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Dry Deposition Methods Based on Turbulence Kinetic Energy: 1. Evaluation of Various Resistances and Sensitivity Studies Using a Single-Point Model
Citation:
Alapaty, K., B. Cheng, J. Bash, J. Munger, J. Walker, AND S. Arunachalam. Dry Deposition Methods Based on Turbulence Kinetic Energy: 1. Evaluation of Various Resistances and Sensitivity Studies Using a Single-Point Model. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES. American Geophysical Union, Washington, DC, 127(22):e2022JD036631, (2022). https://doi.org/10.1029/2022JD036631
Impact/Purpose:
Background: Dry deposition is a two-step transport process of air pollutants from lowest air layer into a thin air layer surrounding objects and then via this thin layer to objects on the surface. Then, surface uptake can cause changes in physical and/or chemical state of the underlying objects (e.g., vegetation) depending upon the chemical and/or biological absorption capacity while usually the slowest process will determine the total rate of pollutant deposition. Thus, dry deposition plays an important role in determining the near surface concentrations of various atmospheric pollutants and it can adversely affect even an ecosystem at local to global scales as well as influence water and carbon cycle and it can have influences on human health via pollutant exposure. Problem: Many varieties of dry deposition methods exist in various air pollution models and the outcome from these models differ causing uncertainty in predicted air concentrations of pollutants and loading of nutrient and pollutants to the surface (e.g., vegetation, water, soil). Lots of resources are used up to intercompare and validate these methods and outcomes and yet there is no universally accepted and usable dry deposition methodology saving resources and focusing research efforts on a single community dry deposition methodology. Approach: The objective of the research is to develop a framework for community methodology for dry deposition for use in regional and global air pollution models. It is achieved by first developing and validating a turbulence velocity scale based on the surface turbulence information that is valid for all situations in the lower part of the atmosphere where pollutants are normally trapped. Then, we hypothesized and proved that the measured friction velocity, used in several resistances’ methods, can be effectively replaced by the new velocity scale multiplied by the von Karman constant. Finally, these new resistance formulations are tested in the Surface Tiled Aerosol and Gas Exchange dry deposition model, which was constructed as a single-point model, in simulating O3 fluxes for a decadal period at Harvard Forest site. Results: The outcome from this work indicate that new formulations work very well in simulating surface latent heat and ozone fluxes when compared to respective simulations using traditional formulations as well as measurements at decadal time scale. Impact: Findings from this research can help improve the capability of dry deposition methods for better estimation of dry deposition fluxes and opens doors for the development of community dry deposition methodology for use in regional and global air quality models.
Description:
Different functions are used to account for turbulence strength in the atmospheric boundary layer for different stability regimes. These functions are one of the sources for differences among different atmospheric models' predictions and associated biases. Also, turbulence strength is underrepresented in some of the resistance formulations. To address these issues with dry deposition, firstly we take advantage of three-dimensional (3-D) turbulence information in estimating resistances by proposing and validating a 3-D turbulence velocity scale that is relevant for different stability regimes of boundary layer. Secondly, we hypothesize and validate that friction velocity measured by 3-D sonic anemometer can be effectively replaced by the new turbulence velocity scale multiplied by the von Karman constant. Finally, we (a) present a set of resistance formulations for ozone (O3) based on the 3-D turbulence velocity scale; (b) intercompare estimations of such resistances with those obtained using existing formulations; and, (c) evaluate simulated O3 fluxes using a single-point dry deposition model against long-term observations of O3 fluxes at the Harvard Forest (MA) site. Results indicate that the new resistance formulations work very well in simulating surface latent heat and O3 fluxes when compared to respective existing formulations and measurements at a decadal time scale. Findings from this research may help to improve the capability of dry deposition schemes for better estimation of dry deposition fluxes and create opportunities for the development of a community dry deposition model for use in regional/global air quality models.
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DOI: Dry Deposition Methods Based on Turbulence Kinetic Energy: 1. Evaluation of Various Resistances and Sensitivity Studies Using a Single-Point Model