Winter pollution set in Greater Mumbai 2 weeks earlier this year: CSE

High winter pollution began in Greater Mumbai and other major cities of Maharashtra two weeks before season, after the novel coronavirus disease pandemic unlockdown opened the economy, the Centre for Science and Environment (CSE) said December 11, 2020.

The non-profit released its analysis on the issue. The analysis is based on publicly available granular real time data (15-minute averages) from the Central Pollution Control Board’s official online portal Central Control Room for Air Quality Management, according to a statement by CSE.

Ten cities — Mumbai, Navi Mumbai, Thane, Kalyan, Pune, Nagpur, Nashik, Aurangabad, Solapur and Chandrapur — were selected for the analysis because real time data was available for them.

Data recorded by 10 air quality monitoring stations in Mumbai, three in Navi Mumbai, two in Chandrapur and one station each in Thane, Kalyan, Pune, Nagpur, Nashik, Aurangabad, and Solapur, was analysed.

Weather data for Mumbai was sourced from the Santa Cruz weather station of the India Meteorological Department.

The overall average level of particulate matter (PM) 2.5 for 11 months in 2020 was considerably lower than the previous year due to the pandemic related to the summer lockdown.

However, the PM2.5 levels in winter rose beyond the standard in the Greater Mumbai region and rest of Maharashtra, the analysis said.

This began in October. The PM2.5 average during that month was 25 per cent higher in Mumbai, 26 per cent in Navi Mumbai and 28 per cent in Kalyan, compared to the corresponding time in 2019.

November was also dirtier, with the monthly average higher by seven per cent in Mumbai, 21 per cent in Navi Mumbai and 31 per cent in Kalyan. Cities outside the Greater Mumbai Region had similar or lower November average as last year.

It was a dirtier Diwali this year in Mumbai. The average PM2.5 level on Diwali day in Mumbai was 76 microgramme per cubic metre (μg / m3) — up from 53 μg / m3 recorded in 2019.

This year, there was about 75 per cent higher rise in hourly PM2.5 concentration between afternoon and night of Diwali that is mostly caused due to firecracker bursting.

The change in hourly PM2.5 concentration between afternoon and night of 2020 Diwali was 145 μg / m3, up from 83 μg / m3 in 2019. Diwali also occurred later in November than the previous year.

“Even though trapping of winter pollution in the Greater Mumbai region is not as high as that of the Indo-Gangetic Plain due to its proximity to sea and better ventilation, the levels increased during winter despite the geographical advantages and favourable meteorology. This indicates high local pollution and strong regional influences,” Anumita Roychowdhury, executive director-research and advocacy, CSE, was quoted as saying in the statement by the non-profit.

The fact that PM2.5 levels in Greater Mumbai rose from October onwards this year, two weeks earlier in the season, was an indication of the changing nature of winter pollution in the area, Roychowdhury said.

Also, the average PM2.5 levels in October and November had been 25-30 per cent higher in Greater Mumbai compared to the previous October and November. “It is clear that this region cannot rely only on its locational advantage of proximity to the sea,” Roychowdhury said.

To avoid winter pollution peaks, all cities of Maharashtra will have to reduce the annual average level of pollution across all cities to meet the national ambient air quality standards and even bring it further down to be closer to the health-based guidelines of the World Health Organization to protect public health, the CSE statement said. 

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