You are here:
Estimating sources, sinks, and fluxes of reactive nitrogen and sulfur within a mixed forest canopy
Citation:
Wu, Z., J. Walker, C. Oishi, G. Katul, T. Duman, X. Chen, D. Schwede, J. Bash, AND J. Iiames. Estimating sources, sinks, and fluxes of reactive nitrogen and sulfur within a mixed forest canopy. Spring 2021 National Atmospheric Deposition Program/Total Deposition Science Committee, Virtual, Virtual, May 10 - 14, 2021.
Impact/Purpose:
Canopy-scale flux measurements and inferential models are useful for developing estimates of net emission or deposition of trace gases and aerosols above forests. However, more detailed measurements and models are needed to relate net fluxes to biological, physical, and chemical processes occurring within the air-canopy-soil system, which occur over multiple time scales. The objective of this work is to develop modeling tools that can be used to link atmosphere-biosphere fluxes of reactive compounds to specific ecosystem compartments (e.g., canopy, understory, ground).
Description:
Estimating the source/sink distribution and vertical fluxes of air pollutants within and above forested canopies is critical for understanding biological, physical, and chemical processes influencing the soil-vegetation-atmosphere exchange. The vertical source-sink profiles of reactive nitrogen and sulfur were examined using multiple inverse modeling methods in a mixed hardwood forest in the southern Appalachian Mountains. Measurements of the vertical concentration profiles of ammonia (NH3), nitric acid (HNO3), sulfur dioxide (SO2), and ammonium (NH4+), nitrate (NO3-), and sulfate (SO42-) in PM2.5 were measured during five intensives between May 2015 and August 2016. The mean concentration profile of NH3 showed decreasing concentrations with decreasing height in the upper canopy and increasing concentrations below the understory toward the forest floor. All other species exhibited patterns of monotonic decreasing concentration from above the canopy to the forest floor. Using the measured concentration profiles, three inverse approaches, including a Eulerian high-order closure model (EUL), a Lagrangian localized near-field (LNF) model, and a new full Lagrangian stochastic model (LSM), were used to simulate the within-canopy flow fields and provide an ensemble estimate of the vertical source-sink flux profiles. The models were evaluated using the within and above canopy eddy covariance flux measurements of sensible heat. Differences between models were analyzed and the flux profiles were used to investigate the origin and fate of reactive nitrogen and sulfur compounds within the canopy. The knowledge gained in this study will benefit the development of soil-vegetation-atmosphere models capable of partitioning canopy-scale deposition of nitrogen and sulfur to specific ecosystem compartments. For presentation at the Spring 2021 National Atmospheric Deposition Program, Total Deposition Science Committee Meeting (Virtual) May 10 - 14, 2021
