非相干宽带腔增强吸收光谱技术应用于大气中HONO和NO2的实时探测

Detection of Atmospheric HONO and NO_2 by Incoherent Broadband Cavity Enhanced Spectroscopy

介绍了基于紫外LED光源的非相干宽带腔增强吸收光谱装置,并将其应用于实际大气中的HONO和NO2浓度的探测。中心波长为365nm的UV-LED出射光被耦合到~1.76m长,由两片高反射率镜片组成的光学谐振腔内,透过腔的光由便携式CCD光谱仪接收。高反射率镜片的反射率由NO2和O2-O2的吸收谱来校正,在353~376nm的测量范围内,最高反射率为0.999 17。在120s的采集时间内,HONO和NO2的探测极限（1σ）分别为0.6和1.8ppbv。将该装置测量的连续56h大气中NO2浓度的变化与配备蓝光转换器的NOx分析仪测量的结果进行比较,线性相关系数R2=0.89,斜率为1.09,截距为3.45。基于该装置探测了实验室大气中的HONO和NO2昼夜浓度变化,24h内的HONO浓度在0~5.3ppbv之间波动,平均浓度为1.8ppbv,NO2浓度变化范围为5~51ppbv,平均浓度为21.9ppbv。

We report on the development of an optical instrument based on LED-IBBCEAS for simultaneous measurements of nitrous acid（HONO）and nitrogen dioxide（NO2）in ambient air.The light emitting from the LED centered at 365 nm was directly focused into the cavity formed with two high reflectivity mirrors,separated by a distance of 1.76 m.The light output of the cavity was received with a portable spectrometer.The mirror reflectivity was calibrated by absorption spectra of NO2 and O2-O2.In the spectral range of 353~376nm,the maximum mirror reflectivity was found to be 0.999 17.Detection limits（1σ）of 0.6ppbv for HONO and 1.8ppbv for NO2 were achieved with an acquisition time of 120 s.In order to test the accuracy of measured results by present setup,concentrations of NO2 were recorded during continuous 56 hours and compared with data from a NOX analyzer equipped with a blue light converter.The least-square fit lines give gradients of 1.09 and respective intercepts of 3.45,with a linear correction factor of 0.89.The concentrations of HONO and NO2 in indoor air were monitored,the concentrations of HONO varied from near 0to 5.3ppbv in 24 hours,the averaged concentration was 1.8ppbv,and the concentrations of NO2 varied from 5to 51 ppbv at the same time,the averaged concentration was 21.9ppbv.