By Subir Bhaumik BBC News, Calcutta

Few vehicles are tested for pollution emissions

Police stations across the Indian city of Calcutta have been equipped with oxygen devices to enable police to offset the effects of pollution.

The extra air is for the benefit of hundreds of traffic policemen in the city who have to brave some of the worst pollution in the world.

The move follows a recent report which said that some 70% of people in the city suffer from respiratory disorders.

It said that traffic police were among the worst hit by poor air quality.

Oxygen concentrators

Ailments include lung cancer, breathing difficulties and asthma, the Chittaranjan National Cancer Institute (CNCI) study said.

The CNCI is one of India's foremost research bodies, and its investigation - published earlier this month - took six years to complete.

In pictures: Calcutta's pollution battle

One of its key findings was a direct link between air pollution among the 18 million people of Calcutta and the high incidence of lung cancer.

Calcutta tops all Indian cities when it comes to lung cancer - at 18.4 cases per 100,000 people - far ahead of Delhi at 13.34 cases per 100,000.

But now the city's 11 traffic offices, where policemen report for duty, have been equipped with oxygen concentrators that are normally used for patients in hospitals.

Calcutta's traffic police chief, Javed Shamim, says his men have the facilities to take oxygen for at least 20 minutes after doing an eight hour shift amid the dust and smoke of the city.

Auto rickshaws are one of the worst pollution offenders

However doctors caution that taking in oxygen may not help the policemen because many of the pollutants are too deeply lodged in their lungs.

Only 10% of Calcutta's 1.5m vehicles have converted to green fuels - and only 20% of those have taken an emission test in the last two years.

Environmentalist Subhas Dutta filed a public interest litigation in the Calcutta High Court in March this year, alleging that the West Bengal government was doing nothing to control air pollution levels.

Deadline

The court ordered the government to reduce vehicle emissions.

"This is a killer but the government is doing nothing to check it," alleged Mr Dutta.

In May 2005, the government set a deadline which ordered all vehicles in Calcutta manufactured before 1990 either to be off the roads or convert to greener fuel like LPG.

Nearly 80% of the city's buses and trucks and nearly 50% of its taxis and auto-rickshaws would have gone off the roads if the government enforced its directive.

The area around Calcutta is covered in smog

But the Calcutta High Court quashed the government directive, and though the government challenged it in a higher bench, the case has yet to come up.

Only 10% of Calcutta's vehicles have converted to greener fuels like LPG.

The worst offenders are around 50,000 auto rickshaws - half of them unregistered - who use "kantatel". This is a fuel made out of a deadly concoction of kerosene and petrol.