Parameterising forest edge deposition using effective roughness length

Advection and inflow effects cause forest edges to experience enhanced dry deposition of atmospheric pollutants. A novel methodology is proposed to parameterise this as a sub-grid scale phenomenon in atmospheric models, based on the calculation of a blending-height based effective roughness length for heterogeneous areas. Numerical simulations were performed using the new parameterisation for a highly fragmented landscape in northern Belgium. Sulphur and nitrogen dry deposition over the first 100 m at the forest edge were found to increase by up to a factor of two, which is in broad agreement with measurements and high-resolution model simulations. It was also found that areas containing sparsely distributed and very small forests are particularly exposed to edge deposition effects.