Dry deposition of acidic air pollutants to tree leaves, determined by a modified leaf-washing technique

Dry deposition fluxes (F-L) of NO3- and SO42- to leaf surfaces were measured for Japanese red pine (Pinus densiflora), Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa), and Japanese white oak (Quercus myrsinaefolia), together with atmospheric concentrations (C-L) of NOx (NO + NO2), T-NO3 (gaseous HNO3 + particulate NO3-) and SOx (gaseous SO2 + particulate SO42-) around the leaves in a suburban area of Japan, using a modified leaf-washing technique. F-L of NO3- and SO42- decreased as follows: pine >> cedar > cypress >= oak and pine >> cedar > oak >= cypress, respectively. F-L of NO3- for all tree species fluctuated synchronously with C-L of T-NO3. F-L of SO42- fluctuated with C-L of SOx, but the dominant pollutant deposited (SO2 or SO42-) appeared to differ for different tree species. Dry deposition conductance (K-L) of T-NO3 and SOx was derived as an F-L/C-L ratio. Seasonal variations of K-L likely reflect the gas/particle ratios of T-NO3 and SOx, which were affected by meteorological conditions such as temperature. Dry deposition velocities (V-d) of T-NO3 and SOx were obtained as the mathematical product of annual mean K-L and the total leaf surface areas in the forests. The comparison of V-d among tree species indicated that the loads of acidic air pollutants were higher to coniferous forests than broad-leaved forest because of the higher K-L and/or larger leaf surface areas. (C) 2008 Elsevier Ltd. All rights reserved.