| Total annual per hectare amounts of sulfur dioxide (SO{dollar}sb2{dollar}) absorbed by forest canopies downwind from an elevated point source were examined by computer simulations and by measurements based on PbO{dollar}sb2{dollar}-sulfation plates. The simulations involved four modules for modelling the release, transport and absorption of SO{dollar}sb2{dollar}: (1) a turbulence module, (2) a dispersion module, (3) a foliar absorption module, and (4) an SO{dollar}sb2{dollar}-loading assessment module. Daily amounts of absorbed SO{dollar}sb2{dollar} were calculated for downwind distances from 0 to 42 km, for smokestack heights from 30 to 200 m, and for different weather conditions, which included neutral conditions, and transitions from stable to unstable conditions. Per hectare rates of SO{dollar}sb2{dollar} deposition and absorption were calculated as affected by wind speed, turbulence, and canopy moisture, from dawn to dusk. Year-round influences of changing weather conditions on the SO{dollar}sb2{dollar} deposition pattern as affected by precipitation, atmospheric stability, wind speeds and wind directions were estimated by way of Monte Carlo simulations. These simulations were calibrated for the area surrounding the SO{dollar}sb2{dollar}-emitting power generator at Grand Lake in Central New Brunswick (SO{dollar}sb2{dollar} emission rate {dollar}sim{dollar} 30,000 tonnes per year). The predicted rates of canopy-absorbed SO{dollar}sb2{dollar} were similar to those obtained with the PbO{dollar}sb2{dollar} plates. The comparison, however, revealed that topography is an important factor in modifying actual SO{dollar}sb2{dollar} absorption rates. In total, the annual amount of SO{dollar}sb2{dollar} absorbed within 42 km of the source was about 2% of the total annual SO{dollar}sb2{dollar} emissions. Increasing the smokestack height from 72 m (current height) to 200 m would reduce this number to about 1%. |
