The first phase of the lockdown, from March 25 to April 15, reduced particulate matter pollution by nearly half in Delhi, according to a report by the Central Pollution Control Board.
“Overall, 46% reduction in PM2.5 and 50% reduction in PM10 was observed during the lockdown period,” the body noted.
This led to nearly a week-long run of the air quality index remaining in the ‘good’ and ‘satisfactory’ categories, as opposed to the unhealthy and hazardous categories the city is more accustomed to. The stint was broken by a dust storm and subsequent change in temperature and dry weather heralding summer.
The improvement in air was due to a reduction in combustion and industrial sources which are common to both the categories of particulate matter. As 81% of Delhi’s nitrous oxide emissions came from the transport sector, restrictions on vehicular activity led to a 56% reduction in NO2 levels and over 37% reduction in carbon monoxide levels during the lockdown period, compared to pre-lockdown times.
There was also a 47% reduction in benzene levels while sulphur dioxide levels reduced only by 20%. This was because 70% of Delhi’s SO2 originates from power plants located around Delhi and power plants continue to operate. Other sources of SO2 were restaurants and some industries, which were operational during the lockdown period along with biomass/refuse burning in some areas in and around Delhi.
Less than average
Moreover, 24-hourly average PM2.5 and PM10 were within National Ambient Air Quality Standards (NAAQS) for 20 and 15 days respectively, while NO2 levels were 75% less than their 24-hourly standard. Also, 24 hourly average levels of PM10, PM2.5 , NO2 and SO2 dropped as low as 24 g/m3, 39g/m3, 15 g/m3 and 10 g/m3 respectively, the report noted.
While significant reduction in NO2 levels was observed in Noida (68%), Ghaziabad (60%) and Gurugram (40%), the same was not observed in Faridabad (17%), where NO2 emissions were found higher during a few days during lockdown. This was likely due to the gas-based power plants in and around Faridabad. Significant reduction in SO2 levels was only seen in Faridabad (47%) and Ghaziabad (22%), while Gurugram (14%) and Noida (10%) recorded relatively limited reductions during the lockdown phase.
As much as 78% of cities in the country that are monitored by the CPCB had their AQI in the good and satisfactory categories, increasing from the average of 44% seen in the pre-lockdown phase.