title: Assessing the influence of secondary organic versus primary carbonaceous aerosols on long-range atmospheric polycyclic aromatic hydrocarbon transport.
abstract: We use the chemical transport model GEOS-Chem to evaluate the hypothesis that atmospheric polycyclic aromatic hydrocarbons (PAHs) are trapped in secondary organic aerosol (SOA) as it forms. We test the ability of three different partitioning configurations within the model to reproduce observed total concentrations in the midlatitudes and the Arctic as well as midlatitude gas-particle phase distributions. The configurations tested are (1) the GEOS-Chem default configuration, which uses instantaneous equilibrium partitioning to divide PAHs among the gas phase, a primary organic matter (OM) phase (absorptive), and a black carbon (BC) phase (adsorptive), (2) an SOA configuration in which PAHs are trapped in SOA when emitted and slowly evaporate from SOA thereafter, and (3) a configuration in which PAHs are trapped in primary OM/BC upon emission and subsequently slowly evaporate. We also test the influence of changing the fraction of PAHs available for particle-phase oxidation. Trapping PAHs in SOA particles upon formation and protecting against particle-phase oxidation (2) better simulates observed remote concentrations compared to our default configuration (1). However, simulating adsorptive partitioning to BC is required to reproduce the magnitude and seasonal pattern of gas-particle phase distributions. Thus, the last configuration (3) results in the best agreement between observed and simulated concentration/phase distribution data. The importance of BC rather than SOA to PAH transport is consistent with strong observational evidence that PAHs and BC are coemitted.
authors.affiliation: Center for Global Change Science and Leading Technology and Policy Initiative and ‡Engineering Systems Division and Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: C L
authors.initials: CL
authors.lastname: Friedman
authors.forename: J R
authors.initials: JR
authors.lastname: Pierce
authors.forename: N E
authors.initials: NE
authors.lastname: Selin
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry*; D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D001110:Arctic Regions; D004784:Environmental Monitoring / Q000379:methods*; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis* / Q000737:chemistry; D053260:Soot / Q000032:analysis / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D011084:Polycyclic Aromatic Hydrocarbons; D053260:Soot