The CSE report says there were 10 days of ‘severe’ and ‘severe-plus’ air quality and one four-day-long smog episode during the winter. , Photo Credit: File Photo SUSHIL KUMAR VERMA

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The winter of 2022 was Delhi’s “cleanest” in the last five years, though its air remains “toxic”. The main determinants for the improved air quality were favorable meteorological conditions as well as a reduction in pollution from farm fires, Delhi-based think tank, the Center for Science and Environment (CSE), said in a report on Monday.

The city-wide winter average for Delhi stood at 160 µg/m³ in the winter that spans from October to January. This was the lowest since wide-scale monitoring started in 2018-19, and the number refers to the PM (particulate matter) 2.5 level, computed by averaging monitoring data from 36 CAAQMS (Continuous Ambient Air Quality Monitoring Stations). PM 2.5 particles are linked to respiratory diseases and responsible for reducing the quality of life.

“This improvement is a combined effect of meteorology and emergency action based on pollution forecasting. There was heavy and extended rainfall in the early phases of the season that prevented smog episodes from building up and also lowered the seasonal average. Despite the decline, Delhi continues to remain the most polluted among the cities and towns of NCR. This downward trend will have to be sustained with much stronger action on vehicles, industry, waste burning, construction, solid fuel and bio mass burning to meet the clean air standard,” the organization said in a press statement.

There was also a decline in peak pollution. This winter, the most polluted day saw the air quality index soar to 401 µg/m³ on November 3 — a five year low. Three of the last five years saw the peak cross 500, with the most being 546 in 2019. To be sure, a value exceeding 400 is still classified as an episode of ‘severe’ pollution. India’s National Ambient Air Quality standards prescribe that the 24-hour PM 2.5 concentration not breach 60 µg/m³.

The CSE’s numbers, sourced from the Central Pollution Control Board (CPCB), suggest that a factor behind reduced pollution last winter was a drop in instances of ‘severe pollution’. There were only 10 days when air quality was ‘severe’ or ‘severe+’ — the highest levels of pollution. In comparison, there were 24 such days in 2021, 23 in 2020, 25 in 2019, and 33 in 2018.

This winter not only saw a lowering in the quantity and intensity of farm stubble fires but also favorable meteorological conditions that were less conducive for the transport of the smoke. Total smoke that fell upon Delhi in from of PM2.5 has been considerably less. CSE estimated that about

As many as 4.1 tonnes of PM2.5 fell over Delhi in the ’22 winter in the form of smoke –37 per cent less than 6.4 tonnes that fell in 2021 and almost half of that in 2020.

“The analysis shows that there were still 10 days of severe and severe-plus air quality and one four-day long smog episode during this winter. In the larger NCR, seasonal averages varied considerably among the cities and towns, but high pollution episodes were synchronized despite large distances,” Avikal Somvanshi, senior program manager, Urban Lab, CSE, said in a statement, “Delhi and the neighboring cities of Faridabad, Ghaziabad, Gurugram and Noida were relatively more polluted than other NCR towns, though not significantly. This is the challenge of this landlocked region that demands even stronger action.”