Report reveals alarming rise in winter pollution in India’s Megacities

Despite belonging to different geo-climatic zones, all mega cities in India faced the challenge of worsening PM2.5 levels during this winter. According to an analysis by the Centre for Science and Environment (CSE), while levels in Delhi have been at their highest, the rest of the cities have similarly seen bad to deteriorating patterns.

Avikal Somvanshi, Senior Programme Manager, CSE stated, “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 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.” 

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

In an earlier feature about North India’s Smog issue, published on Climate Fact Checks, Dr. Partha Jyoti Das, Senior Climate Scientist, and CFC’s in-house expert explained: “PM 2.5 consists of mainly black carbon or carbon soot that is emitted during the process of burning fossil fuels such as coal, petrol, and diesel as well as biomass and biofuels. It is the second major source of global warming after CO2 and is a short-lived climate pollutant (SLCP) responsible for nearly 50% of global warming to date.” 

It is important to note that this alarming rise in winter pollution in India’s Megacities is being reported at a time when the Indian Meteorological Department (IMD) recently declared that India has just experienced its warmest February in 122 years. The country’s temperature was on average 0.28 degrees Celsius higher than typical, with some places seeing readings as high as 2-4 degrees Celsius. This is probably a result of climate change, and the warming trend might continue in the upcoming years. 

All around the nation, notably in the northern states of Delhi, Uttar Pradesh, and Rajasthan, a spike in temperature has been recorded. In February, Delhi saw temperatures 5–6°C above average with 16.2°C, or 3.5°C above average being the city’s recorded minimum temperature while the maximum was 34°C, which is 6°C above average. For more details on this, read the CFC article – After warmest February in 122 years, sweltering summer to arrive early for India in 2023.

What the analysis revealed

Kolkata and Mumbai turned out to be the most polluted after Delhi, while air quality worsened fastest in Bengaluru and Chennai. 

With a winter average PM2.5 level of 151 µg/m³, Delhi remains the most polluted megacity by a large margin – though it has shown improvement over the past few years. But in the other five megacities, average PM2.5 levels this winter 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. 

With 59 g/m3, Hyderabad’s winter average fell slightly short of the standard. Bangalore and Chennai had PM2.5 concentrations of 44 g/m3 and 42 g/m3, respectively, which were comfortably within the 24-hour standard but above the yearly standard.

Compared to the winter of 2021-22, only Delhi has shown an improvement in air quality – its current winter air was 9 percent less polluted. However, winter averages of PM2.5 increased in the remaining five megacities.

When PM2.5 levels in the current winter are compared with the average for the previous three winters, Bengaluru and Chennai’s performance emerges as the worst – their recent winter air was 15 percent more polluted than the average of their last three winters.

Mumbai’s winter air was 14 percent and Hyderabad’s 3 percent more polluted. Kolkata’s overall winter average of PM2.5 has improved compared to the previous three years but is stagnating since 2022. Kolkata’s winter air was 8 percent less polluted compared to the average of the previous three winters. Still, this winter’s pollution level is identical to last winter’s, showing a stagnant trend.

Peak winter pollution in Bengaluru and Hyderabad is the worst in the last four years. On January 27, 2023, the daily PM2.5 levels 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 February 23, 2023, its daily average reached 97 µg/m³.

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

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

Delhi, Kolkata, and Mumbai had lower peaks than the average of the previous three winter peaks. Mumbai’s winter peak was 7 percent lower, Kolkata’s 11 percent lower, and Delhi’s 23 percent lower.

“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 favorable meteorological conditions to contain the peaking of pollution during winters, but their overall city average and levels across locations can cause very high exposures,” said Anumita Roychowdhury, Executive Director-Research and Advocacy, CSE. 

Monthly air quality patterns vary across megacities. Unlike Delhi, which has two pollution crests during the winter season -November and January- other megacities have just one crest. Hyderabad and Bengaluru get the worst air quality in November, whereas Mumbai and Chennai experience it in January. Kolkata’s worst month is December. Apart from Delhi, Kolkata was the most polluted major city in November, December, and January. In February, Mumbai overtook Kolkata.

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

“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,” Senior Programme Manager Somvanshi said.

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 mega cities (excluding Delhi): Kolkata registered 29 days of “very poor” AQI this winter which is second only to Delhi. Mumbai, which had “extremely poor” AQI for seven days, came next. Chennai and Bengaluru registered just one day of “very poor” AQI, while Hyderabad registered zero days with “very poor” AQI.

Despite having a relatively lower number of bad air days, Mumbai had only 12 days of “good” AQI – which was lower than Kolkata’s 14 days. Chennai (43 “good” AQI days) and Bengaluru (33 “good” AQI days) had the maximum number of “good” AQI days among the megacities. 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.

The worst affected locations within megacities had pollution levels 50 percent higher than the city-wide average: There is a considerable variation in air quality among the locations of each megacity, with the worst locations being considerably 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 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 was 64 µg/m³.

Air Pollution and Climate Change

There is an intrinsic connection between air pollution and climate change. The UNEP says that they are two sides of the same coin. In India, air pollution seems to get highlighted only when ‘smog’ like cases surface every year during the winter. But the fact remains that during this time of the year, multiple factors like ‘stubble burning’ and ‘winter conditions’ only amplify an already worsening air quality in the region that is silently contributing to global warming and vice versa. 

“The relationship between air pollution and climate change in the Indian context is obvious. The most important air pollutants like CO2, CO, black carbon, and methane are either greenhouse gases or other forcings having high global warming potential or direct GHGs, contributing to global warming,” said Dr. Das, adding “On the other hand, the major contributors to global warming like CO2, Methane, O3, PM 2.5, etc. constitute some of the main air pollutants in India.” 

Recommendations by the CSE report

The report stated that winter pollution is the region’s litmus test of clean air action. The only way to prevent the high peaks and smog episodes during winter is to ensure sustained improvement in air quality to meet the national ambient air quality standard across the region. This requires region-wide implementation of the following:

• Clean fuels and emissions control systems in the industry
• Massive electrification of the vehicle fleet
• Scaling up of integrated public transport options with vehicle restraint measures like parking restraints
• Waste management based on 100 percent segregation, material recovery, and zero landfill policy
• Clean construction and recycling of C&D waste
• Replacement of solid fuels in households
• Urban greening and dust control 

Executive Director-Research and Advocacy, Roychowdhury said that the situation demands stringent year-round and emergency action during the bad air days to reduce 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 a 40 percent reduction in particulate pollution under the National Clean Air Programme,” Roychowdhury added.