1. Network Assessment Based on Compliance Monitoring (Deviation from NAAQS) 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 Deviation from NAAQS 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. & est. 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. Deviation from NAAQS measures the station’s value for compliance evaluation. The station ranking is according to the absolute difference between the station value and the NAAQS (85 ppb). The highest ranking is for the station whose concentration is closest to the standard (smallest deviation). Stations well above or below the standard concentration are ranked low.

3. Ozone > 85 and and Population Maps The ozone maps (>85 ppb) show that the highest values occur primarily over high population density metropolitan areas. In some areas, e.g. Chicago-Milwaukee, the urban ozone peak is displaced downwind Over the Ohio River basin in addition to the urban ozone islands, there is also a broader regional-scale (1000 km) ozone bulge.

4. Stations with Ozone > 85 ppb: Measured and Estimated Using the measured values, there are 270 stations (52% of 523) with > 85 ppb. Estimating the concentration (by removing each site) yields 277 stations (53%) with > 85 ppb Evidently, removing one station at a time does not change the total number or spatial pattern of the >85 ppb concentration field.

5. Change of Exceedance Classification: Measured and Estimated The characteristic estimation error of ~5-6 ppb changes the classification for a significant number (109 out of 523, 21%) of the stations (left map, yellow stations). The classification flip-flop occurs mainly at the ‘edges’, where the of O3 concentration is near 85 ppb (right map, yellow stations). The flip-flop is rather symmetric: 51 stations changed from > 85 to < 85 while 58 changed vice versa. Evidently, the estimation is mainly influenced by random errors and not by systematic biases.

6. Counties with > 85 ppb O3: Measured and Estimated Noncompliance with NAAQS is only applied if there is a monitor in the violating county The O3 data (AIRS, CastNet, 1993-5) and spatial extrapolation allows concentration estimation over unmonitored counties. It is estimated that over the Eastern US, only a third (214) of the total number of counties with > 85 ppb (664) have ozone monitors, while 2/3 (450) of the counties with > 85 ppb estimated ozone are unmonitored. CastNet stations with >85 ppb account for 11 (5%) of the 214 stations reporting >85 ppb values. Hence, the number and location of ozone monitors is a major factor in determining which and how many counties have > 85 concentration.

7. Absolute Deviation from NAAQS The deviation from NAAQS was calculates as the absolute difference between the measured value and 85 ppb. From regulatory compliance perspective, station that are well above or below the NAAQS are of marginal interest. For compliance, the stations that are of most interest are those with 4 th highest O3 in the vicinity of the standard. In the map, the highlighted (red) areas have concentration near 85 ppb.

8. Ranking by Deviation from NAAQS The deviation from the NAAQS (85 ppb) measures the station importance for compliance. The stations closest to the NAAQS (red dots) occupy much of the central Eastern US, south of the Great Lakes and N. of Tennessee-S. Carolina. The stations with large +/- deviation from NAAQS (blue) are clustered over the megalopolis, Dallas, Houston (O3>85ppb) or over Florida, Upper Midwest (O3<85ppb) From compliance monitoring perspective, the blue stations have the lowest rank.