Lin Peng, Fleming Lauren T, Nizkorodov Sergey A, Laskin Julia, Laskin Alexander
Department of Chemistry , Purdue University , West Lafayette , Indiana 47907-2084 , United States.
Department of Chemistry , University of California , Irvine , California 92697-2025 , United States.
Anal Chem. 2018 Nov 6;90(21):12493-12502. doi: 10.1021/acs.analchem.8b02177. Epub 2018 Oct 18.
Light-absorbing components of atmospheric organic aerosols, which are collectively termed "brown carbon" (BrC), are ubiquitous in the atmosphere. They affect absorption of solar radiation by aerosols in the atmosphere and human health as some of them have been identified as potential toxins. Understanding the sources, formation, atmospheric evolution, and environmental effects of BrC requires molecular identification and characterization of light-absorption properties of BrC chromophores. Identification of BrC components is challenging due to the complexity of atmospheric aerosols. In this study, we employ two complementary ionization techniques, atmospheric pressure photo ionization (APPI) and electrospray ionization (ESI), to obtain broad coverage of both polar and nonpolar BrC components using high-resolution mass spectrometry (HRMS). These techniques are combined with chromatographic separation of BrC compounds with high performance liquid chromatography (HPLC), characterization of their light absorption with a photodiode array (PDA) detector, and chemical composition with HRMS. We demonstrate that this approach enables more comprehensive characterization of BrC in biomass burning organic aerosols (BBOAs) emitted from test burns of sage brush biofuel. In particular, we found that nonpolar BrC chromophores such as PAHs are only detected using positive mode APPI. Meanwhile, negative mode ESI results in detection of polar compounds such as nitroaromatics, aromatic acids, and phenols. For the BrC material examined in this study, over 40% of the solvent-extractable BrC light absorption is attributed to water insoluble, nonpolar to semipolar compounds such as PAHs and their derivatives, which require APPI for their identification. In contrast, the polar, water-soluble BrC compounds, which are detected in ESI, account for less than 30% of light absorption by BrC.
大气有机气溶胶的光吸收成分统称为“棕碳”（BrC），在大气中广泛存在。它们会影响大气中气溶胶对太阳辐射的吸收以及人类健康，因为其中一些已被确定为潜在毒素。了解BrC的来源、形成、大气演变和环境影响需要对BrC发色团的光吸收特性进行分子鉴定和表征。由于大气气溶胶的复杂性，鉴定BrC成分具有挑战性。在本研究中，我们采用两种互补的电离技术，大气压光电离（APPI）和电喷雾电离（ESI），利用高分辨率质谱（HRMS）获得极性和非极性BrC成分的广泛覆盖。这些技术与高效液相色谱（HPLC）对BrC化合物的色谱分离、用光电二极管阵列（PDA）检测器对其光吸收的表征以及用HRMS对化学成分的分析相结合。我们证明，这种方法能够更全面地表征鼠尾草生物燃料试验燃烧排放的生物质燃烧有机气溶胶（BBOA）中的BrC。特别是，我们发现只有使用正模式APPI才能检测到多环芳烃等非极性BrC发色团。同时，负模式ESI可检测到硝基芳烃、芳香酸和酚类等极性化合物。对于本研究中检测的BrC材料，超过40%的可溶剂萃取BrC光吸收归因于水不溶性、非极性至半极性化合物，如多环芳烃及其衍生物，它们的鉴定需要APPI。相比之下，在ESI中检测到的极性、水溶性BrC化合物占BrC光吸收的不到30%。
