Measurements of cloud water deposition on vegetation using a lysimeter and a flux gradient technique

Vertical gradients in wind velocity and liquid water content (LWC) provided cloud deposition fluxes of typically 10 mg m^-2 s^-1 and deposition velocities (v_g) in the range 21 to 39 mm s^-1 for droplets with a number mean radius in the range 6 to 7 μm. In these conditions, the aerodynamic resistance provided the major limitation to deposition rates contributing 60% of the overall transfer resistance. Simultaneous measurements of net water exchange between the atmosphere and the ground using a lysimeter showed that the bulk of the water (typically 80%) was deposited as a vapour flux onto frozen soil within the lysimeter. The measurements show that cloud water deposition at Great Dun Fell (altitude 847 m asl) may increase annual wet deposited SO₄ ^2-, NO₃ ^-, H⁺ and NH₄ ⁺ by 12%, but if such high altitude sites were afforested, the increase would be 44%. -from Authors