PNNL

Abstract

The importance of boundary-layer structures and flow patterns on the air quality of cities located near regions of elevated terrain is well established. Perhaps the most easily recognized effect is the trapping of pollutants in inversions that form in basins or other low lying areas, but other mesoscale meteorological phenomena may be equally significant. While there have been a number of field campaigns in California, relatively few upper-air meteorological measurements have been made in the vicinity of Phoenix and in other major cities in the western U.S. In this paper we discuss three features of the boundary layer observed during the 1998 field campaign that are influenced by the heating and cooling of the terrain surrounding Phoenix: 1) the spatial variation of the mixed layer depth, 2) the capping inversion at the top of the residual layer, and 3) the depth of the atmosphere to which cooling extends during the night. In addition to the measurements, a meteorological and chemical modeling system is used to investigate these features and describe their effect on the vertical transport and mixing of pollutants.