Scientists from the Union ministry of earth sciences have warned about a possible spike in ozone pollution over the next three days because of rising mercury levels. Even though the overall air pollution levels in Delhi was in the moderate zone on Thursday, with the AQI hovering around 141 (on a scale of 0 – 500), scientists said that ozone was one of the main pollutants, along with PM10 and PM2.5. “The mercury is expected to rise over the next three days, which is likely to increase ozone production. The overall pollution levels could rise to poor levels with ozone as one of the lead pollutants,” said a statement issued by Safar, the pollution forecasting agency of the ministry of earth sciences, on Thursday.The India Meteorological Department (IMD) has forecast that the temperature would remain around 40 degrees Celsius over the next three days. On Thursday, the maximum temperature was recorded at 38.8 degrees Celsius. Even though Stratospheric ozone (ozone in the upper reaches of the atmosphere) is good as it absorbs the sun’s harmful ultraviolate rays, it is the ground level ozone — formed when vehicular and industrial fumes undergo chemical reactions in the presence of sunlight — that can cause a variety of health problems including chest pain, coughing, throat irritation, and airway inflammation.“This year ozone level has consistently been elevated because of heat waves in Delhi. There are very few occasions in a year when ozone becomes one of the lead pollutants. Peak summer is one such period,” said a Safar scientist. The Centre for Science and Environment released a report on Wednesday, which also showed that ozone has emerged as a dominant pollutant along with particulate matter on at least 28 days during summer of 2019 (April 1 to June 5) as opposed to only 17 days in 2018 summer.While in 2018 ozone pollution had exceeded the prescribed standards only on five percent days, this year such number of days with high ozone pollution has shot up to 16%. In several residential areas, such as Siri Fort, Aurobindo Marg, RK Puram, JLN Stadium, Dwarka Sector 8 and Rohini, ozone pollution was higher than prescribed on at least 50% days this year. In NCR, Faridabad and Ghaziabad have experienced the biggest spikes. Compared to this, areas such as Aya Nagar, Karni Singh Shooting Range, IGI airport, Lodhi Road, Mandir Marg, Pusa Road, Patparganj, North Campus, ITO and Anand Vihar showed less ozone pollution, with the pollutant exceeding the limit on less than five percent of days. The eight-hour average standard for ozone exposure is 100 microgram per cubic metre. The highest concentration in 2019 went up to 122 microgram per cubic metre, which is 1.22 times higher than the eight-hour average standard. During 2018, it had gone up to 106 microgram per per cubic metre.“This is a matter of serious concern as ozone is a highly reactive gas and can have adverse effect on those suffering from asthma and respiratory conditions. If this trend continues and worsens, the Graded Response Action Plan will also have to initiate action to address the precursor gases that form ozone — NOx, hydrocarbons etc — and crack down on vehicles and industry,” said Anumita RoychowdhuryRo CSE executive director (research and advocacy).