City saw PM2.5 concentration at 4-yr low in ’19

The share of tiny and deadly pollutant particles in Mumbai’s air was the lowest in four years in 2019, but still above the safe limit.

The share of tiny and deadly pollutant particles in Mumbai’s air was the lowest in four years in 2019, but still above the safe limit.

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Mumbai also witnessed its least polluted New Year’s Day on Wednesday from 2016. The air quality index (AQI) remained in the ‘moderate’ category at 175 during the day of January 1, similar to Monday and Tuesday, but by the evening, the AQI increased to 204 (poor) as predicted by System of Air Quality Weather Forecasting and Research (SAFAR) on Monday.

The average concentration of PM2.5 — particulate matter less than 2.5 micron size which can easily enter the lungs and cause health ailments — was 54 microgrammes per cubic metre (µg/m3) in 2019, the lowest since 2016, according to data from SAFAR. In 2018,it was 65 µg/m3; 58 µg/m3 in 2017; and 70 µg/m3 in 2016. The annual safe limit for PM2.5 is 40 µg/m3. Researchers from SAFAR said the percentage share of PM2.5 in PM10 (solid and liquid particles that are more than 10 micrometres in diameter) was at an annual average of 60% in Mumbai in 2018, which increased to 65% in 2019. In Delhi, the percentage share of PM10 reduced from 49% in 2018 to 45% in 2019.

“Around 75-80% air quality monitoring stations showed a decline in PM2.5 concentration in 2019 from previous years,” said Gufran Beig, project director, SAFAR. “There is more awareness about tackling problem pollutant particles like PM2.5 and PM10 in Mumbai. Overall concentration is low due to favourable weather factors in 2019 (Mumbai recorded maximum rain this monsoon since 1958 and five cyclones in Arabian Sea) combined with air pollution abatement efforts by the state government. However, we must remember that efforts need to be escalated to ensure black carbon combustion, composition due to biofuel emissions, and high moisture allowing secondary aerosol formation leading to more toxic density of PM2.5 in PM10 needs to be addressed.”

PM2.5 or smaller particles are the most toxic pollutants to stay in the air for days or weeks, and are carried to lower airways of the lungs and deposited in alveolar wall, causing serious health ailments, said doctors. In 2019, emissions from the industrial sector (36%) were the major source of PM2.5 in Mumbai followed by the residential sector – biofuel emissions (27%), transport (16%), and windblown dust (21%). PM2.5 concentration was the lowest last year, for 24 hours on July 24, 2019, at 11 µg/m3 against the safe limit of 60 µg/m3 for 24 hours. The highest PM2.5 concentration was recorded on January 14 when the concentration was 166 µg/m3. Beig said an increase in wind speed helped disperse pollutants swiftly on Wednesday morning allowing the AQI to be in the ‘moderate’ category but rising humidity in the evening pushed the air quality into the poor category. Firecrackers were used in different parts of the city around 12am on Wednesday but SAFAR did not identify firecrackers as an external emission affecting the AQI.