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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
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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
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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
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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
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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
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
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
Co
nce
ntr
ati
on
(p
pm
)
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
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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
05
10
15202530
354045
Mon
day
Tuesd
ay
Wed
nesd
ay
Thurs
day
Friday
Satur
day
Sunda
y
24
-Ho
ur A
vera
ge P
M10
( g
m-3
)
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Philadelphia PM10 Diurnal Profiles
• 2 stations, 1995 to 1998
28
26
24
22
20
18
16
14
PM
10 C
once
ntra
tion
(g/
m3 )
20151050
Time (hour)
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Philadelphia Site No.4201700128
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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
05
101520
2530
3540
Mon
day
Tuesd
ay
Wed
nesd
ay
Thurs
day
Friday
Satur
day
Sunda
y24
-ho
ur
av
era
ge
PM
10 (
g m
-3)
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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
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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
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Philadelphia PM2.5 Profiles
20
18
16
14
12
10
PM
2.5
Con
cent
ratio
n (
g/m
3 )
2220181614121086420
Time (hour)
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Philadelphia Site No. 3400700038
• 1 station, 1999
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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
0
5
10
15
20
25
30
Mon
day
Tuesd
ay
Wed
nesd
ay
Thurs
day
Friday
Satur
day
Sunda
y24
-ho
ur
av
era
ge
PM
2.5
(g
m-3
)
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Hypothesis Testing
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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
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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
38
37
36
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
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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
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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
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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
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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
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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