Coupling of an agro-ecosystem and air-quality model to link atmospheric particulate matter, nitrogen deposition and short term climate forcers to agricultural activities

Measurements of ammonia fluxes have demonstrated that agricultural management practices impact the magnitude and direction of the flux and that the sources and sinks in agricultural and unmanaged landscapes differ. To capture these observations, the 2012 release of the Community Multiscale Air Quality (CMAQ) model version 5.0 includes an option for coupling national simulations of agricultural practices from the USDA's Environment Policy Integrated Climate (EPIC) model to estimate NH3 emissions from fertilizer application and parameterize the bidirectional air-surface exchange of NH3. This coupled modeling system results in improved evaluations against reduced nitrogen wet deposition and ammonium aerosol observations while linking these environmental and human health issues to agricultural practices. EPIC simulations will be evaluated against reported state wide agricultural yields. Bidirectional NH3 exchange reduced the Continental US annual total N deposition estimates in CMAQ by 5.0% but resulted in much larger regional changes due to a reduction in the NH3 deposition velocity. Satellite, geochemical and air-quality observational needs for more thorough evaluations and the expansion of this model to include soil NOx and N2O emissions will be discussed.