Speaker: Olivia Clifton (NASA/GISS/USRA/NPP)
Topic: Biosphere-atmosphere interactions and impacts on tropospheric chemistry at micrometeorological to regional scales

Exchanges of reactive gases between the biosphere and atmosphere influence tropospheric chemistry, climate, and vegetation health. Dry deposition, an important yet overlooked and uncertain sink of many gases, happens when gases are transported to the Earth's surface via turbulence and are removed from the atmosphere through reactions with various surfaces. Dry deposition through plant stomata (the small pores on leaves used for carbon and water exchange) can injure vegetation with implications for forest and crop health and regional-to-global water and carbon cycling. Turbulence not only transports gases towards the vegetation and soil surfaces to which they can deposit but also spatially separates (segregates) air masses, which may cause ambient chemical reaction rates to speed up or slow down relative to the rates that assume well-mixed conditions. If substantial, segregation in chemistry can alter the land-atmosphere exchanges of gases relevant for tropospheric chemistry. In my talk, I will use global earth system modeling to illustrate the importance of considering variations in dry deposition of ozone in interpreting observed changes in ozone air pollution, and I will show that estimating ozone damage to ecosystems relies on considering often-overlooked interactions between meteorology and plant functioning. I will also show results from a novel tool, a large eddy simulation coupled to a multilayer canopy model and a simplified chemical mechanism. In particular, I will show the impact of segregation on the reactivity of the hydroxyl radical (the most important tropospheric oxidant) inside and above a forest canopy and discuss how segregation and its impact changes with environmental conditions.