【作者】 赵喆；

【导师】 郝吉明；

【作者基本信息】 清华大学 ， 环境科学与工程， 2008， 博士

【摘要】 二次有机气溶胶（secondary organic aerosol,SOA）由于降低能见度、导致气候变化、危害人体健康等负面效应,日益被关注。本研究以排放量大、生成SOA产率高的天然源VOCs物种α-蒎烯为研究对象,通过室内烟雾箱实验系统研究其经光氧化、臭氧氧化生成SOA的过程。光氧化实验在恒温（303K）、恒湿（40%RH）用黑光灯辐照α-蒎烯与NOx的混合物引发;臭氧氧化在黑光灯关闭的条件下通过注入臭氧或α-蒎烯引发,并以甲醇作为OH自由基清除剂。实验过程中,利用扫描迁移率粒子测定仪（SMPS）联合超细凝聚核粒子计数器（CPC）测量颗粒相的粒径分布,利用气相色谱-离子火焰检测器测量α-蒎烯的消耗,并实时记录NOx,O3等气相物种的浓度变化。在无颗粒物种子的条件下,光氧化及臭氧氧化反应生成SOA的产率都可用Odum双产物模型描述。颗粒物粒径分布曲线表明最初颗粒相的形成可由低挥发性氧化产物的均相成核过程解释,随后的粒径的增长由半挥发性有机物在两相的分配决定。干态弱酸性颗粒物种子硫酸铵存在的条件下,α-蒎烯光氧化生成的SOA的时间提前,并且最终产率显著增加,产率的相对增量ΔY*与颗粒物种子的表面积浓度呈较好的线性关系（R²>0.9）。根据反应路径及产物鉴别结果推断,在无机酸性种子气溶胶的催化作用下,α-蒎烯光氧化的主要气相产物蒎酮醛与存在于颗粒相的化合物发生异相反应,生成低聚物（Oligomer）,使得原本存在于气相中的高分子醛类更多地进入颗粒相,使SOA产率的增加。而对于α-蒎烯臭氧氧化的过程,实验结果表明,干态硫酸铵颗粒物种子的存在对SOA产率无影响,对臭氧氧化生成的SOA分子鉴别的结果表明,可鉴别组分中有很高比例的有机羧酸类物质,这一比例远高于光氧化产物,这些有机酸具有较低的挥发性而极易形成颗粒相,并且不参与异相酸催化反应。利用CHEMKIN软件建立化学反应机理模拟平台,辅助进行机理分析,得到本烟雾箱系统的HONO的释放速率为1.65×10^-5 cm³molecule^-1s^-1。由此提供了一种表征实验与箱式模型联合使用确定烟雾箱系统HONO释放速率的方法。更多还原

【Abstract】 Secondary organic aerosol （SOA） has been an issue of enormous interest in recent years because of the possible impacts of SOA on the earth’s radiative balance linked to climate change, visibility degradation, and health effects. In this study, SOA formation potential ofα-pinene, one of the most abundant and reactively biogenic VOCs, was investigated at Tsinghua Indoor Chamber Facility. The photo-oxidation has been initiated by irradiation ofα-pinene/NOx mixture, and ozonolysis has been initiated by injection of ozone orα-pinene under dark condition. Methanol was also injected as OH radical scavenger for ozonolysis experiments. A Scanning Mobility Particle Sizer system （3936, TSI） and a Condensation Particle Counter （3010, TSI） were used to study the SOA formation and a gas chromatograph （GC） equipped with a DB-5 column and a flame ionization detector （FID） was used to measureα-pinene, and the concentration of NO, NO_x-NO and O₃ were recorded simultaneously.For the experiments without seed aerosol, the SOA yield can be regressed by two-product model, and the particle size distribution imply that the SOA were initially formed by homogenous nucleation of products with lower volatility, and the following growth of particle size was due to the gas/particle partitioning process. For the photo-oxidation, the presence of dry ammonia sulfate seed aerosol increased the SOA yield significantly, and a strong linear relationship （r²=0.96） between SOA yield enhancement （ΔY*） and surface concentration of seed aerosol （PMi,s）has been found, denoting that the PMi,s is the control factor for SOA yield enhancement. And the possible reason for the enhancement is due to acid-catalyzed heterogeneous reactions of pinonaldehyde to form oligomer. For ozonolysis, the SOA yield has not been changed by inorganic seed aerosol, because the products are mainly carboxylic acids, which has much lower saturation vapor pressure and thus easily undergo homogeneous nucleation or gas-particle partitioning to be in the aerosol phase.Box simulation was conducted using CHEMKIN software, mechanism analysis with box simulation denoted that, the HONO off-gassing rate are 1.65×10^-5 cm³molecule^-1s^-1.By using the chamber characterization experiments and one box simulation, a method to evaluate the background HONO formation of smog chamber has been established.更多还原