The accurate and precise mass spectrometric measurement of organic compounds in atmospheric aerosol particles is a challenging task that requires analytical developments and adaptations of existing techniques for the atmospheric application. Here we describe the development and characterization of an atmospheric pressure chemical ionization Orbitrap mass spectrometer (APCI-Orbitrap-MS) for the measurement of organic aerosol in real time. APCI is a well-known ionization technique, featuring minimal fragmentation and matrix dependencies, and allows rapid alternation between the positive and negative ionization mode. As a proof of principle, we report ambient organic aerosol composition in real-time, with alternating ionization, high mass resolution (R = 140 000) and accuracy (<2 ppm). The instrument was calibrated in the negative ion mode using 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) model aerosol. We obtain a detection limit of 1.3 ng/m³. Based on the performed calibration using MBTCA particles, the ambient concentration of MBTCA in the particle phase measured in an urban area in Mainz, Germany, ranged between 10 and 80 ng/m³. For the first time, we apply a nontarget screening approach on real-time data, showing molecular variability between ambient day- and nighttime aerosol composition. The detected compounds were grouped in the night- and daytime and analyzed by ultrahigh-resolution MS (UHRMS) visualization methods. Among several prevalent biogenic secondary organic aerosol (BSOA) markers, 24 organic mononitrates and one organic dinitrate were detected. We further estimate that, on average, organic nitrates contribute to 5% and 14% of the measured particulate organic aerosol at day and night, respectively.

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实时超高分辨率质谱：大气有机气溶胶的常压化学电离轨道质谱

大气气溶胶颗粒中有机化合物的准确，精确的质谱测量是一项艰巨的任务，需要对大气应用中的现有技术进行分析开发和调整。在这里，我们描述了用于实时测量有机气溶胶的大气压化学电离Orbitrap质谱仪（APCI-Orbitrap-MS）的开发和表征。APCI是一种众所周知的电离技术，具有最小的碎片化和基质依赖性，并允许在正电离模式和负电离模式之间快速交替。作为原理上的证明，我们实时报告环境有机气溶胶成分，并具有交替电离，高质量分辨率（R= 140 000）和精度（<2 ppm）。使用3-甲基-1,2,3-丁三羧酸（MBTCA）模型气溶胶以负离子模式校准仪器。我们获得的检出限为1.3 ng / m ³。根据使用MBTCA颗粒进行的校准，在德国美因茨市区测量的颗粒相中MBTCA的环境浓​​度范围为10到80 ng / m ³。首次，我们对实时数据应用了非目标筛选方法，显示了白天和晚上周围气溶胶成分之间的分子变异性。在夜间和白天对检测到的化合物进行分组，并通过超高分辨率质谱（UHRMS）可视化方法进行分析。在几种流行的生物成因二级有机气溶胶（BSOA）标记中，检测到24种有机一硝酸盐和一种有机二硝酸盐。我们进一步估计，平均而言，白天和晚上，有机硝酸盐分别占被测颗粒有机气溶胶的5％和14％。