Atmospheric particles play critical roles in climate. However, significant knowledge gaps remain regarding the vertically resolved organic molecular-level composition of atmospheric particles due to aloft sampling challenges. To address this, we use a tethered balloon system at the Southern Great Plains Observatory and high-resolution mass spectrometry to, respectively, collect and characterize organic molecular formulas (MF) in the ground level and aloft (up to 750 m) samples. We show that organic MF uniquely detected aloft were dominated by organonitrates (139 MF; 54% of all uniquely detected aloft MF). Organonitrates that were uniquely detected aloft featured elevated O/C ratios (0.73 ± 0.23) compared to aloft organonitrates that were commonly observed at the ground level (0.63 ± 0.22). Unique aloft organic molecular composition was positively associated with increased cloud coverage, increased aloft relative humidity (∼40% increase compared to ground level), and decreased vertical wind variance. Furthermore, 29% of extremely low volatility organic compounds in the aloft sample were truly unique to the aloft sample compared to the ground level, emphasizing potential oligomer formation at higher altitudes. Overall, this study highlights the importance of considering vertically resolved organic molecular composition (particularly for organonitrates) and hypothesizes that aqueous phase transformations and vertical wind variance may be key variables affecting the molecular composition of aloft organic aerosol.

中文翻译：

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系留气球系统和高分辨率质谱分析显示，与地面相比，高空有机硝酸盐有所增加


大气颗粒物在气候中起着至关重要的作用。然而，由于高空采样的挑战，在垂直解析大气颗粒的有机分子水平组成方面仍然存在重大知识差距。为了解决这个问题，我们使用南部大平原天文台的系留气球系统和高分辨率质谱仪来分别收集和表征地面和高空（高达 750 m）样本的有机分子式 (MF)。我们表明，在高空独特检测到的有机 MF 以有机硝酸盐为主（139 MF；占所有在高空独特检测到的 MF 的 54%）。与地面常见的高空有机硝酸盐 (0.63 ± 0.22) 相比，在高空独特检测到的有机硝酸盐具有较高的 O/C 比 (0.73 ± 0.23)。独特的高空有机分子组成与云层覆盖率的增加、高空相对湿度的增加（与地面相比增加约 40%）和垂直风方差的减少呈正相关。此外，与地面相比，高空样品中 29% 的极低挥发性有机化合物确实是高空样品所独有的，这强调了在更高海拔地区可能形成低聚物。总的来说，这项研究强调了考虑垂直解析的有机分子组成（特别是有机硝酸盐）的重要性，并假设水相变和垂直风变化可能是影响高空有机气溶胶分子组成的关键变量。