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A man take cover to protect themselves from the scorching heat in Delhi. (TOI photo by Rajesh)

NEW DELHI: Day temperatures dropped marginally on Thursday but there was hardly any relief for weather-beaten Delhiites as toxins in the air rose alarmingly due to a cloud cover trapping pollutants. The capital’s air quality index (AQI) breached the ‘severe’ level, going from 219 (poor) on Wednesday to 410 in one of the sharpest single-day spikes in recent months. Fine particle pollution (PM2.5) that AQI measures wasn’t the only threat lurking in the capital’s air. Over the past week, when torrid weather made headlines, levels of the highly toxic ozone (O3) gas were also very high, often double the safe standard of 50 parts per billion.While PM2.5 are minute particles that can enter deep inside a person’s lungs, exposure to O3 can immediately trigger respiratory distress. It can aggravate lung diseases such as asthma and chronic bronchitis and also inflame the airways, causing permanent lung damage in some people, depending on the exposure.“Together, ozone and PM2.5 can play havoc with people’s health. Those exposed to the pollutants, even for a short duration, can suffer respiratory problems,” said Dr Sandeep Salvi, who heads the Chest Research Foundation, Pune. He said asthma and chronic obstructive pulmonary disease (COPD) patients were at high risk.Rise in O3 levels was a direct result of the searing temperatures in the capital. Experts said O3 would continue to be high till there’s rain in the capital. UV levels in Delhi too are way above safe standards.The AQI, meanwhile, unexpectedly rose to ‘severe’ levels for the first time since the winter. PM2.5 reading were as high as 250 micrograms per cubic metres, more than four times the safe standard.Scientists said the dust storm on Thursday early morning led to both PM10 (coarse pollution particles) as well as PM 2.5 levels to peak dramatically.“The levels of PM 2.5 were extremely high after 5am because of the storm. Usually the PM10 levels peak after dust storms but this time the levels of fine particles also went up,” said Gufran Beig, project director of System of Air Quality Weather Forecasting and Research (SAFAR) under the ministry of earth sciences (MoES). The Central Pollution Control Board ’s air quality bulletin, which monitors areas that SAFAR doesn’t, showed air quality in both Delhi and Faridabad to be in the ‘very poor’ category, a level lower than ‘severe’.O3 levels have been consistently high for the last seven days around Delhi University (north campus), Dheerpur and Aya Nagar, with a peak of 120 ppb at Dheerpur. The area around Pusa recorded the minimum O3 levels of about 60-70 ppb.“The temperature in Pusa is also about three to four degrees lower which may have brought down O3 levels. O3 levels go up in the urban heat islands where concrete spaces, vehicular and air conditioner exhausts cause temperatures to rise,” an expert said.“Ozone is created in conditions of high temperature and direct sunlight, accompanied with high levels of oxides of nitrogen (NOx), carbon monoxide (CO) and other volatile organic compounds (VOCs). They peaked this week probably because temperatures were extremely high,” added Beig.Experts said modifying one’s diet and taking more fluids can help fight the health consequences of ozone and PM2.5 exposure. “Fruits and green leafy vegetables contain antioxidants that help fight pollutants by improving the body’s defense mechanism,” said a senior doctor.High vehicular emissions are a major contributor to O3 pollution in the city “Ozone is a very harmful gas. It not directly emitted from any source. Gases from other sources such as NOx and VOCs act as catalysts when there is strong sunlight and heat. The major source of NOx is vehicles. If the government has to control ozone, it has to immediately take action to bring down vehicular emissions,” said Anumita Roychowdhury, head of Centre for Science and Environment (CSE’s) clean air programme.SAFAR along with the Indian Meteorological Department (IMD) recently launched the Ultraviolet (UV) index for Delhi which basically tells people what is their exposure to UV rays on a certain day and whether it is in the no risk, medium risk or high risk categories. SAFAR on Thursday said the UV index for Delhi was 7.2 while the safe range is 1 to 4.CSE’s climate researchers said more heat waves were expected as globally temperatures had risen by an average of 0.8 degrees in the past 100 years. Night-time temperatures were rising too, with Ahmedabad and Delhi recently reporting 39 and 36 degrees Celsius, respectively, at night, they said.