To simulate global mercury (Hg) dynamics in chemical transport models (CTMs), surface-atmosphere exchange of gaseous elemental mercury, Hg⁰, is often parameterized based on a resistance-based dry deposition scheme coupled with a re-emission function from soils. Despite extensive use of this approach, direct evaluations of this implementation against field observations of net Hg⁰ exchange flux are lacking. In this study, we evaluate an existing net exchange parameterization (referred to here as the base model) by comparing modeled fluxes of Hg⁰ to fluxes measured in the field using micrometeorological techniques. Comparisons were performed in two terrestrial ecosystems: a grassland site in Switzerland and an Arctic tundra site in Alaska, U.S. in summer and winter. The base model included the dry deposition and soil re-emission parameterizations from Zhang et al. (2003) and the global CTM GEOS-Chem, respectively. Comparisons of modeled and measured Hg⁰ fluxes showed large discrepancies, particularly in the summer months when the base model overestimated daytime net deposition by approximately 9 and 2 ng m^-2 h^-1 at the grassland and tundra sites, respectively. In addition, the base model was unable to capture a measured nighttime net Hg⁰ deposition and wintertime deposition. We conducted a series of sensitivity analyses and recommend that Hg simulations using CTMs: (i) reduce stomatal uptake of Hg⁰ over grassland and tundra in models by a factor from 5-7; (ii) increase nighttime net Hg⁰ deposition, e.g., by increasing ground and cuticular uptake by reducing the respective resistance terms by factors of 3-4 and 2-4, respectively; and (iii) implement a new soil re-emission parameterization to produce larger daytime emissions and lower nighttime emissions. We conclude that the resistance-based model combined with the new soil re-emission flux parameterization is able to reproduce observed diel and seasonal patterns of Hg⁰ exchange in these ecosystems. This approach can be used to improve model parameterizations for other ecosystems in which flux measurements are available.