Incoherent broad-band cavity-enhanced absorption spectroscopy for simultaneous trace measurements of NO2 and NO3 with a LED source

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NO (x) , SO (x) , CO, and CO2. We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) set-up which uses a LED emitting around 625 nm for the simultaneous detection of NO2 and NO3. The LED light transmitted through a high-finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO2 reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO2 and NO3 concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400 s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2x10(-10) cm(-1), which corresponds to detection limits of 600 pptv for NO2 and 2 pptv for NO3. This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.