A note on aerosol sized particle deposition onto dense and tall canopies situated on gentle cosine hills

Micrometeorological measurements of aerosol sized dry particle deposition velocity (V_d) onto forested canopies have significantly advanced over the past two decades and now include both—airborne and stationary platforms. However, the interpretation of these V_d measurements still relies on stationary and planar homogeneous flow assumptions only appropriate to flat-terrain conditions. Simplified model calculations were used to examine how variations in hill height (H) introduce biases in V_d when assumptions appropriate to flat terrain are applied to periodic and gentle 2-D cosine topography covered with tall and dense forested canopies. It was shown that increasing H reduced the variability in V_d for all aerosol sized particle diameters (d_p) inside the canopy when the hill slope (H/L) remained constant (=0.1), where L is the cosine hill half-length. At the landscape scale, as may be monitored from airborne platforms, assumptions appropriate to flat-terrain appear accurate with increasing H for a constant and gentle H/L (= 0.1). Inside the canopy, variability in V_d tends to be larger than above the canopy for all H values and d_p classes.