7A.2 Effects of satellite clouds-corrected photolysis rates on ozone over CONUS using the WRF-Chem model

Ryu, Young-Hee, Alma Hodzic, Jerome Barre, Gael Descombes, National Center for Atmospheric Research, Patrick Minnis, National Aeronautics and Space Administration/Langley Research Center, and Douglas Spangenberg, Science Systems and Applications

Clouds play a key role in the atmospheric radiation and hence photochemistry. However, it is not well understood how much of the ozone model bias can be attributed to inaccurate cloud predictions in three-dimensional chemistry models. In this study, we use satellite-derived clouds to improve photolysis rates predictions in the WRF-Chem model. Two sets of simulations are performed for 2013 summer: control simulation that uses WRF-generated clouds, and GOES simulation that uses satellite-derived clouds. For GOES simulations, we update cloud optical depth (COD) and bottom and top heights hourly and use the satellite-derived clouds only for photolysis rate computations. The modeled ozone is evaluated against observed ozone during two field campaigns as well as against observations at the EPA ground sites. The comparison with GOES-retrieved COD shows that WRF clouds are in general optically thinner than GOES clouds, which can result in overpredictions of ground ozone. Under cloudy conditions, ozone biases are considerably reduced in the GOES simulations. More interestingly, the ozone biases are more significantly reduced in VOC-limited regimes than in NOx-limited regimes. As one can expect, the difference in ozone concentration between the control and GOES simulations increases as the difference in COD between the two simulations increases.