title: Real-time monitoring of benzene, toluene, and p-xylene in a photoreaction chamber with a tunable mid-infrared laser and ultraviolet differential optical absorption spectroscopy.
abstract: We describe the implementation of a mid-infrared laser-based trace gas sensor with a photoreaction chamber, used for reproducing chemical transformations of benzene, toluene, and p-xylene (BTX) gases that may occur in the atmosphere. The system performance was assessed in the presence of photoreaction products including aerosol particles. A mid-infrared external cavity quantum cascade laser (EC-QCL)-tunable from 9.41-9.88 μm (1012-1063 cm(-1))-was used to monitor gas phase concentrations of BTX simultaneously and in real time during chemical processing of these compounds with hydroxyl radicals in a photoreaction chamber. Results are compared to concurrent measurements using ultraviolet differential optical absorption spectroscopy (UV DOAS). The EC-QCL based system provides quantitation limits of approximately 200, 200, and 600 parts in 10(9) (ppb) for benzene, toluene, and p-xylene, respectively, which represents a significant improvement over our previous work with this laser system. Correspondingly, we observe the best agreement between the EC-QCL measurements and the UV DOAS measurements with benzene, followed by toluene, then p-xylene. Although BTX gas-detection limits are not as low for the EC-QCL system as for UV DOAS, an unidentified by-product of the photoreactions was observed with the EC-QCL, but not with the UV DOAS system.
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada. mparsons@ualberta.ca
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Parsons
authors.forename: Ihor
authors.initials: I
authors.lastname: Sydoryk
authors.forename: Alan
authors.initials: A
authors.lastname: Lim
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: McIntyre
authors.forename: John
authors.initials: J
authors.lastname: Tulip
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jäger
authors.forename: Karen
authors.initials: K
authors.lastname: McDonald
mesh_terms: D001272:Atmosphere / Q000032:analysis*; D001554:Benzene / Q000032:analysis* / Q000528:radiation effects; D003199:Computer Systems; D004784:Environmental Monitoring / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007259:Infrared Rays; D007834:Lasers; D010777:Photochemistry / Q000295:instrumentation; D013057:Spectrum Analysis / Q000295:instrumentation*; D014050:Toluene / Q000032:analysis* / Q000528:radiation effects; D014992:Xylenes / Q000032:analysis* / Q000528:radiation effects
chemical_list: D014992:Xylenes; D014050:Toluene; D001554:Benzene