Special session of California 2000 field study - Air Pollution Modeling and Its Application - page 507

8.2 Meteorological Triggers for Ozone Episodes
in Central California
Ahmet Palazoglu, Angadh Singh, and Scott Beaver
University of California, Davis, CA, USA
Abstract A wind field cluster analysis was performed for the summer ozone
seasons (May-October) of 1996-2004 for the Central California domain. The data
consisted of hourly surface wind speed and direction measurements collected by a
number of surface monitoring networks. For each air basin, we identified days
sharing similar diurnal cycles. Each day and basin was categorized among these
recurring meteorological patterns associated with distinct 500-hPa conditions. We
show how summer air quality is consistently driven by these synoptic (large-scale)
influences - anticyclonic and cyclonic weather systems that develop over the Pacific
Ocean and the southwestern United States. Two such anticyclonic patterns are
shown to trigger the majority of the ozone exceedences. For all Central California
air basins, an eastward sweeping ridge of high pressure originating offshore is
associated with rapidly building ozone levels. For the inland San Joaquin and
Sacramento Valleys, the northward migration of an anticyclone forming over
Mojave Desert and/or Four Corners triggers a number of episodes. These episodic
scenarios are illustrated by examples demonstrating these meteorological triggers.
Keywords CCOS 2000 Field Study, cluster analysis, synoptic meteorology, wind
fields
1. Introduction
The purpose of this study was to determine the relationship between meteorology
and ozone levels throughout the CCOS domain, which includes three major,
coupled air basins in non-attainment of ambient ozone regulations: San Francisco
Bay Area (SFBA), San Joaquin Valley (SJV), and Sacramento Valley (SV).
Robust statistical methods (Beaver and Palazoglu, 2006; Beaver et al., 2008) were
applied to routine surface measurements collected from these basins over nine
extended summer ozone seasons (May-October of 1996-2004), for 1,656 days.
The results were essential for conceptual modeling of Central California summer
air quality; ozone numerical modeling and forecasting; air quality planning;
categorizing transport potential; designing future field monitoring programs;