乙二醛/硫酸铵水相形成二次有机气溶胶机理研究

Secondary organic aerosol(SOA) is the major species in the atmospheric particles and has an Important impact on the atmospheric environment, climate and human health. It is now evident that aqueous-phase processing can be a significant formation and aging pathway of secondary organic aerosol In recent years, the formation of aqueous SOA has been becoming a research hotspot. Aqueous-phase oxidation can convert water-soluble volatile organic compounds (VOCs) into highly oxygenated, less volatile compounds that can contribute to SOA mass upon water evaporation. Inclusion of this SOA formation mechanism may improve agreement between field observations and traditional models, in which SOA formation is governed by the traditional thermodynamic partitioning of gas-phase oxidation products alone. However, due to its complicated nature, many aspects of aqueous-phase processing and its contribution to the SOA budget are still not fully understood..Glyoxal is produced by a wide variety of biogenic and anthropogenic VOCs. In addition to acting as a tracer for SOA formation, glyoxal has been suggested as a direct contributor to SOA. In this study we aim to investigate the processes contributing to overall GL uptake as well as which of these processes are effectively reversible, meaning reversible over aerosol lifetimes. These questions are important for evaluating applicability of laboratory studies to ambient conditions and net SOA yields from GL..Based on the laboratory mimic reactors (smog chamber and flow tube), reactive uptake of glyoxal onto aqueous ammonium sulfate seed aerosol under dark condition will be studied in this work by taking the full advantage of "soft" ionization synchrotron radiation mass spectrometer and aerosol time-of-flight mass spectrometer. In this study we aim to investigate the processes contributing to overall glyoxal uptake as well as which of these processes are effectively reversible, and further quantification of SOA yields as a function of conditions such as relative humidity, gas phase glyoxal mixing ratio, seed aerosol acidity. .Through the serial on-line quantitative and qualitative investigation, the mechanism of the reaction of glyoxal onto aqueous ammonium sulfate seed aerosol will be deeply understand, which is meaningful to the estimate of the effect of aqueous-phase processing on SOA formation..It is expected that this research will contribute to evaluation the effect of aqueous-phase processes contributing to SOA, as well as to reduce of the pollution and the control of the regional haze in China and the national policy making for environment protection.

二次有机气溶胶（SOA）对环境、气候、人类健康有重要影响。近年来的研究表明，水相过程可产生SOA，甚至与传统气相过程对SOA的贡献相当，因而成为研究热点。水溶性有机气体被云、雾及水相气溶胶吸收发生反应，生成低挥发性物质留在颗粒相中生成SOA。由于大气环境的复杂性，目前水相SOA的形成机理还不清楚，需要进一步深入研究。.本项目将基于同步辐射真空紫外单光子电离技术和在线单颗粒质谱技术并综合利用多种谱学手段对实验室模拟反应器中乙二醛/硫酸铵体系的水相反应过程及机理进行研究。重点考察无光照条件下，样品浓度、湿度、酸性等参数对反应的影响。.大气中乙二醛含量很大且有较高的亨利系数，能够通过气液分配转移到水相中，对水相 SOA 的形成有重要贡献，硫酸铵气溶胶是大气中分布最为广泛的吸湿性颗粒物。对该模型体系的研究ji将加深对水相SOA形成机制的理解，对准确评估水相SOA贡献及夜间大气化学都具有重要意义。

研究表明，在某些地区，由水相反应过程生成的水相二次有机气溶胶（aqSOA）的贡献与传统气相过程生成的SOA相当。硫酸铵气溶胶是大气中分布极为广泛的吸湿性颗粒物，乙二醛在大气中分布广泛，具有较高的亨利系数，能够通过气-液分配转移到水相中。对硫酸铵/乙二醛体系水相反应进行深入研究对评估aqSOA贡献，完善SOA形成机制具有重要的作用。.本项目首先综合运用气溶胶飞行时间质谱仪(ATOFMS)、基于同步辐射光源的热解吸/真空紫外飞行时间光电离气溶胶质谱装置(TD-VUV-TOF-PIAMS)、高效液相色谱-电喷雾-离子阱质谱联用(HPLC-ESI-MS)技术，对7种咪唑类物质(咪唑、咪唑-2-甲醛、2-甲基咪唑、4-甲基咪唑、1-乙基咪唑、2-乙基咪唑、1-正丁基咪唑)及硫酸铵-乙二醛水相反应产物进行研究。通过建立咪唑类物质的质谱指纹信息，得到了每种咪唑类物质的光电离效率曲线和电离势信息，并用此信息来鉴定乙二醛/硫酸铵水相反应产物中的咪唑类物质种类。利用同步辐射大科学装置，以在线质谱手段首次在aqSOA中探测到咪唑、咪唑-2-甲醛；通过HPLC-ESI-MS实验识别出aqSOA中含有联咪唑、水合咪唑-2-甲醛、被乙二醛取代的水合咪唑-2-甲醛以及一些大分子聚合物，进一步验证、补充和完善了水相过程及反应机理。.使用液体波导毛细管(LWCC)、总有机碳分析仪(TOC)测量了咪唑类物质及硫酸铵/乙二醛水溶液的吸收光谱。建立了咪唑类物质的光谱指纹，实现了光强的定量检测。利用该指纹谱识别了硫酸铵-乙二醛水相产物中所包含的咪唑类物质。.搭建了吸湿性串联迁移率粒径谱仪对乙二醛/硫酸铵aqSOA的吸湿增长特性进行了研究。发现aqSOA的吸湿增长曲线与硫酸铵有显著不同。随着乙二醛浓度的增加，潮解相对湿度前移，当乙二醛浓度与硫酸铵相当时，aqSOA潮解点消失，粒径随湿度增加连续增长。.利用光化学烟雾箱模拟了乙二醛/硫酸铵aqSOA在大气中的光解老化过程。研究发现在中低相对湿度时光照会造成aqSOA粒径显著减小。.本项目所获结果对于准确评估水相SOA贡献具有极其重要的意义。

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