Atmospheric Science, Department of Chemistry and Molecular Biology, University of Gothenburg, S-412 96 Gothenburg, Sweden.
Environ Sci Technol. 2012 Nov 6;46(21):11660-9. doi: 10.1021/es301750r. Epub 2012 Oct 10.
Limonene has a strong tendency to form secondary organic aerosol (SOA) in the atmosphere and in indoor environments. Initial oxidation occurs mainly via ozone or OH radical chemistry. We studied the effect of O(3) concentrations with or without a OH radical scavenger (2-butanol) on the SOA mass and thermal characteristics using the Gothenburg Flow Reactor for Oxidation Studies at Low Temperatures and a volatility tandem differential mobility analyzer. The SOA mass using 15 ppb limonene was strongly dependent on O(3) concentrations and the presence of a scavenger. The SOA volatility in the presence of a scavenger decreased with increasing levels of O(3), whereas without a scavenger, there was no significant change. A chemical kinetic model was developed to simulate the observations using vapor pressure estimates for compounds that potentially contributed to SOA. The model showed that the product distribution was affected by changes in both OH and ozone concentrations, which partly explained the observed changes in volatility, but was strongly dependent on accurate vapor pressure estimation methods. The model-experiment comparison indicated a need to consider organic peroxides as important SOA constituents. The experimental findings could be explained by secondary condensed-phase ozone chemistry, which competes with OH radicals for the oxidation of primary unsaturated products.
柠檬烯在大气中和室内环境中具有很强的形成二次有机气溶胶（SOA）的趋势。初始氧化主要通过臭氧或 OH 自由基化学发生。我们使用哥德堡低温氧化研究流动反应器和挥发性串联差分迁移率分析仪，研究了存在或不存在 OH 自由基清除剂（2-丁醇）时 O(3)浓度对 SOA 质量和热特性的影响。使用 15 ppb 柠檬烯时，SOA 质量强烈依赖于 O(3)浓度和清除剂的存在。在存在清除剂的情况下，SOA 的挥发性随 O(3)水平的增加而降低，而在没有清除剂的情况下，没有明显变化。开发了一个化学动力学模型，使用可能对 SOA 有贡献的化合物的蒸气压估计值来模拟观察结果。该模型表明，产物分布受 OH 和臭氧浓度变化的影响，这部分解释了观察到的挥发性变化，但强烈依赖于准确的蒸气压估计方法。模型-实验比较表明，需要将过氧化物视为重要的 SOA 成分。实验结果可以用二次凝聚相臭氧化学来解释，该化学与 OH 自由基竞争，以氧化初级不饱和产物。
