Analysis of the dispersion characteristics of the Navajo generating station plume using a Lagrangian Monte-Carlo model

Abstract

The Monte-Carlo Lagrangian particle model MC-LAGPAR developed by Aero Vironment Inc., been used to analyze the dispersion characteristics of the Navajo Generating Station Power Plant plume over the Grand Canyon area. The study was performed on a 26 × 26 grid covering an area of 67,600 km 2. The simulations were performed for the period January 18–22, 1990, a high SO 2 concentration episode during which the plume from the power plant reached Hopi Point, a receptor site on the south rim of the Grand Canyon. The meteorological data used as input to the MC-LAGPAR model were generated by MM4, the Penn State/NCAR mesocale model. The dispersion characteristics of the NGS plume are presented using plan views (XY) of the particles in the computational domain, for different hours of the day. The four-hour average SO 2 concentrations predicted by the model, assuming no SO 2 oxidation and no deposition, are in good agreement with the measurements at Hopi Point. The time at which the peak SO 2 concentration occurs is predicted accurately. This suggests that the power plant was the major contributor to the levels of SO 2 measured during the episodic hours. However, simulations assuming a one-percent-per-hour SO 2 oxidation give sulfate levels that are different from the measurements both in magnitude and in the time at which maximum sulfate level occurs. This suggests other sources than NGS were the major contributor to sulfate at Hopi Point during the January episode.