Application of a statistical trajectory model to the simulation of sulfur pollution over northeastern United States

Abstract

A regional-scale model of atmospheric sulfur pollution is developed for the northeastern United States. The model approximates the long-term average plume from each pollutant source by a series of puffs in which the horizontal distribution of pollutant concentration is assumed to be Gaussian. To construct the puffs, a simulated tracer particle is released twice a day and its location is computed for every 3-h interval by use of observed wind velocities. The location of the center of each puff at certain times after the release is computed by averaging the coordinates of all the particles at the same time after the release and the standard deviations of the coordinates of these particles with respect to the puff center are used to define the size of the puff. The vertical distribution of material in each puff is computed from a numerical integration of a system of two equations which describe the budgets of sulfur dioxide and sulfate, with consideration of inversion height, surface deposition, effective stack height and chemical transformation. These four factors are varied in a series of sensitivity tests for the model. The final concentrations of sulfur dioxide and sulfate at a point of interest are obtained by summing the contributions of all the puffs to that point. In the present simulation, pollutant sources of sulfur dioxide originated from 53 major power plants in the north-eastern United States are considered and maps of predicted sulfur dioxide and sulfate concentrations at 2 m height and of the dry deposition of sulfur have been presented.