Why Ozone is Higher on Weekendsin the South Coast Air Basin:
a 20-Year Perspective
Eric Fujita, William Stockwell, Robert Keislar, and Dave CampbellDivision of Atmospheric Sciences
Desert Research Institute
University and Community College System of Nevada
Reno, Nevada
SCOS97-NARSTO Data Analysis ConferenceDiamond Bar, CA
February 13-15, 2001
1
0.0
0.1
0.2
0.3
0.4
0.51
98
0
19
81
19
82
19
83
19
84
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
Year
Av
era
ge
Ma
x 1
-Hr
Ozo
ne
(p
pm
)
Western Central Eastern
Trends in Average Maximum 1-Hour Ozone from 1980 to 1997 in Western, Central and Eastern South Coast Air Basin
Western: Los Angeles - N. Main, Lynwood, N. Long Beach, Anaheim, and La HabraCentral:Azusa, Glendora, Pomona, and UplandEastern: Riverside and Lake Gregory. 7
0
50
100
150
200
250
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
Year
Num
ber o
f Exc
eeda
nces
1980's
1990's
Trend in Number of Annual Exceedances of the Federal 1-hour Ozone Standard in the South Coast Air Basin from 1976 to 1999
6
Average Daily Maximum Ozone (ppb) in the SoCAB June to October
1981-84
0
40
80
120
160
200
Sun Mon Tue Wed Thu Fri Sat
N. Long Beach
Anaheim
Lynwood
LA-N.Main
Reseda
Burbank
Pico Rivera
La Habra
Azusa
Pomona
Upland
Rubidoux
Average Daily Maximum Ozone (ppb) in the SoCAB June to October
1995-98
0
40
80
120
160
200
Sun Mon Tue Wed Thu Fri Sat
N. Long Beach
Anaheim
Lynwood
LA-N.Main
Reseda
Burbank
Pico Rivera
La Habra
Azusa
Pomona
Upland
Rubidoux
Azusa, Summer 1995
0.00
0.04
0.08
0.12
0.16
0.20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour (PDT)
O3
, NO
an
d N
O2
* (p
pm
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
CO
(p
pm
)
WE O3
WD O3
WE NO
WD NO
WE NO2*
WD NO2*
WE CO
WD CO
CO
NO2
NO
O3
Carry Over
OzoneInhibition
OzoneAccumulation
Post Maximum Ozone
tNO=O3
Azusa, Summer 1995
0.00
0.03
0.06
0.09
0.12
0.15
0.18
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour (PDT)
O3
(pp
m)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
NM
HC
/NO
x
Sun O3
WD O3
Sat O3
Sun HC/NOx
WD HC/NOx
Sat HC/NOx
Average Diurnal Variations in Ozone and HC/NOx Ratios at Azusa in Summer 1995
Twelve-site Average NO and NMHC (from CO) at 4-5 a.m. and 7-8 a.m. (PDT) by Day of the Week in the SoCAB during 1981 to 1998
4-5 a.m. (85-89)4-5 a.m. (90-94)4-5 a.m. (95-98)7-8 a.m. (81-84)7-8 a.m. (85-89)7-8 a.m. (90-94)7-8 a.m. (95-98)
4-5 a.m. (81-84)4-5 a.m. (85-89)4-5 a.m. (90-94)4-5 a.m. (95-98)7-8 a.m. (81-84)7-8 a.m. (85-89)7-8 a.m. (90-94)7-8 a.m. (95-98)
90-94
NMHC (estimated from CO)
0
200
400
600
800
1000
Sun Mon Tue Wed Thu Fri SatN
MH
C (
pp
bC
)
4-5 a.m. (81-84) 4-5 a.m. (85-89)
4-5 a.m. (90-94) 4-5 a.m. (95-98)
7-8 a.m. (81-84) 7-8 a.m. (85-89)
7-8 a.m. (90-94) 7-8 a.m. (95-98)
NO
0
20
40
60
80
100
Sun Mon Tue Wed Thu Fri Sat
NO
(p
pb
)
4-5 a.m. (81-84) 4-5 a.m. (85-89)
4-5 a.m. (90-94) 4-5 a.m. (95-98)
7-8 a.m. (81-84) 7-8 a.m. (85-89)
7-8 a.m. (90-94) 7-8 a.m. (95-98)
Source: Zielinska, 1999 Health Assessment Document for Diesel Emissions: Chapter 2 - Diesel Emissions, atmospheric concentrations, transport and transformation. U.S. EPA Office of Health and Environmental Assessment.
Heavy-Duty Diesel Hydrocarbon Emission Rates Measured on Chassis Dynamometer from Mid-1970s to Mid-1990s for 4-Stroke Engines
y = -0.1971x + 393.65
R2 = 0.4261
0
2
4
6
8
10
12
14
1970 1975 1980 1985 1990 1995 2000
g/m
ile
y = 0.2268x - 426.24
R2 = 0.0108
0
20
40
60
80
100
120
140
1970 1975 1980 1985 1990 1995 2000
g/m
ile
Source: Zielinska, 1999 Health Assessment Document for Diesel Emissions: Chapter 2 - Diesel Emissions, atmospheric concentrations, transport and transformation. U.S. EPA Office of Health and Environmental Assessment.
Heavy-Duty Diesel NOx Emission Rates Measured on Chassis Dynamometer from Mid-1970s to Mid-1990s for 4-Stroke Engines
NO2/NOx
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Sun Mon Tue Wed Thu Fri Sat
ave81-84
ave85-89
ave90-94
ave95-98
Twelve-Site Average NO2/NOx Ratios at 7-8 a.m. (PDT) by Day of the Week
Sunday
0
10
20
30
1982
1984
1986
1988
1990
1992
1994
1996
O3
Acc
umul
atio
n R
ate
(ppb
/hr)
western
central
eastern
Wednesday
0
10
20
30
1982
1984
1986
1988
1990
1992
1994
1996
O3
Acc
umul
atio
n R
ate
(ppb
/hr)
western
central
eastern
3-Year Running Averages of Ozone Accumulation Rates (ppb/hr) in the South Coast Air Basin for Sunday and Wednesday
Wednesday 1981-84
6
7
8
9
10
11
12
13
14
15
N. L
ong
Bea
ch
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e (P
ST
)
0
5
10
15
20
25
30
35
O3
Rat
e (p
pb
/hr)
tO3acc
tNO=O3
Rate
Duration and Rate of Ozone Accumulation on Wednesday During for 1981 - 1984
Sunday 1981-84
6
7
8
9
10
11
12
13
14
15
N. L
ong
Bea
ch
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e (P
ST)
0
5
10
15
20
25
30
35
O3
Rat
e (p
pb/
hr)
tO3acc
tNO=O3
O3 Rate
Duration and Rate of Ozone Accumulation on Sunday During for 1981 - 1984
Sunday - Wednesday (1981-84)
-2
-1
0
1
2
3
4
5N
. Lo
ng B
each
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e C
hang
e (h
ours
)
-10
-8
-6
-4
-2
0
2
4
6
8
10
Rat
e C
hang
e (p
pb/h
r)
Sunday - Wednesday (1985-89)
-2
-1
0
1
2
3
4
5N
. Lo
ng B
each
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e C
hang
e (h
ours
)
-10
-8
-6
-4
-2
0
2
4
6
8
10
Rat
e C
hang
e (p
pb/h
r)
Sunday - Wednesday (1990-94)
-2
-1
0
1
2
3
4
5N
. Lo
ng B
each
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e C
hang
e (h
ours
)
-10
-8
-6
-4
-2
0
2
4
6
8
10
Rat
e C
hang
e (p
pb/h
r)
Sunday - Wednesday (1995-98)
-2
-1
0
1
2
3
4
5N
. Lo
ng B
each
Ana
heim
Lynw
ood
LA-N
.Mai
n
Res
eda
Bur
bank
Pic
o R
iver
a
La H
abra
Azu
sa
Pom
ona
Upl
and
Rub
idou
x
Tim
e C
hang
e (h
ours
)
-10
-8
-6
-4
-2
0
2
4
6
8
10
Rat
e C
hang
e (p
pb/h
r)
Sunday - Wednesday
-15
-10
-5
0
5
10
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
Sun
- W
ed O
3 R
ate
(ppb
/hr)
western central eastern
3-Year Running Averages of Ozone Accumulation Rates (ppb/hr) in the South Coast Air Basin for Sunday Minus Wednesday
Ozone Formation Chemistry
NONO2
h
HCHO, RCHO
HO
HO2
RO2
CO, VOC
H2O2 ROOH
O3
HNO3
NO2 PAN
from RO2
h
O3
from HO2
NO2 + h = O + NO
O + O2 + M = O3 + M
O3 + NO = NO2 + O2
HighVOC/NOx
Low VOC/NOx
O3 inhibition ends about 0.5 to 0.7 hours earlier on Saturdays and about 1.1
to 1.3 hours earlier on Sundays.
O3 inhibition ends earlier in downwind areas and later in areas of highest
density of NO emissions.
The magnitude and spatial patterns of the ozone inhibition periods has not
changed significantly between 1981 to 1998.
Duration of O3 accumulation is shortest in the western basin and longest in the
eastern basin.
Timing of maximum [O3] has not changed over the last two decades in downwind
areas of the basin, but has shifted about 1 to 1.5 hours later in the western and
central basin.
Timing of maximum [O3] does not vary significantly by day of the week.
FINDINGS
During 1981-84, O3 accumulation rates were highest in the central basin and higher
on WDs than WEs at all sites. By 1995-98, rates were highest in the eastern basin
and higher on WEs than WDs in most of the basin.
On average, O3 accumulation rates were cut in half during the 18-year period with
largest reductions in the central basin.
Lower weekend O3 accumulation rates in the 1980s offset shorter O3 inhibition
periods on WEs at central and eastern locations resulting in either no change or
slightly lower [O3] on WEs (i.e., no weekend effect).
In the 1990s, the O3 accumulation rates were generally higher on WEs than WEs.
Coupled with shorter inhibition periods, [O3] was consistently higher on weekends
during the 1990s.
A switch from lower to higher O3 accumulation rates on WEs relative to WDs
coincides with an increase in the magnitude and spatial extent of the weekend
effect.
FINDINGS (Continued)
VOC/NOx 6-9 a.m.(Sat)/VOC/NOx 6-9 a.m.(Wed) ~ 1.05, 1.06, 1.17, and 1.18
VOC/NOx 6-9 a.m.(Sun)/VOC/NOx 6-9 a.m.(Wed) ~ 1.10, 1.17, 1.27 and 1.42
for 1981-84, 1985-89, 1990-94, and 1995-98, respectively. Similar
differences in VOC/NOx ratios during time of maximum ozone.
VOC/NOx 6-9 a.m. during the 1990s are about 7 on weekdays, 8-9 on Saturdays and 9-10 on Sundays. Corresponding ratios at maximum [O3] are 10-11 on weekdays, 12-13 on Saturdays, and 13-14 on Sundays.
While greater carryover of VOC on weekends contributes to larger weekend morning VOC/NOx ratios, most of the increase is due to lower NO emissions during weekend mornings.
FINDINGS (Continued)
Status of ProjectWeekend/Weekday Ozone Observations
in the South Coast Air Basin
• PHASE I: Retrospective Analysis of Ambient and Emissions Data and
Refinement of Hypotheses
– Draft Report 8/23/00
– Final report 12/29/00
• PHASE II: Field Measurements
– Conducted field measurements in late-September to early-October, 2000
– Data Report on 4/15/01
• PHASE III: Data Analysis and Final Report
– Draft Reports on 8/15/01
– Synthesis of Results and final report due 11/15/01
Acknowledgments
• Douglas Lawson, National Renewable Energy Laboratory• Brent Bailey, Coordinating Research Council
• Desert Research Institute– Barbara Zielinska, John Sagebiel, Mark McDaniel, Wendy Goliff, Larry Sheetz, and
Mike Keith – Organic Analytical Laboratory
– John Bowen
• California Air Resources Board– CCOS and CRPAQS
– Monitoring and Laboratory Division
– Research Division and Technical
• Bay Area Air Quality Management District• South Coast Air Quality Management District