[1] Methacrolein (MAC) and methyl vinyl ketone (MVK), two major first-generation products in the oxidation of isoprene, play important roles in tropospheric chemistry. However, little is known about their heterogeneous fate. Here we investigated the heterogeneous reactions of MAC and MVK on particles of silicon dioxide (SiO 2 ), the major constituent of mineral dust in the troposphere, under simulated tropospheric conditions. We first investigated the adsorption and desorption processes. It was found that MAC and MVK molecules were adsorbed onto the surface of SiO 2 particles by van der Waals forces and hydrogen bonding forces in a non-reactive state, and the presence of water vapor did not result in the formation of new substances but could decrease the adsorption ability by consuming isolated hydroxyl groups on the surface of SiO 2 particles. The initial adsorption and desorption rates, initial uptake coefficients, and adsorption concentrations at equilibrium were determined at different relative humidities. Notably, in the desorption process, a considerable amount of MAC or MVK molecules remained on SiO 2 particles in dry air but were almost completely desorbed in high-humid air. We also investigated the heterogeneous ozonolysis of MAC and MVK adsorbed onto SiO 2 particles, determining product yields at different relative humidities. The heterogeneous ozonolysis of MAC and MVK adsorbed onto SiO 2 particles yielded formaldehyde and methylglyoxal as the major secondary carbonyl products and formic acid and acetic acid as the major organic acid products, as in their gas-phase ozonolysis. However, the yield of two major organic peroxides, methyl hydroperoxide and hydroxymethyl hydroperoxide, was much greater in their heterogeneous ozonolysis than in their gas-phase ozonolysis. The mechanisms of heterogeneous ozonolysis of MAC and MVK onto the SiO 2 surface are deduced.
<p><strong>Abstract.</strong> The existence and importance of peroxyformic acid (PFA) in the atmosphere has been under controversy. We present here, for the first time, the observation data for PFA from four field measurements carried out in China. These data provided powerful evidence that PFA can stay in the atmosphere, typically in dozens of pptv level. The relationship between PFA and other detected peroxides was examined. The results showed that PFA had a strong positive correlation with its homolog, peroxyacetic acid, due to their similar sources and sinks. Through an evaluation of PFA production and removal rates, we proposed that the reactions between peroxyformyl radical (HC(O)O<sub>2</sub>) and formaldehyde or the hydroperoxyl radical (HO<sub>2</sub>) were likely to be the major source and degradation into formic acid (FA) was likely to be the major sink for PFA. Based on a box model evaluation, we proposed that the HC(O)O<sub>2</sub> and PFA chemistry was a major source for FA under low NO<sub>x</sub> conditions. Furthermore, it is found that the impact of the HC(O)O<sub>2</sub> and PFA chemistry on radical cycling was dependent on the yield of HC(O)O<sub>2</sub> radical from HC(O) + O<sub>2</sub> reaction. When this yield exceeded 50%, the HC(O)O<sub>2</sub> and PFA chemistry should not be neglected for calculating the radical budget. To make clear the exact importance of HC(O)O<sub>2</sub> and PFA chemistry in the atmosphere, further kinetic, field and modeling studies are required.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.