Some 70% of people in the city of Calcutta suffer from respiratory disorders caused by air pollution, a recent study by a prominent cancer institute in India has concluded.
Ailments include lung cancer, breathing difficulties and asthma, the Chittaranjan National Cancer Institute (CNCI) study says.
The CNCI is one of India's foremost research bodies, and its investigation took six years to complete.
One of its key findings was a direct link between air pollution among the 18m 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.
"Although the defence mechanism of the lungs is activated when exposed to high levels of air pollution, it only aggravates the problem and even leads to genetic disruption," says Twisha Lahiri, who conducted the CNCI study with five other researchers.
The city's highly polluted air is leading to the growing number of lung cancer patients," she said.
The ideal count of Suspended Particulate Matter (SPM) and Respiratory Particulate Matter (RPM) should not exceed 140 and 60 respectively.
But Calcutta's average SPM count is 211 and RPM count is 105. And in the worst polluted traffic intersections, this count can be double the city's average during busy hours.
"Calcutta's air pollution results from the horribly high levels of auto emissions which the authorities have failed to control so far. If this is not checked with a heavy hand, the impact on the health of Calcuttans, particularly children, will be devastating," says city doctor Parthasarthi Dutta.
Dr Dutta said he gets a huge number of patients, young and old, who are suffering from respiratory disorders, neurobehavioral problems and blood abnormalities.
"Such cases are on the rise," he says.
Residents of the city seem to accept their fate with equanimity.
"Anybody who stays outdoors in the city is at grave risk, so I continue to smoke because I will die of cancer in any case," says Shyamol Roy, who runs a roadside food stall.
Cart puller Dinesh Kumar, from neighbouring Bihar, came to Calcutta as a strong young man. Now he suffers breathlessness.
"Doctors told me I may get lung cancer, but I cannot leave the city because I will be out of work," he says.
Schoolgirl Srija Mukherjee has difficulty breathing, her eyes always burn, so her father Arpan Mukherjee sent her off to a boarding school in the hills of the tea-growing district of Darjeeling.
"I cannot risk my daughter's health, she is my only child," says Mr Mukherjee.
Street side occupants - particularly the hawkers who sell stuff - are the worst sufferers , the CNCI study says.
It says that 79% of hawkers who spend a long time outdoors have suffered damaged lungs.
Vehicle mechanics working close to car exhaust pipes were next highest - 60% of them suffered from damaged lungs.
The report says that traffic policemen, drivers and cart pullers who are exposed to vehicle fumes for long hours also suffer from damaged lungs in large numbers.
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.
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.
"It would have thrown Calcutta's transport system into chaos," says Madan Mitra of the Bengal Taxi Association. "The commuter would have suffered."
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.
"Over the past year, only 20% of the city's 1.5m registered vehicles reported for auto emission tests. The rest are getting away spewing out deadly smoke," said car emission expert SM Ghosh.
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.
"The toxic fumes released by them pollutes the city's air more than anything else, but no one can touch the auto-rickshaws because they have powerful trade unions," says environmentalist Subhas Dutta.
"It again becomes an employment issue," he said.