3A.1 Simple urban parameterization for high resolution meteorology and air quality

Pleim, Jonathan, Robert Gilliam, United States Environmental Protection Agency (USEPA), Limei Ran, University of North Carolina, James Kelly, Kirk Baker, and Chris Misenis, USEPA

A simple urban parameterization has recently been developed for the Pleim-Xiu land surface model (PX LSM). The urban scheme leverages accurate, high resolution land use, impervious fraction, and canopy fraction data available in the National Land Cover Database (NLCD) to represent the urban environment. Impervious fraction is used to scale the surface heat capacity and canopy fraction is used to constrain vegetation coverage and adjust LAI. The NLCD has four urban related land use categories with high spatial accuracy that are used to specify roughness length and albedo according density of urban development. Model simulations of WRF using the simple urban scheme in the PX LSM are evaluated and compared to the base PX LSM at several resolutions for three field studies: TexAQS 2006, DISCOVER-AQ 2011 and CARES/CALNEX (2010). The Texas study includes WRF runs at 12 km resolution over the CONUS, 4 km over eastern Texas, and 1 km for Houston as well as 4 km runs of the Community Multiscale Air Quality (CMAQ) model. The California modeling study involves 4 km runs of WRF and CMAQ both offline and using the 2-way coupled WRF-CMAQ. The DISCOVER-AQ study includes model runs at 12 km, 4 km and 1 km covering the Baltimore-Washington area. Preliminary WRF runs have been made and 2-way coupled WRF-CMAQ runs are planned for the DISCOVER-AQ study. The Houston WRF model simulations at 4 and 1 km resolution show reduced near surface stabilty for the runs using the urban scheme that compare better to nighttime tethersonde profiles at the University of Houston. CMAQ runs using the urban WRF runs result in reduced high bias for ground level concentrations of primary species such as NOx and CO. WRF-CMAQ runs for CARES/CALNEX show similarly reduced concentration overpredictions due to reduced nocturnal stability and greater SBL depths in developed areas of California.