Examination of Ozone Sensitivity to Stomatal Conductance in Urban Areas

Abstract Stomatal conductance is a key factor in controlling ozone deposition velocity. Little is known about stomatal conductance and its impacts on air quality in urban areas because urban vegetation in developed land cover types is often omitted in global and regional models. Recent studies show that urban trees have up to three times higher rates of stomatal conductance than their rural counterparts. We update the dry deposition scheme of WRF‐Chem by linking the dry deposition losses of atmospheric species to vegetation physiology and phenology, as WRF‐Chem by default assumes zero stomatal deposition for urban land cover types. We examine ozone sensitivity to a doubled stomatal conductance of urban trees. We find that surface conductance dominates dry deposition velocity in urban areas with 36%–47% from stomatal uptake. We also find that the doubled stomatal conductance reduces the maximum daily 8‐hr ozone concentration by 1.00.4 ppbv on average with a maximum of 2.6 ppbv. These results highlight the importance of accurate characterization of urban vegetation in the development of urban‐scale chemical transport models. Our analyses on the atmospheric processes controlling ozone concentrations indicate a strong coupling between dry deposition and advection that increases with model horizontal resolution. As urban modeling becomes higher resolution, these results emphasize the fact that the interactions between non‐local and local atmospheric processes will be increasingly complex, especially in regions with significant horizontal gradients such as the coastal urban areas. Modeling for such areas needs additional measurements for validation.