The heterogeneous reactions of O₃ with aerosol particles are of central importance to air quality. They are studied extensively, but the molecular mechanisms and kinetics remain unresolved. Based on new experimental data and calculations, we show that long-lived reactive oxygen intermediates (ROIs) are formed. The chemical lifetime of these intermediates exceeds 100 seconds, which is much longer than the surface residence time of molecular O₃ (~10⁻⁹ s). The ROIs explain and resolve apparent discrepancies between earlier quantum mechanical calculations and kinetic experiments. They play a key role in the chemical transformation and adverse health effects of toxic and allergenic air-particulate matter, such as soot, polycyclic aromatic hydrocarbons and proteins. ROIs may also be involved in the decomposition of O₃ on mineral dust and in the formation and growth of secondary organic aerosols. Moreover, ROIs may contribute to the coupling of atmospheric and biospheric multiphase processes.

Filter samples of fine and coarse air particulate matter (PM) collected over a period of one year in central Europe (Mainz, Germany) were analyzed for water-soluble organic compounds (WSOCs), including the α- and β-pinene oxidation products pinic acid, pinonic acid and 3-methyl-1,2,3-butanetricarboxylic acid (3-MBTCA), as well as a variety of dicarboxylic acids and nitrophenols. Seasonal variations and other characteristic features in fine, coarse, and total PM (TSP) are discussed with regard to aerosol sources and sinks in comparison to data from other studies and regions. The ratios of adipic acid and phthalic acid to azelaic acid indicate that the investigated aerosol samples were mainly influenced by biogenic sources. A strong Arrhenius-type correlation was found between the 3-MBTCA concentration and inverse temperature (<i>R</i>² = 0.79, <i>n</i> = 52, <i>E</i>_a = 126 &plusmn; 10 kJ mol⁻¹, temperature range 275–300 K). Model calculations suggest that the temperature dependence observed for 3-MBTCA can be explained by enhanced photochemical production due to an increase of hydroxyl radical (OH) concentration with increasing temperature, whereas the influence of gas-particle partitioning appears to play a minor role. The results indicate that the OH-initiated oxidation of pinonic acid is the rate-limiting step in the formation of 3-MBTCA, and that 3-MBTCA may be a suitable tracer for the chemical aging of biogenic secondary organic aerosol (SOA) by OH radicals. An Arrhenius-type temperature dependence was also observed for the concentration of pinic acid (<i>R</i>² = 0.60, <i>n</i> = 56, <i>E</i>_a = 84 &plusmn; 9 kJ mol⁻¹); it can be tentatively explained by the temperature dependence of biogenic pinene emission as the rate-limiting step of pinic acid formation

Water-soluble proteinaceous matter including proteins and free amino acids (FAAs) as well as some other chemical components was analyzed in fine particulate matter (PM) samples collected over a period of one year in rural Guangzhou. Annual averaged protein and total FAAs concentrations were 0.79 ± 0.47 μg m and 0.13 ± 0.05 μg m, accounting for 1.9 ± 0.7% and 0.3 ± 0.1% of PM, respectively. Among FAAs, glycine was the most abundant species (19.9%), followed by valine (18.5%), methionine (16.1%), and phenylalanine (13.5%). Both proteins and FAAs exhibited distinct seasonal variations with higher concentrations in autumn and winter than those in spring and summer. Correlation analysis suggests that aerosol proteinaceous matter was mainly derived from intensive agricultural activities, biomass burning, and fugitive dust/soil resuspension. Significant correlations between proteins/FAAs and atmospheric oxidant (O) indicate that proteins/FAAs may be involved in O related atmospheric processes. Our observation confirms that ambient FAAs could be degraded from proteins under the influence of O, and the stoichiometric coefficients of the reactions were estimated for FAAs and glycine. This finding provides a possible pathway for the production of aerosol FAAs in the atmosphere, which will improve the current understanding on atmospheric processes of proteinaceous matter.