773 San Marin Drive, Suite 2115, Novato, CA 94998 415.899.0700 

Draft Final Report

2010 OZONE ATTAINMENT DEMONSTRATION 

MODELING FOR THE DENVER 8-HOUR OZONE 

STATE IMPLEMENTATION PLAN CONTROL STRATEGY 

Prepared for: 

Regional Air Quality Council 

1445 Market Street, Suite 260 

Denver, Colorado 80202 

Prepared by: 

Ralph Morris 

Tanarit Sakulyanontvittaya 

Edward Tai 

ENVIRON International Corporation 

773 San Marin Dr. Suite 2115 

Novato, CA 94998 

and 

Dennis McNally 

Cyndi Loomis 

Alpine Geophysics, LLC 

7341 Poppy Way 

Arvada, Colorado 80007 

September 22, 2008
September 2008 

F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\TOC.doc i 

TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY .................................................................................................... ES-1 

Overview of Approach...............................................................................................................ES-1 

2010 Base Case Ozone Projections............................................................................................ES-1 

2010 Control Plan Emission Scenarios......................................................................................ES-3 

2010 Control Plan Ozone Projections........................................................................................ES-4

2010 Unmonitored Area Analysis .............................................................................................ES-5

Alternative 2010 Ozone Projection Results...............................................................................ES-7 

Additional Modeling Metrics.....................................................................................................ES-9 

2010 Control Plan Modeling Conclusions...............................................................................ES-10 

1.0 INTRODUCTION................................................................................................................ 1-1 

1.1 Background................................................................................................................ 1-1 

1.2 Approach.................................................................................................................... 1-1 

1.3 2010 Emissions Modeling Approach......................................................................... 1-4

2.0 2010 OZONE PROJECTIONS........................................................................................... 2-1 

2.1 Introduction................................................................................................................ 2-1 

2.2 Ozone Projection Procedures..................................................................................... 2-1 

2.3 2010 Control Plan Control Measures and Emissions ................................................ 2-2 

2.4 2010 Emission Summary Results .............................................................................. 2-7 

2.5 Ozone Projections for 2010 Control Plans............................................................... 2-10 

2.6 2010 Control Plan Unmonitored Area Analysis ...................................................... 2-13 

3.0 ALTERNATIVE 2010 OZONE PROJECTIONS AND ADDITIONAL MODEL 

METRICS............................................................................................................................. 3-1 

3.1 Introductions .............................................................................................................. 3-1 

3.2 Alternative 2010 Ozone Projections Procedures ....................................................... 3-1 

3.3 Additional Modeling Metrics..................................................................................... 3-7 

4.0 REFERENCES..................................................................................................................... 4-1 
September 2008 

F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\TOC.doc ii 

TABLES 

Table ES-1. Current-year (DVC) and projected future-year (DVF) 

 8-hour ozone Design Values using the CAMx 2006 and 

 2010 base case modeling results........................................................................ES-2 

Table ES-2. Summary of control measures in the 2010 Control 1 and 

 Control 2 emission scenarios .............................................................................ES-3 

Table ES-3. Projected 2010 8-hour ozone Design Values (DVFs) for the 

 2010 Base Case and 2010 Control 1 (Cntl1) and Control 2 (Cntl2) 

 control strategies ................................................................................................ES-4 

Table ES-4. Projected 2010 8-hour ozone Design Values (DVFs) at the 

 Rocky Flats North (RFNO) and Fort Collins West (FTCW) 

 monitoring sites using the EPA guidance default approach, 

 the six alternative projection approaches and the 2010 Base, 

 Control 1 and Control 2 modeling results..........................................................ES-8 

Table 2-1. Summary of control measures in the 2010 Control 1 and 

 Control 2 emission scenarios ............................................................................... 2-6 

Table 2-2. 2006 and 2010 Base Case emission inventories for the 

 Denver 9-county nonattainment area (tons per average episode day). ................ 2-9 

Table 2-3a. Projected 2010 8-hour ozone Design Values (DVFs) for the 

 2010 Base Case and 2010 Control 1 (Cntl1) and Control 2 (Cntl2) 

 control strategies ................................................................................................ 2-11 

Table 2-3b. Relative Response Factors (RRFs) used to project 2010 8-hour 

 ozone Design Values (DVFs) for the 2010 Base Case and two 

 2010 control strategies ....................................................................................... 2-11 

Table 2-3c. Ozone threshold Cutoff Concentration used to project 2010 8-hour 

 ozone Design Values (DVFs) for the 2010 Base Case and two 2010 

 control strategies ................................................................................................ 2-12 

Table 2-3d. Number of days used to project 2010 8-hour ozone Design 

 Values (DVFs) for the 2010 Base Case and two 2010 

 control strategies ................................................................................................ 2-12 

Table 3-1. Projected 2010 8-hour ozone Design Values (DVFs) at the 

 Rocky Flats North (RFNO) and Fort Collins West (FTCW) 

 monitoring sites using the EPA guidance default approach and 

 the six alternative projection approaches and the 2010 Base, 

 Control 1 and Control 2 emission scenarios ........................................................ 3-4 

Table 3-2a. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring 

 sites in the DMA using the EPA guidance default approach, 

 the six alternative projection approaches and the 2010 Base 

 Case modeling results .......................................................................................... 3-5 

Table 3-2b. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring 

 sites in the DMA using the EPA guidance default approach, 

 the six alternative projection approaches and the 2010 Control 1 

 Case modeling results .......................................................................................... 3-5 

Table 3-2c. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring 

 sites in the DMA using the EPA guidance default approach, 

 the six alternative projection approaches and the 2010 

 Control 2 Case modeling results.......................................................................... 3-6 
September 2008 

F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\TOC.doc iii 

Table 3-2d. Ozone cut-off threshold concentrations used in the 2010 8-hour 

 ozone Design Value projections at monitoring sites in the DMA 

 using the EPA guidance default and the six alternative 

 projection approaches .......................................................................................... 3-6 

Table 3-2e. Number of modeling days used in the 2010 8-hour ozone 

 Design Value projections at monitoring sites in the DMA 

 using the EPA guidance default and the six alternative 

 projection approaches .......................................................................................... 3-7 

FIGURES 

Figure ES-1. Interpolated current year 8-hour ozone Design Values 

 (DVC; left) and projected 2010 Base Case 8-hour 

 ozone Design Values..........................................................................................ES-6 

Figure ES-2. Projected 2010 8-hour ozone Design Values (DVF) for 

 the 2010 Control 1 (left) and Control 2 (right) emission scenarios ...................ES-6 

Figure ES-3. Differences in projected 2010 8-hour ozone Design 

 Values (DVF) between the 2010 Control 1 (left) and 2010 

 Control 2 (right) and the 2010 Base Case..........................................................ES-6 

Figure ES-4. Percent change in Total Ozone (left) and Grid Cells (right) 

 greater than 85, 80, 75 and 70 ppb between the 2006 Base Case 

 and the 2010 Base Case (Base), Control 1 (CNTL1) and 

 Control 2 (CNTL2) emission scenarios .............................................................ES-4 

Figure 1-1a. Nested 36/12/4 km modeling domains for the Denver 8-hour 

 ozone modeling study. Blue line domains are for CAMx/SMOKE 

 domains that are nested in the MM5 red line domains ........................................ 1-3 

Figure 1-1b. Nested 12/4 km modeling domains for the Denver CAMx air 

 quality and SMOKE emissions modeling............................................................ 1-3 

Figure 2-1. Interpolated current year 8-hour ozone Design Values (DVC; left) 

 and projected 2010 Base Case 8-hour ozone Design Values............................. 2-14 

Figure 2-2. Projected 2010 8-hour ozone Design Values (DVF) for the 2010 

 Control 1 (left) and Control 2 (right) emission scenarios.................................. 2-14 

Figure 2-3. Differences in projected 2010 8-hour ozone Design Values 

 (DVF) between the 2010 Control 1 (left) and 2010 Control 2 

 (right) and the 2010 Base Case .......................................................................... 2-14 

Figure 3-1a. Arrays of 7 x 7 4 km grid cells around monitors in the DMA............................. 3-2 

Figure 3-1b. Arrays of 5 x 5 (left) and 3 x 3 (right) 4 km grid cells around 

 monitors in the DMA........................................................................................... 3-3 

Figure 3-2a. Percent change in Total Ozone greater than 85, 80, 75 and 

 70 ppb between the 2006 Base Case and the 2010 Base Case 

 (Base), Control 1 (CNTL1) and Control 2 (CNTL2) 

 emission scenarios ............................................................................................... 3-8 

Figure 3-2b. Percent change in Grid Cells greater than 85, 80, 75 and 70 ppb 

 between the 2006 Base Case and the 2010 Base Case (Base), 

 Control 1 (CNTL1) and Control 2 (CNTL2) emission scenarios........................ 3-9 

Figure 3-2c. Percent change in Grid Cell-Hours greater than 85, 80, 75 and 

 70 ppb between the 2006 Base Case and the 2010 Base Case 

 (Base), Control 1 (CNTL1) and Control 2 (CNTL2) emission scenarios.......... 3-10 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-1

EXECUTIVE SUMMARY 

Based on 2005-2007 air quality monitoring data the Denver Metropolitan Area (DMA) violated 

the 0.08 parts per million (ppm) 8-hour ozone National Ambient Air Quality Standard 

(NAAQS). Thus, in November 2007 the DMA reverted to an 8-hour ozone nonattainment area. 

This requires the DMA to develop an 8-hour ozone State Implementation Plan (SIP) that 

demonstrates the area will achieve the 1997 8-hour ozone NAAQS (0.08 ppm) by 2010. The 

Denver Regional Air Quality Council (RAQC), in consultation with the Colorado Department of 

Health and Environment (CDPHE) Air Pollution Control Division (APCD), contracted with 

ENVIRON International Corporation, and their subcontractor Alpine Geophysics, LLC, to 

develop the photochemical modeling databases necessary to demonstrate that the DMA will 

achieve the 0.08 ppm 8-hour ozone NAAQS by 2010. 

OVERVIEW OF APPROACH 

The Comprehensive Air-quality Model with extensions (CAMx; www.camx.com) was set up for 

a June-July 2006 episode on a 36/12/4 km grid with the 4 km domain focused on Colorado. 

Meteorological inputs were prepared using the MM5 meteorological model whose results and 

evaluation are discussed by McNally and co-workers (2008a). An initial emissions inventory 

was prepared using the SMOKE emissions modeling system and a preliminary 2006 base case 

was performed. A preliminary model performance evaluation was conducted and diagnostic 

sensitivity tests performed to identify an optimal model configuration for simulating ozone 

formation in the DMA (Morris et al., 2008b). A revised final CAMx 2006 base case simulation 

was performed and a comprehensive model performance evaluation was conducted (Morris et 

al., 2008c). Although there were some model performance issues on some of the modeling days 

during the June-July 2006 episode, a vast majority of the modeling days achieved EPA’s model 

performance goals and looking at many model performance displays and metrics we concluded 

that the model was simulating the observed ozone sufficiently well for use in making ozone 

projections. Furthermore, on most days the model reproduced the observed VOC/NOx ratios in 

Denver quite well suggesting that the model is simulating the same chemical regimes as 

observed as well. 

2010 BASE CASE OZONE PROJECTIONS 

The procedures given in EPA’s 8-hour ozone modeling guidance were used to project current 

year 8-hour ozone Design Values (DVC) to obtain projected future year 2010 8-hour ozone 

Design Values (DVF) at each of the DMA monitoring sites (EPA, 2007). These procedures use 

the 2006 and 2010 base case modeling results in a relative fashion whereby modeled relative 

response factors (RRFs) are used to scale the current year 8-hour ozone Design Value (DVC) to 

obtain the projected future year 8-hour ozone Design Value (DVF): 

DVF = DVC x RRF 

The 2010 ozone projections were made using EPA’s Modeled Attainment Test Software 

(MATS) tool (http://www.epa.gov/scram001/modelingapps_mats.htm). 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-2

For the Denver 2010 ozone projections, with one exception, the DVCs were based on the 8-hour 

ozone Design Values from the 2005-2007 period (i.e., the three year average of the fourth 

highest daily maximum 8-hour ozone concentration at each monitor). The exception to this was 

for the Fort Collins West (FTCW) monitor that started monitoring in 2006 so a two year average 

of the fourth highest daily maximum 8-hour ozone concentrations was used from 2006-2007 for 

the FTCW DVC. 

Table ES-1 summarizes the projected 8-hour ozone Design Values (DVF) at the DMA 

monitoring sites for the 2010 base case simulation using the CAMx 2006 and 2010 base case 

modeling results and EPA recommended default ozone projection procedures (EPA, 2007). The 

maximum projected 8-hour ozone Design Value is 84 ppb and occurs at both the Rocky Flats 

North (RFNO) and Fort Collins West (FCTW) monitoring sites (see column 5 in Table ES-1). 

As this value is 84 ppb or lower, then the 2010 base case modeling results pass the model 

attainment demonstration test. EPA’s guidance for making 8-hour ozone projections 

recommends truncating the final projected DVF for comparisons with the 85 ppb NAAQS. In 

column 6 of Table ES-1 the DVFs are presented to the nearest tenth of a ppb before truncation, 

in which case we see that the projected 2010 base case DVFs at RFNO and FTCW are both 84.9 

ppb. Also shown in Table ES-1 are the RRFs and the cut-off thresholds used in selecting days 

and number of days used in calculating the RRF. The EPA desire to use at least 10 modeling 

days and a cutoff threshold of 70 ppb or higher is satisfied using the Denver June-July 2006 

modeling period at all monitoring sites. Modeling days are selected based on whether the 2006 

base case model estimated maximum daily maximum 8-hour ozone concentration near a monitor 

(i.e., within 7 x 7 array of 4 km grid cells centered on the monitor) are above the cut-off 

threshold. In order to achieve at least 10 model days for developing the RRFs, the cut-off 

thresholds of 74 ppb to 78 ppb were used depending on the monitor (the key RFNO and FTCW 

monitors using a 78 and 76 ppb cut-off thresholds, respectively). 

Table ES-1. Current-year (DVC) and projected future-year (DVF) 8-hour ozone Design Values 

using the CAMx 2006 and 2010 base case modeling results. 

2005-07 2010 Base Case 

Site ID Monitor Name County DVC DVF DVF RRF Cutoff #days 

80013001 Welby Adams 70.0 70 70.2 1.0042 77.0 11 

80050002 Highland Arapahoe 78.0 77 77.3 0.9916 78.0 14 

80130011 S. Boulder Creek Boulder 81.0 80 80.8 0.9976 78.0 10 

80310002 Denver - CAMP Denver 56.0 56 56.0 1.0017 78.0 10 

80310014 Carriage Denver 74.0 74 74.1 1.0022 78.0 10 

80350004 Chatfield State Park Douglas 84.0 83 83.4 0.9934 78.0 11 

80410013 USAF Academy El Paso 73.0 72 72.0 0.9873 75.0 10 

80410016 Manitou Springs El Paso 74.0 73 73.7 0.9966 74.0 10 

80590002 Arvada Jefferson 79.0 79 79.2 1.0026 78.0 10 

80590005 Welch Jefferson 75.0 75 75.0 1.0004 78.0 10 

80590006 Rocky Flats North Jefferson 85.0 84 84.9 0.9994 78.0 10 

80590011 NREL Jefferson 82.0 82 82.3 1.0039 78.0 11 

80690011 Fort Collins - West Larimer 86.0 84 84.9 0.9874 76.0 10 

80691004 Fort Collins Larimer 74.0 73 73.0 0.9878 76.0 12 

81230009 Greeley - Weld Tower Weld 78.0 77 77.7 0.9964 75.0 10 

GTH161 Gunnison Gunnison 68.0 67 67.8 0.9984 74.0 10 

ROM206 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 

ROM406 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-3

2010 CONTROL PLAN EMISSION SCENARIOS 

2010 ozone projections were made for two 2010 emission control plans: (1) 2010 Control 1 that 

consists of the federally-enforceable control measures that are proposed for the Denver 8-hour 

ozone State Implement plan (SIP); and (2) Control 2 that includes the federally-enforceable 

measures of Control 1 plus additional control measures that are adopted as state-only 

enforceable. The 2010 ozone projections for the two control plans were made using the same 

procedures as for the 2010 base case. Table ES-2 summarizes the control measures for the two 

2010 control plans. 

Table ES-2. Summary of control measures in the 2010 Control 1 and Control 2 emission 

scenarios. 

Strategies Under Development for 2008 Proposed Ozone Action Plan 

(All strategies apply to the entire Denver/North Front Range nonattainment area (NAA) unless otherwise 

noted)

Control 1

Recommended Measures 

for Federally-Enforceable 

State Implementation Plan (SIP) 

Potential 

Emission 

Reduction

Control 2

Recommend Measures 

Adopted and Enforced 

as State-only Measures 

Potential 

Emission 

Reduction

3⁄4 More stringent Reg. 11 I/M cutpoints 

 (Denver area) – adopted, effective 

 May 1, 2008 

~ 1 tpd VOC, 

~3 tpd NOx, 

~13 tpd CO

3⁄4 Inspection/maintenance program in 

 North Front Range (structure to be 

 determined) 

~ 1 tpd VOC,

 ~1 tpd NOx, 

~17 tpd CO 

3⁄4 7.8 RVP gasoline regulatory 

requirement in North Front Range 

(consistent with Denver area) 

~ 3 tpd VOC

3⁄4 Mandatory high-emitter pilot

program (Denver area) – began 

January 1, 2008 

unknown at 

this time 

3⁄4 Tighten up collector plate 

requirements for older vehicles 

(statewide) 

< 1 tpd VOC 

~ 7 tpd CO

3⁄4 Increase condensate tank control 

(95%) 

 for all new/modified tanks >2 tpy 

(2009) 

 for all existing tanks >10 tpy (2010) 

VOC 

~ 6-9 tpd 

~19-30 tpd

3⁄4 Increase condensate tank control 

(95%) 

 for all existing tanks >5 tpy (2011) 

 for all existing tanks >2 tpy (2012) 

VOC 

~ 30-35 tpd 

~9-12 tpd

3⁄4 Pneumatic valves controls - require 

 low/no bleed valves on all new and 

 existing valves by 2009 

~ 23 tpd VOC

3⁄4 Statewide Oil & Gas regulations -- 

 Controls on existing reciprocating 

 internal combustion engines 

unknown at 

this time

3⁄4 Expand Reg. 7 (VOC control 

requirements) to entire NAA

unknown at 

this time

3⁄4 Remove current exemptions in Reg. 

3 for selected small sources required 

to file air pollution emission notices 

and obtain permits

unknown at 

this time

3⁄4 Require Reasonably Available 

 Control Technology (RACT) for minor

 sources in NAA (Reg. 3)

unknown at 

this time

TOTAL 

EMISSION 

REDUCTIONS 

VOC 

NOx 

CO 

~52-66 tpd 

~ 3 tpd 

~13 tpd 

VOC 

NOx 

CO 

~41-49 tpd 

NA 

 >24 tpd
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-4

2010 CONTROL PLAN OZONE PROJECTIONS 

Table ES-3 displays the projected 8-hour ozone DVFs for the 2010 base case and the two 2010 

control plans. The maximum projected 8-hour ozone Design Values for the 2010 Base, Control 

1 and Control 2 emissions scenarios are 84 ppb at the Rocky Flats North (RFNO) and Fort 

Collins West (FTCW) monitoring sites. Thus, the 2010 Base Case and two control scenarios 

pass the modeled attainment demonstration test. However, since there are four monitoring sites 

with projected 2010 DVFs of 82 ppb or higher (84 ppb at RFNO and FTCW, 83 ppb at Chatfield 

and 82 ppb at NREL), an additional weight of evidence (WOE) analysis is required. 

When reporting the DVFs to the nearest tenth of a ppb we see that the projected 2010 DVF for 

the Base Case is 84.9 ppb at both the RFNO and FTCW monitoring sites. The implementation 

of the federally enforceable SIP control measures in the 2010 Control 1 emissions scenario 

reduces the DVFs at the RFNO and FTCW by, respectively, 0.1 and 0.2 ppb (to 84.8 and 84.7 

ppb, respectively). The addition of the state-enforceable control measures in the 2010 Control 2 

scenario reduces the DVFs at RFNO and FRTCW by an additional 0.1 and 0.2 ppb, respectively 

(to 84.7 and 84.5 ppb, respectively). These results are consistent with the 2010 sensitivity 

modeling that found ozone to be more responsive to emission controls at the FTCW than RFNO 

monitoring sites (McNally et al., 2008b). 

Table ES-3. Projected 2010 8-hour ozone Design Values (DVFs) for the 

2010 Base Case and 2010 Control 1 (Cntl1) and Control 2 (Cntl2) control strategies. 

DVF (EPA Recommended) DVF (to nearest 0.1 ppb) 

Name County DVC Base Cntl1 Cntl2 Base Cntl1 Cntl2 

Welby Adams 70.0 70 70 70 70.2 70.2 70.2 

Highland Arapahoe 78.0 77 77 77 77.3 77.2 77.1 

S. Boulder Creek Boulder 81.0 80 80 80 80.8 80.7 80.6 

Denver - CAMP Denver 56.0 56 56 55 56.0 56.0 55.9 

Carriage Denver 74.0 74 74 74 74.1 74.1 74.0 

Chatfield State Park Douglas 84.0 83 83 83 83.4 83.3 83.3 

USAF Academy El Paso 73.0 72 71 71 72.0 71.9 71.9 

Manitou Springs El Paso 74.0 73 73 73 73.7 73.7 73.7 

Arvada Jefferson 79.0 79 79 79 79.2 79.1 79.1 

Welch Jefferson 75.0 75 75 74 75.0 75.0 74.9 

Rocky Flats North Jefferson 85.0 84 84 84 84.9 84.8 84.7 

NREL Jefferson 82.0 82 82 82 82.3 82.2 82.1 

Fort Collins - West Larimer 86.0 84 84 84 84.9 84.7 84.5 

Fort Collins Larimer 74.0 73 72 72 73.0 72.9 72.7 

Greeley-WeldTower Weld 78.0 77 77 77 77.7 77.4 77.0 

Gunnison Gunnison 68.0 67 67 67 67.8 67.8 67.9 

Larimer Larimer 76.0 75 75 75 75.2 75.1 75.1 

Larimer Larimer 76.0 75 75 75 75.2 75.1 75.1 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-5

2010 UNMONITORED AREA ANALYSIS 

EPA’s 8-hour ozone projection procedure also includes an unmonitored area analysis (EPA, 

2007) that has been codified in MATS. The unmonitored area analysis uses the future-year 8-

hour ozone Design Value projection procedure applied to each grid cell in the modeling domain. 

In this procedure, the current-year Design Values (DVC) are interpolated to each grid cell in the 

modeling domain. This interpolation scheme uses the modeled concentration gradients. RRFs 

are then obtained for each grid cell in the modeling domain using essentially the same approach 

as used for the monitored ozone projections, only using the modeling data within each grid cell 

rather than near a grid cell as done for the projections at the monitor. 

Figure ES-1 displays the interpolated current year 8-hour ozone Design Values (DVC) and 

projected 8-hour ozone Design Values (DVFs) for the 2010 Base Case using the MATS 

unmonitored area analysis. Interpolated current year ozone DVCs in excess of 80 ppb are 

estimated to the south, west and northwest of Denver stretching to Fort Collins and then west of 

Fort Collins. In fact, the MATS interpolation procedure estimates 12 grid cells of current-year 

DVCs in excess of the 85 ppb NAAQS occur west of the Fort Collins (Figure ES-1, left). The 

projected DVFs for the 2010 base case (Figure ES-1, right) have greatly reduced the spatial 

extent of the DVFs in excess of 80 ppb and the 12 cells with DVCs exceeding the 85 ppb 

NAAQS have been reduced by half to 6 grid cells in the 2010 base case emissions scenario. 

Figure ES-2 displays the unmonitored area analysis projected DVFs for the 2010 Control 1 (left) 

and 2010 Control 2 (right) emission scenarios. There are slight reductions in the 2010 DVFs 

over the 2010 Base Case, which can be seen more clearly in the difference plots seen in Figure 

ES-3. The 6 remaining grid cells with projected DVFs that are 85 ppb or higher in the 2010 Base 

case are reduced to 4 and 3 grid cells in the, respectively, 2010 Control 1 and Control 2 emission 

scenarios. 

EPA guidance stresses that the unmonitored area test has more uncertainties than the projections 

at the monitors and it should be treated separately from the monitor based attainment 

demonstration test (EPA, 2007). EPA further notes that while it is expected that additional 

emission controls will likely be needed to eliminate predicted exceedances of the ozone NAAQS 

in the monitor based attainment test, the same requirements may not be appropriate in 

unmonitored areas. In any event, EPA recommends that areas of predicted violations in the 

unmonitored area test be scrutinized and understood to determine whether they are likely to 

really exist in the ambient air, or whether they may be caused by an error or uncertainties in the 

modeling system. At a minimum, it may be appropriate to deploy additional ozone monitors to 

such areas. In the case of the Denver ozone modeling, higher ozone concentrations are estimated 

west of Fort Collins than at the locations of the two monitors in Fort Collins on some days and 

this does not appear to be due to an error in the modeling system. Whether it may be due to 

uncertainties in the modeling system can not be determined. However, it does not seem 

implausible that higher ozone values could exist west of the Fort Collins West monitoring site. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-6

Figure ES-1. Interpolated current year 8-hour ozone Design Values (DVC; left) and projected 

2010 Base Case 8-hour ozone Design Values (DVF; right). 

Figure ES-2. Projected 2010 8-hour ozone Design Values (DVF) for the 2010 Control 1 (left) 

and Control 2 (right) emission scenarios. 

Figure ES-3. Differences in projected 2010 8-hour ozone Design Values (DVF) between the 

2010 Control 1 (left) and 2010 Control 2 (right) and the 2010 Base Case. 

 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-7

ALTERNATIVE 2010 OZONE PROJECTION RESULTS 

Several alternative 2010 ozone projection procedures were analyzed for the 2010 Base Case, 

Control 1 and Control 2 emission scenarios to estimate the uncertainties in the projection 

procedures and provide confidence that passing the modeled attainment demonstration test does 

indicate attainment will likely be achieved in 2010 under either the 2010 Base Case, Control 1 or 

Control 2 emission scenarios. These alternative ozone projection procedures differ in the days 

used and how modeled ozone near the monitor is selected to construct the RRFs. Six additional 

ozone projection procedures were analyzed, in addition to the EPA guidance default approach 

discussed previously: 

Minimum 5 Days to Develop RRF using 85-70 ppb Sliding Threshold (5dth): In the EPA 

default approach, days are selected for use RRFs based on whether the maximum daily 

maximum 8-hour ozone concentration near the monitor (with 7 x 7 array of grid cells) in 

the 2006 Base Case is greater than a threshold, with the threshold determined when at 

least 10 days are obtained for the RRF. In this alternative projection approach, we 

require a minimum of 5 modeled days to construct the RRFs. 

Use of 80 ppb Cutoff Threshold and Minimum of 1 Day (1dth80): The second 

alternative ozone projection approach uses an 80 ppb cutoff threshold and RRFs are 

allowed to be calculated with as few as one modeling day. 

Use of 75 ppb (1dth75) and 70 ppb (1dth70) Cutoff Thresholds: In those two alternative 

projection approaches the cutoff threshold is reduced to 75 and 70 ppb. 

Use of 5 x 5 and 3 x 3 Array of Grid Cells: Select the maximum daily maximum 8-hour 

ozone concentration from a 5 x 5 or 3 x 3 array of grid cells centered on the monitor, 

instead of using a 7 x 7 array as used in the EPA default procedure 

Table ES-4 lists the projected 2010 DVFs at the key RFNO and FTCW monitoring sites for the 

EPA guidance default and the six alternative ozone projection procedures discussed above. Also 

shown in Table ES-4 are the ozone cutoff thresholds and number of days used in calculating the 

RRFs for each alternative 2010 ozone project methods and the RFNO and FTCW monitoring 

sites. It should be noted that there is really no one “correct” method for projecting future year 

ozone concentrations that has been proven the most reliable. Methods based on just a few 

number of days have been shown to be less robust than ones based on more days. And it is 

logical that methods based on modeled concentrations closer to the observed 8-hour ozone 

Design Values would be more representative of the conditions that produced those Design 

Values than methods based on days much higher or lower than the Design Values. 

2010 Base Case: For the 2010 Base Case, the projected 2010 DVF using the EPA guidance 

default approach was 84.9 ppb at both the RFNO and FTCW monitoring sites. Some of the six 

alternative projection approaches result in increases, whereas others in decreases in the projected 

2010 DVFs at these two sites relative to the EPA guidance default approach. The projected 

DVFs at RFNO for the 2010 Base Case range from 84.5 to 85.2 with an average value of 84.9 

ppb. A similar range for the FTCW monitor is 84.6 to 85.2 ppb with an average of 84.9 ppb. At 

the RFNO monitoring site, 3 of the 7 projection methods pass the modeled attainment 

demonstration test (43%), while at the FTCW 5 of the 7 methods pass the test (71%). 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-8

2010 Control 1 Case: A majority of the 2010 ozone projection procedures pass the modeled 

attainment demonstration test at both the RFNO (4 out of 7, 57%) and FTCW (6 out of 7, 86%) 

monitoring sites. At the RFNO monitoring site, the projected DVFs for the 2010 Control 1 

scenario range from 84.3 to 85.1 ppb with an average of 84.8 ppb. And at the FTCW monitoring 

site the projected DVFs range from 84.4 to 85.0 ppb with an average of 84.7 ppb. 

2010 Control 2 Case: The 2010 projected DVFs at RFNO for the 2010 Control 2 case are similar 

to the 2010 Control 1 case ranging from 84.3 to 85.1 ppb, with an average of 84.8 ppb. More 

benefits are seen at FTCW where the 2010 projected DVFs range from 84.3 to 84.8 ppb with an 

average of 84.5 ppb. 

An examination of the different 2010 ozone projection methods across monitoring sites shows no 

method is tending toward estimating higher or lower DVFs than the EPA default method across 

all monitoring sites. This is clearly shown in Table ES-4 for the RFNO and FTCW monitoring 

sites where, in most cases, a method in which the projected DVF at RFNO is greater than the 

EPA default method is below the EPA default method at FTCW and vice versa. 

In conclusion, the alternative ozone projection approaches support the findings using the EPA 

default approach that the 2010 Base Case will likely achieve attainment in the Denver region of 

the 0.08 ppm 8-hour ozone NAAQS. The ozone projection methods indicate that there will be 

more certainty that the Denver region will achieve 8-hour ozone attainment in 2010 under the 

2010 Control 1 and Control 2 emission scenarios. 

Table ES-4. Projected 2010 8-hour ozone Design Values (DVFs) at the Rocky Flats North 

(RFNO) and Fort Collins West (FTCW) monitoring sites using the EPA guidance default 

approach, the six alternative projection approaches and the 2010 Base, Control 1 and Control 2 

modeling results. 

Alternative 2010 Ozone Projection Procedures 

Name DVC EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 Avg 

2010 Base Case (Base) DVFs (ppb) 

Rocky Flats North 85.0 84.9 85.2 85.1 84.9 85.0 85.0 84.5 84.9 

Fort Collins - West 86.0 84.9 84.6 84.6 84.9 85.1 84.8 85.2 84.9 

2010 Control Strategy No. 1 (Cntl1) DVFs (ppb) 

Rocky Flats North 85.0 84.8 85.1 85.0 84.8 85.0 84.9 84.3 84.8 

Fort Collins - West 86.0 84.7 84.4 84.4 84.7 84.9 84.6 85.0 84.7 

2010 Control Strategy No. 2 (Cntl2) DVFs (ppb) 

Rocky Flats North 85.0 84.7 85.1 84.9 84.8 84.9 84.8 84.3 84.8 

Fort Collins - West 86.0 84.5 84.3 84.3 84.5 84.7 84.5 84.8 84.5 

Cut-Off Concentration (ppb) 

Rocky Flats North 78 81 80 75 70 76 75 

Fort Collins - West 76 81 80 75 70 75 73 

Number of Days Used 

Rocky Flats North 10 6 7 19 27 11 10 

Fort Collins - West 10 5 5 13 22 10 10 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-9

ADDITIONAL MODELING METRICS 

EPA’s 8-hour ozone modeling guidance recommends calculating additional modeling metrics 

from the current year base case to future year control scenario to assure that they indicate the 

modeled ozone concentrations are going down. These additional modeling metrics examine the 

ozone differences between the current year base case and future year emission scenarios in the 

modeling domain to assure that ozone is going down, on average, across the entire nonattainment 

area (NAA) rather than just limited to a few key monitoring sites. 

The changes in daily maximum 8-hour ozone concentrations between the 2006 Base Case and 

2010 emission scenarios was calculated across grid cells in the Denver NAA and across all days 

in the June-July 2006 modeling episode. The changes 8-hour ozone concentrations are 

calculated for values above four separate threshold concentrations: 85, 80, 75 and 70 ppb. These 

modeling metrics consist of the following: 

Total Ozone: Defined as the difference between the modeled daily maximum 8-hour 

ozone concentrations and the threshold concentration, for modeled values above the 

threshold, summed across all grid cells in the Denver NAA and modeling days during 

June-July 2006. 

Grid Cells: Number of grid cell-days with modeled daily maximum 8-hour ozone 

concentrations greater than the threshold for all grid cells in the NAA and days from the 

June-July 2006 episode. 

Grid Cell-Hours: Number of grid cell-hours with modeled running 8-hour ozone 

concentrations greater than the threshold for all grid cells in the NAA and hours during 

the June-July 2006 episode. 

Figure ES-4 displays the percent change in the Total Ozone and Grid Cells between the 2006 

Base Case and the 2010 emission scenarios (the change in Grid-Cell Hours is similar). There are 

small reductions between 2006 and 2010 in the Total Ozone (~-5%) and Grid Cell (~-3%) 

modeling metrics greater than the 70 ppb threshold. However, the emission reductions between 

2006 and 2010 are having their intended effect in being more effective at reducing the elevated 

8-hour ozone concentrations. For example, the changes in Total Ozone and Grid Cells greater 

than 85 ppb modeling metrics between the 2006 and 2010 Base Cases are -21% and -14% , 

respectively. These reductions are even greater for the 2010 Control 1 case (-28% and -17%) 

and even greater still for the 2010 Control 2 scenario. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Exec_Sum2.doc September 2008 ES-10

Percent Change in Total Ozone for 2010 Base, Cntrl1, and 

Cntrl2

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Base CNTL1 CNTL2

% Change

Total Ozone

85 ppb

Total Ozone

80 ppb

Total Ozone

75 ppb

Total Ozone

70 ppb

Percent Change in Grid Cells for 2010 Base, Cntrl1, and 

Cntrl2

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Base CNTL1 CNTL2

% Change

Grid Cells

85 ppb

Grid Cells

80 ppb

Grid Cells

75 ppb

Grid Cells

70 ppb

Figure ES-4. Percent change in Total Ozone (left) and Grid Cells (right) greater than 85, 80, 75 

and 70 ppb between the 2006 Base Case and the 2010 Base Case (Base), Control 1 (CNTL1) 

and Control 2 (CNTL2) emission scenarios.

2010 CONTROL PLAN MODELING CONCLUSIONS 

The 2010 ozone modeling indicates that the Denver region would achieve attainment of the 1997 

8-hour ozone NAAQS (0.08 ppm) by 2010 under any of the three 2010 emission scenarios 

studied. All three 2010 emission scenarios pass the modeled attainment demonstration test. 

Examining the unmonitored area test, the alternative ozone projection procedures and additional 

modeling metrics we conclude that the two 2010 control strategies provide more certainty that 

ozone attainment will be achieved in 2010 than the 2010 base case. 

There are numerous uncertainties in the modeling analysis. By definition, models are simplistic 

approximations of complex phenomena. The modeling analysis used to asses whether various 

emission reduction measures will bring the Denver area into attainment of the 8-hour ozone 

NAAQS contain many elements that are uncertain (e.g., emissions inputs and projections, 

meteorological inputs, ozone transport, etc.). There are a lot of year-to-year meteorological 

variations in the Denver area that greatly affect the ozone formation potential of the region. For 

example, the most ozone formation conducive year for the DMA in recent record was 2003 that 

was followed by the year with the least ozone formation conducive conditions in 2004. If the 

ozone formation conditions in the next few years are much more severe than seen in the JuneJuly 2006 modeling period, then that could jeopardize achieving attainment in 2010. However, 

for 2008 it appears the opposite is true providing further confidence that the DMA will achieve 

attainment of the 8-hour ozone NAAQS in 2010. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec1_Control_Intro2.doc September 2008 1-1 

1.0 INTRODUCTION 

1.1 BACKGROUND 

Ozone air quality in the Denver Metropolitan Area (DMA) has been near the 8-hour ozone 

National Ambient Air Quality Standard (NAAQS) of 0.08 ppm (exceedance defined by values of 

85 ppb or higher) for several years. In December 2002, the Denver Regional Air Quality 

Council (RAQC) and Colorado Department of Health and Environment (CDPHE) Air Pollution 

Control Division (APCD) and others entered into an 8-hour ozone Early Action Compact (EAC) 

with the U.S. Environmental Protection Agency (EPA). EPA’s EAC allows an area to submit an 

enforceable 8-hour ozone State Implementation Plan (SIP) by March 2004 that demonstrates 

attainment of the 8-hour ozone NAAQS by 2007. In return, EPA will defer the classification of 

an area as nonattainment until 2007. Based on 2005-2007 measured air quality, the DMA 

violated the 0.08 ppm 8-hour ozone NAAQS (i.e., 1997 8-hour ozone NAAQS), so in November 

2007 the DMA reverted to an 8-hour ozone nonattainment area and is required to prepare an 8-

hour ozone State Implementation Plan (SIP) that demonstrates attainment by 2010. The 

contracting team of ENVIRON International Corporation, and their subcontractor Alpine 

Geophysics, LLC, were selected by the RAQC and CDPHE to perform the 2010 8-hour ozone 

attainment demonstration modeling for the new SIP. 

On March 12, 2008, EPA promulgated a new primary ozone NAAQS that has the same form as 

the 1997 ozone NAAQS, but lowers the threshold from 0.08 ppm (85 ppb) to 0.075 ppm (76 

ppb). Of the ~14 ozone monitors in the greater DMA, half have 2005-2007 8-hour ozone DVs 

that are 0.075 ppm or higher. The current Denver 8-hour ozone SIP modeling effort addresses 

the 0.08 ppm 8-hour ozone NAAQS, the new 0.075 ppm 8-hour ozone NAAQS will be 

addressed in future SIP actions. 

1.2 APPROACH 

The fifth generation Mesocale Model (MM5) meteorological model (Anthes and Warner, 1978; 

Dudhia, 1993), the Sparse Matrix Operating Kernel Emissions (SMOKE) modeling system 

(Coats, 1996) and the Comprehensive Air-quality Model with extensions (CAMx) 

photochemical grid model (ENVIRON, 2008) are being used to model ozone in the Denver area 

for a June-July 2006 modeling period for the purposes of demonstrating attainment of the 8-hour 

ozone standard by 2010. The 8-hour ozone modeling activities being performed by the 

ENVIRON/Alpine Modeling Team consists of the following activities: 

• Development of a Denver 8-hour ozone SIP attainment demonstration Modeling Protocol 

(Morris et al., 2007; http://www.ozoneaware.org/documents/DraftFinalProtocolDenver8-

HourOzoneNov282007.pdf); 

• MM5 meteorological modeling and model performance evaluation (McNally et al., 

2008a); 

• Development of a preliminary 36/12/4 km photochemical modeling database for the 

June-July 2006 episode, the DMA, and initial model performance evaluation, sensitivity 

test modeling and identification of optimal model configuration for simulating ozone in 

the DMA (Morris et al., 2008b); 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec1_Control_Intro2.doc September 2008 1-2 

• Final base case modeling and model performance evaluation for the June-July 2006 

DMA episode (Morris et al., 2008c); 

• 2010 base case modeling, emission sensitivity tests and ozone source apportionment 

modeling (McNally et al., 2008b); and 

• 2010 control strategy modeling (this document). 

This document presents the results of the 2010 control strategy modeling. These results include 

the ozone projections for the SIP control plan (Control 1) federally-enforceable control 

measures, as well as the SIP control plan plus additional state-only measures (Control 2). In 

Chapter 2 we present the 2010 ozone projections for the 2010 Base, Control 1 and Control 2 

Cases using the default projection procedures in EPA’s 8-hour ozone modeling guidance (EPA, 

2007) and compare against the model ozone attainment demonstration test. In Chapter 3 we look 

at additional air quality metrics and alternative 2010 ozone projection approaches that are used to 

corroborate the modeled ozone attainment demonstration and is one component of the Weight of 

Evidence (WOE) ozone attainment demonstration. 

Figure 1-1a displays the MM5 (red) and CAMx (blue) 36/12/4 km modeling domains 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 (Figure 1-1a). The CAMx 2006 and 2010 base case modeling results from the 36 km 

continental U.S. domain simulation are then processed to generate BCs for the CAMx 12/4 km 

domain (Figure 1-1b). 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). 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec1_Control_Intro2.doc September 2008 1-3 

-2880-2520-2160-1800-1440-1080 -720 -360 0 360 720 1080 1440 1800 2160 2520 2880

-2160

-1800

-1440

-1080

-720

-360

0

360

720

1080

1440

1800

2160

MM5 36 km

CAMx 36 km

MM5 12km

CAMx 12km

MM5 4km

CAMx 4

Figure 1-1a. Nested 36/12/4 km modeling domains for the Denver 8-hour ozone modeling 

study. Blue line domains are for CAMx/SMOKE domains that are nested in the MM5 red line 

domains. 

-1680-1560-1440-1320-1200-1080 -960 -840 -720 -600 -480 -360 -240 -120 0 120 240

-600

-480

-360

-240

-120

0

120

240

360

480

CAMx 12km

CAMx 4km

Figure 1-1b. Nested 12/4 km modeling domains for the Denver CAMx air quality and SMOKE 

emissions modeling.
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec1_Control_Intro2.doc September 2008 1-4 

1.3 2010 EMISSIONS MODELING APPROACH 

The 2010 base case and control strategy emissions were prepared using the same procedures as 

used to prepare the final 2006 base case emissions scenario (Morris et al., 2008b) and are 

described by McNally and co-workers (McNally et al., 2008b). The CDPHE/APCD provided 

2010 emissions for all anthropogenic emission sources in Colorado except oil and gas (O&G) 

emissions in the Denver-Julesburg Basin for which 2010 emissions from the WRAP Phase III 

O&G emissions development project were utilized (Bar-Ilan et al., 2008b). Outside of Colorado, 

the 2010 anthropogenic emissions were based on the WRAP 2002 and 2018 emissions 

inventories projected to 2010. CAMx-ready emissions were generated using the Sparse Matrix 

Operator Kernel Emissions (SMOKE) emissions modeling system (Coats, 1996) for all 

anthropogenic emissions categories except on-road mobile sources in the DMA, which used the 

Consolidated Community Emissions Processing Tool (ConCEPT) modeling system (Loomis et 

al., 2005) and biogenic emissions. The same biogenic emissions were used for the 2010 base 

case as were used for the final 2006 base case biogenic emissions were based on the Model of 

Emissions of Gases and Aerosols from Nature (MEGAN) biogenic emissions model (Guenther 

and Wiedinmyer, 2004). Emissions from fires were also kept constant between the 2006 base 

case and 2010 base case emission scenarios. 

The 2010 emissions for the two control strategies were either provided by the CDPHE or, for the 

case of on-road mobile sources, modeled using the CONCEPT MV and SMOKE-MOBILE6 onroad mobile source emissions modeling system. Section 2 contains the results of the 2010 

emissions modeling. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-1 

2.0 2010 OZONE PROJECTIONS 

2.1 INTRODUCTION 

This section presents the 2010 ozone Design Value projections for the 2010 base case and the 

two 2010 emission control plans. These two 2010 control plans correspond to: (1) 2010 Control 

1 that consists of the federally-enforceable control measures that are proposed for the Denver 8-

hour ozone State Implement plan (SIP); and (2) Control 2 that includes the federally-enforceable 

measures of Control 1 plus additional control measures that are adopted as state-only 

enforceable. The 8-hour ozone projections are made using the CAMx modeling results for the 

2006 base case (Morris et al., 2008b,c) and the 2010 Base, Control 1 and Control 2 Cases. These 

ozone projections are made using EPA’s Modeled Attainment Test Software (MATS) tool 

(http://www.epa.gov/scram001/modelingapps_mats.htm). The MATS ozone projection 

procedures and 8-hour ozone projections for the 2010 Base Case and 2010 sensitivity 

simulations are described in detail by McNally and co-workers (2008b). Below we provide a 

brief overview of the ozone projection procedures, whose results for the 2010 Base, Control 1 

and Control 2 emissions are presented later in this Chapter. 

2.2 OZONE PROJECTION PROCEDURES 

The Denver 2010 8-hour ozone projections were made following default procedures in EPA’s 

latest modeling guidance (EPA, 2007), with one exception described below. These procedures 

use the model in a relative sense to scale the observed current year 8-hour ozone Design Value 

(DVC) to obtain a future year 8-hour ozone Design Value (DVF). The model derived scaling 

factors are referred to as relative response factors (RRF) and are defined as the ratio of daily 

maximum 8-hour ozone concentrations near a monitor averaged over several days of modeling 

results for the 2010 emissions scenario to the 2006 base case: 

RRF = [Σ 2010 scenario] / [Σ 2006 base] 

DVF = DVC x RRF 

The basic steps in performing the 2010 8-hour ozone projections can be summarized as follows: 

1. Develop an observed current year 8-hour ozone Design Value (DVC) as the starting point 

for the ozone projections. EPA guidance recommends using a three year average of three 

years of Design Values centered on the modeling year, which for the Denver June-July 

2006 episode modeling would mean Design Values from the five year period of 2006-

2008. As the 2008 ozone season is not yet completed, use of this approach for the DVCs 

is not possible. So instead we used the 8-hour ozone Design Values from the 2005-2007 

period that resulted in Denver being classified as nonattainment for the DVCs. 

2. Select the maximum modeled 8-hour ozone concentrations near a monitor for several 

days from the 2006 base and 2010 emission scenarios and take the ratio of their averages 

to construct the monitor-specific RRFs: 

a. By near a monitor EPA guidance suggests using an array of 7 x 7 grid cells 

centered on the monitoring location for the Denver modeling that uses a 4 km grid 

resolution. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-2 

b. By several days EPA recommends RRFs based on at least 10 modeled days and 

recommends selecting days in which the 2006 base case maximum daily 

maximum 8-hour ozone concentrations near a monitor are greater than an ozone 

threshold (cut off). Initially, an ozone threshold of 85 ppb is used. If less than 10 

days are obtained the threshold is reduced by 1 ppb until at least 10 days are 

obtained for the RRF. When the 70 ppb threshold floor is reached and there are at 

least 5 days then the RRF is used. 

3. The RRF is applied to the DVC to obtain the projected DVF for the 2010 emission 

scenarios. The projected DVF is truncated to the nearest ppb. 

4. If the DVFs at all monitoring sites are less than or equal to 84 ppb, then the modeled 

attainment demonstration test is passed. If a DVF at any monitor is 85 ppb or higher, the 

modeled attainment test is not passed. 

5. If there are any DVFs between 82 ppb and 87 ppb then a Weight of Evidence (WOE) 

analysis is required to corroborate the modeled attainment demonstration. 

6. An unmonitored area analysis is also performed that interpolates the DVCs across the 

modeling domain and performs the ozone projections in each grid cell using the 

procedures given above, except using the modeling results within each grid cell rather 

than near the grid cell. 

a. EPA believes that the unmonitored area analysis is more uncertain than the 

monitor based ozone projections, whereas additional emissions reductions are 

likely required to eliminate any projected monitored ozone exceedances, the same 

is not true in the unmonitored area test. 

b. EPA recommends that the reasons behind any unmonitored area test exceedances 

be understood and explained. 

2.3 2010 CONTROL PLAN CONTROL MEASURES AND EMISSIONS 

The same emissions modeling procedures used for the 2006 and 2010 base cases were used for 

the 2010 control plan emission scenarios (Morris et al, 2008a,b; McNally et al., 2008b). The onroad mobile source control measures were modeled using either the CONCEPT MV (area 

covered by the Denver link-based network) or SMOKE-MOBILE6. The other control measures 

were included in emissions files provided by the CDPHE/APCD. Table 2-1 summarizes the 

control measures in the 2010 Control 1 federally-enforceable SIP control strategy and the 2010 

Control 2 that includes the Control 1 control measures as well as additional control measures to 

be adopted by the state of Colorado. 

2.3.1 Measures Proposed for the Federally-Enforceable SIP 

The following measures are proposed for inclusion in the Ozone State Implementation Plan (SIP) 

and were modeled as the 2010 Control 1 emissions scenario. In addition to being adopted and 

enforced by the State of Colorado, these measures will also be federally-enforceable upon 

approval of the SIP revision by EPA. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-3 

1. Adopt more stringent cut-points for inspection/maintenance program in 7-

county Denver metro area

Lower cut-points will identify more high-emitting vehicles that will result in 

repairs to reduce emissions. The Air Quality Control Commission approved 

revisions to Regulation No. 11 implementing these cut-points in March 2008 and 

the changes took effect in May 2008. These revisions are expected to reduce 

mobile source VOC emissions by one ton per day (tpd), NOx emissions by three 

tpd, and carbon monoxide (CO) emissions by 13 tpd. 

2. Require 7.8 pounds per square inch (psi) RVP (Reid Vapor Pressure) 

gasoline in the entire nonattainment area 

Gasoline with 7.8 RVP is already required in the former one-hour ozone 

nonattainment area (most of the 7-county Denver area) and will be required in 

portions of Larimer and Weld counties and eastern portions of Arapahoe and 

Adams counties under this action. This change requires EPA regulatory action, 

which hopefully can be implemented no later than May 2010, if not before. This 

action is expected to provide an additional SIP credit of three tpd VOC emission 

reduction. 

3. Increase control requirements for oil and gas condensate tanks to 95% for all 

new and modified tanks greater than two tons per year (tpy) by 2009 and all 

existing tanks greater than 10 tpy by 2010.

 

 This will replace the current 75% system-wide control requirement in Regulation 

No. 7 and will be implemented as revisions to Regulation No. 7 adopted by the 

AQCC in December 2008. The requirements for new and modified tanks will 

take effect in February 2009 and the requirements for existing tanks greater than 

10 tpy will take effect in May 2010. These controls are expected to reduce VOC 

emissions between 24 and 39 tpd. (The North Front Range Transportation and 

Air Quality Planning Council have endorsed an alternative approach suggested by 

industry that would increase the current system-wide control factor to 90% as a 

SIP measure. This alternative proposal is likely to be considered by the Air 

Quality Control Commission during its upcoming rulemaking pre-hearing 

process.)

4. Require low-bleed control devices on all new and existing pneumatic valves 

in oil and gas operations by 2009 

The AQCC will adopt revisions to Regulation No. 7 in December 2008 effective 

in May 2009 that require low-bleed controllers on valves. Exemptions will be 

granted for operations that require high-bleed controllers on valves for safety 

reasons. These controls are expected to reduce VOC emissions between 19 and 

23 tpd. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-4 

5. Expand current requirements in Regulation No. 7 for Volatile Organic 

Compound (VOC) controls to the entire nonattainment area 

 Control requirements for VOC stationary sources currently pertain only to the 

former one-hour ozone attainment/maintenance area (most of the 7-county 

Denver area). These reasonably available control technology (RACT) 

requirements in Regulation No. 7 will now apply to specific new and existing 

listed source categories and all new and existing major (greater than 100 tons per 

year (tpy)) stationary sources of VOCs in portions of Larimer and Weld counties 

and eastern portions of Adams and Arapahoe counties. These revisions to 

Regulation No. 7 will be adopted by the AQCC in December 2008 and become 

effective in February 2009. The impact of these revisions is difficult to quantify 

since it is unknown how many sources will be affected and the control levels that 

will be required. 

6. Remove current exemptions contained in Regulation No. 3 for selected small 

sources required to file air pollution emission notices and obtain permits 

Regulation No. 3 currently contains exemptions for many small source categories. 

Many of these exemptions pertaining to VOC sources will be removed by the 

AQCC in revisions to Regulation No. 3 in December 2008 and become effective 

in February 2009. This change will result in the identification of more sources of 

VOCs and potentially additional control requirements. The impact of these 

revisions is difficult to quantify since it is unknown how many sources will be 

affected and the control levels that will be required. 

7. Require general application of permit requirements in Regulation No. 3 and 

reasonably available control technology (RACT) for all VOC stationary 

sources greater than two tons per year and NOx stationary sources greater 

than five tons per year in the entire nonattainment area. 

Revisions to Regulation No. 3 implementing these changes were adopted by the 

AQCC in February 2008. The impact of these revisions is difficult to quantify 

since it is unknown how many sources will be affected and the control levels that 

will be required. 

2.3.2 Measures Proposed as State-Only Measures in State Regulation 

 

The following measures will not be included in the federally-enforceable SIP at this time, but 

will be adopted and enforced exclusively under state authority. These measures will provide 

additional reductions of ozone-causing emissions, which will give the region an additional 

margin of safety to maintain compliance with the 1997 8-hour ozone NAAQS and will help the 

region make further progress towards meeting the new EPA standard. 

1. Implement a motor vehicle inspection/maintenance program in the North Front 

Range (Larimer and Weld counties)

 The North Front Range Transportation and Air Quality Planning Council have 

endorsed a proposal to extend the inspection/maintenance (I/M) program structure 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-5 

that currently exists in the Denver metropolitan area to portions of Larimer and Weld 

counties. The program includes IM240 testing, remote-sensing clean screen, gas cap 

checks, and advisory On-Board Diagnostics (OBDII) checks. Revisions to 

Regulation No. 11 implementing this change in the former basic I/M program area in 

Larimer and Weld counties will be proposed to the AQCC in September 2008 for 

adoption in December 2008. The program could become effective in 2010 or a date 

determined by the AQCC. Changes to the boundary of the North Front Range 

program area to include the entire urbanized portion of Larimer and Weld counties 

will likely be considered by the General Assembly during the 2009 session. 

Conservatively, this program is expected to reduce mobile source VOC emissions by 

at least one tpd, NOx emissions by at least one tpd, and CO emissions by at least 17 

tpd. 

The North Front Range Transportation and Air Quality Planning Council also endorse 

an evaluation of the I/M program structure by 2013 that includes consideration of 

expanded OBDII testing and high-emitter identification. 

2. Continue implementing the high-emitter pilot program in the Denver metro area 

A mandatory pilot program using remote sensing technology began January 1, 2008. 

The pilot program will continue through July 2009 after which the results from the 

program will be analyzed. This analysis may lead to implementation of a full-scale 

high-emitter program in the future. Since this pilot program is still underway, the 

emission reduction potential of this program has not yet been identified. However, it 

is a well-established fact that high-emitting vehicles contribute a disproportionate 

amount of pollution to our air. 

 

3. Tighten up collector plate requirements in state law 

Collector plate requirements in current state statute limit emission tests on vehicles 

more than 25 years old. The RAQC and CDPHE are working with stakeholders to 

develop legislation that will limit collector plates to true collector vehicles and close 

the emissions testing loophole for old, non-collector vehicles. The impact from these 

old, non-collector vehicles is difficult to quantify, but it is expected the VOC 

reduction could be around one tpd and the CO reduction could be around seven tpd. 

4. Increase control requirements for oil and gas condensate tanks to 95% for all 

existing tanks greater than 2 tpy 

Regulation No. 7 will be amended by the AQCC in December 2008 to increase the 

number of tanks controlled in the nonattainment area beyond the 10 tpy threshold 

included in the SIP. Control requirements for tanks greater than 5 tpy will take effect 

in May 2011 and tanks greater than 2 tpy will have to meet the requirements by May 

2012. These provisions of Regulation No. 7 will be adopted and enforced as a stateonly control measure and will not be included in the SIP. These controls are expected 

to reduce VOC emissions between 39 and 47 tpd. (The North Front Range 

Transportation and Air Quality Planning Council have endorsed an alternative 

approach suggested by industry that would increase the current system-wide control 

factor to 90% as a SIP measure. This alternative proposal is likely to be considered 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-6 

by the Air Quality Control Commission during its upcoming rulemaking pre-hearing 

process.)

5. Implement control requirements for reciprocating internal combustion engines 

(RICE) statewide 

The control requirements will mirror requirements currently in place in the 

Denver/North Front Range nonattainment area. Revisions to Regulation No. 7 

making these requirements apply statewide will be adopted by the AQCC in 

December 2008 and will become effective by May 1, 2010. The emission reduction 

impact from these statewide controls has not yet been quantified. 

Table 2-1. Summary of control measures in the 2010 Control 1 and Control 2 emission 

scenarios. 

Strategies Under Development for 2008 Proposed Ozone Action Plan 

(All strategies apply to the entire Denver/North Front Range nonattainment area (NAA) unless otherwise noted)

Control 1

Recommended Measures 

for Federally-Enforceable 

State Implementation Plan (SIP) 

Potential 

Emission 

Reduction

Control 2

Recommend Measures 

Adopted and Enforced 

as State-only Measures 

Potential 

Emission 

Reduction

3⁄4 More stringent Reg. 11 I/M cutpoints 

 (Denver area) – adopted, effective 

 May 1, 2008 

~ 1 tpd VOC, 

~3 tpd NOx, 

~13 tpd CO

3⁄4 Inspection/maintenance program in 

 North Front Range (structure to be 

 determined) 

~ 1 tpd VOC,

 ~1 tpd NOx, 

~17 tpd CO 

3⁄4 7.8 RVP gasoline regulatory 

requirement in North Front Range 

(consistent with Denver area) 

~ 3 tpd VOC

3⁄4 Mandatory high-emitter pilot

program (Denver area) – began 

January 1, 2008 

unknown at 

this time 

3⁄4 Tighten up collector plate 

requirements for older vehicles 

(statewide) 

< 1 tpd VOC 

~ 7 tpd CO

3⁄4 Increase condensate tank control 

(95%) 

 for all new/modified tanks >2 tpy 

(2009) 

 for all existing tanks >10 tpy (2010) 

VOC 

~ 6-9 tpd 

~19-30 tpd

3⁄4 Increase condensate tank control 

(95%) 

 for all existing tanks >5 tpy (2011) 

 for all existing tanks >2 tpy (2012) 

VOC 

~ 30-35 tpd 

~9-12 tpd

3⁄4 Pneumatic valves controls - require 

 low/no bleed valves on all new and 

 existing valves by 2009 

~ 23 tpd VOC

3⁄4 Statewide Oil & Gas regulations -- 

 Controls on existing reciprocating 

 internal combustion engines 

unknown at 

this time

3⁄4 Expand Reg. 7 (VOC control 

requirements) to entire NAA

unknown at 

this time

3⁄4 Remove current exemptions in Reg. 

3 for selected small sources required 

to file air pollution emission notices 

and obtain permits

unknown at 

this time

3⁄4 Require Reasonably Available 

 Control Technology (RACT) for minor

 sources in NAA (Reg. 3)

unknown at 

this time

TOTAL 

EMISSION 

REDUCTIONS 

VOC 

NOx 

CO 

~52-66 tpd 

~ 3 tpd 

~13 tpd 

VOC 

NOx 

CO 

~41-49 tpd 

NA 

 >24 tpd
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-7 

2.4 2010 EMISSION SUMMARY RESULTS 

The emission inventories were developed using EPA-approved emissions modeling methods, 

including EPA’s MOBILE6 model and local Vehicle Miles Travelled (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 from Continuous Emissions 

Monitors (CEMs). 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 demographic data for offroad and area sources. 

Highway mobile source emissions within the DMA were based on the CONCEPT MV emissions 

model that uses link-based activity (VMT) data from the Denver Regional Council of 

Governments (DRCOG) and the MOBILE6 emissions model. The SMOKE-MOBILE6 

emissions model was used to estimate on-road mobile source emissions in Larimer and Weld 

Counties not covered by the DRCOG transportation network using the VMT from the North 

Front Range Transportation and Air Quality Planning Council and CDOT. 

 

Non-road source emissions are from the EPA NONROAD 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 the WRAP Phase III oil and gas emissions inventory 

development study (Bar-Ilan, 2008a) and were projected to 2010 using the methodology in the 

WRAP Phase III projection methodology document (Bar-Ilan, 2008b). The WRAP Phase III oil 

and gas inventory was sponsored by the Independent Petroleum Association of Mountain States 

(IPAMS). 

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

inventory. 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 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-8 

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. 

Wildfire emissions were based on MODIS satellite data. Wildfire emissions can vary 

significantly on a day-to-day basis depending on conditions. 

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

2006 and 2010 are presented in Table 2-2. Emissions of NOx and VOCs are in tons per average 

episode day. Because of their large day-to-day variations and small influence in the Denver 

NAA for the June-July 2006 episode, emissions from wildfires are not included in Table 2-2. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-9 

Table 2-2. 2006 and 2010 Base Case emission inventories for the Denver 9-county 

nonattainment area (tons per average episode day). 

2006 2010 

Source Category NOx VOC NOx VOC 

Point Sources 

Electric Generation Units (EGU) 55.6 0.7 58.5 1.6 

External Combustion Boilers 9.5 0.4 10.0 0.5 

Industrial Processes 12.5 10.2 14.0 11.0 

Petroleum and Solvent Evaporation 0.3 19.0 0.3 22.0 

Other 3.1 1.8 3.6 2.0 

Point Sources Subtotal 81.0 32.1 86.4 37.0 

Oil & Gas Point & Area Sources

Condensate Tanks 126.5 129.6 

Other O&G Point Sources 22.6 6.8 23.6 8.6 

Pneumatic Devices (Area Source) 24.8 31.1 

Unpermitted Fugitives (Area Source) 16.2 20.4 

Other Area Sources 17.1 10.8 22.5 13.7 

O&G Point & Area Sources Subtotal 39.7 185.2 46.2 203.3 

Area Sources 

Personal Care Products 7.1 7.0 

Household Products 21.4 17.9 

Automotive Aftermarket Products 11.9 13.0 

Architectural Coatings 20.1 16.8 

Aircraft 7.4 1.3 8.2 1.5 

Railroad 12.8 0.5 13.8 0.6 

Other Coatings/Pesticides/Cooking/ Miscellaneous. 3.9 4.1 

Area Source Subtotal 20.2 66.3 22.1 61.0 

Non-Road Mobile Sources 

Agricultural Equipment 7.0 0.9 6.3 0.7 

Airport Equipment 0.7 0.1 0.6 0.1 

Commercial Equipment 5.3 6.2 5.1 7.0 

Construction and Mining Equipment 35.7 5.5 31.2 4.5 

Industrial Equipment 10.5 2.4 6.9 1.4 

Lawn and Garden Equipment (Commercial) 9.4 35.9 8.9 28.1 

Lawn and Garden Equipment (Residential) 1.2 7.5 1.2 11.8 

Boats/Recreational Equipment/Miscellaneous 0.7 6.9 0.8 7.8 

Non-Road Mobile Source Subtotal 70.5 65.3 61.0 61.3 

On-Road Mobile Sources 

On-Road Mobile (including vehicle refueling) 165.5 129.7 122.9 109.2 

On-Road Mobile Subtotal 165.5 129.7 122.9 109.2 

Anthropogenic Total 376.8 478.6 338.5 471.8 

Biogenic Total 53.0 694.0 53.0 694.0 

Anthropogenic & Biogenic Total 429.8 1172.6 391.5 1165.8 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-10 

2.5 OZONE PROJECTIONS FOR 2010 CONTROL PLANS 

Table 2-3 displays the projected 8-hour ozone DVFs for the 2010 base case and the two 2010 

control plans. Included in this table are the 2010 DVFs (Table 2-3a), the RRFs (Table 2-3b) and 

the cut-off threshold concentrations (Table 2-3c) and the number of modeling days (Table 2-3d) 

used in the construction of the RRFs. The first set of DVFs in Table 2-3a (columns 4-6) follow 

EPA’s guidance approach (EPA, 2007) to truncate the final DVFs to the nearest ppb for 

comparisons with the NAAQS. Whereas the last set of three DVFs for the three 2010 emissions 

scenarios display the DVFs to the nearest tenth of a ppb. The maximum projected 8-hour ozone 

Design Values for the 2010 Base, Control 1 and Control 2 cases are 84 ppb at the Rocky Flats 

North (RFNO) and Fort Collins West (FTCW) monitoring sites. Thus, the 2010 Base Case and 

two control scenarios pass the modeled attainment demonstration test. However, since there are 

four monitoring sites with projected 2010 DVFs of 82 ppb or higher (84 ppb at RFNO and 

FTCW, 83 ppb at Chatfield and 82 ppb at NREL), then additional Weight of Evidence (WOE) 

analysis is required. 

When reporting the DVFs to the nearest tenth of a ppb we see that the maximum projected DVF 

for the 2010 Base Case is 84.9 ppb at both the RFNO and FTCW monitoring sites. The 

implementation of the federally enforceable SIP control measures in the 2010 Control 1 

emissions scenario reduces the DVFs at the RFNO and FTCW monitoring sites by, respectively, 

0.1 and 0.2 ppb (to 84.8 and 84.7 ppb, respectively). The addition of the state-enforceable 

control measures in the 2010 Control 2 scenario reduces the DVFs at the RFNO and FTCW 

monitoring sites by another 0.1 and 0.2 ppb, respectively (to 84.7 and 84.5 ppb, respectively). 

These results are consistent with the 2010 sensitivity modeling that found ozone to be more 

responsive to emission controls at the FTCW than RFNO monitoring sites (McNally et al., 

2008b). 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-11 

Table 2-3a. Projected 2010 8-hour ozone Design Values (DVFs) for the 

2010 Base Case and 2010 Control 1 (Cntl1) and Control 2 (Cntl2) control strategies. 

DVF (EPA Recommended) DVF (to nearest 0.1 ppb) 

Name County DVC Base Cntl1 Cntl2 Base Cntl1 Cntl2 

Welby Adams 70.0 70 70 70 70.2 70.2 70.2 

Highland Arapahoe 78.0 77 77 77 77.3 77.2 77.1 

S. Boulder Creek Boulder 81.0 80 80 80 80.8 80.7 80.6 

Denver - CAMP Denver 56.0 56 56 55 56.0 56.0 55.9 

Carriage Denver 74.0 74 74 74 74.1 74.1 74.0 

Chatfield State Park Douglas 84.0 83 83 83 83.4 83.3 83.3 

USAF Academy El Paso 73.0 72 71 71 72.0 71.9 71.9 

Manitou Springs El Paso 74.0 73 73 73 73.7 73.7 73.7 

Arvada Jefferson 79.0 79 79 79 79.2 79.1 79.1 

Welch Jefferson 75.0 75 75 74 75.0 75.0 74.9 

Rocky Flats North Jefferson 85.0 84 84 84 84.9 84.8 84.7 

NREL Jefferson 82.0 82 82 82 82.3 82.2 82.1 

Fort Collins - West Larimer 86.0 84 84 84 84.9 84.7 84.5 

Fort Collins Larimer 74.0 73 72 72 73.0 72.9 72.7 

Greeley-WeldTower Weld 78.0 77 77 77 77.7 77.4 77.0 

Gunnison Gunnison 68.0 67 67 67 67.8 67.8 67.9 

Larimer Larimer 76.0 75 75 75 75.2 75.1 75.1 

Larimer Larimer 76.0 75 75 75 75.2 75.1 75.1 

Table 2-3b. Relative Response Factors (RRFs) used to project 2010 8-hour ozone Design 

Values (DVFs) for the 2010 Base Case and two 2010 control strategies.

RRF 

Name County DVC base cntl1 cntl2 

Welby Adams 70.0 1.0042 1.0039 1.0031

Highland Arapahoe 78.0 0.9916 0.9900 0.9896

S. Boulder Creek Boulder 81.0 0.9976 0.9963 0.9956

Denver - CAMP Denver 56.0 1.0017 1.0009 0.9999

Carriage Denver 74.0 1.0022 1.0015 1.0005

Chatfield State Park Douglas 84.0 0.9934 0.9921 0.9917

USAF Academy El Paso 73.0 0.9873 0.9857 0.9856

Manitou Springs El Paso 74.0 0.9966 0.9961 0.9962

Arvada Jefferson 79.0 1.0026 1.0022 1.0013

Welch Jefferson 75.0 1.0004 1.0002 0.9999

Rocky Flats North Jefferson 85.0 0.9994 0.9981 0.9973

NREL Jefferson 82.0 1.0039 1.0027 1.0020

Fort Collins - West Larimer 86.0 0.9874 0.9852 0.9836

Fort Collins Larimer 74.0 0.9878 0.9853 0.9832

Greeley-WeldTower Weld 78.0 0.9964 0.9925 0.9883

Gunnison Gunnison 68.0 0.9984 0.9984 0.9987

Larimer Larimer 76.0 0.9903 0.9892 0.9890

Larimer Larimer 76.0 0.9903 0.9892 0.9890
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-12 

Table 2-3c. Ozone threshold Cutoff Concentration used to project 2010 8-hour ozone Design 

Values (DVFs) for the 2010 Base Case and two 2010 control strategies.

Cutoff Concentration 

Name County DVC base cntl1 cntl2 

Welby Adams 70.0 77.0 77.0 77.0

Highland Arapahoe 78.0 78.0 78.0 78.0

S. Boulder Creek Boulder 81.0 78.0 78.0 78.0

Denver - CAMP Denver 56.0 78.0 78.0 78.0

Carriage Denver 74.0 78.0 78.0 78.0

Chatfield State Park Douglas 84.0 78.0 78.0 78.0

USAF Academy El Paso 73.0 75.0 75.0 75.0

Manitou Springs El Paso 74.0 74.0 74.0 74.0

Arvada Jefferson 79.0 78.0 78.0 78.0

Welch Jefferson 75.0 78.0 78.0 78.0

Rocky Flats North Jefferson 85.0 78.0 78.0 78.0

NREL Jefferson 82.0 78.0 78.0 78.0

Fort Collins - West Larimer 86.0 76.0 76.0 76.0

Fort Collins Larimer 74.0 76.0 76.0 76.0

Greeley-WeldTower Weld 78.0 75.0 75.0 75.0

Gunnison Gunnison 68.0 74.0 74.0 74.0

Larimer Larimer 76.0 77.0 77.0 77.0

Larimer Larimer 76.0 77.0 77.0 77.0

Table 2-3d. Number of days used to project 2010 8-hour ozone Design Values (DVFs) for the 

2010 Base Case and two 2010 control strategies.

Number of Day 

Name County DVC base cntl1 cntl2 

Welby Adams 70.0 11 11 11

Highland Arapahoe 78.0 14 14 14

S. Boulder Creek Boulder 81.0 10 10 10

Denver - CAMP Denver 56.0 10 10 10

Carriage Denver 74.0 10 10 10

Chatfield State Park Douglas 84.0 11 11 11

USAF Academy El Paso 73.0 10 10 10

Manitou Springs El Paso 74.0 10 10 10

Arvada Jefferson 79.0 10 10 10

Welch Jefferson 75.0 10 10 10

Rocky Flats North Jefferson 85.0 10 10 10

NREL Jefferson 82.0 11 11 11

Fort Collins - West Larimer 86.0 10 10 10

Fort Collins Larimer 74.0 12 12 12

Greeley-WeldTower Weld 78.0 10 10 10

Gunnison Gunnison 68.0 10 10 10

Larimer Larimer 76.0 10 10 10

Larimer Larimer 76.0 10 10 10
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-13 

2.6 2010 CONTROL PLAN UNMONITORED AREA ANALYSIS 

EPA’s 8-hour ozone projection procedure also includes an unmonitored area analysis (EPA, 

2007) that has been codified in MATS. The unmonitored area analysis uses the future-year 8-

hour ozone Design Value projection procedure applied to each grid cell in the modeling domain. 

In this procedure, the current-year Design Values (DVC) are interpolated to each grid cell in the 

modeling domain. This interpolation scheme uses the modeled concentration gradients. RRFs 

are then obtained for each grid cell in the modeling domain using essentially the same approach 

as used for the monitored ozone projections, only using the modeled data within each grid cell 

rather than near a grid cell as done for the projections at the monitor. 

Figure 2-1 displays the interpolated current year 8-hour ozone Design Values (DVC) and 

projected 8-hour ozone Design Values (DVFs) for the 2010 Base Case using the MATS 

unmonitored area analysis. Interpolated current year ozone DVCs in excess of 80 ppb are 

estimated to the south, west and northwest of Denver stretching to Fort Collins and then west of 

Fort Collins. In fact, the MATS interpolation procedure estimates 12 grid cells of current-year 

DVCs in excess of the 85 ppb NAAQS that occurs west of the Fort Collins (Figure 2-1, left). 

The projected DVFs for the 2010 base case (Figure 2-1, right) have greatly reduced the spatial 

extent of the DVFs in excess of 80 ppb and the 12 cells with DVCs exceeding the 85 ppb 

NAAQS have been reduced by half to 6 grid cells in the 2010 base case emissions scenario. 

Figure 2-2 displays the unmonitored area analysis projected DVFs for the 2010 Control 1 (left) 

and 2010 Control 2 (right) emission scenarios. There are slight reductions in the 2010 DVFs 

over the 2010 Base Case, which can be seen more clearly in the difference plots seen in 

Figure 2-3. The 6 remaining grid cells with projected DVFs that are 85 ppb or higher in the 2010 

Base case are reduced to 4 and 3 grid cells in the, respectively, 2010 Control 1 and Control 2 

emission scenarios. 

EPA guidance stresses that the unmonitored area test has more uncertainties than the projections 

at the monitors and it should be treated separately from the monitor based attainment 

demonstration test (EPA, 2007). EPA further notes that while it is expected that additional 

emission controls will likely be needed to eliminate predicted exceedances of the ozone NAAQS 

in the monitor based attainment test, the same requirements may not be appropriate in 

unmonitored areas. In any event, EPA recommends that areas of predicted violations in the 

unmonitored area test be scrutinized and understood to determine whether they are likely to 

really exist in the ambient air, or whether they may be caused by an error or uncertainties in the 

modeling system. At a minimum, it may be appropriate to deploy additional ozone monitors to 

such areas. In the case of the Denver ozone modeling, higher ozone concentrations are estimated 

west of Fort Collins than at the locations of the two monitors in Fort Collins on some days and 

this does not appear to be due to an error in the modeling system. Whether it may be due to 

uncertainties in the modeling system can not be determined. However, it does not seem 

implausible that higher ozone values could exist west of the Fort Collins West monitoring site. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-14 

Figure 2-1. Interpolated current year 8-hour ozone Design Values (DVC; left) and projected 

2010 Base Case 8-hour ozone Design Values (DVF; right). 

Figure 2-2. Projected 2010 8-hour ozone Design Values (DVF) for the 2010 Control 1 (left) and 

Control 2 (right) emission scenarios. 

Figure 2-3. Differences in projected 2010 8-hour ozone Design Values (DVF) between the 2010 

Control 1 (left) and 2010 Control 2 (right) and the 2010 Base Case. 

 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-1 

3.0 ALTERNATIVE 2010 OZONE PROJECTIONS 

AND ADDITIONAL MODEL METRICS 

3.1 INTRODUCTION 

As noted in Chapter 2, the maximum projected 2010 8-hour ozone Design Value (DVF) at any 

monitor for the 2010 Base, Control 1 and Control 2 emission scenarios is 84 ppb at the Rocky 

Flats North (RFNO) and Fort Collins West (FTCW) monitoring sites, so passes the modeled 

attainment demonstration test. As these DVFs are 82 ppb or higher, then a Weight of Evidence 

(WOE) analysis is required to corroborate the modeled attainment demonstration test. The WOE 

analysis examines observed emissions and air quality data and their trends, assesses the 

conceptual model of ozone formation in the region, examines additional modeling metrics and 

performs additional analysis. All of the elements of the WOE analysis are examined together to 

determine whether the preponderance of evidence suggests that Denver area will in fact achieve 

attainment of the 0.08 ppm 8-hour ozone National Ambient Air Quality Standard (NAAQS) by 

2010. Below we provide additional modeling metrics and alternative ozone projection 

procedures that are one component of a WOE analysis. 

3.2 ALTERNATIVE 2010 OZONE PROJECTIONS PROCEDURES 

Several alternative 2010 ozone projection procedures were analyzed for the 2010 Base Case, 

Control 1 and Control 2 scenarios to estimate the uncertainties in the projection procedures and 

provide confidence that passing the modeled attainment demonstration test does indicate 

attainment will likely be achieved in 2010. These alternative ozone projection procedures differ 

in the days used and how modeled ozone near the monitor is selected to construct the RRFs. Six 

additional ozone projection procedures were analyzed, in addition to the EPA guidance default 

approach discussed in Chapter 2: 

Minimum 5 Days to Develop RRF using 85-70 ppb Sliding Threshold (5dth): In the EPA 

default approach, modeling days are selected for use in constructing RRFs based on 

whether the maximum daily maximum 8-hour ozone concentration near the monitor 

(with 7 x 7 array of grid cells) in the 2006 Base Case is greater than a threshold, with the 

threshold determined when at least 10 days are obtained for the RRF. In this alternative 

projection approach, we require a minimum of 5 modeled days to construct the RRFs. 

Use of 80 ppb Cutoff Threshold and Minimum of 1 Day (1dth80): The second 

alternative ozone projection approach uses an 80 ppb cutoff threshold and RRFs are 

allowed to be calculated with as few as one modeling day. 

Use of 75 ppb (1dth75) and 70 ppb (1dth70) Cutoff Thresholds: These two alternative 

ozone projection approaches use cutoff thresholds of 75 and 70 ppb. 

Use of 5 x 5 and 3 x 3 Array of Grid Cells: Select the maximum daily maximum 8-hour 

ozone concentration from a 5 x 5 or 3 x 3 array of grid cells centered on the monitor, 

instead of using a 7 x 7 array as used in the EPA default procedure. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-2 

In regards to these last two alternative 2010 ozone projection methods, Figure 3-1 displays the 

sizes of the arrays of 7 x 7, 5 x 5 and 3 x 3 4 km grid cells around the monitors in the DMA. 

With the EPA default 7 x 7 array of grid cells around each monitor, there is a lot of overlap of 

the areas searched to obtain the maximum daily maximum 8-hour ozone concentrations near a 

monitor used in the RRFs. This can potentially result in selecting the same modeled 

concentrations from nearby grid cells to develop the RRFs for different monitors. Using the 

tighter 5 x 5 and 3 x 3 array of grid cells centered on each monitor (Figure 3-1b) reduces the 

overlap among nearby monitors and potentially retains the different characteristics of the 

monitoring sites, if such differences were captured by the model. For example, the CAMP, and 

other more urban Denver monitoring sites, are clearly affected by the high NOx concentrations 

that inhibit ozone formation. Use of the 7 x 7 array of grid cells results in selecting maximum 

modeled concentrations that are potentially outside of the influence of the downtown Denver 

high NOx concentrations for use in the RRFs thereby not capturing the NOx inhibition effect of 

these monitoring sites (Figure 3-1). 

Figure 3-1a. Arrays of 7 x 7 4 km grid cells around monitors in the DMA. 

 

-800 -760 -720 -680 -640 -600

-120

-80

-40

0

40

80

120

SBC

ACAD

 ARVA

NREL 

RMNP

FTCW

 GREE

CHAT CHAT

MANI

FTCO

WCTO

 CARR

WELB

HIGH

CAMP

 RFNO

WELC

LOOK

Denver Ozone Monitoring Sites 

with surrounding 7x7 cells
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-3 

 Figure 3-1b. Arrays of 5 x 5 (left) and 3 x 3 (right) 4 km grid cells around monitors in the DMA. 

Table 3-1 lists the projected 2010 DVFs at the RFNO and FTCW monitoring sites for the EPA 

guidance default and the six alternative ozone projection procedures discussed above. Also 

shown in Table 3-1 are the ozone cutoff thresholds and number of days used in calculating the 

RRFs for each alternative 2010 ozone project method and the RFNO and FTCW monitoring 

sites. Results for all monitoring sites in the DMA are shown in Table 3-2. It should be noted 

that there is really no one “correct” method for projecting future year ozone concentrations that 

has been proven the most reliable. Methods based on just a few number of days have been 

shown to be less robust than ones based on more days. And it is logical that methods based on 

modeled concentrations closer to the observed 8-hour ozone Design Values would be more 

representative of the conditions that produced those Design Values than methods based on days 

with much higher or lower ozone concentrations than the Design Values. 

2010 Base Case: For the 2010 Base Case, the projected 2010 DVF using the EPA guidance 

default approach was 84.9 ppb at both the RFNO and FTCW monitoring sites. Some of the six 

alternative projection approaches result in increases, whereas others in decreases relative to the 

EPA default approach in the projected 2010 DVFs at these two sites. The projected DVFs at 

RFNO for the 2010 Base Case range from 84.5 to 85.2 ppb with an average value of 84.9 ppb. A 

similar range for the FTCW monitor is 84.6 to 85.2 ppb with an average of 84.9 ppb. At the 

RFNO monitoring site 3 of the 7 projection methods pass the modeled attainment demonstration 

test (43%), while at the FTCW 5 of the 7 methods pass the test (71%). 

2010 Control 1 Case: A majority of the 2010 ozone projection procedures pass the modeled 

attainment demonstration test at both the RFNO (4 out of 7, 57%) and FTCW (6 out of 7, 86%) 

monitoring sites. At the RFNO monitoring site, the projected DVFs for the 2010 Control 1 

scenario range from 84.3 to 85.1 ppb with an average of 84.8 ppb. And at the FTCW monitoring 

site the projected DVFs range from 84.4 to 85.0 ppb with an average of 84.7 ppb. 

-800 -760 -720 -680 -640 -600

-120

-80

-40

0

40

80

120

SBC

ACAD

 ARVA

NREL 

RMNP

FTCW

 GREE

CHAT CHAT

MANI

FTCO

WCTO

 CARR

WELB

HIGH

CAMP

 RFNO

WELC

LOOK

Denver Ozone Monitoring Sites

with surrounding 3x3 cells

-800 -760 -720 -680 -640 -600

-120

-80

-40

0

40

80

120

SBC

ACAD

 ARVA

NREL 

RMNP

FTCW

 GREE

CHAT CHAT

MANI

FTCO

WCTO

 CARR

WELB

HIGH

CAMP

 RFNO

WELC

LOOK

Denver Ozone Monitoring Sites

with surrounding 5x5 cells
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-4 

2010 Control 2 Case: The 2010 projected DVFs at RFNO for the 2010 Control 2 case are similar 

to the 2010 Control 1 case ranging from 84.3 to 85.1 ppb, with an average of 84.8 ppb. More 

benefits are seen at the FTCW monitoring site where the 2010 projected DVFs range from 84.3 

to 84.8 ppb with an average of 84.5 ppb. 

An examination of the different 2010 ozone projection methods across monitoring sites shows no 

method is trending toward estimating higher or lower DVFs than the EPA default method across 

all monitoring sites. This is clearly shown in Table 3-1 for the RFNO and FTCW monitoring 

sites where, in most cases, a method in which the projected DVF at RFNO is greater than the 

EPA default method is below the EPA default method at FTCW and vice versa. The possible 

exception to this is at the downtown ozone monitors where as the array of grid cells becomes 

smaller, the projected DVF goes up. For example, at the CAMP monitor and the 2010 Control 1 

case the projected DVF using the 7 x 7, 5 x 5 and 3 x 3 array of grid cells are, respectively, 56.0, 

56.9 and 57.5 ppb (Table 3-2). This reflects the selection of modeling results closer to the urban 

core where the model is less responsive. It is encouraging that the EPA default 2010 ozone 

projection approach falls in between the alternative approaches and, in almost all cases, the 

average of the seven ozone projection approaches equals the EPA default method approach. 

In conclusion, the alternative ozone projection approaches support the findings using the EPA 

default approach that the 2010 Base Case will likely achieve attainment in the Denver region of 

the 0.08 ppm 8-hour ozone NAAQS. The ozone projection methods indicate that there will be 

more certainty that the Denver region will achieve 8-hour ozone attainment in 2010 under the 

2010 Control 1 emissions scenario. 

Table 3-1. Projected 2010 8-hour ozone Design Values (DVFs) at the Rocky Flats North 

(RFNO) and Fort Collins West (FTCW) monitoring sites using the EPA guidance default 

approach and the six alternative projection approaches and the 2010 Base, Control 1 and 

Control 2 emission scenarios. 

Alternative 2010 Ozone Projection Procedures 

Name DVC EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 Avg 

2010 Base Case (Base) DVFs (ppb) 

Rocky Flats North 85.0 84.9 85.2 85.1 84.9 85.0 85.0 84.5 84.9 

Fort Collins - West 86.0 84.9 84.6 84.6 84.9 85.1 84.8 85.2 84.9 

2010 Control Strategy No. 1 (Cntl1) DVFs (ppb) 

Rocky Flats North 85.0 84.8 85.1 85.0 84.8 85.0 84.9 84.3 84.8 

Fort Collins - West 86.0 84.7 84.4 84.4 84.7 84.9 84.6 85.0 84.7 

2010 Control Strategy No. 2 (Cntl2) DVFs (ppb) 

Rocky Flats North 85.0 84.7 85.1 84.9 84.8 84.9 84.8 84.3 84.8 

Fort Collins - West 86.0 84.5 84.3 84.3 84.5 84.7 84.5 84.8 84.5 

Cut-Off Concentration (ppb) 

Rocky Flats North 78 81 80 75 70 76 75 

Fort Collins - West 76 81 80 75 70 75 73 

Number of Days Used 

Rocky Flats North 10 6 7 19 27 11 10 

Fort Collins - West 10 5 5 13 22 10 10 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-5 

Table 3-2a. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring sites in the DMA 

using the EPA guidance default approach, the six alternative projection approaches and the 

2010 Base Case modeling results.

2010 Base Case 

Name DVC base 5dth 1dth80 1dth75 1dth70 5x5 3x3 

Welby 70.0 70.2 69.4 69.4 70.3 71.1 70.4 71.4 

Highland 78.0 77.3 76.2 77.4 77.5 78.0 77.6 78.0 

S. Boulder Creek 81.0 80.8 80.5 80.5 80.5 80.5 80.8 80.5 

Denver - CAMP 56.0 56.0 55.8 55.8 56.2 56.7 56.8 57.3 

Carriage 74.0 74.1 73.8 73.8 74.3 75.0 75.0 74.8 

Chatfield State Park 84.0 83.4 83.0 83.3 83.6 84.0 83.2 82.9 

USAF Academy 73.0 72.0 72.4 72.2 72.0 72.2 72.1 72.3 

Manitou Springs 74.0 73.7 73.7 73.6 73.8 73.5 73.6 73.7 

Arvada 79.0 79.2 78.9 78.9 79.4 79.7 79.5 79.4 

Welch 75.0 75.0 75.0 75.0 74.8 74.9 74.5 74.6 

Rocky Flats North 85.0 84.9 85.2 85.1 84.9 85.0 85.0 84.5 

NREL 82.0 82.3 82.6 82.5 82.2 82.0 82.0 81.8 

Fort Collins - West 86.0 84.9 84.6 84.6 84.9 85.1 84.8 85.2 

Fort Collins 74.0 73.0 72.8 72.8 73.0 73.3 73.3 73.6 

Greeley - Weld 78.0 77.7 78.0 77.5 77.7 77.7 77.7 77.8 

Gunnison 68.0 67.8 67.9 68.0 67.9 67.8 67.8 67.8 

Larimer 76.0 75.2 75.0 75.0 75.0 75.2 75.2 75.2 

Larimer 76.0 75.2 75.0 75.0 75.0 75.2 75.2 75.2 

Table 3-2b. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring sites in the DMA 

using the EPA guidance default approach, the six alternative projection approaches and the 

2010 Control 1 Case modeling results.

2010 Control Strategy No. 1 (Cntl1) 

Name DVC EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 

Welby 70.0 70.2 69.2 69.2 70.3 71.2 70.3 71.4 

Highland 78.0 77.2 76.0 77.2 77.4 78.0 77.5 77.9 

S. Boulder Creek 81.0 80.7 80.4 80.4 80.4 80.4 80.7 80.3 

Denver - CAMP 56.0 56.0 55.7 55.7 56.2 56.7 56.9 57.5 

Carriage 74.0 74.1 73.7 73.7 74.3 75.1 75.1 75.0 

Chatfield 84.0 83.3 82.8 83.1 83.6 83.9 83.1 82.8 

USAF Academy 73.0 71.9 72.3 72.1 71.9 72.1 72.0 72.2 

Manitou Springs 74.0 73.7 73.7 73.6 73.8 73.4 73.6 73.7 

Arvada 79.0 79.1 78.9 78.9 79.4 79.7 79.4 79.3 

Welch 75.0 75.0 75.0 75.0 74.7 74.8 74.5 74.5 

Rocky Flats North 85.0 84.8 85.1 85.0 84.8 85.0 84.9 84.3 

NREL 82.0 82.2 82.5 82.4 82.1 82.1 81.9 81.7 

Fort Collins - West 86.0 84.7 84.4 84.4 84.7 84.9 84.6 85.0 

Fort Collins 74.0 72.9 72.7 72.7 72.9 73.1 73.1 73.5 

Greeley - Weld 78.0 77.4 77.7 77.1 77.4 77.4 77.4 77.5 

Gunnison 68.0 67.8 67.9 68.0 67.9 67.8 67.8 67.8 

Larimer 76.0 75.1 74.9 74.9 74.9 75.1 75.1 75.1 

Larimer 76.0 75.1 74.9 74.9 74.9 75.1 75.1 75.1 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-6 

Table 3-2c. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring sites in the DMA 

using the EPA guidance default approach, the six alternative projection approaches and the 

2010 Control 2 Case modeling results.

2010 Control Strategy No. 2 (Cntl2) 

Name DVC EPA 5dth dth80 1dth75 1dth70 5x5 3x3 

Welby 70.0 70.2 69.1 69.1 70.3 71.2 70.3 71.3 

Highland 78.0 77.1 75.9 77.2 77.4 78.0 77.5 77.9 

S. Boulder Creek 81.0 80.6 80.3 80.3 80.4 80.4 80.6 80.3 

Denver - CAMP 56.0 55.9 55.7 55.7 56.2 56.7 56.9 57.5 

Carriage 74.0 74.0 73.6 73.6 74.3 75.0 75.1 75.0 

Chatfield State Park 84.0 83.3 82.7 83.1 83.5 83.9 83.0 82.8 

USAF Academy 73.0 71.9 72.3 72.1 71.9 72.1 72.0 72.2 

Manitou Springs 74.0 73.7 73.7 73.6 73.8 73.4 73.6 73.7 

Arvada 79.0 79.1 78.8 78.8 79.3 79.7 79.3 79.2 

Welch 75.0 74.9 74.9 74.9 74.7 74.8 74.4 74.5 

Rocky Flats North 85.0 84.7 85.1 84.9 84.8 84.9 84.8 84.3 

NREL 82.0 82.1 82.3 82.3 82.1 82.0 81.9 81.6 

Fort Collins - West 86.0 84.5 84.3 84.3 84.5 84.7 84.5 84.8 

Fort Collins 74.0 72.7 72.6 72.6 72.7 73.0 73.0 73.3 

Greeley - Weld 78.0 77.0 77.4 76.7 77.0 77.1 77.1 77.2 

Gunnison 68.0 67.9 67.9 68.0 67.9 67.9 67.9 67.8 

Larimer 76.0 75.1 74.9 74.9 74.9 75.1 75.1 75.1 

Larimer 76.0 75.1 74.9 74.9 74.9 75.1 75.1 75.1 

Table 3-2d. Ozone cut-off threshold concentrations used in the 2010 8-hour ozone Design 

Value projections at monitoring sites in the DMA using the EPA guidance default and the six 

alternative projection approaches.

Cut-Off Concentration (ppb) 

Name EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 

Welby 77.0 80.0 80.0 75.0 70.0 76.0 74.0 

Highland 78.0 83.0 80.0 75.0 70.0 78.0 76.0 

S. Boulder Creek 78.0 80.0 80.0 75.0 70.0 76.0 75.0 

Denver - CAMP 78.0 80.0 80.0 75.0 70.0 74.0 72.0 

Carriage 78.0 80.0 80.0 75.0 70.0 76.0 73.0 

Chatfield State Park 78.0 81.0 80.0 75.0 70.0 78.0 77.0 

USAF Academy 75.0 78.0 80.0 75.0 70.0 75.0 73.0 

Manitou Springs 74.0 78.0 80.0 75.0 70.0 73.0 72.0 

Arvada 78.0 80.0 80.0 75.0 70.0 76.0 75.0 

Welch 78.0 81.0 80.0 75.0 70.0 77.0 76.0 

Rocky Flats North 78.0 81.0 80.0 75.0 70.0 76.0 75.0 

NREL 78.0 81.0 80.0 75.0 70.0 77.0 75.0 

Fort Collins - West 76.0 81.0 80.0 75.0 70.0 75.0 73.0 

Fort Collins 76.0 80.0 80.0 75.0 70.0 75.0 73.0 

Greeley - Weld 75.0 77.0 80.0 75.0 70.0 74.0 73.0 

Gunnison 74.0 78.0 80.0 75.0 70.0 74.0 73.0 

Larimer 77.0 80.0 80.0 75.0 70.0 77.0 76.0 

Larimer 77.0 80.0 80.0 75.0 70.0 77.0 76.0 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-7 

Table 3-2e. Number of modeling days used in the 2010 8-hour ozone Design Value projections 

at monitoring sites in the DMA using the EPA guidance default and the six alternative projection 

approaches.

Number of Days Used 

Name EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 

Welby 11 6 6 13 29 10 10 

Highland 14 5 9 17 37 10 11 

S. Boulder Creek 10 6 6 18 28 12 11 

Denver - CAMP 10 7 7 14 31 12 10 

Carriage 10 6 6 15 32 10 12 

Chatfield State Park 11 5 6 18 33 11 10 

USAF Academy 10 6 3 10 30 10 10 

Manitou Springs 10 5 3 9 25 12 12 

Arvada 10 7 7 16 25 12 11 

Welch 10 5 5 17 31 12 11 

Rocky Flats North 10 6 7 19 27 11 10 

NREL 11 5 6 16 30 13 10 

Fort Collins - West 10 5 5 13 22 10 10 

Fort Collins 12 5 5 14 24 10 10 

Greeley - Weld 10 5 2 10 22 11 11 

Gunnison 10 7 3 9 14 10 10 

Larimer 10 5 5 13 21 10 10 

Larimer 10 5 5 13 21 10 10 

3.3 ADDITIONAL MODELING METRICS 

EPA’s 8-hour ozone modeling guidance recommends calculating additional modeling metrics 

from the current year base case to future year control scenarios to assure that they indicate the 

modeled ozone concentrations are going down. These additional modeling metrics examine the 

ozone differences between the current year base case and future year emission scenarios in the 

modeling domain to assure that ozone is going down, on average, across the entire nonattainment 

area (NAA) rather than just limited to a few key monitoring sites. 

The changes in daily maximum 8-hour ozone concentrations between the 2006 Base Case and 

2010 emission scenarios were calculated across grid cells in the Denver NAA and across all days 

in the June-July 2006 modeling episode. The changes 8-hour ozone concentrations are 

calculated for values above four separate threshold concentrations: 85, 80, 75 and 70 ppb. These 

modeling metrics consist of the following: 

Total Ozone: Defined as the difference between the modeled daily maximum 8-hour 

ozone concentrations and the threshold concentration, for modeled values above the 

threshold, summed across all grid cells in the Denver NAA and modeling days during 

June-July 2006. 

Grid Cells: Number of grid cell-days with modeled daily maximum 8-hour ozone 

concentrations greater than the threshold for all grid cells in the Denver NAA and days 

from the June-July 2006 episode. 

Grid Cell-Hours: Number of grid cell-hours with modeled running 8-hour ozone 

concentrations greater than the threshold for all grid cells in the Denver NAA and hours 

during the June-July 2006 episode. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-8 

Figure 3-2 displays the percent change in the Total Ozone, Grid Cells and Grid Cell-Hours 

between the 2006 Base Case and the 2010 emission scenarios. Using the 70 ppb threshold, there 

are small reductions between 2006 and 2010 in the Total Ozone (~-5%) and Grid Cell (~-3%) 

modeling metrics. However, the emission reductions between 2006 and 2010 are having their 

intended effect in reducing the elevated 8-hour ozone concentrations. For example, the changes 

in Total Ozone, Grid Cells and Grid Cell-Hours greater than the 85 ppb threshold modeling 

metrics between the 2006 and 2010 Base Cases are -21%, -14% and -22%, respectively. These 

reductions are even greater for the 2010 Control 1 case (-28%, -17% and -25%) and even greater 

still for the 2010 Control 2 scenario. 

Percent Change in Total Ozone for 2010 Base, Cntrl1, and 

Cntrl2

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Base CNTL1 CNTL2

% Change

Total Ozone

85 ppb

Total Ozone

80 ppb

Total Ozone

75 ppb

Total Ozone

70 ppb

Figure 3-2a. Percent change in Total Ozone greater than 85, 80, 75 and 70 ppb between the 

2006 Base Case and the 2010 Base Case (Base), Control 1 (CNTL1) and Control 2 (CNTL2) 

emission scenarios. 
 F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-9 

Percent Change in Grid Cells for 2010 Base, Cntrl1, and 

Cntrl2

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Base CNTL1 CNTL2

% Change

Grid Cells

85 ppb

Grid Cells

80 ppb

Grid Cells

75 ppb

Grid Cells

70 ppb

Figure 3-2b. Percent change in Grid Cells greater than 85, 80, 75 and 70 ppb between the 

2006 Base Case and the 2010 Base Case (Base), Control 1 (CNTL1) and Control 2 (CNTL2) 

emission scenarios.
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec4_Refs2.doc September 2008 4-1 

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Denver Regional Air Quality Council, Denver, Colorado. Prepared by ENVIRON 

International Corporation, Novato, CA. February. 

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

Modeling Analysis for the Denver Early Action Compact: 2007 Control Strategy 

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. February. 

Morris R.E., D.E. McNally, T.W. Tesche, G.S. Tonnesen, J.W. Boylan and P. Brewer. 2005a. 

“Preliminary Evaluation of the Community Multiscale Air Quality Model for 2002 over 

the Southeastern United States”. J. Air and Waste Manage. Assoc. 55:1694-1708. 

November. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec4_Refs2.doc September 2008 4-6 

Morris R.E. and G.M. Stella. 2005b. “Quality Assurance Project Plan (Draft) for the 

Association for Southeastern Integrated Planning (ASIP) Emissions and Air Quality 

Modeling to Address 8-Hour Ozone and PM 2.5 Nonattainment in the Southeastern 

States”. Revision 0. Prepared by ENVIRON International Corporation, Novato, CA. 

November. 

Morris, R.E., A. Hoats, S. Lau, B. Koo, G. Tonnesen, C-J. Jung and M. Omary. 2005c. “Air 

Quality Modeling Analysis for CENRAP – Preliminary 2002 Base Case CMAQ and 

CAMx Modeling of the Continental US 36 km Domain and Model Performance 

Evaluation”. Prepared by ENVIRON International Corporation, Novato, CA. April. 

Morris R.E., E. Tai, Y. Jia and M. Jimenez. 2005d. “Photochemical Modeling of the Tulsa and 

Oklahoma City 8-Hour Ozone Early Action Compact (EAC) State Implementation Plan 

(SIP) – Technical Support Document”. Prepared by ENVIRON International 

Corporation, Novato, CA. March. 

Morris R.E. and G. Tonnesen. 2006. “Quality Assurance Project Plan (Draft) for Central 

Regional Air Partnership (CENRAP) Emissions and Air Quality Modeling – Revision 3”. 

 ENVIRON International Corporation, Novato, CA. March. 

Morris, R.E., B. Koo, A. Guenther, G. Yarwood, D. McNally, T.W. Tesche, G. Tonnesen, J. 

Boylan and P. Brewer. 2006. Model sensitivity evaluation for organic carbon using two 

multi-pollutant air quality models that simulate regional haze in the Southeastern United 

States. Atmos. Env. 40 (2006) 4960-4972. 

Morris, R., B. Wang, E. Tai, D. McNally, C. Loomis, G. Stella and T.W. Tesche. 2007. 

Modeling Protocol for the Denver 8-Hour Ozone Attainment Demonstration Modeling. 

ENVIRON International Corporation, Novato, CA. November. 

http://www.ozoneaware.org/documents/DraftFinalProtocolDenver8-

HourOzoneNov282007.pdf. 

Morris, R., S. Kemball-Cook, D. Strohm and L. Parker. Modeling Protocol for the Unita Basin 

Air Quality Study. 2008a. Prepared for Independent Petroleum Association of Mountain 

States (IPAMS). Prepared by ENVIRON International Corporation, Novato, California. 

March 17. 

Morris R., E. Tai, L. Parker, J. Johnson, D. McNally and C. Loomis. 2008b. Initial Ozone 

Model Performance Evaluation of the June-July 2006 Denver Ozone Episode and 

Diagnostic Testing and Analysis. ENVIRON International Corporation, Novato, 

California. Prepared for Denver Regional Air Quality Council (RAQC), Denver, 

Colorado. May 13. 

Morris R., E. Tai, Tanarit Sakulyanontvittaya, D. McNally and C. Loomis. 2008c. Model 

Performance Evaluation for the June-July 2006 Ozone Episode for the Denver 8-Hour 

Ozone State Implementation Plan. ENVIRON International Corporation, Novato, 

California. Prepared for Denver Regional Air Quality Council (RAQC), Denver, 

Colorado. August 29. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec4_Refs2.doc September 2008 4-7 

Pechan. 2005a. “Electric Generating Unit (EGU) Growth Factor Comparison”. Prepared for 

CENRAP Emissions Inventory Workgroup. E.H. Pechan and Associates, Inc. Durham, 

North Carolina. January. 

Pechan. 2005b. Technical Memorandum: Updates to Source Classification Code (SCC) to 

speciation profile cross-reference table. Prepared for CENRAP Emissions Inventory 

Workgroup. E.H. Pechan and Associates, Inc. Durham, North Carolina. April. 

Pechan and CEP. 2005c. “Consolidated of Emissions Inventories”. (Schedule 9; Work Item 3). 

 E.H. Pechan and Associates, Inc. Durham, North Carolina. Carolina Environmental 

Program, University of North Carolina, Chapel, Hill, North Carolina. April. 

Pechan 2005d. “Development of Growth and Control Inputs for CENRAP 2018 Emissions, 

Draft Technical Support Document”. E.H. Pechan and Associates, Inc. Durham, North 

Carolina. Carolina Environmental Program, University of North Carolina, Chapel, Hill, 

North Carolina. May. 

Pechan and CEP. 2005e. “Refinements of CENRAP’s 2002 Emissions Inventories”. (Schedule 

9; Work Item 3). E.H. Pechan and Associates, Inc. Durham, North Carolina. Carolina 

Environmental Program, University of North Carolina, Chapel, Hill, North Carolina. 

August. 

Pechan and CEP. 2004. “Methods for Consolidation of Emissions Inventories”. (Schedule 9; 

Work Item 3). Prepared for CENRAP Emissions Inventory Workgroup. E.H. Pechan and 

Associates, Inc. Durham, North Carolina. Carolina Environmental Program, University 

of North Carolina, Chapel, Hill, North Carolina. 

Pollack, A., C. Lindhjem, T. Stoeckenius, C. Tran, G. Mansell, M. Jimenez, G. Wilson and S. 

Coulter-Burke. 2004. Evaluation of the U.S. EPA MOBILE6 Highway Vehicle 

Emissions Factor Model, Final Report, CRC Project E-64. ENVIRON International. 

Pollack, A.K, L. Chan, P. Chandraker, J. Grant, C. Lindhjem, S. Rao, J. Russell and C. Tran. 

2006. “WRAP Mobile Source Emission Inventories Update”. ENVIRON International 

Corporation, Novato, CA. May. 

http://www.wrapair.org/forums/ef/UMSI/0606_WRAP_Mobile_Source_EI_Final_Report

.pdf

Rodriguez, M., M. Barna, K. Gebhart, B. Schichtel and W. Malm. 2008. Regional Air Quality 

Model Simulation of the Rocky Mountain Atmosphere Nitrogen and Sulfur Study: 

Preliminary Results and Analysis. Presented at Air & Waste Management Association’s 

Aerosol & Atmospheric Optics: Visual Air Quality and Radiation conference, Moab, 

Utah, April 28 – May 2 

Seaman, N.L. 2000. Meteorological modeling for air quality assessments. Atmos. Environ., 

Vol. 34, No. 12-14, 2231-2260. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec4_Refs2.doc September 2008 4-8 

Seaman, N.L., D.R. Stauffer, and L.M. Lario. 1995. A multiscale four-dimensional data 

assimilation system applied to the San Joaquin Valley during SARMAP. Part I: Modeling 

design and basic performance characteristics. J. Appl. Meteo., Vol. 34, pp. 1739-1761. 

Stauffer, D.R. and N.L. Seaman. 1990. Use of four-dimensional data assimilation in a limitedarea mesoscale model. Part I: Experiments with synoptic data. Mon. Wea. Rev., 118, 

1250-1277. 

Tesche, T.W., D.E. McNally, C. Loomis, R.W. Morris and G.E. Mansell. 2003. “Revised 

Ozone Modeling Protocol -- Air Quality Modeling Analysis for the Denver Early Action 

Ozone Compact: Modeling Protocol, Episode Selection, and Domain Definition”. 

Prepared by Alpine Geophysics, LLC, Ft. Wright, Kentucky and ENVIRON International 

Corporation, Novato, CA. Prepared for Mr. Gerald Dilley, Denver Regional Air Quality 

Council. May. 

Tesche, T.W., R.E. Morris, G. Tonnesen, D.E. McNally, J. Boylan, and P. Brewer. 2005a . 

CMAQ/CAMx annual 2002 performance evaluation over the eastern U.S. Atmospheric 

Environment. 

Tonnesen, G., R.E. Morris, J. Vimont, M. Uhl, K. Briggs and T. Moore. 2003. “The WRAP 

Regional Modeling Center – Application and evaluation of regional visibility models.” 

Presented at AWMA Annual Meeting and Exhibition. June. 

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2005. “Final Report for the 

Western Regional Air Partnership (WRAP) Regional Modeling Center (RMC) for the 

Project Period March 1, 2004, through February 28, 2005”. Prepared for WRAP 

Regional Modeling Center (RMC). August. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2004_RMC_final_report_main_body.pdf

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2006. “Final Report for the 

Western Regional Air Partnership (WRAP) 2002 Visibility Model Performance 

Evaluation”. Prepared for WRAP Regional Modeling Center (RMC). February. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2002_MPE_report_main_body_FINAL.pdf

Yarwood, G., R.E. Morris, M.A. Yocke, H. Hogo and T. Chico. 1996. Development of a 

Methodology for Source Apportionment of Ozone Concentration Estimates from a 

Photochemical Grid Model. Presented at the 89th AWMA Annual Meeting, Nashville 

TN, June 23-28. 

Yarwood, G., S. Shepard, G. Wilson and A. Guenther. 2007. “User’s Guide to the Global 

Biosphere Emissions and Interactions System (GloBEIS) – Version 3.2”. Prepared by 

ENVIRON International Corporation, Novato, CA. November. 

(http://www.globeis.com/data/Users_Guide_Globeis_v3.2.Jan23_2008.pdf). 

Xiu, A. and J.E. Pleim. 2000. Development of a land surface model. Part I: application in a 

mesoscale meteorology model. J. App. Met., 40, pp. 192-209. 
F:\Denver_O3_2008\Reports\2010_Control_Strategy\draft#2\Sec4_Refs2.doc September 2008 4-8 

Seaman, N.L., D.R. Stauffer, and L.M. Lario. 1995. A multiscale four-dimensional data 

assimilation system applied to the San Joaquin Valley during SARMAP. Part I: Modeling 

design and basic performance characteristics. J. Appl. Meteo., Vol. 34, pp. 1739-1761. 

Stauffer, D.R. and N.L. Seaman. 1990. Use of four-dimensional data assimilation in a limitedarea mesoscale model. Part I: Experiments with synoptic data. Mon. Wea. Rev., 118, 

1250-1277. 

Tesche, T.W., D.E. McNally, C. Loomis, R.W. Morris and G.E. Mansell. 2003. “Revised 

Ozone Modeling Protocol -- Air Quality Modeling Analysis for the Denver Early Action 

Ozone Compact: Modeling Protocol, Episode Selection, and Domain Definition”. 

Prepared by Alpine Geophysics, LLC, Ft. Wright, Kentucky and ENVIRON International 

Corporation, Novato, CA. Prepared for Mr. Gerald Dilley, Denver Regional Air Quality 

Council. May. 

Tesche, T.W., R.E. Morris, G. Tonnesen, D.E. McNally, J. Boylan, and P. Brewer. 2005a . 

CMAQ/CAMx annual 2002 performance evaluation over the eastern U.S. Atmospheric 

Environment. 

Tonnesen, G., R.E. Morris, J. Vimont, M. Uhl, K. Briggs and T. Moore. 2003. “The WRAP 

Regional Modeling Center – Application and evaluation of regional visibility models.” 

Presented at AWMA Annual Meeting and Exhibition. June. 

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2005. “Final Report for the 

Western Regional Air Partnership (WRAP) Regional Modeling Center (RMC) for the 

Project Period March 1, 2004, through February 28, 2005”. Prepared for WRAP 

Regional Modeling Center (RMC). August. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2004_RMC_final_report_main_body.pdf

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2006. “Final Report for the 

Western Regional Air Partnership (WRAP) 2002 Visibility Model Performance 

Evaluation”. Prepared for WRAP Regional Modeling Center (RMC). February. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2002_MPE_report_main_body_FINAL.pdf

Yarwood, G., R.E. Morris, M.A. Yocke, H. Hogo and T. Chico. 1996. Development of a 

Methodology for Source Apportionment of Ozone Concentration Estimates from a 

Photochemical Grid Model. Presented at the 89th AWMA Annual Meeting, Nashville 

TN, June 23-28. 

Yarwood, G., S. Shepard, G. Wilson and A. Guenther. 2007. “User’s Guide to the Global 

Biosphere Emissions and Interactions System (GloBEIS) – Version 3.2”. Prepared by 

ENVIRON International Corporation, Novato, CA. November. 

(http://www.globeis.com/data/Users_Guide_Globeis_v3.2.Jan23_2008.pdf). 

Xiu, A. and J.E. Pleim. 2000. Development of a land surface model. Part I: application in a 

mesoscale meteorology model. J. App. Met., 40, pp. 192-209.