High sensitivity detection of NO2 employing off-axis integrated cavity output spectroscopy coupled with multiple line integrated spectroscopy

摘要

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 km 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 tunable 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 vs. concentration of NO2, we report an effective sensitivity of detection of 10 ppt for NO2. To the best of our knowledge, this is among the most sensitive levels of detection of NO2 to date. A sensitive sensor for the detection of NO2 will be helpful to monitor the ambient air quality, combustion emissions from the automobiles, power plants, aircraft and for the detection of nitrate based explosives (which are commonly used in improvised explosives (IEDs)). Additionally such a sensor would be valuable for the study of complex chemical reactions that undergo in the atmosphere resulting in the formation of photochemical smog, tropospheric ozone and acid rain.