Gas phase formation of extremely oxidized pinene reaction products in chamber and ambient air
Gas phase formation of extremely oxidized pinene reaction products in chamber and ambient air
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DOI：
10.5194/acp-12-5113-2012
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发表时间：
2012-01-01
影响因子：
6.3
通讯作者：
Mentel, Th F.
中科院分区：
文献类型：
--
作者：
Ehn, M.;Kleist, E.;Mentel, Th F.
此前曾在芬兰海蒂亚拉的北方森林中观察到高分子量（300-650 Da）自然带电负离子。这项工作进行的长期测量表明，在海蒂亚拉，春季和秋季之间几乎每个晚上都能观察到这些离子。在 Julich 植物大气室 (JPAC) 中低 OH 条件下对 α-蒎烯 (C10H16) 氧化进行额外测量时，可以以惊人的细节再现环境质谱图。这些离子被鉴定为硝酸根离子 (NO3-) 和 α-蒎烯氧化产物的簇，氧碳比达到 0.7-1.3，同时保留了大部分最初的 10 个碳原子。将离子归因于簇而不是单个分子是基于对 HSO4- (Hyytiala) 和 C3F5O2- (JPAC) 簇中相同的极度氧化有机物的额外观察。离子光谱中最丰富的产物被确定为 C10H14O7、C10H14O9、C10H16O9 和 C10H14O11。形成这些分子的机制尚不清楚，但最初的反应很可能是臭氧对双键的攻击，因为离子主要在黑暗条件下观察到。 β-蒎烯在相同条件下也形成高度氧化的产物，但效率较低，主要是 C-9 化合物，这在 Hyytiala 中未观察到，其中 β-蒎烯平均丰度比 α-蒎烯低 4-5 倍。此外，为了解释高O/C和相对高的H/C，我们认为偕二醇和/或氢过氧化物基团可能很重要。我们估计中性极度氧化产物总和的夜间浓度约为 0.1-1 ppt（类似于 10(6)-10(7) 摩尔 cm(-3)）。这与海蒂亚拉白天的气态 H2SO4 含量范围相似。由于这些高度氧化的有机物大约重 3 倍，并且蒸汽压可能极低，因此它们在新气溶胶颗粒形成和生长的初始步骤中的作用可能很重要，需要在未来进行更详细的探索。
High molecular weight (300-650 Da) naturally charged negative ions have previously been observed at a boreal forest site in Hyytiala, Finland. The long-term measurements conducted in this work showed that these ions are observed practically every night between spring and autumn in Hyytiala. The ambient mass spectral patterns could be reproduced in striking detail during additional measurements of alpha-pinene (C10H16) oxidation at low-OH conditions in the Julich Plant Atmosphere Chamber (JPAC). The ions were identified as clusters of the nitrate ion (NO3-) and alpha-pinene oxidation products reaching oxygen to carbon ratios of 0.7-1.3, while retaining most of the initial ten carbon atoms. Attributing the ions to clusters instead of single molecules was based on additional observations of the same extremely oxidized organics in clusters with HSO4- (Hyytiala) and C3F5O2- (JPAC). The most abundant products in the ion spectra were identified as C10H14O7, C10H14O9, C10H16O9, and C10H14O11. The mechanism responsible for forming these molecules is still not clear, but the initial reaction is most likely ozone attack at the double bond, as the ions are mainly observed under dark conditions. beta-pinene also formed highly oxidized products under the same conditions, but less efficiently, and mainly C-9 compounds which were not observed in Hyytiala, where beta-pinene on average is 4-5 times less abundant than alpha-pinene. Further, to explain the high O/C together with the relatively high H/C, we propose that geminal diols and/or hydroperoxide groups may be important. We estimate that the night-time concentration of the sum of the neutral extremely oxidized products is on the order of 0.1-1 ppt (similar to 10(6)-10(7) molec cm(-3)). This is in a similar range as the amount of gaseous H2SO4 in Hyytiala during day-time. As these highly oxidized organics are roughly 3 times heavier, likely with extremely low vapor pressures, their role in the initial steps of new aerosol particle formation and growth may be important and needs to be explored in more detail in the future.