Synthesis of Carboxylic Acid and Dimer Ester Surrogates to Constrain the Abundance and Distribution of Molecular Products in α-Pinene and β-Pinene Secondary Organic Aerosol.,Environmental Science & Technology

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Synthesis of Carboxylic Acid and Dimer Ester Surrogates to Constrain the Abundance and Distribution of Molecular Products in α-Pinene and β-Pinene Secondary Organic Aerosol.
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2020-08-19 , DOI: 10.1021/acs.est.0c01566
Christopher M Kenseth ₁ , Nicholas J Hafeman ₁ , Yuanlong Huang ₂ , Nathan F Dalleska ₃ , Brian M Stoltz ₁ , John H Seinfeld ₄

Affiliation

Liquid chromatography/negative electrospray ionization mass spectrometry [LC/(−)ESI-MS] is routinely employed to characterize the identity and abundance of molecular products in secondary organic aerosol (SOA) derived from monoterpene oxidation. Due to a lack of authentic standards, however, commercial terpenoic acids (e.g., cis-pinonic acid) are typically used as surrogates to quantify both monomeric and dimeric SOA constituents. Here, we synthesize a series of enantiopure, pinene-derived carboxylic acid and dimer ester homologues. We find that the (−)ESI efficiencies of the dimer esters are 19–36 times higher than that of cis-pinonic acid, demonstrating that the mass contribution of dimers to monoterpene SOA has been significantly overestimated in past studies. Using the measured (−)ESI efficiencies of the carboxylic acids and dimer esters as more representative surrogates, we determine that molecular products measureable by LC/(−)ESI-MS account for only 21.8 ± 2.6% and 18.9 ± 3.2% of the mass of SOA formed from ozonolysis of α-pinene and β-pinene, respectively. The 28–36 identified monomers (C_7–10H_10–18O_3–6) constitute 15.6–20.5% of total SOA mass, whereas only 1.3–3.3% of the SOA mass is attributable to the 46–62 identified dimers (C_15–19H_24–32O_4–11). The distribution of identified α-pinene and β-pinene SOA molecular products is examined as a function of carbon number (n_C), average carbon oxidation state

, and volatility (C*). The observed order-of-magnitude difference in (−)ESI efficiency between monomers and dimers is expected to be broadly applicable to other biogenic and anthropogenic SOA systems analyzed via (−) or (+) LC/ESI-MS under various LC conditions, and demonstrates that the use of unrepresentative surrogates can lead to substantial systematic errors in quantitative LC/ESI-MS analyses of SOA.

中文翻译：

羧酸和二聚酯替代物的合成，以限制α-in烯和β-P烯二次有机气溶胶中分子产物的丰度和分布。

液相色谱/负电喷雾电离质谱法[LC /（-）ESI-MS]通常用于表征源自单萜氧化的二次有机气溶胶（SOA）中分子产物的身份和丰度。但是，由于缺乏可靠的标准，通常使用市售的萜烯酸（例如，顺-羽酸）作为替代品来定量单体和二聚体SOA成分。在这里，我们合成了一系列对映纯，pin烯衍生的羧酸和二聚酯同系物。我们发现，二聚酯的（-）ESI效率是顺式的19-36倍-松酸，表明二聚体对单萜SOA的质量贡献在过去的研究中被高估了。使用测得的羧酸和二聚物酯的（-）ESI效率作为更具有代表性的替代物，我们确定可通过LC /（-）ESI-MS测量的分子产物仅占质量的21.8±2.6％和18.9±3.2％分别由α-pine烯和β-pine烯的臭氧分解形成的SOA。鉴定出的28–36个单体（C _7–10 H _10–18 O _3–6）占SOA总质量的15.6–20.5％，而SOA质量的仅1.3–3.3％归因于46–62鉴定的二聚体（ C _15–19 H _24–32 O _4–11）。检查确定的α-pine烯和β-pine烯SOA分子产物的分布与碳数（n _C），平均碳氧化态

和挥发性（C *）的关系。预计单体和二聚体之间观察到的（-）ESI效率的数量级差异将广泛适用于在各种LC条件下通过（-）或（+）LC / ESI-MS分析的其他生物和人为SOA系统，并证明使用无代表性的替代物可能导致SOA定量LC / ESI-MS分析中的重大系统错误。

更新日期：2020-10-21

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