PNNL

Abstract

During a four-week period in May and June of 1998, meteorological and chemical measurements were made as part of an field campaign carried out in the Phoenix area. Data from the field campaign provide the first detailed measurements of the properties of the convective boundary layer in this area and of the effects of these properties on ozone levels. The meteorological and chemical measurements have been combined with results from a set of meteorological, particle, and chemistry models to study ozone production, transport, and mixing in the vicinity of Phoenix. Good agreement between the simulations and observations was obtained, and the results have been used to illustrate several important factors affecting ozone patterns in the region. Heating of the higher terrain north and east of Phoenix regularly produced thermally-driven circulations from the south and southwest through most of the boundary layer during the afternoon, carrying the urban ozone plume to the northeast. The combination of deep mixed layers and moderate winds aloft provided good ventilation of the Phoenix area on most days so that multi-day buildups of locally-produced ozone did not appear to contribute significantly to ozone levels during the study period. Simulations showed the sensitivity of daytime surface ozone mixing ratios to vertical mixing processes, demonstrating the dependence of afternoon surface ozone mixing ratios on reservoirs of ozone located above the growing convective boundary layer. The model results also indicated that ozone production in the region is VOC-limited.