City’s air quality improves as vehicles stay off roads

The city has witnessed a sharp decline in major pollutants following the restrictions imposed under the current coronavirus lockdown.

The city has witnessed a sharp decline in major pollutants following the restrictions imposed under the current coronavirus lockdown.

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As most people are working from home, Mumbai has seen an unprecedented fall in vehicular traffic, resulting in a 45% drop in average nitrogen oxide (NOx) concentration recorded during the first three weeks of March as compared to 2018 and 2019, according to a report by the System of Air Quality Weather Forecasting and Research (SAFAR) under the Ministry of Earth Sciences published on Saturday. NOx is a major component of vehicle exhaust.

“By comparing NOx levels during March 2018 and 2019, we found a considerable reduction [approximately 30%] in NOx concentration from March 2 to March 16,” said Gufran Beig, project director, SAFAR.

The highest amount of NOx reduction was recorded at 75% at Bandra Kurla Complex. The area witnesses maximum vehicular traffic in the city. Nerul, Navi Mumbai and Worli both recorded a marked decline in NOx, the SAFAR report said.

While Colaba, Malad, Andheri, and Mazagaon recorded no change, Borivli and Bhandup recorded the lowest levels of particulate matter during this period.

Drop-in pollutant concentration was attributed to lesser vehicular emissions. “Fossil fuel emission, mainly coming from vehicular traffic, is one of the major sources of NOx (approximately 60-80%) and PM2.5 (35-50%). Hence, for any change in vehicle numbers, the strongest indicator is falling NOx. However, the reduction of vehicles reduces PM2.5 as secondary particulates but increases resuspended dust emissions faster. Thus, there is a fine balance, and weather factors such as high wind speed and rise in temperatures help reduce particulates. This was seen on Saturday,” said Beig. Saturday saw the cleanest air day this year so far with the overall air quality index (AQI) at 65, falling under the ‘satisfactory’ category. Before Saturday, an AQI 78 (satisfactory) was recorded on January 29.

“On March 16, a spike in pollutants was observed owing to a possible rise in vehicular movement and other polluting sources in anticipation of directions issued under the COVID-19 outbreak. Also, unfavourable weather conditions during this period cannot be ruled out. Thereafter, pollutants began reducing, and an overall average NOx reduction at 45% was recorded for Mumbai for March 2020 so far,” said Beig.

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