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Small, deadly and diesel-driven
- Why The Telegraph has been running a clean-air campaign

The Calcutta air is not just foul -- it’s fatal.

The smaller the polluting particle, the more potent it is. And about 70 per cent of the respirable suspended particulate matter (RSPM) in the Calcutta air is 3.3 microns or less. This is small enough to reach the innermost areas of the lungs — brochii and alveoli — causing irreparable damage, says a survey.

Till now, 10 microns or less has been the standard index of respirable air pollution. But a recent study carried out by the West Bengal Pollution Control Board (PCB) and the environment department of Jadavpur University (JU) has lowered the micron count (to 3.3 and less), raised the danger level (from damaging to deadly) and pinned the pollution blame (on diesel-driven vehicles).

“This study, carried out for the first time in the country, is vital, as the small and deadly particulate matters of 3.3 micron or less have been found to dominate the city air. These small particles are deadly, as they go deep into the lungs,” explained a researcher with the project.

Titled ‘Distribution of Particulate Matter in sub-PM 10 fraction in Ambient Air of Calcutta’, the study aims “to prepare a database on exact distribution of different micron categories of particulate matter in Calcutta’s ambient air”.

The study was carried out in and around seven stretches of the city — Moulali, Ultadanga, Gariahat, Park Street, Rajabazar, Park Circus and Salt Lake — from October 2002 to January 2003.

“The specified sample points were chosen as we wanted to study the status of air-pollution exposure to children. The chosen spots were either close to schools or had several students passing through. We got an indication of the ambient air these children are exposed to, for four to six hours daily, five days a week,” added another researcher.

Samples were raised continuously for 24 hours and fractions measured through an instrument called the Anderson sampler. The findings are frightening, warn experts. If particulate fractions of 3.3 microns and below constituted, on an average, about 70 per cent of the air monitored, at Park Street and Rajabazar, the polluting count touched 80 per cent. What’s more, at all the sampling sites, the concentration of particles in the 0 to 2-micron range was found to be “maximum”.

“In effect, it means that these small and deadly particles — emitted primarily by diesel-driven vehicles — constitute about half the total suspended particulate of the city air,” said a PCB researcher. “We plan to study the health effects of the exposure during the subsequent editions of this ongoing project with the help of the students,” he added.

The PCB-JU environment department study findings would explain the World Bank report, stating that there had been 5,726 estimated “air pollution-related premature deaths” in the city during 1991-92. And a similar study by the Centre for Science & Environment that put the “death due to pollution” figure at 10,647 for the year 1995. Between 1991 and 1995, the estimated number of hospitalisations and sickness related to air pollution in the city also rose to 55 lakh from 30 lakh.

“One of our previous studies carried out by Chittaranjan Cancer Hospital and the zoology department of Calcutta University also showed that an average Calcuttan is 10 times more exposed to air pollution than somebody living outside the city area, due to the high levels of vehicular pollution,” said a scientist involved with the present study.

Yet, the state transport department continues to fight for — not against — the fume-belching vehicles that blacken our lungs and choke our city.

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