Pune: The Pune metropolitan region ranked third among 10 most polluted cities surveyed in India with a 500% increase this year in ground-level ozone — a highly toxic gas caused by vehicular pollution — compared to 2023, said a study by researchers at the Centre for Science and Environment. Researchers said exposure for eight hours to the poisonous gas could lead to serious respiratory and cardiovascular problems and for 24 hours could be fatal for vulnerable people. Ozone gas is formed by reactions between nitrogen dioxide emitted by vehicles and the burning of substances and oxygen in the presence of sunlight.
While the ozone gas layer is protective in the stratosphere, it is fatal for people at ground level. The study said that in Pune, the gas is formed in areas with heavy vehicular pollution and eventually settles in green spaces. Dr Sundeep Salvi, director of Pulmocare Research and Education Foundation, told TOI that ozone does have a significant impact on the lungs and gets deposited in airways.
It manifests mainly into upper respiratory tract infections. “It can worsen asthma, and people with comorbidities, children and senior citizens are heavily affected, because it makes the tract irritable and vulnerable to catching bacterial as well as viral infections. We had a very hot summer this year and ground-level ozone must have increased with motor vehicle pollutants, air and sunlight.
This was primarily the reason behind respiratory issues this summer,” he added. Avikal Somvanshi, head, Urban Lab, Centre for Science and Environment (CSE) and co-author of the study, told TOI, “Once the ground-level ozone is formed, it reacts with nitrogen oxide (NO2) again and gets subdued. However, its continuous formation produces high levels of toxic gas which move to green areas with less NO2 and form pockets of these chambers across the city.
Savitribai Phule Pune University (SPPU) has a lot of big green areas where the gas deposits and its levels increase.” The study explored the increase based on data from 2020 to 2024 from the Central Pollution Control Board (CPCB)’s Continuous Ambient Air Quality Monitoring System (CAAQMS) of which there are 12 in Pune and three in Pimpri Chinchwad. The monitors measure the gas only at one- and eight-hour averages and gas concentration every 15 minutes.
However, the safety standard is defined only for one-hour and eight-hour averages. According to CPCB standards, the safe limit for ground-level ozone is 100 microgramme per cubic metre and anything above is exceedance. This summer, exceedance was reported on 58 days.
In mid-May, six of 16 stations in Pune metropolitan region reported exceedance, making the situation the worst the region had seen in five years. It also marked the 500% increase from last year. Somvanshi said, “The reason is drastic increase in vehicular pollution in Pune over the last five years.
The toxic gases concentrate in areas with congestion and also add to the release of natural gases from municipal solid waste. The excessive heat wave observed in 2024 was a primary reason for the increase.” A senior official from the PMC environment department told TOI that the number of vehicles registered with a BSVI engine, which is more advanced, had increased in 2024.
“This will help us mitigate the problem of toxic gases. We have been promoting CNG, electric buses, electric personal vehicles and Metro transportation. The traffic police has also taken action to reduce congestion in areas to prevent concentration of the ozone gas.
Unfortunately, over the past few years, the city’s population has drastically increased and along with it the number of vehicles. Excessive air pollution is an obvious byproduct. As far as we know, we have kept nitrogen dioxide levels under control.
” Meanwhile, the study identified SPPU as most chronically affected by ground-ozone pollution, exceeding the standard for 119 days, so far, this year. It was followed by Gavalinagar and Thergaon in Pimpri with 119 days and 99 days of exceedance each. Shivajinagar’s pollution was calculated with PM2.
5 levels making its AQI the worst in the city, though the ozone gas was still at a minimum. Researchers said the hourly peak on average had gone up by 200% from 2020. The maximum eight-hour average was recorded at SPPU when the level hit 212.
7 μg/m3 on March 22. “It was startling to see cities smaller than Delhi and Mumbai with such high levels of ozone gas,” Somvanshi said about Pune ranking the third most polluted among the 10 cities surveyed. Ground-level ozone should ideally become negligible in the night air, said researchers.
However, night ozone was still observed almost exceeding up to 100 μg/m3 most frequently at Gavalinagar in Pimpri and SPPU. Ozone gas also traps heat, which is attributed to the high night temperatures observed in Pune, this year. “The gas has an immediate impact unlike PM2.
5 which affects a person due to long-term exposure. Ozone gas is correlated to the most number of deaths from air pollution. In order to mitigate the problem, vehicular congestion must be reduced, emission testing done and instruments to process nitrogen dioxide installed within vehicles.
Taking a walk at the park becomes dangerous if levels are so high,” said Somvanshi. Even though the ground-level ozone exceedance is the worst during summer months, it remains a year-long problem for Pune which provides hot and sunny weather conditions for the gas to build up. Air pollution activist Hema Chari Madabhushi told TOI, “We had always known that ozone gas formation was occurring dangerously in the city, but didn’t know how bad it was.
Especially near SPPU, the traffic is extremely congested and all heritage trees along the road have been chopped. It causes a significant amount of air pollution.” She said children, senior citizens, traffic police personnel and autorickshaw drivers were at greater risk now, considering how much pollution occurs along roadsides.
“Ozone is affecting temperatures, increasing heat island effect and also impacting precipitation. The civic body needs to take the study seriously and must immediately focus on ensuring back-to-back and well-connected public transportation, otherwise the problem will never be resolved,” Madabhushi added..
