Rain washes away pollution, improves air quality in city

Heavy rain in July and in the past few days in August has brought down air pollution in the capital with the air quality index reported as being at a “good” scale.

Due to the showers, Particulate Matter (PM) 2.5 levels have fallen down substantially and the air quality index was reported as “good” for six days and “moderate” for three days in the first nine days of August, according to a leading atmospheric scientist.

The PM 2.5 levels in the first nine days of this month was 51 microgram per cubic metre. The maximum permissible limit of PM 2.5 levels as set up the Central Pollution Control Board is 60 ig/m3.

“Pollution is well within the permissible range in most areas,” Dr Gufran Beig, project director of the country’s first ever System of Air Quality Weather Forecasting and Research (SAFAR), said.

The PM levels from August 1 to August 9 are 58, 62, 61, 59, 50, 58, 58, 63, 49 respectively, according to data collected at Lodhi Road by SAFAR, which is developed by Pune-based Indian Institute of Tropical Meteorology (IITM), an autonomous body under the Ministry of Earth Sciences. 

He said even if it doesn’t rain for the next three days, air quality will be in the acceptable range. But if it doesn’t rain for more than a week, levels will start shooting up again.

“The particulate matters get washed off due to rain and hence pollution falls,” Beig said.  The levels were under the satisfactory limits in July as well; 73 per cent of the total number of days in July was under the “good” category, while 20 and seven per cent under the “moderate” and “poor” categories respectively.

However, gaseous pollutants do not get washed away by rain as they are very light, but the level of some of them like ozone production depends on sunlight and if weather is cloudy or rainy, then these gases do not get much affected.

“But if monsoonal winds are coming from cleaner area, then they sweep away these pollutants with cleaner winds and hence their level will also go down,” Dr Beig said.

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