Evaluation of and updates to the oxidized reactive nitrogen gaseous dry-deposition parameterization from the GEOS-Chem model, including a pathway for ground surface NO2 hydrolysis

Abstract

Dry deposition is a major loss pathway for reactive nitrogen species from the atmospheric boundary layer. We evaluate isolated components of the parameterization for species-specific gaseous dry-deposition velocity Vd(x) for HNO3 and NO2 from the GEOS-Chem chemical transport model by running a stand-alone version of Vd code in single-point mode to enable a more direct comparison to field observations. Improved measurement-model agreement results mainly from (i) updates to the calculation of molecular diffusivities and (ii) the representation of ground surface NO2 hydrolysis in the formulation of non-stomatal uptake. We evaluate the parameterization for non-stomatal dry deposition of NO2 by comparing to eddy-covariance-inferred nocturnal Vd(NO2) over Harvard Forest. We address a large low bias (-80 %) in simulated nocturnal Vd(NO2) by representing NO2 heterogeneous hydrolysis on deposition surfaces, paying attention to chemical flux divergence, soil NO emission, and canopy surface area effects. Finally, we evaluate the updated oxidized reactive nitrogen (NOy) dry-deposition parameterization by comparing to eddy-covariance-inferred Vd(NOy) over Harvard Forest, finding that a modest nocturnal low bias (-19 %) remains in simulated Vd(NOy) due to the compensating effects of updates to the calculation of molecular diffusivities (28 % reduction in nocturnal Vd(NOy)) and the representation of NO2 heterogeneous hydrolysis (25 % increase in nocturnal Vd(NOy)). These developments are a first step towards a tractable representation of NO2 hydrolysis in a dry-deposition scheme and have important implications for the near-surface NO2 lifetime through a mechanism involving HONO emission.