A synoptic climatology of surface-level ozone in eastern Wisconsin

Areas in Eastern Wisconsin typically experience exceedances of the federal health standard for ozone (120 ppb) several times each summer. Since transport has been shown (e.g., Dye et al., 1995) to be a key element in these exceedances, the primary objective of this research project was to investigate and analyze--in a climatological context--the relationship between tropospheric ozone and atmospheric circulation in Eastern Wisconsin. The chief methodological tool employed was a "synoptic climatology".; An additional goal was to achieve a better understanding--in climatological terms--of the relative contributions to ozone exceedance events in Eastern Wisconsin from the local, meso, and synoptic scales. For this goal, methodologies were employed to better resolve the commingled space and time scales that are an integral part of Eastern Wisconsin's ozone problem. The third and final objective of the investigation, was the climatological validation of Dye et al.'s (1995) conceptual model of ozone formation and transport.; One working hypothesis was that long-term climatology does not support the contention that during episodes of elevated ozone, approximately one-half of Eastern Wisconsin's total ozone actually enters the LMAQR from the Eastern and Southern United States (WI DNR, 1994). A second working hypothesis was that contributions at the mesoscale--from the Chicago-Gary-Milwaukee source areas--are the "critical" component for ozone "exceedance" events in Eastern Wisconsin.; This research has: (1) revealed a strong association between ozone exceedances in Eastern Wisconsin and the location of an anticyclone to the east/southeast of Eastern Wisconsin; (2) demonstrated that a strong relationship exists between ozone exceedances in Eastern Wisconsin and southwesterly synoptic-scale flow across Eastern Wisconsin; (3) validated--in a climatological context--Dye et. al.'s (1995) conceptual model of ozone formation and transport; (4) shown that model results which indicate approximately one half of Eastern Wisconsin's ozone during ozone episodes is derived from sources located in the Eastern and Southern U.S., may not be "climatologically" correct; (5) indicated that ozone and precursors generated from source areas at the mesoscale level, may be the quintessential component for exceedances in Eastern Wisconsin; and (6) suggested that the Chicago-Gary area in all likelihood is a larger contributor to exceedances in Eastern Wisconsin than the greater Milwaukee area.