In a first-ever study using ozone data collected by commercial aircraft, researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder found that levels of the pollutant in the lowest part of Earth’s atmosphere have increased across the Northern Hemisphere over the past 20 years. That’s even as tighter controls on emissions of ozone precursors have lowered ground-level ozone in some places, including North America and Europe…
In an open-access study published August21 in the journal Science Advances, the team found an overall increase in ozone levels above the Northern Hemisphere.
Tropospheric ozone is an important greenhouse gas, is detrimental to human health and crop and ecosystem productivity, and controls the oxidizing capacity of the troposphere. Because of its high spatial and temporal variability and limited observations, quantifying net tropospheric ozone changes across the Northern Hemisphere on time scales of two decades had not been possible. Here, we show, using newly available observations from an extensive commercial aircraft monitoring network, that tropospheric ozone has increased above 11 regions of the Northern Hemisphere since the mid-1990s, consistent with the OMI/MLS satellite product. The net result of shifting anthropogenic ozone precursor emissions has led to an increase of ozone and its radiative forcing above all 11 study regions of the Northern Hemisphere, despite NOx emission reductions at midlatitudes.
“That’s a big deal because it means that as we try to limit our pollution locally, it might not work as well as we thought,” said Audrey Gaudel, a CIRES scientist working in the NOAA Chemical Sciences Laboratory and the study’s lead author…
In the so-called “lower troposphere,” which is closest to Earth’s surface, ozone has decreased above some mid-latitude regions, including Europe and the United States, where ozone precursor emissions have decreased.
The researchers found those reductions were offset by increases higher in the troposphere — with the net result being an overall ozone increase from the surface to 12 km… The model showed that increased emissions in the tropics were likely driving the observed increase of ozone in the Northern Hemisphere.