The national air quality index (AQI) programmes will allow the authorities to represent concentrations of eight key air pollutants that pose risks to human health through single numbers to classify air quality as good, satisfactory, moderate, poor, very poor or severe.

“This index will provide citizens one number, one colour and one description, and inform them about the quality of air they’re breathing,” Prakash Javadekar, the Union environment and forests minister, said today, releasing a document outlining the AQI system.

“This is another step towards a cleaner India,” Javadekar said.

The Central Pollution Control Board had assigned a panel of environmental scientists the task of developing the AQI as an information dissemination system to serve as an alternative to the current air quality indicators — a series of concentrations of different air pollutants.

The AQI will assign the air quality over a city or a site within a city a number between 0 and 500, with good air quality represented by a figure between 0 and 50 and severe air pollution indicated by a figure over 401. (See chart)

“We’ve taken into account the potential health impacts of all the eight pollutants to develop this classification system,” said Mukesh Sharma, a professor of civil engineering at the Indian Institute of Technology, Kanpur, who led a research team that developed the software programs for the AQI.

Under the AQI classification, an air quality number between 0 and 50 will have “minimal impact” on health, a number between 51 and 100 may cause “minor breathing discomfort to sensitive people”, while a number between 401 and 500 may cause respiratory impact even on “healthy people, and serious health impacts on people with lung and heart disease and these impacts may be experienced even during light physical activity.”

The pollution control board wants the AQI system implemented in 20 state capitals and 46 other cities with populations of a million or more in the first phase over the next five years, a senior pollution control board official said.

Although the AQI was developed by a panel of scientific and technical experts in consultation with respiratory disease specialists, the official said, its technical details will be available on the pollution board website for 45 days seeking additional comments from other experts.

“We’re hoping some cities could start issuing numbers by this December,” the official said.

The AQI will combine the concentrations of carbon monoxide, ozone, nitrogen dioxide, sulphur dioxide, ammonia, lead and particulate matter smaller than 10 microns and 2.5 microns to generate a single number indicating the quality of air.

“It’s hard for people to interpret concentrations, the single number will tell them the quality of air from the health point of view,” Sharma said. “For example, he said, a concentration of 300 micrograms per cubic metre of particulate matter PM10 would map on the AQI to a value of 350, which would instantly tell us that the air quality is poor.”

A pollution board official said a large city could have several sites monitoring the concentrations of pollutants — and each site may issue its own number.

The non-government Centre for Science and Environment has hailed the ministry’s decision to introduce the AQI as a health advisory that will quickly inform the public about the quality of air in their neighbourhood or cities.

“We’ve been waiting for something like this a long time,” said Anumita Roychowdhury, the head of the CSE’s air pollution team. “Such numbers are needed to demystify air quality data, promote public awareness and build public pressure for effective air pollution control.” Several cities such as Beijing, Paris and Mexico City, she said, have already implemented similar air quality index numbers.