Early lockdown in Delhi had less impact on air quality: Report

The first Covid-19 lockdowns led to significant changes in urban air pollution levels in Delhi and other major cities around the world, but the changes were smaller than expected, a new study by an international team of experts led by the University of Birmingham has concluded.

Published in ‘Science Advances’ on Thursday, the researchers evaluated changes in ambient NO2 (nitrogen dioxide), O3 (ozone) and fine particle (PM2.5) concentrations arising from lockdown emission changes in 11 global cities: Beijing, Wuhan, Milan, Rome, Madrid, London, Paris, Berlin, New York, Los Angeles and Delhi after developing new corrections for the impact of weather and seasonal trends.

The experts discovered that the beneficial reductions in NO2 due to the lockdowns were smaller than expected, after removing the effects of weather. They also found in parallel that the lockdowns caused (weather-corrected) concentrations of ozone in cities to increase.

Scientists at Birmingham used machine learning to strip out weather impacts and seasonal trends before analysing the data: site-specific hourly concentrations of key pollutants from December 2015 to May 2020.

The study also revealed that concentrations of PM2.5, which can worsen medical conditions such as asthma and heart disease, decreased in all cities studied except London and Paris.

Lead-author Zongbo Shi of the University of Birmingham said: “Rapid, unprecedented reduction in economic activity provided a unique opportunity to study the impact of interventions on air quality. 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 than 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,” the expert added.