Surprise find ing on air quality

AIR pollution levels across the world decreased during the early lockdowns of 2020 but not as much as expected, according to a study led by scientists from the University of Birmingham in the UK.

The study measured levels of nitrogen dioxide, ozone and fine particle concentrations in 11 cities last year, among them Beijing, Wuhan, Milan, Rome, Madrid, London, Paris, Berlin, New York, Los Angeles and Delhi. The results were published in Science Advances in January.

The researchers found that, after adjusting for weather effects, the reduction in nitrogen dioxide was less than they had expected, while lockdowns caused concentrations of ozone to increase.

Fine particle concentrations decreased in all the cities except London and Paris.

Zongbo Shi, a professor of atmospheric biogeochemistry at the university and lead author of the study, said: “Emission changes associated with the early lockdown restrictions led to abrupt changes in air pollutant levels but their impacts on air quality were more complex that we thought and smaller than we expected.

“Weather changes can mask changes in emissions on air quality. Importantly, our study has provided a new framework for assessing air pollution interventions by separating the effects of weather and season from the effects of emission changes,” he said.