Simulating sulfur dioxide plume dispersion and subsequent deposition downwind from a stationary point source: A model

Dispersion and subsequent deposition of SO2 downwind from a stationary point source are affected by several transport processes: buoyancy at the source, advection, and air turbulence en route from the source to the area of impact. In this paper, SO2 transport processes are simulated by way of Lagrangian air parcel trajectory simulations. In these simulations, the source releases air parcels in puffs. The calculations cover both daytime and night-time conditions and take into account: (i) solar geometry, (ii) diurnal variations of wind speed and air turbulence, (iii) resistance to the transfer of SO2 from the air to the land, and (iv) flat terrain. Deposition to the forest is determined by calculating the rate of SO2 flux from individual air parcels to the land according to the parcel's velocity and an assumed air-to-surface SO2 transfer coefficient. Daily cumulative SO2 deposition rates are calculated by summing the simulated diffusional fluxes of SO2 from air to land over each simulated time step. Daily cumulative SO2 amounts are calculated for downwind distances from 0 to 42 km, for smokestack heights from 30 to 200 m, and for each day of the year according to historical year-round and local weather patterns representative of days with neutral conditions and days with transitions from stable to unstable conditions. Annual per hectare rates of SO2 deposition are calculated by way of Monte Carlo simulations, according to historical patterns for daily wind, atmospheric stability, and precipitation. These simulations are calibrated for the area surrounding a coal-burning power generator at Grand Lake in south-central New Brunswick, Canada. Calculated concentrations for SO2 were similar to those obtained with a mobile SO2 detection unit and a SO2-monitoring unit 42 km NE from the emission source. Cumulative SO2 deposition rates were reasonably similar to those obtained with PbO2 sulfation plates. A detailed comparison revealed topography was an important factor in modifying actual cumulative SO2 deposition rates.