Concentrations of H2CO in the part-per-billion by volume (ppbv) range are determined in gaseous mixtures containing large excesses of NO2, CH3CHO, and N2 by the use of photoacoustic spectroscopy (PAS). Mixtures containing H2CO as a minority component are prepared by gas permeation methods and examined by pulsed laser PAS in the ultraviolet and visible spectral regions. The relative concentrations of the major components of each mixture are an order of magnitude or more larger than the H2CO component under study. PA spectra with 0.5-cm−1 resolution in the 302.5-303.8 nm region are presented in Fig. 3 and are used to identify spectral signatures needed for selective detection. The dependence of PA signals on concentration is determined separately for each of the three polyatomic components in samples with N2. An experimental protocol for quantitatively measuring H2CO concentrations near 50 ppbv in NO2, CH3CHO, and N2 mixtures is described.
M. Boutonnat, D. A. Gilmore, K. A. Keilbach, N. Oliphant, and G. H. Atkinson, "Photoacoustic Detection of Formaldehyde as a Minority Component in Gas Mixtures," Appl. Spectrosc. 42, 1520-1524 (1988)