Pollution in March spikes after winter-like wind lull

Pune: Winter pollution is a given each year, but air quality improves considerably during summer.
But this March seems different, data from System of Air Quality and Weather Forecasting and Research (SAFAR), Indian Institute of Tropical Meteorology (IITM), indicates.

The last eight days of March show high particulate pollution levels in the city, where pollutants have not only crossed the maximum permissible limit but are also significantly higher than the same period in 2017, and in the winter month of December 2017.

Pune's air quality index has plunged to a dirty 'yellow' like Mumbai this summer, from the clean 'green' of the same period, last year. SAFAR scientists said though this is normal for Mumbai, it is an anomaly for Pune.

A comparison with the same period last year shows that the average 24-hour values of the pollutant PM 2.5 (particles less than 2.5 micrometers in diameter), which is considered more harmful than other pollutants, shot up by over 30% to even 50% during different days in March 2018.

PM 2.5 levels during the last few days were also significantly higher than those recorded during some days in December.

Gufran Beig, project director of SAFAR, said colder temperature in winter causes the boundary layer of the atmosphere to descend. This, coupled with calm winds during winter, causes pollutants to get trapped near the earth’s surface, hindering their dispersal. This is why pollution surges during winter.

However, though temperatures during the last few days have soared, touching 35 degrees celsius and even crossing this mark in some locations, pollution seems to be hanging around.

“Normally, as temperatures increase, wind speed also tends to rise simultaneously. The wind speed should have increased in March this year. But it has not happened. Pune’s air quality index, which usually depicts ‘green’ in March—indicative of a ‘satisfactory’ air quality—has plunged to ‘yellow’, indicating moderate air quality, which is still not healthy,” Beig said.

A ‘moderate’ air quality is normal for Mumbai this time of the year, it is unusual for Pune, he added. “Though the reasons behind a decreasing wind speed are still being debated, the general view is that stagnant wind conditions are on the rise,” he said.

He said that road construction works, which seem to have increased in the city lately, contribute more to PM 10 (particles less than 10 micrometers in diameter) and relatively less to PM 2.5.