Mumbai Faces Alarming Ground-Level Ozone Pollution Amid Nationwide Urban Air Quality Crisis
Reported by Akshata Pawar
Mumbai, 16th July 2025: Mumbai, India’s financial capital, has emerged as one of the key urban centres battling an alarming spike in ground-level ozone pollution this summer, according to a detailed analysis released by the Centre for Science and Environment (CSE) today.
The new study, conducted by CSE’s Urban Lab under its ‘Air Quality Tracker’ initiative, highlights that major metros across India — including Kolkata, Bengaluru, Hyderabad, and Chennai — have experienced severe ozone pollution in recent months. While Delhi was not part of this particular analysis, CSE has previously flagged a similar trend for the capital.
Between March 1 and May 31 this year, Mumbai saw ozone levels breach the permissible eight-hour standard on 32 out of 92 days, marking it as one of the worst-affected metros despite a 42% improvement over the same period last year. The worst-hit locality was Chakala, with 29 days of exceedance, followed by Byculla and Kherwadi.
“Ozone is not emitted directly like other pollutants but forms from a complex chemical reaction involving nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide under sunlight,” explained Anumita Roychowdhury, Executive Director at CSE. “Unchecked, this could become a serious public health crisis.”
CSE’s report reveals that Mumbai’s ozone pollution is no longer limited to just summer months. During winter 2024–25, the city experienced 87 days of ozone exceedance, a 10% increase over the previous winter, an unusual seasonal trend typically associated with cooler northern cities.
Another worrying sign is the longer persistence of ozone in the evening hours, even after sunset, indicating changing atmospheric chemistry or shifts in precursor emissions. While daily peak ozone levels this summer have dropped by 35% compared to last year, the complex interplay between ozone and other pollutants like NO₂ continues to shape the city’s air quality patterns.
“Chakala’s data is particularly concerning because it consistently shows high levels of both NO₂ and ozone,” said Sharanjeet Kaur, Deputy Programme Manager at the CSE Urban Lab. “This contradicts the usual trend where high NO₂ suppresses ozone formation, suggesting hyper-local anomalies driven by meteorological and traffic-related factors.”
The CSE study used real-time granular data from 80 official air monitoring stations across five metros. The eight-hour ozone standard — as per international norms — was considered breached even if a single monitoring station in a city reported exceedance. This approach underlines the severity of localised exposure risks.
Other key findings include:
Bengaluru saw a 29% rise in ozone exceedance days compared to last year.
-Kolkata and Hyderabad recorded significant improvements in summer ozone levels, but winter trends remained concerning, especially in Howrah, which recorded 81 winter exceedance days, up from just 14 the previous year.
-Chennai saw 15 exceedance days this summer — a dramatic increase from zero last year.
Ozone pollution, CSE warns, is a regional issue. While it may be formed in polluted urban areas, it can drift into cleaner suburban and rural regions, harming agriculture and food security. Its health impacts include inflammation of the airways, increased asthma attacks, and worsened respiratory conditions, especially in children, the elderly, and individuals with pre-existing lung diseases.
A Call for Urgent Action
Roychowdhury emphasized the need to integrate ozone mitigation into urban clean air strategies, saying, “Cities that have successfully brought down particulate pollution are now facing a rise in ozone and NOx levels — a pattern we must urgently avoid.”
CSE recommends:
-Stringent control of emissions from vehicles, industries, and waste burning
-Widespread adoption of zero-emission technologies
-Improved and localized ozone monitoring
-Integration of ozone control into the Graded Response Action Plan (GRAP)
-Development of regional ozone action plans to prevent cross-boundary pollution impact
