A week after Diwali, fluctuating temperatures have caused air quality levels in Mumbai to oscillate between moderate and poor.
While cooler nights come as a relief for Mumbaiites, it led to a drop in air quality, to 216 on Monday. Temperatures fell 3.4 degrees below normal, to 18.5 degrees Celsius. Pollution levels are expected to increase marginally on Tuesday, with the System of Air Quality Weather Forecasting and Research (SAFAR) predicting an AQI of 218 (poor).
Air quality index (AQI) levels between 201-300 falls under the ‘poor’ category and 301-400 is ‘very poor’ — indicating a health risk for people sensitive to air pollution.
While the national capital has been reeling under a severe pollution crisis since Diwali, with AQI levels above 500, or ‘severe’, Mumbai has experienced relatively cleaner air through the week after Diwali.
On Diwali (October 30), the city recorded an AQI of 279 (poor), followed by spike a day after Diwali (October 31) at 315 (very poor) and finally 221 on November 1.
Over the last seven days, however, air quality improved to ‘moderate’ levels on most days, except on November 4 (when a ‘poor’ AQI of 204) was recorded, and on Monday.
SAFAR researchers said the drop in night temperatures from 20 to 18 degrees Celsius allowed pollutant particles to settle closer to the city’s surface.
“Inversion, in which pollutants do not get dispersed easily because of cold temperatures, caused air quality to drop to poor in Mumbai. A drop in wind speed and low moisture levels allows pollutants to be further trapped,” said Neha S Parkhi, senior programme manager, SAFAR.
Officials from the weather bureau said low minimum temperatures are likely to continue, but an increase in moisture levels may help check Mumbai’s pollution levels.
“Currently, cold winds over the city are coming from the eastern and north-eastern parts of the country. While they are bringing temperatures down, they are not dry, which means pollutants will not easily settle over the city surface,” said KS Hosalikar, deputy director general, western region, India Meteorological Department. “This, along with setting in of sea breeze in Mumbai will keep pollution levels between the ‘moderate’ and ‘poor’ categories.”
Five of 10 locations where air quality is measured in Mumbai recorded ‘poor’ levels on Monday, while five others fell under the ‘moderate’ category. Andheri, Bandra Kurla Complex, Mazgaon and Malad were the most polluted locations in the city, while Navi Mumbai on the outskirts too, recorded high pollution (see box).