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 B ig Meadows, Virginia. Three methodologies were employed to analyze the 6-ye ar ozone data set (1989-1994) from this elevated, regional, background moni toring site. (1) A. springtime case study showed that repeated dynamic proc esses associated with three consecutive cold-front passages were related to a cyclic pattern in ozone variation. Back-trajectory analysis suggests a s tratospheric as well as anthropogenic influence on the enhanced ozone event s. (2) Analyses of the meteorology and back trajectories associated with da ytime ozone events above the 90th percentile and below the 10th percentile revealed strong contrasts in transport history. Enhanced events were strong ly associated with dry high-pressure conditions and half were associated wi th descent through surface anticyclones. Conversely, the depleted-ozone tra jectories were typically associated with low-pressure systems and were more likely to be associated with ascending or low-level flow than descending f low. (3) Back trajectories were grouped according to similar transport path s to try to explain ozone variance by air-mass transport. In a previous stu dy, segregation of ozone values by transport path explained a relatively la rge amount of the ozone variance: at Bermuda. However, in our study, this a pproach explained only a small portion of the ozone variance. We attribute the differences in explained variance at the two sites to complex interacti ons between transport and photochemistry over the continent and a simplifie d transport regime over the western North Atlantic Ocean.