The evolution of the boundary layer and its effect on air chemistry in thePhoenix area

During a 4-week period in May and June of 1998, meteorological and chemical measurements were made as part of a field campaign carried out in the Phoe nix area. Data from the field campaign provide the first detailed measureme nts of the properties of the convective boundary layer in this area and of the effects of these properties on ozone levels. The meteorological and che mical measurements have been combined with results from a set of meteorolog ical, particle, and chemistry models to study ozone production, transport, and mixing in the vicinity of Phoenix. Good agreement between the simulatio ns and observations was obtained, and the results have been used to illustr ate several important factors affecting ozone patterns in the region. Heati ng of the higher terrain north and east of Phoenix regularly produced therm ally driven circulations from the south and southwest through most of the b oundary layer during the afternoon, carrying the urban ozone plume to the n ortheast. The combination of deep mixed layers and moderate winds aloft pro vided good ventilation of the Phoenix area On most days so that multiday bu ildups of locally produced ozone did not appear to contribute significantly to ozone levels during the study period. Sensitivity simulations determine d that 20 to 40% of the afternoon surface atone mixing ratios (correspondin g to 15 to 35 ppb) were due to vertical mixing processes that entrained res ervoirs of ozone into the growing convective boundary layer. The model resu lts also indicated that ozone production in the region is volatile organic compound limited.