The state government has sought details from auto emission testing centres of all vehicles that have failed pollution checks since August to prepare a list of polluting vehicles.

In a letter to 103 testing centres in Calcutta and Howrah, the transport department has sought a detailed report with the number of vehicles (commercial as well as private), types of vehicles and the make of their engines.

The data will be used to understand if the automated testing centres upload test figures on the Vahaan website and prepare a rough estimate of polluting vehicles around the time when the air quality index is “unhealthy” in Howrah and Calcutta, a transport department official said.

The air quality data provided by the Central Pollution Control Board revealed the level of PM 2.5 — an ultra-fine toxic pollutant — at Victoria Memorial at 7pm on Wednesday was 144, “unhealthy for sensitive groups”.

The level of PM2.5 at Padmapukur in Howrah on Tuesday was 156, “unhealthy.”

“We want to identify the types of vehicles that have failed the pollution tests and classify them as commercial or private,” the transport official said.

“We will then track these vehicles to see if they made necessary changes to clear the pollution test.”

In 2016, the National Green Tribunal had said that vehicular emission and “resuspension of road dust” had a direct correlation to the amount of particulates in the air in urban areas.

Prolonged exposure to particulates can trigger a host of critical ailments, including lung cancer, health experts have said.

The transport department has restricted BS III vehicles and tried to phase out 15-year-old ones in an attempt to tackle air pollution.

Recently, the department has started a system where details of a vehicle is uploaded on a website and only if it clears all the parameters can the vehicle undergo a pollution test.

In September, the National Green Tribunal had imposed a fine of Rs 10 crore on the Bengal government for failing to check air pollution despite repeated orders.

“Vehicular pollution is definitely a grave issue here.

Over 54 per cent of total vehicles plying in Calcutta and Howrah are very old and nearly 90 per cent of public buses run on diesel and are BS III,” environment activist Subhas Datta said.

“If you add low vehicular speed and high vehicle density to this, you have a deadly mix.”

Chief secretary Rajiva Sinha has convened a meeting on Friday to take stock of the measures that various departments, including environment, transport, urban development, and police have taken so far.