The nighttime nitrogen oxides, NO3听and N2O5, are reactive species that drive atmospheric chemical transformations in the dark. 听The nitrate radical, NO3, has strong visible absorption bands near 662 nm. 听The combination of cavity ring down spectroscopy (CRDS) at this wavelength with chemical titration via NO provides a sensitive and specific听颈苍-蝉颈迟耻听measurement of this compound, with sensitivity to 0.2 part per trillion by volume (pptv) in a 1-second average. 听Thermal conversion of dinitrogen pentoxide, N2O5, in a separate channel allows for its detection with similar sensitivity.
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The NOAA six听channel CRDS instrument measures NO3听and N2O5together with NO, NO2, NO y and O3. 听It has been deployed on aircraft, ships, tall towers and at ground sites听around the world. 听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.
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References
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Brown, S.S., H. Stark, S.J. Ciciora, and A.R. Ravishankara, In-situ measurement of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy. Geophys. Res. Lett., 2001. 28(17): p. 3227-3230.听听