Application of a variable pressure infrared spectrometer for formaldehyde measurements in indoor and outdoor environments

摘要

Pollutants detection by tunable diode laser spectroscopy is conventionally achieved by scanning the emission frequency of the laser around an isolated absorption line of the species under investigation. Absolute quantification relies on the comparison of the measured absorption signal with the absorption signal of a calibrated sample at the same pressure, or with a calculated line profile when the spectroscopic parameters are available and accurate. We developed an alternative procedure : with the laser emission frequency actively stabilized on top of the absorption line, both the pressure inside the cell and the absorption signal are measured while the cell is progressively filled with the sample up to about 12 Torr. The slope at origin of the signal vs. pressure curve is proportional to the concentration in the sample and absolute concentration is obtained with a calibrated mixture injected into the cell at regular intervals. This procedure, which proves as efficient as the conventional one, has been applied together with a mobile spectrometer to the quantification of formaldehyde in outdoor and indoor (buildings and cars) environments.