International Corporation Air Sciences

Technical Support Document 

CARBON MONOXIDE MODELING 

FOR THE CLARK COUNTY MAINTENANCE PLAN 

Prepared for 

Clark County 

Department of Air Quality and Environmental Management 

500 S. Grand Central Parkway 

PO Box 551776 

Las Vegas, NV 89155-1776 

Prepared by 

Chris Emery 

Gary Wilson 

Stella Shepard 

John Grant 

ENVIRON International Corporation 

773 San Marin Drive, Suite 2115 

Novato, CA 94998 

May 19, 2008 

 773 San Marin Drive, Suite 2115, Novato, CA 94998 415.899.0700 
May 2008 

G:\Las Vegas CO MP\TSD\TOC.doc i 

TABLE OF CONTENTS 

Page 

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

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

1.2 Modeling for the Maintenance Plan........................................................................... 1-3 

2. EMISSION PROCESSING................................................................................................. 2-1 

2.1 Overview of Approach............................................................................................... 2-1 

2.2 On-Road Mobile Sources........................................................................................... 2-1 

2.3 Non-Road Emission Categories............................................................................... 2-18 

2.4 Area Sources ............................................................................................................ 2-20 

2.5 Point Sources ........................................................................................................... 2-20 

2.6 Summary of Total Emissions................................................................................... 2-21 

3. MODELING RESULTS...................................................................................................... 3-1 

3.1 Overview of Approach............................................................................................... 3-1 

3.2 UAM Simulations ...................................................................................................... 3-2 

3.3 Microscale Modeling ................................................................................................. 3-9 

3.4 Estimating On-Road Emission Budgets................................................................... 3-11 

4. SECTION 110(l) REQUIREMENTS.................................................................................. 4-1 

4.1 Ozone ......................................................................................................................... 4-1 

4.2 Particulate Matter....................................................................................................... 4-2 

REFERENCES.......................................................................................................................... R-1 

TABLES 

Table 2-1 MOBILE6.2 input parameters for Las Vegas runs .............................................. 2-3 

Table 2-2 Adjustment factor to scale link-level emissions to account for mass 

transit and traffic control measures...................................................................... 2-6 

Table 2-3 2008 VMT by facility type. Totals are shown as output by 

TransCAD, and after seasonal, day-of-week, and public transit 

adjustments .......................................................................................................... 2-8 

Table 2-4 2010 VMT by facility type. Totals are shown as output by 

TransCAD, and after seasonal, day-of-week, and public transit 

adjustments .......................................................................................................... 2-9 

Table 2-5 2020 VMT by facility type. Totals are shown as output by 

TransCAD, and after seasonal, day-of-week, and public transit 

adjustments ........................................................................................................ 2-10 
May 2008 

G:\Las Vegas CO MP\TSD\TOC.doc ii 

Table 2-6 Component and total on-road mobile source CO emissions (TPD) 

for all future years from the AIR version of MOBILE6.................................... 2-12 

Table 2-7 Component and total on-road mobile source CO emissions (TPD) 

for all future years from the Sierra-modified version of MOBILE6 ................. 2-12 

Table 2-8 Annual CO emissions reported for Nellis AFB (TPY)...................................... 2-18 

Table 2-9 Summary of inputs used for NONROAD modeling future years...................... 2-19 

Table 2-10 Modeling CO point source emission estimates (TPD) ...................................... 2-21 

Table 2-11 Summary of total daily CO emissions (TPD) in the UAM CO 

Maintenance Plan. On-road mobile emissions are taken from the 

AIR version of MOBILE6 ................................................................................. 2-21 

Table 3-1 Domain-peak 8-hour CO (ppm) from each UAM simulation ............................. 3-2 

Table 3-2 Peak 8-hour average CO concentrations (ppm) predicted by UAM, 

CAL3QHC, and UAM+CAL3QHC for each future year and for 

each of the Five Points intersections. Note that peaks reported for 

each of the models and their combined effect occur over different 

8-hour periods .................................................................................................... 3-10 

Table 3-3 Peak total UAM + EDMS 8-hour CO concentrations (ppm) at all 

three airports and for all future years evaluated. Values shown for 

McCarran airport occur at the peak publicly accessible receptor...................... 3-10 

Table 3-4 Grid definition of the central urban sub-domain................................................ 3-11 

Table 3-5 Weekday domain-wide on-road emission increase, net on-road 

emission increase that includes an additional 60% increase outside 

the central urban sub-domain, resulting UAM predicted peak CO, 

and resulting total and sub-domain on-road emission budgets 

(December 9) for each future year..................................................................... 3-12 

Table 3-6 Peak 8-hour average CO concentrations (ppm) predicted by UAM, 

CAL3QHC, and UAM+CAL3QHC for each future year, and for 

each of the Five Points intersections. UAM and CAL3QHC results 

are taken from the on-road sensitivity scaling tests. Note that 

peaks reported for each of the models and their combined effect 

occur over different 8-hour periods ................................................................... 3-12 

Table 3-7 Peak total UAM + EDMS 8-hour CO concentrations (ppm) at all 

three airports and for all future years evaluated. Values shown for 

McCarran airport occur at the peak publicly accessible receptor. 

UAM results are taken from the on-road sensitivity scaling tests ..................... 3-13 

Table 4-1 Total PM10 Mobile Source Emissions for 2006.................................................. 4-2 

Table 4-2 2006 24-Hour Controlled PM10 Emissions......................................................... 4-3 

FIGURES 

Figure 2-1 Hourly weekend and weekday start distributions (fraction) 

provided by Clark County, used to temporally allocate emissions 

derived from TransCAD. ..................................................................................... 2-4 

Figure 2-2 Fraction of original weekday start distribution (from Figure 2-1) 

and start distributions in all future years for the Las Vegas 

Boulevard area calculated from the TransCAD origin trips by TAZ 

(from the 2005 CO SIP Revision)........................................................................ 2-5 
May 2008 

G:\Las Vegas CO MP\TSD\TOC.doc iii 

Figure 2-3 Hourly start emission factors from the MOBILE6 runs: “Sun EF” 

is the Sunday profile used for all start emissions; “Mon EF” is the 

Monday profile used for start emissions outside of the LVB area; 

and “LVB Mon EF” is the Monday profile used for start emissions 

within the LVB area............................................................................................. 2-5 

Figure 2-4 Weekday and Sunday hourly VMT distribution.................................................. 2-7 

Figure 2-5 Spatial distribution of total on-road mobile source CO emissions on 

December 9 for the 2008 future year (using AIR version of MOBILE6) ......... 2-13 

Figure 2-6 Spatial distribution of total on-road mobile source CO emissions on 

December 9 for the 2010 future year (using AIR version of MOBILE6) ......... 2-14 

Figure 2-7 Spatial distribution of total on-road mobile source CO emissions on 

December 9 for the 2020 future year (using AIR version of MOBILE6) ......... 2-15 

Figure 2-8 Spatial distribution of total on-road mobile source CO emissions on 

December 9 for the 2020 future year (taken from the 2005 CO SIP 

Revision)............................................................................................................ 2-16 

Figure 2-9 Difference in total on-road mobile source CO emissions on December 9 

for the 2020 future year. The field shown in Figure 2-8 is subtracted 

from the field shown in Figure 2-7 .................................................................... 2-17 

Figure 2-10 Hourly activity profile used to temporally allocate non-road emissions ........... 2-20 

Figure 2-11 Spatial distribution of total surface gridded CO emissions on December 9 

for the 2008 future year (using AIR version of MOBILE6).............................. 2-22 

Figure 2-12 Spatial distribution of total surface gridded CO emissions on December 9 

for the 2010 future year (using AIR version of MOBILE6).............................. 2-23 

Figure 2-13 Spatial distribution of total surface gridded CO emissions on December 9 

for the 2020 future year (using AIR version of MOBILE6).............................. 2-24 

Figure 3-1 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2008 (AIR version of MOBILE6) ................................... 3-3 

Figure 3-2 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2010 (AIR version of MOBILE6) ................................... 3-4 

Figure 3-3 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2020 (AIR version of MOBILE6) ................................... 3-5 

Figure 3-4 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2008 (Sierra-modified version of 

MOBILE6)........................................................................................................... 3-6 

Figure 3-5 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2010 (Sierra-modified version of 

MOBILE6)........................................................................................................... 3-7 

Figure 3-6 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2020 (Sierra-modified version of 

MOBILE6)........................................................................................................... 3-8 

Figure 3-7 Location of the central urban sub-domain used in the UAM 

sensitivity tests (heavy red line)......................................................................... 3-11 
May 2008 

G:\Las Vegas CO MP\TSD\TOC.doc iv 

Figure 3-8 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2008 with increased on-road mobile source 

emissions to reach peak CO just under 9.0 ppm (AIR version of 

MOBILE6)......................................................................................................... 3-14 

Figure 3-9 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2010 with increased on-road mobile source 

emissions to reach peak CO just under 9.0 ppm (AIR version of 

MOBILE6)......................................................................................................... 3-15 

Figure 3-10 Spatial distribution of UAM predicted 8-hour maximum CO 

concentrations (ppm) for the December 8-9, 1996 episode using 

emission forecasts for 2020 with increased on-road mobile source 

emissions to reach peak CO just under 9.0 ppm (AIR version of 

MOBILE6)......................................................................................................... 3-16 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_1_Intro.doc 1-1

1. INTRODUCTION 

1.1 BACKGROUND 

The Las Vegas Valley is a large desert basin at about 2000 feet elevation, surrounded by 

mountain ranges up to 11,900 feet, making it quite susceptible to air pollution problems. This 

area includes the City of Las Vegas, the City of North Las Vegas, and the City of Henderson. 

The remainder constitutes unincorporated areas of Clark County. Clark County has been the 

fastest growing area of the United States over the past 50 years, with a current population of 

nearly 2,000,000 (UNLV, 2008). During the winter months, cold air masses stagnate over the 

region, and nightly temperature inversions trap pollutants within the valley. The overnight 

buildup of pollutants has historically caused violations of the national carbon monoxide standard 

in a limited area surrounding the East Charleston (now Sunrise Acres) monitoring station. This 

monitoring site in the vicinity of converging major transportation corridors named the “Five 

Points,” where three state highways intersect. Additionally, the site is located within a local 

depression where air pollution often collects. 

The 1990 Clean Air Act Amendments (CAAA) established two National Ambient Air Quality 

Standards (NAAQS) for carbon monoxide (CO). The first sets a maximum allowable 

concentration of 35 parts per million (ppm) averaged over 1 hour, and the second sets a 

maximum concentration of 9 ppm1 averaged over 8 hours. Areas that exceed one or both of the 

ambient standards more than two times in a two-year period are in violation and are thus 

classified as non-attainment areas for carbon monoxide. 

Although the Las Vegas Valley has never exceeded the 1 hour CO NAAQS, it has previously 

exceeded the 8 hour standard at least once per year on a winter seasonal basis. The last 

exceedance of the 8-hour standard occurred in 1998 in the Five Points area and measured 10.3 

ppm. There have been no CO exceedances since 1998. This downtrend is the direct result of the 

implementation of local CO control measures and the tighter federal motor vehicle emission 

standards. 

1.1.1 CO Regulatory History 

The number and severity of historical 8-hour CO violations caused the U.S. Environmental 

Protection Agency (EPA) to automatically designate the Valley as a “moderate” nonattainment 

area upon enactment of the 1990 CAAA on November 15, 1990. Moderate nonattainment areas 

were required to implement emission control measures as “expeditiously as practicable” in order 

to attain the CO NAAQS by December 31, 1995. Clark County implemented the set of controls 

required by the Clean Air Act for CO nonattainment areas, and made great strides towards 

attaining the 8-hour standard. However, due to phenomenal growth within the Las Vegas 

Valley, it fell short of meeting the NAAQS by the applicable attainment date. EPA then granted 

Clark County a one year extension to demonstrate compliance with the NAAQS. Still, the Las 

Vegas Valley was not successful in achieving compliance by December 31, 1996. 

 

1 Note that when rounding is taken into account, the CO concentration required to exceed the 8-hour standard is 9.5 

ppm. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_1_Intro.doc 1-2

According to CAAA requirements, the EPA reclassified the Las Vegas Valley as a “serious” 

nonattainment area for carbon monoxide on October 2, 1997. A deadline of May 1999 (18 

months from the notice publication date) was set for submission of a State Implementation Plan 

(SIP) that demonstrated attainment by December 31, 2000. The resulting 2000 CO State 

Implementation Plan (SIP) for Clark County contained local measures for attaining the 

standards, including wintertime gasoline specifications. In June 2005 the EPA found that the 

valley had attained the standards by the applicable attainment date. 

Later, Clark County submitted a 2005 CO SIP Revision, which included revised and improved 

methodologies for estimating on-road mobile source emissions (the chief component of CO 

emissions in the valley), and extended future year estimates of CO concentrations out to 2030 to 

demonstrate maintenance of the standards and to establish conformity emission budgets for 

multiple future years. No changes in actual control regulations were incorporated into the 2005 

CO SIP Revision. 

1.1.2 Previous CO Modeling 

Between 1996-2000, the Clark County Department of Comprehensive Planning developed 

computer models for valley-wide carbon monoxide to provide technical support for the control 

measures being evaluated for the 2000 CO SIP. This modeling was developed and conducted 

according to CAAA requirements and followed EPA modeling guidance specific to 8-hour CO 

SIP demonstrations. Modeling was conducted for three historical CO episodes in 1995-96 using 

a combination of numerical models, each focusing upon a specific scale and issue. The Urban 

Airshed Model (UAM) was used to simulate episodic urban-scale CO patterns on a grid with 1-

km spacing over the entire developed portion of the Las Vegas Valley; the CAL3QHC 

intersection model was used to simulate micro-scale CO patterns at the “Five Points” 

intersections; and the EDMS airport model was used to simulate fine-scale emissions and CO 

concentration patterns at the three civil airports in the area, including McCarran International 

Airport, North Las Vegas, and Henderson. 

At the time, 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 EPA’s 

MOBILE5b emission factor model, the Direct Travel Impact Model (DTIM), and vehicle volume 

information provided by the Regional Transportation Commission (RTC) via their TRANPLAN 

transportation demand model (TDM). Ultimately the 2000 CO SIP was based on modeling 

results for the single best performing episode of the three: the night of December 8-9 (SundayMonday), 1996. 

In 2005, the Clark County Department of Air Quality and Environmental Management updated 

their UAM CO modeling and conformity analysis using the latest tools, data resources, and 

methodologies available to estimate CO emissions. From the revised modeling results, Clark 

County submitted the 2005 CO SIP Revision. Continuing with the use of the previous 

UAM/CAL3QHC/EDMS modeling datasets developed for the December 8-9, 1996 episode, 

specific updates to the emission inventories were made, including modifications to on-road 

mobile, non-road mobile, civil airports, railroads and point sources. New spatial distributions 

were developed for area sources from updated land use projections. The future years modeled in 

this update included: 2006, 2010, 2015, 2020, and 2030. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_1_Intro.doc 1-3

The greatest effort in the 2005 CO modeling update focused on the on-road mobile source 

inventory estimates. MOBILE5b was replaced by the latest version of the model, 

MOBILE6.2.03. The TRANPLAN TDM link-level traffic volumes were replaced with 

improved and broader datasets generated using the GIS-based TransCAD TDM. DTIM was 

replaced by two new programs, one to process the link-based emissions and another to process 

start and intra-zonal emissions based on traffic analysis zones (TAZ). Additionally, NEVESbased non-road emission estimates were replaced with EPA’s NONROAD2004 model, run with 

Clark County input data and activity profiles. Railroad estimates were improved based on a 

study conducted by Mactec (2003). Finally, improvements were incorporated for the CO 

emission inventories from the three civil airports. The latest version of EDMS was used, which 

introduced the AERMOD dispersion model and included emission factor inputs from 

MOBILE6.2. 

1.2 MODELING FOR THE MAINTENANCE PLAN 

Clark County is in the process of requesting a reclassification of its CO designation from nonattainment to attainment by EPA. As part of this re-designation request, the EPA has expressed a 

desire for the DAQEM to perform new modeling calculations using current population variables 

in the most recent TransCAD TDM for the Las Vegas Valley in its CO Maintenance Plan. 

The modeling conducted in support of the CO Maintenance Plan followed the procedures 

developed for the 2005 CO SIP Revision. However, updated TransCAD TDM output was used, 

in parallel to the recent ozone SIP modeling, in addition to new wintertime fuel specifications. 

In addition, emissions from Nellis Air Force Base were updated according to the latest 

information from DAQEM. The following future years were simulated: 2008, 2010, and 2020. 

Note that the original 2006 future year modeled in the 2005 CO SIP Revision was replaced with 

the 2008 future year in this work. 

The revised CO UAM modeling used RTC TransCAD runs that they performed in 2006 to 

define on-road mobile source activity and distributions, in a manner consistent with the ozone 

SIP modeling. Start and running exhaust emissions were calculated and distributed in time and 

space in the same manner as performed for the CO SIP revision with modifications as necessary 

to accommodate the different TAZ definitions in the updated TransCAD model. Although the 

current I/M program was maintained in all future years, a new fuel was specified for all years 

comprising a 13.5 RVP with the current 3.5% oxygenate, with no further fuel controls (no CBG, 

no TCM adjustments, and no alternative fuel programs for government fleets). EPA's 

MOBILE6.2 (Air Improvement Resource’s version, which allows more detail in the database 

output to support the processing for this particular approach) was run for all years. Additionally, 

Sierra Research's modified version of MOBILE6.2, which improves the estimate of RVP effects 

on later model vehicles (Sierra Research, 2003), was used for all three future years to develop an 

alternative set of on-road mobile emissions. The NONROAD2005 model was used to calculate 

non-road emissions for the new gasoline specifications in all years; this model is also consistent 

with the version used in the ozone SIP. 

Given that the original 2006 future year in the 2005 CO SIP Revision was replaced with the 2008 

future year in this work, stationary CO emissions needed to be generated for 2008. Area 

emissions were interpolated from the existing 2006 and 2010 inventories and allocated in space 

using 2006 spatial surrogates. Civil airport and railroad emissions were similarly interpolated. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_1_Intro.doc 1-4

Since point source emissions are held constant for all years, they were used for 2008 without 

modification. 

UAM was run for the 2008, 2010, and 2020 future years using the revised emission inventories. 

Following the methodology used in the 2005 CO SIP Revision, UAM was run in two ways: one 

in which all emissions were included in the model, and another in which emissions from the 

three civil airports were removed to minimize double-counting of airport impacts when UAM 

results are combined with EDMS results. Note that EDMS was not re-run in this project; EDMS 

model results from the 2005 SIP Revision were used without modification for 2010 and 2020. It 

is also important to note that traffic volumes on the major roadways within the McCarran airport 

property are included in both EDMS and TransCAD. As a result, the EDMS+UAM CO 

concentration results for McCarran reflect a double-counting of portions of the on-road mobile 

source emissions on that property, and so the CO concentrations reported for McCarran are 

conservative (i.e., high) estimates. EDMS receptor concentrations for 2008 were interpolated 

from 2006 and 2010. CAL3QHC was re-run in this project for the three “Five Points” 

intersections for all years using the updated traffic volumes and emission factors. 

Section 2 of this report describes the development of the model-ready emission inventories. 

Section 3 describes the CO modeling using UAM and CAL3QHC, and reports the peak 8-hour 

results from UAM, UAM+CAL3QHC, and UAM+EDMS. Final on-road emission budgets are 

also reported in Section 3. Section 4 addresses the requirements of Clean Air Act Section 110(l) 

concerning changes to local control measures and their potential impacts on reasonable further 

progress and other pollutants. 
May 2008 

 

2. EMISSION PROCESSING

2.1 OVERVIEW OF APPROACH 

The estimation of CO emissions for the CO Maintenance Plan followed the procedures 

developed for the 2005 CO SIP Revision. However, updated TransCAD TDM output was used, 

in parallel to the recent ozone SIP modeling, in addition to new wintertime fuel specifications. 

The new wintertime fuel specifications affected MOBILE6 on-road emission factors and 

NONROAD emission estimates. In addition, emissions from Nellis Air Force Base were 

updated according to the latest information from DAQEM. The following future years were 

simulated: 2008, 2010, and 2020. Note that the original 2006 future year in the 2005 CO SIP 

Revision was replaced with the 2008 future year in this work. 

The revised CO UAM modeling used RTC TransCAD runs that they performed in 2006 to 

define on-road mobile source activity and distributions, consistent with the ozone SIP modeling. 

Start and running exhaust emissions were calculated and distributed in time and space in the 

same manner as performed for the CO SIP revision with modifications as necessary to 

accommodate the different TAZ definitions in the updated TransCAD model. Although the 

current I/M program was maintained in all future years, a new fuel was specified for all years 

comprising a 13.5 RVP with the current 3.5% oxygenate, with no further fuel controls (no CBG, 

no TCM adjustments, and no alternative fuel programs for government fleets). EPA's 

MOBILE6.2 (Air Improvement Resource’s version, which allows more detail in the database 

output to support the processing for this particular approach) was run for all years. Additionally, 

Sierra Research's modified version of MOBILE6.2, which improves the estimate of RVP effects 

on later model vehicles (Sierra Research, 2003), was used for all three future years to develop an 

alternative set of on-road mobile emissions. The NONROAD2005 model was used to calculate 

non-road emissions for the new gasoline specifications in all years; this model is also consistent 

with the version used in the ozone SIP. 

Given that the original 2006 future year in the 2005 CO SIP Revision was replaced with the 2008 

future year in this work, stationary CO emissions needed to be generated for 2008. Area 

emissions were interpolated from the existing 2006 and 2010 inventories and allocated in space 

using 2006 spatial surrogates. Civil airport and railroad emissions were similarly interpolated. 

Since point source emissions are held constant for all years, they were used for 2008 without 

modification. 

2.2 ON-ROAD MOBILE SOURCES 

DAQEM provided RTC’s TransCAD model output for each of the future years: 2006, 2008, 

2010, and 2020. The TransCAD model output provided link-level volumes (number of vehicles) 

and trip origins and destinations for the following seven diurnal periods: midnight – 7 AM, 7 

AM – 9 AM, 9 AM – 2 PM, 2 PM – 4 PM, 4 PM – 6 PM, 6 PM – 8 PM, 8 PM – midnight. 

When modeling Sunday, the period data were first summed together over all seven periods and 

then redistributed to hourly values using a weekend temporal distribution. When modeling 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-1
May 2008 

 

Monday, the period totals were maintained as output by TransCAD. They were further 

disaggregated into hourly values by applying the fraction of each hour within each period from 

the weekday distribution. 

2.2.1 MOBILE6 Inputs 

Future year MOBILE6 inputs were compiled according to the 2005 CO SIP Revision and fuel 

specifications selected by DAQEM (Table 2-1). For each future year, eight input files were 

created, for each of the four roadway types (freeway, arterial, local, and ramp) both for weekday 

and weekend. For Freeway and Arterial, the model was run for speeds between 5 and 65 mph 

for every 1 mph increment. The Local roadway type was set at 12.9 mph, and the Ramp 

roadway type was set to 34.6 mph by MOBILE6 itself. 

No CNG fleets were assumed to be present in the future years. The current I/M program was 

maintained for all future years. Note that MOBILE6 I/M effectiveness was set to 100%; Clark 

County has developed a white paper to justify this value for Las Vegas (Clark County, 2005). 

For the VMT mix, values generated from a 2002 traffic study conducted by RTC in Las Vegas 

(Orth-Rodgers and Associates, 2003) were used, which yielded VMT for 5 vehicle types that 

were further broken down into 16 vehicle types based on MOBILE6 default VMT mix for 2002. 

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

adjustments, or hourly activity profiles, so the same settings were used for all future years. 

Following the approach from the 2005 CO SIP Revision, a first set of MOBILE6 runs was 

conducted using the start distribution contained in the sdist.lv file (shown in Figure 2-1). These 

emission factors were applied to the whole domain except for a small region around Las Vegas 

Boulevard. A second set of MOBILE6 runs was conducted to better estimate the specific 

weekday start emission factors along the Las Vegas Boulevard (LVB), where the start activity is 

not centered within residential areas, but rather parking lots near casinos (and thus are not 

characteristic of typical commute activity profiles). A more representative start distribution was 

calculated as the fraction of TransCAD origin trips occurring over all TAZs along the boulevard 

from all periods available in the TransCAD output. Figure 2-2 shows the weekday start 

distributions for all future years along the Las Vegas Boulevard. Given the similarity of the 

future year start distributions, the composite start distribution was applied to all future years for 

the region around the Las Vegas Boulevard. Figure 2-3 compares the hourly MOBILE6 start 

emission factor profiles for Sunday (entire domain), Monday (LVB area), and Monday 

(remainder of the domain). 

2.2.2 TransCAD Link Activity Adjustments 

The TransCAD volume data is representative of an annual average weekday. The link-level 

activity was adjusted from annual average to December by a factor of 1.000. The activity data 

were scaled to Sunday estimates by weighting the Sunday day-of-week factor by the average 

weekday factor. The Sunday activity adjustment was 0.743. Activity was not adjusted for 

Monday. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-2
May 2008 

 

Table 2-1. MOBILE6.2 input parameters for Las Vegas runs. 

M6 Input Parameter Weekday Parameters Weekend Parameters Source 

42.0 44.0 49.0 51.0 55.0 

58.0 64.0 66.0 66.0 66.0 

62.0 58.0 55.0 53.0 51.0 

50.0 48.0 47.0 45.0 44.0 

44.0 43.0 42.0 42.0 

42.0 44.0 49.0 51.0 55.0 

58.0 64.0 66.0 66.0 66.0 

62.0 58.0 55.0 53.0 51.0 

50.0 48.0 47.0 45.0 44.0 

44.0 43.0 42.0 42.0 

same 

temperatures 

used as in 

previous work 

HOURLY TEMPERATURES 

REGISTRATION DIST LV_reg02.RDT LV_reg02.RDT provided by 

Clark County 

0.5042 0.0767 0.2552 

0.0779 0.0358 0.0080 

0.0002 0.0001 0.0003 

0.0007 0.0003 0.0000 

0.0000 0.0024 0.0011 

0.0030 0.0008 0.0007 

0.0002 0.0016 0.0025 

0.0031 0.0113 0.0072 

0.0008 0.0013 0.0019 

0.0015 

0.5042 0.0767 0.2552 

0.0779 0.0358 0.0080 

0.0002 0.0001 0.0003 

0.0007 0.0003 0.0000 

0.0000 0.0024 0.0011 

0.0030 0.0008 0.0007 

0.0002 0.0016 0.0025 

0.0031 0.0113 0.0072 

0.0008 0.0013 0.0019 

0.0015 

provided by 

Clark County 

VMT FRACTIONS BY 

VEHICLE TYPE 

VMT BY HOUR Hvmt_lv.wek Hvmt_lv.wnd provided by 

Clark County 

START DIST sdist.lv sdist.lv provided by 

Clark County 

provided by 

Clark County OXYGENATED FUELS 0.00 1.00 0.00 0.035 1 0.00 1.00 0.00 0.035 1 

83 81 50 22222 

22222222 2 11 090. 

22212112 

83 81 50 22222 

22222222 2 11 090. 

22212112 

provided by 

Clark County ANTI-TAMP PROG 

provided by 

Clark County > Exhaust I/M program #1 

 1 1983 2050 1 TRC 

2500/IDLE 

 1 1983 2050 1 TRC 

2500/IDLE I/M PROGRAM 

I/M MODEL YEARS 1 1968 1995 1 1968 1995 

I/M VEHICLES 1 22222 22222222 2 1 22222 22222222 2 

I/M STRINGENCY 1 22 1 22 

I/M COMPLIANCE 1 90 1 90 

I/M WAIVER RATES 1 0.1 0.1 1 0.1 0.1 

I/M EFFECTIVENESS 1.00 1.00 1.00 1.00 1.00 1.00 

I/M GRACE PERIOD 1 2 1 2 

I/M CREDIT FILE tech12.d tech12.d 

> Exhaust I/M program #2 

 2 1983 2050 1 TRC 

OBD I/M 

 2 1983 2050 1 TRC 

OBD I/M I/M PROGRAM 

I/M MODEL YEARS 2 1996 2050 2 1996 2050 

I/M VEHICLES 2 22222 22222222 2 2 22222 22222222 2 

I/M STRINGENCY 2 22 2 22 

I/M COMPLIANCE 2 90 2 90 

I/M WAIVER RATES 2 0.1 0.1 2 0.1 0.1 

I/M GRACE PERIOD 2 2 2 2 

> Evap I/M program #3 

 3 1983 2050 1 TRC 

EVAP OBD 

 3 1983 2050 1 TRC 

EVAP OBD I/M PROGRAM 

I/M MODEL YEARS 3 1996 2050 3 1996 2050 

I/M VEHICLES 3 22222 11111111 1 3 22222 11111111 1 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-3
May 2008 

 

M6 Input Parameter Weekday Parameters Weekend Parameters Source 

I/M COMPLIANCE 3 90 3 90 

I/M WAIVER RATES 3 0.1 0.1 3 0.1 0.1 

I/M GRACE PERIOD 3 2 3 2 

CALENDAR YEAR 2009, 2011, 2021 2009, 2011, 2021 

EVALUATION MONTH 1 1 

WE VEH US no yes 

FUEL RVP 13.5 13.5 provided by 

Clark County 

FUEL PROGRAM 1 1 provided by 

Clark County 

Average Gasoline Fuel 

Sulfur Content = 30 ppm 

Average Gasoline Fuel 

Sulfur Content = 30 ppm 

Maximum Gasoline Fuel 

Sulfur Content = 80 ppm 

Maximum Gasoline Fuel 

Sulfur Content = 80 ppm 

DIESEL SULFUR 15,15,15 15,15,15 provided by 

Clark County 

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 4 812 16 20

Hour beginning

Fraction of Daily Total

24

Weekday

Weekend

Figure 2-1. Hourly weekend and weekday start distributions (fraction) provided by Clark 

County, used to temporally allocate emissions derived from TransCAD. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-4
May 2008 

 

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

Fraction of Daily Total 

Original Starts

2000

2006

2010

2015

2020

2030

Figure 2-2. Fraction of original weekday start distribution (from Figure 2-1) and start 

distributions in all future years for the Las Vegas Boulevard area calculated from the TransCAD 

origin trips by TAZ (from the 2005 CO SIP Revision). 

0

0.002

0.004

0.006

0.008

0.01

0.012

123456789

101112131415161718192021222324

Hour

g/mile

Mon EF Sun EF LVB Mon EF

Figure 2-3. Hourly start emission factors from the MOBILE6 runs: “Sun EF” is the Sunday 

profile used for all start emissions; “Mon EF” is the Monday profile used for start emissions 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-5
May 2008 

 

outside of the LVB area; and “LVB Mon EF” is the Monday profile used for start emissions within 

the LVB area. 

Prior to calculating the link-based emissions, the link volumes were first adjusted to observed 

traffic counts by facility type. Then, the adjusted link volumes were adjusted to bring the total 

volume into agreement with the VMT reported through the Highway Performance Monitoring 

System (HPMS). The overall HPMS adjustment was a single factor multiplied uniformly to the 

volumes to bring the total into agreement with HPMS. The HPMS adjustment factor used was 

1.0628, based on the ozone SIP work. 

Within each of the seven periods, the data were further disaggregated using the default weekday 

(Dec. 9) distribution for Monday. For Sunday, the data were summed to obtain the daily total 

before re-distributing into the hours using the default weekend (Dec. 8) distribution. The same 

VMT distributions that were used for the 2005 CO SIP Revision were used for the future years, 

as illustrated in Figure 2-4. 

After the link data were temporally allocated to hourly values, the hourly speeds were adjusted 

using the following Bureau of Public Roads (BPR) curve, where the volume to capacity ratio was 

capped at 1.25: 

( ) ⎥⎦

⎤ ⎢⎣⎡ +

= B

ff

a

C A V

S

S

*1

where: 

Sa = adjusted link speed (mph) 

S = reported link free flow speed (mph) ff

V = total link volume (vehicles OR vehicles per hour) 

C = total link capacity (vehicles OR vehicles per hour) 

For freeways, interstates, system ramps, and expressways, 

 A = 0.66 B = 7.2 

For major arterials, minor arterials, collectors, ramps, and other, 

 A = 0.76 B = 5.9 

The link-level emissions were adjusted upward by the factors shown in Table 2-2 to capture 

transit activity (values provided by DAQEM). Link-level emissions were not adjusted for 

TCMs. 

Table 2-2. Adjustment factor to scale link-level emissions to account for mass transit and traffic 

control measures. 

Year Transit Adjustment Factor TCM Adjustment Factor 

2008 1.004438 1.000 

2010 1.003913 1.000 

2020 1.003192 1.000 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-6
May 2008 

 

On-Road Hourly VMT Distribution

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

Percent

Dec. 8 Dec. 9

Figure 2-4. Weekday and Sunday hourly VMT distribution. 

2.2.3 Link-Level Running Emissions 

The TransCAD link level volumes were first adjusted by the count correction factor and the 

HPMS adjustment. Then, they were disaggregated to hourly volumes. The speed was adjusted 

using the hourly volume to capacity ratio in the BPR curve. The MOBILE6 emission factor for 

that hour and adjusted speed was multiplied by the hourly link volume to determine hourly 

emissions. The hourly emissions were further adjusted to December, day of week, transit 

activity, and TCM’s in CNTLEM within the EPS3 processing. Tables 2-3 through 2-5 present 

tabulations of VMT by facility type for each future year, as directly reported by TransCAD, and 

after the adjustments described above. 

2.2.4 Start Emissions 

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

using the weekday VMT distribution show in Figure 2-4. The start emissions were calculated by 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-7
May 2008 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-8

multiplying the hourly VMT by the hourly MOBILE6 start emission factors. The hourly link 

start emissions were then totaled over the entire network and redistributed to TAZ, based on the
May 2008 

Table 2-3. 2008 VMT by facility type. Totals are shown as output by TransCAD, and after seasonal, day-of-weadjustments. 

Modeled 

Group Code Facility Type 

2006 

DVMT 

Count DVMT DVMT DVMT DVMT 

Correction 

Factor 

Corrected to 

Count 

Corrected to 

HPMS 

Adjusted to 

December 

Adjusted for 

Transit 

0 External Connector 607,755 0.9102 553,178 587,918 587,918 590,527 1 System Ramp 341,326 1.4572 497,380 528,616 528,616 530,962 2 Minor Arterial 5,439,127 0.9774 5,316,203 5,650,060 5,650,060 5,675,135 3 Major Arterial 15,344,935 0.9468 14,528,584 15,440,979 15,440,979 15,509,507 4 Freeway on- or off-ramp 1,226,843 1.0633 1,304,503 1,386,425 1,386,425 1,392,578 5 Interstate 10,477,414 1.0043 10,522,467 11,183,278 11,183,278 11,232,909 6 Freeway 4,567,426 1.1169 5,101,358 5,421,723 5,421,723 5,445,785 7 Expressway 198,762 1.9272 383,054 407,110 407,110 408,916 8 Collector 3,310,084 1.1742 3,886,701 4,130,786 4,130,786 4,149,118 9 Centroid Connector 3,255,261 1.1742 3,822,327 4,062,369 4,062,369 4,080,398 

10 Local 15,271 1.1742 17,931 19,057 19,057 19,141 11 HOV Lane 243,363 1.1169 271,812 288,882 288,882 290,164 

Intrazonal 106,738 1 106,738 113,442 113,442 113,945 

Daily Total 45,134,305 46,312,237 49,220,645 49,220,645 49,439,086 Transit adjustment 1.004438 HPMS adjustment 1.0628 December adjustment 1.000 Sunday adjustment 0.743 Monday adjustment 1.000 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 
May 2008 

Table 2-4. 2010 VMT by facility type. Totals are shown as output by TransCAD, and after seasonal, day-of-weadjustments. 

Modeled 

Group Code Facility Type 

2010 

DVMT 

Count DVMT DVMT DVMT DVMT 

Correction 

Factor 

Corrected to 

Count 

Corrected to 

HPMS 

Adjusted to 

December 

Adjusted for 

Transit 

0 External Connector 631,693 0.9102 574,967 611,075 611,075 613,466 1 System Ramp 356,340 1.4572 519,259 551,868 551,868 554,028 2 Minor Arterial 6,100,189 0.9774 5,962,325 6,336,759 6,336,759 6,361,555 3 Major Arterial 16,609,483 0.9468 15,725,859 16,713,443 16,713,443 16,778,842 4 Freeway on- or off-ramp 1,347,467 1.0633 1,432,762 1,522,739 1,522,739 1,528,697 5 Interstate 11,303,566 1.0043 11,352,171 12,065,087 12,065,087 12,112,298 6 Freeway 5,395,363 1.1169 6,026,081 6,404,519 6,404,519 6,429,580 7 Expressway 193,598 1.9272 373,103 396,534 396,534 398,085 8 Collector 3,498,212 1.1742 4,107,601 4,365,558 4,365,558 4,382,641 9 Centroid Connector 3,581,532 1.1742 4,205,435 4,469,537 4,469,537 4,487,026 

10 Local 15,632 1.1742 18,355 19,507 19,507 19,584 11 HOV Lane 486,752 1.1169 543,654 577,795 577,795 580,056 

Intrazonal 121,457 1 121,457 129,084 129,084 129,589 

Daily Total 49,641,284 50,963,026 54,163,504 54,163,504 54,375,446 Transit adjustment 1.003913 HPMS adjustment 1.0628 December adjustment 1.000 Sunday adjustment 0.743 Monday adjustment 1.000 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 
\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 

Table 2-5. 2020 VMT by facility type. Totals are shown as output by TransCAD, and after seasonal, day-of-weadjustments. 

Group Code Facility Type 

Modeled 

2020 

DVMT 

Count 

Correction 

Factor 

DVMT 

Corrected to 

Count 

DVMT 

Corrected to 

HPMS 

DVMT 

Adjusted to 

December 

DVMT 

Adjusted for 

Transit 

0 External Connctor 789,029 0.9102 718,174 763,276 763,276 765,712 1 System Ramp 535,150 1.4572 779,821 828,794 828,794 831,439 2 Minor Arterial 8,695,678 0.9774 8,499,155 9,032,902 9,032,902 9,061,735 3 Major Arterial 19,167,364 0.9468 18,147,660 19,287,333 19,287,333 19,348,898 4 Freeway on- or off-ramp 1,707,664 1.0633 1,815,759 1,929,789 1,929,789 1,935,949 5 Interstate 15,636,220 1.0043 15,703,456 16,689,633 16,689,633 16,742,906 6 Freeway 7,464,694 1.1169 8,337,317 8,860,901 8,860,901 8,889,185 7 Expressway 7,652 1.9272 14,746 15,672 15,672 15,722 8 Collector 4,146,492 1.1742 4,868,811 5,174,573 5,174,573 5,191,090 9 Centroid Connector 4,693,489 1.1742 5,511,095 5,857,191 5,857,191 5,875,887 

10 Local 15,818 1.1742 18,573 19,739 19,739 19,802 11 HOV Lane 1,160,461 1.1169 1,296,119 1,377,515 1,377,515 1,381,912 

Intrazonal 168,722 1 168,722 179,317 179,317 179,890 

Daily Total 64,188,433 65,879,409 70,016,635 70,016,635 70,240,128 Transit adjustment 1.003192 HPMS adjustment 1.0628 December adjustment 1.000 Sunday adjustment 0.743 

1.000 

May 2008 G:

Monday adjustment 
May 2008 

fraction of period-specific trip origins for each TAZ over the total number of trip origins over all 

TAZs. For Sunday, the TransCAD data is not representative of a typical weekend profile, so the 

hourly VMT was estimated by first totaling all the period VMT to a daily value, then it was 

distributed to hourly values using the weekend profile in Figure 2-4. The Sunday start emissions 

were then calculated by multiplying the hourly VMT by the MOBILE6 hourly emission factors 

for all hours. The emissions were totaled over the entire network and then spatially distributed to 

each TAZ using a single ratio of the daily total TAZ trip origins to the daily total of all trip 

origins over the domain. 

The future year start emissions were calculated twice; once using the MOBILE6 emission factors 

generated using the sdist.lv hourly start distribution (Figure 2-1), and once using the MOBILE6 

emission factors generated using the modified start distribution discussed above to reflect the 

activity along the Las Vegas Boulevard (Figure 2-2). 

Following the methodology in the 2005 CO SIP Revision, 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 receives 25% of the start 

emissions from that TAZ, the surrounding 8 grid cells receive 60% of the start emissions (7.5% 

per cell), and the outside 16 grid cells receive 15% of the start emissions (0.9375% per cell). 

2.2.5 Intrazonal Activity 

The intrazonal VMT was calculated assuming a default length of 1 mile for each intrazonal trip 

(as is described in the 2004-2005 Regional Transportation Plan documentation [FY 2004-2025 

RTP and FY 2004-2006 TIP, Chapter 5, page 5-16]). 

2.2.6 Total On-Road Emissions 

Table 2-6 lists the component and total on-road mobile source emissions for all future years 

using the AIR version of MOBILE6. For comparison, Table 2-7 lists the component and total 

on-road emissions using the Sierra-modified version of MOBILE6. Figures 2-5 through 2-7 

present the future year spatial distribution of the total on-road mobile source emissions for 

December 9, 1996 using the AIR version of MOBILE6. 

The combination of updated TransCAD traffic volumes and higher MOBILE6 emission factors 

due to fuel changes results in much higher on-road mobile emissions out to 2020 than reported in 

the 2005 CO SIP Revision. Figure 2-8 displays the 2020 on-road mobile sources from the 2005 

CO SIP Revision (compare to Figure 2-7). Figure 2-9 shows the difference in mobile source 

emissions between Figures 2-8 and 2-7. Note that higher emission factors and higher traffic 

volumes in the Las Vegas Boulevard and McCarran airport areas result in the largest increases in 

those areas. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-12
May 2008 

Table 2-6. Component and total on-road mobile source CO emissions (TPD) for all future years 

from the AIR version of MOBILE6. 

2008 2010 2020 

Sunday 12/8/2005 

Links - Running 206.6 204.6 188.9 

Starts 157.3 158.8 167.6 

Intrazonals 0.7 0.8 0.8 

Total 364.6 364.2 357.3 

Monday 12/9/2005 

Links - Running 277.6 275.1 253.7 

Starts 300.6 303.4 319.4 

Intrazonals 1.1 1.2 1.3 

Total 579.3 579.7 574.4 

Table 2-7. Component and total on-road mobile source CO emissions (TPD) for all future years 

from the Sierra-modified version of MOBILE6. 

2008 2010 2020 

Sunday 12/8/2005 

Links - Running 167.2 163.7 146.1 

Starts 150.3 151.1 158.3 

Intrazonals 0.6 0.7 0.7 

Total 318.1 315.5 305.1 

Monday 12/9/2005 

Links - Running 224.3 219.6 195.8 

Starts 286.3 287.8 300.5 

Intrazonals 1.0 1.0 1.1 

Total 511.6 508.4 497.4 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-13
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

 On-Road CO Emissions

2008 Future Year (EPA M6)

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

Figure 2-5. Spatial distribution of total on-road mobile source CO emissions on December 9 for 

the 2008 future year (using AIR version of MOBILE6). 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-14
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 On-Road CO Emissions

2010 Future Year (EPA M6)

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

Figure 2-6. Spatial distribution of total on-road mobile source CO emissions on December 9 for 

the 2010 future year (using AIR version of MOBILE6).

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-15
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 On-Road CO Emissions

2020 Future Year (EPA M6)

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

Figure 2-7. Spatial distribution of total on-road mobile source CO emissions on December 9 for 

the 2020 future year (using AIR version of MOBILE6).

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-16
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 On-Road CO Emissions

2020 Future Year (2005 SIP)

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

Figure 2-8. Spatial distribution of total on-road mobile source CO emissions on December 9 for 

the 2020 future year (taken from the 2005 CO SIP Revision).

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-17
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

Difference in 2020 On-Road CO Emissions

 2008 MP - 2005 SIP

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Max Difference: 1.7 TPD

Figure 2-9. Difference in total on-road mobile source CO emissions on December 9 for the 

2020 future year. The field shown in Figure 2-8 is subtracted from the field shown in Figure 2-7.

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-18
May 2008 

2.3 NON-ROAD EMISSION CATEGORIES 

2.3.1 Airports 

In 2003, Clark County and their contractor Ricondo and Associates developed a detailed 

emissions inventory at the three county civil airports (McCarran, North Las Vegas, and 

Henderson), and performed dispersion modeling using the Federal Aviation Administration’s 

EDMS model (Ricondo, 2003, 2005). The latest version of EDMS was used, which introduced 

the AERMOD dispersion model. On-road mobile sources were estimated using Clark County 

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

To properly account for the contributions of civil airports toward the valley-wide distribution of 

CO during the December 8-9 episode, the UAM emissions inventory included the EDMS airport 

emission estimates. Airport emissions for the 2010 and 2020 future years were taken from the 

2005 CO SIP Revision, which in turn were based upon the work of Ricondo (2003, 2005). 

Emission estimates for 2008 were derived by linearly interpolating total airport emissions 

between 2006 and 2010. 

The emission estimates for Nellis AFB were updated in the current modeling project based on 

data provided by DAQEM. Table 2-8 shows annual total CO emissions reported for Nellis. 

Emissions for this facility were allocated to each hour of the episode assuming a flat temporal 

profile (i.e., no monthly, daily, or hourly variations). 

Table 2-8. Annual CO emissions reported for Nellis AFB (TPY). 

Year CO (TPY) 

2008 1266.03 

2010 1305.74 

2020 1476.60 

Following the 2005 CO SIP Update, airport emissions were placed evenly across the grid cells in 

which the airports reside. 

2.3.2 Locomotives 

The 2005 CO SIP Update included estimates of railroad emissions for 2001 based on the work of 

Mactec (2003). Switching and line-haul locomotive emissions were allocated to the grid 

according to the location of yards and railroad line segments, respectively. Projections for 2006, 

2010, and 2020 were developed for the 2005 CO SIP Update. Estimates for 2008 were 

determined by interpolated between 2006 and 2010. 

Railroad maintenance emissions were estimated in the 2005 CO SIP Update using EPA’s 

NONROAD Model. In this project, railroad equipment emissions for 2010 and 2020 were taken 

from the previous SIP, and estimates for 2008 were similarly determined by interpolated between 

2006 and 2010. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-19
May 2008 

2.3.3 Other Non-Road Categories 

Weekday and weekend emissions for Clark County were estimated using EPA’s NONROAD 

Model (Core Model Version 2005a, February 2006) for the years 2008, 2010, and 2020. The 

period type was set to Winter Season, and emissions were reported as tons per day. Clark 

County was modeled as a “Southwest” region instead of the default “Central West” region. 

Table 2-9 summarizes the NONROAD Model input parameters for each future year. All inputs 

except for the gasoline specifications were taken from the 2005 CO SIP Update. 

Table 2-9. Summary of inputs used for NONROAD modeling future years. 

2008 2010 2020 

 

 Weekday 

(tpd) 

Weekend 

(tpd) 

Weekday 

(tpd) 

Weekend Weekday Weekend 

(tpd) (tpd) (tpd) 

Period Type Monthly Monthly Monthly Monthly Monthly Monthly 

Typical 

Day 

Typical 

Day 

Typical 

Day 

Typical 

Day 

Typical 

Day 

Typical 

Summation Type Day 

Year of Episode 2008 2008 2010 2010 2020 2020 

Month of Year Dec. Dec. Dec. Dec. Dec. Dec. 

Weekend or weekday Weekday Weekend Weekday Weekend Weekday Weekend 

Fuel RVP for gas 13.5 13.5 13.5 13.5 13.5 13.5 

Oxygen Weight % 3.50 3.50 3.50 3.50 3.50 3.50 

Gas sulfur % 0.003 0.003 0.003 0.003 0.003 0.003 

Diesel sulfur % 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 

CNG/LPG sulfur % 0.003 0.003 0.003 0.003 0.003 0.003 

Minimum temper. (F) 42 42 42 42 42 42 

Maximum temper. (F) 66 66 66 66 66 66 

Average temper. (F) 51.9 51.9 51.9 51.9 51.9 51.9 

Altitude of region low low low low low low 

Airport ground support equipment (GSE) was removed from the NONROAD emissions 

estimates because they were reported as part of the EDMS (civil airports) and Nellis AFB 

inventories. Recreational marine estimates were also removed since the major water areas in 

Clark County lie outside of the modeling domain. Railroad maintenance/equipment emissions 

were removed from the NONROAD estimates as emissions for this category were taken from the 

2005 CO SIP Update. 

Figure 2-10 shows the distribution used to temporally allocate non-road sources. Non-road 

emissions in 2010 and 2020 were allocated to the grid using surrogates developed specifically for 

those years from GIS-based landuse datasets as part of the 2005 CO SIP Update. Non-road 

emissions for 2008 were spatially allocated using the 2006 gridding surrogates from the 2005 CO 

SIP Update. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-20
May 2008 

0

0.02

0.04

0.06

0.08

0.1

0.12

13579

11131517192123

Hour

Figure 2-10. Hourly activity profile used to temporally allocate non-road emissions. 

2.4 AREA SOURCES 

The 2010 and 2020 area source estimates were taken from the 2005 CO SIP Update with no 

changes. Values were interpolated to 2008 from the 2006 and 2010 estimates. Since 2006 and 

2010 area sources were spatially allocated using different gridding surrogates, special processing 

was required to perform the interpolation to 2008. First, the 2010 area source estimates were 

processed to the grid using 2006 spatial surrogates. Then 2008 area source estimates were 

calculated by interpolated between 2006 and 2010 on a cell-by-cell and hour-by-hour basis. 

Therefore, the 2008 area sources are represented on the grid by 2006 spatial surrogates, similarly 

to the non-road sources. 

2.5 POINT SOURCES 

The point source inventory from the 2000 CO SIP and 2005 SIP Update was used for this 

modeling. At that time, Clark County provided a point source emission inventory for future 

years that included updated stack parameters and emissions based on “Potential To Emit” (PTE) 

levels for seven specific facilities. The UAM future year inventories included PTE levels plus a 

70 ton/year buffer for these sources. All future year modeling used the same future year point 

source data. Table 2-10 shows a breakdown by elevated and low-level point sources. 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-21
May 2008 

Table 2-10. Modeling CO point source emission estimates (TPD). 

 Future Years 

Elevated 15.53

Low Level 0.28

Total 15.82

2.6 SUMMARY OF TOTAL EMISSIONS 

Table 2-11 presents a summary of total daily CO emissions by source category, including onroad emissions (based on the AIR version of MOBILE6), for all future years. Figures 2-11 

through 2-13 show the spatial distribution of total CO emissions on December 9 for all future 

years. 

Table 2-11. Summary of total daily CO emissions (TPD) in the UAM CO Maintenance Plan. 

On-road mobile emissions are taken from the AIR version of MOBILE6. 

2008 2010 2020 

Sunday 12/8

On-Road 364.6 364.2 357.3 

Henderson Airport 1.5 1.6 2.6 

McCarran Airport 30.9 33.2 43.2 

North Las Vegas Airport 5.2 5.2 5.5 

Nellis AFB 3.5 3.6 4.0 

Area Sources 13.6 14.3 18.1 

Non-Road 39.9 42.5 49.7 

Point Sources 15.8 15.8 15.8 

Railroad 0.2 0.2 0.3 

Total 475.1 480.6 496.5 

Monday 12/9

On-Road 579.3 579.7 574.4 

Henderson Airport 1.2 1.3 2.0 

McCarran Airport 30.9 33.2 43.2 

North Las Vegas Airport 4.1 4.1 4.3 

Nellis AFB 3.5 3.6 4.0 

Area Sources 13.9 14.7 18.6 

Non-Road 57.7 60.8 71.2 

Point Sources 15.8 15.8 15.8 

Railroad 0.3 0.3 0.4 

Total 706.7 713.5 733.9 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-22
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 Total CO Emissions

2008 Future Year (EPA M6)

0.6

1.2

1.8

2.4

3

3.6

4.2

4.8

5.4

6

Figure 2-11. Spatial distribution of total surface gridded CO emissions on December 9 for the 

2008 future year (using AIR version of MOBILE6). 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-23
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 Total CO Emissions

2010 Future Year (EPA M6)

0.6

1.2

1.8

2.4

3

3.6

4.2

4.8

5.4

6

Figure 2-12. Spatial distribution of total surface gridded CO emissions on December 9 for the 

2010 future year (using AIR version of MOBILE6). 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-24
May 2008 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

TPD

 Total CO Emissions

2020 Future Year (EPA M6)

0.6

1.2

1.8

2.4

3

3.6

4.2

4.8

5.4

6

Figure 2-13. Spatial distribution of total surface gridded CO emissions on December 9 for the 

2020 future year (using AIR version of MOBILE6). 

G:\Las Vegas CO MP\TSD\Sec_2_Emissions.doc 2-25
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-1 

3. MODELING RESULTS

3.1 OVERVIEW OF APPROACH 

The UAM was provided with the updated future year CO emission inventories for 2008, 2010, 

and 2020 (as described in Section 2) and run for the December 8-9, 1996 historical CO event. 

All other environmental parameters were taken from the original modeling as documented in the 

2000 CO SIP and the 2005 CO SIP Update. The UAM was used to determine peak 8-hour CO 

levels in the basin for each future year. 

Modeling was performed to address UAM valley-wide CO distributions, intersection “hot spot” 

modeling with CAL3QHC, and EDMS micro-scale results reported by Ricondo (2003, 2005). 

With regard to the airports, it was necessary to run UAM twice using two different inventories 

per future year: 

1. Valley-wide CO and micro-scale intersection modeling – including updated EDMS 

emissions in the UAM; 

2. Micro-scale airport CO modeling – removing EDMS airport emissions from the UAM 

inventory in order to minimize double-counting. 

EDMS results from the Ricondo (2003, 2005) analyses were combined with the revised UAM 

model predictions for the future years of 2008, 2010, and 2020 to estimate 8-hour CO 

concentrations for the duration of the episode on and around the airport properties. Note that the 

EDMS results previously reported for 2006 and 2010 (from the 2005 CO SIP Update) were 

interpolated to derive 2008 EDMS concentrations. 

For hotspot intersection modeling, the CAL3QHC model was used to model three intersections: 

Charleston/Eastern, Charleston/Fremont and Eastern/Fremont, which are referred to collectively 

as the “Five Points” area. EPA (1992, 1995) guidance for screening level modeling of these 

three intersections was followed. The ambient temperature for each hour of the episode (needed 

to estimate emissions with the MOBILE6 model), and the wind direction and speed (needed for 

the CAL3QHC dispersion estimates) were taken from the original UAM/CAL3QHC modeling 

documented in the 2000 SIP. The same MOBILE6 inputs documented for the on-road emissions 

calculations in Section 2 were used to estimate emission factor inputs for CAL3QHC. Traffic 

volumes for all links associated with the three intersections were scaled according to the 

differences between the current TransCAD volumes and those used in the 2005 CO SIP Update. 

Since there were no 2008 volumes from the TransCAD results reported in the 2005 CO SIP 

Update, they were derived by scaling from 2006 (original TransCAD volumes) to 2008 (current 

TransCAD volumes). The CAL3QHC model output was added to the background UAM levels 

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

Additional UAM simulations were run with scaled-up on-road CO emissions for each future year 

to develop on-road mobile emission budgets that demonstrate compliance with the 8-hour CO 

standard. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-2 

3.2 UAM SIMULATIONS 

The UAM was used to simulate the emissions and transport of carbon monoxide throughout the 

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

UAM was run from 1500 LST December 8 to 1100 LST December 9 to cover the most cold, 

stagnant and stable portion of the episode during which CO was observed to build up. The UAM 

was run using two sets of emission inputs, as described in Section 2: 

1. On-road mobile sources estimated using the AIR version of MOBILE6; 

2. On-road mobile sources estimated using the Sierra-modified version of MOBILE6. 

Figures 3-1 through 3-3 display predicted 8-hour maximum CO concentrations in the modeling 

domain using the AIR version of MOBILE6 for the years 2008, 2010, and 2020, respectively. 

UAM predictions show that the 8-hour CO standard of 9 ppm will not be violated anywhere 

within the domain. Three distinct areas of CO maxima occur in the simulation: (1) near the 

“elbow” of U.S. 95 in northeast Las Vegas; (2) around the intersection of U.S. 95 and I-15; and 

(3) along the Las Vegas Boulevard “strip” near the intersection with Spring Mountain Road and 

extending to McCarran airport. 

Similar patterns are seen when using emissions derived from the Sierra-modified version of 

MOBILE6, although the CO concentration patterns are lower overall in each year (Figures 3-4 

through 3-6). The domain-peak 8-hour CO concentrations are tabulated below for each year and 

MOBILE6 run. 

Table 3-1. Domain-peak 8-hour CO (ppm) from each UAM simulation. 

Peak 8-hour CO 

Year AIR MOBILE6 Sierra-modified MOBILE6 

2008 8.8 8.4 

2010 8.5 8.1 

2020 7.7 7.1 

Note that the contribution of McCarran airport to local CO concentrations in that area steadily 

increases over this period. This is due to the projected growth in airport activities as reported by 

Ricondo (2003, 2005). In each successive year through 2020, however, the contribution from 

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

Las Vegas to the northern boundary of McCarran airport along Tropicana Boulevard. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-3 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2008 Future Year (EPA M6)

Peak = 8.8 ppm

5

6

7

8

9

10

11

12

Figure 3-1. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2008 (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-4 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2010 Future Year (EPA M6)

Peak = 8.5 ppm

5

6

7

8

9

10

11

12

Figure 3-2. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2010 (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-5 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2020 Future Year (EPA M6)

Peak = 7.7 ppm

5

6

7

8

9

10

11

12

Figure 3-3. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2020 (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-6 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2008 Future Year (Sierra M6)

Peak = 8.4 ppm

5

6

7

8

9

10

11

12

Figure 3-4. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2008 (Sierra-modified version of 

MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-7 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2010 Future Year (Sierra M6)

Peak = 8.1 ppm

5

6

7

8

9

10

11

12

Figure 3-5. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2010 (Sierra-modified version of 

MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-8 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2020 Future Year (Sierra M6)

Peak = 7.1 ppm

5

6

7

8

9

10

11

12

Figure 3-6. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2020 (Sierra-modified version of 

MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-9 

3.3 MICROSCALE MODELING 

Future year UAM simulation results were used to provide estimates of background ambient CO 

levels for micro-scale modeling performed for the “Five Points” hot spot intersection and for the 

three civil airports in the modeling domain (McCarran, Henderson Executive, and North Las 

Vegas). UAM concentrations from the appropriate grid cells were simply added to the 

concentrations predicted at each micro-scale receptor to obtain a total (background + microscale) CO concentration. Note that the UAM simulations reported here utilized on-road mobile 

emissions generated from the AIR version of MOBILE6 only. Procedures for running 

CAL3QHC and combining with UAM predictions followed the same methodology as described 

in the 2000 CO SIP and 2005 CO SIP Revision. Results are presented in the following subsections. 

3.3.1 CAL3QHC Intersection Modeling 

The CAL3QHC model was used to model three intersections: Charleston/Eastern, 

Charleston/Fremont and Eastern/Fremont, which are referred to collectively as the “Five Points” 

area. The ambient temperature for each hour of the episode (needed to estimate emissions with 

the MOBILE6 model), and the wind direction and speed (needed for the CAL3QHC dispersion 

estimates) were taken from the original modeling documented in the 2000 SIP. The AIR version 

of MOBILE6 was used to provide emission factor inputs for idle and 30 MPH for each hour and 

each year. Traffic volumes for all links associated with the three intersections were scaled 

according to the differences between the current TransCAD volumes and those used in the 2005 

CO SIP Update. For 2010 and 2020, scaling factors were developed according to the differences 

between the current and 2005 SIP TransCAD volumes averaged over the four UAM grid cells 

that contain the Five Points intersections. Since there were no 2008 volumes from the 2005 SIP 

TransCAD, scaling factors were derived to scale from 2006 to 2008 according to the difference 

between the current 2008 and original 2006 TransCAD volumes. The scaling factors are listed 

below for each year: 

 Year CAL3QHC Volume Scaling

 2008 1.28 

 2010 1.19 

 2020 1.26 

The CAL3QHC model output was added to the background UAM levels to estimate 8-hour CO 

concentrations for the duration of the episode. Table 3-2 presents the individual peak 8-hour 

average CO concentrations predicted by UAM, CAL3QHC, and their combination, in each of the 

future years and for each of the three intersections in the “Five Points” area. Note that the peak 

8-hour periods among the UAM, CAL3QHC, and UAM+CAL3QHC results occur at different 

times. All values are well below the 9 ppm standard. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-10 

Table 3-2. Peak 8-hour average CO concentrations (ppm) predicted by UAM, CAL3QHC, and 

UAM+CAL3QHC for each future year and for each of the Five Points intersections. Note that 

peaks reported for each of the models and their combined effect occur over different 8-hour 

periods. 

Eastern/Charleston Eastern/Fremont Fremont/Charleston Year UAM CAL3QHC CAL3QCH+UAM CAL3QHC CAL3QHC+UAM CAL3QHC CAL3QHC+UAM 

2008 6.6 2.1 8.1 1.8 7.7 1.0 7.0 

2010 6.4 1.9 7.7 1.7 7.4 1.0 6.7 

2020 5.8 1.5 6.9 1.4 6.7 0.8 6.0 

3.3.2 EDMS Airport Modeling 

The UAM was run for all future years with exactly the same inputs as described in Section 3.2; 

however, airport emissions for the three civil airports in the domain were removed from the 

UAM inventory to minimize double counting to the extent possible. It is important to note that 

traffic volumes on the major roadways within the McCarran airport property are included in both 

EDMS and TransCAD. As a result, the EDMS+UAM CO concentration results for McCarran 

reflect a double-counting of portions of the on-road mobile source emissions on that property, 

and so the CO concentrations reported for McCarran are conservative (i.e., high) estimates. 

As part of the 2005 CO SIP Revision, Clark County provided EDMS simulation results for 2005, 

2010, 2015 and 2020, based on the work of Ricondo (2003, 2005). The EDMS results reported 

for 2006 and 2010 were interpolated to derive 2008 EDMS receptor concentrations. EDMS 

concentrations were combined with the UAM model predictions for 2008, 2010, and 2020 to 

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

properties. Note that the receptor grid for North Las Vegas airport was reduced to the immediate 

area surrounding the airport, and thus results shown in Table 3-3 are lower than reported in the 

2005 CO SIP Revision. 

In each of these years, several receptors at McCarran airport reported total 8-hour CO 

concentrations (sum of EDMS and UAM components) above the 8-hour CO standard of 9 ppm. 

Note, however, that all receptors above the 9 ppm standard in all future years evaluated occurred 

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

receptors in publicly restricted areas removes all exceedance estimates. Table 3-3 presents the 

peak total 8-hour CO concentration at all three 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 3-3. Peak total UAM + EDMS 8-hour CO concentrations (ppm) at all three airports and 

for all future years evaluated. Values shown for McCarran airport occur at the peak publicly 

accessible receptor. 

Airport 2008 2010 2020 

McCarran 7.8 7.7 8.9 

Henderson Executive 1.3 1.4 3.0 

North Las Vegas 3.5 3.4 2.9 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-11 

3.4 ESTIMATING ON-ROAD EMISSION BUDGETS 

The UAM was used to refine the estimation of future year on-road mobile CO emission budgets 

for the central, most urbanized portion of the modeling domain. The definition of the central 

urban sub-domain is given in Table 3-4 and shown in Figure 3-7. On-road mobile source 

emissions calculated from the AIR version of MOBILE6 were scaled up over the entire domain 

to the point at which the peak 8-hour CO concentration reached 8.9 ppm in each of the future 

years. Additionally, the on-road mobile source emissions outside the central urban sub-domain 

Table 3-4. Grid definition of the central urban sub-domain. 

 Column Row UTM East UTM North 

Low-left 11 19 652.000 3991.000 

Upper-Right 36 45 678.000 4018.000 

642 652 662 672 682 692

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3973

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UTM Northing (km)

Figure 3-7. Location of the central urban sub-domain used in the UAM sensitivity tests (heavy 

red line).
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-12 

were increased by an additional 60% in each year to reach a maximum peak 8-hour CO 

concentration of just under 9.0 ppm in either the peak UAM grid cell, the peak UAM+ 

CAL3QHC receptor, or the peak UAM+EDMS receptor. UAM results from this analysis are 

presented in Table 3-5. Plots of UAM daily maximum CO concentrations for each future year 

are shown in Figures 3-8 through 3-10. 

 

Table 3-5. Weekday domain-wide on-road emission increase, net on-road emission increase 

that includes an additional 60% increase outside the central urban sub-domain, resulting UAM 

predicted peak CO, and resulting total and sub-domain on-road emission budgets (December 9) 

for each future year. 

Year 

Domain-Wide 

On-Road 

Emissions 

Increase 

Net On-Road 

Emissions 

Increase 

Peak 8-hr 

CO (ppm) 

Total Domain 

On-Road 

Emissions 

(TPD) 

Sub-Domain 

On-Road 

Emissions 

(TPD) 

2008 0.5% 13% 8.87 658 457 

2010 4.0% 18% 8.88 686 464 

2020 5.0% 23% 8.12 704 435 

Future year CAL3QHC intersection results were similarly scaled up by the domain-wide on-road 

emission increases shown in the second column of Table 3-5. Table 3-6 presents the individual 

peak 8-hour average CO concentrations predicted by UAM, CAL3QHC, and their combination, 

in each of the future years and for each of the three intersections in the “Five Points” area. Note 

that the peak 8-hour periods among the UAM, CAL3QHC, and UAM+CAL3QHC results occur 

at different times. All values remain well below the 9 ppm standard. 

Table 3-7 presents the peak total UAM + EDMS 8-hour CO concentration from each UAM run 

listed in Table 3-5 (without airports included). Note that EDMS results were not scaled up as onroad motor vehicle emissions consist of a fraction of the total EDMS inventory, and much of the 

on-road emissions on airport property are already double counted as described earlier. 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 3-6. Peak 8-hour average CO concentrations (ppm) predicted by UAM, CAL3QHC, and 

UAM+CAL3QHC for each future year, and for each of the Five Points intersections. UAM and 

CAL3QHC results are taken from the on-road sensitivity scaling tests. Note that peaks reported 

for each of the models and their combined effect occur over different 8-hour periods. 

Eastern/Charleston Eastern/Fremont Fremont/Charleston Year UAM CAL3QHC CAL3QCH+UAM CAL3QHC CAL3QHC+UAM CAL3QHC CAL3QHC+UAM 

2008 6.7 2.1 8.2 1.8 7.8 1.0 7.0 

2010 6.7 2.0 8.0 1.8 7.7 1.0 7.0 

2020 6.1 1.6 7.2 1.4 7.0 0.8 6.3 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-13 

Table 3-7. Peak total UAM + EDMS 8-hour CO concentrations (ppm) at all three airports and 

for all future years evaluated. Values shown for McCarran airport occur at the peak publicly 

accessible receptor. UAM results are taken from the on-road sensitivity scaling tests. 

Airport 2008 2010 2020 

McCarran 7.88 7.77 8.98 

Henderson Executive 1.38 1.50 3.38 

North Las Vegas 3.53 3.51 3.10 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-14 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

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4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2008 Future Year (EPA M6)

Peak = 8.87 ppm

5

6

7

8

9

10

11

12

Figure 3-8. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2008 with increased on-road 

mobile source emissions to reach peak CO just under 9.0 ppm (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-15 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2010 Future Year (EPA M6)

Peak = 8.88 ppm

5

6

7

8

9

10

11

12

Figure 3-9. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) for 

the December 8-9, 1996 episode using emission forecasts for 2010 with increased on-road 

mobile source emissions to reach peak CO just under 9.0 ppm (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_3_Modeling.doc 3-16 

642 652 662 672 682 692

UTM Easting (km)

3973

3983

3993

4003

4013

4023

UTM Northing (km)

ppm

UAM Max 8-hour CO Concentrations

 2020 Future Year (EPA M6)

Peak = 8.12 ppm

5

6

7

8

9

10

11

12

Figure 3-10. Spatial distribution of UAM predicted 8-hour maximum CO concentrations (ppm) 

for the December 8-9, 1996 episode using emission forecasts for 2020 with increased on-road 

mobile source emissions to reach peak CO just under 9.0 ppm (AIR version of MOBILE6). 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_4_Section110.doc 4-1 

4. SECTION 110(l) REQUIREMENTS 

Before the EPA can redesignate the Las Vegas Valley nonattainment area to attainment – based 

on the proposed changes contained in this plan – the provisions of CAAA Section 110(a)(2) and 

Section 110(l) must be satisfied. Section 110(a)(2) addresses the general requirements for SIPs. 

Section 110(l) requires that any SIP revision not interfere with requirements for attainment or 

reasonable further progress regarding other criteria pollutants, or with any other CAAA 

requirements. The requirements of Section 110(l) are addressed here. 

The maintenance plan proposes to relax one federally enforceable control measure – the reduced 

RVP gasoline program – and removes three other control measures: the CBG wintertime 

program, TCM/TDM, and the Alternative Fuels Program. However, the TCM/TDM and the 

Alternative Fuels Program will be retained in the plan as contingency measures. The following 

analysis demonstrates that the control measure changes proposed in this CO maintenance plan 

will not interfere with Clark County’s progress towards attaining the 8-hour ozone NAAQS, or 

with continued attainment of the PM10 NAAQS. Nevada is currently designated as attainment/ 

unclassifiable for PM2.5 under Section 107(d) of the CAAA; therefore, no analysis is required 

on PM2.5 NAAQS impacts. 

4.1 OZONE 

4.1.1 Reduced RVP Gasoline and CBG Wintertime Programs 

Relaxation of the RVP for wintertime fuels and elimination of the CBG wintertime program are 

not expected to interfere with attainment of the 8-hour ozone standard because both are 

wintertime programs. Elevated levels of ozone normally occur during the summertime because 

heat and sunlight are needed to produce the chemical reactions between nitrogen oxides (NOx) 

and volatile organic compounds (VOC) that form ground-level ozone. 

4.1.2 TCM/TDM 

CAAA Section 187(b)(2) requires areas classified as serious nonattainment to adopt TCMs as 

provided in Section 182(d)(1). The RTC adopted Resolutions No. 177 and No. 186 (2000 CO 

SIP, Appendix D), which indicated support and established the guidelines for administering a 

voluntary employer-based commuter incentive program (VMEP), also known as CAT MATCH. 

In 1997, EPA released a policy document that set forth guidance and interpretation on the 

enforceability of VMEPs (Memo from R. Wilson dtd. 10/24/97). It said that state and local 

agencies “are not responsible, necessarily, for implementing a program dependent on voluntary 

actions” (2000 CO SIP, Appendix A). Furthermore, policy directs that the total amount of 

emission reductions from voluntary measures shall not exceed 3 percent of the statutory 

requirements of the CAAA with respect to any SIP submittal. 

DAQEM is evaluating the benefits of VMEPs in conjunction with the development of an ozone 

SIP; discontinuation of CO SIP credits from the TCM/TDM is not expected to interfere. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_4_Section110.doc 4-2 

4.1.3. Alternative Fuels Program for Government Fleets 

The state of Nevada developed the Alternative Fuels Program as a result of the Energy Policy 

Act of 1992, which required federal, state, and fuel provider fleets to acquire alternative fuel 

vehicles. The law establishing this program is set forth in NRS Chapter 486a, which authorizes 

the State Environmental Commission to promulgate implementing regulations. Those 

regulations are set forth in NAC Chapter 486a. 

DAQEM is evaluating the benefits of the Alternative Fuel Program in conjunction with the 

development of an ozone SIP; discontinuation of CO SIP credits from the program is not 

expected to interfere. 

4.2 PARTICULATE MATTER 

Relaxation of the RVP requirement for wintertime fuels, elimination of the CBG wintertime 

program, and discontinuation of CO SIP credits from the TCM/TDM and the Alternative Fuels 

Program are not expected to interfere with continued attainment of the 24-hour PM10 standard 

because DAQEM has demonstrated that motor vehicle exhaust is an insignificant source of 

PM10 in the Las Vegas Valley (PM10 State Implementation Plan for Clark County, 2001; 

Milestone Achievement Report for Clark County, 2007). 

DAQEM’s determination of source significance was based primarily on the J.D. Smith annual 

inventory and the 24-hour micro-inventories at five representative sites, supplemented by 

reviews of the 1998 valley-wide annual emission inventory and Chemical Mass Balance 

modeling. The emission inventories/projections in the Milestone Achievement Report for Clark 

County (2007) show that motor vehicle exhaust makes an insignificant contribution to PM10 

concentrations. 

Table 4-1 shows total PM10 mobile source emissions for the Las Vegas Valley in 2006. The 

contribution of vehicle exhaust to total PM10 mobile source emissions is less than 1 percent. 

Table 4-1. Total PM10 Mobile Source Emissions for 2006.

On-Road Mobile Source Category Tons per Day (tpd) 

Paved road dust (includes construction and unpaved shoulder track-out) 83.53 

Private unpaved roads 9.34 

Highway construction projects activities 1.34 

Highway construction projects - wind erosion 3.13 

Vehicular sulfate PM 0.02 

Vehicle tire wear 0.37 

Vehicle brake wear 0.55 

Vehicle exhaust 0.53 

Total PM10 mobile source emissions 98.81 

Source: PM10 Milestone Achievement Report for Clark County, June 2007. 
May 2008 

G:\Las Vegas CO MP\TSD\Sec_4_Section110.doc 4-3 

Table 4-2 shows that mobile source emission programs, such as reduced RVP, CBG, 

TCM/TDM, and alternative fuel fleets, have a negligible effect in reducing 24-hour PM10 

concentrations in the Las Vegas Valley. 

Table 4-2. 2006 24-Hour Controlled PM10 Emissions. 

On-Road Mobile Source Category Uncontrolled PM10

(tpd) 

Controlled PM10 

(tpd) 

Percent 

Reduction 

Paved road dust (includes construction track-out) 83.53 59.31 29.00 

Unpaved road dust 9.34 3.27 65.00 

Highway construction projects activities 1.34 0.43 68.00 

Highway construction projects–wind erosion 3.13 0.91 71.00 

Vehicle sulfate PM 0.02 0.02 0.00 

Vehicle tire wear 0.37 0.37 0.00 

Vehicle brake wear 0.55 0.55 0.00 

Vehicle exhaust 0.53 0.53 0.00 

Total 98.81 65.38 33.83% 

Source: PM10 Milestone Achievement Report for Clark County, June 2007. 
May 2008 

G:\Las Vegas CO MP\TSD\References.doc R-1 

REFERENCES 

Clark County. 2000. “Carbon Monoxide State Implementation Plan: Las Vegas Valley 

Nonattainment Area, Clark County, Nevada.” Prepared by the Clark County Department 

of Air Quality and Environmental Management (August 2000). 

Clark County. 2005. “Carbon Monoxide State Implementation Plan Revision: Las Vegas Valley 

Nonattainment Area, Clark County, Nevada.” Prepared by the Clark County Department 

of Air Quality and Environmental Management (October 2005). 

Clark County. 2005. “Effectiveness of The Clark County Vehicle Inspection And Maintenance 

Program.” Appendix C of the 2005 Carbon Monoxide State Implementation Plan for 

Clark County. Prepared by the Clark County Department of Air Quality and 

Environmental Management (October 2005). 

 

EPA. 1992. “Guideline for Modeling Carbon Monoxide from Roadway Intersections,” EPA454/R-92-005, November 1992. 

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 (revised), U.S. 

EPA OAQPS, Research Triangle Park, NC. September 1995. 

Mactec. 2003. “Clark County-Wide Inventory of Non-road Engines Project.” Prepared for the 

Clark County Department of Air Quality and Environmental Management. 

Orth-Rodgers and Associates, Inc. 2003. “Air Quality Vehicle Distribution Study and 

Modeling.” Prepared for the Regional Transportation Commission of Southern Nevada. 

Regional Transportation Commission (RTC). “FY 2004-2025 RTP and FY 2004-2006 (TIP), 

Chapter 5”, Regional Transportation Commission of Southern Nevada. 

Ricondo. 2003. “Carbon Monoxide Emissions Inventory and Dispersion Modeling Study 

Update 2003.” Prepared for Clark County Department of Aviation, by Ricondo & 

Associates, San Francisco, CA (November, 2003). 

Ricondo. 2005. “Addendum to the 2003 Carbon Monoxide Emissions Inventory and Dispersion 

Modeling Study.” Memorandum to Dennis Mewshaw, Clark County Department of 

Aviation, from Adrian Jones, Ricondo & Associates, San Francisco, CA (May 19, 2005). 

Sierra Research. 2003. “Review of Current and Future CO Emissions from On-Road Vehicles 

in Selected Western Areas.” Prepared for Western States Petroleum Association, by 

Sierra Research, Inc., Report No. SR03-01-01 (January 28, 2003). 

UNLV. 2008. http://cber.unlv.edu/pop.html.