67% drop in NO2, 39% in particulate matter during three phases of lockdown

A 67% drop in nitrogen dioxide (NO2) levels while a 39% drop for particulate matter (PM2.5 and PM10) were recorded during three phases of the lockdown in the city

A 67% drop in nitrogen dioxide (NO2) levels while a 39% drop for particulate matter (PM2.5 and PM10) were recorded during three phases of the lockdown in the city as compared to the same period in 2019, states an analysis by the System of Air Quality Weather Forecasting and Research (SAFAR).

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The three phases, first period from March 25 to April 14, second from April 15 to May 3, and the third from May 4 to 17, saw maximum percentage decline for NO2 during the first two weeks (72.4%). PM2.5 levels fell maximum during lockdown 2.0 by (50.3%). PM10 also saw maximum reduction during the second phase by 52.6%. However, there was a lower percentage reduction in all three pollutants NO2 (59.5%), PM2.5 (32.3%), and PM10 (24.6%) during lockdown 3.0, as compared to levels during the same period in 2019.

Nitrogen dioxide is a toxic gas that contributes to aerosol formation that can worsen respiratory conditions formed from the burning of coal, oil, and vehicular emissions. PM2.5 is breathable particulate matter which is 2.5 microns in size or smaller while PM10 are larger particles. Both can cause health complications.

“The analysis shows us that the reduction percentage kept declining with time because values were getting saturated at the lowest possible natural levels or background levels,” said Gufran Beig, director, SAFAR. “This means that during the first phase maximum reduction in vehicular emission allowed NO2 levels to fall to its lowest but reduction in PM levels fell by around 34% because they are secondary pollutants from vehicular emissions. However, by the second phase, NO2 gradually declined from the background level while PM levels fell to its lowest. By the third, percentage reduction gradually declined as base levels for both pollutants were reached in previous phases.”

On comparing drop in pollutant percentages with other cities, Pune showed a maximum decline in NO2 followed by Mumbai, Ahmedabad and Delhi, while PM decline was maximum in Ahmedabad, Delhi, followed by Mumbai and Pune. “The impact of unseasonal showers helped reduced pollutant concentrations for cities like Pune and Delhi during lockdown 3.0,” added Beig.

While the analysis of the fourth lockdown 4.0 is being compiled by his team, Beig added that with pre-monsoon showers predicted for Mumbai next week, low pollution levels are expected to maintain. “The impact on monsoon will show a further decline and how much more background pollutant levels can fall during lockdown 5.0,” said Beig.

PM concentration, year’s lowest on Saturday

The concentration of PM2.5 was the lowest this year, at 15 micrograms per cubic metre (µg/m3), on Saturday morning which increased to 22 µg/m3 by the evening. SAFAR said the drop was due to a light drizzle between Friday night and Saturday morning. The World Health Organization (WHO) PM2.5 safe standard for 24 hours is 25 µg/m3, while the national safe standard is 60 µg/m3.