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

Draft Final Report

2010 OZONE PROJECTIONS FOR THE 2010 BASE CASE 

AND 2010 SENSITIVITY TESTS AND 2010 OZONE SOURCE 

APPORTIONMENT MODELING FOR THE DENVER 

8-HOUR OZONE STATE IMPLEMENTATION PLAN 

Prepared for: 

Regional Air Quality Council 

1445 Market Street, Suite 260 

Denver, Colorado 80202 

Prepared by: 

Dennis McNally 

Cyndi Loomis 

Alpine Geophysics, LLC 

7341 Poppy Way 

Arvada, Colorado 80007 

Ralph Morris 

Tanarit Sakulyanontvittaya 

Edward Tai 

ENVIRON International Corporation 

773 San Marin Dr. Suite 2115 

Novato, CA 94998 

September 8, 2008
September 2008 

i 

TABLE OF CONTENTS 

Page 

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

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

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

 2010 Sensitivity Test Results...............................................................................................ES-4 

 2010 Ozone Source Apportionment Modeling....................................................................ES-7 

 Conclusions of 2010 Ozone Projections And 

 Emissions Sensitivity Tests..........................................................................................ES-11 

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

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

1.2 Purpose............................................................................................................................. 1-1 

1.3 Overview of Modeling Approach .................................................................................... 1-2 

1.4 2010 Emissions Modeling Approach............................................................................... 1-3 

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

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

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

 2.3 Ozone Projections for the 2010 Base Case...................................................................... 2-3 

 2.4 2010 Sensitivity Tests.................................................................................................... 2-10 

3.0 2010 APCA SOURCE APPORTIONMENT..................................................................... 3-1 

3-1 Introduction...................................................................................................................... 3-1 

3-2 Technical Description ...................................................................................................... 3-1 

3-3 Application Methodology ................................................................................................ 3-6 

3-4 Analysis Methodology and Results ................................................................................. 3-8 

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

APPENDICES 

Appendix A: Projected 2010 8-Hour Ozone Design Values (DVF) 

at DMA Monitoring Sites for the 2010 Base Case and 2010 

Emission Sensitivity Scenarios 
September 2008 

ii 

Appendix B: Differences in projected 2010 8-hour ozone Design 

 Values between the 2010 Sensitivity tests and the 2010 

 Base Case using the MATS Unmonitored Area Test 

 Projection Procedure 

Appendix C: Ozone Source Apportionment Modeling Results for each 

Monitor in the Denver Nonattainment Area with Daily Maximum 

8-Hour ozone > 70 ppb and the 2010 Base Case Emissions Scenario 

using the Anthropogenic Precursor Culpability Assessment (APCA) Source 

Apportionment Approach 

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-3 

Table ES-2. Results of the Denver 2010 emission sensitivity tests.......................................ES-6 

Table 2-1. Fourth highest daily maximum 8-hour ozone 

 concentrations ppm) at monitoring sites in the 

 Denver area during 2005, 2006 and 2007 and 

 2005-2007 8-hour ozone Design Values that is 

 used as the current-year Design Value (DVC) 

 starting point for the 2010 8-hour ozone projections........................................... 2-3 

Table 2-2. Summary of 2006 and 2010 base case VOC, NOx and 

 CO emissions in Colorado for July 21-23, 2006 ................................................. 2-4 

Table 2-3. Current-year (DVC) and projected future-year (DVF) 

 8-hour ozone Design Values using the CAMx 2006 and 

 2010 base case modeling results.......................................................................... 2-5 

Table 2-4. Description of 2010 sensitivity tests performed using the 

 Denver CAMx 12/4 km modeling system ......................................................... 2-11 

Table 2-5. Results of 2010 sensitivity tests......................................................................... 2-13 

Table 3-1. Source apportionment source groups for Denver SIP 2010 modeling ................ 3-7 

Table 3-2. Source apportionment source regions for Denver SIP 2010 modeling................ 3-7 

FIGURES 

Figure ES-1. Current-year interpolated 8-hour ozone Design 

 Values (DVC; left) and projected future-year 8-hour 

 ozone Design Values (DVF; right) for the 2010 base case simulation..............ES-3 

Figure ES-2a. Rocky Flats North source apportionment for 29 July 

 including boundary conditions...........................................................................ES-9 

Figure ES-2b. Rocky Flats North source apportionment for 29 July 

 excluding boundary conditions..........................................................................ES-9 

Figure ES-2c. Rocky Flats North source apportionment for 29 July 

 attributable to anthropogenic NOx emissions..................................................ES-10 

Figure ES-2d. Rocky Flats North source apportionment for 29 July 

 attributable to anthropogenic and biogenic VOC emissions............................ES-10 
September 2008 

iii 

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

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

 domains that are nested in the MM5 red line domains ........................................ 1-2 

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

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

Figure 2-1. Difference plots in daily maximum 8-hour ozone 

 concentrations between the 2010 and 2006 base case 

 CAMx simulations for July 29 (top left), June 27 (top right), 

 June 28 (bottom left) and June 12 (bottom right), 2006 ...................................... 2-6 

Figure 2-2. 2010 minus 2006 base case emissions difference plots 

 for NOx (left) and VOC....................................................................................... 2-7 

Figure 2-3a. Current-year 8-hour ozone Design Values (DVC) interpolated 

 by the MATS tool ................................................................................................ 2-8 

Figure 2-3b. Projected 2010 8-hour ozone Design Values (DVF) 

 generated by the MATS tool for the 2010 base 

 case emissions scenario........................................................................................ 2-9 

Figure 3-1. Source apportionment source regions in 12km CAMx domain........................... 3-7 

Figure 3-2. Source apportionment source regions in 4km CAMx domain............................. 3-8 

Figure 3-3a. Rocky Flats North source apportionment for 29 July including 

 boundary conditions........................................................................................... 3-10 

Figure 3-3b. Rocky Flats North source apportionment for 29 July 

 excluding boundary conditions.......................................................................... 3-10 

Figure 3-3c. Rocky Flats North source apportionment for 29 July 

 attributable to anthropogenic NOx sources........................................................ 3-11 

Figure 3-3d. Rocky Flats North source apportionment for 29 July 

 attributable to anthropogenic VOC sources....................................................... 3-11 

Figure 3-3a. Fort Collins West source apportionment for 29 July including 

 boundary conditions........................................................................................... 3-12 

Figure 3-3b. Fort Collins West source apportionment for 29 July excluding 

 boundary conditions........................................................................................... 3-12 

Figure 3-3c. Fort Collins West source apportionment for 29 July attributable 

 to anthropogenic NOx sources........................................................................... 3-13 

Figure 3-3d. Fort Collins West source apportionment for 29 July attributable 

 to anthropogenic VOC sources .......................................................................... 3-13 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-1 

EXECUTIVE SUMMARY 

Due to violations of the 0.08 parts per million (ppm) 8-hour ozone National Ambient Air Quality 

Standard (NAAQS) based on 2005-2007 air quality data, in November 2007 the Denver 

Metropolitan Area (DMA) reverted to an 8-hour ozone nonattainment area. This requires the 

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

will achieve the 0.08 ppm 8-hour ozone NAAQS by 2010. The Denver Regional Air Quality 

Council (RAQC), in consultation with the Colorado Department of Health and Environment 

(CDPHE) Air Pollution Control Division (APCD), contracted with ENVIRON International 

Corporation and their subcontractor Alpine Geophysics, LLC to develop the photochemical 

modeling databases necessary to demonstrate that the DMA will achieve the 0.08 ppm 8-hour 

ozone NAAQS by 2010. 

OVERVIEW OF APPROACH 

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

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

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

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

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

performed. A preliminary model performance evaluation was conducted and diagnostic 

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

formation in the DMA (Morris et al., 2008b). A revised final CAMx 2006 base case (Run 17) 

simulation was performed and a comprehensive model performance evaluation was conducted 

(Morris et al., 2008c). Although there were some model performance issues on some of the 

modeling days during the June-July 2006 episode, usually due to an ozone underestimation bias, 

on a vast majority of the modeling days the ozone model performance achieved EPA’s model 

performance goals that along with the other model performance metrics indicated that the model 

was simulating the observed ozone sufficiently well for use in making ozone projections. 

Furthermore, on most days the model reproduced the observed VOC/NOx ratios in Denver quite 

well suggesting that the model is simulating the same chemical regimes as observed as well. 

2010 BASE CASE OZONE PROJECTIONS 

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

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

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

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

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

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

DVF = DVC x RRF 

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

ozone Design Values from the 2005-2007 period (i.e., the three year average of the fourth 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-2 

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 that the two year 

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

2007 for FTCW. 

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 described above. 

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

Flats North (RFNO) and Fort Collins West (FCTW) monitoring sites (see column 5 in Table ES1). As this value is 84 ppb or lower, then the 2010 base case modeling results pass the modeled 

attainment demonstration test. However, because the maximum projected 8-hour ozone Design 

Values lie between 82 and 87 ppb, then a WOE analysis is required. Although the EPA 8-hour 

ozone projection procedure is to truncate the final projected DVF for comparisons with the 

NAAQS, in column 6 of Table ES-1 we present the DVFs to the nearest tenth of a ppb before 

truncation. In this 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 modeled days is 

satisfied using the Denver June-July 2006 modeling period. In order to achieve that many 

modeled days, the cut-off threshold had to be reduced from 74 ppb to 78 ppb depending on the 

monitor, with the RFNO and FTCW monitors using a 78 and 76 ppb thresholds, respectively. 

The level of ozone reductions in the projected Design Values appears to be greater the further 

away from central Denver the monitor resides. In fact, ozone is estimated to increase very 

slightly at the monitors in or immediately downwind of the urban core. This is due to the 

reductions in on-road mobile sources NOx emissions that increase ozone in the urban core. The 

ozone increases are due to less ozone titration due to reduction in the primary emitted NOx 

emissions and/or less inhibition effect that high NOx concentrations have on ozone formation. 

As one moves away from the Denver urban core, the ozone increases between 2006 and 2010 

turn into no change and then to ozone decreases. The distance from the Denver urban core when 

the ozone increases change to ozone decreases varies by day due to changes in emissions (e.g., 

weekday versus weekend day) and changes in meteorology. The RFNO monitor lies near the 

modeled ozone increase-to-decrease cross over distance, which explains why the model 

projected 2010 Design Value is relative insensitive to the changes in emissions from 2006 to 

2010 at this site (85.0 to 84.9 ppb, a 0.1 ppb reduction); of the 10 days used to construct the RRF 

for RFNO there are some days of ozone increases and some with ozone decreases. At the FTCW 

monitoring site, on the other hand, the model is more responsive (1.1 ppb ozone reduction) as it 

is an area where the modeled ozone changes either stay the same or are reduced between 2006 

and 2010. 

Figure ES-1 display the results of EPA’s unmonitored area analysis for the 2010 base case. 

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 (Figure ES-1, left). In fact, the unmonitored area 

procedure estimates that there are current-year DVCs in excess of the 85 ppb NAAQS occurring 

in 12 grid cells to the west of the Fort Collins monitoring sites. 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 occurring to the south, west and northwest of Denver and the 12 cells with DVCs exceeding 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-3 

the 85 ppb NAAQS have been reduced by half to 6 grid cells in the 2010 base case emissions 

scenario. EPA stresses that the unmonitored area analysis is much more uncertain than the 

modeled attainment test at the monitors. And whereas additional emissions controls would likely 

be needed to eliminate continued violations at the monitor, such actions may not be appropriate 

for the unmonitored area analysis. 

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

using the CAMx 2006 and 2010 base case modeling results. 

2005-07 2010 Base Case 

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

80013001 Welby Adams 70.0 70 70.2 1.0042 77.0 11 

80050002 Highland Arapahoe 78.0 77 77.3 0.9916 78.0 14 

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

80310002 Denver - CAMP Denver 56.0 56 56.0 1.0017 78.0 10 

80310014 Carriage Denver 74.0 74 74.1 1.0022 78.0 10 

80350004 Chatfield State Park Douglas 84.0 83 83.4 0.9934 78.0 11 

80410013 USAF Academy El Paso 73.0 72 72.0 0.9873 75.0 10 

80410016 Manitou Springs El Paso 74.0 73 73.7 0.9966 74.0 10 

80590002 Arvada Jefferson 79.0 79 79.2 1.0026 78.0 10 

80590005 Welch Jefferson 75.0 75 75.0 1.0004 78.0 10 

80590006 Rocky Flats North Jefferson 85.0 84 84.9 0.9994 78.0 10 

80590011 NREL Jefferson 82.0 82 82.3 1.0039 78.0 11 

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

80691004 Fort Collins Larimer 74.0 73 73.0 0.9878 76.0 12 

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

GTH161 Gunnison Gunnison 68.0 67 67.8 0.9984 74.0 10 

ROM206 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 

ROM406 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 

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

future-year 8-hour ozone Design Values (DVF; right) for the 2010 base case simulation. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-4 

2010 SENSITIVITY TEST RESULTS 

Sixteen (16) 2010 emissions reductions sensitivity tests were conducted with the CAMx 

modeling system. Most of these emission reduction sensitivity tests reduced VOC and/or NOx 

emissions from a specific source category either just within the Denver nonattainment area 

(NAA) or within the entire state of Colorado. Ozone projections were made at each of the 

monitoring sites for each of the 2010 sensitivity tests. We also performed the unmonitored area 

analysis for each sensitivity test to better understand the spatial extent of any ozone benefits or 

adverse effects. All sensitivity tests modified emissions from the 2010 base case emissions 

scenario. 

Table ES-2 displays the results of the 2010 sensitivity tests in terms of VOC, NOx and CO 

emission reductions from the 2010 base case, changes in projected 8-hour ozone Design Values 

at the key RFNO and FTCW monitoring sites, maximum difference in 2010 8-hour ozone 

Design Values anywhere in the DMA and maximum difference in daily maximum 8-hour ozone 

concentrations anywhere in the DMA and on any of the modeling days. 

Mobile Source Emissions: The first three sensitivity tests examined the sensitivity of 2010 

ozone projections to on-road mobile source emissions. Reducing on-road mobile sources VOC 

emissions 20% in the DMA reduces the projected DVFs at RFNO and FTCW by 0.2 and 0.1 

ppb, respectively. The 7 psi RVP gasoline in on-road mobile source gasoline vehicles reduces 

the DVFs by 0.1 ppb at both monitors. And the zero percent ethanol penetration scenario in the 

on-road and non-road mobile source gasoline engines increases the DVF at RFNO by 0.1 ppb, 

and has no effect at FTCW. 

Oil and Gas VOC Emissions: VOC emissions from O&G sources in the NAA were reduced by 

20% (b1-sens04) and 40% (b1-sens04d) in two of the 2010 emissions sensitivity tests. The O&G 

VOC emission reductions had little effect at the RFNO monitor, but reduced the projected DVF 

at the FTCW monitor by 0.1 and 0.2 ppb, respectively. The spatial maps of differences in the 

DVFs show a large area of ozone benefits due to the O&G VOC reductions centered on the 

O&G production area in Weld County. The RFNO monitor is right at the edge of this benefits 

area. Note that the Denver EAC SIP modeling of the June-July 2002 episode saw more transport 

from the Weld County O&G production area down to the RFNO monitor, so these results are 

partly an artifact of the meteorological conditions of the June-July 2006 modeling period. The 

O&G VOC emissions clearly have an effect on ozone formation in the Fort Collins area. In fact, 

the 6 grid cells west of Fort Collins that are projected to still violate the 0.08 ppm 8-hour ozone 

NAAQS in the 2010 base case (Figure ES-1, right) are reduced to 4 and 3 grid cells in the 20% 

and 40% O&G VOC emission reduction sensitivity scenarios. Clearly VOC emission reductions 

from O&G sources in Weld County would benefit ozone attainment in the Fort Collins area and 

likely elsewhere in the Denver NAA under other meteorological conditions. 

Combined VOC & NOx Sensitivity Simulations: Sensitivity simulations b1-sens04b and b1-

sens04c looked at combined VOC and NOx emissions reductions from area, non-road point and 

O&G emissions in the NAA. Although both simulations reduced VOC emissions by 20%, NOx 

emissions were reduced by 20% in sens04b and by 30% in sens04c allowing us to isolate the 

effects of the NOx controls. Several of the other sensitivity tests also allow us to isolate the 

effects of the VOC and NOx controls in these two sensitivity tests for each source category. The 

b1-sens04b 20% VOC/NOx emissions reduction scenario reduces the DVF at RFNO by 0.5 ppb. 

This is due to reductions in the RFNO ozone DVF of approximately 0.1 ppb from area source 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-5 

VOC (b1-sens07), 0.1 ppb from O&G VOC (b1-sens04), 0.2 ppb from non-road VOC (b1-

sens06) and 0.2 ppb from point and O&G source NOx (b1-sens05). An additional 0.2 ppb ozone 

reduction in the RFNO DVF is obtained when the NOx reduction is increased from 20% to 30%. 

At the FTCW monitor, the effects of the NOx emission reductions alone are even greater. The 

20% VOC/NOx reduction gives a 1.1 ppb reduction in the ozone DVF at the FTCW monitor; 

increasing the NOx reduction by another 10% increases the ozone reduction at the FTCW 

monitor by another 0.5 ppb (total 1.6 ppb reduction). This suggests that a majority of the ozone 

benefits at FTCW are due to the NOx emission reductions. Although as noted above, VOC 

emission reductions from O&G sources in the NAA are also beneficial for reducing ozone in the 

Forth Collins area. With the exception of a couple grid cells of isolated ozone increases, the 

effects of the combined VOC/NOx controls are wide-spread reductions in ozone throughout the 

DMA. 

State-Wide Sensitivity: The state-wide sensitivity tests produce nearly the same ozone benefits 

at DMA monitors as the controls in the NAA alone. This is seen most clearly by comparing b1-

sens05 with b1-sens08 that examine a 20% reduction in NOx emissions from point and O&G 

sources in, respectively, the NAA and Colorado. They produce the same ozone reduction at 

RFNO (0.2 ppb) and the state-wide reduction produces slightly more ozone reduction at FTCW 

(0.6 ppb) than the NAA controls alone (0.5 ppb). At this time we have only evaluated the effects 

of the state-wide emission reduction sensitivity tests within the DMA. There are likely more 

ozone benefits due to the Colorado state-wide emission reductions outside of the DMA that may 

be important given the new lower (March 2008) ozone NAAQS. 

Bark Beetle Sensitivity: The effects of accounting for the Bark Beetle infestation on biogenic 

emissions have small effects on the DVFs in the DMA (0.1 ppb reduction). Thus, the 2010 

Denver ozone projections are not affected by the Bark Beetle infestation. 

The 2010 emissions sensitivity tests show higher ozone sensitivity to reducing NOx emissions 

than reducing VOC emissions. Although there are small areas of ozone increases due to NOx 

emissions reductions in the Denver urban core, and at the locations (grid cells) of some point 

sources, the overall ozone reduction benefits of the NOx controls outweigh the ozone increases. 

Furthermore, the locations of the highest ozone increases due to NOx reductions are monitoring 

sites with low ozone concentrations. Although the ozone benefits of VOC reductions do not 

seem as great as those from NOx reductions, VOC emissions reductions do reduce ozone 

somewhat and do not exhibit any ozone increases as seen with the NOx emissions reductions. In 

particular, the VOC emissions reductions from O&G sources have ozone benefits in the Fort 

Collins area and particular the key FTCW ozone monitor. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 

Table ES-2. Results of the Denver 2010 emission sensitivity tests.

Emissions (TPD) % Anthro (%) 

DV Ozone 

(PPB) 

G

Ozo

Test Description CO VOC NOx CO VOC NOx RFNO FTCW Ma

2006.a3 

Current Year 8-Hour Ozone Design Value 85 86 

b1 2010 Base Case -386.0 -42.2 -50.1 -10.2% -5.3% -5.6% 84.9 84.9 b1-sns01 20% VOC On-Road NAA 0.0 -22.8 0.0 0.0% -3.0% 0.0% -0.2 -0.1 0.1 b1-sns02 

Evap VOC On-Road in NAA (7 psi RVP) -46.9 -9.8 -0.3 -1.4% -1.3% 0.0% -0.1 -0.1 0.1 

b1-sns03 0% Ethanol in NAA 323.3 -3.8 -2.0 9.5% -0.5% -0.2% 0.1 0.0 0.4 b1-sns04 20% VOC O&G in NAA 0.0 -48.2 0.0 0.0% -6.4% 0.0% 0.0 -0.1 0.0 b1-sns04b 

20% VOC & NOx Ar, Pnt, Non-Rd and O&G in NAA 0.0 -72.5 -41.3 0.0% -9.6% -4.9% -0.5 -1.1 1.8 

b1-sns04c 

20% VOC & 30% NOx Ar, Pnt, Non-Rd, O&G in NAA 0.0 -72.5 -62.0 0.0% -9.6% -7.4% -0.7 -1.6 2.8 

b1-sns04d 40% VOC O&G in NAA 0.0 -96.3 0.0 0.0% -12.7% 0.0% -0.1 -0.2 0.1 b1-sns05 20% NOx Pnt & O&G NAA 0.0 0.0 -20.6 0.0% 0.0% -2.5% -0.2 -0.5 0.3 b1-sns06 20% VOC Non-Rd in NAA 0.0 -12.7 0.0 0.0% -1.7% 0.0% -0.2 -0.1 0.0 b1-sns07 20% VOC Area in NAA 0.0 -7.5 0.0 0.0% -1.0% 0.0% -0.1 -0.1 0.0 b1-sns08 20% NOx Pnt & O&G CO 0.0 0.0 -78.0 0.0% 0.0% -9.3% -0.2 -0.6 1.1 b1-sns09 20% VOC O&G in CO 0.0 -67.2 0.0 0.0% -8.9% 0.0% 0.0 -0.1 0.1 b1-sns10 

20% VOC & NOx Point & O&G in CO 0.0 -77.5 -78.0 0.0% -10.2% -9.3% -0.3 -0.6 0.9 

b1-sns11 

20% NOx Point & O&G in NAA + 20% NOx Pawnee 0.0 0.0 -23.0 0.0% 0.0% -2.7% -0.2 -0.5 0.3 

b1-sns12a 

Effects of increase in Bark Beetle 2006 to 2010 -8.4 -87.8 -0.3 -0.2% -11.6% 0.0% 0.0 -0.1 0.1 

b1-sns12b 

Effects of 2010 Bark Beetle infestation -21.1 -233.5 -0.8 -0.6% -30.8% -0.1% -0.1 -0.1 0.1 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-7

2010 OZONE SOURCE APPORTIONMENT MODELING 

The Anthropogenic Precursor Culpability Assessment (APCA) version of the CAMx ozone 

source apportionment was applied using the 2010 base case inventory with the emissions 

segregated into 8 source categories and 11 source regions. The source categories are presented 

in Table ES-3 and the geographic source regions are given in Table ES-4. Ozone source 

apportionment is obtained for each source group, which consist of a source region and source 

category (e.g., on-road mobile sources from the 7-County Denver Metro area). As the 

contributions of ozone from initial concentrations (IC) and boundary conditions (BC) are always 

obtained, this results in ozone source apportionment to 90 separate source groups in the Denver 

ozone source apportionment modeling (90 = 8 x 11 + 2). 

The CAMx ozone source apportionment uses reactive tracers that operate in parallel to the host 

model. For each source group, there are four tracers corresponding to the source group’s VOC 

and NOx concentrations (Vi and Ni) and ozone formed that is attributable to the source groups 

VOC concentrations (O3Vi) or NOx concentrations (O3Ni). In the original Ozone Source 

Apportionment Technology (OSAT) ozone source apportionment approach implemented in 

CAMx, when ozone is formed in a grid cell it is attributable to a source group based on the 

relative contributions of the source groups VOC or NOx concentration to the total VOC or NOx 

concentration in that grid cell based on a determination of whether the ozone formed was under 

VOC-limited or NOx-limited conditions. Thus, in OSAT the O3V and O3N reactive tracers 

indicate how much of the ozone is formed under VOC-limited versus NOx-limited conditions. 

This results in OSAT assigning ozone to biogenic VOCs, which is not necessarily control 

strategy relevant information as they are uncontrollable. The APCA version of source 

apportionment only assigns ozone formed to biogenic (uncontrollable) sources when it is due to 

the interaction of biogenic VOC with biogenic NOx. When ozone is formed under VOC-limited 

conditions due to the interaction of biogenic VOC with anthropogenic NOx, a case where OSAT 

would assign it to the biogenic VOC (O3V) source group, APCA redirects the assignment to the 

anthropogenic NOx (O3N) source group. Thus, with APCA the O3V and O3N tracers no longer 

represent ozone formed under VOC-limited and NOx-limited conditions. 

The source apportionment results were analyzed at each of the ozone monitor sites in the DMA. 

At each monitor location, for each day, the 8-hour average ozone results for each period over 70 

ppb were averaged to develop a composite contribution. 

Example displays for a high ozone day (July 29th) at the Rocky Flats North monitor are presented 

in Figure ES-2. APCA ozone source apportionment modeling results for other days and other 

monitors are presented in Appendix C. The results show significant day-to-day and monitor-tomonitor variations. Figure ES-2a presents the ozone results including the boundary conditions, 

that is, the contribution from sources outside the 12 km domain. Of the 76.1 ppb of ozone 

estimated at the monitor, ~48 ppb (two-thirds) was transported into the 12 km domain and ~18 

ppb (one-third) was attributed to sources in the seven-county Denver Metro area. Figure ES-2b 

presents the same results as ES-2a, but without the boundary conditions plotted and the vertical 

scale expanded to better resolve the source region contributions. This figure shows that of the 

~18 ppb from Metropolitan Denver sources, ~10 ppb was from motor vehicles, ~5 ppb was from 

non-road mobile sources with the balance from other sources. Figure ES-2c presents the ozone 

formed that is attributable to anthropogenic NOx concentrations, whereas Figure ES-2d presents 

the ozone formed attributable to anthropogenic and biogenic VOC concentrations. These two 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-8

figures suggest that emission reductions from anthropogenic NOx sources will be more effective 

at reducing ozone in the model than reductions from anthropogenic VOC sources, although both 

VOC and NOx controls will reduce ozone. The Fort Collins West monitor shows similar 

contributions as the Rocky Flats North monitor except the highest contributions are from sources 

in the Larimer/Weld County source region and oil and gas sources from Larimer/Weld county 

have a large contribution. 

The source apportionment results vary by day and by location. However, several overall trends 

emerge, namely: 

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

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

• At the Denver Metropolitan monitors the largest contributors are Denver Metropolitan 

metro area motor vehicle and non-road sources; 

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

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

Metropolitan sources; 

• The majority of the ozone formed is attributable to anthropogenic NOx emissions. 

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

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

For instance, the source apportionment modeling in support of the Denver Early Action Compact 

using a 2002 ozone episode showed more impact of sources in Northern Colorado into the 

Denver Metropolitan area. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-9

Figure ES-2a. Rocky Flats North source apportionment for 29 July including boundary 

conditions. 

Figure ES-2b. Rocky Flats North source apportionment for 29 July excluding boundary 

conditions. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-10

Figure ES-2c. Rocky Flats North source apportionment for 29 July attributable to 

anthropogenic NOx emissions. 

Figure ES-2d. Rocky Flats North source apportionment for 29 July attributable to 

anthropogenic and biogenic VOC emissions. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Exec_Sum1.doc August 2008 ES-11

CONCLUSIONS OF 2010 OZONE PROJECTIONS AND 

EMISSIONS SENSITIVITY TESTS 

The 2010 emissions reduction sensitivity tests and 2010 ozone source apportionment modeling 

provide consistent results. The source apportionment modeling estimates that when daily 

maximum 8-hour ozone concentrations are greater than 70 ppb then approximately two-thirds of 

the ozone in the DMA is coming from outside of the Denver 12 km modeling domain (roughly 

outside of Colorado and adjacent states). Most of the remainder one-third of the ozone comes 

from sources within the Denver 9-county NAA. For the Rocky Flats North monitoring site on 

July 29, 2006, the 2010 ozone source apportionment results suggest that half of the locally 

generated ozone comes from on-road mobile sources, with ~1/4 from non-road mobile source, 

1/8 from EGU point sources and the remainder 1/8 from area, non-EGU and oil and gas (O&G) 

sources from the 7-County Denver area. For the Forth Collins West monitoring sites a similar 

breakdown in source categories is seen only sources from Larimer/Weld Counties contribute 

more than sources from the 7-County DMA and O&G emissions from Larimer/Weld Counties 

are major contributors as well. 

The APCA ozone source apportionment attributes most of the ozone formed to anthropogenic 

NOx emissions rather than anthropogenic and biogenic VOC emissions. This suggests that 

anthropogenic NOx control may be a viable path toward reducing ozone concentrations. The 

2010 sensitivity modeling also suggests that NOx emissions reductions are effective at reducing 

ozone concentrations. However, the 2010 emissions sensitivity tests also saw areas where the 

NOx emission reductions resulted in ozone increases. These areas include isolated grid cells at 

the locations of some point sources and within the Denver urban core. The extent of the ozone 

increases due to the NOx controls in the Denver urban core varied day-to-day due to changes in 

emissions (e.g., weekday versus weekend day) and meteorology. However, the overall benefits 

for reducing ozone from the NOx controls out weigh the adverse effects of the ozone increases, 

although care should be taken in the level and types of NOx emissions controlled to limit the 

adverse effects. Although the VOC emission reductions do not produce as large ozone reduction 

as the NOx controls at some key sites (e.g., Fort Collins West), they always reduce ozone or 

have no effect and no adverse effects of VOC emissions reductions are seen. 

Thus, an ozone reduction path using either NOx and/or VOC emission reductions appear to be a 

viable paths in the Denver area. The VOC emission reductions always reduce ozone or have no 

or very little effect. Although the ozone reductions due to the NOx controls are larger and more 

widespread, there are also local ozone increases due to the NOx controls that need to be 

considered. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec1_2010_Intro1.doc August 2008 1-1 

1.0 INTRODUCTION 

1.1 BACKGROUND 

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

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

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

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

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

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

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

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

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

violated the 0.08 ppm 8-hour ozone NAAQS, so in November 2007 the DMA reverted to an 8-

hour ozone nonattainment area and is required to prepare an 8-hour ozone State Implementation 

Plan (SIP) that demonstrates attainment by 2010. The contracting team of ENVIRON 

International Corporation, and their subcontractor Alpine Geophysics, LLC, were selected by the 

RAQC and CDPHE to perform the 2010 8-hour ozone attainment demonstration modeling for 

the new SIP. 

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

the 0.08 ppm 8-hour ozone NAAQS, but lowers the threshold from 0.08 ppm (85 ppb) to 0.075 

ppm (75 ppb). Of the ~14 ozone monitors in the greater DMA, half have 2005-2007 8-hour 

ozone DVs that are 75 ppb or higher. The current Denver 8-hour ozone SIP modeling effort 

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

addressed in the future. 

1.2 PURPOSE 

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

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

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

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

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

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

ENVIRON/Alpine Modeling Team consists of the following activities: 

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

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

HourOzoneNov282007.pdf); 

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

2008a); 

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

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

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

the DMA (Morris et al., 2008b); 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec1_2010_Intro1.doc August 2008 1-2 

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

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

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

modeling (this document); and 

• 2010 control strategy modeling (in progress). 

1.3 OVERVIEW OF MODELING APPROACH 

Figure 1-1a displays the MM5 (red) and CAMx (blue) 36/12/4 km modeling domains used in the 

Denver 8-hour ozone modeling study. The CAMx model was first applied to the 36 km 

continental U.S. domain using boundary conditions (BCs) from a global climate air quality 

model (Figure 1-1a). The CAMx 2006 and 2010 base case modeling results from the 36 km 

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

domain (Figure 1-1b) and the, respectively, 2006 12/4 km base case and 2010 12/4 km base case 

and sensitivity simulations. The CAMx simulations for the 12/4 km domains were run using 

two-way interactive grid nesting (i.e., pollutants can flow back and forth between the 12 km and 

4 km domains to account for recirculation). 

-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.
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec1_2010_Intro1.doc August 2008 1-3 

-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

Denver CAMx 12 and 4 km Domain

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

emissions modeling.

1.4 2010 EMISSIONS MODELING APPROACH 

The 2010 base case emissions were prepared using the same procedures as used to prepare the 

final 2006 base case emissions scenario (Morris et al., 2008b). The CDPHE/APCD provided 

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

the Denver-Julesburg Basin for which 2010 emissions from the WRAP Phase III O&G emissions 

development project were utilized (Bar-Ilan et al., 2008b). Outside of Colorado the 2010 

anthropogenic emissions were based on the WRAP 2002 and 2018 emissions inventories. 

CAMx-ready emissions were generated using the Sparse Matrix Operator Kernel Emissions 

(SMOKE) emissions modeling system (Coats, 1996) for all anthropogenic emissions categories 

except on-road mobile sources in the DMA, which used the Consolidated Community Emissions 

Processing Tool (ConCEPT) modeling system (Loomis et al., 2005). The same biogenic 

emissions were used for the 2010 base case as were used for the final 2006 base case biogenic 

emissions were based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) 

biogenic emissions model (Guenther and Wiedinmyer, 2004). Emissions from fires were also 

kept constant between the 2006 base case and 2010 base case emission scenarios. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-1 

2.0 2010 OZONE PROJECTIONS 

2.1 INTRODUCTION 

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

2010 emission sensitivity scenarios. These projections are made using the CAMx modeling 

results for the 2006 base case (Morris et al., 2008b,c) and the 2010 base case and emission 

sensitivity scenarios. The EPA Modeled Attainment Test Software (MATS) tool was used to 

make the 2010 8-hour ozone Design Value projections. 

2.2 OZONE PROJECTION PROCEDURES 

The EPA modeling guidance for 8-hour ozone attainment demonstration modeling contain 

specific procedures that use current-year and future-year modeling results in a relative fashion to 

scale current-year observed 8-hour ozone Design Values to project future-year 8-hour ozone 

Design Values for comparisons with the NAAQS (EPA, 2007). The EPA guidance projection 

procedures were used to estimate 2010 8-hour ozone Design Values for the 2010 base case and 

2010 sensitivity simulations. If the future-year Design Value for a monitor is less than or equal 

to 84 ppb, the modeled attainment test is passed. If the future-year Design Value is greater than 

or equal to 85 ppb, the modeled attainment test is not passed. If the future-year Design Value 

lies between 82 and 87 ppb, a weight of evidence (WOE) determination is required that provides 

corroborative information that attainment will be achieved in the future-year. 

The EPA guidance procedure for projecting future-year 8-hour ozone Design Values has been 

codified in EPA’s Modeled Attainment Test Software (MATS; 

http://www.epa.gov/ttn/scram/modelingapps_mats.htm). This procedure starts with a currentyear observed 8-hour ozone Design Value (DVC) for each monitor. The modeling results are 

then used to scale the observed 8-hour ozone DVC to obtain a future-year 8-hour ozone Design 

Value projection (DVF). This is done through the calculation of model-estimated relative 

response factors (RRFs) that are the ratio of the model-estimated 8-hour ozone concentrations for 

the future-year to current-year emission scenarios. The RRF is monitor-specific and is used to 

scale the current year observed design value (DVC) to estimate the projected future-year 8-hour 

ozone design value (DVF): 

DVF = DVC x RRF 

The RRF is defined as the ratio of the average of the maximum 8-hour ozone concentrations 

“near a monitor” for the future-year emissions scenario to the average for the current year base 

case emissions scenario. The EPA default definition of “near a monitor” is to select the 

maximum model-estimated daily maximum 8-hour ozone concentrations from an array of grid 

cells centered on the monitor. The size of the array of grid cells centered on the monitor is grid 

cell size dependent and for the 4 km grid cell resolutions used in the Denver modeling, EPA 

recommends use of an array of 7 x 7 grid cells centered on the monitor (EPA, 2007). 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-2 

EPA’s 8-hour ozone modeling guidance includes the following language for selecting the 

current-year observed 8-hour ozone design values that are used in the modeled attainment 

demonstration test: 

“For the modeled attainment tests we recommend using the average of the three design 

value periods which include the baseline inventory year...The average of the three design 

value periods best represents the baseline concentration, while taking into account the 

variability of meteorology and emissions (over a five year period).” (EPA, 2007, pg. 22). 

For the Denver modeling that used the 2006 baseline inventory and modeling year, that would 

mean the current year 8-hour ozone Design Value (DVC) would be based on the average of three 

years of Design Values from 2004-2006, 2005-2007 and 2006-2008. As the 2008 ozone season 

is not yet complete, the 2006-2008 8-hour ozone Design Values can not yet be calculated. We 

considered using the average of two years of Design Values from 2004-2006 and 2005-2007, but 

in that case none of the DVCs would be violating the 8-hour ozone NAAQS. Thus, we used the 

2005-2007 Design Value as the starting current-year Design Value (DVC) in the 2010 ozone 

projections for all monitors but one. This is appropriate as the 2005-2007 8-hour ozone Design 

Values are the very ones that resulted in Denver being declared an 8-hour ozone nonattainment 

area in November 2007. The one exception to this is for the Fort Collins West monitor that 

started operating in 2006 so a “2-year” 8-hour ozone Design Value will be used (i.e., average of 

fourth highest daily maximum 8-hour ozone concentrations from 2006 and 2007). Table 2-1 

displays the fourth highest daily maximum 8-hour ozone concentrations at monitors in the 

Denver area and the 2005-2007 Design Values that were used as the DVC starting point for the 

future-year ozone projections. The use of these DVCs was agreed to by RAQC, CDPHE and 

EPA early on in the process and was stated in the Modeling Protocol (Morris et al., 2007). 

EPA recommends that at least of 10 modeling days be included in the calculation of the RRFs 

and future-year design values with an absolute 5 day minimum. The criterion for using an 

episode day in calculating the episode average Design Value for that monitor is that the modeled 

daily maximum 8-hour ozone near the monitor exceeds a minimum threshold value. EPA 

recommends use of an 85 ppb threshold in the future-year 8-hour ozone Design Value 

calculations, but if insufficient number of days are available to calculate the RRFs then this 

threshold can be reduced by 1 ppb until sufficient modeling days are obtained, or until a 70 ppb 

floor is obtained. When the 70 ppb threshold floor is reached and there are less than 5 days 

available for calculating a RRF, then no RRF is calculated. For the Denver June-July 2006 

modeling, we were able to calculate RRFs for all monitors in the DMA using 10 days or more of 

modeling results and never achieved the 70 ppb threshold floor. 

In the final step of the modeled attainment test, the projected future-year 8-hour ozone Design 

Value is truncated to the nearest ppb and then compared with the NAAQS; if it is 84 ppb or 

lower at all monitors in the area then the modeled attainment test is passed. As noted above, 

even if the modeled attainment test is passed, if there are any projected 8-hour ozone Design 

Values above 82 ppb, then a weight of evidence (WOE) analysis is required that presents 

corroborative evidence that attainment would be achieved. Even if the modeled attainment test 

is not passed, if the projected future-year 8-hour ozone Design Values at all monitors are 87 ppb 

or lower, a WOE attainment demonstration may still be conducted. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-3 

Table 2-1. Fourth highest daily maximum 8-hour ozone concentrations (ppm) at monitoring 

sites in the Denver area during 2005, 2006 and 2007 and 2005-2007 8-hour ozone Design 

Values that is used as the current-year Design Value (DVC) starting point for the 2010 8-hour 

ozone projections. 

Site Name 

2005

4th Maximum 

8-Hour Average 

Value (ppm) 

2006

4th Maximum 

8-Hour Average 

Value (ppm) 

2007

4th Maximum 

8-Hour Average 

Value (ppm) 

2005 - 2007 

3-Year Average 

4th Maximum 

Value (ppm) 

Welby 0.073 0.069 0.070 0.070 

Highland 0.080 0.081 0.075 0.078 

S. Boulder Creek 0.076 0.082 0.085 0.081 

Denver – CAMP 0.051 0.062 0.057 0.056 

Carriage 0.074 0.072 0.076 0.074 

Chatfield State Park 0.084 0.086 0.082 0.084 

USAF Academy 0.077 0.072 0.071 0.073 

Manitou Springs 0.075 0.076 0.072 0.074 

Arvada 0.078 0.082 0.078 0.079 

Welch 0.064 0.081 0.080 0.075 

Rocky Flats North 0.077 0.090 0.090 0.085 

NREL 0.079 0.083 0.085 0.082 

Fort Collins – West --- 0.087 0.085 0.086* 

Fort Collins 0.076 0.078 0.069 0.074 

Greeley – Weld Tower 0.078 0.082 0.074 0.078 

Rocky Mountains NP 0.075 0.076 0.078* 0.076 

* Fort Collins West monitor started in 2006 so a 2-year average 4th maximum 8-hour ozone concentrations is used

EPA’s 8-hour ozone projection procedure also includes an unmonitored area analysis that has 

also been codified in MATS. The unmonitored area analysis uses the future-year 8-hour ozone 

Design Value projection procedure described above applied to each grid cell in the modeling 

domain. In this procedure, the current-year Design Values (DVC) are first interpolated to each 

grid cell in the modeling domain. This interpolation scheme uses the modeled concentration 

gradients in its interpolation procedures. RRFs are then obtained for each grid cell in the 

modeling domain using the procedures described above except using the actual modeled daily 

maximum 8-hour ozone concentrations in each grid cell (co-located) rather than values near the 

grid cell. The same rules are used to assure there are sufficient days to calculate a robust and 

reliable RRF. Namely, pick the highest days above a threshold value so that at least 10 modeling 

days are used in the RRFs by reducing the threshold from 85 ppb until the 70 ppb floor is 

reached. If with the 70 ppb floor there are 5 or more days the RRF is still used. However, for 

grid cells in which there are less than 5 modeling days with daily maximum 8-hour ozone 

concentrations greater than 70 ppb no RRF is calculated and consequently no 2010 projected 

DVF is obtained for that grid cell. 

2.3 OZONE PROJECTIONS FOR THE 2010 BASE CASE 

The EPA recommended procedures for projecting future year 8-hour ozone Design Values and 

the MATS tool were used with the CAMx 2006 and 2010 base case modeling results to project 

2010 8-hour ozone Design Values at monitors in the Denver area. Table 2-2 shows the total 

VOC, NOx and CO emissions in Colorado for the 2006 and 2010 base case and three 

representative days from the June-July 2006 modeling period (including a weekday and weekend 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-4 

days). The anthropogenic emissions are for the state of Colorado, whereas the biogenic 

emissions are for the 4 km grid domain, which matches the state of Colorado reasonably well 

(see Figure 1-1). The anthropogenic VOC, NOx and CO emissions are projected to be reduced 

by 5.3%, 3.3% and 10.1% between 2006 and 2010 on the weekday selected (July 21). When 

accounting for the presence of biogenic emissions, the percent reduction of NOx and CO 

emissions between 2006 and 2010 are reduced a little, but for the VOC emissions the 5.3% 

reduction in anthropogenic VOC emissions is reduced to 0.6% reduction when accounting for 

total emissions state-wide in Colorado. 

Table 2-2. Summary of 2006 and 2010 base case VOC, NOx and CO emissions in Colorado 

for July 21-23, 2006. 

Anthropogenic Biogenic 

2006 

Base 

2010 

Base 

Difference 

(TPD) 

Difference 

(%) (TPD) 

VOC (TPD) 

July 21 (Friday) 807.0 764.0 -43.0 -5.3% 3795.1 

July 22 (Saturday) 807.2 775.0 -32.2 -4.0% 4596.3 

July 23 (Sunday) 799.0 771.1 -27.8 -3.5% 4960.3 

NOx (TPD) 

July 21 (Friday) 862.6 833.8 -28.8 -3.3% 39.4 

July 22 (Saturday) 715.3 713.0 -2.3 -0.3% 42.4 

July 23 (Sunday) 704.4 699.1 -5.3 -0.7% 51.2 

CO (TPD) 

July 21 (Friday) 3840.2 3452.3 -388.0 -10.1% 575.1 

July 22 (Saturday) 4281.9 3979.4 -302.5 -7.1% 647.7 

July 23 (Sunday) 4284.6 4016.9 -267.7 -6.2% 722.6 

Table 2-3 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 described above. The 

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

North (RFNO) and Fort Collins West (FCTW) monitoring sites (see column 5). As this value is 

84 ppb or lower, then the 2010 base case modeling results pass the modeled attainment 

demonstration test. However, because the maximum projected 8-hour ozone Design Values lie 

between 82 and 87 ppb, then a WOE analysis is required. Although the EPA 8-hour ozone 

projection procedure is to truncate the final projected DVF for comparisons with the NAAQS, in 

column 6 we present the DVFs to the nearest tenth of a ppb before truncation. In this case we 

see that the projected 2010 base case DVFs at RFNO and FTCW are both 84.9 ppb. 

Also shown in Table 2-3 is the RRF and the cut-off threshold used in selecting days and number 

of days used in calculating the RRF. The EPA desire to use at least 10 modeled days is satisfied 

using the Denver June-July 2006 modeling period. In order to achieve that many modeled days, 

the cut-off threshold had to be reduced to 74 ppb to 78 ppb depending on the monitor, with the 

RFNO and FTCW monitors using a 78 and 76 ppb threshold, respectively. 

The level of ozone reductions in the projected Design Values appears to be greater the further 

away from central Denver the monitor resides. In fact, ozone is estimated to increase very 

slightly at the monitors in or immediately downwind of the urban core. This is due to the 

reductions in on-road mobile sources NOx emissions that increase ozone in the urban core. This 

ozone increase due to NOx emission reductions is due to less ozone titration from a reduction of 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-5 

the primary emitted NO emissions (NO + O3 Æ NO2 +O2) and/or less NOx inhibition effect on 

ozone formation that high NOx concentrations have as a termination step to the radical cycle 

(NO2 + OH Æ HNO3). This effect is seen in difference plots in daily maximum 8-hour ozone 

concentrations between the 2010 and 2006 base case simulations shown in Figure 2-1 for four 

days. These four days were selected because they were four common days out of the ~10 that 

were used in the 2010 Design Value projections for both the RFNO and FTCW monitoring sites. 

Most of the NOx emission reductions between the 2006 and 2010 base cases occur in the DMA, 

as shown in Figure 2-2. This is the area that experiences ozone increases from 2006 to 2010 

(Figure 2-1). As one moves away from the Denver urban core, the ozone increases between 

2006 and 2010 turn into no change and then to ozone decreases. The distance from the Denver 

urban core when the ozone increases change to ozone decreases varies by day due to changes in 

emissions (e.g., weekday versus weekend day) and changes in meteorology. The RFNO monitor 

lies near the modeled ozone increase-to-decrease cross over distance, which explains why the 

model projected 2010 Design Value is relative insensitive to the changes in emissions from 2006 

to 2010 at this site (85.0 to 84.9 ppb, a 0.1 ppb reduction); of the 10 days used to construct the 

RRF for RFNO there are some days of ozone increases and some with ozone decreases. This 

effect is seen in the ozone difference plots for four of the ten days used in developing the RRF 

for the RFNO monitoring site. At the FTCW monitoring site, on the other hand, the model is 

more responsive (1.1 ppb ozone reduction) as it is an area far enough away from the Denver 

urban core where the modeled ozone changes either stay the same or are reduced between 2006 

and 2010. 

Table 2-3. Current-year (DVC) and projected future-year (DVF) 8-hour ozone Design Values 

using the CAMx 2006 and 2010 base case modeling results. 

2010 Base Case 

Site ID Monitor Name County 

2005-07

DVC DVF DVF RRF Cutoff #days 

80013001 Welby Adams 70.0 70 70.2 1.0042 77.0 11 

80050002 Highland Arapahoe 78.0 77 77.3 0.9916 78.0 14 

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

80310002 Denver - CAMP Denver 56.0 56 56.0 1.0017 78.0 10 

80310014 Carriage Denver 74.0 74 74.1 1.0022 78.0 10 

80350004 Chatfield State Park Douglas 84.0 83 83.4 0.9934 78.0 11 

80410013 USAF Academy El Paso 73.0 72 72.0 0.9873 75.0 10 

80410016 Manitou Springs El Paso 74.0 73 73.7 0.9966 74.0 10 

80590002 Arvada Jefferson 79.0 79 79.2 1.0026 78.0 10 

80590005 Welch Jefferson 75.0 75 75.0 1.0004 78.0 10 

80590006 Rocky Flats North Jefferson 85.0 84 84.9 0.9994 78.0 10 

80590011 NREL Jefferson 82.0 82 82.3 1.0039 78.0 11 

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

80691004 Fort Collins Larimer 74.0 73 73.0 0.9878 76.0 12 

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

GTH161 Gunnison Gunnison 68.0 67 67.8 0.9984 74.0 10 

ROM206 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 

ROM406 Larimer Larimer 76.0 75 75.2 0.9903 77.0 10 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-6 

Figure 2-1. Difference plots in daily maximum 8-hour ozone concentrations between the 2010 

and 2006 base case CAMx simulations for July 29 (top left), June 27 (top right), June 28 

(bottom left) and June 12 (bottom right), 2006. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-7 

Figure 2-2. 2010 minus 2006 base case emissions difference plots for NOx (left) and VOC 

(right). 

Figure 2-3 displays the results of the 8-hour ozone DVF projections using the unmonitored area 

analysis from MATS. Figure 2-3a displays the interpolated fields of the current year Design 

Values (DVCs). 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 

procedures estimates that current-year DVCs in excess of the 85 ppb NAAQS occur in 12 grid 

cells to the west of the Fort Collins sites (Figure 2-3a). The projected DVFs for the 2010 base 

case (Figure 2-3b) have greatly reduced the spatial extent of the DVFs in excess of 80 ppb 

occurring to the south, west and northwest of Denver and the 12 cells with DVCs exceeding the 

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

scenario. 

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

at the monitors and it should be treated separately from the monitor based attainment test (EPA, 

2007). EPA further notes that while it is expected that additional emission controls are needed to 

eliminate predicted violations of the monitor based test, the same requirements may not be 

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

violations in the unmonitored area test be scrutinized and understood to determine whether they 

are likely to exist in the ambient air or whether they may be caused by an error or uncertainties in 

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

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

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

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

due to uncertainties in the modeling system can not be determined. However, the placement of 

the Fort Collins West monitor west of the original Fort Collins monitor in 2006 has found much 

higher observed ozone in the ambient air, it does not seems implausible that even higher values 

could exist even further west from Fort Collins. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-8 

Figure 2-3a. Current-year 8-hour ozone Design Values (DVC) interpolated by the MATS tool. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-9 

Figure 2-3b. Projected 2010 8-hour ozone Design Values (DVF) generated by the MATS tool 

for the 2010 base case emissions scenario.
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-10 

2.4 2010 SENSITIVITY TESTS 

Sixteen (16) 2010 emissions reductions sensitivity tests were conducted with the CAMx 

modeling system. Most of these emission reduction sensitivity tests reduced VOC and/or NOx 

emissions from a specific source category either just within the Denver nonattainment area 

(NAA) or within the entire state of Colorado. Ozone projections were made at each of the 

monitoring sites for each of the 2010 sensitivity tests. We also performed the unmonitored area 

analysis for each sensitivity test to better understand the spatial extent of any ozone benefits or 

adverse effects. Table 2-4 describes each of the sensitivity tests. All sensitivity tests modified 

emissions from the 2010 base case emissions scenario. 

The first three sensitivity tests examined the sensitivity of 2010 ozone formation to on-road 

mobile sources emissions within the Denver NAA. The first 2010 sensitivity test (b1-sens01) 

examined a 20% across-the-board reduction in VOC emissions from on-road mobile sources in 

the NAA. The second sensitivity test examined the effects of reducing evaporative VOC 

emissions from on-road mobile sources by specifying a baseline gasoline Reid Vapor Pressure 

(RVP) of 7 psi. Thus, with the assumed 85% ethanol market penetration in 2010 with a 1 psi 

waiver and a 7.8 psi RVP for the base case gasoline, this results in a reduction in the average 

RVP of gasoline in the Denver NAA from 8.65 psi in the 2010 base case to 7.85 psi in the b1-

sen02 2010 sensitivity case. The third mobile source sensitivity test assumed zero ethanol 

market penetration in the NAA and accompanying changes in on-road and non-road mobile 

gasoline engines’ VOC, NOx and CO emissions. 

The next 11 sensitivity tests listed in Table 2-4 (b1-sens04 to b1-sens11) are self explanatory 

with reductions in VOC and/or NOx from specifically identified source categories either just 

within the Denver NAA or throughout Colorado. 

The final two sensitivity tests were designed to assess the sensitivity that the Bark Beetle 

infestation would have on biogenic VOC emissions and projected 2010 ozone concentrations. 

The MEGAN biogenic emissions model was used to estimate the effects the Bark Beetle 

infestation would have on biogenic emissions. The 2006 and 2010 base case MEGAN biogenic 

emissions simulations assumed no Bark Beetle infestation. Estimates of the spatial extent of the 

Bark Beetle infestation from 2006 and 2010 were obtained from Dr. Christine Wiedinmyer of the 

National Center for Atmospheric Research (NCAR) and MEGAN was rerun assuming that 

biogenic emissions were reduced over the infestation areas to obtain two new sets of biogenic 

emission inputs accounting for the extent of Bark Beetle infestation in 2006 and 2010. The first 

Bark Beetle infestation sensitivity test was designed to determine whether the reductions in 

biogenic emissions due to the changes in Bark Beetle infestation between 2006 and 2010 would 

affect the 2010 ozone projections (b1-sens12a). This was accomplished by reducing biogenic 

emissions from the MEGAN no Bark Beetle simulation used in the 2006 and 2010 base case 

simulations by the reductions in the biogenic emissions estimates between the MEGAN 2006 

and 2010 Bark Beetle infestation emissions estimates. The second Bark Beetle sensitivity test 

was designed to determine whether the differences of with or without Bark Beetle effects on 

biogenic emission would affect ozone formation so used the MEGAN 2010 Bark Beetle 

infestation biogenic emission estimates with all other emissions identical to the 2010 base case 

simulation. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-11 

Table 2-4. Description of 2010 sensitivity tests performed using the Denver CAMx 12/4 km 

modeling system. 

Sens Test Description 

2006.a3 2006 base case and current year 8-hour Ozone Design Value (DVC) 

b1 2010 Base Case 

b1-sns01 20% reduction in VOC on-road mobile sources in NAA 

b1-sns02 Evaporative VOC on-road mobile sensitivity in NAA using 7 psi RVP gasoline 

b1-sns03 0% Ethanol penetration in NAA 

b1-sns04 20% reduction in VOC from O&G sources in NAA 

b1-sns04b 20% reduction in VOC & NOx from area, point, non-road and O&G sources in NAA 

b1-sns04c 20% VOC & 30% NOx reduction in area, point, non-road and O&G sources in NAA 

b1-sns04d 40% reduction in VOC from O&G sources in NAA 

b1-sns05 20% reduction in NOx from point & O&G sources in NAA 

b1-sns06 20% reduction in VOC from non-road mobile sources in NAA 

b1-sns07 20% reduction in VOC from area sources in NAA 

b1-sns08 20% reduction in NOx from point & O&G sources in Colorado 

b1-sns09 20% reduction in VOC from O&G sources in Colorado 

b1-sns10 20% reduction in VOC & NOx from point & O&G sources in Colorado 

b1-sns11 20% reduction in NOx from point & O&G in NAA + 20% reduction in NOx from Pawnee 

b1-sns12a Effects of increase in Bark Beetle infestation 2006 to 2010 

b1-sns12b Effects of 2010 Bark Beetle infestation 

Table 2-6 displays the results of the 2010 sensitivity tests in terms of VOC, NOx and CO 

emission reductions from the 2010 base case, changes in projected 8-hour ozone Design Values 

at the key RFNO and FTCW monitoring sites, maximum difference in 2010 8-hour ozone 

Design Values anywhere in the DMA and maximum difference in daily maximum 8-hour ozone 

concentrations anywhere in the DMA and on any of the modeling days. Projected 8-hour ozone 

Design Values for the 2010 sensitivity tests and all of the monitoring sites are given in Appendix 

A. Spatial maps of differences in the projected DVFs between the 2010 sensitivity simulations 

and the 2010 base case are shown in Appendix B. 

Mobile Source Emissions: Reducing on-road mobile sources VOC emissions 20% in the DMA 

reduces the projected DVFs at RFNO and FTCW by 0.2 and 0.1 ppb, respectively. The 7 psi 

RVP gasoline in on-road mobile source gasoline vehicles reduces the DVFs by 0.1 ppb at both 

monitors. And the zero percent ethanol penetration scenario in the on-road and non-road mobile 

source gasoline engines increases the DVF at RFNO by 0.1 ppb, and has no effect at FTCW. 

The spatial maps (Appendix B) show that the reductions in the DVF due to the 20% mobile 

sources VOC control are small, in the 0.05 to 0.5 ppb range across the DMA. The reductions for 

the 7 psi scenario are even smaller. And the ozone increases in the no ethanol scenario are 

comparable to the reductions in the 20% VOC mobile scenario. 

Oil and Gas VOC Emissions: VOC emissions from O&G sources in the NAA were reduced by 

20% (b1-sens04) and 40% (b1-sens04d) in two of the 2010 emissions sensitivity tests. The O&G 

VOC emission reductions had little effect at the RFNO monitor, but reduced the projected DVF 

at the FTCW monitor by 0.1 and 0.2 ppb, respectively. The spatial maps of differences in the 

DVFs show a large area of ozone benefits due to the O&G VOC reductions centered on the 

O&G production area in Weld County. The RFNO monitor is right at the edge of this benefits 

area. Note that the Denver EAC SIP modeling of the June-July 2002 episode saw more transport 

from the Weld County O&G production area down to the RFNO monitor, so these results are 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 2-12 

partly an artifact of the meteorological conditions of the June-July 2006 modeling period. The 

O&G VOC emissions clearly have an effect on ozone formation in the Fort Collins area. In fact, 

the 6 grid cells west of Fort Collins that are projected to still violate the 0.08 ppm 8-hour ozone 

NAAQS in the 2010 base case (Figure 2-3b) are reduced to 4 and 3 grid cells in the 20% and 

40% O&G VOC emission reduction sensitivity scenarios. Clearly VOC emission reductions 

from O&G sources in Weld County would benefit ozone attainment in the Fort Collins area and 

likely elsewhere in the Denver NAA under other meteorological conditions. 

Combined VOC & NOx Sensitivity Simulations: Sensitivity simulations b1-sens04b and b1-

sens04c looked at combined VOC and NOx emissions reductions from area, non-road point and 

O&G emissions in the NAA. Although both simulations reduced VOC emissions by 20%, NOx 

emissions were reduced by 20% in sens04b and by 30% in sens04c allowing us to isolate the 

effects of the NOx controls. Several of the other sensitivity tests also allow us to isolate the 

effects of the VOC and NOx controls in these two sensitivity tests for each source category. The 

b1-sens04b 20% VOC/NOx emissions reduction scenario reduces the DVF at RFNO by 0.5 ppb. 

This is due to reductions in the RFNO ozone DVF of approximately 0.1 ppb from area source 

VOC (b1-sens07), 0.1 ppb from O&G VOC (b1-sens04), 0.2 ppb from non-road VOC (b1-

sens06) and 0.2 ppb from point and O&G source NOx (b1-sens05). An additional 0.2 ppb ozone 

reduction in the RFNO DVF is obtained when the NOx reduction is increased from 20% to 30%. 

At the FTCW monitor, the effects of the NOx emission reductions alone is even greater. The 

20% VOC/NOx reduction gives a 1.1 ppb reduction in the ozone DVF at the FTCW monitor, 

increasing the NOx reduction by another 10% increases the ozone reduction at the FTCW 

monitor by another 0.5 ppb (total 1.6 ppb reduction). This suggests that a majority of the ozone 

benefits at FTCW are due to the NOx emission reductions. Although as noted above, VOC 

emission reductions from O&G sources in the NAA are also beneficial for reducing ozone in the 

Forth Collins area. With the exception of a couple grid cells of isolated ozone increases, the 

effects of the combined VOC/NOx controls are wide-spread reductions in ozone throughout the 

DMA (Appendix B). 

State-Wide Sensitivity: The state-wide sensitivity tests produce nearly the same ozone benefits 

at DMA monitors as the controls in the NAA alone. This is seen most clearly by comparing b1-

sens05 with b1-sens08 that examine a 20% reduction in NOx emissions from point and O&G 

sources in, respectively, the NAA and Colorado. They produce the same ozone reduction at 

RFNO (0.2 ppb) and the state-wide reduction produces slightly more ozone reduction at FTCW 

(0.6 ppb) than the NAA controls alone (0.5 ppb). At this time we have only evaluated the effects 

of the state-wide emission reduction sensitivity tests within the DMA. There are likely more 

ozone benefits due to the Colorado state-wide emission reductions outside of the DMA that may 

be important given the new lower (March 2008) ozone NAAQS. 

Bark Beetle Sensitivity: The effects of accounting for the Bark Beetle infestation on biogenic 

emissions have small effects on the DVFs in the DMA (0.1 ppb reduction). An examination of 

the difference plots in Appendix B shows small areas of ozone decreases in the DMA and small 

areas of ozone increases on the western slopes of the Rocky Mountains. This is because ozone 

formation in the DMA occurs under a mixture of VOC-limited and NOx-limited conditions, 

whereas ozone formation in the western slope is primarily NOx-limited. The Bark Beetle 

infestation reduces VOC emissions that in turn reduce ozone in the DMA under VOC-limited 

ozone formation conditions. However, over the western slope small ozone increases occur 

because of the reduction in biogenic VOC emissions which in turn reduce the reaction of olefin 

VOC species (e.g., isoprene) with ozone thereby increasing ozone concentrations slightly.
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec2_2010-DV1.doc August 2008 

Table 2-5. Results of 2010 sensitivity tests. 

Emissions (TPD) % Anthro (%) 

DV Ozone 

(PPB) 

G

Ozo

Test Description CO VOC NOx CO VOC NOx RFNO FTCW Ma

2006.a3 

Current Year 8-Hour Ozone Design Value 85 86 

b1 2010 Base Case -386.0 -42.2 -50.1 -10.2% -5.3% -5.6% 84.9 84.9 b1-sns01 20% VOC On-Road NAA 0.0 -22.8 0.0 0.0% -3.0% 0.0% -0.2 -0.1 0.1 b1-sns02 

Evap VOC On-Road in NAA (7 psi RVP) -46.9 -9.8 -0.3 -1.4% -1.3% 0.0% -0.1 -0.1 0.1 

b1-sns03 0% Ethanol in NAA 323.3 -3.8 -2.0 9.5% -0.5% -0.2% 0.1 0.0 0.4 b1-sns04 20% VOC O&G in NAA 0.0 -48.2 0.0 0.0% -6.4% 0.0% 0.0 -0.1 0.0 b1-sns04b 

20% VOC & NOx Ar, Pnt, Non-Rd and O&G in NAA 0.0 -72.5 -41.3 0.0% -9.6% -4.9% -0.5 -1.1 1.8 

b1-sns04c 

20% VOC & 30% NOx Ar, Pnt, Non-Rd, O&G in NAA 0.0 -72.5 -62.0 0.0% -9.6% -7.4% -0.7 -1.6 2.8 

b1-sns04d 40% VOC O&G in NAA 0.0 -96.3 0.0 0.0% -12.7% 0.0% -0.1 -0.2 0.1 b1-sns05 20% NOx Pnt & O&G NAA 0.0 0.0 -20.6 0.0% 0.0% -2.5% -0.2 -0.5 0.3 b1-sns06 20% VOC Non-Rd in NAA 0.0 -12.7 0.0 0.0% -1.7% 0.0% -0.2 -0.1 0.0 b1-sns07 20% VOC Area in NAA 0.0 -7.5 0.0 0.0% -1.0% 0.0% -0.1 -0.1 0.0 b1-sns08 20% NOx Pnt & O&G CO 0.0 0.0 -78.0 0.0% 0.0% -9.3% -0.2 -0.6 1.1 b1-sns09 20% VOC O&G in CO 0.0 -67.2 0.0 0.0% -8.9% 0.0% 0.0 -0.1 0.1 b1-sns10 

20% VOC & NOx Point & O&G in CO 0.0 -77.5 -78.0 0.0% -10.2% -9.3% -0.3 -0.6 0.9 

b1-sns11 

20% NOx Point & O&G in NAA + 20% NOx Pawnee 0.0 0.0 -23.0 0.0% 0.0% -2.7% -0.2 -0.5 0.3 

b1-sns12a 

Effects of increase in Bark Beetle 2006 to 2010 -8.4 -87.8 -0.3 -0.2% -11.6% 0.0% 0.0 -0.1 0.1 

b1-sns12b 

Effects of 2010 Bark Beetle infestation -21.1 -233.5 -0.8 -0.6% -30.8% -0.1% -0.1 -0.1 0.1 

2010 Base Case emission reductions from 2006 levels, all other emission reductions from 2010Base Cases * Maximum difference in 2010 design value anywhere on the 4km grid. **Maximum difference in daily maximum 8-hour ozone concentration anywhere on the 4km grid. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-1 

3.0 2010 APCA SOURCE APPORTIONMENT 

3.1 INTRODUCTION 

This section presents the 2010 ozone source apportionment modeling. This analysis is made 

using the CAMx modeling results for the 2010 base case emissions using the June-July 2006 

episode (Morris et al., 2008b,c). This section begins with a technical description of the 

technique, followed by the application methodology and concluding with the analysis 

methodology and results. 

3.2 TECHNICAL DESCRIPTION 

Photochemical grid models are used to develop NOx and/or VOC emission reduction strategies 

to attain ozone air quality objectives. Traditionally, the development of an ozone attainment 

strategy involves iteration through many photochemical grid model scenarios to identify which 

pollutants, source categories and source regions should be controlled. It is impractical to analyze 

every potential control strategy and so there is potential for implementing controls on sources 

that contribute little to the high ozone levels or, conversely, not controlling sources that do 

contribute. 

3.2.1 Introduction to OSAT 

ENVIRON developed an ozone source attribution approach that has become known as the 

“Ozone Source Apportionment Technology”, or OSAT (Yarwood et al., 1996). This method 

was implemented in the CAMx photochemical grid model. OSAT provides a method for 

estimating the contributions of multiple source areas, categories, and pollutant types to ozone 

formation in a single model run. 

The main challenges in developing and implementing a methodology to track the spatial and 

temporal relationships between separate groups of emission sources and ozone formation are: 

• Accounting not only for the presence of ozone precursors from a given source region at a 

given receptor location, but also accurately estimating the cumulative contribution to 

ozone production of those precursors while they were en-route to the receptor. 

• Insuring compatibility with the underlying air quality model formulation so that derived 

source-receptor relationships will be consistent with model response to emission changes. 

• Providing sufficient spatial and temporal resolution while managing, within practical 

constraints, the computer resources required to run the software tool. 

The methodology is designed so that all ozone and precursor concentrations are attributed among 

the selected source groupings at all times. Thus, for all receptor locations and times, the ozone 

(or ozone precursor concentrations) predicted by CAMx is attributed among the source 

groupings selected for OSAT. The methodology also estimates the fractions of ozone arriving at 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-2 

the receptor that were formed en-route under VOC- or NOX-limited conditions. This information 

indicates how ozone concentrations at the receptor will respond to reductions in VOC and NOX

precursor emissions. 

The biggest limitation of this, or any other, ozone source apportionment approach likely results 

from the non-linear nature of the chemical interactions between emissions from different source 

groupings and their effect on ozone formation. This means that as soon as the emission 

inventory is perturbed, the source receptor relationships begin to change. Thus, OSAT can only 

estimate the contribution to ozone from a specific source grouping under the current emissions 

scenario. It cannot directly quantify the ozone reductions that will result from an emission 

control strategy because the CAMx response may well be non-linear with the magnitude of the 

control applied (e.g. 20 percent or 60 percent control) and the presence/absence of other 

simultaneous controls on other source groupings. 

However, this fundamental truth of photochemical modeling does not limit the usefulness of 

OSAT: arguably it increases its usefulness. At any rate, it suggests the following approach to 

control strategy development with OSAT. For the base CAMx scenario, OSAT could be used to 

identify specific source groupings for which ozone reductions from emissions controls would be 

maximized. Just as important, OSAT will identify source groupings for which emissions 

controls are not effective at reducing ozone concentrations. The most effective and feasible 

control measures identified in this way can be applied to the emission inventory, leading to a 

revised CAMx scenario with different (lower) emissions. If additional controls are needed, 

OSAT could be applied again to identify the most effective control measures under the new 

conditions. Development of the control plan will still proceed by an iterative process, but OSAT 

can be used to guide the process to develop (and justify) more refined, better-targeted and more 

cost-effective ozone control strategies. 

3.2.2 OSAT/APCA Technical Formulation 

CAMx has been extended to accommodate extra tracer species needed to perform ozone source 

apportionment. For each user-specified source grouping (geographical area/emissions category) 

there are two distinct types of tracer species, “timing tracers”1

 and “ozone reaction tracers.” The 

timing tracers are used to track the temporal relationships between precursor emissions and 

ozone formation. The ozone reaction tracers track the fate of ozone precursors (NOX and VOC) 

emissions from each source grouping plus the ozone formation attributed to those emissions. 

The methodology requires that all ozone precursors be tracked so that all contributions to ozone 

can be accounted for, thus ozone and precursors originating from the model boundary and initial 

concentrations are also tracked as separate source groupings (however, no timing tracers are 

allocated to the initial or boundary conditions). The following sub-sections describe the 

methodologies employed for the timing and ozone reaction tracers. 

OSAT tracks ozone formation from user defined source groups using reactive “ozone-tracers” 

that run in parallel to the CAMx host model. OSAT does not affect the host CAMX model 

calculations; rather it extracts information on ozone formation source-relationships from the 

model in a mass consistent fashion. There are four ozone-reaction tracers per source area to 

account for the contributions of emissions of separate source areas to the complex process of the 

 

1

 Note that “timing tracers” were not used in the Denver ozone source apportionment modeling so are not discussed further. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-3 

ozone formation activity. It is important to recall that the mass of NOX or VOC from a given 

source area that may be present at a given receptor at a selected hour is often not particularly 

relevant to the amount of ozone present there at that time. Rather, it is the contribution to ozone 

formation activity of source areas’ NOX and VOC emissions en-route to a receptor that must be 

determined. The ozone-reaction tracers are designed to integrate these en-route contributions to 

ozone production/destruction activity. 

Ozone formation involves both NOX and VOCs, and the NOX and VOCs participating in ozone 

formation in any particular grid cell/time step may have originated from different source 

groupings. The ozone formation process can be controlled more by the availability of VOCs or 

NOX, depending upon the relative abundance of both precursors, and ozone formation is 

described either as VOC-limited or NOX-limited, respectively. When ozone production at a 

given location and time is NOX-limited it makes sense to attribute ozone production to source 

groupings based on their contributions to the local NOX and similarly to allocate based on VOC 

contributions when ozone formation is VOC-limited. Consequently, separate tracers are used to 

track ozone formation occurring under NOX-and VOC-limited conditions. 

The four types of ozone-reaction tracers that are tracked for each source grouping (i.e., 

geographic area/source category, boundary conditions or initial conditions) are explained below. 

The name of each tracer uniquely identifies the source grouping it represents: 

 Ni = NOX tracer for source grouping i. Emitted with the same spatial and temporal 

distribution as NOX emissions for source grouping i. Decays with local 

dNOX/dt for each grid cell/time step. 

 Vi = VOC tracer for source grouping i. Emitted with the same spatial and temporal 

distribution as VOC emissions for source grouping i. Decays with local 

dVOC/dt for each grid cell/time step. Note that VOC tracers are defined as 

single carbon species, so their concentrations are numerically equal in ppb and 

ppbC units. 

 O3Vi = Tracer of ozone formation under VOC limited conditions attributed to source 

grouping i. If ozone formation is determined to be VOC-limited for a given 

grid cell/time step, O3Vi is formed in proportion to local dO3/dt in proportion 

weighted by the distribution of VOC precursors (Vi). 

 O3Ni = Tracer of ozone formation under NOX limited conditions attributed to source 

grouping i. If ozone formation is determined to be NOX-limited for a given 

grid cell/time step, O3Ni is formed in proportion to local dO3/dt in proportion 

weighted by the distribution of NOX precursors (Ni). 

The ozone reaction tracer methodology was designed to be inherently mass consistent with 

CAMx. In other words, the sums of the NOX, VOC and ozone tracers should remain consistent 

with their standard CAMx counterparts as follows: 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-4 

∑ ∑

∑ ∑

∑

= +

=

= +

i i

i

i

O O V O N

V CB VOCs

N NO NO

3 3 3

4

2

The tracer families, Ni and Vi, track NOX and VOC emissions from each source grouping to 

allow attribution of ozone formation as it occurs throughout CAMx. The rates of emission of the 

Ni and Vi tracers are set equal to the total NOX and VOC emissions in the inventory for a source 

grouping, respectively. For the Vi tracers, the emissions are set equal on a ppmC basis. For the 

initial condition (IC) source grouping, the NIC and VIC tracers are initialized from the CAMx 

initial concentration fields and receive no more mass input after the start of the simulation. For 

the boundary condition (BC) source grouping, the fluxes of NOX and VOC entering CAMx from 

the boundaries are effectively interpreted as emissions of the NBC and VBC tracers at the model 

boundaries. Unlike emission source groupings, boundary and initial conditions also introduce 

ozone directly into CAMx. Since there is no way of determining whether the ozone in the 

boundary and initial conditions was formed under VOC or NOX limited conditions, this ozone is 

divided equally between O3N and O3V tracers. However, subsequent ozone formation within 

CAMx from boundary and initial condition VOCs and NOX is allocated to O3V and O3N tracers 

on the basis of whether ozone formation occurred under VOC or NOX limited conditions. 

The Ni, Vi, O3Ni and O3Vi tracers are deposited at rates determined by the standard CAMx 

deposition calculation on a surface grid cell by grid cell basis. For NOX, the deposition velocity 

for each tracer Ni [Vd( Ni)] is set equal to the concentration weighted average of the deposition 

velocities for NO and NO2: 

Similarly, the deposition velocity for each tracer Vi is set equal to the concentration weighted 

average of the deposition velocities for the VOC species (the concentration weighting is 

performed on a ppmC basis). The deposition velocity for the O3N and O3V tracers is set equal 

to the ozone deposition velocity. 

The Ni, Vi, O3Ni and O3Vi tracers are transported and diffused in the horizontal and vertical 

using the same transport and diffusion fluxes used in the host model for NOx, VOC and ozone, 

respectively. 

The Ni tracer mass in each grid cell at each time step decays according to the chemical change in 

the CAMx predicted NOX (ΔNOX) weighted by the tracer contribution to the total of NOX tracers 

from all source groupings: 

The Vi tracer mass in each grid cell at each time step decays according to the chemical change in 

the CAMx predicted VOC (ΔVOC) weighted by the tracer contribution to the total of VOC 

( ) ( ) ( )

2

2 2

NO NO

NO V NO NO V NO V N D D

d i

+

× + × =

∑ = + Δ ×

i

i

i i x N

N N N NO
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-5 

tracers from all source groupings. However, because the reactivity of VOCs from different 

source groupings can be different, a weighting factor based on the OH-reactivity of each V tracer 

(kOHi) is also introduced. The kOHi for each source grouping is calculated at the start of each 

simulation period (typically one day) by averaging the OH rate constants of the speciated VOC 

emissions for each source grouping. The V tracer mass in each grid cell at each time step decays 

at a rate determined by the following equation: 

The O3N and O3V tracers for each source grouping accumulate a weighted fraction of the ozone 

production activity (PO3) and ozone destruction activity (DO3) that occurs in each grid cell at 

each time step. The process of apportioning PO3 and DO3 across O3N and O3V tracers occurs 

as follows: 

 1. Determine whether the local (grid cell/time step) ozone production process is NOX or 

VOC limited. As described in detail below, the determination is based on the ratio of 

the local HNO3 and H2O2 production rates. If the H2O2/HNO3 production ratio is 

greater than 1/3 during a time step, then ozone formation is NOX limited. If this ratio 

is less than or equal to 1/3, then ozone formation is VOC limited. 

 2. For allocating ozone production under conditions determined to be: 

(a) NOX limited: allocate PO3 across O3N tracers 

(b) VOC limited: allocate PO3 across O3v tracers based on maximum 

incremental reactivity (MIR) factors 

 

 3. For ozone destruction, allocate across all ozone tracers. 

 

 where X = N and V. 

This is the algorithm used for OSAT ozone source apportionment. The Anthropogenic Precursor 

Culpability Assessment (APCA) method of ozone source apportionment in CAMx was used in 

the Denver 2010 modeling uses a different algorithm for allocating ozone production, as 

described below. 

The MIRs used in equation (5) are the weighted average MIRs for the emissions in each source 

group. The MIR approach was developed by Carter (1994) to approximate the ozone forming 

potential of VOCs accounting for both kinetic and mechanistic reactivity effects. The MIR 

∑( ) ×

× = + Δ ×

i i

i i

i i V kOH

V kOH V V VOC

∑ = + ×

i

i

i i N

N O N O N PO3 3 3

∑ ×

× = + ×

i i

i i

i i V MIR

V MIR O V O V PO3 3 3

∑ = + ×

i

i

i i X

X O3X O3X DO3
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-6 

represents the ozone formation potential of the VOC mixture accounting for the VOC reactions 

with OH as well as the effects of all of the VOC products that produce ozone formation. The 

VOC + OH reaction is the main VOC destruction mechanism so it is appropriate to weight the 

VOC destruction across the VOC reactive tracers by their composite reaction rate with OH 

(kOH). 

The determination of whether the ozone produced is under more VOC-limited or NOx-limited 

conditions is based on the main radical termination reactions in the atmosphere. Under VOClimited conditions the instantaneous production of HNO3 is higher, whereas under NOx-limited 

conditions the instantaneous production of H2O2 is higher. Thus a ratio of the production of 

these two species is used to determine whether ozone formation was more VOC-limited or NOxlimited, which was extensively tested in the development of OSAT (ENVIRON, 2008). 

Anthropogenic Precursor Culpability Assessment (APCA). APCA differs from OSAT in 

recognizing that certain emission groups are not controllable (e.g., biogenic emissions) and that 

apportioning ozone production to these groups does not provide information that is relevant to 

control strategies. To address this, in situations where OSAT would attribute ozone production 

to non-controllable (i.e., biogenic) emissions, APCA re-allocates that ozone production to the 

controllable portion of precursors that participated in ozone formation with the non-controllable 

precursor. In the case where biogenic emissions are the uncontrollable source category, APCA 

would only attribute ozone production to biogenic emissions when ozone formation is due to the 

interaction of biogenic VOC with biogenic NOX. When ozone formation is due to biogenic VOC 

and anthropogenic NOX under VOC-limited conditions (a situation in which OSAT would 

attribute ozone production to biogenic VOC), APCA re-directs that attribution to the 

anthropogenic NOX precursors present. The use of APCA instead of OSAT results in more 

ozone formation attributed to anthropogenic NOX sources and less ozone formation attributed to 

biogenic sources. APCA is not really a “source apportionment” technique because it expresses 

biases as to which sources should be implicated (i.e., those that are controllable), hence it is 

referred to as a “culpability assessment.” . 

3.3 APPLICATION METHODOLOGY 

The APCA version of the CAMx ozone source apportionment was applied using the 2010 base 

case inventory with the emissions segregated into 8 source categories and 11 source regions. 

The source categories are presented in Table 3-1. A list of the source regions is presented in a 

tabular form in Table 3-2 and in graphical form in Figures 3-1 and 3-2 for the 12 km and 4 km 

CAMx domains, respectively. Note that in some cases only small portions of states on the 

periphery of the 12 km grid are included in the analysis. Further note that source regions are 

defined on a grid cell basis, with each grid cell assigned to the region with the largest area. Thus, 

it is possible for sources on the border of a region to get assigned to an adjacent region. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-7 

Table 3-1. Source apportionment source groups for Denver SIP 2010 modeling. 

Source Apportionment Source Groups

Biogenic/Fires 

On-road Motor Vehicles 

Non-road 

Oil and Gas 

Area Sources 

Industrial Point Sources 

Electric Generation Units 

Boundary and Initial Conditions 

Table 3-2. Source apportionment source regions for Denver SIP 2010 modeling. 

Source Apportionment Source Regions

7-County Denver Metro 

Larimer/Weld Counties 

Northeastern Colorado 

Southeastern Colorado 

Southwestern Colorado 

Northwestern Colorado 

Wyoming, Idaho, Oregon 

Utah, Nevada, California 

Arizona, New Mexico 

Kansas, Texas, Oklahoma, Missouri, Arkansas 

Nebraska, South Dakota, Minnesota, Iowa 

Figure 3-1. Source apportionment source regions in 12km CAMx domain. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-8 

Figure 3-2. Source apportionment source regions in 4km CAMx domain. 

3.4 ANALYSIS METHODOLOGY AND RESULTS 

The source apportionment results were analyzed at the ozone monitor sites used in the ozone 

attainment test presented in Section 2 of this report. At each monitor location, for each day, the 

8-hour average ozone results for each period over 70 ppb were averaged to develop a composite 

contribution. 

Example displays for a high ozone day (July 29th) at the Rocky Flats North and Fort Collins 

West monitors, the two monitors with the highest future year design values are presented in this 

section. APCA ozone source apportionment modeling results for other days and other monitors 

are presented in Appendix C. The results show significant day-to-day and monitor-to-monitor 

variation. The Rocky Flats North results are presented in Figure 3-3. Figure 3-3a presents the 

ozone results including the boundary conditions, that is, the contribution from sources outside 

the 12 km domain. Of the 76.1 ppb of ozone estimated at the monitor, ~48 ppb was transported 

into the 12 km domain and ~18 ppb was attributed to sources in the seven-county Denver Metro 

area. Figure 3-3b presents the same results as 3-3a, but without the boundary conditions plotted 

and the vertical scale expanded to better resolve the source region contributions. This figure 

shows that of the ~18 ppb from Metro Denver sources ~10 ppb was from motor vehicles, ~5 ppb 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-9 

was from non-road mobile sources with the balance from other sources. Figure 3-3c presents the 

ozone formed under anthropogenic NOx-limited conditions, that is, ozone formed under 

conditions where the model is responsive to NOx controls or since the APCA version of source 

apportionment was used, ozone formed under VOC-limited conditions due to the interaction of 

biogenic VOC with anthropogenic NOx. Figure 3-3d presents the ozone formed under 

anthropogenic VOC-limited conditions, that is, ozone formed under conditions where the model 

is responsive to VOC controls. These two figures suggest that emission reductions from NOx 

sources will be more effective at reducing ozone in the model than reductions from VOC 

sources, although both VOC and NOx controls will reduce ozone. Analogous plots for the Fort 

Collins West monitor are presented in Figure 3-4 that show similar contributions as the Rocky 

Flats North monitor, except the highest contributions are from sources in the Larimer/Weld 

County source region and oil and gas sources from Larimer/Weld County have a large 

contribution which they didn’t at Rocky Flats North. 

The source apportionment results vary by day and by location. However, several overall trends 

emerge, namely: 

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

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

• At the Denver Metropolitan monitors, the largest contributors are Denver Metropolitan 

area motor vehicle and non-road sources; 

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

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

Metropolitan sources; 

• The majority of the ozone is attributable to anthropogenic NOx emissions. 

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

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

For instance, the source apportionment modeling in support of the Denver Early Action Compact 

(Morris et. Al., 2004f,g) using the 2002 ozone episode showed more impact of sources in 

Larimer/Weld Counties into the Denver Metropolitan area. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-10 

Figure 3-3a. Rocky Flats North source apportionment for 29 July including boundary 

conditions. 

Figure 3-3b. Rocky Flats North source apportionment for 29 July excluding boundary 

conditions. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-11 

Figure 3-3c. Rocky Flats North source apportionment for 29 July attributable to anthropogenic 

NOx sources. 

Figure 3-3d. Rocky Flats North source apportionment for 29 July attributable to anthropogenic 

VOC sources. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-12 

Figure 3-3a. Fort Collins West source apportionment for 29 July including boundary conditions. 

Figure 3-3b. Fort Collins West source apportionment for 29 July excluding boundary 

conditions. 
 F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec3_2010-apca1.doc August 2008 3-13 

Figure 3-3c. Fort Collins West source apportionment for 29 July attributable to anthropogenic 

NOx sources. 

Figure 3-3d. Fort Collins West source apportionment for 29 July attributable to anthropogenic 

VOC sources. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-1 

4.0 REFERENCES 

Anthes, R.A. 1977. “A Cumulus Parameterization Scheme Utilizing a One-Dimensional Cloud 

Model”, Mon. Wea. Rev., Vol. 105, pp. 270-286. 

Anthes, R.A. and T.T. Warner. 1978. “The Development of Mesoscale Models Suitable for Air 

Pollution and Other Mesometeorological Studies”, Mon. Wea. Rev., Vol. 106, pp, 1045-

1078. 

Barna, M., W. Malm, B. Schichtel, K. Gebhart and M. Rodriguez. 2008. Prediction Total 

Nitrogen Deposition at National Parks. Presented at Air & Waste Management 

Association’s Aerosol & Atmospheric Optics: Visual Air Quality and Radiation 

conference, Moab, Utah, April 28 – May 2. 

Bar-Ilan, A., R. Friesen, A. Pollack and A. Hoats. 2007. “WRAP Area Source Emissions 

Inventory Projections and Control Strategy Evaluation Phase II”. ENVIRON 

International Corporation, Novato, CA. July. 

http://www.wrapair.org/forums/ssjf/documents/eictts/OilGas/2007-

07_Phase%20II_O&G_Draft_Final_Report-v7-23.pdf. 

Bar-Ilan, A., J. Grant, R. Friesen, A. Pollack, D. Henderer, Daniel Pring and Kathleen Sgamma. 

2008a. Development of Baseline 2006 Emissions from Oil and Gas Activity in the 

Denver Julesburg Basin. ENVIRON International Corporation, Novato, California. April 

30. (http://www.wrapair.org/forums/ssjf/documents/eictts/OilGas/2008-

04_%2706_Baseline_Emissions_DJ_Basin_Technical_Memo_(04-30).pdf). 

Bar-Ilan, A., J. Grant, R. Friesen, A. Pollack, D. Henderer, Daniel Pring and Kathleen Sgamma. 

2008b. Development 2010 Oil and Gas Emissions Projections for the Denver Julesburg 

Basin. ENVIRON International Corporation, Novato, California. April 30. 

(http://www.wrapair.org/forums/ssjf/documents/eictts/OilGas/2008-

04_%2710_Projection_Emissions_DJ_Basin_Technical_Memo(04-30).pdf).pdf). 

Carter, W.P.L. 1994. Development of ozone reactivity scales for volatile organic compounds. J. 

Air & Waste Manage. Assoc., 44, 881-899. 

Coats, C.J. Jr. 1996. High-performance algorithms in the Sparse Matrix Operator Kernel 

Emissions (SMOKE) modeling system. Proc. Ninth AMS Joint Conference on 

Applications of Air Pollution Meteorology with AWMA. Amer. Meteor. Soc., Atlanta, 

GA, 584-588. 

Dudhia, J. 1993. "A Non-hydrostatic Version of the Penn State/NCAR Mesoscale Model: 

Validation Tests and Simulation of an Atlantic Cyclone and Cold Front". Mon. Wea. Rev., 

Vol. 121. pp. 1493-1513. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-2 

Emery, C., E. Tai, and G. Yarwood. 2001. “Enhanced Meteorological Modeling and 

Performance Evaluation for Two Texas Episodes”. Prepared for the Texas Natural 

Resources Conservation Commission. Prepared by ENVIRON International Corp, 

Novato, CA. 

ENVIRON. 2008. User’s Guide – Comprehensive Air Quality Model with Extensions – Version 

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

February. 

EPA. 2007. “Guidance on the Use of Models and Other Analyses for Demonstrating Attainment 

of Air Quality Goals for Ozone, PM2.5 and Regional Haze”. U.S. Environmental 

Protection Agency, Research Triangle Park, NC. EPA-454/B-07-002. April. 

EPA. 2005a. “Guidance on the Use of Models and Other Analyses in Attainment 

Demonstrations for the 8-hr Ozone NAAQS”. U.S. Environmental Protection Agency, 

Atmospheric Sciences Modeling Division, Research Triangle Park, N.C. October. 

EPA. 2005b. “Technical Support Document for the Final Clean Air Interstate Rule – Air Quality 

Modeling”. U.S. Environmental Protection Agency, Office of Air Quality and Planning 

Standards, Research Triangle Park, North Carolina, 27711. March. 

EPA. 2005c. “Regional Haze Regulations and Guidelines for Best Available Technology 

(BART) Determinations”. Fed. Reg./Vol. 70, No. 128/Wed. July. Rules and Regulations, 

pp. 39104-39172. 40 CFR Part 51, FRL-7925-9, RIN AJ31. 

EPA. 2003a. “A Conceptual Model to Adjust Fugitive Dust Emissions to Account for Near 

Source Particle Removal in Grid Model Applications”. Prepared by Tom Pace, U.S. EPA, 

August. http://www.epa.gov/ttn/chief/emch/invent/statusfugdustemissions_082203.pdf. 

EPA. 2003b. National emission inventory QA and augmentation. Memorandum. Prepared by 

Anne Pope, U.S. EPA, June. 

http://www.epa.gov/ttn/chief/emch/invent/qaaugmementationmemo_99nei_60603.pdf

EPA. 2001. “Guidance Demonstrating Attainment Air Quality Goals for PM2.5 and Regional 

Haze”. Draft Final (17 February 2005), U.S. Environmental Protection Agency, 

Atmospheric Sciences Modeling Division, Research Triangle Park, N.C. 

EPA. 1999. “Draft Guidance on the Use of Models and Other Analyses in Attainment 

Demonstrations for the 8-hr Ozone NAAQS”. Draft (May 1999), U.S. Environmental 

Protection Agency, Office of Air Quality Planning and Standards, Research Triangle 

Park, N.C 

EPA. 1991. "Guidance for Regulatory Application of the Urban Airshed Model (UAM), "Office 

of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research 

Triangle Park, N.C. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-3 

ERG. 2006a. “WRAP Point and Area Source Emissions Projections for the 2018 Base Case”. 

Eastern Research Group, Inc., Sacramento, California. January. 

http://www.wrapair.org/forums/ssjf/documents/eictts/docs/WRAP_2018_EI-Version_1-

Report_Jan2006.pdf. 

ERG. 2006b. “Mexico National Emissions Inventory, 1999”. Eastern Research Group, Inc, 

Sacramento, California and TransEngineering, El Paso, Texas. October. 

http://www.epa.gov/ttn/chief/net/mexico/1999_mexico_nei_final_report.pdf. 

Gao, Y.-R., Y.-H. Kuo, J. Dudhia, and D.B. Barsons. 2000. Four-dimensional variational data 

assimilation of heterogeneous mesoscale observations for a strong convective case. Mon. 

Wea. Rev., 128, 619-643. 

Gephart, K.A., B.A. Schitel, M.G. Barna, M.A. Rodriguez and J. Hand. 2007. Meteorological 

Issues Associated with Nitrogen and Sulfur Deposition at Rocky Mountain National Park, 

Colorado. National Park Service, Air Resources Division, Fort Collins, Colorado. 

Presented at Air and Waste Management Association Meeting, Pittsburgh, PA, Paper No. 

492. June. 

Gery, M. W., G.Z. Whitten, J.P. Killus, and M.C. Dodge. 1989. A photochemical mechanism 

for urban and regional-scale computer modeling. J. Geophys. Res. 94, 12925-12956. 

Grell, G. A., J. Dudhia, and D. R. Stauffer. 1994. "A Description of the Fifth Generation Penn 

State/NCAR Mesoscale Model (MM5). NCAR Tech. Note, NCAR TN-398-STR, 138 pp. 

Guenther, A. and C. Wiedinmyer. 2004. User’s Guide to the Model of Emissions of Gases and 

Aerosols from Nature (MEGAN). National Center for Atmospheric Research (NCAR), 

Boulder, Colorado (http://acd.ucar.edu/~christin/megan1.0_userguide.pdf). 

Jacob, D.J., R. Park and J.A. Logan. 2005. “Documentation and Evaluation of the GEOSCHEM Simulation for 2002”. Provided to the VISTAS Group. Harvard University. 

June. 

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

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

Emissions Modeling Community. Presented at the 14th International Emission Inventory 

Conference “Transforming Emission Inventories – Meeting Future Challenges Today”, 

Las Vegas, Nevada, April 11-14. 

(http://www.epa.gov/ttn/chief/conference/ei14/session11/loomis.pdf) 

MACTEC. 2006. “Documentation of the Base G 2002 Base Year, 2009 and 2018, Emission 

Inventories for VISTAS”. Prepared for Visibility Improvement State and Tribal 

Association of the Southeast (VISTAS). MACTEC, Inc., Gainesville, Florida. 

Mansell, G.E. and T. Dinh. 2003a. “Emission Inventory Report, Air Quality Modeling Analysis 

for the Denver Early Action Ozone Compact: Development of the 2002 Base Case 

Modeling Inventory”. Prepared for Denver Regional Air Quality Council prepared by 

ENVIRON International Corporation, Novato, CA. September. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-4 

Mansell, G.E. and T. Dinh. 2003b. “Emission Inventory Report Addendum, Air Quality 

Modeling Analysis for the Denver Early Action Ozone Compact: Development of the 

2002 Base Case Modeling Inventory”. Prepared for Denver Regional Air Quality 

Council. Prepared by ENVIRON International Corporation, Novato, CA. September. 

Mansell, G.E. and T. Dinh. 2003c. “Emission Inventory Report, Air Quality Modeling Analysis 

for the Denver Early Action Ozone Compact: Development of the 2007 Base Case 

Modeling Inventory”. Prepared for Denver Regional Air Quality Council. Prepared by 

ENVIRON International Corporation, Novato, CA. October. 

Mansell, G., S. Lau, J. Russell and M. Omary. “Fugitive Wind Blown Dust Emissions and Model 

Performance Evaluation – Phase II”. ENVIRON International Corporation, Novato 

California and University of California at Riverside. May. 

http://www.wrapair.org/forums/dejf/documents/WRAP_WBD_PhaseII_Final_Report_050506.pdf

.

McNally, D., T.W. Tesche and R. Morris. 2003. “Air Quality Modeling Analysis For The 

Denver Early Action Ozone Compact: Evaluation of MM5 Simulations of The Summer 

’02 Denver Ozone Season and Embedded High 8-hr Ozone Episodes”. Alpine 

Geophysics, LLC, Ft. Wright, Kentucky. July. 

McNally, D., G. Schewe, J. Johnson and R. Morris. 2008. “Evaluation of Preliminary MM5 

Meteorological Model Simulation for the June-July 2006 Denver Ozone SIP Modeling 

Period Focused on Colorado”. Prepared by Alpine Geophysics, LLC and ENVIRON 

International Corporation. Prepared for Denver Regional Air Quality Council (RAQC). 

February. 

Morris, R.E. and G.E. Mansell. 2003a. Preliminary CAMx Base Case ozone modeling for the 

June-July 2002 Denver Ozone Episode. Memorandum. Prepared for Gerald Dilley, 

Denver Regional Air Quality Council prepared by ENVIRON International Corporation, 

Novato, CA. October. 

Morris, R.E., G.E. Mansell, D.A. McNally and T.W. Tesche. 2003b. Update on Ozone 

Modeling to Support Denver 8-Hour Early Action Compact. Presented at Denver EAC 

Modeling Review Panel (MRP) Meeting October, Denver, Colorado. 

http://www.raqc.org/ozone/EAC/MRP/Oct17/Environ_101703.pdf 

Morris, R.E., B. Koo, S. Lau, T.W. Tesche, D. McNally, C. Loomis, G. Stella, G. Tonnesen and 

Z. Wang. 2004a. “VISTAS Emissions and Air Quality Modeling – Phase I Task 4cd 

Report: Model Performance Evaluation and Model Sensitivity Tests for Three Phase I 

Episodes”. Prepared for the VISTAS Technical Analysis Committee. Prepared by 

ENVIRON International Corporation, Alpine Geophysics, LLC, and the University of 

California, Riverside (CE-CERT). 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-5 

Morris, R.E., D. McNally, T. Tesche, G. Tonnesen, J. Boylan and P. Brewer. 2004b. “Regional 

Haze Modeling over the VISTAS States: Preliminary Verification of Models-3/CMAQ 

for the 2002 Annual Period.” Presented at AWMA Visibility Conference, Asheville, 

North Carolina. October. 

Morris R.E., T.W. Tesche and G.S. Tonnesen. 2004c. “Quality Assurance Project Plan (Draft) 

for the Visibility Improvements for State and Tribal Associations for the Southeastern 

States (VISTAS) Emissions and Air Quality Modeling”. Revision 0. ENVIRON 

International Corporation, Novato, CA. November. 

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

Modeling Analysis for the Denver Early Action Compact: Preliminary Photochemical 

Base Case Modeling and Model Performance Evaluation for the Summer ’02 Denver 

Ozone Season and Embedded High 8-Hour Ozone Episodes”. Prepared for Denver 

Regional Air Quality Council, Denver, Colorado. Prepared by ENVIRON International 

Corporation, Novato, CA. November.

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

Modeling Analysis for the Denver Early Action Compact: 2007 Base Case, Control 

Strategy and Sensitivity Analysis Modeling”. Prepared for Denver Regional Air Quality 

Council, Denver, Colorado. Prepared by ENVIRON International Corporation, Novato, 

CA. January.

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

Modeling Analysis for the Denver Early Action Compact: 2007 Emissions Reduction 

Sensitivity Modeling. Prepared for Colorado Department of Health and Environment and 

Denver Regional Air Quality Council, Denver, Colorado. Prepared by ENVIRON 

International Corporation, Novato, CA. February. 

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

Modeling Analysis for the Denver Early Action Compact: 2007 Control Strategy 

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

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

ENVIRON International Corporation, Novato, CA. February. 

Morris R.E., D.E. McNally, T.W. Tesche, G.S. Tonnesen, J.W. Boylan and P. Brewer. 2005a. 

“Preliminary Evaluation of the Community Multiscale Air Quality Model for 2002 over 

the Southeastern United States”. J. Air and Waste Manage. Assoc. 55:1694-1708. 

November. 

Morris R.E. and G.M. Stella. 2005b. “Quality Assurance Project Plan (Draft) for the Association 

for Southeastern Integrated Planning (ASIP) Emissions and Air Quality Modeling to 

Address 8-Hour Ozone and PM 2.5 Nonattainment in the Southeastern States”. Revision 

0. Prepared by ENVIRON International Corporation, Novato, CA. November. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-6 

Morris, R.E., A. Hoats, S. Lau, B. Koo, G. Tonnesen, C-J. Jung and M. Omary. 2005c. “Air 

Quality Modeling Analysis for CENRAP – Preliminary 2002 Base Case CMAQ and 

CAMx Modeling of the Continental US 36 km Domain and Model Performance 

Evaluation”. Prepared by ENVIRON International Corporation, Novato, CA. April. 

Morris R.E., E. Tai, Y. Jia and M. Jimenez. 2005d. “Photochemical Modeling of the Tulsa and 

Oklahoma City 8-Hour Ozone Early Action Compact (EAC) State Implementation Plan 

(SIP) – Technical Support Document”. Prepared by ENVIRON International 

Corporation, Novato, CA. March. 

Morris R.E. and G. Tonnesen. 2006. “Quality Assurance Project Plan (Draft) for Central 

Regional Air Partnership (CENRAP) Emissions and Air Quality Modeling – Revision 3”. 

 ENVIRON International Corporation, Novato, CA. March. 

Morris, R.E., B. Koo, A. Guenther, G. Yarwood, D. McNally, T.W. Tesche, G. Tonnesen, J. 

Boylan and P. Brewer. 2006. Model sensitivity evaluation for organic carbon using two 

multi-pollutant air quality models that simulate regional haze in the Southeastern United 

States. Atmos. Env. 40 (2006) 4960-4972. 

Morris, R., B. Wang, E. Tai, D. McNally, C. Loomis, G. Stella and T.W. Tesche. 2007. 

Modeling Protocol for the Denver 8-Hour Ozone Attainment Demonstration Modeling. 

ENVIRON International Corporation, Novato, CA. November. 

http://www.ozoneaware.org/documents/DraftFinalProtocolDenver8-

HourOzoneNov282007.pdf. 

Morris, R., S. Kemball-Cook, D. Strohm and L. Parker. Modeling Protocol for the Unita Basin 

Air Quality Study. 2008a. Prepared for Independent Petroleum Association of Mountain 

States (IPAMS). Prepared by ENVIRON International Corporation, Novato, California. 

March 17. 

Morris R., E. Tai, L. Parker, J. Johnson, D. McNally and C. Loomis. 2008b. Initial Ozone 

Model Performance Evaluation of the June-July 2006 Denver Ozone Episode and 

Diagnostic Testing and Analysis. ENVIRON International Corporation, Novato, 

California. Prepared for Denver Regional Air Quality Council (RAQC), Denver, 

Colorado. May 13. 

Morris R., E. Tai, Tanarit Sakulyanontvittaya, D. McNally and C. Loomis. 2008c. Model 

Performance Evaluation for the June-July 2006 Ozone Epsiiode for the Denver 8-Hour 

Ozone State Implementation Plan. ENVIRON International Corporation, Novato, 

California. Prepared for Denver Regional Air Quality Council (RAQC), Denver, 

Colorado. August 29. 

Pechan. 2005a. “Electric Generating Unit (EGU) Growth Factor Comparison”. Prepared for 

CENRAP Emissions Inventory Workgroup. E.H. Pechan and Associates, Inc. Durham, 

North Carolina. January. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-7 

Pechan. 2005b. Technical Memorandum: Updates to Source Classification Code (SCC) to 

speciation profile cross-reference table. Prepared for CENRAP Emissions Inventory 

Workgroup. E.H. Pechan and Associates, Inc. Durham, North Carolina. April. 

Pechan and CEP. 2005c. “Consolidated of Emissions Inventories”. (Schedule 9; Work Item 3). 

E.H. Pechan and Associates, Inc. Durham, North Carolina. Carolina Environmental 

Program, University of North Carolina, Chapel, Hill, North Carolina. April. 

Pechan 2005d. “Development of Growth and Control Inputs for CENRAP 2018 Emissions, 

Draft Technical Support Document”. E.H. Pechan and Associates, Inc. Durham, North 

Carolina. Carolina Environmental Program, University of North Carolina, Chapel, Hill, 

North Carolina. May. 

Pechan and CEP. 2005e. “Refinements of CENRAP’s 2002 Emissions Inventories”. (Schedule 

9; Work Item 3). E.H. Pechan and Associates, Inc. Durham, North Carolina. Carolina 

Environmental Program, University of North Carolina, Chapel, Hill, North Carolina. 

August. 

Pechan and CEP. 2004. “Methods for Consolidation of Emissions Inventories”. (Schedule 9; 

Work Item 3). Prepared for CENRAP Emissions Inventory Workgroup. E.H. Pechan and 

Associates, Inc. Durham, North Carolina. Carolina Environmental Program, University 

of North Carolina, Chapel, Hill, North Carolina. 

Pollack, A., C. Lindhjem, T. Stoeckenius, C. Tran, G. Mansell, M. Jimenez, G. Wilson and S. 

Coulter-Burke. 2004. Evaluation of the U.S. EPA MOBILE6 Highway Vehicle 

Emissions Factor Model, Final Report, CRC Project E-64. ENVIRON International. 

Pollack, A.K, L. Chan, P. Chandraker, J. Grant, C. Lindhjem, S. Rao, J. Russell and C. Tran. 

2006. “WRAP Mobile Source Emission Inventories Update”. ENVIRON International 

Corporation, Novato, CA. May. 

http://www.wrapair.org/forums/ef/UMSI/0606_WRAP_Mobile_Source_EI_Final_Report.

pdf

Rodriguez, M., M. Barna, K. Gebhart, B. Schichtel and W. Malm. 2008. Regional Air Quality 

Model Simulation of the Rocky Mountain Atmosphere Nitrogen and Sulfur Study: 

Preliminary Results and Analysis. Presented at Air & Waste Management Association’s 

Aerosol & Atmospheric Optics: Visual Air Quality and Radiation conference, Moab, 

Utah, April 28 – May 2 

Seaman, N.L. 2000. Meteorological modeling for air quality assessments. Atmos. Environ., Vol. 

34, No. 12-14, 2231-2260. 

Seaman, N.L., D.R. Stauffer, and L.M. Lario. 1995. A multiscale four-dimensional data 

assimilation system applied to the San Joaquin Valley during SARMAP. Part I: Modeling 

design and basic performance characteristics. J. Appl. Meteo., Vol. 34, pp. 1739-1761. 
F:\Denver_O3_2008\Reports\2010_Sens_OSAT\draft#1\Sec4_Refs1.doc August 2008 4-8 

Stauffer, D.R. and N.L. Seaman. 1990. Use of four-dimensional data assimilation in a limitedarea mesoscale model. Part I: Experiments with synoptic data. Mon. Wea. Rev., 118, 

1250-1277. 

Tesche, T.W., D.E. McNally, C. Loomis, R.W. Morris and G.E. Mansell. 2003. “Revised Ozone 

Modeling Protocol -- Air Quality Modeling Analysis for the Denver Early Action Ozone 

Compact: Modeling Protocol, Episode Selection, and Domain Definition”. Prepared by 

Alpine Geophysics, LLC, Ft. Wright, Kentucky and ENVIRON International Corporation, 

Novato, CA. Prepared for Mr. Gerald Dilley, Denver Regional Air Quality Council. 

May. 

Tesche, T.W., R.E. Morris, G. Tonnesen, D.E. McNally, J. Boylan, and P. Brewer. 2005a . 

CMAQ/CAMx annual 2002 performance evaluation over the eastern U.S. Atmospheric 

Environment. 

Tonnesen, G., R.E. Morris, J. Vimont, M. Uhl, K. Briggs and T. Moore. 2003. “The WRAP 

Regional Modeling Center – Application and evaluation of regional visibility models.” 

Presented at AWMA Annual Meeting and Exhibition. June. 

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2005. “Final Report for the 

Western Regional Air Partnership (WRAP) Regional Modeling Center (RMC) for the 

Project Period March 1, 2004, through February 28, 2005”. Prepared for WRAP Regional 

Modeling Center (RMC). August. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2004_RMC_final_report_main_body.pdf

Tonnesen, G., Z. Wang, M. Omary, C-J. Chien, Y. Wang, R. Morris, S. Kemball-Cook, Y. Jia, S. 

Lau, B. Koo, Z. Adelman, A. Holland and J. Wallace. 2006. “Final Report for the 

Western Regional Air Partnership (WRAP) 2002 Visibility Model Performance 

Evaluation”. Prepared for WRAP Regional Modeling Center (RMC). February. 

http://pah.cert.ucr.edu/aqm/308/reports/final/2002_MPE_report_main_body_FINAL.pdf

Yarwood, G., R.E. Morris, M.A. Yocke, H. Hogo and T. Chico. 1996. Development of a 

Methodology for Source Apportionment of Ozone Concentration Estimates from a 

Photochemical Grid Model. Presented at the 89th AWMA Annual Meeting, Nashville 

TN, June 23-28. 

Yarwood, G., S. Shepard, G. Wilson and A. Guenther. 2007. “User’s Guide to the Global 

Biosphere Emissions and Interactions System (GloBEIS) – Version 3.2”. Prepared by 

ENVIRON International Corporation, Novato, CA. November. 

(http://www.globeis.com/data/Users_Guide_Globeis_v3.2.Jan23_2008.pdf). 

Xiu, A. and J.E. Pleim. 2000. Development of a land surface model. Part I: application in a 

mesoscale meteorology model. J. App. Met., 40, pp. 192-209.