Ozone pollution no longer just a summer phenomenon, says CSE study
Ozone pollution that is previous thought to be a summer phenomenon is becoming more widespread in Delhi and NCR cities such as Ghaziabad, Gurugram, Noida, Greater Noida, Faridabad and Meerut, a study by Centre for Science and Environment (CSE) said on Saturday. Ozone is a highly reactive gas and harmful for those suffering from respiratory conditions. Depending on the level of exposure, it can cause coughing and sore or scratchy throat, inflame and damage the airways and make the lungs more susceptible to infection. The study assessed trends during different seasons – summer (March-June), winter (October-February) and monsoon (July-September), between 2018 and 2021 (up to July 18). The analysis is based on the real-time (15-minute averages) data sourced from the Central Pollution Control Board (CPCB). It has been captured from CPCB’s 81 air quality monitoring stations across Delhi and the national capital region (NCR). The primary emission sources of ozone include those from vehicles, power plants, factories, and other combustion sources. These undergo cyclic reactions in the presence of sunlight to generate ground level ozone. According to the report, the trends were calculated in terms of number of days when the daily level exceeded the 8-hour standard. The national ambient air quality standard for ozone (8-hourly) is 100 ug/m3. The report said the top 10 high-ozone locations include stations from south Delhi as well as small cities in the region. In south Delhi, stations such as Dr KS Shooting Range (233 days), Siri Fort (150 days), Nehru Nagar (174 days), and Sri Aurobindo Marg (126 days) make up four of the top five most polluted spots in Delhi. In Lyutens’ Delhi, Jawaharlal Nehru Stadium (116 days) and National Stadium (82 days) had relatively high numbers of exceedance days, or days when the concentration was high for over 80 days. North, east and west Delhi districts also had a few stations recording high exceedance, the study said. They included Sonia Vihar (142 days), but these are not as closely situated as in the case of south Delhi, it said. The study also points out that even during the lockdowns imposed during 2020-21, when the concentration of particulate matter in the air reduced, the ozone levels remained the same. CSE executive director Anumita Roychowdhury said so far the focus has only been on mitigating particulate matter pollution, but ozone is now a round-the-year problem requiring urgent attention of clean air programmes. “The risk from ozone is often not well understood, as the current regulatory practice of spatially averaging the data from all monitoring stations blunts the curve. As ozone is a highly reactive gas and even short-term exposure can aggravate respiratory conditions leading to emergency hospital admission, it requires a different approach to risk assessment,” she said. Avikal Somvanshi, programme manager in CSE’s Urban Lab team of the Sustainable Cities programme, said this analysis shows that the number of days not meeting the ozone standards has begun to increase even during winter months, making the winter smog more toxic.
