Modelling of soil emissions of nitrous oxide for global studies

The global inventory of annual N₂O emissions is in general agreement with source estimates inferred from inverse modeling. The pathways for loss of soil nitrogen in the humid tropics of Costa Rica were analyzed by compiling soil nitrogen budgets for a deforestation sequence. Most of the nitrogen loss occurs through denitrification. The enhanced N₂O emission caused by deforestation may be an important global source. Global monthly estimates of N₂O emissions were used to prescribe a three-dimensional atmospheric transport model. The simulated northern hemispheric (NH) N₂O surface concentration of about 1 ppb higher than in the southern hemisphere (SH) agrees with atmospheric observations.

Predicted concentrations for the NH were somewhat higher in summer than in winter, whereas the atmospheric N₂O concentration measurements show no seasonal variation. The small seasonality in modeled atmospheric N2O concentrations for the SH is more consistent with measurements. Omission of soil N₂O consumption and episodic emissions in temperate ecosystems, and possible underestimation of N2O emissions from combustion in winter may exaggerate the simulated seasonal trends in the NH. Also, seasonal trends in atmospheric N₂O concentrations remain unobserved, because of the remote location of most monitoring stations and the lack of precision of atmospheric N₂O measurements.