The Submicron Atmospheric Aerosol as a Carrier of Reactive Chemical Species: Case of Peroxides

Abstract

The submicron atmospheric aerosol carries short-lived, reactive chemical species, including hydrogen peroxide and organic peroxides, at concentrations as high as 1 mM in the associated water. This conclusion is based on equilibrium calculations and (limited) experimental data. Hydrogen peroxide and hydroxymethylhydroperoxide (HOCH₂OOH) are especially likely to be found in the aqueous component of the atmospheric aerosol because of their very high Henry's law constants. Aerosol phase concentrations of hydrogen peroxide fall within a range in which significant biochemical effects have been observed when respiratory tract epithelial cells are treated with hydrogen peroxide solutions. This may help to explain the results of epidemiological studies that have shown that adverse health effects are associated with fine aerosols and/or sulfates. The submicron sulfate-containing aerosol is itself frequently a product of chemical reactions involving hydrogen peroxide, and hence a surrogate for the peroxide and associated reactive species. That is, the epidemiological results may signal a response to atmospheric peroxides rather than to sulfates. This hypothesis supports reduction of the total submicron aerosol mass as a way to reduce adverse health effects, because the total submicron mass is closely linked to the aqueous component that carries the reactive species. To test this hypothesis, studies are needed of the effects of exposures of cellular layers and/or animals to submicron hydrogen peroxide- containing aerosols that also contain salts such as ammonium sulfate.