The Atmospheric Chemistry and Canopy Exchange Simulation System for Ammonia (ACCESS-NH3): Formulation and Application to Measurements from a Deciduous Forest Canopy

As nitrogen oxide and sulfur dioxide emissions decrease in the U. S. as a result of air quality regulations, ammonia (NH₃) is being recognized as playing an increasingly important role in fine particle (PM_2.5) formation. If regulations on NH₃ emissions are implemented in the future, it will be necessary to have reliable models of NH₃ bi-directional exchange over a variety of land use types to help formulate effective control or mitigation strategies. The Atmospheric Chemistry and Canopy Exchange Simulation System for Ammonia (ACCESS-NH3) is a multilayer, single column model that simulates the bi-directional transport and exchange of ammonia throughout the soil-plant-atmosphere continuum. In this presentation, the ACCESS-NH3 modeling system is described and results from its application to a deciduous forest canopy are presented. NH₃ concentration and flux measurements, along with micrometeorological and environmental observations, were made within and above a forest canopy at the U. S. Forest Service’s Coweeta Hydrologic Laboratory in southwestern North Carolina during the summer of 2015. ACCESS-NH3 has been applied to the data obtained during this field experiment to evaluate the model and to assess how NH₃ interacts with a deciduous forest canopy and how these interactions vary as a function of environmental conditions. Results from these evaluations and simulations will be presented.