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Winter damper & hilsa hope for Calcutta
Pollutants robbing weather of chill

Calcutta, Jan. 6: The high concentration of fine particulate pollutants in Calcutta’s air and the fumes from diesel-run vehicles may be helping warm the city’s winters and disturb its normal monsoon trends apart from choking people’s lungs, experts say.

Calcutta has had a prolonged chill this winter but that is more of an aberration: overall, winters in the city have become “significantly warmer”, studies have found.

“The aerosols — fine particulate matter embedded in water droplets — can influence local warming and the monsoon pattern,” J. Srinivasan, professor at the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science, Bangalore, said today at the Indian Science Congress here.

Srinivasan later told The Telegraph that though aerosols and other particulate matter were earlier thought to only contribute to cooling by resisting the Sun’s rays, it was now established that particulate matter containing black carbon could play a role in warming the climate.

Anumita Roy Choudhury, a transport pollution expert from the Delhi-based Centre for Science and Environment, was more categorical.

“While the sulphate particulate and its aerosol contributes to cooling, particulates with black carbon absorb heat and contribute to warming,” she said.

“Calcutta is a fit case for the second phenomenon as it has very high concentrations of particulates from fossil fuels, especially diesel, which contain black carbon. The warming impact of black carbon emissions from diesel vehicles is now established.”

A Pune University study of long-term temperature trends in India’s four biggest cities in the 20th century, based on India Meteorological Department (IMD) data, shows that Calcutta’s minimum winter temperatures have risen by about 1.09C in the past 100 years. The study linked this to increased urbanisation.

IMD experts agree that the monsoon has become significantly irregular in the city, and particularly skewed over the past decade.

According to the Centre for Science and Environment, Calcutta may be considered the country’s “diesel capital”, with nearly 65 per cent of all its vehicles and nearly 99 per cent of its commercial vehicles being run on diesel.

“Besides, nearly 65 per cent of city vehicles are over 15 years old. Although 15-year-old commercial vehicles have been banished from the city’s core areas after a high court order in 2008, the situation has not changed much in Greater Calcutta,” an expert said.

Srinivasan said: “While the complete role of diesel-driven particulate matter in climate change is yet to be confirmed, there is no doubt about the negative effects of such toxic particulates on health. Your government should act in this direction.”