Influence of Organized Turbulence on OH Reactivity at a Deciduous Forest

Abstract

Abstract Oxidation of reactive carbon fuels climate‐ and pollution‐relevant chemistry. Deciduous forests are important sources of reactive carbon (particularly isoprene). Organization in turbulence can physically separate (“segregate”) oxidants from reactive carbon, causing oxidation to increase or decrease relative to the (ubiquitous) assumption of well‐mixed conditions. We use large eddy simulation coupled to a multilayer canopy model and simplified chemistry to quantify the impact of segregation on near‐canopy hydroxyl radical (OH) reactivity. Simulations mimic summer clear‐sky midday and morning conditions at a homogeneous deciduous forest. OH‐isoprene segregation alters OH reactivity inside the canopy by up to 9%, but the impact strongly depends on height, soil NO emissions, and sunlight. Uniquely, we identify the drivers of changes by isolating the roles of isoprene and OH. Our findings also suggest that segregation may create discrepancies between direct measurements and bottom‐up estimates of OH reactivity, separate from the issue of mischaracterized or unknown OH sinks.