773 San Marin Drive, Suite 2115, Novato, CA 94998 415.899.0700 Draft Final Report

FINAL 2010 OZONE ATTAINMENT DEMONSTRATION
MODELING FOR THE DENVER 8-HOUR OZONE
STATE IMPLEMENTATION PLAN

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

January 12, 2009F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy\Draft_Final\TOC.doc January 2009 i TABLE OF CONTENTS

Page

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

Overview of Approach.........................................................................................................ES -1 Final 2010 Control Strategy.................................................................................................ES -1 2010 Ozone Projections .......................................................................................................E S-2 2010 Ozone Attainment Demonstration Modeling..............................................................ES-5

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

1.1 Background................................................................................................................. ..... 1-1 1.2 Approach................................................................................................................... ....... 1-1 1.3 2010 Emissions Modeling Approach............................................................................... 1-4

2. 2010 OZONE ATTAINMEANT DEMONSTRATION ................................................... 2-1

2.1 Introduction............................................................................................................... ....... 2-1 2.2 Ozone Projection Procedures........................................................................................... 2-1
2.3 Ozone Attainment Demonstrati on for the 2010 Base Case and the Final 2010 Control Strategy............................................................................................. 2-3
2.4 Attainment Demonstration Conclusions........................................................................ 2-12

3. ALTERNATIVE 2010 OZONE PROJECTIONS
AND ADDITIONAL MODEL METRICS ........................................................................ 3-1

3.1 Introduction.............................................................................................................. ........ 3-1 3.2 Alternative 2010 Ozone Projection Procedures............................................................... 3-1 3.3 Additional Modeling Metrics........................................................................................... 3-7

4. REFERENCES.................................................................................................................. ... 4-1

TABLES

T able ES-1. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy .............................................ES-3 Table 1-1. 2006 Base Case (2006.a 3), 2010 Base Case (2010.b1) and Final 2010 Control Strategy (2010.b1-fsip) VOC, NOx and CO emissions (tons per day) across Colorado............................................................ 1-5 Table 2-1a. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy ............................................... 2-4 Table 2-1b. Relative Response Factors (RRFs) used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and the Final 2010 Control Strategy................................................................................. 2-5F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy\Draft_Final\TOC.doc January 2009 ii Table 2-1c. Ozone threshold Cutoff Con centration used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy................................................................................. 2-6 Table 2-1d. Number of days used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy................................................................................................... 2-7 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 EP A guidance default approach and the six alternative projection ap proaches and the 2010 Base, Control 1
and Control 2 emission scenarios ........................................................................ 3-4 Table 3-2a. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring sites in the DMA using the EP A guidance default approach, the six alternative projection appr oaches and the 2010 Base Case modeling results................................................................................................... 3-5 Table 3-2b. Projected 2010 8-hour ozone Design Values (DVFs) at monitoring sites in the DMA using the EP A guidance default approach, the six alternative projection approaches and the Final 2010 Control Strategy modeling results................................................................................................... 3-5
Table 3-2c. 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 default and the six alternative projection approaches............................................................................................................ 3-6 Table 3-2d. Number of modeling days us ed in the 2010 8-hour ozone Design Value projections at monitoring sites in the DMA using the EPA guidance default and the six alternative projection approaches.......................................... 3-7

FIGURES

Figure ES-1. Interpolated current year 8-hour ozone Design Values and projected 2010 Base Case 8-hour ozone Design Values.............................ES-4 Figure ES-2. Projected 2010 8-hour ozone Design Values (DVF) for
the Final 2010 Control Strate gy and differences in projected
2010 DVFs between the 2010 Base Case and Final 2010 Control Strategy (2010 Control – 2010 Base).................................................................ES-5 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 doma ins for the Denver CAMx air quality and SMOKE emissions modeling........................................................................ 1-3 Figure 2-1. Interpolated cu rrent year observed 8-hour oz one Design Values (DVCs) using the MATS tool (ppb).................................................................................. 2-9 Figure 2-2. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010
Base Case emissions scenar io using the MATS tool (ppb) ............................... 2-10 Figure 2-3. Projected 2010 8-hour ozone Design Values (DVFs) for the Final 2010 Control Strategy emissions scen ario using the MATS tool (ppb) ..................... 2-11F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy\Draft_Final\TOC.doc January 2009 iii Figure 2-4. Differences in projected 2010 8-hour ozone Design Values (DVFs)
between the 2010 Base Case and the Final 2010 C ontrol Strategy emissions scenarios using the MA TS tool (2010 Control – 2010 Base). .......... 2-12 Figure 3-1a. Arrays of 7 x 7 4 km grid cells around monitors in the DMA............................. 3-2 Figure 3-1b. Arrays of 5 x 5 (left) and 3 x 3 (right) 4 km grid cells a
round monitors in the DMA................................................................................. 3-3 Figure 3-2a. Percent change in To tal Ozone greater than 85, 80, 75 and 70 ppb between the 2006 Base Case and the 2010 Base Case (Base) and Final 2010 Control Strategy (FSIP) 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 a nd the 2010 Base Case (Base) and Final 2010 Control Strategy (FSIP) emission scenarios...................................... 3-9F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Final\Exec_Sum2.doc January 2009 ES-1 EXECUTIVE SUMMARY

Based on 2005-2007 air quality monitoring data, the Denver Metropolitan Area (DMA) violated the 0.08 parts per million (ppm) 8-hour ozone National Ambient Air Quality Standard (NAAQS). Thus, in November 2007 the DMA 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 Divisi on (APCD), contracted with ENVIRON International Corpor ation, 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 Model with extensions (CAMx; www.camx.com ) was applied to the June-July 2006 episode using 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 McNall y and co-workers (2008a). An initial emissions inventory was prepared using the SMOKE emissions modeling system and a preliminary 2006 base case modeling was performed. A preliminary mode l performance evaluation was conducted and diagnostic sensitivity tests perf ormed to identify an optimal model configuration for simulating ozone formation in the DMA (Morris et al., 2 008a). A revised final CAMx 2006 base case simulation was performed and a comprehensiv e model performance evaluation was conducted (Morris et al., 2008b). Although th ere were some model performa nce issues on some of the modeling days during the June-Jul y 2006 episode, a vast majority of the modeling days achieved EPA’s model performance goals and after the ex amination of many model performance displays
and metrics we concluded that the model was simulating the obser ved ozone sufficiently well for use in making future year ozone pr ojections (Morris et al., 2008b).

FINAL 2010 CONTROL STRATEGY

The Final 2010 Control Strategy was based on a slight modification of the CDPHE’s Ozone Action Plan – Alternative Proposal #2 (CDPHE, 2008) presented at the Colorado Air Quality Control Commission (AQCC) hearing Decembe r 11-12, 2008 (AQCC, 2008). The Denver 8- hour ozone SIP modeling demonstrates that at tainment of the 0.08 pp m ozone NAAQS will be
achieved in 2010 under the 2010 Base Case emissions scenario. The Final 2010 Control Strategy contained two additional federally-enforceable control measures beyond the 2010 Base Case (CDPHE, 2008; AQCC, 2008) that provides more certa inty that ozone attainment will be
achieved in 2010:

• 85% control of VOC emissions on all conde nsate tanks with annual VOC emissions greater than 2 t ons per year; and

• Revisions to condensate tank flaring controls that phases in the auto igniters on flares controlling tanks greater than or equal to 50 TPY by May 1, 2009 and on all remaining tanks greater than 2 TPY in the Denver NAA by May 1, 2010.F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Final\Exec_Sum2.doc January 2009 ES-2 These control measures reduce VOC emissions from oil and gas (O&G) development sources that are primarily located in Weld County in the DMA. Acro ss Colorado, the Final 2010 Control Strategy reduces anthropogenic VOC emissions by -3.6% from 2010 Base Case conditions.

2010 OZONE PROJECTIONS

The procedures given in EPA’s 8-hour ozone modeling guidance we re used to project current year 8-hour ozone Design Values (DVC) to ob tain projected future year 2010 8-hour ozone Design Values (DVF) at each of the DMA monito ring sites (EPA, 2007). These procedures use the modeling results for the 2006 base case and 2010 emission scenarios in a relative fashion where modeled relative response factors (RRFs) are used to scale the current year observed 8- hour ozone Design Value (DVC) to obtain the projected future ye ar 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).

For the Denver 2010 ozone projections, with on e exception, the DVCs we re 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 st arted monitoring in 2006 so a two year average of the fourth highest daily maximum 8-hour oz one concentrations was used based on ozone observations from the 2006-2007 period.

Table ES-1 displays the projected future year 2010 8-hour ozone Design Values (DVFs) for the
2010 Base Case and the Final 2010 Control Strate gy emission scenarios. The first set of DVFs in Table ES-1 (columns 4 and 5) follow EPA’ s guidance approach (EPA , 2007) to truncate the final DVFs to the nearest ppb for comparison with the NAAQS. Whereas the last set of DVFs
for the 2010 Base Case and Final 2010 Control Strategy (columns 6 and 7 in Table ES-1) display
the DVFs to the nearest te nth of a ppb so that we can disti nguish any differences in the ozone projections between the 2010 Base Case a nd Final 2010 Control Strategy. The maximum projected 8-hour ozone Design Valu e for the 2010 Base Case and Final 2010 Control Strategy is 84 ppb at the Rocky Flats North (RFNO) and Fort Collins West (FTCW) monitoring sites. As all projected 2010 8-hour ozone Design Values ar e below 85 ppb, the 2010 Base Case and Final 2010 Control Strategy both pass the modeled ozone attainment demonstra tion 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 Chat field and 82 ppb at NREL), th en 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 two additional control measures in the Fina l 2010 Control Strategy reduces the DVF at the FTCW monitoring site by 0.1 ppb (84.8 ppb) and has no effect at the RFNO monitoring site (84.9 ppb). Of the 18 site s listed in Table 2-3, the Final 2010 Control Strategy is projected to reduce the 2010 DVF by 0.1 ppb at four sites and by 0.2 ppb at one site,F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Final\Exec_Sum2.doc January 2009 ES-3 with the remainder of the monitoring sites ha ving identical 2010 DVFs for the 2010 Base Case and Final 2010 Control Strategy. The largest ozone reduction due to the control measures in the Final 2010 Control Strategy (0.2 ppb) occurs at the Weld C ounty Tower monitoring site (Greely), which is not surprising given that it is the closest monitor to the O&G developments that occur primarily in Weld County which is where the largest VOC emission reductions occur
in the Final 2010 Control Stra tegy control measures.

Table ES-1. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy.

2010 DVF (EPA Guidance) 2010 DVF (nearest 0.1 ppb)

Name County DVC (2005- 2007) Base Case Final Strategy Base Case Final Strategy Welby Adams 70.0 70 70 70.2 70.2 Highland Arapahoe 78.0 77 77 77.3 77.3

S. Boulder Creek Boulder 81.0 80 80 80.8 80.7

Denver - CAMP Denver 56.0 56 56 56.0 56.0 Carriage Denver 74.0 74 74 74.1 74.1 Chatfield State Park Douglas 84.0 83 83 83.4 83.4 USAF Academy El Paso 73.0 72 72 72.0 72.0 Manitou Springs El Paso 74.0 73 73 73.7 73.7

Arvada Jefferson 79.0 79 79 79.2 79.1

Welch Jefferson 75.0 75 75 75.0 75.0 Rocky Flats North Jefferson 85.0 84 84 84.9 84.9

NREL Jefferson 82.0 82 82 82.3 82.2

Fort Collins - West Larimer 86.0* 84 84 84.9 84.8

Fort Collins Larimer 74.0 73 73 73.0 73.0 Greeley-WeldTower Weld 78.0 77 77 77.7 77.5

Gunnison Gunnison 68.0 67 67 67.8 67.8

Larimer Larimer 76.0 75 75 75.2 75.2

Larimer Larimer 76.0 75 75 75.2 75.2
* Fort Collins West DVC based on two-years of measured data. With the 2008 zone season data now available the 2006-2008 8-hour ozone Design Value at Fort Collins is now 82 ppb.

EPA’s 8-hour ozone projection procedure also includes an unm onitored area analysis (EPA, 2007) that has been codified in MATS. The unmonitored area analysis uses the future-year 8- hour ozone Design Value projection procedure applie d 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 modeli ng domain using essentially the same approach as used for the monitored ozone projections.

Figure ES-1 displays the interpolated current ye ar 8-hour ozone Design Values (DVC; left) and projected 8-hour ozone Design Values (DVFs) fo r the 2010 Base Case (right) 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 west of th e Fort Collins (Figure ES-1, left). The projected DVFs for the 2010 base case (Figure ES-1, right) have greatly reduced the spatialF:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Final\Exec_Sum2.doc January 2009 ES-4 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 unmonitored area anal ysis projected DVFs for the Final 2010 Control Strategy (left) and the differences in the 2010 DVFs between the 2010 Base Case and Final 2010 Control Strategy (right). There are slight reductions in the 20 10 DVFs in the Final 2010 Control Strategy over the 2010 Base Case, which can be seen more clearly in the difference plot seen in Figure ES-2 (right). The 6 remain ing grid cells with projected DVFs that are 85 ppb or higher in the 2010 Base case are reduced to 5 grid cells in the Final 2010 Control Strategy.

EPA guidance stresses that the unmonitored area te st has more uncertainties than the projections at the monitors and it should be treated sepa rately from the monitor based attainment demonstration test (EPA, 2007). EPA further notes that while it is expected that additional emission controls will likely be needed to el iminate predicted exceedan ces 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 predicted violations in the
unmonitored area test be scru tinized and understood to determin e whether they are likely to really exist in the ambient air, or whether they may be caused by an erro r or uncertainties in the modeling system. It may be appropriate to deploy additional ozone monitors to such areas. In the case of the Denver ozone modeling, higher ozone concentrations are estimated west of Fort
Collins than at the locations of the two monitors in Fort Collins on some days and this does not appear to be due to an error in the modeling sy stem. Whether it may be due to uncertainties in the modeling system can not be determined. Howe ver, it does not seem implausible that higher
ozone values could exist west of th e Fort Collins West monitoring site.

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).F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Final\Exec_Sum2.doc January 2009 ES-5 Figure ES-2. Projected 2010 8-hour ozone Design Values (DVF) for the Final 2010 Control Strategy (left) and differences in projected 2010 DVFs between the 2010 Base Case and Final 2010 Control Strategy (2010 Control – 2010 Base) (right).

2010 OZONE ATTAINMENT DEMONSTRATION MODELING

The 2010 ozone modeling indicates th at the Denver region would ach ieve attainment of the 1997 0.08 ppm 8-hour ozone NAAQS by 2010 under both the 2010 Base Case and Final 2010 Control Strategy. Both 2010 emission scenarios pass the m odeled attainment demonstration test at the monitoring sites (EPA, 2007). Examining the un monitored area analysis, both 2010 emission scenarios have several grid cells (5-6) that ar e projected to still exceed the ozone NAAQS in 2010. However, these residual 2010 ozone exceedan ces were due to the assumed 86 ppb current year DVC at the Fort Collins West monitoring s ite that is based on two years (2005-2007) of
ozone observations. The inclusion of ozone obs ervations from 2008 results in an 8-hour ozone Design Value for the Fort Collins West monitori ng site of 82 ppb, which if used for the DVC
would eliminate the residual ozone exceedance areas in the unmonitored area analysis. Although
both 2010 emissions scenarios demonstrate a ttainment of the ozone NAAQS in 2010, the
additional controls in the Final 2010 Control Strategy provide more certainty that ozone
attainment will be achieved in 2010 than the 2010 Base Case.

There are numerous uncertainties in the modeling analysis. By definition, models are simplistic approximations of complex phenomena. The mode ling analysis used to asses whether various emission reduction measures will bring the Denve r area into attainment of the 8-hour ozone NAAQS contain many elements that are uncerta in (e.g., emissions i nputs and projections, meteorological inputs, ozone transpor t, etc.). There is a lot of year-to-year variability in the meteorological for the Denver area that greatly affects the ozone formation potential of the region. For example, the most ozone formati on conducive year for the DMA in recent record was 2003 that was followed by the year with the least ozone formation conducive conditions in
2004. If the ozone formation conditions in the next few years are much more severe than seen in the June-July 2006 modeling period, then that c ould jeopardize achieving attainment in 2010. However, at least 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_Fi nal_Control_Strategy\Draft_Fi nal\Sec1_2010Final_Intro2.doc January 2009 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 early enforceable 8-hour ozone State Im plementation Plan (SIP) by March 2004 that
demonstrates attainment of the 8-hour ozone NAAQS by 2007. In return, EPA will defer the
classification of an area as nonattainment until 2007. Based on 2005-2007 measured air quality, the DMA violated the 1997 0.08 ppm 8-hour ozone NAAQS, so in November 2007 the DMA
reverted to an 8-hour ozone nonattainment area and is required to prepare an 8-hour ozone SIP that demonstrates attainment by 2010. The c ontracting team of ENVIRON International Corporation, and their subcontra ctor Alpine Geophysics, LLC, we re selected by the RAQC and CDPHE to perform the 2010 8-ho ur ozone attainment demons tration modeling for the new
Denver 8-hour ozone 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.

This document presents the ozone attainment de monstration modeling of the 2010 Base Case and Final 2010 Control Strategy for the Denver 8-hour ozone SIP that was approved by the Colorado Air Quality Control Commissi ons (AQCC) during their December 11-12, 2008 hearing.

1.2 APPROACH

The Denver 8-hour ozone attainment demons tration modeling was performed using the following meteorological, emissions and photoch emical grid models: the fifth generation Mesocale Model (MM5) meteorological model (A nthes and Warner, 197 8; 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). These models were applie d to a June-July 2006 modeling period for the purposes of demonstrating attainment of the 8-h our ozone standard by 2010. Figure 1-1 displays the 36/12/4 km modeling domains used fo r the MM5 and SMOKE/CAMx modeling. CAMx simulations were first performe d for the 36 km continental U.S. Inter-RPO modeling domain and the results processed to generate boundary c onditions (BCs) for the 12 km modeling domain (i.e., one-way grid nesting between the 36 km and 12 km CAMx domains). CAMx was then
used to simulate ozone formation within the 12/4 km modeling domain using two-way interactive grid nesting (Figure 1-1b). On ce the 12 km BCs were defined from the 2006 andF:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Fi nal\Sec1_2010Final_Intro2.doc January 2009 1-2 2010 36 km CAMx simulations, sensitivity and contro l strategy evaluations runs were made on the 12/4 km modeling domain. The Denver 8- hour ozone SIP modeling work was performed mostly during the 2008 calendar year and produced the following reports:

• Development of a Denver 8-hour ozone SIP a ttainment demonstration Modeling Protocol (Morris et al., 2007).

o http://www.ozoneaware.org/documen ts/DraftFinalProtocolDenver8- HourOzoneNov282007.pdf

• MM5 meteorological modeling and model pe rformance evaluation (McNally et al., 2008a).

o http://www.ozoneaware.org/documents/MM5_Eval_DENSIP_Feb25_2008.pdf

• 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., 2008a).

o http://www.ozoneaware.org/documents /Prelim_Ozone_Eval_Denver_SIP_Feb27 _2008.pdf

• Final base case modeling and model perfor mance evaluation for the June-July 2006 DMA episode (Morris et al., 2008b).

o http://www.ozoneaware.org/documents /modeling/Denver_2006MPE_DraftFinal_ Aug29_2008.pdf

• 2010 base case modeling, emission sensitivity tests and ozone source apportionment modeling (McNally et al., 2008b).

o http://www.ozoneaware.org/doc uments/modeling/Exec_Sum1.pdf

• 2010 control strategy and attainment demons tration modeling (Morris et al., 2008c).

o http://www.ozoneaware.org/documents/m odeling/Denver_2010ControlStrat_Draf t_Sep22_2008.pdf

The last report listed above (Morris et al., 2008c) presented ozone attainment demonstration modeling for a 2010 Base Case, a proposed 2 010 SIP Control Strategy (Cntl1) and a 2010 Control Strategy that included the proposed federa lly-enforceable SIP control measures as well as additional state-only control measures (C ntl2). The Colorado Air Quality Control Commission (AQCC) held a hearing on the proposed Denver 8-hour ozone 2010 SIP Control Strategy and passed a motion for a slightly modi fied Ozone Action Plan to produce a Final 2010 Control Strategy for the Denver 8-ho ur ozone SIP (AQCC, 2008).F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Fi nal\Sec1_2010Final_Intro2.doc January 2009 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 fo r the Denver 8-hour ozone modeling study. Blue line domains are for CAMx/SMOKE domains that are nested in the MM5 red line
domains.

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

CAMx 12km CAMx 4km

Figure 1-1b. Nested 12/4 km modeling domains for the Denver CAMx air quality and SMOKE emissions modeling.F:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Fi nal\Sec1_2010Final_Intro2.doc January 2009 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 fi nal 2006 base case emissions scenario (Morris et al., 2008a,b) and the 2010 Base Case and emissions sensitivity scenarios and are described by McNally and co-workers (McNally et al., 2008b). The CDPHE/APCD provided 2010 emi ssions for all anthropogenic emission sources in Colorado except for on -road mobile sources and 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 utili zed (Bar-Ilan et al., 2008a,b). Outside of Colorado, the 2010 anthropogenic emissions were based 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 and were based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) biogenic emissions model (Guenther and Wiedinmyer, 2004). Emissions from fires were al so kept constant between the 2006 base case
and 2010 emission scenarios.

Colorado emissions for the 2010 Base Case a nd Final 2010 Control Strategy were either provided by the CDPHE or, in the case of on-road mobile source s, modeled using the CONCEPT MV and SMOKE-MOBILE6 on-road mobile source emissions modeling systems. Table 1-1 summarizes the VOC, NOx and CO emissions with in the 4 km Colorado domain (Figure 1-1b) for the 2006 Base Case, the 2010 Base Case and the Final 2010 Control Strategy. Between the 2006 and 2010 Base Case emissions scenarios, VOC , NOx and CO emissions are estimates to be reduced by, respectively, 42 tons per day (TPD ) (-1%), 50 TPD (-5%) and 386 TPD (-10%).
Note that the emissions in Table 1-1 ar e model-ready emissions for the July 27, 2006 representative day (Thursday) and may differ from the planning inventories and other modeling days. In particular, the model-ready emissions ha ve day-specific adjustments for several source categories (e.g., on-road mobile sources and bi ogenic emissions) and the VOC emissions have been speciated into the CB05 chemical mechanis m used in the CAMx photochemical grid model so that any organic compounds that are considered non-reactive in the or iginal VOC inventories have been dropped for ozone modeling.

The Denver 8-hour ozone SIP Final 2010 Control Strategy implemented tw o additional control measures over the 2010 Base Case (AQCC, 2008):

• 85% control of VOC emissions on all conde nsate tanks with annual VOC emissions greater than 2 t ons per year; and

• Revisions to condensate tank flaring controls that phases in the auto igniters on flares controlling tanks greater than or equal to 50 TPY by May 1, 2009 and on all remaining tanks greater than 2 TPY in the Denver NAA by May 1, 2010.

The two control measures in the Final 2010 Cont rol Strategy results mainly in VOC emission
reductions over the 2010 Base Case. Across Colorado, the 2010 Final Control Strategy
emissions scenario has 28 TPD less VOC emissions than the 2010 Base Case. This results in a -3.6 percent reduction in anthropogenic and a -0.6% reduction in total VOC emissions across Colorado over the 2010 Base Case due to the impl ementation of the two control measures in theF:\Denver_O3_2008\Reports\2010_Fi nal_Control_Strategy\Draft_Fi nal\Sec1_2010Final_Intro2.doc January 2009 1-5 Final 2010 Control Strategy. Note that the flar ing used in the condensate tank VOC control measure in the Final 2010 Control Strategy results in increases in NOx and CO emissions over
the 2010 Base Case. NOx and CO emissions are estimated to be 0.04 and 0.21 TPD higher in the Final 2010 Control Strategy than th e 2010 Base Case, respectively. However, these increases in NOx and CO emissions are minor representing less than 0.01% of th e Colorado NOx and CO
emissions.

Table 1-1. 2006 Base Case, 2010 Base Case and Final 2010 Control Strategy VOC, NOx and CO emissions (tons per day) across the Colorado 4 km domain.

Total Colorado Emissions (tons/day) July 27, 2006

Emissions Scenario CO (tons/day) NOx (tons/day) VOC * (tons/day)

Total Colorado Emissions

2006 Base Case 4401.1 930.7 4671.4

2010 Base Case 4015.2 880.7 4629.2 Final 2010 Control Strategy 4015.4 880.7 4601.6 Biogenic Emissions for Colorado 4 km Grid 2006 MEGAN Biogenics 618.4 44.2 3871.5 Anthropogenic Colorado Emissions

2006 Base Case 3782.8 886.5 799.9

2010 Base Case 3396.8 836.5 757.7 Final 2010 Control Strategy 3397.0 836.5 730.1 Percent Change in Total Colorado Emissions

2006 Base Case -- -- --

2010 Base Case -8.8% -5.4% -0.9% Final 2010 Control Strategy -8.8% -5.4% -0.9% Percent Anthropogenic in Total Colorado Emissions

2006 Base Case -- -- --

2010 Base Case -10.2% -5.6% -5.3% Final 2010 Control Strategy -10.2% -5.6% -8.7%

* VOC emissions from CBO5 chemical mechanism.F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-1 2.0 2010 OZONE ATTAINMEANT DEMONSTRATION

2.1 INTRODUCTION

This section presents the 2010 ozone Design Value projections for the 2010 Base Case and the Final 2010 Control Strategy approved by the Colora do Air Quality Control Commissions at their December 11-12, 2008 hearing (AQCC, 2008). The fu ture year ozone projections demonstrate
that the Denver area will achieve the 0.08 ppm 8-hour ozone NAAQS by 2010 under the 2010
Base Case conditions. The 2010 Final Control Strategy includes federally-enforceable control
measures that will be included in the Denver 8-hour ozone State Implementation Plan (SIP) that provide additional certainty that ozone attainment will be achieved in 2010. The 8-hour ozone projections are made using the CAMx modeling results for the 2006 Base Case (Morris et al., 2008a,b) and the 2010 Base Case and Final 2010 C ontrol Strategy emission scenarios. These ozone projections are made usin g EPA’s Modeled Attainment Test Software (MATS) tool that
can be found at:

• http://www.epa.gov/scram001/modelingapps_mats.htm

The procedures used by MATS to make ozone pr ojection are described in detail by McNally and co-workers (2008b) that presente d the 8-hour ozone projections for the Denver 2010 Base Case and 2010 sensitivity simulations. Below we provi de a brief overview of the ozone projection procedures used by MATS, whos e results for the 2010 Base Case and Final 2010 Control Strategy are presented later in this Chapter.

2.2 OZONE PROJECTION PROCEDURES

The Denver 2010 8-hour ozone projections were made using default procedur es in EPA’s latest modeling guidance (EPA, 2007), with one exception th at is described below. These procedures
use the model in a relative sens e to scale the observed current year 8-hour ozone Design Value (DVC) to obtain a future year 8-hour ozone De sign Value (DVF). The model derived scaling
factors are referred to as relati ve 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 case]

DVF = DVC x RRF

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

1. Develop an observed current year 8-hour oz one Design Value (DVC) at each monitoring site that serves as the starting point for the ozone projections.

EPA guidance recommends using an average of three years of 8-hour ozone Design Values centered on the modeling year, wh ich for the Denver June-July 2006 episode modeling would mean averaging 8-hour ozone Design Values from the 2004-2006, 2005- 2007 and 2006-2008 periods. This results in aver aging the fourth highest daily maximumF:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-2 8-hour ozone concentration at a monitor acro ss five years of data centered on 2006 using weighting factors of 1, 2, 3, 2, and 1 for th e years 2004-2008, respectively. However, for the Denver 2010 8-hour ozone projections th e “five year Design Value” approach recommended in EPA’s guidance was not used as the DVCs for the following reasons:

a. The Denver 2010 ozone projections were initially made before the 2008 ozone season was completed so use of the “five year Design Value” approach for the DVCs that included 2008 observations was not possible.

b. Using such a “five year Design Value “ approach would result in the DVCs that attain the 0.08 ppm 8-hour oz one NAAQS for all monitors in the Denver region,
which seemed inconsistent with the de signation of the Denver area as 8-hour
ozone nonattainment in November 2007.

Thus instead, with one exception, for the DVC s the 8-hour ozone Design Values from the 2005-2007 three year period that resulted in Denver being classifi ed as nonattainment were used. The exception is for the Fort Collins West ozone monitor that started monitoring in 2006 so the DVC was based on th e average fourth highest measured 8-hour ozone for two years (2006-2007).

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.

b. By several days EPA recommends RRFs based on at least 10 modeled days and recommends selecting days in which the 2006 base case highest daily maximum
8-hour ozone concentrations near a monito r are greater than an ozone threshold (cut off). Initially, an ozone threshold of 85 ppb is used. If less than 10 days are obtained the threshold is reduced by 1 ppb until at least 10 days are obtained for the RRF. When the 70 ppb threshold floor is reached and there are at least 5 days
then the RRF is used. If there are less than 5 modeled days with the 2006 base case highest daily maximum 8-hour ozone c oncentration near the monitor greater or equal to 70 ppb, then no RRF and 2010 ozone projection is made for that monitoring site.

3. The RRF is applied to the DVC to obtai n 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 e qual 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 projections in each grid cell using theF:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-3 procedures given above, excep t using the modeling results within each grid cell rather than near the grid cell.

a. EPA believes that the unmonitored area analysis is more uncertain than the monitor based ozone projections, whereas additional emissions reductions are likely required to eliminate any projected monitored ozone exceedances, the same
is not true in the unmonitored area test.

b. EPA recommends that the reasons behind any unmonitored area test exceedances be understood and explained.

2.3 OZONE ATTAINMENT DEMONSTR ATION FOR THE 2010 BASE CASE AND
THE FINAL 2010 CONT ROL STRATEGY

The same emissions modeling procedures used for the 2006 Base Case and 2010 sensitivity tests and preliminary control strategies were used for the 2010 Base Case and Final 2010 Control Strategy (Morris et al, 2008c,d; McNally et al., 2008b). The on-ro ad mobile source emissions were modeled using either the CONCEPT MV (a rea covered by the Denve r link-based network)
or SMOKE-MOBILE6. The two control measures for the Final 2010 C ontrol Strategy were included in emissions files prov ided by the CDPHE/APCD. Tabl e 1-1 presented in Chapter 1
summarizes the emissions within the Colorado 4 km grid domain for the 2006 Base Case, 2010 Base Case and Final 2010 Control Strategy. Th e Final 2010 Control Strategy was based on a slight modification to the CDPHE’s Ozone Ac tion Plan – Alternative Proposal #2 (CDPHE, 2008) presented at the Colorado Air Quality Control Commission hearing December 11-12, 2008 (AQCC, 2008) and contained tw o federally-enforceable control measures beyond the 2010 Base
Case: 85% condensate tank VOC controls on tanks greater than 2 tpy and revised controls on condensate flaring.

2.3.1 Attainment Demonstratio n at the Monitoring Sites

Table 2-1 displays the projecte d future year 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and the Final 2010 Control Strategy emission scenarios. Included in this table are the 2010 DVFs (Table 2-1a) and the RRFs (Table 2-1b) the ozone cut-off threshold concentrations (Table 2-1c) and the number of modeling days (Table 2-1d) used in the
construction of the RRFs. The first set of DVFs in Table 2-1a (columns 4 and 5) follow EPA’s guidance approach (EPA, 2007) to truncate the final DVFs to th e nearest ppb for comparison with the NAAQS. Whereas the last set of DVFs for the 2010 Base Case and Final 2010 Control Strategy display the DVFs to the nearest tenth of a ppb so that we can distinguish any differences in the ozone projections between the 2010 Base Case and Final 2010 Control Strategy. The maximum projected 8-hour ozone Design Value for the 2010 Base Case and Final 2010 Control Strategy is 84 ppb at the Rocky Flats North (RFNO) and Fort Co llins West (FTCW) monitoring sites. As all projected 2010 8-hour ozone Desi gn Values are below 85 ppb, the 2010 Base Case and Final 2010 Control Strategy both pass the m odeled ozone attainment demonstration test. However, since there are four monitoring si tes 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.F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-4 When reporting the DVFs to the nearest tenth of a ppb we see that the maximum projected DVF for the 2010 Base Case is 84.9 ppb at both the RF NO and FTCW monitoring s ites (Table 2-1a). The implementation of the federally-enforceable SI P control measures in the Final 2010 Control Strategy reduces the DVF at the FTCW monito ring site by 0.1 ppb (84.8 ppb) and has no effect at the RFNO monitoring site ( 84.9 ppb). Of the 18 sites listed in Table 2-1, the Final 2010 Control Strategy is projected to reduce the 2010 DVF by 0.1 ppb at four sites and by 0.2 ppb at one site, with the remainder of the monitoring sites having identical DVFs for the 2010 Base Case and Final 2010 Control Strategy. The larges t ozone reduction due to the control measures
in the Final 2010 Control Strate gy (0.2 ppb) occurs at the Weld County Tower monitoring site (Greely), which is not surprising given that it is the closest monitor to the O&G developments that occur primarily in Weld County, which is where the largest VOC emission reductions occur
due to the Final 2010 Control Stra tegy control measures. These re sults are consistent with the 2010 sensitivity modeling that found ozone to be more responsive to emission controls at the FTCW than RFNO monitoring si tes (McNally et al., 2008b).

Table 2-1a. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy.

2010 DVF (EPA Guidance) 2010 DVF (nearest 0.1 ppb)

Name County DVC (2005- 2007) Base Case Final Strategy Base Case Final Strategy Welby Adams 70.0 70 70 70.2 70.2 Highland Arapahoe 78.0 77 77 77.3 77.3

S. Boulder Creek Boulder 81.0 80 80 80.8 80.7

Denver - CAMP Denver 56.0 56 56 56.0 56.0 Carriage Denver 74.0 74 74 74.1 74.1 Chatfield State Park Douglas 84.0 83 83 83.4 83.4 USAF Academy El Paso 73.0 72 72 72.0 72.0 Manitou Springs El Paso 74.0 73 73 73.7 73.7

Arvada Jefferson 79.0 79 79 79.2 79.1

Welch Jefferson 75.0 75 75 75.0 75.0 Rocky Flats North Jefferson 85.0 84 84 84.9 84.9

NREL Jefferson 82.0 82 82 82.3 82.2

Fort Collins - West Larimer 86.0* 84 84 84.9 84.8

Fort Collins Larimer 74.0 73 73 73.0 73.0 Greeley-WeldTower Weld 78.0 77 77 77.7 77.5

Gunnison Gunnison 68.0 67 67 67.8 67.8

Larimer Larimer 76.0 75 75 75.2 75.2

Larimer Larimer 76.0 75 75 75.2 75.2
* Fort Collins West DVC based on two-years of meas ured data. With the 2008 zone season data now available the 2006-2008 8-hour ozone Design Value at Fort Collins is now 82 ppb.F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-5 Table 2-1b. Relative Response Factors (RRFs) used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and the Final 2010 Control Strategy.

RRF

Name County DVC Base Case Final Strategy Welby Adams 70.0 1.0042 1.0040 Highland Arapahoe 78.0 0.9916 0.9915

S. Boulder Creek Boulder 81.0 0.9976 0.9974

Denver - CAMP Denver 56.0 1.0017 1.0014 Carriage Denver 74.0 1.0022 1.0019 Chatfield State Park Douglas 84.0 0.9934 0.9933 USAF Academy El Paso 73.0 0.9873 0.9873 Manitou Springs El Paso 74.0 0.9966 0.9966

Arvada Jefferson 79.0 1.0026 1.0023

Welch Jefferson 75.0 1.0004 1.0002 Rocky Flats North Jefferson 85.0 0.9994 0.9992

NREL Jefferson 82.0 1.0039 1.0036

Fort Collins - West Larimer 86.0 0.9874 0.9869

Fort Collins Larimer 74.0 0.9878 0.9871 Greeley-WeldTower Weld 78.0 0.9964 0.9944

Gunnison Gunnison 68.0 0.9984 0.9984

Larimer Larimer 76.0 0.9903 0.9902

Larimer Larimer 76.0 0.9903 0.9902F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-6 Table 2-1c. Ozone threshold Cutoff Concentration used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy.

Cutoff Concentration

Name County DVC Base Case Final Strategy Welby Adams 70.0 77.0 77.0 Highland Arapahoe 78.0 78.0 78.0

S. Boulder Creek Boulder 81.0 78.0 78.0

Denver - CAMP Denver 56.0 78.0 78.0 Carriage Denver 74.0 78.0 78.0 Chatfield State Park Douglas 84.0 78.0 78.0 USAF Academy El Paso 73.0 75.0 75.0 Manitou Springs El Paso 74.0 74.0 74.0

Arvada Jefferson 79.0 78.0 78.0

Welch Jefferson 75.0 78.0 78.0 Rocky Flats North Jefferson 85.0 78.0 78.0

NREL Jefferson 82.0 78.0 78.0

Fort Collins - West Larimer 86.0 76.0 76.0

Fort Collins Larimer 74.0 76.0 76.0 Greeley-WeldTower Weld 78.0 75.0 75.0

Gunnison Gunnison 68.0 74.0 74.0

Larimer Larimer 76.0 77.0 77.0

Larimer Larimer 76.0 77.0 77.0F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-7 Table 2-1d. Number of days used to project 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case and Final 2010 Control Strategy.

Number of Day

Name County DVC Base Case Final Strategy Welby Adams 70.0 11 11 Highland Arapahoe 78.0 14 14

S. Boulder Creek Boulder 81.0 10 10

Denver - CAMP Denver 56.0 10 10 Carriage Denver 74.0 10 10 Chatfield State Park Douglas 84.0 11 11 USAF Academy El Paso 73.0 10 10 Manitou Springs El Paso 74.0 10 10

Arvada Jefferson 79.0 10 10

Welch Jefferson 75.0 10 10 Rocky Flats North Jefferson 85.0 10 10

NREL Jefferson 82.0 11 11

Fort Collins - West Larimer 86.0 10 10

Fort Collins Larimer 74.0 12 12 Greeley-WeldTower Weld 78.0 10 10

Gunnison Gunnison 68.0 10 10

Larimer Larimer 76.0 10 10

Larimer Larimer 76.0 10 10F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-8 2.3.2 Unmonitored Area Analysis

EPA’s 8-hour ozone projection procedure also includes an unm onitored area analysis (EPA, 2007) that has been codified in MATS. The unmonitored area analysis uses the future-year 8- hour ozone Design Value projection procedure applie d 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 interpolat ion scheme uses the modeled c oncentration gradients so that the gridded DVCs may have some locations th at are higher than the observed DVCs at the monitoring sites. RRFs are then obtained fo r each grid cell in the modeling domain using essentially the same approach as used for the monitored ozone projections, only RRFs are based
on the model estimates within eac h grid cell rather than near a grid cell as done for the projections at the monitor.

Figure 2-1 displays the interpol ated current year 8-hour ozone Design Values (DVC) using the MATS unmonitored area analysis. Interpolated current year ozone DVCs in excess of 80 ppb are estimated to the south, west and northwest of Denver stretching to Fort Collins and then west of Fort Collins. In fact, the MATS interpolation procedure estima tes 12 grid cells of current-year DVCs in excess of the 0.08 ppm NAAQS (i.e., 85 ppb or higher) that occur west of Fort Collins (Figure 2-1).

The projected DVFs for the 2010 Base Case (Figure 2-2) have grea tly reduced the spatial extent of the DVFs in excess of 80 ppb and the 12 ce lls with DVCs exceeding the 0.08 ppm NAAQS have been reduced by half to 6 grid cells in the 2010 Base Case emissions scenario. Note that
the unshaded areas in the unmon itored area analysis 2010 ozone pr ojections are areas in which there were less than 5 days with 2006 Base Ca se daily maximum 8-hour ozone estimates of 70 ppb or greater so no 2010 ozone projecti on were made for those grid cells.

Figure 2-3 displays the unmon itored area analysis projected DVFs for the Final 2010 Control Strategy emissions scenario. There are slight reductions in the 2010 DVFs over the 2010 Base Case, which can be seen more clearly in the 2010 DVF difference plot shown in Figure 2-4. The 6 remaining exceedance grid cells with projected DVFs that are 85 ppb or higher in the 2010 Base case are reduced to 5 grid cells under the Final 2010 Control Strategy.

EPA guidance stresses that the unmonitored area te st has more uncertainties than the projections at the monitors and it should be treated sepa rately from the monitor based attainment demonstration test (EPA, 2007). EPA further notes that while it is expected that additional emission controls will likely be needed to el iminate predicted exceedan ces 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 predicted violations in the
unmonitored area test be scru tinized and understood to determin e whether they are likely to really exist in the ambient air, or whether they may be caused by an erro r or uncertainties in the modeling system. It may be appropriate to deploy additional ozone monitors to such areas. In the case of the Denver ozone modeling, higher ozone concentrations are estimated west of Fort
Collins than at the locations of the two monitors in Fort Collins on some days and this does not appear to be due to an error in the modeling sy stem. Whether it may be due to uncertainties in the modeling system can not be determined. Howe ver, it does not seem implausible that higher
ozone values could exist west of the Fort Collins West monitoring site. These high 2010 projected ozone DVFs west of Fort Collins are driven by the high DVC of 86 ppb at the FTCWF:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-9 monitor that is based on two-years (2006-2007) of monitoring data. When a third year of monitoring data is included (2008) the 8-hour ozone Design Value at FTCW is reduced from 86 ppb to 82 ppb. If the 82 ppb lower actual 8-hour ozone Design Value was used for the DVC at
the FTCW monitor in the unmonitored area anal ysis instead of 86 ppb, there would be no grid cells exceeding the 8-hour ozone NAAQS in th e unmonitored area analysis for both the 2010
Base Case and Final 2010 Contro l Strategy emission scenarios.

Figure 2-1. Interpolated current year observed 8-hour ozone Design Values (DVCs) using the MATS tool (ppb).F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-10 Figure 2-2. Projected 2010 8-hour ozone Design Values (DVFs) for the 2010 Base Case emissions scenario using the MATS tool (ppb).F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-11 Figure 2-3. Projected 2010 8-hour ozone Design Values (DVFs) for the Final 2010 Control Strategy emissions scenario using the MATS tool (ppb).F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec2_2010Final_AttainDemo2.doc January 2009 2-12 Figure 2-4. Differences in projected 2010 8-hour ozone Design Values (DVFs) between the 2010 Base Case and the Final 2010 Control Strategy emissions scenarios using the MATS tool (2010 Control – 2010 Base).

2.4 ATTAINMENT DEMONSTRATION CONCLUSIONS

The photochemical modeling of the Denver regi on demonstrates that the 2010 Base Case
emissions scenario is sufficient to achieve attainment of the 0.08 ppm ozone NAAQS by 2010.
The additional control measures in the Final 2010 Control Strate gy provide additional assurances
that ozone attainment will be achieved in the Denver area by 2010.F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 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 Case and Final 2010 C ontrol Strategy is 84 ppb at the Rocky Flats North (RFNO) and Fort Collins West (FTCW) mon itoring sites, so both 2010 emission scenarios pass the modeled attainment demonstration test . As these projected 2010 DVFs are 82 ppb or higher, then a Weight of Ev idence (WOE) analysis is requi red to corroborate the modeled attainment demonstration test. The WOE analys is examines observed emissions and air quality data and their trends, assesses the conceptual m odel 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 wh ether the preponderance of evidence suggests that
Denver area will in fact achieve attainment of the 0.08 ppm 8- hour ozone National Ambient Air Quality Standard (NAAQS) by 2010. Below we provide add itional modeling metrics and alternative ozone projection procedures th at are one component of a WOE analysis.

3.2 ALTERNATIVE 2010 OZONE PR OJECTION PROCEDURES

Several alternative 2010 ozone proj ection procedures were analy zed for the 2010 Base Case, and Final 2010 Control Strategy emission scenarios to estimate the unce rtainties in th e projection procedures and provide confiden ce that passing the modeled atta inment demonstration test does indicate attainment will likely be achieved in 2010. These alternative ozone projection procedures differ in the days used and how modeled ozone near the monitor is selected to construct the RRFs. Six additional ozone projecti on procedures were analyzed, in addition to the EPA guidance default approach discussed in Chapter 2:

Minimum 5 Days to Develop RRF us ing 85-70 ppb Sliding Threshold (5dth) : In the EPA default approach, modeling days are selected for use in constructing RRFs based on whether the maximum daily maximum 8-hour ozone concentration near the monitor (with 7 x 7 array of grid cells) in the 2006 Base Case is greater than a threshold, with the threshold determined when at least 10 days are obtained for the RRF. In this alternative projection approach, we require a minimum of 5 modeled days to construct the RRFs.

Use of 80 ppb Cutoff Threshold and Minimum of 1 Day (1dth80) : The second alternative ozone projection approach us es 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_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 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 monitors in the DMA. With the EPA default 7 x 7 array of grid cells around each monitor, there is a lot of overlap of the areas searched to obtain the maximum daily maximum 8-hour ozone concentrations near a monitor used in the RRFs. This can potentially result in selecting the same maximum 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 cen tered on each monitor (Figure 3-1b) reduces the overlap among nearby monitors and potentially retains the different characteristics of the monitoring sites, if such differences were captured by the model. For example, the CAMP monitor, and other more urban Denver monitoring sites, is clearly affected by the high NOx concentrations in metropolitan Denver that inhibit ozone forma tion. Use of the 7 x 7 array of grid cells results in selecting maximum modeled c oncentrations that are potentially outside of the influence of the high NOx concentration region for use in the RRFs thereby not capturing the NOx inhibition effect of these monitoring sites in the metropolitan Denver region (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_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 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 2010 Base Case and Final 2010 Control Strategy us ing the EPA guidance default and the six alternative ozone projection proce dures discussed above. Also s hown in Table 3-1 are the ozone cutoff thresholds and number of days used in calculating the RRFs fo r each alternative 2010 ozone project method and the RFNO and FTCW monitoring sites. Results for all monitoring
sites in the DMA are shown in Table 3-2. It should be noted that there is really no one “correct” method for projecting future year ozone concentra tions that has been proven the most reliable. Methods based on just a few number of days have been shown to be less robust than ones based on more days. And it is logical that methods based on modeled concentr ations closer to the observed 8-hour ozone Design Values would be mo re representative of the conditions that produced those Design Values th an methods based on days with much higher or lower ozone concentrations than the Design Values.

2010 Base Case : For the 2010 Base Case, the projected 2010 DVF using the EPA guidance default approach was 84.9 ppb at both the RFNO a nd FTCW monitoring sites. Some of the six alternative projection approaches re sult in increases, whereas others in decreases in the projected DVF relative to the EPA default approach at th ese two sites. The projected DVFs at RFNO for the 2010 Base Case range from 84.5 to 85.2 ppb with an average value of 84.950 ppb. A similar range for the FTCW monitor is 84.6 to 85.2 ppb with an av erage of 85.013 ppb. At the RFNO monitoring site, 3 of the 7 projection methods pa ss the modeled attainment demonstration test (43%), while at the FTCW 5 of th e 7 methods pass the test (71%).

Final 2010 Control Strategy : The 2010 ozone projections at th e RFNO monitoring site for the Final 2010 Control Strategy are the same as for the 2010 Base Case using all the alternative projections procedures (e.g., av erage 84.950 ppb). At the at th e FTCW monitoring site, the projected DVFs for the Final 2010 Control Strategy range from 84.6 to 85.1 ppb with an average of 84.963 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_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 3-4 An examination of the different 2010 ozone proj ection methods across mon itoring 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 the projected DVF at RF NO 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 downt own ozone monitors where as th e array of grid cells becomes smaller, the projected DVF goes up. For example, at the CAMP monitor and the 2010 Base Case the projected DVF using the 7 x 7, 5 x 5 and 3 x 3 array of grid cells are, respectively, 56.0, 56.8 and 57.3 ppb (Table 3-2a). This reflects the sele ction of modeling results closer to the urban core where the model is less responsive and wher e ozone increases from the 2006 to 2010 due to NOx emissions reductions (NOx disbenefits). It is encouraging that the EPA default 2010 ozone projection approach falls in betw een the alternative appr oaches and, in most cases, the average of the seven ozone projection approaches is close to the EPA default method approach.

In conclusion, the alte rnative ozone projection approaches support the findings using the EPA default approach that the 2010 Base Case will like ly 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 achie ve 8-hour ozone attainment in 2010 under the Final 2010 Control Strategy.

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 84.950 Fort Collins - West 86.0 84.9 84.6 84.6 84.9 85.1 84.8 85.2 85.013 Final 2010 Control Strategy DVFs (ppb) Rocky Flats North 85.0 84.9 85. 2 85.1 84.9 85.0 85.0 84.5 84.950 Fort Collins - West 86.0 84.8 84.6 84.6 84.8 85.0 84.8 85.1 84.963 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_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 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 si x 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 si x alternative projection approaches and the Final 2010 Control Strategy modeling results. Final 2010 Control Strategy
Name DVC EPA 5dth 1dth80 1dth75 1dth70 5x5 3x3 Welby 70.0 70.2 69.4 69.4 70.3 71.1 70.3 71.3 Highland 78.0 77.3 76.2 77. 4 77.5 78.0 77.6 78.0 S. Boulder Creek 81.0 80.7 80.5 80.5 80.5 80.5 80.8 80.4 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 84.0 83.4 82. 9 83.3 83.6 83.9 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 79.1 78.9 78. 9 79.3 79.7 79.4 79.3
Welch 75.0 75.0 75.0 75. 0 74.7 74.9 74.5 74.5 Rocky Flats North 85.0 84.9 85.2 85.1 84.9 85.0 85.0 84.5
NREL 82.0 82.2 82.5 82. 5 82.2 82.0 82.0 81.8 Fort Collins - West 86.0 84. 8 84.6 84.6 84.8 85.0 84.8 85.1 Fort Collins 74.0 73.0 72. 8 72.8 73.0 73.2 73.2 73.6 Greeley - Weld 78.0 77.5 77.8 77.3 77.5 77.5 77.6 77.7 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 75.2F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 3-6 Table 3-2c. 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_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 3-7 Table 3-2d. 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 c ontrol scenarios to assure that they indicate the modeled ozone concentrations are going down. These additional modeling metrics examine the
ozone differences between the curr ent 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 concentrations between the 2006 Base Case and 2010 emission scenarios were calculated across grid cells in the Denver NAA and across all days in the June-July 2006 modeling episode. Th e changes 8-hour ozone concentrations are calculated for values above four separate th reshold 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 co ncentration, 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 fo r all grid cells in the Denver NAA and days from the June-July 2006 episode.

Figure 3-2 displays the percent change in the Total Ozone and Grid Cells between the 2006 Base
Case and the 2010 Base Case and Final 2010 Control Strategy emission scenarios. Using the 70 ppb threshold, there are small reductions between 2006 and 2010 in the Total OzoneF:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 3-8 (approximately -5%) and Grid Cell (approximat ely -3.5%) modeling metrics. However, the
emission reductions between 2006 and 2010 are havi ng their intended effect by having more reductions in the higher 8-hour ozone concentra tions in the Denver region. For example, the changes in Total Ozone and Grid Cells with ozone greater than the 85 p pb threshold are reduced by approximately -21% and -14%, respectively. Th ese reductions are even greater for the Final 2010 Control Strategy scen ario than the 2010 Base Case. Fo r example, the Total Ozone above 85 ppb is reduced by -21.9% in the 2010 Base Ca se and reduced event more (-23.4%) in the Final 2010 Control Strategy.



### Percent Change in Total Ozone for 2010 Base and 2010
FSIP

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

Base FSIP% 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) and Final 2010 Control Strategy (FSIP)
emission scenarios.F:\Denver_O3_2008\Reports\2010_Final_Control_Strategy \Draft_Final\Sec3_Control_ModelMetrics2.doc January 2009 3-9 

### Percent Change in Grid Cells for 2010 Base and 2010 FSIP

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

Base FSIP% 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) and Final 2010 Control Strategy (FSIP)
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