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

Abstract

Dispersion and subsequent deposition of SO 2 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, SO 2 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 SO 2 from the air to the land, and (iv) flat terrain. Deposition to the forest is determined by calculating the rate of SO 2 flux from individual air parcels to the land according to the parcel's velocity and an assumed air-to-surface SO 2 transfer coefficient. Daily cumulative SO 2 deposition rates are calculated by summing the simulated diffusional fluxes of SO 2 from air to land over each simulated time step. Daily cumulative SO 2 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 SO 2 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 SO 2 were similar to those obtained with a mobile SO 2 detection unit and a SO 2-monitoring unit 42 km NE from the emission source. Cumulative SO 2 deposition rates were reasonably similar to those obtained with PbO 2 sulfation plates. A detailed comparison revealed topography was an important factor in modifying actual cumulative SO 2 deposition rates.