Ozone pollution higher in Delhi, poses serious health risk: Study

Ozone level has increased manifold in the national capital due to severe heat wave this season posing a serious health risk, a recent study has revealed and suggested aggressive control of industrial and vehicular emissions. According to the air quality index (AQI), released everyday by Central Pollution Control Board (CPCB), ozone is emerging as a dominant pollutant along with particulate matter (PM), especially in Delhi and NCR areas, said environment think tank CSE.

"It is shocking to note that according to the AQI which the CPCB releases every day, ozone, along with particulate matter, has been the dominant pollutant of the day on 28 days between April 1 and June 5, 2019. "During the same period in 2018, ozone was the dominant pollutant along with particulate matter on only 17 days," the study by Centre for Science and Environment (CSE) said.

After tracking the daily ozone data, the CSE has found that this summer, when the capital witnessed searing heat wave, average ozone levels exceeded the prescribed standard on 16 per cent of the days overall, compared to 5 per cent of the days during the same period in 2018. The eight-hour average standard for ozone exposure is 100 microgram per cubic metre (cu m).

The study said the highest concentration in 2019 went up to 122 microgram per cu m, which is 1.22 times higher than the eight-hour average standard. During 2018, it had gone up to 106 microgram per cu m which is 1.1 times higher than the standard. Environment expert  and CSE Executive Director Anumita Roychowdhury said, "If this trend continues and worsens, the Graded Response Action Plan (GRAP) will also have to initiate action to address the precursor gases that form ozone -- NOx, hydrocarbons etc -- and crack down on vehicles and industry."

The NGO has tracked the daily ozone data released by the CPCB for Delhi and the National Capital Region (NCR) for the period April 1-June 15, 2019. Ozone is a unique problem that is dependent on emissions of gases from different sources as well as on the atmospheric conditions, CSE said, adding the combination of high gaseous emissions and intense summer conditions with severe heat waves can aggravate this problem.

In several residential and industrial locations, the number of days crossing the limit was very high ranging from 53 to 92 per cent of the days, it said. "This is a matter of serious concern as ozone is a highly reactive gas and can have immediate adverse effect on those suffering from asthma and respiratory conditions," Roychowdhury said, adding the intense heat wave this summer could have influenced the trend.

"There is a special reason for tracking ozone during summer as it is not directly emitted from any source. Other gases such as nitrogen oxide and volatile organic compounds that are emitted from combustion sources like vehicles, industry or power plants, react in the air under the influence of sunlight and temperature to form ozone. "Summer months, with their high sunshine and high ambient temperatures, increase our vulnerability to ozone impacts. It seems the intense heat wave experienced this summer may have influenced this trend in the region, which is already suffering from severe air pollution," she said.

According to the CSE report, the data is available for the year 2018 from 31 monitoring stations in Delhi and from 36 stations for the year 2019. The study revealed that ozone level was high in the NCR towns of Faridabad, which has experienced the highest share of days - 80 per cent -- when ozone crossed the eight-hourly standards.

This is followed by Ghaziabad with 67 per cent and Gurugram with 21 per cent of days. Noida shows much less impact with only 1 per cent of the days exceeding the standards. "In the month of May, 2019, close to 20 per cent of the days exceeded the standards compared to 3 per cent in May, 2018. Similarly, while during June, 2018 not a single day had violated the ozone standard, 27 per cent of the days in June, 2019 crossed the limit.

"Only April, 2018 had comparatively higher share of days violating standards (10 per cent) compared to 7 per cent during April 2019," the study said. Identifying hot spots in the national capital with higher concentration of ozone, the study said that in prominent residential areas it has exceeded more, like in Siri Fort where 76 per cent of the days in the period under analysis exceeded the ozone standards while at Sri Aurobindo Marg it was 87 per cent.

Areas like R K Puram (53 per cent), JLN Stadium (71 per cent), Dwarka Sector 8 (68 per cent) and Rohini (63 per cent) too had high ozone levels. "The industrial and institutional areas are in an equally bad situation. Bawana (78 per cent of the days in the period under analysis), Jahangirpuri (67 per cent), Najafgarh (92 per cent), and Narela (80 per cent). This is bad news as it indicates increased and extended exposure for people living in these areas almost on a daily basis," the study said.

The city's average could have been worse if some locations did not have low levels, it said, adding in Aya Nagar, Karni Singh Shooting Range, IGI airport, Lodhi Road, Mandir Marg, Pusa Road, Patparganj, North Campus, ITO and Anand Vihar less than 5 per cent of the days have experienced the exceedance. This is a complex atmospheric chemistry and needs investigation, CSE pointed out while warning that the number of days crossing the standard have certainly gone up this summer and can be a serious health crisis if the levels begin to increase hereafter.

"As the AQI is beginning to show ozone as a dominant pollutant, this will require strong action to cut down gaseous emissions from combustion sources - vehicles and industry. "The new source assessment studies of 2018 have already implicated vehicles as the highest source of NOx (which is a key culprit in the ozone recipe) -- according to the SAFAR study of 2018, vehicles in Delhi are responsible for 62.5 per cent and industry 24.4 per cent of the total NOx load from all sources.

"The Teri-ARAI study of 2018 had found vehicles responsible for 81 per cent. NOx mainly catalyses reaction between gases in the air," the CSE said.