Aqueous-phase autoxidation in the atmosphere: fate and formation of organic peroxides

Autoxidation is a widely recognized mechanism known to initiate the degradation of food and lipids and modify organic matter in the atmosphere. Given the low NOx concentration in aqueous media (e.g., cloud water and fog droplets), autoxidation can become vital to facilitate the formation of highly oxygenated molecules such as organic peroxides (ROOH and ROOR). Here, we have identified aqueous-phase autoxidation-initiated hydroperoxides in varying organic precursors, including a laboratory model compound and monoterpene oxidation products. Our results show that autoxidation-initiated ROOHs are suppressed at enhanced precursor and oxidant concentrations. Furthermore, we observed an exponential increase in the yield of ROOHs when UV light with longer wavelengths was used in the experiment, comparing UVA, UVB, and UVC. Water-soluble organic compounds represent a significant fraction of ambient cloud water component (up to 500 µM. Thus, aqueous-phase autoxidation can become an important oxidation pathway for water-soluble species and as such facilitate the formation of ROOHs, thereby adding to the climate and health burden of atmospheric particulate matter.