Comprehensive identification of aerosol sources and their constituent organic compounds requires aerosol-phase molecular-level characterization with a high time resolution. While real-time chemical characterization of aerosols is becoming increasingly common, information about functionalization and structure is typically obtained from offline methods. This study presents a method for determining the presence of carboxylic acid functional groups in real time using extractive electrospray ionization mass spectrometry based on measurements of [M – H + 2Na]⁺ adducts. The method is validated and characterized using standard compounds. A proof-of-concept application to α-pinene secondary organic aerosol (SOA) shows the ability to identify carboxylic acids even in complex mixtures. The real-time capability of the method allows for the observation of the production of carboxylic acids, likely formed in the particle phase on short time scales (<120 min). Our research explains previous findings of carboxylic acids being a significant component of SOA and a quick decrease in peroxide functionalization following SOA formation. We show that the formation of these acids is commensurate with the increase of dimers in the particle phase. Our results imply that SOA is in constant evolution through condensed-phase processes, which lower the volatility of the aerosol components and increase the available condensed mass for SOA growth and, therefore, aerosol mass loading in the atmosphere. Further work could aim to quantify the effect of particle-phase acid formation on the aerosol volatility distributions.

中文翻译：

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使用萃取电喷雾电离质谱法实时鉴定气溶胶相羧酸的产生


气溶胶来源及其有机化合物的全面识别需要具有高时间分辨率的气溶胶相分子级表征。虽然气溶胶的实时化学表征变得越来越普遍，但有关功能化和结构的信息通常是通过离线方法获得的。本研究提出了一种基于 [M – H + 2Na] ⁺ 加合物测量的提取电喷雾电离质谱法实时确定羧酸官能团存在的方法。该方法使用标准化合物进行验证和表征。对 α-蒎烯二次有机气溶胶 (SOA) 的概念验证应用表明，即使在复杂的混合物中也能识别羧酸。该方法的实时能力允许观察可能在短时间内（<120 分钟）在颗粒相中形成的羧酸的产生。我们的研究解释了先前的发现，即羧酸是 SOA 的重要组成部分，以及 SOA 形成后过氧化物官能化的快速减少。我们表明这些酸的形成与颗粒相中二聚体的增加相称。我们的结果表明，SOA 通过凝相过程不断演化，这降低了气溶胶成分的挥发性，并增加了 SOA 生长的可用凝结质量，从而增加了大气中的气溶胶质量负载。进一步的工作旨在量化颗粒相酸形成对气溶胶挥发性分布的影响。