FIG. 6. (A) Chlorofluorocarbon and SF6 concentrations measured in August 2003 samples from the Northern High Plains rangeland site IMP (symbols) compared with simulated profiles (lines) for porosity, moisture content, and tortuosity data shown in Table 2; and (B) match of simulated (lines) seasonally distributed root-zone N2O production of 0.04 kg N2O-N ha–1 yr–1 to measured concentrations. X in line represents mean and range of groundwater (GW) equivalent equilibrium concentration in water-vapor-saturated air.