National Ambient Air Quality Standards

India's National Ambient Air Quality Standards (NAAQS) specify acceptable concentrations of pollutants in outdoor air to protect human health and the environment. They provide pollutant-specific benchmarks over defined averaging periods, allowing measured air quality to be assessed against a common national standard.

Purpose of the standards

The central purpose is to establish a consistent basis for identifying and controlling air pollution, rather than judging air quality only by visible smoke or public complaints.

• The standards seek to protect human health, vegetation and property from the harmful effects of air pollution.
• They provide benchmarks for assessing air quality across locations and tracking changes over time.
• They help identify areas where pollution control is needed and support the setting of priorities for air-quality management.
• They provide a reference for assessing whether pollution-control measures are improving ambient air quality.

Legal basis and pollutants covered

The Central Pollution Control Board (CPCB) is empowered to lay down air-quality standards under Section 16(2)(h) of the Air (Prevention and Control of Pollution) Act, 1981. The revised NAAQS notified in 2009 cover 12 pollutants.

• The pollutants are sulphur dioxide, nitrogen dioxide, PM10, PM2.5, ozone, lead, carbon monoxide, ammonia, benzene, benzo(a)pyrene, arsenic and nickel.
• Standards specify both pollutant concentrations and averaging periods because short-term exposure and sustained exposure require different assessment.
• The standards apply to industrial, residential, rural and other areas, with separate annual limits for sulphur dioxide and nitrogen dioxide in notified ecologically sensitive areas.

How the standards guide air-quality management

Monitoring results are compared with the relevant standard to assess compliance and identify pollution problems. For example, the PM2.5 limits are 40 micrograms per cubic metre as an annual average and 60 micrograms per cubic metre over 24 hours.

• Comparison with the appropriate averaging period helps distinguish persistent pollution from shorter-duration episodes.
• Exceedances provide a basis for investigating pollution sources and planning measures such as industrial pollution control, cleaner transport and dust management.
• Ambient standards are not emission standards: NAAQS concern the concentration in outdoor air, whereas emission standards regulate pollutants released by particular sources.
• NAAQS establish the benchmark to be achieved; effective improvement also requires monitoring, source control and implementation by responsible authorities.