Evaluation and updates to the oxidized reactive nitrogen trace gas dry deposition parameterization from the GEOS-Chem CTM, 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. Represented in chemical transport models (CTMs) as a first-order process, time-varying rate coefficients are parameterized and expressed via species-specific deposition velocities (V_d(x)). We evaluate isolated components of the parameterization for V_d in the GEOS-Chem CTM by extracting the trace gas dry deposition algorithm and reimplementing in single-point-mode to enable more direct comparison to field observations. Resistances to surface uptake follow a modified version of the ‘big-leaf’ Wesely parameterization, which previous studies have shown applies poorly to off-target species such as NO₂ under conditions favoring non-stomatal uptake. We evaluate non-stomatal dry deposition of NO₂ by comparing to eddy covariance observed nocturnal V_d(NO₂) over Harvard Forest. We eliminate a large low bias (-80 %) in simulated nocturnal V_d(NO₂) by representing NO₂ heterogeneous hydrolysis on deposition surfaces, paying attention to chemical flux divergence, soil NO emission, as well as canopy surface area effects. Finally, we evaluate the updated oxidized reactive nitrogen (NO_y) dry deposition parameterization for GEOS-Chem by comparing to eddy covariance observed V_d(NO_y) over Harvard Forest, finding a modest nocturnal low bias (-19 %) remains in simulated V_d(NO_y) due to the compensating effects of updates to the calculation of molecular diffusivities (28 % reduction in nocturnal V_d(NO_y)) and representation of NO₂ heterogenous hydrolysis (25 % increase in nocturnal V_d(NO_y)). These developments are applicable to models across scales, having important implications for near-surface NO₂ lifetime through a mechanism involving HONO emission.