Abstract We investigate secondary organic aerosol (SOA) and gas phase organic acid yields from the sequential photooxidation of seven monoterpene isomers (α-pinene, β-pinene, limonene, sabinene, terpinolene, α-terpinene, and γ-terpinene) using an Oxidative Flow Reactor under dry conditions. SOA yields were highest for terpinolene (33% at 5.7 days of aging), followed by sabinene, β-pinene, α-pinene, limonene, γ-terpinene, and α-terpinene. Isomers with exocyclic double bonds (i.e. immediately adjacent to a ring) had higher SOA yields than those with endocyclic double bonds, or with double bonds that are unattached to a ring structure. SOA yields increased with OH exposure, highlighting the limitation of using single values for SOA yield in modeling studies, and the need for isomer-specific SOA parameterizations. SOA yields were adequately fit by a one-product model and in broad agreement with previous studies. SOA yields linearly increased with organic aerosol mass concentration, possibly the result of high OH loading and short residence times in the flow reactor. Gas phase yields of formic, acetic, butyric, and methacrylic acid (or their isomers) followed very different patterns as a function of OH exposure from SOA yields, and were poorly correlated with OH rate constants. These observations suggest that higher volatility (fragmentation) products of monoterpene photooxidation were produced and lost on different timescales from the production and condensation of lower-volatility (functionalization) products. Formic acid yields ranged from 0.06 to 9.3% across all OH exposures. Formic acid yields from γ-terpinene (0.36–3%) monotonically increased with OH exposure, unlike the other monoterpene isomers, which exhibited initial increases in formic acid yields with OH exposure, followed by decreases at higher OH concentrations. This difference in organic acid yield trends is consistent with the distribution of carbon-containing species identified by chemical ionization mass spectrometry.

中文翻译：

---

七种单萜连续光氧化产生的 SOA 和气相有机酸

摘要 我们研究了七种单萜异构体（α-蒎烯、β-蒎烯、苎烯、蒎烯、萜品油烯、α-萜品烯和 γ-萜品烯）的连续光氧化产生的二次有机气溶胶 (SOA) 和气相有机酸产率。干燥条件下的流动反应器。萜品油烯的 SOA 产量最高（老化 5.7 天时为 33%），其次是槭烯、β-蒎烯、α-蒎烯、苎烯、γ-松油烯和 α-松油烯。具有环外双键（即紧邻环）的异构体比具有环内双键或具有未连接到环结构的双键的异构体具有更高的 SOA 产率。SOA 产量随着 OH 暴露而增加，突出了在建模研究中使用单一 SOA 产量值的局限性，以及对异构体特定 SOA 参数化的需求。SOA 产量由单一产品模型充分拟合，并且与以前的研究大体一致。SOA 产量随有机气溶胶质量浓度线性增加，这可能是流动反应器中高 OH 负载和短停留时间的结果。甲酸、乙酸、丁酸和甲基丙烯酸（或它们的异构体）的气相产率随着 OH 暴露与 SOA 产率的变化而遵循非常不同的模式，并且与 OH 速率常数的相关性较差。这些观察结果表明，单萜光氧化的高挥发性（断裂）产物在低挥发性（官能化）产物的产生和缩合的不同时间尺度上产生和丢失。所有 OH 暴露的甲酸产率范围为 0.06% 至 9.3%。γ-萜品烯的甲酸产率 (0. 36–3%）随着 OH 暴露单调增加，这与其他单萜异构体不同，其他单萜异构体随着 OH 暴露显示甲酸产率的初始增加，随后在更高的 OH 浓度下降低。这种有机酸产率趋势的差异与化学电离质谱法确定的含碳物质的分布一致。