Winter air pollution & smog: CSE study notes fresh patterns

The overall average level of particulate matter 2.5 for the all 11 months in 2020 so far was considerably lower than the previous year, but the levels in winter went up to make the air “very poor” to “severe” levels across Delhi-NCR.

This implied that lower average level of PM2.5 throughout the year due to the lockdown imposed to curb the novel coronavirus disease (COVID-19) spread could not prevent the winter spike.

This was among the key highlights of an analysis done by the Delhi-based think tank Centre for Science and Environment. The daily PM2.5 levels increased by about 8-11 times between August — the cleanest month of 2020 — and November across Delhi-NCR.

This rise varied from 9.5 times increase in Delhi to 11 times in Ghaziabad; followed by Noida (9.2 times), Gurugram (6.4 times) and Faridabad (6.2 times).

CSE compared the annual averages of the cities and towns of the larger NCR region with that of Delhi and the big four (Gurugram, Faridabad, Noida and Ghaziabad).

It showed that even with much lower annual average level of PM2.5, other smaller NCR cities and towns experienced almost the same maximum levels during winter when the entire region is in an airlock.

Among other highlights of the analysis were:

• Winter air turned dramatically toxic as the share of PM2.5 in overall PM10 increased significantly: The percentage share of PM2.5 in the overall PM10 rose to over 70 per cent during the onset of winter from 47 per cent during the smog episodes in early November. The share of PM2.5 in PM10 was highest on Diwali, reaching over 80 per cent at many locations.
• The air quality for some days in November improved substantially without rains but with overall improvement in wind patterns. There are three days during the second half of November when the air quality improved to “moderately polluted” category in Delhi. This is the same as 2019, but the clean-up in 2019 was induced by rains.
• Local pollution across the monitoring locations in Delhi showed wider variations between the lower and upper ranges of pollution. This was in contrast to the range of variations noted last year, which was more upper bound.
• For example, on the peak smog day in November 2020, the PM2.5 levels in several stations varied from a lower bound 108 microgram per cubic meter (μg / m3) at NSIT to 699 μg / m3 at Mundka. In 2019, however, the variation was noted at a higher range — between 351 μg / m3 at Shadipur to 725 μg / m3 at Alipur — while the overall level stayed above 374 μg / m3.
• The smoke from crop stubble fire started impacting Delhi more discerningly from October 10, 2020 onwards. This was a week earlier than 2019, when it started on October 16, according to the CSE analysis. There were seven days in 2020 when the contribution of smoke to Delhi’s PM2.5 concentration exceeded 30 per cent in contrast to three days in 2019 and 2018.

According to Anumita Roychowdhury, CSE executive director-research and advocacy:

 “There was a change in the pattern this year that showed up in lesser number of smog episodes compared to last year, wider variation on location-wise concentration with more lower bound ranges compared to last year, higher number of days with greater contribution from the stubble burning among others. There are also days when pollution levels have dropped to moderate level even without rains but better wind conditions.”

She added there was a need to enforce power plant standards, eliminate coal from the industry, scale up public transport and vehicle restraint measures and manage waste to have a zero waste and zero landfill strategy.

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