Chapter 55 - Environmental Pollution Control [PDF]

Part VII - The Environment

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Chapter 55 - Environmental Pollution Control ENVIRONMENTAL POLLUTION CONTROL AND PREVENTION Jerry Spiegel and Lucien Y. Maystre Over the course of the twentieth century, growing recognition of the environmental and public health impacts associated with anthropogenic activities (discussed in the chapter Environmental Health Hazards) has prompted the development and application of methods and technologies to reduce the effects of pollution. In this context, governments have adopted regulatory and other policy measures (discussed in the chapter Environmental Policy) to minimize negative effects and ensure that environmental quality standards are achieved. The objective of this chapter is to provide an orientation to the methods that are applied to control and prevent environmental pollution. The basic principles followed for eliminating negative impacts on the quality of water, air or land will be introduced; the shifting emphasis from control to prevention will be considered; and the limitations of building solutions for individual environmental media will be examined. It is not enough, for example, to protect air by removing trace metals from a flue gas only to transfer these contaminants to land through improper solid waste management practices. Integrated multimedia solutions are required.

The Pollution Control Approach The environmental consequences of rapid industrialization have resulted in countless incidents of land, air and water resources sites being contaminated with toxic materials and other pollutants, threatening humans and ecosystems with serious health risks. More extensive and intensive use of materials and energy has created cumulative pressures on the quality of local, regional and global ecosystems. Before there was a concerted effort to restrict the impact of pollution, environmental management extended little beyond laissez-faire tolerance, tempered by disposal of wastes to avoid disruptive local nuisance conceived of in a short-term perspective. The need for remediation was recognized, by exception, in instances where damage was determined to be unacceptable. As the pace of industrial activity intensified and the understanding of cumulative effects grew, a pollution control paradigm became the dominant approach to environmental management. Two specific concepts served as the basis for the control approach: · the assimilative capacity concept, which asserts the existence of a specified level of emissions into the environment which does not lead to unacceptable environmental or human health effects · the principle of control concept, which assumes that environmental damage can be avoided by controlling the manner, time and rate at which pollutants enter the environment Under the pollution control approach, attempts to protect the environment have especially relied on isolating contaminants from the environment and using end-of-pipe filters and scrubbers. These solutions have tended to focus on media-specific environmental quality objectives or emission limits, and have been primarily directed at point source discharges into specific environmental media (air, water, soil).

Applying Pollution Control Technologies Application of pollution control methods has demonstrated considerable effectiveness in controlling pollution problems - particularly those of a local character. Application of appropriate technologies is based on a systematic analysis of the source and nature of the emission or discharge in question, of its interaction with the ecosystem and the ambient pollution problem to be addressed, and the development of appropriate technologies to mitigate and monitor pollution impacts. In their article on air pollution control, Dietrich Schwela and Berenice Goelzer explain the importance and implications of taking a comprehensive approach to assessment and control of point sources and non-point sources of air pollution. They also highlight the challenges - and opportunities - that are being addressed in countries that are undergoing rapid industrialization without having had a strong pollution control component accompanying earlier development. Marion Wichman-Fiebig explains the methods that are applied to model air pollutant dispersion to determine and characterize the nature of pollution problems. This forms the basis for understanding the controls that are to be put into effect and for evaluating their effectiveness. As the understanding of potential impacts has deepened, appreciation of effects has expanded from the local to the regional to the global scale. Hans-Ulrich Pfeffer and Peter Bruckmann provide an introduction to the equipment and methods that are used to monitor air quality so that potential pollution problems can be assessed and the effectiveness of control and prevention interventions can be evaluated. John Elias provides an overview of the types of air pollution controls that can be applied and the issues that must be addressed in selecting appropriate pollution control management options. The challenge of water pollution control is addressed by Herbert Preul in an article which explains the basis whereby the earth’s natural waters may become polluted from point, non-point and intermittent sources; the basis for regulating water pollution; and the different criteria that can be applied in determining control programmes. Preul explains the manner in which discharges are received in water bodies, and may be analysed and evaluated to assess and manage risks. Finally, an overview is provided of the techniques that are applied for large-scale wastewater treatment and water pollution control. A case study provides a vivid example of how wastewater can be reused - a topic of considerable significance in the search for ways that environmental resources can be used effectively, especially in circumstances of scarcity. Alexander Donagi provides a summary of the approach that has been pursued for the treatment and groundwater recharge of municipal wastewater for a population of 1.5 million in Israel.

Comprehensive Waste Management Under the pollution control perspective, waste is regarded as an undesirable by-product of the production process which is to be contained so as to ensure that soil, water and air resources are not contaminated beyond levels deemed to be acceptable. Lucien Maystre provides an overview of the issues that must be addressed in managing waste, providing a conceptual link to the increasingly important roles of recycling and pollution prevention. In response to extensive evidence of the serious contamination associated with unrestricted management of waste, governments have established standards for acceptable practices for collection, handling and disposal to ensure environmental protection. Particular attention has been paid to the criteria for environmentally safe disposal through sanitary landfills, incineration and hazardous-waste treatment. To avoid the potential environmental burden and costs associated with the disposal of waste and promote a more thorough stewardship of scarce resources, waste minimization and recycling have received growing attention. Niels Hahn and Poul Lauridsen provide a summary of the issues that are addressed in pursuing recycling as a preferred waste management strategy, and consider the potential worker exposure implications of this.

Shifting Emphasis to Pollution Prevention End-of-pipe abatement risks transferring pollution from one medium to another, where it may either cause equally serious environmental problems, or even end up as an indirect source of pollution to the same medium. While not as expensive as remediation, end-of-pipe abatement can contribute significantly to the costs of production processes without contributing any value. It also typically is associated with regulatory regimes which add other sets of costs associated with enforcing compliance. While the pollution control approach has achieved considerable success in producing short-term improvements for local pollution problems, it has been less effective in addressing cumulative problems that are increasingly recognized on regional (e.g., acid rain) or global (e.g., ozone depletion) levels. The aim of a health-oriented environmental pollution control programme is to promote a better quality of life by reducing pollution to the lowest level possible. Environmental pollution control programmes and policies, whose implications and priorities vary from country to country, cover all aspects of pollution (air, water, land and so on) and involve coordination among areas such as industrial development, city planning, water resources development and transportation policies. Thomas Tseng, Victor Shantora and Ian Smith provide a case study example of the multimedia impact that pollution has had on a vulnerable ecosystem subjected to many stresses - the North American Great Lakes. The limited effectiveness of the pollution control model in dealing with persistent toxins that dissipate through the environment is particularly examined. By focusing on the approach being pursued in one country and the implications that this has for international action, the implications for actions that address prevention as well as control are illustrated. As environmental pollution control technologies have become more sophisticated and more expensive, there has been a growing interest in ways to incorporate prevention in the design of industrial processes - with the objective of eliminating harmful environmental effects while promoting the competitiveness of industries. Among the benefits of pollution prevention approaches, clean technologies and toxic use reduction is the potential for eliminating worker exposure to health risks. David Bennett provides an overview of why pollution prevention is emerging as a preferred strategy and how it relates to other environmental management methods. This approach is central to implementing the shift to sustainable development which has been widely endorsed since the release of the United Nations Commission on Trade and Development in 1987 and reiterated at the Rio United Nations Conference on Environment and Development (UNCED) Conference in 1992. The pollution prevention approach focuses directly on the use of processes, practices, materials and energy that avoid or minimize the creation of pollutants and wastes at source, and not on “add-on” abatement measures. While corporate commitment plays a critical role in the decision to pursue pollution prevention (see Bringer and Zoesel in Environmental policy), Bennett draws attention to the societal benefits in reducing risks to ecosystem and human health—and the health of workers in particular. He identifies principles that can be usefully applied in assessing opportunities for pursuing this approach.

AIR POLLUTION MANAGEMENT Dietrich Schwela and Berenice Goelzer Air pollution management aims at the elimination, or reduction to acceptable levels, of airborne gaseous pollutants, suspended particulate matter and physical and, to a certain extent, biological agents whose presence in the atmosphere can cause adverse effects on human health (e.g., irritation, increase of incidence or prevalence of respiratory diseases, morbidity, cancer, excess mortality) or welfare (e.g., sensory effects, reduction of visibility), deleterious effects on animal or plant life, damage to materials of economic value to society and damage to the environment (e.g., climatic modifications). The serious hazards associated with radioactive pollutants, as well as the special procedures required for their control and disposal, also deserve careful attention. The importance of efficient management of outdoor and indoor air pollution cannot be overemphasized. Unless there is adequate control, the multiplication of pollution sources in the modern world may lead to irreparable damage to the environment and mankind. The objective of this article is to give a general overview of the possible approaches to the management of ambient air pollution from motor vehicle and industrial sources. However, it is to be emphasized from the very beginning that indoor air pollution (in particular, in developing countries) might play an even larger role than outdoor air pollution due to the observation that indoor air pollutant concentrations are often substantially higher than outdoor concentrations. Beyond considerations of emissions from fixed or mobile sources, air pollution management involves consideration of additional factors (such as topography and meteorology, and community and government participation, among many others) all of which must be integrated into a comprehensive programme. For example, meteorological conditions can greatly affect the ground-level concentrations resulting from the same pollutant emission. Air pollution sources may be scattered over a community or a region and their effects may be felt by, or their control may involve, more than one administration. Furthermore, air pollution does not respect any boundaries, and emissions from one region may induce effects in another region by longdistance transport. Air pollution management, therefore, requires a multidisciplinary approach as well as a joint effort by private and governmental entities.

Sources of Air Pollution The sources of man-made air pollution (or emission sources) are of basically two types: · stationary, which can be subdivided into area sources such as agricultural production, mining and quarrying, industrial, point and area sources such as manufacturing of chemicals, nonmetallic mineral products, basic metal industries, power generation and community sources (e.g., heating of homes and buildings, municipal waste and sewage sludge incinerators, fireplaces, cooking facilities, laundry services and cleaning plants) · mobile, comprising any form of combustion-engine vehicles (e.g., light-duty gasoline powered cars, light- and heavy-duty diesel powered vehicles, motorcycles, aircraft, including line sources with emissions of gases and particulate matter from vehicle traffic). In addition, there are also natural sources of pollution (e.g., eroded areas, volcanoes, certain plants which release great amounts of pollen, sources of bacteria, spores and viruses). Natural sources are not discussed in this article.

Types of Air Pollutants Air pollutants are usually classified into suspended particulate matter (dusts, fumes, mists, smokes), gaseous pollutants (gases and vapours) and odours. Some examples of usual pollutants are presented below: Suspended particulate matter (SPM, PM-10) includes diesel exhaust, coal fly-ash, mineral dusts (e.g., coal, asbestos, limestone, cement), metal dusts and fumes (e.g., zinc, copper, iron, lead) and acid mists (e.g., sulphuric acid), fluorides, paint pigments, pesticide mists, carbon black and oil smoke. Suspended particulate pollutants, besides their effects of provoking respiratory diseases, cancers, corrosion, destruction of plant life and so on, can also constitute a nuisance (e.g., accumulation of dirt), interfere with sunlight (e.g., formation of smog and haze due to light scattering) and act as catalytic surfaces for reaction of adsorbed chemicals. Gaseous pollutants include sulphur compounds (e.g., sulphur dioxide (SO 2 ) and sulphur trioxide (SO 3 )), carbon monoxide, nitrogen compounds (e.g., nitric oxide (NO), nitrogen dioxide (NO 2 ), ammonia), organic compounds (e.g., hydrocarbons (HC), volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH), aldehydes), halogen compounds and halogen derivatives (e.g., HF and HCl), hydrogen sulphide, carbon disulphide and mercaptans (odours). Secondary pollutants may be formed by thermal, chemical or photochemical reactions. For example, by thermal action sulphur dioxide can oxidize to sulphur trioxide which, dissolved in water, gives rise to the formation of sulphuric acid mist (catalysed by manganese and iron oxides). Photochemical reactions between nitrogen oxides and reactive hydrocarbons can produce ozone (O 3 ), formaldehyde and peroxyacetyl nitrate (PAN); reactions between HCl and formaldehyde can form bis-chloromethyl ether. While some odours are known to be caused by specific chemical agents such as hydrogen sulphide (H 2 S), carbon disulphide (CS2 ) and mercaptans (R-SH or R1-S-R2) others are difficult to define chemically. Examples of the main pollutants associated with some industrial air pollution sources are presented in table 55.1 (Economopoulos 1993). Table 55.1 Common atmospheric pollutants and their sources Category

Source

Emitted pollutants

Agriculture

Open burning

SPM, CO, VOC

Mining and quarrying

Coal mining

SPM, SO 2 , NO x , VOC



Crude petroleum and natural gas production

SO 2



Non-ferrous ore mining

SPM, Pb



Stone quarrying

SPM

Manufacturing

Food, beverages and tobacco

SPM, CO, VOC, H 2 S



Textiles and leather industries

SPM, VOC



Wood products

SPM, VOC



Paper products, printing

SPM, SO 2 , CO, VOC, H 2 S, RSH

Manufacture of chemicals

Phthalic anhydride

SPM, SO 2 , CO, VOC



Chlor-alkali

Cl2



Hydrochloric acid

HCl



Hydrofluoric acid

HF, SiF4



Sulphuric acid

SO 2 , SO 3



Nitric acid

NO x



Phosphoric acid

SPM, F2



Lead oxide and pigments

SPM, Pb



Ammonia

SPM, SO 2 , NO x , CO, VOC, NH 3



Sodium carbonate

SPM, NH 3



Calcium carbide

SPM



Adipic acid

SPM, NO x , CO, VOC



Alkyl lead

Pb



Maleic anhydride and terephthalic acid

CO, VOC



Fertilizer and pesticide production

SPM, NH 3



Ammonium nitrate

SPM, NH 3 , HNO 3



Ammonium sulphate

VOC



Synthetic resins, plastic materials, fibres

SPM, VOC, H 2 S, CS2



Paints, varnishes, lacquers

SPM, VOC



Soap

SPM



Carbon black and printing ink

SPM, SO 2 , NO x , CO, VOC, H2S



Trinitrotoluene

SPM, SO 2 , NO x , SO 3 , HNO 3

Petroleum refineries

Miscellaneous products of petroleum and coal

SPM, SO 2 , NO x , CO, VOC

Non-metallic mineral Glass products products manufacture

SPM, SO 2 , NO x , CO, VOC, F



Structural clay products

SPM, SO 2 , NO x , CO, VOC, F2



Cement, lime and plaster

SPM, SO 2 , NO x , CO

Basic metal industries Iron and steel

SPM, SO 2 , NO x , CO, VOC, Pb



Non-ferrous industries

SPM, SO 2 , F, Pb

Power generation

Electricity, gas and steam

SPM, SO 2 , NO x , CO, VOC, SO 3 , Pb

Wholesale and retail trade

Fuel storage, filling operations

VOC

Transport



SPM, SO 2 , NO x , CO, VOC, Pb

Community services

Municipal incinerators

SPM, SO 2 , NO x , CO, VOC, Pb

Source: Economopoulos 1993

Clean Air Implementation Plans Air quality management aims at the preservation of environmental quality by prescribing the tolerated degree of pollution, leaving it to the local authorities and polluters to devise and implement actions to ensure that this degree of pollution will not be exceeded. An example of legislation within this approach is the adoption of ambient air quality standards based, very often, on air quality guidelines (WHO 1987) for different pollutants; these are accepted maximum levels of pollutants (or indicators) in the target area (e.g., at ground level at a specified point in a community) and can be either primary or secondary standards. Primary standards (WHO 1980) are the maximum levels consistent with an adequate safety margin and with the preservation of public health, and must be complied with within a specific time limit; secondary standards are those judged to be necessary for protection against known or anticipated adverse effects other than health hazards (mainly on vegetation) and must be complied “within a reasonable time”. Air quality standards are short-, medium- or long-term values valid for 24 hours per day, 7 days per week, and for monthly, seasonal or annual exposure of all living subjects (including sensitive subgroups such as children, the elderly and the sick) as well as nonliving objects; this is in contrast to maximum permissible levels for occupational exposure, which are for a partial weekly exposure (e.g., 8 hours per day, 5 days per week) of adult and supposedly healthy workers. Typical measures in air quality management are control measures at the source, for example, enforcement of the use of catalytic converters in vehicles or of emission standards in incinerators, land-use planning and shut-down of factories or reduction of traffic during unfavourable weather conditions. The best air quality management stresses that the air pollutant emissions should be kept to a minimum; this is basically defined through emission standards for single sources of air pollution and could be achieved for industrial sources, for example, through closed systems and high-efficiency collectors. An emission standard is a limit on the amount or concentration of a pollutant emitted from a source. This type of legislation requires a decision, for each industry, on the best means of controlling its emissions (i.e., fixing emission standards). The basic aim of air pollution management is to derive a clean air implementation plan (or air pollution abatement plan) (Schwela and Köth-Jahr 1994) which consists of the following elements: · description of area with respect to topography, meteorology and socioeconomy · emissions inventory · comparison with emission standards · air pollutant concentrations inventory · simulated air pollutant concentrations · comparison with air quality standards · inventory of effects on public health and the environment · causal analysis · control measures · cost of control measures · cost of public health and environmental effects · cost-benefit analysis (costs of control vs. costs of efforts) · transportation and land-use planning · enforcement plan; resource commitment · projections for the future on population, traffic, industries and fuel consumption · strategies for follow-up. Some of these issues will be described below.

Emissions Inventory; Comparison with Emission Standards The emissions inventory is a most complete listing of sources in a given area and of their individual emissions, estimated as accurately as possible from all emitting point, line and area (diffuse) sources. When these emissions are compared with emission standards set for a particular source, first hints on possible control measures are given if emission standards are not complied with. The emissions inventory also serves to assess a priority list of important sources according to the amount of pollutants emitted, and indicates the relative influence of different sources—for example, traffic as compared to industrial or residential sources. The emissions inventory also allows an estimate of air pollutant concentrations for those pollutants for which ambient concentration measurements are difficult or too expensive to perform.

Air Pollutant Concentrations Inventory; Comparison with Air Quality Standards The air pollutant concentrations inventory summarizes the results of the monitoring of ambient air pollutants in terms of annual means, percentiles and trends of these quantities. Compounds measured for such an inventory include the following: · sulphur dioxide · nitrogen oxides · suspended particulate matter · carbon monoxide · ozone · heavy metals (Pb, Cd, Ni, Cu, Fe, As, Be) · polycyclic aromatic hydrocarbons: benzo(a)pyrene, benzo(e)pyrene, benzo(a)anthracene, dibenzo(a,h)anthracene, benzoghi)perylene, coronen · volatile organic compounds: n-hexane, benzene, 3-methyl-hexane, n-heptane, toluene, octane, ethyl-benzene xylene (o-,m-,p-), n-nonane, isopropylbenzene, propylbenezene, n-2-/3-/4ethyltoluene, 1,2,4-/1,3,5-trimethylbenzene, trichloromethane, 1,1,1 trichloroethane, tetrachloromethane, tri-/tetrachloroethene. Comparison of air pollutant concentrations with air quality standards or guidelines, if they exist, indicates problem areas for which a causal analysis has to be performed in order to find out which sources are responsible for the non-compliance. Dispersion modelling has to be used in performing this causal analysis (see “Air pollution: Modelling of air pollutant dispersion”). Devices and procedures used in today’s ambient air pollution monitoring are described in “Air quality monitoring”.

Simulated Air Pollutant Concentrations; Comparison with Air Quality Standards Starting from the emissions inventory, with its thousands of compounds which cannot all be monitored in the ambient air for economy reasons, use of dispersion modelling can help to estimate the concentrations of more “exotic” compounds. Using appropriate meteorology parameters in a suitable dispersion model, annual averages and percentiles can be estimated and compared to air quality standards or guidelines, if they exist.

Inventory of Effects on Public Health and the Environment; Causal Analysis Another important source of information is the effects inventory (Ministerium für Umwelt 1993), which consists of results of epidemiological studies in the given area and of effects of air pollution observed in biological and material receptors such as, for example, plants, animals and construction metals and building stones. Observed effects attributed to air pollution have to be causally analysed with respect to the component responsible for a particular effect—for example, increased prevalence of chronic bronchitis in a polluted area. If the compound or compounds have been fixed in a causal analysis (compound-causal analysis), a second analysis has to be performed to find out the responsible sources (source-causal analysis).

Control Measures; Cost of Control Measures Control measures for industrial facilities include adequate, well-designed, well-installed, efficiently operated and maintained air cleaning devices, also called separators or collectors. A separator or collector can be defined as an “apparatus for separating any one or more of the following from a gaseous medium in which they are suspended or mixed: solid particles (filter and dust separators), liquid particles (filter and droplet separator) and gases (gas purifier)”. The basic types of air pollution control equipment (discussed further in “Air pollution control”) are the following: · for particulate matter: inertial separators (e.g., cyclones); fabric filters (baghouses); electrostatic precipitators; wet collectors (scrubbers) · for gaseous pollutants: wet collectors (scrubbers); adsorption units (e.g., adsorption beds); afterburners, which can be direct-fired (thermal incineration) or catalytic (catalytic combustion). Wet collectors (scrubbers) can be used to collect, at the same time, gaseous pollutants and particulate matter. Also, certain types of combustion devices can burn combustible gases and vapours as well as certain combustible aerosols. Depending on the type of effluent, one or a combination of more than one collector can be used. The control of odours that are chemically identifiable relies on the control of the chemical agent(s) from which they emanate (e.g., by absorption, by incineration). However, when an odour is not defined chemically or the producing agent is found at extremely low levels, other techniques may be used, such as masking (by a stronger, more agreeable and harmless agent) or counteraction (by an additive which counteracts or partially neutralizes the offensive odour). It should be kept in mind that adequate operation and maintenance are indispensable to ensure the expected efficiency from a collector. This should be ensured at the planning stage, both from the know-how and financial points of view. Energy requirements must not be overlooked. Whenever selecting an air cleaning device, not only the initial cost but also operational and maintenance costs should be considered. Whenever dealing with high-toxicity pollutants, high efficiency should be ensured, as well as special procedures for maintenance and disposal of waste materials. The fundamental control measures in industrial facilities are the following: Substitution of materials. Examples: substitution of less toxic solvents for highly toxic ones used in certain industrial processes; use of fuels with lower sulphur content (e.g., washed coal), therefore giving rise to less sulphur compounds and so on. Modification or change of the industrial process or equipment. Examples: in the steel industry, a change from raw ore to pelleted sintered ore (to reduce the dust released during ore handling); use of closed systems instead of open ones; change of fuel heating systems to steam, hot water or electrical systems; use of catalysers at the exhaust air outlets (combustion processes) and so on. Modifications in processes, as well as in plant layout, may also facilitate and/or improve the conditions for dispersion and collection of pollutants. For example, a different plant layout may facilitate the installation of a local exhaust system; the performance of a process at a lower rate may allow the use of a certain collector (with volume limitations but otherwise adequate). Process modifications that concentrate different effluent sources are closely related to the volume of effluent handled, and the efficiency of some air-cleaning equipment increases with the concentration of pollutants in the effluent. Both the substitution of materials and the modification of processes may have technical and/or economic limitations, and these should be considered. Adequate housekeeping and storage. Examples: strict sanitation in food and animal product processing; avoidance of open storage of chemicals (e.g., sulphur piles) or dusty materials (e.g., sand), or, failing this, spraying of the piles of loose particulate with water (if possible) or application of surface coatings (e.g., wetting agents, plastic) to piles of materials likely to give off pollutants. Adequate disposal of wastes. Examples: avoidance of simply piling up chemical wastes (such as scraps from polymerization reactors), as well as of dumping pollutant materials (solid or liquid) in water streams. The latter practice not only causes water pollution but can also create a secondary source of air pollution, as in the case of liquid wastes from sulphite process pulp mills, which release offensive odorous gaseous pollutants. Maintenance. Example: well maintained and well-tuned internal combustion engines produce less carbon monoxide and hydrocarbons. Work practices. Example: taking into account meteorological conditions, particularly winds, when spraying pesticides. By analogy with adequate practices at the workplace, good practices at the community level can contribute to air pollution control - for example, changes in the use of motor vehicles (more collective transportation, small cars and so on) and control of heating facilities (better insulation of buildings in order to require less heating, better fuels and so on). Control measures in vehicle emissions are adequate and efficient mandatory inspection and maintenance programmes which are enforced for the existing car fleet, programmes of enforcement of the use of catalytic converters in new cars, aggressive substitution of solar/battery-powered cars for fuel-powered ones, regulation of road traffic, and transportation and land use planning concepts. Motor vehicle emissions are controlled by controlling emissions per vehicle mile travelled (VMT) and by controlling VMT itself (Walsh 1992). Emissions per VMT can be reduced by controlling vehicle performance - hardware, maintenance - for both new and in-use cars. Fuel composition of leaded gasoline may be controlled by reducing lead or sulphur content, which also has a beneficial effect on decreasing HC emissions from vehicles. Lowering the levels of sulphur in diesel fuel as a means to lower diesel particulate emission has the additional beneficial effect of increasing the potential for catalytic control of diesel particulate and organic HC emissions. Another important management tool for reducing vehicle evaporative and refuelling emissions is the control of gasoline volatility. Control of fuel volatility can greatly lower vehicle evaporative HC emissions. Use of oxygenated additives in gasoline lowers HC and CO exhaust as long as fuel volatility is not increased. Reduction of VMT is an additional means of controlling vehicle emissions by control strategies such as · use of more efficient transportation modes · increasing the average number of passengers per car · spreading congested peak traffic loads · reducing travel demand. While such approaches promote fuel conservation, they are not yet accepted by the general population, and governments have not seriously tried to implement them. All these technological and political solutions to the motor vehicle problem except substitution of electrical cars are increasingly offset by growth in the vehicle population. The vehicle problem can be solved only if the growth problem is addressed in an appropriate way.

Cost of Public Health and Environmental Effects; Cost-Benefit Analysis The estimation of the costs of public health and environmental effects is the most difficult part of a clean air implementation plan, as it is very difficult to estimate the value of lifetime reduction of disabling illnesses, hospital admission rates and hours of work lost. However, this estimation and a comparison with the cost of control measures is absolutely necessary in order to balance the costs of control measures versus the costs of no such measure undertaken, in terms of public health and environmental effects.

Transportation and Land-Use Planning The pollution problem is intimately connected to land-use and transportation, including issues such as community planning, road design, traffic control and mass transportation; to concerns of demography, topography and economy; and to social concerns (Venzia 1977). In general, the rapidly growing urban aggregations have severe pollution problems due to poor land-use and transportation practices. Transportation planning for air pollution control includes transportation controls, transportation policies, mass transit and highway congestion costs. Transportation controls have an important impact on the general public in terms of equity, repressiveness and social and economic disruption - in particular, direct transportation controls such as motor vehicle constraints, gasoline limitations and motor vehicle emission reductions. Emission reductions due to direct controls can be reliably estimated and verified. Indirect transportation controls such as reduction of vehicle miles travelled by improvement of mass transit systems, traffic flow improvement regulations, regulations on parking lots, road and gasoline taxes, car-use permissions and incentives for voluntary approaches are mostly based on past trial-and-error experience, and include many uncertainties when trying to develop a viable transportation plan. National action plans incurring indirect transportation controls can affect transportation and land-use planning with regard to highways, parking lots and shopping centres. Long-term planning for the transportation system and the area influenced by it will prevent significant deterioration of air quality and provide for compliance with air quality standards. Mass transit is consistently considered as a potential solution for urban air pollution problems. Selection of a mass transit system to serve an area and different modal splits between highway use and bus or rail service will ultimately alter land-use patterns. There is an optimum split that will minimize air pollution; however, this may not be acceptable when non-environmental factors are considered. The automobile has been called the greatest generator of economic externalities ever known. Some of these, such as jobs and mobility, are positive, but the negative ones, such as air pollution, accidents resulting in death and injury, property damage, noise, loss of time, and aggravation, lead to the conclusion that transportation is not a decreasing cost industry in urbanized areas. Highway congestion costs are another externality; lost time and congestion costs, however, are difficult to determine. A true evaluation of competing transportation modes, such as mass transportation, cannot be obtained if travel costs for work trips do not include congestion costs. Land-use planning for air pollution control includes zoning codes and performance standards, land-use controls, housing and land development, and land-use planning policies. Land-use zoning was the initial attempt to accomplish protection of the people, their property and their economic opportunity. However, the ubiquitous nature of air pollutants required more than physical separation of industries and residential areas to protect the individual. For this reason, performance standards based initially on aesthetics or qualitative decisions were introduced into some zoning codes in an attempt to quantify criteria for identifying potential problems. The limitations of the assimilative capacity of the environment must be identified for long-term land-use planning. Then, land-use controls can be developed that will prorate the capacity equitably among desired local activities. Land-use controls include permit systems for review of new stationary sources, zoning regulation between industrial and residential areas, restriction by easement or purchase of land, receptor location control, emission-density zoning and emission allocation regulations. Housing policies aimed at making home ownership available to many who could otherwise not afford it (such as tax incentives and mortgage policies) stimulate urban sprawl and indirectly discourage higher-density residential development. These policies have now proven to be environmentally disastrous, as no consideration was given to the simultaneous development of efficient transportation systems to serve the needs of the multitude of new communities being developed. The lesson learnt from this development is that programmes impacting on the environment should be coordinated, and comprehensive planning undertaken at the level where the problem occurs and on a scale large enough to include the entire system. Land-use planning must be examined at national, provincial or state, regional and local levels to adequately ensure long-term protection of the environment. Governmental programmes usually start with power plant siting, mineral extraction sites, coastal zoning and desert, mountain or other recreational development. As the multiplicity of local governments in a given region cannot adequately deal with regional environmental problems, regional governments or agencies should coordinate land development and density patterns by supervising the spatial arrangement and location of new construction and use, and transportation facilities. Land-use and transportation planning must be interrelated with enforcement of regulations to maintain the desired air quality. Ideally, air pollution control should be planned for by the same regional agency that does land-use planning because of the overlapping externalities associated with both issues.

Enforcement Plan, Resource Commitment The clean air implementation plan should always contain an enforcement plan which indicates how the control measures can be enforced. This implies also a resource commitment which, according to a polluter pays principle, will state what the polluter has to implement and how the government will help the polluter in fulfilling the commitment.

Projections for the Future In the sense of a precautionary plan, the clean air implementation plan should also include estimates of the trends in population, traffic, industries and fuel consumption in order to assess responses to future problems. This will avoid future stresses by enforcing measures well in advance of imagined problems.

Strategies for Follow-up A strategy for follow-up of air quality management consists of plans and policies on how to implement future clean air implementation plans.

Role of Environmental Impact Assessment Environmental impact assessment (EIA) is the process of providing a detailed statement by the responsible agency on the environmental impact of a proposed action significantly affecting the quality of the human environment (Lee 1993). EIA is an instrument of prevention aiming at consideration of the human environment at an early stage of the development of a programme or project. EIA is particularly important for countries which develop projects in the framework of economic reorientation and restructuring. EIA has become legislation in many developed countries and is now increasingly applied in developing countries and economies in transition. EIA is integrative in the sense of comprehensive environmental planning and management considering the interactions between different environmental media. On the other hand, EIA integrates the estimation of environmental consequences into the planning process and thereby becomes an instrument of sustainable development. EIA also combines technical and participative properties as it collects, analyses and applies scientific and technical data with consideration of quality control and quality assurance, and stresses the importance of consultations prior to licensing procedures between environmental agencies and the public which could be affected by particular projects. A clean air implementation plan can be considered as a part of the EIA procedure with reference to the air.

AIR POLLUTION: MODELLING OF AIR POLLUTANT DISPERSION Marion Wichmann-Fiebig International Monitoring Programmes International agencies such as the World Health Organization (WHO), the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) have instituted monitoring and research projects in order to clarify the issues involved in air pollution and to promote measures to prevent further deterioration of public health and environmental and climatic conditions. The Global Environmental Monitoring System GEMS/Air (WHO/ UNEP 1993) is organized and sponsored by WHO and UNEP and has developed a comprehensive programme for providing the instruments of rational air pollution management (see figure 55.1. The kernel of this programme is a global database of urban air pollutant concentrations of sulphur dioxides, suspended particulate matter, lead, nitrogen oxides, carbon monoxide and ozone. As important as this database, however, is the provision of management tools such as guides for rapid emission inventories, programmes for dispersion modelling, population exposure estimates, control measures, and costbenefit analysis. In this respect, GEMS/Air provides methodology review handbooks (WHO/UNEP 1994, 1995), conducts global assessments of air quality, facilitates review and validation of assessments, acts as a data/information broker, produces technical documents in support of all aspects of air quality management, facilitates the establishment of monitoring, conducts and widely distributes annual reviews, and establishes or identifies regional collaboration centres and/or experts to coordinate and support activities according to the needs of the regions. (WHO/UNEP 1992, 1993, 1995) The Global Atmospheric Watch (GAW) programme (Miller and Soudine 1994) provides data and other information on the chemical composition and related physical characteristics of the atmosphere, and their trends, with the objective of understanding the relationship between changing atmospheric composition and changes of global and regional climate, the long-range atmospheric transport and deposition of potentially harmful substances over terrestrial, fresh-water and marine ecosystems, and the natural cycling of chemical elements in the global atmosphere/ocean/biosphere system, and anthropogenic impacts thereon. The GAW programme consists of four activity areas: the Global Ozone Observing System (GO3OS), global monitoring of background atmospheric composition, including the Background Air Pollution Monitoring Network (BAPMoN); dispersion, transport, chemical transformation and deposition of atmospheric pollutants over land and sea on different time and space scales; exchange of pollutants between the atmosphere and other environmental compartments; and integrated monitoring. One of the most important aspects of the GAW is the establishment of Quality Assurance Science Activity Centres to oversee the quality of the data produced under GAW. Figure 55.1 Global Environmental Monitoring System/Air pollution management

The aim of air pollution modelling is the estimation of outdoor pollutant concentrations caused, for instance, by industrial production processes, accidental releases or traffic. Air pollution modelling is used to ascertain the total concentration of a pollutant, as well as to find the cause of extraordinary high levels. For projects in the planning stage, the additional contribution to the existing burden can be estimated in advance, and emission conditions may be optimized. Depending on the air quality standards defined for the pollutant in question, annual mean values or short-time peak concentrations are of interest. Usually concentrations have to be determined where people are active - that is, near the surface at a height of about two metres above the ground.

Parameters Influencing Pollutant Dispersion Two types of parameters influence pollutant dispersion: source parameters and meteorological parameters. For source parameters, concentrations are proportional to the amount of pollutant which is emitted. If dust is concerned, the particle diameter has to be known to determine sedimentation and deposition of the material (VDI 1992). As surface concentrations are lower with greater stack height, this parameter also has to be known. In addition, concentrations depend on the total amount of the exhaust gas, as well as on its temperature and velocity. If the temperature of the exhaust gas exceeds the temperature of the surrounding air, the gas will be subject to thermal buoyancy. Its exhaust velocity, which can be calculated from the inner stack diameter and the exhaust gas volume, will cause a dynamic momentum buoyancy. Empirical formulae may be used to describe these features (VDI 1985; Venkatram and Wyngaard 1988). It has to be stressed that it is not the mass of the pollutant in question but that of the total gas that is responsible for the thermal and dynamic momentum buoyancy. Meteorological parameters which influence pollutant dispersion are wind speed and direction, as well as vertical thermal stratification. The pollutant concentration is proportional to the reciprocal of wind speed. This is mainly due to the accelerated transport. Moreover, turbulent mixing increases with growing wind speed. As so-called inversions (i.e., situations where temperature is increasing with height) hinder turbulent mixing, maximum surface concentrations are observed during highly stable stratification. On the contrary, convective situations intensify vertical mixing and therefore show the lowest concentration values. Air quality standards - for example, annual mean values or 98 percentiles - are usually based on statistics. Hence, time series data for the relevant meteorological parameters are needed. Ideally, statistics should be based on ten years of observation. If only shorter time series are available, it should be ascertained that they are representative for a longer period. This can be done, for example, by analysis of longer time series from other observations sites. The meteorological time series used also has to be representative of the site considered - that is, it must reflect the local characteristics. This is specially important concerning air quality standards based on peak fractions of the distribution, like 98 percentiles. If no such time series is at hand, a meteorological flow model may be used to calculate one from other data, as will be described below.

Concepts of Air Pollution Modelling As mentioned above, dispersion of pollutants is dependent on emission conditions, transport and turbulent mixing. Using the full equation which describes these features is called Eulerian dispersion modelling (Pielke 1984). By this approach, gains and losses of the pollutant in question have to be determined at every point on an imaginary spatial grid and in distinct time steps. As this method is very complex and computer time consuming, it usually cannot be handled routinely. However, for many applications, it may be simplified using the following assumptions: · no change of emission conditions with time · no change of meteorological conditions during transport · wind speeds above 1 m/s. In this case, the equation mentioned above can be solved analytically. The resulting formula describes a plume with Gaussian concentration distribution, the so called Gaussian plume model (VDI 1992). The distribution parameters depend on meteorological conditions and downwind distance as well as on stack height. They have to be determined empirically (Venkatram and Wyngaard 1988). Situations where emissions and/or meteorological parameters vary by a considerable amount in time and/or space may be described by the Gaussian puff model (VDI 1994). Under this approach, distinct puffs are emitted in fixed time steps, each following its own path according to the current meteorological conditions. On its way, each puff grows according to turbulent mixing. Parameters describing this growth, again, have to be determined from empirical data (Venkatram and Wyngaard 1988). It has to be stressed, however, that to achieve this objective, input parameters must be available with the necessary resolution in time and/or space. Concerning accidental releases or single case studies, a Lagrangian or particle model (VDI Guideline 3945, Part 3) is recommended. The concept thereby is to calculate the paths of many particles, each of which represents a fixed amount of the pollutant in question. The individual paths are composed of transport by the mean wind and of stochastic disturbances. Due to the stochastic part, the paths do not fully agree, but depict the mixture by turbulence. In principle, Lagrangian models are capable of considering complex meteorological conditions - in particular, wind and turbulence; fields calculated by flow models described below can be used for Lagrangian dispersion modelling.

Dispersion Modelling in Complex Terrain If pollutant concentrations have to be determined in structured terrain, it may be necessary to include topographic effects on pollutant dispersion in modelling. Such effects are, for example, transport following the topographic structure, or thermal wind systems like sea breezes or mountain winds, which change wind direction in the course of the day. If such effects take place on a scale much larger than the model area, the influence may be considered by using meteorological data which reflect the local characteristics. If no such data are available, the three-dimensional structure impressed on the flow by topography can be obtained by using a corresponding flow model. Based on these data, dispersion modelling itself may be carried out assuming horizontal homogeneity as described above in the case of the Gaussian plume model. However, in situations where wind conditions change significantly inside the model area, dispersion modelling itself has to consider the three-dimensional flow affected by the topographic structure. As mentioned above, this may be done by using a Gaussian puff or a Lagrangian model. Another way is to perform the more complex Eulerian modelling. To determine wind direction in accord with the topographically structured terrain, mass consistent or diagnostic flow modelling may be used (Pielke 1984). Using this approach, the flow is fitted to topography by varying the initial values as little as possible and by keeping its mass consistent. As this is an approach which leads to quick results, it may also be used to calculate wind statistics for a certain site if no observations are available. To do this, geostrophic wind statistics (i.e., upper air data from rawinsondes) are used. If, however, thermal wind systems have to be considered in more detail, so called prognostic models have to be used. Depending on the scale and the steepness of the model area, a hydrostatic, or the even more complex non-hydrostatic, approach is suitable (VDI 1981). Models of this type need much computer power, as well as much experience in application. Determination of concentrations based on annual means, in general, are not possible with these models. Instead, worst case studies can be performed by considering only one wind direction and those wind speed and stratification parameters which result in the highest surface concentration values. If those worst case values do not exceed air quality standards, more detailed studies are not necessary. Figure 55.2, figure 55.3 and figure 55.4 demonstrate how the transport and dispension of pollutants can be presented in relation to the influence of terrain and wind climatologies derived from consideration of surface and geostrophic wind frequencies. Figure 55.2 Topographic structure of a model region

Figure 55.3 Surface frequency distributions as determined from geostrophic frequency distribution

Figure 55.4 Annual mean pollutant concentrations for a hypothetical region calculated from the geostrophic frequency distribution for heterogeneous wind fields

Dispersion Modelling in Case of Low Sources Considering air pollution caused by low sources (i.e., stack heights on the order of building height or emissions of road traffic) the influence of the surrounding buildings has to be considered. Road traffic emissions will be trapped to a certain amount in street canyons. Empirical formulations have been found to describe this (Yamartino and Wiegand 1986). Pollutants emitted from a low stack situated on a building will be captured in the circulation on the lee side of the building. The extent of this lee circulation depends on the height and width of the building, as well as on wind speed. Therefore, simplified approaches to describe pollutant dispersion in such a case, based solely on the height of a building, are not generally valid. The vertical and horizontal extent of the lee circulation has been obtained from wind tunnel studies (Hosker 1985) and can be implemented in mass consistent diagnostic models. As soon as the flow field has been determined, it can be used to calculate the transport and turbulent mixing of the pollutant emitted. This can be done by Lagrangian or Eulerian dispersion modelling. More detailed studies - concerning accidental releases, for instance - can be performed only by using non-hydrostatic flow and dispersion models instead of a diagnostic approach. As this, in general, demands high computer power, a worst case approach as described above is recommended in advance of a complete statistical modelling.

AIR QUALITY MONITORING Hans-Ulrich Pfeffer and Peter Bruckmann Air quality monitoring means the systematic measurement of ambient air pollutants in order to be able to assess the exposure of vulnerable receptors (e.g., people, animals, plants and art works) on the basis of standards and guidelines derived from observed effects, and/or to establish the source of the air pollution (causal analysis). Ambient air pollutant concentrations are influenced by the spatial or time variance of emissions of hazardous substances and the dynamics of their dispersion in the air. As a consequence, marked daily and annual variations of concentrations occur. It is practically impossible to determine in a unified way all these different variations of air quality (in statistical language, the population of air quality states). Thus, ambient air pollutant concentrations measurements always have the character of random spatial or time samples.

Measurement Planning The first step in measurement planning is to formulate the purpose of the measurement as precisely as possible. Important questions and fields of operation for air quality monitoring include: Area measurement: · representative determination of exposure in one area (general air monitoring) · representative measurement of pre-existing pollution in the area of a planned facility (permit, TA Luft (Technical instruction, air)) · smog warning (winter smog, high ozone concentrations) · measurements in hot spots of air pollution to estimate maximum exposure of receptors (EU-NO 2 guideline, measurements in street canyons, in accordance with the German Federal Immission Control Act) · checking the results of pollution abatement measures and trends over time · screening measurements · scientific investigations - for example, the transport of air pollution, chemical conversions, calibrating dispersion calculations. Facility measurement: · measurements in response to complaints · ascertaining sources of emissions, causal analysis · measurements in cases of fires and accidental releases · checking success of reduction measures · monitoring factory fugitive emissions. The goal of measurement planning is to use adequate measurement and assessment procedures to answer specific questions with sufficient certainty and at minimum possible expense. An example of the parameters that should be used for measurement planning is presented in table 55.2 , in relation to an assessment of air pollution in the area of a planned industrial facility. Recognizing that formal requirements vary by jurisdiction, it should be noted that specific reference here is made to German licensing procedures for industrial facilities. Table 55.2 Parameters for measurement planning in measuring ambient air pollution concentrations (with example of application) Parameter

Example of application: Licensing procedure for industrial facilities in Germany

Statement of the question

Measurement of prior pollution in the licensing procedure; representative random probe measurement

Area of measurement

Circle around location with radius 30 times actual chimney height (simplified)

Assessment standards (place and time Threshold limits IW1 (arithmetic mean) and IW2 dependent): characteristic values to (98th percentile) of TA Luft (Technical be obtained from measurement data instruction, air); calculation of I1 (arithmetic mean) and I2 (98th percentile) from measurements taken for 1 km2 (assessment surface) to be compared with IW1 and IW2 Ordering, choice and density of measurement sites

Regular scan of 1km2 , resulting in “random” choice of measurement sites

Measurement time period

1 year, at least 6 months

Measurement height

1.5 to 4 metres above ground

Measurement frequency

52 (104) measurements per assessment area for gaseous pollutants, depending on the height of the pollution

Duration of each measurement

1/2 hour for gaseous pollutants, 24 hours for suspended dust, 1 month for dust precipitation

Measurement time

Random choice

Measured object

Air pollution emitted from the planned facility

Measurement procedure

National standard measurement procedure (VDI guidelines)

Necessary certainty of measurement results

High

Quality requirements, quality control, VDI guidelines calibration, maintenance Recording of measurement data, validation, archiving, assessment

Calculation of quantity of data I1V and I2V for every assessment area

Costs

Depend on measurement area and objectives

The example in table 55.2 shows the case of a measurement network that is supposed to monitor the air quality in a specific area as representatively as possible, to compare with designated air quality limits. The idea behind this approach is that a random choice of measurement sites is made in order to cover equally locations in an area with varying air quality (e.g., living areas, streets, industrial zones, parks, city centres, suburbs). This approach may be very costly in large areas due to the number of measurement sites necessary. Another conception for a measurement network therefore starts with measurement sites that are representatively selected. If measurements of differing air quality are conducted in the most important locations, and the length of time that the protected objects remain in these “microenvironments” is known, then the exposure can be determined. This approach can be extended to other microenvironments (e.g., interior rooms, cars) in order to estimate the total exposure. Diffusion modelling or screening measurements can help in choosing the right measurement sites. A third approach is to measure at the points of presumed highest exposure (e.g., for NO 2 and benzene in street canyons). If assessment standards are met at this site, there is sufficient probability that this will also be the case for all other sites. This approach, by focusing on critical points, requires relatively few measurement sites, but these must be chosen with particular care. This particular method risks overestimating real exposure. The parameters of measurement time period, assessment of the measurement data and measurement frequency are essentially given in the definition of the assessment standards (limits) and the desired level of certainty of the results. Threshold limits and the peripheral conditions to be considered in measurement planning are related. By using continuous measurement procedures, a resolution that is temporally almost seamless can be achieved. But this is necessary only in monitoring peak values and/or for smog warnings; for monitoring annual mean values, for example, discontinuous measurements are adequate. The following section is dedicated to describing the capabilities of measurement procedures and quality control as a further parameter important to measurement planning.

Quality Assurance Measurements of ambient air pollutant concentrations can be costly to conduct, and results can affect significant decisions with serious economic or ecological implications. Therefore, quality assurance measures are an integral part of the measurement process. Two areas should be distinguished here. Procedure-oriented measures Every complete measurement procedure consists of several steps: sampling, sample preparation and clean-up; separation, detection (final analytical step); and data collection and assessment. In some cases, especially with continuous measurement of inorganic gases, some steps of the procedure can be left out (e.g., separation). Comprehensive adherence to procedures should be strived for in conducting measurements. Procedures that are standardized and thus comprehensively documented should be followed, in the form of DIN/ISO standards, CEN standards or VDI guidelines. User-oriented measures Using standardized and proven equipment and procedures for ambient air pollutant concentration measurement cannot alone ensure acceptable quality if the user does not employ adequate methods of quality control. The standards series DIN/EN/ISO 9000 (Quality Management and Quality Assurance Standards), EN 45000 (which defines the requirements for testing laboratories) and ISO Guide 25 (General Requirements for the Competence of Calibration and Testing Laboratories) are important for user-oriented measures to ensure quality. Important aspects of user quality control measures include: · acceptance and practice of the content of the measures in the sense of good laboratory practice (GLP) · correct maintenance of measurement equipment, qualified measures to eliminate disruptions and ensure repairs · carrying out calibrations and regular checking to ensure proper functioning · carrying out interlaboratory testing.

Measurement Procedures Measurement procedures for inorganic gases A wealth of measurement procedures exists for the broad range of inorganic gases. We will differentiate between manual and automatic methods. Manual procedures

In the case of manual measurement procedures for inorganic gases, the substance to be measured is normally adsorbed during the sampling in a solution or solid material. In most cases a photometric determination is made after an appropriate colour reaction. Several manual measurement procedures have special significance as reference procedures. Because of the relatively high personnel cost, these manual procedures are conducted only rarely for field measurements today, when alternative automatic procedures are available. The most important procedures are briefly sketched in table 55.3 . Table 55.3 Manual measurement procedures for inorganic gases Material Procedure

Execution

Comments

SO 2

Absorption in tetrachloromercurate solution (wash bottle); reaction with formaldehyde and pararosaniline to red-violet sulphonic acid; photometric determination

EU-reference measurement procedure; DL = 0.2 µg SO 2 ; s

Removal of interfering substances by concentrated H 3 PO 4 ; adsorption on silica gel; thermal desorption in H 2 -stream and reduction to H 2 S; reaction to molybdenum-blue; photometric determination

DL = 0.3 µg SO 2 ;

TCM procedure

SO 2

Silica gel procedure

= 0.03 mg/m3 at 0.5 mg/m3

s = 0.03 mg/m3 at 0.5 mg/m3

NO 2

Saltzman procedure

Absorption in reaction solution while forming a red azo dye (wash bottle); photometric determination

Calibration with sodium nitrite; DL = 3 µg/m3

O3

Potassium iodide procedure

Formation of iodine from aqueous potassium iodide solution (wash bottle); photometric determination

DL = 20 µg/m3 ; rel. s = ± 3.5% at 390 µg/m3

F-

Silver bead procedure; variant 1

Sampling with dust preseparator; enrichment of F- on sodium carbonate-coated silver beads; elution and measurement with ion-sensitive lanthanum fluoride-electrode chain

Inclusion of an undetermined portion of particulate fluoride immissions

F-

Silver bead procedure; variant 2

Sampling with heated membrane filter; enrichment of F- on sodium carbonate-coated silver beads; determination by electrochemical (variant 1) or photometric (alizarin-complexone) procedure

Danger of lower findings due to partial sorption of gaseous fluoride immissions on membrane filter; DL = 0.5 µg/m3

Cl-

Mercury rhodanide procedure

Absorption in 0.1 N sodium hydroxide solution (wash bottle); reaction with mercury rhodanide and Fe(III) ions to iron thiocyanato complex; photometric determination

DL = 9 µg/m3

Cl2

Methyl-orange procedure

Bleaching reaction with methyl-orange solution (wash bottle); photometric determination

DL = 0.015 mg/m3

NH 3

Indophenol procedure

Absorption in dilute H 2 SO 4 (Impinger/wash bottle); conversion with phenol and hypochlorite to indophenol dye; photometric determination

DL = 3 µg/m3 (impinger); partial inclusion of compounds and amines

NH 3

Nessler procedure

Absorption in dilute H 2 SO 4 (Impinger/wash bottle); distillation and reaction with Nessler’s reagent, photometric determination

DL = 2.5 µg/m3 (impinger); partial inclusion of NH 4 +compounds and amines

H2S

Molybdenum-blue procedure

Absorption as silver sulphide on glass beads treated with silver sulphate and potassium hydrogen sulphate (sorption tube); released as hydrogen sulphide and conversion to molybdenum blue; photometric determination

DL = 0.4 µg/m3

H2S

Methylene blue procedure

Absorption in cadmium hydroxide suspension while forming CdS; conversion to methylene blue; photometric determination

DL = 0.3 µg/m3

DL = detection limit; s = standard deviation; rel. s = relative s. A special sampling variant, used primarily in connection with manual measurement procedures, is the diffusion separation tube (denuder). The denuder technique is aimed at separating the gas and particle phases by using their different diffusion rates. Thus, it is often used on difficult separation problems (e.g., ammonia and ammonium compounds; nitrogen oxides, nitric acid and nitrates; sulphur oxides, sulphuric acid and sulphates or hydrogen halides/halides). In the classic denuder technique, the test air is sucked through a glass tube with a special coating, depending on the material(s) to be collected. The denuder technique has been further developed in many variations and also partially automated. It has greatly expanded the possibilities of differentiated sampling, but, depending on the variant, it can be very laborious, and proper utilization requires a great deal of experience. Automated procedures

There are numerous different continuous measuring monitors on the market for sulphur dioxide, nitrogen oxides, carbon monoxide and ozone. For the most part they are used particularly in measurement networks. The most important features of the individual methods are collected in table 55.4 . Table 55.4 Automated measurement procedures for inorganic gases Material

Measuring principle

Comments

SO 2

Conductometry reaction of SO 2 with Exclusion of interferences with H 2 O 2 in dilute H 2 SO 4 ; measurement selective filter (KHSO 4 /AgNO 3 ) of increased conductivity

SO 2

UV fluorescence; excitation of SO 2 molecules with UV radiation (190– 230 nm); measurement of fluorescence radiation

Interferences, e.g., by hydrocarbons, must be eliminated with appropriate filter systems

NO/NO 2

Chemiluminescence; reaction of NO with O 3 to NO 2 ; detection of chemiluminescence radiation with photomultiplier

NO 2 only indirectly measurable; use of converters for reduction of NO 2 to NO; measurement of NO and NO x (=NO+NO 2 ) in separate channels

CO

Non-dispersive infrared absorption; Reference: (a) cell with N 2 ; measurement of IR absorption with (b) ambient air after removal of CO; specific detector against reference cell (c) optical removal of CO absorption (gas filter correlation)

O3

UV absorption; low-pressure Hg lamp Reference: ambient air after removal as radiation source (253.7 nm); of ozone (e.g., Cu/MnO 2 ) registration of UV absorption in accordance with Lambert-Beer’s law; detector: vacuum photodiode, photosensitive valve

O3

Chemiluminescence; reaction of O 3 with ethene to formaldehyde; detection of chemiluminescence radiation with photomultiplier

Good selectivity; ethylene necessary as reagent gas

It should be emphasized here that all automatic measurement procedures based on chemical-physical principles must be calibrated using (manual) reference procedures. Since automatic equipment in measurement networks often runs for extended periods of time (e.g., several weeks) without direct human supervision, it is indispensable that their correct functioning is regularly and automatically checked. This generally is done using zero and test gases that can be produced by several methods (preparation of ambient air; pressurized gas cylinders; permeation; diffusion; static and dynamic dilution). Measurement procedures for dust-forming air pollutants and its composition Among particulate air pollutants, dustfall and suspended particulate matter (SPM) are differentiated. Dustfall consists of larger particles, which sink to the ground because of their size and thickness. SPM includes the particle fraction that is dispersed in the atmosphere in a quasi-stable and quasi-homogenous manner and therefore remains suspended for a certain time. Measurement of suspended particulate matter and metallic compounds in SPM

As is the case with measurements of gaseous air pollutants, continuous and discontinuous measurement procedures for SPM can be differentiated. As a rule, SPM is first separated on glass fibre or membrane filters. It follows a gravimetric or radiometric determination. Depending on the sampling, a distinction can be made between a procedure to measure the total SPM without fractionation according to the size of the particles and a fractionation procedure to measure the fine dust. The advantages and disadvantages of fractionated suspended dust measurements are disputed internationally. In Germany, for example, all threshold limits and assessment standards are based on total suspended particulates. This means that, for the most part, only total SPM measurements are performed. In the United States, on the contrary, the so-called PM-10 procedure (particulate matter ≤ 10mm) is very common. In this procedure, only particles with an aerodynamic diameter up to 10 mm are included (50 per cent inclusion portion), which are inhalable and can enter the lungs. The plan is to introduce the PM-10 procedure into the European Union as a reference procedure. The cost for fractionated SPM measurements is considerably higher than for measuring total suspended dust, because the measuring devices must be fitted with special, expensively constructed sampling heads that require costly maintenance. Table 55.5 contains details on the most important SPM measurement procedures. Table 55.5 Measurement procedures for suspended particulate matter (SPM) Procedure

Measuring principle

Comments

Small filter device

Non-fractionated sampling; air flow rate 2.7–2.8 m3 /h; filter diameter 50 mm; gravimetric analysis

Easy handling; control clock; device operable with PM-10 preseparator

LIB device

Non-fractionated sampling; air flow rate 15-16 m3 /h; filter diameter 120 mm; gravimetric analysis

Separation of large dust quantities; advantageous for analysis of dust components; control clock

High-Volume-Sampler Inclusion of particles up to approx. 30 µm diameter; air flow rate approx. 100 m3 /h; filter diameter 257 mm; gravimetric analysis

Separation of large dust quantities, advantageous for analysis of dust components; relatively high noise level

FH 62 I

Continuous, radiometric dust measuring device; nonfractionating sampling; air flow rate 1 or 3 m3 /h; registration of dust mass separated on a filter band by measuring attenuation of -radiation (krypton 85) in passage through exposed filter (ionization chamber)

Gravimetric calibration by dusting of single filters; device also operable with PM-10 preseparator

BETA dust meter F 703

Continuous, radiometric dust measuring device; nonfractionated sampling; air flow rate 3 m3 /h; registration of dust mass separated on a filter band by measuring attenuation of radiation (carbon 14) in passage through exposed filter (Geiger Müller counter tube)

Gravimetric calibration by dusting of single filters; device also operable with PM-10 preseparator

TEOM 1400

Continuous dust measuring Relationship between frequency device; non-fractionated lowering and dust mass must be sampling; air flow rate 1 m3 /h; established through calibration dust collected on a filter, which is part of a self-resonating, vibrating system, in side stream (3 l/min); registration of the frequency lowering by increased dust load on the filter

Recently, automatic filter changers have also been developed that hold a larger number of filters and supply them to the sampler, one after another, at timed intervals. The exposed filters are stored in a magazine. The detection limits for filter procedures lie between 5 and 10 µg/m3 of dust, as a rule. Finally, the black smoke procedure for SPM measurements has to be mentioned. Coming from Britain, it has been incorporated into EU guidelines for SO 2 and suspended dust. In this procedure, the blackening of the coated filter is measured with a reflex photometer after the sampling. The black smoke values that are thus photometrically obtained are converted into gravimetric units (µg/m3 ) with the help of a calibration curve. Since this calibration function depends to a high degree on the composition of the dust, especially its soot content, the conversion into gravimetric units is problematic. Today, metal compounds are often routinely determined in suspended dust immission samples. In general, the collection of the suspended dust on filters is followed by a chemical dissolution of the separated dusts, since the most common final analytical steps presuppose converting the metallic and metalloid compounds in an aqueous solution. In practice, the most important methods by far are atom absorption spectroscopy (AAS) and spectroscopy with plasma excitation (ICP-OES). Other procedures for determining metallic compounds in suspended dust are x-ray fluorescence analysis, polarography and neutron activation analysis. Although metallic compounds have been measured for more than a decade now as a component of SPM in outside air at certain measurement sites, important unanswered questions remain. Thus the conventional sampling by separating the suspended dust on filters assumes that the separation of the heavy metal compounds on the filter is complete. However, earlier indications have been found in the literature questioning this. The results are very heterogeneous. A further problem lies in the fact that different compound forms, or single compounds of the respective elements, cannot be distinguished in the analysis of metallic compounds in suspended dust using the conventional measurement procedures. While in many cases adequate total determinations can be made, a more thorough differentiation would be desirable with certain especially carcinogenic metals (As, Cd, Cr, Ni, Co, Be). There are often big differences in the carcinogenic effects of elements and their individual compounds (e.g., chromium compounds in oxidation levels III and VI - only those in level VI are carcinogenic). In such cases a specific measurement of the individual compounds (species analysis) would be desirable. Despite the significance of this problem, only first attempts at species analysis are being made in measurement technique. Measurement of dustfall and metallic compounds in dustfall

Two fundamentally different methods are used to collect dustfall: · sampling in collecting vessels · sampling on adhesive surfaces. A popular procedure for measuring dustfall (deposited dust) is the so-called Bergerhoff procedure. In this procedure the entire atmospheric precipitation (dry and wet depositions) is collected over 30± 2 days in vessels about 1.5 to 2.0 metres above the ground (bulk deposition). Then the collecting vessels are taken to the lab and prepared (filtered, water evaporated, dried, weighed). The result is calculated on the basis of the surface area of the collecting vessel and exposure time in grams per square meter and day (g/m2 d). The relative detection limit is 0.035 g/m2 d. Additional procedures for collecting dustfall include the Liesegang-Löbner device and methods which collect the deposited dust on adhesive foils. All measurement results for dustfall are relative values that depend on the apparatus used, as the dust separation is influenced by the flow conditions at the device and other parameters. The differences in the measurement values obtained with the different procedures can reach 50 per cent. Also important is the composition of the deposited dust, such as the content of lead, cadmium and other metallic compounds. The analytical procedures used for this are basically the same as those used for suspended dust. Measuring special materials in dust form

Special materials in dust form include asbestos and soot. Collecting fibres as air pollutants is important since asbestos has been classified as a confirmed carcinogenic material. Fibres with a diameter of D ≤ 3mm and a length of L ≥ 5mm, where L:D ≥ 3, are considered carcinogenic. Measurement procedures for fibrous materials consist of counting, under the microscope, fibres that have been separated on filters. Only electron microscopic procedures can be considered for outside air measurements. The fibres are separated on gold-coated porous filters. Prior to assessment in an electron scan microscope, the sample is freed of organic substances through plasma incineration right on the filter. The fibres are counted on part of the filter surface, randomly chosen and classified by geometry and type of fibre. With the help of energy dispersive x-ray analysis (EDXA), asbestos fibres, calcium sulphate fibres and other inorganic fibres can be differentiated on the basis of elemental composition. The entire procedure is extremely expensive and requires the greatest care to achieve reliable results. Soot in the form of particles emitted by diesel motors has become relevant since diesel soot was also classified as carcinogenic. Because of its changing and complex composition and because of the fact that various constituents are also emitted from other sources, there is no measurement procedure specific to diesel soot. Nevertheless, in order to say something concrete about the concentrations in ambient air, soot is conventionally defined as elemental carbon, as a part of total carbon. It is measured after sampling and an extraction step and/or thermal desorption. Determination of the carbon content ensues through burning in an oxygen stream and coulometric titration or non-dispersive IR detection of the carbon dioxide formed in the process. The so-called aethalometer and the photoelectric aerosol sensor are also used for measuring soot, in principle.

Measuring Wet Depositions Together with dry deposition, wet deposition in rain, snow, fog and dew constitute the most important means by which harmful materials enter the ground, water or plant surfaces from the air. In order to clearly distinguish the wet deposition in rain and snow (fog and dew present special problems) from the measurement of total deposition (bulk deposition, see section “Measurement of dustfall and metallic compounds” above) and dry deposition, rain catchers, whose collection opening is covered when there is no rain (wet-only sampler), are used for sampling. With rain sensors, which mostly work on the principle of conductivity changes, the cover is opened when it starts to rain and closed again when the rain stops. The samples are transferred through a funnel (open area approx. 500 cm2 and more) into a darkened and if possible insulated collection container (of glass or polyethylene for inorganic components only). In general, analysing the collected water for inorganic components can be done without sample preparation. The water should be centrifuged or filtered if it is visibly cloudy. The conductivity, pH value and important anions (NO 3 – , SO 4 2– , Cl– ) and cations (Ca2+, K +, Mg2+, Na+, NH 4 + and so on) are routinely measured. Unstable trace compounds and intermediate states like H 2 O 2 or HSO 3 – are also measured for research purposes. For analysis, procedures are used that are generally available for aqueous solutions such as conductometry for conductivity, electrodes for pH values, atom adsorption spectroscopy for cations (see section “Measuring special materials in dust form”, above) and, increasingly, ion exchange chromatography with conductivity detection for anions. Organic compounds are extracted from rain water with, for example, dichloromethane, or blown out with argon and adsorbed with Tenax tubes (only highly volatile materials). The materials are then subjected to a gas chromatographic analysis (see “Measurement procedures for organic air pollutants”, below). Dry deposition correlates directly with ambient air concentrations. The concentration differences of airborne harmful materials in rain, however, are relatively small, so that for measuring wet deposition, wide-mesh measuring networks are adequate. Examples include the European EMEP measurement network, in which the entry of sulphate and nitrate ions, certain cations and precipitation pH values are collected in approximately 90 stations. There are also extensive measurement networks in North America.

Optical Long-Distance Measurement Procedures Whereas the procedures described up to now catch air pollution at one point, optical long-distance measuring procedures measure in an integrated manner over light paths of several kilometres or they determine the spatial distribution. They use the absorption characteristics of gases in the atmosphere in the UV, visible or IR spectral range and are based on the LambertBeer law, according to which the product of light path and concentration are proportional to the measured extinction. If the sender and receiver of the measuring installation change the wavelength, several components can be measured in parallel or sequentially with one device. In practice, the measurement systems identified in table 55.6 play the biggest role. Table 55.6 Long-distance measurement procedures Procedure

Application

Advantages, disadvantages

Fourier transform IR range (approx. 700–3,000 cm– infrared spectroscopy 1 ), several hundred metres light (FTIR) path. Monitors diffuse surface sources (optical fence), measures individual organic compounds

+ Multi-component system + dl a few ppb – Expensive

Differential optical Light path to several km; measures + Easy to handle absorption SO 2 , NO 2 , benzene, HNO 3 ; + Successful performance test spectrometry (DOAS) monitors linear and surface + Multi-component system – High dl under conditions of sources, used in measuring poor visibility (e.g.fog) networks Long-distance laser absorption spectroscopy (TDLAS)

Research area, in low-pressure cuvettes for OH-

+ High sensitivity (to ppt) + Measures unstable trace compounds – High cost – Difficult to handle

Differential Absorption LIDAR (DIAL)

Monitors surface sources, large surface immission measurements

+ Measurements of spatial distribution + Measures inaccessible places (e.g., smoke gas trails) – Expensive – Limited component spectrum (SO 2 , O 3 , NO 2 )

LIDAR = Light detection and ranging; DIAL = differential absorption LIDAR.

Measurement Procedures for Organic Air Pollutants The measurement of air pollution containing organic components is complicated primarily by the range of materials in this class of compounds. Several hundred individual components with very different toxicological, chemical and physical characteristics are covered under the general title “organic air pollutants” in the emissions registers and air quality plans of congested areas. Especially due to the great differences in potential impact, collecting relevant individual components has more and more taken the place of previously used summation procedures (e.g., Flame Ionization Detector, total carbon procedure), the results of which cannot be assessed toxicologically. The FID method, however, has retained a certain significance in connection with a short separation column to separate out methane, which is photochemically not very reactive, and for collecting the precursor volatile organic compounds (VOC) for the formation of photo-oxidants. The frequent necessity of separating the complex mixtures of the organic compounds into relevant individual components makes measuring it virtually an exercise in applied chromatography. Chromatographic procedures are the methods of choice when the organic compounds are sufficiently stable, thermally and chemically. For organic materials with reactive functional groups, separate procedures that use the functional groups’ physical characteristics or chemical reactions for detection continue to hold their ground. Examples include using amines to convert aldehydes to hydrazones, with subsequent photometric measurement; derivatization with 2,4-dinitrophenylhydrazine and separation of the 2,4hydrazone that is formed; or forming azo-dyes with p-nitroaniline for detecting phenols and cresols. Among chromatographic procedures, gas chromatography (GC) and high-pressure liquid chromatography (HPLC) are most frequently employed for separating the often complex mixtures. For gas chromatography, separation columns with very narrow diameters (approx. 0.2 to 0.3 mm, and approx. 30 to 100 m long), so-called high-resolution capillary columns (HRGC), are almost exclusively utilized today. A series of detectors are available for finding the individual components after the separation column, such as the above-mentioned FID, the ECD (electron capture detector, specifically for electrophilic substitutes such as halogen), the PID (photo-ionization detector, which is especially sensitive to aromatic hydrocarbons and other -electron systems), and the NPD (thermo-ionic detector specifically for nitrogen and phosphorus compounds). The HPLC uses special through-flow detectors which, for example, are designed as the through-flow cuvette of a UV spectrometer. Especially effective, but also especially expensive, is the use of a mass spectrometer as a detector. Really certain identification, especially with unknown mixtures of compounds, is often possible only through the mass spectrum of the organic compound. The qualitative information of the so-called retention time (time the material remains in the column) that is contained in the chromatogram with conventional detectors is supplemented with the specific detection of the individual components by mass fragmentograms with high detection sensitivity. Sampling must be considered before the actual analysis. The choice of sampling method is determined primarily by volatility, but also by expected concentration range, polarity and chemical stability. Furthermore, with non-volatile compounds, a choice must be made between concentration and deposition measurements. Table 55.7 provides an overview of common procedures in air monitoring for active enrichment and chromatographic analysis of organic compounds, with examples of applications. Table 55.7 Overview of common chromatographic air quality measurement procedures of organic compounds (with examples of applications) Material group

Concentration Sampling, preparation range

Hydrocarbons C1 -C9

µg/m3

Gas mice (rapid sampling), gas-tight syringe, cold trapping in front of capillary column (focusing), thermal desorption

GC/FID

Low-boiling hydrocarbons, highly volatile halogenated hydrocarbons

ng/m3 -µg/m3

Evacuated, passivated high-grade steel cylinder (also for clean air measurements) Sampling dispatch through gas loops, cold trapping, thermal desorption

GC/FID/ECD/PID

Organic compounds in boiling point range C6 -C30 (60-350 °C)

µg/m3

Adsorption on activated carbon, (a) desorption with CS2 (b) desorption with solvents (c) headspace analysis

Capillary GC/FID

Organic compounds in boiling point range 20-300 °C

ng/m3 -µg/m3

Adsorption on organic polymers (e.g., Tenax) or Capillary molecular carbon sieve (carbopack), thermal GC/FID/ECD/MS desorption with cold trapping in front of capillary column (focusing) or solvent extraction

Modification for lowboiling compounds (from -120 °C)

ng/m3 -µg/m3

Adsorption on cooled polymers (e.g. thermogradient tube), cooled to -120 °C, use of carbopack

Capillary GC/FID/ECD/MS

High boiling organic compounds partially attached to particles (esp. PAH, PCB, PCDD/PCDF), high sampling volume

fg/m3 -ng/m3

Sampling on filters (e.g., small filter device or high volume sampler) with subsequent polyurethane cartridges for gaseous portion, solvent desorption of filter and polyurethane, various purification and preparatory steps, for PAH also sublimation

Capillary GCGCMS (PCDD/PCDF), capillary GC-FID or MS (PAH), HPLC fluorescence detector (PAH)

High boiling organic fg/m3 -ng/m3 compounds, esp. PCDD, PCDF, PBDD, PBDF, low sampling volume

Adsorption on organic polymers (e.g., polyurethane foam cylinder) with prior filters (e.g., glass fibre) or inorg. adsorp. (e.g., silica gel), extraction with solvents, various purification and preparatory steps, (including multicolumn chromatography), derivatizing for chlorophenols

HRGC/ECD

High boiling organic compounds bound to particles, e.g., components of organic aerosols, deposition samples

Separation of aerosols on glass fibre filters (e.g., high or low volume sampler) or dust collection on standardized surfaces, extraction with solvents (for deposition also of remaining filtered water), various purification and preparation steps

HRGC/MS HPLC (for PAHs)

ng/m3 ng-µg/g aerosol pg-ng/m2 day

Final analytical step

GC = gas chromatography; GCMS = GC/mass spectroscopy; FID = flame ionization detector HRGC/ECD = high resolution GC/ECD; ECD = electron capture detector HPLC = high performance liquid chromatography. PID = photo-ionization detector. Deposition measurements of organic compounds with low volatility (e.g., dibenzodioxins and dibenzofurans (PCDD/PCDF), polycyclic aromatic hydrocarbons (PAH)) are gaining in importance from the perspective of environmental impact. Since food is the main source of human intake, airborne material transferred onto food plants is of great significance. There is, however, evidence that material transfer by way of particulate deposition is less important than dry deposition of quasi-gaseous compounds. For measuring total deposition, standardized devices for dust precipitation are used (e.g., Bergerhoff procedure), which have been slightly modified by darkening as a protection against the entry of strong light. Important technical measurement problems, such as the resuspension of already separated particles, evaporation or possible photolytic decomposition, are now being systematically researched in order to improve the less-than-optimal sampling procedures for organic compounds.

Olfactometric Investigations Olfactometric immission investigations are used in monitoring to quantify odour complaints and to determine baseline pollution in licensing procedures. They serve primarily to assess whether existing or anticipated odours should be classified as significant. In principle, three methodological approaches can be differentiated: · measurement of the emission concentration (number of odour units) with an olfactometer and subsequent dispersion modelling · measurement of individual components (e.g., NH 3 ) or mixtures of compounds (e.g., gas chromatography of gases from landfills), if these adequately characterize the odour · odour determinations by means of inspections. The first possibility combines emission measurement with modelling and, strictly speaking, cannot be classified under the term air quality monitoring. In the third method, the human nose is used as the detector with significantly reduced precision as compared to physical-chemical methods. Details of inspections, measurement plans and assessing the results are contained, for example, in the environmental protection regulations of some German states.

Screening Measurement Procedures Simplified measurement procedures are sometimes used for preparatory studies (screening). Examples include passive samplers, test tubes and biological procedures. With passive (diffusive) samplers, the material to be tested is collected with freely flowing processes such as diffusion, permeation or adsorption in simple forms of collectors (tubes, plaques) and enriched in impregnated filters, meshes or other adsorption media. So-called active sampling (sucking the sample air through a pump) thus does not occur. The enriched quantity of material, analytically determined according to definite exposure time, is converted into concentration units on the basis of physical laws (e.g., of diffusion) with the help of collection time and the collector’s geometric parameters. The methodology stems from the field of occupational health (personal sampling) and indoor air measurement, but it is increasingly being used for ambient air pollutant concentration measurements. An overview can be found in Brown 1993. Detector tubes are often used for sampling and quick preparatory analysis of gases. A certain test air volume is sucked through a glass tube that is filled with an adsorptive reagent that corresponds with the test objective. The contents of the tube change colour depending on the concentration of the material to be determined that is present in the test air. Small testing tubes are often used in the field of workplace monitoring or as a quick procedure in cases of accidents, such as fires. They are not used for routine ambient air pollutant concentration measurements due to the generally too high detection limits and too limited selectivity. Detector testing tubes are available for numerous materials in various concentration ranges. Among the biological procedures, two methods have become accepted in routine monitoring. With the standardized lichen exposure procedure, the mortality rate of the lichen is determined over the exposure time of 300 days. In another procedure, French pasture grass is exposed for 14±1 days. Then the amount of growth is determined. Both procedures serve as summary determinations of air pollutant concentration effects.

Air Quality Monitoring Networks Around the world, the most varied types of air quality networks are utilized. A distinction should be drawn between measurement networks, consisting of automatic, computer-controlled measuring stations (measurement containers), and virtual measurement networks, which only define the measurement locations for various types of air pollutant concentration measurements in the form of a preset grid. Tasks and conceptions of measurement networks were discussed above. Continuous monitoring networks Continuously operating measurement networks are based on automatic measuring stations, and serve primarily for air quality monitoring of urban areas. Measured are air pollutants such as sulphur dioxide (SO 2 ), dust, nitrogen monoxide (NO), nitrogen dioxide (NO 2 ), carbon monoxide (CO), ozone (O 3 ), and to an extent also the sum of the hydrocarbons (free methane, Cn H m) or individual organic components (e.g., benzene, toluene, xylenes). In addition, depending on need, meteorological parameters such as wind direction, wind speed, air temperature, relative humidity, precipitation, global radiation or radiation balance are included. The measuring equipment operated in measurement stations generally consists of an analyser, a calibration unit, and control and steering electronics, which monitors the whole measuring equipment and contains a standardized interface for data collection. In addition to the measurement values, the measuring equipment supplies so-called status signals on errors and the operating status. The calibration of the devices is automatically checked by computer at regular intervals. As a rule, the measurement stations are connected with fixed data lines, dial connections or other data transfer systems to a computer (process computer, workstation or PC, depending on the scope of the system) in which the measurement results are entered, processed and displayed. The measurement network computers and, if necessary, specially trained personnel monitor continuously whether various threshold limits are exceeded. In this manner critical air quality situations can be recognized at any time. This is very important, especially for monitoring critical smog situations in winter and summer (photo-oxidants) and for current public information. Measurement networks for random sample measurements Beyond the telemetric measurement network, other measuring systems for monitoring air quality are used to varying extents. Examples include (occasionally partially automated) measurement networks to determine: · dust deposition and its components · suspended dust (SPM) and its components · hydrocarbons and chlorinated hydrocarbons · low volatile organic materials (dioxins, furans, polychlorinated biphenyls). A series of substances measured in this manner have been classified as carcinogens, such as cadmium compounds, PAHs or benzene. Monitoring them is therefore particularly important. To provide an example of a comprehensive programme, table 55.8 summarizes the air quality monitoring that is systematically conducted in North Rhine-Westphalia, which with 18 million inhabitants is the most populous state in Germany. Table 55.8 Systematic air quality monitoring in North-Rhine-Westphalia (Germany) Continuous measuring system

Partially automated measuring system

Discontinuous measuring system/Multi-component measurements

Sulphur dioxide Nitrogen monoxide Nitrogen dioxide Carbon monoxide Suspended particulate matter (SPM) Ozone Hydrocarbons Wind direction Wind speed Air temperature Air pressure Relative humidity Radiation balance Precipitation

SPM composition: Lead Cadmium Nickel Copper Iron Arsenic Beryllium Benzo[a]pyrene Benzo[e]pyrene Benzo[a]anthracene Dibenzo[a,h]anthracene Benzo[ghi)perylene Coronene

Benzene and other hydrocarbons Halogenated hydrocarbons Dust deposition and material composition Soot Polychlorinated biphenyls Polyhalogenated dibenzodioxins and dibenzofurans (PCDD/PCDF)

AIR POLLUTION CONTROL John Elias

Management of Air Pollution The objective of a manager of an air pollution control system is to ensure that excessive concentrations of air pollutants do not reach a susceptible target. Targets could include people, plants, animals and materials. In all cases we should be concerned with the most sensitive of each of these groups. Air pollutants could include gases, vapours, aerosols and, in some cases, biohazardous materials. A well designed system will prevent a target from receiving a harmful concentration of a pollutant. Most air pollution control systems involve a combination of several control techniques, usually a combination of technological controls and administrative controls, and in larger or more complex sources there may be more than one type of technological control. Ideally, the selection of the appropriate controls will be made in the context of the problem to be solved. · What is emitted, in what concentration? · What are the targets? What is the most susceptible target? · What are acceptable short-term exposure levels? · What are acceptable long-term exposure levels? · What combination of controls must be selected to ensure that the short-term and long-term exposure levels are not exceeded? Table 55.9 describes the steps in this process. Table 55.9 Steps in selecting pollution controls Step 1: Define emissions.

The first part is to determine what will be released from the stack. All potentially harmful emissions must be listed. The second part is to estimate how much of each material will be released. Without this information, the manager cannot begin to design a control programme.

Step 2: Define target groups.

All susceptible targets should be identified. This includes people, animals, plants and materials. In each case, the most susceptible member of each group must be identified. For example, asthmatics near a plant that emits isocyanates.

Step 3: Determine acceptable exposure levels.*

An acceptable level of exposure for the most sensitive target group must be established. If the pollutant is a material that has cumulative effects, such as a carcinogen, then long-term exposure levels (annual) must be set. If the pollutant has short-term effects, such as an irritant or a sensitizer, a short-term or perhaps peak exposure level must be set.**

Step 4: Select controls.

Step 1 identifies the emissions, and Step 3 determines the acceptable level. In this step, each pollutant is checked to ensure that it does not exceed the acceptable level. If it exceeds the acceptable level, additional controls must be added, and the exposure levels checked again. This process continues until all exposures are at or below the acceptable level. Dispersion modelling can be used to estimate exposures for new plants or to test alternative solutions for existing facilities.

* When setting exposure levels in Step 3, it must be remembered that these exposures are total exposures, not just those from the plant. Once the acceptable level has been established, background levels, and contributions from other plants must be subtracted to determine the maximum amount that the plant can emit without exceeding the acceptable exposure level. If this is not done, and three plants are allowed to emit at the maximum, the target groups will be exposed to three times the acceptable level. ** Some materials such as carcinogens do not have a threshold below which no harmful effects will occur. Therefore, as long as some of the material is allowed to escape to the environment, there will be some risk to the target populations. In this case a no effect level cannot be set (other than zero). Instead, an acceptable level of risk must be established. Usually this is set in the range of 1 adverse outcome in 100,000 to 1,000,000 exposed persons. Some jurisdictions have done some of the work by setting standards based on the maximum concentration of a contaminant that a susceptible target can receive. With this type of standard, the manager does not have to carry out Steps 2 and 3, since the regulating agency has already done this. Under this system, the manager must establish only the uncontrolled emission standards for each pollutant (Step 1), and then determine what controls are necessary to meet the standard (Step 4). By having air quality standards, regulators can measure individual exposures and thus determine whether anyone is exposed to potentially harmful levels. It is assumed that the standards set under these conditions are low enough to protect the most susceptible target group. This is not always a safe assumption. As shown in table 55.10, there can be a wide variation in common air quality standards. Air quality standards for sulphur dioxide range from 30 to 140 µg/m3 . For less commonly regulated materials this variation can be even larger (1.2 to 1,718 µg/m3 ), as shown in table 55.11 for benzene. This is not surprising given that economics can play as large a role in standard setting as does toxicology. If a standard is not set low enough to protect susceptible populations, no one is well served. Exposed populations have a feeling of false confidence, and can unknowingly be put at risk. The emitter may at first feel that they have benefited from a lenient standard, but if effects in the community require the company to redesign their controls, or install new controls, costs could be higher than doing it correctly the first time. Table 55.10 Range of air quality standards for a commonly controlled air contaminant (sulphur dioxide) Countries and territories

Long-term sulphur dioxide air quality standards (µg/m3 )

Australia

50

Canada

30

Finland

40

Germany

140

Hungary

70

Taiwan

133

Table 55.11 Range of air quality standards for a less commonly controlled air contaminant (benzene) City/State

24-hour air quality standard for benzene (µg/m3 )

Connecticut

53.4

Massachusetts

1.2

Michigan

2.4

North Carolina

2.1

Nevada

254

New York

1,718

Philadelphia

1,327

Virginia

300

The levels were standardized to an averaging time of 24 hours to assist in the comparisons. (Adapted from Calabrese and Kenyon 1991.) Sometimes this stepwise approach to selecting air pollution controls is short circuited, and the regulators and designers go directly to a “universal solution”. One such method is best available control technology (BACT). It is assumed that by using the best combination of scrubbers, filters and good work practices on an emission source, a level of emissions low enough to protect the most susceptible target group would be achieved. Frequently, the resulting emission level will be below the minimum required to protect the most susceptible targets. This way all unnecessary exposures should be eliminated. Examples of BACT are shown in table 55.12 . Table 55.12 Selected examples of best available control technology (BACT) showing the control method used and estimated efficiency Process

Pollutant

Control method

Estimated efficiency

Soil remediation

Hydrocarbons

Thermal oxidizer

99

Kraft pulp mill recovery boiler

Particulates

Electrostatic precipitator

99.68

Production of fumed Carbon monoxide silica

Good practice

50

Automobile painting Hydrocarbons

Oven afterburner

90

Electric arc furnace

Particulates

Baghouse

100

Petroleum refinery, catalytic cracking

Respirable particulates

Cyclone + Venturi scrubber

93

Medical incinerator

Hydrogen chloride

Wet scrubber + dry scrubber

97.5

Coal-fired boiler

Sulphur dioxide

Spray dryer + absorber

90

Waste disposal by dehydration and incineration

Particulates

Cyclone + condenser 95 + Venturi scrubber + wet scrubber

Asphalt plant

Hydrocarbons

Thermal oxidizer

99

BACT by itself does not ensure adequate control levels. Although this is the best control system based on gas cleaning controls and good operating practices, BACT may not be good enough if the source is a large plant, or if it is located next to a sensitive target. Best available control technology should be tested to ensure that it is indeed good enough. The resulting emission standards should be checked to determine whether or not they may still be harmful even with the best gas cleaning controls. If emission standards are still harmful, other basic controls, such as selecting safer processes or materials, or relocating in a less sensitive area, may have to be considered. Another “universal solution” that bypasses some of the steps is source performance standards. Many jurisdictions establish emission standards that cannot be exceeded. Emission standards are based on emissions at the source. Usually this works well, but like BACT they can be unreliable. The levels should be low enough to maintain the maximum emissions low enough to protect susceptible target populations from typical emissions. However, as with best available control technology, this may not be good enough to protect everyone where there are large emission sources or nearby susceptible populations. If this is the case, other procedures must be used to ensure the safety of all target groups. Both BACT and emission standards have a basic fault. They assume that if certain criteria are met at the plant, the target groups will be automatically protected. This is not necessarily so, but once such a system is passed into law, effects on the target become secondary to compliance with the law. BACT and source emission standards or design criteria should be used as minimum criteria for controls. If BACT or emission criteria will protect the susceptible targets, then they can be used as intended, otherwise other administrative controls must be used.

Control Measures Controls can be divided into two basic types of controls - technological and administrative. Technological controls are defined here as the hardware put on an emission source to reduce contaminants in the gas stream to a level that is acceptable to the community and that will protect the most sensitive target. Administrative controls are defined here as other control measures. Technological controls Gas cleaning systems are placed at the source, before the stack, to remove contaminants from the gas stream before releasing it to the environment. Table 55.13 shows a brief summary of the different classes of gas cleaning system. Table 55.13 Gas cleaning methods for removing harmful gases, vapours and particulates from industrial process emissions Control method

Examples

Description

Efficiency

Gases/Vapours







Condensation

Contact condensers Surface condensers

The vapour is cooled and condensed to a liquid. This is inefficient and is used as a preconditioner to other methods

80+% when concentration >2,000 ppm

Absorption

Wet scrubbers (packed or plate absorbers)

The gas or vapour is collected in a liquid.

82–95% when concentration 100 ppm

Adsorption

Carbon Alumina Silica gel Molecular sieve

The gas or vapour is collected on a solid.

90+% when concentration 1,000 ppm

Incineration

Flares Incinerator Catalytic incinerator

An organic gas or vapour is oxidized by heating it to a Not recommended when concentration high temperature and holding it at that temperature for 2,000 ppm

Particulates





Inertialseparators

Cyclones

Particle-laden gases are forced to change direction. 70–90% The inertia of the particle causes them to separate from the gas stream. This is inefficient and is used as a preconditioner to other methods.

Wet scrubbers

Venturi Wetted filter Tray or sieve scrubber

Liquid droplets (water) collect the particles by For 5 µm particles, 98.5% at 6.8 w.g.; impaction, interception and diffusion. The droplets and 99.99+% at 50 w.g. their particles are then separated from the gas stream. For 1 µm particles, 45% at 6.8 w.g.; 99.95 at 50 w.g.

Electrostatic precipitators

Plate-wire Flat-plate Tubular Wet

Electrical forces are used to move the particles out of the gas stream onto collection plates

95–99.5% for 0.2 µm particles 99.25–99.9+% for 10 µm particles

Filters

Baghouse

A porous fabric removes particulates from the gas stream. The porous dust cake that forms on the fabric then actually does the filtration.

99.9% for 0.2 µm particles 99.5% for 10 µm particles



The gas cleaner is part of a complex system consisting of hoods, ductwork, fans, cleaners and stacks. The design, performance and maintenance of each part affects the performance of all other parts, and the system as a whole. It should be noted that system efficiency varies widely for each type of cleaner, depending on its design, energy input and the characteristics of the gas stream and the contaminant. As a result, the sample efficiencies in table 55.13 are only approximations. The variation in efficiencies is demonstrated with wet scrubbers in table 55.13 . Wet scrubber collection efficiency goes from 98.5 per cent for 5 µm particles to 45 per cent for 1 µm particles at the same pressure drop across the scrubber (6.8 in. water gauge (w.g.)). For the same size particle, 1 µm, efficiency goes from 45 per cent efficiency at 6.8 w.g. to 99.95 at 50 w.g. As a result, gas cleaners must be matched to the specific gas stream in question. The use of generic devices is not recommended. Waste disposal

When selecting and designing gas cleaning systems, careful consideration must be given to the safe disposal of the collected material. As shown in table 55.14 , some processes produce large amounts of contaminants. If most of the contaminants are collected by the gas cleaning equipment there can be a hazardous waste disposal problem. Table 55.14 Sample uncontrolled emission rates for selected industrial processes Industrial source

Emission rate

100 ton electric furnace

257 tons/year particulates

1,500 MM BTU/hr oil/gas turbine

444 lb/hr SO 2

41.7 ton/hr incinerator

208 lb/hr NO x

100 trucks/day clear coat

3,795 lb/week organics

In some cases the wastes may contain valuable products that can be recycled, such as heavy metals from a smelter, or solvent from a painting line. The wastes can be used as a raw material for another industrial process - for example, sulphur dioxide collected as sulphuric acid can be used in the manufacture of fertilizers. Where the wastes cannot be recycled or reused, disposal may not be simple. Not only can the volume be a problem, but they may be hazardous themselves. For example, if the sulphuric acid captured from a boiler or smelter cannot be reused, it will have to be further treated to neutralize it before disposal. Dispersion

Dispersion can reduce the concentration of a pollutant at a target. However, it must be remembered that dispersion does not reduce the total amount of material leaving a plant. A tall stack only allows the plume to spread out and be diluted before it reaches ground level, where susceptible targets are likely to exist. If the pollutant is primarily a nuisance, such as an odour, dispersion may be acceptable. However if the material is persistent or cumulative, such as heavy metals, dilution may not be an answer to an air pollution problem. Dispersion should be used with caution. Local meteorological and ground surface conditions must be taken into consideration. For example, in colder climates, particularly with snow cover, there can be frequent temperature inversions that can trap pollutants close to the ground, resulting in unexpectedly high exposures. Similarly, if a plant is located in a valley, the plumes may move up and down the valley, or be blocked by surrounding hills so that they do not spread out and disperse as expected. Administrative controls In addition to the technological systems, there is another group of controls that must be considered in the overall design of an air pollution control system. For the large part, they come from the basic tools of industrial hygiene. Substitution

One of the preferred occupational hygiene methods for controlling environmental hazards in the workplace is to substitute a safer material or process. If a safer process or material can be used, and harmful emissions avoided, the type or efficacy of controls becomes academic. It is better to avoid the problem than it is to try to correct a bad first decision. Examples of substitution include the use of cleaner fuels, covers for bulk storage and reduced temperatures in dryers. This applies to minor purchases as well as the major design criteria for the plant. If only environmentally safe products or processes are purchased, there will be no risk to the environment, indoors or out. If the wrong purchase is made, the remainder of the programme consists of trying to compensate for that first decision. If a low-cost but hazardous product or process is purchased it may need special handling procedures and equipment, and special disposal methods. As a result, the low-cost item may have only a low purchase price, but a high price to use and dispose of it. Perhaps a safer but more expensive material or process would have been less costly in the long run. Local ventilation

Controls are required for all the identified problems that cannot be avoided by substituting safer materials or methods. Emissions start at the individual worksite, not the stack. A ventilation system that captures and controls emissions at the source will help protect the community if it is properly designed. The hoods and ducts of the ventilation system are part of the total air pollution control system. A local ventilation system is preferred. It does not dilute the contaminants, and provides a concentrated gas stream that is easier to clean before release to the environment. Gas cleaning equipment is more efficient when cleaning air with higher concentrations of contaminants. For example, a capture hood over the pouring spout of a metal furnace will prevent contaminants from getting into the environment, and deliver the fumes to the gas cleaning system. In table 55.13 it can be seen that cleaning efficiencies for absorption and adsorption cleaners increase with the concentration of the contaminant, and condensation cleaners are not recommended for low levels (