title: Synergy between secondary organic aerosols and long-range transport of polycyclic aromatic hydrocarbons.
abstract: Polycyclic aromatic hydrocarbons (PAHs), known for their harmful health effects, undergo long-range transport (LRT) when adsorbed on and/or absorbed in atmospheric particles. The association between atmospheric particles, PAHs, and their LRT has been the subject of many studies yet remains poorly understood. Current models assume PAHs instantaneously attain reversible gas-particle equilibrium. In this paradigm, as gas-phase PAH concentrations are depleted due to oxidation and dilution during LRT, particle-bound PAHs rapidly evaporate to re-establish equilibrium leading to severe underpredictions of LRT potential of particle-bound PAHs. Here we present a new, experimentally based picture in which PAHs trapped inside highly viscous semisolid secondary organic aerosol (SOA) particles, during particle formation, are prevented from evaporation and shielded from oxidation. In contrast, surface-adsorbed PAHs rapidly evaporate leaving no trace. We find synergetic effects between hydrophobic organics and SOA - the presence of hydrophobic organics inside SOA particles drastically slows SOA evaporation to the point that it can almost be ignored, and the highly viscous SOA prevents PAH evaporation ensuring efficient LRT. The data show the assumptions of instantaneous reversible gas-particle equilibrium for PAHs and SOA are fundamentally flawed, providing an explanation for the persistent discrepancy between observed and predicted particle-bound PAHs.
authors.affiliation: Pacific Northwest National Laboratory, Richland, Washington 99354, USA. alla.zelenyuk@pnnl.gov
authors.forename: Alla
authors.initials: A
authors.lastname: Zelenyuk
authors.forename: Dan
authors.initials: D
authors.lastname: Imre
authors.forename: Josef
authors.initials: J
authors.lastname: Beránek
authors.forename: Evan
authors.initials: E
authors.lastname: Abramson
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Wilson
authors.forename: Manish
authors.initials: M
authors.lastname: Shrivastava
mesh_terms: D000327:Adsorption; D000336:Aerosols / Q000737:chemistry*; D000393:Air Pollutants / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D013058:Mass Spectrometry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D014835:Volatilization
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D005740:Gases; D011084:Polycyclic Aromatic Hydrocarbons