HR: 0800h
AN: A51C-0070    [Abstracts]
TI: Off-Axis Cavity Ring-Down Spectroscopy and Field Measurements of Dinitrogen Pentoxide at High-Latitudes
AU: * Apodaca, R L
EM: ftrla@uaf.edu
AF: University of Alaska Fairbanks, Geophysical Institute, Department of Chemistry and Biochemistry, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Huff, D M
EM: fsdmh22@uaf.edu
AF: University of Alaska Fairbanks, Geophysical Institute, Department of Chemistry and Biochemistry, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Simpson, W R
EM: ffwrs@uaf.edu
AF: University of Alaska Fairbanks, Geophysical Institute, Department of Chemistry and Biochemistry, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Ayers, J D
EM: ayersj@cortland.edu
AF: SUNY-Cortland, Department of Chemistry, Bowers Hall, Cortland, NY 13045 United States
AU: Baer, D S
EM: d.baer@lgrinc.com
AF: Los Gatos Research, 67 East Evelyn Avenue Suite 3, Mountain View, CA 94041 United States
AB: In the nighttime atmosphere, dinitrogen pentoxide (N₂O₅) plays a major role in the fate of nitrogen oxides. Dinitrogen pentoxide is formed by reaction of NO₂ with ozone to form NO₃, which then combines with another NO₂ molecule. Subsequently, N₂O₅ can undergo heterogeneous hydrolysis forming nitric acid. The deposition of nitric acid results in removal of nitrogen oxides from the atmosphere and is of growing interest as to the impact on the affected ecosystem. Cold temperatures and long nights favor this dark NO_x oxidation pathway during high-latitude winter, spring, and fall. Recent technical advances have allowed in-situ NO₃ and N₂O₅ detection. Existing NO₃ and N₂O₅ detectors often possess features making them difficult to deploy and operate in field studies. In this work we describe a new technique, off-axis cavity ring-down spectroscopy (oa-CRDS), with features that are favorable for field operation. We also demonstrate the first application of oa-CRDS to the measurement of N₂O₅ from ambient air. Off-axis cavity ring-down spectroscopy employs off-axis coupling of light into the cavity, eliminating the rigorous spatial and spectral optical alignment required with traditional CRDS. As such, oa-CRDS is virtually insensitive to vibration and temperature fluctuations, features that are highly desirable in field instrumentation. High sensitivity and resistance to baseline drift is preserved in the oa-CRDS method by maintaining temporal-domain measurements, a feature lost with intensity-domain-based instrumentation. High data collection rates are another feature of this system, with the ability to sample at 500 Hz or greater, limited only by the ring-down time of the cavity. An oa-CRDS field instrument was developed using a small, inexpensive, technical grade, continuous-wave diode laser. The field instrument is housed in a light weight, portable, weatherproof case, containing all of the optical and electronic components. The oa-CRDS instrument was compared to a previously characterized continuous-wave cavity ring-down spectroscopy-based instrument using measurements of ambient air in Fairbanks, AK. We observed very good agreement (R² = 0.97) between measurements made by the two systems. Absorption sensitivity and detection limits for the oa-CRDS system compare favorably with more traditional CRDS systems and are discussed. Measurements from the oa-CRDS instrument are reported and discussed for subarctic pollution in the Fairbanks, AK airshed.
DE: 4251 Marine pollution (0345, 0478)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005