Abstract
Abstract. While nitrogen (N) is an essential element for life, human population growth and demands for energy, transportation and food can lead to excess nitrogen in the environment. A modeling framework is described and implemented to promote a more integrated, process-based and system-level approach to the estimation of ammonia (NH3) emissions which result from the application of inorganic nitrogen fertilizers to agricultural soils in the United States. The United States Department of Agriculture (USDA) Environmental Policy Integrated Climate (EPIC) model is used to simulate plant demand-driven fertilizer applications to commercial cropland throughout the continental US. This information is coupled with a process-based air quality model to produce continental-scale NH3 emission estimates. Regional cropland NH3 emissions are driven by the timing and amount of inorganic NH3 fertilizer applied, soil processes, local meteorology, and ambient air concentrations. Initial fertilizer application often occurs when crops are planted. A state-level evaluation of EPIC-simulated, cumulative planted area compares well with similar USDA reported estimates. EPIC-annual, inorganic fertilizer application amounts also agree well with reported spatial patterns produced by others, but domain-wide the EPIC values are biased about 6% low. Preliminary application of the integrated fertilizer application and air quality modeling system produces a modified geospatial pattern of seasonal NH3 emissions that improves current simulations of observed atmospheric particle nitrate concentrations. This modeling framework provides a more dynamic, flexible, and spatially and temporally resolved estimate of NH3 emissions than previous factor-based NH3 inventories, and will facilitate evaluation of alternative nitrogen and air quality policy and adaptation strategies associated with future climate and land use changes.
Highlights
Background and introductionNitrogen (N) is an essential element required for the growth and maintenance of all biological tissues, but human population growth and increased demands for energy, transportation and food have lead to dramatic increases in N production (Galloway et al, 2008)
This inventory was developed from a combination of emission factors and inverse modeling (Gilliland et al, 2006) that assumes unidirectional emission from soil and vegetation canopies; NH3 is known to exhibit bi-directional behavior (Sutton et al, 1995), and recent studies suggest that inclusion of bi-directional NH3 behavior will alter regional nitrogen budget simulations in ways that are important for ecosystem and human health (Dennis et al, 2010)
A methodology has been described that facilitates assessment of the process-driven regional-to-national response of agricultural soil emissions of NH3 to changing land use, policy and climate under a set of user-defined fertilizer management conditions and nationally consistent, spatially and temporally resolved inputs for the conterminous US
Summary
Nitrogen (N) is an essential element required for the growth and maintenance of all biological tissues, but human population growth and increased demands for energy, transportation and food have lead to dramatic increases in N production (Galloway et al, 2008). Ammonia emissions originating from soils receiving commercial N fertilizer applications account for 33 % of all agricultural NH3 emissions This inventory was developed from a combination of emission factors and inverse modeling (Gilliland et al, 2006) that assumes unidirectional emission from soil and vegetation canopies; NH3 is known to exhibit bi-directional behavior (Sutton et al, 1995), and recent studies suggest that inclusion of bi-directional NH3 behavior will alter regional nitrogen budget simulations in ways that are important for ecosystem and human health (Dennis et al, 2010). Cooter et al (2010) confirm that this same paradigm can simulate the measured magnitude and temporal variability of post-application inorganic fertilizer NH3 emissions from grain-corn soils in the US southern Coastal Plain This approach promises to improve current unidirectional, factor-based inventories, but its national-scale implementation is challenging. The discussion that follows describes the development of such a fertilizer simulation system, evaluates two key aspects of this system, and closes with an example of the integration of this information into a regional air quality model application with bi-directional ammonia flux
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