NEW DELHI: The analysis of summer air quality during the national lockdown which started on March 25 presented a mixed trend. While the PM2.5 and NO2 curves fell and flattened dramatically in cities, a phenomenon that hogged the national attention is the increase in tropospheric ozone pollution which even breached standards in several cities, according to the Centre for Science and Environment (CSE).
The CSE looked at data on two major air pollutants emitted from burning fossil fuels: nitrogen dioxide (NO2) and fine particulate matter known as PM2.5.
The CSE did an analysis of 22 mega and metropolitan cities in India. The cities covered by the CSE analysis are Delhi-NCR (including Faridabad, Ghaziabad, Gurugram and Noida), Kolkata, Chennai, Mumbai, Ahmedabad, Ujjain, Bengaluru, Hyderabad, Jaipur, Jodhpur, Patna, Vishakapatnam, Amritsar, Howrah, Pune, Guwahati, Lucknow, and Kochi.
There was a rapid rise in PM2.5 during the lockdown relaxation and rise in pollution levels during Lockdown 4.0 when restrictions were relaxed.
The average level for lockdown 4.0 compared to the average of the cleanest of the other lockdown phases was higher in Chennai by 118 per cent; in Jaipur and Amritsar by 109 per cent; in Visakhapatnam by 108 per cent; in Pune by 80 per cent; and in Delhi by 43 per cent.
According to CSE researchers, ozone is primarily a sunny weather problem in India that otherwise remains highly variable during the year. It is a highly reactive gas; even short-term exposure (one hour) is dangerous for those with respiratory conditions and asthma.
Ozone is not directly emitted by any source but is formed by photochemical reactions between oxides of nitrogen (NOx) and other volatile organic compounds (VOCs) and gases in the air under the influence of sunlight and heat. Ozone can be controlled only if gases from all sources are controlled.
Anumita Roychowdhury, executive director-research, and advocacy, CSE said: “This pandemic-led change in air quality has helped us understand summer pollution. Normally, every year, winter pollution is what draws our attention. The characteristics of summer pollution are different: there are high winds, intermittent rains and thunderstorms, and high temperatures and heatwaves. This is in contrast to winter - with its inversion, lower mixing height of air, and cold and calm conditions that trap the air and the pollutants in it.”
If the maximum eight-hour average for 24 hours is considered (as the environment Protection Agency does to capture the health risks), then more than two-thirds of the lockdown days in Delhi-NCR cities and Ahmedabad had at least one station that exceeded the standard. In Ahmedabad, the city-wide maximum eight-hour average exceeded the standard on 43 days; in Ujjain, it exceeded on 38 days.