STUDIES OF DEPOSITION IN HILL CLOUD

The occurrence of cloud at ground level over hills is particularly difficult to categorise and quantify in complex mountainous terrain, and has constituted a major part of our studies as described below. For routine calculations, concentrations in hill cloud have to be estimated from daily observations at the limited national network of air and precipitation monitoring stations, coupled with meteorological data, leading to additional complications. Further approximations have to be made to calculate deposition rates, and the preliminary estimates of bulk annual deposition given in this paper. However the observed pattern of forest damage raises questions about the large variations in exposure of individual trees, and the relevance of bulk annual deposition estimates averaged over large areas. A tentative approach to identifying particularly damaging episodic conditions for tree foliage is also outlined. © 1990 Società Italiana di Fisica.