DOE OSTI · 3011602
Aldehyde cool-flame chemistry explains a missing source of organic acids
Abstract
Combustion emission is a significant source of organic acids, impacting atmospheric chemistry and climate. Their formation mechanisms, however, remain poorly understood, leading to underestimation in kinetic models. We investigate the cool-flame oxidation of key combustion intermediates—C 1 –C 4 aldehydes and benzaldehyde. Using in-situ synchrotron vacuum ultraviolet photoionization mass spectrometry, we observe the direct conversion of aldehydes to organic acids, a process enhanced by HO 2 radicals. Quantum chemistry calculations reveal that the reaction of RC(O)O 2 with HO 2 on the singlet potential energy surface contributes to organic acids. Incorporating this pathway into a kinetic model significantly improves organic acid prediction. Despite the high-temperature nature of engine combustion, significant spatial and temporal inhomogeneities (e.g., near-wall regions and crevice volumes) lead to localized cool-flame conditions, facilitating organic acid formation and emission. Elucidating the acid formation under cool-flame conditions provides a critical mechanism for accurately modelling anthropogenic organic acid emissions and developing mitigation strategies.
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Liu, Bingzhi [University of Science and Technology of China, Anhui (China)], Dong, Bin [University of Science and Technology of China, Anhui (China)], Wang, Huanhuan [University of Science and Technology of China, Anhui (China)] (ORCID:0000000334003800), Ruan, Shanshan [University of Science and Technology of China, Anhui (China)], Zhu, Qingbo [University of Science and Technology of China, Anhui (China)], Chen, Weiye [University of Science and Technology of China, Anhui (China)], Wang, Liuyuan [University of Science and Technology of China, Anhui (China)], Zhu, Long [University of Science and Technology of China, Anhui (China)], Xing, Lili [Henan University of Science and Technology (China)], Truhlar, Donald G. [University of Minnesota, Minneapolis, MN (United States)] (ORCID:0000000277427294), Wang, Zhandong [University of Science and Technology of China, Anhui (China)] (ORCID:0000000315352319). 2025-12-26. Aldehyde cool-flame chemistry explains a missing source of organic acids. https://doi.org/10.1038/s41467-025-67986-w
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