Reactive aldehyde chemistry explains the missing source of hydroxyl radicals

Hydroxyl radicals (OH) determine the tropospheric self-cleaning capacity, thus regulating air quality and climate. However, the state-of-the-art mechanisms still underestimate OH at low nitrogen oxide and high volatile organic compound regimes even considering the latest isoprene chemistry. Here we propose that the reactive aldehyde chemistry, especially the auto-xidation of carbonyl organic peroxy radicals (R(CO)O2) derived from higher aldehydes, is a noteworthy OH regeneration mechanism that overwhelms the contribution of the isoprene autoxidation, the latter has been proved to largely contribute to the missing OH source under high isoprene condition. As diagnosed by the quantum chemical calculations, the R(CO)O2 radicals undergo fast H-migration to produce unsaturated hydroperoxyl-carbonyls that generate OH through rapid photolysis. This chemistry could explain almost all unknown OH sources in areas rich in both natural and anthropogenic emissions in the warm seasons, and may increasingly impact the global self-cleaning capacity in a future low nitrogen oxide society under carbon neutrality scenarios.

Xinping Yang, Haichao Wang, Keding Lu, Xuefei Ma, Zhaofeng Tan, Bo Long, Xiaorui Chen, Chunmeng Li, Tianyu Zhai, Yang Li, Kun Qu, Yu Xia, Yuqiong Zhang, Xin Li, Shiyi Chen, Huabin Dong, Limin Zeng, Yuanhang Zhang