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
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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.
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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
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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)
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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?
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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?
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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.
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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
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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
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Results – Salt Lake City
Computed averages from the daily results
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Results – Las Vegas
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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
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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
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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
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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.
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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%
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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
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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.
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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
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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
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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
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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
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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.
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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)
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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.
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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