Ozone build-up: Delhi-NCR and other metropolitan areas of India confront new air quality crisis

Each year during winter, Delhi-NCR hits the headlines due to severe air pollution that surpasses all permissible limits. However, there is now another major concern. According to an analysis by the Centre for Science and Environment (CSE), ground-level ozone increased in 10 metropolitan areas of India this summer, with Delhi being the most affected, as reported by TOI. The report further highlighted that Delhi-NCR recorded 176 days of exceedance during the study period, followed by Mumbai and Pune with 138 days.

According to CSE, it is common for ground-level ozone to exceed safety standards during summer in some locations in Delhi-NCR. However, this year, the number of stations exceeding the standard across core NCR reached 17.6, the highest in the last five years. Previously, only 9.4 stations exceeded the standard daily on average. This number gradually increased, reaching 14.6 stations with exceeded limits in the summer of 2020.

The report notes that ideally, ground-level ozone should be negligible at night. However, it has been growing rapidly, with a surge in ozone levels after sunset in all 10 metropolitan areas.


Why is ground-level ozone considered dangerous?
According to the report, ground-level ozone is a highly reactive gas that can create serious health problems. “Those with respiratory conditions, asthma, chronic obstructive pulmonary disease, children with developing lungs, and older adults are at serious risk. The gas can inflame and damage airways, make lungs susceptible to infection, aggravate asthma, emphysema, and chronic bronchitis, and increase the frequency of asthma attacks,” said Anumita Roychowdhury, Executive Director of Research and Advocacy at CSE.

Another concern is that even in Delhi’s green neighborhoods, high levels of ground-level ozone were recorded, including areas like Dr Karni Singh Shooting Range and Lodhi Colony. “This is consistent with the science that ozone drifts and gathers in areas with relatively lower amounts of gaseous pollutants. Thus, relatively cleaner areas, including urban peripheries, can have comparatively higher ozone concentrations,” added Roychowdhury.

Avikal Somvanshi, Programme Manager at Urban Lab, CSE, who led the study, said, “Even though ground-level ozone exceedance is typically worse during summer months, data from the 10 metropolitan areas analyzed in our study shows that it is a year-round problem.”

CSE asserted that the country should develop a robust public information and dissemination system to alert the public wherever ozone build-up occurs.