New studies reveal drastic fall in global NO2 levels during lockdown

Nitrogen dioxide (NO2) pollution over northern China, Western Europe and the U.S. decreased significantly in early 2020 when compared to the same time last year, two new studies have found.

Published in Geophysical Research Letters, researchers used satellite measurements of air quality to estimate the changes in NO2 over the major epicentres of the outbreak: China, South Korea, Italy, Spain, France, Germany, Iran and the United States.

They found that NO2 pollution decreased by an average of 40% over Chinese cities and by 20% to 38% over Western Europe and the United States during the 2020 lockdown, as compared to the same time in 2019.

However, the study found NO2 did not decrease over Iran, one of the earliest and hardest-hit countries. The authors suspect this is because complete lockdowns weren’t in place until late March and before that, stay-at-home orders were largely ignored. The authors did see a dip in emissions during the Iranian New Year holiday after March 20, but this dip is observed during the celebration every year.

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Jenny Stavrakou, an atmospheric scientist at the Royal Belgian Institute for Space Aeronomy in Brussels and co-author of one of the papers said such a significant drop in emissions is unprecedented since air quality monitoring from satellites began in the 1990s. The only other comparable events are short-term reductions in China’s emissions due to strict regulations during events like the 2008 Beijing Olympics.

However, the drop in NO2 pollution has caused an increase in surface ozone levels in China, according to one of the new studies. Ozone is a secondary pollutant formed when sunlight and high temperature catalyze chemical reactions in the lower atmosphere. Ozone is harmful to humans at ground-level, causing pulmonary and heart disease.

Ms Stavrakou said: ‘Maybe this unintended experiment could be used to understand better the emission regulations. It is some positive news among a very tragic situation.’

Read the full paper here. 

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