Development of Multi-Layer Dry Deposition Mechanisms in Canopy-App

Dry deposition serves as one of the major sinks for air pollutants. Historically, simplified ‘big leaf’ approaches are used in community chemical transport models, neglecting the explicit vertical structure and the physical, dynamical, and chemical variations within vegetation canopies. In this study, a multi-layer dry deposition model is being adapted, focusing on a more accurate estimation of dry deposition rate and flux. Here the multi-layer dry deposition model is adapted from the Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS), with updates to the molecular diffusivity coefficients, reactivity coefficients, and Henry’s law coefficients for 31 gas species from the ‘RACM2_plus’ mechanism. This new model can run both offline and online within the canopy-app (https://github.com/noaa-oar-arl/canopy-app), which is being developed by NOAA Air Resources Laboratory (ARL), aiming to be incorporated into NOAA United Forecast System (UFS) weather and atmospheric composition modeling suite. Canopy-app computes select variables and adjustment factors used for efficiently modulating atmospheric quantities (such as gas-phase chemical species) due to vertically resolved canopy effects. The multi-layer dry deposition codes in the offline/stand-alone version of canopy-app use top-layer boundary (i.e., above-canopy) inputs driven by the UFS-based Global Forecast System (GFS) surface/meteorological data (e.g, 2-meter temperature and humidity, 10-meter winds, downward shortwave radiation, surface pressure, and supplemental/satellite-based vegetative canopy inputs). The output of canopy-app will include dry deposition velocities for numerous chemical species, with user-flexibility in selecting different model algorithms/schemes and tunable parameters. Ultimately, we envision that the canopy-app with a new multi-layer dry deposition module will serve as an inline component in several operational and community air quality models. The performance of this new multi-layer dry deposition model will be evaluated against observations collected both within the U.S. and globally. Ongoing work includes extending the canopy-app multi-layer dry deposition to include aerosols as well.