The Union ministry of environment and forests has described Calcutta’s air quality as “significantly” worse than the national standard, saying that it is the state government’s responsibility to clean it up.

“The West Bengal Pollution Control Board is duty-bound to monitor the ambient air quality in Calcutta and to take all steps for air quality control,” the ministry has said in an affidavit filed before Calcutta High Court.

It requested the court to monitor steps to combat air pollution.

Although the ministry did not accuse the state government, of which the pollution board is an organ, of failure to improve the air quality, the comment that it is far worse than the national standard is indictment enough.

The ministry has also left Calcutta out of a study of air pollution in large cities because the state did not show any interest.

State government sources said the pollution control board argued that the Asian Development Bank (ADB) had conducted a similar study on Calcutta in 2004-05.

“There were a lot of problems in the report and questions were raised about the veracity of the ADB findings,” said a senior board official.

Subhash Dutta, who brought the matter of air pollution to the court’s notice, said he would mention Calcutta’s omission from the study — undertaken for Delhi, Mumbai, Bangalore, Chennai, Kanpur and Pune — at the next hearing.

“The biggest contributors to pollution in Calcutta are old vehicles, which constitute around 54 per cent of the city’s vehicular population. The state government has done nothing to phase out these vehicles,” said Dutta.

Phasing out of old vehicles is a political issue in Bengal as the transport sector is a key constituency of the CPM.

The affidavit recommended concerted action, under the monitoring of the high court,for phasing out old vehicles.

“It is for the Union ministry of surface transport and the state transport department to take appropriate action in this regard,” it said.

Under the Air Act 1981, the state environment department and the pollution control board are responsible for ensuring healthy air quality within their territorial jurisdiction.

In all other cities, state governments have initiated the phasing out of old vehicles and introduced cleaner fuel, like LPG.

“It’s a fact that we have a role in the process,” said environment secretary M.L. Meena.