Introduction to Air Pollution

View Slides on Introduction Part 1 & Part 2

In this chapter you will learn:

bullet What is air pollution and what are the various factors contributing to air pollution?
bullet History of air pollution.
bullet What is an air pollutant and what are the various common air pollutants?
bullet What are the various sources of air pollutants?
bullet What is an emission inventory?
bullet 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:

bullet Are we doing something about solving these problems?
bullet Do we know enough about the conditions under which a pollution episode occurs?
bullet What are the regulations?
bullet 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:
bullet Air pollution affects every one of us.
bullet Air pollution can cause health problems and, may be, death.
bullet Air pollution reduces crop yields and affects animal life.
bullet 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 ( )

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.


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 C2H3NO, 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

A detailed list of major accidents involving hazardous substances is available on the web site of the United Nations Environmental Program;



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.


   There are two units of measurement. They are as follows:

bullet  µg/m3
bullet  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

P1V1/T1 = P2V2/T2



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

bullet Areas where air pollution levels persistently exceed national air quality standards.
bullet Locations of air pollution monitoring sites, operated by state and local agencies.
bullet The 25 largest individual sources of each pollutant in the United States.
bullet Location of major stationary sources of air pollution.
The following table shows the criteria air pollutant monitors in the US from 1970 to 1990.
Year PM10 O3 NO2 SO2 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 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 
Percentage Decrease in 
Carbon Monoxide  38 25
Lead 67 44
Nitrogen Dioxide (NO2) 14 1(NO2)
Ozone (Pre-existing NAAQS) (1 hour) 19 20(VOC)
Ozone (Revised NAAQS) (8 hour) 16  
PM10 26 12
Sulfur Dioxide (SO2) 39 12

Sulfur Dioxide

Sulfur dioxide is considered a primary precursor of acidic precipitation. The sources of SO2 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 SO2 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 is a gaseous, secondary pollutant and is formed during photochemical smog in the atmosphere. The interaction of NO2 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 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 CO2 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 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. 







Sulfur Dioxide

( SO2 )


gaseous compound made up of sulfur and oxygen



coal-burning power plants and industries


industrial boilers and processes


coal-burning stoves







eye irritation


dead aquatic life


lung damage


reacts in atmosphere resulting in acidic precipitation


deteriorate buildings and statues


damage forests

Hydrocarbons Composed of hydrogen and carbon.

dry cleaning operations.


auto paint shop


chemical plants


auto emissions


service stations


waste facilities


( O3 )

gaseous pollutant


vehicle exhaust



lung damage


eye irritation


respiratory tract problem

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

diesel engines


power plants


steel industry, flour mills


windblown dust


wood stoves



damage crops


lung damage


reduce visibility


discolor buildings and statues


eye irritation

Nitrogen Oxides ( NOx ) several gaseous compounds made up of nitrogen and oxygen
bullet vehicles
bullet industrial boilers
bullet industrial processes
bullet power plants
bullet commercial and residential heaters
bullet coal-burning stoves
bullet natural gas pipelines


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


metallic element


bullet vehicles burning leaded gasoline
bullet power plants
bullet metal refineries


bullet brain, kidney damage
bullet contaminated crops and livestock
bullet smog


Carbon Monoxide ( CO )


colorless, odorless gas


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


bullet headaches, reduced mental alertness, death
bullet heart damage
bullet 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 (<10 µm) 100
Pb Lead particles 5
* VOCs are not criteria pollutants, but they are precursors of  criteria pollutant ozone (smog).


Toxic air pollutants may originate from natural sources such as volcanoes as well as from manmade sources such as stationary and mobile sources. The stationary sources serve as major contributors to air pollution, since they include factories, refineries, or power pollutants, which are constantly emitting pollutants into the atmosphere. 

Pie Chart of Mobile Source


 Based on 1996 National Toxics Inventory data, major sources account for about 26 percent of air toxics emissions, smaller area sources and other sources (such as forest fires) for 24 percent, and mobile sources for 50 percent. Accidental releases, which also contribute air toxics to the atmosphere, are not included in these estimates.


The Clean Air Act amendments of 1990 provided a list of 189 chemicals to be regulated under the hazardous air pollutant provision of the act. A complete list of chemicals is given in Appendix C.

On June 18, 1995, the US EPA has removed Caprolactum from the above list based on a July 1993 petition filed by Allied Signal, BASF, and DSM chemicals North America. The chemical is used in the manufacture of synthetic nylon fiber.

The toxic air pollutants in US are reported to the public via the Toxic Release Inventory (TRI).
TRI information is briefly summarized in a word document. For that information Click Here. In 1995, the toxic substances released to air, land, water and underground totaled 1.66 billion lb., compared to 1.75 billion lb. in 1994. The total TRI releases in 1995 were 45.6% below baseline year.


The top 20 sources of toxic chemicals are presented in the table below: (in short tons)

Source : EPA Document

For a citizen's guide to evaluating exposures to toxic air pollutants, and some related links,  Click Here.



The sources may be classified as primary or secondary, mobile or stationary, combustion or non combustion, point or area and natural (biogenic) sources.
The following table shows the constituents of atmospheric fine particles (<2.5mm) and their major sources, classified as primary and secondary and further as natural and anthropogenic. 

Source US EPA document :

Point sources include stationary facilities that emit sufficient amounts of pollutants to be worth listing. Area sources are all other point sources that individually emit small amount of pollutants. Dry cleaners in a city are an example of area sources. They contribute significantly to pollution as a group. Mobile sources include automobiles, trucks, air planes, ships, boats and lawnmowers. Natural sources are soil, water, vegetables, volcanic eruptions and lightning strikes.

Sources may also be classified the way they generate emissions: transportation, stationary combustion sources, industrial processes, solid waste disposal facilities and miscellaneous. The U.S. Environmental Protection Agency uses the above classification for reporting air emissions to the public. The general definitions are as follows:

Transportation sources: This category includes most emissions produced from transportation sources during the combustion process. The internal combustion engines fueled by gasoline and diesel are the biggest sources in this category. The other sources include trains, ships, lawnmowers, farm tractors, planes, and construction machinery.


Stationary combustion sources: In this category the sources only produce energy and the emission is a result of fuel combustion. The sources include power plants as well as home heating furnaces.


Industrial Processes: The sources which emit pollutants during manufacturing of products are included in this category. Petrochemical plants, petrochemical refining, food and agriculture industries, chemical processing, metallurgical and mineral product factories and wood processing industries are the major sources of air emissions. The smaller sources include dry- cleaning, painting and degreasing operations.


Solid Waste Disposal: This category includes facilities that dispose off unwanted trash. Refuse incineration and open burning are important sources.


Miscellaneous: The sources which do not fit in the above four categories are listed under this title. These sources include forest fires, house fires, agriculture burning, asphalt road paving and coal mining.

The pollutants typically released from the above sources are given in the table.
Transportation sources
carbon monoxide ( CO ), lead ( Pb ), nitrogen oxides ( NOx ), ozone ( O3 )
Stationary sources
carbon monoxide ( CO ), lead ( Pb ), nitrogen oxides ( NOx), particulate matter, sulfur dioxide (SO2)
Industrial processes
carbon monoxide ( CO ), lead ( Pb ), nitrogen oxides ( NOx), particulate matter, sulfur dioxide (SO2)
Solid Waste Disposal
carbon monoxide ( CO )
Miscellaneous ( forest fires, asphalt road paving, coal mining etc. )
carbon monoxide ( CO ), nitrogen oxides ( NOx), particulate matter, sulfur dioxide (SO2)

 The following table indicates a table serves to illustrate the nationwide primary PM10 emission estimates from mobile and stationary sources, 1985 to 1993.

  Source US EPA document:


In order to communicate with the public, regulatory agencies in various countries have developed different air pollution indices. The idea is to translate technical information on concentration levels of various pollutants into a simple and easy to understand language for the public.

The U.S. Environmental Protection Agency has developed the pollutant standard index (PSI) for introducing consistency in providing information regarding the air quality throughout the U.S. The system is based on a scale of 0-500. The computed index below 100 indicates that the air quality is within acceptable range. A value over 100 implies potential health problems. The alerts are issued at 200, 300 and 400 levels. Five pollutants (carbon monoxide, sulfur dioxide, total suspended particulate, ozone and nitrogen dioxide) are included in the index. The reported index is based on the highest index value of any of the five pollutants.

The concentration associated with the index value is given in Table, and the health effects are discussed in the following table.

U.S. Pollutant Standard Index  ( Source U.S. EPA )

(24 hr)
(24 hr)
(8 hr)
(24 hr)
(24 hr)
50 % of 

Associated Health Effects With U.S. Pollutant Standard Index  ( Source U.S. EPA )


Index Value
Health Effect Descriptor
General Health Effects
Cautionary Statements
400 - 500
Premature death of ill & elderly. Healthy
people will experience adverse symptoms
that affect their normal activity.
All persons should remain indoors,
keeping windows & doors closed. All
persons should minimize physical 
exertion & avoid automobile traffic
300 - 400
Premature onset of certain diseases in 
addition to significant aggravation of
symptoms & decreased exercise tolerance 
in healthy persons
Elderly & persons with existing diseases
should stay indoors & avoid physical 
exertion. General population should
avoid outdoor activity.
200 - 300
Very Unhealthy
Significant aggravation of symptoms &
decreased exercise tolerance in persons
with heart or lung disease with widespread
symptoms in the healthy population
Elderly & persons with existing heart 
or lung disease should stay indoors & 
reduce physical activity
100 - 200 
Mild aggravation of symptoms with susceptible
persons, with irritation symptoms in the 
healthy population
Persons with existing heart or
respiratory ailments should reduce physical
exertion & outdoor activity
50 - 100
0 - 50
a : No index values reported at concentration levels below those specified by " Alert Level " criteria.
b : Annual primary NAAQS
c : 400*10-6 gm/m3 was used instead of the O3 Alert Level of 200*10-6 gm/m3


 Emission Inventory is a study of the pollutant emission estimates from sources in a given area. The development of emission inventory is important for a company as well as for the pollution control agencies. The inventory allows an environmental scientist to locate pollution sources, to define types and amounts of emission from each source, to define physical characteristics of sources, to determine emission frequency and duration of each pollutant exposure, to determine relative contributions to pollution problem in the area due to individual sources or a group of sources, to determine pollution controls needed to protect public health, and to provide a data base for air quality modeling and risk assessment.


Development  of  an Emission Inventory :The emission inventories have been developed by a plant, local agency, or a nation. The development of a good inventory requires substantial resources and careful planning. Several steps are involved in the development of an emission inventory. The details depend on the area coverage, nature of sources, and purpose. Some of the basic steps are listed below:


Planning: This step defines scope and purpose of inventory. The following points are considered during this step :the pollutants to be enlisted in the inventory are specified along with the methods to collect/estimate data, and the use of this data and the geographical area involved are determined. The legal authority and the responsibility of specific groups within the organization to acquire data is considered along with an assessment of cost, and resources.


Data Collection: This stage follows the plan of action set in planning stage. During this phase emissions are classified, pollutant sources are located and classified, and the quality and quantity of materials handled, processed, or burned in each source is determined.

The data required to develop an inventory for a plant may be collected by mail survey which is the most common and economical technique for developing an initial regional or national emission inventory. Plant inspection is the most accurate method of data collection and is used to examine various processes, to interview with the staff and to carry out source emission testing, if necessary. The manufacturer specifications are also studied. It is more time consuming than mail surveys, and is usually used only at important point sources in the plant. Field surveys are similar to plant surveys, and used mainly to gather data about small area sources. Data is often found in industrial and government files, periodicals, trade journals and scientific publications. These publications often contain process activity level, and control device description. However they do not provide raw emission data, and rely upon estimates of emissions from published data on related sources. This method is  usually used as a last resort method.

The kind of information collected during the development of an emission inventory includes general source information ( location, ownership, and nature of business ), process information ( type of equipment, type of reactions ), activity levels (amount of fuel and materials ( input ), amount of production (output) of the plant ), control device information ( type of air pollution control devices )and information required to estimate emissions ( temperature, tank conditions, hours of operation, seasonal variation ).
For mobile sources information include year of vehicle, type of vehicle and vehicle.


Data Analysis: After the data have been gathered, several analyses are made to check the accuracy of the collected information and to develop concise information for further use. It includes calculation of emission rate for each pollutant by using :


stack monitoring data, when available,


use of emission factors from AP-42,


mass balance, and


engineering calculations.

One or more techniques could be used for emission rate calculations. Continuous monitoring is the most accurate but the most expensive method.

Emission rate is the weight of a pollutant emitted per unit time. Emission factor is an estimate of the rate at which a pollutant is released into the atmosphere as a result of some activity. An example of the calculation of emission rate using an emission factor is shown below:


The values of emission factors can be obtained from AP-42. Average emission factors from many similar facilities are also used in the absence of plant specific data.

Area and mobile source emissions are also estimated using emission factors. Biogenic emissions are difficult to calculate. A mathematical model is used to calculate emissions based on the type of vegetation, temperatures, scalar radiation and land use of the area.


Reporting Data: Depending on regulations the information is filed with local, regional and national pollution control agencies. For example in the U.S. data gathered by state agencies are reported to U.S. EPA's computerized National Emissions Data System. NEDS is a computerized data system developed for storage and retrieval of source and emission data, and is used to generate national emissions reports, fuel summary listings, and other data reports.

The Emission Inventory developed may be used for :

identifying types of pollutants emitted from specific sources,


determining the magnitude or amount of emissions from those sources,


developing emission distributions in time and space,


calculating emission rates under specific plant operating conditions, and


finding out the relation of ambient air pollutant concentrations to specific sources.

The US EPA has developed two major emission inventories: The first inventory is for criteria pollutants, and the second inventory is for toxic substances known as (Toxic Release Inventory - TRI ).

The following figure shows the National Toxic Inventory’s 189 hazardous air pollutant (HAP) emissions by state. 

Source : US EPA Document

Both the inventories have been very useful in identifying and solving air pollution problems. New regulations were proposed in the U.S. based on results obtained from these inventories. The fees charged by the state agencies under Title V of the 1990 Clean Air Act Amendments are designed using information from emission inventories. The requests to construct/modify existing and proposed sources are analyzed with the help of emission inventory data.

An example of a regional emission inventory is Great Lakes Regional Air Toxics Emissions Inventory developed by Great Lakes Commission ( So far the emission inventory has focused on individual, manufacturing, and commercial sources in eight Great Lakes states. Future plans include the incorporation of 72 chemicals and compounds emitted by mobile sources in the area.

Environmental managers can use emission inventory to estimate fees, to eliminate or to improve processes responsible for releasing large amounts of raw material, to implement control technology and to change processes for improving product quality.

More complete emission inventory information can be obtained by Clicking Here.



Asia represents a major source of air pollution as a result of rapid population growth, explosive industrialization, and few environmental regulations.

Due to the use of high sulfur coal to generate energy, the cities in China are heavily polluted by sulfur dioxide and particulate. The average ash content of Chinese coal is 27%. The sulfur content varies upto 5%. The combustion sources include small domestic stoves as well as large industrial plants. China produces over 15 million tons of SO2 and 20 million tons of particulate. Industrial emissions of carbon dioxide and greenhouse gases are emitted in large quantities in China. Nitrogen oxide emissions are likely to increase as the production of cars will increase in China. China employs very little air pollution control technology. Acid rain is an important issue in China.

The following figure shows Air pollution Index for major Chinese cities during Aug. 28, 1998 to Sept. 3, 1998. (Refer Chart)

Guangzhou and Shanghai were mainly polluted by nitrogen dioxide. The critical pollutant in Beijing was the total suspended particle from coal burning, construction projects and dust-raising winds.

Air pollution is a serious problem in major cities in India. Delhi's pollution scenario is India's grimmest, and leads the other metros in vehicular pollution levels. The presence of suspended particulate matter is due to the use of coal in power plants. More than 45 million metric tons of ash is produced annually due to the use of low quality coal. In 23 Indian cities with populations of more than one million, auto exhausts and industrial emissions dangerously cross limits . Recent studies reveal that the number of patients with respiratory diseases and allergies has roughly doubled since the start of the 1990s. In Calcutta winter levels for particulate matter are 12 times above the standards. In Mumbai's (Bombay) "gas chamber", the eastern suburb of Chembur, pollution figures zoom to 10 times above the safe levels. India's metropolitan vehicle population has roughly tripled since 1990. The most damaging pollutants come from petrol driven cars and two wheelers. On July 5, 1997, IPAN (Indian Public Affairs Network) published an article of how the growing catalytic converter use could ease Asian cities’ air pollution.

The air quality in Indonesia in deteriorating rapidly with industrial expansion. In the capital city, Jakarta, brownish yellow clouds of lead laden smog are common from 2.5 million vehicles. During several periods in 1997, Malaysia experienced haze conditions due to particulate matter from fires burning in Indonesia. Based upon readings from the Malaysian Air Pollutant Index, the air pollution levels registered in the "unhealthy" and occasionally in the "very unhealthy" ranges.

SO2 is a problem area in South Korea and is being controlled by the use of air pollution control equipment.

Vehicle emissions contribute most significantly to Hong Kong's air pollution problems, diesel powered engines being the prime culprit. In 1996 there were some 300,000 vehicles on Hong Kong's road, and one in three were diesel vehicles that covered two third of the mileage recorded by the total vehicle fleet. Today there are around 480,000 vehicles in Hong Kong, with diesel vehicles accounting for about 60% of the overall mileage.

To read and download a synopsis on PBT (Persistent Bioaccumulative and Toxic) chemicals click here.

More on the state of 'Air Pollution in Asia'


Air pollution is an important problem facing by our society. The solutions require a global approach. The international agencies (e.g. UN) are playing an active role in developing treaties (see chapter on regulations). The level of activity to control air pollution varies from one nation to another. A part of the pollution problem is caused by our desire to progress. The progress leads to movement of more people to a developed area and increased consumption of resources. The solution to the pollution problem involves politics, economics, science, technology, sociology and life style changes.

Not understanding the consequences of pollution is also part of the problem. For years, people thought that they could safely get rid of garbage, sewage, exhaust, and other waste products by throwing them away, flushing them down the drain, or releasing them into the air. Thus basic awareness and appropriate education in conjunction with that awareness is called for.

Are we prepared to change our lifestyle to reduce air pollution? This question will come over again and again as we prepare ourselves for the next century.




Find out the legal definition of air pollution in your area.


What can you do to reduce air pollution as a result of personal activities?


Discuss the possible causes of air pollution in your community.


List the five largest sources of air pollution in your state.


Describe an air pollution accident in your state .


Collect air pollution news items from your local newspaper.


What is the difference between smoke, fume and dust?


Compile a list of five major toxic air pollutants in your state.


Name five major sources of toxic air pollutants in your city.


What is an emission inventory?


Find a story in your local newspaper or on the Internet. Discuss the air pollution problem in the news.


What is meant by Global warming? State any two effects.


What is an air pollutant?


What are the units of measurement for air pollutants?


List out the common air pollutants we face in our day-to-day life.


What is a toxic air pollutant?


What are the various ill-effects of toxic air pollutants?


What are the amendments done to CAA? State them in brief.


State the various types of sources of air pollutants and also cite examples for them.


What is the procedure EPA follows to categorize  the sources of air pollutants and what are the various sources in this procedure?


What is an Air Quality Index?


List out a few websites in the field of air pollution.


List out the various ranges of Air Quality Index and the various health effects to the corresponding ranges.


What are the various steps involved in an emission inventory?


Give an equation to calculate Emission Rate?


What are the various uses of Emission Inventory?


Cite any 5 air pollution accidents in Asia.


Write down the important points discussed in this section.




A power plant emits 60 kg of fly ash per hour from its main stack. The effluent flow rate in the stack is 1m3/sec. What is the concentration of the fly ash in discharged gas. Express your results in mg/m3.


A nation has 200 coal fired power plants and produces 0.2 x 1012 watts of electricity per year. The average sulfur content in coal used by the power plants is 1.8%. The average energy content of coal is 28 x 106 J/kg. Compute the amount of sulfur emitted from the power plants in one year.


Interview five students on the subject of air pollution. Prepare a report on their views on a personal computer.


Compute the fraction of U.S. NOx emissions contributed by transportation sources and industrial processes in 1980 and 1990.


Consider a coal fired plant with 92.5% efficient S02 scrubbers and an oil fired plant with no scrubber: Assume the coal used has a heat content of 14,000 Btu/lb and contains 3.5% sulfur, and that the oil has a heat content of 1.5(10)5 Btu/gallon and contains 0.9% sulfur. Determine which power plant emits more SO2 per unit of electricity produced.


The eight hour standard for CO is 10 mg/m3. Calculate the equivalent concentration in parts per million.


Compute the density of dry air and humid air at the same temperature and pressure. State your assumptions and comment on your results.


Calculate the density of a mixture of 90% air and 10% SO2 at a temperature of 100o C and a pressure of 1.10 atm.


Determine the absolute and gauge pressures exerted at the bottom of a column of liquid 11 meters high with a density of 1 kg/m3







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Slide show on the basics of air pollution

Slide show on the basics of air pollution

Asian Air Pollution

Asian Air Pollution


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