基于LED光源的非相干宽带腔增强吸收光谱技术探测HONO和NO_2

摘要

An application of incoherent broadband cavity enhanced absorption spectroscopy with a near-ultraviolet LED（λ_（peak）≈372 nm and FWHM is 13 nm） to simultaneously detecting HONO and NO_2 is described.The light emitted from the LED is collimated and then coupled into an 70 cm long high finesse cavity formed with two high reflectivity mirrors.The spectra are respectively recorded when the cell is filled with He and then N_2,and the mirror reflectivity is determined from the change in transmitted intensity due to the difference in Rayleigh scattering cross-section between He and N_2.The maximum of mirror reflectivity is 0.99962 at 390 nm in a spectral region of 360-390 nm,and corresponding maximum of light path length is about 1.71 km when NO_2/HONO mixture is measured.The concentrations of HONO and NO_2 are obtained using least-squares fit.Detection sensitivity（1σ） of 0.6 ppbv for HONO and 1.9 ppbv for NO_2 are achieved using an acquisition time of 1000 s.The experimental results demonstrate the possible application of this technology to in situ monitoring the trace gases in the atmosphere.%介绍了基于近紫外发光二极管LED（中心波长约372 nm,半高宽13 nm）光源的非相干宽带腔增强吸收光谱技术,同时用于探测痕量气体HONO和NO_2.LED出射光经准直后耦合进入长度为70 cm,由两块高反射率镜片组成的高精密光学腔内.分别测量了氮气消光谱和氦气消光谱,通过两者瑞利散射截面的差异而引起光谱强度的变化来标定镜片反射率.在360—390 nm反演波段内,镜片反射率在390 nm处最大且为0.99962,对应测量NO_2/HONO混合物时的最大光程约1.71 km,并利用最小二乘拟合反演出了HONO和NO_2的浓度值.当光谱采集时间为1000 s时,HONO和NO_2的探测灵敏度（1σ）分别为0.6 ppbv和1.9 ppbv.实验结果表明,该技术为实现大气痕量气体的高灵敏度在线监测提供了另一种可能的途径.