Ozone is not found naturally at ground-level; it is a product of a reaction of oxygen, volatile hydrocarbons and the oxides of nitrogen, which are emitted by vehicles. It tends to peak during the high temperatures of summer.

An analysis by the Centre for Science and Environment (CSE) of summertime ozone levels in April-May this year found that the hourly levels at Lodhi Estate, a green and posh part of the city, had peaked at “close to three times the standard.”

“Even when there has been intermittent rain that brought down the temperature and blocked the sun, thus reducing ozone levels, the gas would bounce back very quickly after the rains were over,” said the CSE report.

Targeting the cause of ground-level ozone, the Delhi Government is monitoring particulate matter in the air such as dust and smoke. “Ozone is dangerous at lower levels of the atmosphere, especially in smoggy conditions. But we are not monitoring it specifically, as we are already monitoring the factors that cause it, like nitrogen oxides,” said Delhi Government Environment and Forest Secretary Ashwani Kumar.

Doctors accept that awareness about the adverse health effects of ozone is not widespread. “But this doesn’t stop the rampage of that growing air pollution is causing to the health of city dwellers. We are seeing a steep rise in respiratory problems,” said Dr. Anil Bansal from Delhi Medical Association.

Studies have shown that the upper respiratory tract isn’t as effective in scrubbing ozone from the air that we inhale, as other pollutants like sulphur dioxide or chlorine gas, which are more soluble in water.

The majority of the ozone inhaled reaches the lower respiratory tract and dissolves into a thin layer of epithelial lining fluid throughout the conducting airways of the lung thus damaging it, according to scientific papers.