Abstract：
Carbonyls are ubiquitous in the troposphere and play a crucial role in atmospheric oxidation capacity (AOC), particularly in photochemistry-active regions such as the Tibetan Plateau (TP). However, the composition and evolution of carbonyls over the TP is still poorly understood due to a lack of comprehensive observations and modelling. Here, we conducted an intensive field measurement of 37 carbonyls and their precursors at a suburban site in Lhasa during summer 2022. Markedly higher levels of carbonyls (7.24 ± 3.83 ppbv) were found during ozone pollution episodes, with 36 % higher than those during non-episodes. Formaldehyde was the most abundant carbonyl (38 %), which primarily originating from photochemical secondary formations. Simulations using the Rapid adaptive Optimization Model for Atmospheric Chemistry (ROMAC) indicated strong AOC in Lhasa, with the daytime maximum of ·OH and ·HO2 of 9.8 × 106 and 4.2 × 108 molecules cm-3, respectively, which were even higher than that in most of the megacities in China. Notably, AOC significantly enhanced with the increasing carbonyls during the episodes, with the concentrations of ·OH and ·HO2 were boosted 21 % and 67 % than those during non-episodes, respectively. Budget analysis revealed that the ·HO2 + NO (88 %) and ·OH + VOC (74 %) pathways dominated the generation and loss of ·OH, respectively. And for ·HO2, they were ·RO2 + NO (67 %) and ·HO2 + NO (83 %). This study provides valuable insights into the strong AOC in the ecologically-fragile and climate-sensitive TP region, and highlighted the crucial role of anthropogenic-biogenic interactions in the active photochemistry of TP.
摘要：
羰基化合物在对流层中普遍存在，在大气氧化能力（AOC）中起着至关重要的作用。特别是在光化学活跃的地区，如青藏高原（TP）。然而,由于缺乏全面的观察和建模，人们对TP上羰基的组成和演化仍然知之甚少。这里,2022年夏季，我们在拉萨郊区进行了37种羰基化合物及其前体的密集现场测量。在臭氧污染事件中发现了更高水平的羰基化合物（7.24±3.83ppbv），比非发作期高出36%。甲醛是最丰富的羰基（38％），主要来自光化学次级地层。使用大气化学快速自适应优化模型（ROMAC）进行的模拟表明，拉萨的AOC很强，·OH和·HO2的白天最大值分别为9.8×106和4.2×108分子cm-3，甚至高于中国大多数特大城市的水平。值得注意的是,在发作期间，随着羰基化合物的增加，AOC显着增强，·OH和·HO2的浓度比非发作期分别增加了21%和67%，分别。预算分析表明，·HO2NO（88％）和·OHVOC（74％）途径主导了·OH的产生和损失，分别。对于·HO2，它们是·RO2NO（67％）和·HO2NO（83％）。这项研究为生态脆弱和气候敏感的TP地区强大的AOC提供了宝贵的见解，并强调了人为-生物相互作用在TP活性光化学中的关键作用。
