Differences in the Temporal and Spatial Distribution of Ground-Level Ozone in Large Urban, Small Urban and Rural Areas in Georgia, USA

Many large consolidated metropolitan areas, several small urban centers, and even some rural regions do not meet the new 8-hour ozone National Ambient Air Quality Standard. 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 this study, we evaluated differences in the temporal and spatial distribution of ground-level ozone in large urban, small urban and rural areas. We used a Kolmorogov-Zurbenko (KZ) filter to decompose ozone time series at each of 58 sites in and around Georgia into five components based on frequency: intra-day, diurnal, synoptic, seasonal and long term. The relative contribution of each component to ozone variability at each site was then assessed. 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. We consider that these differences are chemical in nature and result from nighttime loss (scavenging by fresh NO emissions in the city) and possibly lower daytime production efficiency of ozone in the more metropolitan areas. This is thought to be a reasonable explanation and the purpose of further research, to compare production efficiencies, differences in composition, and to determine the feasability of treating these differences differently from a policy and regulation perspective. In a separate analysis, we assume the synoptic scale components generally represent the shared regional influence of weather. In this sense, the correlation of the synoptic time series among sites is used to define a spatial area of influence that delineates urban airsheds from rural airsheds, and identifies areas in which the urban and rural airsheds interface.