Air Pollution

Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases and is an important source of morbidity and mortality.

World Health Organization defined it as the presence of materials in the air, which are harmful to the living beings once they cross their threshold concentration levels.The foreign bodies, gases and so on act as air pollutants.It is the most extensive and worst form of pollution.

Types of Air Pollution-

There are two types of air pollutants, namely primary and secondary.

Primary Pollutants

Primary pollutants enter the atmosphere directly from the source. Some important primary pollutants are as follows.
1. Suspended particulate matter (SPM)
2. Oxides of carbon
3. Hydrocarbons (Methane)
4. Sulphur oxides (SOx)
5. Nitrogen oxides (NOx)
6. Chlorofluorocarbons (CFCs)
7. Lead

Secondary Pollutants

Secondary pollutants are not directly emitted from sources. These pollutants are formed as a result of chemical reactions between the primary pollutants
and certain atmospheric constituents, in the presence of sunlight. Sulphates, nitrates and organic particles can be transported over large distances, such as hundreds and even thousands of kilometres. Some important secondary pollutants are as follows.
1. Sulphur trioxide: It is a compound formed when sulphur dioxide reacts with oxygen. It combines with water to form sulphuric acid.
2. Smog formation: Smog is an odd combination of smoke and fog. The effect of smog is maximum just before sunrise as smog particles that are entrapped
between cold air are unable to rise.
Two types of smog are prevalent as per records.

(a) Sulphurous or London smog:

It affected London for a very long time and hence, its name. It is also termed as ‘reducing smog’ as its mixture of components is chemically reducing in nature. This is due to the presence of sulphur dioxide in air. It is more prevalent during the morning hours of winter season when the relative humidity is high and air near the ground is also cooler. London smog causes throat irritation and difficulty in breathing.

(b) Photochemical or Los Angeles smog:

This type of smog is due to the presence of oxides of nitrogen in the atmosphere, formed as a result of vehicular exhaust. It is formed due to chemical reactions involving ozone, nitrogen oxide, hydrocarbons and peroxyacetyl nitrate (PAN) in the presence of sunlight. This phenomenon mainly occurs during warm sunny days as sunlight is required to carry out photochemical reaction in seasons when the sky is clear. Photochemical smog consists of brown hazy fumes. It irritates the eyes and lungs, causes cracking of rubber and extensive damage to plant life.

(c) Ground level ozone:

Tropospheric or ground level ozone is formed from photochemical reaction between two major classes of air pollutants, such as volatile organic compounds (VOCs) and nitrogen oxides.

3. Acid rain:

Acid rain is caused by a chemical reaction that begins when compounds like sulphur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen and other chemicals to form more acidic pollutants known as acid rain.

Aerosols:

They are stable suspensions of solid or liquid particles in the air. Aerosols affect weather conditions by blocking solar radiation. The deposition of aerosols on leaves affects the process of photosynthesis.
• Mist: Aerosols consisting of liquid droplets.
• Dust: Aerosols consisting of solid particles.
• Fume: Aerosols consisting of hot vapours of metals.
• Smoke is also an aerosol, which is a mixture of liquid and solid particles as a result of burning.
• Plume: It is a geometrical form of smoke.
• Smog is the mixture of smoke and fog
• Dust: Aerosols consisting of solid particles.
• Fume: Aerosols consisting of hot vapours of metals.
• Smoke is also an aerosol, which is a mixture of liquid and solid particles as a result of burning.
• Plume: It is a geometrical form of smoke.
• Smog is the mixture of smoke and fog

Major Air Pollution-Related Chemical Substances

Pollutants Source Pathological effect on human beings

Ozone (Ground level) Vehicular exhaust Lung function – aggravation of asthma,

emphysema, and chronic bronchitis

Lead Leaded petrol Central Nervous System, interference with

development of RBCs

Sulphur dioxide Thermal power plant and industries respiratory problem, reduces exchange of

gases from lung surface

Nitrogen oxides Thermal power plant Heart and lung problems, Bronchitis, asthma, and

also carcinogenic issues

Carbon monoxide Incomplete combustion of fossil fuels, wood Reduces oxygen-carrying capacity of blood,

stoves and cigarette smoking. breathing problems

Hydrogen sulphide Oil refineries and chemical industries. Nausea, irritation of eyes and throat

Hydrogen cyanide Blast furnace, fumigation and chemical industry. Headache, dry throat, indistinct vision, and

dysfunction of nerve cells

Ammonia Fertilizer industry, dye making, bleaching and

explosives. Acidification of water bodies at high level

Phosgene Chemical and dye-making industry. Pulmonary oedema

Volatile organic compounds Vaporize easily and some examples are gasoline, benzene, etc. Smog formation

The following are the major government initiatives to monitor air pollution.

1. National Air Quality Monitoring Programme
2. National Ambient Air Quality Standards
3. System of Air Quality and Weather Forecasting

1. National Air Quality Monitoring Programme:

The Central Pollution Control Board is executing a nation-wide programme of ambient air quality

monitoring known as National Air Quality Monitoring Programme (NAMP).

National Air Quality Index (NAQI) was launched on 17 October 2014 to disseminate information on

air quality in an easily understandable form for the general public. The measurement of air quality is

based on the pollutants mentioned below:

(a) PM10 – Particulate matter (Size less than

10 μm)

(b) PM2.5 – Particulate matter (Size less than

2.5 μm)

(d) SO2

(e) CO

(f) Ozone

(g) Ammonia

(h) Lead

The unit of measurements in case of pollutants mentioned above is microgram per cubic metre

except in the case of CO where it is milligram. The AQI is classified along one of the six

categories.

(a) Good (0–50)

(b) Satisfactory (51–100)

(d) Poor (201–300)

(e) Very Poor (301–400)

(f) Severe (401–500)

National Ambient Air Quality Standards: It may be noted that ambient air quality standards are

specified separately in India for around 12 pollutants including the 8 that constitute the NAQI. The

additional four pollutants are arsenic, nickel, benzene and benzopyrene. PM2.5 is particularly dangerous

and can cause adverse health effects owing to its greater penetrability into the human respiratory

system and eventual accumulation in human organs and blood. PM concentrations are higher in winter

season and are lower during monsoon months. SO2 levels are within the prescribed National

Ambient Air Quality Standards in residential areas of all the cities. Decreasing trend may be due to various

interventions that have taken place in recent years, such as reduction of sulphur in diesel, use of

cleaner fuel such as CNG in Delhi, implementation of Bharat Stage-III emission norms. In addition,

there has been a change in the use of domestic fuel from coal to LPG, which may have contributed to

reduction in ambient levels of SO2. NO2 levels are within the prescribed National Ambient Air Quality Standards in residential areas of most of the cities. The reasons for low levels of

NO2 may be various measures taken, such as banning of old vehicles, better traffic management, etc. Despite an increase in the number of vehicles, CO levels have reduced during last few years. The decrease may be attributed to measures, such as the conversion of three-wheelers of CNG.

3. System of Air Quality and Weather Forecasting:

The Ministry of Earth Sciences (MoES), the Government of India has introduced a major national

initiative, ‘System of Air Quality and Weather Forecasting and Research’ known as ‘SAFAR’ for greater

metropolitan cities of India to provide location-specific information on air quality in near real-time

and its forecast 1–3 days in advance for the first time in India. It has been combined with the

early warning system on weather parameters. The SAFAR system is developed by the Indian Institute of tropical Meteorology, Pune. WHO has its own standards. Across the globe, most of the emissions that reach the atmosphere come from coal (43%) followed by oil (33%).