Large Eddy Simulation of the Interaction Between Biogenic Volatile Organic Compound Transport and Chemistry Within a Tropical Forest Canopy

Abstract

A multitude of biogenic volatile organic compounds (BVOCs) are emitted within the canopy air-space of tropical forests. These compounds undergo reactions with atmospheric oxidants (eg. Ozone O3, the nitrate NO3 or the hydroxyl OH radicals), which mainly originate above the canopy, and reaction products can subsequently condense to form secondary organic aerosols. Canopy resolving Large Eddy Simulation (LES) combined with a representation of atmospheric chemistry presents a valuable tool for a better understanding of the interaction between chemistry and transport processes. This requires the adequate resolution of concentration fields of reactants (BVOCs and oxidants) as well as the flow field inside the canopy. We present the results of an LES study with 17 layers inside the forest (2 m vertical resolution), which includes a simplified BVOC chemistry in order to estimate the export of BVOCs and their principal reaction products such as methyl vinyl ketone (MVK) and methacrolein (MACR) from a tropical canopy. These results are compared to field measurements of ozone, nitrogen oxides, isoprene, monoterpenes as well as MVK and MACR observed during a field campaign at the Cuieiras Biological Reserve K34 (2°36’32” S, 60° 12’33” W) tower from April 2014 to January 2015.