Meteorological controls on ozone at an elevated eastern United States regional background monitoring site

To determine synoptic- and regional-scale meteorological controls on ozone upwind of the North Atlantic Ocean, we developed an ozone climatology for Big Meadows, Virginia. Three methodologies were employed to analyze the 6-year ozone data set (1989-1994) from this elevated, regional, background monitoring site. (1) A. springtime case study showed that repeated dynamic processes associated with three consecutive cold-front passages were related to a cyclic pattern in ozone variation. Back-trajectory analysis suggests a stratospheric as well as anthropogenic influence on the enhanced ozone events. (2) Analyses of the meteorology and back trajectories associated with daytime ozone events above the 90th percentile and below the 10th percentile revealed strong contrasts in transport history. Enhanced events were strongly associated with dry high-pressure conditions and half were associated with descent through surface anticyclones. Conversely, the depleted-ozone trajectories were typically associated with low-pressure systems and were more likely to be associated with ascending or low-level flow than descending flow. (3) Back trajectories were grouped according to similar transport paths to try to explain ozone variance by air-mass transport. In a previous study, segregation of ozone values by transport path explained a relatively large amount of the ozone variance: at Bermuda. However, in our study, this approach explained only a small portion of the ozone variance. We attribute the differences in explained variance at the two sites to complex interactions between transport and photochemistry over the continent and a simplified transport regime over the western North Atlantic Ocean.