CHENNAI: Manali in north Chennai is emerging as the country’s most severe hotspot for ground-level ozone pollution, with a monitoring station in the industrial suburb recording 500 micrograms per cubic metre of ozone on May 19, the highest level reported anywhere in India this year, according to Central Pollution Control Board (CPCB) data.
The area has repeatedly recorded elevated ozone levels this year, with another monitoring station in Manali registering 361 micrograms per cubic metre on May 3. The readings indicate that the north Chennai industrial belt is among the country’s most polluted regions for ground-level ozone.
A senior official from the Centre for Research on Energy and Clean Air (CREA) said ozone concentrations in Manali exceeded the national air quality standard on 24 days in May.
“The recorded values crossed the national standard of 100 micrograms per cubic metre, which is based on an eight-hour average,” the official said.
Manali houses several petrochemical industries, oil refineries, fertiliser plants and thermal power stations. However, the Tamil Nadu Pollution Control Board (TNPCB) said industries alone cannot be blamed for the elevated ozone levels, pointing to vehicular emissions and volatile organic compounds as major contributors.
According to TNPCB, Manali’s Air Quality Index (AQI) has improved from 118 in 2018 to 64 in 2026, while 15 of the 17 highly polluting industries in the area have switched to cleaner fuels such as compressed natural gas (CNG), LPG and naphtha.
Ground-level ozone is a harmful pollutant formed when nitrogen oxides and volatile organic compounds react in the presence of sunlight. Unlike the ozone layer in the upper atmosphere, which shields the Earth from harmful ultraviolet radiation, ground-level ozone can pose risks to human health and the environment.