北京城市大气高含氧有机分子的定量测量 #br#

大气高含氧有机分子是二次有机气溶胶的重要前体物。使用气态硫酸分子作为大气高含氧有机分子的替代 物评估其在硝酸根-大气常压界面化学电离飞行时间质谱离子化过程中的电离效率, 并基于高分辨率差分电迁移率粒 径谱仪串联飞行时间质谱建立了质谱传输效率的矫正方法, 从而建立了大气高含氧有机分子的半定量方法。在此基 础上开展了北京冬季大气高含氧有机分子的外场观测, 识别了约一百一十个大气高含氧有机分子, 表征了它们的浓度 变化趋势和化学组成特征。研究发现羟基自由基在大气高含氧有机分子生成过程中具有重要作用, 而氮氧化合物也 会参与其中。从挥发性分布看, 该地区冬季高含氧有机分子中归于极低挥发性有机化合物 (ELVOC) 的最多, 低挥发性 有机化合物 (LVOC) 次之, 表明该地区大气高含氧有机分子在大气颗粒物上的凝结对二次有机气溶胶的形成具有重要 贡献。

Quantitative Measurement of Highly Oxygenated Organic Molecules in Urban Beijing #br#

Highly oxygenated organic molecules (HOMs) are important precursors for secondary organic aerosols (SOAs). Gaseous sulfuric acid was used as an analogue of HOMs to estimate the ionization efficiency of HOMs in a chemical ionization atmospheric-pressure-interface time-of-flight mass spectrometer (CI-APi-ToF) equipped with a nitrate chemical ionization source, then a mass-dependent transmission correction for HOMs was performed using a high-resolution half-mini differential mobility analyzer (HR-DMA) in tandem of the ToF-MS, and hence a semiquantitative method of atmospheric HOMs was established. Based on the method established, a field campaign was then carried out in Beijing from February to March 2018, during which about 110 HOMs species were identified together with their temporal profiles and elemental composition. The observation indicates that hydroxyl radicals play an important role in the formation of HOMs, whereas nitrogen oxides are also involved. Most of the observed HOMs can be classified as extremely low volatility organic compounds (ELVOCs), and followed by low volatility organic compounds (LVOCs), which implies that condensation of HOMs contributes to the formation of secondary organic aerosol in this particular region.