Science.-Pandemic closures rapidly reduced global ozone pollution

06-10-2021 Negative tropospheric ozone anomaly at the height of local lockdowns due to the coronavirus pandemic POLICY RESEARCH AND TECHNOLOGY NASA


When lockdowns during the coronavirus pandemic reduced local nitrogen oxide emissions, the effect on ozone pollution was global and unexpectedly rapid.

As the coronavirus pandemic slowed global trade in early 2020, emissions of nitrogen oxides (NOx), which create ozone, a hazard to human health and the climate, fell 15% globally, with reductions locals as high as 50%, according to a study led by scientists at NASA’s Jet Propulsion Laboratory.

As a result of the lower NOx emissions, by June 2020, global ozone levels had fallen to a level that lawmakers thought would take at least 15 years to reach by conventional means, such as regulations, NASA reports.

The study shows that innovative technologies and other solutions aimed at reducing NOx locally have the potential to rapidly improve air quality and climate globally. It has been published in Science Advances.

Ozone protects us from destructive solar radiation when it is high above Earth in the stratosphere. Closer to the ground, however, it has other lasting impacts. Ozone at the surface was estimated to have caused 365,000 deaths worldwide in 2019 by damaging the lungs of vulnerable people, such as young children and people with asthma. Similarly, it damages the respiratory systems of plants, their ability to photosynthesize, thus reducing plant growth and crop yields. And at the top of the troposphere, it is a powerful greenhouse gas that increases global temperatures.

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When the world was locked in by the coronavirus pandemics, scientists had an unprecedented opportunity to study how human activity interacts with processes in the Earth’s natural system at regional and global scales.

A team of international researchers led by JPL scientist Kazuyuki Miyazaki took this opportunity to investigate the two main oxides of nitrogen: nitrogen oxide and nitrogen dioxide, collectively referred to as NOx.

They traced the chain of events from reducing fossil fuel use during closures to reducing local NOx emissions and finally reducing global tropospheric ozone pollution. The stricter the blockade imposed by a nation, the greater the reduction in emissions. For example, China’s stay-at-home orders in early February 2020 produced a 50% drop in NOx emissions in some cities within a few weeks; most US states achieved a 25% drop later in the spring.

The overall result of reduced NOx emissions was a 2% drop in global ozone, half the amount expected to be produced by the most aggressive NOx emission controls considered by the Intergovernmental Panel on Climate Change, the authorized body of international climate experts for a period of 30 years.

Ozone reductions from reduced NOx emissions spread rapidly around the world and from the surface upward more than 6 miles (10 kilometers). “I was very surprised at how big the impact on global ozone was,” said JPL scientist Jessica Neu, co-author of the new study. “We expected a more local response on the surface.”

The reactions that turn NOx into ozone require sunlight and depend on many additional factors, such as the weather and what other chemicals are in the air. These factors interact in so many ways that, in some circumstances, reducing NOx emissions actually increases ozone. Therefore, researchers cannot understand or predict ozone concentrations from NOx emissions data alone. That requires a more thorough analysis, like this study.

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The researchers used measurements of NOx, ozone and other atmospheric gases from five Earth-observing satellites from NASA and ESA. They inserted the multiple satellite observations into four numerical models of atmospheric chemical reactions and weather, using a data analysis system developed at JPL. They found that changes in atmospheres from the models matched well with satellite observations and reproduced known increases and decreases in emissions as regions moved in and out of lockdowns. These findings indicate that both global NOx emissions and ozone will rise again as the world economy accelerates again.

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