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Global warming is an environmental phenomenon caused by natural and anthropogenic air pollution. It refers to rising air and ocean temperatures around the world. This temperature rise is at least partially caused by an increase in the amount of greenhouse gases in the atmosphere. Greenhouse gases trap heat energy in the Earth’s atmosphere. (Usually, more of Earths heat escapes into space.) Carbon dioxide is a greenhouse gas that has had the biggest effect on global warming. Carbon dioxide is emitted into the atmosphere by burning fossil fuels (coal, gasoline, and natural gas). Humans have come to rely on fossil fuels to power cars and planes, heat homes, and run factories. Doing these things pollutes the air with carbon dioxide. Other greenhouse gases emitted by natural and artificial sources also include methane, nitrous oxide, and fluorinated gases. Methane is a major emission from coal plants and agricultural processes. Nitrous oxide is a common emission from industrial factories, agriculture, and the burning of fossil fuels in cars. Fluorinated gases, such as hydrofluorocarbons, are emitted by industry. Fluorinated gases are often used instead of gases such as chlorofluorocarbons (CFCs). CFCs have been outlawed in many places because they deplete the ozone layer. Worldwide, many countries have taken steps to reduce or limit greenhouse gas emissions to combat global warming. The Kyoto Protocol, first adopted in Kyoto, Japan, in 1997, is an agreement between 183 countries that they will work to reduce their carbon dioxide emissions.


  1. Ambient Air Quality Standards in India

Ambient air quality refers to the condition or quality of air surrounding us in the outdoors. National Ambient Air Quality Standards are the standards for ambient air quality set by the Central Pollution Control Board (CPCB) that is applicable nationwide. The CPCB has been conferred this power by the Air (Prevention and Control of Pollution) Act, 1981.

Air (Prevention and Control of Pollution) Act 1981 was enacted by the Central Government with the objective of arresting the deterioration of air quality. The Air (Prevention and Control of Pollution) Act 1981 describes the main functions of the Central Pollution Control Board (CPCB) as follows:

  • To advise the Central Government on any matter concerning the improvement of the quality the air and the prevention, control and abatement of air pollution.
  • To plan and cause to be executed a nation-wide programme for the prevention, control and abatement of air pollution.
  • To provide technical assistance and guidance to the State Pollution Control Board.
  • To carry out and sponsor investigations and research related to prevention, control and abatement of air pollution.
  • To collect, compile and publish technical and statistical data related to air pollution; and
  • To lay down and annul standards for the quality of air

The mandate provided to the CPCB under the Air (Prevention and Control of Pollution) Act empowers it to set standards for the quality of air.

The current National Ambient Air Quality Standards were notified on 18 November 2009 by the Central Pollution Control Board. 

Table 1: National Ambient Air Quality Standards

PollutantTime Weighted AverageConcentration in Ambient Air



 Rural and 

Other Areas


Sensitive Area 

(notified by Central Government)

Sulphur Dioxide


24 hours**
50 8020 80

Nitrogen Dioxide


24 hours**
40 8030 80

Particulate Matter

 (size less than 

10 µm) or PM10 µg/m3

24 hours**
60 10060 100

Particulate Matter

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

24 hours**
40 6040 60
Ozone (O3) µg/m38 hours*
1 hour**
100 180100 180
Lead (Pb)
24 hours**
0.50 1.00.50 1.0

Carbon Monoxide 

(CO) mg/m3

8 hours*
1 hour**
02 0402 04
Ammonia (NH3) µg/m3Annual*
24 hours**
100 400100 400
Benzene (C6H6) µg/m3Annual*55
Benzo(a)Pyrene (BaP)- particulate phase only,
Nickel (Ni),
* 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 8 hourly or 1 hourly monitored values, as applicable, shall be complied with 98% of the time, they may exceed the limits but not on two consecutive days of monitoring.
Source: National Ambient Air Quality Standards, Central Pollution Control Board Notification in the Gazette of India, Extraordinary, New Delhi, 18th November, 2009


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