Nighttime Nitrogen Oxides
The nighttime nitrogen oxides, NO3 and N2O5, are reactive species that drive atmospheric chemical transformations in the dark. The nitrate radical, NO3, has strong visible absorption bands near 662 nm. The combination of cavity ring down spectroscopy (CRDS) at this wavelength with chemical titration via NO provides a sensitive and specific in-situ measurement of this compound, with sensitivity to 0.2 part per trillion by volume (pptv) in a 1-second average. Thermal conversion of dinitrogen pentoxide, N2O5, in a separate channel allows for its detection with similar sensitivity.
The NOAA six channel CRDS instrument measures NO3 and N2O5together with NO, NO2, NO y and O3. It has been deployed on aircraft, ships, tall towers and at ground sites around the world. A separate two-channel instrument the measures only NO3and N2O5has been a versatile instrument for ground-based measurements and laboratory studies, also in a number of locations worldwide.
References
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