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