Influence of synoptic and mesoscale meteorology on ozone pollution potential for San Joaquin Valley of California

The distribution of historical ozone levels for a region is tabulated as a function of its prevailing synoptic and mesoscale influences. Meteorological patterns are determined sequentially from extended records of hourly surface wind measurements sampling relevant low-level flows. A visualization method is presented to readily indicate the likelihoods for exceedances to occur under a variety of meteorological conditions. The study domain is San Joaquin Valley (SJV) of California, which is divided into three subregions (North. Central, and South). Each day from May-October of 1996-2004 is labeled using synoptic (single-day) and mesoscale (intra-day) patterns. Emissions levels are assumed roughly constant for this period following the introduction of reformulated gasoline to California. Synoptic motions largely control the regional SJV ozone pollution potential: the same single-day patterns are identified for all three SJV subregions. Additionally, a unique mesoscale flow feature is identified in each subregion that strongly affects its ozone levels: flows through minor Coast Range gaps for N-SJV, the Fresno Eddy for C-SJV, and flows through Mojave Pass for S-SJV. The strength of each mesoscale feature is characterized using 1-h surface u or v wind components that explain local ozone pollution potentials. (C) 2008 Elsevier Ltd. All rights reserved.