AQI notifies the public about the declining air quali ty level of each city and what the possible associated health hazards. The pollution board will study air pollution levels in 13 cities - Delhi, Agra, Kanpur, Lucknow, Varanasi, Faridabad, Ahmedabad, Chennai, Bengaluru, Hyderabad, Jodhpur, Mumbai and Pune -round-the-clock. Particulate matters in 180 Indian cities are six times higher than WHO standard.

Air Quality Index is the only tool that provides the correct information about air quality to people. An expert group comprising medical professionals, air quality experts, academics, advocacy groups, and state pollution control boards has been constituted and a technical study was awarded to IIT-Kanpur. , said a CPCB official.

The AQI has seven sub-categories, namely good, satisfactory, moderately polluted, poor, very poor, and severe.

"The proposed AQI will consider eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short term (up to 24-hourly averaging period) National Ambient Air Quality Standards are prescribed. The PCB right now has only two automatic air-quality monitoring machines, while the reading of manual machines are inconsistent," said Somendra Mohan Ghosh, an automobile emission expert.

Likely health impacts for different AQI categories and pollutants have also been suggested, with inputs from medical experts of the group.

India, being the world's third-largest emitter of greenhouse gases, has pledged to limit the amount of carbon dioxide per unit of GDP. Even China had done the same.

According to WHO study, 15 Indian cities are among the top 20 in the world as far as fine particulate matter (PM2.5) is concerned.

The indexing becomes relevant after India's commitment at the global climate summit at Paris. India has promised to reduce the pollution by 35% from the pre-2005 environment.