title: Off-axis cavity ringdown spectroscopy: application to atmospheric nitrate radical detection.
abstract: Atmospheric nitrate radicals (NO3) are detected using off-axis cavity ringdown spectroscopy (CRDS) for the first time to our knowledge with a room-temperature continuous-wave (cw) diode laser operating near 662 nm. A prototype instrument was constructed that achieved a 1sigma absorption sensitivity of 5 x 10(-10) cm(-1) Hz(-1/2), corresponding to a 1.4 part per trillion by volume 2sigma detection limit in 4.6 s at 80 degrees C. This sensitivity is a significant improvement over a recent implementation of off-axis cavity-enhanced absorption spectroscopy and comparable to that of the most advanced cw CRDS and pulsed CRDS applications for atmospheric detection of NO3. A comparison of measurements of ambient air in Fairbanks, Alaska, recorded with the off-axis CRDS instrument and a previously characterized conventional cw CRDS instrument showed good agreement (R2 = 0.97).
authors.affiliation: Geophysical Institute and Department of Chemistry and Biochemistry, University of Alaska, Fairbanks, Fairbanks, Alaska 99775, USA.
authors.forename: James D
authors.initials: JD
authors.lastname: Ayers
authors.forename: Randy L
authors.initials: RL
authors.lastname: Apodaca
authors.forename: William R
authors.initials: WR
authors.lastname: Simpson
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Baer
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere / Q000032:analysis*; D004784:Environmental Monitoring / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007834:Lasers; D009566:Nitrates / Q000032:analysis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000295:instrumentation* / Q000379:methods
chemical_list: D000393:Air Pollutants; D009566:Nitrates