Synergy between Secondary Organic Aerosols and Long-Range Transport of Polycyclic Aromatic Hydrocarbons

• Published in: Environmental science & technology Vol. 46; no. 22; pp. 12459 - 12466
• Main Authors: Zelenyuk, Alla, Imre, Dan, Beránek, Josef, Abramson, Evan, Wilson, Jacqueline, Shrivastava, Manish
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.11.2012
• Subjects: Adsorption; aerosols; Aerosols - chemistry; Air Pollutants - chemistry; Applied sciences; Atmospheric aerosols; Atmospheric pollution; Equilibrium; Evaporation; Exact sciences and technology; gases; Gases - chemistry; Hydrophobic surfaces; hydrophobicity; Mass Spectrometry; Models, Chemical; Organic chemistry; Oxidation; Oxidation-Reduction; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Polycyclic aromatic hydrocarbons; Polycyclic Aromatic Hydrocarbons - chemistry; Volatilization; Hydrocarbon; Secondary pollutant; Polycyclic aromatic compound; Mutagen; Synergism; Persistent organic pollutant; Transport process; Carcinogen; Long range pollutant transport; Adsorbed state; Aerosols; Air pollution; Organic compounds
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/es302743z

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.