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Ozone Data Sources

Ozone monitoring studies have identified different O₃ exposure profiles at high elevations (greater than 4,900 feet) than at lower elevations (less than 1,600 feet) and near sea level (Aneja and others 1994). Levels of O₃ in mountains are lower than in lowlands during the daytime. Near sea level, O₃ levels are very high during the day, often exhibiting a distribution characteristic of the peak hours for automobile traffic. The concentrations in the mountainous areas of the South have important implications for forest health. The ambient O₃ concentrations are sufficiently high to induce injury to sensitive native vegetation in the Blue Ridge Mountains (Skelly and Hildebrand 1995). In addition, some areas in the region are downwind of significant NO_x and VOC emission sources. For example, regionally high O₃ levels found in the Blue Ridge Mountains and Shenandoah Valley of Virginia result from a combination of upwind emission sources located in the industrial Midwest and specific weather patterns (Wolff and others 1977). These weather-related O₃ episodes may be attributed to a combination of local- and regional-scale factors: (1) higher than normal ambient temperatures, (2) wind speeds and directions associated with stationary high-pressure systems that produce local air stagnation, and (3) lower than normal relative humidity (Aneja and Li 1990).