Denver Metropolitan Area and North Front Range 8-Hour 

Ozone State Implementation Plan 

Emissions Inventory 

DRAFT FINAL 

October 29, 2008 

DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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Table of Contents 

1 Introduction to the Emission Inventory ...................................................................... 1 

2 Summary of Emission Inventory for 2006 and 2010 Base Case ................................ 2 

3 Summary of Emission Inventory for 2010 Control Case............................................ 9 

4 VOC and NOx Motor Vehicle Emission Budgets.................................................... 13 

4.1 Proposed 2010 Emissions Budgets for the Denver Metro and North Front 

Range 8-Hour Ozone Subareas..................................................................................... 15 

5 Highway Vehicle Sources......................................................................................... 17 

5.1 Ethanol Marketshare Assumptions................................................................... 21 

5.2 2006 Base Year Input to the Mobile Model for Adams, Arapahoe, Boulder, 

Broomfield, Denver, Douglas and Jefferson Counties................................................. 22 

5.3 2006 Base Year Input to the Mobile Model for Larimer and Weld Counties . 23 

5.4 2010 Base Year Input to the Mobile Model for Adams, Arapahoe, Boulder, 

Broomfield, Denver, Douglas and Jefferson Counties................................................. 23 

5.5 2010 Base Year Input to the Mobile Model for Larimer and Weld Counties .. 24 

5.6 2010 Control Case Input to the Mobile Model for Adams, Arapahoe, Boulder, 

Broomfield, Denver, Douglas, and Jefferson Counties................................................ 25 

5.7 2010 Control Case Input to the Mobile Model for Larimer and Weld Counties

 26 

6 Non-Road Mobile Sources........................................................................................ 27 

6.1 Locomotive Emissions...................................................................................... 28 

6.2 Aircraft and Airport Emissions – Denver International Airport....................... 28 

7 Stationary Sources .................................................................................................... 29 

7.1 Area Sources (Non-Oil and Gas)...................................................................... 29 

7.2 Point Source Emissions..................................................................................... 30 

7.2.1 Electrical Generation Utilities (EGUs)..................................................... 30 

7.3 Oil and Gas Emissions...................................................................................... 32 

7.3.1 Calculation of Emission Reductions From the Oil and Gas Industry....... 33 

8 References................................................................................................................. 39 
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List of Tables 

Table 1. Demographic Data ............................................................................................... 3 

Table 2. Base Case Inventories for 8-Hour Ozone DMA/NFR NAA ................................ 8 

Table 3. VOC Base Case and Control Case Emission Inventory ..................................... 11 

Table 4. NOx Base Case and Control Case Emission Inventory...................................... 12 

Table 5. Subarea and Nonattainment Area-Wide 2010 Motor Vehicle Emission Budgets

................................................................................................................................... 15 

Table 6. Distribution of VMT between the Budget Subareas (2010)............................... 16 

Table 7. Emissions summary for July 11 -17 Period from CAMx Ozone Modeling ....... 19 

Table 8. 2006 Emissions Modeling Comparison.............................................................. 20 

Table 9. 2010 Emissions Modeling Comparison.............................................................. 20 

Table 10. 2006 Base Year NONROAD Model Input....................................................... 27 

Table 11. 2010 Base Year and Control Case NONROAD Model Input .......................... 27 

Table 12. Non-Oil and Gas Area Sources - Comparison of 2002 and 2005 NEI............ 29 

Table 13. Reconstructed Count of Small Tanks with VOC Emissions Less than 5 Tons 

per Year..................................................................................................................... 35 

Table 14. Small Condensate Tanks................................................................................... 36 

Table 15. Large Condensate Tanks................................................................................... 37 

Table 16. Nonattainment Area Pneumatic Devices Emissions......................................... 38 

List of Figures 

Figure 1. Denver Metro Area and North Front Range 8-Hour Ozone Emission Budget 

Subareas.................................................................................................................... 14 

Figure 2. Number of Large Tanks by Emission Rate ....................................................... 34 
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1 Introduction to the Emission Inventory 

This portion of the Technical Support Document (TSD) provides greater detail and 

technical information to supplement the description of the Emission Inventory presented 

in other Denver Metro Area and North Front Range 8-hour ozone state implementation 

plan (SIP) documents. 

For additional detail on the emission inventory, see: 

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

“2010 Ozone Attainment Demonstration Modeling for the Denver 8-Hour Ozone 

State Implementation Plan Control Strategy.” ENVIRON International 

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

Council (RAQC), Denver, Colorado. September 22, 2008. 

<http://www.colorado.gov/airquality/documents/deno308/Denver_2010ControlStr

at_Draft_Sep22_2008.pdf> 

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

“Model Performance Evaluation for the June-July 2006 Ozone Episode for the 

Denver 8-Hour Ozone State Implementation Plan.” ENVIRON International 

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

Council (RAQC), Denver, Colorado. August 29, 2008. 

<http://www.colorado.gov/airquality/documents/deno308/Denver_2006MPE_Draf

tFinal_Aug29_2008.pdf
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2 Summary of Emission Inventory for 2006 and 2010 Base Case 

This section presents emissions inventories for the SIP nonattainment area, 2006 base 

case, and the 2010 base case used in the modeling scenarios. Inventories for the 8-hour 

ozone control area 2010 control case modeling are presented later in this document and 

include the additional control measures that are included in the attainment 

demonstration for the 8-hour ozone National Ambient Air Quality Standard (NAAQS). All 

of the base and control case inventories are for the 8-hour ozone nonattainment area 

(NAA), which includes the counties of Denver, Jefferson Douglas, Broomfield, Boulder, 

Adams, Arapahoe, and portions of Weld1

 and Larimer2 counties. These inventories in 

tons per summer day (tpsd) represent emissions estimates for an average episode day 

during the peak summer ozone season (May through September). 

The emission estimates were developed based on the most recent vehicle miles traveled 

(VMT) estimates contained in: 1) Denver Regional Council of Government’s (DRCOG) 

conformity analysis for the updated fiscally constrained element of the 2035 Regional 

Transportation Plan; 2) North Front Range Transportation and Air Quality Planning 

Council’s (NFRTAQPC) 2035 Regional Transportation Plan; 3) the Air Pollution Control 

Division (APCD) estimates of VMT derived from data provided by the Colorado 

Department of Transportation (CDOT); and 4) Population estimates from the State 

Demographer. Demographic data are presented in Table 1. 

1 That portion of Weld County that lies south of a line described as follows: Beginning at a point on Weld County’s 

eastern boundary and Logan County’s western boundary intersected by 40 degrees, 42 minutes, 47.1 seconds north 

latitude, proceed west on 40 degrees, 42 minutes, 47.1 seconds north latitude until this line intersects Weld County’s 

western boundary and Larimer County’s eastern boundary. 

2 That portion of Larimer County (including part of Rocky Mountain National Park) that lies south of a line described 

as follows: Beginning at a point on Larimer County’s eastern boundary and Weld County’s western boundary 

intersected by 40 degrees, 42 minutes, and 47.1 seconds north latitude, proceed west to a point defined by the 

intersection of 40 degrees, 42 minutes, 47.1 seconds north latitude and 105 degrees, 29 minutes, and 40.0 seconds west 

longitude, thence proceed south on 105 degrees, 29 minutes, 40.0 seconds west longitude to the intersection with 40 

degrees, 33 minutes and 17.4 seconds north latitude, thence proceed west on 40 degrees, 33 minutes, 17.4 seconds 

north latitude until this line intersects Larimer County’s western boundary and Grand County’s eastern boundary. 
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Table 1. Demographic Data 

The 2006 and 2010 base case inventories incorporate the control measures in place at 

that time. Control measures in place in 2006 and assumed for 2010 include: 

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

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

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

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

gasoline standards become effective. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

to a national RVP limit of 7.8 pounds per square inch (psi) to reduce fuel 

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

psi RVP waiver for ethanol. 

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

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

of 9.0 psi to reduce fuel volatility. For ethanol-blended fuels, the RVP limit is 10.0 

psi due to the federal 1.0 psi RVP waiver for ethanol. 

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

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

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

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

For purposes of the base case 2010 mobile source inventory, the RVP of the 

base gasoline is assumed to be 7.8 psi for the Denver metropolitan portion of 

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

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

with an ethanol share of 25%. 

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

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

emissions of volatile organic compounds from condensate collection, storage, 

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

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

reduction from uncontrolled emissions of volatile organic compounds from new 

and existing oil and gas exploration and production operations located within the 

8-hour ozone nonattainment area designated by EPA for operators with total 

emissions greater than 30 tons per year. The 2006 base case estimate was 
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developed from actual reported emissions based on the system-wide 47.5% 

reduction requirement. 

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

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

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

season, with technology that achieves a 95% reduction in VOC emissions. The 

2010 base case emissions estimate assumes the 75% system-wide reduction 

requirement. 

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

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

locomotive standards do not go into effect until 2015 and therefore were not 

included in the 2010 inventories. 

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

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

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

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

sources. Estimates for future emissions are based on the above-mentioned tools and the 

EPA’s Economic Growth and Analysis System (EGAS) model for estimating future point 

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

demographic data for off-road and area sources. The technical support document 

contains detailed information on model assumptions and parameters for each source 

category. 

Highway mobile source emissions are from the ENVIRON Consolidated Community 

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

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

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

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

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

and garden equipment and construction equipment. Oil and gas source emissions are 

from the revised Independent Petroleum Association of Mountain States (IPAMS) 

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

methodology document. The IPAMS inventory was sponsored by the IPAMS and is 

Phase III of a regional oil and gas emission inventory for the Inter-Mountain West jointly 

with the Western Regional Air Partnership (WRAP). 

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

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

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

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

in the EPA May 30, 2007 Emission Reduction Credit Memo were applied to the 

projected 2010 non-oil and gas area source inventory. A check on the non-oil and gas 

area sources estimates comparing the recently available 2005 NEI emissions data is 

shown later in this document. An inventory completed in 2005 for Denver International 

Airport (DIA) was used for aircraft and airport non-road source emissions from DIA for 

both 2006 and 2010. 

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

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

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

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

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

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

produced a global data base of land use data, the MEGAN Driving Variable Database 

Version 1.2, for use with MEGAN. Surface temperatures are provided by the Mesoscale 

Meteorological Model (MM5) modeling. 
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Summaries of the VOC and NOx base case inventories for the nonattainment area for 

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

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

the TSD.

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

background ozone concentrations in the modeling effort. Wildfire emissions can vary 

significantly on a day-to-day basis depending on conditions.
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Table 2. Base Case Inventories for 8-Hour Ozone DMA/NFR NAA 
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3 Summary of Emission Inventory for 2010 Control Case 

Reductions from the control measures described in the “Denver Metro Area & North 

Front Range 8-Hour Ozone Attainment Plan” have been applied to the 2010 base case 

emissions inventories to provide an additional safety margin as follows: 

• Reid Vapor Pressure of base gasoline to be 7.8 pounds per square inch (psi) 

(maintains 1.0 psi waiver for ethanol-blended gasoline at 85% market share) in 

North Front Range--estimated 3 tons per day (tpd) VOC reduction to direct 

onroad mobile source emissions and in refueling (gas station) emissions. 

• Controls on new condensate tanks ≥ 2 tons per year (tpy) and existing tanks ≥10 

tpy--estimated 24 tpd reduction in VOC based on an assumed Rule Effectiveness 

adjustment of 0.83 applied to the calculated actual emissions reduction. 

• New and existing pneumatic control devices required to be low-bleed devices-- 

approximately 19 tpd VOC reduction based on an assumed Rule Effectiveness 

adjustment of 0.83. 

• Tighten Regulation No. 11 I/M cut-points--1 tpd VOC, 3 tpd NOx and 13 tpd CO. 

• Additional Regulation No. 3 and No. 7 changes--no additional credit assumed. 

Rule Effectiveness (RE) reflects the actual ability of a regulatory program for controlled 

point sources or source categories to achieve the emissions reductions required by 

regulation. During the Air Quality Control Commission (AQCC) 2006 rule making on 

Regulation No. 7 revisions related to controls on condensate tank emissions, new EPA 

guidance on RE was reviewed. In consultation with EPA Region 8 staff, an RE of 0.83 

was established for the oil and gas industry facilities. This essentially discounts the 

calculated reduction estimates by 17%. The previously agreed upon RE of 0.83 was 

assumed for condensate tank controls and pneumatic devices for the purposes of 

facilitating the 2010 base case and control case modeling. 

The APCD has recently analyzed both the weekly compliance rate through reporting and 

compliance rate of random inspections on condensate controls for the 2007 peak ozone 
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season for each of the companies with total system wide VOC emissions of 30 tpy. The 

analysis indicates an 83% compliance rate based on weekly reporting and a 91% 

compliance rate based on random inspections. Based on this analysis and the proposed 

revisions to strengthen Regulation No. 7, the State believes a rule effectiveness factor of 

at least 0.83 is still valid. Analysis supporting the final RE used in modeling is found in a 

separate TSD. 

The total emission reduction, compared to the 2006, for these control strategies 

(together with the federal and existing state controls assumed for the 2010 base case) is 

approximately 47 tpd VOC and 3 tpd NOx in the 8-hour nonattainment area (However, 

the total VOC reduction could be as great as 70 tpd without the rule effectiveness 

reduction.). The resulting 2010 control inventory based on the total control package 

noted above is presented in Table 3 (VOC) and Table 4 (NOx) for the 8-hour 

nonattainment area. All inventories presented as tons per summer day (tpsd) in this 

section represent a typical average episode day. In the photochemical modeling, all 

anthropogenic source categories are varied by day of the week, time of day, 

temperature, location, speciation and other factors. Biogenic sources are varied by 

differing meteorological conditions and diurnally varied by temperature.
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Table 3. VOC Base Case and Control Case Emission Inventory 
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Table 4. NOx Base Case and Control Case Emission Inventory 
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4 VOC and NOx Motor Vehicle Emission Budgets 

According to EPA regulations and guidance, the SIP may establish a budget or budgets 

that apply to the entire nonattainment area, and/or subarea budgets for each 

metropolitan planning organization or subarea within the nonattainment area. 

For purposes of this SIP, motor vehicle emissions budgets for VOC and NOx are 

established for the 2010 attainment year. Budgets are specifically established for two 

sub-regional areas and for the entire nonattainment area for purposes of transportation 

conformity. The two subareas are defined as follows and shown in Figure 1: 

• Southern Subarea - Area denoted by the ozone nonattainment area south of the 

Boulder County northern boundary and extended through southern Weld County 

to the Morgan County line. This area includes the nonattainment portion of 

DRCOG’s’ regional planning area and the southern Weld County portion of the 

Upper Front Range Transportation Planning Region (TPR). 

• Northern Subarea - Area denoted by the ozone nonattainment area north of the 

Boulder County northern boundary and extended through southern Weld County 

to the Morgan County line. This area includes the North Front Range 

Transportation and Air Quality Planning Council transportation planning area as 

well as the northern ozone nonattainment area portion the Upper Front Range 

TPR in Larimer and Weld counties. 

When subarea budgets are created in the SIP, the sum of the subarea budgets must 

equal the total allowable emissions the area can have from the transportation sector and 

still lead to attainment of the standard. If each subarea meets its motor vehicle emission 

budgets or if the total emissions for the entire nonattainment area (the sum of the 

subareas) are less than or equal to the budget for the entire nonattainment area, then 

the entire area will meet the total SIP’s purpose of attaining the relevant standard. 
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Figure 1. Denver Metro Area and North Front Range 8-Hour Ozone Emission Budget Subareas
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4.1 Proposed 2010 Emissions Budgets for the Denver Metro and North 

Front Range 8-Hour Ozone Subareas 

Table 5 shows both the regional motor vehicle emissions budgets and the separate 

motor vehicle emissions budgets for the ozone precursors VOC and NOx for the two 

subareas discussed above. 

Table 5. Subarea and Nonattainment Area-Wide 2010 Motor Vehicle Emission Budgets 

The 2010 VMT estimates were used with 2010 emission factors obtained from the EPA 

MOBILE6.2 Emission Factor Model to calculate emissions. The two subarea budgets 

presented in the table add to the sum of the total 2010 motor vehicle emissions for the 

entire nonattainment area in the 2010 base case inventory (See Table 2), which 

demonstrates attainment of the standard. 

For the underlying transportation modeling, the roadway and transit links in DRCOG’s 

2005 and 2015 Cycle 2 (2007) networks were truncated to include only the portion of the 

network within the 8-hour ozone nonattainment area. VMT estimates from these 

networks were interpolated to obtain 2006 and 2010 baseline VMT estimates for 

purposes of developing the SIP emissions inventories. Likewise, the 2005 and 2015 

(2007) networks from the North Front Range MPO were truncated to include only the 
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portion of the network within the 8-hour ozone nonattainment area. The VMT estimates 

were interpolated to obtain 2006 and 2010 baseline VMT estimates. Where there was 

overlap between the North Front Range (NFR) and DRCOG networks in Weld County, 

the DRCOG network was used. In areas where there was no MPO network, the Federal 

Highway Authority (FHWA) Highway Performance Management System (HPMS) and 

Colorado Department of Transportation (CDOT) networks, plus a growth factor, were 

used to calculate VMT. 

Table 6 summarizes the VMT estimates for each of the budget subareas. The total VMT 

is identical to the 2010 base case VMT estimates in Table 2.

Table 6. Distribution of VMT between the Budget Subareas (2010) 

The 2006 and 2010 VMT estimates were used with emission factors obtained from the 

EPA Mobile 6.2 Emission Factor Model to calculate emissions. Emissions were 

calculated on a link-by-link basis. Speeds were obtained from the MPO transportation 

networks and the roadway speed limit was used for CDOT links. The ambient 

temperatures for the regional emissions analysis were derived from the meteorological 

modeling performed for the attainment demonstration for a typical ozone episode period. 

The motor vehicle mix was obtained from the CDOT automated traffic counters.
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5 Highway Vehicle Sources 

Emissions modeling was conducted using two systems, the Sparse Matrix Operating 

Kernel Emissions (SMOKE) model (Coats, 1996) and the Consolidated Community 

Emissions Processing Tool (CONCEPT) (Loomis et al., 2005). The CONCEPT linkbased mobile emissions modeling system was used to generate the on-road mobile 

source emissions the Denver Regional Council of Governments (DRCOG) portion of the 

8-hour ozone nonattainment area (NAA). The SMOKE emissions modeling system does 

not generate link-based mobile source emissions and was used for the less critical areas 

of the NAA. SMOKE used countywide vehicle miles traveled (VMT) data from Larimer 

and Weld Counties not covered by the DRCOG transportation network. It used VMT 

from the North Front Range Transportation and Air Quality Planning Council (NFR) and 

Colorado Department of Transportation (CDOT), together with spatial surrogates. 

SMOKE assumes a constant speed across all VMT of the same roadway type. 

The CONCEPT MV emissions model estimates and grids link-level emissions using the 

output from DRCOG Transportation Demand Model (TDM). The TDM provides VMT or 

volume for multi-hour periods, and CONCEPT uses temporal allocation factors and VMT 

mix fractions to estimate hourly emissions for each vehicle class for each roadway Type 

and speed. 

EPA’s EPA Mobile 6.2 Emission Factor Model (MOBILE6) is executed within CONCEPT 

to generate the gram/mile (for running emissions) and gram/trip (for trip start and trip 

ends) emission factors. The emission factors depend on meteorological data 

(temperature and humidity), which are obtained from MM5 meteorological modeling runs 

for every grid cell in the modeling domain, and the speeds associated with each link. 

CONCEPT then estimates emissions for each emissions mode by multiplying the activity 

data (VMT or trips by vehicle class) by the appropriate MOBILE6 emission factors. For 

each hour of each episode day, for each link in each grid cell, CONCEPT uses the grid 
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cell ID, county, temperature increase bin, road type, and speed to determine the correct 

emission factor for each vehicle class, pollutant and (non-start) emission mode. 

Emissions for each vehicle class, emission type, and pollutant are estimated as the 

product of the emission factor and the VMT on that link associated with the vehicle class 

and speed. 

Both CONCEPT and SMOKE use temporal adjustments to adjust VMT for the day of 

week. Both models also speciate the emissions as required for input to an air quality 

model. The result of both CONCEPT and SMOKE was an hourly, gridded, speciated 

inventory for a two-month period ready for input to the Comprehensive Air-quality Model 

with extensions (CAMx) air quality model (ENVIRON, 2008). 

For the SIP summary inventory tables (Table 2, Table 3, and Table 4) and for the Motor 

Vehicle Emissions Budgets in Table 5, a single number for highway vehicle emissions is 

needed. The basic technique used in the CONCEPT model was used to calculate 

emissions for the SIP and the Emission Budgets. The principal difference was that 

emissions were calculated on a daily basis instead of an hourly basis. 

The 2006 and 2010 VMT estimates were used with emission factors obtained from the 

EPA Mobile 6.2 Emission Factor Model to calculate emissions. Emissions were 

calculated on a link-by-link basis. Speeds were obtained from the MPO transportation 

networks and the roadway speed limit was used for CDOT links. The ambient 

temperatures for the regional emissions analysis were derived from the meteorological 

modeling performed for the attainment demonstration for a typical ozone episode period. 

The motor vehicle mix was obtained from the CDOT automated traffic counters. 

For the CONCEPT area modeling (Adams. Arapahoe, Boulder, Broomfield, Denver, 

Douglas, Jefferson and a portion of Weld counties), the ambient temperature used for 

modeling is: MIN/MAX TEMPERATURE: 42.6 101.2. 
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For the SMOKE area modeling (Larimer, and most of Weld counties), the ambient 

temperature used for modeling is: MIN/MAX TEMPERATURE: 59.0 89.0. 

Table 7 presents a summary of the CONCEPT and SMOKE highway vehicle modeling 

used in the CAMx ozone modeling for the July 11-17 period for the base case in 2006 

and 2010. 

Table 7. Emissions summary for July 11 -17 Period from CAMx Ozone Modeling 

July11-17 Emissions Summary for July 11 –17 Ozone Modeling 

(tons/day) weekday

CONCEPT 2006 Fri Sat Sun Mon Tue Wed Thu average

NOX 139.4 102.8 85.2 119.6 120.9 130.9 137.7 129.7

TOG 115.2 88.6 78.5 90.9 87.4 97.1 108.1 99.7

CO 934.2 750.7 663.5 801.8 806.8 862.7 890.1 859.1

 

CONCEPT 2010 

NOX 104.0 77.1 64.1 89.3 90.3 97.7 102.7 96.8

TOG 94.4 74.8 66.8 74.7 71.8 79.3 88.6 81.8

CO 751.9 604.6 532.7 642.5 653.3 697.9 716.4 692.4

SMOKE 2010 

NOx 26.2 22.4 20.4 24.0 23.5 23.8 25.7 24.7

TOG 16.1 15.2 14.5 15.3 14.4 14.7 15.6 15.2

CO 192.5 169.9 155.1 174.9 182.4 180.4 190.2 184.1

TOTAL 2010 

NOx 130.2 99.5 84.4 113.3 113.8 121.6 128.4 121.4

TOG 110.5 90.0 81.2 90.0 86.2 94.0 104.3 97.0

CO 944.4 774.5 687.9 817.4 835.7 878.3 906.6 876.5

Table 8 and Table 9 compare the CONCEPT and SMOKE output summary on a 

weekday average basis with the single number used in summary Table 2, Table 3, and 

Table 4 and in the Motor Vehicle Emissions Budgets in Table 5. As can be seen, the 

single numbers calculated for the SIP and Emission Budgets are a reasonable 

representation of the emissions used in the ozone modeling. 
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Table 8. 2006 Emissions Modeling Comparison 

 July11-17 CONCEPT MODEL SIP Method 

week day average DRCOG tons % diff

NOX 129.7 135.4 4.4%

TOG/VOC 99.7 100.4 0.6%

CO 859.1 930.3 8.3%

Smoke* non-DRCOG tons % diff

NOX 39.611 28.5 -28.0%

TOG/VOC 21.177 20.4 -3.5%

CO 276.492 196.8 -28.8%

 NAA TOTAL 2006 SIP NAA TOTAL % diff

NOX 169.3 163.9 -3.2%

TOG/VOC 120.9 120.8 -0.1%

CO 1135.6 1127.1 -0.8%

 * 2006 Smoke is from Tuesday July 18, 2006 

Table 9. 2010 Emissions Modeling Comparison 

 

July11-17 CONCEPT 

MODEL SIP Method 

week day average 

DRCOG 2010 

tons % diff

NOX 96.8 100.4 3.7%

TOG/VOC 81.8 86.9 6.3%

CO 692.4 775.5 12.0%

 Smoke 

non-DRCOG 

tons % diff

NOX 24.650 22.5 -8.7%

TOG/VOC 15.236 19.5 27.8%

CO 184.083 189.2 2.8%

 NAA TOTAL 2010 SIP NAA TOTAL % diff

NOX 121.4 122.9 1.2%

TOG/VOC 97.0 106.4 9.7%

CO 876.5 964.7 10.1%
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

21

5.1 Ethanol Marketshare Assumptions 

The 2006 60% ethanol marketshare for Denver is based on actual sampling. The 

increase in 2010 accounts for marketshare trends, most notably actual sampling in 2005 

and 2007 showing an 85% ethanol marketshare. Actual sampling was also used to 

calculate the 60% NFR marketshare for 2006. However, because over the years prior to 

2008 the NFR sampling has been done on a smaller scale, and sample locations have 

not been as rigorously selected, the Division did not feel as comfortable projecting out a 

marketshare to 2010, and accordingly, conservatively estimated that the 2010 

marketshare in the NFR would be 25% consistent with the marketshare utilized in the 

EAC modeling. In retrospect, the Division agrees that for consistency sake, the same 

projecting out methodology used in Denver should have been used for the NFR, 

notwithstanding the smaller sample set. Nevertheless, based on the ethanol sensitivity 

tests for 2010, 0% vs 100% ethanol market penetration for the entire NAA area does not 

change the outcome of the ozone modeling attainment demonstration at the key 

monitors (e.g., Rocky Flats North and Fort Collins West). Therefore, it can be concluded 

that changing the ethanol market penetration for the NFR from 25% to a higher 

percentage based on projecting out from a limited sample set would have a negligible 

effect on ozone. 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

22

5.2 2006 Base Year Input to the Mobile Model for Adams, Arapahoe, 

Boulder, Broomfield, Denver, Douglas and Jefferson Counties

REBUILD EFFECTS : 0.10 

EXPAND EVAPORATIVE : 

EXPAND EXHAUST : 

I/M PROGRAM : 1 1982 2050 2 T/O 2500/IDLE 

I/M MODEL YEARS : 1 1982 2050 

I/M VEHICLES : 1 11111 22222222 2 

I/M STRINGENCY : 1 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 1 95.0 

I/M WAIVER RATES : 1 .00 .57 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 1 5 

I/M PROGRAM : 2 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 2 1982 2050 

I/M CUTPOINTS : 2 06CUTPC.D 

I/M VEHICLES : 2 21111 11111111 1 

I/M STRINGENCY : 2 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 2 95.0 

I/M WAIVER RATES : 2 .00 .64 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 2 5 

I/M PROGRAM : 3 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 3 1982 2050 

I/M CUTPOINTS : 3 06CUTPT.D 

I/M VEHICLES : 3 12222 11111111 1 

I/M STRINGENCY : 3 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 3 95.0 

I/M WAIVER RATES : 3 .00 .91 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 3 5 

I/M PROGRAM : 4 1998 2050 2 T/O GC 

I/M MODEL YEARS : 4 1982 2050 

I/M VEHICLES : 4 22222 11111111 1 

I/M COMPLIANCE : 4 94.8 (Compliance data from insp. year 2001) 

I/M WAIVER RATES : 4 .00 .91 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 4 5 

ANTI-TAMP PROG : 

82 75 02 22222 22222222 2 12 095. 22111112 

FUEL PROGRAM : 4 

 88.0 116.0 122.0 124.0 74.0 57.0 57.7 30.0 

 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 

1000.0 1000.0 1000.0 1000.0 303.0 303.0 248.0 87.0 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 

OXYGENATED FUELS : 0.000 0.600 0.000 0.035 2 

FUEL RVP : 7.7 

REG DIST : REG_MET.D 

 </run> 

 <scenario> 

ALTITUDE : 2 

5.3 2006 Base Year Input to the Mobile Model for Larimer and Weld 

Counties 

REBUILD EFFECTS : 0.10 

EXPAND EVAPORATIVE : 

EXPAND EXHAUST : 

FUEL PROGRAM : 4 

 88.0 116.0 122.0 124.0 74.0 57.0 57.7 30.0 

 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 

1000.0 1000.0 1000.0 1000.0 303.0 303.0 248.0 87.0 

 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 

OXYGENATED FUELS : 0.000 0.600 0.000 0.035 2 

FUEL RVP : 7.4 

REG DIST : REG_LAR.D 

 </run> 

 <scenario> 

ALTITUDE : 2 

5.4 2010 Base Year Input to the Mobile Model for Adams, Arapahoe, 

Boulder, Broomfield, Denver, Douglas and Jefferson Counties

REBUILD EFFECTS : 0.35 

I/M PROGRAM : 1 1982 2050 2 T/O 2500/IDLE 

I/M MODEL YEARS : 1 1982 2050 

I/M VEHICLES : 1 11111 22222222 2 

I/M STRINGENCY : 1 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 1 95.0 

I/M WAIVER RATES : 1 .00 .57 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 1 5 

I/M PROGRAM : 2 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 2 1982 2050 

I/M CUTPOINTS : 2 10CUTPC.D 

I/M VEHICLES : 2 21111 11111111 1 

I/M STRINGENCY : 2 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 2 95.0 

I/M WAIVER RATES : 2 .00 .64 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 2 5 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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I/M PROGRAM : 3 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 3 1982 2050 

I/M CUTPOINTS : 3 10CUTPT.D 

I/M VEHICLES : 3 12222 11111111 1 

I/M STRINGENCY : 3 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 3 95.0 

I/M WAIVER RATES : 3 .00 .91 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 3 5 

I/M PROGRAM : 4 1998 2050 2 T/O GC 

I/M MODEL YEARS : 4 1982 2050 

I/M VEHICLES : 4 22222 11111111 1 

I/M COMPLIANCE : 4 94.8 (Compliance data from insp. year 2001) 

I/M WAIVER RATES : 4 .00 .91 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 4 5 

ANTI-TAMP PROG : 

82 75 02 22222 22222222 2 12 095. 22111112 

FUEL PROGRAM : 3 

OXYGENATED FUELS : 0.000 0.850 0.000 0.035 2 

FUEL RVP : 7.8 

REG DIST : REG_MET.D 

5.5 2010 Base Year Input to the Mobile Model for Larimer and Weld 

Counties 

REBUILD EFFECTS : 0.35 

EXPAND EVAPORATIVE : 

EXPAND EXHAUST : 

FUEL PROGRAM : 3 

OXYGENATED FUELS : 0.000 0.250 0.000 0.035 2 

FUEL RVP : 9.0 

REG DIST : REG_LAR.D 

 </run> 

 <scenario> 

ALTITUDE : 2 

The REBUILD EFFECTS command allows the user to change the Rebuild program 

effectiveness rate used to reduce heavy-duty diesel vehicle NOx off-cycle emissions. 

The command was used by the contractors in the SIP modeling, and was set to be 

consistent with the values used in other SIPs ( those done by NESCAUM and LADCO). 

The command reduces the credit assigned to this program from the default effectiveness 

rate of 90%. 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

25

5.6 2010 Control Case Input to the Mobile Model for Adams, Arapahoe, 

Boulder, Broomfield, Denver, Douglas, and Jefferson Counties 

REBUILD EFFECTS : 0.35 

EXPRESS HC AS VOC : 

 

I/M PROGRAM : 1 1982 2050 2 T/O 2500/IDLE 

I/M MODEL YEARS : 1 1982 2050 

I/M VEHICLES : 1 11111 22222222 2 

I/M STRINGENCY : 1 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 1 95.0 

I/M WAIVER RATES : 1 .00 .57 (Pre 81 rate n/a, post 80 rates from 

insp. year 2001) 

I/M GRACE PERIOD : 1 5 

I/M PROGRAM : 2 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 2 1982 2050 

I/M CUTPOINTS : 2 10CPCb.D 

I/M VEHICLES : 2 21111 11111111 1 

I/M STRINGENCY : 2 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 2 95.0 

I/M WAIVER RATES : 2 .00 .26 (Pre 81 rate n/a, post 80 rates from 

insp. year 2007) 

I/M GRACE PERIOD : 2 5 

I/M PROGRAM : 3 1982 2050 2 T/O IM240 

I/M MODEL YEARS : 3 1982 2050 

I/M CUTPOINTS : 3 10CPTb.D 

I/M VEHICLES : 3 12222 11111111 1 

I/M STRINGENCY : 3 10.0 (Set to min. allowed, pre 81 stringency not 

applicable) 

I/M COMPLIANCE : 3 95.0 

I/M WAIVER RATES : 3 .00 .16 (Pre 81 rate n/a, post 80 rates from 

insp. year 2007) 

I/M GRACE PERIOD : 3 5 

I/M PROGRAM : 4 1998 2050 2 T/O GC 

I/M MODEL YEARS : 4 1982 2050 

I/M VEHICLES : 4 22222 11111111 1 

I/M COMPLIANCE : 4 94.8 (Compliance data from insp. year 2001) 

I/M WAIVER RATES : 4 .00 .26 (Pre 81 rate n/a, post 80 rates from 

insp. year 2007) 

I/M GRACE PERIOD : 4 5 

ANTI-TAMP PROG : 

82 75 02 22222 22222222 2 12 095. 22111112 

 

REG DIST : ..\..\regdist\Reg_Met.D 

FUEL PROGRAM : 3 

FUEL RVP : 7.8 

OXYGENATED FUELS : .000 .850 .000 .035 2 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

26

MIN/MAX TEMPERATURE: 42.6 101.2

5.7 2010 Control Case Input to the Mobile Model for Larimer and Weld 

Counties 

REBUILD EFFECTS : 0.35 

REG DIST : ..\..\regdist\REG_LAR.D 

FUEL PROGRAM : 3 

OXYGENATED FUELS : 0.000 0.850 0.000 0.035 2 

FUEL RVP : 7.8 

MIN/MAX TEMPERATURE: 42.6 101.2 

The control case uses more stringent I/M cutpoints in the Denver area, along with 

updated I/M program effectiveness parameters, and 7.8 RVP gasoline in Larimer and 

Weld Counties. 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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6 Non-Road Mobile Sources 

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

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

lawn and garden equipment and construction equipment. 

Inputs to the NONROAD Model are shown in Table 10 and Table 11. 

Table 10. 2006 Base Year NONROAD Model Input 

Fuel RVP (psi) : 8.20 

Fuel Oxygen weight %: 2.04 

Gasoline Sulfur % : 0.0339 

Diesel Sulfur % : 0.0500 

Marine Diesel Sulfur: 0.0500 

LPG/CNG Sulfur % : 0.0030 

Minimum Temperature : 58.00 

Maximum Temperature : 91.00 

Average Ambient Temp: 77.30 

Table 11. 2010 Base Year and Control Case NONROAD Model Input 

Fuel RVP for gas : 8.8 

Oxygen Weight % : 2.97 

Gas sulfur % : 0.0011 

Diesel sulfur % : .0050 

Marine Dsl sulfur %: .0050 

CNG/LPG sulfur % : 0.003 

Minimum temper. (F): 58.0 

Maximum temper. (F): 91.0 

Average temper. (F): 77.3 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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6.1 Locomotive Emissions 

Locomotive emissions from the 2002 NEI were grown by population growth and the 

effect of EPA final locomotive Tier 3 standards were considered and included, where 

appropriate, in the 2010 area source estimates. The effect of the standards were 

calculated based on “Regulatory Impact Analysis: Control of Emissions of Air Pollution 

from Locomotive Engines and Marine Compression Ignition Engines Less than 30 Liters 

Per Cylinder” (EPA, March 2008). 

6.2 Aircraft and Airport Emissions – Denver International Airport 

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

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

(Ricondo & Associates, June 2005). 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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7 Stationary Sources 

7.1 Area Sources (Non-Oil and Gas) 

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

pesticides, etc) are from the 2002 EPA National Emissions Inventory (NEI), grown to 

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

now has a 2005 NEI available, it is only a placeholder Inventory because there are major 

revisions to the NEI methodology that are to be implemented with the 2008 NEI. For 

area sources, the 2002 and 2005 NEIs are identical, as seen in Table 12. 

Table 12. Non-Oil and Gas Area Sources - Comparison of 2002 and 2005 NEI 

9 County Metro Area 2005 NEI tons/year 9 County Metro Area 2002 NEI tons/year 

TIER1NAME TIER3NAME VOC SCC6_DESC SCC8_DESC VOC 

SOLVENT UTILIZATION architectural 5,354.36 Architectural Coatings Total: All Solvent Types 5354.36

 

 All Household Products Total: All Solvent Types 1740.26

 All Products/Processes Total: All Solvent Types 79.29

 

Automotive Aftermarket 

Products Total: All Solvent Types 2505.13

 Household Products Total: All Solvent Types 2731.89

 Personal Care Products Total: All Solvent Types 1522.11

SOLVENT UTILIZATION 

consumer 

solvents 8,578.68 Consumer Solvents SUM 8578.68

 

Pesticide Application: 

Agricultural All Processes 379.76

 Pesticide Application Total: All Solvent Types 379.76

SOLVENT UTILIZATION 

pesticide 

application 759.52 Pesticide SUM 759.52

SOLVENT UTILIZATION traffic markings 374.10 Traffic Markings Total: All Solvent Types 374.1

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

in the EPA May 30, 2007 Emission Reduction Credit Memo were applied to the 

projected 2010 non-oil and gas area source inventory. Non-oil and gas point source 

emissions were grown to 2010 by the EPA EGAS economic model, and by adding 

sources for which permits have been issued. 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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7.2 Point Source Emissions 

Point source emissions were taken from Air Pollution Control Division's (APCD) Air 

Pollutant Emission Notice (APEN) database. All sources in Colorado emitting criteria 

and/or hazardous air pollutants (HAPs), including those emitting such ozone formation 

contributors (OFCs) as volatile organic compounds (VOCs) and criteria pollutants such 

as nitrogen oxides (NOx) specifically, are required to submit an APEN. The de minimis 

level for reporting criteria pollutants is 1 ton/year (tpy) in nonattainment areas and 2 

tons/year in attainment areas (actual uncontrolled emissions). In addition, source 

inspections, the active contacting of sources identified from mailing lists, and stricter 

permitting requirements contribute to the APCD’s knowledge of potential emissions 

sources of OFCs. For HAPs the de minimis levels for reporting vary based on a 

combination of the specific HAP's toxicity and scenarios for its release, but can be as 

low as 50 pounds/year. Estimates for future emissions are based on the EPA’s 

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

sources activity. 

7.2.1 Electrical Generation Utilities (EGUs) 

Continuous Emissions Monitoring (CEM) data for electrical generation utilities (EGUs) in 

the vicinity of Denver were used for the 2006 Actual Base Case emissions inventory. 

The data were analyzed to also develop point source emissions for the 2006 Typical 

Base Case emissions inventory. The CEM data analysis resulted in emissions that were 

lower than the reported APEN emissions. Because of this, EGU emissions for 2010 

were not grown using EGAS. Instead, the 2006 reported APEN emissions were used. 

For the photochemical modeling, actual hourly CEM emission data were modeled for the 

2006 model performance evaluation runs. Then, using the CEM data, "typical" temporal 

emissions profiles were developed. These temporal profiles were designed to reflect the 

expected emissions patterns for the local area and meteorological conditions being 

modeled. That is, the temporal profiles derived from the CEM data were used to 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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disaggregate the annual emissions to the daily and hourly estimates required for input to 

the photochemical model 

To account for growth in EGU emissions from recently permitted emission units that are 

not included in the 2006 APEN inventory but expected to be in operation by 2010, caseby-case review was conducted to determine the actual emissions for 2010. Specifically: 

• Comanche Power Plant. The new Unit 3 was permitted subject to netting under 

Regulation No. 3. As part of the SIP inventory development process, it was 

determined that the actual emissions from all three Comanche units in 2006 

would be a reliable estimate of actual emissions in 2010 for NOx and SO2. 

However, since the increase in CO and VOC emissions from Unit 3 were not 

accounted for in the 2006 emissions estimates from Unit 1 and Unit 2, the 

increase in CO and VOC emissions from the new Unit 3 were added to the 2010 

inventory. 

• Fort Saint Vrain Power Plant. Permitted emission limits for two new turbines were 

included in the 2010 inventory. 

• Plains End Generating Station. Permitted emission limits for fourteen new 

natural-gas fired ICE units were included in the 2010 inventory. 

• Platte River Power Authority – Rawhide Power Plant. Permitted emission limits 

for a new turbine was included in the 2010 inventory. 

• Spindle Hill Energy. Permitted emission limits for new turbines were included in 

the 2010 inventory. 

• Tri-State Generation Craig Plant. A permit modification at this facility was subject 

to netting under Regulation No. 3. It was determined that the actual emissions for 

this facility in 2006 are a reliable estimate of actual emissions in 2010. 

 
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7.3 Oil and Gas Emissions 

Oil and gas source emissions are based on estimates from the WRAP Phase III oil and 

gas emissions inventory development study, which was sponsored by the Independent 

Petroleum Association of Mountain States (IPAMS): 

http://www.wrapair.org/forums/ssjf/documents/eictts/OilGas/2008-

04_%2706_Baseline_Emissions_DJ_Basin_Technical_Memo_(04-30).pdf

or 

http://www.colorado.gov/airquality/documents/deno308/2008-

04_2706_Baseline_Emissions_DJ_Basin_Technical_Memo_(04-30).pdf 

WRAP Phase III oil and gas emissions were projected to 2010 using the methodology in 

the WRAP Phase III projection methodology document: 

http://www.wrapair.org/forums/ssjf/documents/eictts/OilGas/2008-

04_%2710_Projection_Emissions_DJ_Basin_Technical_Memo(04-30).pdf

or 

http://www.colorado.gov/airquality/documents/deno308/2008-

04_2710_Projection_Emissions_DJ_Basin_Technical_Memo(04-30).pdf 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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7.3.1 Calculation of Emission Reductions From the Oil and Gas Industry 

7.3.1.1 Condensate Tank Emissions Controls 

Uncontrolled emissions from condensate tanks are from the IPAMS inventory. The 

modifications to Regulation 7 would control emissions from all tanks greater than 10 tons 

per year by 95% and new and modified small tanks greater than 2 tons per year by 95%. 

The basic equation for calculating controlled emissions is as follows. 

Equation 1: 

 Controlled emissions = Uncontrolled emissions X (1 – CE x RE x RP)

Where CE is the control efficiency (95%), RE is the rule effectiveness (a discount to 

account for less than perfect compliance, calculated elsewhere in the TSD as 83% or 

0.83) and RP is rule penetration, calculated below. 

7.3.1.1.1 Small Tanks (Less than 5 tons per year): 

The 2007 Air Pollution Emission Notice (APEN) data (the latest complete year) was used 

as the basis to calculate the average effectiveness of emissions controls for tanks. 

Since only data for units with emissions of more than 5 tons per year were required to be 

submitted, the data are essentially nonexistent for small tanks and unreliable. The 

APEN data are limited to tanks greater than 5 tons per year within the 8-Hour Ozone 

Nonattainment Area (NAA). 

Given this, two approaches could be used to estimate the number of small tanks for 

each range of emissions (greater than zero to 1 ton per year, greater than 1 to 2 tons per 

year, greater than 2 to 3 tons per year, greater than 3 to 4 tons per year, and greater 

than 4 to 5 tons per year). One approach would be to assume a statistical distribution 

and try to use data from large tanks to infer information about small tanks.. Another 

approach is to develop a mathematical model to predict the number of small units. 

The Division investigated both approaches and provided some preliminary results to 

stakeholders based on the first approach. However, upon further review, the Division 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

34

decided that the second approach would provide a more technically defensible result 

because there is insufficient data to determine the type of statistical distribution to apply 

to small tanks. 

A regression modeling approach was chosen. It uses the large tank APEN data to 

construct a regression analysis for the relationship between the number of units in each 

range of 1-ton interval of emissions and the emission rate. This regression is presented 

below in Figure 2 below. 

Figure 1: Number of Large 

Tanks by Emission Rate

Greater Than 5 tons per year (2007 Inventory Year APENS)

y = -0.0042x3 + 0.5721x2 - 25.761x + 406.42

R2

 = 0.971

-100

0

100

200

300

400

500

0 10 20 30 40 50 60 7

Emissions (tons per year)

Number of Tanks

0

Figure 2. Number of Large Tanks by Emission Rate 

The regression equation has an R2 value of 0.97. That is, the regression equation fits the 

data well. A fundamental assumption in this approach is that the same equation will be a 

good predictor for the number of small tanks beyond the range of available APEN data. 

Based on the regression equation in the Figure 1, (y = -0.0042x3

 + 0.5721x2 - 25.761x + 

406.42) where y is the number of units at each emission interval and x is the emission 

rate in each 1 ton per year interval, the number of units in each interval of small tank 

emissions was determined. 

Evaluating the equation for the interval from 3 to 4 (3), we find: 

Y = -0.0042x(3)3

 + 0.5721x(3)2 - 25.761x(3) + 406.42 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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Y = -0.1134 + 5.1489 + -77.283 + 406.42 

Y = 334.1525

The results of the reconstructed count and corresponding emissions in tons per year are 

given in Table 13 below. 

Table 13. Reconstructed Count of Small Tanks with VOC Emissions Less than 5 Tons 

per Year 

ton/year interval Count Total Emissions 

0 

reconstructed 

count (t/y - 0.5) x Count 

1 381 191 

2 357 536 

3 334 835 

4 312 1,093 

5 291 1,311 

The last column of Table 13 is calculated by multiplying the count by the assumed 

average emission rate for each interval (assumed to be the midpoint of the interval – that 

is 1.5 for the 1 to 2 interval). This column represents the total emissions of all sources in 

each interval. So for the interval 3 we have: 

emissions = 2.5 x 334 = 835 tons per year 

The emissions from 2 to 5 tons per year sum to 3,240 tons (835 + 1093 + 1311). The 

emissions from 0 to 5 tons per year sum to 3,966 tons. Dividing 3,240 by 3,966 gives 

the fraction of emissions affected by controlling units with emissions greater than 2 tons 

per year. This fraction, 0.82, is also called “Rule Penetration” (RP). 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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Table 14 summarizes the results of Equation 1 and the IPAMS inventory for small 

condensate tanks. 

Table 14. Small Condensate Tanks 

County 

2006 

Uncontrolled 

Emissions T/Y 

Growth 

Factor 

2010 

Uncontrolled 

Emissions T/Y 

New 

Emissions 

Uncontrolled 

OLD 

Emissions 

2010 

Uncontrolled CE RP RE 

New 

Emissions 

2010 

Controlled 

OLD 

Emissions 

2010 

Controlled 

OLD 

Controlled 

+ NEW 

Controlled 

ADAMS 173.7 0.730 126.86 126.86 0 0.82 0.83 0 126.9 126.86

ARAPAHOE 23.9 0.730 17.47 17.47 0 0.82 0.83 0 17.5 17.47

BOULDER 56.6 0.730 41.32 41.32 0 0.82 0.83 0 41.3 41.32

BROOMFLD 13.6 0.730 9.92 9.92 0 0.82 0.83 0 9.9 9.92

DENVER 6.3 0.730 4.58 4.58 0 0.82 0.83 0 4.6 4.58

LARIMER 36.5 0.730 26.63 26.63 0 0.82 0.83 0 26.6 26.63

WELD 5,208.8 1.302 6,784.40 393.90 6,390.51 0.95 0.82 0.83 140 6390.5 6,530.70

TOTAL 5,519.4 7,011.17 372.94 6,617.27 140 6,617.27 6,757.46

Total 

Tons/Day 15.1 19.2 1.0 18.1 0.4 18.1 18.5 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

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7.3.1.1.2 Large Tanks (Greater than 5 tons per year) 

Table 15 summarizes the results of Equation 1 and the IPAMS inventory for large 

condensate tanks. The rule penetration for large tanks was calculated from the APEN 

data, and is the fraction of large tanks that have emissions greater than 10 tons per year. 

Table 15. Large Condensate Tanks 

County 

2006 

Uncontrolled 

Emissions 

T/Y 

Growth 

Factor 

2010 

Uncontrolled 

Emissions T/Y 

Control 

Factor RP RE 

New 

Emissions 

2010 

Controlled 

OLD 

Emissions 

2010 

Controlled 

Controlled 

2010 T/Y 

ADAMS 2,644.7 0.730 1,930.99 1,930.99 0.95 0.884 0.830 0 584.7 584.74

ARAPAHOE 364.2 0.730 265.89 265.89 0.95 0.884 0.830 0 80.5 80.52

BOULDER 861.5 0.730 629.02 629.02 0.95 0.884 0.830 0 190.5 190.48

BROOMFLD 206.7 0.730 150.93 150.93 0.95 0.884 0.830 0 45.7 45.70

DENVER 95.4 0.730 69.65 69.65 0.95 0.884 0.830 0 21.1 21.09

LARIMER 555.1 0.730 405.33 405.33 0.95 0.884 0.830 0 122.7 122.74

WELD 79,287.7 1.302 103,271.06 5,995.83 97,275.23 0.95 0.884 0.830 1,268 29456.6 30,724.73

TOTAL 84,015.4 1.27028 106,722.87 5,676.88 100,727.03 1,268.12 30,501.88 31,770

Total 

T0ns/Day 230.2 292.4 15.6 276.0 3.5 83.6 87.0

In applying Equation 1 in Table 15, rule penetration is as shown in the table for existing 

tanks, but is 1.00 for new and modified tanks, since all new and modified tanks are 

controlled. 
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

38

7.3.1.2 Pneumatic Device Emissions Controls 

Uncontrolled emissions from Pneumatic Devices are from the IPAMS inventory. The 

modifications to Colorado Air Quality Control Commission Regulation 7 would require 

the use of low-bleed devices, which have been determined elsewhere in the TSD to 

control emissions from Pneumatic Devices by 74.8% (using enhanced maintenance). 

The basic equation for calculating controlled emissions is Equation 1. The result of 

applying Equation 1 to the IPAMS inventory is shown in Table 16, below. The rule 

penetration is 1.00 because all devices in the NAA are to be controlled. The calculation 

of rule effectiveness is discussed elsewhere in the TSD. 

Table 16. Nonattainment Area Pneumatic Devices Emissions 

Nonattainment Area Pneumatic Devices Emissions (tons/year) 

County 

2010 

Uncontrolled 

Emissions 

T/Y 

Control 

Factor

Rule 

Penetration

Rule 

Effectiveness 

Pneumatic 

Devices 

Controlled 

2010 T/Y 

ADAMS 595 0.748 1 0.83 226

ARAPAHOE 68 0.748 1 0.83 26

BOULDER 167 0.748 1 0.83 63

BROOMFLD 42 0.748 1 0.83 16

DENVER 23 0.748 1 0.83 9

LARIMER 65 0.748 1 0.83 25

WELD 10,395 0.748 1 0.83 3,940

Grand Total 11,355 4,304

Tons Per 

Day 31.1 11.8
DRAFT FINAL - Denver Metro Area/North Front Range 8-hr Ozone SIP – Emission Inventory 

39

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