Weekday/Weekend O 3 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

Introduction CARB, NREL, CRC Data analysis Modeling Field study CRC Project A-36B is a data analysis project to study weekday/weekend differences in O 3 and PM in areas outside CA CRC Project A-36B is a data analysis project to study weekday/weekend differences in O 3 and PM in areas outside CA Chicago Philadelphia Atlanta

Objectives At 3 urban locations outside CA, study the day-of-the-week dependence of –diurnal profile of hourly O 3 concentrations –daily maximum 1-hour and 8-hour O 3 –PM 10 and PM 2.5 Test hypotheses for the “weekend effect” Identify changes in the weekday/weekend difference over a longer period

Technical Approach

Ozone Monitoring Sites AreaNo. SitesYears (1) Months Atlanta 8 5Mar/Apr - Oct/Nov 3 1 Chicago 21 5Apr - Oct or Jan - Dec 5 2/3 Philadelphia 6 5Mar - Nov or Jan - Dec (1)

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

Atlanta, GA; Friday Monday

Chicago, IL; Sunday Wednesday

Philadelphia, PA; Sunday Friday

Maximum One-Hour Concentrations

Maximum One-Hour Concentrations Mean and Standard Deviation

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

Hypothesis Testing by the Shift Method Example: Friday-Monday O 3 Difference Distribution of the difference Bootstrap mean difference 5.3 ppb Observed difference 5.2 ppb Hypothesized difference 0 ppb (Null hypothesis) Null distribution Probability that the observed difference (5.2 ppb) occurs by chance if the true difference is 0 ppb Bootstrap distribution

Atlanta, GA; Maximum One-Hour O 3 Average Values: 8 out of 11 sites show statistically significant (1) differences –High O 3 on Fridays (7) and Saturdays (1) –Low O 3 on Mondays (7) and Sundays (1) Median Values (7) and 90th Percentile (10) –High O 3 on Fridays –Low O 3 on Mondays, Sundays, and Tuesdays Exceedances of the NAAQS occurred on Fridays (41), Thursdays (40), Saturdays (31) (1) 10% confidence level

Maximum One-Hour Concentrations Mean and Standard Deviation

Chicago, IL; Maximum One-Hour O 3 Average Values: 25 out of 26 sites show statistically significant differences –High O 3 on Sundays (23) and Saturdays (2) –Low O 3 on Tuesdays (12), Wednesdays (10), Other Weekdays (5) Median Values (24) –High O 3 on Sundays; Low O 3 during midweek 90th Percentile (25) –High O 3 on Saturdays and Sundays; low O 3 early work week

Maximum One-Hour Concentrations Mean and Standard Deviation

Philadelphia, PA; Maximum One-Hour O 3 Average Values: all 6 sites show statistically significant differences –High O 3 on Sundays (4) and Saturdays (2) –Low O 3 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

Maximum 8-Hour O 3 Concentrations Atlanta –Day-of-week differences in 8-hour O 3 is less significant than 1-hour O 3 –High concentrations on Fridays (4 sites) and Saturdays (4) Chicago –Day-of-week difference in 8-hour O 3 similar to 1-hour O 3 ; individual sites may show higher or lower differences –High concentrations on Sundays; low during midweek

Philadelphia –Weekly cycle more apparent in 8-hour than in 1-hour concentrations –High O 3 on weekends, low late work week Maximum 8-Hour O 3 Concentrations (continued)

PM 10 at Chicago, IL; (  g/m 3 )

24-Hour Average PM 10 High 24-hour averaged PM on Tuesdays and Fridays, low PM on weekends Statistics significant (5%) at all 5 sites (  g/m 3 )

Hour-of-week Profiles of NO x

Correlation Between O 3 and NO x

Summary Atlanta: O 3 weekly buildup –High O 3 on Fridays, low O 3 on Mondays Chicago: O 3 weekend effect –High O 3 on Sundays, low O 3 during midweek Philadelphia: O 3 weekend effect –High O 3 on Sundays, low O 3 during late work week Chicago: PM high during the week, low on weekends

Future Work Use VOC/NO x ratio to bypass the confounding effects of meteorology Test hypotheses Test historical trends Need access to EPA’s AIRS database!!!!!!! –VOC –PM 10 for Atlanta, Philadelphia –Availability of PM 2.5