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AGU: Journal of Geophysical Research, Atmospheres


Index Terms

  • 0305 - Aerosols and particles
  • 0365 - Troposphere: composition and chemistry
  • 0345 - Pollution: urban and regional
  • 0368 - Troposphere: constituent transport and chemistry
  • 0360 - Radiation: transmission and scattering

Paper in Press


Characterization of speciated aerosol direct radiative forcing over California

Key Points
  • Evaluate model performance with various meteorological and aerosol measurements
  • Understand seasonal and spatial variation of speciated aerosols over California
  • Diagnose direct radiative forcings for individual aerosol species


Chun Zhao

L. Ruby Leung

Richard C. Easter

Jenny L Hand

Jeremy Avise

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 PM<sub>2.5</sub> 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<sup>-2</sup> (winter minimum) to 3 W m<sup>-2</sup> (summer maximum). EC is the largest contributor in summer (-1.1 W m<sup>-2</sup> and ~35%), and sulfate is the largest in winter (-0.45 W m<sup>-2</sup> and ~30%). In the atmosphere, total aerosol introduces a warming effect of about 0.5 W m<sup>-2</sup> (winter minimum) to 2 W m<sup>-2</sup> (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<sup>-2</sup> through the seasons with sulfate as the biggest contributor of -0.4 W m<sup>-2</sup> (winter minimum) to -0.7 W m<sup>-2</sup> (summer maximum). EC produces a TOA warming of up to about 0.7 W m<sup>-2</sup>, while all other aerosol species produce a TOA cooling. The diagnostic method implemented in WRF-Chem can be applied to other regions to understand the roles of different aerosols on the direct radiative forcing and regional climate.

Received 28 June 2012; accepted 28 November 2012.

Citation: Zhao, C., L. R. Leung, R. C. Easter, J. L. Hand, and J. Avise (2012), Characterization of speciated aerosol direct radiative forcing over California, J. Geophys. Res., doi:10.1029/2012JD018364, in press.