Modeling of boundary layer processes affecting ozone in the complex terrains of California during PreCalNex 2009 field campaign

Airborne LIDAR measurements of ozone during PreCalNex field campaign (July 11 - 20 2009) provide useful data sets to examine boundary layer processes coupled with sea-land breeze and/or slope flows in South Coast and Central Valley regions in California. We simulated meteorology and ozone plumes in the complex terrains of California using the Weather Research and Forecasting – Chemistry (WRF-Chem) model with input from the US EPA's 2005 National Emission Inventory for the field campaign period. The model nested domain includes the entire California with 4 x 4 km² horizontal resolution. The model-simulated meteorology was evaluated with the observations by the surface stations. Model near-surface temperature agreed well with the observations in South Coast and Central Valley areas. However, the model simulations were much drier than the measurements in Central Valley, indicating the need of proper representation of irrigated soil moisture and temperature in the model. During the field campaign, LIDAR observations detected high ozone plumes in Banning Pass, San Gabriel Mountain, San Bernardino Mountain, and slopes in Tulare County. On July 17, deep vertical lofting of ozone into the lower free troposphere due to the mountain-chimney effect was found near the San Gabriel Mountains. The location and time of ozone plumes in the model simulations agree well with those in the observations including the elevated ozone plume near the San Gabriel Mountains. It implies reasonable model simulations of three-dimensional transport process by synoptic system, sea-land breeze and slope flows. However, the simulated ozone layers are more than twice as thick as the measurements in the mountain slope and the gap regions. To explain this discrepancy, we will present the dependencies of model boundary layer height, convective clouds, and winds on horizontal and vertical grid configuration and physical options. Their implications for ozone simulations will also be discussed.