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Summertime Droughts Lead to Worsening Ozone Pollution in U.S. Southeast


A new study, funded in part by CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) program, adds to the evidence that drought can lead to worsening ozone pollution in some regions of the US. Researchers from the University of Houston, Rice University, and NOAA/Global Systems Laboratory used 15-years of surface ozone observations and weekly US Drought Monitor indices to investigate the differences in ozone response to drought across the US and determine what role ozone chemistry plays in causing such differences. They found an increase in summertime ozone in the US southeast during drought conditions, but no change or even a decrease in the US west. By modeling the ozone chemistry at the different observation sites, the research team was able to determine that isoprene, a key precursor of ozone, drove the opposite responses. 

Published in the Journal of Geophysical Research: Atmospheres, this study underscores the key role isoprene plays in ozone production under drought conditions. In California, ozone decreased along with decreasing isoprene emissions. In Georgia, on the other hand, isoprene increased under drought conditions causing production of ozone to increase as well. According to the researchers, the differences in isoprene changes during drought between California and Georgia are likely due to the different responses of plants to water stress. Californian plants experience longer severe water stress and are more likely to be under chronic water stress even in non-drought conditions leading to immediate isoprene decline during drought. For researchers, this means drought duration, in addition to drought severity, should be included when modeling drought impacts on atmospheric composition. 

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