A new nation-wide analysis by Centre for Science and Environment (CSE) says that in the summer of 2024, the levels of ground-level ozone in the air went up in the 10 major metropolitan areas of India.

These areas and cities include Bengaluru Metropolitan Area (Karnataka), Chennai Metropolitan Area (Tamil Nadu), Delhi-NCR, Greater Ahmedabad (Gujarat), Greater Hyderabad (Telangana), Greater Jaipur (Rajasthan), Kolkata Metropolitan Area (West Bengal), Greater Lucknow (Uttar Pradesh), Mumbai Metropolitan Region (Maharashtra) and Pune Metropolitan Region (Maharashtra).

Says Anumita Roychowdhury, executive director, research and advocacy, CSE: “Ground-level ozone, a highly reactive gas, has serious health consequences. Those with respiratory conditions, asthma and chronic obstructive pulmonary disease – as well as children with premature lungs and older adults — are at serious risk. This can inflame and damage airways, make lungs susceptible to infection, aggravate asthma, emphysema, and chronic bronchitis and increase the frequency of asthma attacks leading to increased hospitalisation.”

The 2020 State of Global Air report states that age-standardised rates of death attributable to ground-level ozone is among the highest in India. The seasonal eight-hour daily maximum concentrations have recorded one of the highest increases in India between 2010 and 2017 – about 17 per cent.

Ozone needs special attention — ground-level ozone is not directly emitted from any source. It is produced from complex interaction between nitrogen oxides (NOx) and volatile organic compounds (VOCs) that are emitted from vehicles, power plants, factories, and other combustion sources and undergo cyclic reactions in the presence of sunlight to generate ground-level ozone. VOCs can also be emitted from natural sources, such as plants.

Roychowdhury points out that as the National Clean Air Programme (NCAP) gears up for its second phase, “its reform agenda has to address the multi-pollutant crisis and the combined threat from PM2.5, ozone, nitrogen oxides and other gases. Global experience shows that there is usually a trade-off — as particulate pollution gets reduced, the problem of NOx and ground-level ozone increases. This requires significant tightening of the regulatory benchmark for ozone to address the toxic emissions from industry, vehicles, households and open burning”.  

According to Avikal Somvanshi, programme manager, Urban Lab, CSE, who has led the CSE study, “in 2024, we have found that the geographical spread of the problem is much wider than what we had seen in the lockdown summer of 2020 in most metropolitan areas. This time’s toxic build-up has lasted longer in locations affected by the problem. Even the smaller metropolitan areas have witnessed rapid increase. In metropolitan areas in the south and western coastal belt, the problem is not limited only to the summer months.”