Fluxes of Fine Particles Over a Semi-Arid Pine Forest: Possible Effects of a Complex Terrain

Abstract

Semi-arid forests are of growing importance due to expected ecosystem transformations following climatic changes. Dry deposition of atmospheric aerosols was measured for the first time in such an ecosystem, the Yatir forest in southern Israel. Size-segregated flux measurements for particles ranging between 0.25 μm and 0.65 μm were taken with an optical particle counter (OPC) using eddy covariance methodology. The averaged deposition velocity (Vd ) at this site was 3.8 ± 4.5 mm s−1 for 0.25–0.28 μm particles, which is in agreement with deposition velocities measured in mid and northern latitude coniferous forests, and is most heavily influenced by the atmospheric stability and turbulence conditions, and to a lesser degree by the particle size. Both downward and upward fluxes were observed. Upward fluxes were not associated with a local particle source. The flux direction correlated strongly with wind direction, suggesting topographical effects. We hypothesize that a complex terrain and a patchy fetch affec...