Deep-UV Broadband Cavity-Enhanced Absorption Spectroscopy: application to sensitive real-time detection of the aromatic pollutants Benzene, Toluene, and Xylene (BTX)

Benzene, toluene and xylene (BTX) are serious air pollutants emitted by the chemical industry. Real-time monitoring of these air pollutants would be a valuable tool to regulate emissions of these compounds and reduce the harm they cause to human health. Here we demonstrate the first detection of BTX using Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS). The instrument was operated in the deep-ultraviolet spectral region between 252 and 286 nm, where aromatic compounds have intense  π→π*  absorption bands. The mirror reflectivity was calibrated by two methods and exceeded 99.63% at 266 nm. At an integration time of 60 s, the 1σ measurement sensitivity was estimated to be 1.4 ppbv (1σ) for benzene, 8.7 ppbv (1σ) for toluene, 7.3 ppbv (1σ) for m-xylene and 3.0 ppbv (1σ) for p-xylene, respectively. The absorption cross-sections of BTX were measured in this work with an uncertainty of 10% at a resolution of 0.74 nm and were in good agreement with earlier studies, after accounting for differences in spectral resolution. To demonstrate the ability of the instrument to quantify complex mixtures, the concentrations of m-xylene and p-xylene were retrieved under five different mixing ratios. The IBBCEAS approach allows real time, in situ measurements with high selectivity, and may be valuable in applications not suited to long-path approaches like DOAS. Instrumental improvements and strategies for different atmospheric and analytical applications are discussed.