Ambient formaldehyde detection with a laser spectrometer based on difference-frequency generation in PPLN

A laser spectrometer based on difference-frequency generation in periodical ly poled LiNbO3 (PPLN) has been used to quantify atmospheric formaldehyde w ith a detection limit of 0.32 parts per billion in a given volume (ppbV) us ing specifically developed data-processing techniques. With state-of-the-ar t fiber-coupled diode-laser pump sources at 1083 nm and 1561 nm, difference -frequency radiation has been generated in the 3.53-mum (2832-cm(-1)) spect ral region. Formaldehyde in ambient air in the 1- to 10-ppb V range has bee n detected continuously for nine and five days at two separate field sites in the Greater Houston area operated by the Texas Natural Resource Conserva tion Commission (TNRCC) and the Houston Regional Monitoring Corporation (HR M). The acquired spectroscopic data are compared with results obtained by a well-established wet-chemical 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamin e (PFBHA) technique.