1. Network Assessment Based on Daily Max Ozone Concentration Prepared for EPA OAQPS Richard Scheffe by Rudolf B. Husar and Stefan R. Falke Center for Air Pollution Impact and Trend Analysis, CAPITA Washington University, St. Louis December 2000

2. Network Assessment Based on Ozone Concentration AQ Management ActivityGeographic Info. Need Station Measure Risk assessmentPollutant concentration 4 th highest O3 Risk AssessmentPersons/Station Compliance evaluationConc. vicinity to NAAQS Deviation from NAAQS Reg./local source attribution & trackingSpatial coverage Area of Sampling Zone All aboveEstimation uncertainty Meas. & estimate difference Persons in sampling zone There are at least five different measures that represent the information need for (1) risk assessment, (2) compliance monitoring and (3) tracking are listed below. The daily max O3 concentration measures the environmental stress on the population. The specific measure used id the 4th highest 8hr daymax ozone averaged over 93-95. Using this objective measure, the station with the largest daily max is ranked #1.

3. The Ozone Database used for Network Assessment The ozone datasets were quality controlled and fused from the AIRS (491 stations) and CastNet (32 stations). The AIRS sites are clustered mainly in urban-metropolitan areas while the CastNet sites cover rural regions. The concentration metric used were the 4 th highest daily 8 hr average during 1993-95 and the 90%-tile daily max ozone, 1990-95. This integrated ozone data set was used for the OTAG Air Quality Analysis Workgroup.

4. 4 th Highest and 90 th Percentile Ozone Concentration The two ozone concentration metric show very similar spatial pattern. The peak values occur in metro areas over the NE Megalopolis, Atlanta, Houston, Dallas, downwind of Chicago and a broad area over the Ohio River Valley. At the edges (four ‘corners’) of EUS, the O3 levels are near the troposphereic background.

5. Ranking by Daily Max Concentration The daily max concentration is a factor in health risk. The stations with the highest O3 levels (red) are located over the NE Megalopolis, Ohio River Valley and the urban center in the Southeast: Dallas, Houston, Atlanta. The stations with the lowest O3 levels (blue) are located throughout the remainder EUS. Contiguous regions of low O3 are found in Florida, Upper Midwest, and the inland part of the Northeast. From O3 exposure perspective, the blue stations are ranked lowest.