Modeling bio-atmospheric coupling of the nitrogen cycle through NOx emissions and NOy deposition

The tropospheric and terrestrial nitrogen cycles are connected to one another through the emissions of NOx and NHx from soils and vegetation and the subsequent redeposition of these compounds and their products elsewhere. These connections play an important role in the Earth system influencing tropospheric concentrations of NOx, O3, and CO2. Estimates of the biogenic sources of NOx, soil emissions and biomass burning, are amongst the most variable terms in the global budget of NOx and are eclipsed only by lightning. A 3-D chemistry transport model, IMAGES, was used to examine how soil emissions and biomass burning influence tropospheric concentrations of NOx and O3 as well as NOy deposition. Soil and biomass burning emissions of NOx contributed the most to atmospheric NOx concentrations closest to the surface and south of 30°N. The influence of these emissions on tropospheric O3 and NOx concentrations dissipated with height suggesting that these surface emissions are most important to surface ozone concentrations. The removal of either the soil or biomass burning source resulted in a 5-20% difference in tropospheric O3 concentrations over large regions of the atmosphere. Both sources are also important contributors to N deposition, particularly south of 30°N which, in turn, can generate significant carbon storage. These exercises demonstrate both the importance and complexity of the connections between atmospheric chemistry and the terrestrial biosphere.