Droplet Assisted Ionization (DAI) is a relatively new method for online analysis of aerosol droplets that enables measurement of the rate of an aerosol reaction. Here, we used DAI to study the reaction of carbonyl functionalities in secondary organic aerosol (SOA) with Girard's T (GT) reagent, a reaction that can potentially be used to enhance the detection of SOA in online measurements. SOA was produced by α-pinene ozonolysis. Particulate matter was collected on a filter, extracted, and mixed with GT reagent in water. While the reaction hardly proceeded at all in bulk solution, products were readily observed with DAI when the solution was atomized to produce micron-size droplets. Varying the droplet transit time between the atomizer and mass spectrometer allowed the reaction rate constant to be determined, which was found to be 4 orders of magnitude faster than what would be expected from bulk solution kinetics. Decreasing the water content of the droplets, either by heating the capillary inlet to the mass spectrometer or by decreasing the relative humidity of the air surrounding the droplets in the transit line from the atomizer to the mass spectrometer, enhanced product formation. The results suggest that reaction enhancement occurs at the droplet surface, which is consistent with previous reports of reaction acceleration during mass spectrometric analysis, where a bulk solution is analyzed with an ionization method that produces aerosol droplets.

中文翻译：

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通过液滴辅助电离研究有机气溶胶的反应动力学：相对于本体溶液，液滴的反应性增强。

液滴辅助电离（DAI）是一种相对较新的在线分析气溶胶液滴的方法，可以测量气溶胶反应的速率。在这里，我们使用DAI研究了有机有机气溶胶（SOA）中的羰基官能团与吉拉德T（GT）试剂的反应，该反应可以潜在地用于增强在线测量中SOA的检测。SOA是通过α-pine烯臭氧分解产生的。将颗粒物收集在过滤器上，萃取，并与GT试剂在水中混合。尽管几乎没有在本体溶液中进行反应，但是当溶液雾化以产生微米大小的液滴时，很容易用DAI观察到产物。通过改变雾化器和质谱仪之间的液滴通过时间，可以确定反应速率常数，发现它比本体溶液动力学所预期的快4个数量级。通过加热毛细管到质谱仪的入口或通过降低从雾化器到质谱仪的传输线中液滴周围的空气的相对湿度来降低液滴的水含量，可增强产品的形成。结果表明，反应增强发生在液滴表面，这与以前在质谱分析过程中反应加速的报道一致，在质谱分析中，本体溶液是使用产生气溶胶液滴的电离方法进行分析的。通过加热毛细管到质谱仪的入口或通过降低从雾化器到质谱仪的传输线中液滴周围的空气的相对湿度，可以增强产品的形成。结果表明，反应增强发生在液滴表面，这与以前在质谱分析过程中反应加速的报道一致，在质谱分析中，本体溶液是使用产生气溶胶液滴的电离方法进行分析的。通过加热毛细管进入质谱仪的入口或通过降低从雾化器到质谱仪的传输线中液滴周围的空气的相对湿度，可以增强产品的形成。结果表明，反应增强发生在液滴表面，这与以前在质谱分析过程中反应加速的报道一致，在质谱分析中，本体溶液是使用产生气溶胶液滴的电离方法进行分析的。