Abstract Submission - L. Emmenegger - Empa
Advances in infrared spectroscopy for conducted and diffuse emissions.
Infrared spectroscopy is gaining increasing importance in emissions monitoring as a non-invasive and highly compound specific technique. A number of different systems are commercially available and have been certified by MCERTS and TUV. The concepts, advantages and limitations are well illustrated by two distinct techniques: Fourier Transform Infrared Spectroscopy (FTIR) and Quantum Cascade Laser Absorption Spectroscopy. (QCLAS)
An FTIR spectrometer obtains infrared spectra by collecting an interferogram across all infrared frequencies. Typically, this is done at ambient pressure where absorption patterns are such that a spectral resolution of less than 0.5 cm-1 is sufficient for the simultaneous identification and quantification of a wide range of substances. Various calibration schemes as well as retrieval algorithms can be applied. [1-4] Quantum cascade lasers (QCLs) are novel laser sources in the mid infrared (MIR, 3-30 μm) spectral region where most gaseous molecules have their fundamental absorption bands. QCLs are small, reliable, tunable and can be matched to a spectral range of strong ro-vibrational lines of various molecules. The application of QCLs to gas analysis has been demonstrated for many substances, including NH3, CO, CO2, N2O, C2H4, HCHO, NO and NO2. Furthermore, isotopes such as 12CO2 and 13CO2 can be distinguished with very high precision. QCLAS can be used at ambient pressure – for example in open path systems – or at a pressure of a few hPa. [5-7]
Depending on the application, both approaches are adequate, as will be shown by examples for stationary sources, car exhaust and diffuse emissions.
