Cavity ring down spectroscopy (CRDS) is a high sensitivity absorption technique that exploits an optical cavity, in this case, two high reflectivity mirrors aligned parallel to one another, to achieve optical paths up to 100 km in a 50 - 100 cm听cell. 听Diode lasers are readily available at 405 nm, near the maximum in the absorption spectrum of nitrogen dioxide,听NO2, enabling measurement with a precision to 20 parts per trillion by volume (pptv) at 1 second time resolution with an accuracy better than 5%. 听Quantitative inlet conversions provide simultaneous measurements of nitric oxide (NO), ozone (O3) and total reactive nitrogen (NOy).
The Nitrogen Oxide Cavity Ring Down Spectrometer (NOxCaRD) is a four-channel instrument for NO, NO2, NOy, and O3. 听It is well-suited for light aircraft and mobile laboratories and has participated in the recent FAST-LVOS and听听field studies, among others.
References
Brown, S.S., H.J. An, M. Lee, J.H. Park, S.D. Lee, D.L. Fibiger, E.E. McDuffie, W.P. Dub茅, N.L. Wagner, and K.E. Min, Cavity Enhanced Spectroscopy for Measurement of Nitrogen Oxides in the Anthropocene: Results from the Seoul Tower during MAPS 2015. Faraday Discussions, 2017. 200: p. 529-557.听
Wild, R.J., P.M. Edwards, W.P. Dub茅, K. Baumann, E.S. Edgerton, P.K. Quinn, J.M. Roberts, A.W. Rollins, P.R. Veres, C. Warneke, E.J. Williams, B. Yuan, and S.S. Brown, A Measurement of Total Reactive Nitrogen, NOy, together with NO2, NO and O3 via Cavity Ring-Down Spectroscopy. Environ. Sci. Technol., 2014. 48: p. 9609-9615.听听
Washenfelder, R.A., W.P. Dub茅, N.L. Wagner, and S.S. Brown, Measurement of atmospheric ozone by cavity ring-down spectroscopy. Environ. Sci. Technol., 2011. 45: p. 2938-2944.听
Fuchs, H., W.P. Dub茅, B.M. Lerner, N.L. Wagner, E.J. Williams, and S.S. Brown, A sensitive and versatile detector for atmospheric NO2 and NOx based on blue diode laser cavity ring-down spectroscopy. Environ. Sci. Technol., 2009. 43: p. 7831-7836.听听