Ozone pollution in India increased during lockdown

Air pollution decrease in India during the Covid-19 lockdown was not as high as originally thought. 

To get a clearer picture of air pollution in India, researchers at the University of York looked at nitrogen oxide (NOx), particulate matter (PM2.5) and ozone (O3) pollution. 

They used hourly data from air quality monitoring stations and compared this data to the same dates from the previous three years to evaluate changes due to lockdown. 

When taking observational data into account, the researchers found that NOx and PM2.5 fell up to 57% and 75% respectively.

But when meteorology was factored in, those percentages fell to less than 8% for PM2.5 and between 5 and 30% in both cities, while O3 increased. 

According to the researchers, although the air did look cleaner, this allowed more sunshine to get through, creating conditions for ozone to increase. 

The researchers also found that local sources of emissions, such as vehicles and the burning of fuels, had less influence on air pollution levels than regional emissions sources, while weather events and atmospheric chemical processes contributed independently to air pollutant levels.

‘To accurately quantify the impact of the Covid-19 lockdown on air pollutant levels, meteorology and atmospheric chemistry needs to be considered in addition to emissions,’ says York University postdoctoral researcher Leigh Crilley, who led the Faculty of Science research along with York Associate Professor Cora Young and team.

‘Our research shows the decline in local emissions had less influence on the decrease in air pollutants than first thought.’

‘We demonstrate that regional sources, such as rural and agriculturally based emissions, that may have been less affected by the lockdown, have a significant influence on PM2.5 levels in Delhi and Hyderabad after weather-normalization. This indicates that future PM2.5 mitigation strategies should focus on national-scale, as well as local sources,’ says Young.

‘Overall, this study highlights the impact of emissions, meteorology and chemistry on air pollution and that all three should be considered when assessing the effects of any short-term intervention on air pollutants.’