Evaluation of HNO ₃ , SO ₂ , and NH ₃ 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.