Effect of the Variability of the Radiative Properties of Light Absorbing Particles (LAC)

1. Effect of the Variability of the Radiative Properties of Light Absorbing Particles (LAC) on the Aerosol Direct Forcing in the ACE Asia Region R.W. Bergstrom1, P. Pilewskie2 *, P. B. Russell2, S. Ramirez1, T. C. Bond3 1Bay Area Environmental Research Institute, 2NASA Ames Research Center, 3University of Illinois, *now at University of Colorado Overview Recent field studies (ACE Asia, APEX, TRACE-P) have shown that the mass absorption properties (MAE) of black carbon (or light absorbing carbon) particles in the East Asia region appear to vary between 5 m2/gm to 20 m2/gm. Bond and Bergstrom (2004) show that the absorption properties of LAC depend upon the type of combustion source and range from amorphous carbon-like particles with a low MAE to graphite-like carbon particles with a high MAE. In this poster we explore the effect of the variability in the radiative properties of LAC (or BC) particles on the direct forcing (TOA and Surface). Using April 12, 2001 as our test case we take the aerosol optical depth and single scattering albedo results from MATCH model simulations done by Bill Collins, David Filmore and Phil Rasch of NCAR for the ACE Asia field campaign. Using a detailed radiative transfer model we compute the direct aerosol forcing. Then, we calculate the difference in the TOA and surface direct aerosol radiative forcing for a 50% decrease of the absorption properties of BC minus that of a 50% increase of the absorption properties of the BC particles. This result (shown at the very bottom of the poster) indicates that the observed variability leads to a maximum difference of the 24 hour average direct forcing of 6 w/m2 (TOA) and 11 w/m2 (Surface) due simply to the uncertainty of the absorption properties of BC. This result emphasizes the need for detailed measurements and analysis of the absorption properties of atmospheric BC (or LAC) particles For a description of the MATCH model, see Collins et al., (2002) For a description of the radiative transfer model, see Bergstrom et al., (2004). Combined Dust and BC absorption properties One of difficulties with measurements of the aerosols in the East Asia region is that dust and bc are oftenare combined. Bergstrom et al (2004) estimated the single scattering albedo of the resulting aerosol. The figure below shows the range of possible single scattering albedos for the observed dust-bc combination aerosol. MATCH results for aerosol optical depth for April 12, 2001 SeaWiFS Aerosol Optical Depth analysis from A. Higurashi. For description of the method, see Higurashi and Nakajima 2002 Comparision of the MATCH predicted aerosol single scattering albedo to the values observed by Bergstrom et al (2004) at 33N,128E on April 12, 2001. All Results shown for April 12, 2001 MATCH model simulation results provided by Bill Collins, David Filmore and Phil Rasch of NCAR Topography Black Carbon Dust SO2/Sulfate Source Function Optical Depths TOA forcing Surface forcing Total aerosol with 50% less absorbing BC - 50% more absorbing BC References: Alfaro, S. C., et al. (2003), Chemical and optical characterization of aerosols measured in spring 2002 at the ACE-Asia supersite, Zhenbeitai,China, J. Geophys. Res., 108(D23), 8641, doi:10.1029/2002JD003214. Anderson, T., S. et al (2003), Variability of aerosol optical properties derived from in situ aircraft measurements during ACE-Asia, J. Geophys. Res., 108(D23),8647, doi:10.1029/2002JD003247. Bond and Bergstrom (2004) Light absorption by atmospheric carbon: An investigative review, in preparation. Bergstrom et al, (2004) Spectral Absorption by Aerosols during ACE Asia, J.Geophys Res., 109, D19S15, doi:10.1029/2003JD004467, in press. Collins, et al, (2002) Simulation of aerosol distributions and radiative forcing for INDOEX: Regional climate impacts, J.Geophys Res., 107, ( D19), 8028, doi:10.1029/2000JD000032 Higurashi, A., and T. Nakajima (2002), Detection of aerosol types over the East China Sea near Japan from four-channel satellite data, Geophys. Res.Lett., 29(17), 1836, doi:10.1029/2002GL015357. Holler, R., K. Ito, S. Tohno, and M. Kasahara (2003), Wavelength dependent aerosol single-scattering albedo: Measurements and model calculations fo ra coastal site near the Sea of Japan during ACE-Asia, 706 J. Geophys. Res.,108(D23), 8648, doi:10.1029/2002JD003250. Li, L., H. Fukushima, R. Fruin, B. G. Mitchell, M. He, I. Uno, T. Takamura, andS. Ohta (2003), Influence of submicron absorptive aerosol on SeaWiFS derived marine reflectance during ACE-Asia, J. Geophys. Res., 108(D15), 4472,doi:10.1029/2002JD002776 Effect of Variability of BC on TOA and Surface Forcing