Uptake and reaction of atmospheric organic vapours on organic films

Abstract

Films composed in whole or in part of organic compounds represent an important atmospheric interface. Urban surfaces are now known to be coated with a film ("grime") whose chemical composition somewhat resembles that of urban atmospheric aerosols. Such films may act as media in which atmospheric trace gases may be sequestered (leading to their removal from the gas phase); they may also act as reactive media, either as a "solvent" or as a source of reagents. Organic coatings on aqueous surfaces are also important, not just on ocean and lake surfaces ("biofilms") but also on the surfaces of fogwaters and atmospheric aerosol particles. We have initiated experimental uptake studies of trace gases into simple proxies for urban organic films using two techniques: a Knudsen cell effusion reactor and a laser-induced fluorescence method. We will discuss our first results on non-reactive uptake of organic compounds by organic films we use as proxies for urban grime coatings. In general, the measured uptake coefficients appear to track the octanol-air partition coefficients, at least qualitiatively. We have also measured the kinetics of reactions between gas-phase ozone and small polycyclic aromatic hydrocarbons (PAHs), when these are adsorbed at the air-aqueous interface or incorporated into an organic film. Reactions at the "clean" air-water interface and at a coated interface consisting of a monolayer of various amphiphilic organic compounds all follow a Langmuir-Hinshelwood mechanism, in which ozone first adsorbs to the air-aqueous interface, then reacts with already adsorbed PAH. By contrast, the reaction in the pure organic film occurs in the bulk phase. Under some circumstances, heterogeneous oxidation of PAHs by ozone may be as important in the atmosphere as their gas phase oxidation by OH.

Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City

“…As reaction with OH is the dominant loss process of gas-phase PAHs (Atkinson and Arey, 1994), we therefore investigate the heterogeneous reaction rate of OH with particle-phase PAHs to determine its role in the loss of PAHs in Mexico City. Heterogeneous oxidation by ozone may also be an important sink for PAHs (Donaldson et al, 2005), so the results presented here represent a lower limit of their reactive decay.…”

Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range

“…We hypothesize that reactions between O 3 and organic surfaces (i.e., soil, organic films) could be one non-photochemical surface-level source of alkanoic acids near the site, though unlikely to account for the entire source. Reactions of O 3 on organic surfaces such as organic films (Donaldson et al, 2005), plant surfaces (Cape et al, 2009;Jud et al, 2016), and human skin (Liu et al, 2016(Liu et al, , 2017 have been reported previously. Soil organic matter and organic films are often rich in alkenes (Vancampenhout et al, 2009;Donaldson et al, 2005;Simpson et al, 2006), which undergo ozonolysis reactions in the presence of O 3 (Criegee, 1975;Wolff et al, 1997).…”

“…Reactions of O 3 on organic surfaces such as organic films (Donaldson et al, 2005), plant surfaces (Cape et al, 2009;Jud et al, 2016), and human skin (Liu et al, 2016(Liu et al, , 2017 have been reported previously. Soil organic matter and organic films are often rich in alkenes (Vancampenhout et al, 2009;Donaldson et al, 2005;Simpson et al, 2006), which undergo ozonolysis reactions in the presence of O 3 (Criegee, 1975;Wolff et al, 1997). Hydroxyalkyl hydroperoxides formed via the ozonolysis of alkenes can further decompose to alkanoic acids (Moortgat et al, 1997;Anglada et al, 2002;Hasson et al, 2003;.…”

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O<sub>3</sub>, NO<sub>2</sub>, H<sub>2</sub>O, OH and NO<sub>3</sub>

“…2004; Mmereki et al, 2004;Donaldson et al, 2005;Kahan et al, 2006;Kwamena et al, 2006Kwamena et al, , 2007. The investigated PAHs comprise benzo[a]pyrene (BaP), anthracene, naphthalene, pyrene, phenanthrene, benzo[a]anthracene (BaA), perylene, and fluoranthene.…”