Impact of the Criegee Intermediate on the Formation of Secondary Organic Aerosols during E-4-Hexen-1-ol Ozonolysis.

Abstract

Criegee intermediates (CIs), which are active species in the troposphere, play an important role in the formation of secondary organic aerosols (SOA). In this study, matrix isolation technology combined with a vacuum Fourier transform infrared spectrometer (MIFT-IR) and smog chamber method were used to study the typical green leaf volatiles (E-4-hexen-1-ol, E4H1O) ozonolysis process. The infrared characteristic peak resulting from the O-O stretching vibration of CH₃CHOO was identified at 882 cm^-1. And the characteristic infrared peaks of CH₂OHCH₂CH₂CHOO were not detected, possibly due to the presence of extremely rapid unimolecular reaction channels. To investigate the subsequent atmospheric reaction process of these two CIs, additional smog chamber experiments with the E4H1O-O₃ system were conducted to investigate the impact on SOA formation mechanisms. The ordered oligomers derived from the continuous oligomerization of RO₂ radicals with several CIs were identified as the primary components of SOA without the addition of sulfur dioxide (SO₂). The addition of SO₂ in the concentration range of 14-159 ppb, acting as a scavenger for CIs, led to the disappearance of the oligomers, while the yield of SOA continued to increase. The reasons for the increased mass concentration of SOA may be a change in the chemical composition. The escalating concentrations of SO₂ underwent reactions with CIs (or OH radicals) to generate H₂SO₄, subsequently elevating the acidity of the particles. The acid particles resulted in the changes in SOA composition, leading to the production of organic sulfates (OSs), thereby contributing to the increase in SOA yield. A number of OSs were detected in the presence of SO₂, which may result from the heterogeneous reaction of oxygen-containing species with sulfuric acid under acidic conditions. Additionally, non-sulfur-containing molecular structures of emerging C_xH_yO_z products in the particle phase were also identified. Our findings provided detailed molecular insights into the mechanism of E4H1O ozonolysis and its impact on SOA formation from the perspective of Criegee chemistry.