The North Carolina 

8-Hour Ozone Attainment Demonstration 

for the 

Charlotte-Gastonia-Rock Hill, NC-SC 

8-Hour Ozone Nonattainment Area 

(Cabarrus, Gaston, Lincoln, 

Mecklenburg, Rowan, Union Counties and 

Coddle Creek and Davidson Townships in Iredell County) 

Prepared by: 

North Carolina Department of Environment and Natural Resources 

Division of Air Quality 

June 15, 2007
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone i 

North Carolina Attainment Demonstration June 15, 2007 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone ii 

North Carolina Attainment Demonstration June 15, 2007 

PREFACE 

This document contains North Carolina's modeling demonstration that the Charlotte-GastoniaRock Hill, North Carolina-South Carolina 8-hour ozone nonattainment area will meet the 

National Ambient Air Quality Standard for 8-hour ozone by June 15, 2010. This area includes 

the entire counties of Cabarrus, Gaston, Lincoln, Mecklenburg, Rowan and Union Counties; 

Coddle Creek and Davidson Townships in Iredell County; and the Rock Hill Metropolitan 

Planning Organization boundary in York County, South Carolina. 
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North Carolina Attainment Demonstration June 15, 2007 

EXECUTIVE SUMMARY 

INTRODUCTION

Ozone, a strong chemical oxidant, adversely impacts human health through effects on respiratory 

function and can also damage forests and crops. Ozone is not emitted directly by the utilities, 

industrial sources or motor vehicles but instead, is formed in the lower atmosphere, the 

troposphere, by a complex series of chemical reactions involving nitrogen oxides (NOx), 

resulting from the utilities, combustion processes and motor vehicles, and reactive volatile 

organic compounds (VOCs). VOCs include many industrial solvents, such as toluene, xylene 

and hexane as well as the various hydrocarbons (HC) that are evaporated from the gasoline used 

by motor vehicles or emitted through the tailpipe following combustion. Additionally, VOCs are 

emitted by natural sources such as trees and crops. 

Ozone formation is promoted by strong sunlight, warm temperatures and light winds. High 

concentrations tend to be a problem in the eastern United States only during the hot summer 

months when these conditions frequently occur. Therefore, the U. S. Environmental Protection 

Agency (USEPA) mandates seasonal monitoring of ambient ozone concentrations in North 

Carolina from April 1 through October 31 (40 CFR 58 App. D, 2.5). 

NATIONAL AMBIENT AIR QUALITY STANDARD (NAAQS)

The USEPA promulgated a new 8-hour ozone NAAQS in July 1997, setting the standard at 0.08 

parts per million (ppm) averaged over an 8-hour period. An exceedance of the 8-hour ozone 

NAAQS occurs when a monitor measures ozone above 0.084 ppm (per the rounding 

convention). A violation of the NAAQS occurs when the average of the annual fourth highest 

daily maximum 8-hour ozone values over three consecutive years is equal to or greater than 

0.085 ppm. This three-year average is termed the design value for the monitor. The design 

value for a nonattainment area is the highest monitor’s design value in the area. 

NATURE OF PROBLEM IN NORTH CAROLINA

In April 2004, the USEPA designated areas as nonattainment for the 8-hour ozone NAAQS 

based upon air quality monitoring data measured during the 2001, 2002 and 2003 ozone seasons. 

These designations became effective on June 15, 2004. In North Carolina, there were seven 

areas designated as nonattainment (see Figure 1). 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone iv 

North Carolina Attainment Demonstration June 15, 2007 

Figure 1. 8-hour Ozone Nonattainment Boundaries for North Carolina 

This submittal covers the North Carolina portion of the Charlotte-Gastonia-Rock Hill, North 

Carolina-South Carolina (the Metrolina area) 8-hour ozone nonattainment area. This area was 

designated under subpart 2 since the area’s 1-hour ozone design value was 0.129 ppm. Areas 

with 1-hour design values at 0.121 ppm or greater were designated under subpart 2, since this 

threshold was the low end of the classification table in Section 181(a)(1) of the Clean Air Act. 

The USEPA determined during the designation process that this was the appropriate treatment of 

the classification table under the 8-hour standard. With a regional 2001-2003 8-hour ozone 

design value of 0.100 ppm, the Metrolina area was classified as moderate. This nonattainment 

area includes the entire counties of Cabarrus, Gaston, Lincoln, Mecklenburg, Rowan and Union 

Counties; Coddle Creek and Davidson Townships in Iredell County; and the Rock Hill 

Metropolitan Planning Organization boundary in York County, South Carolina. 

CONTROLS APPLIED

Several control measures already in place or being implemented over the next few years will 

reduce stationary point, highway mobile, and nonroad mobile sources emissions. The expected 

Federal and State control measures were modeled for the attainment year of 2009. 

The Federal control measures that were modeled included the Tier 2 vehicle standards; the 

heavy-duty gasoline and diesel highway vehicle standards; low sulfur gasoline and diesel fuels, 

large nonroad diesel engines standards; the nonroad spark-ignition engines and recreational 

engines standard; and the Clean Air Interstate Rule. 

The State control measures that were modeled included the Clean Air Bill, in which the vehicle 

emissions inspection and maintenance program was expanded from 9 counties to 48; the NOx 

SIP Call Rule, which will reduce summertime NOx emissions from power plants and other 

industries; and the Clean Smokestacks Act, which will reduce NOx emissions beyond the 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone v 

North Carolina Attainment Demonstration June 15, 2007 

requirements of the NOx SIP Call Rule and will require coal-fired power plants to meet an 

annual NOx emissions cap. 

ATTAINMENT TEST RESULTS

The attainment test is not based on absolute modeling results, but rather relative reductions of 

ozone and is only applied at grid cells near the monitors. However, reviewing the modeling 

results of how the predicted ozone decreases in the future years and how wide spread the 

reductions are play an important role for the State in determining if additional controls should be 

considered. 

The air quality modeling is used in a relative sense by determining what the relative reduction in 

ozone occurred between the baseline year (2002) and the attainment year (2009). Table 1 lists 

the attainment test results for the Metrolina area. The first two columns are the monitoring site 

and the county in which the site is located. The next three columns are the modeling base year 

design value (DVB), the relative response factor (RRF) and the future design value (DVF). 

According to the USEPA’s guidance, areas with future design values between 0.082 and 0.087 

ppm need to provide additional weight of evidence that the area will attain the 8-hour ozone 

NAAQS. Four of the monitors in the Metrolina area fall within the range requiring additional 

weight of evidence to demonstrate attainment. 

Table 1 Attainment Test Results 

2009 

Monitoring Site County 

DVB (ppm) 

5-year weighted 

2000-2004 RRF DVF 

(ppm) 

Arrowood Mecklenburg 0.0847 0.892 0.075 

County Line Mecklenburg 0.0973 0.874 0.085 

Crouse Lincoln 0.0907 0.868 0.078 

Enochville Rowan 0.0970 0.870 0.084 

Garinger (Plaza) Mecklenburg 0.0953 0.883 0.084 

Monroe Union 0.0870 0.884 0.076 

Rockwell Rowan 0.0973 0.862 0.083 

York York, SC 0.0830 0.861 0.071 

The North Carolina Division of Air Quality (NCDAQ) provided strong weight of evidence that 

the Metrolina nonattainment area will attain the 8-hour ozone NAAQS by 2009. These included 

looking at alternative methods to calculate the future design values, air quality metrics, current 

air quality data and the emission reductions still to occur in 2007, 2008 and 2009, and additional 

measures that were not included in the air quality modeling. 

The NCDAQ believes that the modeling attainment demonstration, in conjunction with the 

weight of evidence analyses, provides the necessary evidence that the Metrolina nonattainment 

area will attain the NAAQS by the prescribed attainment date. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone vi 

North Carolina Attainment Demonstration June 15, 2007 

TABLE OF CONTENTS 

PREFACE ii

EXECUTIVE SUMMARY iii

1.0 INTRODUCTION 1

1.1 What is tropospheric ozone?................................................................................................ 1 

1.2 What is the National Ambient Air Quality Standard? ......................................................... 1 

1.3 Nature of Problem in North Carolina .................................................................................. 2 

1.4 Conceptual Description of Ozone Formation in the Metrolina Area................................... 4 

1.5 Clean Air Act Requirements................................................................................................ 7 

2.0 ATTAINMENT DEMONSTRATION METHODS AND INPUTS 9

2.1 Analysis Method.................................................................................................................. 9 

2.2 Model Selection ................................................................................................................. 10 

2.2.1 Selection of Photochemical Grid Model..................................................................... 10 

2.2.2 Selection of Meteorological Model ............................................................................ 11 

2.2.3 Selection of Emissions Processing System................................................................. 13 

2.3 Episode Selection............................................................................................................... 14 

2.3.1 Overview of USEPA Guidance on Ozone .................................................................. 14 

2.3.2 Episode Selection........................................................................................................ 14 

2.4 Modeling Domains ............................................................................................................ 16 

2.4.1 Horizontal Modeling Domain ..................................................................................... 16 

2.4.2 Vertical Modeling Domain ......................................................................................... 17 

2.5 Emission Inventory............................................................................................................ 18 

2.5.1 Stationary Point Sources ............................................................................................. 19 

2.5.2 Stationary Area Sources.............................................................................................. 21 

2.5.3 Off-Road Mobile Sources ........................................................................................... 21 

2.5.4 Highway Mobile Sources............................................................................................ 22 

2.5.5 Biogenic Emission Sources......................................................................................... 22 

3.0 Model Performance Evaluation 24

3.1 Domain-Wide Performance ............................................................................................... 25 

3.1.1 Spatial Plots ................................................................................................................ 26 

3.1.2 Scatter Plots ................................................................................................................ 34 

3.1.3 Time Series Plots ........................................................................................................ 38 

3.1.4 Domain-Wide Summary ............................................................................................. 40 

3.2 Metrolina Nonattainment Area Model Performance Evaluation....................................... 40 

3.2.1 Time Series Plots ........................................................................................................ 40 

3.2.2 Area and Monitor Statistics ........................................................................................ 44 
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4.0 CONTROLS APPLIED 45

4.1 Federal Control Measures.................................................................................................. 45 

4.1.1 Tier 2 Vehicle Standards............................................................................................. 45 

4.1.2 Heavy-Duty Gasoline and Diesel Highway Vehicles Standards ................................ 45 

4.1.3 Large Nonroad Diesel Engines Rule........................................................................... 45 

4.1.4 Nonroad Spark-Ignition Engines and Recreational Engines Standard ....................... 46 

4.1.5 NOx SIP Call in Surrounding States........................................................................... 46 

4.1.6 Clean Air Interstate Rule............................................................................................. 46

4.2 State Control Measures...................................................................................................... 47 

4.2.1 Clean Air Bill.............................................................................................................. 47 

4.2.2 NOx SIP Call Rule...................................................................................................... 48 

4.2.3 Clean Smokestacks Act............................................................................................... 48 

4.2.4 Open Burning Bans..................................................................................................... 48

4.2.5 Clean Air Interstate Rule............................................................................................. 49

5.0 ATTAINMENT DEMONSTRATION 50

5.1 Attainment Test Introduction............................................................................................. 50 

5.2 Attainment Test Results..................................................................................................... 51 

5.3 Supporting Weight of Evidence......................................................................................... 51 

5.3.1 Alternative DVF Calculation ...................................................................................... 52 

5.3.2 Air Quality Modeling Metrics .................................................................................... 53 

5.3.3 Air Quality Modeling Results From Other Studies .................................................... 54 

5.3.4 Air Quality Trends and Additional Reductions in Emissions..................................... 55 

5.3.5 Local Measures not Modeled...................................................................................... 57 

5.4 Unmonitored Area Analysis .............................................................................................. 58 

5.4 Data Access........................................................................................................................ 58 

6.0 OTHER CLEAN AIR ACT REQUIREMENTS 59

6.1 RACT/RACM Requirements............................................................................................. 60 

6.2 Reasonable Further Progress ............................................................................................. 62

6.3 Actual Emissions Inventory............................................................................................... 65 

6.4 Emissions Inventory Statement ......................................................................................... 65 

6.5 Periodic Emissions Inventory ............................................................................................ 65

6.6 Permit Program Requirements........................................................................................... 66 

6.7 Gasoline Vapor Recovery.................................................................................................. 66 

6.8 Inspection and Maintenance Program................................................................................ 66 

6.9 Other Measures.................................................................................................................. 67 

6.10 Compliance with Section 110(a)(2)................................................................................. 67 

6.11 Equivalent Techniques..................................................................................................... 67 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone viii 

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6.12 Contingency Measures..................................................................................................... 67 

7.0 MOTOR VEHICLE EMISSION BUDGETS 69

7.1 Transportation Conformity ................................................................................................ 69 

7.2 Highway Mobile Source VOC Insignificance ................................................................... 69 

7.3 Motor Vehicle Emission Budgets...................................................................................... 70 

LIST OF TABLES 

Table 1 Attainment Test Results.................................................................................................... v 

Table 1.2-1 Subpart 2 Classifications and Attainment Dates ........................................................ 2 

Table 1.3-1 Metrolina Air Quality Data Designations were Based Upon ...................................... 4 

Table 2.4.2-1: Vertical Layer Definition For MM5 and CMAQ.................................................. 18 

Table 3.1-1. 12-km Domain Model Statistics for 8-Hour Ozone ................................................. 26 

Table 3.2.2-1. Metrolina Nonattainment Area Monitor Statistics ............................................... 44 

Table 5.3-1 Attainment Test Results ........................................................................................... 51 

Table 5.3.1-1 5-Year Average Alternative Attainment Test Results for 2009 ............................ 52 

Table 5.3.3-1 Metrolina DVFs based on EAC Modeling ............................................................ 54 

Table 5.3.3-2 Metrolina DVFs based on the USEPA’s CAIR Modeling .................................... 55 

Table 5.3.4-1 Design Values (ppm) for the North Carolina Monitors in the Metrolina Area...... 55 

Table 5.3.4-2 Utility NOx Emission Reductions since 2006 Ozone Season............................... 57 

Table 6.2-1 Metrolina Nonattainment Area 2002 Baseline VOC Emissions (tons/day)............. 64 

Table 6.2-2 Metrolina Nonattainment Area 2008 Baseline VOC Emissions (tons/day)............. 64 

Table 6.2-3 Metrolina Nonattainment Area 15% RFP Analysis .................................................. 64 

Table 7.3-1 Highway Mobile Source NOx Emissions Metrolina Nonattainment Area .............. 71 

Table.7.3-2 County Level NOx MVEB for 2009 ........................................................................ 72 
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LIST OF FIGURES 

Figure 1. 8-hour Ozone Nonattainment Boundaries for North Carolina ...................................... iv 

Figure 1.3-1 8-hour ozone nonattainment boundaries for North Carolina .................................... 2 

Figure 1.3-2 Monitor locations in the Metrolina area.................................................................... 3 

Figure 1.4-1 Location of electric generating facilities in and near the Metrolina nonattainment 

area.................................................................................................................................................. 5 

Figure 1.4-2 2002 NOx emissions for the Metrolina nonattainment area and neighboring 

counties ........................................................................................................................................... 6 

Figure 2.4.1-1: The MM5 horizontal domain is the outer most, blue grid, with the CMAQ 36-km 

domain nested in the MM5 domain. ............................................................................................. 16

Figure 2.4.1-2: A more detailed view of the 12-km grid over the VISTAS region...................... 17 

Figure 3.1.1-1 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for May 25, 2002......................................................................... 27 

Figure 3.1.1-2 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for June 3, 2002........................................................................... 28 

Figure 3.1.1-3 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for June 12, 2002......................................................................... 29 

Figure 3.1.1-4 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for July 3, 2002. .......................................................................... 30 

Figure 3.1.1-5 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for July 17, 2002. ........................................................................ 31 

Figure 3.1.1-6 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for August 2, 2002. ..................................................................... 32 

Figure 3.1.1-7 Spatial plots for modeled predicted and observed peak 1-hour (top) and 8-hour 

(bottom) ozone concentrations for August 10, 2002. ................................................................... 33 

Figure 3.1.2-1 8-hour ozone scatter plot for North Carolina 12-km grid for June 2002 ............. 34 

Figure 3.1.2-2 8-hour ozone scatter plots for North Carolina 12-km grid for July 2002 ........... 35 

Figure 3.1.2-3 8-hour ozone scatter plots for North Carolina 12-km grid for August 2002 ....... 35 

 Figure 3.1.2-4 8-hour ozone scatter plots for South Carolina 12-km grid for June 2002........... 36 

Figure 3.1.2-5 8-hour ozone scatter plots for South Carolina 12-km grid for July 2002 ............ 37 

Figure 3.1.2-6 8-hour ozone scatter plots for South Carolina 12-km grid for August 2002 ....... 37 

Figure 3.1.3-1 Time series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for June 2002................................................................................................... 38 

Figure 3.1.3-2 Time series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for July 2002. .................................................................................................. 39 

Figure 3.1.3-3 Times series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for August 2002 .............................................................................................. 39 

Figure 3.2.1-1 Time series plots of model predicted versus 8-hour ozone concentrations for 

County Line monitor for June (top), July (middle) and August (bottom). ................................... 42 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone x 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.2.1-2 Time series plots of model predicted versus 8-hour ozone concentrations for 

Enochville monitor for June (top), July (middle) and August (bottom)....................................... 43 

Figure 4.2.1-1 North Carolina’s NOx Inspection and maintenance phase-in map...................... 47 

Figure 5.3.4-1 Location and size of the Duke Energy facilities located in the vicinity of the 

Metrolina nonattainment area. ...................................................................................................... 56 
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North Carolina Attainment Demonstration June 15, 2007 

LIST OF APPENDICES 

Appendix A: Policy and Memorandums 

Appendix B: Stakeholders Correspondence Regarding Motor Vehicle Emissions Budgets

Appendix C: Air Quality Data 

Appendix D: Modeling Protocol 

Appendix E: Emissions Inventory Summary

Appendix F: Emissions Inventory Documentation

Appendix G: Quality Assurance of Emissions Inventory

Appendix H: Emissions Modeling Documentation of Deviations from Defaults 

Appendix I: Meteorological Development Documentation 

Appendix J: Model Performance Evaluation

Appendix K: Modeling Results

Appendix L: Attainment Test 

Appendix M: Adopted State Measures

Appendix N: Grid Resolution Journal Article 

Appendix O: Reasonable Further Progress Documentation 

Appendix P: Contingency Measures Documentation

Appendix Q: Supporting Documentation from VISTAS 

Appendix R: Hearing Report, Comments Received and Responses 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 1 

North Carolina Attainment Demonstration June 15, 2007 

1.0 INTRODUCTION 

1.1 What is tropospheric ozone? 

Ozone, a strong chemical oxidant, adversely impacts human health through effects on respiratory 

function and can also damage forests and crops. Ozone is not emitted directly by the utilities, 

industrial sources or motor vehicles but instead, is formed in the lower atmosphere, the 

troposphere, by a complex series of chemical reactions involving nitrogen oxides (NOx), 

resulting from the utilities, combustion processes and motor vehicles, and reactive volatile 

organic compounds (VOCs). VOCs include many industrial solvents, such as toluene, xylene 

and hexane as well as the various hydrocarbons (HC) that are evaporated from the gasoline used 

by motor vehicles or emitted through the tailpipe following combustion. Additionally, VOCs are 

emitted by natural sources such as trees and crops. 

Ozone formation is promoted by strong sunlight, warm temperatures and light winds. High 

concentrations tend to be a problem in the eastern United States only during the hot summer 

months when these conditions frequently occur. Therefore, the U. S. Environmental Protection 

Agency (USEPA) mandates seasonal monitoring of ambient ozone concentrations in North 

Carolina from April 1 through October 31 (40 CFR 58 App. D, 2.5). 

1.2 What is the National Ambient Air Quality Standard? 

In 1997 the USEPA revised the primary (health) and secondary (welfare) national ambient air 

quality standard (NAAQS) for ground-level ozone (40 CFR 50.9), setting the standard at 0.08 

parts per million (ppm) averaged over an 8-hour period. The USEPA was sued on this action 

and in May 1999 the U. S. Court of Appeals for the D. C. Circuit remanded the 8-hour ozone 

standard back to the USEPA. In 2001, the USEPA proposed a response to the remand and 

reaffirmed the standard. Finally, in 2003 the 8-hour ozone standard became effective. The 

USEPA made nonattainment designations for the 8-hour ozone standard on April 30, 2004 with 

an effective date of June 15, 2004. 

An exceedance of the 8-hour ozone NAAQS occurs when a monitor measures ozone above 

0.084 ppm (per the rounding convention). A violation of the NAAQS occurs when the average 

of the annual fourth highest daily maximum 8-hour ozone values over three consecutive years is 

greater than or equal to 0.085 ppm. This three-year average is termed the design value for the 

monitor. The design value for a nonattainment area is the highest monitor’s design value in the 

area. 

Since the 1977 amendments to the Clean Air Act (CAA), areas of the country that violated the 

ambient standard for a particular pollutant were formally designated as nonattainment for that 

pollutant. This formal designation concept was retained in the 1990 Amendments (CAAA), but 

additionally, areas designated as nonattainment for the 1-hour ozone standard were to be 

classified as to the degree of nonattainment. Five categories were created (section 181 of the 

1990 CAAA). In increasing severity, these were marginal, moderate, serious, severe and 

extreme. The attainment dates for these areas were based upon this classification. The highest 

monitor design value in a nonattainment area was used to determine its classification. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 2 

North Carolina Attainment Demonstration June 15, 2007 

With the implementation of the 8-hour ozone standard, an area could be designated under section 

172 of the 1990 CAAA (subpart 1) as “basic” and would have 5 years from designation to attain 

the standard or could be designated under section 181 (subpart 2) and classified as one of the five 

categories listed above with attainment dates based on the classification (Table 1.2-1). Areas 

with an 1-hour ozone design value greater than 0.121 ppm were classified under subpart 2 and all 

other areas were classified under subpart 1. 

Table 1.2-1 Subpart 2 Classifications and Attainment Dates 

Classification Design Value Range (ppm) Attainment Date 

Marginal 0.085 up to 0.092 June 15, 2007 

Moderate 0.092 up to 0.107 June 15, 2010 

Serious 0.107 up to 0.120 June 15, 2013 

Severe 15 0.120 up to 0.127 June 15, 2019 

Severe 17 0.127 up to 0.187 June 15, 2021 

Extreme 0.187 and above June 15, 2024 

1.3 Nature of Problem in North Carolina 

On April 15, 2004, the USEPA designated areas as nonattainment for the 8-hour ozone NAAQS 

based upon air quality monitoring data measured during the 2001, 2002 and 2003 ozone seasons. 

These designations became effective on June 15, 2004. In North Carolina, there were seven 

areas designated as nonattainment (Figure 1.3-1). 

Figure 1.3-1 8-hour ozone nonattainment boundaries for North Carolina 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 3 

North Carolina Attainment Demonstration June 15, 2007 

The Charlotte-Gastonia-Rock Hill, North Carolina-South Carolina (referred to as the Metrolina 

area) 8-hour ozone nonattainment area was designated under subpart 2 since that area’s 1-hour 

ozone design value was 0.129 ppm. With a regional 2001-2003 8-hour ozone design value of 

0.100 ppm, the Metrolina area was classified as moderate. This nonattainment area includes the 

entire counties of Cabarrus, Gaston, Lincoln, Mecklenburg, Rowan and Union Counties; Coddle 

Creek and Davidson Townships in Iredell County; and the Rock Hill Metropolitan Planning 

Organization boundary in York County, South Carolina. 

Figure 1.3-2 displays where the monitors are located in the counties affected by the Metrolina 

nonattainment designation. The air quality data that the designations were based on is listed in 

Table 1.3-1. This table includes all of the monitors within the Metrolina nonattainment area and 

the York County monitor for completeness, even though it is located outside of the 

nonattainment boundary. The historic air quality data for the monitors in the Metrolina area is 

listed in Appendix C. 

Figure 1.3-2 Monitor locations in the Metrolina area 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 4 

North Carolina Attainment Demonstration June 15, 2007 

Table 1.3-1 Metrolina Air Quality Data Designations were Based Upon 

4th Highest 8-hour Ozone Value Monitor County 2001 2002 2003 2001-2003 

Design Value

Crouse Lincoln 0.094 0.095 0.089 0.092 

County Line Mecklenburg 0.099 0.107 0.088 0.098 

Garinger (Plaza) Mecklenburg 0.099 0.103 0.086 0.096 

Arrowood Mecklenburg 0.086 0.094 0.073 0.084 

Enochville Rowan 0.103 0.108 0.087 0.099 

Rockwell Rowan 0.097 0.106 0.098 0.100 

Monroe Union 0.081 0.100 0.083 0.088 

York York, SC 0.080 0.096 0.076 0.084 

Bolded values represents violations of the 8-hour ozone NAAQS. 

1.4 Conceptual Description of Ozone Formation in the Metrolina Area 

The full conceptual description of ozone formation in North Carolina and the Metrolina 

nonattainment area is discussed in Appendix D. This section will focus on the conceptual 

description of ozone formation in the Metrolina area. 

As stated earlier, ozone forms through the reaction of NOx and VOC emissions. Due to 

generally warm and moist climate of the Carolinas, vegetation abounds in many forms. The 

emissions from natural sources, such as vegetation, are referred to as biogenic emissions and 

account for approximately 90% of the total VOC emissions in the Carolinas. This results in the 

Carolinas being a NOx limited environment, which means that reductions in NOx emissions will 

have the greatest impact on reducing ozone formation in the Carolinas, including the Metrolina 

area. 

North Carolina’s most populous metropolitan regions are located in the central portions or the 

Piedmont of the state. The three largest cities (Charlotte, Greensboro, and Raleigh) form a 

partial crescent extending from the southwest to the northeast. This combination of metropolitan 

regions is often referred to as the Piedmont Crescent. A network of interstate and intrastate 

highways interconnects these three largest cities and further extends into adjoining states in a 

general southwest to northeast pattern. The mobile-based NOx emissions follow these highway 

networks with the highest emissions occurring in or near the city centers. The industrial point 

sources with both anthropogenic NOx and VOC emissions are also generally located in close 

proximity to the cities and the major road networks. Finally, North Carolina’s largest NOx point 

sources are electric generating facilities, which are spatially scattered around state but are most 

heavily concentrated near the Piedmont Crescent. Figure 1.4-1 displays the location of the 

electric generating facilities in and near the Metrolina nonattainment area. 
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North Carolina Attainment Demonstration June 15, 2007 

Figure 1.4-1 Location of electric generating facilities in and near the Metrolina 

nonattainment area. 

By combining each of the major emission source categories (biogenic source VOC emissions 

and mobile sources (highway and non-road) and electric generating facilities NOx emissions), 

the highest concentrations of precursor pollutants for ozone formation are focused throughout the 

Piedmont Crescent, which includes the Metrolina area. Therefore, the greatest potential for 

ozone formation, with the right weather conditions, is also in this central portion of North 

Carolina. 

Figure 1.4-2 displays the breakdown of man-made NOx emissions in and near the Metrolina 

nonattainment area. This figure shows that in the Metrolina area, including the counties that 

neighbor the nonattainment area, point source and highway mobile source NOx emissions 

account for over three quarters on the NOx emissions. The majority of the point source NOx 

emissions come from the electric generating facilities. Therefore, these sources that most impact 

ozone formation in the Metrolina region are highway mobile sources and electric generating 

facilities. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 6 

North Carolina Attainment Demonstration June 15, 2007 

Figure 1.4-2 2002 NOx emissions for the Metrolina nonattainment area and neighboring 

counties 

In addition to the emissions, meteorology plays an important role in ozone formation as well. 

Almost all high ozone episodes occurring in the Southeastern United States will have some 

common meteorological characteristics, including warm temperatures, lower relative humidity, 

little or no precipitation, and relatively light winds. These conditions are nearly universally 

indicative of regional high-pressure patterns causing large-scale sinking (subsiding) air at various 

levels of the atmosphere. The differences in the position, strength, and movement of these high 

pressure areas, along with differences in various mid-to-upper level wind patterns, allow staff to 

discern five meteorological scenarios, or “regimes”, in which high ozone episodes are likely to 

occur in the Carolinas. These meteorological regimes are discussed in detail in Appendix D.

The regional transport of ozone into the Metrolina area also contributes to the high ozone values 

observed in the Metrolina area. Just outside the borders of the Carolinas is a collection of large 

metropolitan regions. These metropolitan regions have similar emissions profiles and 

frequencies of high ozone concentrations leading to exceedances of the 8-hour ozone NAAQS. 

It is reasonable to conclude that precursor pollutants, as well as formed ozone, can be transported 

from any of these larger metropolitan regions into the Carolinas with an appropriate wind flow 

orientation from one or more of these regions. In recognition of the effects of regional transport 

of ozone, the USEPA has promulgated two rules to help reduce the effects of transported 

pollutants; the NOx SIP Call Rule and the Clean Air Interstate Rule. 

In additional to regional transport, recirculated pollution around the Metrolina area affects high 

ozone events. Winds in the lower and middle atmosphere can shift around in a variety of 

directions. In the most frequent scenarios, winds transition from one direction to another in a 

clockwise fashion during the extent of the complete synoptic cycle or scenario. This clockwise 

shifting of the winds is a key characteristic of eastward-moving high pressure systems in the 

Northern Hemisphere. In a large recirculation pattern, plume(s) of precursor pollutants and 

formed ozone may leave the Metrolina area one day, travel across multiple regions, then return 

to the very air shed from where it started within a matter of days. Throughout the journey of air 

parcels in this type pattern, precursor pollutants and ozone are constantly being exchanged and 

added to the air parcels from each source sector and metropolitan region along the way, 

Point

25%

Area

4% Nonroad Mobile

17%

Highway Mobile

54%
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irrespective of any geo-political boundaries. In such smaller scale recirculation patterns, 

precursor pollutants and ozone from two neighboring metropolitan regions can exchange back 

and forth over a series of days, especially as a strong area of high-pressure moves from west to 

east across the region. 

To summarize the conceptual description of ozone formation in the Metrolina area, various 

meteorological regimes in conjunction with biogenic VOC emissions and man-made NOx 

emissions can result in high ozone values in the Metrolina area. Reductions in highway mobile 

source and electric generating facility NOx emissions in and near the Metrolina area will have 

the greatest impact on reducing ozone formation. 

1.5 Clean Air Act Requirements 

Sections 172(c), 182(a) and 182 (b) of the CAA, as amended, contain the requirements for ozone 

nonattainment areas. As a subpart 2 moderate ozone nonattainment area, the Metrolina area 

must meet the requirements for both a marginal and moderate area, as well as the general 

requirements contained in Section 172(c). These requirements are listed below and are discussed 

in more details in Section 6. 

Section 172(c) Nonattainment Plan Provisions

(1) Reasonable available control measures (RACM) 

(2) Reasonable further progress (RFP) 

(3) Actual emissions inventory and periodic emissions inventory 

(4) New source review (NSR) 

(5) Permit requirements for new and modified sources 

(6) Other measures as may be necessary to provide attainment by specified attainment date 

(7) Compliance with Section 110(a)(2) 

(8) Equivalent techniques 

(9) Contingency measures 

Section 182(a) Plan Submissions and Requirements for Marginal Areas

(1) Actual emissions inventory in accordance with 172(c)(3) 

(2) Corrections to SIP 

 (A) Reasonably available control technology (RACT) 

 (B) Motor vehicle inspection and maintenance (I/M) 

 (C) Permit programs 

(3) Periodic emissions inventory 

 (A) General – emission inventory every three years until area is redesignated to 

attainment. 

 (B) Annual emissions statement requirement for sources 25 tons per year or greater 

of VOC or NOx. 

Section 182(b) Plan Submissions and Requirements for Moderate Areas

(1) Reasonable further progress 
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(2) Reasonable available control technology 

(3) Gasoline vapor recovery 

(4) Motor vehicle I/M 

(5) Offset requirements of at least 1.15 to 1. 
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2.0 ATTAINMENT DEMONSTRATION METHODS AND INPUTS 

The attainment modeling for the Metrolina nonattainment area was performed in conjunction 

with the regional haze modeling being done by the Southeast Regional Planning Organization, 

Visibility Improvement State and Tribal Association of the Southeast (VISTAS) and the fine 

particulate matter (PM2.5) and ozone modeling being done by the Association of Southeastern 

Integrated Planning (ASIP). VISTAS and ASIP are run by the ten Southeast states (Alabama, 

Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, Virginia 

and West Virginia. Since the regional haze and PM2.5 modeling uses annual simulations and 

includes an intermediate year that is the attainment year required for the Metrolina nonattainment 

area, the North Carolina Division of Air Quality (NCDAQ) decided to use the this modeling for 

its attainment demonstration. The sections below outline the methods and inputs used by 

VISTAS/ASIP for the regional modeling. 

2.1 Analysis Method 

The modeling analysis is a complex technical evaluation that begins by selection of the modeling 

system. VISTAS decided to use the following modeling system: 

• Meteorological Model: The Pennsylvania State University/National Center for 

Atmospheric Research (PSU/NCAR) Mesoscale Meteorological Model (MM5) is a 

nonhydrostatic, prognostic meteorological model routinely used for urban- and regionalscale photochemical, fine particulate matter, and regional haze regulatory modeling 

studies. 

• Emissions Model: The Sparse Matrix Operator Kernel Emissions (SMOKE) modeling 

system is an emissions modeling system that generates hourly gridded speciated emission 

inputs of mobile, nonroad mobile, area, point, fire and biogenic emission sources for 

photochemical grid models. 

• Air Quality Model: USEPA’s Models-3/ Community Multiscale Air Quality (CMAQ) 

modeling system is an ‘One-Atmosphere’ photochemical grid model capable of 

addressing ozone, particulate matter (PM), visibility and acid deposition at regional scale 

for periods up to one year. 

Additionally, an historical year is selected to model that represent typical meteorological 

conditions in the Southeast when high ozone, PM2.5 and poor visibility are observed throughout 

the Region. Once the historical year is selected, meteorological inputs are developed using the 

meteorological model. Emission inventories are also developed for the historical year and 

processed through the emissions model. These inputs are used in the air quality model to predict 

ozone, PM2.5 and visibility, with the results compared to the historic data. The model 

performance is evaluated by comparing the modeled predicted data to the historic air quality 

data. 

Once model performance is deemed adequate, typical baseline and future year emissions are 

processed through the emissions model. For this demonstration, the baseline year was 2002, 
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which corresponds with the same year as the historic meteorology used in the modeling. The 

attainment future year NCDAQ is using for this demonstration is 2009, since mandatory 

attainment date for the Metrolina area is June 15, 2010. The attainment date is set prior to the 

completion of the 2010 ozone season, therefore the attainment of the NAAQS would have to be 

met by the end of the 2009 ozone season. These emissions are processed through the air quality 

model with the meteorological inputs. The air quality modeling results are used to determine a 

relative reduction in future ozone, which is used in the attainment demonstration. 

The complete modeling protocol used for this analysis can be found in Appendix D. 

2.2 Model Selection 

To ensure that a modeling study is defensible, care must be taken in the selection of the models 

to be used. The models selected must be scientifically appropriate for the intended application 

and be freely accessible to all stakeholders. Scientifically appropriate means that the models 

address important physical and chemical phenomena in sufficient detail, using peer-reviewed 

methods. Freely accessible means that model formulations and coding are freely available for 

review and that the models are available to stakeholders, and their consultants, for execution and 

verification at no or low cost. 

The following sections outline the criteria for selecting a modeling system that is both defensible 

and capable of meeting the study's goals. These criteria were used in selecting the modeling 

system used for this modeling attainment demonstration. 

2.2.1 Selection of Photochemical Grid Model 

Criteria

For a photochemical grid model to qualify as a candidate for use in an attainment demonstration 

of the 8-hour ozone NAAQS, a State needs to show that it meets several general criteria: 

• The model has received a scientific peer review 

• The model can be demonstrated applicable to the problem on a theoretical basis 

• Data bases needed to perform the analysis are available and adequate 

• Available past appropriate performance evaluations have shown the model is not biased 

toward underestimates or overestimates 

• A protocol on methods and procedures to be followed has been established 

• The developer of the model must be willing to make the source code available to users 

for free or for a reasonable cost, and the model cannot otherwise be proprietary. 

Overview of CMAQ

The photochemical model selected for this study was CMAQ version 4.4. For more than a 

decade, the USEPA has been developing the Models-3 CMAQ modeling system with the 
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overarching aim of producing a ‘One-Atmosphere’ air quality modeling system capable of 

addressing ozone, fine particulate matter, visibility and acid deposition within a common 

platform. The original justification for the Models-3 development emerged from the challenges 

posed by the 1990 CAAA and the USEPA’s desire to develop an advanced modeling framework 

for ‘holistic’ environmental modeling utilizing state-of-science representations of atmospheric 

processes in a high performance computing environment. The USEPA completed the initial 

stage of development with Models-3 and released the CMAQ model in mid 1999 as the initial 

operating science model under the Models-3 framework. The most recent rendition is CMAQ 

version 4.4, which was released in October 2004. 

Another reason for choosing CMAQ as the atmospheric model is the ability to do oneatmospheric modeling. Since NCDAQ will be using the same modeling exercise for the ozone 

and PM2.5 attainment demonstrations SIPs, as well as the regional haze SIP, having a model that 

can handle both ozone and particulate matter is essential. A number of features in CMAQ’s 

theoretical formulation and technical implementation make the model well suited for annual PM 

modeling. 

The configuration used for this modeling demonstration, as well as a more detailed description of 

the CMAQ model, can be found in the Modeling Protocol (Appendix D). 

2.2.2 Selection of Meteorological Model 

Criteria

Meteorological models, either through objective, diagnostic, or prognostic analysis, extend 

available information about the state of the atmosphere to the grid upon which photochemical 

grid modeling is to be carried out. The criteria for selecting a meteorological model are based on 

both the models ability to accurately replicate important meteorological phenomena in the region 

of study, and the model's ability to interface with the rest of the modeling systems -- particularly 

the photochemical grid model. With these issues in mind, the following criteria were established 

for the meteorological model to be used in this study: 

• Non-Hydrostatic Formulation 

• Reasonably current, peer reviewed formulation 

• Simulates Cloud Physics 

• Publicly available on no or low cost 

• Output available in I/O API format 

• Supports Four Dimensional Data Assimilation (FDDA) 

• Enhanced treatment of Planetary Boundary Layer heights for AQ modeling 
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Overview of MM5

The non-hydrostatic MM5 model is a three-dimensional, limited-area, primitive equation, 

prognostic model that has been used widely in regional air quality model applications. The basic 

model has been under continuous development, improvement, testing and open peer-review for 

more than 20 years and has been used worldwide by hundreds of scientists for a variety of 

mesoscale studies. 

MM5 uses a terrain-following non-dimensionalized pressure, or "sigma", vertical coordinate 

similar to that used in many operational and research models. In the non-hydrostatic MM5, the 

sigma levels are defined according to the initial hydrostatically-balanced reference state so that 

the sigma levels are also time-invariant. The gridded meteorological fields produced by MM5 

are directly compatible with the input requirements of ‘one atmosphere’ air-quality models using 

this coordinate. MM5 fields can be easily used in other regional air quality models with different 

coordinate systems by performing a vertical interpolation, followed by a mass-conservation readjustment. 

Distinct planetary boundary layer (PBL) parameterizations are available for air-quality 

applications, both of which represent sub-grid-scale turbulent fluxes of heat, moisture and 

momentum. One scheme uses a first-order eddy diffusivity formulation for stable and neutral 

environments and a modified first-order scheme for unstable regimes. The other scheme uses a 

prognostic equation for the second-order turbulent kinetic energy, while diagnosing the other key 

boundary layer terms. 

Initial and lateral boundary conditions are specified for real-data cases from mesoscale threedimensional analyses performed at 12-hour intervals on the outermost grid mesh selected by the 

user. Surface fields are analyzed at three-hour intervals. A Cressman-based technique is used to 

analyze standard surface and radiosonde observations, using the National Meteorological 

Center's spectral analysis, as a first guess. The lateral boundary data are introduced using a 

relaxation technique applied in the outermost five rows and columns of the coarsest grid domain. 

Results of detailed performance evaluations of the MM5 modeling system in regulatory air 

quality application studies have been widely reported in the literature (e.g., Emery et al., 1999; 

Tesche et al., 2000, 2003) and many have involved comparisons with other prognostic models 

such as the Regional Atmospheric Modeling System (RAMS) and the Systems Application 

International Mesoscale Model. The MM5 enjoys a far richer application history in regulatory 

modeling studies compared with RAMS or other models. Furthermore, in evaluations of these 

models in over 60 recent regional scale air quality application studies since 1995, it has generally 

been found that the MM5 model tends to produce somewhat better photochemical model inputs 

than alternative models. 

The configuration used for this modeling demonstration, as well as a more detailed description of 

the MM5 model, can be found in the Modeling Protocol (Appendix D). 
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2.2.3 Selection of Emissions Processing System 

Criteria

The principal criterion for an emissions processing system is that it accurately prepares 

emissions files in a format suitable for the photochemical grid model being used. The following 

list includes clarification of this criterion and additional desirable criteria for effective use of the 

system. 

• File System Compatibility with the I/O API 

• File Portability 

• Ability to grid emissions on a Lambert Conformal projection 

• Report Capability 

• Graphical Analysis Capability 

• MOBILE6 Mobile Source Emissions 

• Biogenic Emissions Inventory System version 2 (BEIS-3) 

• Ability to process emissions for the proposed domain in a reasonable amount of time. 

• Ability to process control strategies 

• No or low cost for acquisition and maintenance 

• Expandable to support other species and mechanisms 

Overview of SMOKE

The SMOKE Emissions Processing System Prototype was originally developed at the Microcomputing Center of North Carolina. As with most ‘emissions models’, SMOKE is principally 

an emission processing system and not a true emissions modeling system in which emissions 

estimates are simulated from ‘first principles’. This means that, with the exception of mobile 

and biogenic sources, its purpose is to provide an efficient, modern tool for converting emissions 

inventory data into the formatted emission files required by an air quality simulation model. For 

mobile sources, SMOKE actually simulates emissions rates based on input mobile-source 

activity data, emission factors and outputs from transportation travel-demand models. 

SMOKE was originally designed to allow emissions data processing methods to utilize emergent 

high-performance-computing as applied to sparse-matrix algorithms. Indeed, SMOKE is the 

fastest emissions processing tool currently available to the air quality modeling community. The 

sparse matrix approach utilized throughout SMOKE permits both rapid and flexible processing 

of emissions data. The processing is rapid because SMOKE utilizes a series of matrix 

calculations instead of less efficient algorithms used in previous systems. The processing is 

flexible because the processing steps of temporal projection, controls, chemical speciation, 

temporal allocation, and spatial allocation have been separated into independent operations 

wherever possible. The results from these steps are merged together at a final stage of 

processing. 
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SMOKE contains a number of major features that make it an attractive component of the 

modeling system. The model supports a variety of input formats from other emissions 

processing systems and models. It supports both gridded and county total land use scheme for 

biogenic emissions modeling. SMOKE can accommodate emissions files from up to 10 

countries and any pollutant can be processed by the system. 

For additional information about eh SMOKE model please refer to Modeling Protocol 

(Appendix D). 

2.3 Episode Selection 

A crucial step to SIP modeling is the selection of episodes to model. Several considerations need 

to be weighed before settling on not only which days to model, but how many days for each 

episode. This section details the guidance and process by which episodes were selected for the 

8-hour Ozone SIP modeling package. 

2.3.1 Overview of USEPA Guidance on Ozone 

The USEPA’s September 2006 draft final guidance, Guidance on the Use of Models and Other 

Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5 and Regional 

Haze, (referred to as Attainment Guidance) sets out specific criteria for the selection of episodes 

to model for attainment of the 8-hour ozone NAAQS. First, episodes should include days 

encompassing a variety of meteorological conditions, including varying wind directions, for days 

exceeding 0.084 ppm. Additionally, episodes should be selected that contain days close (within 

± 0.010 ppm) to the current design value (DVC). Episodes should also be chosen around days 

for which there are extensive air quality and meteorology measurements, including 

measurements aloft, measurements of indicator species and/or precursor measurements. Finally, 

a sufficient number of days should be selected to ensure robust attainment tests at violating 

monitoring sites. 

In addition to these primary criteria, the USEPA also suggests a set of secondary criteria that 

may be used in the selection of episodes. This set of criteria allows states to give preference to 

previously modeled episodes. This is a very valuable consideration, as the USEPA points out, 

since it can save modeling resources and effort. Additional considerations include selecting 

episodes maximizing the number of days and sites observing a violation, selecting episodes 

which include weekends, and the selection of episodes meeting primary and secondary criteria in 

other nonattainment areas, when participating in regional modeling. Using these criteria laid out 

by the USEPA, the data available was systematically examined to determine the best episodes 

for modeling.

2.3.2 Episode Selection 

With the advances in computing and storage technologies, and aided by regional modeling 

efforts, NCDAQ intends to move toward the modeling of the peak ozone season for the 8-hour 

ozone attainment demonstration SIP. By modeling the peak season, several criteria are covered, 

including the modeling of weekends and a sufficient number of days to ensure a robust modeled 
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attainment test. Modeling the peak ozone season will also accomplish the goal of encompassing 

a myriad of meteorological conditions that influence ozone concentrations. 

Efforts were made to determine an appropriate period to model. The selection process started 

with an examination of the 8-hour ozone maxima for the 1997 through 2004 seasons to 

determine which season may yield the most days to be included for study. Following the second 

primary criteria, the number of days each monitoring site observed a value within 0.010 ppm of 

the design value was tabulated using the recently suggested 5 year average (the 3 year average 

design value). 

It was found that, overall, 2002 had the most days within 0.010 ppm of the design values, and 

generally had the most exceedance days for the individual monitoring sites. When 2002 was not 

the highest year, it was generally either the second or third highest, for either design value 

convention. Since 2002 was the base year for the VISTAS modeling as well, choosing the 2002 

ozone season for the episode allowed the NCDAQ and the other States involved in ASIP to use 

the VISTAS modeling for the attainment demonstration for ozone. 

The months of May through September 2002 were typical of the meteorology one would expect 

for an active ozone season, namely warmer and drier than average. Temperatures were 1-2 oF 

warmer than average across the state and throughout the Mid-Atlantic States and the 

precipitation values were 4-6 inches below normal for most of North Carolina. The dry 

conditions were also present for much of the coastal Mid-Atlantic States. The warmer and drier 

conditions led to lower soil moisture throughout much of the East coast, which would reduce the 

evaporation of moisture into the air, thus lowering dewpoint temperatures. With less available 

moisture in the atmosphere, cloud cover was decreased, which lead to more sunlight, increased 

photochemistry, and higher levels of ozone across the state. 

Additionally, the episode classification further verifies that the 2002 ozone season is a 

representative year for use in attainment demonstration modeling. The 2002 ozone season 

encompass all five meteorological scenarios: eastern stacked highs, frontal approaches, Canadian 

highs, modified Canadian highs, progressive Canadian highs and the subcategory of tropical 

influence. Thus, the 2002 season provides an excellent case to evaluate various control strategies 

for maintaining the NAAQS for ozone. 

For these reasons, the 2002 ozone season was selected for the episode to model for the 

attainment demonstration. Further details of the episode selection process, episode classification 

procedures, as well as the episodes classifications for the 2002 ozone season can be found in the 

Modeling Protocol (Appendix D). 
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2.4 Modeling Domains 

2.4.1 Horizontal Modeling Domain 

The CMAQ model was run in one-way nested grid mode. This allowed the larger outer domains 

to feed concentration data to the inner nested domain. One-way nesting is believed to be 

appropriate for the generally stagnant conditions experienced during North Carolina ozone 

episodes. Two-way nesting was not considered due to numerical and computational uncertainty 

associated with the technique. 

The horizontal coarse grid modeling domain boundaries were determined through a national 

effort to develop a common grid projection and boundary. Since this national modeling domain 

was used in the VISTAS regional haze modeling, it was used for the attainment demonstration as 

well. A smaller 12-km grid, modeling domain was selected in an attempt to balance location of 

areas of interest, such as ozone and fine particulate matter nonattainment areas, as well as Class 1 

and wilderness areas for regional haze. Processing time was also a factor in choosing a smaller 

12-km grid, modeling domain. 

The coarse 36-km horizontal grid domain covers the continental United States. This domain was 

used as the outer grid domain for MM5 modeling with the CMAQ domain nested within the 

MM5 domain. Figure 2.4.1-1 shows the MM5 horizontal domain as the outer most, blue grid 

with the CMAQ 36-km domain nested in the MM5 domain. 

Figure 2.4.1-1: The MM5 horizontal domain is the outer most, blue grid, with the CMAQ 

36-km domain nested in the MM5 domain. 
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To achieve finer spatial resolution in the VISTAS states, a one-way nested high resolution 

(12-km grid resolution) was used. Figure 2.4.1-2 shows the 12-km grid, modeling domain for 

the VISTAS region. This is the modeling domain on which the attainment test results are based. 

The NCDAQ did a study to determine if using a finer grid resolution provided different 

modeling results. Since the USEPA’s attainment test uses the modeling results to determine the 

relative reductions in ozone between the base year and the future year, the NCDAQ determined 

that effectively the same attainment test results are obtained from 12-km grid modeling or 4-km 

grid modeling. Since 4-km grid modeling takes significantly more time and resources to run, the 

NCDAQ decided to use the VISTAS 12-km grid modeling results for this attainment 

demonstration. A copy of a journal article describing the results of the grid resolution study can 

be found in Appendix N. 

Figure 2.4.1-2: A more detailed view of the 12-km grid over the VISTAS region. 

2.4.2 Vertical Modeling Domain 

The CMAQ vertical structure is primarily defined by the vertical grid used in the MM5 

modeling. The MM5 model employed a terrain following coordinate system defined by 

pressure, using 34 layers that extend from the surface to the 100 mb. Table 2.4.2-1 lists the layer 

definitions for both MM5 and for CMAQ. A layer-averaging scheme is adopted for CMAQ to 

reduce the computational cost of the CMAQ simulations. The effects of layer averaging were 

evaluated in conjunction with the VISTAS modeling effort and was found to have a relatively 

minor effect on the model performance metrics when both the 34 layer and a 19 layer CMAQ 

models were compared to ambient monitoring data. 
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Table 2.4.2-1: Vertical Layer Definition For MM5 and CMAQ 

MM5 Simulation CMAQ 19 Layers

Layer Sigma Pressure 

(mb) 

Height 

(m) 

Depth 

(m) 

Layer Sigma Pressure 

(mb) 

Height 

(m) 

Depth 

(m) 

34 0.000 100 14662 1841 19 0.000 100 14662 6536

33 0.050 145 12822 1466 0.050 145 

32 0.100 190 11356 1228 0.100 190 

31 0.150 235 10127 1062 0.150 235 

30 0.200 280 9066 939 0.200 280 

29 0.250 325 8127 843 18 0.250 325 8127 2966

28 0.300 370 7284 767 0.300 370 

27 0.350 415 6517 704 0.350 415 

26 0.400 460 5812 652 0.400 460 

25 0.450 505 5160 607 17 0.450 505 5160 1712

24 0.500 550 4553 569 0.500 550 

23 0.550 595 3984 536 0.550 595 

22 0.600 640 3448 506 16 0.600 640 3448 986

21 0.650 685 2942 480 0.650 685 

20 0.700 730 2462 367 15 0.700 730 2462 633

19 0.740 766 2095 266 0.740 766 

18 0.770 793 1828 259 14 0.770 793 1828 428

17 0.800 820 1569 169 0.800 820 

16 0.820 838 1400 166 13 0.820 838 1400 329

15 0.840 856 1235 163 0.840 856 

14 0.860 874 1071 160 12 0.860 874 1071 160

13 0.880 892 911 158 11 0.880 892 911 158

12 0.900 910 753 78 10 0.900 910 753 155

11 0.910 919 675 77 0.910 919 

10 0.920 928 598 77 9 0.920 928 598 153

9 0.930 937 521 76 0.930 937 

8 0.940 946 445 76 8 0.940 946 445 76

7 0.950 955 369 75 7 0.950 955 369 75

6 0.960 964 294 74 6 0.960 964 294 74

5 0.970 973 220 74 5 0.970 973 220 74

4 0.980 982 146 37 4 0.980 982 146 37

3 0.985 986.5 109 37 3 0.985 986.5 109 37

2 0.990 991 73 36 2 0.990 991 73 36

1 0.995 995.5 36 36 1 0.995 995.5 36 36

0 1.000 1000 0 0 0 1.000 1000 0 0 

2.5 Emission Inventory 

There are five different emission inventory source classifications, stationary point and area 

sources, off-road and on-road mobile sources, and biogenic sources. Stationary point sources are 

those sources that emit greater than a specified tonage per year and the data is provided at the 

facility level. Stationary area sources are those sources whose emissions are relatively small but 
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due to the large number of these sources, the collective emissions could be significant (i.e., dry 

cleaners, service stations, etc.). These types of emissions are estimated on the county level. Offroad mobile sources include equipment that can move, but do not use the roadways, i.e., lawn 

mowers, construction equipment, railroad locomotives, aircraft, etc. The emissions from these 

sources, like stationary area sources, are estimated on the county level. On-road mobile sources 

are automobiles, trucks, and motorcycles that use the roadway system. The emissions from these 

sources are estimated by vehicle type and road type and are summed to the county level. 

Biogenic sources are the natural sources like trees, crops, grasses and natural decay of plants. 

The emissions from these sources are estimated on a county level. 

In addition to the various source classifications, there are also various types of emission 

inventories. The first is the actual base year inventory. This inventory is the base year emissions 

that correspond to the meteorological data, for this modeling effort is 2002. These emissions are 

used for evaluating the air quality model performance. 

The second type of inventory is the typical base year inventory. This inventory is similar to the 

actual base year, however for sources that may have significant changes from year-to-year, a 

more typical emission value is used. In this modeling effort, typical emissions were developed 

for the electric generating units (EGUs) and the wildland fire emissions. The air quality 

modeling results using these emissions are used in calculating the relative reresponse factors 

used in the attainment demonstration test. 

The future year base inventory is an inventory developed for some future year for which 

attainment of the ozone standard is needed. For this modeling project, the future year inventory 

will be 2009, the last complete year for which the standard must be attained. It is the future base 

year inventory that control strategies and sensitivities are applied to determine what controls 

beyond those measures already included in the future year base inventory, to which source 

classifications must be made in order to attain and maintain the ozone standard. 

In the sections that follow, a synopsis of the inventories used for each source classifications are 

discussed. The detail discussions of the emissions inventory development can be found in 

Appendix F and emission summaries by county for the Metrolina nonattainment area, as well as 

for the State are in Appendix E. 

2.5.1 Stationary Point Sources 

Point source emissions are emissions from individual sources having a fixed location. Generally, 

these sources must have permits to operate and their emissions are inventoried on a regular 

schedule. Large sources having emissions of 100 tons per year (tpy) of a criteria pollutant, 

10 tpy of a single hazardous air pollutant (HAP), or 25 tpy total HAP are inventoried annually. 

Smaller sources have been inventoried less frequently. The point source emissions data can be 

grouped into the EGU sources and the other point sources, i.e., non-EGUs. Appendix F.1 

documents the point source modeling inventory development in more details. Appendix E 

provides tables of the point sources in the Metrolina nonattainment area and the average daily 

peak ozone season emissions. 
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Electric Generating Units

The actual base year inventory for the EGU sources used 2002 continuous emissions monitoring 

(CEM) data reported to the USEPA’s Acid Rain program or 2002 hourly emissions data 

provided by stakeholders. This data provides hourly emissions profiles that can be used in the 

modeling of these large sources of NOx and helps to provide more accurate modeling of these 

sources. 

Since the NOx emissions from EGU sources are a significant part of the emissions inventory, a 

typical base year emissions inventory was developed for these sources to avoid anomalies in 

emissions due to variability in meteorology, economic and outage factors in 2002. This 

approach is consistent with the USEPA’s modeling guidance. To develop a typical year 2002 

emissions inventory for EGU sources, for each unit the average CEM heat input for 2000 

through 2004 was divided by the 2002 actual heat input to generate a unit specific normalizing 

factor. This normalizing factor was then multiplied by the 2002 actual emissions. The heat 

inputs for the period 2000 through 2004 were used since the modeling current design values use 

monitoring data from this same 5-year period. If a unit was shutdown for an entire year during 

the 2000 through 2004 period, the average of the years the unit was operational was used. If a 

unit was shutdown in 2002, but not permanently shutdown, the emissions and heat inputs for 

2001 (or 2000) were used in the normalizing calculations. 

As part of the VISTAS modeling, VISTAS and the Midwest Regional Planning Organization 

contracted with ICF Resources, L.L.C., to generate future year emission inventory for the electric 

generating sector of the contiguous United States using the Integrated Planning Model (IPM). 

IPM is a dynamic linear optimization model that can be used to examine air pollution control 

policies for various pollutants throughout the contiguous United States for the entire electric 

power system. The dynamic nature of IPM enables the projection of the behavior of the power 

system over a specified future period. The optimization logic determines the least-cost means of 

meeting electric generation and capacity requirements while complying with specified 

constraints including air pollution regulations, transmission bottlenecks, and plant-specific 

operational constraints. The versatility of IPM allows users to specify which constraints to 

exercise and populate IPM with their own datasets. 

The IPM modeling runs took into consideration the USEPA’s Clean Air Interstate Rule (CAIR) 

implementation and North Carolina’s Clean Smokestacks Act compliance plans for Duke Power 

and Progress Energy. 

Other Point Sources

For the non-EGU sources, the same inventory will be used for both the actual and typical base 

year emissions inventories. The non-EGU category will use annual emissions as reported for the 

Consolidated Emissions Reporting Rule (CERR) for the year 2002. These emissions were 

temporally allocated to month, day, and hour using source category code (SCC) based allocation 

factors using the SMOKE emissions model. 
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North Carolina Attainment Demonstration June 15, 2007 

The general approach for assembling future year data was to use recently updated growth and 

control data consistent with USEPA’s CAIR analyses. This data was supplemented with state 

specific growth factors and stakeholder input on growth assumptions. 

2.5.2 Stationary Area Sources 

Stationary area sources include sources whose emissions are relatively small but due to the large 

number of these sources, the collective emissions could be significant (i.e., combustion of fuels 

for heating, structure fires, service stations, etc.). Emissions are estimated by multiplying an 

emission factor by some known indicator of collective activity, such as fuel usage, number of 

household or population. Stationary area source emissions are estimated on the county level. 

A portion of the area source 2002 base year inventory for North Carolina was developed by the 

NCDAQ and provided to the VISTAS/ASIP contractor. The VISTAS/ASIP contractor 

calculated the remaining portion of the area source inventory. The sources estimated by the 

contractor include emissions from animal husbandry, wildland fires, and particulate matter from 

paved and unpaved roads. For the other states within the modeling domain, the state supplied 

data or the CERR data for 2002 was used. 

The actual base year inventory will serve as the typical base year inventory for all area source 

categories except for wildland fires. For this source category, development of a typical year fire 

inventory provided the capability of using a comparable data set for both the base year and future 

years. Thus, fire emissions would remain the same for air quality modeling in both the base and 

any future years. The VISTAS Fire Special Interest Work Group was consulted and decided to 

use State level ratios of acres over a longer term record (three or more years) developed for each 

fire type relative to 2002. The 2002 acreage was then scaled up or down based on these ratios to 

develop a typical year inventory. 

For categories other than wildland fires, the VISTAS/ASIP contractor generated the future base 

year emissions inventory used in the attainment demonstration modeling. Growth factors 

supplied from the states or the USEPA’s CAIR emission projections were applied to project the 

controlled emissions to the appropriate year. In some cases, the USEPA’s Economic Growth and 

Analysis System Version 5 growth factors were used if no growth factor was available from 

either the states or the CAIR growth factor files. 

Appendix F.2 provides a detailed discussion of the area source inventory. Appendix E provides 

emission summaries by area source category for average peak ozone season day. 

2.5.3 Off-Road Mobile Sources 

Non-road mobile sources include equipment that can move, but do not use the roadways, such as 

construction equipment, aircraft, railroad locomotives, lawn and garden equipment, etc. For the 

majority of the non-road mobile sources, the emissions were estimated using the USEPA’s 

NONROAD2005c model. For the three source categories not included in the NONROAD 

model, i.e., aircraft engines, railroad locomotives and commercial marine, more traditional 
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North Carolina Attainment Demonstration June 15, 2007 

methods of estimating the emissions were used. The same inventory will be used for both the 

actual and typical base year emissions inventories for the non-road mobile sources. 

For the source categories estimated using the USEPA’s NONROAD model, the model was used 

to create a future base year inventory. The NONROAD model takes into consideration rules that 

are in effect that could impact the emissions from these source categories. For the four largest 

airports in North Carolina, the FAA’s Terminal Area Forecast was used to project growth in 

aircraft emissions. For the commercial marine, railroad locomotives and the remaining airport 

emissions, the VISTAS/ASIP contractor calculated the future base year emissions using detailed 

inventory data (both before and after controls) for 1996 and 2010 obtained from the USEPA’s 

Clean Air Interstate Rule Technical Support Document. When available, state specific growth 

factors were used. 

Appendix F.2 provides a detailed discussion of the nonroad mobile source inventory. Average 

daily emission summaries by nonroad source category can be found in Appendix E. 

2.5.4 Highway Mobile Sources 

In order to accurately model the mobile source emissions in the Metrolina nonattainment area, 

the newest version of the MOBILE model, MOBILE6.2, was used. Key inputs for the MOBILE 

model include information on the age of vehicles on the roads, the average speed on the roads, 

the mix of vehicles on the roads, any control technologies in place in an area to reduce emissions 

for motor vehicles (e.g., emissions inspection programs), and temperature. The MOBILE model 

inputs were developed through interagency consultation with the transportation partners for this 

area. 

The MOBILE model takes into consideration rules that are in effect that impact the emissions 

from this source sector. For highway mobile sources, the actual and typical year emissions were 

the same and the MOBILE model was run using input data reflective of 2002. The same model 

then is run for the future year emissions inventory using input data reflective of 2009. The 2002 

and 2009 vehicle miles traveled (VMT), speeds, vehicle age and vehicle mix data was obtained 

from the North Carolina Department of Transportation (NCDOT). For urban areas in North 

Carolina that run travel demand models (TDMs), VMT and speed data from TDMs were used. 

The Metrolina area is one of the areas that run a TDM, and the TDM domain covers the entire 

nonattainment area. 

For a detailed discussion about the mobile source inventory development used in the attainment 

demonstration modeling, please refer to Appendix F.3. Emission summaries by county for the 

mobile source sector can be found in Appendix E. 

2.5.5 Biogenic Emission Sources 

Biogenic emissions were prepared with the SMOKE-BEIS3 (Biogenic Emission Inventory 

System 3 version 0.9) preprocessor. SMOKE-BEIS3 is basically the Urban Airshed Model 

(UAM)-BEIS3 model, but also includes modifications to use MM5 data, gridded land use data, 
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North Carolina Attainment Demonstration June 15, 2007 

and science updates. The emission factors that are used in SMOKE-BEIS3 are the same as the 

emission factors in UAM-BEIS3. 

The basis for the gridded land use data used by BEIS3 is the county land use data in the Biogenic 

Emissions Landcover Database version 3 (BELD3) provided by the USEPA. A separate land 

classification scheme, based upon satellite (AVHRR, 1 km spatial resolution) and census 

information, aided in defining the forest, agriculture and urban portions of each county. 
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North Carolina Attainment Demonstration June 15, 2007 

3.0 Model Performance Evaluation 

There are many aspects of model performance. This section will focus primarily on the methods 

and techniques recommended by the USEPA for evaluating the performance of the air quality 

model. Before the air quality model can be fully evaluated, an understanding of the 

meteorological modeling performance is needed to understand potential biases and errors that 

may be passed from the meteorological model directly into the air quality model. The 

meteorological modeling evaluation is fully documented in Appendix I and is briefly 

summarized in the next few paragraphs. 

Generally speaking, the meteorological modeling performance was quite good at both the 36-km 

and 12-km grid resolutions. Synoptic features were routinely accurately predicted and the 

meteorological model showed considerable skill in replicating the state variables 

(e.g. temperature, mixing ratio, relative humidity, wind speed and direction, cloud cover, and 

precipitation). The meteorological modeling performance statistics fell within expected and 

acceptable ranges of error during the majority of the 2002 modeled year. 

The meteorological modeling performance for North Carolina was very similar to the 

performance for the VISTAS/ASIP region for the 12-km modeling domain. Again, large-scale 

meteorological patterns were accurately predicted. The meteorological model demonstrated 

substantial skill throughout the entire year and was especially skillful during the summertime 

season from May through September. 

For the North Carolina portion of the 12km modeling domain, the temperature bias was near zero 

in May, June, and August. July had a slight negative temperature bias near –0.25 Kelvin (K), 

and September had a negative temperature bias of –0.1 K. The mixing ratio bias was near 

0 gram/kilogram (g/kg) in May through July and then fell to –0.2 g/kg in August and to -0.6 in 

September. The relative humidity bias generally hovered around ± 3% throughout the summer. 

Cloud coverage bias peaked near 10% in July and was biased less than 5% during the other 

summertime months. Wind direction was the most erratic of the measurements. The direction 

bias in North Carolina was more pronounced than for the full 12-km domain, being more 

negative May through July, and more positive in August and September. When considering all 

wind measurements, the wind speed was 0.8 to 1.0 meters per second (m/s) too strong. When 

omitting calm observations, the bias falls to 0.2 to 0.5 m/s. Additionally, the meteorological 

model noticeably overestimated the amount of summertime precipitation but not the spatial 

coverage of measurable precipitation. 

Overall, excess wind speeds, increased relative humidity, more daytime cloud cover, and 

precipitation overestimations will likely contribute to slight under predictions of the daily 

maximum peak ozone concentration in the air quality model. The NCDAQ believes that the 

meteorological model performance is adequate for this modeling exercise and should produce 

credible inputs for the air quality modeling for the attainment demonstration for the Metrolina 

area. 

With the meteorological modeling performance summarized, the first step in the air quality 

modeling process is to verify the model’s performance in terms of its ability to predict the ozone 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 25 

North Carolina Attainment Demonstration June 15, 2007 

in the right locations and at the right levels. To do this, the actual base year model predictions 

are compared to the ambient data observed in the historical season. This verification is a 

combination of statistical and graphical evaluations. If the model appears to be producing ozone 

in the right locations for the right reasons, then the model can be used as a predictive tool to 

evaluate various control strategies and their effects on ozone. The purpose of the model 

performance evaluation is to assess how accurately the model predicts ozone levels observed in 

the historical season. The key statistical measures that were used to evaluate model performance 

are as follows: 

1. Comparison of modeled mean of ozone to the observed mean of ozone. This metric is an 

evaluation of how, on average across the modeling period, the model compares to the 

observed values. 

2. Bias in the model is calculated by taking the difference between the modeled mean and 

the observed mean. 

3. Normalized bias is calculated by taking the bias for each observation/prediction pair, and 

then dividing by the number of pairs that are used in the calculations. The USEPA 

recommends that normalized bias fall between ± 5 – 15 percent. 

4. Gross error. For the entire modeling domain, gross error for all pairs above 60 parts per 

billion (ppb) of ozone was calculated. For the Metrolina nonattainment area, the gross 

error was calculated on the daily 8-hour ozone maximums. The USEPA guidance 

suggests that gross error can be interpreted as precision of the model. This metric is 

typically used to compare various modeling applications. The USEPA recommends that 

the gross error of all pairs >60 ppb be less than 30-35 percent. 

These statistics will be presented in the sections that follow for the entire 12-km modeling 

domain and for the Metrolina nonattainment area. 

Another method of evaluating model performance is reviewing spatial plots and time series plots 

of the modeled versus observed data. These graphical plots aid in getting a better understanding 

of how the model is performing over the whole domain. 

Only the model performance evaluation for the 12-km grid domain will be discussed in the 

subsections to follow. For the full model performance evaluation for both the 36-km and 12-km 

grid domains, please refer to Appendix J. 

3.1 Domain-Wide Performance 

The 8-hour ozone statistical data was calculated for the 12-km domain for the ASIP states, North 

Carolina and South Carolina and is presented in Tables 3.1-1. The mean normalized bias was 

well within the recommended ± 5-15 percent for the entire season (May through September). 

When looking at the individual monthly statistics for August and September in North Carolina 

and South Carolina, the mean normalized bias was slightly outside the suggested range. This 

suggests an under prediction of ozone toward the end of the summer, however the NCDAQ does 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 26 

North Carolina Attainment Demonstration June 15, 2007 

not believe this slight under prediction for August and September impacts the overall modeling 

results. The mean normalized gross error was significantly below the 30-35 percent range at the 

60 ppb threshold for all regions. These statistical metrics were used as a first screening of the 

model performance. 

Table 3.1-1. 12-km Domain Model Statistics for 8-Hour Ozone 

Region/Month Modeled 

Mean (ppb) 

Observed 

Mean (ppb) 

Mean Bias 

(ppb) 

Mean 

Normalized 

Bias (%) 

Mean 

Normalized 

Gross Error 

(%) 

ASIP States combined 

May 61.26 67.69 -6.44 -8.96 12.47 

June 62.62 70.99 -8.37 -11.37 14.02 

July 62.73 70.85 -8.12 -10.90 14.74 

August 61.33 72.57 -11.24 -14.92 16.98 

September 60.81 71.98 -11.17 -14.98 17.07 

Mean (May-September) 61.75 70.82 -9.07 -12.23 15.06 

North Carolina 

May 64.06 69.05 -5 -6.86 10.76 

June 62.21 71.82 -9.62 -13.03 14.47 

July 62.94 72.10 -9.16 -12.09 14.63 

August 60.60 73.92 -13.33 -17.40 18.34 

September 57.90 69.37 -11.46 -16.11 17.68 

Mean (May-September) 61.54 71.25 -9.71 -13.10 15.18 

South Carolina 

May 63.87 67.71 -3.85 -5.31 9.66 

June 61.95 70.92 -8.97 -12.10 13.52 

July 60.89 70.24 -9.35 -12.73 14.75 

August 59.77 71.39 -11.62 -16.03 16.64 

September 61.18 72.62 -11.44 -15.22 16.32 

Mean (May-September) 61.53 70.58 -9.05 -12.28 14.18 

3.1.1 Spatial Plots 

Appendix J has all of the domain-wide spatial plots of modeled 1-hour and 8-hour maximum 

ozone with the observations overlaid for the days used in the relative response factor 

calculations. In this section, only representative days will be displayed (Figures 3.1.1-1 and 

3.1.1-7). Overall the model does well with the spatial extent of the higher ozone concentrations. 

There is a slight under prediction of the ozone in the model, most notably in the 1-hour ozone 

plots. Higher ozone concentrations are seen in the urban areas, where it would be expected. In 

general, the NCDAQ believes the model does an acceptable job capturing the spatial distribution 

and concentration of ozone in the Metrolina region. 
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North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-1 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for May 25, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 28 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-2 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for June 3, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 29 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-3 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for June 12, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 30 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-4 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for July 3, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 31 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-5 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for July 17, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 32 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-6 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for August 2, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 33 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.1-7 Spatial plots for modeled predicted and observed peak 1-hour (top) and 

8-hour (bottom) ozone concentrations for August 10, 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 34 

North Carolina Attainment Demonstration June 15, 2007 

3.1.2 Scatter Plots 

The NCDAQ is most concerned about how the model performed for North and South Carolina 

and secondarily for the whole 12-km domain. For this reason, the scatter plots below are for the 

two states and the domain-wide scatter plots can be found in Appendix J. The model 

performance scatter plots of modeled predicted versus observed for 1-hour and 8-hour ozone has 

been compiled for each month used in the attainment test (May through September). Only the 8-

hour ozone scatter plots for the three months (June through August) in which the majority of the 

modeled days used in the relative response factor are shown. Although there are some outliers, 

the overall performance is good for the 2002 ozone season. The majority of the points fall within 

the acceptable limits of good model performance. 

North Carolina scatter plots

Figure 3.1.2-1 through 3.1.2-3 displays the scatter plots for 8-hour ozone for June, July and 

August for all of the monitoring sites in North Carolina. The 1-hour ozone scatter plots and the 

remaining 8-hour ozone scatter plots can be found in Appendix J. Overall, for the North 

Carolina monitoring sites the model performance is good. Although there are some days where 

over predictions and under predictions are observed, in general most days fall within acceptable 

ranges of the 1:1 line. 

Figure 3.1.2-1 8-hour ozone scatter plot for North Carolina 12-km grid for June 2002 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 35 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.2-2 8-hour ozone scatter plots for North Carolina 12-km grid for July 2002 

Figure 3.1.2-3 8-hour ozone scatter plots for North Carolina 12-km grid for August 2002 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 36 

North Carolina Attainment Demonstration June 15, 2007 

South Carolina scatter plots

Figure 3.1.2-4 through 3.1.2-6 displays the scatter plots for 8-hour ozone for June, July and 

August for all of the monitoring sites in South Carolina. The 1-hour ozone scatter plots and the 

remaining 8-hour ozone scatter plots can be found in Appendix J. Overall, the model 

performance is good for the South Carolina monitoring sites. Again, although there are some 

days where over predictions and under predictions are observed, in general most days fall within 

acceptable ranges of the 1:1 line. 

 Figure 3.1.2-4 8-hour ozone scatter plots for South Carolina 12-km grid for June 2002 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 37 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.2-5 8-hour ozone scatter plots for South Carolina 12-km grid for July 2002 

Figure 3.1.2-6 8-hour ozone scatter plots for South Carolina 12-km grid for August 2002 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 38 

North Carolina Attainment Demonstration June 15, 2007 

3.1.3 Time Series Plots 

Following are 8-hour time series plots from the 12 km domain for the North Carolina monitors 

for June through August. The time series presents the observed values (black *’s) and the 

predicted values (green lines) by month. The 1-hour and 8-hour ozone time series plots for the 

ASIP region, North Carolina and South Carolina can be found in Appendix J. 

The model predicts the overall diurnal pattern well, however it tends to under predict peak values 

and over predict minimum values. In particular the last few days of August shows the model not 

handling the prediction of the absolute value of ozone well. Overall, the model is within 

acceptable tolerances for model performance. 

Figure 3.1.3-1 Time series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for June 2002. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 39 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.1.3-2 Time series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for July 2002. 

Figure 3.1.3-3 Times series plot of model predicted versus mean 8-hour observed for North 

Carolina monitors for August 2002 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 40 

North Carolina Attainment Demonstration June 15, 2007 

3.1.4 Domain-Wide Summary 

Overall, the model performance for North Carolina and South Carolina throughout the ozone 

season is good. For the most part, mean normalized bias and mean normalized gross error are 

within the recommended limits for good model performance. The model seems to do a good job 

capturing ozone concentrations through various episode-clean out cycles. There are some 

instances of under and over predictions, but for the majority of the time the model does well 

simulating the afternoon ozone peak throughout North Carolina and South Carolina. The scatter 

plots show that the model did well. The NCDAQ believes that the model performance is well 

within the limits of acceptable performance established in the USEPA’s Guidance On The Use 

Of Models And Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, 

PM2.5, and Regional Haze (“Attainment Guidance”). 

3.2 Metrolina Nonattainment Area Model Performance Evaluation 

Below is the model performance evaluation for the Metrolina nonattainment area. Included are 

visual (e.g. time series) and statistical measures. These evaluation products include: 

1. Time series plots showing how the model’s predicted ozone compares to the observed 

ozone at the monitor within the same grid cell. This is considered the most stringent of 

the model performance evaluation procedures since it requires the evaluation of the 

model’s ability to predict the observed ozone in the location where it was observed over 

all hours of the episode. 

2. Statistical measures for entire nonattainment area and by monitor in the region. 

Statistical measures include mean bias, mean normalized bias, and mean normalized 

gross error. Like the time series, the statistics compare the observed ozone at the monitor 

to the grid cell where the monitor is located. 

3.2.1 Time Series Plots 

The following are the June through August time series plots for the 12km grid domain for the 

County Line and Enochville monitors located in Mecklenburg and Rowan Counties, 

respectively. The time series presents the observed values (green line) and the predicted values 

(red line). Presented here are just the 8-hour ozone plots for these two monitors, all of the May 

through September, 1-hour and 8-hour ozone time series plots for the monitors in the 

nonattainment area can be found in Appendix J. 

As with the larger domain time series plots, the air quality model tends to slightly under predict 

peak 8-hour ozone values. The over prediction of the nighttime minimum issue is more 

noticeable in the individual monitoring site time series, especially these more urbanized sites due 

to the higher night time nitrogen oxide (NOx) environment found in such a urban area. The NOx 

emissions titrate the ozone after sunset and the ozone levels decrease dramatically. The air 

quality model does not replicate this type of phenomenon very well. The nighttime minimum 

over prediction is not an issue with respect to the modeled attainment test and is therefore not of 
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North Carolina Attainment Demonstration June 15, 2007 

significant concern in this modeling exercise. The ability of the air quality model to accurately 

capture the synoptic cycles from high ozone episodes to very clean periods is best demonstrated 

in these individual monitor time series. Despite the under prediction of some of the 8-hour 

ozone daily maximum and the over night over predictions, the NCDAQ concludes that the air 

quality modeling continues to meet all requirements for further application in the modeled 

attainment test. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 42 

North Carolina Attainment Demonstration June 15, 2007 

Figure 3.2.1-1 Time series plots of model predicted versus 8-hour ozone concentrations for 

County Line monitor for June (top), July (middle) and August (bottom). 
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North Carolina Attainment Demonstration June 15, 2007 

Figure 3.2.1-2 Time series plots of model predicted versus 8-hour ozone concentrations for 

Enochville monitor for June (top), July (middle) and August (bottom). 
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North Carolina Attainment Demonstration June 15, 2007 

3.2.2 Area and Monitor Statistics 

Table 3.2.2-1 displays the model performance statistics comparing the modeled 8-hour ozone 

mean and the observed 8-hour ozone mean at each monitor in the Metrolina area, as well as the 

combined statistics for all of the monitors in the Metrolina area. The statistics represent the May 

through September time period.

Table 3.2.2-1. Metrolina Nonattainment Area Monitor Statistics 

Monitor Modeled 

Mean (ppb)

Observed 

Mean (ppb)

Mean Bias 

(ppb) 

Mean 

Normalized 

Bias (%) 

Mean 

Normalized 

Gross Error 

(%) 

Metrolina Area 66.87 75.75 -8.75 -10.72 15.04 

Crouse 69.0 76.0 -6.0 -7.232 12.050 

County Line 66.0 76.0 -11.0 -13.777 17.861 

Garinger (Plaza) 69.0 74.0 -5.0 -5.872 14.354 

Arrowood 69.0 77.0 -8.0 -9.248 13.835 

Enochville 66.0 76.0 -10.0 -12.223 14.812 

Rockwell 68.0 77.0 -9.0 -11.230 14.767 

Monroe 63.0 75.0 -12.0 -14.677 17.048 

York County, SC 65.0 75.0 -9.0 -11.471 15.549 

It is recommended that the combined mean normalized bias fall within ± 5-15 percent and the 

combined mean normalized gross error not exceed the 30-35 percent range. For a specific 

monitor, it is recommended that the mean normalized bias fall within ± 20 percent. From the 

table above it is demonstrated that the mean bias, mean normalized bias, and mean normalized 

gross error were all within recommended and accepted ranges. 

A slight under prediction of 8-hour ozone was also observed at this more refined level of analysis 

and was similar to what was seen at the larger state and VISTAS/ASIP region levels. Individual 

monthly statistics are not presented here due to the very limited number of modeled and 

observed data pairs at just the eight Metrolina ozone monitoring sites. Whole season statistics 

are more representative of how this air quality modeling will be applied in the modeled 

attainment test discussed in Appendix L. Across the whole season, the Metrolina region as a 

whole, as well as the individual ozone monitoring sites, had mean normalized bias statistics in 

the suggested ± 5-15 percent range and mean normalized gross error statistics in the suggested 

30-35 percent range given a 60 ppb threshold. 
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North Carolina Attainment Demonstration June 15, 2007 

4.0 CONTROLS APPLIED 

Several control measures already in place or being implemented over the next few years will 

reduce stationary point, highway mobile, and nonroad mobile sources emissions. The Federal 

and State control measures were modeled for all of the future years and are discussed in the 

sections below. 

4.1 Federal Control Measures 

4.1.1 Tier 2 Vehicle Standards 

Federal Tier 2 vehicle standards will require all passenger vehicles in a manufacturer’s fleet, 

including light-duty trucks and Sport Utility Vehicles (SUVs), to meet an average standard of 

0.07 grams of NOx per mile. Implementation began in 2004, and should be completely phased 

in by 2007. The Tier 2 standards will also cover passenger vehicles over 8,500 pounds gross 

vehicle weight rating (the larger pickup trucks and SUVs), which are not covered by the current 

Tier 1 regulations. For these vehicles, the standards will be phased in beginning in 2008, with 

full compliance in 2009. The new standards require vehicles to be 77% to 95% cleaner than 

those on the road today. The Tier 2 rule also reduced the sulfur content of gasoline to 30 ppm 

starting in January of 2006. Most gasoline sold in North Carolina prior to January 2006 had a 

sulfur content of about 300 ppm. Sulfur occurs naturally in gasoline, but interferes with the 

operation of catalytic converters on vehicles resulting in higher NOx emissions. Lower-sulfur 

gasoline is necessary to achieve the Tier 2 vehicle emission standards. 

4.1.2 Heavy-Duty Gasoline and Diesel Highway Vehicles Standards 

New USEPA standards designed to reduce NOx and VOC emissions from heavy-duty gasoline 

and diesel highway vehicles began to take effect in 2004. A second phase of standards and 

testing procedures, beginning in 2007, will reduce particulate matter from heavy-duty highway 

engines, and will also reduce highway diesel fuel sulfur content to 15 ppm since the sulfur 

damages emission control devices. The total program is expected to achieve a 90% reduction in 

particulate matter (PM) emissions and a 95% reduction in NOx emissions for these new engines 

using low sulfur diesel, compared to existing engines using higher-content sulfur diesel. 

4.1.3 Large Nonroad Diesel Engines Rule 

In May 2004, the USEPA promulgated new rules for large nonroad diesel engines, such as those 

used in construction, agricultural, and industrial equipment, to be phased in between 2008 and 

2014. The nonroad diesel rules also reduce the allowable sulfur in nonroad diesel fuel by over 

99%. Nonroad diesel fuel currently averages about 3,400 ppm sulfur. The rule limits nonroad 

diesel sulfur content to 500 ppm in 2006 and 15 ppm in 2010. The combined engine and fuel 

rules would reduce NOx and PM emissions from large nonroad diesel engines by over 90%, 

compared to current nonroad engines using higher-content sulfur diesel.
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North Carolina Attainment Demonstration June 15, 2007 

4.1.4 Nonroad Spark-Ignition Engines and Recreational Engines Standard 

The new standard, effective in July 2003, regulates NOx, HC and CO for groups of previously 

unregulated nonroad engines. The new standard will apply to all new engines sold in the United 

States and imported after these standards begin and will apply to large spark-ignition engines 

(forklifts and airport ground service equipment), recreational vehicles (off-highway motorcycles 

and all-terrain-vehicles), and recreational marine diesel engines. The regulation varies based 

upon the type of engine or vehicle. 

The large spark-ignition engines contribute to ozone formation and ambient CO and PM levels in 

urban areas. Tier 1 of this standard was implemented in 2004 and Tier 2 is scheduled to start in 

2007. Like the large spark-ignition, recreational vehicles contribute to ozone formation and 

ambient CO and PM levels. For the off-highway motorcycles and all-terrain-vehicles, model 

year 2006, the new exhaust emissions standard was phased-in by 50% and for model years 2007 

and later at 100%. Recreational marine diesel engines over 37 kilowatts are used in yachts, 

cruisers, and other types of pleasure craft. Recreational marine engines contribute to ozone 

formation and PM levels, especially in marinas. Depending on the size of the engine, the 

standard began phasing-in in 2006. 

When all of the nonroad spark-ignition engines and recreational engines standards are fully 

implemented, an overall 72% reduction in HC, 80% reduction in NOx, and 56% reduction in CO 

emissions are expected by 2020. These controls will help reduce ambient concentrations of 

ozone, CO, and fine PM. 

4.1.5 NOx SIP Call in Surrounding States 

In October 1998, the USEPA made a finding of significant contribution of NOx emissions from 

certain states and published a rule that set ozone season NOx budgets for the purpose of reducing 

regional transport of ozone (63 FR 57356). This rule, referred to as the NOx SIP Call, called for 

ozone season controls to be put on utility and industrial boilers, as well as internal combustion 

engines in 22 states in the Eastern United States. A NOx emissions budget was set for each state 

and the states were required to develop rules that would allow the state to meet their budget. A 

NOx trading program was established, allowing sources to buy credits to meet their NOx budget 

as opposed to actually installing controls. The emission budgets were to be met by the beginning 

of 2004. Even with the trading program, the amount of ozone season NOx emissions has 

decreased significantly in and around North Carolina. 

4.1.6 Clean Air Interstate Rule 

On May 12, 2005, the USEPA promulgated the “Rule To Reduce Interstate Transport of Fine 

Particulate Matter and Ozone (Clean Air Interstate Rule); Revisions to Acid Rain Program; 

Revisions to the NOX SIP Call”, referred to as CAIR. This rule established the requirement for 

States to adopt rules limiting the emissions of NOx and sulfur dioxide (SO2) and a model rule for 

the states to use in developing their rules. The purpose of the CAIR is to reduce interstate 

transport of precursors to fine particulate and ozone. 
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North Carolina Attainment Demonstration June 15, 2007 

The CAIR applies to (1) any stationary, fossil-fuel-fired boiler or stationary, fossil-fuel-fired 

combustion turbine serving at any time, since the start-up of a unit’s combustion chamber, a 

generator with nameplate capacity of more than 25 MWe producing electricity for sale and (2) 

for a unit that qualifies as a cogeneration unit during the 12-month period starting on the date 

that the unit first produces electricity and continues to qualify as a cogeneration unit, a 

cogeneration unit serving at any time a generator with nameplate capacity of more than 25 MWe 

and supplying in any calendar year more than one-third of the unit’s potential electric output 

capacity or 219,000 MWh, whichever is greater, to any utility power distribution system for sale 

This rule provide annual state caps for NOx and SO2 in two phases, with the Phase I caps for 

NOx and SO2 starting in 2009 and 2010, respectively. Phase II caps become effective in 2015. 

The USEPA is allowing the caps to be met through a cap and trade program if a state so chooses 

to participate in the program. 

4.2 State Control Measures 

North Carolina has adopted a number of regulations and legislation to address pollution issues 

across the State. These include the Clean Air Bill, the NOx SIP Call Rule, the Clean 

Smokestacks Act and the Open Burning Rule. All of these regulations were modeled in the 

attainment demonstration. These regulations are summarized below and the actual regulations 

and legislation can be viewed in Appendix M. 

4.2.1 Clean Air Bill 

The 1999 Clean Air Bill expanded the vehicle emissions inspection and maintenance program in 

North Carolina from 9 counties to 48 counties between July 1, 2002 and January 1, 2006 

(Figure 4.2.1-1). Vehicles are tested using the onboard diagnostic system (OBDII), an improved 

method of testing, which indicates NOx emissions, among other pollutants. The previously used 

tailpipe test (i.e., idle test) did not measure NOx. Mecklenburg and Gaston Counties were 

required to have the idle test inspection and maintenance program due to the 1-hour ozone 

nonattainment/maintenance status of those counties. The idle test only tested VOC and CO 

emissions. Starting in 2006, the idle test was replaced with the OBDII test in these two counties. 

Figure 4.2.1-1 North Carolina’s NOx Inspection and maintenance phase-in map 
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North Carolina Attainment Demonstration June 15, 2007 

The effective dates for the counties in the Metrolina nonattainment area are listed below. 

County Date County Date 

Cabarrus July 1, 2002 Mecklenburg July 1, 2002 

Gaston July 1, 2002 Rowan July 1, 2003 

Iredell July 1, 2003 Union July 1, 2002 

Lincoln January 1, 2004 

 4.2.2 NOx SIP Call Rule 

In response to the USEPA’s NOx SIP call, North Carolina adopted rules to control the emissions 

of NOx from large stationary combustion sources. These rules cover (1) fossil fuel-fired 

stationary boilers, combustion turbines, and combined cycle systems serving a generator with a 

nameplate capacity greater than 25 megawatts and selling any amount of electricity, (2) fossil 

fuel-fired stationary boilers, combustion turbines, and combined cycle systems having a 

maximum design heat input greater than 250 million British thermal units per hour, and (3) 

reciprocating stationary internal combustion engines rated at equal or greater than 2400 brake 

horsepower (3000 brake horsepower for diesel engines and 4400 brake horsepower for dual fuel 

engines). As part of the NOx SIP call, the USEPA rules established a NOx budget for sources in 

North Carolina and other states. 

Besides amending existing NOx rules and adopting new NOx rules specifically to address the 

USEPA NOx SIP call, the North Carolina rules also require new sources to control emissions of 

NOx. The objective of this requirement is (1) to aid in meeting the NOx budget for North 

Carolina for minor sources and (2) to aid in attaining and maintaining the ambient air quality 

standard for ozone in North Carolina. 

North Carolina’s NOx SIP Call rule was predicted to reduce summertime NOx emissions from 

power plants and other industries by 68% by 2006. In October 2000, the North Carolina 

Environmental Management Commission adopted rules requiring the reductions. 

4.2.3 Clean Smokestacks Act 

In June 2002, the North Carolina General Assembly enacted the Clean Smokestacks Act, 

requiring coal-fired power plants to reduce annual NOx emissions by 78% by 2009. These 

power plants must also reduce annual sulfur dioxide emissions by 49% by 2009 and by 74% by 

2013. The Clean Smokestacks Act reduces NOx emissions beyond the requirements of the NOx 

SIP Call Rule. One of the first state laws of its kind in the nation, this legislation provides a 

model for other states in controlling multiple air pollutants from older coal-fired power plants. 

4.2.4 Open Burning Bans 

The North Carolina Environmental Management Commission (EMC) approved revisions to the 

open burning regulation banning open burning on forecasted code orange and higher air quality 

action days for those counties that the NCDAQ forecasts ozone and fine particulate matter. The 
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North Carolina Attainment Demonstration June 15, 2007 

NCDAQ has forecasted ozone for the Metrolina area since 1998, and in 2002 started forecasting 

fine particulate matter year round. Therefore, the following counties in the Metrolina area are 

subject to this rule: Cabarrus, Gaston, southern Iredell, Lincoln, Mecklenburg, Rowan, and 

Union. 

4.2.5 Clean Air Interstate Rule 

In response to the USEPA’s CAIR, the NCDAQ developed a state CAIR. Under the USEPA’s 

rule, North Carolina has caps as follows: 

• Annual NOx: 62,183 tons for 2009-2014 and 

51,819 tons for 2015 and each year thereafter; 

• Ozone season NOx: 28,392 tons for 2009-2014 and 

23,660 tons for 2015 and each year thereafter; 

• Annual SO2: 137,342 tons for 2010-2014 and 

96,139 tons for 2015 and each year thereafter. 

The State’s NOx allocations have been distributed among the covered facilities. The USEPA 

will determine the SO2 allocations, which are based on the acid rain program. For the most part 

the proposed rules incorporate the USEPA’s model rule. The USEPA’s model rule for 

definitions; permitting; monitoring, reporting, and recordkeeping; trading and banking; 

designated representative; opt-in provision, and new source growth are incorporated by 

reference. 

The rule requires the EMC to periodically review the allocations in 2010 and every five years 

thereafter and to decide whether to reallocate. This rule does not preclude the EMC from 

adopting additional emission reduction requirements for covered sources if necessary to attain or 

maintain an ambient air quality standard. 

The EMC adopted North Carolina’s CAIR on March 9, 2006 and the rule became effective 

July 1, 2006. 
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5.0 ATTAINMENT DEMONSTRATION 

5.1 Attainment Test Introduction 

The modeled attainment test is the practice of using air quality modeling results for baseline and 

future years to determine if an area is expected to attain the NAAQS. For the 8-hour ozone 

NAAQS, the baseline and future model estimates are used in a “relative” rather than “absolute” 

sense. Specifically, the ratio of the air quality model’s future to current predictions is calculated 

at each ozone monitoring site. These monitoring site-specific ratios are called relative response 

factors (RRFs). Future ozone design values (DVFs) are then estimated at each monitor by 

multiplying the monitor-specific baseline ozone design value (DVB) by the modeled RRF for 

each monitor. If all of the predicted monitor-specific DVFs in a given area are less than or equal 

to 0.084 ppm, the attainment test is passed and the area is said to demonstrate attainment. 

Equation 5.1-1 presents the modeled attainment test, applied at monitoring site “x” as described 

in Section 4.0 of the USEPA’s Attainment Guidance. 

 (DVF) = (RRF) x (DVB) Equation 5.1-1 

Where (DVB) = the baseline design value monitored at site "x", ppm 

= the average (of the three) design value periods which include the baseline 

inventory year (i.e. the average of the 2000-2002, 2001-2003, and 2002-2004 

design vales periods for the 2002 baseline inventory year). 

 (RRF) = the ratio of the future 8-hr daily maximum concentration predicted "nearby" a 

monitor (averaged over each day of the episode) to the current 8-hr daily 

maximum concentration predicted "nearby" the monitor (averaged over each 

day of the episode). 

 (DVF) = the estimated future design value, ppm. 

It is important to consider an array of cells “nearby” a monitor rather than focusing on the 

individual cell containing the monitor. This allows for variations in the model performance 

where the peak ozone may not occur in the grid cell that contains the monitor but rather nearby 

the monitor. 

The RRF is calculated by taking the ratio of the future year modeling 8-hour ozone daily 

maximum to the current year modeling 8-hour ozone daily maximum “near” the monitor 

averaged over all of the episode days (Equations 5.1-2). 

RRF = mean future yr. 8-hr daily max “near” monitor “x” Equation 5.1-2 

 mean current yr. 8-hr daily max “near” monitor “x” 

The DVC, for purposes of the modeled attainment test, is defined in the USEPA’s Attainment 

Guidance the average of the three design value periods that straddle the baseline inventory year 
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(e.g., the average of the 2000-2002, 2001-2003, and 2002-2004 design value periods for a 2002 

baseline inventory year). 

5.2 Attainment Test Results 

As stated above, the attainment test is not based on absolute modeling results but rather relative 

reductions of ozone and is only applied at the monitors. However, reviewing the modeling 

results of how the predicted ozone decreases in the future years and how wide spread the 

reductions are plays an import role for the State in determining if additional controls should be 

considered. The modeling results for each day used in the RRF calculations are available in 

Appendix K. Additionally, discussions about how this modeling demonstration meets the 

screening test for areas away from the monitoring sites and additional matrices performed to 

support the attainment test results are in Appendix L. 

The USEPA’s Attainment Guidance states that future design values (DVFs) that fall below 

0.082 ppm demonstrate attainment and little weight of evidence is needed. For monitors with 

DVFs between 0.082 ppm and 0.087 ppm, a weight of evidence demonstration must be 

submitted that supports a demonstration of attainment. For DVFs greater than 0.087 ppm, the 

Attainment Guidance states that more qualitative results are less likely to support a conclusion 

differing from the outcome of the modeled attainment test. 

Table 5.3-1 lists the attainment test results for the Metrolina nonattainment . The first column is 

the monitoring site, followed by the base year design value discussed in Section 5.1. The next 

series of columns are the calculated RRF and the resulting DVF for the attainment year 2009. 

Monitors with DVFs that fall in the additional weight of evidence requirement are bolded. 

Table 5.3-1 Attainment Test Results 

2009 

Monitoring Site County 

DVB (ppm) 

5-year weighted 

2000-2004 RRF DVF 

(ppm) 

Arrowood Mecklenburg 0.0847 0.892 0.075 

County Line Mecklenburg 0.0973 0.874 0.085 

Crouse Lincoln 0.0907 0.868 0.078 

Enochville Rowan 0.0970 0.870 0.084 

Garinger (Plaza) Mecklenburg 0.0953 0.883 0.084 

Monroe Union 0.0870 0.884 0.076 

Rockwell Rowan 0.0973 0.862 0.083 

York York, SC 0.0830 0.861 0.071 

5.3 Supporting Weight of Evidence 

As part of the weight of evidence determination, the following analyses will be evaluated: 

alternative DVFs calculations, metrics of air quality modeling results, air quality modeling 

results from other studies, observed air quality trends and additional reductions in emissions, and 
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North Carolina Attainment Demonstration June 15, 2007 

local measures not modeled. The weight of evidence determination is a supplement to the 

modeled attainment test and further supports that the area will attain the NAAQS for 8-hour 

ozone by June 15, 2010. 

The NCDAQ believes that the weight of evidence provided in the sections below is strong 

evidence that the Metrolina nonattainment area will attain the 8-hour ozone NAAQS by 2009.

5.3.1 Alternative DVF Calculation 

The NCDAQ uses the USEPA recommended method of calculating the DVB in its modeled 

attainment test. However, the NCDAQ has commented several times on various draft versions 

of the attainment guidance that we do not believe that a weighted DVB is appropriate and that a 

DVB calculated using a straight average minimizes the impacts of any abnormally hot/dry or 

cool/wet meteorological conditions. As part of the weight of evidence demonstration, the 

NCDAQ proposes an alternative method to calculate the DVB and presents the modeled 

attainment test results with this alternative DVB. 

The USEPA recommends calculating the DVB by averaging the three design value periods that 

straddle the baseline inventory year. This methodology results in a center weighting of annual 

4th highest ozone concentrations around the baseline inventory year because the three design 

value periods averaged contain overlapping data. A weighted DVB can be significantly affected 

by an abnormally hot/dry or cool/wet year, if the year happens to be the center weighted year. 

To minimize potential impacts of any abnormal meteorological conditions while still considering 

ozone conditions across a 5-year span, an alternative DVB calculation that does not weight any 

of the years more than another, but is the straight average of annual 4th highest ozone 

concentrations for the 5-year span centered on the baseline inventory year was considered. 

The 5-year straight average DVB is applied to the remainder of the modeled attainment test 

equations and the resulting DVFs are shown in Table 5.3.1-1 at each monitoring site in the 

Metrolina region. 

Table 5.3.1-1 5-Year Average Alternative Attainment Test Results for 2009 

Monitoring Site County 

Alternative DVB

2000-2004 

(ppm) 

RRF DVF 

(ppm) 

Arrowood Mecklenburg 0.0834 0.892 0.074 

County Line Mecklenburg 0.0956 0.874 0.083 

Crouse Lincoln 0.0892 0.868 0.077 

Enochville Rowan 0.0944 0.870 0.082 

Garinger (Plaza) Mecklenburg 0.0938 0.883 0.082 

Monroe Union 0.0846 0.884 0.074 

Rockwell Rowan 0.0946 0.862 0.081 

York York, SC 0.0798 0.861 0.068 
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North Carolina Attainment Demonstration June 15, 2007 

The alternative DVFs are slightly lower at each monitoring site compared to the attainment test 

DVFs. These differences were expected as 2002 was an abnormally hot and dry year throughout 

the Southeast resulting ozone concentrations that were much higher than in the surrounding years 

of 2000, 2001, 2003, and 2004. Thus, the recommended DVB calculation weighted these high 

air quality conditions several times more than in the NCDAQ alternative DVB calculations. The 

NCDAQ firmly believes that the straight five-year average approach to the DVB calculation is 

more appropriate and minimizes dramatic fluctuations in meteorological and air quality 

conditions from year to year. This would be true whether the center weighted year was an 

abnormally hot/dry year or a cool/wet year. 

While none of the monitoring sites in the Metrolina region had DVF values at or above 

0.085 ppm using the NCDAQ alternative DVB calculation, there are still three monitors that 

have DVFs that fall between 0.082 and 0.087 ppm. This continues to indicate that some 

additional weight of evidence should still be included to demonstrate attainment. 

5.3.2 Air Quality Modeling Metrics 

A series of five additional air quality modeling outputs or metrics is recommended to provide 

assurance the modeled attainment demonstration indicates attainment. These metrics look at the 

relative change between the baseline and future years modeling and help to demonstrate how 

widespread the improvement in air quality is expected in the future. These metrics include: 

• The relative change in surface grid-hours greater than 0.084ppm. This is the number of 

grid cells in a Metrolina region with predicted hourly 8-hour ozone concentrations greater 

than 0.084 ppm. The relative change is the percent reduction from the baseline year to 

the future year. 

• The relative change in the number of grid cells with predicted 8-hour daily maximums 

greater than 0.084 ppm. This metric uses the modeled daily maximum 8-hour ozone 

concentrations greater than 0.084 ppm. The relative change is the percent reduction from 

the baseline year to the future year. 

• The relative change in the sum of hourly predictions greater than 0.084 ppm. This metric 

is the sum of all grid cells with predicted hourly 8-hour ozone concentrations greater than 

0.084 ppm. The relative change is the percent reduction from the baseline year to the 

future year. 

• The relative change in the sum of the predicted 8-hour daily maximums greater than 

0.084 ppm. This metric uses the modeled daily maximum 8-hour ozone concentrations 

greater than 0.084 ppm. The relative change is the percent reduction from the baseline 

year to the future year. 

• The change in the Air Quality Index (AQI) counts. The AQI counts metric is a count of 

the number of grid cells with predicted maximum 8-hour ozone concentrations sorted 

within each of the color codes as defined by the USEPA’s AQI. 

The USEPA recommended that these metrics should be at least 80% or higher in order to provide 

weight of evidence that an area would attain the ozone NAAQS. The air quality modeling metric 

analyses demonstrated significant reductions of greater than 85%, in all metrics, in the 2009 
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North Carolina Attainment Demonstration June 15, 2007 

attainment year of modeled days above the NAAQS in the Metrolina nonattainment area. A full 

discussion of the metrics and the results can be found in Appendix L. 

5.3.3 Air Quality Modeling Results From Other Studies 

Another recommended weight of evidence analysis is to review other air quality modeling results 

that included the Metrolina nonattainment area to determine how other modeling results compare 

to the attainment demonstration. There are two air quality modeling studies to which results are 

available for the Metrolina area. 

The first is the Early Action Compact (EAC) modeling that the NCDAQ performed for the EAC 

areas within North Carolina. Since the modeling domain for this analysis covered the majority 

of North Carolina, including the Metrolina nonattainment area, the modeling results can be easily 

compared to the attainment demonstration. Although there are some differences between the two 

modeling exercises, the modeling results for 2012 show all of the monitors well below the 8-hour 

ozone NAAQS, with the highest monitor having a DVF of 0.081 ppm. 

Table 5.3.3-1 Metrolina DVFs based on EAC Modeling 

2012 

Monitoring Site County DVB 

(ppm) RRF DVF 

(ppm) 

Arrowood Mecklenburg 0.092 0.848 0.078 

County Line Mecklenburg 0.101 0.802 0.081 

Crouse Lincoln 0.092 0.826 0.076 

Enochville Rowan 0.099 0.818 0.081 

Garinger (Plaza) Mecklenburg 0.098 0.816 0.080 

Monroe Union 0.088 0.795 0.070 

Rockwell Rowan 0.100 0.800 0.080 

It should be noted that for the Greensboro/Winston-Salem/High Point EAC area, the EAC 

attainment test results predicted the highest monitor in the area to be at 83 ppb in 2007. 

However the current 2004-2006 design value for that area is 80 ppb, below what was projected 

and a year earlier. 

Another air quality modeling exercise that contained results for the Metrolina nonattainment area 

is the USEPA’s modeling for the Clean Air Interstate Rule (CAIR). The Technical Support 

Document for the final CAIR, March 2005, provided modeling results with and without the 

implementation for the CAIR. These modeling results are listed in the table below. 
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North Carolina Attainment Demonstration June 15, 2007 

Table 5.3.3-2 Metrolina DVFs based on the USEPA’s CAIR Modeling 

DVF (ppb) County DVB 

(ppb) 2010 Base 2010 CAIR 

Lincoln 92.3 76.1 74.5 

Mecklenburg 100.3 82.5 81.4 

Rowan 99.7 81.3 80.1 

Union 87.7 71.9 71.1 

York, SC 83.3 70.0 68.5 

The USEPA’s modeling results predicts that the Metrolina nonattainment area should be below 

the 8-hour ozone standard by 2010. Although this is one year later than the attainment year for 

the Metrolina area, the USEPA’s 2010 CAIR DVFs are 3 to 4 ppb lower than what the NCDAQ 

is showing in the attainment demonstration, and supports weight of evidence that the Metrolina 

area will attain the 8-hour ozone standard by its attainment year of 2009. 

5.3.4 Air Quality Trends and Additional Reductions in Emissions 

Since the 8-hour ozone designation for the Metrolina area, the 8-hour ozone design values have 

improved significantly. The 2001-2003 design value period had values as high as 0.100 ppm and 

six out of the seven North Carolina monitors in the area were violating the NAAQS. Each year 

since, the design values have decreased and/or the number of violating monitors in the region has 

decreased. With the latest design value period, 2004-2006, the highest violating monitor has a 

value of 88 ppb and there are only three monitors that exceed the NAAQS (See Table 5.3.4-1) 

Table 5.3.4-1 Design Values (ppm) for the North Carolina Monitors in the Metrolina Area 

Monitoring Site County 2001-2003 2002-2004 2003-2005 2004-2006 

Arrowood Mecklenburg 0.084 0.081 0.078 0.080 

County Line Mecklenburg 0.098 0.092 0.087 0.088 

Crouse Lincoln 0.092 0.086 0.081 0.079 

Enochville Rowan 0.099 0.091 0.085 0.085 

Garinger (Plaza) Mecklenburg 0.096 0.091 0.086 0.088 

Monroe Union 0.088 0.085 0.079 0.078 

Rockwell Rowan 0.100 0.094 0.088 0.083 

York York, SC 0.084 0.081 0.075 0.076 

The current ozone design values are very close to the predicted attainment year design values, 

however, there are still significant nitrogen oxides (NOx) emission reductions that are expected 

between now and the attainment year. Although most of these expected NOx emission 

reductions have been included in the attainment demonstration modeling, it does not appear the 

model is responsive enough to expected emission reductions. 
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As mentioned in Section 1.4, the Metrolina area is a NOx limited area and the major sources of 

NOx emissions in the region comes from mobile sources and electric generating facilities. 

Reduction of emissions from these two source sectors can significantly influence the ozone 

formation in this region. The NCDAQ has estimated that there will be approximately 7.6 tons 

per day of NOx emissions reduced each year from the mobile sector. These reductions are the 

result of Federal motor vehicle and equipment standards for both highway vehicles and off-road 

equipment. 

Another source of NOx emission reductions that are expected to occur between now and the 

attainment year are from the electric generating facilities located in and near the Metrolina 

nonattainment area. Several of the Duke Energy units are still expected to have controls installed 

over the next two years. Figure 5.3.4-1 displays the location and size of the Duke Energy 

facilities located in the vicinity of the Metrolina nonattainment area. Table 5.3.4-2 lists the units 

that are in and around the Metrolina area and shows the year the controls are expected to come 

on line and the estimated amount of NOx emissions reductions for the ozone season. 

Figure 5.3.4-1 Location and size of the Duke Energy facilities located in the vicinity of the 

Metrolina nonattainment area. 
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North Carolina Attainment Demonstration June 15, 2007 

Table 5.3.4-2 Utility NOx Emission Reductions since 2006 Ozone Season 

Facility County Technology Operational 

Date 

Ozone Season 

Reductions 

(tons/season) 

Allen Steam Station 

 Unit 2 

 Unit 3 

Gaston SNCR 

SNCR 

Spring 2007 

Fall 2007 

~300 

Buck Steam Station 

 Units 3 & 4 

 Units 5 & 6 

Rowan Low NOx Burners 

SNCR 

Spring 2007 

Fall 2006 

~350 

Riverbend 

 Unit 4 

 Unit 5 

 Unit 6 

 Unit 7 

Gaston 

SNCR 

SNCR & Burners 

SNCR & Burners 

SNCR 

Spring 2007 

Spring 2007 

Fall 2006 

Fall 2006 

~325 

Marshall Steam Station 

 Unit 2 

 Unit 3 

 Unit 4 

Catawba SNCR 

SCR 

SNCR 

Spring 2007 

Fall 2008 

Fall 2006 

~2,300 

Total expected reduction = 3,275 tons/ozone season 

SNCR = Selective Non-Catalytic Reduction 

SCR = Selective Catalytic Reduction 

The combination of the mobile source and utility NOx emission reductions that are expected in 

the Metrolina area between the end of the 2006 ozone season and before the beginning of the 

attainment year 2009 is significant. Since the 2004-2006 design values are just above the 

standard, the additional NOx emission reductions in the area should ensure that the Metrolina 

area would attain the NAAQS by the prescribed attainment year. 

5.3.5 Local Measures not Modeled 

A significant source of NOx emission reductions that has not been included in the modeling is 

the addition of a SCR unit at Marshall Unit 3. As can be seen in Figure 5.3.4-1 in the previous 

section, the Marshall Steam Station is located directly north and adjacent to the Metrolina 

nonattainment area. The additional NOx emission reductions expected at this facility will have 

an impact on the ozone formation in the Metrolina area on days when the winds are coming from 

the North/Northwest and on days when there is recirculation occurring. This SCR unit should be 

installed the Fall of 2008 and will be operational before the beginning of 2009. 

In addition to the Marshall NOx emission reductions, the Metrolina area has a number of groups 

that are working towards decreasing emissions. These measures are voluntary measures that 

although may not account for large emission reductions, they are directionally correct. A few of 

the known measures that are under way in the Metrolina area include: I-77 High Occupancy 

Vehicle (HOV) lane in Mecklenburg County, truck stop electrification in Rowan County, express 
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North Carolina Attainment Demonstration June 15, 2007 

bus routes, pedestrian walkways and bikeways projects, idle reduction policies, biodiesel use and 

diesel retrofit projects. Discussions of these measures can be found in Appendix L. 

5.4 Unmonitored Area Analysis 

The modeled attainment test does not address future air quality at locations where there is not an 

ozone monitor nearby. To guard against the possibility that air quality levels could exceed the 

standard in areas with limited monitoring, Section 3.4 of the Attainment Guidance suggest that 

additional review is “necessary, particularly in nonattainment areas where the ozone or PM2.5 

monitoring network just meets or minimally exceeds the size of the network required to report 

data to Air Quality System (AQS).” This review is intended to ensure that a control strategy 

leads to reductions in ozone at other locations that could have baseline (and future) design values 

exceeding the NAAQS were a monitor deployed there. The test is called an “unmonitored area 

analysis”. The purpose of the analysis is to use a combination of model output and ambient data 

to identify areas that might exceed the NAAQS if monitors were located there. 

NCDAQ believes that the density of its’ monitoring network relieves the necessity of applying 

this additional analysis. With an average of one monitor per 3,077 km2

, this is one of the densest 

statewide ozone monitoring networks in the nation. Additionally, the monitor density across the 

Metrolina nonattainment area is more than twice that of the statewide monitor density (on 

average a monitor every 1,278 km2

). 

The Modeled Attainment Test Software (MATS) tool has been developed by the USEPA to 

spatially interpolate data, adjust the spatial fields based on model output gradients, and multiply 

the fields by model calculated RRFs for analysis of unmonitored areas. However, this tool has 

just recently been released with documentation, June 2007, and the NCDAQ has not had 

sufficient time to review documentation and fully understand the output from this tool, nor has 

the tool been peer reviewed. The NCDAQ is committed to evaluate the MATS tool output and 

any peer review comments that are submitted to determine if additional monitoring or further 

NOx controls may be needed to ensure attainment of the NAAQS throughout the Metrolina 

region. 

5.4 Data Access 

The modeling input and output files are very large and it would not be reasonable to submit all of 

these files with the SIP attainment demonstration. These include all files used to process the 

emissions, meteorology and air quality models and any other files used to develop the modeling. 

To request access to these files please contact the Division of Air Quality, Attainment Planning 

Branch Chief at 919.733.3340. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 59 

North Carolina Attainment Demonstration June 15, 2007 

6.0 OTHER CLEAN AIR ACT REQUIREMENTS 

Sections 172(c), 182(a) and 182 (b) of the CAA, as amended, contain the requirements for ozone 

nonattainment areas. As a subpart 2 moderate ozone nonattainment area, the Metrolina area 

must meet the requirements for both a marginal and moderate area, as well as the general 

requirements contained in Section 172(c). These requirements are listed below and are discussed 

in more detail in the following chapter, although it should be noted that they have been grouped 

to avoid duplication of the discussion. 

Section 172(c) Nonattainment Plan Provisions

(1) Reasonable available control measures (RACM) 

(2) Reasonable further progress (RFP) 

(3) Actual emissions inventory and periodic emissions inventory 

(4) New source review (NSR) 

(5) Permit requirements for new and modified sources 

(6) Other measures as may be necessary to provide attainment by specified attainment date 

(7) Compliance with Section 110(a)(2) 

(8) Equivalent techniques 

(9) Contingency measures 

Section 182(a) Plan Submissions and Requirements for Marginal Areas

(1) Actual emissions inventory in accordance with 172(c)(3) 

(2) Corrections to SIP 

 (A) Reasonably available control technology (RACT) 

 (B) Motor vehicle inspection and maintenance (I/M) 

 (C) Permit programs 

(3) Periodic emissions inventory 

 (A) General – emission inventory every three years until area is redesignated to 

attainment. 

 (B) Annual emissions statement requirement for sources 25 tons per year or greater 

of VOC or NOx. 

Section 182(b) Plan Submissions and Requirements for Moderate Areas

(1) Reasonable further progress 

(2) Reasonable available control technology 

(3) Gasoline vapor recovery 

(4) Motor vehicle I/M 

(5) Offset requirements of at least 1.15 to 1. 
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North Carolina Attainment Demonstration June 15, 2007 

6.1 RACT/RACM Requirements 

Section 172(c)(1) of the CAA requires SIPs to provide for the implementation of all reasonably 

available control measures (RACM) to demonstrate attainment as expeditiously as practicable. 

A subset of RACM is RACT, which relates specifically to stationary point sources. Section 

182(b)(2) of the CAA requires RACT rules be adopted for all point sources of VOC and NOx 

with potential to emit at least 100 tons per year or greater. The RACT rules were due on 

September 15, 2006. The NCDAQ was unable to complete the rule adoption process by that 

date. However, a public hearing was held on the RACT rules on October 4, 2006, and the EMC 

officially adopted the rules on January 11, 2007. The rules became effective on March 1, 2007. 

Sources subject to the rule must submit a permit application and compliance schedule by 

August 1, 2007, with final compliance no later than April 1, 2009. The RACT rules are 

contained in 15A NCAC 02D.0902, .0909, .1402 and .1403 and are provided in Appendix M. 

 In the mid 1990s, the NCDAQ completed a technical analysis and determined that the entire 

state is NOx limited and that the control program for reducing ozone should be focused on NOx 

emission reductions, since roughly 90 percent of the VOC emissions in North Carolina originate 

from biogenic sources, and not man-made sources. When the 8-hour ozone standard was 

promulgated in 1997, the NCDAQ evaluated the 8-hour ozone levels in North Carolina and 

realized at that time that attainment of the new standard was going to be a significant challenge 

for the state. The NCDAQ began the process of legislative and rulemaking changes that were 

deemed necessary for the state to attain the 8-hour ozone standard in late 1997, which addressed 

many of the RACM available. As such, work began to demonstrate the need for an aggressive 

inspection and maintenance program. This resulted in the 1999 session of the General Assembly 

passing the Clean Air Bill, which required the testing of vehicles in 48 counties across the state. 

The EMC adopted the NOx SIP Call rule in 2000 and the open burning rule in 2004. The 2002 

session of the General Assembly passed the Clean Smokestacks Act. Details of these control 

measures are discussed in Section 4.2 of this document. 

Since the Clean Smokestacks Act, the NOx SIP Call rule and the RACT rule address the 

implementation of RACM for point sources, the remaining source sectors were examined for 

potential control measures that would expedite attainment of the NAAQS. Area source NOx 

emissions are a very small fraction of the NOx emissions in the Metrolina area, accounting for 

only four percent of the total NOx. The only reasonably controlled area source is open burning, 

since the remaining NOx sources include structure fires and forest fires, which cannot be 

controlled. With the adoption of the open burning rule in 2004, RACM for area sources is 

addressed. 

This left the focus of the RACM evaluation on the nonroad and on-road mobile sectors. The 

NCDAQ considered the following measures: 

 An I/M program for on-road heavy-duty diesel engines 

 An I/M program for on-road light-duty diesel engines 

 Requirements for clean diesel technology for all construction equipment on large 

construction projects 

 Mandatory VMT reduction program on ozone episode days 

 Anti-idling program for heavy-duty engines (on-road and non-road) 
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North Carolina Attainment Demonstration June 15, 2007 

The first two measures, I/M programs for diesel engines, is not viable at this time since the 

technology is not yet available on heavy-duty diesel engines and is just beginning to be available 

for some light-duty diesel vehicles, but not all. For the remaining measures, the NCDAQ 

concluded that these measures would require significant stakeholder involvement, and additional 

time to study the cost-benefit of these measures. An estimated timeline for implementation of 

the remaining control measures is outlined below. 

June 2007 – December 2007 Research and perform the cost-benefit analysis of these 

measures 

January 2008 – September 2008 Draft rules for viable measures, organize a list of 

stakeholders and hold several stakeholder meetings to 

address concerns in draft rules 

July 2008 Take concept of draft rules to the Air Quality Committee 

(AQC) 

September 2008 Present draft rules to AQC and request permission to take 

draft rules to the EMC. 

November 2008 Present draft rules to the EMC and request permission to 

take the rules to public hearing. 

January 2009 Take rules to public hearing and provide 30 days to public 

comments. 

February 2009 – April 2009 Address comments received at public hearing and prepare 

hearing report for AQC and EMC. 

May 2009 Take final rules to EMC and request adoption of final rules. 

July 2009 If 10 letters requesting legislative review are not received, 

rules become effective and time for implementation 

outlined in rule (6 months to 2 years depending on rule) 

May 2010 If 10 letters received requesting legislative review received, 

legislative review process would begin. 

As outlined above, these measures cannot be implemented by May 1, 2009 and measures 

implemented after this date cannot advance the June 2010 attainment date. However, these 

measures will continue to be studied as the NCDAQ considers what additional emission 

reductions may be needed in the Metrolina area to show maintenance of the 8-hour ozone 

standard. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 62 

North Carolina Attainment Demonstration June 15, 2007 

6.2 Reasonable Further Progress 

Section 182(b)(1) of the CAA mandates a 15 percent VOC emission reduction, accounting for 

growth, in the first 6 years after the baseline year (2002) for moderate and above ozone 

nonattainment areas. Thus for the Metrolina nonattainment area, a reasonable further progress 

(RFP) analysis between 2002 and 2008 is required. Although the Charlotte-Gastonia 1-hour 

ozone nonattainment area (comprised of Mecklenburg and Gaston Counties) was classified as 

moderate following the 1990 CAAA, the area had measured attainment of the 1-hour standard 

prior to the 15 percent Rate of Progress (ROP) requirement coming due on November 15, 1993. 

Therefore, this area did not implement a 15 percent ROP plan under the 1-hour standard, and the 

RFP requirement must be met through VOC reductions only, consistent with the CAA. 

The methodology the NCDAQ used to calculate the RFP target levels of VOC emissions is based 

on the method developed in the CAAA, while taking into account the restrictions on creditable 

emissions and the need to use the 2002 inventory as a baseline. The CAAA of 1990 specified 

four types of measures that were not creditable toward the 15 percent RFP requirement. These 

were: 

(1) Any measure relating to motor vehicle exhaust or evaporative emissions promulgated by 

the Administrator by January 1, 1990. 

(2) Regulations concerning Reid Vapor Pressure (RVP) promulgated after 1990 or required 

under section 211(h). 

(3) Measures required under section 182(a)(2)(A) to correct deficiencies in SIPs regarding 

VOC RACT regulations required prior to enactment of the CAA Amendments of 1990. 

(4) State regulations submitted to correct deficiencies in I/M existing or required programs. 

These four types of measures were all expected to result in a decrease in emissions between 1990 

and 1996. Of these four types of measures, RACT and I/M program corrections and the 1992 

RVP requirements were completely in place by 1996 and therefore are already accounted for in 

the 2002 baseline. As a result, they would produce no additional reductions between 2002 and 

2008 or later milestone years. 

However, the pre-1990 Federal Motor Vehicle Control Program (FMVCP) will continue to 

provide additional benefits during the first two decades of the 21st century as remaining vehicles 

meeting pre-1990 standards are removed from the vehicle fleet. Because these benefits are not 

creditable for RFP purposes, in order to calculate the target level of emissions for future RFP 

milestone years, you must first calculate the reductions that would occur over these future years 

as a result of the pre-1990 FMVCP. The NCDAQ used Method 1 to account for non-creditable 

reductions when calculating RFP targets for the 2008 milestone year. They are consistent with 

requirements of sections 182(b)(1)(C) and (D) and 182(c)(2)(B) of the CAAA. The NCDAQ did 

not have VOC RACT regulations in the Metrolina region prior to the enactment of the 1990 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 63 

North Carolina Attainment Demonstration June 15, 2007 

CAAA, thus only the on-road mobile source sector required an estimation of non-creditable 

emissions. 

Method 1: For areas that must meet a 15 percent VOC reduction requirement by 2008: 

(A) Estimate the actual anthropogenic base year VOC inventory in 2002 with all 2002 

control programs in place for all sources. 

(B) Using the same highway vehicle activity inputs used to calculate the actual 2002 

inventory, run the appropriate motor vehicle emissions model for 2002 and for 2008 

with all post-1990 CAA measures turned off. Any other local inputs for vehicle I/M 

programs should be set according to the program that was required to be in place in 

1990. Fuel RVP should be set at 9.0 or 7.8 depending on the RVP required in the 

local area as a result of fuel RVP regulations promulgated in June, 1990. 

(C) Calculate the difference between the 2002 and 2008 VOC emission factors calculated 

in Step B and multiply by 2002 vehicle miles traveled (VMT). The result is the VOC 

emissions reductions that will occur between 2002 and 2008 without the benefits of 

any post-1990 CAA measures. These are the non-creditable reductions that occur 

over this period. 

(D) Subtract the non-creditable reductions calculated in Step C from the actual 

anthropogenic 2002 inventory estimated in Step A. This adjusted VOC inventory is 

the basis for calculating the target level of emissions in 2008. 

(E) Reduce the adjusted VOC inventory calculated in Step D by 15 percent. The result is 

the target level of VOC emissions in 2008 in order to meet the 2008 RFP 

requirement. The actual projected 2008 inventory for all sources with all control 

measures in place and including projected 2008 growth in activity must be at or 

lower than this target level of emissions. 

The NCDAQ’s 2002 baseline VOC emissions for the Metrolina area are presented in 

Table 6.2-1. The 2008 VOC emission estimates are included in Table 6.2-2. Table 6.2-3 below 

provides the summary 15% RFP analysis showing the projected 2008 VOC emissions for the 

area, 188.1 tons/day are well below the target level of emissions, 263.9 tons/day, as calculated 

using Method 1. Further details about the RFP calculation can be found in Appendix O. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 64 

North Carolina Attainment Demonstration June 15, 2007 

Table 6.2-1 Metrolina Nonattainment Area 2002 Baseline VOC Emissions (tons/day) 

County Point Area Non-Road Highway 

Mobile Total 

Cabarrus 2.2 6.0 2.7 21.5 32.4 

Gaston 2.5 8.9 2.9 13.5 27.8 

Iredell (partial) 0.9 1.9 0.9 5.1 8.8 

Lincoln 2.1 3.1 1.3 7.1 13.6 

Mecklenburg 5.7 29.4 24.1 68.0 127.2 

Rowan 6.3 5.6 2.3 14.8 29.0 

Union 1.0 6.4 4.7 13.0 25.1 

Total 20.7 61.3 38.9 143.0 263.9 

Table 6.2-2 Metrolina Nonattainment Area 2008 Baseline VOC Emissions (tons/day) 

County Point Area Non-Road Highway 

Mobile Total 

Cabarrus 2.3 5.9 1.5 12.5 22.2 

Gaston 2.7 9.4 2.0 9.0 23.1 

Iredell (partial) 0.7 1.8 0.5 4.2 7.2 

Lincoln 2.1 2.9 0.8 4.8 10.6 

Mecklenburg 5.9 30.1 13.0 35.4 84.4 

Rowan 6.0 5.6 1.5 9.7 22.8 

Union 1.2 5.7 1.7 9.2 17.8 

Total 20.9 61.4 21.0 84.8 188.1 

Table 6.2-3 Metrolina Nonattainment Area 15% RFP Analysis 

Metrolina 15% RFP Analysis VOC 

(tons/day) Step from Method 1 

Total 2002 Base year anthropogenic VOC emissions 263.9 Step A 

Non-creditable VOC reductions 11.3 Step C 

2002 base year minus the non-creditable emissions 252.6 Step D 

2008 target level of VOC emissions 214.7 Step E 

2008 projected VOC emissions 188.1 Projection < Target RFP goal met 

* See Appendix O for details on the development of these numbers. 

The NCDAQ must show continued progress from 2008 through the attainment date (June 15, 

2010). To do so, the NCDAQ calculated the expected benefits from the fleet turnover for the onroad and off-road mobile sectors. In 2009 and 2010, the NCDAQ expects approximately 7.6 

tons per day of NOx emissions reductions from this fleet turnover. The NCDAQ did not 

calculate future expected VOC emissions reductions in 2009 and 2010 since the area is NOx 

limited, but additional VOC emission reductions are expected from the fleet turnover of the onroad mobile sector. The NCDAQ believes these additional reductions demonstrate continued 

reasonable further progress toward attainment beyond 2008. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 65 

North Carolina Attainment Demonstration June 15, 2007 

Another requirement of RFP is that VOC motor vehicle emission budgets for transportation 

conformity need to be set for the RFP year 2008. The NCDAQ has determined that mobile 

source VOC emissions are insignificant to ozone formation in the Metrolina nonattainment area 

(see Appendix F.3). Therefore, the RFP motor vehicle emission budgets are not required. 

6.3 Actual Emissions Inventory 

Section 182(a)(1) and Section 172(c)(3) require the development of a comprehensive, accurate 

current inventory of actual emissions from all sources of VOC and NOx in the nonattainment 

area. Such inventory was due two years after designation of the 8-hour ozone nonattainment 

areas, or by June 15, 2006. The NCDAQ met this requirement through the submittal of the 2002 

emission inventories under the Consolidated Emission Reporting Rule (CERR) for the North 

Carolina counties in this nonattainment area. 

The NCDAQ submitted statewide emissions for area, nonroad mobile and highway mobiles 

sources. For stationary point sources, The NCDAQ submitted inventories for those counties 

without a local program. The Mecklenburg County Land Use and Environmental Services 

Agency - Air Quality submitted an emission inventory for stationary point sources located within 

Mecklenburg County. 

The final 2002 emission inventories used in the attainment demonstration will go through the 

public hearing process with the full attainment demonstration, which will include any updates or 

revisions that are necessary since the CERR submittal. 

6.4 Emissions Inventory Statement 

Section 182(a)(3)(B) requires the SIP to contain a requirement for all owners or operators of 

stationary sources located in the nonattainment area and that emit either VOC or NOx to submit 

a statement of actual emissions annually. The State may waive the requirement for sources that 

emit less than 25 tons per year of NOx or VOC emissions. The requirement for such emissions 

statements has been in place in the old 1-hour ozone nonattainment areas including CharlotteGastonia (Mecklenburg and Gaston Counties) under 15A NCAC 02Q .0207 since July 1, 1994. 

The NCDAQ took an amendment to this rule to public hearing on March 14, 2007 to add the 

new 8-hour ozone counties in the Charlotte-Gastonia-Rock Hill nonattainment area. The 

NCDAQ anticipates that the EMC will adopt this amended rule at its May 10, 2007 meeting, and 

that the rule will become effective on August 1, 2007. The NCDAQ will submit the amended 

rule to the USEPA as soon as it becomes effective. 

6.5 Periodic Emissions Inventory 

Section 172(c)(3) and 182(a)(3)(A) require periodic inventory submittals. Specifically, Section 

182(a)(3)(A) requires the inventory be submitted every three years until the area is redesignated 

to attainment. The NCDAQ plans to meet this requirement through the CERR submittal. As 

such, The NCDAQ will submit the 2005 emissions inventory on or before June 1, 2007. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 66 

North Carolina Attainment Demonstration June 15, 2007 

6.6 Permit Program Requirements 

Sections 172(c)(5) and 182(a)(2)(C) require a permit program consistent with the requirements 

of Section 173. Additionally, Section 182(b)(5) requires an offset requirement of 1.15 to 1. On 

November 30, 2005, the NCDAQ submitted amendments to the nonattainment new source 

review (NNSR) rules contained in 15A NCAC 2D .0531 to the USEPA for review and approval. 

These rules adopted the new offset requirement. Further, on March 16, 2007, the NCDAQ 

submitted amendments to 15A NCAC 2D .0530 Prevention of Significant Deterioration (PSD) 

permitting rules to the USEPA. The NCDAQ believes that the adoption and submittal of the 

NNSR and the PSD rules meet the “prevention of significant deterioration” requirement of 

Section 110(a)(2)(D)(i) since major sources in North Carolina are subject to PSD and NNSR 

programs. Finally, the NCDAQ adopted an Emissions Banking Rule, 15A NCAC 2D .2300 to 

establish a bank where sources could place their shutdown credits, as well as credits achieved 

through installing controls that go above and beyond what is required. The NCDAQ believes it 

has met the permit program requirements for a moderate nonattainment area. 

6.7 Gasoline Vapor Recovery 

Section 182(b)(3) of the CAA requires moderate and above ozone nonattainment areas to 

implement Stage II vapor recovery programs. However, Section 202(a)(6) of the CAA states 

that the section 182(b)(3) Stage II requirement shall not apply in moderate areas after onboard 

refueling vapor recovery (ORVR) rules are promulgated. The USEPA promulgated the ORVR 

regulations on April 16, 1994. Therefore, 8-hour ozone moderate areas designated in 2004 are 

not subject to the Stage II vapor recovery program requirements. 

As such, the NCDAQ removed the pre-piping requirements that were contained in the 1-hour 

maintenance plan for the Charlotte-Gastonia area. The attainment plan and contingency plan 

contained in this submittal addresses the necessary controls to attain the 8-hour standard in the 

Metrolina region. Since the area is NOx-limited and the Stage II program is not required, the 

NCDAQ believes removing the pre-piping requirement is appropriate. The removal of the prepiping requirement was done through a separate SIP revision. The public hearing was held on 

October 4, 2006, the EMC approved the rule change on January 11, 2007 and the rule became 

effective on March 1, 2007. No emission changes are expected from this rule change since the 

pre-piping for Stage II does not result in any emission reductions. 

6.8 Inspection and Maintenance Program 

Section 182(b)(4) requires moderate and above ozone nonattainment areas to implement a 

vehicle I/M program. To meet this requirement for the Charlotte-Gastonia 1-hour ozone 

nonattainment area, a decentralized idle test was implemented in Mecklenburg County on April 

1, 1991, and in Gaston County on July 1, 1992. Additionally, the State required the program to 

also be implemented in Cabarrus and Union Counties, and the program became effective on July 

1, 1993. The program required testing for CO and VOC emissions. Following the promulgation 

of the new 8-hour standard in 1997, the North Carolina General Assembly passed the Clean Air 

Bill in the 1999 session. The Clean Air Bill required that the I/M test be changed to be the 

Acceleration Simulation Mode (ASM) or dynamometer testing for both NOx and VOC 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 67 

North Carolina Attainment Demonstration June 15, 2007 

emissions. The Clean Air Bill also mandated that the program be phased in 48 counties across 

the state between 2002 and 2006, and that the idle test be phased out in 2006 in the nine counties 

in which the program was required. In the 2000 session of the General Assembly, the testing 

was changed again to be On-Board Diagnostics (OBD-II) since this equipment was significantly 

cheaper and also allowed testing for NOx and VOC emissions from automobiles. The following 

rules were amended to reflect the legislative requirements of the Clean Air Bill: 15A NCAC 

02D .1001, .1002, .1004, .1005. The NCDAQ believes that the Clean Air Bill and associated 

rule changes meet the requirements of Section 182(b)(4). 

6.9 Other Measures 

Section 1729(c)(6) requires the nonattainment SIPs to include enforceable limitation and other 

control measures, along with schedules for compliance as needed to demonstrate attainment. 

Section 4.0 of this document discusses in detail the Federal and State measures that are necessary 

for attainment. Appendix M contains the rules and compliance schedules. 

6.10 Compliance with Section 110(a)(2) 

Section 172(c)(7) requires nonattainment SIPs to meet the applicable provisions of Section 

110(a)(2). The NCDAQ has reviewed the requirements of Section 110(a)(2) and has concluded 

that the prior rule submittals, along with this attainment demonstration plan address the relevant 

requirements. 

6.11 Equivalent Techniques 

The NCDAQ believes that the procedures for modeling, emissions inventory and planning 

follow the USEPA guidance and is not requesting approval for equivalent techniques, as 

envisioned under Section 172(c)(8). 

6.12 Contingency Measures 

Section 172(c)(9) requires that the nonattainment SIPs contain specific measures that would take 

effect upon a State’s failure to attain the ozone standard in a given area, without further action by 

the State or the USEPA. Guidance from the USEPA indicates that the measures should be 

approximately three percent of the baseline emissions, so that reasonable progress level of 

reduction could be expected to occur in the year following the failure to attain. The NCDAQ 

elected to adopt NOx only contingency measures since the area is NOx limited. The contingency 

plan consists of Federal and State measures. The Federal measures result from the fleet turnover 

of the light and heavy-duty engine standards from the on-road mobile sector and the non-road 

engine standards. These measures are already adopted and the fleet turnover will occur without 

further action by either the State or the USEPA. The fleet turnover will result in approximately 

7.6 tons/day NOx emission reductions, or about 2.7% of the base emissions. The analysis of 

these emission reductions is included in Appendix P. 

The State measure is lowering the NOx RACT applicability level from 100 tons per year 

potential emissions to 50 tons per year potential emissions. The NCDAQ took this rule to public 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 68 

North Carolina Attainment Demonstration June 15, 2007 

hearing on March 14, 2007. The NCDAQ anticipates that the EMC will adopt this amended rule 

at its May 10, 2007 meeting, and that the rule will become effective on July 1, 2007. The 

NCDAQ will submit the amended rule to the USEPA as soon as it becomes effective. The draft 

rule is included in Appendix M. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 69 

North Carolina Attainment Demonstration June 15, 2007 

7.0 MOTOR VEHICLE EMISSION BUDGETS 

7.1 Transportation Conformity 

The purpose of transportation conformity is to ensure that Federal transportation actions 

occurring in nonattainment and maintenance areas do not hinder the area from attaining and 

maintaining the 8-hour ozone standard. This means that the level of emissions estimated by the 

NCDOT or the metropolitan planning organizations for the Transportation Implementation Plan 

(TIP) and Long Range Transportation Plan must not exceed the motor vehicle emission budgets 

(MVEBs) as defined in this attainment demonstration. 

7.2 Highway Mobile Source VOC Insignificance 

Section 93.109(k) in the Transportation Conformity Rule Amendments for the new 8-hour ozone 

and fine particulate matter NAAQS addresses areas with insignificant motor vehicle emissions. 

The rule suggests that such a finding would be based on a number of factors, including the 

percentage of motor vehicle emissions in the context of the total SIP inventory, the current state 

of air quality as determined by monitoring data for that NAAQS, the absence of SIP motor 

vehicle control measures, and historical trends and future projections of the growth of motor 

vehicle emissions. Although there is a vehicle control measure in place in the Metrolina area, an 

inspection and maintenance program, the current program was established for additional 

reductions in NOx emissions. There are incidental VOC emission reductions as a result of this 

program (~ 8%), however it is not believed the reduction of VOC emissions resulted in 

decreased ozone levels. 

The NCDAQ has examined the sources of VOC emissions and their contribution to ozone 

formation in North Carolina. Due to the generally warm and moist climate of North Carolina, 

vegetation abounds in many forms, and forested lands naturally cover much of the state. The 

biogenic sector is the most abundant source of VOC emissions in North Carolina and accounts 

for approximately 90% of the total VOC emissions statewide. The overwhelming abundance of 

biogenic VOC emissions makes the majority of North Carolina a NOx limited environment for 

the formation of ozone. This holds true in the Metrolina area. 

Additionally, the NCDAQ has performed a number of modeling sensitivities to determine the 

impact of highway mobile source VOCs on ozone formation in the Metrolina area. The results 

of these sensitivities indicate no change in future ozone concentrations in the Metrolina area 

when highway mobile VOC emissions are significantly changed (e.g., 50% decrease). These 

sensitivities are discussed in more detail in Appendix F.3. 

The NCDAQ believes highway mobile VOCs are insignificant contributors to ozone formation 

in the Metrolina nonattainment area. Emission estimates indicate highway mobile VOC is a 

small percentage of the total VOC emissions inventory. Highway mobile VOC emissions are 

projected to decrease into the future, notwithstanding VMT increases. Emission sensitivity 

modeling indicates no change in future ozone concentrations when VOC emissions are 

significantly changed. For these reasons, the NCDAQ presented the VOC insignificance concept 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 70 

North Carolina Attainment Demonstration June 15, 2007 

to the transportation partners and all agreed through the interagency consultation that VOC 

emissions were insignificant. Therefore, the NCDAQ will not be setting MVEB for VOC for the 

North Carolina portion of the Metrolina nonattainment area. The NCDAQ will revisit the setting 

of MVEB for VOC if there is indication that the Metrolina area has become VOC sensitive for 

ozone formation. 

An affirmative insignificance finding from the USEPA only relieves the transportation partners 

from a regional emissions analysis for VOC emissions for this area and does not relieve them of 

the other transportation conformity requirements. The transportation partners will need to note 

the VOC insignificance finding (if found adequate and approved by the USEPA) in future 

conformity determinations. 

7.3 Motor Vehicle Emission Budgets 

As part of the consultation process on setting MVEBs, the NCDAQ sent out a request for 

comment on setting the geographic extent of the MVEBs to all of the transportation partners. A 

copy of the letter can be found in Appendix B. In the letter, the NCDAQ expressed its 

preference for setting county level budgets and some of the reasons why the NCDAQ believed 

county level budgets were appropriate. 

The NCDAQ received comments from several of the transportation partners regarding the 

geographic extent of the MVEBs. Some of the partners wanted county-by-county budgets; 

others wanted regional budgets. Copies of the letters received can be found in Appendix B. 

Upon careful consideration of all arguments, the NCDAQ decided to move forward with setting 

county level MVEBs. The NCDAQ believes that since mobile source NOx emissions play a 

significant role in the ozone formation in the Metrolina area, it is important that the large 

counties in the area meet the county level NOx MVEBs that closely represents the emissions that 

were modeled for the attainment demonstration. 

A requirement of RFP is that VOC motor vehicle emission budgets for transportation conformity 

need to be set for the RFP year 2008. Since the NCDAQ has determined that mobile source 

VOC emissions are insignificant to ozone formation in the Metrolina nonattainment area (see 

Appendix F.3), the 2008 RFP motor vehicle emission budgets are not required. 

The MVEBs will be set for the attainment year 2009. By the time the MVEBs are approved by 

the USEPA, the next transportation conformity regional emissions analysis should be for years 

2009 and beyond. Therefore, MVEBs will not be set for the baseline year 2002. 

Although the emissions are usually expressed in terms of tons per day, the MVEBs will be set in 

terms of kilograms (kg) per day. The reason for the change is because the MOBILE model 

generates the emissions factors in grams per mile. In past conformity exercises, there have been 

some issues with conversion to tons per day, as well as concerns with how the MVEBs were 

rounded to the hundredth place. Setting MVEBs in kilograms per day will avoid these issues in 

future conformity determinations. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 71 

North Carolina Attainment Demonstration June 15, 2007 

The mobile inputs used to develop the MVEBs were developed through interagency consultation 

with the transportation partners for this area. These inputs were consistent with what was used in 

the attainment demonstration modeling, and do not represent a significant change to the 

emissions. These changes include: 

• Time of day speeds and vehicle miles traveled for Iredell, Mecklenburg and Union 

Counties were used in response to comments. 

• Vehicle age distribution and vehicle mix were revised to reflect new data available, in 

response to comments. 

• Temperature, relative humidity and barometric pressure assumptions were developed 

using the average 2002 July meteorological data for the region. 

The table below shows the North Carolina counties with their highway mobile NOx emissions 

expressed in tons per day and the corresponding kilograms per day values for 2009. 

Table 7.3-1 Highway Mobile Source NOx Emissions Metrolina Nonattainment Area 

2009 County Tons/day Kg/day 

Cabarrus 8.57 7,788 

Gaston 9.48 8,602 

Iredell* 5.61 5,094 

Lincoln 3.65 3,317 

Mecklenburg 32.27 29,270 

Rowan 8.45 7,675 

Union 5.57 5,070 

Total 73.09 66,353 

* Iredell County emissions for nonattainment area only. 

The NCDAQ will set MVEB, for transportation conformity purposes, as county budgets within 

the Metrolina nonattainment area for 2009. Tables 7.3-2 below list out the NOx MVEBs in 

kilograms per day, for transportation conformity purposes, by county. Upon the USEPA’s 

affirmative adequacy finding for these county level sub-area MVEBs, these MVEBs will become 

the applicable MVEBs for each county. 
The Charlotte-Gastonia-Rock Hill, NC-SC 8-Hour Ozone 72 

North Carolina Attainment Demonstration June 15, 2007 

Table.7.3-2 County Level NOx MVEB for 2009 

County MVEB 

(Kilograms/day) 

Cabarrus 7,788 

Gaston 8,602 

Iredell* 5,094 

Lincoln 3,317 

Mecklenburg 29,270 

Rowan 7,675 

Union 5,070 

* Iredell County MVEB for nonattainment area only