title: Extremely sensitive detection of NO₂ employing off-axis integrated cavity output spectroscopy coupled with multiple-line integrated absorption spectroscopy.
abstract: We report on the development of a new sensor for NO₂ with ultrahigh sensitivity of detection. This has been accomplished by combining off-axis integrated cavity output spectroscopy (OA-ICOS) (which can provide large path lengths of the order of several kilometers in a small volume cell) with multiple-line integrated absorption spectroscopy (MLIAS) (where we integrate the absorption spectra over a large number of rotational-vibrational transitions of the molecular species to further improve the sensitivity). Employing an external cavity quantum cascade laser operating in the 1601-1670 cm⁻¹ range and a high-finesse optical cavity, the absorption spectra of NO₂ over 100 transitions in the R band have been recorded. From the observed linear relationship between the integrated absorption versus concentration of NO₂ and the standard deviation of the integrated absorption signal, we report an effective sensitivity of detection of approximately 28 ppt (parts in 10¹²) for NO₂ To the best of our knowledge, this is among the most sensitive levels of detection of NO₂ to date.
authors.affiliation: Department of Physics, Adelphi University, Garden City, New York 11530, USA. Rao@adelphi.edu
authors.forename: Gottipaty N
authors.initials: GN
authors.lastname: Rao
authors.forename: Andreas
authors.initials: A
authors.lastname: Karpf
mesh_terms: D000042:Absorption; D003201:Computers; D004784:Environmental Monitoring / Q000379:methods; D004867:Equipment Design; D005740:Gases / Q000032:analysis; D007834:Lasers; D009585:Nitrogen Dioxide / Q000737:chemistry*; D055095:Optics and Photonics; D010777:Photochemistry / Q000379:methods; D010825:Physics / Q000379:methods; D015203:Reproducibility of Results; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D005740:Gases; D009585:Nitrogen Dioxide