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 13, 2011 

Prepared by: 

North Carolina Department of Environment and Natural Resources 

Division of Air Quality 
 (This page intentionally left blank)
Greensboro/Winston-Salem/High Point area i 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

PREFACE 

This document contains North Carolina's Section 110(a)(1) Maintenance Plan for the 8-hour 

ozone National Ambient Air Quality Standard (NAAQS) for the Greensboro/WinstonSalem/High Point 1-hour ozone maintenance area. 
Greensboro/Winston-Salem/High Point area ii 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

EXECUTIVE SUMMARY 

Introduction 

Ozone is formed by a complex set of chemical reactions involving volatile organic compounds 

(VOCs), nitrogen oxides (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 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 and is hence 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. 

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 Resourses and the United States 

Environmental Protection Agency (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 designated the Triad area for the 1997 8-hour ozone standard and 

deferred the effective date. The Triad EAC area met all of their milestones and attained the 1997 
Greensboro/Winston-Salem/High Point area iii 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

8-hour ozone standard by the December 2007 deadline. The USEPA designated the Triad area 

as attainment/unclassifiable in April 2008. 

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 and 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. 

Conclusion 

The emission inventory comparison demonstrates that the estimated emissions are expected to 

decrease from the attainment inventory year through the end future year. Additionally, the 

ambient air quality data demonstrates that the Triad maintenance area has continued to maintain 

and is well below the 1997 8-hour ozone standard. The North Carolina Division of Air Quality 

(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 iv 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

TABLE OF CONTENTS 

PREFACE ........................................................................................................................................ i

EXECUTIVE SUMMARY ............................................................................................................ ii

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

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

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

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

2.0 MAINTENANCE PLAN .................................................................................................... 4

2.1 EMISSION INVENTORIES ............................................................................................... 4

2.2 MAINTENANCE DEMONSTRATION ............................................................................. 8

2.3 AMBIENT AIR QUALITY MONITORING ...................................................................... 9

2.4 CONTINGENCY PLAN ................................................................................................... 12

2.4.1 Overview ..................................................................................................................... 12

2.4.2 Primary and Secondary Triggers ................................................................................ 12

2.4.3 Action Resulting From Trigger Activation ................................................................. 13

2.5 VERIFICATION OF CONTINUED ATTAINMENT ....................................................... 14

3.0 CONCLUSION ................................................................................................................. 14
Greensboro/Winston-Salem/High Point area 1 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

1.0 INTRODUCTION 

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 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’s design value in the area. 

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. 

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 
Greensboro/Winston-Salem/High Point area 2 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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 

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

2008. 

Forsyth Guilford

Rockingham

Lincoln

Mecklenburg Rowan

Davie

Chatham

Caswell Person

Granville

Wake

Durham

Franklin

Johnston

Edgecombe

Pitt

Cunberland

Union

Cabarrus

Gaston

Randolph

Stokes

Yadkin

Northhampton

New Hanover New 

Madison

Buncombe

Yancey

Alexander

Caldwell

Martin

Duplin

Swain

Haywood

Camden

Nash

Orange

Alamance

Davidson

Harnett

Cleveland

Anson

Richmond

Robeson Bladen

Columbus

Brunswick

Pender

Sampson

Onslow

Jones

Carteret

Craven

Pamilico

Hyde

Beaufort

Washington

Tyrrell Dare

Greene

Wayne

Wilson

Ashe Warren

McDowell

Rutherford

Polk

Henderson

Cherokee

Graham

Clay

Macon

Transylvania

Jackson

Catawba Burke

Watauga

Alleghany

Surry

Wilkes

Iredell

Stanly

M ontgomery

Moore

Hoke

Scotland

Avery

Vance

Halifax

Bertie

Hertiford

Gates

Chowan

Perquimons

Pasquotank

Currituck

Lee

Mitchell

Lenoir

Ozone Nonattainment – Designated 1992

Ozone Nonattainment – Designated 1978

Forsyth Guilford

Rockingham

Lincoln

Mecklenburg Rowan

Davie

Chatham

Caswell Person

Granville

Wake

Durham

Franklin

Johnston

Edgecombe

Pitt

Cunberland

Union

Cabarrus

Gaston

Randolph

Stokes

Yadkin

Northhampton

New Hanover New 

Madison

Buncombe

Yancey

Alexander

Caldwell

Martin

Duplin

Swain

Haywood

Camden

Nash

Orange

Alamance

Davidson

Harnett

Cleveland

Anson

Richmond

Robeson Bladen

Columbus

Brunswick

Pender

Sampson

Onslow

Jones

Carteret

Craven

Pamilico

Hyde

Beaufort

Washington

Tyrrell Dare

Greene

Wayne

Wilson

Ashe Warren

McDowell

Rutherford

Polk

Henderson

Cherokee

Graham

Clay

Macon

Transylvania

Jackson

Catawba Burke

Watauga

Alleghany

Surry

Wilkes

Iredell

Stanly

M ontgomery

Moore

Hoke

Scotland

Avery

Vance

Halifax

Bertie

Hertiford

Gates

Chowan

Perquimons

Pasquotank

Currituck

Lee

Mitchell

Lenoir

Ozone Nonattainment – Designated 1992

Ozone Nonattainment – Designated 1978

Forsyth Guilford

Rockingham

Lincoln

Mecklenburg Rowan

Davie

Chatham

Caswell Person

Granville

Wake

Durham

Franklin

Johnston

Edgecombe

Pitt

Cunberland

Union

Cabarrus

Gaston

Randolph

Stokes

Yadkin

Northhampton

New Hanover New 

Madison

Buncombe

Yancey

Alexander

Caldwell

Martin

Duplin

Swain

Haywood

Camden

Nash

Orange

Alamance

Davidson

Harnett

Cleveland

Anson

Richmond

Robeson Bladen

Columbus

Brunswick

Pender

Sampson

Onslow

Jones

Carteret

Craven

Pamilico

Hyde

Beaufort

Washington

Tyrrell Dare

Greene

Wayne

Wilson

Ashe Warren

McDowell

Rutherford

Polk

Henderson

Cherokee

Graham

Clay

Macon

Transylvania

Jackson

Catawba Burke

Watauga

Alleghany

Surry

Wilkes

Iredell

Stanly

M ontgomery

Moore

Hoke

Scotland

Avery

Vance

Halifax

Bertie

Hertiford

Gates

Chowan

Perquimons

Pasquotank

Currituck

Lee

Mitchell

Lenoir

Ozone Nonattainment – Designated 1992

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

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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

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: 

• 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 
Greensboro/Winston-Salem/High Point area 4 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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. 

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 
Greensboro/Winston-Salem/High Point area 5 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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, highway 

mobile and off-road 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. 

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. 
Greensboro/Winston-Salem/High Point area 6 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

Table 2.1-1. Point Source Emissions 

County 

NOx Emissions 

(tons/day) 

VOC Emissions 

(tons/day) 

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. 

Table 2.1-2. Area Source Emissions 

County 

NOx Emissions 

(tons/day) 

VOC Emissions 

(tons/day) 

2007 2011 2018 2007 2011 2018 

Davidson 0.62 0.60 0.55 6.83 7.10 6.91 

Davie 0.21 0.22 0.23 4.68 5.03 6.51 

Forsyth 0.99 1.04 1.11 16.53 18.63 22.31 

Guilford 2.01 2.01 1.99 22.62 24.20 28.80 

Triad Total 3.83 3.87 3.88 50.66 54.96 64.53 

For highway mobile sources, the USEPA’s Motor Vehicle Emission Simulator (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 highway 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 
Greensboro/Winston-Salem/High Point area 7 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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. Highway Mobile Source Emissions 

County 

NOx Emissions 

(tons/day) 

VOC Emissions 

(tons/day) 

2007 2011 2018 2007 2011 2018 

Davidson 15.08 11.70 4.24 6.60 5.03 2.42 

Davie 5.03 3.50 2.08 1.85 1.41 0.90 

Forsyth 27.73 17.26 10.84 12.05 6.75 4.23 

Guilford 42.78 32.10 18.84 17.41 12.97 7.82 

Triad Total 90.62 64.56 36.00 37.91 26.16 15.37 

Off-road mobile sources are equipment that can move but do not use the roadways, i.e., lawn 

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

category are calculated using the USEPA’s NONROAD2008a nonroad mobile 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 multiply 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 mobile 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 off-road mobile source emissions are presented in Table 2.1-4. 

Table 2.1-4. Off-Road Mobile Source Emissions 

County 

NOx Emissions 

(tons/day) 

VOC Emissions 

(tons/day) 

2007 2011 2018 2007 2011 2018 

Davidson 3.56 2.75 1.89 1.97 1.52 1.02 

Davie 0.78 0.63 0.38 1.32 1.16 0.83 

Forsyth 4.94 3.99 2.40 3.79 2.93 2.12 

Guilford 11.83 9.59 6.11 8.33 6.50 4.84 

Triad Total 21.11 16.96 10.78 15.41 12.11 8.81 
Greensboro/Winston-Salem/High Point area 8 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

2.2 MAINTENANCE DEMONSTRATION 

Maintenance is demonstrated when the future years total man-made emissions are less than the 

2007 attainment inventory emissions. Table 2.2-1 summarizes the total man-made emissions for 

the Triad area. 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. 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 2.2-1. Total Man-Made Emissions for the Triad Area 

County 

NOx Emissions 

(tons/day) 

VOC Emissions 

(tons/day) 

2007 2011 2018 2007 2011 2018 

Davidson 21.99 17.94 9.88 19.23 17.50 14.29 

Davie 6.08 4.41 2.75 8.04 7.79 8.43 

Forsyth 35.88 24.47 16.5 36.4 32.34 32.69 

Guilford 57.68 44.76 28.00 58.04 53.35 51.10 

Triad Total 121.63 91.58 57.13 121.71 110.98 106.51 

Table 2.2-2 Maintenance Demonstration for the Triad Area 

Year NOx TPD VOC TPD 

2007 121.63 121.71 

2011 91.58 110.98 

2018 57.13 106.51 

Difference from 

2007 to 2018 -64.50 -15.20 

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 can be 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. 
Greensboro/Winston-Salem/High Point area 9 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

TABLE 2.2-3 Safety Margins for the Triad Areas 

Year NOx TPD VOC TPD 

2007 N/A N/A 

2011 -30.05 -10.73 

2018 -64.50 -15.2 

2.3 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 2.3-1). These monitors were installed in accordance with the 40 CFR 58. 

Figure 2.3-1 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 2.3-2. 
Greensboro/Winston-Salem/High Point area 10 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

Figure 2.3-2 Current Triad Ozone Monitoring Network 

Tables 2.3-1 and 2.3-2, respectively, show the 8-hour ozone air quality data and corresponding 

design values for the monitors in the Triad area from 2001 through 2010. As you can see from 

Table 2.3-2, all of the monitors in the Triad area have continued to maintain the 1997 8-hour 

ozone standard since being designated attainment in 2008. 

Table 2.3-1 Triad Area’s 4th Highest 8-hour Ozone Values(2001-2010) 

Monitor 4th

 Highest 8-hour Ozone Values (ppm) 

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Cooleemee 

Davie County 0.094 0.098 0.089 0.073 0.084 0.080 0.085 0.081 0.068 --- 

Mocksville 

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

Hattie Ave. 

Forsyth County 0.094 0.099 0.087 0.075 0.074 0.082 0.082 0.081 0.068 0.081

Union Cross 

Forsyth County 0.094 0.093 0.081 0.078 0.080 0.082 0.083 0.078 0.068 0.078

Shiloh Church 

Forsyth County 0.096 0.094 0.074 0.071 0.078 0.067 0.076 0.077 0.066 0.076

Cherry Grove 

Caswell County 0.087 0.095 0.083 0.074 0.076 0.075 0.082 0.080 0.067 0.073

McLeansville 

Guilford County 0.086 0.104 0.079 0.071 0.081 --- --- --- --- --- 

Mendenhall 

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

Bethany 

Rockingham County 0.094 0.096 0.083 0.074 0.078 0.075 0.082 0.084 0.068 0.074
Greensboro/Winston-Salem/High Point area 11 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

Table 2.3-1 Continued: Triad Area’s 4th Highest 8-hour Ozone Values(2001-2010) 

Monitor 4th

 Highest 8-hour Ozone Values (ppm) 

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 

Sophia 

Randolph County 0.085 0.092 0.078 0.076 --- --- --- --- --- --- 

Pollirosa 

Forsyth County 0.082 0.088 0.078 0.072 --- --- --- --- --- --- 

Clemmons 

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

Table 2.3-2 Triad Area’s Design Values (2001-2010) 

Monitor Design Value (ppm) 

01-03 02-04 03-05 04-06 05-07 06-08 07-09 08-10 

Cooleemee 

Davie County 0.093 0.086 0.082 0.079 0.083 0.082 0.078 --- 

Mocksville 

Davie County --- --- --- --- --- --- --- --- 

Hattie Ave. 

Forsyth County 0.093 0.087 0.078 0.077 0.079 0.081 0.077 0.076 

Union Cross 

Forsyth County 0.089 0.084 0.079 0.080 0.081 0.081 0.076 0.074 

Shiloh Church 

Forsyth County 0.088 0.079 0.074 0.072 0.073 0.073 0.073 0.073 

Cherry Grove 

Caswell County 0.088 0.084 0.077 0.075 0.077 0.079 0.076 0.073 

McLeansville 

Guilford County 0.089 0.084 0.077 0.076 --- --- --- --- 

Mendenhall 

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

Bethany 

Rockingham 

County 

0.091 0.084 0.078 0.075 0.078 0.080 0.078 0.075 

Sophia 

Randolph County 0.085 0.082 --- --- --- --- --- --- 

Pollirosa 

Forsyth County 0.082 0.079 --- --- --- --- --- --- 

Clemmons 

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

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

---- 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 12 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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. 

2.4 CONTINGENCY PLAN 

2.4.1 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. 

2.4.2 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 
Greensboro/Winston-Salem/High Point area 13 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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 

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. 

2.4.3 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 1 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, 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,. 
Greensboro/Winston-Salem/High Point area 14 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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. 

2.5 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. 

3.0 CONCLUSION 

The emission inventory comparison demonstrates that the estimated emissions are expected to 

decrease from the attainment inventory year through the end future year. Additionally, the 

ambient air quality data demonstrates that the Triad maintenance area has continued to maintain, 

and is well below, the 1997 8-hour ozone standard. 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 
Greensboro/Winston-Salem/High Point area 15 

110(a)(1) Maintenance Plan for 8-Hour Ozone April 13, 2011 

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

8-hour ozone standard have been met.