非相干宽带腔增强吸收光谱技术应用于实际大气亚硝酸的测量

Incoherent broadband cavity enhanced absorption spectroscopy for measurements of atmospheric HONO

介绍了基于紫外发光二极管光源的非相干宽带腔增强吸收光谱技术,并用于实际大气亚硝酸(HONO)和二氧化氮(NO_2)的同时测量.分析了腔内气体的瑞利散射对测量的影响,测试了紫外发光二极管光源的稳定性,使用氦气和氮气的瑞利散射差异性标定了镜片反射率随波长的变化曲线,在HONO吸收峰(368.2 nm)处镜片反射率约为0.99965.应用Allan方差统计方法确定出测量光谱最佳采集时间为320 s,对应的HONO和NO_2的探测限(1σ)分别为0.22 ppb和0.45 ppb.使用非相干宽带腔增强吸收光谱测量装置对大气HONO和NO_2进行了连续三日的实际观测,将测量得到的HONO浓度变化与差分吸收光谱测量装置的测量结果进行对比,线性相关系数R^2为0.917.

We report the development of an incoherent broadband cavity enhanced absorption spectroscopy（IBBCEAS） based on an ultraviolet light emitting diode（UV-LED）,and the IBBCEAS instrument is used for simultaneously measuring of the atmospheric HONO and NO2.The cavity-enhanced method is characterized by high sensitivity and spatial resolution.The incoherent broadband light is focused into a high-finesse optical cavity,two highly reflecting mirrors form the ends of the cavity,and the light is then trapped between the two highly reflecting mirrors,resulting in long photon residence time and long optical path length.The effects of the Rayleigh scattering of the gases in the cavity and stability of the UV-LED light source were discussed in this paper.The reflectivity of the highly reflecting mirror was calibrated by the difference of Rayleigh scattering of He and N2,and the optimum averaging time of the IBBCEAS instrument was confirmed to be 320 s by the Allan variance analysis.Detection limits（la） of 0.22 ppb for HONO and 0.45 ppb for NO2 were achieved with an optimum acquisition time of 320 s.In order to test the accuracy of measured results by the IBBCEAS instrument,concentrations of HONO and NO2 were recorded during about continuous three days by the IBBCEAS instrument and compared with the results obtained by a different optical absorption spectroscopy（DOAS）instrument.The results of HONO show a linear correction factor（R^2） of 0.917,in a slope of 0.897 with an offset of0.13 ppb;NO2 concentration measured by the IBBCEAS instrument accords well with the result obtained by the DOAS instrument,with a linear correlation of R^2 = 0.937,in a slope of 0.914 with an offset of-0.17 ppb.