Atmos. Chem. Phys. Discuss., 9, 16011-16050, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Investigation of downscaling techniques for the linkage of global and regional air quality modeling
Y. F. Lam and J. S. Fu
Dept. of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN, USA

Abstract. Recent year, downscaling global atmospheric model outputs for the USEPA Community Multiscale Air Quality (CMAQ) Initial (IC) and Boundary Conditions (BC) have become practical because of the rapid growth of computational technologies that allow global simulations can be completed within a reasonable time and have better performance. The traditional method of generating IC/BC by profile data has lost its advocators due to the weakness of the limited horizontal and vertical variations found on the gridded boundary layers. In this paper, we are in effort to investigate the effects of using profile IC/BC and global atmospheric model data. We utilize the GEOS-Chem model outputs to generate time-varied and layer-varied IC/BC for year 2002 using our newly development of tropopause determining algorithm. The purpose of the study is to determine the tropopause effect to the downscaling process. From the results, we have found that without considering tropopause in the downscaling process created unrealistic O3 concentrations in IC/BC at the upper boundary conditions for regional tropospheric model. This phenomenon has caused over-prediction of surface O3 in CMAQ. And it is greatly affected by temperature and latitudinal location. With the implementation of our algorithm, we have successfully resolved the incompatibility issues in the vertical layer structure between global and regions chemistry models to yield better surface O3 predictions than profile IC/BC on both summer and winter conditions. At the same time, it improved the vertical O3 distribution of CMAQ outputs. The algorithm can be applied to a global atmospheric model which performs a reasonable outcome to determine the tropopause.

Citation: Lam, Y. F. and Fu, J. S.: Investigation of downscaling techniques for the linkage of global and regional air quality modeling, Atmos. Chem. Phys. Discuss., 9, 16011-16050, doi:10.5194/acpd-9-16011-2009, 2009.
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