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Rationale. Previous studies have demonstrated associations of high ozone levels with increased epidemiologic as well as lung function measures of asthma activity. Objectives. In an observational study during the summer months, we hypothesized that higher ambient ozone levels are associated with more frequent symptoms, higher airway and systemic inflammation, as well as worse lung function in asthmatics as compared with non-asthmatic individuals. Methods. Thirty-eight asthmatics and thirteen healthy control subjects residing in metropolitan Atlanta were enrolled during peak ozone season. Medical histories, quality-of-life questionnaires, spirometry, serum immunoglobulin (IgE), peripheral eosinophil counts, and exhaled nitric oxide (NO) were obtained during study visits. Personal ozone exposures over the 2 days before presentation were estimated based on location and activity surveys. Main results. Upper airway symptoms were more frequent in asthmatics. Higher levels of ozone were associated with worse airflow obstruction, lower quality of life scores, greater eosinophilia, and higher exhaled NO levels in asthmatics. Finally, both asthmatics and non-asthmatics with allergies showed associations between air quality and airway inflammation. Conclusions: In adults with asthma but not controls studied during peak ozone season, increasing ozone exposure predicted lower lung function and increased biomarkers of respiratory and systemic inflammation. These associations were enhanced in atopic participants, both with and without asthma. Importantly, the study findings were noted while atmospheric ozone levels were predominantly within the current and revised national air quality standards. [ABSTRACT FROM AUTHOR]