MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

FOR THE MARICOPA COUNTY AREA

MARCH 2013
MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

FOR THE MARICOPA COUNTY AREA

Prepared by:

March 2013

Technical Assistance Provided By:

Arizona Department of Environmental Quality

Arizona Department of Transportation

Maricopa County Air Quality Department

U.S. Environmental Protection Agency
MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

FOR THE MARICOPA COUNTY AREA

TABLE OF CONTENTS

CHAPTER PAGE

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

OUTLINE OF THE MAG 2013 CARBON MONOXIDE

MAINTENANCE PLAN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

TWO CONTINUED ATTAINMENT OF THE CARBON MONOXIDE

STANDARDS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

HISTORICAL PERSPECTIVE. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

CARBON MONOXIDE MONITORING NETWORK. . . . . . . . . . . 2-1

MONITORING RESULTS AND CONTINUED ATTAINMENT

DEMONSTRATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

QUALITY ASSURANCE PROGRAM. . . . . . . . . . . . . . . . . . . . . . 2-2

THREE MAINTENANCE PLAN.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

MAINTENANCE PLAN CONTROL MEASURES. . . . . . . . . . . . . 3-1

EMISSIONS INVENTORIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

MAINTENANCE DEMONSTRATION.. . . . . . . . . . . . . . . . . . . . . 3-5

MONITORING NETWORK AND VERIFICATION OF

CONTINUED ATTAINMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

CONTINGENCY PROVISIONS. . . . . . . . . . . . . . . . . . . . . . . . . 3-19

TRANSPORTATION CONFORMITY BUDGET. . . . . . . . . . . . . 3-20

SUBSEQUENT MAINTENANCE PLAN REVISIONS.. . . . . . . . 3-22

REFERENCES.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23

i
MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

FOR THE MARICOPA COUNTY AREA

LIST OF TABLES

TABLE PAGE

2-1 2008 Carbon Monoxide Monitoring Data Summary for the Maricopa 

County Maintenance Area.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2-2 2009 Carbon Monoxide Monitoring Data Summary for the Maricopa 

County Maintenance Area.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2-3 2010 Carbon Monoxide Monitoring Data Summary for the Maricopa 

County Maintenance Area.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2-4 2011 Carbon Monoxide Monitoring Data Summary for the Maricopa 

County Maintenance Area.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

3-1 Maintenance Measures in the 2013 Carbon Monoxide

Maintenance Plan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3-2 Average Weekday Emissions during the Winter Season in the 

Carbon Monoxide Modeling Domain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3-3 Average Weekday Emissions during the Winter Season in the

Carbon Monoxide Maintenance Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3-4 Total Carbon Monoxide Emissions in the 

Carbon Monoxide Modeling Domain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-5 UAM/CAL3QHC Maximum Eight-Hour Carbon Monoxide Concentration

Adjustments and Scaled Estimates for 2025.. . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-6 Maximum CAL3QHC Eight-Hour Carbon Monoxide 

Concentrations in 2025. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

3-7 Second Highest Eight-Hour Carbon Monoxide Concentrations at 

Monitors in Maricopa County for 1996-2011. . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3-8 Carbon Monoxide Monitoring Sites in Maricopa County. . . . . . . . . . . . . . . . 3-18

ii
MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

FOR THE MARICOPA COUNTY AREA

LIST OF FIGURES

FIGURE PAGE

2-1. Carbon Monoxide Maintenance Area and Carbon Monoxide

Monitoring Sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2-2. Carbon Monoxide Trends (2004-2011). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

3-1. 2008 and 2025 Carbon Monoxide Emissions by Source Category

for the Carbon Monoxide Modeling Domain. . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3-2. 2008 and 2025 Carbon Monoxide Emissions by Source Category

for the Carbon Monoxide Maintenance Area.. . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3-3. Carbon Monoxide Modeling Domain and Maintenance Area. . . . . . . . . . . . . 3-8

3-4. Historical One-Hour and Eight-Hour Carbon Monoxide Monitoring

Data and Projections for the West Phoenix Monitoring Site. . . . . . . . . . . . . 3-14

3-5. Normalized Diurnal Cycles of Wind Speed, Temperature, Mixing Height

and Maximum Eight-Hour Carbon Monoxide Concentrations. . . . . . . . . . . . 3-16

iii
MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN FOR THE MARICOPA

COUNTY AREA

APPENDICES

APPENDIX A

Exhibit I: 2008 Periodic Emissions Inventory for Carbon Monoxide for the

Maricopa County, Arizona Maintenance Area. Maricopa County Air

Quality Department. November 2012.

Exhibit 2: Technical Support Document in Support of the MAG 2013 Carbon

Monoxide Maintenance Plan for the Maricopa County Area. March

2013.

APPENDIX B

Exhibit 1: Public Hearing Process Documentation

Exhibit 2: Certification of Adoption

iv
CHAPTER ONE

INTRODUCTION

The Maricopa County nonattainment area has attained the National Ambient Air Quality

Standards for carbon monoxide and has been redesignated as a maintenance area by the

Environmental Protection Agency (EPA). In 1978, the Governor of Arizona designated the

Maricopa Association of Governments (MAG) as the lead air quality planning agency for

Maricopa County in accordance with the Clean Air Act Section 174(a). Together with the

State, MAG is responsible for determining which elements of the State Implementation

Plan will be planned, implemented and enforced by State and local governments in

Arizona. In 1992, the Arizona Legislature recertified MAG as the regional air quality

planning agency in accordance with Section 174 of the 1990 Clean Air Act Amendments

(A.R.S. Section 49-406A.). MAG coordinates with the Arizona Department of

Environmental Quality, Arizona Department of Transportation, and the Maricopa County

Air Quality Department in developing the plans necessary to attain and maintain the

national standards. 

There have been no violations of the one-hour carbon monoxide standard since 1984 and

no violations of the eight-hour standard since 1996. The Revised MAG 1999 Serious Area

Carbon Monoxide Plan demonstrated attainment by 2000 and was submitted to EPA in

2001. The MAG Carbon Monoxide Redesignation Request and Maintenance Plan

demonstrated maintenance of the carbon monoxide standards through 2015 and was

submitted to EPA in 2003. On March 9, 2005, EPA published final approval of the Serious

Area Plan, Maintenance Plan, and redesignation of the Maricopa County area to

attainment status, effective April 8, 2005.

Section 175A(b) of the Clean Air Act requires that eight years after redesignation of an

area as an attainment area, an additional plan revision for maintaining the primary air

quality standard for ten years after the expiration of the initial ten year period must be

submitted to EPA. In accordance with the Clean Air Act, the MAG 2013 Carbon Monoxide

Maintenance Plan has been prepared. The plan demonstrates continued maintenance of

the carbon monoxide standards through 2025 with a maximum eight-hour concentration

of 4.0 parts per million and establishes a 2025 motor vehicle emissions budget of 559.4

metric tons per day for the carbon monoxide maintenance area.

OUTLINE OF THE MAG 2013 CARBON MONOXIDE MAINTENANCE PLAN

The purpose of this document is to present the MAG 2013 Carbon Monoxide Maintenance

Plan for the Maricopa County Area. The plan was prepared to address the relevant

portions of the September 4,1992 EPA memorandum entitled, “Procedures for Processing

Requests to Redesignate Areas to Attainment” that are pertinent to maintenance plans.

1-1
The MAG 2013 Carbon Monoxide Maintenance Plan is composed of the following major

sections:

1. Introduction (This Chapter) - Includes a general discussion of the prior

Serious Area Plan and Maintenance Plan approvals, redesignation to

attainment status, and the outline of the MAG 2013 Carbon Monoxide

Maintenance Plan.

2. Continued Attainment of the Carbon Monoxide Standards - Includes the

historical perspective; carbon monoxide monitoring network; monitoring

results and continued attainment demonstration; and quality assurance

program.

3. Maintenance Plan - Includes the maintenance plan control measures;

emissions inventories; maintenance demonstration; monitoring network and

verification of continued attainment; contingency provisions; transportation

conformity budget; and subsequent maintenance plan revisions.

1-2
CHAPTER TWO

CONTINUED ATTAINMENT OF THE CARBON MONOXIDE STANDARDS

Attainment of the National Ambient Air Quality Standards for carbon monoxide (CO) is

demonstrated when two consecutive years of monitoring data for each site show no more

than one exceedance per year of the eight-hour (9 ppm) and one-hour (35 ppm) standards. 

The following information demonstrates that the Maricopa County maintenance area has

continued to attain the national standards for carbon monoxide for the past 15 years. This

is based on quality assured monitoring data representing all carbon monoxide monitoring

locations in the maintenance area.

HISTORICAL PERSPECTIVE

Data from the regional monitoring network indicates that the Maricopa County maintenance

area has not experienced a violation of the eight-hour standard for carbon monoxide since

1996. The last violation of the one-hour standard was recorded in 1984. In addition, both

the frequency of exceedance days and the magnitude of observed CO concentrations have

declined dramatically since air quality monitoring began in the late 1960's.

In contrast to the lack of eight-hour violations since 1996, eighty-six exceedance days were

recorded in 1984. There was a noticeable decline in the number of exceedance days from

1984 through 1990. In 1994 through 1996 period, there were a total of eight exceedance

days, three each in 1994 and 1995, and two in 1996. There were two violation sites in

1994 (West Indian School and West Phoenix sites), and one each in 1995 and 1996 (both

at the Phoenix Grand Avenue microscale monitor). A single exceedance of the eight-hour

standard occurred in 1999 at the Phoenix Grand Avenue site, but this one exceedance did

not constitute a violation of the standard. There have been no exceedances of the CO

standard since 1999.

The Maricopa County maintenance area has been in attainment of the National Ambient

Air Quality Standards for carbon monoxide since 1997 and has had a continuous

downward trend in concentrations. In the past ten years, the annual eight-hour maximum

concentration has decreased by approximately 57 percent, from 7.5 ppm in 2001 to

3.2 ppm in 2011. Since 2008, the maximum eight-hour concentrations reported at the CO

monitoring locations have been less than half of the 9 ppm standard (9.4 ppm due to

rounding).

CARBON MONOXIDE MONITORING NETWORK

The ambient air monitoring network for carbon monoxide in the Maricopa County

maintenance area consists of 12 State and Local Air Monitoring Stations (SLAMS). The

Buckeye station is located west of the maintenance area in Maricopa County and also

monitors carbon monoxide. Twelve of these sites are operated by the Maricopa County

2-1
Air Quality Department and one monitor is operated by the Arizona Department of

Environmental Quality. The CO monitoring sites are identified, along with summary data

from 2008 through 2011, in Tables 2-1 through 2-4. Figure 2-1 shows the geographical

distribution of the regional monitoring network.

MONITORING RESULTS AND CONTINUED ATTAINMENT DEMONSTRATION

The monitoring data presented in Tables 2-1 through 2-4 verify that the Maricopa County

maintenance area has remained in attainment of the national standards for carbon

monoxide, in accordance with the federal requirements of 40 CFR 50.8. Data recovery

rates for the monitors exceed the 75 percent completeness requirements for all years and

all state and federal quality assurance procedures have been followed. Figure 2-2

illustrates the downward trend in the second-highest carbon monoxide concentrations at

all monitors in the maintenance area.

QUALITY ASSURANCE PROGRAM

Carbon monoxide data for the Maricopa County area has been collected and qualityassured in accordance with 40 CFR, Part 58, Appendix A “Quality Assurance

Requirements for SLAMS, SPMs, and PSD Air Monitoring” and EPA’s “Quality Assurance

Handbook for Air Pollution Measurement Systems: Volume II: Ambient Air Quality

Monitoring Program”. The data are recorded in the EPA Air Quality System and are

available for public review through sources such as the EPA AirData website and air quality

monitoring reports produced by the Maricopa County Air Quality Department and the

Arizona Department of Environmental Quality.

2-2
TABLE 2-1

2008 CARBON MONOXIDE MONITORING DATA SUMMARY

FOR THE MARICOPA COUNTY MAINTENANCE AREA

STANDARDS: 1-HOUR: 35 PPM; 8-HOUR: 9 PPM*

Site Name

1-Hour 8-Hour

Max

ppm

2

nd

 Max

ppm

Max

ppm

2

nd

 Max

ppm

Buckeye, 26449 W. 100th Dr.s+0.7 0.7 0.5 0.5

Central Phoenix, 1645 E. Roosevelt 3.6 3.5 2.6 2.2

Dysart, 16825 N. Dysart Rd.s1.5 1.4 1.0 1.0

Glendale, 6001 W. Olive

s

2.1 2.0 1.6 1.5

Greenwood, 1128 N. 27th Ave. 3.0 3.0 2.7 2.4

JLG Supersite, 4530 N. 17th Ave. 3.1 3.1 2.5 2.4

Mesa, 310 S. Brookss1.7 1.7 1.4 1.3

North Phoenix, 601 E. Butler Dr.s2.1 2.0 1.3 1.3

South Phoenix, 33 W. Tamarisk Ave.s 3.7 3.2 2.2 2.0

South Scottsdale, 2857 N. Miller Rd.s

2.0 2.0 1.5 1.4

Tempe, 1525 S. College Ave.s2.4 2.3 1.8 1.4

West Chandler, 275 S. Elliss1.8 1.7 1.4 1.4

West Indian School, 3315 W. Indian

School Rd.

3.9 3.6 2.8 2.8

West Phoenix, 3847 W. Earll 4.7 4.5 3.1 3.0

* Due to mathematical rounding, values $ 35.5 and 9.5 ppm are necessary to exceed the

standard.

S Seasonal monitor operating September 1st to April 1st.

+

The Buckeye monitor is located outside the carbon monoxide maintenance area.

Sources: Environmental Protection Agency Air Quality System; Maricopa County Air

Quality Department 2008-2011 Air Monitoring Network Reviews.

2-3
TABLE 2-2

2009 CARBON MONOXIDE MONITORING DATA SUMMARY

FOR THE MARICOPA COUNTY MAINTENANCE AREA

STANDARDS: 1-HOUR: 35 PPM; 8-HOUR: 9 PPM*

Site Name

1-Hour 8-Hour

Max

ppm

2

nd

 Max

ppm

Max

ppm

2

nd

 Max

ppm

Buckeye, 26449 W. 100th Dr.s+1.2 1.1 0.6 0.5

Central Phoenix, 1645 E. Roosevelt 3.6 3.0 2.2 2.1

Dysart, 16825 N. Dysart Rd.s1.0 0.9 0.9 0.8

Glendale, 6001 W. Olive

s

2.0 1.9 1.3 1.2

Greenwood, 1128 N. 27th Ave. 3.5 3.2 2.6 2.4

JLG Supersite, 4530 N. 17th Ave. 2.9 2.8 2.3 2.3

Mesa, 310 S. Brookss2.0 1.9 1.5 1.3

North Phoenix, 601 E. Butler Dr.s5.9 2.1 1.3 1.3

South Phoenix, 33 W. Tamarisk Ave.s 4.1 3.4 2.6 2.2

South Scottsdale, 2857 N. Miller Rd.s

2.9 1.9 1.4 1.4

Tempe, 1525 S. College Ave.s4.0 3.6 2.9 2.1

West Chandler, 275 S. Elliss2.1 2.1 1.7 1.5

West Indian School, 3315 W. Indian

School Rd.

5.6 5.0 4.2 3.3

West Phoenix, 3847 W. Earll 4.9 4.8 4.6 3.3

* Due to mathematical rounding, values $ 35.5 and 9.5 ppm are necessary to exceed the

standard.

S Seasonal monitor operating September 1st to April 1st.

+

The Buckeye monitor is located outside the carbon monoxide maintenance area.

Sources: Environmental Protection Agency Air Quality System; Maricopa County Air

Quality Department 2008-2011 Air Monitoring Network Reviews.

2-4
TABLE 2-3

2010 CARBON MONOXIDE MONITORING DATA SUMMARY

FOR THE MARICOPA COUNTY MAINTENANCE AREA

STANDARDS: 1-HOUR: 35 PPM; 8-HOUR: 9 PPM*

Site Name

1-Hour 8-Hour

Max

ppm

2

nd

 Max

ppm

Max

ppm

2

nd

 Max

ppm

Buckeye, 26449 W. 100th Dr.s+1.9 1.3 0.6 0.6

Central Phoenix, 1645 E. Roosevelt 3.2 3.2 2.4 2.2

Dysart, 16825 N. Dysart Rd.s2.0 1.8 0.9 0.6

Glendale, 6001 W. Olive

s

9.0 8.9 3.0 1.5

Greenwood, 1128 N. 27th Ave. 4.3 3.9 3.0 2.3

JLG Supersite, 4530 N. 17th Ave. 2.9 2.7 2.1 2.1

Mesa, 310 S. Brookss2.0 2.0 1.4 1.4

North Phoenix, 601 E. Butler Dr.s2.9 2.4 1.7 1.6

South Phoenix, 33 W. Tamarisk Ave.s 4.4 4.3 3.1 3.1

South Scottsdale, 2857 N. Miller Rd.s

2.1 2.0 1.6 1.6

Tempe, 1525 S. College Ave.s3.4 2.4 1.9 1.6

West Chandler, 275 S. Elliss2.0 2.0 1.9 1.6

West Indian School, 3315 W. Indian

School Rd. (Closed June 30, 2010) #

3.7 3.3 2.3 2.3

West Phoenix, 3847 W. Earll 4.3 4.2 3.3 3.2

* Due to mathematical rounding, values $ 35.5 and 9.5 ppm are necessary to exceed the

standard.

S Seasonal monitor operating September 1st to April 1st.

#

Less than 75 percent data available.

+

The Buckeye monitor is located outside the carbon monoxide maintenance area.

Sources: Environmental Protection Agency Air Quality System; Maricopa County Air

Quality Department 2008-2011 Air Monitoring Network Reviews.

2-5
TABLE 2-4

2011 CARBON MONOXIDE MONITORING DATA SUMMARY

FOR THE MARICOPA COUNTY MAINTENANCE AREA

STANDARDS: 1-HOUR: 35 PPM; 8-HOUR: 9 PPM*

Site Name

1-Hour 8-Hour

Max

ppm

2

nd

 Max

ppm

Max

ppm

2

nd

 Max

ppm

Buckeye, 26449 W. 100th Dr.s+1.8 1.2 0.9 0.8

Central Phoenix, 1645 E. Roosevelt 3.8 3.5 2.1 2.1

Dysart, 16825 N. Dysart Rd.s1.0 0.9 0.5 0.5

Glendale, 6001 W. Olive

s

1.9 1.8 1.3 1.2

Greenwood, 1128 N. 27th Ave. 3.0 2.9 2.5 2.5

JLG Supersite, 4530 N. 17th Ave.#2.5 2.5 2.3 2.1

Mesa, 310 S. Brookss1.9 1.8 1.5 1.3

North Phoenix, 601 E. Butler Dr.s2.9 2.7 1.6 1.5

South Phoenix, 33 W. Tamarisk Ave.s 3.0 2.9 2.6 2.0

South Scottsdale, 2857 N. Miller Rd.s

1.8 1.7 1.4 1.3

Tempe, 1525 S. College Ave.s3.6 3.4 3.2 2.9

West Chandler, 275 S. Elliss1.8 1.7 1.4 1.3

West Phoenix, 3847 W. Earll 4.4 3.9 3.0 2.9

* Due to mathematical rounding, values $ 35.5 and 9.5 ppm are necessary to exceed the

standard.

S Seasonal monitor operating September 1st to April 1st.

#

Less than 75 percent data available.

+

The Buckeye monitor is located outside the carbon monoxide maintenance area.

Sources: Environmental Protection Agency Air Quality System; Maricopa County Air

Quality Department 2008-2011 Air Monitoring Network Reviews.

2-6
2-7

ARICOPA 

ASSOCIATION of 

GOVERNMENTS 

Prepared by the Maricopa Association of Governments, December 2012 

FIGURE 2-1 CARBON MONOXIDE MAINTENANCE AREA 

AND CARBON MONOXIDE MONITORING SITES 

Legend 

Carbon Monoxide Maintenance Area 

• Carbon Monoxide Monitoring Site 

Freeway 

Planned Freeway 

Major Roads 

N 

Monitoring Site Name 

BE Buckeye 

CP Central Phoenix 

DY Dysart 

GL Glendale 

GR Greenwood 

JLG JLG Supers ite 

M E Mesa 

NP North Phoenix 

SP South Phoenix 

ss South Scottsdale 

1E Tempe 

MAP AREA 

While every effort has been made to ensure the accuracy of this 

information, the Maricopa Association of Governments makes no 

warranty, expressed or implied, as to its accuracy and expressly 

disclaims liability for the accuracy thereof. 

I:\Projects\air_quality\Maps\85x11 \co_mntrs_201 1.mxd 
* Due to mathematical rounding, values $ 9.5 ppm are necessary to exceed the standard.

Second-Highest Concentration

8-Hour Average Values

WP TE,WP

WP WP

WP

W WPI

8-hour standard = 9.4 ppm*

WP

FIGURE 2-2

CARBON MONOXIDE TRENDS

(2004-2011)

Monitors Where the Second-Highest Reading Occurred

(TE) Tempe

(WI) West Indian School Road

(WP) West Phoenix

Source: Environmental Protection Agency Air Quality System.

2-8
CHAPTER THREE

MAINTENANCE PLAN

No violation of the one-hour National Ambient Air Quality Standard for carbon monoxide

has occurred in Maricopa County since 1984 and no violation of the eight-hour carbon

monoxide standard has been recorded at any monitor since 1996. The Revised MAG

1999 Serious Area Carbon Monoxide Plan for the Maricopa County Nonattainment Area

was submitted to the Environmental Protection Agency (EPA) in 2001 (MAG, 2001). The

Carbon Monoxide Redesignation Request and Maintenance Plan for the Maricopa County

Nonattainment Area was submitted to EPA in 2003 (MAG, 2003). 

The Revised 1999 Serious Area Carbon Monoxide Plan demonstrated attainment of the

carbon monoxide standards by 2000. The 2003 Carbon Monoxide Maintenance Plan 

demonstrated continued maintenance of the carbon monoxide standards through 2015. 

EPA approved the Revised 1999 Serious Area Carbon Monoxide Plan and the 2003

Carbon Monoxide Maintenance Plan and redesignated the Maricopa County area to

attainment, effective April 8, 2005 (EPA, 2005). 

Section 175A(b) of the Clean Air Act Amendments states that “8 years after redesignation

of any area as an attainment area under section 107(d), the State shall submit to the

Administrator an additional revision of the applicable State implementation plan for

maintaining the national primary ambient air quality standard for 10 years after the

expiration of the initial 10-year period”. Thus, a second carbon monoxide maintenance

plan for the years 2016 through 2025 for the Maricopa county area is required for submittal

to EPA by April 8, 2013. 

This second carbon monoxide maintenance plan (hereafter referred to as the 2013 CO

Maintenance Plan) demonstrates maintenance of the National Ambient Air Quality

Standards for carbon monoxide in the Maricopa County area through 2025 and establishes

a 2025 conformity budget for onroad mobile source emissions using the latest version of

the EPA Motor Vehicle Emission Simulator (MOVES) model, MOVES2010b. The 2008

Periodic Emissions Inventory for Carbon Monoxide for the Maricopa County, Arizona

Maintenance Area is also included in Appendix A, Exhibit 1.

MAINTENANCE PLAN CONTROL MEASURES

The Maricopa County area will continue to implement the maintenance measures in the

2003 Carbon Monoxide Maintenance Plan. The first nine measures in Table 3-1 were

used for numeric credit in demonstrating maintenance of the carbon monoxide standards

through 2015. These measures are described in Chapter Two of the 2003 CO

Maintenance Plan. The tenth measure, Expansion of Area A Boundaries, was one of three

contingency measures in the 2003 Carbon Monoxide Maintenance Plan. This measure

is described in Section VII-2-2 of the Technical Support Document in Appendix A, Exhibit 

3-1
TABLE 3-1

MAINTENANCE MEASURES IN THE 2013 CARBON MONOXIDE MAINTENANCE

PLAN

 1. California Phase 2 Reformulated Gasoline with 3.5% Oxygen Content From

November 1 Through March 31

 2. Off-Road Vehicle and Engine Standards

 3. Phased-In Emission Test Cutpoints

 4. One-time Waiver from Vehicle Emissions Test

 5. Defer Emissions Associated with Government Activities

 6. Coordinate Traffic Signal Systems

 7. Develop Intelligent Transportation Systems

 8. Tougher Enforcement of Vehicle Registration and Emissions Test Compliance

 9. Clean Burning Fireplace Ordinances

10. Expansion of Area A Boundaries 

3-2
2 of the 2003 Carbon Monoxide Maintenance Plan (MAG, 2003). The reason for converting

this measure from contingency to maintenance in the 2013 Carbon Monoxide Maintenance

Plan is discussed below. 

In November 2012, EPA proposed to approve the 110(l) SIP revision submitted by the

Arizona Department of Environmental Quality (ADEQ, 2009; ADEQ, 2011) that will eliminate

the requirement for motorcycles to participate in the Arizona vehicle emissions inspection

and maintenance (VEI) program (EPA, 2012a). EPA has indicated that the benefits of the

contingency measure, Expansion of Area A Boundaries, in the 2003 Carbon Monoxide

Maintenance Plan may be used to offset the increase in emissions attributable to the

exemption of motorcycles from the VEI program. Like other contingency measures in the

2013 CO Maintenance Plan, this measure was implemented early, in accordance with EPA

guidance (EPA, 1993). 

Therefore, the Expansion of Area A Boundaries is included as a maintenance measure in

the 2013 Carbon Monoxide Maintenance Plan. As discussed in the Contingency Provisions

section of this chapter, ADEQ has made a commitment to re-institute the VEI program

requirement for motorcycles, if there is a future violation of the carbon monoxide standard.

EMISSIONS INVENTORIES

The emissions inventories used in performing the maintenance demonstration are presented

in Table 3-2, for 2006, 2008, 2015 and 2025 in the carbon monoxide modeling domain, and

Table 3-3, for 2008 and 2025 in the CO maintenance area. The 2008 emissions in both

tables are based on the latest periodic emissions inventory (PEI) for carbon monoxide (CO)

contained in Appendix A, Exhibit 1 (MCAQD, 2012). The PEI estimates CO emissions for

a typical weekday during the winter months, November - January.

Emission reduction credit for two measures in Table 3-1, California Phase 2 Reformulated

Gasoline and Off-Road Vehicle and Engine Standards, is reflected in the emissions

inventories shown in Tables 3-2 and 3-3. The EPA MOVES2010b model estimates that

California Phase 2 Reformulated Gasoline will reduce CO emissions by 128.9 metric tons

per day in 2025, a reduction in CO maintenance area emissions of about 17 percent. The

EPA NONROAD2008a model estimates that Off-Road Vehicle and Engine Standards will

reduce CO emissions by 15.0 metric tons per day in 2025, which represents a two percent

reduction in CO maintenance area emissions. 

While other maintenance measures in Table 3-1 will continue to be implemented, their

collective carbon monoxide reduction impact in 2025 is anticipated to be less than one

percent. Therefore, no numeric credit has been taken for these measures in the

maintenance demonstration. In addition to Reformulated Gasoline and Off-Road Vehicle

and Engine Standards, the maintenance demonstration in this plan is dependent upon the

emission reduction benefits of tighter federal emission standards for new onroad and

nonroad engines, fuel requirements, and continuing fleet turnover to lower emissions from

onroad and nonroad vehicles. These emission reduction benefits are reflected in the onroad

and nonroad emissions shown in Tables 3-2 and 3-3.

3-3
TABLE 3-2

AVERAGE WEEKDAY EMISSIONS DURING THE WINTER SEASON

IN THE CARBON MONOXIDE MODELING DOMAIN

Source

Category

CO Emissions (metric tons/day)

2006 2008 2015 2025

Point 0.4 0.7 18.0 18.0

Area 26.4 25.8 29.6 33.1

Nonroad 227.1 187.0 133.1 129.4

Onroad 549.1 410.0 297.9 223.4

Total 803.0 623.5 478.6 403.9

TABLE 3-3

AVERAGE WEEKDAY EMISSIONS DURING THE WINTER SEASON

IN THE CARBON MONOXIDE MAINTENANCE AREA

Source

Category

CO Emissions

(metric tons/day)

2008 2025

Point 0.7 19.8

Area 37.8 47.3

Nonroad 281.5 213.1

Onroad 581.6 359.4

Total 901.6 639.6

3-4
The data used to derive growth factors for estimating point and area source emissions were

derived from the MAG Socioeconomic Projections of Population, Housing and Employment

by Municipal Planning Area and Regional Analysis Zone in Maricopa County (MAG, 2007). 

These projections, which cover the period 2010 through 2030, are based on the 2005

Special U.S. Census conducted in Maricopa County and were approved by the MAG

Regional Council in May 2007. 

Onroad mobile source emissions for the 2013 Carbon Monoxide Maintenance Plan were

estimated using the MOVES2010b model and traffic assignment data output by the MAG

TransCAD travel demand model. The socioeconomic projections adopted by the MAG

Regional Council in 2007 were also used as input to the travel demand model. 

Nonroad equipment emissions were developed with the EPA NONROAD2008a model, using

default NONROAD2008a activity growth rates for Maricopa County, with one exception. 

Equipment population and activity levels for commercial lawn and garden equipment were

based on a survey performed as part of Cap and Trade Oversight Committee work

(ENVIRON, 2003). 

The Emissions and Dispersion Modeling System (EDMS) and Federal Aviation

Administration Terminal Area Forecast system database were used to estimate future

emissions for all airports, except Luke Air Force Base (AFB). Luke AFB emissions were

derived from the 2008 Mobile Source Emissions Inventory for Luke AFB (Weston, 2010) and

the F-35A Training Basing Environmental Impact Statement (USAF, 2012).

Details regarding the technical inputs and assumptions used in preparing the emissions

inventories are provided in Chapter II of the TSD (Appendix A, Exhibit 2). The percentage

contributions of CO emissions by source category are illustrated in Figures 3-1 and 3-2 for

the CO modeling domain and maintenance area, respectively. 

MAINTENANCE DEMONSTRATION

The 2013 Carbon Monoxide Maintenance Plan relies on a series of technical analyses to

demonstrate maintenance of the National Ambient Air Quality Standards for carbon

monoxide through 2025. The maintenance demonstration assumes that the measures in

Table 3-1 will continue to be implemented through 2025.

Three different modeling analyses were performed to estimate the effects of growth and

emission reduction strategies on future carbon monoxide concentrations in the Maricopa

County area. In addition, two weight of evidence evaluations were conducted using actual

trends in air quality and meteorological data to reinforce the modeling analyses. The results

of these five quantitative assessments provide assurance that there will continue to be

compliance with the federal carbon monoxide standards through 2025.

A modeling protocol was developed to detail the technical approaches and assumptions to

be used in demonstrating maintenance of the federal standards for carbon monoxide. The

modeling protocol is contained in Appendix I of the Technical Support Document for the

2013 CO Maintenance Plan (TSD), contained in Appendix A, Exhibit 2. 

3-5
FIGURE 3-1

2008 AND 2025 CARBON MONOXIDE EMISSIONS BY SOURCE CATEGORY FOR

THE CARBON MONOXIDE MODELING DOMAIN

 

FIGURE 3-2

2008 AND 2025 CARBON MONOXIDE EMISSIONS BY SOURCE CATEGORY FOR

THE CARBON MONOXIDE MAINTENANCE AREA

 

3-6
For the maintenance demonstration, two sets of carbon monoxide emissions inventories

were developed representing: (1) the carbon monoxide modeling domain in 2006, 2008,

2015, and 2025 and (2) the carbon monoxide maintenance area in 2008 and 2025. The

carbon monoxide modeling domain and maintenance area are illustrated in Figure 3-3. The

modeling domain covers 792 square miles, while the maintenance area represents 1,814

square miles. Both of these areas are located within Maricopa County.

The 2008 Periodic Emissions Inventory for Carbon Monoxide in the Maricopa County

Maintenance Area is provided in Appendix A, Exhibit 1 (MCAQD, 2012). This inventory was

used to establish the 2008 base case emissions, back-cast the 2006 emissions, and project

the 2015 and 2025 future emissions with control measures in place. 

The modeling for the 2013 CO Maintenance Plan was conducted using three approaches:

(1) an emissions inventory comparison, (2) a scaling of the Urban Airshed Model/CAL3QHC

maximum concentration, and (3) a CAL3QHC intersection hotspot analysis. The first

approach demonstrates maintenance of the standard by showing a continuing decrease in

emissions levels in 2015 and 2025 compared with emissions levels in 2006 and 2008. The

second approach scales the UAM/CAL3QHC maximum eight-hour concentrations for 2006

and 2015 derived from the 2003 CO Maintenance Plan based on the ratio of future year to

base year total anthropogenic carbon monoxide emissions. The scaled UAM/CAL3QHC

maximum concentration in 2025 was used to demonstrate maintenance of the eight-hour

carbon monoxide standard. 

In the third approach, CAL3QHC modeling was performed for six intersections which are

expected to experience the heaviest traffic volumes and congestion in 2025. The CAL3QHC

maximum eight-hour CO concentration projected for each intersection was added to the

estimated background concentration for 2025. The combined background and CAL3QHC

maximum eight-hour concentration at each intersection was also used to demonstrate

maintenance of the eight-hour carbon monoxide standard in 2025.

In addition to the three modeling approaches described above, two weight of evidence

analyses were performed to demonstrate maintenance through 2025. These include an

evaluation of historical one-hour and eight-hour carbon monoxide concentration trends at

monitoring sites and a regional meteorological analysis. For the first weight of evidence

analysis, historical CO concentration trends for each monitoring site were developed and the

trend was extended to 2015 and 2025 using regression analysis. For the second weight of

evidence approach, a meteorological analysis was performed to demonstrate that the

historical improvements in CO concentrations in the Maricopa County area are not due to

unusually favorable meteorological conditions. 

Summaries of the five technical analyses conducted as part of the maintenance

demonstration are described in the subsections that follow. Details regarding these

analyses and underlying technical assumptions are documented in Section IV of the TSD

(Appendix A, Exhibit 2).

3-7
FIGURE 3-3 

CARBON MONOXIDE MODELING DOMAIN AND MAINTENANCE AREA

3-8

.· 

;ii Palo Verde 

Me iteRedhawk 

on . .Valley Energy 

0 2.25 4.5 

• BE 

·. 

• ;ii Power Plant _ 

c::J CO Modeling Domain 

CJ CO M a intenance Area 

c:::::J M aricopa Cou nty 
Emissions Inventory Comparison

The emissions in the carbon monoxide modeling domain shown in Table 3-2 were estimated

using the latest emissions models and planning assumptions. Table 3-4 compares the total

2006 and 2015 CO emissions in Table 3-2 with emissions derived with older models and

assumptions as part of the 2003 CO Maintenance Plan. In order to estimate the maximum

eight-hour CO concentration in 2025, the maximum concentration in 2006 of 5.3 ppm at the

West Indian School monitor was multiplied by the ratio of 403.9 metric tons per day in 2025

divided by 803.0 tons per day in 2006. This results in an estimated maximum eight-hour

concentration in the CO modeling domain of 2.7 parts per million (ppm) in 2025. 

Table 3-3 indicates that total emissions in the CO maintenance area are 639.6 metric tons

per day in 2025 and 901.6 metric tons per day in 2008. Applying this ratio to the maximum

eight-hour CO concentration of 3.1 ppm at the West Phoenix monitor in 2008, results in an

estimated maximum eight-hour CO concentration of 2.2 ppm In 2025. These two emissions

inventory comparisons reveal that the maximum concentration will remain well below the

eight-hour standard of 9 ppm in both the CO modeling domain and the CO maintenance

area through 2025. 

Scaled UAM/CAL3QHC Maximum Eight-Hour Concentrations

In the MAG 2003 CO Maintenance Plan, the eight-hour carbon monoxide concentrations in

the modeling domain were estimated for the years 2006 and 2015 using the EPA-approved

Urban Airshed Model (UAM) and intersection hotspot model (CAL3QHC). Since the

UAM/CAL3QHC predictions were derived from the emissions inventories based on older

versions of models (e.g., MOBILE6) available at the time the MAG 2003 CO Maintenance

Plan was developed, emissions inventories for the years 2006 and 2015, as well as the

maintenance year 2025, were newly developed, as shown in Table 3-4, using the latest

versions of models and updated input data. The UAM/CAL3QHC projections for the years

2006 and 2015 were adjusted by the ratio of the new to old emissions inventory totals. The

adjusted 2006 and 2015 UAM/CAL3QHC estimates from the MAG 2003 CO Maintenance

Plan were scaled for the maintenance year 2025. 

Although the Phoenix Grand Avenue and West Indian School monitors were deactivated in

1993 and 2010, respectively, modeling conducted for the Revised MAG 1999 Serious Area

CO Plan (MAG, 2001) and the MAG 2003 CO Maintenance Plan (MAG, 2003) projected

that these monitored intersections would have some of the highest levels of traffic

congestion and CO concentrations in future years. In addition, the West Indian School

monitor recorded the peak CO concentration of 10.5 ppm during the 1994 episode that was

modeled in both plans. The adjusted and scaled maximum concentrations for these two

intersections, as well as the highest eight-hour CO concentrations predicted by

UAM/CAL3QHC in the modeling domain, are shown in Table 3-5. The scaled maximum

UAM/CAL3QHC eight-hour CO concentration for 2025 is 4.0 ppm, which is less than half

the eight-hour CO standard of 9 ppm. 

3-9
TABLE 3-4

TOTAL CARBON MONOXIDE EMISSIONS IN THE CARBON MONOXIDE MODELING

DOMAIN

Source

Total CO Emissions (metric tons/day)

2006 2015 2025

2003 CO Maintenance Plan 912.3 901.2 N/A

2013 CO Maintenance Plan 803.0 478.6 403.9

TABLE 3-5

UAM/CAL3QHC MAXIMUM EIGHT-HOUR CARBON MONOXIDE CONCENTRATION

ADJUSTMENTS AND SCALED ESTIMATES FOR 2025

 (units = ppm)

2006 2015 2025

UAM/

CAL3QHC Adjusted

UAM/

CAL3QHC Adjusted

Based on

2006

Based on

2015

WI Monitor* 7.28 6.41 6.59 3.50 3.22 2.95

WI Receptor #9 8.25 7.26 8.08 4.29 3.65 3.62

WI Receptor #8 8.08 7.11 7.84 4.16 3.58 3.51

WI Receptor #20 7.85 6.91 7.44 3.95 3.48 3.33

PHGA Monitor** N/A N/A N/A N/A N/A N/A

PHGA Receptor #30 8.24 7.25 7.81 4.15 3.65 3.50

PHGA Receptor #46 8.08 7.11 7.45 3.96 3.58 3.34

PHGA Receptor #29 8.03 7.07 7.39 3.92 3.56 3.31

UAM/CAL3QHC

Maximum 8.92 7.85 8.06 4.28

3.95

(rounded

to 4.0)

3.61

WI = West Indian School

PHGA = Phoenix Grand Avenue

*The WI Monitor was deactivated on June 30, 2010

**The PHGA monitor values were not available (N/A) for the 1994 episode modeled with

UAM/CAL3QHC (MAG, 2001; MAG, 2003), because the monitor was deactivated on March 31,

1993, due to impending reconstruction of the adjacent intersection.

*** The UAM/CAL3QHC maximum was rounded to one decimal place.

3-10
Intersection Hotspot Analysis

The three intersections projected to have the highest traffic volumes and the three

intersections projected to have the worst traffic congestion were identified using the MAG

TransCAD traffic assignment for the year 2025. Detailed data sets were collected for each 

of the six intersections and they were modeled using CAL3QHC to determine the maximum

eight-hour CO concentration in 2025. The modeling input assumptions and results are

detailed in Section III of the TSD (Appendix A, Exhibit 2). The background eight-hour CO

concentration used for all intersections was determined to be 1.3 ppm. The maximum eighthour CO concentration in 2025, which is the sum of the intersection maximum impact and

the background concentration, was projected to be 1.7 ppm at two intersections: 16th Street

and Camelback Road and Priest Drive and Southern Avenue, as shown in Table 3-6. The

results from the CAL3QHC intersection hotspot analysis support the conclusion that high

traffic volumes and congestion will not contribute to exceedances of the eight-hour carbon

monoxide standard in 2025.

Continued Monitored Attainment

In addition to the three modeling analyses described above, MAG conducted two weight of

evidence evaluations to support the maintenance demonstration. The first of these

assessed the historical trends in one-hour and eight-hour concentrations measured at

carbon monoxide monitors in the Maricopa County area. To demonstrate attainment,

carbon monoxide concentrations at each monitor should not exceed the one-hour standard

of 35 ppm more than once per year for two consecutive years. In addition, the eight-hour

standard of 9 ppm can not be exceeded more than once per year for two consecutive years. 

The trends in the second-highest eight-hour carbon monoxide concentrations at eighteen

monitors for the years 1996 - 2011 are shown in Table 3-7. Similar tables showing the

highest and second-highest one-hour CO concentrations and highest eight-hour CO

concentrations recorded at these eighteen monitors are shown in Section IV-3-1 of the TSD

(Appendix A, Exhibit 2). The one-hour carbon monoxide standard has not been violated at

any monitor since 1984. The highest and second highest one-hour CO concentrations at

all monitors in 2011 were 4.4 ppm and 3.9 ppm, respectively.

The second-highest eight-hour carbon monoxide concentration of 10.0 ppm was recorded

at the Grand Avenue monitor in 1996. Since then, no monitor has violated the eight-hour

CO standard. Eight-hour CO concentrations have continued to decline over the past

decade. The highest and second highest eight-hour CO concentrations in 2011 were 3.2

ppm and 2.9 ppm, respectively.

To predict future concentrations based on the historical monitored carbon monoxide

concentrations, a regression analysis was performed using data recorded at fourteen CO

monitors for the period 1980 to 2011. The regression equations were used to project carbon

monoxide concentrations to 2015 and 2025. Figure 3-4 shows the historical and projected 

3-11
TABLE 3-6

MAXIMUM CAL3QHC EIGHT-HOUR CARBON MONOXIDE CONCENTRATIONS

 IN 2025

 (units = ppm)

Intersection

CAL3QHC

Maximum

One-Hour CO

Concentration

Maximum

Eight-Hour CO

Concentration

Background

CO

Concentration

Total

Maximum

Eight-Hour CO

Concentration

16th St & Camelback Rd 0.5 0.4

1.3

1.7

107th Ave & Grand Ave 0.4 0.3 1.6

Priest Dr & Southern Ave 0.5 0.4 1.7

7

th Ave & Van Buren St 0.4 0.3 1.6

Germann Rd & Gilbert Rd 0.4 0.3 1.6

Thomas Rd & 27th Ave 0.4 0.3 1.6

3-12
TABLE 3-7

SECOND HIGHEST EIGHT-HOUR CARBON MONOXIDE CONCENTRATIONS AT MONITORS IN MARICOPA COUNTY

FOR 1996-2011

 (units = ppm)

Site ID Site Name Abbr

2

nd

 highest non-overlapping 8-hour CO concentrations

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

04-013-0013 South Phoenix (old)* SP 5.1 4.4 4.7 4.1

04-013-0016 W Indian School Rd WI 8.3 7.2 8.1 7.6 6.8 6.0 5.4 5.3 4.6 4.8 4.5 3.9 2.8 3.3 2.3

04-013-0019 West Phoenix WP 8.2 7.0 7.1 7.5 7.2 6.6 5.5 5.5 5.1 4.6 4.6 4.1 3.0 3.3 3.2 2.9

04-013-0022 Grand Ave GA 10.0 7.8 6.8 8.1 6.0 6.2 5.5

04-013-1003 Mesa ME 3.8 4.5 3.7 4.0 3.2 2.7 3.5 2.2 1.7 2.4 2.0 2.0 1.3 1.3 1.4 1.3

04-013-1004 North Phoenix NP 3.7 3.4 5.6 3.5 3.1 2.5 2.7 2.1 2.0 2.2 1.9 1.6 1.3 1.3 1.6 1.5

04-013-2001 Glendale GL 3.7 3.0 3.4 3.5 3.2 2.8 2.7 2.3 2.1 2.3 1.8 1.6 1.5 1.2 1.5 1.2

04-013-3002 Central Phoenix CP 7.5 7.2 6.3 6.0 5.2 4.1 4.1 3.8 3.3 3.8 3.2 2.9 2.2 2.1 2.2 2.1

04-013-3003 South Scottsdale SS 4.9 4.2 3.5 4.1 3.1 3.1 2.8 2.2 2.4 2.4 1.9 1.6 1.4 1.4 1.6 1.3

04-013-3005 Gilbert GI 2.2 2.7 2.4 2.0

04-013-3006 Maryvale MA 6.3 5.9 6.7 7.0 5.3 5.0 4.1 2.9

04-013-3009 West Chandler (old)* WC 2.7 2.7 2.8 2.3

04-013-3010 Greenwood GR 6.9 6.8 6.7 5.6 4.6 5.1 5.1 4.3 4.1 3.5 3.0 2.4 2.4 2.3 2.5

04-013-4003 South Phoenix (new)

* SP 4.4 4.8 3.4 3.7 3.3 3.3 3.2 2.7 2.3 2.0 2.2 3.1 2.0

04-013-4004 West Chandler (new)

* WC 2.2 2.1 2.2 2.6 2.1 2.0 2.0 1.5 1.4 1.5 1.6 1.3

04-013-4005 Tempe TE 3.2 3.1 3.4 2.4 1.7 2.4 2.4 1.9 1.4 2.1 1.6 2.9

04-013-4007 Surprise SU 1.1 1.1 0.8

04-013-4010 Dysart DY 1.1 1.1 1.2 0.8 1.3 1.0 0.8 0.6 0.5

04-013-4011 Buckeye BE 0.4 0.9 0.6 0.8 0.5 0.5 0.6 0.8

04-013-9997 Super Site SUPR 6.5 6.5 5.2 4.2 4.2 4.0 3.6 2.9 2.9 2.4 2.3 2.1 2.1

Maximum 10.0 7.8 8.1 8.1 7.2 6.6 5.5 5.5 5.1 4.8 4.6 4.1 3.0 3.3 3.2 2.9

* South Phoenix and West Chandler monitors (old) were relocated to the new South Phoenix and West Chandler sites in 1999 and 2000, respectively.

3-13
FIGURE 3-4

HISTORICAL ONE-HOUR AND EIGHT-HOUR CARBON MONOXIDE MONITORING

DATA AND PROJECTIONS FOR THE WEST PHOENIX MONITORING SITE

3-14

West Phoenix Site 

40 .--------------------------------------------------------------------. 

1-HourCO Standard(35 ppm) 35 ...................................... .. .. .. .................. ........................... ~ •• -... ~ ..................... -

30 

10 

8-HourCO Standard(9 ppm) 

-::~-~;: :fa ---- 3.6 pp;n- ... . . ;t:. ' ... 2 .0 pm .......... .'I..' 

0 +-------,-------.--------.-------.-------.-------.------ .7 ppm ____________ pm 

5 

1980 1985 1990 1995 2000 2005 20 10 20 15 2020 2025 

Year 

--2nd Highest 1-Hour CO - 2nd Highest 8-Hour CO 
trends in the second-highest one-hour and eight-hour CO concentrations at the West

Phoenix monitor. The West Phoenix site has the highest projected eight-hour CO

concentrations of 2.7 ppm in 2015 and 1.6 ppm in 2025. Similar graphs for the other

thirteen monitors are provided in Section IV-3-1 of the TSD (Appendix A, Exhibit 2). The

projected carbon monoxide concentrations based on historical data provide additional

evidence that the Maricopa County area will continue to maintain the one-hour and eighthour standards through 2025.

Meteorological Analysis

A meteorological analysis was performed to support the premise that the measured

decreases in carbon monoxide concentrations are attributable to permanent and

enforceable emission reductions, not unusually favorable meteorological conditions. The

permanent and enforceable measures that have achieved continuing reductions in carbon

monoxide concentrations, despite major increases in population, employment and vehicle

travel in the region, are described in the Revised MAG 1999 Serious Area Carbon Monoxide

Plan (MAG, 2001). For this purpose, long-term historical conditions for key meteorological

parameters, including temperature, wind speed, wind direction, atmospheric stability, and

mixing height, have been analyzed. The detailed results of this analysis are documented

in Section IV-3-2 of the TSD (Appendix A, Exhibit 2).

Four different meteorological analyses were performed to demonstrate that the continuing

trend in declining carbon monoxide concentrations in the Maricopa County area has not

been due to favorable meteorological conditions. Figure 3-5 shows the results of one of

these four analyses. This analysis was performed using meteorological data and eight-hour

carbon monoxide concentrations for the winter seasons of 1994-2011. This graph shows

clearly that maximum CO concentrations have declined, while daily wind speeds,

temperatures, and mixing heights have not varied significantly over the same period. 

The conclusions of the four meteorological analyses are summarized below:

• The maximum eight-hour CO concentrations have continued to decline, even though

meteorological conditions during those years have not differed significantly from the

1994 episode meteorological conditions.

• The eight-hour CO concentrations have declined, while the daily variations in wind

speeds, temperatures and mixing heights have not varied significantly over time.

• The one-hour CO concentrations have continued to decrease over time regardless

of meteorological conditions.

• Daily maximum eight-hour CO concentrations below the CO standard were

predominant during the period 1997 through 2011 under the same range of wind

speeds and mixing heights.

3-15
FIGURE 3-5

NORMALIZED DIURNAL CYCLES OF WIND SPEED, TEMPERATURE, MIXING

HEIGHT AND MAXIMUM EIGHT-HOUR CARBON MONOXIDE CONCENTRATIONS

3-16
Maintenance Demonstration Summary

Together, the three modeling and two weight of evidence analyses described above support

a definitive conclusion that carbon monoxide concentrations will remain well below the onehour and eight-hour standards through 2025. The following maximum eight-hour carbon

monoxide concentrations were projected for 2025: 

Emissions Inventory Comparison - 2.7 ppm (modeling domain); 2.2 ppm (maintenance area)

Scaled UAM/CAL3QHC Maximum Eight-Hour Concentrations - 4.0 ppm (modeling domain)

Intersection Hotspot Analysis - 1.7 ppm (near two high traffic/congested intersections)

Continued Monitored Attainment - 1.6 ppm (2nd-high at the West Phoenix monitor)

The maximum 2025 eight-hour carbon monoxide concentration projected by these four

analyses was 4.0 ppm, which was based on scaled UAM/CAL3QHC modeling results from

the 2003 CO Maintenance Plan. This maximum concentration in 2025 is less than half the

eight-hour carbon monoxide standard of 9 ppm. 

The Meteorological Analysis provides additional convincing evidence that the major

reductions in carbon monoxide concentrations since 1994, despite increases in regional

population, employment, and vehicle travel over this period, can be attributed to permanent

and enforceable federal and local measures in the EPA-approved carbon monoxide plans

for the region (MAG, 2001; MAG, 2003), rather than favorable meteorological conditions.

MONITORING NETWORK AND VERIFICATION OF CONTINUED ATTAINMENT

The ambient air quality monitoring network in Maricopa County is designed to assess the

extent of air pollution, ensure compliance with national legislation, evaluate control options,

and provide data for air quality modeling. In accordance with 40 CFR Part 58, the Maricopa

County Air Quality Department (MCAQD) currently maintains twelve carbon monoxide

monitoring sites in Maricopa County, while the Arizona Department of Environmental Quality

(ADEQ) operates the Supersite in central Phoenix. Table 3-8 lists the carbon monoxide

monitoring sites and their addresses.

MCAQD and ADEQ will continue to operate an appropriate air quality monitoring network

to collect and provide air quality data for use in demonstrating ongoing attainment of the

carbon monoxide standards. If the ambient levels of carbon monoxide concentrations rise

and threaten to exceed the federal standards, the reasons for these occurrences will be

investigated and appropriate actions will be taken. In compliance with 40 CRF Part 58

Subpart B, an annual air monitoring network review will be conducted to determine whether

the network meets the monitoring objectives defined in Appendix D of 40 CFR Part 58,

whether new sites are needed, and whether existing sites are no longer needed and can be

terminated. 

3-17
TABLE 3-8

CARBON MONOXIDE MONITORING SITES IN MARICOPA COUNTY

Site ID Site Name Abbr Address City

04-013-0016 West Indian School Rd* WI 33rd Ave & W Indian School Rd Phoenix

04-013-0019 West Phoenix WP 39th Ave & Earll Dr Phoenix

04-013-1003 Mesa ME Broadway Rd & Alma School Rd Mesa

04-013-1004 North Phoenix NP 7

th St & Dunlap Ave Phoenix

04-013-2001 Glendale GL 59th Ave & W Olive Glendale

04-013-3002 Central Phoenix CP 16th St & Roosevelt St Phoenix

04-013-3003 South Scottsdale SS Miller Rd & Thomas Rd Scottsdale

04-013-3010 Greenwood GR 27th Ave & Interstate 10 Phoenix

04-013-4003 South Phoenix SP Central Ave & Broadway Rd Phoenix

04-013-4004 West Chandler WC Ellis St & Frye Rd Chandler

04-013-4005 Tempe TE College Ave & Apache Blvd Tempe

04-013-4010 Dysart DY Dysart Rd & Bell Rd Surprise

04-013-4011 Buckeye BE Hwy 85 & MC 85 Buckeye

04-013-9997 Supersite SUPR 4530 N 17th Ave Phoenix

* Closed in 2010.

3-18
CONTINGENCY PROVISIONS

Section 175A(d) of the Clean Air Act requires that the maintenance plan contain contingency

provisions to ensure prompt actions to correct any violation of the carbon monoxide standard

which occurs after redesignation to attainment. A contingency plan is not required to contain

fully adopted contingency measures. However, the plan should contain clearly identified

contingency measures to be adopted, a schedule and procedure for adoption and

implementation, and a specific time limit for action by the State. In addition, specific

indicators should be identified which will be used to determine when the contingency

measures need to be implemented (EPA, 1992). The 2013 Carbon Monoxide Maintenance

Plan addresses each of these requirements below. 

Two contingency measures in this plan were also contingency measures in the EPAapproved 2003 CO Maintenance Plan: Gross Polluter Option for I/M Program Waivers and

Increased Waiver Repair Limit Options (MAG, 2003). A third contingency measure, 

Reinstatement of the VEI Program for Motorcycles, has been added to the 2013 CO

Maintenance Plan. 

Consistent with EPA guidance on early implementation of contingency measures, the two

contingency measures that were approved in the 2003 CO Maintenance Plan have already

been implemented in the CO maintenance area (EPA, 1993). No emission reduction credit

for these two contingency measures was taken in this maintenance demonstration. 

A description of the contingency measures in the 2003 CO Maintenance Plan is provided

in Section VII-2-2 of the Technical Support Document in Appendix A, Exhibit 2 (MAG, 2003). 

The reasons for converting the Expansion of Area A Boundaries from a contingency

measure in the 2003 CO Maintenance Plan to a maintenance measure in the 2013 Carbon

Monoxide MaintenancePlan and the addition of a new contingency measure, Reinstatement

of the VEI Program for Motorcycles, are discussed below.

In November 2012, EPA proposed to approve the 110(l) SIP revision submitted by the

Arizona Department of Environmental Quality (ADEQ, 2009; ADEQ, 2011) that will eliminate

the requirement for motorcycles to participate in the Arizona vehicle emissions inspection

and maintenance (VEI) program (EPA, 2012a). EPA has indicated that the benefits of the

contingency measure, Expansion of Area A Boundaries, in the 2003 CO Maintenance Plan

may be used to offset the increase in emissions attributable to the exemption of motorcycles

from the VEI program. Like other contingency measures in the 2003 CO Maintenance Plan,

this measure was implemented early, in accordance with EPA guidance (EPA, 1993). 

The motorcycle exemption is estimated to increase total carbon monoxide emissions in Area

A by 0.264 metric tons per day or 0.027 percent, while the 2003 CO Maintenance Plan

estimated that the expansion of Area A boundaries mandated by S.B. 1427 in 1998 reduced

total CO emissions by 0.1 percent in 2000. Since the Expansion of Area A Boundaries will

be used to offset the VEI exemption, it has been converted from a contingency measure in

the 2003 Maintenance Plan to a committed maintenance measure in the 2013 Carbon

Monoxide Maintenance Plan. 

3-19
As indicated in the ADEQ SIP revision that will exempt motorcycles from VEI testing, CAA

section 175A(d) requires that the State adopt as a contingency measure any control

measure that was approved in the SIP prior to redesignation, but which the State

subsequently repeals or relaxes (ADEQ, 2009; EPA, 2012a). In this instance, because the

EPA-approved VEI program applied to motorcycles at the time the Maricopa County area

was redesignated to attainment of the carbon monoxide standards in 2005, Reinstatement

of the VEI Program for Motorcycles must also be adopted as a contingency measure in the

2013 Carbon Monoxide Maintenance Plan. 

The ADEQ SIP revision proposes a contingency measure to reinstate VEI testing for

motorcycles in Area A if a violation of the carbon monoxide standard occurs. If a violation

of the eight-hour carbon monoxide standard occurs (i.e., the second-highest reading at the

same monitor over two consecutive years is 9.5 ppm or higher), reinstatement of the

motorcycle VEI program will be implemented according to the following schedule: ADEQ

will request that the Arizona State Legislature reinstate emissions testing of motorcycles by

October following the violation. In January 2013, ADEQ will request that the Legislature

enact new legislation to reinstate emissions testing of motorcycles previously exempted by

the revised SIP in the Phoenix vehicle emissions testing area, beginning January 1 of the

following year (ADEQ, 2009).

In general, the success of an air quality program is measured by the concentrations

recorded at the monitors. In order to ensure that violations of the carbon monoxide

standards do not occur in the future, ambient air quality monitoring data will be examined

to determine if additional contingency measures are needed. Two verified eight-hour carbon

monoxide readings exceeding 9.0 ppm at one monitor during the same winter season

(November - January) will trigger consideration of additional measures, which may include

the strengthening of contingency measures that have already been implemented. When the

trigger is activated, additional measures would be considered on the following schedule: (A)

verification of the monitoring data to be completed three months after activation of the

trigger; (B) applicable measures to be considered for adoption six months after the date

established in (A); and (C) resultant committed measures to be implemented within twelve

months after the adoption date in (B).

 

TRANSPORTATION CONFORMITY BUDGET

In accordance with the 1990 Clean Air Act Amendments (CAAA), transportation conformity

requirements are intended to ensure that transportation activities do not result in air quality

degradation. Section 176 of the Amendments requires that transportation plans, programs,

and projects conform to applicable air quality plans before the transportation action is

approved by a Metropolitan Planning Organization (MPO). The designated MPO for

Maricopa County is the Maricopa Association of Governments. 

Section 176(c) of the 1990 CAAA provides the framework for ensuring that Federal actions

conform to air quality plans under section 110. Conformity to an implementation plan means

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that proposed activities must not: (1) cause or contribute to any new violation of any

standard in any area, (2) increase the frequency or severity of any existing violation of any

standard in any area, or (3) delay timely attainment of any standard or any required interim

emission reductions or other milestones in any area.

EPA transportation conformity regulations establish criteria involving comparison of

projected transportation plan emissions with the motor vehicle emissions assumed in

applicable air quality plans. These regulations define the term “motor vehicle emissions

budget” as meaning “the portion of the total allowable emissions defined in a revision of the

applicable implementation plan (or in an implementation plan revision which was endorsed

by the Governor or his or her designee) for a certain date for the purpose of meeting

reasonable further progress milestones or attainment demonstrations, for any criteria

pollutant or its precursors, allocated by the applicable implementation plan to highway and

transit vehicles.”

The MAG 2003 CO Maintenance Plan, submitted to EPA in May 2003, established two

transportation conformity budgets for the carbon monoxide modeling domain: a 2006 CO

emissions budget of 699.7 metric tons per day and a 2015 CO budget of 662.9 metric tons

per day. EPA found the 2006 and 2015 carbon monoxide budgets to be adequate for

conformity purposes, effective October 14, 2003. In addition, these budgets were approved

by EPA as part of the MAG 2003 CO Maintenance Plan, effective April 8, 2005. Currently,

the approved 2006 budget applies to conformity horizon years from 2006 through 2014 and

the 2015 budget applies to horizon years after 2014.

Table 3-3 indicates that the onroad mobile source emissions for the CO maintenance area

will be 359.4 metric tons per day in 2025. EPA has indicated a new version of MOVES may

be released in 2013 that “will incorporate multiple sources of new emissions data” and “it is

too early in the development process for us to estimate the overall direction and magnitude

of the emissions changes” (EPA, 2012b). To ensure that increases in carbon monoxide

emission rates in future versions of the MOVES model do not cause exceedances of the

2025 conformity budget, it is proposed that a “safety margin” be applied to the 2025 onroad

mobile source emissions produced by MOVES2010b. 

Table 3-3 indicates that the 2008 carbon monoxide emissions estimated by MOVES2010b

for the maintenance area are 581.6 metric tons per day. The maximum eight-hour carbon

monoxide concentration in 2008 was 3.1 ppm (at the West Phoenix monitor), which is only

one-third of the standard. Figure IV-1 in the TSD (Appendix A, Exhibit 2) indicates that

carbon monoxide concentrations have declined since 2008 at all monitors and are projected

to remain far below the 2008 concentrations at every monitoring site. The hotspot analysis

also revealed that the traffic at high volume and heavily congested intersections will increase

eight-hour carbon monoxide concentrations by a maximum of 0.4 ppm in 2025. Therefore,

an increase in the 2025 conformity budget to a level below the 2008 emissions will not result

in an exceedance of the carbon monoxide standard. 

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It is proposed that the safety margin represent 90 percent of the difference between the

2008 and 2025 carbon monoxide emissions, which is 200.0 metric tons per day. When

added to the 2025 carbon monoxide emissions of 359.4 metric tons per day, this establishes

a new 2025 conformity budget of 559.4 metric tons per day for the CO maintenance area. 

It is important to note that the 2025 budget for the CO maintenance area is less than the

2006 and 2015 conformity budgets for the CO modeling domain, even though the

maintenance area is more than twice the size of the modeling domain.

Once EPA finds the new 2025 budget to be adequate (or approves the 2025 budget as part

of the MAG 2013 CO Maintenance Plan), the 2025 budget for the CO maintenance area will

be applied in regional conformity analyses conducted by MAG for horizon years 2025 and

beyond. The 2006 and 2015 conformity budgets approved by EPA as part of the MAG 2003

CO Maintenance Plan, effective April 8, 2005, will continue to be applied in conformity

analyses for horizon years prior to 2025. The approved 2006 carbon monoxide budget of

699.7 metric tons per day for the CO modeling domain will be applied in regional conformity

analyses for horizon years 2006 through 2014 and the approved 2015 carbon monoxide

budget of 662.9 metric tons per day for the CO modeling domain will be applied for horizon

years 2015 through 2024.

SUBSEQUENT MAINTENANCE PLAN REVISIONS

Section 175A(b) of the Clean Air Act requires that a maintenance plan be submitted to EPA

eight years after the original redesignation request and maintenance plan has been 

approved (i.e., by April 8, 2013). The purpose of this second maintenance plan is to

demonstrate maintenance of the federal carbon monoxide standards for an additional ten

years (2016-2025) following the first ten-year period (2006-2015).

No additional revisions of the carbon monoxide maintenance plan are anticipated at this

time. If EPA reduces the carbon monoxide standards, the Maricopa Association of

Governments, as the designated Regional Air Quality Planning Agency for the Maricopa

County area, will work with ADEQ, MCAQD, ADOT and EPA to revise the State

Implementation Plan, if necessary to demonstrate attainment and maintenance of the new

carbon monoxide standards.

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REFERENCES

ADEQ, 2009. Arizona Department of Environmental Quality. Arizona State Implementation

Plan Revision, Exemption of Motorcycles from Vehicle Emissions Inspections and

Maintenance Program Requirements in Area A. November 6, 2009.

ADEQ, 2011. Arizona Department of Environmental Quality. Arizona State Implementation

Plan Revision, Exemption of Motorcycles from Vehicle Emissions Inspections and

Maintenance Program Requirements in Area A. January 11, 2011.

ENVIRON, 2003. Maricopa County 2002 Comprehensive Emission Inventory for the Cap

and Trade Oversight Committee. Final Report prepared for Arizona Department of

Environmental Quality. October. 8, 2003.

EPA, 1992. U.S. Environmental Protection Agency. Procedures for Processing Requests to

Redesignate Areas to Attainment. September 4, 1992.

EPA, 1993. U.S. Environmental Protection Agency. Early Implementation of Contingency

Measures for Ozone and Carbon Monoxide (CO) Nonattainment Areas. August 13, 1993.

EPA, 2005. U.S. Environmental Protection Agency. Approval and Promulgation of

Implementation Plans and Designation of Areas for Air Quality Planning Purposes: Arizona. 

Federal Register, March 9, 2005, Vol. 70, No. 45, p. 11553. 

EPA, 2012a. U.S. Environmental Protection Agency. Approval and Promulgation of

Implementation Plans and Designation of Areas for Air Quality Planning Purposes: Arizona;

Motor Vehicle Inspection and Maintenance Programs. Federal Register, November 5, 2012,

Vol. 77, No. 214, p. 66422. 

EPA, 2012b. E-mail from Gary Dolce, EPA, to Taejoo Shin, MAG. October 25, 2012.

MAG, 2001. Maricopa Association of Governments. Revised MAG 1999 Serious Area

Carbon Monoxide Plan for the Maricopa County Nonattainment Area. March 2001.

MAG, 2003. Maricopa Association of Governments. Carbon Monoxide Redesignation

Request and Maintenance Plan for the Maricopa County Nonattainment Area. May 2003.

MAG, 2007. Maricopa Association of Governments. Socioeconomic Projections

Documentation. May 2007.

MCAQD, 2012. Maricopa County Air Quality Department. 2008 Periodic Emissions

Inventory for Carbon Monoxide for the Maricopa County, Arizona Maintenance Area. 2012.

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USAF, 2012. United States Air Force. F-35A Training Basing Environmental Impact

Statement, Final Volume 1. June 2012.

Weston, 2010. Weston Solutions Inc. 2008 Mobile Source Air Emissions Inventory for Luke

Air Force Base. Report prepared for the Air Education and Training Command (AETC), US

Air Force, Randolph AFB, TX. June 2010.

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