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.