Sulfuric acid in the atmosphere can participate in acid-catalyzed and acid-driven reactions, including those within secondary organic aerosols (SOA). Previous studies have observed enhanced absorption at visible wavelengths and significant changes in the chemical composition when SOA was exposed to sulfuric acid. However, the specific chromophores responsible for these changes could not be identified. The goals of this study are to identify the chromophores and determine the mechanism of browning in highly acidified α-pinene SOA by following the behavior of specific common α-pinene oxidation products, namely, cis-pinonic acid and cis-pinonaldehyde, when they are exposed to highly acidic conditions. The products of these reactions were analyzed with ultra-performance liquid chromatography coupled with photodiode array spectrophotometry and high-resolution mass spectrometry, UV–vis spectrophotometry, and nuclear magnetic resonance spectroscopy. cis-Pinonic acid (2) was found to form homoterpenyl methyl ketone (4), which does not absorb visible radiation, while cis-pinonaldehyde (3) formed weakly absorbing 1-(4-(propan-2-ylidene)cyclopent-1-en-1-yl)ethan-1-one (5) and 1-(4-isopropylcyclopenta-1,3-dien-1-yl)ethan-1-one (6) via an acid-catalyzed aldol condensation. This chemistry could be relevant for environments characterized by high sulfuric acid concentrations, for example, during the transport of organic compounds from the lower to the upper atmosphere by fast updrafts.

中文翻译：

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在强酸性条件下老化的顺式蒎醛的发色团的形成

大气中的硫酸可以参与酸催化和酸驱动的反应，包括二次有机气溶胶 (SOA) 中的反应。先前的研究观察到，当 SOA 暴露于硫酸时，可见光波长的吸收增强，化学成分发生显着变化。然而，无法确定导致这些变化的特定发色团。本研究的目的是通过跟踪特定常见 α-蒎烯氧化产物（即顺式蒎烯酸和顺式蒎醛）的行为，识别发色团并确定高度酸化的 α-蒎烯 SOA 中褐变的机制。暴露于强酸性条件下。使用超高效液相色谱结合光电二极管阵列分光光度法和高分辨率质谱法、紫外可见分光光度法和核磁共振光谱法对这些反应的产物进行分析。顺式-蒎酸( 2 )被发现形成高萜基甲基酮( 4 )，其不吸收可见辐射，而顺式-蒎醛( 3 )形成弱吸收的1-(4-(丙-2-亚基)环戊-1 -en-1-基)乙-1-酮( 5 )和1-(4-异丙基环戊-1,3-二烯-1-基)乙-1-酮( 6 )通过酸催化羟醛缩合。这种化学反应可能与以高硫酸浓度为特征的环境有关，例如，在有机化合物通过快速上升气流从低层大气输送到高层大气的过程中。