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, 2008September 2008

F:\Denver_O3_2008\Reports\2010_C ontrol_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 Pr ojections Procedures ....................................................... 3-1 3.3 Additional Modeling Metrics..................................................................................... 3-7

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

F:\Denver_O3_2008\Reports\2010_C ontrol_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 me asures 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 Contro l 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 projec tion approaches and the 2010 Base,
Control 1 and Cont rol 2 modeling results..........................................................ES-8 Table 2-1. Summary of control me asures 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 Contro l 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 Con centration 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 oz one Design Values (DVFs) at the Rocky Flats North (RFNO) and Fort Collins West (FTCW) monitoring sites using the EP A guidance default approach and the six alternative projec tion 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 th e EPA guidance default approach, the six alternative projec tion 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 th e EPA guidance default approach, the six alternative projecti on 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 th e EPA guidance default approach, the six alternative proj ection approaches and the 2010 Control 2 Case modeling results.......................................................................... 3-6September 2008

F:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\TOC.doc iii Table 3-2d. Ozone cut-off threshold con centrations used in the 2010 8-hour ozone Design Value projections at monitoring sites in the DMA using the EPA guidance de fault 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 de fault 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 Cont rol 2 (right) emission scenarios ...................ES-6 Figure ES-3. Differences in pr ojected 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 Oz one (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 mode ling 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 De sign 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 Contro l 2 (right) emission scenarios.................................. 2-14 Figure 2-3. Differences in project ed 2010 8-hour ozone Design Values (DVF) between the 2010 Cont rol 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) an d 3 x 3 (right) 4 km grid cells around
monitors in the DMA........................................................................................... 3-3 Figure 3-2a. Percent change in Tota l 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 C ontrol 2 (CNTL2) emission scenarios.......... 3-10F:\Denver_O3_2008\Reports\2010_Control_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-1 EXECUTIVE SUMMARY

Based on 2005-2007 air quality monitoring data th e Denver Metropolitan Ar ea (DMA) violated the 0.08 parts per million (ppm) 8-hour ozone National Ambient Air Quality Standard (NAAQS). Thus, in November 2007 the DMA reve rted 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 Corporat ion, and their subcontractor Alpine Geophysics, LLC, to develop the photochemical modeling databases n ecessary to demonstrate that the DMA will achieve the 0.08 ppm 8- hour ozone NAAQS by 2010.

OVERVIEW OF APPROACH

The Comprehensive Air-quality Mo del 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 th e 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 mode ling system and a preliminary 2006 base case was performed. A preliminary model perfor mance evaluation was conducted and diagnostic sensitivity tests performed to identify an optimal model conf iguration for simulating ozone formation in the DMA (Morris et al., 2008b). A revised final CAMx 200 6 base case simulation was performed and a comprehensive model perf ormance evaluation was conducted (Morris et al., 2008c). Although there were so me model performance issues on some of the modeling days during the June-July 2006 episode, a vast major ity of the modeling days achieved EPA’s model performance goals and looking at many model perf ormance displays and metrics we concluded that the model was simulating the observed oz one sufficiently well for use in making ozone projections. Furthermore, on most days the m odel 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 obt ain projected future year 2010 8-hour ozone Design Values (DVF) at each of the DMA monito ring 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-h our 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/sc ram001/modelingapps_mats.htm).F:\Denver_O3_2008\Reports\2010_Control_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-2 For the Denver 2010 ozone projections, with on e exception, the DVCs were based on the 8-hour ozone Design Values from the 2005-2007 period (i .e., the three year av erage 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 ma ximum 8-hour ozone concentrati ons 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) mon itoring sites (see column 5 in Table ES-1). As this value is 84 ppb or lower, then th e 2010 base case modeling results pass the model attainment demonstration test. EPA’s gui dance 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. Modeli ng days are selected based on whether the 2006 base case model estimated maximum daily maximu m 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 m odel days for developing the RRFs, the cut-off thresholds of 74 ppb to 78 ppb were used depe nding 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 Boul der 81.0 80 80.8 0.9976 78.0 10
80310002 Denver - CAMP Denv er 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 10F:\Denver_O3_2008\Reports\2010_Control_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-3 2010 CONTROL PLAN EMISSION SCENARIOS

2010 ozone projections were made for two 2010 em ission control plans: (1) 2010 Control 1 that consists of the federally-enforceable control me asures that are proposed for the Denver 8-hour ozone State Implement plan (SIP); and (2) C ontrol 2 that includes the federally-enforceable measures of Control 1 plus a dditional 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 tpdF:\Denver_O3_2008\Reports\2010_Control_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-4 2010 CONTROL PLAN OZONE PROJECTIONS

Table ES-3 displays the projected 8-hour oz one 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 No rth (RFNO) and Fort Collins West (FTCW) monitoring sites. Thus, the 2010 Base Case and two control scenarios pass the modeled attainment demons tration 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) analys is 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 meas ures 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-en forceable control measures in the 2010 Control 2
scenario reduces the DVFs at RFNO and FRTC W by an additional 0.1 and 0.2 ppb, respectively (to 84.7 and 84.5 ppb, respectively). These results are consiste nt 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 Boulde r 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 75.1F:\Denver_O3_2008\Reports\2010_Control_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-5 2010 UNMONITORED AREA ANALYSIS

EPA’s 8-hour ozone projection procedure also in cludes an unmonitored area analysis (EPA, 2007) that has been codified in MATS. The unm onitored 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 us es the modeled concentration gradients. RRFs are then obtained for each grid cell in the mode ling 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 fo r 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 cu rrent year ozone DVCs in excess of 80 ppb are estimated to the south, west and northwest of De nver 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 cell s in the 2010 base case emissions scenario.

Figure ES-2 displays the unmon itored area analysis projected DVF s 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 differenc e plots seen in Figure ES-3. The 6 remaining grid cells with projec ted 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 te st has more uncertainties than the projections
at the monitors and it should be treated se parately from the monitor based attainment demonstration test (EPA, 2007). EPA further notes that while it is expe cted that additional emission controls will likely be needed to el iminate predicted exceedances of the ozone NAAQS in the monitor based attainment test, the sa me requirements may not be appropriate in unmonitored areas. In any event, EPA recommends that areas of predic ted violations in the
unmonitored area test be scruti nized and understood to determin e 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 appr opriate to deploy additional ozone monitors to
such areas. In the case of the Denver ozone m odeling, higher ozone concen trations are estimated
west of Fort Collins than at the locations of th e 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 valu es could exist west of the Fort Collins West monitoring site.F:\Denver_O3_2008\Reports\2010_Control_St rategy\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_St rategy\draft#2\Exec_Sum2.doc September 2008 ES-7 ALTERNATIVE 2010 OZONE PROJECTION RESULTS

Several alternative 2010 ozone projection proced ures were analyzed for the 2010 Base Case,
Control 1 and Control 2 emission scenarios to estimate the un certainties in the projection procedures and provide confidence that passing the modeled attain ment 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 procedur es differ in the days
used and how modeled ozone near the monitor is selected to construct th e RRFs. Six additional ozone projection procedures were analyzed, in addition to the EPA guida nce default approach discussed previously:

Minimum 5 Days to Develop RRF usi ng 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 m onitor (with 7 x 7 arra y of grid cells) in the 2006 Base Case is greater than a threshol d, 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 th reshold 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 a rray 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 th e key RFNO and FTCW monitoring sites for the EPA guidance default and the six alternative ozon e 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 on e “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 r obust than ones based on more days. And it is logical that methods based on modeled concentr ations closer to the observed 8-hour ozone Design Values would be more representative of the conditi ons 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 a nd FTCW monitoring sites. Some of the six alternative projection approaches re sult in increases, whereas others in decreases in the projected
2010 DVFs at these two sites rela tive 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 projec tion 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_St rategy\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 si te, the projected DVFs for the 2010 Control 1 scenario range from 84.3 to 85.1 ppb with an av erage 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 fo r 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 proj ected DVFs range from 84.3 to 84.8 ppb with an average of 84.5 ppb.

An examination of the different 2010 ozone proj ection 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 th e projected DVF at RFNO is greater than the
EPA default method is below the EPA defa ult method at FTCW and vice versa.

In conclusion, the alternative ozone projection approaches s upport the findings using the EPA default approach that the 2010 Base Case will lik ely achieve attainment in the Denver region of the 0.08 ppm 8-hour ozone NAAQS. The ozone proj ection 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 10F:\Denver_O3_2008\Reports\2010_Control_St rategy\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 co ntrol 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 do wn, on average, across th e entire nonattainment area (NAA) rather than just limite d to a few key monitoring sites.

The changes in daily maximum 8-hour ozone co ncentrations between the 2006 Base Case and
2010 emission scenarios was calcula ted across grid cells in the Denver NAA and across all days in the June-July 2006 modeling episode. Th e changes 8-hour ozone concentrations are calculated for values above four separate thre shold concentrations: 85, 80, 75 and 70 ppb. These modeling metrics consis t of the following:

Total Ozone : Defined as the difference between the modeled daily maximum 8-hour
ozone concentrations and the threshold c oncentration, 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 th e threshold for all grid cells in the NAA and days from the June-July 2006 episode.

Grid Cell-Hours : Number of grid cell-hours wi th modeled running 8-hour ozone concentrations greater than the threshold for all grid cel ls in the NAA and hours during the June-July 2006 episode.

Figure ES-4 displays the percen t change in the Total Ozone and Grid Cells between the 2006
Base Case and the 2010 emission scen arios (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 thresh old. 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_St rategy\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 MODE LING 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 th e modeled attainment demonstration test. Examining the unmonitored area test, the alterna tive ozone projection pro cedures and additional modeling metrics we conclude that the two 2010 c ontrol strategies provid e 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 mode ling analysis used to asses whether various emission reduction measures will bring the De nver area into attainment of the 8-hour ozone NAAQS contain many elements that are uncerta in (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 theozone formation conditions in the next few years are much more severe than seen in the JuneJuly 2006 modeling period, then that could jeop ardize 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 Denve r Metropolitan Area (D MA) 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 in to an 8-hour ozone Early Action Compact (EAC) with the U.S. Environmental Protection Agency (E PA). 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. Base d on 2005-2007 measured air quality, the DMA violated the 0.08 ppm 8-hour oz one NAAQS (i.e., 1997 8-hour oz one NAAQS), so in November
2007 the DMA reverted to an 8-hour ozone nonatta inment area and is required to prepare an 8- hour ozone State Implementation Plan (SIP) that demonstrates at tainment 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 grea ter DMA, half have 2005-2007 8-hour ozone DVs that are 0.075 ppm or higher. The current De nver 8-hour ozone SIP modeling effort addresses the 0.08 ppm 8-hour ozone NAAQS, the ne w 0.075 ppm 8-hour ozone NAAQS will be
addressed in future SIP actions.

1.2 APPROACH

The fifth generation Mesocale Model (MM5) me teorological 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 be ing 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 m odeling activities being performed by the ENVIRON/Alpine Modeling Team consis ts of the following activities:

• Development of a Denver 8-hour ozone SIP a ttainment demonstration Modeling Protocol (Morris et al., 2007; http://www.ozoneaware.org/documents /DraftFinalProtocolDenver8- HourOzoneNov282007.pdf );

• MM5 meteorological modeling and model pe rformance 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 initia l 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 perfor mance 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 resu lts of the 2010 control strategy m odeling. 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 attainme nt 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 demonstr ation and is one component of the Weight of Evidence (WOE) ozone attainment demonstration.

Figure 1-1a displays the MM5 (r ed) 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 condi tions (BCs) from a globa l 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 pr ocessed to generate BCs for the CAMx 12/4 km domain (Figure 1-1b). The CAMx simulations fo r 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 t he 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 emissi ons scenario (Morris et al., 2008b) and are described by McNally and co-workers (McNa lly et al., 2008b). Th e CDPHE/APCD provided 2010 emissions for all anthropogenic emission s ources 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 utilize d (Bar-Ilan et al., 2008b). Outside of Colorado, the 2010 anthropogenic emissions were ba sed on the WRAP 2002 and 2018 emissions inventories projected to 2010. CA Mx-ready emissions were generated using the Sparse Matrix Operator Kernel Emissions (SMOKE) emissi ons modeling system (Coats, 1996) for all anthropogenic emissions categories except on-road mobile sources in the DMA, which used the Consolidated Community Emissi ons Processing Tool (ConCEPT) modeling system (Loomis et al., 2005) and biogenic emissions. The same bi ogenic 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 we re 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 us ing 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_C ontrol_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 Valu e projections for the 2010 base case and the two 2010 emission control plans. These two 2010 control plans correspo nd to: (1) 2010 Control 1 that consists of the federally-enforceable cont rol 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 a dditional 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 us ing EPA’s Modeled Attainment Test Software (MATS) tool (http://www.epa.gov/scram001/modelingapps_ma ts.htm). The MATS ozone projection procedures and 8-hour ozone projections fo r 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 procedur es, whose results for the 2010 Base, Control 1 and Control 2 emissions are presen ted later in this Chapter.

2.2 OZONE PROJECTION PROCEDURES

The Denver 2010 8-hour ozone projec tions were made following de fault procedures in EPA’s latest modeling guidance (EPA, 2007), with one ex ception 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 relativ e 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 scen ario 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 y ear 8-hour ozone Design Value (DVC) as the starting point for the ozone projections. EPA guidance recomm ends 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 Valu es 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 th e 8-hour ozone Design Values from the 2005-2007 period that resulted in Denver being cl assified 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 scenario s 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 De nver modeling that uses a 4 km grid
resolution.F:\Denver_O3_2008\Reports\2010_C ontrol_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 wh ich 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 th reshold of 85 ppb is used. If less than 10 days are obtained the threshold is re duced by 1 ppb until at least 10 days are obtained for the RRF. When the 70 ppb thre shold floor is reached and there are at least 5 days then the RRF is used.
3. The RRF is applied to the DVC to obta in 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 th e modeled attainment demonstration.
6. An unmonitored area analysis is also perf ormed that interpolates the DVCs across the modeling domain and performs the ozone pr ojections in each grid cell using the procedures given above, except using the mode ling results within each grid cell rather than near the grid cell.

a. EPA believes that the unmonitored area an alysis 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 CONTRO L 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 federall y-enforceable SIP control strategy and the 2010
Control 2 that includes the Control 1 control measur es as well as additiona l 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 St ate 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 measur es will also be federally-enforceable upon approval of the SIP revision by EPA.F:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-3 1. Adopt more stringent cut-points for in spection/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 Ai r Quality Control Commission approved revisions to Regulation No. 11 implemen ting these cut-points in March 2008 and the changes took effect in May 2008. Th ese 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 additi onal SIP credit of th ree tpd VOC emission
reduction.

3. Increase control requirements for oil a nd 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 requi rements 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 alternat ive 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 it s 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 Regulat ion No. 7 in December 2008 effective in May 2009 that require low-bleed contro llers 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_C ontrol_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/mai ntenance area (most of the 7-county Denver area). These reasonably av ailable control technology (RACT) requirements in Regulation No. 7 will now apply to specific new and existing listed source categories and all new and ex isting 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 Arap ahoe 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 exemp tions 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 identi fication of more sources of VOCs and potentially additional control requirements. The impact of these revisions is difficult to quantify sinc e it is unknown how many sources will be
affected and the control le vels that will be required.

7. Require general application of permit requirements in Regulation No. 3 and reasonably available control technol ogy (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 implemen ting these changes were adopted by the AQCC in February 2008. The impact of th ese 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 th e 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 gi ve 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 toward s meeting the new EPA standard.

1. Implement a motor vehicle inspection/ma intenance 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 inspectio n/maintenance (I/M) program structureF:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-5 that currently exists in the Denver metropol itan area to portions of Larimer and Weld counties. The program includes IM240 testing, remote-sensing clean screen, gas cap checks, and advisory On-Board Diag nostics (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 pr oposed to the AQCC in September 2008 for adoption in December 2008. The program coul d 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 urbani zed 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 leas t one tpd, and CO emissions by at least 17 tpd.

The North Front Range Transportation and Ai r Quality Planning Council also endorse an evaluation of the I/M pr ogram structure by 2013 that includes consideration of expanded OBDII testing and high-emitter identification.

2. Continue implementing the high-emitter pilot program in th e 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 stat e 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 pl ates to true collector vehicles and close the emissions testing loophole for old, non-coll ector 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 th e CO reduction could be around seven tpd.

4. Increase control requirements for oil a nd gas condensate tanks to 95% for all existing tanks greater than 2 tpy

Regulation No. 7 will be amended by th e AQCC in December 2008 to increase the
number of tanks controlled in the no nattainment area beyond the 10 tpy threshold included in the SIP. Control requirements fo r 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 w ill 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 a nd 47 tpd. (The North Front Range Transportation and Air Quality Planning C ouncil have endorsed an alternative approach suggested by industr y that would increase the current system-wide control
factor to 90% as a SIP measure. This alte rnative proposal is likel y to be consideredF:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-6 by the Air Quality Control Commission dur ing its upcoming rulemaking pre-hearing process.)

5. Implement control requirements for recipr ocating internal combustion engines (RICE) statewide

The control requirements will mirror re quirements currently in place in the Denver/North Front Range nonattainment ar ea. Revisions to Regulation No. 7 making these requirements apply statewid e will be adopted by the AQCC in December 2008 and will become effective by May 1, 2010. The emission reduction impact from these statewide cont rols 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 Ra nge 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 tpdF:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-7 2.4 2010 EMISSION SUMMARY RESULTS

The emission inventories were developed us ing EPA-approved emissions modeling methods, including EPA’s MOBILE6 model and local Vehi cle Miles Travelled (VMT) data for on-road
mobile source emissions, EPA’s non-road model a nd local demographic information for area and off-road sources, and reported actual emissions for point sources from Continuous Emissions
Monitors (CEMs). Estimates for future emi ssions are based on the above-mentioned tools and the EPA’s Economic Growth and Analysis Syst em (EGAS) model for estimating future point sources activity, VMT growth for on-road mob ile 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 transporta tion 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 WR AP Phase III oil and gas emissions inventory development study (Bar-Ilan, 2008a) and were pr ojected to 2010 using the methodology in the WRAP Phase III projection methodology document (B ar-Ilan, 2008b). The WRAP Phase III oil and gas inventory was sponsored by the Independ ent Petroleum Association of Mountain States
(IPAMS).

Non-oil and gas area source emissi ons (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 redu ctions listed in the EPA May 30, 2007 Emission Reduction Credit Memo were applied to th e projected 2010 non-oil and gas area source inventory. An inventory completed in 2005 for De nver 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 fr om Nature (MEGAN) Biogenic Emissions ModelF:\Denver_O3_2008\Reports\2010_C ontrol_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 Mesos cale Meteorological Model (MM5) modeling.

Wildfire emissions were based on MODIS sate llite data. Wildfire emissions can vary significantly on a day-to-day basis depending on conditions.

Summaries of the VOC and NOx base case invent ories 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 fr om wildfires are not included in Table 2-2.F:\Denver_O3_2008\Reports\2010_C ontrol_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 (Are a Source) 24.8 31.1 Unpermitted Fugitives (A rea 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 1165.8F:\Denver_O3_2008\Reports\2010_C ontrol_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 oz one 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 th e 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) m onitoring 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 th e 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 scenar io reduces the DVFs at the RFNO and FTCW monitoring sites by another 0.1 and 0.2 ppb, resp ectively (to 84.7 and 84.5 ppb, respectively).
These results are consistent w ith 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_C ontrol_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 Boulde r 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 Boul der 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 0.9890F:\Denver_O3_2008\Reports\2010_C ontrol_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 10F:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec2_Control_AttainDemo2.doc September 2008 2-13 2.6 2010 CONTROL PLAN UNMONIT ORED AREA ANALYSIS

EPA’s 8-hour ozone projection procedure also in cludes an unmonitored area analysis (EPA, 2007) that has been codified in MATS. The unm onitored 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 us es the modeled concentration gradients. RRFs are then obtained for each grid cell in the mode ling 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 fo r the projections at the monitor.

Figure 2-1 displays the interp olated current year 8-hour oz one Design Values (DVC) and projected 8-hour ozone Design Values (DVFs) for the 2010 Base Case using the MATS unmonitored area analysis. Interpolated cu rrent year ozone DVCs in excess of 80 ppb are estimated to the south, west and northwest of De nver 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 we st of the Fort Collins (Figure 2-1, left). The projected DVFs for the 2010 base case (Figure 2-1, right) have greatl y 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 cell s in the 2010 base case emissions scenario.

Figure 2-2 displays the unmonito red area analysis projected DVF s 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 differe nce plots seen in Figure 2-3. The 6 remaining grid cells with pr ojected 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 te st has more uncertainties than the projections
at the monitors and it should be treated se parately from the monitor based attainment demonstration test (EPA, 2007). EPA further notes that while it is expe cted that additional emission controls will likely be needed to el iminate predicted exceedances of the ozone NAAQS in the monitor based attainment test, the sa me requirements may not be appropriate in unmonitored areas. In any event, EPA recommends that areas of predic ted violations in the
unmonitored area test be scruti nized and understood to determin e 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 appr opriate to deploy additional ozone monitors to
such areas. In the case of the Denver ozone m odeling, higher ozone concen trations are estimated
west of Fort Collins than at the locations of th e 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 valu es could exist west of the Fort Collins West monitoring site.F:\Denver_O3_2008\Reports\2010_C ontrol_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_C ontrol_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 Co llins 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 co rroborate 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 Nati onal 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 PR OJECTIONS PROCEDURES

Several alternative 2010 ozone projection proced ures 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 a ttainment demonstrati on test does indicate attainment will likely be achieved in 2010. Thes e 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 anal yzed, in addition to the EPA guidance default approach discussed in Chapter 2:

Minimum 5 Days to Develop RRF usi ng 85-70 ppb Sliding Threshold (5dth) : In the EPA default approach, modeling days are select ed 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 grea ter than a threshold, with the threshold determined when at least 10 days ar e 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 a rray 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_C ontrol_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-2 In regards to these last two alternative 2010 ozone projection me thods, 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 mo nitors 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 potenti ally result in selecting the same modeled concentrations from nearby grid cells to deve lop the RRFs for different monitors. Using the tighter 5 x 5 and 3 x 3 array of grid cells ce ntered on each monitor (F igure 3-1b) reduces the overlap among nearby monitors and potentially retains the different characteristics of the monitoring sites, if such differences were captu red by the model. For example, the CAMP, and
other more urban Denver monitori ng sites, are clearly affected by the high NOx concentrations
that inhibit ozone formation. Use of the 7 x 7 ar ray of grid cells results in selecting maximum modeled concentrations that are potentially ou tside of the influence of the downtown Denver high NOx concentrations for use in the RRFs there by 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 cellsF:\Denver_O3_2008\Reports\2010_C ontrol_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 us ed in calculating the RRFs for each alternative 2010 ozone projec t 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 “corr ect” method for projecting future ye ar ozone concentrations that has been proven the most reliable. Methods ba sed 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 con centrations 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 a nd FTCW monitoring sites. Some of the six alternative projection approaches re sult in increases, whereas others in decreases relative to the EPA default approach in the projected 2010 DVFs at these two sites. Th e 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 aver age of 84.9 ppb. At the RFNO monitoring site 3 of the 7 projection met hods 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 si te, the projected DVFs for the 2010 Control 1 scenario range from 84.3 to 85.1 ppb with an av erage 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 cellsF:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-4 2010 Control 2 Case : The 2010 projected DVFs at RFNO fo r 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 si te where the 2010 projec ted DVFs range from 84.3 to 84.8 ppb with an average of 84.5 ppb.

An examination of the different 2010 ozone proj ection 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 fo r the RFNO and FTCW monitoring sites where, in most cases, a method in which th e projected DVF at RFNO is greater than the
EPA default method is below the EPA default me thod at FTCW and vice versa. The possible exception to this is at the downtown ozone monito rs 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 sele ction 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 betw een the alternative approaches and, in almost all cases, the average of the seven ozone projection approach es equals the EPA default method approach.

In conclusion, the alternative ozone projection approaches s upport the findings using the EPA default approach that the 2010 Base Case will lik ely achieve attainment in the Denver region of the 0.08 ppm 8-hour ozone NAAQS. The ozone proj ection 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 10F:\Denver_O3_2008\Reports\2010_C ontrol_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 75.1F:\Denver_O3_2008\Reports\2010_C ontrol_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 76.0F:\Denver_O3_2008\Reports\2010_C ontrol_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 co ntrol 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 do wn, on average, across th e entire nonattainment area (NAA) rather than just limite d to a few key monitoring sites.

The changes in daily maximum 8-hour ozone co ncentrations 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. Th e changes 8-hour ozone concentrations are calculated for values above four separate thre shold concentrations: 85, 80, 75 and 70 ppb. These modeling metrics consis t of the following:

Total Ozone : Defined as the difference between the modeled daily maximum 8-hour
ozone concentrations and the threshold c oncentration, 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 cel ls in the Denver NAA and days from the June-July 2006 episode.

Grid Cell-Hours : Number of grid cell-hours wi th modeled running 8-hour ozone concentrations greater than the threshold for all grid cel ls in the Denver NAA and hours during the June-July 2006 episode.F:\Denver_O3_2008\Reports\2010_C ontrol_Strategy\draft#2\Sec3_Control_ModelMetrics2.doc September 2008 3-8 Figure 3-2 displays the percent change in th e 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 th e 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 el evated 8-hour ozone concentrations. For example, the changes in Total Ozone, Grid Cells and Grid Cell-H ours 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_C ontrol_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)
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Xiu, A. and J.E. Pleim. 2000. Development of a land surface model. Part I: application in a mesoscale meteorology model. J. App. Met.

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