International Corporation

Air Sciences 

### sierra research

Final Report

WINTERTIME GASOLINE

FUEL SPECIFICATIONS STUDY

Prepared for

Randy White Robert Tekniepe Clark County Department of Air Quality and Environmental Management 500 S. Grand Central Parkway Las Vegas, NV 89106

Prepared by

Chris Emery

Susan Kemball-Cook Sneha Jagtap Gary Wilson ENVIRON International Corporation 101 Rowland Way, Suite 200

Novato, California 94945

Siona Delaney James Lyons Sierra Research, Inc.

1801 J Street Sacramento, CA 95814

January 17, 2008

101 Rowland Way, Suite 220, Novato, CA 94945 415.899.0700Final / January 17, 2008

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### i TABLE OF CONTENTS

Page

1. INTRODUCTION................................................................................................................ ....1

1.1 Background....................................................................................................................1 1.2 Project Concept........................................................................................................... ...1

2. HISTORICAL CARBON MONOXIDE TRENDS...............................................................3

2.1 The Data.........................................................................................................................3

2.2 Results.................................................................................................................. ..........3

3. WINTERTIME GASOLINE OPTIONS .............................................................................10

3.1 Background..................................................................................................................10

3.2 Fuel Scenarios............................................................................................................ ..11 3.3 Analysis Methodology.................................................................................................11

3.4 Results................................................................................................................... .......12

4. EVALUATION OF TRANSITIONAL PERIOD GASOLINE OPTIONS ......................14

5. CO EMISSIONS INVE NTORY AND UAM MODELING ................................................16

5.1 CO Emissions Processing Approach ...........................................................................16

5.2 CO Emission Results ...................................................................................................17 5.3 UAM Modeling Results...............................................................................................17

6. REGULATORY IMPACTS OF WINTER GASOLINE OPTIONS .................................22

6.1 Regulations on Clark County Gasoline .......................................................................22 6.2 Regulatory Impacts of Gasoline Options.....................................................................23

REFERENCES..................................................................................................................... ........24

APPENDICES

Appendix A: NAC 590.065 Gasoline: Adoption of specification guides by reference; exemption from strict compliance with standards; limitations on vapor pressure;

limitations on contents Appendix B: Clark County Air Quality Regulations: Section 53 - Oxygenated Gasoline ProgramFinal / January 17, 2008

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### ii TABLES

Table 2-1. Annual 1 st 

### maximum 8-hour ambient CO concentrations from Clark County, NV. ..........................................................................................5

Table 2-2. Annual 2 nd 

### maximum 8-hour ambient CO concentrations from Clark County, NV. ..........................................................................................5 Table 3-1. Wintertime gasoline fuel requirements for Clark County .....................................10 Table 3-2. Inputs for Clark County (winter 2006 gasoline)....................................................12 Table 3-3. Approximate increase in CO g/mi emissions associated with Clark County winter gasoline fuel scenarios .........................................................13

Table 4-1. Wintertime Gasoline Fuel Requirements for Clark County ..................................14 Table 5-1. Domain-wide on-road CO emission components and totals (TPD) by future year ....................................................................................18

Table 5-2. Domain-wide and central sub-domain total on-road CO emissions (TPD) by future year. Only values for Monday,

December 9 are shown...........................................................................................18 Table 5-3. Total domain-wide CO emissions (TPD) by future year used for UAM modeling of each fuel scenario ..............................................................18 Table 5-4. Peak predicted 8-hour CO (ppm) from the UAM CO SIP modeling system. The “SIP” column shows the replicated CO SIP values. The 8-hour CO NAAQS is 9 ppm...............................................20 Table 5-5. Peak 8-hour average CO concentrations (ppm) predicted by UAM, CAL3QHC, and UAM+CAL3QHC for each of the Five

Points intersections. .............................................................................................21 Table 5-6. Peak total UAM, EDMS, and total UAM+EDMS 8-hour CO concentrations (ppm) at all three airports evaluated. ...........................................21

FIGURES

Figure 2-1. Upper panel: Las Vegas Valley carbon monoxide monitoring site as of the year 2000. ...........................................................................................6 Figure 2-2. Time series of 1 st 

### and 2 nd 

### maximum 8-hour ambient CO concentrations for Clark County, NV ......................................................................7 Figure 2-3. Monthly 1 st 

### maximum 8-hour CO concentration in Clark County, Nevada..............................................................................................8 Figure 2-4. Monthly 2 nd 

### Maximum 8-Hour CO Concentration in Clark County, Nevada..............................................................................................8 Figure 2-5. First maximum 8-hour ambient CO concentration at each monitor in the Las Vegas Valley over the time period 1990-2006..........................9 Figure 2-6. Number of exceedances of the 8-hour CO standard at monitors in the Las Vegas Valley during the period 1990-2006 ............................................9 Figure 3-1. On-road mobile CO effects of Clark County winter gasoline

fuel reformulation ..................................................................................................13 Figure 5-1. Total domain-wide CO emissions (TPD) by future year used for UAM modeling of each fuel scenario. Weekday values are shown ...............19Final / January 17, 2008

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### 1 1. INTRODUCTION

1.1 BACKGROUND

The U.S. Environmental Protection Agency (EPA) has established two National Ambient Air Quality Standards (NAAQS) for carbon monoxide (CO): 35 parts per million (ppm) averaged over one hour; and 9 ppm averaged over eight hours. CO cannot exceed the 8-hour NAAQS at any monitoring site more than once per year, meaning that the annual second-highest concentration above the NAAQS defines an exceedance and is used to establish the design value (DV) for the area. Because of the rounding convention used by EPA, a concentration of 9.5 ppm

is needed to violate the 8-hour standard.

The Las Vegas Valley has historically violated the 8-hour CO standard during the winter

months. The 1-hour CO standard has never been exceeded. During cold, clear, stagnant periods, pollutants emitted in the evening and morning hours are trapped within the valley in very shallow layers near the ground, and slowly move with overnight drainage flows into the lowest areas of the basin. Subsequent to the Clean Air Act Amendments of 1990, the EPA designated the valley as a “moderate” nonattainment area for 8-hour CO. Ultimately, the area was

reclassified as a “serious” area in the mid-1990’s after continued exceedances of the CO

standard.

The resulting 2000 CO State Implementation Plan (SIP) for Clark County contained local measures for attaining the standards, and in June 2005 the EPA found that the valley had attained the standards by the applicable date of December 31, 2000. The 2000 CO SIP includes three control measures that affect Clark County gasoline specifications during the CO season (October – March); oxygenated fuel using 10% ethanol by volume and at least 3.5% oxygen content by weight; 9.0 psi Reid Vapor Pressure (RVP) requirement with a 1.0 psi waiver for >9% ethanol; and Cleaner Burning Gasoline (CBG) specifications to reduce emissions of sulfur and aromatic hydrocarbons.

Later, Clark County submitted a 2005 CO SIP Re vision, 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 “out” years. No changes in actual control regulations were incorporated into the 2005

CO SIP Revision.

1.2 PROJECT CONCEPT

The Clark County Department of Air Quality and Environmental Management (DAQEM) commissioned an independent analysis of the current wintertime gasoline specifications that apply in the Las Vegas Valley, as well as an evaluation of possible changes to those specifications, and/or their period of appli cability. The DAQEM contracted with ENVIRON International Corporation and Sierra Research, Inc. to assist in this wintertime gasoline study.Final / January 17, 2008

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### 2 ENVIRON and Sierra performed the following analyses, and results are documented in this report as noted:

 Summarized the historical CO trends in the Las Vegas Valley from 1990 through 2005 (Section 2);

 Evaluated various wintertime gasoline options available to Clark County in light of EPA’s regulations limiting “boutique” fuels (Section 3);

 Evaluated various options for addressing the transitions to and from winter gasolines available to Clark County (Section 4);

 Estimated on-road mobile source CO emission totals and assessed future year CO concentration peaks using the Urban Airshed Model (UAM) for two gasoline options in a manner consistent with the 2005 SIP Revision (Section 5);

 Summarized the regulatory impacts associated with each of the identified wintertime gasoline options (Section 6).Final / January 17, 2008

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### 3 2. HISTORICAL CARBON MONOXIDE TRENDS

This section presents a summary of ENVIRON’s analysis of ambient CO trends in the Las Vegas Valley between 1990 and 2006. This analysis was based on 8-hour CO data provided by the Clark County DAQEM.

2.1 THE DATA

CO data presented below were measured by the Las Vegas Valley carbon monoxide airmonitoring network that was initially administered by the Air Quality Division of the Clark County Health District, and later by the DAQEM. For this analysis, continuous daily 8-hour CO data were extracted from the EPA Air Quality System (AQS) by DAQEM for the entire period of January 1990 through Spring 2006, and provided to ENVIRON. Daily maximum 8-hour CO concentrations were extracted from these data over each CO season, which extends from October through March. Each monitor in the network continuously measures ambient CO levels using a Dasibi Carbon Monoxide Analyzer (Model 3003) which employs the Gas Filter Correlation technique. Figure 2-1 shows the Las Vegas Valley CO monitoring system as of 2000 (upper panel) and 2005 (lower panel). These figures are taken from the Las Vegas CO State Implementation Plans (Clark County Board of Commissioners, 2000; 2005) and do not show all monitors that recorded data during the 1990-2005 period. Note in particular the location of the City Center monitor, as this is the monitor with the longest continuous ambient CO time series. A full accounting of all stations and the times during which they were active is given in Tables

2-1 and 2-2.

2.2 RESULTS

The first and second CO concentration maxima for each monitor for each year during the time period 1990-2006 are shown in tabular form in Tables 2-1 and 2-2. While CO concentrations are measured year-round, ambient data were analyzed over the October-March CO season each year, and the year label indicates the October 1 start date. For example, the year 1995 indicates the October 1995 – May 1996 period. The 1 st 

### and 2 nd 

### maxima (taken over all monitors) for each year are shown in graphical form in Figure 2-2. The 8-hour NAAQS of 9 ppm 1 

### is shown in red in Figure 2-2. Both the first and second maxima show a steadily declining trend during the 1990-2006 period. The first and second maxima have not exceeded the 8-hour CO standard since 1998. The most recent value of the first maximum (5.3 ppm) is well below the 8-hour standard, as is the most recent value of the 2 nd 

### maximum (5.0 ppm).

Figures 2-3 and 2-4 show the monthly 1 st 

### and 2 nd 

### maximum CO concentration taken over all LasVegas monitors as a function of time and month. Only the months of the CO season (OctoberMarch) are shown. The 1 st 

### (Figure 2-3) and 2 nd 

### (Figure 2-4) maxima are each represented by a surface. The surfaces are domed across the months, indicating that yearly maximum CO concentrations generally occurred during December-January. This is consistent with the cold temperatures and strong atmospheric stability frequently occurring during these months, as these

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

ppm.Final / January 17, 2008

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### 4 conditions are conducive to high CO concentrations. Note that the only exceedance of the 8- hour CO standard during the months of March or October came in March of 1996. During the last 10 years, then, there has not been a singl e exceedance of the 8-hour standard during October or March. The downward slope of the 1 st 

### and 2 nd 

### maximum surfaces as time progresses from 1990-2006 indicates the overall reduction in CO concentrations in the Las Vegas Valley. The 1 st



### and 2 nd 

### maximum CO values have declined for all months from 1990 to 2006.

Figure 2-5 shows the first maximum 8-hour ambient CO level by monitor as a function of year. By examining these time series, we can evaluate whether there are shifts in the locations of peak CO concentrations over the years. The only monitors that exceeded the 8-hour CO standard are

the East Charleston and the Sunrise Acres mon itors. Comparison of Figure 2-5 and Figure 2-2 shows that the highest 1 st 

### maximum 8-hour CO times series over all monitors (Figure 2-2) is simply the 1 st 

### maximum CO at East Charleston from 1990-1996 and the 1 st 

### maximum CO at Sunrise Acres from 1997-2005. There are no significant shifts in the location of the peak CO concentrations over the years. Monitors with relatively high maximum CO (Sunrise Acres, E. Sahara) at the beginning of the period are the monitors with highest maximum CO concentrations throughout, and the monitors with relatively low CO maxima (Pittman, Craig Road) at the start of their operation show relatively low CO maxima throughout.

There is only one monitor with a continuous time series extending from 1990-2005. The City Center monitor shows a trend of decreasing CO over the period of interest. This decreasing trend is apparent in nearly all of the other mon itors. The only monitor to show an increase in CO over the lifetime of the monitor is Craig Road, and its first maximum 8-hour value never rises above 2 ppm, which is well below the 8-hour standard.

Several of the monitors in the Las Vegas Valley showed an increase in 1 st 

### maximum CO concentrations during the 1996-1998 period (e.g. Sunr ise Acres, City Center, S. LV Blvd.), but all of these returned to a decreasing trend in the 1999-2005 period.

Figure 2-6 shows the number of exceedances of the 8-hour CO standard across all monitors in the Las Vegas Valley monitoring network during the period 1990-2006. From a high value of 13 in 1990, the number of exceedances has shown an overall declining trend, with some interannual variability likely due to weather conditions. Since 1998, there have been no exceedances of the

8-hour CO standard.

In summary, the 8-hour CO trend data show that the 1 st 

### and 2 nd 

### maxima CO concentrations in the Las Vegas Valley have decreased significantly during the 1990-2005 time period. This result is not sensitive to the choice of location within the Valley or to the month of the CO season examined. Peak CO values generally occurred during the months of December and January. No

exceedances of the 8-hour CO standard have occurred since 1998.Final / January 17, 2008

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### 5 Table 2-1. Annual 1 st maximum 8-hour ambient CO concentrations from Clark County, NV.

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

0007 S.E. Valley --- --- --- --- --- --- --- --- 2.1 1.8 1.5 1.4 1.4 1.1 --- --- ---
0016 City Center 8.6 7.4 7.4 7.4 7.6 6.9 6.8 5.7 7.7 5.7 5.1 4.4 4.0 3.7 3.7 3.7 2.9

0557 East Charleston 15.9 12.6 12.1 11.9 10.9 10.3 10.3 6.7 --- --- --- --- --- --- --- --- ---

0561 Sunrise Acres --- --- --- --- --- --- 8.3 10.0 10.3 8.6 7.3 6.5 6.6 5.5 5.8 5.3 5.3
0020 Craig Road --- --- --- --- --- 0.9 1.7 1.7 2.0 1.2 1.5 1.4 1.8 0.9 --- --- ---
0043 Paul Meyer Park --- --- --- --- --- --- --- --- 1.7 2.1 1.8 1.1 1.9 1.2 --- --- ---

0107 Pittman --- --- --- --- --- 2.7 3.0 2.7 2.5 2.5 2.3 2.5 2.3 --- --- --- ---
0298 Green Valley --- --- --- --- --- --- --- --- 2.1 2.0 1.8 1.6 1.4 1.3 --- --- ---

0538 Winterwood --- --- --- --- --- --- --- --- 6.3 5.7 4.1 4.5 3.6 3.9 3.3 3.7 2.9

0539 E. Sahara --- --- --- --- --- --- --- --- 7.9 7.0 5.8 6.3 4.9 5.1 5.2 4.6 4.2

0562 Crestwood --- --- --- --- --- --- 6.5 6.0 6.4 6.3 5.2 4.5 3.8 --- --- --- ---
0601 Boulder City --- --- --- --- --- --- --- --- 0.7 0.6 1.2 0.7 0.7 0.3 --- --- ---
1022 E. Flamingo --- --- --- --- --- 4.6 5.0 4.5 5.3 5.7 5.1 4.3 3.5 --- --- --- ---

1023 S. LV Blvd. --- --- --- --- --- --- 4.8 5.2 5.6 5.0 3.9 3.7 3.0 3.0 2.9 2.3 2.0

2002 J.D. Smith --- --- --- --- --- --- --- --- 6.8 6.1 4.7 5.6 4.7 4.9 3.8 4.1 3.7

0563 Freedom Park --- --- --- --- --- --- --- --- --- --- 5.5 5.3 5.2 5.0 4.9 4.6 ---

0021 Shadow Lane --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

1021 --- --- --- --- --- --- --- --- --- --- --- --- 4.0 3.6 4.1 4.2 3.1 1st Maximum 8-Hour Concentration (ppm) Monitor Site

6.5 6.6 5.5 5.8 10.0 8.6 Maximum 1st Max 8-Hour

Concentration 5.3 Annual 1 s t Maximum 8-Hour CO Concentrations in Clark County, Nevada (Based on October to March Data)

15.9 12.6 12.1 11.9 10.9 5.3 10.3 10.3 10.3 7.3

Table 2-2. Annual 2 nd maximum 8-hour ambient CO concentrations from Clark County, NV.

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

0007 S.E. Valley --- --- --- --- --- --- --- --- 2.0 1.7 1.5 1.3 1.3 1.0 --- --- ---

0016 City Center 7.8 7.1 6.1 7.2 7.2 6.4 6.6 5.5 7.3 5.7 4.7 4.3 3.8 3.6 3.5 3.6 2.9

0557 East Charleston 14.2 12.1 11.0 11.1 10.6 9.4 10.1 6.5 --- --- --- --- --- --- --- --- ---

0561 Sunrise Acres --- --- --- --- --- --- 8.1 9.0 10.1 8.2 7.1 6.3 6.0 5.3 5.1 5.2 5.0

0020 Craig Road --- --- --- --- --- 0.8 1.6 1.5 1.8 0.8 1.4 1.3 1.0 0.9 --- --- ---

0043 Paul Meyer Park --- --- --- --- --- --- --- --- 1.7 1.9 1.6 1.0 1.5 1.2 --- --- ---

0107 Pittman --- --- --- --- --- 2.6 2.8 2.6 2.5 2.4 2.1 2.3 2.2 --- --- --- ---

0298 Green Valley --- --- --- --- --- --- --- --- 1.8 1.9 1.7 1.5 1.3 1.3 --- --- ---

0538 Winterwood --- --- --- --- --- --- --- --- 5.1 5.4 3.7 3.9 3.5 3.8 3.1 3.2 2.5

0539 E. Sahara --- --- --- --- --- --- --- --- 6.8 6.9 5.7 5.6 4.8 4.9 4.7 4.5 3.9

0562 Crestwood --- --- --- --- --- --- 5.4 5.9 6.2 5.8 4.7 4.3 3.8 --- --- --- ---

0601 Boulder City --- --- --- --- --- --- --- --- 0.7 0.6 1.0 0.6 0.7 0.3 --- --- ---

1022 E. Flamingo --- --- --- --- --- 4.5 4.4 4.3 5.0 5.4 4.7 4.1 3.2 --- --- --- ---

1023 S. LV Blvd. --- --- --- --- --- --- 4.6 4.9 5.1 4.4 3.7 3.4 2.9 3.0 2.6 2.3 1.9

2002 J.D. Smith --- --- --- --- --- --- --- --- 6.6 5.8 4.7 5.1 4.5 4.8 3.7 3.9 3.5

0563 Freedom Park --- --- --- --- --- --- --- --- --- --- 5.2 5.5 4.8 4.5 4.8 4.1

0021 Shadow Lane

--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

1021 Katie Ave. --- --- --- --- --- --- --- --- --- --- --- --- 3.6 3.5 3.7 3.8 3.0

8.2 7.1 6.3 5.0 6.0 5.3 5.1 5.2 9.4 10.1 9.0 10.1 12.1 11.0 11.1 10.6 Maximum 2nd Max 8-Hour

Concentration Monitor Site

14.2 Annual 2 nd Maximum 8-Hour CO Concentrations in Clark County, Nevada (Based on October to March Data)

2nd Maximum 8-Hour Concentration (ppm)Final / January 17, 2008

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### 6 Figure 2-1 . Upper panel: Las Vegas Valley carbon monoxide monitoring site as of the year 2000. Figure from the Carbon Monoxide State Implementation Plan for the Las Vegas Valley (Clark County Board of Commissioners, 2000). Lower panel: Las Vegas Valley carbon monoxide monitoring site as of the year 2005. Figure from the Carbon Monoxide State Implementation Plan for the Las Vegas Valley (Clark County Board of Commissioners, 2005).Final / January 17, 2008

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### 7 1st and 2nd Maximum 8-Hour CO Levels in Clark County, Nevada
(Based on October to March Data)

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Calendar YearCO Concentration (ppm)

8-Hour CO Standard (9.5 ppm)

First Maximum

Second Maximum

Figure 2-2. Time series of 1 st and 2 nd maximum 8-hour ambient CO concentrations for Clark County, NV. Data are analyzed during the October-March CO season, and the year label indicates the October start date. For example, the year 1995 indicates the October 1995- May 1996 time period.Final / January 17, 2008

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### 8 1990

1992

1994

1996

1998

2000
2002

2004

2006OctoberNovemberDecemberJanuaryFebruaryMarch 1.5 3.5 5.5 7.5 9.5 11.5 13.5 15.5 

## Monthly 1st Maximum 8-Hour CO Concentration in Clark County, NV

13.5-15.5

11.5-13.5

9.5-11.5

7.5-9.5

5.5-7.5

3.5-5.5

1.5-3.5

Figure 2-3. Monthly 1 st maximum 8-hour CO concentration in Clark County, Nevada.

1990

1992

1994

1996
1998

2000

2002

2004

2006OctoberNovemberDecemberJanuaryFebruaryMarch 1.5 3.5 5.5 7.5 9.5 11.5 13.5 15.5 

## Monthly 2nd Maximum 8-Hour CO Concentration in Clark County, NV

13.5-15.5

11.5-13.5

9.5-11.5

7.5-9.5

5.5-7.5

3.5-5.5

1.5-3.5

Figure 2-4. Monthly 2 nd Maximum 8-Hour CO Concentration in Clark County, Nevada.Final / January 17, 2008

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### 9 First Maximum 8-Hour Ambient CO Levels by Monitor

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.019901991199219931994199519961997199819992000200120022003200420052006



### YearCO (ppm) CO 8-Hour NAAQS

S.E. Valley

City Center

East Charleston

Sunrise Acres

Craig Road

Paul Meyer Park

Pittman

Green Valley

Winterwood

E. Sahara

Crestwood

Boulder City

E. Flamingo

S. LV Blvd.

J.D. Smith

Freedom Park

Shadow Lane

Figure 2-5. First maximum 8-hour ambient CO concentration at each monitor in the Las Vegas Valley over the time period 1990-2006.



## Number of Exceedances of the 8-Hour CO Standard in the Las Vegas Valley

13

6

2 3 4

1 3

1 2

00000000 

### 0 3 6 9 12 1519901991199219931994199519961997199819992000200120022003200420052006Exceedances

Figure 2-6. Number of exceedances of the 8-hour CO standard at monitors in the Las Vegas Valley during the period 1990-2006.Final / January 17, 2008

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### 10 3. WINTERTIME GASOLINE OPTIONS

Sierra Research assessed the on-road vehicle carbon monoxide (CO) emissions impacts of possible reformulations of the Clark County wint ertime gasoline specifications. After a review of recently promulgated federal regulations regarding “boutique” fuels and consultation with DAQEM, several agreed-upon fuel scenarios were analyzed. In this analysis, the impacts of the different fuel scenarios on fleet average CO emission factors generated by MOBILE6.2 were investigated. Based on these results, DAQEM selected two fuel scenarios for a more detailed evaluation using the methodology documented in the 2005 CO SIP Revision for air quality planning purposes in Clark County.

3.1 BACKGROUND

Winter gasoline sold in Clark County is currently subject to RVP limits as well as specifications for oxygenate, sulfur, and aromatic content. The RVP specification is imposed by Nevada statute, while oxygenate, aromatic, and sulfur content specifications are imposed by sections 53 and 54 of the Clark County Air Quality Regula tions. The current wintertime gasoline fuel requirements in Clark County are summarized in Table 3-1.

Table 3-1. Wintertime gasoline fuel requirements for Clark County. Fuel Property Standard Reid Vapor Pressure (RVP) Max 9.0 psi (10.0 psi for fuel with 9+ vol % EtOH)

Sulfur Content Max 80 ppmw; Flat limit of 40 ppmw

Aromatic Content Max 30 vol %; Flat limit of 25 vol % Oxygen Content Min 3.5 wt %



### According to recently promulgated federal regulations (Federal Register, 2006), winter gasoline sold in Clark County is considered to be a “boutique” fuel due to the sulfur and aromatic limits imposed by sections 53 and 54. These regulations, which are intended to restrict the creation of new boutique fuels, preclude any changes to the Clark County winter aromatic and sulfur limits except for their elimination. Further, once eliminated these limits cannot be reinstated.

Given the restrictions on boutique fuels, Clark County has limited options with respect to changes in its wintertime gasoline specifications, which are summarized below.

1. With respect to the sulfur and aromatics limits, the only choices are retention of the existing limits or their elimination. It should be noted that the existing sulfur limit has been rendered obsolete by the more stringent federal Tier 2 gasoline limit on sulfur

content.

2. Because Clark County is still designated as a “serious” nonattainment area with respect to attainment of the eight-hour CO NAAQS, winter gasoline is still required by the Clean Air Act to contain at least 2.7% oxygen by weight, which limits the changes that can be made to the existing 3.5 wt% oxygen requirement. However, it is possible thatFinal / January 17, 2008

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### 11 redesignation of Clark County to attainment with respect to the CO NAAQS could allow the elimination of the oxygenate requirement.

3. Finally, there are no impediments to changes in the winter RVP limit for Clark County gasoline other than the necessity of demonstrating, via a SIP revision or as part of maintenance plan if redesignation occurs, that such changes will not lead to nonattainment of the CO NAAQS.

3.2 FUEL SCENARIOS

Based on the above, the following matrix of fuel scenarios was developed for analysis:

1. Elimination of the 9 psi winter RVP requirement in favor of enforcement of the ASTM limit for gasoline sold in Clark County during the winter months, which can go as high as 15 psi (ASTM, 2006);

2. Relaxation of the 3.5 wt% oxygen limit to 2.7 wt%;

3. Elimination of the vapor pressure requirement and relaxation of the oxygenate requirement (combination of scenarios 1 and 2);

4. Elimination of the aromatic and sulfur content requirements;

5. Elimination of the aromatic, sulfur, and RVP requirements (combination of scenarios 1 and 4);

6. Elimination of the aromatic and sulfur requirements and relaxation of the oxygenate requirement to 2.7 wt% (combination of scenarios 2 and 4);

7. Elimination of the RVP, aromatic, and su lfur requirements with relaxation of the oxygenate requirement (combination of scenarios 1, 2, and 4); and

8. Elimination of all wintertime gasoline requirements (i.e., using no oxygenates in the gasoline along with eliminating the aromatic, sulfur and RVP requirements).

3.3 ANALYSIS METHODOLOGY

The different fuel scenarios were analyzed for winter conditions during the years 2006, 2010, 2015, 2020, 2025, and 2030. Each winter year assumes a fleet distribution equivalent to January of the following year (e.g., winter 2006 = January 2007). This analysis focused on effects of the fuel scenarios on fleet-average CO emission factors, which have units of grams per mile.Final / January 17, 2008

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### 12 For changes in RVP and oxygenate content, CO impacts were assessed using EPA’s

MOBILE6.2 emission factor model 2 

### using Clark County specific input data derived from the latest CO SIP (Clark County Board of Commissi oners, 2005). The runs reflected area-specific winter temperatures, registration distribution, di stribution of vehicle miles traveled (VMT) by vehicle class and hour of day, distribution of vehicle starts by hour of day, and inspection and maintenance (I/M) parameters.

This was done by inputting the 2006 winter fuel properties for Clark County and estimating the CO effects of revising the aromatics content to reflect the 2006 nationwide average. Winter gasoline fuel properties for Clark County and the nationwide average aromatic level were taken from Winter 2006 Alliance of Automobile Manufacturers (AAM) Fuel Survey Data (AAM, 2006). The Clark County gasoline properties are shown in Table 3-2. The average nationwide

aromatic content was 23.1%.

Table 3-2. Inputs for Clark County (winter 2006 gasoline). Fuel Property Clark County Gasoline MTBE (wt% oxygen) 0 ETBE (wt% oxygen) 0 Ethanol (wt% oxygen) 3.47 TAME (wt% oxygen) 0 Sulfur (ppm) 31

RVP (psi) 8.8 E200 (%) 46.4 E300 (%) 78.7 Aromatics (vol%) 20.2

Olefins (vol%) 6.7 Benzene (vol%) 0.60



### 3.4 RESULTS

Figure 3-1 shows a graphical illustration of the on-road vehicle CO emission impacts for all the fuel scenarios, and Table 3-3 summarizes the percentage increase in emissions associated with all the fuel scenarios. As one would expect, eliminating all wintertime gasoline fuel requirements in Scenario 8 leads to the highest CO emissions, which are 20% to 30% higher than the baseline depending on the year.

The largest single impact on CO emissions is associated with eliminating the RVP requirement, which leads to an increase of 16% to 18%. It should be noted that the MOBILE6 algorithm for modeling RVP impacts on CO emissions is quite dated and has been shown to be of questionable validity for the later model-year vehicles that dominate this analysis (Sierra Research, 2005). Therefore, the impact of elimination of the RVP requirement on CO emissions based on MOBILE6 is likely to be considerably overstated.

2 Version 6.2.03 dated September 2003.Final / January 17, 2008

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### 13 0 2 4 6 8 10 12 14

2006 2010 2015 2020 2025 2030

Calendar YearFleet Average CO Emissions (g/mi)

Baseline Case

Fuel Scenario 1

Fuel Scenario 2

Fuel Scenario 3

Fuel Scenario 4

Fuel Scenario 5

Fuel Scenario 6

Fuel Scenario 7

Fuel Scenario 8

Figure 3-1. On-road mobile CO effects of Clark County winter gasoline fuel reformulation.

Table 3-3. Approximate increase in CO g/mi emissions associated with Clark County winter gasoline fuel scenarios.

Scenario 2006 2010 2015 2020 2025 2030 1. Eliminate RVP Requirement 18% 18% 17% 16% 16% 16% 2. Relax Oxy Requirement 2% 1% 1% 1% 1% 1% 3. Eliminate RVP + Relax Oxy Requi rement 20% 19% 18% 17% 17% 17%
4. Eliminate Aromatics + Sulfur R equirement 1% 1% 1% 1% 1% 1%
5. Eliminate Aromatics + Sulfur + RVP Requirement 19% 19% 18% 18% 18% 18% 6. Eliminate Aromatics + Sulfur Requirement and Relax Oxy Requirement 3% 3% 2% 2% 2% 2%
7. Eliminate RVP + Aromatics + Sulfur and Relax Oxy Requirement 22% 21% 19% 19% 18% 18% 8. Eliminate All Requirements a 29% 25% 22% 21% 20% 20%

a Clark County will need to be redesignated to attainment for CO during the winter to allow for the use of no oxygenates.



### As shown in Figure 3-1 and Table 3-3, eliminating the aromatics and sulfur limits would have a very small impact on CO emissions, as would relaxing the 3.5 wt% oxygen content requirement to 2.7 wt%. Based on the data presented in Table 3-3, complete elimination of the oxygenate requirement would increase CO emissions by a bout 10% in 2006, but that would drop to about 2% by 2030 due to turnover of the fleet.Final / January 17, 2008

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### 14 4. EVALUATION OF TRANSITIONAL PERIOD GASOLINE OPTIONS

The availability of gasoline in Clark County during the winter is affected by the specifications imposed on that fuel by state and local requirements. At present, winter gasoline sold in Clark County is subject to controls on RVP and oxygenate, sulfur, and aromatic content. The current specifications and control periods are summarized in Table 4-1.

Table 4-1. Wintertime Gasoline Fuel Requirements for Clark County.

Fuel Property Standard Control

Period

RVP Max 9.0 psi (10.0 psi for fuel with 9+ vol % EtOH a ) 10/1 – 3/31 Oxygen Content Min 3.5 wt % 10/1 – 3/31

Sulfur Content Max 80 ppmw; Flat limit of 40 ppmw 11/1 – 3/31

Aromatic Content Max 30 vol %; Flat limit of 25 vol % 11/1 – 3/31

a Nevada statutes impose a limit of 10% ethanol by volume for on-road gasoline.



### The winter RVP specification in Clark County is imposed by Nevada statute 3 

### between October 1 and March 31, and the statute provides no transition period. The minimum oxygen content requirement is set forth in Section 53 of the Clark County Air Quality Regulations and applies between October 1 and March 31; the aromatic and sulfur content specifications are set forth in Section 54 of the Clark County Air Quality Re gulations and apply between November 1 and March 31. Both Sections 53 and 54 have enforcement provisions that effectively require gasoline being delivered to retail stations to meet the requirements 15 days before the actual

effective date.

Based on a review of the regulations, examination of AAM fuel survey data for Los Angeles, Phoenix, and Las Vegas, discussions with fuel suppliers, and review of the Kinder Morgan pipeline system in the Pacific Region, it is the winter fuel specifications themselves, particularly the RVP and oxygenate requirements, rather than the transition periods, that present the greatest issues with respect to fuel supply in Clark County.

Beginning with the RVP requirement, Clark Count y and Phoenix are the only two areas that enforce a low wintertime RVP requirement. In addition, both Clark County and Phoenix are generally supplied with gasoline from refineries in southern California. The low RVP requirement leads to tightened gasoline supply in Clark County (and Phoenix) because it precludes the sale in Clark County of the conventional and reformulated gasoline sold throughout the rest of the U.S., including California, during the winter. The fact that most of the low RVP gasoline sold in Clark County and Phoeni x comes from southern California refineries leaves gasoline supply to those areas vulnerable to refinery upsets.

Clark County’s high oxygen content requirement and relatively long winter oxygenate period increase the amount of ethanol that has to be available for the production of compliant gasoline. To the extent that ethanol supplies are limited or become disrupted, the supply of gasoline in Clark County will also be similarly impacted.

3 Nevada Administrative Code § 590.065Final / January 17, 2008

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### 15 As described in Section 3, the Clark County winter sulfur content requirement became superfluous with the implementation of the federa l Tier 2 gasoline sulfur limits and the winter aromatic content requirements do not appear to impose any significant burden on fuel suppliers. Therefore, these requirements are not a significant issue with respect to the supply of gasoline to Clark County.

As discussed in Section 3, the emissions impacts of eight potential winter gasoline scenarios in Clark County were analyzed, and the potential impact of all eight scenarios on the availability of gasoline in Clark County were reviewed. Because each of the scenarios relaxes current constraints on the specifications of gasoline sold in Clark County, there should in general be no adverse impacts relative to current gasoline supply if any of the scenarios are selected for implementation.

As discussed above, elimination of the winter RVP requirement is the scenario that is likely to have the greatest positive impact on gasoline supply to Clark County. There are several reasons for this. First, it would allow C4 and C5 hydrocarbons to be blended into gasoline destined for Clark County, thereby increasing the volume of available gasoline. Secondly, it would greatly increase the supply pool of gasoline that could be shipped to Clark County during the winter

months.

As also discussed above, elimination, rather than relaxation, of the oxygen content requirement would also be expected to remove a potential limitation on the supply of gasoline to Clark County. Note that eliminating the requirement would not prohibit the sale of oxygenated gasoline in Clark County, it would merely not require it, which would provide suppliers with greater flexibility. It should also be noted that while Clark County cannot completely eliminate the winter oxygenate requirement without being redesignated as in attainment with the NAAQS for CO and demonstrating the ability to maintain compliance with the NAAQS without oxygenated gasoline, the number of months when oxygenated gasoline is required could be reduced. Based on the analysis of winter CO concentrations in Section 2, it appears that, at a minimum, oxygenate requirements could be eliminat ed during the months of October, February, and March. The Clean Air Act requires a minimu m of four months of oxygenate use during the CO nonattainment period, but would allow less time if “the State can demonstrate that because of meteorological conditions, a reduced period will assure that there will be no exceedances of the carbon monoxide standard outside of such reduced period.”Final / January 17, 2008

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### 16 5. CO EMISSIONS INVE NTORY AND UAM MODELING

This section presents an assessment of CO emissions and UAM modeling for two of the eight wintertime gasoline options presented to the Clar k County (DAQEM) as described in Section 3. ENVIRON ran the MOBILE6 on-road emission factor model for the current wintertime gasoline and two fuel options for the following years: 2006, 2010, 2015, 2020, and 2030. These three sets of emissions data were combined with year-specific traffic pattern data developed as part of the 2005 CO SIP revision (referred to hereafter as the “CO SIP”) to derive several sets of UAM model-ready basin-wide gridded on-road emissi on input files per future year. The on-road inventories were then combined with pre-existing model-ready stationary and non-road CO emissions files (also from the CO SIP) so that the UAM could be run to project the resulting CO

emissions into CO concentration distributions . Following the CO SIP, UAM was run for the various future year emission scenarios using meteorological inputs representative of the historical December 8-9, 1996 CO episode.

The modeling reported here was performed to show that the two wintertime fuel options selected for analysis will not result in exceedances of the EPA 8-hour CO NAAQS in any of the future years listed above, given the projected roadway network and traffic activity projections assumed

in the CO SIP.

5.1 CO EMISSIONS PROCESSING APPROACH

Sierra Research presented the DAQEM with eight wintertime gasoline options as part of its work described in Section 3. In consultation with DAQEM staff, two of these options were selected for the development of UAM CO emission inventories and air quality model projections:

#1: Elimination of the 9 psi winter RVP requirement in favor of enforcement of the 13.5 psi ASTM limits for gasoline sold in Clark County during the winter months;

and

#8: Elimination of all wintertime gasoline requirements.

ENVIRON quantified emission impacts of each opti on. The starting point for this analysis was the on-road mobile source emissions processing t ools, scripts, and programs developed by Clark County and ENVIRON during the development of th e CO SIP. The current wintertime gasoline and each of the two gasoline options were first defined in the inputs to the EPA’s MOBILE6.2 on-road emission factor model using the various fuel parameters listed in Section 3. The current wintertime gasoline was re-run through the standard EPA MOBILE6.2 model to replicate the CO SIP numbers. For both fuel scenarios #1 and #8, two versions of the MOBILE6.2 model were run; the standard version from EPA, and a modifi ed version from Sierra Research that improved the estimates of RVP effects for late model vehicles (Sierra Research, 2003). The modified model uses alternative RVP correction factors for later model vehicles (post 1990 model year vehicles) derived from available “paired” test data at the time (i.e., test data from the same

vehicle tested on two different fuels with di fferent RVP levels while holding other fuel parameters constant to the extent possible). On-road emission inventory results from both models are shown to provide a direct comparison of the effect.Final / January 17, 2008

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### 17 The MOBILE model was run in a manner exactly equivalent to the approach used in developing the SIP emissions inventory, with each run at 1- degree temperature intervals. All other inputs remained identical to the assumptions and parameters defined in the SIP processing. The output from the matrix of MOBILE runs were then combined with link-specific traffic activity, trip lengths, volumes, and speeds derived from pre-ex isting output from the Regional Transportation Commission’s TRANSCAD traffic demand model to generate gridded, hourly on-road mobile source emission rates on the CO SIP modeling grid. The DAQEM and ENVIRON staff worked together closely to develop a very deta iled and complex methodology to apply MOBILE emission factors to the various data provi ded by TRANSCAD. Hence, ENVIRON already possessed all of the necessary TRANSCAD output , and processing tools/scripts from the previous work, from which to develop the mobile source emissions in a manner that was completely consistent with the emission budgets reported in the CO SIP.

5.2 CO EMISSION RESULTS

Mobile emission totals relative to the SIP on-road emissions inventory were tabulated for each of the future years: 2006, 2010, 2015, 2020, and 2030. Table 5-1 compares the domain-wide emissions for just the on-road components for: (1) the re-generated CO SIP case (“SIP”) using EPA’s MOBILE6.2; (2) scenario #1 using EPA’s MOBILE6.2; (3) scenario #1 using Sierra’s MOBILE6.2; (4) scenario #8 using EPA’s MOBILE6.2; and (5) scenario #8 using Sierra’s MOBILE6.2. Table 5-2 compares the total on-road CO inventory for the entire domain and the total on-road CO inventory for just the central portion of the modeling domain that covers the most urbanized portion of the grid 4 

### . We refer to this smaller area of the grid as the central subdomain.

Comparison of the re-generated “SIP” on-road emission values in Table 5-1 against the actual

CO SIP values 5 

### shows that the re-generated start emissions on Monday, December 9 are approximately 5 TPD higher than the CO SIP start emissions. We tracked this back to a small error in the emissions processing conducted for the CO SIP modeling application; therefore, the values in Table 5-1 are correct. Table 5-3 shows the total (on-road + non-road + stationary) CO inventories for the entire UAM modeling domain. Figure 5-1 shows these results graphically for Monday, December 9.

5.3 UAM MODELING RESULTS

ENVIRON conducted a “roll-forward” projection of future CO concentrations that would result from the two gasoline options. The future years of 2006, 2010, 2015, 2020, and 2030 were analyzed. Specifically, we identified how each option would impact the forecasts of the

4 See Section 4.4 of the 2005 CO SIP Technical Support Do cument for a definition of this sub-domain (Clark County Board of Commissioners, 2005).

5 Table 2-15, Section 2.3.6 of the 2005 CO SIP Technical Support Document (Clark County Board of Commissioners, 2005).Final / January 17, 2008

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### 18 Table 5-1. Domain-wide on-road CO emission com ponents and totals (TPD) by future year.

SIP EPA M6 Fuel#1 EPA M6 Fuel#1 Sierra M6 Fuel#8 EPA M6 Fuel# 8 Sierra M6

Year Category 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec

2006 Intrazonal 0.56 0.89 0.65 1.05 0.58 0.94 0.74 1.18 0.66 1.06

Starts 125.22 241.6 134.38 260.57 129.38 249.94 149.7 290.31 144.35 278.93

Links 150.64 204.61 193.78 265.65 160.59 219.65 215.85 295.93 179.75 245.88

Total 276.42 447.1 328.81 527.27 290.55 470.53 366.29 587.42 324.76 525.87

2010 Intrazonal 0.83 1.35 0.97 1.58 0.86 1.4 1.06 1.72 0.93 1.52

Starts 136.04 262.55 145.31 281.71 138.75 268 154.49 299.46 147.67 285.17

Links 150.26 205.29 195.65 267.98 157.66 215.44 212.54 291.14 171.83 234.84

Total 287.13 469.19 341.93 551.27 297.27 484.84 368.09 592.32 320.43 521.53

2015 Intrazonal 0.67 1.08 0.78 1.27 0.68 1.1 0.84 1.35 0.72 1.16

Starts 138.56 267.28 147.36 285.42 139.62 269.35 152.84 295.94 144.83 279.3

Links 137.32 187.7 178.62 244.79 139.36 190.48 192.27 263.52 150.24 205.4

Total 276.55 456.06 326.76 531.48 279.66 460.93 345.95 560.81 295.79 485.86

2020 Intrazonal 0.72 1.16 0.83 1.35 0.72 1.16 0.88 1.42 0.76 1.22

Starts 139.35 268.58 147.88 286.13 139.77 269.41 150.67 291.37 142.35 274.24

Links 133.15 182 173.12 237.18 134.03 183.21 184.39 252.67 142.89 195.37

Total 273.22 451.74 321.83 524.66 274.52 453.78 335.94 545.46 286 470.83

2030 Intrazonal 0.71 1.14 0.82 1.34 0.71 1.14 0.86 1.39 0.74 1.19

Starts 152.68 294.3 161.83 313.08 152.68 294.3 163.94 317 154.6 297.84

Links 142.66 194.67 185.4 253.52 142.66 194.67 196.75 269.09 151.55 206.85

Total 296.05 490.11 348.05 567.94 296.05 490.11 361.55 587.48 306.89 505.88

Table 5-2. Domain-wide and central sub-domain total on-road CO emissions (TPD) by future year. Only values for Monday, December 9 are shown.

Year SIP

EAP M6 Fuel #1

EPA M6 Fuel #1
Sierra M6 Fuel #8

EPA M6 Fuel #8
Sierra M6

2006 Total 447.10 527. 27 470.53 587.42 525.87

Sub-domain 352.43 415.63 370.94 463.08 414.61

2010 Total 469.19 551. 27 484.84 592.32 521.53

Sub-domain 350.36 412.19 362.18 443.01 389.68

2015 Total 456.06 531. 48 460.93 560.81 485.86

Sub-domain 323.73 378.27 327.23 399.30 345.09

2020 Total 451.74 524. 66 453.78 545.46 470.83

Sub-domain 311.48 363.14 312.94 377.83 324.92

2030 Total 490.11 567. 94 490.11 587.48 505.88

Sub-domain 320.50 373.17 320.50 386.39 331.11

Table 5-3. Total domain-wide CO emissions (TPD) by future year used for UAM modeling of
each fuel scenario.

SIP EPA M6 Fuel #1

EPA M6 Fuel #1
Sierra M6 Fuel #8

EPA M6 Fuel #8
Sierra M6

Year 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec 8-Dec 9-Dec

2006 392.65 587.26 446.04 667.42 407.79 610.69 483.53 727.57 441.90 666.03

2010 415.89 622.46 470.69 704.54 426.03 638.10 496.85 745.59 449.19 674.80

2015 417.84 624.20 468.06 699.62 420.94 629.07 487.22 728.95 437.07 654.00

2020 427.79 635.99 476.42 708.91 429.10 638.03 490.51 729.71 440.59 655.07

2030 477.39 706.83 529.39 784.66 477.38 706.83 542.89 804.22 488.23 722.60Final / January 17, 2008

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### 19 Domain-Wide Total CO Emissions Monday, December 9

0 100 200 300 400 500 600 700 800 900

2006 2010 2015 2020 2030

YearTPD SIP EPA M6 Fuel #1 EPA M6 Fuel #1 Sierra M6 Fuel #8 EPA M6 Fuel #8 Sierra M6

Figure 5-1. Total domain-wide CO emissions (TPD) by future year used for UAM modeling of each fuel scenario. Weekday values are shown.



### historical exceedance-level CO episode in each future year as modeled in the CO SIP. The mobile source inventories for each gasoline option were first combined with the other stationary and non-road emission components, and the resulting total CO inventory was then run through the UAM. The modeled impact on simulated peak CO relative to the NAAQS is reported in Table 5-4. Note that the ~5 TPD error found for start emissions on December 9 has no impact on the peak CO reported for the “SIP” scenario, as these numbers are identical to the CO SIP

values.

As this task was originally intended to demonstrate, in a general manner, the relationship between projected on-road emissions and resulting peak CO concentrations over the entire domain, hotspot and airport modeling were not regenerated for the fuel scenarios analyzed here. Furthermore, the procedure of separately scaling up on-road emissions within and outside of the central sub-domain was not performed as it was in the CO SIP 6



### .

The 2006 and 2010 “sub-domain” emission totals shown in Table 5-2 for Scenario #8 using the EPA MOBILE6 model are higher than the maximum scaled-up CO sub-domain budgets shown in Table 4-8 of the 2005 CO SIP Technical Suppor t Document. One might expect that sub-

6 Increasing on-road emissions within and outside of the central sub-domain was performed in the modeling

conducted for the SIP revision to demonstrate continued main tenance of the CO standard while allowing for larger separate emission budgets within the sub-domain and in outer areas (see Table 4-8 of the 2005 CO SIP Technical Support Document).Final / January 17, 2008

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### 20 Table 5-4. Peak predicted 8-hour CO (ppm) from the UAM CO SIP modeling system. The “SIP” column shows the replicated CO SIP values. The 8-hour CO NAAQS is 9 ppm.

Year SIP

EPA M6 Fuel #1

EPA M6 Fuel #1
Sierra M6 Fuel #8

EPA M6 Fuel #8
Sierra M6

2006 7.4 7.8 7.7 8.6 8.5

2010 7.2 7.6 7.4 8.1 7.9

2015 6.5 6.8 6.6 7.2 6.9

2020 6.7 7.1 6.7 7.2 6.8

2030 8.0 8.3 8.0 8.4 8.0



### domain emissions that exceed the budgets established in Table 4-8 should result in peak CO exceeding the 9 ppm standard. Table 4-8 is based on the simple upward linear scaling of mobile source CO emissions according to the individual factors listed for each future year. However, the fuel scenarios run in the current assessment changed the spatial characterization of CO emissions. This is because removing the RVP limit leads to different effects to start and running exhaust emissions, and different start distributi ons are defined within the modeling domain (one for Las Vegas Boulevard, and one for everywhere else). Since the spatial start distributioncauses a change in the spatial increase of CO emissions, it is possible to achieve higher subdomain CO emissions than shown in Table 4-8 that result in peak CO concentrations below the 9 ppm standard. In other words, peak CO responds not only to emission increases, but also to

where the CO is increased.

The higher sub-domain emissions shown in Table 5-2 for 2006 and 2010 under fuel Scenario #8 using EPA’s MOBILE6 model also has ramifica tions for the hot-spot and airport modeling results reported in the 2005 CO SIP. 7 

### As stated above, we did not re-run the hot-spot and airport models for this analysis. Instead, we developed a simpler approach in which we scaled the 2006 and 2010 hot-spot and airport results from Tables 4-4 and 4-5 in the Technical Support Document by the relative increase in the on-road sub-domain emissions shown in Table 5-2 of this report. The resulting Scenario #8 scaling factors are 1.31 for 2006 and 1.27 for 2010, based on the weekday (December 9) emissions growth. For the hot-spot intersections, we scaled both the UAM and hot-spot model results since they are almost entirely associated with on-road CO emissions. For the airport results, we scaled only the UAM component, since the airport model results are dominated by CO emissions from aircraft and stationary CO sources that would not be impacted by a change in gasoline as in Scenario #8. Note that this scaling approach is conservative since it is based on on-road emissions growth only, while developing a scaling approach based on the total sub-domain emissions (to include stationary and area sources) would reduce the scaling factors.

Table 5-5 displays the scaled hot-spot modeling results and Table 5-6 displays the scaled airport model results to reflect Scenario #8 with the EPA MOBILE6 model. With the scaling applied, peak 8-hour CO concentrations remain well below the 9 ppm standard for both years.

7 See Tables 4-4 and 4-5 in the 2005 CO SIP Technical Support Document.Final / January 17, 2008

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### 21 Table 5-5. Peak 8-hour average CO concentrations (ppm) predicted by UAM, CAL3QHC, and UAM+CAL3QHC for each of the Five Points intersections. Note that peaks reported for each of the models and their combined effects occur over different 8-hour periods. Results are based on scaling factors developed from the sub-domai n on-road emissions differences shown in Table 5-2 for fuel Scenario #8 using EPA MOBILE6.

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

2006 6.41 2.15 8.04 1. 68 7.41 0.93 6.67

2010 5.87 1.69 7.12 1. 45 6.76 0.88 6.11

Table 5-6. Peak total UAM, EDMS, and total UAM+EDMS 8-hour CO concentrations (ppm) at all three airports evaluated. Values shown for McCarran airport occur at the peak publiclyaccessible receptor. Results are based on scaling factors developed from the sub-domain onroad emissions differences shown in Table 5-2 for fuel Scenario #8 using EPA MOBILE6. Airport 2006 2010 McCarran Total (CO SIP) 7.47 7.14 EDMS (CO SIP) 6.21 5.89 UAM (CO SIP) 1.26 1.25 UAM (Scenario #8) 1.65 1.58
Scenario #8 Total 7.86 7.48 Henderson Executive (CO SIP) 1.12 1.36 EDMS (CO SIP) 0.42 0.42 UAM (CO SIP) 0.70 0.94 UAM (Scenario #8) 0.91 1.20
Scenario #8 Total 1.34 1.61 North Las Vegas (CO SIP) 5.01 5.04 EDMS (CO SIP) 0.40 0.36 UAM (CO SIP) 4.61 4.68 UAM (Scenario #8) 6.04 5.94
Scenario #8 Total 6.44 6.30Final / January 17, 2008

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### 22 6. REGULATORY IMPACTS OF WINTER GASOLINE OPTIONS

After discussions with DAQEM on the preferred winter and transitional period gasoline options for Clark County, the regulatory impacts of select winter gasoline scenarios were evaluated. All relevant federal, state, and county regulations were reviewed, and the required modifications to address the winter gasoline scenarios and remove overlaps and conflicts between the laws, statutes, and regulations were identified. The fo llowing winter gasoline scenarios were selected

for evaluation:

• 

### Elimination of the 9 psi winter RVP requirement (Fuel Scenario 1);

• 

### Elimination of RVP and oxygenate, aromatic and sulfur content requirements (Fuel Scenario 8); and

• 

### Elimination of the RVP, aromatic and sulfur content requirements (Fuel Scenario 8) and a shortening of the winter oxygenate period to November through January.

The existing statutes and regulations and the required modifications associated with the aforementioned winter gasoline scenarios are discussed below.

6.1 REGULATIONS ON CLARK COUNTY GASOLINE

The current requirements imposed on winter gasoline in Clark County are summarized in Table 4-1. Following is a discussion of each fuel prope rty standard on the federal, state, and local

levels.

Reid Vapor Pressure (RVP) : The RVP specification in Clark County is imposed by Nevada

statute 8 

### between October 1 and March 31. The RVP limit of 9 psi (10.0 psi for summertime ethanol gasoline) is more stringent than the ASTM performance standards in Nevada during the winter, and no federal standards exist for winter conventional gasoline. Upon elimination of the RVP limit in the Nevada Administrative Code, the ASTM limits for southern Nevada would apply.

Oxygen Content : The minimum oxygen content of 3.5% by weight for Clark County winter gasoline is required under Section 53 of the Clark County Air Quality Regulations during the months of October through March. This requirement is more stringent than the federal winter oxygenate requirement for Clark County. Because the Las Vegas Valley within Clark County is designated under the Clean Air Act (CAA) as a “serious” nonattainment area for the eight-hour CO National Ambient Air Quality Standard (NAAQS) during the winter, a federal minimum oxygen content requirement of 2.7% by weight is mandated. 9 

### Within the same CAA section, a minimum four-month period of oxygenate use is required during the CO nonattainment period,

unless “the State can demonstrate that because of meteorological conditions, a reduced period

8 Nevada Administrative Code § 590.065

9 Clean Air Act Title § 211(m)(2)Final / January 17, 2008

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### 23 will assure that there will be no exceedances of the carbon monoxide standard outside of such reduced period.”

Clark County has had no violations of the CO standard NAAQS since 1998 and it appears that the County could seek redesignation to attainment . Redesignation could allow the elimination of the winter oxygenate requirement.

Aromatics and Sulfur Content : The aromatic and sulfur content specifications for Clark County winter gasoline are found in Section 54 of the Clark County Air Quality Regulations, and apply between November 1 and March 31. According to recently promulgated federal regulations (Federal Register, 2006), winter gasoline sold in Clark County is considered to be a “boutique” fuel due to the local controls on sulfur and aromatics. These federal regulations, which are intended to restrict the creation of new boutique fuels, preclude any changes to the Clark County winter aromatic and sulfur limits except for their elimination. Further, once eliminated, these limits cannot be reinstated. The Clark County sulfur specification, however, has been rendered redundant by the more stringent federal Tier 2 sulfur standard.

6.2 REGULATORY IMPACTS OF GASOLINE OPTIONS

The regulatory impacts of the winter gasoline op tions affect the one Nevada statute and two Clark County Air Quality Regulations identified above. Any additional federal, state, or local statutes or regulations that would be impacted were not identified. The required changes to existing statues and regulations necessary to implement the selected scenarios are discussed

below.

Elimination of 9 psi RVP Limit : The amendments to the Nevada Administrative Code (NAC) necessary to eliminate the existing 9 psi winter RVP limit in Clark County are shown in track changes in Appendix A. In addition, the language of the statute was updated to reflect the most recent version of the ASTM gasoline standards.

Elimination of Other Winter Gasoline Requirements : As noted above, the oxygenate, sulfur, and aromatic content requirements for winter gasolin e in Clark County are specified in Sections 53 and 54 of the Clark County Air Quality Regulations . Elimination of these requirements could be achieved by the elimination of these two sections of the Clark County Air Quality Regulations. In addition to repeal of Sections 53 and 54, it is important to note that the Nevada State Implementation Plan (SIP), which was approve d by EPA to include winter Cleaner Burning Gasoline, will need to be revised in accordance w ith Title 40 of the Code of Federal Regulations (CFR) Part 51 in order to completely eliminate the sulfur and aromatic requirements.

Shortening of the Winter Oxygenated Gasoline Period : Shortening of the winter oxygenated gasoline period to the months of November th rough January would require modifying Section 53 of the Clark County Air Quality regulations. Th e necessary modifications are shown in track changes in Appendix B.Final / January 17, 2008

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### 24 REFERENCES

Alliance of Automobile Manufacturers. 2006. “Alliance of Automobile Manufacturers North American Fuel Survey Motor Gasoline Winter 2006.”

ASTM. 2006. “Standard Specification for Automotive Spark-Ignition Fuel.” ASTM Standard D 4814-06, ASTM International (November 2006).

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