Calcutta, Dec. 16: Ambarish Choudhury has never touched a cigarette in his life.

So four months ago, when the family physician told him he had lung cancer, the 45-year-old?s first reaction was disbelief.

What he did not realise was even if he stayed away from the potentially lethal puff, the city?s air is foul enough for a breath of death.

?People are yet to realise that the high level of air pollution, caused by auto-emissions, is also a major contributor to the high incidence of lung cancer in the city,? Subir Gangopadhyay, a leading oncologist and former head of radiotherapy, Medical College and Hospital, said today.

The comment came a day after the Bengal government managed to slip out of the high court?s focus after twice failing deadlines to meet tailpipe emission norms. So far, only three auto emission testing centres ? which can measure levels of pollution under the new norms notified by Delhi ? have been ?upgraded? instead of the 50 the state said it would set up.

Oncologists say the highly carcinogenic unsaturated hydrocarbons, emitted from diesel exhausts, get deposited in the lungs. Within a few years, the carcinogens cause malignancy.

Similarly, chemical carcinogens, floating in Calcutta?s atmosphere, can also damage the lungs if inhaled regularly over a long period of time.

?Air pollution, rampant in Calcutta, can be said to be the single largest cause of lung cancer,? said Kalyan Bhattacharya, head of radiotherapy at NRS Medical College and Hospital.

A recent survey by the Chittaranjan National Cancer Institute revealed that lung function of 56 per cent of the city?s adults was impaired. The survey was conducted in the city as well as in the districts.

?What is astounding is that only 2 per cent of the total lung cancer patients hail from all the districts of Bengal,? Gangopadhyay said, quoting National Cancer Registry figures.

?Diesel exhaust does choke up the lungs and cause cancer and that perhaps explains why lung cancer patients are more in the cities, specially in a polluted city like Calcutta than perhaps somewhere in Bankura,? said cancer surgeon Gautam Mukhopadhyay.

Figures from state-run hospitals for the past decade underline how far Calcutta?s foul air has wreaked havoc. Of the over 200,000 cancer patients diagnosed and treated at government hospitals during the period, 15 per cent had lung cancer, Gangopadhyay and other oncologists said.

?Most of the lung cancer victims,? they added, ?are non-smokers?. Of them, at least 20 per cent were women who came from a middle-class background and had nothing to do with tobacco.

According to health department statistics, state-run hospitals in the city report around 70 new patients everyday, of whom over 15 per cent suffer from lung cancer.

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