More Stagnant Air on the Rise, Upping Ozone Risk

When the air is stagnant and there is little air circulation, hot weather can trigger high levels of air pollution that can have health consequences for millions of Americans.  With stagnant air now occurring more frequently in much of the country, and projected to continue increasing, the combination of heat and stagnant air are primed to counteract efforts to reduce ground-level ozone pollution and continue to put thousands of lives at risk every year.

In a new analysis, Climate Central’s States at Risk project has investigated how stagnant summer air conditions have been increasing in much of the nation and explored the relationship between this stagnant air and ozone levels in major U.S. cities in the Lower 48 states.
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More Stagnant Air
We have found that 66 percent of the U.S. has experienced an overall increase in the number of days with stagnant air since the 1970s.  This increase is consistent with what you expect in a warming world, where rising temperatures are expected to increase stationary air masses as overall air circulation slows down.
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Stagnation and Ozone in U.S. Cities
Given that stagnant air events in many U.S. cities have been rising, and are projected to continue increasing if greenhouse gas emissions keep growing, we have also explored the relationship between stagnant air and high ozone levels in several major U.S. cities.

Drawing on air quality data since 1980, we found that in many cities, and particularly those in the Northeast and the Midwest, summers with more stagnant air events also had more days with unhealthy levels of ozone.  A high ozone day was one when concentrations exceeded those levels classified by the EPA as unsafe into one of the four unsafe categories.

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