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Publication Date
7 March 2013

Characterization of Speciated Aerosol Direct Radiative Forcing Over California



The WRF-Chem model, with added capability of diagnosing the direct radiative forcing of individual aerosol species, is used to characterize the spatial and seasonal distribution of speciated aerosol direct radiative forcing over California. Overall, the simulation in 2005 is able to reproduce the observed spatial and seasonal distribution of total PM2.5 mass concentration and the relative contribution from individual aerosol species. On statewide average over California, all aerosol species reduce the surface net radiation fluxes with a total by about 1.5 W m-2 (winter minimum) to 3 W m-2 (summer maximum). EC is the largest contributor in summer (-1.1 W m-2 and  35%), and sulfate is the largest in winter (-0.45 W m-2 and  30%). In the atmosphere, total aerosol introduces a warming effect of about 0.5 W m-2 (winter minimum) to 2 W m-2 (summer maximum). EC and dust contribute about 75-95% and 1-10% of the total warming through the seasons, respectively. At the top of atmosphere (TOA), the overall total aerosol direct radiative effect is cooling of -1.0 W m-2 through the seasons with sulfate as the biggest contributor of -0.4 W m-2 (winter minimum) to -0.7 W m-2 (summer maximum). EC produces a TOA warming of up to about 0.7 W m-2, while all other aerosol species produce a TOA cooling. The diagnostic method implemented in WRFChem can be applied to other regions to understand the roles of different aerosols on the direct radiative forcing and regional climate.

“Characterization Of Speciated Aerosol Direct Radiative Forcing Over California”. 2013. Journal Of Geophysical Research - Atmospheres. doi:10.1029/2012JD018364.
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