Anthropogenic reactive nitrogen production has increased significantly since the preindustrial with a large environmental impact. Most of this increase can be attributed to the use of synthetic nitrogen fertilizers for agricultural purposes (~120 Tg N yr-1). The recycling of nitrogen through manure has also had a profound impact on the environment, given the large increase in manure production since the preindustrial (~120 Tg N yr-1). Presently, agricultural reactive nitrogen emissions, primarily of ammonia, make up the largest fraction of emitted reactive nitrogen emissions to the atmosphere. As reactive nitrogen cascades through the environment it impacts air quality and climate. Reactive nitrogen emissions from manure and synthetic fertilizer contribute significantly to air quality degradation:  the emissions of NOX result in substantial ozone production and the emissions of ammonia impact atmospheric PM10 and PM2.5. Agricultural emissions of ammonia are the largest source category for PM2.5 over large portions of the globe. The emissions of N2O from agricultural practices act to warm the climate and to impact the stratospheric ozone layer. Nitrogen deposition stemming from manure and synthetic fertilizer application exerts a substantial lever on the atmospheric carbon cycle through its impact on plant growth.

Agricultural reactive nitrogen emissions of NOX, N2O and NH3 are expected to increase in the future with an intensification and expansion of agriculture. Climate change is expected to further augment these increases. A further enhancement in the future impact of these reactive nitrogen emissions is expected due to future reductions in sulfate and NOX emissions through environmental legislation. For example, the global burden of accumulation mode nitrate aerosols in 2100 is predicted to be 2.6 times the present day burden due to increased future ammonia emissions. Despite its importance and societal relevance the representation of emissions of reactive nitrogen from agricultural processes has been treated in such a rudimentary manner in Earth System Models that the resulting impacts are highly uncertain. Specifically: (1) ammonia emissions from agriculture are generally crudely estimated with no explicit climate dependence or even seasonal variation; (2) emissions of NOX and N2O from agriculture are generally not considered or are considered very simplistically; (3) the emissions and deposition of reactive nitrogen are treated separately and thus are not treated as a coupled process; and (4) explicit organic and synthetic fertilizer application and manure generation are not explicitly tied to the biogeochemical cycling of nitrogen and its impact on the carbon cycle..

The overall question we seek to answer through the proposed research is: What are the climate and air-quality impacts of agricultural practices on the nitrogen cycle and how will these change with climate, with changes in agricultural practices and with increases in food demand? We intend to address this through the following tasks: Add reactive nitrogen cycling into the ACME model through explicit modeling of agricultural practices of fertilizer and manure management; couple the resultant emissions of NOX, N2O and NH3 from agricultural practices to the atmospheric model; evaluate the resultant emissions and atmospheric concentration and distribution of reactive nitrogen species; simulate the resultant impact of agriculture on air quality and climate for current and future conditions under a number of different scenarios and agricultural management practices.