During COVID-19 shutdowns last year, ozone levels in the lower atmosphere fell by seven percent across much of the Northern Hemisphere, according to a new study from the German weather service Deutscher Wetterdienst, with CIRES and NOAA co-authors. The researchers analyzed data from 45 stations that used balloon soundings and remote sensing instruments to measure ozone throughout the atmosphere.

“The COVID-19 lockdowns are an unplanned global scale atmospheric experiment. We can learn many things from this—for example, what internationally coordinated emission controls could achieve for air quality worldwide,” said Wolfgang Steinbrecht, head of the ozone group at Deutscher Wetterdienst and lead author of the study published in Geophysical Research Letters.

Ozone in the lower atmosphere (the troposphere) acts as an air pollutant and much of it is produced by human activity, while ozone in the stratosphere (above the troposphere) occurs naturally and protects us from the Sun’s harmful ultraviolet rays.

Last year, worldwide actions to contain the COVID‐19 virus closed factories, grounded airplanes and greatly reduced travel and transportation. Less fuel was burned and less exhaust was emitted, and as a result, atmospheric concentrations of nitrogen oxides and volatile organic compounds (VOCs) decreased. These substances are important for ozone production and destruction in the troposphere.

The researchers measured ozone using primarily ozonesondes on weather balloons that fly from the ground up to 30 kilometers (km) in altitude. During spring and summer last year, they found significantly reduced ozone concentrations in the troposphere across the mid-latitude and polar regions of the Northern Hemisphere, and less than in any other year since at least 2000.

“Reduced emissions in spring and summer months due to the COVID‐19 crisis lowered ozone production and very likely caused the ozone reductions we observed,” said Owen Cooper, a CIRES scientist working in the NOAA Chemical Sciences Laboratory and one of the paper’s co-authors. 

For this study, researchers from CIRES and NOAA’s Global Monitoring Laboratory provided the ozonesonde observations above Boulder, Trinidad Head, California and Hilo, Hawaii. CIRES researchers in NOAA’s Chemical Sciences Laboratory provided advice on statistical methods and contributed to the data interpretation.

This story was adapted from a press release by Deutscher Wetterdienst. Deutscher Wetterdienst and AGU have also issued a joint press release, in English.