Evaluation of HNO₃, SO₂, and NH₃ in the Surface Tiled Aerosol and Gaseous Exchange (STAGE) option in the Community Multiscale Air Quality Model version 5.3.2 against field-scale, in situ and satellite observations

Abstract. The Surface Tiled Aerosol and Gaseous Exchange (STAGE) model was developed for estimating dry deposition and bidirectional exchange for field-scale applications and use within the CMAQ v5.3.2 regional scale model. The model was evaluated against micrometeorological flux measurements of NH₃, HNO₃, and SO₂ at a managed grassland and NH₃ in a cultivated corn (Zea Mays) field. When using field-scale observations for soil and vegetation NH₃ compensation points, modelled fluxes for all species agreed well, within or near the reported measurement uncertainty. However, when using the CMAQ v5.3.2 values for NH₃ emission potentials at the Duke Forest grassland site, the model estimated mean net deposition rate was 1.3 ng m^-2 h^-1 while the observed mean NH₃ evasive flux was 8.4 ng m^-2 h^-1. Modelled NH₃ concentration fields evaluated against Cross-Track Infrared Sounder (CrIS) satellite observations indicates a broad underestimation of NH₃ concentrations by approximately 1 to 2 ppb in the U.S. Great Plains. The results from the grassland field data and indicates that there is likely an underestimation of the evasive NH₃ flux in grassland sites due to the model's default tabular values of the vegetation/litter NH₄⁺ concentrations. The STAGE's model sensitivity to soil and vegetation emission potentials indicates that regional scale model results for NH₃ can be further improved with additional micrometeorological flux and vegetation and soil chemistry measurements over different land use types, soil types, and vegetation phenological stages.