The average PM2.5 level in the city’s air was 10 micrograms per cubic meter of air in a week in August

The city suffered its worst air pollution in two years in the first week of December, says a study by the Delhi-based Centre for Science and Environment (CSE).

According to the study, the average PM2.5 level in the city’s air was 10 micrograms per cubic meter of air in a week in August, when the air was the cleanest compared with other months of the year. It jumped to 130 in the first week of December.

Across the river, in Howrah, too, the December air has been found to be critically polluted. The corresponding PM2.5 level are 19 and 136.

Environment scientists said August was the cleanest because of a combination of reasons, including limited economic activity in early stages of unlocking and meteorological factors such as rain, which had considerably neutralised the pollution load.

“In the first week of December, Calcutta has experienced its worst week and peak in last two years so far with PM2.5 level,” the report states.

“There were a few days when Calcutta and Howrah air pollution levels were higher than Delhi,” it says.

Experts associated with the study — which analysed the winter air data from October 1 to December 6, generated at all automatic air pollution measuring stations in the city —  pointed out that the combination of heightened economic activity and meteorological factors have contributed to the jump in pollution.

Indian Meteorological Department (IMD) said visibility had dropped considerably, a tell-tale indicator of heightened pollution. The wind speed has been low, a typical winter phenomenon, leading to slow dispersal of pollutants.

“The visibility in Alipore this morning was between 60 and 100 metres. Under normal circumstances it remains about 1,000 metres. The wind speed also remained relatively low,” said G.K. Das, of IMD Calcutta.

The CSE study found that the air quality recorded by the automatic monitoring station on the BT Road campus of Rabindra Bharati University reached “severe” in the first week of December. At the other six stations in the city, the quality was “very poor”.

According to the study, the average PM2.5 level in the city’s air was 10 micrograms per cubic meter of air. It jumped to 130 micrograms in the first week of December. 

“The disturbing part is the finding that the share of PM2.5 has increased significantly within PM 10,” said Anumita Roy Choudhury, an air pollution expert of the CSE who led the study.

Ultrafine PM2.5 is considered much more lethal compared with the relatively coarser PM10. “The percentage share of PM2.5 in overall PM10 has gone up to 60 per cent during high pollution episodes from around mid-November and remained high at over 50 per cent since then,” the report says.

“The spike in pollution can be attributed to anthropogenic well as meteorological factors. The cooler December air leads to an inversion phenomenon that results in trapping pollutants closer to the ground. Heightened economic activity, too, has contributed to the rise in pollution,” said Roy Choudhury.

“This is a typical and predictable winter trend when continuous emissions from local sources, including vehicles, industry, construction and episodic pollution from biomass burning, get trapped because of meteorological changes,” said Avikal Somvanshi, from the CSE air pollution team.

Roy Chowdhury stressed the need for “systemic changes” to reduce the city’s air pollution. “Systemic changes like switching public transport to cleaner fuels or phasing out old commercial vehicles will take time, but these changes will lead to a drop in the city’s air pollution level,” she said.

The report published by the CSE said that the three-year annual average of Calcutta’s air quality was 41 per cent poorer than the standards set by the Central Pollution Control Board for the country. For Howrah, it was 42 per cent poorer.

Asked about the study, Kalyan Rudra, the chairman of the state pollution control board, said: “I have not seen the CSE report. Unless one critically considers the impact of meteorological factors, it becomes a one-sided report.”

Kolkata air pollution: worst week in two years – Telegraph India