PNNL

Abstract

Biomass burning (BB) emits enormous amounts of aerosol particles and gases into the atmosphere and thereby significantly influences regional air quality and global climate. A dominant particle type from BB is spherical organic aerosol particles called tarballs (TBs). Currently, TBs can only be identified from their uniquely spherical shapes, observed using microscopy, leaving many unanswered questions related to TB-formation mechanisms, optical properties, and emission inventory. As a result, TBs are not considered in most climate models. Here, we show that TBs transform in BB plumes from primary emitted liquid organic particles through chemical processes within ~3 hours. We find that the ratios of N and O to K, a conserved tracer, and viscosity increase with particle age by the formation of organic compounds that contain nitrogen and carboxylic acid functional groups. The properties of these types of organic compounds suggest that TBs can possess enhanced light absorption and hygroscopicity. The TB-formation mechanism implies that TBs can occur in many BB plumes across the globe and should thus be incorporated into models for accurate assessments of BB particle evolution and of BB impacts on regional and global climate.