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In this study we revisit one of the simplest RO2 + RO2 reactions: the self-reaction of the ethene derived hydroxyperoxy radical formed via sequential addition of ·OH and O2 to ethene. Previous studies of this reaction suggested that the branching to ‘accretion products,’ compounds containing the carbon backbone of both reactants, was minimal. Here, CF3O− GC-CIMS is used to quantify the yields of ethylene glycol, glycolaldehyde, a hydroxy hydroperoxide produced from RO2 + HO2, and a C4O4H10 accretion product. These experiments were performed in an environmental chamber at 993 hPa and 294 K. We provide evidence that the accretion product is likely dihydroxy diethyl peroxide (HOC2H4OOC2H4OH = ROOR) and forms in the gas-phase with a branching fraction of 23 ± 5%. We suggest a new channel in the RO2+RO2 chemistry leading directly to the formation of HO2 (together with glycolaldehyde and an alkoxy radical). Finally, by varying the ratio of the formation rate of RO2 and HO2 in our chamber, we constrain the ratio of the rate coefficient for the reaction of RO2 + RO2 to that of RO2 + HO2 and find that this ratio is .22±.07, consistent with previous flash photolysis studies. 

RO 2 + OH reactions at atmospheric conditions lead to widespread levels of the previously omitted strong oxidizing agent ROOOH. 

Dimethyl sulfide (DMS), emitted from the oceans, is the most abundant biological source of sulfur to the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect Earth’s radiative balance by scattering solar radiation and serving as cloud condensation nuclei. We report the atmospheric discovery of a previously unquantified DMS oxidation product, hydroperoxymethyl thioformate (HPMTF, HOOCH 2 SCHO), identified through global-scale airborne observations that demonstrate it to be a major reservoir of marine sulfur. Observationally constrained model results show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth. Analyses of these observations show that HPMTF chemistry must be included in atmospheric models to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.