Do Organized Turbulent Motions Influence Ozone Dry Deposition to Forests?

Abstract:

Dry deposition is an important sink of tropospheric ozone and influences background and episodic ozone air pollution. Plant canopies remove a large amount of ozone through uptake by plant stomata, leaf cuticles, and soil. Stomatal uptake of ozone injures vegetation, thereby altering local-to-global water and carbon cycling. Observed ozone fluxes are used to inform dry deposition parameterizations in chemical transport models, but represent the influence of several complex processes. Understanding these processes is fundamental to building the process-oriented knowledge needed to estimate past and future changes in the ozone depositional sink and damage to plants. Here we constrain the influence of spatial structure in canopy turbulence on ozone dry deposition using large eddy simulation coupled to a multilayer canopy model. In particular, we probe whether organized turbulence segregates areas of efficient leaf uptake from areas of high or low ozone. We simulate three different deciduous forests with leaf area, soil moisture, and humidity varying across the cases. Sensitivity simulations perturb atmospheric stability, ozone dry deposition, or ozone entrainment. We find that the covariance between ozone mixing ratios and leaf uptake in the canopy is negligible compared to the mean leaf uptake of ozone, implying no need to account for segregation in ozone dry deposition in interpreting flux observations or building dry deposition parameterizations. Counteracting meteorological influences on the ozone depositional sink versus the direct influence of the depositional sink on ozone mixing ratios contributes to low segregation.