World Environment Day 2023: CSE finds ground-level ozone pollution in Delhi-NCR all-year problem, persists at nights too

New Delhi and South Delhi areas were worst affected by ground-level ozone between March 1, 2023 and May 30, 2023

By Nandita Banerji
Published: Monday 05 June 2023
Ground-level ozone usually exceeds the safety standard on all summer days in some locations in Delhi-NCR every year. Photo: iStock__

The ground-level ozone pollution affecting parts of the Delhi-National Capital Region (NCR) was lower this year than in the last five years, but the duration of its exceedance was higher, a new analysis by New Delhi-based non-profit Centre for Science and Environment (CSE) has found. 

New Delhi and South Delhi areas were worst affected by ground-level ozone pollution between March 1, 2023 and May 30, 2023. The non-profit issued an alert on rising ozone pollution and multi-pollutant crisis in the national capital on World Environment Day 2023.

Read more: China’s anti-pollution measures have backfired

The analysis was based on Central Pollution Control Board (CPCB) data on ozone levels from 58 stations across Delhi-NCR. 

Ground-level ozone remains a problem at night too, CSE found. “Ground-level ozone should ideally become negligible in the night air, but Delhi-NCR has been witnessing a rare phenomenon where ozone levels remain elevated hours after sunset,” the analysis added. 

Even winter months in Delhi-NCR faced excess ozone levels, making it an all-year problem. Cold and foggy conditions in the winter can inhibit the formation of ground-level ozone, but ozone levels exceeded the standard at multiple stations on 26 days in January this year.

Ground-level ozone is not directly emitted from any source. It is produced from complex interaction between nitrogen oxides, volatile organic compounds, carbon monoxide that are emitted from vehicles, power plants, factories, and other combustion sources. 

These compounds undergo cyclic reactions in the presence of sunlight to generate ground-level ozone.

Anumita Roychowdhury, executive director for research and advocacy, CSE said:

The standard practice of CPCB to average out the data of all stations to determine daily air quality index cannot capture the public health risk from this short-lived and hyper-localised pollutant. This underestimates the severity of the local build-up and high toxic exposures in the hotspots.

Read more: Parts of US, Europe and Asia still grappling with problem of high level of ozone pollution

There were fewer instances of heatwaves in Delhi-NCR this summer, meaning the geographical spread of ground-level ozone pollution has been the lowest in March and April this year when compared to data over the past five years, according to the report. 

The spatial spread, or the number of stations exceeding the standard for ground-level ozone across the city, has been much lower this year. However, the duration for exceeding the limits has increased, the analysis said.

Ground-level ozone usually exceeds the safety standard on all summer days in some locations in Delhi-NCR every year.

“On average, 10 stations have exceeded the standard daily this summer, which is 33 per cent lower from the mean of the previous four summers,” the paper said.

This summer, at the stations which reported exceedance, the rolling eight-hour average stayed above standard for 4.9 hours, up from 4.6 hours observed the last summer. 

New Delhi and South Delhi neighbourhoods were worst affected by ground-level ozone pollution, CSE further found. Nehru Nagar, located in the southern part of the city, is the most chronically affected in the core Delhi-NCR. The area has exceeded the standard in this location for 75 days this March-May. 

Other locations with the most ground-level ozone exceedances were Sri Aurobindo Marg, Dr KS Shooting range, Mandir Marg, Alipur and Patparganj in Delhi. Sanjay Nagar and Vasundhara in Ghaziabad, Gwal Pahari in Gurugram and Knowledge Park in Greater Noida were affected in NCR. 

Read more: Air pollution second leading risk factor for death across Africa

Locations with the lowest ground-level ozone pollution in the core Delhi-NCR include Punjabi Bagh, Ashok Vihar, Siri Fort, Chandni Chowk, North Campus, and Pusa in Delhi. For NCR, it was Sector 16A and 11 and New Industrial Town in Faridabad and Sector 1 in Noida. 

Central Delhi and Gurugram are facing a worsening trend, recording a high jump in the number of exceedance days. Ground-level ozone hotspots are also located in areas with low levels of nitrogen dioxide, carbon monoxide and fine particulate matter 2.5. 

Ozone is emerging as a serious public health issue in India, according to health evidence. Age-standardised rates of death attributable to ground-level ozone are among the highest in India, found the 2020 State of Global Air report.

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