Mumbai: Pollution levels on Diwali (Sunday) and the day after (Monday) were far less in Mumbai as compared to Delhi.
A Diwali 2016 pollution report by the System of Air Quality Weather Forecasting and Research (SAFAR) identified Mumbai’s air quality index (AQI) – pollutant measuring indicator — at 278 (poor) on Diwali, 315 (very poor) for the day after Diwali and 221 (poor) on Tuesday. Delhi recorded an AQI of 452 (severe) on Diwali, 500+ on Monday and 500 (severe) on Tuesday.
Mumbai also fared better than Pune the day after Diwali, as the latter saw a spike from 192 (moderate) on Sunday to 340 (very poor) on Monday.
AQI levels between 100 and 200 fall under ‘moderate’ category, 201-300 fall under the ‘poor’ and 301-400 under the ‘very poor’ category, indicating a health risk for people sensitive to air pollution. Levels above 400 fall under the ‘severe’ category, indicating serious risk of respiratory effects for the general public.
Researchers said weather factors played a major role in high pollution levels in both Mumbai and Delhi. “With the additional source of firecrackers, Mumbai experienced a drop in wind speed from a day before Diwali (10-11 km an hour) to Sunday (at 6 km/h). However, on the the same days, Delhi saw less than 1 km/h wind speed,” said Gufran Beig, project director, SAFAR. “When wind speed drops, pollutants form a thick layer closer to the earth’s surface through inversion.”
He said while this thick layer of smoke locked in pollutants 10m from the surface at Delhi, which led to smog formation, the layer was much higher from the ground in Mumbai and was dispersed much faster by Tuesday afternoon.
SAFAR officials also said external emissions readings (mostly firecrackers) were at par with last year’s emissions in Mumbai. However, this was not the case for Pune. “The use of firecrackers combined with open burning emissions in Mumbai was similar to previous years, but the spike in pollution at Pune was mainly from firecracker emissions this year,” said Neha S Parkhi, senior programme officer, SAFAR.
Meanwhile, the report identified Malad (311) as the most-polluted location for the city, this Diwali, followed by Andheri (306), Nerul (Navi Mumbai at 309) and Bandra-Kurla Complex (298). The least-polluted locations were Colaba and Borivli — both recorded ‘poor’ air quality.
The lead pollutants in Mumbai were PM2.5 — small pollutant particles that can enter the lungs and PM10 — slightly larger, coarser particles. Both were twice above the safe limit. As against the permissible limit of 60 microgrammes per cubic metre (µg/m3) for PM2.5, levels were as high as 114 µg/m3 on Sunday and 145.9µg/m3 on Monday in Mumbai. Similarly, PM10 levels were 181 µg/m3 on Sunday and 224µg/m3 Monday. The safe limit is 100µg/m3.