AGS-PRF: Molecular Level Characterization of Amino Acids in Atmospheric Aerosols

本博士后研究重点是研究大气中的氨基酸及其对大气颗粒氮含量的贡献。它将建立一种表征气相和颗粒相氨基酸的仪器方法。将对最近几次野外活动的样品进行氨基酸含量分析。这一项目将增进对导致氨基酸排放的自然和人为生物活动如何影响地球氮循环的了解。本项目的具体目标是：(1)利用化学标准对目标氨基酸的半挥发性热解吸气溶胶气相色谱/质谱仪（SV-TAG）进行校准，并将其与气相仪、簇化学电离质谱仪（Cluster CIMS）、粒子相仪、电子冲击或真空紫外电离耦合高分辨率飞行时间质谱仪（GCxGC-EI/VUV-HR-TOFMS）进行比较；(2)从SV-TAG数据中识别和量化氨基酸，并过滤之前在亚马逊雨林、美国东南部和室内教室进行的实地活动中收集的样本；(3)确定不同环境大气气溶胶中目标游离氨基酸的分配系数。预测和测量的分配系数之间的巨大差异表明游离氨基酸在颗粒中凝结和反应。这支持了氨基酸在颗粒阶段反应形成稳定、低挥发性化合物的假设，这些化合物有助于在大气颗粒和雾/云滴中观察到过量的氮（即总氮和无机氮量之间的差异）。

This Postdoctoral Research Fellowship is focused on the investigation of amino acids in the atmosphere and their contribution to the nitrogen content of atmospheric particles. It will establish an instrumental method for characterizing amino acids in gas and particle phases. Samples from several recent field campaigns will be analyzed for amino acid content. This project will improve the understanding of how biological activities, both natural and anthropogenic, that lead to the emission of amino acids influence Earth's nitrogen cycle. The specific objectives of the proposed project are to: (1) Calibrate the Semi-Volatile Thermal desorption Aerosol Gas chromatograph/mass spectrometer (SV-TAG) for targeted amino acids by using chemical standards, and compare it to a gas phase instrument, Cluster Chemical Ionization Mass Spectrometer (Cluster CIMS), and a particle phase instrument, two-dimensional GC with electron impact or vacuum UV ionization coupled to a high resolution time-of-flight MS (GCxGC-EI/VUV-HR-TOFMS); (2) Identify and quantify amino acids from SV-TAG data and filter samples collected during previous field campaigns in the Amazon Rainforest, Southeastern United States, and an indoor classroom; and (3) Determine the partitioning coefficients of targeted free amino acids in atmospheric aerosols from various environments. Large discrepancies between predicted and measured partitioning coefficients indicate that free amino acids are condensing and reacting in the particles. This supports the hypothesis that amino acids react in the particle phase to form stable, low volatility compounds that contribute to the observed excess nitrogen (i.e., difference between total nitrogen and inorganic nitrogen amounts) in atmospheric particles and fog/cloud droplets.