Ozone Modeling over the Western U.S. -- Impact of National Controls
on Ozone Trends in the Future
Rural/Urban Ozone in the Western United States -- March 10, 2004
Pat Dolwick, Carey Jang, Sharon PhillipsU.S. EPA – Office of Air Quality Planning and Standards
Purpose/Outline
Purpose: • Present some limited results from EPA ozone
modeling simulations estimating future trends in ozone over the western U.S.
Outline:• Expected ozone trends over western U.S.
• Modeling ozone in the western U.S. w/ CMAQ
• Effect of intercontinental transport on ozone
Expected Ozone Trends – Federal Emissions Reductions Eastern U.S. EGU NOx controls
• Modeling studies have shown impacts from eastern U.S. NOx in Big Bend N.P. and Dallas.
• Total NOx reduction of ~ 28%, beginning 5/03
Tier 2 / Gasoline Sulfur• Issued in 2000 • SUVs, light trucks, vans subject to same
emissions standards as cars (0.07 gpm NOx)• 77-95% less NOx emissions from category• Effective in model year 2004, phase in (07/09)
Contribution to High Ozone in the Dallas Region
CAMx source apportionment: Source: IAQR
7010
3
34
2 1
11
1
1
1
1
Expected Ozone Trends – Federal Emissions Reductions Heavy Duty Engine & Diesel Sulfur
• Issued in 2001• Emissions standards for heavy-duty trucks and buses, plus
fuel sulfur limits• 95% less NOx emissions from category• Effective in model year 2006/07, phase in (09/10)
NonRoad Engine & Diesel Sulfur • Proposed in 2003, Expected final in April 2004 • Emissions standards for construction, agricultural, and
industrial equipment• 90% less NOx emissions from category• Effective in model year 2008, phase in through 2014
-60
-50
-40
-30
-20
-10
0
AZ CO ID OR UT
State / Base Case
Per
cent
Cha
nge
(%)
2020 B
2020 C
2030 B
2030 C
Expected Ozone Trends – Future NOx Emissions Changes
Expected Ozone Trends – NonRoad Emissions
Expected Ozone Trends – NonRoad Modeling Analyses
CAMx, v3.10 36/12 km 11 layers, 4.8 km Two July 96
episodes (25 days) 2020 base/control 2030 base control
Expected Ozone Trends – NonRoad Modeling Analyses
Mean normal. bias = -21% Gross error = 26% Improvement from Tier 2
• CARB Emissions• BEIS3 Emissions
Only 3 subregions met EPA recommended targets, but went forward w/ analysis given use of model in relative mode.
-30
-20
-10
0
10
20
30
40
Perc
ent
AverageAccuracy ofthe Peak
MeanNormalizedBias
MeanNormalizedGross Error
Expected Ozone Trends – NonRoad Modeling Analyses
Most portions of the western U.S. are projected to have a reduction of 2-10 ppb in peak 8-hr ozone levels by 2020
Greater reductions in majority of CA
Disbenefits in LA, SF, DEN (small) & PHX (small)
Expected Ozone Trends – NonRoad Modeling Analyses
Most portions of the western U.S. are projected to have a reduction of 2-10 ppb in peak 8-hr ozone levels by 2030
Greater reductions in majority of CA
Disbenefits in LA, SF, & PHX
Expected Ozone Trends – Relative Reduction Factors Use relative change in model ozone (base vs. future) in
conjunction with present-day design values to estimate the design value in the future.• NR analyses used 1999-2001 ambient data
• For this presentation, used preliminary 2001-2003 ambient data
• Only uses predictions >= 70 ppb
• Compares 9-cell average, multi-day mean, 8-hr max
Explained in more detail in EPA 8-Hour modeling guidance
Legend
53 - 70
71 - 79
80 - 84
85 - 89
90 - 94
95 - 129
Number of Counties
(97)
(108)
(151)
(71)
(67)
Nonroad (CAMX) 8 hour
(27)
1999-2001 Design Values
1999-2001 Eight Hour Ozone Design Values
Projected 2020 Eight Hour Ozone Design Values
Legend
DV2020B
43 - 70
71 - 79
80 - 84
85 - 89
90 - 94
95 - 133
Number of Counties
(154)
(39)
(16)
(9)
(5)
Nonroad (CAMX) 8 hour
(299)
2020 Base Design Values
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Maricopa
Pima
Expected Ozone Trends – NR Modeling: Arizona
Expected Ozone Trends – NR Modeling: Colorado
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Jefferson
Larimer
Expected Ozone Trends – NR Modeling: Nevada
50
55
6065
70
75
80
8590
95
100
2001-2003 2020 B 2020 C 2030 B 2030 C
Clark
Expected Ozone Trends – NR Modeling: New Mexico
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Bernalillo
Dona Ana
San Juan
Expected Ozone Trends – NR Modeling: Oregon
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Clackamas
Columbia
Lane
Marion
Expected Ozone Trends – NR Modeling: Utah
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Davis
Salt Lake
Utah
Weber
Expected Ozone Trends – NR Modeling: Washington
50556065707580859095
100
2001-2003
2020 B 2020 C 2030 B 2030 C
Clark
King
Pierce
Thurston
Expected Ozone Trends – NonRoad Modeling Analyses
8-hour ozone levels are generally expected to decrease slightly in the Western U.S. over the next 10-25 years• Decrease of ~ 5%: Albuquerque, Denver, Phoenix,
Salt Lake City, Tucson, & rural areas
• Larger decreases: Portland, Seattle
• Model results uncertain (your results may vary)
• Certain Western U.S. cities are likely to maintain design values near/just below the NAAQS over the next 0-20 years w/o local control • – will depend on year-to-year meteorological variability.
CMAQ Western U.S. Ozone Modeling
EPA has modeled ozone over the western U.S. using several model configurations
• Proof of Concept (left): 1996 episode, 36/12km, 2001 release of CMAQ
• Continental U.S.: entire year of 1996, 36km, 2002 release of CMAQ
• Continental U.S.: entire year of 2001, 36km, 2004 release of CMAQ, in progress
CMAQ Western U.S. Ozone Modeling – 1996 Application
Model performance evaluation indicated greater negative bias in the western U.S. in the summer than in 36/12 CAMx
• Mean normalized bias = -11.7%• Normalized gross error = 23.2 %• East US (annual): bias = -1.2%; error
= 18.6%• West US (annual): bias = -26.5%;
error = 29.9%• East US (summer): bias = 0.8%;
error = 18.7%• West US (summer): bias = -27.0%;
error = 30.5%
CMAQ Western U.S. Ozone Modeling – 1996 Application
RRF-derived estimates of future design values differ across 3 models• CMAQ and CAMx are more
similar than REMSAD
In future, EPA hopes to consolidate ozone and PM modeling into a single, comprehensive modeling platform
505560657075808590
Mar
icopa
Jeffe
rson Cl
ark
Salt L
ake
Clac
kam
as King
AZ CO NV UT OR WA
1999-2001 DV
2030 Base (36 kmCMAQ)
2030 Base (36/12 km CAMX)
2030 Base (36km REMSAD)
Default BCs/ICs : EPA Default Profile v6b• Ozone = 35 ppb
GCMx (GEOS-CHEM + Default) BCs/ICs : 21 key species from “GEOS-CHEM” + the rest from “Default” (Needed for CMAQ runs)• Ozone ~ 10-25 ppb (surface)
• Ozone ~ 200 ppb (top model layer, 400-100 mb)
Highlights of differences using GCMx BCs/ICs• July 2001 (monthly avg.):
• Lower O3 (3~10 ppb) over the west coast
• Moderately higher PM 2.5 (mainly PM sulfate) over U.S.
Effect of Intercontinental Transport – Sensitivity Tests
((July July monthly avg., 2001)monthly avg., 2001)
O3 diff. (GEOS/CHEM BCs/ICs – Default BCs/ICs)
O3 O3 (%)
Source: Jang (2004), personal communication
((July July 22, 2001)22, 2001)
O3 diff. (GCM BCs/ICs – Default BCs/ICs)
O3 (daily avg.) O3 (8-hr max)
Source: Jang (2004), personal communication