A two‐photon laser‐induced fluorescence field instrument for ground‐based and airborne measurements of atmospheric NO

Authors:
  • JBJ. D. Bradshaw
    J. D. Bradshaw
  • MRM. O. Rodgers
    M. O. Rodgers
  • SSS. T. Sandholm
    S. T. Sandholm
  • SKS. KeSheng
    S. KeSheng
  • DDD. D. Davis
    D. D. Davis
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Abstract
This paper reports on a new two‐photon laser‐induced fluorescence (TP‐LIF) sensor capable of making routine measurements at the few parts per trillion volume level. This direct spectroscopic detection method has been demonstrated to be a reliable instrument while performing both on the ground and in the air. As currently designed it is unique in being “signal” rather than “signal‐to‐noise” limited. The latter characteristic enables the TP‐LIF sensor to make atmospheric measurements of NO under environmental conditions that might normally be considered unsuitable for a laser technique. These include clouds, rain, and, in general, high‐atmospheric‐aerosol loading conditions. Of special interest is the insensitivity of the TP‐LIF NO instrument to changes in pressure while operating in the troposphere. This characteristic has enabled this sensor to be used to record real‐time altitude profiles of NO. Future improvements should make possible two measurement opportunities: (1) NO flux measurements via the airborne eddy‐correlation method and (2) nitrogen isotopic distribution measurements (e.g., N15O16 versus N14O16) as a means of identifying specific NOx, sources.

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