Because of its wide coverage over much of the globe, biomass burning has been widely studied in the context of direct radiative forcing. Such study is warranted as smoke particles scatter and at times absorb solar radiation efficiently. Further, as much of what is known about smoke transport and impacts is based on remote sensing mea-5 surements, the optical properties of smoke particles have far reaching effects into numerous aspects of biomass burning studies. Global estimates of direct forcing have been widely varying, ranging from near zero to −1 W m −2 . A significant part of this difference can be traced to varying assumptions on the optical properties of smoke. This manuscript is the third part of four examining biomass-burning emissions. Here 10 we review and discuss the literature concerning measurement and modeling of optical properties of biomass-burning particles. These include available data from published sensitivity studies, field campaigns, and inversions from the Aerosol Robotic Network (AERONET) of Sun photometer sites. As a whole, optical properties reported in the literature are varied, reflecting both the dynamic nature of fires, variations in smoke ag-15 ing processes and differences in measurement technique. We find that forward modeling or "internal closure" studies ultimately are of little help in resolving outstanding measurement issues due to the high degree of degeneracy in solutions when using "reasonable" input parameters. This is particularly notable with respect to index of refraction and the treatment of black carbon. Consequently, previous claims of column 20 closure may in fact be more ambiguous. Differences between in situ and retrieved ω o values have implications for estimates of mass scattering and mass absorption efficiencies. In this manuscript we review and discuss this community dataset. Strengths and lapses are pointed out, future research topics are prioritized, and best estimates and uncertainties of key smoke particle parameters are provided. Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Print Version Interactive Discussion © EGU 2004 20compared to solutions from inversion methods. In all of these sections we explore differences in particle properties by region and fire chemistry, and attempt to reconcile differences that exist between investigation techniques. In conclusion we discuss our findings and present what we feel are reasonable parameters with likely uncertainties for smoke properties. Suggestions are made for future research. Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Print Version Interactive Discussion © EGU 2004 2. Field measurements and bulk empirical parameterisations Bulk empirical modeling is often used for first order evaluations of the perturbation of the clear sky radiative balance by aerosol particles. Examples of the application of the bulk method to global radiative flux include Charlson et al. (1991) and Chylek and Wong (1995) for anthropogenic sulfates a...

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