Ozone dry deposition through plant stomata: Multi-model comparison with flux observations and the role of water stress as part of AQMEII4 Activity 2.

Abstract

A substantial portion of tropospheric ${\text{O}}_3$ dry deposition occurs after diffusion of ${\text{O}}_3$ through plant stomata. Simulating stomatal uptake of ${\text{O}}_3$ in 3D atmospheric chemistry models is important in the face of increasing drought induced declines in stomatal conductance and enhanced ambient ${\text{O}}_3$ . Here, we present a comparison of the stomatal component of ${\text{O}}_3$ dry deposition $\left({\text{eg}}_{\text{s}}\right)$ from chemical transport models and estimates of ${\text{eg}}_{\text{s}}$ from observed ${\text{CO}}_2$ , latent heat, and ${\text{O}}_3$ flux. The dry deposition schemes were configured as single-point models forced with data collected at flux towers. We conducted sensitivity analyses to study the impact of model parameters that control stomatal moisture stress on modeled ${\text{eg}}_{\text{s}}$ . Examining six sites around the northern hemisphere, we find that the seasonality of observed flux-based ${\text{eg}}_{\text{s}}$ agrees with the seasonality of simulated ${\text{eg}}_{\text{s}}$ at times during the growing season with disagreements occurring during the later part of the growing season at some sites. We find that modeled water stress effects are too strong in a temperate-boreal transition forest. Some single-point models overestimate summertime ${\text{eg}}_{\text{s}}$ in a seasonally water-limited Mediterranean shrubland. At all sites examined, modeled ${\text{eg}}_{\text{s}}$ was sensitive to parameters that control the vapor pressure deficit stress. At specific sites that experienced substantial declines in soil moisture, the simulation of ${\text{eg}}_{\text{s}}$ was highly sensitive to parameters that control the soil moisture stress. The findings demonstrate the challenges in accurately representing the effects of moisture stress on the stomatal sink of ${\text{O}}_3$ during observed increases in dryness due to ecosystem specific plant-resource interactions.