Loss of unburned-fuel hydrocarbons from combustion aerosols during atmospheric transport

Urban, coal-fired power plant, coastal, and marine aerosols were compared in terms of pyrogenic (PHC) and unburned-fuel (FHC) hydrocarbon contributions. It was observed that the relative content of FHC decreased from near combustion source to remote samples. Artificially irradiated and aerated combustion aerosols also exhibited selective loss of FHC along with photoreactive compounds. Furthermore, different correlation to soot content has been obtained for the two fractions in marine aerosols. We suggest that PHC and FHC present a decoupled association to soot Whereas soot-compound interactions protect PHC from major transformations, FHC occur more exposed to vapor/particle partitioning. This is consistent with the decoupled size distribution of the two fractions in aged aerosols: PHC mostly occur in small (soot-rich) particles whereas FHC distribute onto all sizes. Our findings are relevant to source reconciliation modeling and aerosol chemistry.