Lockdown helps city breathe easy
STUDY OF THREE PHASES Steep drop in nitrogen dioxide levels; SO2 concentration in air rises
have found that the average concentration of most pollutants in the city’s air fell during the first three phases of the lockdown (from March 25 to May 18).
An analysis of pollutant data available from the monitoring stations of the Central Pollution Control Board (CPCB), done by Urbanemissions.info, found that the levels of five out of six pollutants were lower in the last two months, as compared to prelockdown levels.
Urbanemissions.info, an air pollution research group, studied the concentration of particulate matter (PM2.5, PM10), nitrogen dioxide (NO2), sulphur dioxide (SO2), ozone (O3), and carbon monoxide (CO) over the 54 days of lockdown, divided into three phases. The first phase of the lockdown was from March 25 to April 14; the second, from April 15 to May 3; and the third, from May 4 to May 17. Levels were compared with a 30-day average (February 20 to March 22) during the pre-lockdown period. While levels for most pollutants dipped, SO2 saw a spike during lockdown.
Average levels of PM2.5 — breathable particulate matter of 2.5 micron size or smaller — fell from 45 microgrammes per cubic metre (µg/m3) during pre-lockdown to 27.8 µg/m3 during the first phase and then to 23.3 µg/m3 and 22.6 µg/m3 in second and third phases respectively. A similar trend was observed for CO and O3. The most substantial decline was witnessed for NO2 — produced by burning of coal, oil, and emissions from vehicles — which fell from pre-lockdown levels of 37.5 µg/m3 to 9.8 µg/m3 during the first phase; 7.3 µg/m3 in the second; and rose to 9.8 µg/m3 in the third.
Sarath Guttikunda, founder and director, Urbanemissions.info, said, “In Mumbai, most of the traffic was down, which followed up with reduction in dust resuspension. Emissions from the construction sector were not there while residential open waste burning was limited. Light industry operations too were not there while migration of most low-income groups resulted in reduced biofuel emissions from cooking.”
However, the levels of SO2 — a colourless gas with pungent odour and taste that causes respiratory diseases such as asthma, bronchitis and emphysema — spiked during the lockdown. While it fell from 15.4 µg/m3 pre-lockdown to 12.5 µg/m3 during the first phase, a surge was seen during the second (24.6 µg/m3) and third phases (36.2 µg/m3). A marginal spike in PM10 (larger, coarser particles) was also witnessed during the third phase.