The ongoing lockdown due to COVID-19 pandemic has pushed pollution levels in Delhi to a 5-year low and, across India, the number of cities that recorded ‘good’ on the air quality index jumped from 6 — on March 16 — to 30 as on March 29, according to data from the Central Pollution Control Board.
PM 2.5, the most dangerous pollutant, measured at the pollution monitoring station in Anand Vihar, New Delhi, ranged from 16 μg/m³ - 42 μg/m³ (microgram per metre cubed) from March 25 to April 1, the first week of the lockdown.
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By comparison, PM 2.5 had ranged from 72-187 μg/m³ during the corresponding period last year, and 72-171 μg/m³ in 2018. In 2016, it spanned 49-116 μg/m³, station data on the website of the CPCB shows.
It wasn’t possible to compare the air quality index, which is a weighted average of the contribution of several pollutants, in this week from that in previous years, as such data wasn’t available on the website.
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The CPCB in a report on the impact of the ‘Janata curfew’ on March 22 , said that on the day before, AQI was ‘Moderate (101-250)’ in Delhi. “Overall, up to 44% reduction in PM10 levels was observed in Delhi during March 22-23, 2020, compared to previous day. The PM2.5 reduction was 8% on the curfew day but declined to 34% next day owing to negligible combustion activities on March 22-23, 2020, in and around the city.”
The key factor that triggered the decline was the number of on-road vehicles, which contributed to a 51% reduction in NOx levels and a 32% reduction in carbon monoxide levels during March 22-23 as compared to March 21.
Unlike in the winter months, Delhi and other regions of the Indo Gangetic Plains generally tend to have better air quality in March, aided by consistent wind and sunlight, which help flush out pollutants. “The impact of meteorological factors was partially favourable... however the reduction in air pollution can be largely attributed to transport and commercial-industrial restrictions,” the CPCB said in its report.
Research studies have attributed the key sources of PM2.5 in summer to be: dust and construction activities (35%), transport sector (20%) and industry (20%).
During the lockdown PM10 and PM2.5 levels were reduced by about 35-40%. The cessation of industries contributed to this reduction by 10%, vehicles 10-15% and dust another 10-15%, the organisation calculated.
As on March 29, a total 91 cities were under ‘Good’ (0-50) and ‘Satisfactory (51-100)’ categories, with 30 cities with ‘Good’ AQI values. However, Lucknow, Muzaffarpur, Kalyan, Guwahati and Singrauli were under ‘Poor’ category during March 25-28. High emission levels in Lucknow and Guwahati were noted for PM2.5, attributable to ‘local’ combustion related activities. As on March 29, no city was under ‘Poor’ AQI (251-300) category.