Differences in Ozone Production Efficiencies in Large Urban, Small Urban and Rural Areas in Georgia, USA

The implementation of the new 8-hour ozone National Ambient Air Quality Standard forces not only many large consolidated metropolitan areas, but also several small urban centers, and even some rural regions into non-attainment status. The importance of chemical and physical mechanisms affecting ozone formation, accumulation, transport, and destruction in such areas may be different and thus, require different approaches for managing the air pollution. In previous studies, we evaluated differences in the temporal distribution of ground-level ozone in large urban, small urban and rural areas. The temporal analysis suggested that the seasonal components in rural areas play a larger role in ozone variability than they do in more urbanized areas. The rural areas also have a higher long-term baseline relative to the more urban areas. Here, we consider that these differences are chemical in nature and result from nighttime loss and possibly lower daytime production efficiency of ozone in the more metropolitan areas. O₃ and NO_y collected during the summer of 2002 are used to differentiate composition and production efficiencies of ozone between large metropolitan and small urban air in the southeastern United States. Results indicate that the small urban locations produce ozone twice as efficiently as observed at the metropolitan Atlanta sites with respect to NO_y. Data generated with the Community Multi-scale Air Quality (CMAQ) modeling system was used to compare modeled results to the stationary observations. Model results reflect that small urban locations produce ozone twice as efficiently as the large metropolitan Atlanta.