Jang Myoseon, Carroll Brian, Chandramouli Bharadwaj, Kamens Richard M
Department of Environmental Sciences and Engineering, CB 7431, Rosenau Hall, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Environ Sci Technol. 2003 Sep 1;37(17):3828-37. doi: 10.1021/es021005u.
Aerosol growth by the heterogeneous reactions of different aliphatic and alpha,beta-unsaturated carbonyls in the presence/absence of acidified seed aerosols was studied in a 2 m long flow reactor (2.5 cm i.d.) and a 0.5-m3 Teflon film bag under darkness. For the flow reactor experiments, 2,4-hexadienal, 5-methyl-3-hexen-2-one, 2-cyclohexenone, 3-methyl-2-cyclopentenone, 3-methyl-2-cyclohexenone, and octanal were studied. The carbonyls were selected based on their reactivity for acid-catalyzed reactions, their proton affinity, and their similarity to the ring-opening products from the atmospheric oxidation of aromatics. To facilitate acid-catalyzed heterogeneous hemiacetal/acetal formation, glycerol was injected along with inorganic seed aerosols into the flow reactor system. Carbonyl heterogeneous reactions were accelerated in the presence of acid catalysts (H2SO4), leading to higher aerosol yields than in their absence. Aldehydes were more reactive than ketones for acid-catalyzed reactions. The conjugated functionality also resulted in higher organic aerosol yieldsthan saturated aliphatic carbonyls because conjugation with the olefinic bond increases the basicity of the carbonyl leading to increased stability of the protonated carbonyl. Aerosol population was measured from a series of sampling ports along the length of the flow reactor using a scanning mobility particle sizer. Fourier transform infrared spectrometry of either an impacted liquid aerosol layer or direct reaction of carbonyls as a thin liquid layer on a zinc selenide FTIR disk was employed to demonstrate the direct transformation of chemical functional groups via the acid-catalyzed reactions. These results strongly indicate that atmospheric multifunctional organic carbonyls, which are created by atmospheric photooxidation reactions, can contribute significantly to secondary organic aerosol formation through acid-catalyzed heterogeneous reactions. Exploratory studies in 25- and 190-m3 outdoor chambers were also implemented to demonstrate the formation of high molecular weight organic structures. The reaction of ozone with alpha-pinene to generate secondary organic aerosols (SOAs) was performed in the presence of background aerosol consisting of a mixture of wood soot and diesel soot. Results strongly suggest that indigenous sulfuric acid associated with the combustion of fossil fuels (e.g., diesel soot) can initiate acid-catalyzed heterogeneous reactions of SOAs on the particle phase.
在黑暗条件下，于一个2米长的流动反应器（内径2.5厘米）和一个0.5立方米的特氟龙薄膜袋中，研究了不同脂肪族和α,β - 不饱和羰基化合物在有无酸化种子气溶胶存在时通过非均相反应的气溶胶增长情况。对于流动反应器实验，研究了2,4 - 己二烯醛、5 - 甲基 - 3 - 己烯 - 2 - 酮、2 - 环己烯酮、3 - 甲基 - 2 - 环戊烯酮、3 - 甲基 - 2 - 环己烯酮和辛醛。选择这些羰基化合物是基于它们对酸催化反应的反应活性、质子亲和力以及与芳烃大气氧化开环产物的相似性。为促进酸催化的非均相半缩醛/缩醛形成，将甘油与无机种子气溶胶一起注入流动反应器系统。在酸催化剂（硫酸）存在下，羰基非均相反应加速，导致气溶胶产率高于无酸催化剂时。对于酸催化反应，醛比酮更具反应活性。共轭官能团也导致有机气溶胶产率高于饱和脂肪族羰基化合物，因为与烯烃键共轭会增加羰基的碱性，从而导致质子化羰基的稳定性增加。使用扫描迁移率粒径分析仪从沿着流动反应器长度的一系列采样口测量气溶胶粒子群。通过对撞击的液体气溶胶层进行傅里叶变换红外光谱分析，或者将羰基化合物作为薄液体层直接反应在硒化锌傅里叶变换红外光谱盘上，来证明通过酸催化反应化学官能团的直接转化。这些结果有力地表明，由大气光氧化反应产生的大气多功能有机羰基化合物可通过酸催化的非均相反应对二次有机气溶胶的形成有显著贡献。还在25立方米和190立方米的室外舱中进行了探索性研究，以证明高分子量有机结构的形成。在由木烟和柴油烟混合物组成的背景气溶胶存在下，进行了臭氧与α - 蒎烯反应生成二次有机气溶胶（SOA）的实验。结果有力地表明，与化石燃料燃烧（如柴油烟）相关的原生硫酸可引发颗粒相上SOA的酸催化非均相反应。
