稳定态Criegee中间体(SCIs)是大气化学过程重要的活性中间体，其可通过和SO2反应生成气态硫酸进而对大气中新粒子生成(NPF)和云凝结核(CCN)产生影响。由于SCIs+SO2的反应速率常数很难实现直接测定，大气科学界对其上述作用机制依然存在未知。本项目拟首先应用新建的大气光化学烟雾箱对不同类型的SCIs与SO2的反应动力学常数进行测定，并阐明其与SCIs+H2O反应和SCIs光解反应的竞争机制；进而采用实验室模拟和MCM模型相结合的研究手段，通过模型拟合在线观测的大气中活性自由基、气态硫酸、SO2以及各种VOCs关键活性组分的浓度变化，定量研究SCIs的生成和反应机制；最后结合在交通流量最大的市区点位以及BVOCs释放量较大的城郊下风向森林地区等典型区域对NPF的外场观测数据，使用改进后的多相模型RACM/CAPRAM深入解析SCIs对大气硫酸与NPF的贡献。

Stabilized Criegee intermediates (SCIs), produced from the ozonolysis of alkenes, play an important role in atmospheric chemical processes, as they contribute to both new particle formation and the growth of the ultrafine particles to CCN sizes via their reaction with SO2. However, the quantitative effects of the reaction SCIs+SO2 remain uncertain because it has been impossible to make direct measurements of the rate constants. So far, only simplest SCIs such as CH2OO have been investigated recently; experimental studies on SCIs with complicated structure are rarely reported. Air pollution in China is still severe within high concentrations of alkenes and ozone, as SCIs precursors, which may lead to high levels of atmospheric H2SO4 and new particle formation (NPF) in the presence of high concentration SO2. To better understand the SCIs initiated oxidation mechanism of SO2 to H2SO4 in the real atmosphere and further influence on the atmospheric new particle formation and climate, kinetic and mechanistic studies are required. This work will firstly explore the kinetics of SO2 reaction with different type of SCIs, formed from the ozonolysis of ethylene, propene, isoprene and terpenes under real atmospheric conditions in a newly built simulation chamber (20 m3). The contribution of SCIs to atmospheric H2SO4 formation competing with the reaction of SCIs+H2O and photolysis of SCIs will also be assessed through the laboratory experiments. Then, a sophisticated chemical box model based on the Master Chemical Mechanism will be deployed to probe the chemistry occurring in the atmospheric simulation chamber: input the kinetic data obtained and reaction pathways under different relative humidity (RH) conditions to simulate the variations of the reactants and the key products/intermediate products and compare with the observation. Then, field observations will be conducted at both downtown site and suburban area site in North China Plain (NCP) area, Shandong Province, to characterize the atmospheric concentrations of VOCs, H2SO4, SO2, O3, and OH/HO2/RO2 radicals etc. and particle size distribution (specially 0.4-40 nm) and their chemical compositions (especially SO42-). Finally, to evaluate the role of the SCIs in atmospheric sulfate formation (e.g. organic sulfate and/or H2SO4) and further in atmospheric new particle formation under clean and polluted atmospheric environment, the modified SCIs chemical mechanisms with a series of kinetic parameters for different SCIs reactions with SO2 (laboratory results) and its regional concentration (field measurement) will be introduced into a multi-phase chemical box model based on the RACM/CAPRAM mechanism (http://projects.tropos.de/capram/).