Modeling Bi-Directional Fluxes of NH3 in a Forest Ecosystem Using SURFATM-NH3 Model: A Study with a Dataset from a Deciduous Montane Forest in the Southeastern U.S.

Ammonia (NH₃) is the most abundant alkaline component in the atmosphere, is therefore of great importance in the neutralization of atmospheric acids and formation of aerosol particles. Numerous studies have been published investigating the effects of NH₃ fluxes on agricultural ecosystems since emissions of atmospheric NH₃ are mainly related to agriculture. However, NH₃ emissions also occur from natural sources and may affect sensitive ecosystems such as forests. Understanding and prediction the biosphere-atmosphere interactions of NH₃ in a forest canopy is challenging due to the complex nature of this ecosystem. A two-layer NH₃ compensation point model SURFATM-NH₃ is used to investigate the NH₃ flux partitioning between the ground layer, cuticle and stomata compartments for a deciduous forest ecosystem. As key parameters the model uses an energy budget model that makes possible to simulate surface temperature for which volatilization is very sensitive, as well as measured and estimated soil and stomatal emission potentials. The model simulates the energy balance, surface temperature and NH₃ fluxes. Modeling results are evaluated with a data set obtained from a field study carried out in a forest canopy at the U. S. Forest Service’s Coweeta Hydrologic Laboratory in southwestern North Carolina during 2015 and 2016. The comparison of modeled and measured results will be presented and the sources of NH₃ will be examined, giving propositions for future model improvements.