Clean air during Durga Puja, but Kolkata AQI backslides as winter approaches

An analysis of the air quality index during Durga Puja showed that Kolkata enjoyed clean air during the festival, but pollution worsened to usual levels almost immediately afterwards.

An analysis of the air quality index (AQI) during Durga Puja showed that Kolkata enjoyed clean air during the festival, but pollution worsened to usual levels almost immediately afterwards.

Traffic regulations were imposed in the city from October 17 to 24 this year; apart from relieving pandal hoppers and daily commuters, and helping to maintain emergency services, this move also reduced air pollution levels. The rainy weather during the festival, when lakhs of people descended on the city, also improved the air quality.

The mean daily AQI dropped steadily from 122.75 on October 18 (moderate) to 74.41 (satisfactory) on October 23 on the eve of Navami, and then dipped further to 44.39 (good) on October 24 on the eve of Maha Dashami. While PM10 levels had been slightly above the 60 ug/m3 permissible limit prescribed the Central Pollution Control Board, the PM2.5 concentration was marginally below the prescribed 40 ug/m3 limit. Both saw a drastic drop on Maha Dashami itself, on October 24.

After Durga Puja, however, air quality deteriorated drastically, following the removal of traffic regulations. The AQI promptly spiked back to the moderate category, hitting 102.51 by October 27. The AQI data was compiled by SwitchON Foundation, based on an analyisis of data from several stations of the West Bengal Pollution Control Board, placed in different parts of Kolkata.

“The air quality improved pleasantly during the Durga Puja festivals, but it has regrettably deteriorated to pre-puja levels once more. This decline can be largely attributed to reduced vehicle movement and weather events,” said Vinay Jaju, managing director of the SwitchON Foundation.

Experts emphasises that the October 10 traffic notification from the Kolkata Police, which prohibited all types of goods vehicles on the city’s roads between 8 a.m. and 4 a.m. (except emergency services) from October 17 to 24, helped improve air quality.

The presence of low-pressure systems and the rainfall, particularly during the last day of Durga Puja, also contributed to a reduction in air pollution within the city. This favourable weather condition alleviated the usual pollution concerns associated with the festive season, when lakhs of people descend on the streets.