Pollution level in 4 major cities (Mumbai, Delhi,
Kolkata & Chennai) before lockdown and at the
present.
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Answer:
Explanation:
Transport pollution levels declined by three-fourth across Mumbai and Pune between March 24 and April 25 (lockdown period), as compared to the period between February 20 and March 20, revealed an analysis published by the System of Air Quality Weather Forecasting and Research (SAFAR) on Sunday.
Meanwhile, the pollutant-measuring indicator, air quality index (AQI), in Mumbai was 37 (good), making it the cleanest air day so far this year, while Pune recorded 47, also under the ‘good’ category.
The month-wise comparison of air quality levels for four cities – Mumbai, Delhi, Pune and Ahmedabad – also revealed that the highest reduction was witnessed in nitrogen dioxide (NO2) levels for Pune at 70%, followed by Mumbai (69%). Delhi and Ahmedabad recorded a 33% and 30% decline in NO2 levels. Average NO2 concentration fell from 23 parts per billion (ppb) before lockdown month to 7 ppb during lockdown for Mumbai, and 24 ppb to 7 ppb for Pune.
“Drastic NO2 decline in Mumbai and Pune indicate that vehicular emissions play a major role in contributing to overall air pollution. Stringent restrictions imposed during the lockdown helped in bringing down the pollution level. Even industrial emissions were lower. However, in Delhi and Ahmedabad this was not the case because under minor influence of external emissions, mild dust storms allowed pollutant particles to be suspended closer to the surface,” said Gufran Beig, director, SAFAR.
Toxic gases such as NO2 are formed by burning of coal, oil, and emissions from vehicles that worsen respiratory conditions.
“NO2 or other oxides of nitrogen can lead to chemical deposition in the lungs, leading to inflammation of the lung tissue. Prolonged exposure weakens the lungs leading to serious ailments,” said Dr Sanjeev Mehta, pulmonologist (chest specialist), Lilavati Hospital, Bandra.
SAFAR also recorded reduction in PM2.5 levels, which showed maximum decline at Ahmedabad at 51%, followed by Mumbai 49%, Pune 39% and Delhi 31%. PM2.5 is breathable particulate matter comprising solid and liquid particles of 2.5 microns in size or smaller.
“Unlike NO2, PM2.5 is influenced by other factors including meteorological conditions. All four cities witnessed weather disturbances leading to fluctuating particulate matter concentration during lockdown,” said Beig.
Independent researchers said a comparative analysis for air quality is more valid when done for the same period year-on-year.
“When we compared month-wise averages, meteorological conditions between two months may be very different from each other which may not establish the reduced impact of external emissions within a city,” said Ronak Sutaria, founder and director, UrbanSciences.
Meanwhile, the Central Pollution Control Board (CPCB) also recently published its analysis of Mumbai’s air quality between March 16 and April 15. The analysis revealed that Mumbai had witnessed a 40% reduction in PM2.5, 43% decline in PM10 (larger coarser particles), 77% reduction in NO2, 59% fall in average benzene levels (contributes to volatile organic compounds) and 50% drop in sulphur dioxide (SO2 – colourless gas with pungent odour that causes respiratory diseases).
“The absence of non-essential vehicles, combustion activities in industries and commercial construction sites during the period may be attributable to the decline,” the analysis stated.
The lowest 24 hourly average for PM10 was 54 microgrammes per cubic metre against the safe limit of 100 µg/m3, PM2.5 was 20 µg/m3 against safe limit of 60 µg/m3, and NO2 levels at 5 µg/m3 against 80 µg/m3 safe limit.
“Hourly decline in all pollutants was observed due to restriction on construction activities, less road dust resuspension, and to some extent curb on industrial activities. Absence of emission sources was seen missing at night early morning that would otherwise accumulate before lockdown,” said a senior CPCB official.