The Transport of Atmospheric Pollutants in the Complex Terrain of the Phoenix Area

Atmospheric aerosol data was collected during two Phoenix Air-Flow Experiments (PAFEX). The overall goal of the experiments is to develop an improved air pollution model for use in urban areas of complex terrain such as Phoenix. The complex-terrain features influence the winds, producing various air flows within the region. The interaction of these flows are difficult to simulate through the use of current air pollution models. The aerosol data are important to measure because certain particle types can be used as tracer particles of the air flow, lending information about the winds that can be used in the models.

During the winter experiment, PAFEX-I, which took place near central Phoenix during early 1998, aerosol data was collected as a function of time and height. The observed aerosol concentrations indicate that the transport of the particles is driven predominantly by the terrain flows. The iron oxide type is one of the more abundant aerosol types observed. This aerosol group appears to consistently follow the air flow and may be good for tracer particles.

Ozone and aerosol ground measurements were collected during PAFEX-II, which took place in the east valley during the summer of 1998. The observations show the transport of an ozone plume, which originated in central Phoenix and moved eastward by the upvalley regional terrain flow. This terrain flow occurs daily in the Phoenix area during the summer. Simulations carried out with the HOTMAC mesescale model also show how the pollution plume spreads eastward due to the upvalley flow during the day time and how it is reversed at night due to katabatic winds. The aerosol concentration, however, does not follow such a consistent trend, which suggests that the aerosol types dominating the data set were transported from different origins, and likely by different flows, than the ozone. Sulfate is one of the dominant aerosol types, and particles of that type may serve as useful tracer particles once the source can be determined.