A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO(2) in air with a sensitivity of better than 100 ppt. The modulation techniques employed to achieve this sensitivity are described in detail, and the noise mechanisms, which currently limit the detectable absorption coefficients to greater, similar 10(-7) m(-1), are examined.

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A laser absorption spectrometer is described which employs a wavelength tunable diode laser in conjunction with a multipass White cell. The instrument is sensitive to absorption coefficients as low as 3 x 10(-8) m(-1) and is designed for use as a portable pollution monitor. The performance of the instrument is illustrated by describing the measurement of three gases commonly found in the atmosphere: SO(2) and N(2)O with sensitivities of 1 ppb and NH(3) with a sensitivity of better than 0.1 ppb. The linearity of response and calibration of the instrument are also discussed in some detail.

Accurate measurements of the wavenumbers of more than 100 lines in the nu(3) band of ozone have been made using a tunable semiconductor diode laser and a temperature-stabilized germanium etalon. The accuracy for the line centers is estimated to be within 3-10 MHz and compares well with the accuracy attained using more complicated heterodyne techniques. The relevance of these results to ozone monitoring instruments based on CO(2) lasers is discussed. The tunability of the diode laser is also exploited to monitor ambient concentrations of ozone in the presence of interfering molecular species. A detection sensitivity of ~0.5 ppb of ozone is demonstrated.