An aircraft gas chromatograph-mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow
An aircraft gas chromatograph-mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow
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DOI：
10.5194/amt-10-5089-2017
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发表时间：
2017-12-22
影响因子：
3.8
通讯作者：
Williams, Jonathan
中科院分区：
文献类型：
--
作者：
Bourtsoukidis, Efstratios;Helleis, Frank;Williams, Jonathan
挥发性有机化合物（VOCs）对全球空气质量和对流层氧化过程非常重要。除了地面测量外，还可以通过现场空中测量来研究此类物种在运输过程中的化学演变。一般来说，飞机仪表需要比地面系统灵敏、坚固，并以更高的频率采样，同时其结构必须符合严格的机械和电气安全标准。在这里，我们提出了一种新的有机快速鉴定分析系统（索菲亚），这是一种定制的快速气相色谱-质谱（GC-MS）系统，具有2-3 min的时间分辨率和定量大气中卤代烃混合比的能力（例如氯甲烷）、碳氢化合物（例如异戊二烯）、含氧VOC（丙酮、丙醛、丁酮）和芳烃（例如苯、甲苯）的含量从低于ppt到ppb。相对高的时间分辨率是一个新的低温预浓缩单元，快速冷却（+/-6摄氏度秒（-1））的样品富集陷阱到140摄氏度，和一个新的色谱炉设计的快速冷却速率（+/-30摄氏度秒（-1））和随后的热稳定的结果。索菲亚于2015年8月安装在高空和远程研究飞机（HALO）上，用于氧化机制观测（OMO）活动，旨在调查热带对流层上部的亚洲季风污染流出。除了一个全面的仪器表征，我们提出了一个例子季风烟羽穿越飞行作为一个案例研究，以证明仪器的能力。碳氢化合物，卤化碳和氧化VOC数据索菲亚的一氧化碳（CO）和甲烷（CH 4）的混合比进行了比较，用于定义污染羽。通过使用过量（ExMR）和归一化的过量混合比（NEMR）的污染可以归因于两个空气质量的明显不同的起源，确定的后向轨迹分析。这项工作赞同使用索菲亚的飞机操作，并证明了相对较高的频率，多组分测量在大气化学研究的价值。
Volatile organic compounds (VOCs) are important for global air quality and oxidation processes in the troposphere. In addition to ground-based measurements, the chemical evolution of such species during transport can be studied by performing in situ airborne measurements. Generally, aircraft instrumentation needs to be sensitive, robust and sample at higher frequency than ground-based systems while their construction must comply with rigorous mechanical and electrical safety standards. Here, we present a new System for Organic Fast Identification Analysis (SOFIA), which is a custom-built fast gas chromatography-mass spectrometry (GC-MS) system with a time resolution of 2-3 min and the ability to quantify atmospheric mixing ratios of halocarbons (e.g. chloromethanes), hydrocarbons (e.g isoprene), oxygenated VOCs (acetone, propanal, butanone) and aromatics (e.g. benzene, toluene) from sub-ppt to ppb levels. The relatively high time resolution is the result of a novel cryogenic pre-concentration unit which rapidly cools (+/-6 degrees C s(-1)) the sample enrichment traps to 140 degrees C, and a new chromatographic oven designed for rapid cooling rates (+/-30 degrees C s(-1)) and subsequent thermal stabilization. SOFIA was installed in the High Altitude and Long Range Research Aircraft (HALO) for the Oxidation Mechanism Observations (OMO) campaign in August 2015, aimed at investigating the Asian monsoon pollution outflow in the tropical upper troposphere. In addition to a comprehensive instrument characterization we present an example monsoon plume crossing flight as a case study to demonstrate the instrument capability. Hydrocarbon, halocarbon and oxygenated VOC data from SOFIA are compared with mixing ratios of carbon monoxide (CO) and methane (CH4), used to define the pollution plume. By using excess (ExMR) and normalized excess mixing ratios (NEMRs) the pollution could be attributed to two air masses of distinctly different origin, identified by back-trajectory analysis. This work endorses the use of SOFIA for aircraft operation and demonstrates the value of relatively high-frequency, multicomponent measurements in atmospheric chemistry research.