A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

[摘要] Because of its wide coverage over much of the globe, biomass burning hasbeen widely studied in the context of direct radiative forcing. Such studyis warranted as smoke particles scatter and at times absorb solar radiationefficiently. Further, as much of what is known about smoke transport andimpacts is based on remote sensing measurements, the optical properties ofsmoke particles have far reaching effects into numerous aspects of biomassburning studies. Global estimates of direct forcing have been widelyvarying, ranging from near zero to −1 W m^-2. A significant part of thisdifference can be traced to varying assumptions on the optical properties ofsmoke. This manuscript is the third part of four examining biomass-burningemissions. Here we review and discuss the literature concerning measurementand modeling of optical properties of biomass-burning particles. Theseinclude available data from published sensitivity studies, field campaigns,and inversions from the Aerosol Robotic Network (AERONET) of Sun photometersites. As a whole, optical properties reported in the literature are varied,reflecting both the dynamic nature of fires, variations in smoke agingprocesses and differences in measurement technique. We find that forwardmodeling or ''internal closure'' studies ultimately are of little help inresolving outstanding measurement issues due to the high degree ofdegeneracy in solutions when using ''reasonable'' input parameters. This isparticularly notable with respect to index of refraction and the treatmentof black carbon. Consequently, previous claims of column closure may in factbe more ambiguous. Differences between in situ and retrieved ω_ovalues have implications for estimates of mass scattering and massabsorption efficiencies. In this manuscript we review and discuss thiscommunity dataset. Strengths and lapses are pointed out, future researchtopics are prioritized, and best estimates and uncertainties of key smokeparticle parameters are provided.

[学科分类] 大气科学