Abstract. Eighteen free amino acids (FAAs) were quantified in cloud water sampled at the puy de Dôme station (PUY – France) during 13 cloud events. This quantification has been performed without concentration neither derivatization, using LC-MS and the standard addition method to avoid matrix effects. Total concentrations of FAAs (TCAAs) vary from 1.2 µM to 7.7 µM, Ser (Serine) being the most abundant AA (23.7 % in average) but with elevated standard deviation, followed by Glycine (Gly) (20.5 %), Alanine (Ala) (11.9 %), Asparagine (Asn) (8.7 %), and Leucine/Isoleucine (Leu/I) (6.4 %). The distribution of AAs among the cloud events reveals high variability. TCAA constitutes between 0.5 and 4.4 % of the dissolved organic carbon measured in the cloud samples. AAs quantification in cloud water is scarce but the results agree with the few studies that investigated AAs in this aqueous medium. The environmental variability is assessed through a statistical analysis. This work shows that AAs are correlated with the time spent by the air masses in the boundary layer, especially over the sea surface before reaching the PUY. The cloud microphysical properties fluctuation does not explain the AAs variability in our samples confirming previous studies at PUY. We finally assessed the sources and the atmospheric processes that potentially explain the prevailing presence of certain AAs in the cloud samples. The initial relative distribution of AAs in biological matrices (proteins extracted from bacterial cells or mammalian cells, for example) could explain the dominance of Ala, Gly and Leu/I. AA composition of aquatic organisms (i.e., diatoms species) could also explain the high concentrations of Ser in our samples. The analysis of the AAs hydropathy also indicates a higher contribution of AAs (80 % in average) that are hydrophilic or neutral revealing the fact that other AAs (hydrophobic) are less favorably incorporated into cloud droplets. Finally, the atmospheric aging of AAs has been evaluated by calculating atmospheric lifetimes considering their potential transformation in the cloud medium by biotic or abiotic (mainly oxidation) processes. The most concentrated AAs encountered in our samples present the longest atmospheric lifetimes and the less dominant are clearly efficiently transformed in the atmosphere, potentially explaining their low concentrations. However, this cannot fully explain the relative contribution of several AAs in the cloud samples. This reveals the high complexity of the bio-physico-chemical processes occurring in the multiphasic atmospheric environment.

中文翻译：

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puy de Dôme 站（法国）云水中游离氨基酸的定量

摘要。在 13 次云事件期间，在 puy de Dôme 站（PUY – 法国）采样的云水中的 18 种游离氨基酸 (FAA) 被量化。这种量化是在没有浓缩和衍生化的情况下进行的，使用 LC-MS 和标准添加方法来避免基质效应。FAA (TCAA) 的总浓度从 1.2 µM 到 7.7 µM 不等，Ser（丝氨酸）是最丰富的 AA（平均 23.7%）但标准偏差较高，其次是甘氨酸（Gly）（20.5%）、丙氨酸（Ala） ) (11.9 %)、天冬酰胺 (Asn) (8.7 %) 和亮氨酸/异亮氨酸 (Leu/I) (6.4 %)。AA 在云事件中的分布显示出高度可变性。TCAA 占云样品中测量的溶解有机碳的 0.5% 至 4.4%。云水中的 AA 量化很少，但结果与少数研究这种水介质中的 AA 的研究一致。通过统计分析评估环境可变性。这项工作表明 AA 与边界层中的气团所花费的时间相关，尤其是在到达 PUY 之前的海面。云微物理特性的波动并不能解释我们样本中的 AA 变异性，这证实了 PUY 之前的研究。我们最终评估了可能解释云样本中某些 AA 普遍存在的来源和大气过程。AA 在生物基质中的初始相对分布（例如从细菌细胞或哺乳动物细胞中提取的蛋白质）可以解释 Ala、Gly 和 Leu/I 的优势。IE，硅藻物种）也可以解释我们样品中高浓度的 Ser。对 AA 亲水性的分析还表明亲水性或中性 AA 的贡献较高（平均 80%），揭示了其他 AA（疏水性）不太容易融入云滴的事实。最后，考虑到它们在云介质中通过生物或非生物（主要是氧化）过程的潜在转变，通过计算大气寿命来评估 AA 的大气老化。在我们的样品中遇到的浓度最高的 AA 具有最长的大气寿命，而较不显着的 AA 在大气中明显有效地转化，这可能解释了它们的低浓度。然而，这并不能完全解释云样本中几种 AA 的相对贡献。