A diode laser based gas monitor suitable for measurement of trace gas exchange using micrometeorological techniques

A fast response, sensitive, field-worthy trace gas analyzer (TGA), based on the principle of diode laser absorption spectroscopy has been developed. The TGA is suitable for in situ trace gas flux measurements using micrometeorological techniques, and is capable of achieving total system noise levels of less than 1, 2, or 4 part per billion by volume (ppbv) rms for N2O, NH3, and CH4, respectively, for a 5-s integration period, and less than 50 pptv for 1-h averaging periods. This sensitivity is accomplished using a unique approach to digital signal processing and a single-path sample absorption cell, both of which reduce noise due to optical fringes. The instrument is also capable of rapid sampling rates (10 samples/s) sufficient for eddy correlation (EC) measurements when used with the appropriate flow system design. The TGA software and electronics have been designed to interface directly with micrometeorological instrumentation such as sonic anemometers, facilitating the use with the eddy correlation and gradient techniques. The operation, characteristics, and practical aspects of employing the TGA with micrometeorological techniques are reviewed. Gradient flux data for N2O and CH4 from field study measurements is from two plots are presented. The results demonstrate the capabilities of the TGA to make sensitive, continuous measurements of trace gas fluxes using micrometeorological techniques, allowing the assessment of the immediate and long-term impact of treatments or perturbations to natural and agricultural systems. (C) 2002 Elsevier Science B.V. All rights reserved.