Weekday/Weekend O3 and PM Differences in Three Cities Outside California

CRC Project A-36B

Betty K. Pun and Christian SeigneurAER, San Ramon, CA

Warren WhiteWashington University, St. Louis, MO

“Weekend Effect” Research Workgroup Meeting6 September 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 O3 and PM in areas outside CA

CRC Project A-36B is a data analysis project to study weekday/weekend differences in O3 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 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

Technical Approach

Airshed Selection

Data Compilation

Characterization of Day-of-the-W eek Behavior (Ozone, PM)

Hypothesis 1 :Changes in

VO C/NO x Ratio

Hypothesis 2 :Friday/Saturday

N ight Traffic

Hypothesis 3:Tem poral

Traffic P rofiles

Hypothesis 4:Spatia l Traffic

P rofiles

Hypothesis 5:O ther Non-

m obile Sources

Hypothesis 6:PM Effect on

Photochem istry

SynthesisCA Studies

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

Atlanta Site No. 1513500024

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (hours)

Ozo

ne

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(p

pm

)

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Sunday

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

Atlanta Site 1312100488

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15202530

354045

Mon

day

Tuesd

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-Ho

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( g

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Philadelphia PM10 Diurnal Profiles

• 2 stations, 1995 to 1998

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PM

10 C

once

ntra

tion

(g/

m3 )

20151050

Time (hour)

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

Philadelphia Site No.4201700128

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

Philadelphia Site 4201700128

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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

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

Philadelphia PM2.5 Profiles

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PM

2.5

Con

cent

ratio

n (

g/m

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2220181614121086420

Time (hour)

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

Philadelphia Site No. 3400700038

• 1 station, 1999

Philadelphia PM2.5 Day-of-the-week Behavior

24-hour average:

– Highest on Saturdays, Tuesdays; lowest on Thursdays

– Differences significant at 10% level

Philadelphia Site 3400700038

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Hypothesis Testing

Hypothesis: VOC/NOx Ratio

• VOC/NOx ratio increases during weekend

Atlanta ChicagoPhiladelphia

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

Hypothesis: VOC/NOx Ratio

• Correlation between O3 and VOC/NOx ratio (grouped by day of the week)

Atlanta ChicagoPhiladelphia

Correlation coef. 0.04 0.98 0.67

R2 0.00 0.96 0.4542

41

40

39

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Dai

ly M

axim

um O

3 (

ppb)

3.63.43.23.02.82.62.42.2

24-Hour Average VOC/NOx (ppbC/ppb)

Chicago

67

66

65

64

63

62

61

Dai

ly M

axim

um O

3 (

ppb)

8.58.07.57.06.56.05.5

24-hour Average VOC/NOx (ppbC/ppb)

Atlanta

Hypothesis: Friday/Saturday Night Traffic

• 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 weekendsAtlanta 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

Increased traffic on Friday and Saturday evenings leads to increased carry-over of precursors and increased O3 formation potential on the weekends

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

Hypothesis: Precursor Carry-over

• 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

Carry-over of precursors from one day to the next is the driving force for the weekly cycle of O3

Hypothesis: PM Affects Photochemistry

• 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

Reduction in fine PM emissions during weekends results in increased photochemical activity and O3

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