Air Pollution


Before starting any discussion about air pollution, it becomes important to study about atmosphere where air pollutants are discharged. The atmosphere is very dynamic in nature therfore in this unit we will be studing about atmospheric dynamics and air pollution.

  1. Atmosphere

Atmosphere is a protective blanket of gases surrounding the earth which sustains life on earth and saves it from the hostile environment of outer space

  • Maintain heat balance
  • Vital carrier of water from ocean to land as part of hydrological cycle
  • Absorb cosmic rays

Composition of clean dry air:

  Air Pollution

Pollution is a word used for any contaminant which is not expected to be in air we breathe. There are many definitions for air pollution.

World Health Organisation (WHO)

The presence in the out-door atmosphere of substances or contaminants put there by man, in quantities or concentrations and of a duration as to cause any; discomfort to a substantial number of  inhabitants of a district of which are injurious to public health or to human, plant or animal life or property or which interfere with the reasonable comfortable enjoyment of life and property throughout the state or through such territories or areas of the state as shall be affected thereby

Bureau of Indian Standards (BIS)

The presence in ambient atmosphere of substances generally resulting from activities of man, in sufficient concentration present for a sufficient time and under circumstances which interfere significantly with the comfort health or welfare of persons or with the full use of enjoyment of property

American Medical Association (AMA)

Excessive concentration of foreign material in the air which adversely affect the well being of individual and causes damage to the property

  Sources and classification of Air Pollution

The sources of air pollution can be natural which occure due to natural calamities and changes and manmade which are of anthropogenic origin.

Classification of Air Pollution

The basic three criteria for dividing the air pollutants are based on their origin, chemical composition and states of matter

Classification of Air Pollution

Point source:  A point source is a single, identifiable source of air pollutant emissions (for example, the emissions from a combustion furnace, flue gas stack). Point sources are also characterized as being either elevated or at ground-level

Line source: A line source is one-dimensional source of air pollutant emissions (for example, the emissions from the vehicular traffic on a roadway)

Area source: An area source is a two-dimensional source of diffuse air pollutant emissions (for example, the emissions from a forest fire, a landfill or the evaporated vapors from a large spill of volatile liquid)

Volume source: A volume source is a three-dimensional source of diffuse air pollutant emissions. Essentially, it is an area source with a third (height) dimension (for example, the fugitive gaseous emissions from piping, valves and other equipment at various heights within industrial facilities).


  Harmful impacts of Air Pollution

The extent to which an individual is harmed by air pollution usually depends on the total exposure to the damaging chemicals, i.e., the duration of exposure and the concentration of the chemicals 

Short-term effects include irritation to the eyes, nose and throat, and upper respiratory infections such as bronchitis and pneumonia. Other symptoms can include headaches, nausea, and allergic reactions

Long-term health effects can include chronic respiratory disease, lung cancer, heart disease, and even damage to the brain, nerves, liver, or kidneys. Continual exposure to air pollution affects the lungs of growing children and may aggravate or complicate medical conditions in the elderly


Sources, Health and Welfare Effects for Criteria Pollutants




Health Effects

Welfare Effects

Carbon Monoxide (CO)

Colorless, odorless gas

Motor vehicle exhaust, indoor sources include kerosene or wood burning stoves.

Headaches, reduced mental alertness, heart attack, cardiovascular diseases, impaired fetal development, death.

Contribute to the formation of smog.

Sulfur Dioxide (SO2)

Colorless gas that dissolves in water vapor to form acid, and interact with other gases and particles in the air.

Coal-fired power plants, petroleum refineries, manufacture of sulfuric acid and smelting of ores containing sulfur.

Eye irritation, wheezing, chest tightness, shortness of breath, lung damage.

Contribute to the formation of acid rain, visibility impairment, plant and water damage, aesthetic damage.

Nitrogen Dioxide (NO2)

Reddish brown, highly reactive gas.

Motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels.

Susceptibility to respiratory infections, irritation of the lung and respiratory symptoms (e.g., cough, chest pain, difficulty breathing).

Contribute to the formation of smog, acid rain, water quality deterioration, global warming, and visibility impairment.

Ozone (O3)

Gaseous pollutant when it is formed in the troposphere.

Vehicle exhaust and certain other fumes.  Formed from other air pollutants in the presence of sunlight.

Eye and throat irritation, coughing, respiratory tract problems, asthma, lung damage.

Plant and ecosystem damage.

Lead (Pb)

Metallic element

Metal refineries, lead smelters, battery manufacturers, iron and steel producers.

Anemia, high blood pressure, brain and kidney damage, neurological disorders, cancer, lowered IQ.

Affects animals and plants, affects aquatic ecosystems.

Particulate Matter (PM)

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

Diesel engines, power plants, industries, windblown dust, wood stoves.

Eye irritation, asthma, bronchitis, lung damage, cancer, heavy metal poisoning, cardiovascular effects.

Visibility impairment, atmospheric deposition, aesthetic damage.

  When we say its pollution…???

Just watching excess of smoke coming out of chimney or lot of dust and fumes does not define pollution. Pollution is determined by the value of certain concentration of pollutant present in air for a particular duration. The ambient readings are matched with acceptable standards given by CPCB, MoEF in India. The standards are presently given for 12 pollutants, and are updated time to time. Any value higher then these standards are said to be pollution.


National Ambient Air Quality Standards, CPCB 2009



Time weighted average

Concentration in Ambient Air




Rural and

other areas

Ecologically Sensitive Area (notified by Central Government)



Sulphur Dioxide (SO2), µg/m3





24 hours**





Nitrogen Dioxide (NO2) µg/m3





24 hours**





PM10 (Particulate Matter size less than 10 µm) µg/m3





24 hours**





PM2.5 (Particulate Matter size less than 2.5 µm) µg/m3





24 hours**





Ozone (O3) µg/m3

8 Hours**




1 Hour**





Lead (Pb) µg/m3




24 hours**




Carbon Monoxide (CO) mg/m3

8 Hours



1 Hour




Ammonia (NH3) µg/m3




24 hours**




Benzene (C6H6) µg/m3





Benzo-pyrene (BaP) particulate phase only ng/m3





Arsenic (Ar ) ng/m3





Nickel (Ni) ng/m3




* Annual arithmetic mean of minimum 104 measurements in a year at a particular site taken twice a week 24 hourly at uniform intervals.

**24 hourly or 08 hourly or 01 hourly monitored values, as applicable, shall be compiled with 98% of the time in a year. 2% of the time, they may exceed the limits but not on two consecutive days of monitoring


The last column in the above mentioned table is ecologically sensitive area, most of the student consider them to be hospitals which is incorrent. MoEF also gives a list of ecologically sensitive area which includes:


Ecologically sensitive areas as per Central Govt.

  • Religious and historical places
  • Archeological monuments/sites
  • Scenic Areas
  • Coastal Resorts, Coastal areas (corals, mangroves, breeding and spawning areas)
  • Estuaries, Gulf area
  • Biosphere Reserve
  • National Parks, Sanctuaries, Natural Lakes, swamps, wetlands etc
  • Seismic Zones
  • Tribal Settlement
  • Area under scientific and geological interest
  • Defence installations those of security importance
  • International Borders
  • Airports          

  Air Pollution dispersion and meteorology

Air pollution mainly affects you if you are near the source or the air is carrying the pollutants towards you. Therefore; the movement of air and how it carries the pollutants is very important. None of the study on air pollutaion is complete without meteorological data. In the coming section we are going to discuss the dynamics of atmosphere and its effect on air pollution dispersion.


Meteorology is the study of the changes in temperature, air pressure, moisture, and wind direction in the troposphere.  It is a science that studies atmospheric phenomena, especially those that relate to weather.


Relevant Factors of environment and meteorology that plays important role is dispersion are:

  Environmental Factor

Stack height: the height of the stack is the major factor which decides the dispersion of pollutants in air. The more is the height of the stack the more is the dispersion and least is the ground level concentration (GLC) of the pollutants.

The physical height of the stack and the maximum plume rise notify the type of dispersion of pollutant in the atmosphere.

Rate of release of gases: the flow rate of the gases from the chimney decided the amount of the pollutant that will be released in the atmosphere at given interval of time.

Mixing height: mixing height is the vertical height in the atmosphere where rigorous mixing of the pollutants takes place. It is the layer from where dispersion starts.

Temperature of outflow gas: the temperature of the outflow gas governs the sinking or raising of the air parcel depending on the temperature of the ambient atmosphere at the time of emission.

  Meteorological Factors

Ambient temperature: the temperature of the atmosphere is the regulating force for the dispersion of pollutants as it is responsible for the stable or unstable condition that prevails in atmosphere.

Wind speed and direction: the transport of air parcel is only due to the blow of wind. The factor also helps in site selection of industrial zones as governs the prediction of impacts.

Wind rose diagram -defined as graphical representation of wind speed and direction of a particular location. Wind speed less that 1.8 km/hr is called calm. Get data from IMD (Head office Pune). Nearby IMD (80km vicinity) or Automatic weather station. Example of windrose diagram is given below.

Wind Vane for direction;

anemometer for wind speed 


automatic weather station


Solar radiation: insolation affects the ambient temperature and also contributes in stability classification. Instrument: Pyranometer, Sunshine recorder etc.

Precipitation: the pattern that is the quantity and distribution of rainfall play important role in air pollution dispersion. Rain Gauge

Turbulence: the rapid mixing and transport of pollutants is governed by turbulence (disturbance) in the atmosphere. The formation of eddies takes place due to turbulence which is responsible for vertical and horizontal mixing of pollutants in the atmosphere. The turbulence in the atmosphere can be mechanical due to buildings, mountains etc and can be thermal due to temperature difference.

Temperature is the major meteorological parameter that decides the stability condition prevailing in the atmosphere and hence decides the fate of the pollutants. The temperature regime changes when we move from troposphere to exosphere.

The atmosphere is broadly divided into four regions. It extends upto 500km with temperature varying from minimum of -92OC to maximum of 12000C.


  Atmospheric Facts

  • 99% of atmosphere mass is within 30 km of earth surface
  • Most of earth phenomenon occur in troposphere and it contains 80% of the total atmospheric mass
  • Maximum ozone layer is found b/w 25 – 30 km range and its concentration in 10 ppm. It is measured in Dobson Units (DU)
  • 100 DU=1mm of pure ozone gas at normal temperature and pressure at sea level



Altitude range (Km)

Temperature range OC

Lapse rate







15 to -56




-56 to -2




-2 to -92




-92 to 1200



 This distribution of temperature determines the fate of pollutants. In next tutorial we will study the meteorological factors in details and how they contribute in pollution dispersion.



When studing the atmospheric parameters; it becomes important to know about some instruments used to measure these parameters.

A radiosonde is a battery-powered instrument package carried into the atmosphere usually by a weather baloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. A radiosonde that is dropped from an airplane and falls, rather than being carried by a balloon is called a dropsonde


Modern radiosondes measure or calculate the following variables:


Radiosondes measuring ozone concentration are known as ozonesondes.

  Life Cycle of Air Pollutants

  Dry and Wet Deposition

Dry deposition is the direct deposition of particulates and gaseous pollutants on the surface of building and structures.

Wet deposition is when air pollutants mix with rain water and precipitate on earth surface. Example Acid rain



  Air Pollution Inventorization