Technical note: Laboratory evaluation of a tunable diode laser system for eddy covariance measurements of ammonia flux

A tunable diode laser trace gas analyzer (TGA 100, Campbell Scientific, Logan, Utah) was evaluated in the laboratory for its ability to measure ammonia fluxes using the eddy covariance technique. A random noise generator was used in the laboratory to switch sampling between high and low concentration air streams to simulate a range of eddy sizes with a known input. A mechanical switching system was developed to prevent pressure fluctuations during switching associated with valves. A half-power point of 0.4 Hz was found for 50 m of sampling tubing. Resolution, determined through laboratory tests, was conservatively estimated between 0.2 and 1 μg m−2 s−1.