 "Delhi-NCR hit by summer ozone crisis once again, shows CSE analysis")
Centre for Science and Environment (CSE), a think tank based in Delhi, on Monday, issued an alert on rising ozone pollution and the multi-pollutant crisis that Delhi and the National Capital Region (NCR) are facing during summer.
A recent analysis conducted by the CSE said that ground-level ozone exceedance is reported on nearly all days of summer. The report released on Sunday, the eve of World Environment Day 2023, revealed that while the region continues to face a multi-pollutant crisis, the levels of ozone this summer are lower than in previous years. However, if not addressed, this issue could escalate into a serious public health crisis in the coming years. Over the last five years, it has been noted that ground-level ozone has been an all-season problem but it is exceptionally worse in the months of April and May, said CSE in its report.
According to Anumita Roychowdhury, Executive Director of Research and Advocacy at CSE, the focus on particulate pollution has overshadowed the urgent need to address toxic gases. “Inadequate monitoring, limited data, and inappropriate methods of trend analysis have weakened the understanding of this growing public health hazard. Learn from the advanced economies that after controlling particulate pollution have fallen into the grip of rising nitrogen oxides (NOx) and ozone crisis. India should prevent this trap,” she said.
What is ground-level ozone?
Ground-level ozone is a highly toxic gas formed by the interaction of nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide (CO) emitted from vehicles, power plants, factories, and other combustion sources. VOCs can also be emitted from natural sources, such as plants. According to CSE, the complex chemistry of ground-level ozone makes it a challenging pollutant to track and mitigate.
These pollutants undergo cyclic reactions in the presence of sunlight, resulting in the formation of ground-level ozone.
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The problem extends beyond cities, as ozone can also drift long distances, becoming a regional pollutant that affects both public health and crop production. Therefore, ground-level ozone hotspots are often located in areas with low levels of NO2, CO, and PM2.5 because it dissipates faster in highly polluted areas.
Status of ozone exceedance and worst affected areas in Delhi-NCR
“Due to the very toxic nature of ground-level ozone, the national ambient air quality standard for ozone has been set for only short-term exposures (one-hour and eight-hour averages), and compliance is measured by the number of days that exceed the standards. Compliance requires that the standards are met 98 per cent of the time of the year. It may exceed the limits on two per cent of the days in a year, but not on two consecutive days of monitoring,” says Avikal Somvanshi, senior programme manager, Urban Lab at CSE.
She explained that there should not be more than eight days in a year when the ozone standard is breached, and not on two consecutive days. However, the CSE report has revealed that ground-level ozone has become a year-long problem in Delhi-NCR, with only nine days this year so far recording no exceedance among any air quality monitoring stations in the region.
The analysis conducted by CSE examined data from 58 official stations across Delhi-NCR, tracking ozone exceedance during the summer from 2019 to May 2023. It found that ground-level ozone exceedances were reported on nearly all days of summer. This summer ground-level ozone exceedances were reported on 87 days between 1 March and 30 May. The Central Pollution Control Board (CPCB) has set a cap of 200 µg/m3 for ground-level ozone.
New Delhi and South Delhi are the most severely affected areas, with Nehru Nagar reporting the highest number of exceedance days. Other affected areas include Ghaziabad, Gurugram, and Greater Noida. In terms of improvement, Siri Fort, Sector 16A in Faridabad, and Indirapuram and Loni in Ghaziabad registered significant reductions in exceedance days.
The analysis also revealed that night-time ground-level ozone persists in the air hours after sunset, which is a rare phenomenon observed in Delhi-NCR, according to CSE. Night-time ozone was reported on 28 days in May.
Why does ozone need special attention?
Ground-level ozone poses a significant public health risk, especially for individuals with respiratory conditions such as asthma, and chronic obstructive pulmonary disease (COPD), and vulnerable populations such as children and older adults. Exposure to ozone can inflame and damage airways, increase the susceptibility to respiratory infections, exacerbate asthma and other respiratory conditions, and lead to hospitalisations.