The flip side of the unusually chilly winter that Calcutta craved and got this season is a spurt in the particulate content of the city’s already noxious night air.
A measure of how polluted the night air has been lately is the pollution control board’s reading of 735.8 micrograms of respirable particulate matter per cubic metre of air at Rabindra Bharati University on BT Road at midnight on New Year’s Eve.
For the entire first week of January, the average RPM in the city was 232.32 micrograms, lower than its night-pollution level but close to two-and-a-half times the national standard of 100 micrograms per cubic metre.
Respirable particulate matter is tiny enough to be inhaled but the health implications are huge.
“As the automatic air-pollution data generated at Rabindra Bharati suggests, busier the traffic at night, more the pollution. BT Road has a high density of goods vehicles at night,” a pollution control board official said.
The crackdown on polluting vehicles in Calcutta has long gone cold and it needed a chillier than usual winter to bring the government’s pollution-control bluff back into focus. “A comparison of the daily average concentration of RPM levels with that of night time shows that during winter, the night-time readings are more than the daily average concentration (of particulates) in Calcutta,” states a recently released PCB report based on collated data from 2011 and 2012.
More frightening is the level of PM2.5, the tiniest yet deadliest particulates of 2.5 micron or less in diameter. The first week of January saw the presence of PM2.5 in the city air soar to 184.8 micrograms per cubic metre, three times the permissible limit of 60.
Jadavpur University’s pro vice-chancellor Siddhartha Datta, who is an expert on the subject, said the impact of air pollution was heightened on winter nights because of inversion. “Cooler night temperatures trap air pollutants close to the ground and pollution levels become very high. Almost static air adds to the trend.”
Temperatures had been consistently below normal from late December until last week, barring a couple of days in between.
The weather may have played its part in Calcuttans inhaling more toxic particulate matter this winter but the buck stops at babuland, where there has been little effort against pollution by commercial vehicles despite judicial directives.
Environment activist Subhas Datta pegs the number of fume-belching, overweight trucks trundling through town at 50,000 in a single night. Add to that the banned taxis older than 15 years that ply on city roads at night and you have the perfect smokescreen.