A nationwide analysis conducted by the Centre for Science and Environment (CSE) reveals a significant rise in ground-level ozone concentrations across ten major metropolitan areas in India during the summer of 2024. The affected cities include Bengaluru, Chennai, Delhi-NCR, Greater Ahmedabad, Greater Hyderabad, Greater Jaipur, Kolkata, Greater Lucknow, Mumbai, and Pune.

Anumita Roychowdhury, Executive Director of Research and Advocacy at CSE, underscores the health risks associated with ground-level ozone. "This highly reactive gas poses serious health hazards, particularly for individuals with respiratory conditions such as asthma and chronic obstructive pulmonary disease, as well as children and the elderly," Roychowdhury explains. The gas inflames airways, increases susceptibility to infections, and can exacerbate chronic respiratory conditions, leading to more frequent hospitalizations.

The 2020 State of Global Air report highlights that India experiences some of the highest age-standardized rates of death attributable to ground-level ozone. Between 2010 and 2017, the country saw a 17% increase in the seasonal eight-hour daily maximum concentrations of this pollutant.

Ground-level ozone is not directly emitted but forms through complex interactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. These pollutants originate from vehicles, power plants, factories, and other combustion sources. VOCs can also be emitted naturally from plants.

As the National Clean Air Programme (NCAP) approaches its second phase, Roychowdhury emphasizes the need for a comprehensive approach to tackle the multi-pollutant crisis, which includes ground-level ozone. “There is often a trade-off where reducing particulate pollution can lead to increased NOx and ground-level ozone. We need stricter regulatory benchmarks for ozone and better controls on emissions from industries, vehicles, households, and open burning,” she says.

Avikal Somvanshi, Programme Manager at CSE, highlights the broader geographic spread of ozone pollution in 2024 compared to the lockdown summer of 2020. This year’s data shows a prolonged toxic buildup in affected areas, including smaller metropolitan regions. The issue is now observed to persist beyond summer in some locations.

The study, which covers data from April 1 to July 18, 2024, uses real-time data from the Central Pollution Control Board’s (CPCB) online portal. The analysis reveals that ground-level ozone exceedances were reported across all ten metropolitan areas, with Delhi-NCR experiencing the highest number of exceedance days at 176. Mumbai and Pune follow with 138 days each.

The report notes a dramatic increase in exceedances in smaller metropolitan areas, with Ahmedabad showing a 4,000% rise, followed by Pune at 500% and Jaipur at 152%. This is contrasted with a decrease in exceedances in Kolkata and Chennai.

The intensity of ground-level ozone pollution remains high across all metropolitan areas, with Jaipur recording the highest regional average and peak levels. Despite the highest number of exceedance days being in Delhi-NCR and Mumbai, Jaipur’s air has been found to be the most toxic in terms of regional averages and peaks.

The study also points out that ground-level ozone levels remain elevated even at night in all metropolitan areas, with Mumbai reporting the most instances of night-time exceedance.

Sharanjeet Kaur, Programme Officer at CSE, calls for improvements in monitoring and trend analysis methods. The current compliance standards, which allow exceedances on a limited number of days, do not adequately address the local impacts of ozone pollution. The report suggests that a city-wide average is insufficient to capture the severity of ground-level ozone pollution and its health implications.

As ground-level ozone continues to pose a year-round challenge, particularly in sunny and less polluted areas, Roychowdhury stresses the need for an immediate and robust response. “The NCAP must refine its strategy to address not only PM10 but also ozone and its precursors. Effective action requires stringent controls on emissions and improved public awareness systems,” she concludes.

This analysis underscores the urgent need for comprehensive policies and public health interventions to mitigate the growing threat of ground-level ozone pollution in India’s urban centers.