CHENNAI: Manali recorded India’s highest ground-level ozone reading this year of 500 micrograms per cubic metre on May 19, according to Central Pollution Control Board (CPCB) data, even as environmental regulators point to improvements in the region’s air quality. A second monitoring station in the area peaked at 361 micrograms per cubic metre on May 3, placing the industrial cluster (in northern Chennai), home to petrochemical plants, oil refineries, fertiliser units and thermal power stations, among the country’s worst ozone hotspots this summer.
Manoj Kumar, analyst at the Centre for Research on Energy and Clean Air, said, “Analysis of CPCB data showed that Manali exceeded the National Ambient Air Quality Standards for ozone on 24 days during May 2026, based on the prescribed 8-hour average concentration standard of 100 micrograms per cubic metre.
“Ozone is one of the few pollutants that tend to increase during summer as intense sunlight accelerates chemical reactions between nitrogen oxides and volatile organic compounds (VOCs),” he added.
However, Tamil Nadu Pollution Control Board (TNPCB) officials caution against drawing conclusions solely from peak ozone readings.
“We cannot simply say industries alone are responsible. The bigger problem currently is the vehicular emissions, which is also a source of VOCs. Industrial clusters will inevitably have cumulative impacts,” a senior TNPCB official said.
According to TNPCB data, the Air Quality Index (AQI) in Manali has improved from 118.9 in 2018 to 64 in 2026. Of the 19 highly polluting 17-category industries in the area, 15 have switched from furnace oil to cleaner fuels such as recompressed liquefied natural gas (R-LNG), LPG and naphtha.
“The government took a policy decision to move industries away from furnace oil to gaseous fuels specifically to reduce baseline pollution levels seven years ago. And it’s yielding results today,” the TNPCB official said.
But Shweta Narayan, campaign lead at Global Climate and Health Alliance and author of ‘Cradle to Grave’ report, said, “Ozone forms when volatile organic compounds combine with other chemicals in the presence of sunlight. Carbon-focused solutions alone will not address this problem. Industries need better leak detection systems, improved operational practices and transparent emissions monitoring.”
She argued that many ozone-forming emissions originate from so-called fugitive emissions like leaks during storage, transportation and handling of chemicals rather than from smokestacks alone.
“Industries can invest in better leak detection and repair programmes, improve operational efficiency and adopt cleaner production systems. The question is whether there is sufficient accountability and enforcement to ensure these measures are implemented,” she added.
Independent public policy analyst Dharmesh Shah said, “Pollution Release and Transfer Registry (PRTR) would give India what every effective pollution control system needs: transparency. By making information on industrial emissions publicly available, a PRTR empowers regulators, communities, researchers, and businesses to identify pollution hotspots, and also strengthens accountability.”