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Weekday/Weekend O 3 and PM Differences in Three Cities Outside California

This research study examines the day-of-the-week dependence of O3 and PM concentrations in three urban locations outside California. The objective is to test the hypotheses for the "weekend effect" and identify changes in weekday/weekend differences over a longer period. The study utilizes data analysis, modeling, and field studies to analyze the diurnal profile of O3 concentrations, daily maximums, and 1-hour/8-hour averages of O3 and PM10/PM2.5.

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Weekday/Weekend O 3 and PM Differences in Three Cities Outside California

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  1. Weekday/Weekend O3 and PM Differences in Three Cities Outside California Betty K. Pun and Christian Seigneur AER, San Ramon, CA Warren White Washington University, St. Louis, MO “Weekend Effect” Research Workgroup Meeting 13 April 2000

  2. Introduction Chicago Philadelphia • CARB, NREL, CRC • Data analysis • Modeling • Field study Atlanta CRC Project A-36B is a data analysis project to study weekday/weekend differences in O3 and PM in areas outside CA

  3. Objectives • At 3 urban locations outside CA, study the day-of-the-week dependence of • diurnal profile of hourly O3 concentrations • daily maximum 1-hour and 8-hour O3 • PM10 and PM2.5 • Test hypotheses for the “weekend effect” • Identify changes in the weekday/weekend difference over a longer period

  4. Technical Approach

  5. Ozone Monitoring Sites Area No. Sites Years(1) Months Atlanta 8 5Mar/Apr - Oct/Nov 3 1 Chicago 21 5 Apr - Oct or Jan - Dec 5 2/3 Philadelphia 6 5 Mar - Nov or Jan - Dec (1) 1995 - 1999

  6. Hour-of-the-Week Analysis Hourly Data Record by Site • Ozone • Atlanta, GA • Chicago, IL • Philadelphia, PA • PM • Chicago, IL Group by Day of Week Group by Hour of Day Average Concentration of Each Hour

  7. Atlanta, GA; 1995 - 1999 Friday Monday

  8. Chicago, IL; 1995 - 1999 Sunday Wednesday

  9. Philadelphia, PA; 1995 - 1999 Sunday Friday

  10. Maximum One-Hour Concentrations

  11. Maximum One-Hour Concentrations Mean and Standard Deviation

  12. Bootstrap Sampling Bootstrap Samples Observed Data Sampling with replacement . . . The population distribution of any statistic can be approximated by the distribution of that statistic derived from the bootstrap samples

  13. Hypothesis Testing by the Shift MethodExample: Friday-Monday O3 Difference Probability that the observed difference (5.2 ppb) occurs by chance if the true difference is 0 ppb Null distribution Bootstrap distribution Distribution of the difference Hypothesized difference 0 ppb (Null hypothesis) Observed difference 5.2 ppb Bootstrap mean difference 5.3 ppb

  14. Atlanta, GA; Maximum One-Hour O3 • Average Values: 8 out of 11 sites show statistically significant(1) differences • High O3 on Fridays (7) and Saturdays (1) • Low O3 on Mondays (7) and Sundays (1) • Median Values (7) and 90th Percentile (10) • High O3 on Fridays • Low O3 on Mondays, Sundays, and Tuesdays • Exceedances of the NAAQS occurred on Fridays (41), Thursdays (40), Saturdays (31) (1) 10% confidence level

  15. Maximum One-Hour Concentrations Mean and Standard Deviation

  16. Chicago, IL; Maximum One-Hour O3 • Average Values: 25 out of 26 sites show statistically significant differences • High O3 on Sundays (23) and Saturdays (2) • Low O3 on Tuesdays (12), Wednesdays (10), Other Weekdays (5) • Median Values (24) • High O3 on Sundays; Low O3 during midweek • 90th Percentile (25) • High O3 on Saturdays and Sundays; low O3 early work week

  17. Maximum One-Hour Concentrations Mean and Standard Deviation

  18. Philadelphia, PA; Maximum One-Hour O3 • Average Values: all 6 sites show statistically significant differences • High O3 on Sundays (4) and Saturdays (2) • Low O3 on Fridays (3), Wednesdays (2), and Thursdays • Median Values (3) • High on Sundays; Low during late week • 90th Percentile (6) • High on Weekends and Mondays; low on Fridays

  19. Maximum 8-Hour O3 Concentrations • Atlanta • Day-of-week differences in 8-hour O3 is less significant than 1-hour O3 • High concentrations on Fridays (4 sites) and Saturdays (4) • Chicago • Day-of-week difference in 8-hour O3 similar to 1-hour O3; individual sites may show higher or lower differences • High concentrations on Sundays; low during midweek

  20. Maximum 8-Hour O3 Concentrations (continued) • Philadelphia • Weekly cycle more apparent in 8-hour than in 1-hour concentrations • High O3 on weekends, low late work week

  21. PM10 at Chicago, IL; 1995 - 1999 (mg/m3)

  22. 24-Hour Average PM10 • High 24-hour averaged PM on Tuesdays and Fridays, low PM on weekends • Statistics significant (5%) at all 5 sites (mg/m3)

  23. Hour-of-week Profiles of NOx

  24. Correlation Between O3 and NOx

  25. Summary • Atlanta: O3 weekly buildup • High O3 on Fridays, low O3 on Mondays • Chicago: O3 weekend effect • High O3 on Sundays, low O3 during midweek • Philadelphia: O3 weekend effect • High O3 on Sundays, low O3 during late work week • Chicago: PM high during the week, low on weekends

  26. Future Work • Use VOC/NOx ratio to bypass the confounding effects of meteorology • Test hypotheses • Test historical trends • Need access to EPA’s AIRS database!!!!!!! • VOC • PM10 for Atlanta, Philadelphia • Availability of PM2.5

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