# Aqueous-phase reactive species formed by fine particulate matter from remote forests and polluted urban air

page10440In the aqueous phase, fine particulate matter can form reactive species (RS) that influence the aging, properties, and health effects of atmospheric aerosols. In this study, we explore the RS yields of aerosol samples from a remote forest (Hyytiälä, Finland) and polluted urban locations (Mainz, Germany; Beijing, China), and we relate the RS yields to different chemical constituents and reaction mechanisms. Ultra-high-resolution mass spectrometry was used to characterize organic aerosol composition, electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique was applied to determine the concentrations of inline-formulaRadical⚫OH, Oinline-formula $M2inlinescrollmathml{}_{normal 2}^{\mathrm{Radicalnormal ⚫}-}$ 12pt16ptsvg-formulamathimg0745b536dd0e5fe0f2cc8f1f9cffd00f acp-21-10439-2021-ie00001.svg12pt16ptacp-21-10439-2021-ie00001.png , and carbon- or oxygen-centered organic radicals, and a fluorometric assay was used to quantify Hinline-formula2Oinline-formula2. The aqueous Hinline-formula2Oinline-formula2-forming potential per mass unit of ambient PMinline-formula2.5 (particle diameter inline-formula< 2.5 inline-formulaµm) was roughly the same for all investigated samples, whereas the mass-specific yields of radicals were lower for sampling sites with higher concentrations of PMinline-formula2.5. The abundances of water-soluble transition metals and aromatics in ambient PMinline-formula2.5 were positively correlated with the relative fraction of inline-formulaRadical⚫OH and negatively correlated with the relative fraction of carbon-centered radicals. In contrast, highly oxygenated organic molecules (HOM) were positively correlated with the relative fraction of carbon-centered radicals and negatively correlated with the relative fraction of inline-formulaRadical⚫OH. Moreover, we found that the relative fractions of different types of radicals formed by ambient PMinline-formula2.5 were comparable to surrogate mixtures comprising transition metal ions, organic hydroperoxide, Hinline-formula2Oinline-formula2, and humic or fulvic acids. The interplay of transition metal ions (e.g., iron and copper ions), highly oxidized organic molecules (e.g., hydroperoxides), and complexing or scavenging agents (e.g., humic or fulvic acids) leads to nonlinear concentration dependencies in aqueous-phase RS production. A strong dependence on chemical composition was also observed for the aqueous-phase radical yields of laboratory-generated secondary organic aerosols (SOA) from precursor mixtures of naphthalene and inline-formulaβ-pinene. Our findings show how the composition of PMinline-formula2.5 can influence the amount and nature of aqueous-phase RS, which may explain differences in the chemical reactivity and health effects of particulate matter in clean and polluted air.

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Tong, Haijie / Liu, Fobang / Filippi, Alexander / et al: Aqueous-phase reactive species formed by fine particulate matter from remote forests and polluted urban air. 2021. Copernicus Publications.

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