Learning Objectives

To make the students aware of history of air pollution; definition of air pollution and various types of sources and classification of air pollutants.

Lecture 1 Lecture 2 Lecture 3

Air Pollutants

  • Primary air pollutants - Materials that when released pose health risks in their unmodified forms or those emitted directly from identifiable sources.

  • Secondary air pollutants - Primary pollutants interact with one another, sunlight, or natural gases to produce new, harmful compounds

Primary Air Pollutants

  • Five major materials released directly into the atmosphere in unmodified forms.
    -Carbon monoxide
    -Sulfur dioxide
    -Nitrogen oxides
    -Particulate matter

Carbon Monoxide

  • Produced by burning of organic material (coal, gas, wood, trash, etc.)

  • Automobiles biggest source (80%)

  • Cigarette smoke another major source

  • Toxic because binds to hemoglobin, reduces oxygen in blood

  • Not a persistent pollutant, combines with oxygen to form CO2

  • Most communities now meet EPA standards, but rush hour traffic can produce high CO levels

Sulphur Dioxide

  • Produced by burning sulfur containing fossil fuels (coal, oil)

  • Coal-burning power plants major source

  • Reacts in atmosphere to produce acids

  • One of the major components of acid rain

  • When inhaled, can be very corrosive to lung tissue

  • London
    -1306 banned burning of sea coal
    -1952 “killer fog”: 4,000 people died in 4 weeks
    • tied to sulfur compounds in smog


Nitrogen Oxides

  • Produced from burning of fossil fuels

  • Contributes to acid rain, smog

  • Automobile engine main source

  • New engine technology has helped reduce, but many more cars


  • Hydrocarbons - organic compounds with hydrogen, carbon

  • From incomplete burning or evaporated from fuel supplies

  • Major source is automobiles, but some from industry

  • Contribute to smog

  • Improvements in engine design have helped reduce


  • Particulates - small pieces of solid materials and liquid droplets (2.5 mm and 10 mm)

  • Examples: ash from fires, asbestos from brakes and insulation, dust

  • Easily noticed: e.g. smokestacks

  • Can accumulate in lungs and interfere with the ability of lungs to exchange gases.

  • Some particulates are known carcinogens

  • Those working in dusty conditions at highest risk (e.g., miners)

  • Respirable Suspended Particulate Matter (RSPM) -PM1 having size <= 1µm: effects in alveoli
    -PM2.5 having size <= 2.5µm: effects trachea
    -PM10 having size <= 10µm: effects in nasal part only<

Secondary Pollutants

  • Ozone
  • PAN (peroxy acetyl nitrate)
  • Photochemical smog
  • Aerosols and mists (H2SO4)


  • Ozone (O3) is a highly reactive gas composed of three oxygen atoms.

  • It is both a natural and a man-made product that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere).

  • Tropospheric ozone – what we breathe -- is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOX).


Smog is caused by the interaction of some hydrocarbons and oxidants under the influence of sunlight giving rise to dangerous peroxy acetyl nitrate (PAN).

Photochemical smog

Photochemical smog is a mixture of pollutants which includes particulates, nitrogen oxides, ozone, aldehydes, peroxyethanoyl nitrate (PAN), unreacted hydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.

Aerosols and mists (H2SO4)

Aerosols and mists are very fine liquid droplets that cannot be effectively removed using traditional packed scrubbers.  These droplets can be formed from gas phase hydrolysis of halogenated acids (HCl, HF, HBr), metal halides, organohalides, sulfur trioxide (SO3), and phosphorous pentoxide (P2O5). 


1. Can you explain the word ‘episode’ used in air pollution?
2. Can you think why ‘mountains in a basin like area’ make the pollutants susceptible to accumulation?
3. Can you tell two words making the word ‘smog’?
4. Do you know that ‘soot’ is unburnt/burnt carbon particle?
5. Why Earth Day is celebrated? Explain.
6. Can you explain the significance of World Environment Day?
7. What does ‘Earth Summit's means?
8. Are CO and NOx ‘indicators or ‘pollutants’?
9. Can you list direct/indirect consequences of human activity causing air pollution?
10. Differentiate among personal/occupational/community air exposure.
11. Is environmental tobacco smoke (ETS) personal/occupational / community exposures?
12. Explain various spheres of the Earth.
13. Explain various sources of air pollution.
14. Differentiate between troposphere/stratosphere/mesosphere. Which one is ideal for air pollution studies effecting living beings?
15. Differentiate between criteria/non-criteria/hazardous pollutants . Why O3 is not taken as criteria pollutants?