基于LIF方法对柴油车尾气羟基总反应性测量（封面文章）

基于激光诱导荧光原理搭建了用于机动车尾气测量的羟基(OH) 自由基总反应性直接测量系统(LP-LIF-k_OH), 并开展了典型柴油车尾气的转鼓测试, 获得了不同排放水平下重型柴油车尾气OH 自由基总反应性的特征。该系统使用中心波长为266 nm的紫外脉冲激光在流动管中光解臭氧产生过量OH 自由基, 使其与采样进入流动管中的活性气体反应发生浓度衰减; 利用中心波长为308 nm 的脉冲激光作为激发光, OH 自由基吸收激发激光能量后释放荧光光子信号, 利用激光诱导荧光技术记录OH 自由基衰减曲线对衰减过程进行测量; 而通过对衰减曲线进行指数拟合, 即可获得采样气的OH 自由基总反应性(k_OH)。在柴油车尾气中的活性有机物闭合测量实验中, 对国三与国五的柴油车尾气进行k_OH 的测量, 发现柴油车尾气k_OH 的值随着国家排放标准的升高而降低, 不同车辆的k_OH 差别较大, 同一车辆冷启动测得的k_OH 值大于热启动测得的k_OH 值。kOH 的主要贡献来自氮氧化物(55%)、一氧化碳(2%) 和一次排放的挥发性有机物(34%)。最后初步建立了一种利用k_OH 估算柴油车尾气碳氢化合物(HC) 排放因子的方法。

Measurement of OH Reactivity of Diesel Vehicles ExhaustBased on LIF Method

A direct measurement system of OH reactivity for vehicle exhaust measurement (LP-LIF-k_OH) was established based on the principle of laser-induced fluorescence in this work, then the rotary drum test on the exhaust of typical diesel vehicles was carried out and the total OH reactivity of heavy diesel vehicles at different emission levels was obtained. In the system, a pulsed UV laser is used to photolyze ozone to generate OH radical in a flow tube, and a pulse laser with a central wavelength of 308 nm is used to excite OH radicals. By using laser induced fluorescence technique, the decay of OH concentration caused by the reaction with the sampled reactive gases in the flow tube was measured and recorded, and the total reactivity of OH (kOH) with the sample gas can be derived by fitting the decay curve with an exponential function. In the closure experiment of the active organic compounds in the diesel vehicle exhaust gas, the measurement of the k_OH of diesel cars in China emission standard III and China emission standard V was carried out. It is found that the value of diesel exhaust k_OH decreases with the increase of China emission standard, and the kOH measured under cold start is greater than that measured under warm start for the same vehicle. The observed k_OH is mainly contributed from NOx (55%), CO (2%), and the primary emission of VOCs (34%). A method of estimating the HC emission factor of diesel vehicles by using k_OH is proposed to show the necessity of reactivity measurement in vehicle emission.