New Delhi: Cities in India’s eastern states are increasingly falling into the pincer grip of toxic particulate pollution during the winter season – and the problem is spreading quickly to the smaller cities and towns of the region: says the latest assessment by the Centre for Science and Environment released here recently.

The assessment also notes that though the bigger cities in the region – like Patna and Kolkata -- that are part of the National Clean Air Programme, have witnessed a marginal improvement in the winter average of their PM2.5 levels compared to the previous two winters, their levels are still high.

The smaller towns of Bihar, like Begusarai, Bettiah and Siwan in particular, have recorded the worst winter air in the region, with their seasonal average exceeding 200 micrograms per cubic metre. Nitrogen dioxide pollution is also high in the cities and towns of the region, with Arrah in Bihar recording a staggering 113 µg/m³ monthly average for November, notes CSE.

“This analysis is a stark reminder of the rapid spread of pollution. More cities and smaller towns are scaling the pollution height and dotting the pollution map. This once again vindicates the need for strong state-wide and regional management of air pollution. This is needed to control local pollution sources including vehicles, industry, open burning and construction dust, as well as the impact of upwind pollution sources on downwind cities and towns,” says Anumita Roychowhdury, executive director of research and advocacy, CSE.

“Additionally, the data gap is also a challenge in the region. Even though the real-time monitors have increased in the region including in Jharkhand, some of these could not be used due to data gaps and quality issues. Some of these are new and therefore long-term data is not available. The data, thus, is indicative of the current status and seasonal variation in particulate pollution in medium and smaller cities,” says Avikal Somvanshi, senior programme manager, Urban Lab, CSE.

With the winter season coming to an end, the Urban Lab at CSE has analysed air quality trends during the winter months (October 2022 to February 2023) in cities of the eastern states of West Bengal, Bihar and Odisha. This is an assessment of seasonal trends in PM2.5 concentration for the period October 1, 2022, to February 28, 2023, for 2019, 2020, 2021, 2022 and 2023. Winter inversion and cool and calm conditions trap local pollution that is already high. This is part of the third edition of the Urban Lab’s Air Quality Tracker Initiative since 2020-21.

Key findings of the CSE analysis

Eastern states have experienced the most polluted winter season since 2019-20. The average PM2.5 level across nine cities of east India with functional CAAQMS stations since 2019 stood at 97 µg/m³ this winter. The PM2.5 level was 6 per cent higher compared to the average of the previous three winters. The daily peak of the season was recorded on January 1, 2023, and the daily regional average stood at 173 µg/m³. The peak was 24 per cent higher compared to the peak of the 2021-22 winter and 8 per cent higher compared to the mean peak of the previous three winters.

Most cities have experienced worsening winter PM2.5 levels. West Bengal’s winter average PM2.5 this year is 14 per cent higher than that in the previous winter. Bihar registered a 26 per cent rise, and Odisha had a 44 per cent higher winter average compared to the previous winter. On a long-term basis, Bihar registered an 18 per cent increase and Odisha a 4 per cent increase from the mean level of the previous three winters. However, the seasonal air quality in West Bengal this winter is 4 per cent better than the mean of the previous three winters.

In absolute concentration terms, Bihar with an average PM2.5 level of 134 µg/m³ was the most polluted state in the east, followed by West Bengal with an average PM2.5 level of 84 µg/m³; Odisha was third with a seasonal average of 63 µg/m³. Peak pollution is dangerously high in all eastern states. In absolute concentration terms, Bihar’s daily peak PM2.5 level of 287 µg/m³ was the highest among the three states. West Bengal’s peak was 152 µg/m³ and Odisha’s, was 112 µg/m³.

In the long term, the seasonal peak in West Bengal this winter has been 1 per cent better than the mean of the previous three winter peaks. Bihar registered a 26 per cent increase and Odisha a 14 per cent increase in their peaks compared to the mean of the previous three winter peaks. Smaller cities in Bihar are the most polluted in the region. Begusarai was the most polluted city in the east with an average PM2.5 level of 275 µg/m³. It was followed by Siwan with 203 µg/m³, Bettiah (202 µg/m³), Katihar (188 µg/m³), and Saharsa (180 µg/m³). All the top 20 most polluted cities of the east are located in Bihar.

In West Bengal, Asansol, with a winter average of 102 µg/m³ was the most polluted city; it is followed by Howrah (92 µg/m³) at the second spot. Talcher (75 µg/m³) was the most polluted in Odisha – however, adds Somvanshi, “Since only two cities in the state have real-time monitors with adequate data for assessment, it is not possible to capture the larger landscape.” Haldia in West Bengal was the least polluted city among the three states with a PM2.5 average of 46 µg/m³, followed by Siliguri in West Bengal and Manguraha in Bihar with winter averages of 60 µg/m³ and 66 µg/m³, respectively.

Patna registered the highest increase in winter pollution this winter among the major cities in the region. Patna in Bihar and Talcher in Odisha were the worst performers and registered an increase of 39 per cent and 41 per cent from the previous year, respectively. These were followed by Asansol in West Bengal and Gaya in Bihar, which recorded an increase of 38 per cent and 37 per cent, respectively.

Howrah (0 per cent), Kolkata (3 per cent) and Muzaffarpur (8 per cent) registered nil to marginal increases in pollution levels this season compared to the previous winter. Haldia and Durgapur are the only two cities that have shown improvement in air quality this season compared to the corresponding period in the previous year. Durgapur registered the maximum improvement -- 30 per cent lower PM2.5 levels compared to the previous year; Haldia clocked a 19 per cent dip.

There was a significant increase in NO2 concentrations during November compared to the months of October and September. NO2 comes entirely from combustion sources and significantly, from vehicles. Patna registered the greatest increase -- 2.9 times -- with the maximum build-up of NO2 between September and November 2022. Katihar and Rajgir each registered a 2.6 times increase in NO2. Motihari, Kolkata and Howrah registered a 2.3 times hike. In absolute concentration terms, Arrah in Bihar registered the highest NO2 average of 113 µg/m³. It is followed by Bhagalpur with 98 µg/m³ and Siwan with 89 µg/m³. Among West Bengal cities, Asansol with a monthly average of 40 µg/m³ was the most polluted.

The Diwali of this winter was less polluted compared to the previous year’s Diwali for all the major cities in the region. However, the smaller cities of Bihar witnessed the maximum increase in pollution levels on Diwali night. In fact, pollution level on Diwali night (8 pm to 8 am) shot up by 0.2-2.3 times the average level recorded during the seven nights preceding Diwali. Nine out of 32 stations recorded an increase in pollution on the day of Diwali. Motihari in Bihar saw the greatest jump of 2.3 times higher PM2.5 level -- 152 µg/m³ -- on Diwali night. It was followed by Siwan and Bettiah each with 1.8 times higher PM2.5 concentrations. Bihar cities dominate the top 15 list of cities with the most polluted Diwali nights. Among West Bengal cities, Asansol recorded a Diwali night PM2.5 level of 42 µg/m³. Haldia and Manguraha each with 12 µg/m³ had the least polluted Diwali night in the region, followed by Durgapur with 13 µg/m³.