Lockdown did not improve air quality as much as first thought13th January 2021
Covid-19 lockdowns last year saw people in cities across the world breathe cleaner air – but changes in pollution levels were less dramatic than first thought.
That is according to a team of scientists led by the University of Birmingham, who say the weather masked the true impact of lockdowns on pollutants such as particulate matter, nitrogen dioxide and ozone.
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Early assessments of UK air quality estimated a drop in nitrogen dioxide levels – a key pollutant – as high as 60 per cent during the first lockdown. Similar assessments were made for other global cities. But in reality lockdowns only delivered between a 10-50 per cent drop in NO2 levels, the scientists said today.
Meanwhile some cities saw an increase in ozone pollution during lockdown, and London saw levels of harmful particulate matter increase.
“You would have health benefits from the nitrogen dioxide reduction, but that will be offset somewhat by an increase in ozone,” lead author Professor Zongbo Shi told i.
A tougher challenge
The team assessed the air quality in 11 cities around the world, including London, Paris, New York and Beijing, during the first half of 2020. Artificial intelligence was used to strip out the impact of weather trends on pollution, a process Prof Shi described as “de-weathering”.
Their findings suggest cutting air pollution is a more complex task than previously assumed, he warned. “Air quality improvement is likely to be more challenging than we thought,” he said.
Pollution levels were monitored in Paris and other major cities during the pandemic as part of the research (Photo: Getty)
Prof Shi and his co-authors are calling on governments to design air quality strategies that consider the knock-on impacts for all pollutants, to mitigate against the risk of unintended consequences. That should prevent measures to reduce NO2 inadvertently resulting in a rise in ozone or other pollutants, they said.
“Future mitigation measures require a systematic air pollution control approach towards nitrogen dioxide, ozone and particulate matter which is tailored for specific cities, to maximize the overall benefits of air quality changes to human health,” co-author William Bloss, professor of atmospheric sciences at the University of Birmingham, said.
The findings are published in the journal Science Advances.