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Weekday/Weekend O 3 and PM Differences in Three Cities Outside California CRC Project A-36B

Weekday/Weekend O 3 and PM Differences in Three Cities Outside California CRC Project A-36B. Betty K. Pun and Christian Seigneur AER, San Ramon, CA Warren White Washington University, St. Louis, MO “Weekend Effect” Research Workgroup Meeting 6 September 2000. Introduction. Chicago.

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Weekday/Weekend O 3 and PM Differences in Three Cities Outside California CRC Project A-36B

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  1. Weekday/Weekend O3 and PM Differences in Three Cities Outside CaliforniaCRC Project A-36B Betty K. Pun and Christian Seigneur AER, San Ramon, CA Warren White Washington University, St. Louis, MO “Weekend Effect” Research Workgroup Meeting 6 September 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. Summary from Last Progress Report • Ozone Day-of-the-week analysis • Atlanta, GA • High Fridays, low Mondays • Chicago, IL • High Sundays, low Tuesdays, Wednesdays • Philadelphia, PA • High Sundays, low Fridays • PM10 (24-hour average) • Chicago, IL • High during week, low Sundays

  6. Atlanta PM10 Day-of-the-week Behavior • 1 station; July 98 to June 99 • Jagged diurnal profiles • 24-hour average: • Highest on Tuesdays • Lowest on Sundays • Difference significant at 10% level

  7. Philadelphia PM10 Diurnal Profiles • 2 stations, 1995 to 1998

  8. Philadelphia PM10 Day-of-the-week Behavior 24-hour average: • Highest on Wednesdays or Thursdays ; lowest on Sundays • Difference between all weekday-weekend pairs significant at 5% level

  9. Atlanta PM2.5 Day-of-the-week Behavior • 24-hour average PM2.5 data • 8 sites in 1999 • Highest late work week and Saturdays • Thursdays (3), Saturdays (2), Fridays (2)*, Wednesdays (1) • Lowest early work week and Sundays • Mondays (4), Sundays (3), and Tuesdays (1)* • Statistically significant differences at 5 sites * statistically insignificant at 10% level

  10. Chicago PM2.5 Day-of-the-week Behavior • 24-hour average PM2.5 data • 13 sites in 1999 • High concentrations on Saturdays (6), Wednesdays (5), and Fridays (2) • Low concentrations on Tuesdays (11), Thursdays (2) • Statistically significant differences at all sites

  11. Philadelphia PM2.5 Profiles • 1 station, 1999

  12. Philadelphia PM2.5 Day-of-the-week Behavior 24-hour average: • Highest on Saturdays, Tuesdays; lowest on Thursdays • Differences significant at 10% level

  13. Hypothesis Testing

  14. Hypothesis: VOC/NOx Ratio • VOC/NOx ratio increases during weekend Atlanta Chicago Philadelphia Weekday 5.6 - 6.6 2.3 - 2.5 9.4 - 10.5 Weekend 7.9 - 8.4 3.1 - 3.5 11.0 - 14.1 Increase in the VOC/NOx ratio during the weekend leads to increase in O3 in a VOC-sensitive airshed

  15. Hypothesis: VOC/NOx Ratio • Correlation between O3 and VOC/NOx ratio (grouped by day of the week) Atlanta Chicago Philadelphia Correlation coef. 0.04 0.98 0.67 R2 0.00 0.96 0.45

  16. Hypothesis: Friday/Saturday Night Traffic Increased traffic on Friday and Saturday evenings leads to increased carry-over of precursors and increased O3 formation potential on the weekends • Predawn NOx (ppb) lower on weekends Atlanta Chicago Philadelphia Weekday 28 - 38 38 - 51 36 - 43 Weekend 26 - 33 37 - 46 29 - 39 • Predawn CO (ppm) higher on weekends Atlanta Chicago Philadelphia Weekday 0.76 - 0.83 0.69 - 0.73 0.72 - 0.75 Weekend 0.90 - 0.99 0.75 - 0.78 0.87 - 0.91

  17. Hypothesis: Friday/Saturday Night Traffic • Correlation between O3 and predawn NOx Atlanta Chicago Philadelphia Correlation coef. 0.70 - 0.58 - 0.57 R2 0.50 0.34 0.32 • Correlation between O3 and predawn CO Atlanta Chicago Philadelphia Correlation coef. 0.11 0.77 0.92 R2 0.01 0.59 0.85

  18. Hypothesis: Precursor Carry-over Carry-over of precursors from one day to the next is the driving force for the weekly cycle of O3 • Atlanta (sensitive to predawn NOx) Correlation coef. R2 • O3 vs. previous day NOx 0.75 0.56 • O3 vs. previous day NOy 0.87 0.76 • Chicago, Philadelphia (sensitive to predawn CO) Correlation coef. R2 • O3 vs. previous day CO - 0.09, - 0.07 0.01, 0.00 • O3 vs. previous day VOC 0.56, 0.31 0.31, 0.09

  19. Hypothesis: PM Affects Photochemistry Reduction in fine PM emissions during weekends results in increased photochemical activity and O3 • In Atlanta, Chicago, and Philadelphia, PM2.5 is high on Saturdays; evidence is weak for the decrease of fine PM emissions during weekends • Weak correlation between O3 and solar radiation Atlanta Chicago Philadelphia Correlation coef. 0.23 0.63 0.56 R2 0.06 0.39 0.31 • PM2.5 correlates positively with solar radiation

  20. Future Work • Finish testing hypotheses • Changes in activity patterns • Temporal distribution • Spatial distribution • Changes in emission sources (VOC/PM composition) • Analyze historical trends in O3 weekend effect • Complete final report

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