Air Quality Tracker: Delhi National Capital Region

FOCUS

This report was published by the Centre for Science and Environment, a New Delhi based public interest research organisation, on August 6, 2024. It has been written by Avikal Somvanshi and Sharanjeet Kaur. The report presents a study of ground-level ozone in Delhi National Capital Region.  

Ground-level ozone is a short-lived and localised pollutant in urban areas that can lead to severe respiratory distress and impaired pulmonary function. Ozone is produced in the atmosphere when nitrogen oxides (NOx) and volatile organic compounds (VOCs) undergo complex photochemical reactions.

Due to both public interest and policy being concentrated on reducing particulate pollution, there is limited monitoring and information for ozone, the report notes. It uses publicly available granular data from the Central Control Room for Air Quality Management – the official online portal of the Central Pollution Control Board (CPCB) – to analyse trends in 2020-2024 over the summer (1 April-18 July). This data is sourced in 58 official stations in Delhi-NCR. Given the high toxicity of ground-level ozone, the national ambient air quality standard has been set to 100 μg/m3 (microgram per cubic meter) for an exposure of eight hours on average.

This 14-page document is divided into 3 sections: Overview (Section 1); Key highlights (Section 2) and Act Now (Section 3). 

    FACTOIDS

  1. Ground-level ozone exceedance was reported on 102 days in the summer of 2024. 36 stations (out of 59) noted exceedance on 7th May, which was the worst day from spatial spread of ground ozone. Ground-level ozone pollution impacts New Delhi and South Delhi neighbourhoods the worst.

  2. This summer marked the largest spatial spread of increased ground-level ozone in the past 5 years. 17.6 stations (on average) exceeded the daily safety standard this year, with only 9.4 stations in 2023 and 14.6 stations in 2020. The duration of exceedance has also increased to an average of 13.9 hours this year, which is only superseded by the summer of 2020.

  3. Ozone is catalysed by NO2 and even consumed in NO2 limiting reactions - this creates an inverse relationship in the concentrations of ground-level ozone and concentrations of NO2 as well as PM2.5 (fine particulate matter). This leads to ozone hotspots in the “cleaner” areas in Delhi-NCR.

  4. Station-level, measurable data (<200 μg/m3) in ground-level ozone have increased by 6 per cent since lockdown. The maximum 8-hour average at Alipur in Delhi was high as high 194.1 µg/m3 on 9 June 2024. Three more stations broke 190 µg/m3 mark this summer namely, Rohini, Ashok Vihar and Dr K S Shooting Range.

  5. Nighttime ground-level ozone remains far from ideal as 5 stations on average log ozone every night, compared to 7.7 stations in 2020.

  6. Ground-level ozone is a year-round problem. While the exceedances peak in the summer, there has been a concerning increase in ozone pollution across multiple stations after monsoon, particularly October-November. They even occurring during January, despite the typically inhibitory winter weather.


    Focus and Factoids by Punya Pratyusha Sethi.

    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

2024

TAGS

#ozone #air-pollution #Delhi-winters

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