Impact of temperature on the role of Criegee intermediates and peroxy radicals in dimer formation from β-pinene ozonolysis

Stabilized Criegee intermediates (SCIs) and organic peroxy radicals (ROinline-formula₂) are critical in atmospheric oxidation processes and secondary organic aerosol (SOA) formation. However, the influence of temperature on their corresponding reaction mechanisms in SOA formation is unclear. Through utilizing formic acid as a SCI scavenger and regulating the ratio of hydroperoxyl radials (HOinline-formula₂) to ROinline-formula₂ ([HOinline-formula $M5inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimgafc6f326b6a9116dd589e1771ceee7b4 acp-24-167-2024-ie00001.svg40pt14ptacp-24-167-2024-ie00001.png ]) from inline-formula∼ 0.3 to inline-formula∼ 1.9 using different concentrations of CO, the roles of ROinline-formula₂ and SCIs in SOA formation were investigated from 248 to 298 K, particularly for dimer formation in inline-formulaβ-pinene ozonolysis. The SOA yield increased by 21 % from 298 to 273 K, while it decreased by 40 % from 273 to 248 K. Both changing [HOinline-formula $M10inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimg08dba5c3933c332e918a9664ea4f1c8f acp-24-167-2024-ie00002.svg40pt14ptacp-24-167-2024-ie00002.png ] and scavenging SCIs significantly affect SOA yield and composition. SCI reactions accounted for more than 40 % of dimer and SOA mass formation for all temperatures. Increasing [HOinline-formula $M11inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimgca82d30e7902c2c188f846b1d1563088 acp-24-167-2024-ie00003.svg40pt14ptacp-24-167-2024-ie00003.png ] inhibited dimer and SOA formation, and this inhibition became larger with decreasing temperature. Compared to low [HOinline-formula $M12inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimg03d4ec6e320a97ddcc9a24f1b71ced3c acp-24-167-2024-ie00004.svg40pt14ptacp-24-167-2024-ie00004.png ] (0.30–0.34), the dimer abundance at high [HOinline-formula $M13inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimg170579dc363196766dd32858fc73834e acp-24-167-2024-ie00005.svg40pt14ptacp-24-167-2024-ie00005.png ] (1.53–1.88) decreased by about 31 % at 298 K and 70 % at 248 K. [HOinline-formula $M14inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimgb5f66b14725c2eec2238fa677fc87be6 acp-24-167-2024-ie00006.svg40pt14ptacp-24-167-2024-ie00006.png ] has a specific impact on SCI-controlled dimers at lower temperatures by especially influencing the Cinline-formula₉–SCI reactions with ROinline-formula₂. The dimers formed from Cinline-formula₉–SCI reactions with ROinline-formula₂ were estimated to decrease by 61 % at high [HOinline-formula $M19inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimgb163414b39b6b0fd099817e35b5e9ca4 acp-24-167-2024-ie00007.svg40pt14ptacp-24-167-2024-ie00007.png ] compared to low [HOinline-formula $M20inlinescrollmathml{}_{\mathrm{normal\; 2}}]/[{\mathrm{normal\; RO}}_{\mathrm{normal\; 2}}$ 40pt14ptsvg-formulamathimg48a3b986a1eed6dbafa95a99ec3bc5e1 acp-24-167-2024-ie00008.svg40pt14ptacp-24-167-2024-ie00008.png ] at 248 K. The high reactivity and substantial contribution to SOA of inline-formulaβ-pinene-derived SCIs at lower temperatures observed in this study suggest that monoterpene-derived SCI reactions should be accounted for in describing colder regions of the atmosphere.