The impact of different PBL models on meteorology and air quality model results

Parameterizations of vertical transport due to boundary layer turbulence are among the most important components of meteorology and air quality models. However, the PBL schemes employed in meteorology models and those used in air quality models are often quite different. Part of the reason for this is simply different model development histories, but it also seems that the kind of scheme that works well in meteorology models may not work so well in AQ models or vice versa. Mesoscale meteorology models typically include either simple non-local closure schemes or higher-order schemes that involve prognostic equations for turbulent kinetic energy (TKE) and sometimes other higher order terms such as turbulent dissipation or potential temperature variance. The non-local schemes, in particular, have been developed to address the inadequacies of local schemes that cannot produce realistic profiles of both first order quantities and their fluxes in convective conditions. Air quality models typically use simple local closure (eddy diffusivity), although both non-local and higher-order schemes have also been used. A difficulty for air quality models is that chemical profile data for evaluation is very sparse. Thus ground level concentration data is often used for evaluation which may be affected by many other processes.

The goal of this work is to apply consistent PBL models for both meteorology and air quality that perform well in both systems. Thus, non-local and local schemes will be applied in the MM5 and CMAQ models and evaluated with available profile data, primarily from the 2004 ICARTT field campaign. Field evaluation of a new non-local scheme, the Asymmetric Convective Model version 2 (ACM2), will be an integral part of this study.

DISCLAIMER The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.