Smaller Towns In Bihar, Bengal And Odisha Record Higher Pollution This Winter: CSE Analysis

Arun Kumar Das

Apr 04, 2023, 05:25 PM | Updated 05:25 PM IST

The smaller towns of Bihar have recorded the worst winter air in the region. (Representative image).
The smaller towns of Bihar have recorded the worst winter air in the region. (Representative image).
  • This analysis covers 50 continuous ambient air quality monitoring stations (CAAQMS) spread across 32 cities in the three states. The PM 2.5 level was 6 per cent higher compared to the average of previous three winters.
  • Cities in India’s eastern states are increasingly falling into the pincer grip of toxic particulate pollution during winter season.

    This problem is spreading quickly to the smaller cities and towns of the region, says a latest assessment by Centre for Science and Environment (CSE).

    The assessment, released on Tuesday (4 April), 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 PM 2.5 levels compared to the previous two winters, their levels are still high.

    The smaller towns of Bihar — Begusarai, Bettiah and Siwan in particular —have recorded the worst winter air in the region, with their seasonal average exceeding 200 microgram per cubic metre (µg/m³).

    Nitrogen dioxide (NO2) 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 a strong state-wide and regional management of air pollution," says Anumita Roychowdhury, executive director, research and advocacy, CSE.

    "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," she added.

    "Additionally, 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 PM 2.5 concentration for the period between 1 October, 2022 to 28 February, 2023 for 2019, 2020, 2021, 2022 and 2023.

    Winter inversion and cool, 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.

    This analysis covers 50 continuous ambient air quality monitoring stations (CAAQMS) spread across 32 cities in the three states:

    • West Bengal: seven stations in Kolkata, three in Howrah, and one each in Asansol, Siliguri, Durgapur and Haldia. Real time monitors in Durgapur and Haldia became operational only by the end of 2020.

    • Bihar: Six stations in Patna, three each in Gaya and Muzaffarpur, two in Bhagalpur, and one each in Hajipur, Bettiah, Bihar Sharif, Darbhanga, Motihari, Araria, Arrah, Chhapra, Katihar, Kishanganj, Manguraha, Munger, Purnia, Rajgir, Saharsa, Sasaram, Siwan, Aurangabad, Begusarai and Samastipur.

    • Odisha: One real time station each in Talcher and Brajrajnagar. Many new stations have been added in November 2022 — one station each in Baripada, Bileipada, Keonjhar, Nayagarh, Rairangpur, Rourkela, Suakati and Tensa.

    Only a limited long term trend analysis has been possible for the cities that have added stations and monitors relatively recently (like some of the cities in Odisha).

    Jharkhand has no working monitoring stations, and hence, offers no PM 2.5 data for the last two years — which is why its cities have not been included in this analysis.

    This analysis is based on the real time data available from the current working air quality monitoring stations in east India.

    Somvanshi says a huge volume of data points have been cleaned and data gaps addressed based on the United States Environmental Protection Agency (USEPA) method for this analysis.

    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 PM 2.5 level was 6 per cent higher compared to the average of previous three winters.

    The daily peak of the season was recorded on 1 January, 2023 and the daily regional average stood at 173 µg/m³. The peak was 24 per cent higher compared to the peak of 2021-22 winter and 8 per cent higher compared to the mean peak of previous three winters.

    Most cities have experienced worsening of winter PM 2.5 levels: West Bengal’s winter average PM 2.5 this year is 14 per cent higher than that in the previous winter.

    Bihar registered a 26 per cent rise, and Odisha 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 previous three winters. However, the seasonal air quality in West Bengal this winter is 4 per cent better than the mean of previous three winters.

    In absolute concentration terms, Bihar with an average PM 2.5 level of 134 µg/m³ was the most polluted state in the east, followed by West Bengal with 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, 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 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 previous three winter peaks.

    Smaller cities of Bihar are 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 PM 2.5 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 PM 2.5 levels compared to the previous year; Haldia clocked a 19 per cent dip.

    Increasing levels of NO2 in November — 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.

    Diwali pollution was the highest in the small towns of Bihar among the eastern states.

    In fact, pollution level on Diwali night (8pm to 8am) shot up by 0.2-2.3 times the average level recorded during the seven nights preceding Diwali. Bihar cities dominate the top 15 list of cities with the most polluted Diwali nights.

    Among West Bengal cities, Asansol recorded a Diwali night PM 2.5 level of 42 µg/m³.

    Step Up The Action

    Says Roychowdhury: “High winter pollution is an indicator of a deeper and rapid spread of air pollution in the eastern region. As the winter turns hostile due to inversion and cold and calm conditions, pollution gets trapped and spirals.

    This requires an aggressive strategy to control pollution not only in the bigger cities, but also across the region to mitigate pollution from vehicles and transportation, industries, open burning of waste, landfill fires, construction, household use of solid fuels, and other area sources.

    It is necessary to reduce pollution in a targeted manner to meet the clean air standards.” 

    Arun Kumar Das is a senior journalist covering railways. He can be contacted at

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