Air Quality Tracker: Kolkata Metropolitan Area

FOCUS

This report was published by the Centre for Science and Environment, a New Delhi based not-for-profit research and advocacy organisation, on August 6, 2024. It was written by Avikal Somvanshi and Sharanjeet Kaur. The report presents a study of ground-level ozone in Kolkata Metropolitan Area.

Ground-level ozone is a short-lived and hyper-localised pollutant which has serious health consequences for children, older adults, and those with respiratory conditions. However, the chemistry of ground-level ozone is complex which makes it difficult to track and mitigate.

The 2020 State of Global Air report reveals that age-standardised rates of death attributable to ground-level ozone are among the highest in India. Due to the toxic nature of ground-level ozone, there should not be more than 8 days in a year when the ozone standard is violated, and none of the violations should happen on 2 consecutive days. Global experience indicates that as the problem of particulate pollution reduces, the problem of nitrous oxides (NOx) and ground-level ozone increases. Therefore, it is necessary to devise an action plan that controls particulate pollution as well as ozone precursor gases like nitrous oxides.

The authors have used publicly available granular real time data (15-minute averages) from the Central Pollution Control Board’s official online portal, the Central Control Room for Air Quality Management. They have traced trends in ground-level ozone data from 2020 to 2024 from 10 official stations under the Continuous Ambient Air Quality Monitoring System (CAAQMS) that are spread across the Kolkata Metropolitan Area. The report employs the U.S. Environmental Protection Agency approach of computing 8-hour averages for a day and then checking among them the maximum value to determine the daily ground-level ozone pollution level. This is calculated in terms of the number of days when the daily level has exceeded the 8-hour standard, that is, 100 microgram per cubic metre (µg/m3).

This is a 13-page report that is divided into 3 sections: Overview (Section 1); Key Findings (Section 2); and Act Now (Section 3).

    FACTOIDS

  1. Ground-level ozone exceedance was reported on 37 days in the summer of 2024. May 1 was the worst day for ground ozone pollution on which 7 out of 10 stations in Kolkata Metropolitan Area reported exceedance, when the intensity of pollution hit 108 µg/m3.

  2. Spatial spread refers to the number of stations exceeding the standard across Kolkata Metropolitan Area. In 2024, the spatial spread was 2.8 stations per day from January 1 to June 30, which is the highest in the last five years. In the summer of 2023, the spatial spread was 2.7 stations per day, and the figure was 2.6 stations per day in the summer of 2020.

  3. The average duration of exceedance in 2024 was 13.4 hours, as opposed to just 11.7 hours in 2023.

  4. Fort William and Jadavpur monitoring stations were the worst affected by ground ozone pollution in the Kolkata Metropolitan Region, followed by RB University and Bidhannagar. Howrah was the least affected by ground ozone pollution in the region.

  5. Ground-level ozone hotspots are found in areas with low levels of nitrogen dioxide (NO2) and particulate matter 2.5 micrometres or smaller (PM2.5). However, Fort William and RB University defy this phenomenon since they reported high levels of ground-level ozone and NO2 both.

  6. Ground-level ozone in the air after sunset was less in the April of 2024 than it was in the April of 2020 during the covid-19 lockdown. The NO2 emissions of morning and evening rush hour traffic neutralise ground-level ozone at sunrise and sunset, the report states.

  7. The hourly ozone peak level was up by 20 per cent in 2024 compared to lockdown times in 2020. The maximum 8-hour average was recorded at Belur Math, Howrah, when the peak level hit 160.4 µg/m3 on June 18, 2024.

  8. Ground level ozone should ideally be negligible at night but levels in Kolkata Metropolitan Area remained elevated hours after sunset. In 2024, night-time ozone was reported at 0.2 stations on average every night as opposed to 0.1 stations per night in 2020. RB University has reported night-time ozone on 6 nights, making it the highest reported in the region.

  9. Kolkata’s hot and sunny weather conditions make it easy for ground-level ozone to have a wider spatial spread. Due to this, ground-level ozone pollution has become a yearlong problem in Kolkata and is not just restricted to the summer months, although it is the worst during summer months, peaking in April.


    Focus and Factoids by Karen Chhaya.


    PARI Library's health archive project is part of an initiative supported by the Azim Premji University to develop a free-access repository of health-related reports relevant to rural India.

AUTHOR

Avikal Somvanshi and Sharanjeet Kaur

COPYRIGHT

Centre for Science and Environment

PUBLICATION DATE

06 Aug, 2024

TAGS

#ozone #air-pollution #kolkata #environment #air-quality

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