A Process-based Soil Ammonia Emission Model for Agricultural Soils

Ellen Cooter* and Jesse Bash
U.S. Environmental Protection Agency
National Exposure Research Laboratory
Atmospheric Modeling and Analysis Division
Research Triangle Park, NC 27711, USA

Emission of ammonia from fertilized agricultural soils is estimated to account for 35% of all agricultural NH3 emissions (2002 NEI), but few advances have been proposed with regard to process-based modeling of these emissions since early 2000. Current emission estimates rely on historic annual fertilizer sales reports and crop acreages and, although CMAQ v4.7 offers an option to consider the bi-directional flux of ammonia, it still relies heavily on fixed parameter values. These approaches may be sufficient for retrospective analyses, they lack the flexibility to respond to land use or climate changes needed to assess ecosystem exposure to nitrogen and sulfur deposition.

This presentation describes the development and preliminary evaluation of a more process-based, yet operationally practical approach for estimating bi-directional soil ammonia flux from a monitored agricultural field study site at Lillington, NC. While the application of this approach, when combined with modified canopy flux parameterizations results in more accurate temporally resolved flux estimates, it requires additional agricultural management information that is not currently required for routine ammonia emission processing. We propose to develop this information from a national implementation of the USDA Environmental Integrated Climate (EPIC) model. This combination of CMAQ with improved bi-directional ammonia flux and EPIC farm management scenarios will facilitate the exploration of the potential response of air quality and atmospheric nitrogen loadings to ecosystems in response to regional changes in land use, land cover, farm management and climate.

* Phone: 919-541-1334