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