Carbon Monoxide 

State Implementation Plan Revision 

Las Vegas Valley Nonattainment Area 

Clark County, Nevada 

October 2005 

Clark County Department of Air Quality 

and Environmental Management
Carbon Monoxide State Implementation Plan Revision 

ACKNOWLEDGMENTS 

CLARK COUNTY BOARD OF COMMISSIONERS 

Rory Reid, Chair 

Myrna Williams, Vice-Chair 

Tom Collins 

Yvonne Atkinson Gates 

Chip Maxfield 

Lynette Boggs McDonald 

Bruce Woodbury 

OFFICE OF THE COUNTY MANAGER 

Thom Reilly, County Manager 

Darryl Martin, Assistant County Manager 

Elizabeth Macias Quillin, Assistant County Manager 

Virginia Valentine, Assistant County Manager 

DEPARTMENT OF AIR QUALITY AND ENVIRONMENTAL MANAGEMENT 

Christine Robinson, Director 

Lewis Wallenmeyer, Assistant Director 

Alan Pinkerton, Deputy Director 

Dennis Ransel, Planning Manager 

Cheng Shih, Assistant Planning Manager 

John Koswan, Assistant Planning Manager 

Zheng Li, Modeler 

Ebrahim Juma, Senior Air Quality Specialist 

Melissa Hamner, Technical Writer 

REGIONAL TRANSPORTATION COMMISSION 

Bruce Turner, Planning Manager 

Jerry Duke, Assistant Planning Manager 

Brian Hoeft, Principal Planner 

Sarah Sun, Principal Planner 

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Carbon Monoxide State Implementation Plan Revision 

EXECUTIVE SUMMARY 

This document is a revision of the August 2000 Carbon Monoxide State Implementation Plan,

Las Vegas Valley Nonattainment Area, Clark County, Nevada (2000 CO SIP). Its purpose is to 

update carbon monoxide motor vehicle emissions budgets using MOBILE6, the latest model 

approved by the U.S. Environmental Protection Agency (EPA) for use in transportation 

conformity determinations. 

In the mid-1980s, portions of the Las Vegas Valley began violating the carbon monoxide (CO) 

National Ambient Air Quality Standards (NAAQS) during the winter months. The number and 

severity of these violations caused EPA to designate the valley as a “moderate” nonattainment 

area upon enactment of the Clean Air Act Amendments in November 1990. When Clark County 

did not attain the CO standards after a one-year extension to the required attainment date, EPA 

reclassified the valley as a “serious” CO nonattainment area. The county began development of a 

state implementation plan (SIP) to establish measures for attaining the standards by the end of 

2000, and in August 2000 the Clark County Board of County Commissioners adopted the plan. 

EPA issued a final approval of the 2000 CO SIP in September 2004, and in June 2005 EPA 

found that the Las Vegas Valley had attained the standards by the applicable date of December 

31, 2000. 

During the past several years, the valley has experienced substantial improvement in air quality: 

no violations of the 8-hour CO standard have been recorded since 1998. There has been a similar 

reduction in the intensity of CO concentrations. CO exceedances (but not necessarily violations) 

often totaled 40 or more per year in the 1980s. During 1997 and 1998, the valley experienced 

only four unhealthful and three exceedance days. Exceedances and violations of the 8-hour CO 

standard eased by 1999, and there have been no recorded exceedances since then. 

The greatest modeling effort in this CO SIP revision centered on updating the on-road mobile 

source inventory estimates. This revision focused on recalculating the emissions for on-road and 

non-road sources using the newer MOBILE6.2 and NONROAD2004 models, respectively, then 

running the Urban Airshed Model and the CAL3QHC model to determine if the Las Vegas 

Valley will continue to maintain the CO standards through 2030. The results, as Sections 5 and 6 

describe, confirm continued maintenance: model runs for maximum CO levels using 

MOBILE6.2 do not show any violations through 2030. 

DAQEM updated its CO modeling and conformity analysis for this 2005 CO SIP revision using 

the latest tools, data resources, and methodologies available. The 2000 CO SIP was based on 

computer modeling of the single best performing episode of the three originally modeled: the 

night of December 8-9 (Sunday-Monday), 1996. The EPA regional office approved this 

selection, along with a scaling factor that resulted in a maximum predicted concentration of 11.2 

ppm. This SIP revision continues to rely on the December 8-9, 1996 episode as a base case, but 

uses new data on population and travel projections for conducting the MOBILE6.2 analysis. For 

the 1996 base year, the original TRANPLAN output was used to define traffic volume-related 

parameters. For all future years modeled, the Regional Transportation Commission of Southern 

Nevada provided output from the new TransCAD transportation demand model. Population 

iii
Carbon Monoxide State Implementation Plan Revision 

projections (and actual population for 2000) were modified to reflect higher growth rates in the 

county. 

EPA requires that SIPs also provide for maintaining health standards after attainment. This plan 

revision assures the public that implementation of the programs in the 2000 CO SIP and 

maintenance of the CO health standards will continue through 2030. Since Clark County has 

now reached attainment, and the primary source of CO is the on-road mobile sources category, 

projections for a 30-year horizon past the demonstration date have been forecast. With new 

planning tools and better predictive capabilities (such as MOBILE6) available, Clark County will 

continue to reanalyze and confirm long-term maintenance of the CO health standards. 

Since additional modeling will likely be required for maintenance plan submittals from areas 

seeking redesignation, this SIP revision updates the mobile emission model analysis to provide a 

basis for development of a formal CO maintenance plan and a redesignation request in the near 

future. The Las Vegas Valley air quality implementation plan will remain in effect until 

superseded by an approved CO maintenance plan. 

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Carbon Monoxide State Implementation Plan Revision 

TABLE OF CONTENTS 

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

1.1. Problem Statement..................................................................................................... 1-2 

1.2. Physical Description .................................................................................................. 1-2 

1.3. Climatological Setting ............................................................................................... 1-3 

1.4. Organization of this Revision .................................................................................... 1-3 

2. MONITORING NETWORK AND TRENDS IN AIR QUALITY ................................. 2-1

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

2.2. Background................................................................................................................ 2-1 

2.3. Monitoring Network .................................................................................................. 2-1 

2.4. Trends in Carbon Monoxide Air Quality................................................................... 2-3 

2.5. Carbon Monoxide Saturation Study........................................................................... 2-6 

3. EMISSION INVENTORY SUMMARY............................................................................ 3-1

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

3.2. Emissions Summary by Category.............................................................................. 3-2 

3.2.1. On-Road Mobile Emissions........................................................................... 3-3 

3.2.2. Non-Road Mobile Emissions......................................................................... 3-8 

3.2.3. Point Sources ............................................................................................... 3-10 

3.2.4. Area Sources................................................................................................ 3-11 

3.3. Total Annual Emissions........................................................................................... 3-11 

4. CONTROL MEASURES .................................................................................................... 4-1

4.1. Introduction................................................................................................................ 4-1 

4.2. Carbon Monoxide Control Measures......................................................................... 4-1 

5. BASE CASE MODELING.................................................................................................. 5-1

5.1. Introduction................................................................................................................ 5-1 

5.2. Base Case Scenario Modeling ................................................................................... 5-1 

6. DEMONSTRATION OF ATTAINMENT ........................................................................ 6-1

6.1. Introduction................................................................................................................ 6-1 

6.2. Urban Airshed Model Attainment Demonstration..................................................... 6-1 

6.3. Microscale Modeling ................................................................................................. 6-6 

6.3.1. CAL3QHC Intersection Modeling................................................................. 6-7 

6.3.2. Airport Modeling Using the Emissions and Dispersion Modeling System... 6-8 

7. IMPLEMENTATION AND STATE IMPLEMENTATION PLAN COMMITMENTS7-1

7.1. Implementation, Monitoring, and Reporting ............................................................. 7-1 

7.2. Maintenance............................................................................................................... 7-1 

7.3. Mobile Source Emissions Budget.............................................................................. 7-2 

8. REFERENCES..................................................................................................................... 8-1

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Carbon Monoxide State Implementation Plan Revision 

TABLE OF CONTENTS (continued) 

APPENDICES 

APPENDIX A: Technical Support Document............................................................................ A-1 

APPENDIX B: Carbon Saturation Study ....................................................................................B-1 

APPENDIX C: Effectiveness of the Inspection and Maintenance Program ...............................C-1 

APPENDIX D: Airport Modeling Studies.................................................................................. D-1 

APPENDIX E: RTC Support Letter ............................................................................................E-1 

APPENDIX F: Documentation of the Public Review Process....................................................F-1 

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Carbon Monoxide State Implementation Plan Revision 

LIST OF FIGURES 

Figure 2-1. Las Vegas Valley CO Monitoring Sites – 2005................................................... 2-2 

Figure 2-2. Las Vegas Valley CO Air Quality Trends, Number of Exceedances – 

1981-2004. ........................................................................................................... 2-4 

Figure 2-3. Las Vegas Valley CO Air Quality Trends, Annual Peak Concentrations by 

Station – 1981-2004............................................................................................. 2-5 

Figure 3-1. Spatial Distribution of Total CO Emissions for the 1996 Base Case. ............... 3-14 

Figure 3-2. Spatial Distribution of Total Surface Gridded CO Emissions for the 2030 Future 

Year.................................................................................................................... 3-15 

Figure 5-1. Spatial Distribution of UAM Predicted 8-Hour Maximum CO Concentrations 

(ppm) for the December 8-9, 1996 Base Case with Updated On-Road and NonRoad Mobile Emissions. ...................................................................................... 5-3 

Figure 6-1. Spatial Distribution of UAM-Predicted 8-Hour Maximum CO Concentrations 

(ppm) for the December 8-9, 1996 Episode Using Emissions Forecasts 

for 2006................................................................................................................ 6-3 

Figure 6-2. Spatial Distribution of UAM-Predicted 8-Hour Maximum CO Concentrations 

(ppm) for the December 8-9, 1996 Episode Using Emissions Forecasts 

for 2030................................................................................................................ 6-4 

Figure 6-3. Boundaries of the Outer Domain and Subdomains.............................................. 6-5 

Figure 6-4. CAL3QHC Intersection Location Diagram......................................................... 6-7 

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Carbon Monoxide State Implementation Plan Revision 

LIST OF TABLES 

Table 2-1. Las Vegas Valley CO Monitoring Site Locations and Descriptions ................... 2-2 

Table 3-1. Demographic Data Used in Developing Emission Inventories and to Project 

Activity in the 2000 CO SIP................................................................................ 3-1 

Table 3-2. Demographic Data Used in Developing Emission Inventories and to Project 

Activity in the 2005 CO SIP Revision................................................................. 3-2 

Table 3-3. Cross-Reference Between RTC and MOBILE6.2 Facility Types....................... 3-4 

Table 3-4. 1996 VMT by Facility Type ................................................................................ 3-5 

Table 3-5. Component and Total On-Road Mobile Source CO Emissions (TPD) for the 1996 

Base Year............................................................................................................. 3-6 

Table 3-6. Component and Total On-Road Sunday Mobile Source CO Emissions (TPD) for 

All Future Years................................................................................................... 3-8 

Table 3-7. Component and Total On-Road Monday Mobile Source Co Emissions (TPD) for 

All Future Years................................................................................................... 3-8 

Table 3-8. Annual Airport CO Emission Estimates (TPY) for the 1996 Base Year and for 

Future Years 2010, 2015, and 2020 (2006 and 2030 Estimated)......................... 3-9 

Table 3-9. Clark County CO NONROAD Gridded Emission Estimates (TPD)................. 3-10 

Table 3-10. Clark County CO Area Source Gridded Emissions Estimates (TPD) After Season 

and Day-of-Week Adjustments.......................................................................... 3-11 

Table 3-11. Percent Daily Emissions by Source Category and Year.................................... 3-12 

Table 3-12. Summary of Total Daily CO Emissions (TPD) in the UAM CO SIP 

Revision ............................................................................................................. 3-13 

Table 4-1. Adopted CO Control Measures to Reduce On-Road Mobile Source 

Emissions............................................................................................................. 4-2 

Table 4-2. Control Measures Adopted for the 1995 CO SIP and Included as Part of the 2000 

CO SIP and 2005 CO SIP Revision..................................................................... 4-3 

Table 5-1. Summary Performance Statistics for the December 8-9, 1996 Base Case with 

Updated On-Road and Non-Road Mobile Source Emissions.............................. 5-2

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Carbon Monoxide State Implementation Plan Revision 

LIST OF TABLES (continued) 

Table 6-1. Peak 8-Hour CO Concentrations in Future Years................................................ 6-2 

Table 6-2. Grid Definition of the Central Urban Subdomain................................................ 6-2 

Table 6-3. Change in Peak 8-Hour CO from Doubling the Total CO Emissions Inventory 

Outside the Central Urban Subdomain ................................................................ 6-6 

Table 6-4. Weekday On-Road Emissions Increases, UAM-Predicted Peak CO, and Resulting 

Emissions Budget for Each Future Year.............................................................. 6-6 

Table 6-5. Peak UAM + CAL3QHC 8-Hour Average CO Concentrations (ppm) Predicted 

for Each Future Year and for Each Intersection .................................................. 6-7 

Table 6-6. Peak Total UAM + EDMS 8-Hour CO Concentrations (ppm) at All Three 

Airports and for All Three Future Years Evaluated............................................. 6-8 

Table 7-1. 2006 – 2030 MVEB in the Las Vegas Valley...................................................... 7-2 

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Carbon Monoxide State Implementation Plan Revision 

ACRONYMS AND ABBREVIATIONS 

Acronyms 

CAAA 1990 Clean Air Act Amendments 

CO carbon monoxide 

DAQEM Clark County Department of Air Quality and Environmental Management 

EDMS Emissions and Dispersion Modeling System 

EPA U.S. Environmental Protection Agency 

EPS3 Emission Processing System, version 3 

I/M inspection and maintenance (program) 

MVEB motor vehicle emission budget 

NAAQS National Ambient Air Quality Standards 

NAMS National Air Monitoring Station 

RTC Regional Transportation Commission of Southern Nevada 

RTP regional transportation plan 

RVP Reid Vapor Pressure 

SIP state implementation plan 

SLAMS State and Local Air Monitoring Station 

TAZ traffic analysis zone 

TDM transportation demand management 

TSD Technical Support Document (Appendix A) 

UAM Urban Airshed Model 

VMT vehicle miles traveled 

Abbreviations 

ppm parts per million 

TPD tons per day 

TPY tons per year 

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Carbon Monoxide State Implementation Plan Revision 

1. INTRODUCTION 

The 1990 Clean Air Act Amendments (CAAA) redefined the national air pollution abatement 

framework and established ambitious policies to carry out air quality planning and control 

activities. Two National Ambient Air Quality Standards (NAAQS) were established for carbon 

monoxide (CO): the 1-hour standard has a maximum allowable concentration of 35 parts per 

million (ppm), and the 8-hour standard has a maximum average of 9 ppm over an 8-hour period. 

Areas that violate one or both of the NAAQS more than two times in a two-year period are 

classified as CO nonattainment areas. 

In the mid-1980s, portions of the Las Vegas Valley began violating the CO NAAQS during the 

winter months. Although the valley never exceeded the 1-hour standard, it exceeded the 8-hour 

standard at least once each year on a seasonal basis: in winter, local inversions would stagnate air 

masses and trap pollutants. The overnight buildup of pollutants caused violations of the 8-hour 

standard in a limited area surrounding the East Charleston (now Sunrise Acres) monitoring 

station. 

The number and severity of these violations caused the U.S. Environmental Protection Agency 

(EPA) to automatically designate the valley as a “moderate” nonattainment area upon CAAA 

enactment in November 1990. The Clean Air Act and its amendments required that moderate 

nonattainment areas implement the following emission control measures as expeditiously as 

practicable to attain the CO NAAQS by December 31, 1995: 

1. An oxygenated gasoline program during the winter months that requires gasoline to contain 

no less than 2.7 percent oxygen by weight. 

2. An enhanced vehicle inspection and maintenance (I/M) program meeting Clean Air Act 

criteria. 

3. Forecasts of vehicle miles traveled (VMT) in the region, procedures for annual updates and 

reports attesting to the accuracy of the forecasts, and estimates of actual VMT based on 

traffic counts on area roadways. 

4. Contingency measures that must be implemented if actual VMT exceeds forecasted VMT or 

if the area fails to attain the standard by the applicable date. 

5. Transportation control measures necessary to demonstrate attainment of the NAAQS (Clean 

Air Act Section 187(b)(2)). 

6. Implementation of all Reasonably Available Control Measures as quickly as practicable. 

Clark County implemented these controls and made significant progress towards attaining the 

CO NAAQS, but fell short of meeting the standard by the applicable date due to phenomenal 

population growth. Because of improved CO levels from the implementation of control 

measures, EPA granted Clark County a one-year extension to demonstrate compliance. However, 

the county did not succeed and, according to CAAA requirements, EPA reclassified the Las 

Vegas Valley as a “serious” CO nonattainment area. 

October 2005 1-1
Carbon Monoxide State Implementation Plan Revision 

EPA published the notice of violation reclassifying the area in the Federal Register on October 

2, 1997. The agency set a deadline of May 1999 (18 months from the notice publication date) for 

submittal of an implementation plan that would demonstrate attainment of the CO NAAQS by 

December 31, 2000 (i.e., the Carbon Monoxide State Implementation Plan, Las Vegas Valley 

Nonattainment Area, Clark County, Nevada, approved in August 2000 [2000 CO SIP]). The 

CAAA requires that serious nonattainment areas meet all the requirements for moderate areas 

listed previously, in addition to implementing the following measures: 

1. Gasoline sold during the winter months must contain the level of oxygen necessary to attain 

the standard, in combination with other measures. 

2. Employers of 100 or more people must implement a mandatory travel reduction program that 

requires each company to increase average vehicle occupancy for commute trips by at least 

25 percent over the regional average. This requirement can be avoided if the area can show 

that such a program is not needed to demonstrate attainment of the standard or that a 

comparable emission reduction can be achieved by other measures. Congress has since 

eliminated this requirement from the CAAA. 

3. Areas can implement an economic incentive program containing fees and marketable permits 

if emission reduction milestones are not met by December 31, 2000. 

Beginning in 1997, regional transportation plans (RTPs) had to specifically describe the 

transportation system for future horizon years. This requires the Regional Transportation 

Commission of Southern Nevada (RTC) to approve specific projects and programs for 2000, 

2010, and 2020 (and for 2030 in the 2005 CO SIP revision). 

1.1. PROBLEM STATEMENT 

Federal transportation conformity regulations require use of the latest planning assumptions and 

EPA-approved emissions models each time a regional emissions analysis is conducted (after a 

one-year grace period from the time of final EPA approval). The RTC must conduct a new 

regional emissions analysis to update its conformity determinations as part of a new RTP. These 

conformity determinations must be based on budgets from the latest EPA-approved model (i.e., 

MOBILE6.2), and EPA must approve a revised motor vehicle emissions budget (MVEB) before 

the RTC submits the new RTP. 

Section 1.2 of the 2000 CO SIP discusses the reasons for and requirements of the SIP at that 

time. This revision will not repeat this information, but simply reference the 2000 CO SIP. 

1.2. PHYSICAL DESCRIPTION 

The 2000 CO SIP provides a detailed physical description of the Las Vegas nonattainment area. 

October 2005 1-2
Carbon Monoxide State Implementation Plan Revision 

1.3. CLIMATOLOGICAL SETTING 

The 2000 CO SIP provides a detailed description of the climatological setting of the Las Vegas 

Valley. 

1.4. ORGANIZATION OF THIS REVISION 

Each of the following seven sections addresses a specific topic. These generally follow the 

format of the 2000 CO SIP, with one exception: Section 7 of the 2000 SIP, “Additional 

Requirements of the CAAA,” related to contingency measures needed if the valley did not attain 

the CO standard by the December 2000 deadline. Because the valley attained the standard, EPA 

stated in its June 2005 notice that contingency measures and the five percent per year reduction 

in CO emissions were no longer required; therefore, the discussion in Section 7 of the 2000 CO 

SIP is no longer necessary. The remainder of that section, a discussion of VMT projections and 

other control measures, is addressed in Section 7 of this SIP revision. 

Section 2, “Carbon Monoxide Monitoring Network and Trends in Air Quality,” provides updated 

information on the monitoring network and CO air quality trends. 

Section 3, “Emission Inventory Summary,” presents the 1996 base year emissions inventory for 

stationary, area, and mobile sources (on- and off-road), as required under the 1990 CAAA. This 

section was greatly expanded from the 2000 CO SIP to provide the reader with a better 

understanding of the changes required in the mobile source emissions inventory because of the 

MOBILE6.2 program. The section presents future year on-road mobile emissions estimates using 

MOBILE6.2 inputs, which are based on the transportation network defined in the RTC 

TransCAD transportation demand model (TDM). 

Section 4, “Control Measures,” briefly describes the control strategies that reduced CO emissions 

and led to attainment status. 

Section 5, “Base Case Modeling,” describes the modeling process for the base case simulations 

using the Urban Airshed Model (UAM), including the preparation of inputs and model 

performance. 

Section 6, “Demonstration of Attainment,” describes the modeling analysis demonstrating the 

continued attainment of the NAAQS and summarizes CO concentrations with implemented 

control measures. It also explains the use of MOBILE6.2 for conformity and other purposes. 

Section 7, “SIP Commitments/Implementation,” discusses the implementation of control 

measures, monitoring progress, emission budgets, and maintenance of CO attainment. It contains 

an additional discussion of conformity and mobile source emission budgets, including the use of 

new data. 

Section 8, “References,” identifies the reports and studies supporting the 2005 CO SIP revision. 

October 2005 1-3
Carbon Monoxide State Implementation Plan Revision 

Appendices contain the Technical Support Document (TSD) for the 2005 CO SIP revision and 

other supporting studies. 

October 2005 1-4
Carbon Monoxide State Implementation Plan Revision 

2. MONITORING NETWORK AND TRENDS IN AIR QUALITY 

2.1. INTRODUCTION 

This section provides a brief summary of the Las Vegas Valley CO monitoring network as of 

July 2005 and a discussion of the trends in air quality for CO over the past several years. The CO 

monitoring program demonstrates that air quality is improving, and the reasons for this positive 

development are briefly considered. 

2.2. BACKGROUND 

CO occurs in the atmosphere as the result of incomplete combustion of fuels. In Las Vegas, as in 

other urban areas, motor vehicles are the major source of CO emissions, comprising 

approximately 76 percent of total daily emissions in the base year. Stations usually record 

exceedances of the standard in the late afternoon and evening hours. For more details on the 

sources of CO emissions and a breakdown of contribution by category, see Table 3-11. EPA 

established specific standards for CO in 1971 to protect public health and the environment. The 

most stringent standard of 9 ppm is averaged over a rolling 8-hour period; the maximum 

allowable hourly concentration is 35 ppm. The Clean Air Act requires that EPA review the CO 

standard every five years. EPA has made no changes to the current standards. 

2.3. MONITORING NETWORK 

EPA has established ambient air quality monitoring requirements and standards for State and 

Local Air Monitoring Stations (SLAMS) and National Air Monitoring Stations (NAMS). These 

provide for operating schedules, data quality assurance, and design and siting of CO samplers. 

Although EPA monitoring guidelines require only three CO monitors for areas such as Clark 

County, there were eight CO monitors at the beginning of 2005. Table 2-1 provides details about 

the monitoring sites. The monitoring schedule is continuous, and each monitoring station uses 

the Gas Filter Correlation technique. 

By 1999, the CO monitoring network in the Las Vegas Valley had evolved into a system of 15 

monitoring sites. Eight of these were SLAMS sites, and two were NAMS/SLAMS sites. By the 

beginning of 2005, this network had been reduced to eight sites (Table 2-1). The Clark County 

Department of Air Quality and Environmental Management (DAQEM) operates and administers 

the air monitoring system, which is governed by a set of quality assurance and quality control 

procedures approved by EPA and subject to periodic EPA performance audits. Air quality 

monitoring reports are prepared quarterly and submitted to EPA. All sites except the maximum 

concentration Sunrise Acres monitor have population exposure as their objective. Figure 2-1 

shows the current CO monitoring locations. 

October 2005 2-1
Carbon Monoxide State Implementation Plan Revision 

Table 2-1. Las Vegas Valley CO Monitoring Site Locations and Descriptions 

Site Name Address Type Predominant Wind 

Direction 

City Center 559 N. 7th Street NAMS/SLAMS Southwest 

East Sahara 4001 E. Sahara Ave. SLAMS Southwest 

Orr School Maryland Pkwy. & Flamingo Road SLAMS Southwest 

Winterwood 5483 Club House Dr. SLAMS Southeast 

S. Las Vegas Blvd. 3799 South Las Vegas Blvd. SLAMS N.A. 

Sunrise Acres 2501 S. Sunrise Ave. SLAMS Southwest 

J.D. Smith 1301B East Tonopah NAMS/SLAMS Northwest 

Freedom Park1 650 N. Mojave Rd. SLAMS Northwest 

1

Ceased operation April 30, 2005. 

Figure 2-1. Las Vegas Valley CO Monitoring Sites – 2005. 

October 2005 2-2
Carbon Monoxide State Implementation Plan Revision 

2.4. TRENDS IN CARBON MONOXIDE AIR QUALITY 

No site has ever recorded a violation of the 1-hour CO NAAQS (35 ppm) in the Las Vegas 

Valley; exceedance events are limited to the 8-hour national standard of 9 ppm. The East 

Charleston monitoring station recorded 10 violations during the 1991-1992 winter season, but 

the number of violations declined to one in 1995, three in 1996, one in 1997, and two in 1998. 

There were no violations from 1999 through 2004, the most recent data year. This downtrend is 

the direct result of implementing CO control measures. The East Charleston monitoring site 

(relocated and renamed Sunrise Acres in 2000) is adjacent to a junction of major transportation 

corridors where three state highways intersect, known as the Five Points area. The site also sits in 

a topographic bowl where air pollution collects. The highest 8-hour average CO concentration, 

measured at 10.2 ppm, occurred in the Five Points area during the 1996 season. The second 

highest 8-hour concentrations since that time have been 8.2 ppm in 1999, 7.1 ppm in 2000, 

6.3 ppm in 2001, 5.8 ppm in 2002, 5.3 ppm in 2003, and 5.1 ppm in 2004. 

During the past several years, the Las Vegas Valley has experienced substantial improvement in 

air quality: no violations of the 8-hour CO standard have been recorded since 1998. There has 

been a similar reduction in the intensity of CO concentrations. Figures 2-2 and 2-3 illustrate this 

improved CO air quality. 

Apart from recent winter seasons with fewer inversions, annual reductions in the number of 

events and in CO concentrations can be attributed to the following factors: 

1. Improved motor vehicle emissions control technology and the continued replacement of 

older, poorly maintained vehicles with newer, cleaner vehicles. 

2. The wintertime oxygenated, cleaner-burning gasoline program. 

3. Reduced gasoline Reid Vapor Pressure (RVP). 

4. Requirements for annual smog tests for motor vehicles, including medium- and heavy-duty 

gasoline vehicles. 

5. A computerized traffic signal management program. 

6. Use of the east leg (I-515) freeway and other roadway improvements. 

7. Alternative fuel vehicle programs. 

8. Voluntary rideshare programs. 

CO exceedances (but not necessarily violations) of the NAAQS frequently totaled 40 or more per 

year in the 1980s. During 1997 and 1998, the Las Vegas Valley experienced only four 

unhealthful and three exceedance days, all recorded at the Sunrise Acres station. Exceedances 

and violations of the 8-hour CO standard eased by 1999, and there have been no recorded 

exceedances of the CO standard since then. 

October 2005 2-3
Carbon Monoxide State Implementation Plan Revision 

27

32 33

24

41

32

18

22

27

13

6

2 3 4 1 3 1 2 0 0 0 0 

05

101520253035404550

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032

YEAR

DAYS

Exceedances of the EPAStandard for CO

Figure 2-2. Las Vegas Valley CO Air Quality Trends, Number of Exceedances – 1981-2004. 

October 2005 
Carbon Monoxide State Implementation Plan Revision 

0369

1215

1995 1996 1997 1998 1999 2000 2001 2002 2003 200

Year

High 8-Hour Average

Concentration (ppm)

Boulder City* City Center Craig Road*E. Flamingo / Orr E. Sahara Freedom ParkGreen Valley* Henderson* J.D. SmithPaul Meyer Park* S. Las Vegas Blvd Sunrise Acres / E. CWinterwood

EPA 8-Hour Standard

* - Site was discontinued June 30, 2003

Figure 2-3. Las Vegas Valley CO Air Quality Trends, Annual Peak Concentrations by Station – 198

October 2005 
Carbon Monoxide State Implementation Plan Revision 

2.5. CARBON MONOXIDE SATURATION STUDY 

From November 2001 through January 2002, DAQEM conducted an intensive saturation study 

throughout the Las Vegas Valley to measure CO during its historical peak level period (see 

Appendix B). The purpose was to learn about CO concentrations in the valley on a much larger 

geographical basis, to evaluate whether current CO monitors were representing the highest CO 

concentrations, and to better understand the relationship between land use, meteorology, and 

ambient CO concentrations. Beginning with an initial network of 32 continuous CO samplers, 

the program was expanded during the study to 63 stations. Staff operated a mobile van with a CO 

analyzer and positional recording systems during two intensive monitoring periods. 

The study found that DAQEM monitoring sites generally represented the high concentration 

locations for CO in the Las Vegas Valley. Nearly all of the highest 8-hour average CO 

concentrations occurred near the Sunrise Acres site, in an area east of downtown Las Vegas. The 

highest averages were in the 6 ppm range, far below the 9 ppm 8-hour NAAQS for CO. The 

study confirmed that meteorological conditions (e.g., cold winter nights with poor atmospheric 

dispersion) led to the accumulation of CO within 100 feet of the ground in the area around 

Sunrise Acres. At the same time, areas with similar emission sources did not experience high CO 

levels, further confirming the pooling of pollutants in the Sunrise Acres area. A special 

microscale saturation study site near the Fremont Street casino and parking garage area recorded 

the highest one-hour CO level of 18.3 ppm, which is only half the one-hour NAAQS. 

This saturation study confirmed the proper locations for CO monitors in the valley, assisted staff 

in evaluating the results of the modeling work constituting part of this SIP revision, and 

supported decisions about which CO monitors could be safely removed from the Clark County 

air monitoring network in subsequent years. 

October 2005 2-6
Carbon Monoxide State Implementation Plan Revision 

3. EMISSION INVENTORY SUMMARY 

3.1. INTRODUCTION 

The CAAA requires that all nonattainment areas prepare a base year inventory that is 

comprehensive, accurate, and current with respect to actual emissions in the area (Section 

182(a)(1)). The peak season and modeling CO inventories are based on this inventory. This 

section summarizes the 1996 base year CO inventory for the Las Vegas Valley nonattainment 

area, which addresses CO emissions from four major type categories: stationary point sources, 

area sources, on-road mobile sources, and non-road mobile sources. This section provides a brief 

overview of the source categories and the methodologies employed to estimate emissions. For 

the mobile sources, it includes a discussion of changes from the 2000 CO SIP modeling effort 

that used MOBILE5b, which was replaced by MOBILE6.2.03. During the development of the 

2000 CO SIP, CO emissions from on-road mobile sources (by far the largest contributor to the 

overall emission inventory for Las Vegas) were estimated using a combination of MOBILE5b, 

the Direct Travel Impact Model, and volume/roadway link information provided by the RTC in 

its TRANPLAN model. Appendix A provides more detailed information pertaining to this 

inventory. 

The Clark County Health District was the agency originally responsible for preparing and 

submitting the Las Vegas Valley nonattainment area 1996 base year CO emissions inventory. 

Several other local agencies contributed information necessary for preparing emissions 

estimates, including the RTC, the Clark County Department of Aviation, and the Clark County 

Fire Department. The Nevada Department of Transportation, the U.S. Forest Service, and 

Southwest Gas Corporation also provided information for these estimates. 

The 1996 point source inventory was prepared primarily from a mail survey by the Health 

District. Survey results were supplemented by information obtained through personal contacts 

during compliance inspections, and the RTC provided VMT data necessary to calculate on-road 

mobile source emissions. The MOBILE5b model was run to determine vehicle emission factors 

from on-road mobile sources. Table 3-1 contains the Clark County demographic information 

used in the 2000 CO SIP. 

Table 3-1. Demographic Data Used in Developing Emission Inventories 

and to Project Activity in the 2000 CO SIP1

January Population Employment VMT 

1996 1,037,844 493,213 22,469,020 

2000 1,269,600 609,400 24,929,485 

2010 1,790,700 859,500 38,022,330 

2020 2,406,500 1,115,100 57,492,333 

1

Data is based on RTC 1997 estimates and projections. 

The 2000 CO SIP was based on computer modeling (using UAM) of the single best performing 

episode of the three originally modeled: the night of December 8-9 (Sunday-Monday), 1996. The 

October 2005 3-1
Carbon Monoxide State Implementation Plan Revision 

2000 CO SIP and its appendices provide technical documentation for the models, application 

methodologies, performance evaluations, and future year modeling assessments. This SIP 

revision continues to rely on the December 8-9, 1996 episode. 

This 2005 CO SIP revision uses new data on population and VMT projections, especially for 

conducting the MOBILE6.2 analysis. For the 1996 base year, the RTC’s original TRANPLAN 

output was used to define link-based volume (in VMT) and other traffic volume-related 

parameters. No trip tables were available, which allow for the separate estimation of start versus 

running emissions, so 1996 start emissions were spatially allocated using 2000 TransCAD trip 

data, as described later in this section. All original ancillary information, including vehicle fleet 

mix, seasonal/day-of-week adjustment factors, and hourly activity profiles, remained the same as 

in the original model. 

For all future years modeled in this update, the RTC provided output from the new TransCAD 

TDM, which includes link volumes and trip tables for each year. Population projections (and 

actual population for 2000) were modified to reflect higher growth rates in the county. Table 3-2 

contains this new data, including the revised 1996 daily VMT. 

Table 3-2. Demographic Data Used in Developing Emission Inventories 

and to Project Activity in the 2005 CO SIP Revision 

January Population1 Modeled DVMT2

1996 1,037,844 22,395,251 

2006 1,923,420 37,076,414 

2010 2,281,380 47,170,180 

2015 2,687,055 53,973,132 

2020 2,999,953 58,181,118 

2030 3,410,332 65,586,340 

1

Data obtained from the UNLV Center for Business and Economic Research in July 2005. 2

RTC 2005 TransCAD TDM. 

3.2. EMISSIONS SUMMARY BY CATEGORY 

This section is greatly expanded from the original 2000 CO SIP to provide a better understanding 

of the changes required to develop the mobile source emissions inventory. The 1996 base year 

and future year inventories for the point source and area source categories remain essentially the 

same as those reported in the 2000 CO SIP, although direct comparison with Table 3-2 is 

difficult because the 2000 CO SIP tables used average daily CO season emissions and this SIP 

revision contains daily emissions for the two episode days of Sunday and Monday. The non-road 

and on-road mobile source inventories have been greatly revised to reflect new, updated data 

inputs, new models, and a format to accommodate the MOBILE6.2.03 modeling requirements. 

Appendix A provides an expanded explanation of the methodology and results of the mobile 

source inventory changes. 

October 2005 3-2
Carbon Monoxide State Implementation Plan Revision 

3.2.1. On-Road Mobile Emissions 

The greatest effort in this CO modeling update has focused on the on-road mobile source 

inventory estimates. The model used in the 2000 CO SIP effort (MOBILE5b) was replaced by 

the latest version of the model (MOBILE6.2.03). This version updates CO emission rates for 

low-emission and Tier 2 vehicles, along with many other changes. The Air Improvement 

Resource, Inc. version of this model was used because it provides the capability to create a 

condensed database of composite emission factors. This is important for applications where 

numerous MOBILE6 scenarios must be run to generate lookup factors for link-level emissions 

estimates, such as this one. 

For the 1996 base year, the RTC’s original TRANPLAN output was used to define link-based 

volume (in VMT) and other traffic volume-related parameters. All original ancillary information, 

including vehicle fleet mix, seasonal/day-of-week adjustment factors, and hourly activity 

profiles, remained the same as in the original model. 

Since the output data and formats for MOBILE6 are significantly different from those of its 

predecessor, the original program used to estimate link-level CO emissions (i.e., the Direct 

Travel Impact Model) was replaced by two new programs. The first processes link-based 

emissions, and the second processes emissions based on traffic analysis zones (TAZs). Both 

programs produce inputs for the Emission Processing System, version 3 (EPS3). EPS3 is the 

latest version of the EPS program suite used in the original CO SIP model to generate gridded, 

time-resolved, UAM-ready CO emission input files. 

For all future years modeled in this SIP revision, the RTC provided output from the new 

TransCAD TDM, which includes link volumes and trip tables for each year. Base year 

TRANPLAN intrazonal data were provided as volumes by TAZ with a trip length from which 

VMT was calculated. Future year TransCAD intrazonal data were provided as trips by TAZ 

only. The intrazonal trips were assumed to have a trip length of 1 mile, from which VMT was 

calculated. VMT was multiplied by the running exhaust emission factors, then spatially 

distributed using gridded surrogates developed from the definition of the future year TransCAD 

TAZs. 

For both the base and future year link-level emissions, VMT was calculated from the 

transportation model output (link volume multiplied by link length) for each period of the day 

and allocated to each hour using an hourly distribution for each day of the episode. VMT was 

then multiplied by the hourly running exhaust emission factors (in grams per mile) from 

MOBILE6.2, and the total hourly emissions by link were spatially distributed according to the 

link endpoint coordinates. 

Start emissions were calculated by multiplying hourly estimates of link-level VMT by hourly 

MOBILE6.2 start emission factors in grams per mile. The link-level start emissions were then 

totaled over the entire network and spatially distributed using the period-specific transportation 

model trip origin data by TAZ. Since no TRANPLAN trip data by TAZ were available for the 

1996 base year, 1996 start emissions were spatially allocated using 2000 TransCAD trip data. 

October 2005 3-3
Carbon Monoxide State Implementation Plan Revision 

3.2.1.1. Base Year Estimates

Section 2.2 of Appendix A describes the methodology to develop on-road mobile emissions in 

detail. Total on-road mobile source emissions consist of link-level running exhaust emissions, 

start emissions, and emissions from intrazonal trips. The following subsections briefly 

summarize how these emissions were estimated. 

3.2.1.1.1. MOBILE6 Modeling 

Two sets of MOBILE6 runs were performed. The first used start distribution emission factors 

applied to the entire domain, with the exception of a small area along South Las Vegas 

Boulevard. To better understand specific weekday start emission factors along the boulevard, a 

second set of MOBILE6 runs was conducted. Start activity in this region is not typical of 

commute activity profiles, since trips start in casino/resort parking lots rather than in residential 

areas. Based on the two runs, it was decided to apply the modified start distribution for the 

fraction of the 2000 TransCAD origin trips that occur in the TAZs along South Las Vegas 

Boulevard for the base year and all future years. Figure 2-2 in Appendix A shows the results of 

these runs. 

The effectiveness of the Clark County I/M program was set to 100 percent in the MOBILE6 

emission runs. Appendix C justifies this assumption. 

3.2.1.1.2. Link-Level Running Exhaust Emissions 

The 1996 TRANPLAN activity data were adjusted for season, day, hour, and transit activity to 

provide the data for the link-level emissions. The TRANPLAN link activity data consisted of the 

annual daily average volume for each link in the network classified by RTC facility type code. 

Table 3-3 cross-references RTC facility type codes and MOBILE6.2 roadway types. 

Table 3-3. Cross-Reference Between RTC and MOBILE6.2 Facility Types 

RTC Facility Code Description MOBILE6.2 Roadway Type 

0 Externals Freeway 

1 System Ramps Ramp 

2 Minor Arterials Arterial 

3 Major Arterials Arterial 

4 Freeway Ramps Ramp 

5 Interstates Freeway 

6 Freeways Freeway 

7 Expressways Freeway 

8 Collectors Arterial 

9 Centroid Connectors1 Local 

10 Intrazonal Local 1

Centroid connectors were treated as local roads; VMT on the centroid connectors was multiplied by 

MOBILE6 local road emission factors. 

October 2005 3-4
Carbon Monoxide State Implementation Plan Revision 

Running exhaust emissions for the base year were generated using the Air Improvement 

Resource, Inc. version of MOBILE6. This version takes the standard MOBILE6 database output 

and condenses it across model years for each vehicle class. 

In summary, the link-level running exhaust emissions processing steps were: 

1. Adjust daily volumes to hourly volumes using the profiles in Figure 2-3 of Appendix A. 

2. Adjust link speeds using the hourly volume to capacity ratio in the Bureau of Public Roads 

curve (see Section 2.2.2.3 of Appendix A for details). 

3. Calculate the hourly link VMT as the hourly volume multiplied by the link length. 

4. Calculate the link emissions as the link VMT multiplied by the MOBILE6.2 composite 

emission factor for the link roadway type, hour, and adjusted link speed. 

5. Spatially allocate the link emissions to the modeling grid. 

6. Use EPS3 to adjust emissions to an average December day, to Sunday or Monday, and for 

transit activity. 

Table 3-4 shows the tabulations of 1996 VMT by facility type, as reported by TRANPLAN and 

after adjustment. 

Table 3-4. 1996 VMT by Facility Type 

Group Code Facility Type Modeled 

1996 DVMT 

DVMT 

Adjusted to 

December 

DVMT 

Adjusted for 

Transit 

Sunday 

DVMT 

Monday 

DVMT 

0 External Connector 640,605 654,058 655,988 507,734 670,419 

1 System Ramp 69,247 70,701 70,910 54,884 72,470 

2 Minor Arterial 7,469,952 7,626,821 7,649,320 5,920,574 7,817,605 

3 Major Arterial 3,655,890 3,732,664 3,743,675 2,897,605 3,826,036 

4 Freeway On- or 

Off-Ramp 267,725 273,348 274,154 212,195 280,185 

5 Interstate 3,825,715 3,906,055 3,917,578 3,032,205 4,003,764 

6 Freeway 1,202,253 1,227,501 1,231,122 952,888 1,258,207 

7 Expressway 214,096 218,592 219,237 169,690 224,060 

8 Collector 2,776,772 2,835,084 2,843,448 2,200,828 2,906,003 

9 Centroid Connector 2,185,691 2,231,591 2,238,174 1,732,347 2,287,414 

Intrazonal 87,303 89,136 89,399 69,195 91,366 

Daily Total1 22,395,251 22,776,414 22,843,605 17,680,950 23,346,164 

Transit Adjustment 1.00295 

December Adjustment 1.021 

Sunday Adjustment 0.774 

Monday Adjustment 1.022 

1

Totals are shown as output by TRANPLAN and after seasonal, day-of-week, and public transit adjustments. 

October 2005 3-5
Carbon Monoxide State Implementation Plan Revision 

3.2.1.1.3. Base Year Start Emissions 

The daily link-level VMT from TRANPLAN was allocated to hourly values using the dayspecific hourly VMT profile shown in Figure 2-3 of Appendix A. The base year start emissions 

were calculated from the product of hourly link VMT and hourly MOBILE6.2 start emission 

factors. To remain consistent with how future year start emissions would be developed, base year 

start emissions were translated from link-level to TAZ level. A month/season adjustment factor 

of 1.021 was applied to the start emissions to adjust from an average annual day to an average 

December day. 

Day-of-week adjustment factors were applied to adjust from an average annual day to Sunday 

and Monday. The factors used were 0.774 for Sunday and 1.022 for Monday, the same factors 

used in the 2000 CO SIP. The hourly TAZ start emissions were spatially allocated to the grid cell 

containing the TAZ centroid and the 24 surrounding cells in a “wedding cake” fashion: the grid 

cell containing a TAZ centroid received 25 percent of the start emissions from that TAZ, the 

surrounding 8 grid cells received 60 percent of the start emissions (7.5 percent per cell), and the 

outside 16 grid cells received 15 percent of the start emissions (0.9375 percent per cell). Both the 

EPA Region 9 office and the Office of Transportation and Air Quality reviewed this approach 

(EPA 2005). Figure 2-5 in Appendix A shows the spatial distribution of start exhaust emissions 

for the 1996 base case. 

3.2.1.1.4. Base Year Total Emissions 

Table 3-5 lists the component and total on-road mobile source emissions for the 1996 base year. 

Figure 2-6 of Appendix A presents the spatial distribution of the total on-road mobile source 

emissions for December 9, 1996. 

Table 3-5. Component and Total On-Road Mobile Source CO Emissions (TPD1) 

for the 1996 Base Year 

Links - Running Starts Intrazonal Total 

Sunday 12/8 202.75 126.42 0.78 329.95 

Monday 12/9 269.31 241.21 1.03 511.55 

1

Tons per day. 

3.2.1.2. Future Year Estimates

The RTC provided TransCAD model output for each of the future years (2006, 2010, 2015, 

2020, and 2030). The TransCAD model output provided link-level volumes (number of 

vehicles), along with trip origins and destinations, for the following seven time periods: midnight 

to 7 a.m., 7 a.m. to 9 a.m., 9 a.m. to 2 p.m., 2 p.m. to 4 p.m., 4 p.m. to 6 p.m., 6 p.m. to 

8 p.m., and 8 p.m. to midnight. The following subsections briefly summarize how future year 

emissions were estimated. 

October 2005 3-6
Carbon Monoxide State Implementation Plan Revision 

3.2.1.2.1. Future Year MOBILE6 Inputs 

Table 2-6 of Appendix A details how external files were used. Eight input files were created for 

each future year (2006, 2010, 2015, 2020, and 2030), one for weekdays and one for weekends 

for each of the four roadway types: freeway, arterial, local, and ramp. Values from a 2002 Clark 

County traffic study yielded VMT for five vehicle types, which were further broken down into 

sixteen vehicle types based on the MOBILE6 default VMT mix for 2002. Because Clark County 

does not have future year forecasts for vehicle VMT mix, seasonal/day-of-week adjustments, or 

hourly activity profiles, the base year information for these variables was used for all future 

years. 

3.2.1.2.2. Link-Level Running Exhaust Emissions 

Link volumes were first adjusted to observed traffic counts by facility type, then adjustments 

were made for month/season and day of the week. TransCAD volume data is for an average 

weekday, so Sunday activities were adjusted by a 0.774 day-of-week factor. Monday was not 

adjusted because the TransCAD data represent an average weekday. Hourly and speed 

adjustments were made as in the base year approach. 

3.2.1.2.3. Future Year Start Emissions 

Future year start emissions were calculated the same way as base year start emissions. For 

Monday, the hourly VMT was estimated by disaggregating the period VMT to hourly VMT 

using the day-specific hourly VMT profile shown in Figure 2-3 of Appendix A. Tables 2-10 

through 2-14 of Appendix A show the resulting VMT by facility type for 2006, 2010, 2015, 

2020, and 2030. Start emissions were calculated by multiplying the hourly VMT by the hourly 

MOBILE6 start emission factors. 

3.2.1.2.4. Future Year Intrazonal Activity 

Intrazonal VMT was calculated assuming a default length of 1 mile for each intrazonal trip, as 

described in Chapter 5 of the fiscal year 2004-2005 RTP documentation (RTC 2004). 

3.2.1.2.5. Future Year Total Emissions 

Table 3-6 lists the component and total on-road mobile source emissions for all future years on 

the second Sunday of December. 

October 2005 3-7
Carbon Monoxide State Implementation Plan Revision 

Table 3-6. Component and Total On-Road Sunday Mobile Source CO Emissions (TPD) 

for All Future Years 

Sunday 2006 2010 2015 2020 2030 

Links - Running 149.64 150.26 137.32 133.15 142.66 

Starts 125.10 135.93 138.46 139.23 152.54 

Intrazonal 0.57 0.82 0.66 0.71 0.70 

Total 275.30 287.01 276.44 273.09 295.90 

Table 3-7 lists the component and total on-road mobile source emissions for all future years on 

the second Monday of December. 

Table 3-7. Component and Total On-Road Monday Mobile Source Co Emissions (TPD) 

for All Future Years 

Monday 2006 2010 2015 2020 2030 

Links - Running 204.62 205.29 187.70 182.00 194.67 

Starts 235.73 257.33 262.53 264.10 289.81 

Intrazonal 0.88 1.33 1.07 1.14 1.13 

Total 441.23 463.95 451.30 447.24 485.61 

3.2.2. Non-Road Mobile Emissions 

3.2.2.1. Airports

The Las Vegas Valley contains three major civil airports (McCarran International, North Las 

Vegas, and Henderson) and one large military airport (Nellis Air Force Base). In 1999, Clark 

County sponsored an Emissions and Dispersion Modeling System (EDMS) project for the three 

civil airports. The years modeled included the 1996 base year and the future years of 2000, 2010, 

and 2020. UAM results were added to the EDMS receptor concentrations to provide an estimate 

of background concentrations. In 2003, Clark County sponsored an updated modeling project for 

the three civil airports using the latest version of EDMS. On-road mobile sources were estimated 

using Clark County runs of MOBILE6.2. EDMS was run for 2000, 2005, 2010, 2015, and 2020, 

but UAM results were not added to the EDMS receptor results. The 1996 base year was not 

included in this revision because the EDMS contributions to the UAM for the 1996 base year are 

zero: the 10 EDMS receptors used in this analysis showed that no emissions from McCarran 

were dispersed and that McCarran was isolated from the main Las Vegas CO cloud that existed 

well to the north. The revised modeling resulted in predictions above the 8-hour CO standard at 

several receptors in all years; however, these were located in areas not generally accessible to the 

public, primarily aircraft docking areas, the aircraft apron, etc. EPA has indicated it will accept 

the removal of receptors in non-public access areas from consideration, since the sites do not fall 

under the Clean Air Act definition of “public access.” 

To properly account for the contributions of airports to the valley-wide distribution of CO during 

the December 8-9 episode, UAM had to include the updated EDMS airport emissions within the 

gridded inventory. Airport emissions for 1996 were taken from the original EDMS estimates, 

October 2005 3-8
Carbon Monoxide State Implementation Plan Revision 

and emissions for the 2010, 2015, and 2020 future years were taken from the 2003 updated 

EDMS estimates. Table 3-8 shows the annual airport emissions. Values for 2006 were 

interpolated from 2005 and 2010 EDMS estimates; values for 2030 were extrapolated from the 

rate of growth in the 2015 to 2020 EDMS estimates. The original 2000 CO SIP emission 

estimates for Nellis Air Force Base were retained in the UAM modeling. All these estimates, in 

tons per year (TPY), had to be disaggregated to December, Sunday and Monday, and each hour 

of the day. Clark County provided activity data for the civil airports on which to base the 

disaggregation from annual to hourly emission rates, listed in Table 3-2 of Appendix A. 

Table 3-8. Annual Airport CO Emission Estimates (TPY) for the 1996 Base Year1 and for Future 

Years 2010, 2015, and 20202

 (2006 and 2030 Estimated) 

Year McCarran Henderson North Las Vegas 

1996 10,022 536 2,727 

2006 11,600 646 1,848 

2010 13,494 762 1,880 

2015 15,482 949 1,924 

2020 17,553 1,220 1,971 

2030 21,695 1,762 2,063 

1

Ricondo 1999. 

2

Ricondo 2003. 

Airport emissions were placed evenly across the grid cells in which the airports reside. Figures 

3-1 and 3-2 in Appendix A illustrate details on hourly activity for the three civil airports. 

3.2.2.2. Locomotives

In Clark County, only Union Pacific operates locomotives. Two switching facilities are located 

in the county, the downtown (Civic Center) yard and a yard at the Boulder Junction Wye. 

Updated railroad emissions for 2001 based on a recent non-road study (MACTEC 2003) were 

incorporated into this SIP revision. The base year emissions estimates were taken from the 2000 

CO SIP. Locomotive emissions from the non-road study included both line haul and switching; 

for switching, emissions were placed at the same two facilities previously modeled. 

The locomotive activity unit most useful for emission evaluation is fuel consumption. Projected 

fuel consumption from locomotive use is difficult to estimate, especially for a given track 

segment like the one through Clark County. Fuel consumption depends on factors not restricted 

exclusively to number of trains, tons of freight, or business indicators because of efficiency 

improvements to trains or operations. 

To project locomotive activity increases due to growth in business, a time series plot of available 

data on fuel consumption was used. Emission factors were projected using EPA estimates of the 

effect of fleet turnover. Table 3-3 in Appendix A shows the percent reduction in emissions for 

line-haul and switching engines. Locomotive emissions for future years were based on projected 

growth in fuel consumption and reduced by expected emission reductions from new engine 

controls. 

October 2005 3-9
Carbon Monoxide State Implementation Plan Revision 

3.2.2.3. Other Non-Road Categories

Equipment emission estimates for non-road categories other than aircraft and locomotives during 

weekdays and weekends were performed using EPA’s NONROAD model. For the Clark County 

base year inventory, the period type was set to the winter season and emissions were reported as 

tons per day. Airport ground support equipment was removed from the NONROAD emissions 

estimates because it was estimated separately using EDMS, as described previously. 

Recreational marine estimates were also removed because the major water areas in Clark County 

lie outside the modeling domain. Railroad maintenance emissions for the 1996 base case were 

extracted from the NONROAD output and processed with locomotive emissions. 

Table 3-9 summarizes NONROAD model equipment CO emissions estimates for the base year 

and all future years evaluated in the 2005 CO SIP modeling. The emissions shown in this table 

are for the modeling domain only. 

Table 3-9. Clark County CO NONROAD Gridded Emission Estimates (TPD) 

Second Sunday in December Base 2006 2010 2015 2020 2030 

Recreational 2.47 2.40 2.44 2.52 2.58 2.72 

Construction and Mining 17.47 1.28 0.99 0.80 0.68 0.59 

Industrial 1.80 1.34 0.95 0.41 0.25 0.24 

Lawn and Garden 33.56 32.61 36.28 39.97 43.58 50.70 

Agriculture 0.00 0.00 0.00 0.00 0.00 0.00 

Commercial 10.82 12.91 14.86 16.98 19.12 23.23 

Total 66.13 50.53 55.52 60.68 66.22 77.48 

Second Monday in December Base 2006 2010 2015 2020 2030 

Recreational 1.24 1.20 1.22 1.26 1.29 1.36 

Construction and Mining 34.94 2.56 1.98 1.60 1.36 1.18 

Industrial 3.36 2.54 1.74 0.69 0.46 0.43 

Lawn and Garden 42.22 42.24 46.32 51.03 55.66 64.78 

Agriculture 0.00 0.00 0.00 0.00 0.00 0.00 

Commercial 21.64 25.82 29.72 33.97 38.24 46.45 

Total 103.40 74.36 80.98 88.55 97.02 114.20 

Sections 3.1.3.2 and 3.1.3.3 of the TSD (Appendix A) provide additional information on base 

and future year gridding surrogates used for these non-road sources. 

3.2.3. Point Sources 

This SIP revision used the 1996 base year point source inventory from the original 2000 CO SIP. 

Clark County provided an updated point source emission inventory for future years that included 

updated stack parameters and emissions based on potential-to-emit levels for seven specific 

October 2005 3-10
Carbon Monoxide State Implementation Plan Revision 

facilities. UAM future year inventories included potential-to-emit levels plus a 70-TPY buffer 

for these sources. All future year modeling used the same future year point source data. Tables 3-

14 and 3-15 of Appendix A provide future year emissions of these seven facilities and the 

modeled CO point source emission estimates. 

3.2.4. Area Sources 

The 1996 base year area source estimates were taken from the 2000 CO SIP with no changes. 

Base year emissions were projected by growth factors to determine future year emissions for the 

major area source categories. Table 3-10 summarizes episode-specific area source CO emissions 

for the base and project years by eleven subcategories. Table 3-2 of the 2000 CO SIP contains 

information on these subcategories, but only on an average daily CO season emission basis. The 

data in Table 3-10 are for the peak episode in the 1996 base year, so are not directly comparable. 

3.3. TOTAL ANNUAL EMISSIONS 

Table 3-11 summarizes the percent contribution to total episodic daily emissions of the four 

major emission categories for the base year (1996) and a future year (2030), based on the 

modeling performed in this SIP revision. 

Table 3-12 summarizes total daily CO emissions by source category for the 1996 base year and 

all future years. 

Figure 3-1 shows the spatial distribution of total CO emissions for the 1996 base case. Figure 3-2 

shows a similar spatial distribution for the 2030 projection year. 

Table 3-10. Clark County CO Area Source Gridded Emissions Estimates (TPD) After Season and 

Day-of-Week Adjustments 

Second Sunday in December Base 2006 2010 2015 2020 2030 

Electric Utility Generation 0.558 0.687 0.734 0.787 0.840 0.946 

Small Stationary 2.701 3.412 3.680 3.981 4.283 4.885 

Boiler Emissions 0.385 0.486 0.524 0.567 0.610 0.696 

Industrial Natural Gas 0.148 0.186 0.201 0.218 0.234 0.267 

Commercial Natural Gas 0.041 0.051 0.055 0.059 0.063 0.070 

Residential Natural Gas 0.308 0.360 0.380 0.398 0.416 0.452 

Fireplaces 3.033 4.556 5.233 6.133 7.033 8.832 

Brush Fires 1.262 1.896 2.178 2.552 2.927 3.675 

Cigarette Smoking 0.044 0.066 0.076 0.089 0.102 0.128 

Structural Fires 0.646 0.971 1.115 1.307 1.499 1.882 

Vehicular Fires 0.054 0.081 0.093 0.110 0.126 0.158 

 Total 9.181 12.753 14.270 16.200 18.131 21.991 

October 2005 3-11
Carbon Monoxide State Implementation Plan Revision 

Table 3-10. Clark County CO Area Source Gridded Emissions Estimates (TPD) After Season and 

Day-of-Week Adjustments (continued) 

Second Monday in December Base 2006 2010 2015 2020 2030 

Electric Utility Generation 0.558 0.687 0.734 0.787 0.840 0.946 

Small Stationary 2.701 3.412 3.680 3.981 4.283 4.885 

Boiler Emissions 0.385 0.486 0.524 0.567 0.610 0.696 

Industrial Natural Gas 0.369 0.466 0.503 0.544 0.585 0.667 

Commercial Natural Gas 0.103 0.127 0.138 0.148 0.157 0.176 

Residential Natural Gas 0.308 0.360 0.380 0.398 0.416 0.452 

Fireplaces 3.033 4.556 5.233 6.133 7.033 8.832 

Brush Fires 1.262 1.896 2.178 2.552 2.927 3.675 

Cigarette Smoking 0.044 0.066 0.076 0.089 0.102 0.128 

Structural Fires 0.646 0.971 1.115 1.307 1.499 1.882 

Vehicular Fires 0.054 0.081 0.093 0.110 0.126 0.158 

 Total 9.464 13.109 14.654 16.615 18.576 22.497 

Table 3-11. Percent Daily Emissions by Source Category and Year 

Base Year – 1996 Future Year - 2030 Source Category 

Sunday Monday Sunday Monday 

On-Road 74 76 62 68 

Non-Road 23 21 30 26 

Point <1 <1 3 3 

Area 2 1 4 2 

October 2005 3-12
Carbon Monoxide State Implementation Plan Revision 

Table 3-12. Summary of Total Daily CO Emissions (TPD) in the UAM CO SIP Revision 

Second Sunday in December Base 2006 2010 2015 2020 2030 

On-Road Running (Links) 202.75 149.40 150.18 137.31 133.18 142.80 

On-Road Starts 126.42 125.10 135.93 138.46 139.23 152.54 

On-Road Intrazonal 0.78 0.57 0.82 0.66 0.71 0.70 

Henderson Airport 1.12 1.35 1.59 1.99 2.55 3.69 

McCarran Airport 24.69 28.57 33.24 38.14 43.24 53.44 

Nellis Air Force Base 2.86 2.86 2.86 2.86 2.86 2.86 

North Las Vegas Airport 7.58 5.13 5.22 5.35 5.48 5.73 

Area Sources 9.18 12.75 14.27 16.20 18.13 21.99 

Non-road - NONROAD 66.13 50.49 55.50 60.66 66.21 77.44 

Point Sources 3.13 15.82 15.82 15.82 15.82 15.82 

Railway - Line Haul 0.14 0.17 0.19 0.20 0.22 0.27 

Railway - Maintenance 0.03 0.04 0.04 0.04 0.05 0.06 

Total 444.81 392.49 415.73 417.71 427.65 477.19 

Second Monday in December Base 2006 2010 2015 2020 2030 

On-Road Running (Links) 269.31 204.62 205.29 187.70 182.00 194.67 

On-Road Starts 241.09 235.73 257.33 262.53 264.10 289.81 

On-Road Intrazonal 1.03 0.88 1.33 1.07 1.14 1.13 

Henderson Airport 0.88 1.07 1.26 1.57 2.01 2.91 

McCarran Airport 24.69 28.57 33.24 38.14 43.24 53.44 

Nellis Air Force Base 2.86 2.86 2.86 2.86 2.86 2.86 

North Las Vegas Airport 5.98 4.05 4.12 4.22 4.32 4.52 

Area Sources 9.46 13.11 14.65 16.62 18.58 22.50 

Non-road - NONROAD 103.40 74.30 80.94 88.52 96.99 114.17 

Point Sources 3.13 15.82 15.82 15.82 15.82 15.82 

Railway - Line Haul 0.14 0.17 0.19 0.20 0.22 0.27 

Railway - Maintenance 0.11 0.14 0.15 0.16 0.18 0.21 

Total 662.08 581.31 617.17 619.41 631.46 702.31 

October 2005 3-13
Carbon Monoxide State Implementation Plan Revision 

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UTM Easting (km)

3973

3983

3993

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0.0

0.6

1.2

1.8

2.4

3.0

3.6

4.2

4.8

5.4

Total Surface Emissions

Base Year - Dec 9, 1996

CO (tons per day)

Figure 3-1. Spatial Distribution of Total CO Emissions for the 1996 Base Case. 

October 2005 3-14
Carbon Monoxide State Implementation Plan Revision 

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UTM Easting (km)

3973

3983

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0.0

0.6

1.2

1.8

2.4

3.0

3.6

4.2

4.8

5.4

Total Surface Emissions

Future Year - Dec 9, 2030

CO (tons per day)

Figure 3-2. Spatial Distribution of Total Surface Gridded CO Emissions for the 2030 Future Year. 

October 2005 3-15
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October 2005 3-16
Carbon Monoxide State Implementation Plan Revision 

4. CONTROL MEASURES 

4.1. INTRODUCTION 

This SIP revision focused on recalculating the emissions for on-road and non-road sources using 

the newer MOBILE6.2 and NONROAD2004 models, respectively, and then running the UAM 

to determine if the Las Vegas Valley will continue to maintain the CO standards through 2030. 

The results, as Sections 5 and 6 describe in detail, confirm continued maintenance. Accordingly, 

no new control measures are required in this SIP revision, so this section primarily references 

relevant portions of Section 4 of the 2000 CO SIP with some summary information. The impacts 

of the four CO control measures in the 2000 CO SIP were not recalculated in this revision. 

The 2000 CO SIP noted that about 86 percent of the CO emissions in the Las Vegas Valley in 

1996 were produced by on-road motor vehicles. Non-road mobile sources contributed about 11 

percent, and stationary point and area sources accounted for the remaining 3 percent. The 

proportions have changed slightly in this SIP revision due to the new models employed and a 

focus on emissions for a December Sunday-Monday peak episode rather than on average 

seasonal CO emissions. The 1996 base year proportions under the new modeling analysis are 

about 75 percent from on-road sources, 22 percent from non-road mobile sources, and the 

remaining 3 percent from stationary area and point sources. On-road source proportions are less 

in 2030 due to improved vehicle emission controls: they only make up about 65 percent of CO 

emissions. Non-road emissions increase to 28 percent, point sources to 3 percent, and area 

sources to about 4 percent. These data can be examined in detail in Tables 3-11 and 3-12. 

In developing the 2000 CO SIP, Clark County examined the potential for additional control 

measures on each of the four major source categories. After reviewing the impacts on CO 

attainment from each category and the additional measures available to further reduce CO, the 

county decided to focus new control measures on the major on-road category of the emissions 

inventory. Four new control measures were adopted and implemented. Several additional CO 

control measures adopted in the 1967 to 1995 time frame continue to support achievement of the 

CO standards. 

4.2. CARBON MONOXIDE CONTROL MEASURES 

Regulations and resolutions in support of the control measures necessary for CO attainment were 

adopted prior to submittal of the 2000 CO SIP and became effective at the end of 1999. Control 

measures and programs from previous plans, listed in Tables 4-1 and 4-2, served as the 

foundation to which the four new measures were added to achieve attainment of the standard. 

When fully implemented, the four control measures proposed in the 2000 CO SIP, along with all 

the control measures previously implemented, reduced CO emissions from on-road motor 

vehicles by over 22 percent between 1996 and 2000. These measures were a major reason Clark 

County could offset extraordinary population growth and vehicle usage during the 1990s and 

attain the standards by 2001. Section 4.2.1 of the 2000 CO SIP describes in detail the four onroad mobile source control measures. Since the control measures have not changed and 2000 

emission reductions remain as projected by MOBILE5b, Table 4-1 simply summarizes the 

October 2005 4-1
Carbon Monoxide State Implementation Plan Revision 

control measures. Descriptions of the control measures, legislative history, and acceptance 

criteria are provided in Chapter 4 of the 2000 CO SIP. 

Table 4-1. Adopted CO Control Measures to Reduce On-Road Mobile Source Emissions 

Control Measure 

Year 2000 

Emission 

Reduction % 

Daily CO 

Benefit 

(TPD) 

Adoption 

Date Implementing Agency 

Cleaner Burning Gasoline Program 9.80% 31.9 1999 DAQEM 

Voluntary TDM and Transportation 

Control Measures 0.08% 0.3 1999/Ongoing RTC 

I/M Technician Training 2.95% 10.4 1996 

(enhanced) 

NV Department of Motor 

Vehicles & Public Safety 

Alternative Fuels for 

Government Fleets 0.12% 0.4 1995-2001 NV Division of Environmental Protection 

Combined Effect of Controls 12.2% 43.1 

None of the four control measures were rerun individually as part of the MOBILE6.2 analysis. It 

was unnecessary because the measures have been approved and adopted as part of the 2000 CO 

SIP, and UAM runs for maximum CO levels using MOBILE6.2 do not show any violations 

through 2030. 

Section 4.3 of the 2000 CO SIP describes controls on off-road mobile sources. It identifies the 

only direct proactive controls affecting off-road sources, mobile and otherwise, as the 

Wintertime Cleaner Burning Gasoline and Oxygenated Fuel programs. Since this category 

contributes only about 11 percent of the total CO emissions for the Las Vegas Valley, the 2000 

SIP determined that further controlling these emissions would not be cost-effective or practical. 

Section 4.4 of the 2000 CO SIP notes that only 3 percent of CO emissions in the area come from 

stationary point and area sources. Except for permit-related controls resulting from New Source 

Review and New Source Performance standards, no new controls on point and area sources were 

included in the 2000 CO SIP or in this SIP revision. 

Section 4.5 of the 2000 CO SIP discusses previously adopted control measures from the 1995 

CO SIP and how they continue to assist in air quality improvement efforts. Fleet turnover, partly 

from high annual increases in vehicle registrations and new model year vehicles, continues to be 

a major factor in reducing mobile source CO emissions. In 1997, Clark County increased the 

oxygenated fuels weight control regulation from the 2.7 percent credited in the 1995 CO SIP to 

3.5 percent. The I/M program for motor vehicles, in effect since 1978, continues to provide a 

major reduction in CO emissions. As Appendix C points out, the Nevada Legislature modified 

that program slightly in 2005. Table 4-2 lists previously adopted and enforceable CO control 

measures. 

October 2005 4-2
Carbon Monoxide State Implementation Plan Revision 

Table 4-2. Control Measures Adopted for the 1995 CO SIP and Included as Part of the 2000 CO SIP 

and 2005 CO SIP Revision 

Control Measure Adoption Date 

Oxygenated Fuels 1991/1995 

Reduced RVP Gasoline 1995 

Motor Vehicle I/M Program 1978 

Fleet Turnover 1967 

In summary, the primary control measures in the 1995 and 2000 CO SIPs have been adopted and 

implemented. This 2005 CO SIP revision suggests no new measures, since the area attained the 

CO standards and EPA approved the 2000 CO SIP. Furthermore, the modeling conducted as part 

of this revision demonstrates continued attainment of CO standards through at least 2030. 

October 2005 4-3
Carbon Monoxide State Implementation Plan Revision 

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October 2005 4-4
Carbon Monoxide State Implementation Plan Revision 

5. BASE CASE MODELING 

5.1. INTRODUCTION 

This section summarizes the modeling performed to establish that current CO emission inventory 

projections result in continued maintenance of the 8-hour average NAAQS for CO in the Las 

Vegas nonattainment area. Appendix A provides detailed technical documentation of the models 

used for this 2005 CO SIP revision. 

The CAAA requires that serious CO nonattainment areas like the Las Vegas Valley use EPAapproved models to demonstrate attainment. The current models of choice for CO attainment 

demonstrations are (1) the UAM, an urban-scale, three-dimensional, grid-type, numerical 

simulation model; and (2) CAL3QHC, a microscale roadway intersection (i.e., “hot spot”) plume 

model. Since EPA has identified the UAM and CAL3QHC as effective tools for evaluating 

emission control programs, they were selected to demonstrate attainment in the 2000 CO SIP. 

DAQEM updated its UAM CO modeling for this 2005 CO SIP revision using the latest tools, 

data resources, and methodologies available. It based the revised models on the modeling data 

sets developed in the 2000 CO SIP for the December 8-9, 1996 historical event. Section 3 

describes specific updates to the emissions inventories, which include modifications to on-road 

mobile sources, non-road mobile sources, civil airports, railroads, and point sources. Emissions 

estimates for all remaining categories (mainly area sources and Nellis Air Force Base) were 

taken from the previous modeling detailed in the 2000 CO SIP, although new spatial 

distributions were developed for area sources from updated land use projections. 

5.2. BASE CASE SCENARIO MODELING 

The December 1996 base case in the 2000 CO SIP included in its emissions inventory the 

existing I/M program, the 3.5 percent oxygenated fuel program, low RVP gasoline (9 pounds per 

square inch), and other control measures in place or mandated by the CAAA. For the 2005 CO 

SIP revision base case, the UAM was used to simulate the emission and transport of CO 

throughout the Las Vegas Valley during the night of December 8-9, 1996 (Sunday-Monday). 

Specifically, the UAM was run from 1500 local standard time on December 8 to 1100 local 

standard time on December 9 to cover the coldest, most stagnant and stable portion of the 

episode during which CO was observed to build up. Two base case simulations were run: 

A. With revised on-road emission estimates, keeping all the point, area, and non-road 

emissions the same as the 2000 CO SIP model (see Section 4.1.1 of the TSD). 

B. With both revised on-road and non-road emission estimates, keeping all point and area 

emissions the same as the 2000 CO SIP model (see Section 4.1.2 of the TSD). 

In both cases, estimated 1996 airport emissions from Ricondo (1999) were included in the 

emissions inventory. 

October 2005 5-1
Carbon Monoxide State Implementation Plan Revision 

Figure 5-1 shows the UAM-predicted episode maximum 8-hour CO concentrations (in ppm) 

from the base case simulation using the revised on-road and non-road emissions summarized in 

Section 3 and documented in Sections 2 and 3 of the TSD (Appendix A). The two distinct areas 

of CO maxima in the simulation are located near where U.S. Highway 95 makes a sharp turn 

southward in northeast Las Vegas (called the “elbow”) and along South Las Vegas Boulevard 

near the Spring Mountain Road intersection. The peak in the domain is 11.4 ppm along South 

Las Vegas Boulevard. According to the RTC TransCAD model, this is due to the high 

concentration of parking structures in the area. The secondary maximum reaches more than 9 

ppm along U.S. 95 during the morning commute hours on Monday, December 9. Overall, the 

spatial pattern of predicted 8-hour maximum CO agrees with the previous modeling in the 2000 

CO SIP and with the distribution of observed CO for this period. Unlike the modeling 

documented in the 2000 CO SIP, no external scaling was applied to the UAM results in these 

revised runs. 

Modeling for the on-road and non-road revisions was performed using standard and EPA criteria 

model performance statistics; Table 5-1 shows the statistics used for this simulation. The 

statistics are based on pairings of 8-hour CO predictions and observations across all available 

monitoring sites for the period, which include standard EPA-method monitoring conducted by 

Clark County and special saturation monitoring performed for the Las Vegas Phase II field 

monitoring study. The saturation study was conducted during the winter of 1996-97 and 

supplemented the 14 existing CO sites in the county. These statistics show that UAM 

performance is quite good and should be considered acceptable. 

Table 5-1. Summary Performance Statistics for the December 8-9, 1996 Base Case with Updated 

On-Road and Non-Road Mobile Source Emissions 

Peak 8-hour Observation 9.6 ppm, Marnel Field 

Unpaired Peak 11.4 ppm 

Paired Peak 8.1 ppm 

Statistical Measures 

Unpaired Peak Accuracy 19%1

Paired Peak Accuracy -15% 

Peak Timing Error 1 hr 

Average Peak Bias > 5 ppm -3% 

Average Peak Error > 5 ppm 13% 

Average Peak Timing Bias > 5 ppm 2 hr 

Average Peak Timing Error > 5 ppm 2 hr 

Overall Bias > 5 ppm -6% 

Overall Error > 5 ppm 15% 

1

Bold/colored metrics denote EPA criteria statistics. Blue indicates a number within the 

acceptance criteria and red indicates a number outside the acceptance criteria. 

Figure 4-6 of Appendix A shows a time series of observed and predicted hourly CO 

concentrations at each of the 28 available monitoring sites during the 1996-97 study period. 

October 2005 5-2
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5

6

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8

9

10

11

12

ppm

UAM Max 8-hour CO Concentrations

 1996 Base Case (96B08)

Peak = 11.4 ppm

Figure 5-1. Spatial Distribution of UAM Predicted 8-Hour Maximum CO Concentrations (ppm) for 

the December 8-9, 1996 Base Case with Updated On-Road and Non-Road Mobile 

Emissions. 

October 2005 5-3
Carbon Monoxide State Implementation Plan Revision 

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October 2005 5-4
Carbon Monoxide State Implementation Plan Revision 

6. DEMONSTRATION OF ATTAINMENT 

6.1. INTRODUCTION 

Air quality modeling is an integral part of the air quality planning process to attain the NAAQS. 

Section 6 in the 2000 CO SIP summarized the application of the UAM and CAL3QHC models in 

demonstrating attainment of the CO NAAQS by December 31, 2000. The primary purpose for 

conducting UAM area-wide and CAL3QHC roadway intersection modeling is to demonstrate the 

effectiveness of control strategies in attaining the 8-hour average NAAQS for CO. The 

attainment demonstration consists of four parts: 

1. Developing an attainment-year base case emission inventory that reflects the net effect of 

existing required controls and growth projections for all source categories. 

2. Developing future-year emission strategies. 

3. Performing attainment year model simulations to assess control strategies. 

4. Using results from the UAM and CAL3QHC modeling to demonstrate attainment. 

EPA requires the estimated 8-hour average concentrations be below the 9 ppm standard when 

using the UAM area-wide model to demonstrate attainment. EPA also recommends that the 

CAL3QHC model be applied to intersections at potential hot-spot locations. The hot-spot 

modeling analysis combines concentrations from the UAM with those from the CAL3QHC 

microscale model. 

This section outlines the approach taken to incorporate emissions updates into the UAM data set 

and perform revised UAM urban-scale modeling for the future years of 2006, 2010, 2015, 2020, 

and 2030. Additionally, EDMS results from the Ricondo (2003) analyses were combined with 

revised UAM model predictions for the future years of 2006, 2010, 2015, and 2020 to estimate 

8-hour CO concentrations for the duration of the episode on and around the three civil airport 

properties in the valley. The following sections provide details on each of these components. 

6.2. URBAN AIRSHED MODEL ATTAINMENT DEMONSTRATION 

As described below, the UAM used updated emission inventories for point, on-road mobile, and 

non-road mobile sources for the December 8-9, 1996 historical CO event. All other 

environmental parameters were taken from the original modeling documented in the 2000 CO 

SIP. A similar model performance evaluation was conducted for the base year (Table 5-1). The 

UAM was then run with the updated future year inventories for 2006, 2010, 2015, 2020, and 

2030 to determine peak 8-hour CO levels in the valley using the same December 8-9, 1996 

conditions. Figures 6-1 and 6-2 display predicted 8-hour maximum CO concentrations in the 

modeling domain for the years 2006 and 2030, respectively. Section 4.2 of the TSD (Appendix 

A) contains similar displays of UAM maximum 8-hour concentrations for future years 2010, 

2015, and 2020. UAM predictions show that the 8-hour CO standard of 9 ppm will not be 

violated anywhere within the domain. As Table 6-1 shows, peak 8-hour CO decreases in each 

year until 2015 and then begins to increase out to 2030. 

October 2005 6-1
Carbon Monoxide State Implementation Plan Revision 

Table 6-1. Peak 8-Hour CO Concentrations in Future Years 

Year Peak 8-hour CO 

2006 7.4 

2010 7.2 

2015 6.5 

2020 6.7 

2030 8.0 

Figures 6-1 and 6-2 show that the contribution of McCarran International Airport to local CO 

concentrations increases steadily during this period due to the projected growth in airport 

activities reported by Ricondo (2003). In each successive year through 2020, the contribution 

from on-road mobile sources diminishes and the peak moves from the U.S. 95 “elbow” in 

northeast Las Vegas to the northern boundary of McCarran along Tropicana Boulevard. As in the 

1996 base case, a lower secondary peak occurs in the South Las Vegas Boulevard area near 

Spring Mountain Road. That area possesses a high concentration of parking structures, which 

leads to a local maximum in trip starts in the RTC TransCAD model and a local maximum in 

vehicle start emissions in the modeling emission inventory. This poses the potential for an actual 

local emissions hot spot in this area, and Clark County undertook a saturation study in 2002 to 

address this possibility (Appendix B). Although the TransCAD, EPS3, and UAM models show a 

potential emissions hot spot at Spring Mountain Road and South Las Vegas Boulevard, the 2002 

saturation study showed no hot spot at all in that location. 

The UAM was then used to undertake several sensitivity tests to refine the estimation of future 

year on-road mobile CO emission budgets for the central, most urbanized portion of the 

modeling domain. Table 6-2 defines this central urban subdomain, and Figure 6-3 outlines the 

subdomain in relation to the total modeling domain. 

Table 6-2. Grid Definition of the Central Urban Subdomain 

Column Row UTM1 East UTM North 

Low-Left 11 19 652.000 3991.000 

Upper-Right 36 45 678.000 4018.000 1

Universal Transverse Mercator. 

The first analysis tested the assertion that the emissions inventory outside the central urban 

subdomain has no significant impact on CO concentrations downtown, along South Las Vegas 

Boulevard, and in traditional hot-spot areas. Emissions in the outer grid area were doubled for 

each future year, and the UAM was run to show the incremental impact on peak CO 

concentration. As Table 6-3 demonstrates, peak 8-hour CO concentrations changed by a 

maximum of only 0.07 ppm. The location of the predicted peak did not change at all. 

October 2005 6-2
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6

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8

9

10

11

12

ppm

UAM Max 8-hour CO Concentrations

 2006 Future Year

Peak = 7.37 ppm

Figure 6-1. Spatial Distribution of UAM-Predicted 8-Hour Maximum CO Concentrations (ppm) for 

the December 8-9, 1996 Episode Using Emissions Forecasts for 2006. 

October 2005 6-3
Carbon Monoxide State Implementation Plan Revision 

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6

7

8

9

10

11

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ppm

UAM Max 8-hour CO Concentrations

 2030 Future Year

Peak = 7.96 ppm

Figure 6-2. Spatial Distribution of UAM-Predicted 8-Hour Maximum CO Concentrations (ppm) for 

the December 8-9, 1996 Episode Using Emissions Forecasts for 2030. 

October 2005 6-4
Carbon Monoxide State Implementation Plan Revision 

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3993

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Figure 6-3. Boundaries of the Outer Domain and Subdomains. 

October 2005 6-5
Carbon Monoxide State Implementation Plan Revision 

Table 6-3 demonstrates that the model-predicted peak CO is driven by local emission sources in 

the central urban subdomain, and is therefore insensitive to large changes in emissions in outer 

areas. 

Table 6-3. Change in Peak 8-Hour CO from Doubling the Total CO Emissions Inventory Outside 

the Central Urban Subdomain 

Peak 8-hour CO (ppm) Year 

From Table 6-1 Doubled Outer Emissions 

2006 7.37 7.41 

2010 7.17 7.24 

2015 6.47 6.54 

2020 6.74 6.80 

2030 7.96 8.03 

In the second analysis, future year on-road mobile source emissions were scaled up across the 

entire modeling domain to the point at which the peak 8-hour CO concentration reached 8.9 

ppm. The on-road mobile source emissions outside the central urban subdomain were then 

increased by an additional 70 percent in each year to reach a maximum peak 8-hour CO 

concentration of just under 9.0 ppm (Table 6-4). Figures 4-13 through 4-17 of Appendix A show 

plots of daily maximum CO concentrations for each future year. There was no change in the 

location of the predicted peak. No additional hot spots were generated anywhere in the domain 

by increasing the on-road mobile source emissions in the outer portion of the domain by 70 

percent. 

Table 6-4. Weekday On-Road Emissions Increases, UAM-Predicted Peak CO, and Resulting 

Emissions Budget for Each Future Year 

Eastern/Charleston Eastern/Fremont Fremont/Charleston Year UAM CAL3QHC CAL3QHC+UAM CAL3QHC CAL3QHC+UAM CAL3QHC CAL3QHC+UAM

2006 4.89 1.64 6.14 1.28 5.66 0.71 5.09

2010 4.62 1.33 5.61 1.14 5.32 0.69 4.81

2015 4.19 1.16 4.97 0.96 4.76 0.51 4.31

2020 3.97 1.05 4.67 0.88 4.48 0.49 4.07

2030 4.07 1.03 4.83 0.84 4.58 0.50 4.20

Once EPA approves them, the total domain emissions in Table 6-4 will become the MVEBs the 

RTC uses in future conformity analyses. 

6.3. MICROSCALE MODELING 

Future year UAM simulation results provided estimates of background ambient CO levels for 

microscale modeling of the Five Points area hot spot and the three civil airports in the modeling 

domain (McCarran, Henderson, and North Las Vegas). UAM concentrations from the 

appropriate grid cells were simply added to the concentrations predicted at each microscale 

receptor to obtain a total (background + microscale) CO concentration. 

October 2005 6-6
Carbon Monoxide State Implementation Plan Revision 

6.3.1. CAL3QHC Intersection Modeling 

As previously stated, EPA recommends that a microscale hot-spot analysis be conducted as part 

of the attainment demonstration. Selection criteria for intersections to be analyzed include high 

traffic volume, poor levels of service, and close proximity to the monitoring station recording 

exceedances. The Five Points area, which meets all three criteria, was selected for modeling to 

meet the microscale and attainment demonstration requirements. 

For hot-spot modeling, the CAL3QHC model was used to model three intersections: Charleston 

and Eastern, Charleston and Fremont, and Eastern and Fremont (Figure 6-4). EPA (1992, 1995) 

guidance for screening-level modeling of these three intersections was followed. The 

UAM/CAL3QHC model for the 2000 CO SIP provided the ambient temperature for each hour of 

the episode, needed to estimate emissions with the MOBILE6.2 model, and the wind speed and 

direction needed for the CAL3QHC estimates. The CAL3QHC model output was added to the 

background UAM levels to estimate 8-hour CO concentrations for the duration of the episode. 

Figure 6-4. CAL3QHC Intersection Location Diagram. 

Table 6-5 presents the peak UAM + CAL3QHC 8-hour average CO concentrations predicted in 

each of the future years for each of the three intersections in the Five Points area. All values are 

well below the 9 ppm standard. 

Table 6-5. Peak UAM + CAL3QHC 8-Hour Average CO Concentrations (ppm) Predicted for Each 

Future Year and for Each Intersection 

Year Eastern/Charleston Eastern/Fremont Fremont/Charleston 

2006 7.14 6.65 6.12 

2010 6.70 6.43 5.94 

2015 6.53 6.30 5.88 

2020 6.43 6.23 5.83 

2030 6.49 6.22 5.85 

October 2005 6-7
Carbon Monoxide State Implementation Plan Revision 

6.3.2. Airport Modeling Using the Emissions and Dispersion Modeling System 

For microscale airport modeling, the UAM was run for all future years with exactly the same 

inputs described in Section 4.2 of Appendix A; however, airport emissions for the three civil 

airports in the domain were removed from the UAM inventory to avoid double counting. Clark 

County provided EDMS simulations for these airports for 2005, 2010, 2015, and 2020 (Ricondo 

2003). All receptors above the 9 ppm standard in all future years evaluated were located within 

areas that are not publicly accessible, as defined by Ricondo (2005). Disregarding receptors in 

restricted areas, which EPA has indicated is acceptable, removes all exceedance estimates. Table 

6-6 lists the peak total 8-hour CO concentrations at all three civil airports for each future year 

evaluated. Values for McCarran are taken from the peak publicly accessible receptor. All peak 

CO concentrations are below the 9 ppm standard in all years. 

Table 6-6. Peak Total UAM + EDMS 8-Hour CO Concentrations (ppm) at All Three Airports and for 

All Three Future Years Evaluated 

Airport 2005 2010 2015 2020 

McCarran 7.76 7.47 8.09 8.98 

Henderson Executive 1.28 1.61 2.74 3.96 

North Las Vegas 6.07 6.28 6.14 6.08 1

Values shown for McCarran occur at the peak publicly accessible receptor. 

October 2005 6-8
Carbon Monoxide State Implementation Plan Revision 

7. IMPLEMENTATION AND STATE IMPLEMENTATION 

PLAN COMMITMENTS 

The purpose of this 2005 CO SIP revision is to assure the public that implementation of the 

programs in the 2000 CO SIP and maintenance of the CO health standards will continue through 

2030. As noted earlier, EPA has approved the 2000 CO SIP and determined that it attained its 

goal of achieving the CO NAAQS by the end of 2000. However, with new planning tools and 

better predictive capabilities (such as MOBILE6) available, Clark County will continue to 

reanalyze and confirm long-term maintenance of the CO health standards. In addition to the 

practical aspects of meeting the transportation conformity regulatory requirements for new 

emission models, this SIP revision also lays the foundation for development of a formal CO 

maintenance plan and a redesignation request to EPA. The rest of this section describes how the 

2000 CO SIP control measures are being implemented and tracked, and how the revised 

emission budget for mobile sources will provide a basis for the valley to continue to meet federal 

transportation requirements. 

7.1. IMPLEMENTATION, MONITORING, AND REPORTING 

Implementation of the control measures specified in Section 4 is necessary for the Las Vegas 

Valley to continue maintaining the CO NAAQS. The responsibility for implementing these 

control measures lies with DAQEM, the Nevada Division of Environmental Protection, and the 

RTC. Each entity has the personnel, funding, and authority to implement its respective part of 

the proposed primary control measures. Table 4-1 provides the adoption and implementation 

status of each of the four key on-road mobile source control measures. 

In addition to continued implementation of control measures, the 1990 CAAA requires 

continual air quality monitoring. As Section 2 noted, DAQEM currently has eight monitoring 

sites to observe CO levels and will notify the state and EPA of any NAAQS violations or 

exceedances. This coverage is more than adequate for an area and population such as Clark 

County; EPA requires only three monitoring sites for similar-size areas. This network will 

continue to operate in accordance with the requirements of 40 CFR 58, and DAQEM will 

continue to submit quarterly reports to EPA as mandated. DAQEM provided EPA with its 2004 

annual NAMS/SLAMS report in May 2005. 

7.2. MAINTENANCE 

EPA requires that implementation plans also provide for maintaining the standard after 

attainment. Since Clark County has now reached attainment, and the primary source of CO is the 

on-road mobile sources category, VMT projections for a 30-year horizon past the demonstration 

date have been forecast. Since additional modeling will likely be required for maintenance plan 

submittals from areas seeking redesignation, this 2005 CO SIP revision updated the mobile 

emission model analysis to provide a basis for development of a formal CO maintenance plan 

and a redesignation request in the near future. The Las Vegas Valley air quality implementation 

plan will remain in effect until superseded by an approved CO maintenance plan. 

October 2005 7-1
Carbon Monoxide State Implementation Plan Revision 

7.3. MOBILE SOURCE EMISSIONS BUDGET 

Under Section 176(c) of the Clean Air Act, transportation plans, programs, and projects in 

maintenance areas that are funded or approved under Title 23 of the U.S. Code or the Federal 

Transit Act must conform to the on-road MVEBs specified in the applicable SIP. 40 CFR 93.118 

provides the criteria and procedures for MVEBs. 

The MVEB establishes a cap on motor vehicle-related emissions that cannot be exceeded by 

predicted transportation system emissions. The emissions budget applies as a ceiling on 

emissions in the year for which it is defined and for all subsequent years until a different budget 

is defined for another year or a SIP revision modifies the budget. Without a clearly indicated 

intent otherwise expressed in the SIP, the estimate of future transportation network emissions 

used in the milestone or attainment demonstration acts as the MVEB. 

The emissions analysis for conformity determinations must include emissions from the entire 

transportation network within the nonattainment area. In the case of Las Vegas, the 

nonattainment area encompasses both the air quality modeling domain and the transportation 

planning domain. 

The decision on what years to propose for the CO MVEB is a joint policy call between various 

stakeholders, state and federal transportation agencies, and state and local air quality agencies. 

One choice is to identify motor vehicle emissions in the year of the next conformity finding 

(2006) and maintain the budget for all subsequent analysis years (i.e., the interim year 

conformity analyses, the horizon year, and all years beyond the horizon year). In the case of Las 

Vegas, that would mean a total domain budget of 623 TPD in the initial 2006-2009 time frame. 

Table 7-1 reflects the calculated MVEBs based on MOBILE6.2 in this 2005 CO SIP revision. 

Section 6 and Appendix A of this SIP revision provide specific information on how these 

multiyear budget values were derived; DAQEM determined that it would be more accurate to 

establish multiyear budgets for modeling. The MVEBs in Table 7-1 are the budgets Clark 

County proposes for EPA approval and, subsequently, for RTC use in making conformity 

determinations for the next RTP. 

Table 7-1. 2006 – 2020 MVEB in the Las Vegas Valley 

Years Peak 8-hr CO (ppm) MVEB (TPD) 

2006-2009 8.96 623 

2010-2014 8.98 690 

2015-2019 8.98 768 

2020+ 8.97 817 

Amended May 2006 7-2
Carbon Monoxide State Implementation Plan Revision 

8. REFERENCES 

AAR (Association of American Railroads) 2000. “Railroad Ten-Year Trends 1990-1999.” 

Washington, D.C.: Association of American Railroads. 

AAR 2004. “Analysis of Class I Railroads 2002 – Data.” Washington, D.C.: Association of 

American Railroads. Available online at http://www.aar.org/pubstores/listItems.aspx. 

Egami, D., J. Bowen, P. Roberts, S. Reyes, T. Dye, C. Emery, and D. Souten 1998. “The Las 

Vegas Valley Carbon Monoxide Urban Airshed Model Update Project – Phase II: Field Data 

Collection.” Las Vegas, NV: Clark County Department of Comprehensive Planning. 

EIA (Energy Information Administration) 2005. “Distillate Sales by End Use, Annual Data.” 

Washington, D.C.: U.S. Department of Energy. Available online at 

http://www.eia.doe.gov/oil_gas/petroleum/info_glance/distillate.html. 

Emery, C., D. Souten, N. Kumar, F. Lurman, and P. Roberts 1998. “The Las Vegas Valley 

Carbon Monoxide Urban Airshed Model Update Project – Phase II: UAM Base Case and 

Sensitivity Applications.” Las Vegas, NV: Clark County Department of Comprehensive 

Planning. 

EPA (U.S. Environmental Protection Agency) 2005. July 2005 phone call from Karina 

O’Connor, EPA Region 9 Office, San Francisco, CA, to David Calkins, ENVIRON Holdings, 

Inc., Las Vegas, NV, approving use of “wedding cake” grid system for allocating hourly TAZ 

start emissions. 

EPA 1997. “Final Emissions Standards for Locomotives.” EPA420-F-97-048. Washington, 

D.C.: U.S. Environmental Protection Agency. 

EPA 1995. “User’s Guide to CAL3QHC Version 2.0: A Modeling Methodology for Predicting 

Pollutant Concentrations Near Roadway Intersections.” EPA-454/R-92-06. Washington, D.C.: 

U.S. Environmental Protection Agency. 

EPA 1992. “Guideline for Modeling Carbon Monoxide from Roadway Intersections.” EPA454/R-92-005. Washington, D.C.: U.S. Environmental Protection Agency. 

MACTEC 2003. “Clark County-Wide Inventory of Non-road Engines Project.” Las Vegas, NV: 

Clark County Department of Air Quality and Environmental Management. 

October 2005 8-1
Carbon Monoxide State Implementation Plan Revision 

Orth-Rodgers & Associates, Inc. 2003. "Air Quality Vehicle Distribution Study and Modeling." 

Las Vegas, NV: Regional Transportation Commission of Southern Nevada. 

Pollack, A.K., R. Chi, C. Lindhjem, C. Tran, P. Chandraker, P. Heirigs, L. Williams, S.S. 

Delaney, M.A. Mullen, and K.B. Thesing 2004. “Development of WRAP Mobile Source 

Emission Inventories.” Denver, CO: Western Governors’ Association. 

RTC (Regional Transportation Commission of Southern Nevada) 2004. Chapter 5 of FY 2004-

2025 Regional Transportation Plan. Las Vegas, NV: Regional Transportation Commission of 

Southern Nevada. 

Ricondo and Associates, Inc. 1999. “Carbon Monoxide Emissions Inventory and Dispersion 

Modeling.” Las Vegas, NV: Clark County Department of Aviation. 

Ricondo and Associates, Inc. 2003. “Carbon Monoxide Emissions Inventory and Dispersion 

Modeling Study Update 2003.” Las Vegas, NV: Clark County Department of Aviation. 

Ricondo and Associates, Inc. 2005. “Addendum to the 2003 Carbon Monoxide Emissions 

Inventory and Dispersion Modeling Study.” Memorandum dated 5/19/05 from Adrian Jones, 

Ricondo & Associates, San Francisco, CA, to Dennis Mewshaw, Clark County Department of 

Aviation, Las Vegas, NV. 

October 2005 8-2