Business closures and lockdowns to stem the spread of the coronavirus disease 2019 (Covid-19) cut deaths caused by air pollution by an estimated 95,000 globally in 2020, an analysis published by Science Advances found.

Lockdown measures imposed on and off in many countries since the start of the pandemic in March 2020 resulted in up to a 50-percent reduction in concentrations of nitrogen dioxide, a direct emission from vehicles and coal-powered electricity plants, in the air worldwide, the data showed.

However, while lockdowns may have led to a more than 30-percent drop in microscopic particulate matter released into the air as a result of burning fuel, as well as an up to 28-percent decline in ozone in parts of Asia, their effects in Europe and the United States were negligible.

Although the reductions in airborne pollution varied from country to country, they were significant enough in densely populated areas to have a positive, though in most cases modest, effect on related deaths, they said.

“The air pollution declines that we calculated are primarily due to reduced economic activity during the Covid-19 lockdown,” study co-author Guillaume Chossiere said.

“Our study controlled for seasonal and inter-annual trends and found that the stringency of the lockdowns was a statistically significant driver of the decreases,” said Chossiere, a researcher in the Laboratory for Aviation and the Environment at the Massachusetts Institute of Technology in Cambridge.

The findings are based on an assessment of air quality in 36 countries across three continents – North America, Asia and Europe – using satellite imagery and on-the-ground measurements.

The United States saw a more than 4-percent drop in airborne nitrogen oxide levels, but a less than 1-percent decline in ozone, the data showed. Airborne particulate matter levels remained relatively stable nationally as well.

As a result, the United States accounted for a fraction of the reduction in “premature deaths” – or deaths occurring earlier than life expectancy – caused by respiratory illnesses linked with air pollution exposure.

Conversely, China, which, along with the United States, is among the world’s biggest polluters, likely made up nearly 80 percent of the global reduction in premature deaths attributed to air pollution, according to the researchers.

The findings suggest Covid-19 lockdowns “exerted a limited effect” on global air quality, although some parts of East Asia experienced “pronounced improvements,” they said.

“Although the Covid-19 related lockdowns brought significant reductions in economic activities, air pollution levels did not decrease as much as had been speculated at first,” Chossiere said.

“Primary pollution [from] nitrogen dioxide had the largest decreases and associated health benefits, but, with the notable exception of China, secondary air pollution [from] fine particulates and ozone did not bring significant health benefits,” he said.