A Numerical Analysis of Los Angeles Basin Pollution Transport to the Grand Canyon under Stably Stratified, Southwest Flow Conditions

This paper presents a numerical investigation of air pollutant transport from the Los Angeles Basin to Grand Canyon National Park (GCNP) under the stably stratified wintertime, synoptic highpressure conditions that existed during lo-13 February 1987. The Colorado State University Regional Atmospheric Modeling System (CSU-RAMS) is used to develop fields of different atmospheric variables for 54 simulated hours. These fields are applied in a Lagrangian particle dispersion model (LPDM) to simulate the advection of pollutant particles for this period. It is found that under the generally southwest flow conditions presented, particles released from the Los Angeles Basin will impact the Grand Canyon but only in small amounts. By comparing a flat to complex terrain simulation, the importance of the terrain features between Los Angeles and GCNP to the dispersion of Los Angeles Basin pollutants is made obvious. Mountain barriers and undulating land reduce what could otherwise be a very serious pollutant impact on GCNP. Based on these results the conclusion is made that despite southwest average flow aloft during the Winter Haze Intensive Tracer Experiment (WHITEX) period of lo-13 February 1987, Los Angeles Basin pollution did not contribute significantly to the observed visibility reduction in the Grand Canyon during that time period. Key word index: Dispersion, long-range transport, terrain-induced, mesoscale modeling, boundary layer.