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CSE analyses winter air pollution trends in major cities across India

ByNE India Broadcast

Mar 8, 2023

All mega cities in India, irrespective of their locations in different geo-climatic zones, faced the challenge of worsening PM2.5 levels during the winter season of 2022-23. While levels in Delhi have been the highest, the remaining cities have also experienced very poor to worsening trends. 

This has emerged from an analysis of real time PM2.5 data done by Centre for Science and Environment (CSE) in Delhi, Kolkata-Howrah, Mumbai, Hyderabad, Bengaluru and Chennai for the winter period (October 1, 2022-February 28, 2023). The objective of this analysis has been to assess the peer mega cities to understand the longer term seasonal variations and annual trends in particulate pollution.

“While Delhi’s winter air quality hogs all the eyeballs, the rising winter air pollution in other mega cities including Kolkata, Mumbai, Hyderabad, Bengaluru and Chennai, does not get adequate attention. While Delhi has bent its seasonal pollution curve, winter air pollution is high or on the rise in most other mega cities. These cities located outside the northern plains may have more favourable meteorological conditions to contain the peaking of pollution during winters, but their overall city average and levels across locations can cause very high exposures. This demands round the year action to control emissions in cities that are motorising and urbanising rapidly,” says Anumita Roychowdhury, executive director-research and advocacy, CSE.

“Winter season presents a serious challenge in all mega cities despite them being located in different geo-climatic zones with varying meteorological and topographical conditions. The PM2.5 levels remain elevated and peak during winter in all mega cities. This winter, several of these cities (excluding Delhi) recorded higher seasonal PM2.5 averages compared to their previous winter. This clearly indicates that the overall emissions are high or may be rising in those cities,” says Avikal Somvanshi, seniour programme manager, Centre for Science and Environment.

The key highlights

Kolkata and Mumbai the most polluted after Delhi, while air quailty has worsened fastest in Bengaluru and Chennai: Delhi, with a winter average PM2.5 level of 151 µg/m³ remains the most polluted mega city by a large margin – though it has shown improvement over the past few years. But in the other five mega cities, average PM2.5 levels this winter (October 2022 to Feburary 2023) stood at 84 µg/m³ for Kolkata (including Howrah) and 77 µg/m³ for Mumbai — both higher than the 24-hour standard for PM2.5. Hyderabad’s winter average of 59 µg/m³ was just under the standard. Bengaluru with 44 µg/m³ and Chennai with 42 µg/m³ were comfortably under the 24-hour standard, but breeched the annual standard for PM2.5.

  • Compared to the winter of 2021-22, only Delhi has shown an improvement in air quality — its current winter air was 9 per cent less polluted. Winter averages of PM2.5 increased in the remaining five mega cities.
  • When PM2.5 levels in the current winter is compared with the average for the previous three winters, Bengaluru and Chennai’s performance emerges as the worst — their current winter air was 15 per cent more polluted than the average of their previous three winters.
  • Mumbai’s winter air was 14 per cent and Hyderabad’s 3 per cent more polluted.
  • Kolkata’s overall winter average of PM2.5 has improved compared to the previous three years, but is stagnating since last year. Kolkata’s winter air was 8 per cent less polluted compared to the average of previous three winters, but this winter’s pollution level is identical to that of last winter, showing a stagnant trend.

 

Peak winter pollution in Bengaluru and Hyderabad is worst in the last four years: On January 27, 2023, daily PM2.5 level in Bengaluru hit 152 µg/m³ — the highest 24-hour PM2.5 average recorded in the city since 2019. Similarly, Hyderabad registered its highest 24-hour PM2.5 average since 2019 this winter when on Feburary 23, 2023 its daily average reached 97 µg/m³.

Peak daily values this winter for Kolkata, Mumbai and Chennai were not as high as their previous winter peaks but still in the “very poor” AQI category. Kolkata’s winter peak stood at 162 µg/m³ (registered on January 21, 2023); for Mumbai it was 148 µg/m³ (registered on January 18, 2023); and for Chennai it stood at 139 µg/m³ (registered on October 24, 2022). Delhi’s peak pollution this winter stood at 401 µg/m³ (registered on November 3, 2022).

When the PM2.5 peak level of current winter is compared to the average for previous three winters, Bengaluru’s performance works out to be the worst: its winter peak was 68 per cent higher than the average of its previous three winter peaks. Simlarly, Chennai’s winter peak was 28 per cent higher, and Hyderabad’s 8 per cent higher.

Delhi, Kolkata and Mumbai had lower peaks compared to the average of previous three winter peaks. Mumbai’s winter peak was 7 per cent lower, Kolkata’s 11 per cent lower and Delhi’s 23 per cent lower.

Monthly air quality pattern varies across mega cities: Unlike Delhi which has two pollution crests during the winter season (November and January), other mega cities have just one crest. November is the worst air quality month for Hyderabad and Bengaluru, while for Mumbai and Chennai, it has been January. Kolkata’s worst month is December. Kolkata was the most polluted mega city (excluding Delhi) for the months of November, December and January. In Feburary, Mumbai overtook Kolkata.

Winter is a problematic season for all mega cities, but intensity of the problem varies: The days with bad air quality occurred in clusters during the winter season in mega cities. The clustering of bad air days was longer in Delhi, Kolkata, Mumbai and Hyderabad, but of shorter duration in Bengaluru and Chennai. Intensity and duration of these bad air days was long enough in Delhi to get classified as a smog episode. Other than Delhi, compared to the previous winter, the number of bad air days were more in other mega cities.

Kolkata’s longer term seasonal PM2.5 trend was lower but had the highest number of “very poor” AQI days; Mumbai had least number of “good”AQI days among mega cities (excluding Delhi): Kolkata registered 29 days of “very poor” AQI this winter which is second only to Delhi. It was followed by Mumbai that had seven days of “very poor” AQI. Chennai and Bengaluru registered just one day of “very poor” AQI, while Hyderabad registered zero days with “very poor” AQI.

Mumbai had only 12 days of “good” AQI — which was lower than Kolkata’s 14 days — despite having relatively lower number of bad air days. Chennai (43 “good” AQI days) and Bengaluru (33 “good” AQI days) had the maximum number of “good” AQI days among the mega cities. Hyderabad had only 15 “good” AQI days. Delhi was the worst with nine “severe” AQI days, 87 “very poor” days, and a mere five “good” AQI days.

Worst affected locations within mega cities had pollution levels 50 per cent higher than the city-wide average: There is a considerable variation in air quality among the locations of each mega city, with the worst locations being considerabily more polluted than the city-wide average. For Kolkata-Howrah, the most polluted location was Ghusuri in Howrah with a winter average of 128 µg/m³. In Mumbai, the worst air quality was recorded at Bandra-Kurla Complex (BKC) whose seasonal average stood at 122 µg/m³. Alandur was the most polluted location in Chennai with a seasonal average of 71 µg/m³. Zoo Park was the worst affected in Hyderabad with a seasonal average of 71 µg/m³. In Bengaluru, the most polluted location was Bapuji Nagar – the seasonal average was 64 µg/m³.

The way forward

Says Somvanshi: “The winter period is a special challenge in all cities as adverse meteorological conditions trap pollution and increase concentration and exposures. The impact is worse if the overall pollution in the city is high and is worsening.”

Roychowdhury adds: “This demands stringent action round the year as well as emergency action during the bad-air days to bring down the overall pollution levels. Efforts should focus on reducing emissions from vehicles, industry, waste burning, construction, and solid fuels in households, among others. This is also needed to meet the new target of 40 per cent reduction in particulate pollution under the National Clean Air Programme.”  

(A CSE Analysis)

Report- Pratyusha Mukherjee 

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