The National Green Tribunal has directed the state pollution control board to widen the ambit of measuring Calcutta's air pollution.
The steps the eastern zonal bench of the tribunal asked the board to take include measuring PM2.5 at automatic monitoring stations.
The order was passed on a public interest litigation by environment activist Subhas Datta.
PM2.5 (ultrafine particulate matter less than or equal to 2.5micron in size) is considered the most potent pollutant because of its ability to reach the deepest parts of the lungs and trigger several pulmonary diseases, including lung cancer.
The prevalence of the particulate matter in Calcutta's air is now measured manually, though most major cities get their levels measured by automatic monitoring stations.
The city has two automatic and 17 manual air pollution monitoring stations.
The tribunal bench comprising Justice P.K. Roy and P.C. Mishra also directed the board to measure the pollution level in the city on all seven days, instead of only two days, as is the practice.
The board has also been asked to conduct a study to assess the sources and causes of air pollution and set up an auto-emission testing centre every 5sq km.
The bench also wants the results of the emission tests to be made available to the pollution control board online.
The bench accepted a petition by Datta pleading for an order to modify the air pollution expert committee, set up by the tribunal, on the grounds that it lacks expertise.
"If the air pollution level is properly measured, the true picture of the city's air pollution and the role of vehicles will be exposed. We have reasons to believe that the present system of measuring air pollution does not reflect the actual level of pollution in city, which is very close to that of Delhi," Datta said.
A board official said the automatic air pollution measurement centres in the city would soon start recording PM2.5.