Acid-catalyzed Multiphase reaction of Oxygenated Volatile Organic Compounds with Hydrogen Peroxide

The acid-catalyzed multiphase reaction with hydrogen peroxide has been suggested to be a potential pathway for secondary organic aerosol formation from isoprene and its oxidation products. However, knowledge of the chemical mechanism and kinetics for this process is still incomplete. Herein the uptake of several oxygenated volatile organic compounds on H2SO4-H2O2 mixed solutions was investigated using a flow-tube reactor coupled to a mass spectrometer. These OVOCs, including methacrolein, 2-methyl-3-buten-2-ol (MBO232), 2-methyl-2-butanol, 3-buten-2-ol, 2-butanol and 3-methyl-2-buten-1-ol (MBO321) are related to isoprene photooxidation or structurally similar to isoprene. The reactive uptake coefficients were acquired and the reaction pathways were proposed according to the products information.

Isoprene was generated from the reaction of MBO232 and H2SO4. When adding H2O2 into the acid solutions, new peaks were detected by the mass spectrometer, indicating that a different reaction mechanism occurred in H2SO4-H2O2 mixed solution compared to that in H2SO4 solution only. To further survey this chemical mechanism, the uptake of three aliphatic alcohols (2-methyl-2-butanol, 3-buten-2-ol, 2-butanol) on H2SO4-H2O2 mixed solution was studied. Tertiary or allyl alcohols can contribute to organic hydroperoxides (ROOHs) formation but secondary alcohols cannot under through this path according to the experimental results of gas-liquid multiphase reaction. The generation and degradation mechanisms of ROOHs were proposed using various methods, such as isotope labeling, infrared characterization and mass spectrum measurements. Once formed, ROOHs were found to undergo two degradation pathways: the acid-catalyzed rearrangement reaction and the organic hydrogen peroxysulfate formation pathway. As for the MBO321-H2SO4/ H2O2 system, ROOHs were also found in the gas and liquid phase through the acid-catalyzed route, while the formation of acetone and acetaldehyde were also detected which could undergo a rearrangement reaction. Organosulfates, which were proposed to be SOA tracer compounds in the atmosphere, were also produced during the oxidation process. These results indicate that acid-catalyzed multiphase oxidation of typical OVOCs with hydrogen peroxide may contribute to SOA mass under certain atmospheric conditions.