Effect of chemical degradation on BVOC fluxes

Analyses of flux data of volatile organic compounds are usually based on assumption that flux above canopy equals to the emission at the surface. This assumption requires chemical reactions to be slow compared to the turbulent transport, i.e. Damköhler number to be sufficiently low. We explore the effect of chemical degradation on fluxes using stochastic Lagrangian transport model in which the chemical degradation is described as first order decay (SLT-C0). We study cases in which the VOC emission is in the canopy or in the ground level, and vary various parameters, such as chemical lifetime, canopy density, hydrostatic stability, in the model. The magnitude of the chemistry effect on fluxes depends strongly on chemical lifetime and friction velocity. With SLT-C0 model the above canopy fluxes were significantly decreased already at low Damköhler numbers. We will show an example on how much the above canopy flux of selected mono- and sesquiterpenes are decreased in Hyytiälä measurement site, according to SLT-C0 model and oxidant levels measured during HUMPPA-COPEC measurement campaign in August 2010.