Supplement to

Section 110(a)(1) Maintenance Plan 

for the 

1997 8-Hour Ozone Standard

For 

Greensboro/Winston-Salem/High Point 

1-Hour Ozone Maintenance Area

April 12, 2013

Prepared by:

North Carolina Department of Environment and Natural Resources

Division of Air Quality
PREFACE

This document serves as a supplement to the February 4, 2008 110(a)(1) Maintenance Plan for 

the Greensboro/Winston-Salem/High Point ozone maintenance area. This supplement serves as 

the technical support document to request relaxation of current summertime gasoline 

requirement of 7.8 pounds per square inch.
Greensboro/Winston-Salem/High Point Area i

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

INTRODUCTION

This document supplements the 110(a)(1) 1997 8-hour Ozone Standard Maintenance Plan for the 

Greensboro, Winston-Salem, and High Point 1-hour Ozone Maintenance Area (Triad area) that 

was submitted to the United States Environmental Protection Agency (USEPA) on April 13, 

2011. This supplement documents the revisions of the on-road mobile, non-road mobile, and 

area source emissions resulting from the proposed modification of the Reid Vapor Pressure 

(RVP) summertime gasoline requirement from 7.8 pounds per square inch (psi) to 9.0 psi. 

Section 211(h)(1) of the Clean Air Act specifies that during high ozone season, the gasoline 

volatility standard is a maximum of 9.0 psi for ozone attainment areas, and 7.8 psi for ozone 

nonattainment areas. The volatility standard is codified in 40 CFR 80.27(a)(2). 

The RVP is a federal control measure intended to lower air emissions of volatile organic 

compounds (VOC), a precursor to ozone formation. In the mid-to late- 1990s, the discovery that 

a significant amount of VOC emissions comes from natural sources began to change the 

understanding of the atmospheric chemistry, particularly in the southeastern United States. 

Statewide, natural sources account for 90 percent of total VOC emissions. Today, we know that 

controlling ozone throughout North Carolina and much of the southeast is more effectively done 

through emissions reductions of nitrogen oxides (NOx). With this scientific understanding in 

mind, the North Carolina Division of Air Quality (NCDAQ) is requesting the relaxation of the 

7.8 psi RVP requirement in the affected Triad counties. 

This supplement shows that North Carolina can implement the 9.0 psi gasoline without 

interfering with the attainment of the National Ambient Air Quality Standards (NAAQS). The 

NCDAQ’s analysis indicates that increasing the RVP from 7.8 psi to 9.0 psi does not negatively 

impact the redesignation and maintenance demonstration. Therefore, the NCDAQ requests the 

USEPA relax the 7.8 psi RVP requirement and specify 9.0 psi as the applicable gasoline 

volatility standard for the entire maintenance area year round. This action would provide

significant economic relief to North Carolina consumers and businesses as a result of reduced 

fuel costs.

In addition to the revisions to the RVP, there were also some minor revisions to the on-road 

mobile and area source emissions. In the original 110(a)(1) maintenance plan, the on-road 

mobile emissions in Appendix B.3, Table 4.3-1 were incorrect. The on-road mobile emissions 

were not generated with the latest version of the MOtor Vehicle Emissions Simulator (MOVES)

mobile model available at that time, which was MOVES2010a. For this supplement, the 

MOVES2010a was used to generate the on-road mobile emissions for all years – 2007, 2011, 

and 2018. For the area sources, the emissions estimate method used to calculate the underground 

tank breathing and emptying emissions was revised, in addition to the revision to the RVP, 
Greensboro/Winston-Salem/High Point Area ii

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

resulting in changes to the 2007 and 2011 VOC emissions in addition to the 2018 emissions. All 

of these changes are included in this supplement.
Greensboro/Winston-Salem/High Point Area iii

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

REVISED SECTIONS

Attached are the revisions to the 8-hour Ozone Standard 110(a)(1) Maintenance Plan for the 

Greensboro, Winston-Salem, and High Point 1-hour Ozone Maintenance Area. The RVP 

revisions are only applicable to the area, nonroad mobile and on-road mobile sources. To 

appropriately revise the original package, replace the Narrative, Appendix B.2, Appendix B.3 

and Appendix B.4.
Greensboro/Winston-Salem/High Point Area iv

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

EXECUTIVE SUMMARY

Introduction

Ozone is formed by a complex set of chemical reactions involving VOCs, NOx and to a lesser 

extent carbon monoxide (CO). These gases are generated by combustion processes, certain 

industrial processes and even by natural sources such as trees. Tailpipe emissions from on-road 

mobile sources (vehicles) are also significant sources. Even the emissions from such sources as 

boat engines, lawn mowers and construction equipment contribute to the formation of ozone. 

Ozone formation is promoted by strong sunlight, warm temperatures and light winds resulting in 

a problem only during the hot summer months.

The 1997 8-hour ozone National Ambient Air Quality Standard (NAAQS) is 0.08 parts per 

million (ppm). An exceedance of the 8-hour ozone NAAQS occurs when a monitor measures 

ozone above 0.084 ppm on average for an eight-hour period. A violation of this 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 

design value in the area. On March 27, 2008, the United States Environmental Protection 

Agency (USEPA) revised the 8-hour ozone NAAQS to 0.075 ppm (73 Federal Register 16436).

Greensboro/Winston-Salem/High Point Air Quality History

The Greensboro/Winston-Salem/High Point area (referred to as the Triad area) was designated as 

moderate nonattainment for the 1-hour ozone National Ambient Air Quality Standard in 

November 1991. In November 1993, this area was redesignated to attainment/maintenance for 

the 1-hour ozone standard.

In December 2002, the Triad area signed an Early Action Compact (EAC) with the North 

Carolina Department of Environment and Natural Resources and the USEPA for the 1997 8-hour 

ozone standard. The EAC gave the area an opportunity to develop local control strategies to 

meet the 1997 8-hour ozone standard earlier than required by the Clean Air Act. In turn, the 

USEPA agreed to defer the effective date of the nonattainment designation for the EAC areas. If 

an EAC area attained the 1997 8-hour ozone standard by December 31, 2007 and met all of its 

EAC milestones, the USEPA agreed to designate the area as attainment.

In April 2004, the USEPA deferred the effective date of the nonattainment designation of the 

Triad area for the 1997 8-hour ozone standard. The Triad EAC area met all of their milestones 

and attained the 1997 8-hour ozone standard by the December 2007 deadline. The USEPA 

designated the Triad area as attainment/unclassifiable in April 2008. 
Greensboro/Winston-Salem/High Point Area v

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

The Triad area continues to be in compliance with the 1997 8-hour ozone standard. As a result 

of continued improvement in air quality, the USEPA designated the area attainment of the more 

stringent 2008 8-hour ozone NAAQS. However, due to the extreme heat events that affected 

most of the country during a two week period in the summer of 2012, ozone monitors in the 

Triad area measured exceedances of the 2008 8-hour ozone NAAQS.

There are presently three monitors in the Triad area that are violating the 2008 8-hour ozone 

NAAQS based on preliminary 2010-2012 monitoring data. However, all monitors are measuring 

below the current NAAQS for carbon monoxide, fine particulate matter, sulfur dioxide and lead.

Section 110(a)(1) Maintenance Plan Requirements

Section 110(a)(1) of the Clean Air Act requires that each state adopt and submit to the USEPA a 

plan which provides for implementation, maintenance and enforcement of primary standards for 

all areas within the state. The USEPA stated that a 110(a)(1) maintenance plan is required for 

those areas that are designated as attainment/unclassifiable for the 1997 8-hour ozone standard 

and are designated as attainment for the 1-hour ozone standard with an approved maintenance 

plan. The Triad area meets these conditions; therefore, North Carolina is required to submit a 

110(a)(1) maintenance plan for the area. The requirements of the maintenance plan include an 

attainment emissions inventory, a maintenance demonstration with a future inventory year, a 

commitment to continue ambient air quality monitoring, a contingency plan to ensure that any 

violations of the 1997 8-hour ozone standard is promptly corrected and verification of a 

continued attainment tracking mechanism.

Section 110(l) of the Clean Air requires a demonstration that “a revision of an [implementation] 

plan would not interfere with any applicable requirement concerning attainment.” The NCDAQ 

conducted an emissions inventory evaluation for NOx and VOC to examine the rate of change in 

each pollutant in future years. The NCDAQ also completed an in-depth photochemical modeling 

exercise to examine the impact of these emissions changes on expected ozone levels. The results 

are summarized below in section 2.3.

Conclusion

The emissions inventory comparison between the 7.8 psi and 9.0 psi Reid Vapor Pressure (RVP) 

indicates that the estimated future year emissions are slightly higher for NOx and VOC. By 

2018, the effect of relaxing the RVP and other corrections results in an emissions increase of

0.16 tons NOx per day and 1.43 tons VOC per day from all emission sources. This is equivalent 

to a 0.28% and 1.34% increase in total man-made emissions of NOx and VOC, respectively. 

When biogenic VOC emissions from natural sources (117.15 tons per day using USEPA 

Mercury Air Toxics rule modeling) are added to the man-made emissions, the actual VOC 

emissions increase is only 0.64%. 
Greensboro/Winston-Salem/High Point Area vi

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Despite this small increase, the safety margin for the Triad area remains relatively unchanged. 

The differences in NOx and VOC emissions from 2007 through 2018 are -64.34 tons per day and 

-14.34 tons per day, respectively, which demonstrates a downward trend in the emissions. The 

NCDAQ believes these small increases are within the uncertainty of the emissions inventory 

analysis. 

The NCDAQ utilized the USEPA Mercury and Air Toxics (MATS) modeling platform to model 

changes in ozone and particle pollution. The MATS modeling platform was chosen because it is 

fairly recent, has undergone full model performance, and used the MOtor Vehicle Emissions 

Simulator (MOVES) mobile model to generate on-road mobile emissions. The analysis 

incorporated several layers of conservative estimates to determine the maximum impact of the 

RVP relaxation. This includes: (1) selecting the most populous county to represent other 

counties, (2) applying the maximum emissions increase for a given hour to the entire 

summertime period, (3) using the highest emissions increase for a given pollutant to represent 

VOC emissions, and (4) the liberal application of the grid masking. 

The change in ozone concentration at monitors in and near the Triad area caused by the change 

in RVP in the 2016 future year showed no change in ozone concentrations at any of the area 

monitors. Additionally, the planned retirement and conversion of coal-fired electric generating 

units at Buck, Dan River, and Riverbend to natural gas would easily offset NOx emissions 

changes due to the RVP relaxation and reduce ozone levels in the Triad area. A similar 

modeling analysis was conducted for fine particulate matter, and it also showed no potential 

interference. 

The NCDAQ concludes that relaxation of the Federal standard does not interfere with the 

attainment and maintenance of the NAAQS. The NCDAQ has developed a contingency plan 

based on a number of triggers and tracking mechanisms that will ensure that the Triad area 

continues to maintain the 1997 8-hour ozone NAAQS. Therefore, with this submission, the 

NCDAQ believes the requirements of the Section 110(a)(1) maintenance plan for the 1997 8-

hour ozone standard have been met.
Greensboro/Winston-Salem/High Point Area vii

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

TABLE OF CONTENTS

PREFACE....................................................................................................................................... ii

INTRODUCTION ........................................................................................................................... i

REVISED SECTIONS...................................................................................................................iii

EXECUTIVE SUMMARY ........................................................................................................... iv

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

1.1 WHAT IS TROPOSPHERIC OZONE............................................................................. 1-1

1.2 GREENSBORO/WINSTON-SALEM/HIGH POINT AIR QUALITY HISTORY ........ 1-1

1.3 CLEAN AIR ACT SECTION 110(a)(1) MAINTENANCE PLAN REQUIREMENTS. 1-3

1.4 CLEAN AIR ACT SECTION 110(l) DEMONSTRATION REQUIREMENTS ............ 1-4

2.0 MAINTENANCE PLAN................................................................................................. 2-1

2.1 EMISSION INVENTORIES ............................................................................................ 2-1

2.2 MAINTENANCE DEMONSTRATION.......................................................................... 2-4

2.3 CLEAN AIR ACT SECTION 110(l) DEMONSTRATION ............................................ 2-6

2.3.1 INTERFERENCE WITH OZONE NAAQS ................................................................. 2-6

2.3.2 INTERFERENCE WITH CO, PM, SO2, and NO2 NAAQS....................................... 2-20

2.4 AMBIENT AIR QUALITY MONITORING................................................................. 2-22

2.5 CONTINGENCY PLAN ................................................................................................ 2-26

2.5.1 Overview.................................................................................................................. 2-26

2.5.2 Primary and Secondary Triggers.............................................................................. 2-26

2.5.3 Action Resulting From Trigger Activation.............................................................. 2-27

2.6 VERIFICATION OF CONTINUED ATTAINMENT................................................... 2-28

2.7 CONCLUSION............................................................................................................... 2-29
Greensboro/Winston-Salem/High Point Area 1-1

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

1.0INTRODUCTION

1.1 WHAT IS TROPOSPHERIC OZONE

Ozone, a strong chemical oxidant, is the pollutant of main concern. It adversely impacts human 

health through effects on respiratory function and can also damage forests and crops. Ozone is 

not emitted directly by 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), the result of combustion processes, and reactive organic gases. Organic gases, 

also termed volatile organic compounds (VOCs), include many industrial solvents, toluene, 

xylene and hexane as well as the various hydrocarbons that are evaporated from the gasoline 

used by motor vehicles or emitted through the tailpipe following combustion. 

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 only from April 1 through October 31 as described in Title 40 of the Code of Federal 

Regulations Part 58 (40 CFR 58). 

In 1997, the USEPA revised the primary (health) and secondary (welfare) National Ambient Air 

Quality Standards (NAAQS) for ozone by establishing 8-hour standards. An exceedance of the 

8-hour ozone NAAQS occurs when a monitor measures ozone above 0.084 ppm on average for 

an 8-hour period. A violation of this 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. 

On March 26, 2008, the USEPA promulgated a new 8-hour ozone standard. The revised 

standard sets the annual fourth-highest daily maximum 8-hour ozone concentration (averaged 

over 3 years) to 0.075 ppm.

1.2 GREENSBORO/WINSTON-SALEM/HIGH POINT AIR QUALITY HISTORY

Since the 1977 amendments to the Clean Air Act, areas of the country that had not attained 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.
Greensboro/Winston-Salem/High Point Area 1-2

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

The Greensboro/Winston-Salem/High Point area (referred to as the Triad area) was designated 

by the USEPA as “moderate” nonattainment for the 1-hour ozone standard in November 1991. 

The nonattainment area included Davidson, Forsyth and Guilford Counties and a portion of 

Davie County (Figure 1.2-1). The design value was 0.151 ppm for the Triad area, based mainly 

on air quality data from the unusually severe summer of 1988. In November 1992, the State of 

North Carolina submitted a request to redesignate this area to maintenance status, based upon 

three years of clean air quality data (1990 through 1992). The State submitted supplemental 

information to the USEPA in June 1993, and the Triad area was redesignated to 

attainement/maintenance status on November 8, 1993. 

Figure 1.2-1 North Carolina 1-Hour Ozone Nonattainment Areas

For the 1997 8-hour ozone standard, the Triad area signed an Early Action Compact (EAC) with 

the North Carolina Department of Environment and Natural Resources and the USEPA. The 

EAC, signed in December 2002, gave areas the opportunity to develop local control strategies to 

meet the 1997 8-hour ozone NAAQS earlier than required by the Clean Air Act. In turn, the 

USEPA agreed to defer the effective date of the nonattainment designation for these areas. If an 

EAC area attained the 1997 8-hour ozone NAAQS by December 31, 2007 and met all of its EAC 

milestones, the USEPA agreed to designate the area as attainment.

In April 2004, the USEPA designated the Triad area as nonattainment for the 1997 8-hour ozone 

standard and deferred the effective date. The designated area included Alamance, Caswell, 

Davidson, Davie, Forsyth, Guilford, Randolph, and Rockingham Counties (Figure 1.2-2). The 

Triad EAC area met all of their EAC milestones and attained the 1997 8-hour ozone standard by 

North Carolina Ozone Nonattainment Areas

Forsyth Guilford

Rockingham

Lincoln

M ecklenburg

Row an

Davie

Chatham

Casw ell Person

Granville

W ake

DurhamFranklin

Johnston

Edgecom be

Pitt

Cunberland Union

Cabarrus

Gaston

Randolph

Stokes

Y adkin

North- ham pton

New Hanover

M adison

Buncom be

Y ancey

Alexander Caldw ell M artin

Duplin

Sw ain

Hayw ood

Cam den

Nash Orange

Alam ance

Davidson

Harnett

Cleveland

Anson

Richm ond

Robeson Bladen

Colum bus

Brunsw ick

Pender

Sam pson

Onslow

Jones

Carteret

Craven

Pam ilico

Hyde

Beaufort

W ashingtonTyrrell Dare

Greene

W ayne

W ilson

Ashe W arren

M cDow ell

Rutherford Polk

Henderson

Cherokee

Graham

Clay

M acon

Transylvania Jackson

Cataw ba Burke

W atauga

Alleghany

Surry

W ilkes

Iredell

Stanly

M ontgom ery M oore

Hoke

Scotland

Avery

Vance Halifax

Bertie

Hertiford

Gates

Chow an Perquim ons Pasquotank Currituck

Lee

M itchell

Lenoir

Ozone Nonattainment – Designated 1992

Ozone Nonattainment – Designated 1978

North Carolina Ozone Nonattainment Areas

Forsyth Guilford

Rockingham

Lincoln

M ecklenburg

Row an

Davie

Chatham

Casw ell Person

Granville

W ake

DurhamFranklin

Johnston

Edgecom be

Pitt

Cunberland Union

Cabarrus

Gaston

Randolph

Stokes

Y adkin

North- ham pton

New Hanover

M adison

Buncom be

Y ancey

Alexander Caldw ell M artin

Duplin

Sw ain

Hayw ood

Cam den

Nash Orange

Alam ance

Davidson

Harnett

Cleveland

Anson

Richm ond

Robeson Bladen

Colum bus

Brunsw ick

Pender

Sam pson

Onslow

Jones

Carteret

Craven

Pam ilico

Hyde

Beaufort

W ashingtonTyrrell Dare

Greene

W ayne

W ilson

Ashe W arren

M cDow ell

Rutherford Polk

Henderson

Cherokee

Graham

Clay

M acon

Transylvania Jackson

Cataw ba Burke

W atauga

Alleghany

Surry

W ilkes

Iredell

Stanly

M ontgom ery M oore

Hoke

Scotland

Avery

Vance Halifax

Bertie

Hertiford

Gates

Chow an Perquim ons Pasquotank Currituck

Lee

M itchell

Lenoir

Ozone Nonattainment – Designated 1992

Ozone Nonattainment – Designated 1978

Forsyth Guilford

Rockingham

Lincoln

M ecklenburg

Row an

Davie

Chatham

Casw ell Person

Granville

W ake

DurhamFranklin

Johnston

Edgecom be

Pitt

Cunberland Union

Cabarrus

Gaston

Randolph

Stokes

Y adkin

North- ham pton

New Hanover

M adison

Buncom be

Y ancey

Alexander Caldw ell M artin

Duplin

Sw ain

Hayw ood

Cam den

Nash Orange

Alam ance

Davidson

Harnett

Cleveland

Anson

Richm ond

Robeson Bladen

Colum bus

Brunsw ick

Pender

Sam pson

Onslow

Jones

Carteret

Craven

Pam ilico

Hyde

Beaufort

W ashingtonTyrrell Dare

Greene

W ayne

W ilson

Ashe W arren

M cDow ell

Rutherford Polk

Henderson

Cherokee

Graham

Clay

M acon

Transylvania Jackson

Cataw ba Burke

W atauga

Alleghany

Surry

W ilkes

Iredell

Stanly

M ontgom ery M oore

Hoke

Scotland

Avery

Vance Halifax

Bertie

Hertiford

Gates

Chow an Perquim ons Pasquotank Currituck

Lee

M itchell

Lenoir

Ozone Nonattainment – Designated 1992

Ozone Nonattainment – Designated 1978
Greensboro/Winston-Salem/High Point Area 1-3

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

December 2007. The USEPA designated the Triad area as attainment/unclassifiable in April 

2008.

Figure 1.2-2 North Carolina 8-Hour Ozone Nonattainment Areas in 2004

1.3 CLEAN AIR ACT SECTION 110(a)(1) MAINTENANCE PLAN REQUIREMENTS 

Section 110(a)(1) of the Clean Air Act requires that each state adopt and submit to the USEPA a 

plan which provides for implementation, maintenance and enforcement of primary standards for 

all areas within the state. The USEPA guidance (Appendix A) stated that the 110(a)(1) 

maintenance plan is required for those areas that are designated as attainment/unclassifiable for 

the 1997 8-hour ozone standard and are designated as attainment for the 1-hour ozone standard 

with an approved maintenance plan. Therefore, a 110(a)(1) maintenance plan is required for the 

Triad 1-hour ozone maintenance counties.

The requirements for the maintenance plan include the following:
Greensboro/Winston-Salem/High Point Area 1-4

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

 Attainment Emissions Inventory: The attainment emissions inventory should be based on 

actual “typical summer day” emissions of VOCs and NOx. The attainment inventory 

year may be one of any of the three years on which the 8-hour attainment designation was 

based.

 Maintenance Demonstration: The maintenance plan demonstrates how the area will 

remain in compliance with the 8-hour ozone standard for the 10-year period following the 

effective date of designation as attainment/unclassifiable. The future inventory year is 10 

years from the effective date of the attainment designation. The maintenance plan 

compares the emissions for the future inventory year to the attainment inventory year. If 

the future inventory year emissions do not exceed the attainment year emissions then 

maintenance is demonstrated.

 Ambient Air Quality Monitoring: The state should continue to operate air quality 

monitors in accordance with 40 CFR 58 to verify maintenance of the 1997 8-hour ozone 

standard in the area. Any modification to the ambient air monitoring network should be 

accomplished through close consultation with the USEPA Regional Office.

 Contingency Plan: The state must develop a contingency plan that, at a minimum, will 

ensure that any violation of the 1997 8-hour ozone NAAQS is promptly corrected.

 Verification of Continued Attainment: The submittal should indicate how the state will 

track the progress of the maintenance plan. States should develop interim emission 

projection year(s) to show a trend analysis for maintenance of the standard.

In the sections that follow, the North Carolina Division of Air Quality (NCDAQ) will provide 

the technical data necessary to show that the Greensboro/Winston-Salem/High Point area is 

expected to maintain the 1997 8-hour ozone standard and has met the requirements of the 

110(a)(1) maintenance plan.

1.4 CLEAN AIR ACT SECTION 110(l) DEMONSTRATION REQUIREMENTS

Section 110(l) of the Clean Air Act allows for the revision of an implementation plan:

 After reasonable notice and public hearing;

 After the USEPA Administrator has concluded that said implementation plan revision 

will not interfere with attainment and reasonable further progress in emissions reductions.
Greensboro/Winston-Salem/High Point Area 1-5

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

While all Triad area monitors are in attainment of the 1997 8-hour ozone NAAQS and 1-hour 

ozone NAAQS, three monitors are presently in violation of the 2008 8-hour ozone NAAQS. To 

fully satisfy the requirements of section 110(l), emissions inventory analysis with the proposed 

RVP change implemented is documented in Sections 2.1 and 2.2, which show reasonable further 

progress as defined in Section 175, Subpart 1. Additionally, a photochemical modeling exercise 

with updated emissions based on the proposed RVP relaxation in the affected counties was 

conducted, and the findings of this exercise are given in section 2.3.
Greensboro/Winston-Salem/High Point Area 2-1

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

2.0 MAINTENANCE PLAN

2.1 EMISSION INVENTORIES

The 110(a)(1) maintenance plan requires the development of an attainment inventory and a 

future year inventory for VOC and NOx emissions for those areas that were designated as 

attainment for the 1997 8-hour ozone standard and have an approved maintenance plan for the 1-

hour ozone standard. The Triad 1-hour maintenance area, consisting of Davidson, Forsyth and 

Guilford Counties and a part of Davie County, meet the conditions that require the 110(a)(1) 

maintenance plan. 

The attainment inventory year must be one of the three years on which the 8-hour ozone 

attainment designation was based. The USEPA designated the Triad area as attainment in April 

2008 based on the 2005 through 2007 design value. Therefore, the attainment inventory year 

may be 2005, 2006 or 2007. The NCDAQ chose 2007 as the attainment inventory year since an 

emissions inventory had already been developed for this year. The future inventory year is 10 

years from the effective date of the attainment designation. Since the Triad area was designated 

as attainment in 2008, the future inventory year selected was 2018. Finally, the USEPA 

guidance suggested developing an emission inventory for interim years to show a trend analysis. 

The Triad area is an EAC area and the NCDAQ had already submitted modeling demonstrating 

continued maintenance of the 1997 8-hour ozone standard for the years 2012 and 2017, therefore 

only one interim year emission inventory was developed. 

Since the USEPA’s Air Emissions Reporting Requirements (AERR) Rule requires a full 

emissions inventory to be submitted for 2011, the NCDAQ chose 2011 as the interim inventory 

year for this maintenance plan. This will allow the NCDAQ to compare the AERR inventory 

submittal to the estimates in this plan to ensure the area is on track to continue maintenance of 

the 1997 8-hour ozone standard.

As stated earlier, the Triad 1-hour ozone maintenance area consists of Davidson, Forsyth, and 

Guilford Counties and a portion of Davie County. For the purpose of this maintenance plan, an 

emission inventory for all of Davie County will be included.

The emissions inventories are comprised of four major types of sources: point, area, on-road

mobile and nonroad mobile. The projected emissions inventories have been estimated using 

projected rates of growth in population, traffic, economic activity, and other parameters. 

Naturally occurring, or biogenic, emissions are not included in the emissions inventory 

comparison, as these emissions are outside the State’s span of control.
Greensboro/Winston-Salem/High Point Area 2-2

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Point sources are those stationary sources that require an air permit to operate. In general, these 

sources have a potential to emit more than 5 tons per year of a criteria pollutant or its precursors 

from a single facility. The source emissions are tabulated from data collected by direct on-site 

measurements of emissions or mass balance calculations utilizing emission factors from the 

USEPA’s AP-42 or stack test results. There are usually several emission sources for each 

facility. Emission data is collected for each point source at a facility and the data is entered into 

an in-house database system. For the projected years’ inventory, point sources are adjusted by 

growth factors based on Standard Industrial Classification codes. The growth factors are 

generated using the USEPA’s Economic Growth Analysis System version 5.0 (E-GAS 5.0)

program or using growth patterns obtained from County Business Patterns. For detailed 

discussion on how the point sources emission inventory was developed, see Appendix B.1. A 

summary of the point source emissions are presented in Table 2.1-1. No changes to point 

sources emissions are required due to the relaxation of the RVP standard.

Table 2.1-1. Point Source Emissions (tons/day)

County NOx Emissions VOC Emissions

2007 2011 2018 2007 2011 2018

Davidson 2.73 2.89 3.20 3.83 3.85 3.94

Davie 0.06 0.06 0.06 0.19 0.19 0.19

Forsyth 2.22 2.18 2.15 4.03 4.03 4.03

Guilford 1.06 1.06 1.06 9.68 9.68 9.64

Triad Total 6.07 6.19 6.47 17.73 17.75 17.80

Area sources are those stationary sources whose emissions are relatively small but due to the 

large number of these sources, the collective emissions could be significant (i.e., dry cleaners, 

service stations, etc.). For area sources, emissions are estimated by multiplying an emission 

factor by some known indicator of collective activity such as production, number of employees, 

or population. These types of emissions are estimated on the county level. For the projected 

years’ inventory, area source emissions are changed by population growth, projected production 

growth, or when applicable, by E-GAS 5.0 growth factors or using growth patterns obtained 

from County Business Patterns. For detailed discussion on how the area source emission 

inventory was developed, see Appendix B.2. A summary of the area source emissions are 

presented in Table 2.1-2.
Greensboro/Winston-Salem/High Point Area 2-3

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.1-2. Area Source Emissions (tons/day)

Current 7.8 psi RVP 9.0 psi RVP

County NOx Emissions VOC Emissions VOC 

Emissions

2007 2011 2018 2007 2011 2018 2018

Davidson 0.62 0.60 0.55 6.83 7.10 6.91 7.03

Davie 0.21 0.22 0.23 4.68 5.03 6.51 6.51

Forsyth 0.99 1.04 1.11 16.53 18.63 22.31 22.62

Guilford 2.01 2.01 1.99 22.62 24.20 28.80 29.19

Triad Total 3.83 3.87 3.88 50.66 54.96 64.53 65.35

For on-road mobile sources, the USEPA’s MOVES mobile model is run to generate emissions. 

The MOVES model includes the road class vehicle miles traveled (VMT) as an input file and can 

directly output the estimated emissions. For the projected years’ inventories, the on-road mobile 

sources emissions are calculated by running the MOVES mobile model for the future year with 

the projected VMT to generate emissions that take into consideration expected Federal tailpipe 

standards, fleet turnover and new fuels. For detailed discussion on how the on-road mobile 

emission inventory was developed, see Appendix B.3. A summary of the on-road mobile source 

emissions are presented in Table 2.1-3.

Table 2.1-3. On-road Mobile Source Emissions (tons/day)

Current 7.8 psi RVP 9.0 psi RVP

NOx Emissions VOC Emissions

NOx

Emissions

VOC

Emissions

2007 2011 2018 2007 2011 2018 2018 2018

Davidson 15.08 11.70 4.24 6.60 5.03 2.42 4.27 2.48

Davie 5.03 3.50 2.08 1.85 1.41 0.90 2.08 0.90

Forsyth 27.73 17.26 10.84 12.05 6.75 4.23 10.88 4.34

Guilford 42.78 32.10 18.84 17.41 12.97 7.82 18.93 8.04

Triad Total 90.62 64.56 36.00 37.91 26.16 15.37 36.16 15.76

Net Change in Total Future Year Emissions Due to RVP Change 0.16 0.39

% Change in Total Future Year Emissions Due to RVP Change 0.45% 2.54%

The MOVES mobile model estimates a NOx increase of 0.16 tons/day and VOC increase of 0.39 

tons/day in future year 2018 due to RVP relaxation. The NCDAQ is uncertain of the technical 

reason behind the model predicted NOx emissions increases. A discussion of the dependency 

between NOx emissions changes and gasoline RVP was not found in the model documentation, 

and a specific correlation equation could not be identified. 
Greensboro/Winston-Salem/High Point Area 2-4

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Nonroad mobile sources are equipment that can move but do not use the roadways (i.e., lawn 

mowers, construction equipment, railroad locomotives, aircraft). The emissions from this 

category are calculated using the USEPA’s NONROAD2008a nonroad model, with the 

exception of the railroad locomotives and aircraft engine. The railroad locomotive and aircraft 

engine emissions are estimated by taking an activity and multiplying it by an emission factor. 

These emissions are also estimated at the county level. For the projected years’ inventories, the 

emissions are estimated using the USEPA’s NONROAD2008a nonroad model, E-GAS 5.0 

growth factors or projected landing and takeoff data for aircraft. A complete description of how 

these inventories were developed is discussed in detail in Appendix B.4. A summary of the 

nonroad mobile source emissions are presented in Table 2.1-4. The relaxation of the RVP 

standard only affects VOC emissions from nonroad mobile sources as shown in the table below. 

Table 2.1-4. Nonroad Mobile Source Emissions (tons/day)

Current 7.8 psi RVP 9.0 psi RVP

NOx Emissions VOC Emissions

NOx

Emissions

VOC

Emissions

2007 2011 2018 2007 2011 2018 2018 2018

Davidson 3.56 2.75 1.89 1.97 1.52 1.02 1.89 1.05

Davie 0.78 0.63 0.38 1.32 1.16 0.83 0.38 0.83

Forsyth 4.94 3.99 2.40 3.79 2.93 2.12 2.40 2.19

Guilford 11.83 9.59 6.11 8.33 6.50 4.84 6.11 4.96

Triad 

Total

21.11 16.96 10.78 15.41 12.11 8.81 10.78 9.03

2.2 MAINTENANCE DEMONSTRATION

Maintenance is demonstrated when the future year’s total man-made emissions are less than the 

2007 attainment inventory emissions. The 2018 values include the change to the RVP from 

7.8 psi to 9.0 psi. Table 2.2-1 summarizes the total man-made emissions for the Triad 

maintenance area. The RVP change slightly increases the on-road mobile future year (2018) 

NOx emissions by 0.16 tons/day and VOC emissions by 0.39 tons/day based on the MOVES 

model (see Table 2.1-3). For the nonroad mobile sector, there is no change to NOx emissions 

due to the RVP change; however, the VOC emissions increase by 0.22 tons/day. Collectively, 

the total future year man-made NOx and VOC emissions increase by 0.16 tons/day and 

1.43 tons/day, respectively. This is equivalent to a 0.28% and 1.34% increase in total man-made

NOx and VOC emissions, respectively. When biogenic VOC emissions from natural sources 

(117.15 tons/day using USEPA Mercury Air Toxics rule modeling) are added to the man-made 

emissions, actual VOC emissions increase is only 0.64%. 
Greensboro/Winston-Salem/High Point Area 2-5

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.2-1. Total Man-Made Emissions (tons/day) for the Triad Area

County

NOx Emissions VOC Emissions

Current 7.8 psi RVP 9.0 psi 

RVP Current 7.8 psi RVP 9.0 psi RVP

2007 2011 2018 2018 2007 2011 2018 2018

Davidson 21.99 17.94 9.88 9.91 19.31 17.60 14.29 14.50

Davie 6.08 4.41 2.75 2.75 8.04 7.79 8.43 8.43

Forsyth 35.88 24.47 16.50 16.54 36.62 32.63 32.69 33.18

Guilford 57.68 44.76 28.00 28.09 58.31 53.71 51.10 51.83

Triad Total 121.63 91.58 57.13 57.29 122.28 111.73 106.51 107.94

Table 2.2-2 summarizes the NOx and VOC emissions for the entire Triad maintenance area and 

the difference between the attainment and future inventory year. The difference in total manmade NOx emissions from 2007 to 2018 due to the RVP relaxation is a slight increase of -64.50 

tons/day to -64.34 tons/day. Similarly, the difference in VOC emissions from 2007 to 2018 due 

to the RVP relaxation is an increase from -15.20 tons/day to -14.34 tons/day. Since the future 

inventory emissions are less than the attainment inventory emissions, continued maintenance of 

the 1997 8-hour ozone standard in the Triad maintenance area is expected.

Table 2.2-2. Maintenance Demonstration for the Triad Area

Year NOx TPD VOC TPD

2007 121.63 122.28

2011 91.58 111.73

2018 57.29 107.94

Difference from 2007 to 2018 -64.34 -14.34

The difference between the attainment level of emissions from all sources and the projected level 

of emissions from all sources in the maintenance area is considered the “safety margin”. The 

safety margin for each projected year is listed below in Table 2.2-3. As seen in Table 2.2-3, not 

only does the future inventory year demonstrate maintenance of the 1997 8-hour ozone standard, 

the interim inventory year demonstrates a continued trend downward of the emissions. This is 

occurring despite the small increase in 2018 total man-made NOx and VOC emissions due to the 

relaxation of the RVP shown earlier in Table 2.2-1.

Table 2.2-3. Safety Margins for the Triad Area

Year NOx TPD VOC TPD

2007 N/A N/A

2011 -30.05 -10.55

2018 -64.34 -14.34
Greensboro/Winston-Salem/High Point Area 2-6

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.2-1 showed that there is a slight increase in future year NOx and VOC emissions due to 

the relaxation of the RVP, but the relative impact of this increase on the safety margin does not 

alter the downward trend in overall emissions between 2007 and 2018 (see Table 2.2-3). The

NCDAQ does not believe the decline in future year emissions is inconsistent with the 

maintenance demonstration for reasons cited below. 

First, the 2018 emissions are still below the baseline emissions for 2007. Second, the Triad area 

is considered a NOx limited area with respect to ozone formation. This means there are 

significantly more VOC emissions in the atmosphere from natural sources and that reductions in 

man-made VOC emissions, which is the primary purpose of the RVP standard, will not result in 

reductions in ozone formation. Third, the NCDAQ performed a photochemical modeling 

exercise to examine the impact of NOx and VOC emissions increase on ambient ozone 

concentrations. The analysis clearly demonstrates that the slight increase in emissions will result 

in no change to future year ozone concentrations and the potential to interfere with the 

attainment of the 1997 and 2008 8-hour ozone standards is not present (see Section 2.3.1). 

Lastly, the NCDAQ believes that voluntary measures occurring in the Triad region will further 

reduce NOx emissions in the Triad area (see Section 2.3.1). Each of these reasons demonstrates 

that despite the recent violations of the 2008 8-hour ozone standard, the current Federal RVP 

standard is not an effective control strategy to address ozone attainment status in the Triad area. 

A discussion of the RVP relaxation interference with other NAAQS is provided in Section 2.3.2. 

2.3 CLEAN AIR ACT SECTION 110(l) DEMONSTRATION

Relaxation of the Federal gasoline standard requires a demonstration that associated emissions 

increases will not interfere with the attainment of other NAAQS. This section shows that the 

RVP relaxation will not impact compliance with ozone, carbon monoxide (CO), nitrogen dioxide 

(NO2), sulfur dioxide (SO2), and particulate matter (PM) NAAQS.

2.3.1 INTERFERENCE WITH OZONE NAAQS

Currently, all ozone monitors in the Triad area are attaining the 1997 8-hour ozone standard, and 

all but three ozone monitors are attaining the 2008 8-hour ozone standard. The violations 

occurred during the summer of 2012 due to extreme heat episodes that affected most of the 

country in a relatively short period of time.

The NCDAQ has investigated potential contemporaneous, surplus, compensating/equivalent 

emissions reductions, and has identified current and future activities that would compensate for 

the slight increase in NOx and VOC emissions discussed earlier. However, due to restrictions 

set forth requiring emission reduction projects to be located in maintenance areas only, the 
Greensboro/Winston-Salem/High Point Area 2-7

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

NCDAQ is unable to select projects in adjacent counties that affect air quality in the Triad area. 

For example, the Triad area has implemented several large scale renewable energy and energy 

efficiency projects which result in direct emissions reductions at nearby coal-fired electric 

generating units (EGUs). These projects cannot be used to offset emissions increase because the 

affected EGUs are not located in the Triad area. In addition, the planned shutdown of several

coal-fired EGUs by April 2013 cannot be used to compensate for the RVP related emissions 

increases, despite being located within close proximity to the Triad area. The Buck Plant is 

located about a quarter-mile from the Davidson County border. Other nearby EGUs that will 

retire are Riverbend, which is about 37 miles from Davie County and Dan River, which is about 

16.5 miles from the Guilford County line. 

Photochemical Modeling Demonstration

The NCDAQ performed an air quality modeling exercise to show that the relaxation of current 

Federal volatility regulations in the Triad maintenance area is not necessary to maintain or show 

reasonable further progress towards maintaining or attaining the ozone NAAQS. Specifically, 

the relaxation of the current RVP gasoline standard of 7.8 psi to 9.0 psi in Davidson, Davie, 

Forsyth, and Guilford Counties will have little to no impact on ambient concentrations of ozone. 

In addition to modeling the RVP changes, the NCDAQ also modeled the shutdown of nearby 

EGUs to show that the removal of the EGUs offsets the slight increase in emissions due to 

relaxation in gasoline RVP.

The NCDAQ utilized the USEPA Mercury and Air Toxics (MATS) modeling platform to model 

changes in ozone and particle pollution. The MATS modeling platform was chosen because it is 

fairly recent, has undergone full model performance, and used the MOVES mobile model to 

generate on-road mobile emissions. More information on the MATS modeling can be found at 

http://www.epa.gov/mats/actions.html. Both the 2005 base year and the 2016 future year were 

used in the modeling. 2016 was chosen as the future year because it is the latest MATS model 

data available. Tables 2.3-1 – 2.3-6 provide a summary of annual NOx, VOC, and SO2 

emissions in Guilford, Forsyth, Davie, and Davidson Counties where the RVP relaxation is 

proposed, as well as the greater Triad MSA including Buck Steam Station in Rowan County. 
Greensboro/Winston-Salem/High Point Area 2-8

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-1 2005 Annual NOx Emissions for the Triad Area used in the MATS Modeling

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 4516 779 202 194 0 380 6071

Caswell 733 75 137 0 0 47 992

Davidson 4973 776 710 829 0 366 7654

Davie 1829 241 25 14 0 86 2194

Forsyth 9122 1554 189 1734 0 618 13217

Guilford 13105 3410 676 3532 0 960 21683

Randolph 4574 770 140 2531 0 378 8393

Rockingham 2722 395 381 538 1621 243 5901

Rowan(Buck only) 2254

Stokes 1241 161 124 2 20422 84 22033

Surry 3442 436 0 1102 0 231 5212

Yadkin 1975 212 0 5 0 91 2282

4 County RVP Relax 

Area Total

(shown in bold) 29028 5980 1601 6109 0 2030 44749

Triad MSA plus Buck 48231 8808 2584 10481 24297 3485 97886

* Aircraft, locomotive, and marine equipment

Table 2.3-2. 2016 Annual NOx Emissions for the Triad Area used in the MATS modeling 

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 2143 361 156 73 371 3104

Caswell 315 42 89 0 45 491

Davidson 2437 333 450 847 350 4417

Davie 723 125 20 0 83 951

Forsyth 5700 764 134 1888 601 9087

Guilford 7300 1706 518 432 932 10889

Randolph 1649 323 101 35 363 2472

Rockingham 840 176 248 2192 1665 233 5354

Rowan (Buck only) 1597

Stokes 648 88 97 1 4970 80 5885

Surry 1371 204 0 123 222 1920

Yadkin 912 115 0 0 87 1115

4 County RVP Relax 

Area Total

(shown in bold) 16161 2927 1122 3167 0 1966 25344

Triad MSA plus Buck 24039 4238 1813 5591 8232 3369 47282

* Aircraft, locomotive, and marine equipment
Greensboro/Winston-Salem/High Point Area 2-9

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-3. 2005 Annual VOC Emissions for the Triad Area used in the MATS modeling

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 1870 819 9 194 0 3436 6327

Caswell 343 72 5 0 0 405 825

Davidson 1704 672 29 829 0 3124 6359

Davie 368 410 1 14 0 904 1698

Forsyth 3660 1281 8 1734 0 5141 11824

Guilford 4843 2772 29 3532 0 24763 35939

Randolph 1882 632 6 2531 0 3450 8502

Rockingham 1205 451 14 538 7 2215 4431

Rowan (Buck only) 22

Stokes 705 269 5 2 169 793 1943

Surry 1385 481 0 1102 0 1805 4773

Yadkin 688 148 0 5 0 686 1526

4 County RVP Relax 

Area Total

(shown in bold) 10575 5135 67 6109 0 33933 55819

Triad MSA plus Buck 18653 8007 106 10481 199 46722 84169

* Aircraft, locomotive, and marine equipment

Table 2.3-4. 2016 Annual VOC Emissions for the Triad Area used in the MATS modeling

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 1001 425 8 193 3266 4894

Caswell 170 38 3 0 356 567

Davidson 967 337 22 819 2775 4920

Davie 148 281 1 14 813 1257

Forsyth 3411 655 7 1381 4714 10167

Guilford 3328 1453 27 3470 24173 32451

Randolph 738 330 5 2529 3190 6792

Rockingham 352 268 9 537 27 2021 3215

Rowan (Buck only) 42

Stokes 409 184 5 2 182 696 1478

Surry 526 271 0 871 1622 3290

Yadkin 355 76 0 5 595 1031

4 County RVP Relax 

Area Total

(shown in bold) 7854 2725 57 5685 0 32474 48796

Triad MSA plus Buck 11403 4319 88 9822 251 44221 70105

* Aircraft, locomotive, and marine equipment
Greensboro/Winston-Salem/High Point Area 2-10

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-5. 2005 Annual SO2 Emissions for the Triad Area used in the MATS modeling

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 102 67 12 73 0 305 558

Caswell 15 9 9 0 0 94 126

Davidson 119 61 42 245 0 359 827

Davie 45 24 1 0 0 102 172

Forsyth 217 152 11 4108 0 882 5371

Guilford 316 340 39 677 0 947 2320

Randolph 101 60 8 23 0 372 565

Rockingham 59 34 24 835 4253 309 5514

Rowan (Buck only) 92 52 36 1462 9583 300 11525

Stokes 24 18 7 0 96823 209 97081

Surry 75 37 0 104 0 234 450

Yadkin 43 22 0 0 0 221 286

4 County RVP Relax 

Area Total

(shown in bold) 698 577 94 5030 0 2290 8689

Triad MSA plus Buck 1117 824 154 6065 110659 4033 122852

* Aircraft, locomotive, and marine equipment

Table 2.3-6. 2016 Annual SO2 Emissions for the Triad Area used in the MATS modeling

(tons/yr)

On-road

NonroadNon-road 

ALM* Point EGU

Point NonEGU Area Total

Alamance 13 1.1 0.1 73 0 304 392

Caswell 2 0.1 0.0 0 0 94 96

Davidson 18 1.0 0.2 245 0 358 622

Davie 5 0.3 0.0 0 0 102 107

Forsyth 38 1.9 0.0 3835 0 882 4757

Guilford 55 4.2 0.2 679 0 946 1685

Randolph 10 1.0 0.0 23 0 372 406

Rockingham 6 0.5 0.1 45 9211 308 9570

Rowan (Buck only) 10 0.8 0.2 1462 10761 300 12534

Stokes 4 0.2 0.0 0 8731 209 8944

Surry 8 0.6 0.0 104 0 233 345

Yadkin 5 0.2 0.0 0 0 221 226

4 County RVP Relax 

Area Total 116 7 0 4758 0 2287 7170

Triad MSA plus Buck 164 11 1 5003 28704 4028 37910

* Aircraft, locomotive, and marine equipment
Greensboro/Winston-Salem/High Point Area 2-11

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

The USEPA MATS modeling used a national 36 kilometer (km) domain and an eastern US 

12km domain. The NCDAQ modeling was performed using the 12km modeling domain. The 

USEPA is currently using 12km modeling to address the impacts of the proposed Tier 3 Motor 

Vehicle and Emissions Standards. Given that the USEPA is using the 12km modeling for Tier 

3, NCDAQ feels comfortable in using the 12km modeling to estimate the impacts of the change 

in summertime RVP to 9.0 psi. The Eastern modeling region (i.e., Eastern modeling domain) 

extends from Texas northward to North Dakota and eastward to the East Coast. The Eastern 

modeling domain was nested within a coarse grid, 36 x 36 km modeling domain which covers 

the lower 48 states and adjacent portions of Canada and Mexico. The 36 km and 12km modeling 

domains extend vertically from the surface to 100 millibars (approximately 15 km) using a 

sigma-pressure coordinate system. Predictions from the 36 km Continental U.S. (CONUS) 

domain were used to provide initial and boundary concentrations for simulations in the 12 km 

domain. The 36 km and 12 km modeling domains are shown in Figure 2.3-1. Table 2.3-7

provides geographic specifications for these domains.

Figure 2.3-1 Map of the CMAQ photochemical modeling domains. 

(The black outer box denotes the 36 km national modeling domain; the red inner box is the 12 

km western U.S. grid; and the blue inner box is the 12 km eastern U.S. grid.)
Greensboro/Winston-Salem/High Point Area 2-12

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-7. Geographic Elements of Domains used in Photochemical Modeling

Photochemical Modeling Configuration

National Grid Eastern US Fine Grid

Map Projection Lambert Conformal Projection

Grid Resolution 36km 12km

Coordinate Center 97 deg W, 40 deg N

True Latitudes 33 deg N and 45 deg N

Dimensions 148 x 112 x 14 279 x 240 x 14

Vertical Extent 14 Layers: Surface to 100 millibar level

As discussed earlier in Section 2.1, the NCDAQ used the MOVES mobile model to compute 

hourly changes in on-road mobile emissions with RVP settings of 7.8 psi and 9.0 psi. For the 

photochemical modeling evaluation, Guilford County was selected to represent the “highest” 

level of emissions increase expected because it has the greatest population of vehicles within the

Triad maintenance area. Table 2.3-8 summarizes the emissions changes obtained from the 

MOVES model for each pollutant that contributes to ozone formation. Table 2.3-9 shows the 

ratios applied to the species within the CMAQ mobile emissions inputs. 

Table 2.3-8. MOVES 2018 Total Emissions Changes from 7.8 psi to 9.0 psi RVP for 

Guilford County

Pollutant Max % increase Average % increase

Acetaldehyde 0.75% 0.41%

Benzene 0.00% -2.76%

Carbon Monoxide (CO) 2.09% 1.63%

Ethanol 0.00% 0.00%

Formaldehyde 0.00% -1.01%

Hexane 9.20% 2.59%

Methane (CH4) 0.41% 0.20%

Nitrogen Dioxide (NO2) 0.33% 0.19%

Nitrogen Oxide (NO) 0.61% 0.38%

Nitrous Acid (HONO) 0.57% 0.37%

Non-Methane Hydrocarbons 6.95% 1.96%

Oxides of Nitrogen (NOx) 0.57% 0.37%

Styrene 0.89% 0.67%

Toluene 7.67% 2.21%

Total Gaseous Hydrocarbons 6.55% 1.81%

Volatile Organic Compounds (VOC) 7.01% 1.97%

Xylene 8.10% 2.33%
Greensboro/Winston-Salem/High Point Area 2-13

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-9. Ratios applied to CMAQ Mobile Emissions within Davidson, Davie, Forsyth, and 

Guilford Counties

CMAQ Emissions Species Ratio applied

NO 1.0062

NO2 1.0034

CO 1.0209

HONO 1.0057

ALD2 1.0075

CH4 1.0041

Benzene 0.97

FORM 0.998

PAR 1.07

UNR 1.07

ALDX 1.07

ETH 1.07

IOLE 1.07

ISOP 1.07

NVOL 1.07

OLE 1.07

TERP 1.07

UNK 1.07

Typically, the next step is to run SMOKE using the MOVES output. However, NCDAQ is 

unable to run the version of SMOKE used in the MATS modeling. As an alternative, for each 

pollutant, the average and maximum increase at any hour was calculated (see Table 2.3-8). In 

order to generate very conservative estimates of the impacts of the RVP relaxation, the 

maximum percent increase was applied to the mobile emissions for all hours of the June 1st to 

September 15th summertime RVP period. The adjustments were applied to both the 2005 and 

2016 emissions in Guilford, Forsyth, Davie, and Davidson Counties where the RVP relaxation is 

proposed. 

These adjustments were applied to the grid cells covering the four counties. The array of grid 

cells (i.e., grid cell mask) where the RVP emissions changes were applied is shown in Figure 

2.3-2. A grid cell was included in the grid cell mask if as little as 20% of the cell area includes 

one or more of the counties where the RVP relaxation is proposed. The grid cell mask includes 

42 grid cells with an area of 6,048 km2. A typical application of the mask would include 32 grid 
Greensboro/Winston-Salem/High Point Area 2-14

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

cells with an area of 4,608 km2. By comparison, the total area of the four counties is 4,935 km2. 

The 20% threshold grid cell mask used in the modeling will adjust the mobile emissions in a 

larger area than the actual area of the four counties and will lead to conservative modeling 

results.

Figure 2.3-2 Area Mask for Emissions Adjustments Due to Changes in Gasoline RVP

In summary, several layers of conservative estimates were used to determine the maximum 

impact of RVP relaxation. This includes: (1) selecting the most populous county to represent 

other counties, (2) applying the maximum emissions increase for a given hour to the entire 

summertime period, (3) using the highest emissions increase for a given pollutant to represent 

VOC emissions, and (4) the liberal application of the grid masking. 

The NCDAQ used the Community Multiscale Air Quality Modeling System (CMAQ, v.4.71) to 

perform the air quality runs. A total of six runs were made from March 20 to September 30, 

2005. The September 30th model completion date is 2 weeks beyond the RVP period and is well 

beyond the time when the changes in the gasoline RVP would potentially impact model 

predictions. In addition, the month of October contained no days that would impact the ozone 

relative response factors. A total of three runs were made using the 2005 emissions. The first 

run used the default 2005 MATS emissions (BASE05). The second run adjusted the mobile 

emissions due to the change in RVP from 7.8 psi to 9.0 psi during the June 1st to September 15th
Greensboro/Winston-Salem/High Point Area 2-15

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

RVP period (RVP05). The final run simulated the gasoline RVP change along with the switch of 

coal-fired EGUs to combustion turbines at Buck, Dan River, and Riverbend (RVPPT05). Actual 

and projected annual emissions for the three plants are shown in Table 2.3-10 for NOx and Table 

2.3-11 for SO2. Conservatively, emissions at these coal-fired plants were reduced by 85% for 

NOx and 100% for SO2 to simulate the switch to natural gas turbines. Actual NOx reductions 

are closer to 95% at Buck and Dan River, and 100% at Riverbend. (Note that since the 

completion of the modeling, Riverbend is now slated to be shut down completely instead of 

converted to natural gas.)

Table 2.3-10. Actual and Projected NOx Emissions for Buck, Dan River, and Riverbend (tons/yr)

Buck Dan River Riverbend

2005 2195 1542 2542

2006 2146 2276 2270

2007 1660 1535 2243

2014* 111 111 0

2015* 101 107 0

2016* 89 83 0

* Projected emissions

Table 2.3-11. Actual and Projected SO2 Emissions for Buck, Dan River, and Riverbend

(tons/yr)

Buck Dan River Riverbend

2005 9603 4272 13990

2006 9584 7086 15181

2007 10285 7693 15940

2014* 9 9 0

2015* 8 9 0

2016* 7 7 0

* Projected emissions

The 2016 model runs were run in a similar fashion as the 2005 runs. The first run used the 

default 2016 MATS emissions (BASE16). The second run adjusted the mobile emissions due to 

the change in RVP from 7.8 to 9.0 psi during the June 1st to September 15th RVP period 

(RVP16). The final run simulated the gasoline RVP change along with the removal of controlled 

coal fired EGUs at Buck, Dan River, and Riverbend (RVPPT16). The MATS 2016 emissions 

incorrectly contain controlled coal-fired EGUs at these plants. The coal fired EGUs at Dan River 

were retired in 2012, and the units at Buck and Riverbend are scheduled to be retired in April 

2013. For a full list of the runs see Table 2.3-12.
Greensboro/Winston-Salem/High Point Area 2-16

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-12. NCDAQ Model Runs

Model Run Emissions 

Year

Summary

Base05 2005 Default 2005 MATS emissions

RVP05 2005 2005 Emissions adjusted in the RVP counties during June 1st and Sep 

15th

RVPPT05 2005 2005 RVP adjustments with Buck, Dan River, Riverbend -85% NOx, -

100% SO2

Base16 2016 Default 2016 MATS emissions

RVP16 2016 2016 Emissions adjusted in the RVP counties June 1st and Sep 15th

RVPPT16 2016 2016 RVP adjustments with coal-fired EGUs at Buck, Dan River, 

Riverbend removed -100% NOx, -100% SO2

For the 2005 and 2016 model runs, the 2005 monitored design values are set as the ‘base’ ozone 

value. The Model Attainment Test Software is used to compute relative reduction factors 

(RRFs) for each of the sensitivity runs at the area monitors. The 2005 sensitivity runs are 

compared to the Base05 run, and the 2016 sensitivity runs are compared to the Base16 run. RRF 

values of 1.0005 or less would indicate less than a 0.05 ppb rise within the base year or future 

year modeling.

The modeling shows insignificant changes in ozone levels for both 2005 and 2016 due to 

relaxation of the RVP standard. The change in ozone for monitors in and near the Triad area 

generated by the change in RVP in the 2005 base year is shown in Table 2.3-13. There is no

appreciable change in ozone concentrations due to the increase in gasoline RVP. When the 

conversion of the coal-fired EGUs to natural gas is factored in at the three power plants 

(RVPPT05 run, Table 2.3-14), the ozone levels decrease between 0.1 and 0.6 ppb. This 

indicates that the conversion of Buck, Dan River, and Riverbend to natural gas will easily offset 

any slight increase in NOx due to the relaxation of gasoline RVP. 
Greensboro/Winston-Salem/High Point Area 2-17

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-13. Change in Ozone Concentrations and RRFs in the 2005 Base Year Modeling 

with Summertime RVP change to 9.0 psi

Monitor ID County

Base05 

Ozone 

Design 

Value1

(ppb)

RVP05 

Ozone 

Design 

Value2

(ppb) RRF

Change from 

Base05 to 

RVP05 (ppb)

37-033-0001 Caswell 76.3 76.3 1.0002 0.0

37-059-0002 Davie 81.3 81.3 1.0002 0.0

37-067-0028 Forsyth 78.0 78.0 1.0004 0.0

37-067-0030 Forsyth 73.0 73.0 1.0003 0.0

37-067-1008 Forsyth 76.0 76.0 1.0004 0.0

37-067-0027 Forsyth 80.0 80.0 1.0004 0.0

37-081-0011 Guilford 77.0 77.0 1.0005 0.0

37-081-0013 Guilford 82.0 82.0 1.0005 0.0

37-157-0099 Rockingham 77.0 77.0 1.0003 0.0

37-159-0022 Rowan 86.7 86.7 1.0002 0.0

37-159-0021 Rowan 86.7 86.7 1.0001 0.0

1 Default 2005 MATS concentrations

2

2005 concentrations with summertime RVP changed to 9.0 psi

Table 2.3-14 Change in Ozone in the 2005 Base Year Modeling with Summertime RVP 

changed to 9.0 psi and Coal-Fired EGU Emissions Reduced by 85%

Monitor ID County

Base05 

Ozone 

Design 

Value1

(ppb)

RVPPT05 

Ozone 

Design 

Value2

(ppb) RRF

Change from 

Base05 to 

RVPPT05 

(ppb)

37-033-0001 Caswell 76.3 76.2 0.9987 -0.1

37-059-0002 Davie 81.3 80.9 0.9953 -0.4

37-067-0028 Forsyth 78.0 77.9 0.9995 -0.1

37-067-0030 Forsyth 73.0 72.9 0.9997 -0.1

37-067-1008 Forsyth 76.0 75.9 0.9996 -0.1

37-067-0027 Forsyth 80.0 79.8 0.9987 -0.2

37-081-0011 Guilford 77.0 76.9 0.9993 -0.1

37-081-0013 Guilford 82.0 81.9 0.9993 -0.1

37-157-0099 Rockingham 77.0 76.9 0.9995 -0.1

37-159-0022 Rowan 86.7 86.1 0.9939 -0.6

37-159-0021 Rowan 86.7 86.2 0.9952 -0.5

1 Default 2005 MATS concentrations

2

2005 concentrations with summertime RVP changed to 9.0 psi and coal-fired EGU emissions reduced by 

85%
Greensboro/Winston-Salem/High Point Area 2-18

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

The change in ozone concentration at monitors in and near the Triad area caused by the 

relaxation in gasoline RVP in the 2016 future year is shown in Table 2.3-15 (RVP16 run). 

Again, there is no appreciable change in ozone concentrations at any of the area monitors. The 

RVPPT16 run removes controlled coal-fired EGUs at Buck, Dan River, and Riverbend. The 

maximum change in ozone in the RVPPT16 run is a decrease of 0.1 ppb (see Table 2.3-16). The 

shutdown and conversion of the coal fired EGUs to natural gas at Buck, Dan River, and 

Riverbend to natural gas will easily offset any slight increase in NOx due to the relaxation in 

gasoline RVP. 

Table 2.3-15 Change in Ozone Concentrations and RRFs in the 2016 Future Year

Modeling with Summertime RVP changed to 9.0 psi

Monitor ID County

Base16 Ozone 

Design Value1

(ppb)

RVP16 Ozone 

Design Value2

(ppb) RRF

Change from 

Base16 to 

RVP16 (ppb)

37-033-0001 Caswell 76.3 76.3 0.9997 0.0

37-059-0002 Davie 81.3 81.3 0.9988 0.0

37-067-0022 Forsyth 78.0 78.0 1.0001 0.0

37-067-0028 Forsyth 73.0 73.0 1.0002 0.0

37-067-0030 Forsyth 76.0 76.0 1.0001 0.0

37-067-1008 Forsyth 80.0 80.0 1.0001 0.0

37-081-0011 Guilford 77.0 77.0 1.0001 0.0

37-081-0013 Guilford 82.0 82.0 1.0001 0.0

37-157-0099 Rockingham 77.0 77.0 1.0000 0.0

37-159-0021 Rowan 86.7 86.7 0.9988 0.0

37-159-0022 Rowan 86.7 86.7 0.9989 0.0

1 Default 2016 MATS concentrations

2

2016 concentrations with summertime RVP changed to 9.0 psi, coal-fired EGU emissions 

shutdown, and natural gas fired combustion turbines operating
Greensboro/Winston-Salem/High Point Area 2-19

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.3-16 Change in Ozone Concentrations and RRFs in 2016 Future Year Modeling

with Summertime RVP changed to 9.0 psi, Coal-fired EGU emissions shutdown, and 

Natural Gas Fired Combustion Turbines Operating

Monitor ID County

Base16 Ozone 

Design Value1

(ppb)

RVPPT16 

Ozone Design 

Value2(ppb) RRF

Change from 

Base16 to 

RVP16 (ppb)

37-033-0001 Caswell 76.3 76.2 0.9997 -0.1

37-059-0002 Davie 81.3 81.2 0.9988 -0.1

37-067-0022 Forsyth 78 78 1.0001 0.0

37-067-0028 Forsyth 73 73 1.0002 0.0

37-067-0030 Forsyth 76 76 1.0001 0.0

37-067-1008 Forsyth 80 80 1.0001 0.0

37-081-0011 Guilford 77 77 1.0001 0.0

37-081-0013 Guilford 82 82 1.0001 0.0

37-157-0099 Rockingham 77 77 1.0000 0.0

37-159-0021 Rowan 86.7 86.5 0.9988 -0.2

37-159-0022 Rowan 86.7 86.6 0.9989 -0.1

1 Default 2016 MATS concentrations

2

2016 concentrations with summertime RVP changed to 9.0 psi, coal-fired EGU emissions 

shutdown, and natural gas fired combustion turbines operating

In summation, the NCDAQ applied a very conservative modeling approach to estimate the 

increase in emissions due to the relaxation of current gasoline standard of 7.8 psi to proposed 9.0 

psi. Modeling results for 2005 and 2016 show no changes in ozone concentrations at monitors. 

Additionally, the planned shutdown of coal-fired EGUs near the Triad maintenance area will 

reduce ozone levels. The NCDAQ concludes that relaxation of the Federal standard does not 

interfere with the attainment and maintenance of the ozone NAAQS.

Voluntary Efforts to Reduce Air Pollution

The NCDAQ has identified several voluntary programs undertaken by local municipalities, local 

air awareness programs, and other organizations, which target emissions sources that will help 

the Triad area meet the 2008 8-hour ozone standard. A few examples include an annual 

commuter challenge which reduces commuter vehicle miles travelled, a transition to 

electrified/hybrid buses by a municipality, and idle reduction policies, technologies, and 

programs in several Triad counties. Additionally, the NCDAQ has been working with North 

Carolina industries on a voluntary basis to increase energy efficiency at manufacturing facilities. 

Under this partnership, several companies in the Triad area have completed on-site energy 

assessments that have identified cost effective energy efficiency measures with the potential to 
Greensboro/Winston-Salem/High Point Area 2-20

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

reduce air emissions. Table 2.3-17 summarizes the results to date. Actual emission reductions 

would be realized once the companies make decisions on which efficiency measures to 

implement. The NCDAQ and its partners plan to track actual reductions achieved through this 

voluntary program in the coming years. Additional energy assessments are also planned.

Table 2.3-17 Emissions Reductions from Select Voluntary Projects

County Facility

Year Energy 

Assessments 

Conducted 

/Year 

Efficiency 

Measures 

Implemented

NOx VOC

Emission 

Reductions 

Potential 

(tons/yr)

Reductions 

Achieved to 

Date 

(tons/yr)

Emission 

Reductions 

Potential 

(tons/yr)

Reductions 

Achieved to 

Date (tons/yr)

Davidson Furniture Plant 1 2012/ 0.93 0.03

Davidson Furniture Plant 2 2012/ 1.41 0.020

Davidson Furniture Plant 3 2011/2011 0.03 0.01 0.001 0.000

Guilford

Manufacturing 

Plant 1

2012/ 1.06 0.060

Guilford

Manufacturing 

Plant 2

2012/ 1.69 0.090

Total 5.12 0.01 0.200 0.000

2.3.2 INTERFERENCE WITH CO, PM, SO2, and NO2 NAAQS

The current ambient air quality levels for CO is about 25% of the CO standard. Although onroad mobile sources are a large contributor to CO ambient air concentrations, CO emissions 

increase of about 5 tons/day from relaxation of the RVP standard is not expected to affect the 

attainment status of the area. Nonroad and area sources are not large contributors to CO 

emissions.

The revised nitrogen dioxide (NO2) standard was published in the Federal Register on 

February 9, 2010. The monitoring requirements are focused on near-road monitoring; therefore, 

one focus of this standard is on-road mobile sources. To date, none of the near-road NO2
Greensboro/Winston-Salem/High Point Area 2-21

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

monitors have been established in North Carolina. Since there is no data to determine if North 

Carolina is violating or close to exceeding this standard, it is difficult to assess whether 

increasing the RVP will result in a violation of the NO2 standard. However, on-road mobile 

sources are a large contributor of NOx emissions and NO2 is a component of NOx. Based upon 

the MOVES mobile model emission estimations, the RVP relaxation would not increase NO2

concentrations. 

On-road mobile, nonroad mobile, and area sources are not believed to be large contributors to 

directly emitted fine particulate matter less than 2.5 micrometers (PM2.5) or indirectly formed 

PM2.5 concentrations. The photochemical modeling analysis discussed earlier for ozone was also 

used to calculate the changes in PM2.5. The analysis showed no change in particle pollution due 

to changes in RVP in 2005 and 2016 at any of the monitors. 

In North Carolina, directly emitted PM2.5 is a very small component of the overall PM2.5 ambient 

concentrations. The primary species impacting PM2.5 concentrations are the secondarily formed 

sulfates and organic carbons. Sulfates are formed through the chemical reaction of sulfur 

dioxide (SO2) and ammonia and the majority of the organic carbons come from natural sources 

like trees. A 2009 analysis of SO2 emissions, which is a primary contributor to the formation of 

PM2.5 within North Carolina, found about 3.3% of total SO2 emissions came from on-road, 

nonroad and area sources combined, while the remaining 96.7% came from point sources (see 

“Redesignation Demonstration and Maintenance Plan for the Hickory (Catawba County) and 

Greensboro/Winston-Salem/High Point (Davidson and Guilford Counties) Fine Particulate 

Matter Nonattainment Areas”, submitted to the USEPA on December 18, 2009, Figure 4-2, 

p. 4-4). Based on this, it is concluded that the relatively small RVP related emissions change in 

particulate matter will not affect PM2.5 NAAQS.

For the reasons outlined above, it is not likely that increasing the RVP will result in a violation of 

the CO, SO2, PM2.5, and PM10 NAAQS.
Greensboro/Winston-Salem/High Point Area 2-22

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

2.4 AMBIENT AIR QUALITY MONITORING

The NCDAQ has collected ambient monitoring data for the Triad area since the late seventies. 

At the time of the April 2004 8-hour ozone designations, there were nine ozone monitors 

throughout the Triad area, with only six monitors in the Triad 1-hour maintenance counties 

(Figure 2.4-1). These monitors were installed in accordance with 40 CFR 58. 

Figure 2.4-1 Historic Triad Ozone Monitoring Network

Since the 2004 designations, three of the Triad ozone monitors have moved and one monitor has 

shut down. In 2005, the Mendenhall monitor in Guilford County replaced the McLeansville 

monitor and the Forsyth County monitor at Pollirosa moved to Clemmons. Also in 2005, the 

Sophia monitor in Randolph County shutdown. In 2010, the Cooleemee monitor in Davie

County moved to Mocksville. All of these changes to the monitoring network were done in 

consultation with the USEPA and in accordance with 40 CFR 58. The current monitoring 

locations are presented in Figure 2.4-2.
Greensboro/Winston-Salem/High Point Area 2-23

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Figure 2.4-2 Current Triad Ozone Monitoring Network

Tables 2.4-1 and 2.4-2, respectively, show the 8-hour ozone air quality data and corresponding 

design values for the monitors in the Triad area from 2001 through 2010. All of the monitors in 

the Triad area have continued to maintain the 1997 8-hour ozone standard since being designated 

attainment in 2008 (see Table 2.4-2). Since the attainment designation given to the Triad area 

for the more stringent 2008 8-hour ozone standard, three monitors have measured exceedances of 

the standard due to the extreme heat event that affected most of the country during a two week 

period in the summer of 2012.

Table 2.4-1 Triad Area’s 4th Highest 8-hour Ozone Values(2001-2010)

Monitor 4

th Highest 8-hour Ozone Values (ppm)

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012*

Cooleemee

Davie County 0.089 0.073 0.084 0.080 0.085 0.081 0.068 --- --- ---

Mocksville

Davie County --- --- --- --- --- --- --- 0.072 0.072 0.076

Hattie Ave.

Forsyth County 0.087 0.075 0.074 0.082 0.082 0.081 0.068 0.081 0.076 0.079

Union Cross

Forsyth County 0.081 0.078 0.080 0.082 0.083 0.078 0.068 0.078 0.074 0.074

Shiloh Church

Forsyth County 0.074 0.071 0.078 0.067 0.076 0.077 0.066 0.076 --- 0.074

Cherry Grove

Caswell County 0.083 0.074 0.076 0.075 0.082 0.080 0.067 0.073 0.070 0.077

McLeansville

Guilford County 0.079 0.071 0.081 --- --- --- --- --- --- ---

Mendenhall

Guilford County --- --- 0.082 0.080 0.086 0.081 0.072 0.076 0.076 0.078

Bethany

Rockingham County 0.083 0.074 0.078 0.075 0.082 0.084 0.068 0.074 0.071 0.076
Greensboro/Winston-Salem/High Point Area 2-24

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Table 2.4-1 Continued: Triad Area’s 4th Highest 8-hour Ozone Values (2001-2010)

Monitor 4

th Highest 8-hour Ozone Values (ppm)

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012*

Sophia

Randolph County 0.078 0.076 --- --- --- --- --- --- --- ---

Pollirosa

Forsyth County 0.078 0.072 --- --- --- --- --- --- --- ---

Clemmons

Forsyth County --- --- 0.075 0.077 0.078 0.078 0.062 0.081 0.074 0.076

* indicates values calculated with preliminary ozone data for the year 2012

Table 2.4-2 Triad Area’s Design Values (2001-2010)

Monitor Design Value (ppm)

03-05 04-06 05-07 06-08 07-09 08-10 09-11 10-12*

Cooleemee

Davie County 0.082 0.079 0.083 0.082 0.078 --- --- ---

Mocksville

Davie County --- --- --- --- --- --- 0.070 0.073

Hattie Ave.

Forsyth County

0.078 0.077 0.079 0.081 0.077 0.076 0.075 0.078

Union Cross

Forsyth County 0.079 0.080 0.081 0.081 0.076 0.074 0.072 0.075

Shiloh Church

Forsyth County 0.074 0.072 0.073 0.073 0.073 0.073 0.071 0.075

Cherry Grove

Caswell County 0.077 0.075 0.077 0.079 0.076 0.073 0.070 0.073

McLeansville

Guilford County 0.077 0.076 --- --- --- --- --- ---

Mendenhall

Guilford County --- 0.081 0.082 0.082 0.079 0.076 0.074 0.076

Bethany

Rockingham 

County

0.078 0.075 0.078 0.080 0.078 0.075 0.071 0.073

Sophia

Randolph County --- --- --- --- --- --- --- ---

Pollirosa

Forsyth County --- --- --- --- --- --- --- ---

Clemmons

Forsyth County --- 0.076 0.076 0.077 0.072 0.073 0.072 0.077

Bold values indicates violations of the 1997 8-hour ozone standard

* indicates values calculated with preliminary ozone data for the year 2012

---- indicates no data to calculate design value

Underlined data indicates fewer than three years or previous site data in design value calculation 
Greensboro/Winston-Salem/High Point Area 2-25

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

Ambient air quality monitoring is one of the requirements of Section 110 of the Clean Air Act. 

The NCDAQ commits to continue operating the current ozone monitors in the Triad 8-hour 

ozone attainment area, provided sufficient funding is available for continued operation. Any 

monitor shutdowns or relocations will only be made with the approval of the USEPA. No plans 

are underway to discontinue operation, relocate or otherwise affect the integrity of the ambient 

monitoring network in place. The current monitors are operated consistent with 40 CFR 58 and 

any changes will only be made if they are consistent with 40 CFR 58.
Greensboro/Winston-Salem/High Point Area 2-26

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

2.5 CONTINGENCY PLAN

2.5.1 Overview

The two main elements of the North Carolina contingency plan are tracking and triggering 

mechanisms to determine when contingency measures are needed and a process of developing 

and adopting appropriate control measures. There will be three triggers for the contingency plan. 

The primary trigger of the contingency plan will be a violation of the 1997 8-hour ozone 

NAAQS at any of the Triad area monitors. The secondary trigger will be a monitored air quality 

pattern that suggests an actual 1997 8-hour ozone NAAQS violation may be imminent. The 

tertiary trigger will be a monitored fourth high exceedance of the NAAQS. Upon either the 

primary or secondary triggers being activated, the NCDAQ will commence analyses to 

determine what additional measures, if any, will be necessary to attain or maintain the 1997 

8-hour ozone standard. If activation of either the primary or secondary triggers occurs, this plan 

provides a regulatory adoption process for revising emission control strategies. Activation of the 

tertiary trigger will result in an analysis to understand the cause of the exceedance and to identify 

voluntary measures if needed. 

In addition, there will be a tracking mechanism that requires a comparison of the actual 

emissions inventory submitted under the AERR to the projected inventories, and to the 

attainment year inventory contained in this maintenance plan. The AERR reporting years 

coincides with the interim year and is within one year of the final year of the emission 

inventories in this maintenance demonstration.

2.5.2 Primary and Secondary Triggers

The primary trigger of the contingency plan will be a violation of the 1997 8-hour ozone 

standard, or when the three-year average of the 4th highest values is equal to or greater than 

0.085 ppm at a monitor in the Triad maintenance area. The trigger date will be 60 days from the 

date that the State observes a 4th highest value that, when averaged with the two previous ozone 

seasons’ fourth highest values, would result in a three-year average equal to or greater than 

0.085 ppm.

The secondary trigger will apply where no actual violation of the 1997 8-hour ozone standard 

has occurred, but where the State finds monitored ozone levels indicating that an actual ozone 

NAAQS violation may be imminent. A pattern will be deemed to exist when there are two 

consecutive ozone seasons in which the 4th highest values are 0.085 ppm or greater at a single 

monitor within the Triad maintenance area. The trigger date will be 60 days from the date that 
Greensboro/Winston-Salem/High Point Area 2-27

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

the State observes a 4th highest value of 0.085 ppm or greater at a monitor for which the previous 

season had a 4th highest value of 0.085 ppm or greater.

Similarly, the tertiary trigger will not be an actual violation of the 1997 8-hour ozone standard. 

This trigger will be a first alert as to a potential air quality problem on the horizon. The trigger 

will be activated when a monitor in the Triad maintenance area has a 4th highest value of 

0.085 ppm or greater, starting the first year after the maintenance plan has been approved. The 

trigger date will be 60 days from the date that the State observes a 4th highest value of 0.085 ppm 

or greater at any monitor.

2.5.3 Action Resulting From Trigger Activation

Once the primary or secondary trigger is activated, the Planning Section of the NCDAQ shall 

commence analyses including trajectory analyses of high ozone days, and emissions inventory 

assessment to determine those emission control measures that will be required for attaining or 

maintaining the 1997 8-hour ozone standard. By May 1st of the year following the ozone season 

in which the primary or secondary trigger has been activated, North Carolina will complete 

sufficient analyses to begin adoption of necessary rules for ensuring attainment and maintenance 

of the 1997 8-hour ozone NAAQS. The rules would become State effective by the following 

January 1

st, unless legislative review is required.

The measures that will be considered for adoption upon a trigger of the contingency plan 

include: NOx Reasonably Available Control Technology on stationary sources in the Triad

maintenance area, diesel inspection and maintenance program, implementation of diesel retrofit 

programs, including incentives for performing retrofits, and additional controls in upwind areas.

The NCDAQ commits to implement within twenty-four months, or as expeditiously as 

practicable, at least one of the control measures listed above, or other contingency measures that 

may be determined to be more appropriate based on the analysis performed,.

Once the tertiary trigger is activated, the Planning Section of the NCDAQ shall commence 

analyses including meteorological evaluation, trajectory analyses of high ozone days and 

emissions inventory assessment to understand why a 4th highest exceedance of the standard has 

occurred. Once the analyses are completed, the NCDAQ will work with the local air awareness 

program and develop an outreach plan to identify any additional voluntary measures that can be 

implemented. If the 4th highest exceedance occurs early in the season, the NCDAQ will work 

with entities identified in the outreach plan to determine if the measures can be implemented 

during the current season, otherwise, NCDAQ will work with the local air awareness coordinator 

to implement the plan for the following ozone season.
Greensboro/Winston-Salem/High Point Area 2-28

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

2.6 VERIFICATION OF CONTINUED ATTAINMENT

In addition to the contingency measures listed above, the 110(a)(1) maintenance plan should 

indicate how the state will track the progress of the maintenance plan. For the verification of 

continued attainment, the NCDAQ will carry out emission inventory comparisons. The large 

stationary sources are required to submit an emission inventory annually to the NCDAQ. The 

NCDAQ will commit to review these emissions inventories to determine if an unexpected 

growth in NOx emissions in the Triad area may endanger the maintenance of the 1997 8-hour 

ozone standard. Additionally, as new VMT data is provided by the North Carolina Department 

of Transportation, the NCDAQ commits to review this data and determine if any unexpected 

growth in VMT may endanger the maintenance of the 1997 8-hour ozone standard.

Additionally, under the AERR the NCDAQ is required to develop a comprehensive, annual, 

statewide emissions inventory every three years and is due twelve to eighteen months after the 

completion of the inventory year. The AERR inventory years coincides with the interim year 

and is within a year of the final year of the maintenance plan. Therefore, the NCDAQ commits 

to compare the AERR inventories, as they are developed, with the maintenance plan to determine 

if additional steps are necessary for continued maintenance of the 1997 8-hour ozone standard in 

this area. 
Greensboro/Winston-Salem/High Point Area 2-29

Supplement to 110(a)(1) Maintenance Plan for 8-Hour Ozone April 12, 2013

2.7 CONCLUSION

The most recent three years of ozone monitoring data for the Triad maintenance area 

demonstrate compliance with the 1997 8-hour ozone NAAQS. Three monitors are showing 

violations of the 2008 8-hour ozone NAAQS. Since the 1990’s, there have been many major 

programs enacted in North Carolina that have led to significant actual, enforceable emissions 

reductions, which have led to air quality improvements in the Triad area. The planned closing or 

conversion of nearby coal-fired power plants is expected to further improve air quality in the 

Triad maintenance area.

The maintenance plan demonstrates that the projected emissions inventory for 2018 is less than 

the base year emissions inventory without the current RVP requirement of 7.8 psi. The lower 

RVP requirement was implemented as a control measure to reduce VOC emissions. Since VOC 

emissions from biogenic sources dominate in the Southeast, controlling ozone in North Carolina 

is most effectively done through reduction in NOx emissions. The maintenance plan 

demonstrates that the slight increase in NOx emissions predicted by the MOVES model 

correlates to no change in ozone concentrations at monitors in and near the Triad due to the 

relaxation of the RVP standard. It has also been demonstrated that the higher RVP standard will 

not interfere with the attainment of other NAAQS.

This maintenance plan has been prepared to meet the requirements of the 1990 Clean Air Act 

Amendments.