Observational data shows air pollution in India decreased drastically in the first COVID-19 lockdown when emissions from vehicles naturally declined, but researchers say those numbers only tell part of the story — blue skies and an absence of visible smog can be deceiving and hide pollutants that could potentially cause health issues.
Air pollution results from a complex mix of interactions between emissions, meteorology, such as wind direction and rain, as well as chemistry, but looking only at observational data as many recent studies have done without take meteorology into account, skews the numbers.
The researchers found that some air pollutants didn’t drop nearly as much as first thought and even more surprising was that ozone levels increased even as other pollutants decreased. The air looked much cleaner, but that allowed more sunshine to get through, creating conditions for ozone (O3) to increase up to 30 per cent.
«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.»
As the national lockdown in India reduced major urban sources of air pollution, such as traffic, industry and construction, it gave the researchers an opportunity to study the contribution of local sources of air pollutants during normal meteorological conditions.
To get a clearer picture of potential decreases in air pollution, Crilley and Young focussed their study on nitrogen oxides (NOx), fine particulate matter (PM2.5) and O3, as well as what was happening meteorologically at multiple locations within two cities in India — Delhi and Hyderabad — during the start of the first lockdown, from March 24 to April 24, 2020.
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Materials provided by York University. Note: Content may be edited for style and length.