WESTAR Ozone Transport Analysis

Clinton P. MacDonaldDianne S. Miller

Sean RaffuseTim S. Dye

Sonoma Technology, Inc.Petaluma, CA

WESTAR Fall Business MeetingBoise, ID

September 27, 2006STI-3037

2

Overview

Project goal: To quantify the contribution of transported ozone to peak ozone concentrations in six western cities for several years

• Phoenix, AZ• Las Vegas, NV• Denver, CO• Salt Lake City, UT• Farmington, NM• Seattle, WA

3

Source: http://www.al.noaa.gov/WWWHD/Pubdocs/assessment94/common-questions.html

Background – Ozone (1 of 2)

Ozone occurs naturally • Concentrations of

stratospheric ozone up to 12,000 ppb protect earth’s inhabitants from ultraviolet radiation.

• Concentrations of tropospheric ozone are typically 35 to 40 ppb.

Ozone concentrations above natural background levels often occur due to photochemical reactions of NOx and VOCs.

4

Background – Ozone (2 of 2)

Sources of NOx and VOCs • automobile exhaust• solvent fumes• many other anthropogenic emission

sources• natural emissions from trees and

wildfires

5

Background – Peak Local Ozone

Peak local ozone concentrations=

Natural ozone +

Transported ozone (generated from emissions from upwind cities and natural events such as wildfires)

+ Local ozone (generated from local anthropogenic emissions)

6

Questions (1 of 2)

Background ozone• What is the typical natural background

ozone concentration? Transport

• How much ozone, above natural background, was transported into each city?

• What are the typical source areas for transported ozone?

7

Questions (2 of 2)

Local contribution• What amount of locally generated ozone was

produced at each city? Contribution comparison

• On what percentage of high-ozone days was peak local 8-hr ozone dominated by locally generated ozone compared to transported ozone?

• How do these percentages change for each city by transport direction?

• How do the contribution amounts compare among the cities?

8

Methodology (1 of 3)

Peak Local Ozone = Incoming (natural background + transported anthropogenic) + Local Anthropogenic

System developed to calculate incoming ozone

Ran multiple backward trajectories each day for five years (2001–2005, April–October);

Determined the daily peak 8-hr ozone concentration at the last site near which each trajectory passed during daylight hours prior to entering each city; and

Averaged all concentrations to estimate incoming boundary layer concentration each day.

9

Methodology (2 of 3)

Site B is the last site passed, but it is in the buffer.

D is the next nearest site, but Site C is chosen because the trajectory passed Site C after Site D.

The trajectory would be assigned the daily peak 8-hr ozone concentration value from Site C.

If Site C had been passed overnight and Site D passed during the day (10 a.m. to 5 p.m. local time for the city), Site D would have been selected instead.

72-hr backward trajectory

City

10

Methodology (3 of 3)

Peak Local Ozone = Incoming (natural background + transported anthropogenic) + Local Anthropogenic

Date: 07/18/2003Incoming peak 8-hr ozone: 63 ppbNatural background ozone: 35 ppbTransported anthropogenic ozone: 28 ppbLocally generated anthropogenic ozone: 40 ppbPeak local 8-hr ozone: 103 ppbDominant source direction: SE

Salt Lake City

Sample plot showing the trajectories and component concentrations for Salt Lake City on July 18, 2003

11

Results – Salt Lake City

Computed averages from the daily results

12

Results – Las Vegas

13

Results – Locally Generated Ozone

Local contribution for days with ozone >= 70 ppb

0

5

10

15

20

25

30

35

40

45

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40+

Contribution range (ppb)

Num

ber

of D

ays

Average = 8.7 ppb

Las Vegas

0

5

10

15

20

25

30

35

40

45

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40+

Contribution range (ppb)

Nu

mb

er o

f D

ays

Average = 21.8 ppb

Salt Lake City

14

Anthrpogenic Transport contribution for days with ozone >= 70 ppb

0

10

20

30

40

50

60

70

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40+

Contribution range (ppb)

Num

ber

of D

ays

Average = 32.9 ppb Anthrpogenic Transport contribution for days

with ozone >= 70 ppb

0

5

10

15

20

25

30

35

40

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40+

Contribution range (ppb)

Nu

mb

er

of

Da

ys

Average = 20.3 ppb

Las VegasSalt Lake City

Results – Transported Ozone

15

Results – Daily Contribution

Contribution for days with ozone >= 80 pbb

0

20

40

60

80

100

120

7/1

8/2

00

3

7/1

1/2

00

3

6/2

6/2

00

2

6/2

5/2

00

2

7/1

0/2

00

2

8/1

9/2

00

2

7/3

0/2

00

3

8/6

/20

01

7/2

/20

02

8/1

9/2

00

3

7/1

3/2

00

2

7/6

/20

03

7/1

2/2

00

3

7/5

/20

01

7/2

4/2

00

1

7/5

/20

02

8/1

2/2

00

1

6/1

6/2

00

2

6/2

4/2

00

2

7/1

1/2

00

2

7/2

3/2

00

3

7/2

4/2

00

3

7/1

/20

02

5/2

8/2

00

3

6/3

0/2

00

3

7/2

2/2

00

3

6/2

2/2

00

1

8/1

1/2

00

1

7/9

/20

02

8/2

8/2

00

2

7/1

9/2

00

3

8/1

5/2

00

3

8/2

6/2

00

1

6/1

4/2

00

2

6/1

8/2

00

3

7/2

8/2

00

3

Day

Co

nc

en

tra

tio

n (

pp

b)

LocalAnthropogenic TransportNatural

Las VegasSalt Lake City

16

Results – Frequency, Salt Lake City

Day types for days with ozone >= 70 ppb NW

Combination, 30, 63%

Local, 13, 28%

Anthropogenic Transport, 4,

9%

Day types for days with ozone >= 70 ppb NE

Combination, 3, 75%

Local, 0, 0%

Anthropogenic Transport, 1,

25%

Day types for days with ozone >= 70 ppb SW

Combination, 47, 66%

Local, 11, 15%

Anthropogenic Transport, 14,

19%

Day types for days with ozone >= 70 ppb SE

Combination, 4, 67%

Local, 0, 0%

Anthropogenic Transport, 2,

33%

Local days are characterized by local contribution that is at least two-thirds of the ozone beyond natural background.

Transport days are characterized by transport contribution that is at least two-thirds of the ozone beyond natural background.

17

Results – Frequency, Las Vegas

Day types for days with ozone >= 70 ppb NW

Combination, 8, 25%

Local, 1, 3%

Anthropogenic Transport, 23,

72%

Day types for days with ozone >= 70 ppb NECombination, 0,

0%

Local, 0, 0%

Anthropogenic Transport, 3,

100%

Day types for days with ozone >= 70 ppb SW

Combination, 12, 10%

Local, 1, 1%

Anthropogenic Transport, 105,

89%

Day types for days with ozone >= 70 ppb SE

Combination, 10, 37%

Local, 0, 0%

Anthropogenic Transport, 17,

63%

18

Results – Highest Days, Salt Lake City

Contributions and source regions for the five highest ozone days.

Date

Peak Local 8-hr Ozone

Concentration (ppb)

Total Transported Ozone (ppb)

Transported Anthropogenic Ozone (ppb)

Locally Generated

Anthropogenic Ozone (ppb)

Day Type

Probable Source Region(s)

7/18/2003 103 63 28 40 Comb.Southern Nevada, Arizona, Utah

7/11/2003 99 69 34 30 Comb.Northern Nevada, northern California

6/26/2002 96 51 16 45 LocalUtah, Arizona, southern California

6/25/2002 95 55 20 40 LocalSouthern California, southern Nevada, Utah

7/10/2002 94 69 34 25 Comb.Southern Idaho, Oregon

19

Results – Highest Days, Las Vegas

Date

Peak Local 8‑hr Ozone

Concentration (ppb)

Total Transported Ozone (ppb)

Transported Anthropogenic Ozone (ppb)

Locally Generated

Anthropogenic Ozone (ppb)

Day Type

Probable Source Region(s)

8/10/2001 94 72 37 22 Combo.Southern California, Mexico

6/29/2003 94 88 53 6Anthro. Trans.

Nevada, Central California, Pacific Northwest

7/21/2003 93 66 31 27 Combo.Southern Arizona, Mexico

8/11/2001 90 79 44 11Anthro. Trans.

Southern California, Mexico

7/9/2003 90 75 40 15Anthro. Trans.

California

Contributions and source regions for the five highest ozone days.

20

Results – Summary (1 of 2)

CityNatural

BackgroundOzone (ppb)

Average Transported

Anthropogenic Ozone (ppb)

Average Total

Transported Ozone (ppb)

Average Locally

Generated Ozone (ppb)

Average Peak Local 8-hr Ozone

(ppb)

Number of Days

Dominant Source

Direction

Seattle 35 12 47 30 78 22 NW,NE

Salt Lake City 35 20 55 22 77 129 NW,SW

Phoenix 35 22 57 21 78 154 NW,SW

Farmington 35 28 63 11 73 52 NW,SW

Denver 35 28 63 15 79 141 ALL

Las Vegas 35 33 68 9 77 180 SW

Summary of average contributions on days when peak local 8-hr ozone concentrations were at least

70 ppb

21

Results – Summary (2 of 2)

CityNatural

Background Ozone (ppb)

Transported Anthropogenic Ozone (ppb)

Total Transported Ozone (ppb)

Locally Generated

Ozone (ppb)

Peak Local 8-hr Ozone (ppb)

Number of Days

Seattle 35 8 43 47 90 3

Salt Lake City 35 22 57 35 91 16

Phoenix 35 22 57 32 89 19

Denver 35 35 70 23 92 25

Las Vegas 35 39 74 14 88 17

Farmington N/A N/A N/A N/A N/A 0

Summary of average contributions on days when peak local 8-hr ozone concentrations were at least

85 ppb

22

Recommendations (1 of 4)

Expand the data set• Nighttime data• Tribal, industrial, and special study data from various

organizations Use transport information to determine

placement of new rural monitors to better estimate background ozone

Determine whether certain transport directions are excluded because of lack of data• Las Vegas• Arizona – border transport issues

Use 20-year satellite ozone data set to investigate how background ozone levels are changing in time (new idea)

From Final Report and subsequent WESTAR Committee review

23

Recommendations (2 of 4)

Explore the regional and seasonal magnitude of natural background ozone

Investigate sources of ozone• Fires

– Did ozone generated from fire smoke impact ozone concentrations in cities?

– How much ozone was generated by fire smoke?

– How does the contribution of smoke to ozone vary by transport direction, city, and time of year?

• Anthropogenic emissions – Couple emission density maps from the

WRAP modeling with trajectories

24

Recommendations (3 of 4)

Smoke from the Bar Complex and Ralston Fires and certain meteorological conditions led to high ozone in Sacramento.

This was the first two-day Unhealthy ozone episode in September in the past five years.

Estimates reveal that the smoke led to a doubling of NOx emissions for a typical summer day.

Based on historical ozone concentrations on days with similar weather conditions, we estimated that the smoke contributed approximately 10 to 15 ppb to the peak 8-hr average ozone concentrations.

25

Recommendations (4 of 4)

Determine meteorological characteristics often associated with high ozone conditions • Helps organizations determine episodes that

may be caused by natural events• Helps direct the modification of natural

events policies at the national level Compare modeled ozone with results from

this work (lower priority)

26

Final Report

MacDonald C.P., Miller D.S., and Raffuse S.M. (2006) Regional and local contributions to peak local ozone concentrations in six western cities. Final report prepared for the Western States Air Resources Council, Seattle, WA, by Sonoma Technology, Inc., Petaluma, CA, STI-906004-2970-FR, May.

27

Acknowledgments

The authors extend thanks to Bob Lebens of WESTAR for managing this project

and for his important technical advice Other members of the WESTAR ozone work

group for their valuable input: • Steve Arnold, Colorado Department of

Environmental Quality• Mike Sundblom, Arizona Department of

Environmental Quality• Phil Allen, Oregon Department of Environmental

Quality• Brock LeBaron, Bob Clark, and Dave Strohm, Utah

Division of Environment Quality