Coupled Impact of Changing Emissions and Meteorology on Air Quality Inferred from Remote Sensing Observations and Model Simulations

Urban air quality strongly depends on local emissions and meteorological variables. Observations usually are unable to separately quantify the effects of these two processes. We describe a case study of Denver Colorado. We present a method to infer the sensitivity of OH to water vapor mixing ratio using the summertime NO2 column observations combined with the nonlinear relationship between NO2 molecules and OH radicals. A doubling in the water vapor leads to an increase in average OH concentration and a decrease of NO2 lifetime in low winds. The WRF-Chem model has been used to simulate summertime atmospheric composition and deduce the mechanisms of the variation observed from space based instruments.