基于热解腔衰荡光谱技术对二氧化氮和有机硝酸酯同步测量研究

Simultaneous Measurement of Nitrogen Dioxide and Organic Nitrate Based on Thermal Dissociation Cavity Ring-Down Spectroscopy

基于腔衰荡技术搭建了一套热解双腔式腔衰荡光谱(TD-CRDS)探测系统用于环境大气二氧化氮(NO2)和有机硝酸酯(Organic Nitrate,ON)的快速同步测量。二氧化氮是通过其对406 nm处激光的吸收来直接进行测量的,而有机硝酸酯是通过将其在450℃高温下热解为NO2进行间接测量的,在该温度下,ON的转化效率可达到99%。使用中心波长为406.02 nm的激光器,经NO2高分辨吸收截面与激光光谱卷积获得NO2的有效吸收截面为5.74×10^-19 cm^2·molecule^-1;对加热装置进行稳定性测试,确定最佳流速为1 L/min;NO2腔与ON腔同步测量环境大气中的NO2具有非常好的一致性,相关性系数R2为0.99。经优化,本探测系统的探测限可达2.42×10^9 molecule·cm^-3(标准差为3σ,时间分辨率为1 s)。将TD-CRDS系统与长光程差分吸收光谱(LP-DOAS)测量的NO2进行对比,两者一致性较好,R2为0.93,说明系统测量具有较好的准确性。将该系统应用于外场实验中,获得了NO2和ON的浓度序列。

In this study,a two-channel thermal dissociation cavity ring-down spectroscopy(TD-CRDS)system based on cavity ring-down spectroscopy technology was established for the rapid and simultaneous measurement of ambient nitrogen dioxide(NO2)and organic nitrates(ON).NO2 was directly measured by its absorption at 406 nm,while ON was indirectly measured by the NO2 product of its thermal decomposition at 450℃.The ON conversion efficiency reached 99%at this temperature.The effective absorption cross-section of NO2 was obtained by the convolution of the high-resolution absorption cross-section of NO2 using a laser with a central wavelength of 406.02 nm.The laser spectrum was 5.74×10^-19 cm^2·molecule^-1.A stability test of the heating device revealed an optimal flow rate of 1 L/min.The simultaneous measurement of the ambient NO2 by the NO2 and ON cavities exhibited good consistency,with the correlation coefficient R^2=0.99.After optimization,the detection limit of the system reached up to 2.42×10^9 molecule·cm^-3(standard deviation:3σ;temporal resolution:1 s).Comparing the TD-CRDS system with the long-path differential optical absorption spectroscopy(LP-DOAS)in terms of NO2 measurement,good consistency was obtained(R2=0.93),indicating that the system has high measurement accuracy.The TD-CRDS system was applied to field observation,and the time series of NO2 and ON concentration were obtained.