A recent study by the Centre for Science and Environment (CSE) has revealed that ground-level ozone levels in India’s 10 major metropolitan areas have increased significantly during the summer of 2024. The study, which analyzed data from 2020 to 2024, found that ground-level ozone levels have risen by 17% in India between 2010 and 2017.
Ground-level ozone is a highly reactive gas that poses serious health risks to those with respiratory conditions, asthma, and chronic obstructive pulmonary disease. The gas is not directly emitted from any source but is produced through the interaction between nitrogen oxides (NOx) and volatile organic compounds (VOCs) from various sources.
METROPOLITAN AREAS MOST AFFECTED
The study found that ground-level ozone exceedance was reported in all 10 metropolitan areas, with Delhi-NCR being the most affected. The study also found that smaller metropolitan areas have experienced a significant increase in ground-level ozone exceedance, with Ahmedabad registering a 4,000% rise. 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) are the other areas.
IMPACT ON NATIONAL CLEAN AIR PROGRAMME
The study’s findings have significant implications for the National Clean Air Programme (NCAP), which needs to address the multi-pollutant crisis and the combined threat from PM2.5, ozone, nitrogen oxides, and other gases. “India must immediately refine the action strategy for combined control of particulate pollution, ozone, and its precursor gases like NOx to maximise the co-benefits of the action plan,” said Anumita Roychowdhury, executive director, research and advocacy, CSE.
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.”
Adds Somvanshi: “Inadequate monitoring, limited data and inappropriate methods of trend analysis have weakened the understanding of this growing public health hazard. The complex chemistry of ground-level ozone makes it a difficult pollutant to track and mitigate. Due to its toxic nature, ozone’s national ambient air quality standard has been set for only short-term exposures (one-hour and eight-hour averages), and compliance is measured by the number of days that exceed the standards. This requires early action.”
IMMEDIATE ACTION NEEDED
The study’s findings highlight the urgent need for immediate action to address the growing public health hazard of ground-level ozone pollution. India must develop a robust public information and dissemination system to alert the public about ozone exceedance wherever ozone build-up is happening. Additionally, the country needs to develop a comprehensive plan to reduce NOx and VOC emissions from various sources.
The study’s findings emphasize the importance of immediate action to address the growing public health hazard of ground-level ozone pollution. The Indian government must take immediate steps to reduce NOx and VOC emissions, develop a comprehensive plan to reduce particulate pollution, and ensure that public information is disseminated effectively to alert the public about ozone exceedance.
NIGHT-TIME GROUND-LEVEL OZONE CONTINUES TO PERSIST
Ground-level ozone should ideally become negligible in the night air, but all 10 metropolitan areas have been witnessing a rare phenomenon where ozone levels remain elevated hours after sunset. Night-time ozone has been considered when hourly concentration has exceeded the level of 100 µg/m3 between 10PM and 2AM at any station. Mumbai-MMR reported most instances of night-time ground-level ozone, with 171 nights of exceedance. It is followed by Delhi-NCR and Pune with 161 nights and 131 nights respectively. Hyderabad recorded exceedance on 94 nights; Ahmedabad, on 68 nights. Lucknow had 26 exceedance nights while Chennai had 24 and Bengaluru, 22. The least number of exceedanceswas recorded in Kolkata: 17 nights.
High end and green neighbourhoods are worst affected
Dr Karni Singh Shooting Range and Lodi Colony in Delhi, Navy Nagar in Mumbai, Fort William in Kolkata, Kapra in Hyderabad, BMT Layout in Bengaluru, Velachery in Chennai, Savitribai Phule University in Pune, Police Commissionerate in Jaipur, Gomti Nagar in Lucknow and Maninagar in Ahmedabad are all hotspots for ground-level ozone pollution.
“This is consistent with the science that ozone drifts and gathers in areas where comparatively lesser amount of gaseous pollutants are present to further mop it up. Thus, relatively cleaner areas including urban peripheries can have comparatively higher ozone concentration,” says Roychowdhury.
KEY HIGHLIGHTS
* Ground-level ozone levels have increased significantly in India’s 10 major metropolitan areas during the summer of 2024.
* The study found that ground-level ozone levels have risen by 17% in India between 2010 and 2017.
* Ground-level ozone exceedance was reported in all 10 metropolitan areas, with Delhi-NCR being the most affected.
* Smaller metropolitan areas have experienced a significant increase in ground-level ozone exceedance, with Ahmedabad registering a 4,000% rise.
* The study’s findings have significant implications for the National Clean Air Programme (NCAP).