Laser Spectroscopy Sensors for Measurement of Trace Gaseous Formaldehyde

Abstract

A sensitive and direct method to determine atmospheric formaldehyde (HCHO) using laser induced fluorescence spectroscopy (LIF) is described. This technique overcomes the tedious sample collections, water extraction and chemical reactions that are often required in conventional methods. In this LIF approach, the third harmonic of a nontunable Nd:YAG laser at 355 nm is used as a selective excitation wavelength for formaldehyde. Studies at alternative excitation wavelengths have also been performed using 341 nm and 309 nm, which are obtained by Stimulated Raman Scattering of nontunable Nd:YAG laser radiation at 266 nm and 355 nm, respectively. The calibration response is linear in the range of 1-57 ppm and the current limit of detection (LOD) is 0.5 ppm HCHO. It is anticipated that these approaches may be able to avoid interferences that occur in conventional methods for HCHO measurements.