Detection of sulphur dioxide at, and below, the part per billion level using a tunable diode laser

A laser absorption spectrometer is described which employs a wavelength tunable diode laser in conjunction with a multipass White cell. The instrument uses absorption lines in the nu3 band of SO2 to monitor atmospheric SO2 concentrations with sensitivities as high as 0.2 parts per billion (ppb) in a laboratory system. A portable instrument with a fast response time and a sensitivity of 1 ppb is described, and the development of a highly practical field instrument, based on pyroelectric detectors, is discussed.