‘Nitrate radicals’ are likely making air pollution worse in China, India

A new study has found that parts of India and China are hotspots for the night-time production of nitrate radicals that can increase the amount of deadly ozone and PM2.5 particulate matter in the atmosphere.

According to the researchers, the nighttime production of nitrate radicals could make it difficult to improve India's air quality. (Illustrative image) (Express Photo by Prem Nath Pandey)

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Parts of China and India are night-time hotspots for the production of nitrate radicals that could increase the amount of health-threatening ozone and PM2.5 fine particulate matter in the atmosphere, according to a new study published in Nature Geosciences. Nitrate radical is an oxide of nitrogen that consists of three oxygen atoms bound to a nitrogen atom.

While cities in Europe and the United States have experienced a decline in the nocturnal production of nitrate radicals, parts of China and India have experienced a rapid increase. According to Zongbo Shi, co-author of the research article, nitrogen oxides are reactive gases that regulate the formation of air pollutants, including ozone and PM2.5 particles.

“Nitrate radicals will oxidise gas pollutants such as volatile organic compounds(VOCs), which will then generate ozone and secondary organic aerosol. So this deteriorates air quality. Ozone is an air pollutant that affects human health and crop yield. Secondary organic aerosol is an important component of PM2.5,” said Shi to indianexpress.com in an email.

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The study documented the increased production of nitrate radicals in three megacity clusters in China (North China Plain, Yangtze River Delta and Pearl River Delta). It also observed the same phenomenon in parts of India. “Some parts of India (northern India) also see an increase in night-time production of nitrate radicals. If India follows trends seen in Los Angeles and China, it will be harder for India to improve air quality in the future,” added Shi.

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According to the study, if the current trend of increasing ozone pollution continues, this night-time oxidation in China will continue to increase even if nitrate emissions are reduced and controlled.

But, based on trends in Los Angeles since 1980 and global changes since the Covid-19 pandemic, scientists believe that reducing the emissions of VOCs could reduce this night-time oxidation in China and other regions. According to the United States University Corporation for Atmospheric Research, most human-made VOCs come from vehicle exhausts and industrial processes.

According to Shi, the process of nocturnal oxidation driven by nitrate radicals is an important but poorly understood process in atmospheric chemistry. Shi believes that this process must be studied better so that pollution mitigation strategies can be planned better.

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Urban air pollution

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