Automated chamber technique for gaseous flux measurements: Evaluation of a photoacoustic infrared spectrometer‐trace gas analyzer

Experiments were made in order to evaluate the accuracy and sensitivity of a photoacoustic infrared trace gas analyzer (TGA) in conjunction with an automatic opening and closing chamber system developed for near‐continuous (2 min intervals) soil gaseous flux measurements. Humidity interference tests on N 2 O, CH 4 , and CO 2 concentrations measured by the TGA were carried out, and the results showed a linear interference, with correction factors of 3 × 10 −5 x , 1.9 × 10 −3 x and 4.4 × 10 −3 x ( x = H 2 O vapor ppm), respectively. CO 2 interference on N 2 O and CH 4 signals were also linear, with average correction factors of 2.8 × 10 −4 x and 6 × 10 −5 x ( x = CO 2 ppm), respectively. Laboratory intercomparisons between the TGA and GC measurements of N 2 O and CH 4 standards showed good agreement ( R 2 > 0.993), indicating the accuracy of the TGA for measurement of these gases at concentrations up to 100 and 40 ppm N 2 O and CH 4 , respectively. The relatively rapid measurement time for up to five gases simultaneously in 2 min, linearity, and ease of operation of the TGA represent major advantages compared to gas chromatography (GC). The automated chamber system provides a continuous measurement of fluxes with minimum disturbance to the soil environment enclosed by the chamber and provides the means, for example, of quantifying diurnal variability. In situ measurements of N 2 O‐N and CH 4 ‐C fluxes with a sensitivity <10 g ha −1 d −1 (11.6 ng m −2 s −1 ), as well as of CO 2 and water vapor (H 2 O), can be measured by the TGA when used with the automated system, and fluxes at background levels (i.e., from unfertilized soils) can be determined.