Introduction to Air Pollution [PDF]

In the press, air pollution releases from accidents, transportation sources, plants, waste incineration facilities and n

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Introduction to Air Pollution View Slides on Introduction Part 1 & Part 2 In this chapter you will learn: What is air pollution and what are the various factors contributing to air pollution? History of air pollution. What is an air pollutant and what are the various common air pollutants? What are the various sources of air pollutants? What is an emission inventory? Various internet links to know about air pollution. As a result of our awareness toward environment and the allied issues, we are concerned about pollution problems. These concerns range from odor problem to destruction of ozone layer in our atmosphere. The medium for pollution may be air, water and land. Some of the questions which might come to your mind while thinking about pollution are: Are we doing something about solving these problems? Do we know enough about the conditions under which a pollution episode occurs? What are the regulations? How to control emissions? This course is an attempt to answer such questions. Air pollution worldwide is a growing threat to human health and the natural environment. Air pollution may be described as contamination of the atmosphere by gaseous, liquid, or solid wastes or by-products that can endanger human health and welfare of plants and animals, attack materials, reduce visibility (To read about how Haze caused by air pollution can affect visibility Click Here), or produce undesirable odors. Although some pollutants are released by natural sources like volcanoes, coniferous forests, and hot springs, the effect of this pollution is very small when compared to that caused by emissions from industrial sources, power and heat generation, waste disposal, and the operation of internal combustion engines. Fuel combustion is the largest contributor to air pollutant emissions, caused by man, with stationary and mobile sources equally responsible. The air pollution problem is encountered outdoor as well as indoor. To read more about the Outdoor Air Pollution ( Click Here )and to read more about the Indoor Air Pollution Click Here. The indoor air pollution came to our attention during 80's while outdoor air pollution has been around for some time. The major pollutants which contribute to indoor air pollution include radon, volatile organic compounds, formaldehyde, biological contaminants, and combustion by-products such as carbon monoxide, carbon dioxide, sulfur dioxide, hydrocarbons, nitrogen dioxides, and particulate (Read here in EPA page). The major pollutants which contribute to outdoor air pollution are sulfur dioxide, carbon monoxide, nitrogen oxides, ozone, total suspended particulate matter, lead, carbon dioxide, and toxic pollutants. There are several reasons to worry about air pollution. Some are: Air pollution affects every one of us. Air pollution can cause health problems and, may be, death. Air pollution reduces crop yields and affects animal life. Air pollution can contaminate soil and corrode materials. The problems of air pollution in Los Angles, New York city and Chicago, U.S. during the fifties drew attention of regulators in the United States. Conventional pollutants due to auto emissions and smoke stacks were the major thrusts of air pollution during the sixties and seventies. Invisible emissions of toxic pollutants were recognized in the late seventies. The following graph indicates the percent of total suspended particulate based on particle size distribution of California source emissions, in 1986. These emissions increased manifolds since then, making air pollution monitoring, prevention and control inevitable.

Source : US EPA Document (http://www.epa.gov/nceawww1/pdfs/0671ch05.pdf ) The attention also turned to acid rain as a trans-boundary problem following the observations of dying forests in Germany and lake acidification in Scandinavian countries. In early eighties scientists observed a slow down in growth of red spruce in the mountain areas of north-eastern US during the sixties as a result of acid rain. Other problems such as emissions from small sources, area sources, fugitive emissions and carbon dioxide production from combustion came to light as potential pollution problems. Global warming is another international issue being debated by scientists and politicians. The rise in global average temperatures is being related to the increase in concentration of carbon dioxide and green house gases in earth's atmosphere. This is due to burning of fossil fuels, the production of chlorofluorocarbons, deforestation and other forces. The pollution problem in a country depends on business cycles. In the US, business is moving from manufacturing base to service industry. This has also created a need to look at the pollution due to recreational type activities.

AIR POLLUTION ACCIDENTS AND EPISODES The public concern is also based on news stories on air pollution accidents and episodes reported by the media. It is important for us to look at these pollution episodes. During a 3 day fog in 1930, 60 people died in Meuse Valley, Belgium, while 592 people died in Manchester, England in 1931 during a 9 day fog. The 1948 plant emissions and atmospheric conditions in Donora, Penn. USA caused a 4 day fog and 7000 people were reported sick and 20 people died. The 4 day fog of 1952 in London, England resulted in 4000 deaths and concentration levels were several times higher than the current air quality standards in the United States. To read the September, 1998, EPA announcement of the final rule to protect Eastern US from Smog, Click Here. A four hour release of methyl isocyanate at a chemical plant owned by Union Carbide in 1984 killed 2800 people in Bhopal, India and opened the eyes of government agencies and public around the world. This Bhopal gas tragedy can be read in a nutshell in the following table: Accident

Bhopal Gas Tragedy

Location

Bhopal, Madhya Pradesh, India

Year

1984

Pollutant

Methyl isocyanate

Physical Properties of Methyl Isocyanate

Methyl isocyanate is a colorless liquid that has a sharp odor. The odor threshold for methyl isocyanate is 2.1 ppm. The chemical formula for methyl isocyanate is C2 H 3 NO, and the molecular weight is 57.05 g/mol. The vapor pressure for methyl isocyanate is 348 mm Hg at 20 C.

Pathway

Inhalation

# of Deaths

2000

Cause of Death

Primarily : Pulmonary edema Secondary : Respiratory infections such as bronchitis and bronchial pneumonia.

Adverse health effects on

More than 170, 000 survivors

Reproductive adverse effects

Leucorrhea, pelvic inflammatory disease, excessive menstrual bleeding, and suppression of lactation and also stillbirths and spontaneous abortions

This table has been compiled with the data from this EPA web site. As a result new regulations and preventive measures were introduced for air toxins. Public appreciation of radio nuclide emissions increased after the accidents at Three Mile Island, U.S.A. and Chernobyl, in ester while Russia. The accident at Chernobyl in 1986 caused 32 deaths and 135,000 people and their livestock had to be removed from the region for several months. The radiation exposure could increase the cancer death rates in USSR and Europe in coming years. The agricultural activities near the plant have been halted. Click the following link to know the response from EPA regarding Chernobyl accident. Click Here. In the press, air pollution releases from accidents, transportation sources, plants, waste incineration facilities and natural sources receive coverage on a regular basis. The cost of air pollution could easily add up for a nation as well as for an industrial complex. If enough is not done to prevent air pollution problems, it is possible that future generations may see forests on postcards and calendars. For additional information on air pollution episodes in general and some particular episodes in UK during summer, winter and other times, can be obtained from http://www.aeat.co.uk/netcen/airqual/welcome.html A detailed list of major accidents involving hazardous substances is available on the web site of the United Nations Environmental Program; http://www.unepie.org/.

WHAT IS AN AIR POLLUTANT? In our daily life we come across many airborne chemicals. Are all these chemicals termed as air pollutants? This question leads one to define an air pollutant. A contaminant that affects human life, plant life, animal life and property or a contaminant which interferes with the enjoyment of life and property could be termed as an air pollutant. Different countries have different legal definitions for an air pollutant. However, the above definition gives us an idea. The Ohio EPA provides the definition of "Air pollutant" or "air contaminant" as particulate matter, dust, fumes, gas, mist, smoke, vapor or odorous substances, or any combination there of. An air pollutant can be defined based on the concentration of chemical present in environment. The composition of clean air (shown in the following figure) is used as a bench mark. If the concentration of a chemical is above the concentration of chemical present in air, it is then termed as an air pollutant.

There are two basic physical forms of air pollutants. The first is gaseous form. For example, sulfur dioxide, ozone and hydro-carbon vapors exist in the form of a gas. The gases lack definite volume and shape and the molecules are widely separated. The second form of air pollution is particulate matter such as smoke, dust, fly ash and mists. The pollutants are also classified as primary pollutants and secondary pollutants. The primary pollutants remain in the same chemical form as they are released from a source directly into the atmosphere. For example: sulfur dioxide and hydrocarbons. The secondary pollutants are a result of chemical reaction among two or more pollutants. The production of PAN (Peroxyacetyl Nitrate) during photochemical reactions is an example of secondary pollutant.

UNITS FOR THE MEASUREMENT OF CONCENTRATION OF AIR POLLUTANTS There are two units of measurement. They are as follows: µg/m3 ppm (parts per million) One ppm is 1 part in 1,000,000 Density = (Molecular weight of pollutant in gm/mol) / (Volume in l/mol) Concentration in ppm = Concentration in mg/m3 / Density in mg/ml At 00 C and at a pressure of 76 cm of Hg, volume of the air is 22.41 l/mol To obtain volume at any temperature use gas law which is given by P1 V 1 /T1 = P2 V 2 /T2

COMMON AIR POLLUTANTS Let us now turn our attention to common air pollutants. EPA has set national air quality standards for six common pollutants (also referred to as "criteria" pollutants): i. sulfur oxides, ii. carbon monoxide, iii. nitrogen dioxide, iv. ozone, v. total suspended particulate matter, and vi. lead. The other class of air pollutants which are of concern are hazardous and toxic air pollutants. The later area is rapidly expanding because of public pressure, concern over adverse health effects and accidental environmental damage. In this section seven criteria pollutants and some other pollutants are discussed. To view Areas where air pollution levels persistently exceed national air quality standards. Locations of air pollution monitoring sites, operated by state and local agencies. The 25 largest individual sources of each pollutant in the United States. Location of major stationary sources of air pollution. The following table shows the criteria air pollutant monitors in the US from 1970 to 1990. Source: http://www.epa.gov/aboutepa/oar.html Year

PM10

O3

NO 2

SO 2

CO

1970

245

1

43

86

82

1975

1120

321

303

827

494

1980

1135

546

375

1088

511

1985

970

527

305

906

458

1990

720

627

345

743

493

Go to http://www.epa.gov/airdata/ to know air data for various regions. The change in the National Air Quality Concentrations and Emissions (1980-2010) can be found from EPA. The following table shows the percentage change in the National Air Quality Concentrations and Emissions (1988-1997). Pollutant

Percentage Decrease in Concentration 1988-1997

Percentage Decrease in Emissions 1988-1997

Carbon Monoxide

38

25

Lead

67

44

Nitrogen Dioxide (NO 2 )

14

1(NO 2 )

Ozone (Pre-existing NAAQS) (1 hour)

19

20(VOC)

Ozone (Revised NAAQS) (8 hour)

16



PM10

26

12

Sulfur Dioxide (SO 2 )

39

12

Sulfur Dioxide Sulfur dioxide is considered a primary precursor of acidic precipitation. The sources of SO 2 are natural sources such as volcanoes and manmade sources such as power plants and industrial sources that burn coal or fuel. During the burning of fossil fuels 2 lb of SO 2 is produced for each pound of sulfur present in the fuel. It can harm human, and animal lungs, as well as plants and trees. Sulfur dioxide is the main contributor to acid rain. It reacts with the oxygen in the air to become sulfur trioxide, which then reacts with water in the air to form sulfuric acid. Acid rain can slowly kill both animal populations in lakes and rivers and trees and other plants by damaging leaves and root systems. It can deteriorate metal and stone on buildings and statues. The effects of acid rain are not only local, but they can occur hundreds of miles from the sources of sulfur dioxide.

Ozone Ozone is a gaseous, secondary pollutant and is formed during photochemical smog in the atmosphere. The interaction of NO 2 with VOCs produces ozone in the presence of sunlight. If the air over the city does not move, pollutants become trapped close to the earth's surface forming smog and increasing ozone problems which can lead to breathing problems. High ozone levels at the ground level harm plants, including trees and crop plants, and causes the accelerated deterioration of materials such as rubber and fabrics. There is another type of ozone problem which came to attention in late sixties. Concerns were expressed on the destruction of ozone layer due to the use of supersonic transports. At present the destruction of ozone layer in the stratosphere due to the use of certain chemical compounds ( chlorofluorocarbons or CFCs, methane etc. ) is an environmental issue.

Total Suspended Particulate Matter TSP is mostly a primary pollutant, but some of it is formed as secondary pollutant. It consists of soot, dust, tiny objects of liquid, and other material. An increase in the incidence of respiratory diseases and gastric cancer has been linked with the increase in particulate level. The natural sources include volcanoes, forest fires, and desert land. Some manmade sources are steel industry, power plants, and flour mills. Agricultural activities also contribute to TSP loading. Particulate gradually settle back to earth and can cause people to cough, get sore throats, or develop other more serious breathing problems. Particulate matter also causes discoloration of buildings and other structures.

Nitrogen Oxides Nitrogen Oxides are formed naturally by bacteria in soil and play an important role in plant growth. However, nitrogen oxides that enter the air through exhaust from vehicles and some power plants can be harmful. They can combine with water to make acid rain, react in the air to produce ozone and other pollutants, or be harmful by themselves as a gas in the air. Nitrogen dioxide is of greatest concern and is brown- red in color. Nitrogen oxide is relatively less harmful as compared to other oxides of nitrogen.

Carbon Monoxide It is a colorless, odorless and tasteless gas and affects the central nervous system of humans. The gas is emitted when vehicles burn gasoline and when kerosene and wood stoves are used to heat homes. The gas reduces the ability of hemoglobin to carry oxygen to body tissue. The effects of carbon monoxide include headaches, reduced mental alertness, heart damage; it may even cause death, and it contributes to smog.

Lead Lead is fairly abundant and is derived from ore bearing minerals. The gray metal can be easily molded, formed and worked. It can withstand weathering and chemical erosion. Lead has been used in the manufacture of pipes, paint house hold pottery, gasoline additives and storage batteries. In the U.S. the major source of lead mining is the state of Missouri. Automobiles and leaded gasoline are major sources of atmospheric lead. Lead was more of a problem a few years ago when all vehicles used gasoline with lead additives. When lead gasoline is burned, lead is released into the air. When people or animals breathe lead over a period of time, it accumulates in their bodies and can cause brain or kidney damage. Today most cars use unleaded gasoline, but there is still much leaded gasoline being sold, and lead continues to be a major pollutant, especially in cities.

Carbon Dioxide Carbon dioxide emissions have increased significantly during 19th century because of the use of coal, oil and natural gas. It finds uses as a refrigerant, in fire extinguishers and in beverage carbonation. Higher concentrations can affect respiratory function and cause excitation followed by depression of the central nervous system. Contact with liquefied CO 2 can cause frostbite. Workers briefly exposed to very high concentrations have effects like damage to the retina, sensitivity to light (photophobia), abnormal eye movements, constriction of visual fields, and enlargement of blind spots.

Hydrocarbons Hydrocarbons are composed of only hydrogen and carbon. The volatile organic compounds (VOC) are the compounds which take part in atmospheric photochemical process. VOCs are composed of hydrogen and carbon, and may also contain elements such as oxygen, nitrogen, sulfur, chlorine, and fluorine. VOC emissions are produced during combustion and their rate of production is affected by time in combustion chamber, fuel and air mix, temperature, turbulence, pressure and design of chamber. The manmade sources of hydrocarbons include dry cleaning operations, auto paint shop, chemical plants, auto emissions, service stations and waste facilities. The VOCs are used in the manufacture of glue and paints as solvents A summary of the major air pollutants and their effects is given in the following table.

MAJOR AIR POLLUTANTS POLLUTANT

DESCRIPTION

Sulfur Dioxide

SOURCE (s) coal-burning power plants and industries industrial boilers and processes coal-burning stoves refineries heaters

gaseous compound made up of sulfur and oxygen

( SO2 )





EFFECTS eye irritation dead aquatic life lung damage reacts in atmosphere resulting in acidic precipitation deteriorate buildings and statues damage forests

dry cleaning operations. auto paint shop chemical plants auto emissions service stations waste facilities

Hydrocarbons

Composed of hydrogen and carbon.

Ozone

gaseous pollutant

vehicle exhaust

( O3 )



diesel engines power plants steel industry, flour mills windblown dust wood stoves

very small particles of soot, dust, or other matter, including tiny droplets of liquids

Particulate Matter

lung damage eye irritation respiratory tract problem damage crops lung damage reduce visibility discolor buildings and statues eye irritation



several gaseous compounds made up of nitrogen and oxygen

Nitrogen Oxides ( NOx )

vehicles industrial boilers industrial processes power plants commercial and residential heaters coal-burning stoves natural gas pipelines

lung damage forms acid rain, damaging forests, buildings, & statues forms ozone and other pollutants (smog)

vehicles burning leaded gasoline power plants metal refineries

brain, kidney damage contaminated crops and livestock smog

Lead ( Pb )

metallic element





Carbon Monoxide ( CO )

colorless, odorless gas





vehicles burning gasoline indoor sources include kerosene- or wood- burning stoves dry cleaners



headaches, reduced mental alertness, death heart damage smog

The table below lists criteria pollutants and the threshold amounts for designation as large sources. Criteria Pollutant Emission Thresholds (Tons/Year) CO Carbon Monoxide gas 1000 NO2 Nitrogen Dioxide gas 100 SO2 Sulfur Dioxide gas 100 VOC Volatile Organic Compounds * 100 PT Particulate Matter (total) 100 PM10 Particulate Matter (

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