开放光路非相干宽带腔增强吸收光谱技术测量大气NO2

采用蓝色发光二极管(LED)作为非相干宽带腔增强吸收光谱技术(IBBCEAS)系统光源,测量了436～470nm波段内NO2样气的吸收,验证IBBCEAS的高探测灵敏度。通过氮气和氦气两者瑞利散射截面的差异标定了镜片在430～490nm波段内的反射率,并利用纯氧中氧气二聚体(O2-O2)在477nm处的吸收验证了镜片反射率标定的准确性。镜片反射率在461nm处最大且为0.99937,光学腔长度为73.5cm时的最大有效光程为1.17km。当光谱采集时间为20s时,NO2的探测灵敏度(1σ)达到了0.25×10-9。进行了开放光路下环境大气中NO2和O2-O2在454～486nm波段内的吸收测量,结果表明大气中气溶胶等颗粒物的Mie散射消光降低了IBBCEAS仪器的探测灵敏度(1.04×10-9)。大气中O2-O2的测量为IBBCEAS吸收光程的在线标定提供了一种可行的途径。

Open-Path Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for Measurements of Atmospheric NO2

The absorption of NO2 samples in the region of 436~470 nm was measured by incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) with a blue light emitting diode (LED) to demonstrate the performance of IBBCEAS. Mirror reflectivity at 430~490 nm is determined from the changes in transmitted intensity through the cavity due to Rayleigh scattering when the cavity is filled with pure N2 and He, and validated with the help of the absorption at 477 nm of O2-O2 collisional pair in pure oxygen. The maximum mirror reflectivity of 0.99937 is found at 461 nm, which corresponds to an effective path length of about 1.17 km based on a 73.5 cm-long cavity. Detection sensitivity (1σ) of 0.25×10-9 with an acquisition time of 20 s is achieved. The absorptions of NO2 and O2-O2 collisional pair in ambient air are simultaneously measured by IBBCEAS in open-path mode. Measuring results demonstrate that the performance of the IBBCEAS instrument deteriorats due to aerosol extinction. It is a possible solution to realize in situ calibration of absorption light path of IBBCEAS instrument by measuring O2-O2 in atmospheric air.