State of Colorado Implementation Plan to Meet the Requirements of

Clean Air Act Section 110 (a)(2)(D)(i)(I)

Interstate Transport Regarding the 1997 8-Hour Ozone Standard

December 9, 2008

Colorado Department of Public Health and Environment

Air Pollution Control Division

4300 Cherry Creek Drive South

Denver, Colorado 80246

Adopted by the Air Quality Control Commission

December 12, 2008
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

i
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

ii

Table of Contents

1. OZONE-SPECIFIC PROVISIONS TO MEET THE REQUIREMENTS OF CAA 110(A)(2)(D)(I)(I) –

INTERSTATE TRANSPORT .......................................................................................................................................1

1.1. INTRODUCTION ...............................................................................................................................................1

1.2. COLORADO OZONE MONITORING NETWORK..................................................................................................2

1.3. OZONE MONITORING NETWORK IN NEARBY STATES .....................................................................................7

1.4. OZONE TRANSPORT CONCLUSIONS FROM THE DMA/NFR PHOTOCHEMICAL MODELING ............................10

1.4.1. Emission Inventories and 2006 and 2010 Base Case..............................................................................11

1.4.2. Discussion of 2010 Base Case CAMx Modeling Results.........................................................................15

1.5. DENVER METRO AREA/NORTH FRONT RANGE OZONE NONATTAINMENT AREA CONTRIBUTION TO 

DOWNWIND LOCATIONS .............................................................................................................................................18

1.6. SECTION 110(A)(2)(D)(I)(I) – OZONE TRANSPORT CONCLUSIONS ...............................................................20

2. REFERENCES ....................................................................................................................................................22

List of Tables

Table 1: 2008 1-Hour Ozone Monitored Concentration (updated through Sept. 30, 2008)............. 4

Table 2: 2008 8-Hour Ozone Monitored Concentration (updated through Sept. 30, 2008)............. 5

Table 3: 8-Hour Design Value Using the 3-Year (2006-2008) Average of the Fourth Maximum 

Ozone Concentration ................................................................................................................. 6

Table 4: 2005-2007 3-Year Fourth Highest Average Monitoring Concentrations from Kansas, 

Nebraska, New Mexico, Utah and Wyoming............................................................................ 7

Table 5. Base Case Inventories for 8-Hour Ozone DMA/NFR NAA Photochemical Modeling.... 14

List of Figures

Figure 1. Location of Front Range Ozone Monitors ......................................................................... 2

Figure 2. Location of Statewide Ozone Monitors.............................................................................. 3

Figure 3: 8-Hour Ozone Nonattainment Areas.................................................................................. 9

Figure 4. Nested 12/4 km modeling domains for the Denver CAMx air quality and SMOKE 

emissions modeling.................................................................................................................. 10

Figure 5. Projected 2010 8-hour ozone Design Values (DVF)........................................................ 15

Figure 6. Rocky Flats North source apportionment for 29 July including boundary conditions. ... 16

Figure 7: Spatial extent of the 8-hour ozone concentrations that occurred between 10am and 6pm 

local time on June 27, 2002 through July 1, 2002 ................................................................... 19
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

iii
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

1

1. Ozone-Specific Provisions to Meet the Requirements of 

CAA 110(a)(2)(D)(i)(I) – Interstate Transport

1.1. Introduction

The purpose of this document is to provide a plan for the State of Colorado to meet the 

requirements of the Clean Air Act Section 110 (a)(2)(D)(i)(I) Interstate Transport 

requirements regarding the 0.08 parts per million (ppm) 8-Hour Ozone National Ambient 

Air Quality Standard (NAAQS). This addresses the applicable components of 

110(a)(2)(D)(i)(I) demonstrating adequate provisions to prevent emissions from Colorado 

from interfering with attainment or maintenance of the federal ozone NAAQS in any other 

state. This analysis does not address ozone transport for the revised 0.075 ppm 8-Hour 

Ozone NAAQS. 

This document replaces the section titled “Ozone-Specific Provisions” in the document 

“State of Colorado Implementation Plan to Meet the Requirements of Clean Air Act 

Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone and PM2.5

NAAQS.”

Currently, the Denver area is the only area in U.S. Environmental Protection Agency 

(EPA) Region VIII that is designated as nonattainment for the 8-hour ozone NAAQS of 

0.08 ppm. 

In this report, relevant information from the Denver Metropolitan Area and North Front 

Range (DMA/NFR) 8-hour Ozone State Implementation Plan (SIP) process, the Denver 

Early Action Compact (EAC) process, ambient ozone data for Colorado, ambient ozone 

data for nearby states from the EPA Air Quality System (AQS) database, and other 

information is used to demonstrate that Colorado does not contribute significantly to 

nonattainment in, or interfere with maintenance by, any other state with respect to the 0.08 

ppm ozone NAAQS. 
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

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1.2. Colorado Ozone Monitoring Network

The 2007/2008 ozone ambient air monitoring network in the Denver area and along the 

northern Front Range consists of 13 stations operated by the Colorado Air Pollution 

Control Division (APCD) and one station operated by the National Park Service (NPS) in 

Rocky Mountain National Park. There have been other stations that have operated in the 

past. The geographical distribution of the Front Range monitors is presented in Figure 1.

As shown in Figure 1, the ozone monitors are primarily located in urbanized areas along 

the Front Range corridor. The monitors are located in areas where the highest ozone 

concentrations have been monitored historically and where elevated ozone is expected to 

occur. High ozone concentrations along the Front Range occur near the areas with high 

emissions density and dense population. In addition, elevated ozone is observed along 

elevated terrain to the west of the DMA/NFR Nonattainment Area. All of these monitors 

are designated by the U.S. Environmental Protection Agency as “equivalent” analyzers and 

follow all quality assurance requirements as specified in 40 CFR Part 58, Appendix A.

Figure 1. Location of Front Range Ozone Monitors
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

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Figure 2 shows other ozone monitoring sites that exist in Colorado for 2008. These are 

operated by either Colorado, the Southern Ute Tribe, or various Federal agencies. All of 

these sites use monitors that are designated as “equivalent” analyzers by the U.S. 

Environmental Protection Agency. As shown, most of the sites are in the southwest corner 

of Colorado, either within or near the San Juan oil and gas development area.

Figure 2. Location of Statewide Ozone Monitors

Table 1, Table 2, and Table 3 present the monitoring data for the DMA/NFR NAA 

monitoring sites (including the NPS Rocky Mountain National Park monitoring site) as 

well as for other sites in Colorado. In Table 3, the fourth maximum 8-hour ozone 

concentrations along with the 3-year average of the fourth maximum concentrations at each 

site are presented. As shown in both Table 1 and Table 3, the Denver area is currently 

meeting the 8-hour and former 1-hour ozone NAAQS for all sites, except for the 8-Hour 

NAAQS at Rocky Flats North with a design value of 0.86 ppm.
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

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Table 1: 2008 1-Hour Ozone Monitored Concentration (updated through Sept. 30, 2008)

1st Max Date 2nd Max Date 3rd Max Date 4th Max Date

AQS 

Number Site Name 1-Hour 1st Max 1-Hour 2nd Max 1-Hour 3rd Max 1-Hour 4th Max

(ppm) 1-Hour (ppm) 1-Hour (ppm) 1-Hour (ppm) 1-Hour

08-001-3001 Welby 0.100 08/29 0.095 08/05 0.092 07/10 0.089 06/20

08-005-0002 * Highland 0.065 04/04 0.064 04/08 0.064 04/18 0.062 04/19

08-013-0011 S. Boulder Creek 0.089 07/10 0.089 07/25 0.086 07/16 0.085 05/31

08-031-0014 Carriage 0.094 08/05 0.090 08/29 0.089 07/10 0.085 06/20

08-031-0025 ** Denver - Animal 

Shelter 0.100 07/10 0.098 08/05 0.087 06/20 0.087 08/24

08-035-0004 Chatfield State Park 0.101 07/10 0.098 06/20 0.095 08/29 0.092 08/24

08-041-0013 Colo. Spgs. -

Academy 0.085 05/24 0.083 07/10 0.082 08/06 0.080 07/18

08-041-0016 Manitou Springs 0.087 05/24 0.085 08/06 0.083 07/10 0.083 07/11

08-045-0012 ** Rifle - Health 0.081 07/09 0.080 07/10 0.075 08/19 0.074 07/11

08-059-0002 Arvada 0.093 08/05 0.093 08/29 0.092 07/10 0.088 07/25

08-059-0005 Welch 0.102 07/10 0.090 06/20 0.088 08/05 0.088 08/29

08-059-0006 Rocky Flats - N 0.088 07/10 0.088 07/18 0.088 08/29 0.087 07/02

08-059-0011 NREL 0.097 08/29 0.093 07/10 0.092 08/05 0.092 08/24

08-067-7001 *** So. Ute -

Ignacio 0.076 06/04 0.075 05/31 0.073 05/03 0.072 05/3

08-067-7003 *** So. Ute -

Bondad 0.080 06/04 0.078 05/31 0.077 05/27 0.071 04/21

08-067-???? USFS - Shamrock 0.081 06/04 0.079 06/10 0.077 02/29 0.077 05/30

08-069-0007 Rocky Mountain 

Nat'l Park 0.092 07/09 0.090 07/31 0.090 08/28 0.085 05/22

08-069-0011 Ft. Collins - West 0.093 08/19 0.092 07/09 0.092 07/18 0.088 07/24

08-069-1004 Ft. Collins - CSU 0.082 08/19 0.080 07/09 0.079 08/30 0.078 07/24

08-077-0020 ** Palisade - Water 0.081 07/09 0.079 07/10 0.075 07/08 0.074 07/05

08-083-0006 ** Cortez 0.078 07/23 0.074 07/13 0.072 08/05 0.071 07/25

08-083-0101 Mesa Verde Nat’l 

Park 0.075 05/01 0.075 06/04 0.074 05/31 0.072 04/30

08-123-0009 Greeley - Weld 

Tower

0.094 08/20 0.092 07/24 0.089 08/01 0.087 08/04

NOTES: 

* Highland site shut down on 4/21/08 for approx. 6-months. 

** Denver - Animal Shelter site commenced on 4/22/08, Rifle - Health commenced on 6/20/08, 

Palisade - Water commenced on 5/30/08 and Cortez commenced on 6/17/08.

*** Southern Ute sites data only thru 6/30/08.
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

5

Table 2: 2008 8-Hour Ozone Monitored Concentration (updated through Sept. 30, 2008)

1st Max Date 2nd Max Date 3rd Max Date 4th Max Date

AQS 

Number Site Name 8-Hour 1st Max 8-Hour 2nd Max 8-Hour 3rd Max 8-Hour 4th Max

(ppm) 8-Hour (ppm) 8-Hour (ppm) 8-Hour (ppm) 8-Hour

08-001-3001 Welby 0.085 07/10 0.083 08/29 0.077 07/18 0.076 06/20

08-005-0002 * Highland 0.062 04/04 0.060 04/08 0.060 04/18 0.059 04/05

08-013-0011 S. Boulder Creek 0.080 07/10 0.076 05/31 0.076 07/09 0.076 07/18

08-031-0014 Carriage 0.081 07/10 0.075 08/29 0.073 06/20 0.072 07/26

08-031-0025 ** Denver - Animal 

Shelter 0.086 07/10 0.072 08/29 0.071 07/13 0.070 07/26

08-035-0004 Chatfield State Park 0.090 07/10 0.082 06/30 0.080 06/20 0.080 06/27

08-041-0013 Colo. Spgs. -

Academy 0.078 05/24 0.077 07/10 0.073 08/06 0.070 07/18

08-041-0016 Manitou Springs 0.080 05/24 0.076 07/10 0.074 07/11 0.072 07/31

08-045-0012 ** Rifle - Health 0.076 07/09 0.076 07/10 0.069 08/19 0.066 07/13

08-059-0002 Arvada 0.081 08/29 0.080 07/10 0.077 06/20 0.074 08/05

08-059-0005 Welch 0.095 07/10 0.079 06/20 0.077 07/18 0.073 08/19

08-059-0006 Rocky Flats - N 0.083 07/10 0.080 07/18 0.079 05/31 0.079 08/29

08-059-0011 NREL 0.085 07/10 0.085 08/29 0.077 06/20 0.076 06/02

08-067-7001 *** So. Ute -

Ignacio 0.069 06/04 0.067 06/10 0.066 05/10 0.066 06/13

08-067-7003 *** So. Ute -

Bondad 0.073 06/04 0.067 05/27 0.067 05/31 0.067 06/05

08-067-???? USFS - Shamrock 0.074 06/04 0.073 06/10 0.071 06/13 0.069 05/30

08-069-0007 Rocky Mountain 

Nat'l Park 0.081 07/09 0.077 05/25 0.077 07/31 0.076 05/31

08-069-0011 Ft. Collins - West 0.081 07/18 0.079 07/09 0.078 05/25 0.076 07/24

08-069-1004 Ft. Collins - CSU 0.070 05/25 0.070 07/09 0.068 07/18 0.066 05/31

08-077-0020 ** Palisade - Water 0.077 07/09 0.075 07/10 0.070 05/31 0.070 07/29

08-083-0006 ** Cortez 0.067 08/02 0.066 07/23 0.065 08/07 0.064 08/05

08-083-0101 Mesa Verde Nat’l 

Park 0.071 06/04 0.070 04/30 0.069 04/21 0.069 06/10

08-123-0009 Greeley - Weld 

Tower 0.077 07/24 0.076 08/20 0.075 07/26 0.073 08/01

NOTES: 

* Highland site shut down on 4/21/08 for approx. 6-months. 

** Denver - Animal Shelter site commenced on 4/22/08, Rifle - Health commenced on 6/20/08, 

Palisade - Water commenced on 5/30/08 and Cortez commenced on 6/17/08.

*** Southern Ute sites data only thru 6/30/08.
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

6

Table 3: 8-Hour Design Value Using the 3-Year (2006-2008) Average of the Fourth Maximum Ozone 

Concentration

Site Name AQS #

4th

Maximum

2006

8-Hour 

Average

Value (ppm)

4th

Maximum

2007

8-Hour 

Average

Value (ppm)

4th

Maximum

2008

8-Hour 

Average

Value (ppm)

Design Value

(2006 – 2008)

3-Year 

Average

4th Maximum

Value (ppm)

Welby 08-001-3001 0.069 0.070 0.076 0.071

* Highland 08-005-0002 0.081 0.075 0.059 0.071

S. Boulder Creek 08-013-0011 0.082 0.085 0.076 0.081

Carriage 08-031-0014 0.072 0.076 0.072 0.073

** Denver - Animal 

Shelter 08-031-0025 --- --- 0.070 ---

Chatfield State Park 08-035-0004 0.086 0.082 0.080 0.082

USAF Academy 08-041-0013 0.072 0.072 0.070 0.071

Manitou Springs 08-041-0016 0.076 0.072 0.072 0.073

** Rifle - Health 08-045-0012 --- --- 0.066 ---

Arvada 08-059-0002 0.082 0.079 0.074 0.078

Welch 08-059-0005 0.081 0.080 0.073 0.078

Rocky Flats - North 08-059-0006 0.090 0.090 0.079 0.086

NREL 08-059-0011 0.083 0.085 0.076 0.081

*** So. Ute - Ignacio 08-067-7001 --- --- 0.066 ---

*** So. Ute - Bondad 08-067-7003 0.063 0.071 0.067 0.067

USFS - Shamrock 08-067-???? 0.074 0.069 0.069 0.070

Rocky Mountain Nat’l 

Park 08-069-0007 0.076 0.078 0.076 0.076

Fort Collins - West 08-069-0011 0.087 0.085 0.076 0.082

Fort Collins - CSU 08-069-1004 0.078 0.069 0.066 0.071

** Palisade - Water 08-077-0020 --- --- 0.070 ---

** Cortez 08-083-0006 --- --- 0.064 ---

Mesa Verde Nat’l Park 08-083-0101 0.074 0.070 0.069 0.071

Greeley - Weld Tower 08-123-0009 0.082 0.074 0.073 0.076

NOTES: 

* Highland site shut down on 4/21/08 for approx. 6-months. 

** Denver - Animal Shelter site commenced on 4/22/08, Rifle - Health commenced on 6/20/08, 

Palisade - Water commenced on 5/30/08 and Cortez commenced on 6/17/08.

*** Southern Ute sites data only thru 6/30/08. Ignacio data invalid for 01/2005 to 08/2007.
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

7

1.3. Ozone Monitoring Network in Nearby States

Table 4 present 8-hour ozone monitoring data from the surrounding states of Nebraska, Kansas, 

New Mexico, Wyoming, and Utah. Table 4 and show that none of the monitors in surrounding 

states exceed the 8-hour ozone standard except for Davis County Utah. Therefore, to the extent 

that the network is representative of all areas, it can be concluded that the DMA/NFR sources do 

not significantly contribute to the 8-hour ozone standard violations at these down wind locations or 

even further downwind. In addition, Colorado does not significantly contribute to violations 

upwind including Davis County Utah. Utah’s 8-hour proposed 8-hour maintenance plan for the 

1997 8-hour ozone standard does not suggest that Colorado interferes with the maintenance of the 

standard in Davis County Utah.

Table 4: 2005-2007 3-Year Fourth Highest Average Monitoring Concentrations from Kansas, Nebraska, 

New Mexico, Utah and Wyoming 

Site ID State County

EPA 

Region

2005

8-hr 

Ozone

4th Max

(ppm)

2006

8-hr 

Ozone

4th Max

(ppm)

2007

8-hr Ozone

4th Max

(ppm)

3-yr

Avg. of

4th Max

(ppm)

20-045-0004 KS Douglas 7 0.073 0.081 End 2007 N/A

20-091-0010 KS Johnson 7 0.081 0.076 0.071 0.076

20-103-0003 KS Leavenworth 7 0.077 0.074 0.080 0.077

20-107-0002 KS Linn 7 0.075 0.079 0.070 0.074

20-173-0001 KS Sedgwick 7 0.065 0.065 0.059 0.063

20-173-0010 KS Sedgwick 7 0.074 0.073 0.060 0.069

20-191-0002 KS Sumner 7 0.078 0.080 0.070 0.076

20-195-0001 KS Trego 7 0.071 0.076 0.068 0.071

20-209-0021 KS Wyandotte 7 0.079 0.081 0.073 0.077

31-055-0028 NE Douglas 7 0.069 0.072 0.066 0.069

31-055-0032 NE Douglas 7 0.067 0.066 0.056 0.063

31-055-0035 NE Douglas 7 0.070 0.067 0.061 0.066

31-109-0016 NE Lancaster 7 0.056 0.056 0.054 0.055

35-001-0019 NM Bernalillo 6 0.073 0.073 0.070 0.072

35-001-0023 NM Bernalillo 6 0.072 0.073 0.069 0.071

35-001-0024 NM Bernalillo 6 0.074 0.074 0.068 0.072

35-001-0027 NM Bernalillo 6 0.073 0.072 0.071 0.072

35-001-0029 NM Bernalillo 6 0.071 0.070 0.067 0.069

35-001-1012 NM Bernalillo 6 0.077 0.047 0.074 0.066

35-001-1013 NM Bernalillo 6 0.077 0.071 0.071 0.073

35-001-1014 NM Bernalillo 6 0.072 0.072 0.064 0.069

35-013-0008 NM Dona Ana 6 0.070 0.072 0.068 0.070

35-013-0017 NM Dona Ana 6 0.070 0.073 0.070 0.071

35-013-0020 NM Dona Ana 6 0.072 0.072 0.068 0.070

35-013-0021 NM Dona Ana 6 0.076 0.080 0.076 0.077

35-013-0022 NM Dona Ana 6 0.070 0.073 0.073 0.072

35-013-0023 NM Dona Ana 6 0.066 0.070 0.062 0.066
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

8

Table 4 (continued) 2005-2007 3-Year Fourth Highest Average Monitoring Concentrations from Kansas, 

Nebraska, New Mexico, Utah and Wyoming 

Site ID State County

EPA 

Region

2005

8-hr 

Ozone

4th Max

(ppm)

2006

8-hr

Ozone

4th Max

(ppm)

2007

8-hr Ozone

4th Max

(ppm)

3-yr

Avg. of

4th Max

(ppm)

35-015-1005 NM Eddy 6 0.067 0.076 0.066 0.069

35-017-1003 NM Grant 6 0.071 0.067 0.062 0.066

35-025-0008 NM Lea 6 0.074 0.075 0.064 0.071

35-029-0003 NM Luna 6 Start 2006 0.053 0.062 N/A

35-043-1001 NM Sandoval 6 0.069 0.064 0.063 0.065

35-043-1003 NM Sandoval 6 0.075 0.074 0.071 0.073

35-043-9004 NM Sandoval 6 0.076 0.072 0.067 0.071

35-045-0009 NM San Juan 6 0.075 0.063 0.069 0.069

35-045-0018 NM San Juan 6 Start 2006 0.079 0.079 N/A

35-045-1005 NM San Juan 6 0.072 0.071 0.073 0.072

49-003-0003 UT Box Elder 8 0.079 0.078 0.077 0.078

49-003-7001 UT Box Elder 8 0.075 0.076 0.078 0.076

49-005-0004 UT Cache 8 0.069 0.073 0.074 0.072

49-011-0004 UT Davis 8 0.092 0.082 0.082 0.085

49-035-0003 UT Salt Lake 8 0.083 0.084 0.082 0.083

49-035-2004 UT Salt Lake 8 0.086 0.082 0.082 0.083

49-035-3006 UT Salt Lake 8 0.082 0.082 0.079 0.081

49-035-3007 UT Salt Lake 8 0.085 0.080 0.080 0.081

49-035-3008 UT Salt Lake 8 0.080 0.082 0.079 0.080

49-037-0101 UT San Juan 8 0.069 0.070 0.072 0.070

49-045-0003 UT Tooele 8 0.080 0.079 0.076 0.078

49-049-0002 UT Utah 8 0.078 0.074 0.075 0.075

49-049-5008 UT Utah 8 0.080 0.077 0.078 0.078

49-049-5010 UT Utah 8 0.080 0.079 0.077 0.078

49-053-0130 UT Washington 8 0.091 0.072 0.071 0.078

49-057-0007 UT Weber 8 0.081 0.083 0.080 0.081

49-057-1003 UT Weber 8 0.084 0.083 0.082 0.083

56-005-0123 WY Campbell 8 0.063 0.072 0.072 0.069

56-005-0456 WY Campbell 8 0.063 0.065 0.072 0.066

56-035-0098 WY Sublette 8 0.075 0.069 0.068 0.070

56-035-0099 WY Sublette 8 0.079 0.072 0.067 0.072

56-035-0100 WY Sublette 8 0.066 0.074 0.066 0.068

56-037-0200 WY Sweetwater 8 Start 2006 0.067 0.064 N/A

56-039-1011 WY Teton 8 0.060 0.069 0.065 0.064

Figure 3 presents a map of all the U.S. nonattainment areas for the 1997 8-hour ozone 

standard.. Since the surrounding states of Kansas, Nebraska, Wyoming, Utah, and New 

Mexico do not have violations the 8-hour NAAQS for ozone, it can be reasonably 

concluded that Colorado sources do not significantly affect the ozone nonattainment areas 
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

9

even further downwind such as Dallas-Forth Worth and St. Louis nonattainment areas. In 

addition, it is unlikely that Colorado would significantly affect nonattainment areas that are 

typically “upwind” such as Las Vegas and Phoenix. However, it is recognized that, under 

the types of synoptic scale meteorological regimes that occur during some regional ozone 

episodes, simple terms like “upwind” and “downwind” may not be applicable. Thus, 

photochemical modeling is needed to study the distribution of ozone under a variety of 

meteorological regimes.

Figure 3: 8-Hour Ozone Nonattainment Areas
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

10

1.4. Ozone Transport Conclusions from the DMA/NFR 

Photochemical Modeling 

The DMA/NFR photochemical model domain was defined on a nested 36-kilometer (km), 

12 km, and a 4 km nested-grid structure. This structure was utilized in conjunction with 

the Comprehensive Air-quality Model with extensions (CAMx) air quality model 

(ENVIRON, 2008). CAMx, SMOKE (Coats, 1996), and CONCEPT MS (Loomis et al., 

2005) air quality and emissions modeling was performed for the June-July 2006 period. 

Nested 36/12/4 km modeling domains were used in the Denver 8-hour ozone modeling 

study. The CAMx model was first applied to the 36 km continental U.S. domain using 

boundary conditions (BCs) from a global climate air quality model. The CAMx 2006 and 

2010 base case modeling results from the 36 km continental U.S. domain simulation were 

then processed to generate BCs for the CAMx 12/4 km domain (Figure 4) for the 2006 12/4 

km base case and 2010 12/4 km base case and sensitivity simulations. The CAMx 

simulations for the 12/4 km domains were run using two-way interactive grid nesting (i.e., 

pollutants can flow back and forth between the 12 km and 4 km domains to account for 

recirculation). The larger 36km domain was selected to address the impact of boundary 

condition uncertainties for the Front Range area of Colorado, as APCD was concerned 

there may be transport from Southern California and Texas. The 12 km grid resolution 

domain essentially covers the central Rocky Mountain States or portions thereof (i.e., 

Arizona, Colorado, New Mexico, Utah and Wyoming.) The 4 km nested-grid covers most 

of the state of Colorado. 

Figure 4. Nested 12/4 km modeling domains for the Denver CAMx air quality and SMOKE emissions 

modeling.
Colorado Department of Public Health and Environment / Air Pollution Control Division

State of Colorado Implementation Plan to Meet the Requirements of 

Clean Air Act Section 110 (a)(2)(D)(i)(I) - Interstate Transport Regarding 8-Hour Ozone

11

1.4.1. Emission Inventories and 2006 and 2010 Base Case

The photochemical modeling for the “2010 base case” emissions scenario performed for 

the DMA/NFR Ozone SIP process demonstrates compliance in the Front Range Region 

with the 8-hour 0.08 ppm ozone NAAQS. Control measures in place in 2006 and assumed 

for 2010 include:

1. Federal tailpipe standards and regulations, including those for small engines and 

non-road mobile sources. Credit is taken for these federal requirements but they are 

not part of the Colorado SIP. The credits change from 2006 to 2010 as the United 

States Environmental Protection Agency (EPA) Tier II and low sulfur gasoline 

standards become effective.

2. Air Quality Control Commission Regulation No. 11--covering the Automobile 

Inspection and Readjustment (A.I.R.) program in place during the 2006 ozone 

season, which includes an enhanced Inspection/Maintenance (I/M). For 2006, a 

maximum of 10% fleet coverage is assumed, and for 2010, a maximum of 50% 

fleet coverage is assumed for the remote sensing clean screen program in the 

Denver metro area (DMA) based on Regulation No. 11.

3. Air Quality Control Commission Regulations No. 3, No. 6, No. 7, and Common 

Provisions--covering gasoline station and industrial source control programs. The 

Common Provisions, Parts A and B of Regulation No. 3, and the volatile organic 

compounds (VOC) control requirements of Regulation No. 7 are already included 

in the approved SIP. Regulation No. 6 and Part C of Regulation No. 3 implement 

the federal standards of performance for new stationary sources and the federal 

operating permit program. This reference to Regulation No. 6 and Part C of 

Regulation No. 3 shall not be construed to mean that these regulations are included 

in the SIP.

4. Since 2004, gasoline sold in the Denver metro area during the summer Reid Vapor 

Pressure (RVP) ozone season (June 1 to September 15) has been subject to a 

national RVP limit of 7.8 pounds per square inch (psi) to reduce fuel volatility. For 

ethanol-blended fuels, the RVP limit is 8.8 psi due to the federal 1.0 psi RVP 

waiver for ethanol. 

Since 1991, gasoline sold in the Larimer and Weld area during the summer ozone 

season (June 1 to September 15) has been subject to a national RVP limit of 9.0 psi 

to reduce fuel volatility. For ethanol-blended fuels, the RVP limit is 10.0 psi due to 

the federal 1.0 psi RVP waiver for ethanol. 

For 2006, the RVP of gasoline for the Denver metropolitan portion of 

nonattainment area was determined by survey to be at 8.2 psi, with an ethanol 

market share of 60%, and for the Larimer and Weld portion of the nonattainment 

area the RVP was determined to be 8.4 psi with the same ethanol share of 60%. For 

purposes of the base case 2010 mobile source inventory, the RVP of the base 
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gasoline is assumed to be 7.8 psi for the Denver metropolitan portion of 

nonattainment area, with an ethanol market share of 85%, and for the Larimer and 

Weld portion of the nonattainment area the RVP was assumed to be 9.0 psi with an 

ethanol share of 25%.

5. The EPA approved the EAC Ozone Action Plan (OAP) on August 19, 2005. The 

OAP included an amendment to Regulation No. 7 requiring the reduction of flash 

emissions of volatile organic compounds from condensate collection, storage, 

processing and handling operations by May 1, 2005. This initial rule required the 

installation of air pollution control technology to achieve a system-wide 47.5% 

reduction from uncontrolled emissions of volatile organic compounds from new and 

existing oil and gas exploration and production operations located within the 8-hour 

ozone nonattainment area designated by EPA for operators with total emissions 

greater than 30 tons per year. The 2006 base case estimate was developed from 

actual reported emissions based on the system-wide 47.5% reduction requirement. 

6. In February 13, 2008, the EPA approved revisions to Regulation No. 7 to require 

the system-wide reduction of condensate tank flash VOC emissions of 75% for the 

2007 ozone season by May 1, 2007 and 78% reduction for the 2012 ozone season, 

with technology that achieves a 95% reduction in VOC emissions. The 2010 base 

case emissions estimate assumes the 75% system-wide reduction requirement.

7. The effect of EPA final locomotive Tier 3 standards were considered and included, 

where appropriate, in the 2010 area source estimates. Tier 4 locomotive standards 

do not go into effect until 2015 and therefore were not included in the 2010 

inventories.

All of the inventories in this 8-hour Ozone Attainment SIP were developed using EPA 

approved emissions modeling methods, including EPA’s MOBILE6 model and local VMT 

data for on-road mobile source emissions, EPA’s non-road model and local demographic 

information for area and off-road sources, and reported actual emissions for point sources. 

Estimates for future emissions are based on the above-mentioned tools and the EPA’s 

Economic Growth and Analysis System (EGAS) model for estimating future point sources 

activity, VMT growth for on-road mobile sources, and 2010 and 2012 demographic data 

for off-road and area sources. The technical support document contains detailed 

information on model assumptions and parameters for each source category. 

Highway mobile source emissions are from the ENVIRON Consolidated Community 

Emissions Processing Tool (CONCEPT) model inventory, which is based on DRCOG 

VMT data and MOBILE6 input data provided by APCD and expanded to the entire NAA 

based on VMT from the North Front Range Transportation and Air Quality Planning 

Council and CDOT.

Non-road source emissions are from the EPA Non-Road Model. This model includes the 

impact of future controls on non-road engines, which is used in equipment such as lawn 

and garden equipment and construction equipment. Oil and gas source emissions are from 
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the revised Independent Petroleum Association of Mountain States (IPAMS) inventory, 

and were projected to 2010 using the methodology in the IPAMS projection methodology 

document. The IPAMS inventory was sponsored by the IPAMS and is Phase III of a 

regional oil and gas emission inventory for the Inter-Mountain West jointly with the 

Western Regional Air Partnership (WRAP). 

Non-oil and gas area source emissions (including heating, consumer solvent use, aircraft 

and railroads, etc.) are from the 2002 EPA National Emissions Inventory (NEI), grown to 

2006 and 2010 by population growth from data from the State Demographer. Consumer 

solvent emission reductions based on 75% of the per-person reductions listed in the EPA 

May 30, 2007 Emission Reduction Credit Memo were applied to the projected 2010 nonoil and gas area source inventory. A check on the non-oil and gas area sources estimates 

comparing the recently available 2005 NEI emissions data is shown later in this document. 

An inventory completed in 2005 for Denver International Airport (DIA) was used for 

aircraft and airport non-road source emissions from DIA for both 2006 and 2010.

Non-oil and gas point source emissions were grown to 2010 by the EPA EGAS economic 

model, and by adding sources for which permits have been issued. 

Emissions of VOC and nitrogen oxides (NOx) from biogenic sources have been generated 

by the Model of Emissions of Gases and Aerosols from Nature (MEGAN) Biogenic 

Emissions Model using land cover data base of biomass type and density and hourly 

meteorology data. The National Center of Atmospheric Research (NCAR) has produced a 

global data base of land use data, the MEGAN Driving Variable Database Version 1.2, for 

use with MEGAN. Surface temperatures are provided by the Mesoscale Meteorological 

Model (MM5) modeling. 

Summaries of the VOC and NOx base case inventories for the nonattainment area for 2006 

and 2010 are presented in Table 5. Emissions of NOx and VOCs are in tons per average 

episode day. Additional detail on the categories of emissions can be found in the TSD.

Wildfire emissions, though not included in tables, have been considered for the background 

ozone concentrations in the modeling effort. Wildfire emissions can vary significantly on a 

day-to-day basis depending on conditions.
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Table 5. Base Case Inventories for 8-Hour Ozone DMA/NFR NAA Photochemical Modeling
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1.4.2. Discussion of 2010 Base Case CAMx Modeling Results

Currently, Colorado’s highest emissions density is along the Front Range. As shown in 

Figure 5 Photochemical Modeling done for the DMA/NFR SIP process shows that the 

highest 2010 ozone design values along the foothills west of Denver and Fort Collins. 

Ozone concentrations decrease rapidly to the east of Denver. The maximum projected 2010 

base case 8-hour ozone Design Value of 84 ppb occurs at both the Rocky Flats North and 

Fort Collins West monitoring sites. As this value is 84 ppb or lower, the 2010 base case 

modeling results pass the EPA modeled attainment demonstration test. Although the EPA 

8-hour ozone projection procedure is to truncate the final projected DVF for comparisons 

with the NAAQS, the projected 2010 base case future years design value is 84.9 ppb 

(Morris, et al, 2008a). White (unshaded) areas in Figure 5 have future design value of less 

than 63.8 ppb.

Figure 5. Projected 2010 8-hour ozone Design Values (DVF)

Figure 6 presents the ozone source apportionment results, including the boundary 

conditions. The boundary conditions (BCs) show the contribution from sources outside the 
Colorado Department of Public Health and Environment / Air Pollution Control Division

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12 km domain (see Figure 4) for a given high ozone day (results vary by day). On this day, 

of the 76.1 ppb of ozone estimated at the monitor, approximately 48 ppb was transported 

into the 12 km domain and approximately 8 ppb was attributed to sources in the sevencounty Denver Metro area (Morris, et al, 2008a) while the rest was from other counties in 

Colorado or from other states. This suggests that, on this day, ozone was generated 

primarily by global/continental scale “background” and local sources of emissions in the 

Denver Metro area. Transport from nearby states was relatively small. 

Figure 6. Rocky Flats North source apportionment for 29 July including boundary conditions.

Conclusions from ozone source apportionment results (Morris, et al, 2008a) vary by day 

and by location. However, several overall trends emerged, namely: 

• Regional ozone transport into the 12 km domain is the largest contributor, often 

accounting for more than two-thirds of the total ozone;

• At the Denver Metropolitan monitors the largest contributors are Denver 

Metropolitan metro area motor vehicle and non-road sources;

• At the Fort Collins and Greeley monitors, the largest contributors tend to be 

Larimer and Weld County motor vehicles, non-road sources and oil and gas 

sources, and Denver Metropolitan sources; 

• The majority of the ozone formed is attributable to anthropogenic NOx emissions.
Colorado Department of Public Health and Environment / Air Pollution Control Division

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In interpreting these results, it is important to keep in mind that the source apportionment 

results are based on the Denver SIP 2006 modeling episode and are meteorologically 

dependent For instance, the source apportionment modeling in support of the Denver 

Early Action Compact using a 2002 ozone episode (Morris, et al, 2004a) showed more 

impact from sources in northern Colorado in the Denver Metropolitan area.

Other ozone transport studies also confirm that Denver is impacted by ozone from areas 

well outside of Colorado. A report sponsored by the Western States Air Resources Council 

(WESTAR) indicates that, when ozone is greater than 85 ppb in Denver, natural 

background accounts for 37.5% of the total concentration, transported anthropogenic 

generated ozone is 37.5%, and the local anthropogenic ozone contribution is about 25% 

(MacDonald, et. al, 2006).

A common theme at all ozone monitors is that a majority of the peak 8-hour ozone is due to 

ozone transport from sources outside of Colorado and outside the 12km domain boundary. 

Source apportionment modeling indicates that transport into the region accounts for 

approximately 60-75% of the ozone formation in the DMA/NFR. This indicates that the 

DMA/NFR is more of a receptor of ozone and ozone precursors rather than a producer of 

ozone and precursors that transports ozone to areas outside of the Front Range. While the 

modeling suggests that the transport of ozone and/or ozone precursors is a significant issue 

in the west, the magnitude of ozone transport from Colorado to other states is too low to 

significantly contribute to nonattainment in, or interfere with maintenance by, any other 

state with respect to the 0.08 ppm ozone NAAQS.
Colorado Department of Public Health and Environment / Air Pollution Control Division

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1.5. Denver Metro Area/North Front Range Ozone Nonattainment 

Area Contribution to Downwind Locations

As part of the Denver EAC, source apportionment modeling was conducted to evaluate the 

spatial extent of the 8-hour ozone impacts due to emissions from various source regions in 

Colorado. A similar analysis was not done as part of the DMA/NFR ozone SIP analysis, 

however, a similar conclusion would be expected. The conclusion is that ozone formed 

specifically from sources in the DMA/NFR nonattainment area decreases rapidly in 

concentration over the eastern plains of Colorado. Therefore, the photochemical modeling 

that was done for both the DMA/NFR ozone SIP and the Denver EAC suggest that ozone 

and/or ozone precursors from the Front Range do not contribute significantly to downwind 

monitors in other states. 

Figure 7 displays the spatial extent of the 8-hour ozone concentrations that occurred 

between 10am and 6pm local time (the time when the daily maximum 8-hour ozone 

typically occur) on June 27, 2002 through July 1, 2002 due to all emissions (anthropogenic 

and biogenic) from the DMA. As shown in Figure 7, which represents a high ozone 

episode in Denver, the DMA can contribute approximately 10 ppb of ozone at the eastern 

border of Colorado. However, the concentration gradient falls off quickly and emissions 

from the DMA are not expected to be a significant contributor to any ozone nonattainment 

area downwind of the Front Range. Weld, Elbert, Morgan, Larimer, El Paso and other 

counties contribute even less ozone to the Colorado border states with a maximum 

contribution of 5-10 ppb. 
Colorado Department of Public Health and Environment / Air Pollution Control Division

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Figure 7: Spatial extent of the 8-hour ozone concentrations that occurred between 10am and 6pm local time 

on June 27, 2002 through July 1, 2002 
Colorado Department of Public Health and Environment / Air Pollution Control Division

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1.6. Section 110(a)(2)(D)(i)(I) – Ozone Transport Conclusions

With respect to the 0.08 ppm ozone NAAQS, emission control programs in the Colorado 

SIP are expected to adequately protect downwind neighboring states from interstate 

transport of ozone, per Clean Air Act (CAA) Section 110(a)(2)(D)(i)(I). 

Ambient monitoring data in and around Colorado support the assertion that Colorado does 

not contribute significantly to nonattainment in, or interfere with maintenance by, any other 

state with respect to the 1997 8-hour ozone NAAQS of 0.08 ppm. Colorado is unlikely to 

interfere with maintenance of the 8-hour ozone standard in downwind or potentially 

downwind states is supported by monitoring data collected in neighboring states (see Table 

4) and the results of photochemical modeling analysis as discussed in Section 1.4.2 and 1.5. 

Specifically:

1. Ozone concentrations measured at Kansas, Nebraska, and Wyoming monitors closest 

to Colorado are significantly below the nonattainment threshold. In addition, the 

results of the photochemical analysis discussed in the sections noted above show that 

the ozone values in the easternmost Colorado counties are sufficiently low to make it 

unlikely for ozone transport from Colorado to interfere with maintenance of the 1997 

NAAQS in downwind state.

2. A review of recent ozone observations from the EPA AQS database shows that, with 

the exception of a single monitor in Jefferson County, Colorado (i.e., Rocky Flats 

North), all monitoring sites in Colorado and adjacent states that are likely to be 

impacted by Colorado demonstrated attainment of the 0.08 ppm 8-hour ozone NAAQS 

for the three year period of 2005-2007. Since ozone monitors in adjacent states comply 

with the 0.08 ppm NAAQS, it logically follows that Colorado does not cause or 

contribute to monitored violations or interfere with maintenance of the 0.08 ppm ozone 

NAAQS in any other state.

3. For Rocky Flats North, which is the only monitor in Colorado that has levels above 

the 0.08 ppm ozone NAAQS, the preliminary three-year average (2006-2008) fourth 

high value is 0.086 parts per million (ppm), which is only slightly above the 0.08 ppm 

ozone NAAQS.

4. Observations from current networks show that the highest ozone levels in Colorado 

occur along the Colorado Front Range and not in other areas of Colorado.

5.Ozone monitoring data from the surrounding states that are most likely to be 

impacted by Colorado (i.e., Nebraska, Kansas, New Mexico, Wyoming, and Utah) 

show that none of the monitors exceed the 0.08 ppm 8-hour ozone standard. Since the 

areas represented by these monitors are in monitored attainment, it is highly unlikely 

that existing 0.08 ppm ozone nonattainment areas beyond these areas are significantly 

affected by emissions from Colorado. The nearest 0.08 ppm ozone nonattainment areas 

to DMA/NFR Nonattainment Area are:

a. Phoenix, Arizona (Basic Area for 8-Hour ozone) at a distance of 586 miles;
Colorado Department of Public Health and Environment / Air Pollution Control Division

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b. Las Vegas, Nevada (Basic Area for 8-hour ozone) at a distance of 628 

miles;

c. Dallas, Texas (Moderate 8-hour ozone nonattainment area) at a distance of 

663 miles; and

d. St. Louis, Missouri (Moderate 8-hour ozone nonattainment area) at a 

distance of 796 miles. 

Photochemical modeling and other technical analyses performed for the Denver Early 

Action Compact (EAC) and the Denver Metro Area and North Front Range (DMA/NFR) 

8-hour Ozone SIP support the assertion that Colorado does not contribute significantly to 

nonattainment in, or interfere with maintenance by, any other state with respect to the 0.08 

ppm ozone NAAQS. Specifically:

1. The Denver 8-hour Ozone SIP photochemical modeling for 2010 and the associated 

weight of evidence analyses suggest that the DMA/NFR nonattainment area and 

downwind areas already comply or will comply with the 0.08 ppm ozone NAAQS 

by 2010.

2. Photochemical modeling shows that elevated ozone concentration levels generated 

from local emissions decrease rapidly with distance.

3. A review of photochemical modeling performed for both the DMA/NFR Ozone SIP 

and the Denver EAC, including boundary condition analyses, suggests that the 

magnitude of ozone transport from Colorado to other states is too low to 

significantly contribute to nonattainment in, or interfere with maintenance by, any 

other state with respect to the 0.08 ppm ozone NAAQS.

In summary, a review of monitoring data, photochemical modeling, and weight of evidence 

analyses generated for the DMA/NFR SIP process suggests that the transport of ozone and 

ozone precursors from Colorado does not cause or significantly contribute to nonattainment in, 

or interfere with maintenance by, any other state with respect to the 0.08 ppm 8-hour ozone 

NAAQS. This analysis does not address ozone transport for the revised 0.075 ppm 8-Hour 

Ozone NAAQS.
Colorado Department of Public Health and Environment / Air Pollution Control Division

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2. REFERENCES

Coats, C.J. Jr. “High-performance algorithms in the Sparse Matrix Operator Kernel Emissions 

(SMOKE) modeling system.” Proc. Ninth AMS Joint Conference on Applications of Air 

Pollution Meteorology with AWMA. Amer. Meteor. Soc., Atlanta, GA, 584-588. 1996.

ENVIRON. User’s Guide – Comprehensive Air Quality Model with Extensions – Version 

4.40. ENVIRON International Corporation, Novato, CA http://www.camx.com. February 

2008.

Loomis, C., J. Wilkinson, J. Haasbeek, A. Pollack and M. Jansen. 2005. “ConCEPT –

Consolidated Community Emissions Processing Tool, An Open-Source Tool for the Emissions 

Modeling Community.” Presented at the 14th International Emission Inventory Conference 

“Transforming Emission Inventories – Meeting Future Challenges Today”, Las Vegas, 

Nevada, April 11- 14. <http://www.epa.gov/ttn/chief/conference/ei14/session11/loomis.pdf>

MacDonald, C., Miller, D., Raffuse, S., 2006. Regional and Local Contributions to Peak Local 

Ozone Concentrations in Six Western Cities. Sonoma, Technology, Inc., Petaluma, CA. 

Prepared for WESTAR Council of Governments.. May 16

Morris R., E. Tai, Tanarit Sakulyanontvittaya, D. McNally and C. Loomis. 2008a. 2010 Ozone 

Projections for the 2010 Base Case and 2010 Sensitivity Tests and 2010 Ozone Source 

Apportionment Modeling for the Denver 8-Hour Ozone State Implementation Plan. ENVIRON 

International Corporation, Novato, California. Prepared for Denver Regional Air Quality 

Council (RAQC), Denver, Colorado. September 8.

Morris R., E. Tai, Tanarit Sakulyanontvittaya, D. McNally and C. Loomis. 2008b. 2010 Ozone 

Attainment Demonstration Modeling for the Denver 8-Hour Ozone State Implementation Plan 

Control Strategy. ENVIRON International Corporation, Novato, California. Prepared for 

Denver Regional Air Quality Council (RAQC), Denver, Colorado. September 22.

Morris, R.E., G.E. Mansell, E. Tai, D.A. McNally and T.W. Tesche. 2004a. Air Quality 

Modeling Analysis for the Denver Early Action Compact: Ozone Source Apportionment 

Modeling for the Denver EAC. Prepared for the Colorado Department of Health and 

Environment and Denver Regional Air Quality Council, Denver, Colorado. Prepared by 

ENVIRON International Corporation, Novato, CA. May 31..

Utah Air Quality Board, 8-Hour Ozone Maintenance Provision for Salt Lake and Davis 

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