USE OF A LONG-PATH INFRARED GAS MONITOR FOR MEASUREMENT OF NITROUS-OXIDE FLUX FROM SOIL

The Siemens-Plessey, Hawk long-path infrared gas monitor, an instrument originally designed for identification of leaks of pollutant gases from industrial sources, has been applied successfully to the measurement of nitrous oxide, N2O, fluxes from soil. The Hawk system was tuned to the 2180-2200 cm-1 region of the IR spectrum and thus dedicated to the measurement of N2O alone. The response to increasing concentrations of N2O in the absorption path was linear over the range measured, from ambient (0.31 parts per million by volume (ppmv)) up to 4.3 ppmv. The system was compared with a Bomem Fourier transform infrared (FTIR) spectrometer within an ultralarge chamber (60 m2) . The responses of the two instruments were very closely correlated, and the FTIR was used to provide an absolute calibration of the Hawk. Flux measurements by the Hawk/ultralarge chamber system, on a fertilized grassland site on a clay soil in central Scotland, were compared with those measured by conventional small-chamber/gas chromatography methods, using small chambers both within the ultralarge chamber and elsewhere on the experimental site. The results obtained by the different methods were compatible, taking into account the high degree of spatial variability observed at this site. We conclude that the Hawk/large chamber combination shows considerable potential for measuring fluxes from areas 10(2)-10(3) times larger than those covered by conventional small chambers and from sites where the heterogeneity (including the presence of experimental plots with different treatments) precludes the use of micrometeorological methods.