Understanding ozone‐meteorology correlations: A role for dry deposition

Abstract Observations of coincident high relative humidity and low surface ozone are common in air quality data sets, but models underpredict the strength of this correlation. We perform a statistical analysis of 28 years of ozone and meteorology observations taken as part of the Clean Air Status and Trends Network across the United States and find that vapor pressure deficit (VPD) is the strongest predictor of midday ozone in the spring, summer, and fall, and this correlation is strongest at sites with the largest leaf area index. We argue that stomatal regulation of dry deposition, which is known to have a VPD dependence that is not typically included in model parameterizations, can explain this relationship. Using a box model of ozone production and loss, we show that a negative ozone‐humidity slope is only achieved by the inclusion of VPD‐dependent dry deposition, suggesting that this mechanism may explain the observed ozone‐humidity correlation.