Abstract
A major research area in atmospheric chemistry focuses on the formation of secondary organic aerosol (SOA), which contains a large variety of low-volatility organic compounds when generated by the ozonolysis of monoterpenes. Thus, we apply quantum chemistry and kinetic calculations to investigate the ozonolysis of citral, which begins with the formation of primary ozonides (POZs) that decompose into Criegee intermediates (CIs). Although CIs have been previously implicated in tropospheric oxidation, the majority are simple compounds for their class, such as CH2OO· or CH3CHOO·. This study, however, reports on the generation and reaction kinetics of larger CIs, which have been shown to oxidize NO and SO2 into NO2 and SO3, respectively, leading to the production of nitric acid and sulfuric acid. Furthermore, the reactions between these CIs, and H2O and SO2 may serve as the dominant mechanism for removing the former from the troposphere, thereby determining the atmospheric CI concentrations. The low-volatility organic compounds potentially arising from the ozonolysis of citral, including aldehydes (–C(=O)H), ketones (–C(=O)–), alcohols (–OH), and hydroperoxides (–OOH), can form SOA through the nucleation, condensation, and/or partitioning of the condensed and gaseous phases.
Highlights
Atmospheric aerosols significantly affect the earth’s radiation balance by absorbing and scattering solar radiation, leading to a decrease in atmospheric visibility and contributing to climate change
Atmospheric aerosols are mainly classified as either primary aerosols which are directly discharged into the atmosphere by an exhaust source, or secondary aerosols formed in the atmosphere from chemical reaction with gaseous components (Atkinson and Arey, 2003; Hallquist et al, 2009)
The proposed reaction mechanism for monoterpene ozonolysis starts with O3 addition to C=C double bonds, which lead to the formation of primary ozonide (POZ)
Summary
Atmospheric aerosols significantly affect the earth’s radiation balance by absorbing and scattering solar radiation, leading to a decrease in atmospheric visibility and contributing to climate change. The proposed reaction mechanism for monoterpene ozonolysis starts with O3 addition to C=C double bonds, which lead to the formation of primary ozonide (POZ). Sipilä et al (2014) reported that the reaction between SO2 and CIs formed from monoterpene ozonolysis is an important source of atmospheric sulfate and SOAs. In addition, Ye et al (2018) studied α-pinene and limonene ozonolysis in the presence of SO2, finding that the reaction of SO2 with CIs was responsible for altering SOAs yields. Ye et al (2018) studied α-pinene and limonene ozonolysis in the presence of SO2, finding that the reaction of SO2 with CIs was responsible for altering SOAs yields These experimental studies indicated that bimolecular CIs reactions were related to SOAs formation, the chemical processes behind these interactions are not yet fully understood. Neral was used to theoretically explore the gas-phase ozonolysis of citral in the presence of H2O, NO and SO2, providing novel insights on the formation mechanisms of SOAs during monoterpenes ozonolysis and further deepening our understanding of the atmospheric SOAs
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