UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION IX 

75 Hawthorne Street 

San Francisco, CA 94105

October 31, 2013

Memorandum

To: Docket for the EPA Action on the Maricopa Association of Governments’ 2009 Ozone 

Maintenance Plan - Docket ID EPA-R09-OAR-2013-0686

From: Ginger Vagenas, Air Planning Office, EPA Region 9

RE: Adequacy Documentation for Motor Vehicle Emission Budgets in the February 2009

Ozone Maintenance State Implementation Plan for the Phoenix-Mesa Nonattainment 

Area 

Attached to this memorandum is the adequacy documentation for the motor vehicle emission budgets in 

the Maricopa Association of Governments’ February 2009 Eight-Hour Ozone Redesignation Request 

and Maintenance Plan for the Maricopa Nonattainment Area. Note that the official name (i.e., the name 

appearing in 40 CFR 81.303) for the nonattainment area is “Phoenix-Mesa.”
 

Evaluation of the Motor Vehicle Emissions Budgets in the

Maricopa Association of Government’s Eight-Hour Ozone Redesignation Request and Maintenance Plan for the Maricopa Nonattainment Area

February 2009

(1997 8-hour Ozone NAAQS)

Reviewed by Ginger Vagenas, October 2013

Adequacy Review Criteria

40 CFR part 93

Is Criterion

Satisfied?

Reference in SIP Document/Comments

Sec. 93.118(e)(4)(i) The plan was endorsed by the 

Governor (or designee) and was 

subject to a public hearing.

Y

The March 23, 2009 transmittal letter, which serves to adopt and submit MAG’s 

Eight-hour Ozone Redesignation Request and Maintenance Plan for the 

Maricopa County Nonattainment Area, was signed by ADEQ’s acting director, 

Patrick J. Cunningham, who is the Governor’s designee. 

A public hearing was held on January 22, 2009 and is documented in Enclosure 3 

of the submittal letter. See Appendix B of MAG’s Eight-hour Ozone 

Redesignation Request and Maintenance Plan for the Maricopa County 

Nonattainment Area.

Sec. 93.118(e)(4)(ii) The plan was developed through 

consultation with federal, state 

and local agencies; full 

implementation plan 

documentation was provided and 

EPA’s stated concerns, if any, 

were addressed.

Y

Documentation accompanying the plan describes the manner in which the public 

and governmental agencies are consulted. The Maricopa Association of 

Governments (MAG), which is the regional air quality planning agency for 

Maricopa County, coordinates with the Arizona Department of Environmental 

Quality (ADEQ), the Arizona Department of Transportation (ADOT) and the 

Maricopa County Air Quality Department in developing air quality plans. The 

plan was reviewed and approved by the Maricopa Association of Government’s 

Air Quality Technical Advisory Committee, the MAG Management Committee, 

and the MAG Regional Council. See Chapter 1, Introduction. EPA, ADEQ, 

Maricopa County, and ADOT received a copy of the draft plan in November 

2008. EPA’s comments were addressed.

Sec. 93.118(e)(4)(iii) The motor vehicle emission 

budgets are clearly identified and 

precisely quantified. Y

The motor vehicle emissions budgets (MVEBs) are included in Chapter 3 of the 

maintenance plan. The current maintenance plan establishes budgets for the 

year 2025 (VOC = 43.8 metric tons per day; NOx = 101.8 metric tons per day). 

See pages 3-19 and 3-20 of the maintenance plan and section IV.9 of the 

technical support document (Appendix A, Exhibit 2).
 

Sec. 93.118(e)(4)(iv) The motor vehicle emissions 

budgets, when considered 

together with all other emission 

sources, is consistent with 

applicable requirements for 

maintenance.

Y

MAG increased the the 2025 VOC and NOx emissions from onroad mobile 

sources in the eight-hour ozone modeling domain in order to address the 

“inherent uncertainties associated with the use of the latest planning 

assumptions in conformity analyses.” MAG distributed the increase spatially 

based on the proportion of onroad mobile emissions assigned to each four 

kilometer grid cell. See page 3-20 of the Ozone Maintenance Plan. While the 

MVEBs are derived from the modeling domain, they reflect only the motor 

vehicle emissions from within the nonattainment area.

Even with the 10 percent safety margin added to the on-road emissions, the 

overall projected emissions in the Phoenix-Mesa area are consistent with 

continued maintenance of the 1997 ozone standard.

The Ozone Maintenance Plan demonstrates that the level of emissions 

contained in the motor vehicle emissions budgets, with all other emissions 

sources, will provide for maintenance of the 1997 ozone NAAQS through 2025. 

See Chapter 3. 

Sec. 93.118(e)(4)(v) The plan shows a clear 

relationship among the emissions 

budget(s), control measures and 

the total emissions inventory.

Y

The emissions inventory for all point, area, and motor vehicle sources is

described in Section IV.2. of MAG’s Technical Support Document (included in 

the submittal as Appendix A, Exhibit 2), as well as in Chapter 3. See, for example, 

tables 3-6, 3-7, and 3-8. The documentation in these portions of the plan clearly 

shows the relationship among the inventories, control measures, and MVEBs, 

which are used in the modeling of continued maintenance.

Emission factors for vehicle classes were calculated using MOBILE6.2, which was 

the then-current version of the model that is used to estimate motor vehicle 

emission factors. The calculated emission factors were multiplied by the 

estimates of vehicle miles of travel (VMT) to generate emission estimates for 

onroad mobile sources. ADOT’s 2005 Highway Performance Monitoring System 

(HPMS)1and the 2005 traffic assignment prepared by MAG using the EMME/2 

travel demand model provided data for the VMT estimates.

The projected emissions inventory and MVEBs take into account reductions from 

the maintenance measures, but do not include reductions from implementation 

 

1

http://tpd.azdot.gov/data/reports/vmt2005.php
 

of the contingency measures.

Sec. 93.118(e)(4)(vi) Revisions to previously submitted 

control strategy or maintenance 

plans explain and document any 

changes to any previous 

submitted budgets and control 

measures; impacts on point and 

area source emissions; any 

changes to established safety 

margins (see §93.101 for 

definition), and reasons for the 

changes (including the basis for 

any changes to emission factors 

or estimates of VMT.

N/A

EPA previously approved 2008 budgets for VOC (67.9 metric tons per day) and 

NOx (138.3 metric tons per day) that were included in the attainment plan. See 

77 FR 35285; June 13, 2012.This maintenance plan does not revise previously 

submitted plans or budgets. The budgets established in this plan are for the year 

2025, and do not modify the currently approved 2008 budgets for VOC and NOx. 

Sec. 93.118(e)(5) EPA has reviewed the State’s 

compilation of public comments 

and response to comments that 

are required to be submitted 

with any implementation plan.

Y

No written comments were received during the comment period on the draft

plan. One commenter presented verbal testimony at the public hearing held on 

January 22, 2009. Those comments and MAG’s responses are included in 

Appendix B, Exhibit 1 of the submitted maintenance plan.

We have reviewed the compilation of comments and responses and find the 

responses to be acceptable. No issues that might have affected our adequacy 

finding remain unanswered.