Measurements of NO concentrations at sub-ppm levels in vehicle exhaust are needed for emissions certification of future ultra-low emission vehicles. We demonstrate a wavelength-modulation, laser-based, NO detection system suitable for this purpose. A quantum cascade distributed feedback laser (QC-DFB) operating continuous wave (cw) at ∼100 K is frequency modulated at f = 10 kHz and locked to the center of a transition at ∼1921 cm−1 in the fundamental band of NO. The demodulated signal at 2 f of the beam passing through the sample cell directly measures the NO concentration. The cell is a multipass Herriott-type with a 100-m path length. Doppler broadening, pressure broadening, and unresolved Λ doubling combine to yield a pressure for optimum sensitivity of 100 torr and a modulation amplitude of ∼600 MHz. A flowing gas system is used to avoid problems with adsorption and desorption of NO from the cell walls. The reduced pressure eliminates interference from other gas species. Detection of NO concentrations in the few parts-per-billion (ppb) range is demonstrated in diluted exhaust-gas bag samples collected in the vehicle certification process.

AbstractThe dispersion of La2O3, which appears to be the best of the known additives for inhibiting sintering of high‐surface‐area aluminas, in substrates consisting largely of γ‐Al2O3 with minor components of transition aluminas (σ‐ and Θ‐Al2O3) is studied by CO chemisorption, AES, Raman spectroscopy, and XRD.