Pollution

Delhi is India’s most polluted megacity, but others are catching up: CSE report

CSE analyses winter pollution data from Delhi, Kolkata-Howrah, Mumbai, Hyderabad, Bengaluru and Chennai; only the national capital has shown improvement

 
By DTE Staff
Published: Tuesday 07 March 2023
Kolkata and Mumbai are the most polluted cities after Delhi, while air quality has worsened in Bengaluru and Chennai. Photo: iStock.__

All megacities 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, according to a new analysis by the Delhi-based non-profit Centre for Science and Environment (CSE).

While PM2.5 levels in Delhi have been the highest, the remaining cities have also experienced very poor to worsening trends, the document released on March 7, 2023, noted.


Also read: This winter was the cleanest in NCR since 2018, finds CSE; Delhi air most toxic


The non-profit analysed real-time PM2.5 data from October 1, 2022, to February 28, 2023, from Delhi, Kolkata-Howrah, Mumbai, Hyderabad, Bengaluru and Chennai. This analysis aimed at assessing the peer megacities to understand the longer-term seasonal variations and annual trends in particulate pollution.

Anumita Roychowdhury, executive director, research and advocacy, CSE, said:

While Delhi’s winter air quality hogs all the eyeballs, the rising winter air pollution in other megacities, including Kolkata, Mumbai, Hyderabad, Bengaluru and Chennai, do not get adequate attention. While Delhi has bent its seasonal pollution curve, winter air pollution is high or on the rise in most other megacities.

These cities, located outside the northern plains, may have more favourable meteorological conditions to contain the peaking of pollution during winter. Still, 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, Roychowdhury added.

“Winter season presents a serious challenge in all these megacities despite them being located in different geo-climatic zones with varying meteorological and topographical conditions,” said Avikal Somvanshi, senior programme manager, CSE.

The PM2.5 levels remain elevated and peak during winter in all megacities. 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, Somvanshi added.

Beyond Delhi

Kolkata and Mumbai are the most polluted cities after Delhi, while air quality has worsened at the fastest rate in Bengaluru and Chennai, the study found.

Delhi, with a winter average PM2.5 level of 151 µg/m³, remains the most polluted megacity by a large margin — though it has shown improvement over the past few years. In Kolkata, average PM2.5 levels this winter stood at 84 µg/m³; for Mumbai, it was at 77 µg/m³ — 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 breached the annual standard for PM2.5.

Compared to the winter of 2021-22, only Delhi has shown an improvement in air quality. Delhi’s winter air this year was nine per cent less polluted. On the other hand, winter averages of PM2.5 increased in the remaining five megacities. 


Read more: ‘Air pollution cuts India’s average life expectancy by 5 years’


When PM2.5 levels in the current winter are compared with the average for the previous three winters, the performance of Bengaluru and Chennai emerges as the worst — 15 per cent more polluted than the average of their last three winters. 

Mumbai’s winter air was 14 per cent more polluted than last year, and Hyderabad’s was three per cent more polluted.

Kolkata’s overall winter average of PM2.5 has improved compared to the previous three years but has been stagnating since last year, the report added.

Kolkata’s winter air was eight per cent less polluted than the average of the previous three winters. Still, this winter’s pollution level is identical to that of last winter, showing a stagnant trend.

In the last four years, peak pollution levels in winter have been worst for Bengaluru and Hyderabad. On January 27, 2023, the 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 on February 23, 2023, when its daily average reached 97 µg/m³.

Peak daily values for Kolkata, Mumbai and Chennai this winter were not as high as previous records but were still in the “very poor” AQI category.

When PM2.5 peak levels of the current winter are compared to the average for the previous three winters, Bengaluru’s performance is the worst — 68 per cent higher than the average of its previous three winter peaks. Similarly, Chennai’s winter peak was 28 per cent higher and Hyderabad’s eight per cent higher.


Read more: Action must on hotspots to curb air pollution in Delhi


Delhi, Kolkata and Mumbai had lower peak levels than the average of the previous three winter peaks. Mumbai’s peak levels was seven per cent lower, Kolkata’s 11 per cent lower and Delhi’s 23 per cent lower.

Monthly air quality patterns varied across megacities, the study noted. Unlike Delhi, which has two pollution crests during winter (November and January), other megacities have just one crest.

November is the month with the worst air quality for Hyderabad and Bengaluru, while for Mumbai and Chennai, it is January; for Kolkata, it is December. Kolkata was the most polluted megacity (excluding Delhi) for November, December and January. In February, Mumbai overtook Kolkata.

Winter is a problematic season for all megacities, but the analysis found that the intensity of the problem varies. The days with bad air quality occurred in clusters in megacities. The clustering of bad air days was longer in Delhi, Kolkata, Mumbai and Hyderabad but of shorter duration in Bengaluru and Chennai.

The intensity and duration of days with bad air quality were 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 was more in other megacities.

Kolkata’s longer-term seasonal PM2.5 trend was lower but had the highest number of “very poor” AQI days; Mumbai had the least number of “good” AQI days among megacities (excluding Delhi). 

Kolkata registered 29 days of “very poor” AQI this winter, second only to Delhi. It was followed by Mumbai, which 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 — lower than Kolkata (14 days). This is despite the city having a relatively lower number of bad air days.

Chennai (43) and Bengaluru (33) had the maximum number of “good” AQI days among the megacities. Hyderabad had only 15 “good” AQI days. Delhi recorded the worst, with nine “severe” AQI days, 87 “very poor” days and a mere five “good” AQI days.

There is a considerable variation in air quality among the locations of each megacity, with the worst-affected locations being considerably more polluted than the city-wide average.

Worst affected locations within megacities had pollution levels 50 per cent higher 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; here seasonal average was 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 here was 64 µg/m³.

The winter period is a special challenge in all cities as adverse meteorological conditions trap pollution and increase concentration and exposure. The impact is worse if the overall pollution in the city is high and worsening, said Somvanshi.

This demands stringent action around the year as well as emergency action during the bad-air days to bring down the overall pollution levels, said Roychowdhury.

“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,” added Roychowdhury.

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