International Collaboration in Chemistry: Chemical Nature and Origins of Atmospheric Brown Carbon Aerosol

美国国家科学基金会化学分部的环境化学科学项目支持Judith C. Chow、Lung-Wen Anton Chen和Douglas H Lowenthal教授提交的国际化学合作（ICC）提案。他们试图通过美国和德国研究人员之间的国际合作，更好地了解棕色碳（BrC）的化学性质，并解决有关BrC来源的假设。棕色碳是大气气溶胶中一类特殊的吸光有机物，对地球的辐射平衡有直接和间接的影响。BrC被认为来源于生物质燃烧羽流和光化学形成的二次有机气溶胶中有机化合物的氧化和/或寡聚化。本项目通过完善和应用一种新的测量方法，提高了对BrC化学性质及其来源的认识。该方法结合了源和环境气溶胶样品的热/光学特性，以及使用软电离和硬电离方法对释放气体进行质谱检测。沙漠研究所（DRI）开发的热/光学碳分析仪与德国罗斯托克大学（UR）开发的光电离飞行时间质谱仪（TOF-MS）一起增强了多元素和光谱检测能力。BrC和黑碳（BC）可以通过光谱光吸收测量来量化，并在不同温度下形成的气体中使用分子模式/源特征进行研究。BrC与有机基团的关系，特别是在高温馏分（可能来自高分子量多羧酸）中观察到的羧基，将被研究。将建立一个主要气溶胶类型的二维质谱热图库，包括实验室生成的模型气溶胶，真实世界的新鲜和老化源排放，以及来自城市和非城市环境的源混合物。当与先进的化学计量分析相结合时，该库将促进源归因。导出的剖面可以应用于全球排放清单，该清单目前仅包含用于模拟全球辐射平衡的BC分量。本研究的广泛影响包括：1)促进了美国和德国大学之间的学术交流；2)在两国培养博士生，加强环保人才队伍；3)内华达州高中和社区大学环境科学教师的研究经历；4)通过改进BC和BrC的区域和全球排放估算，提高其作为短期气候强迫因子的模型效应的能力。

The Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation supports the research Professors Judith C. Chow, Lung-Wen Anton Chen and Douglas H Lowenthal who submitted an International Collaboration in Chemistry (ICC) proposal. They seek to better understand the chemical nature of brown carbon (BrC) and address the hypotheses regarding BrC sources through an international collaboration between U.S. and German researchers. Brown carbon is a special class of light-absorbing organic matter in atmospheric aerosols that has direct and indirect effects on the Earth's radiation balance. BrC is believed to derive from the oxidation and/or oligomerization of organic compounds in biomass burning plumes and photochemically-formed secondary organic aerosol. This project improves understanding of the BrC's chemical nature and its sources by perfecting and applying a new measurement method. This method combines thermal/optical characterization of source and ambient aerosol samples with mass spectroscopic detection of the evolved gases using soft and hard ionization methods. A thermal/optical carbon analyzer developed at the Desert Research Institute (DRI) is enhanced for multi-elemental and spectral detection with photo-ionization time-of-flight mass spectrometers (TOF-MS) developed at the University of Rostock (UR) in Germany. BrC and black carbon (BC) can then be quantified from spectral light absorption measurements and studied with molecular patterns/source signatures in gases evolved at different temperatures. The relationship of BrC to organic groups, particularly carboxyls observed in higher temperature fractions (likely originating from high-MW polycarboxylic acids), will be investigated. A library consisting of two-dimensional MS-thermograms for major aerosol types, including laboratory-generated model aerosols, real-world fresh and aged source emissions, and source mixtures from urban and non-urban environments will be established. This library will facilitate source attribution when coupled with advanced chemometric analyses. The derived profiles can be applied to global emission inventories that currently contain only a BC component for modeling the global radiation balance.Broader impacts of this study include: 1) increasing academic exchanges between U.S. and German universities; 2) training doctoral candidates in both countries to enhance the environmental workforce; 3) research experiences for environmental science instructors from Nevada high schools and community colleges; and 4) improving the ability to better model effects of BC and BrC as short-term climate forcers by improving their regional and global emission estimates.