UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION III

1650 Arch Street

Philadelphia, Pennsylvania 19103

DATE: February 6, 2014

SUBJECT: Technical Support Document for the Pittsburgh Area’s Carbon Monoxide Second 

Limited Maintenance Plan

FROM: Emlyn Vélez-Rosa, Environmental Engineer

Office of Air Program Planning

TO: File \s\

THRU: Cristina Fernandez, Associate Director

Office of Air Program Planning

I. INTRODUCTION

On July 18, 2011, the Commonwealth of Pennsylvania (“the Commonwealth”) submitted a 

revision to the Pennsylvania State Implementation Plan (SIP), containing a carbon monoxide 

(CO) second maintenance plan for the Pittsburgh Area, which is comprised by portions of 

Allegheny County. The SIP revision was supplemented on November 26, 2013. The SIP 

revision ensures maintenance of the CO National Ambient Air Quality Standards (NAAQS) in 

portions of the Allegheny County for a second ten-year period, from 2013 to 2022. 

II. BACKGROUND 

A. Designations

Carbon monoxide is a colorless, odorless gas emitted from combustion processes. Nationally 

and, particularly in urban areas, the majority of CO emissions to ambient air come from mobile 

sources. CO can cause harmful health effects by reducing oxygen delivery to the body's organs 

(like the heart and brain) and tissues. At extremely high levels, CO can cause death. 

The U.S. Environmental Protection Agency (EPA) initially established the CO NAAQS on April 

30, 1971 (36 FR 8186). The primary standards, protective of public health, were set at 9 parts 

per million (ppm) as an 8-hour average, and 35 ppm, as a 1-hour average, neither to be exceeded 

more than once per year. Later in 1971, EPA set the secondary standards identical to the primary 

standards for protection of the public welfare. See 40 CFR 50.8. In a review of the standards 

completed in 1985 (50 FR 37484, September 13, 1985), EPA retained the primary standard, but 
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revoked the secondary standard due to lack of evidence of direct adverse effect on public welfare 

at or near ambient concentrations. Although the air quality criteria have changed over the past 

two decades, the CO primary standard has been retained without revision. 

On September 12, 1978 (43 FR 40513), EPA designated for the first time portions of Allegheny 

County as a CO nonattainment area, referred to as the Pittsburgh Area. The Pittsburgh Area was 

defined to include the high traffic density areas within Central Business District of Allegheny 

County and certain other high traffic density areas. The Central Business District is defined as 

the area enclosed by the Allegheny River, the Monongahela River, and 579 interstate highway, 

while “the other high traffic density areas” are defined as the Oakland neighborhood of 

Pittsburgh, Pennsylvania.

In the 1990 Amendments, U.S. Congress added a provision under section 186(a) of the Clean Air 

Act (CAA) which authorized EPA to classify nonattainment areas according to the degree of 

severity of the nonattainment problem. Specifically, CAA section 186(a)(1) provides that each 

area designated nonattainment for CO should be classified at the time of such designation as 

“Moderate” (9.1 -16.4 ppm) or “Serious” (16.5 ppm and above) based on the design value of the

area. Additionally, under section 107(d)(a)(C), at the date of enactment of the CAA

Amendments, all areas of the country were designated with respect to ozone and CO in 

accordance with the pre-enactment designations by operation of the law. 

On November 6, 1991 (56 FR 56694), EPA made final designations and classifications for all 

areas in the country for all the six criteria pollutants. The designations and classifications for CO 

(post-enactment of 1990 CAA Amendments) were based on quality assured monitoring data for 

years 1988-1989. The Pittsburgh Area maintained its pre-enactment designation as a CO 

nonattainment area by operation of law. In this designation process, EPA determined that the

Pittsburgh Area was a “nonclassifiable” area with respect CO NAAQS, based on the fact that the 

1988-1989 air quality design values for the Area were below the lowest CO nonattainment 

classification of “Moderate” (below 9.1 ppm). 

B. Compliance with CO NAAQS

A monitor is meeting the CO NAAQS if over a 2-year period the second-highest 1-hour value is 

less than or equal to 35 ppm, and the second-highest, non-overlapping 8-hour value is less than 

or equal to 9 ppm. These calculated values are referred as the 1-hour and the 8-hour design 

value, respectively. A design value is calculated to compare to the NAAQS and determine 

compliance. The CO design values are usually discussed in terms of the 8-hour CO NAAQS, 

rather than the 1-hour NAAQS, because the 8-hour NAAQS is typically the standard of concern. 

The design value of an area is the highest site-specific design value of the monitors located 

within the area. A CO nonattainment area is considered for redesignation if the design value of 

the Area is below the standards, that is, if there are no violations of the CO NAAQS for two 

consecutive years. The method for calculating CO design values is presented in detail in EPA’s 

June 18, 1990 memorandum, “Ozone and Carbon Monoxide Design Value Calculations.” 
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C. Redesignation to Attainment and Maintenance Plan

EPA may redesignate areas to attainment if sufficient monitoring data are available to warrant 

such change and the area meets the criteria contained in section 107(d)(3)(E) of the CAA. These 

criteria include, among others, a full approval of a maintenance plan that covers at least 10 years 

after redesignation, and meets the requirements of section 175A of the CAA. In addition, section 

175A of the CAA require states to submit a revision to the maintenance plan eight years after 

redesignation to provide for maintenance of the NAAQS for 10 years following the end of the 

first 10-year maintenance period. To address potential future NAAQS violations, the 

maintenance plan must contain contingency measures, with a schedule for implementation 

adequate to assure prompt correction of any air quality problems. 

On August 17, 2001, the Commonwealth submitted to EPA a redesignation request and a 

maintenance plan for the Pittsburgh Area for the CO NAAQS. EPA allowed the Commonwealth 

to develop a “limited maintenance plan” (LMP) for the Pittsburgh Area in addressing the 

maintenance plan requirements, and thus meeting the applicable requirements for redesignation. 

According to EPA’s October 6, 1995 guidance “Limited Maintenance Plan Option for 

Nonclassifiable CO Nonattainment Areas,” the LMP option is only available to nonclassifiable 

CO nonattainment areas with design values at or below the 85 percent (%) of the level of the 8-

hour CO NAAQS, or 7.65 ppm. The LMP option allows the areas meeting this requirement to 

submit a less rigorous maintenance plan than generally required for the CO NAAQS. Since the 

Pittsburgh Area was designated as a “nonclassifiable” nonattainment area and the Area’s 8-hour 

design value at the time of redesignation was 3.9 ppm, based on 1998-1999, EPA concurred with 

the Commonwealth’s determination of submitting an LMP for the Area. On November 12, 2002

(67 FR 68521), EPA granted the Commonwealth’s redesignation request and approved as a SIP 

revision the maintenance plan for the Pittsburgh Area. The SIP revision ensured maintenance of 

the standard until January 2013. 

On July 18, 2011, the Pennsylvania Department of Environmental Protection (PADEP) 

submitted, on behalf of Allegheny County Health Department (ACHD), as a SIP revision a 

second 10-year CO maintenance plan for the Pittsburgh Area. In recognition of the continuing 

record of monitoring data showing ambient CO 8-hour concentrations in the Pittsburgh Area well 

below 7.65 ppm, ACHD once more chose the LMP option for the development of this second 

maintenance plan. Further discussion of the maintenance plan requirements and the LMP option 

is provided in section III of this document.

III. EPA’S REQUIREMENTS

Section 175A defines the general framework of a maintenance plan. The maintenance plan will 

constitute a SIP revision and must provide for maintenance of the relevant NAAQS for at least 

10 years after redesgination. Section 175A further states that the plan shall contain such 
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additional measures, if any, as may be necessary to ensure such maintenance. In addition, the 

maintenance plan should contain such contingency measures as EPA deems necessary to ensure 

prompt correction or any violation of the NAAQS. 

According to EPA’s September 4, 1992 Guidance Memorandum “Procedures for Processing 

Requests to Redesignate Areas to Attainment,” the following requirements should be addressed 

by a maintenance plan: 

(1) Attainment Inventory: The state should develop an attainment emissions inventory to 

identify the level of emissions in the area which is sufficient to attain the NAAQS. This 

inventory should be consistent with EPA’s most recent guidance on emissions inventories 

for nonattainment areas available at the time and should include the emissions during the 

time period associated with the monitoring data showing attainment. Emissions of CO 

are generally expected to be the highest during the winter season. Thus, for CO 

nonattainment areas, the inventory should be based on actual “typical winter day”

emissions for the time period associated with the monitoring data showing attainment of 

the standard. For more information on developing seasonal CO emissions inventories, 

refer to EPA’s guidance documents “Emissions Inventory Requirements for Carbon 

Monoxide State Implementation Plans” (EPA-450/4-91-011, March 1991) and 

“Procedures for the Preparation of Emissions Inventories for Carbon Monoxide and 

Precursors of Ozone; Volume I” (EPA-450/4-91-016, May 1991).

(2) Maintenance Demonstration: A state may generally demonstrate maintenance of the 

NAAQS by either showing that the future emissions of a pollutant or its precursors will 

not exceed the level of the attainment inventory, or by modeling to show that the future 

mix of sources and emission rates will not cause a violation of the NAAQS. In both 

instances, the demonstration should be for a period of 10 years following the

redesignation. In either case, to satisfy the demonstration requirement the state should 

project emissions for the 10-year period following redesignation. The projected inventory 

should consider future growth, should be consistent with the attainment inventory, and 

should document data inputs and assumptions. 

(3) Monitoring Network: The state should continue to operate an appropriate air quality 

monitoring network, in accordance with 40 CFR part 58, to verify the attainment status of 

the area. The maintenance plan should contain provisions for continued operation of the 

air quality monitors that will provide such verification. 

(4) Verification of Continued Attainment: Each state should ensure that it has the legal 

authority to implement and enforce all measures necessary to attain and maintain the 

NAAQS. One measure to demonstrate attainment and maintenance is the acquisition of 

ambient and air source emissions data. The state submittal should indicate how the state 

will track the progress of the maintenance plan.

(5) Contingency Plan: The state is required to adopt contingency provisions, as necessary, 
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to promptly correct any violation of the NAAQS that occurs after redesignation of the 

area. In order for the maintenance plan to be approved, a state is not required to have full 

adopted contingency measures that will take effect without further action by the state; 

however, the contingency plan is considered to be an enforceable part of the SIP and 

should ensure that the contingency measures are adopted expediently once they are 

triggered. The plan should clearly identify the measures to be adopted, a schedule and 

procedure for adoption and implementation, and a specific time limit for action by the 

state. As necessary, the state should also identify specific indicators, or triggers, which 

will be used to determine when the contingency measures need to be implemented.

Additionally, transportation conformity requirements apply to nonattainment areas and 

maintenance areas operating under maintenance plans. Transportation conformity is required 

under section 176(c) of the CAA to ensure that federally supported highway, transit projects, and 

other activities are consistent with (conform to) the purpose of the SIP. The CAA requires 

federal actions in nonattainment and maintenance areas to “conform to” the goals of SIP. This 

means that such actions will not cause or contribute to violations of a NAAQS; worsen the 

severity of an existing violation; or delay timely attainment of any NAAQS or any interim 

milestone. EPA has established criteria and procedures for Federal agencies to follow in 

determining conformity of their actions. EPA’s rule governing transportation plans and Federally 

supported highway, transit projects, and other activities is referred to as the Transportation 

Conformity Rule (see 40 CFR part 93, subpart A), and EPA’s rule governing all other types of 

Federal agency actions is referred to as the General Conformity Rule (see 40 CFR part 93, 

subpart B).

Under the Transportation Conformity Rule, metropolitan planning organizations (MPOs) in 

nonattainment and maintenance areas coordinate with state air quality and transportation 

agencies, EPA, Federal Highway Administration (FHWA), and Federal Transit Administration 

(FTA) to demonstrate that their metropolitan transportation plans and transportation 

improvement plans conform to applicable SIPs. This is typically determined by showing that 

estimated emissions from existing and planned highway and transit systems are less than or equal 

to the motor vehicle emissions budgets (MVEBs) contained in a SIP. For their maintenance 

areas, states must submit to EPA motor vehicle emissions budgets (MVEBs) for the last year of 

the maintenance plan. As with nonattainment areas, all maintenance areas that submit emissions 

budgets would be allowed to use the budgets for conformity purposes after EPA finds the budget 

adequate.

Limited Maintenance Plan Option

For nonclassifiable CO areas seeking redesingation to attainment whose design value at the time 

of redesignation is 85 percent or less than the 8-hour CO NAAQS, or 7.65 ppm, a state may 

choose to submit a less rigorous maintenance plan than generally required. This option is termed

a limited maintenance plan (LMP). EPA believes that the full maintenance plan requirements do 

not need to be applied to these areas because they have achieved air quality levels well below the 
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standard without application of control measures required by the CAA for moderate and serious 

nonattainment areas. Also, these areas do not have either a recent history of monitored violations 

of the CO NAAQS or a long prior history of monitored air quality problems. Therefore, EPA 

believes that for a limited maintenance area, the air quality along with the continued applicability 

of prevention of significant deterioration (PSD) permitting requirements, any control measures 

already in the SIP, and Federal measures, should provide adequate assurance of maintenance over 

the10-year maintenance period. The same applies for areas submitting their second maintenance 

plans.

To qualify for the LMP option, the CO design value for the area, based on the eight consecutive 

quarters (two years of data) used to demonstrate attainment must be at or below 7.65 pm for the 

8-hour CO NAAQS. Additionally, the design value for the area must continue to be at or below 

the 7.65 pm for the 8-hour CO NAAQS until the time of EPA’s final action. 

According to EPA’s October 6, 1995 guidance “Limited Maintenance Plan Option for Nonclassifiable CO Nonattainment Areas,” a LMP submittal must include the following: 

(1) Attainment emission inventory: The same requirement continues to apply.

(2) Maintenance demonstration: In an LMP, the maintenance demonstration requirement 

is considered to be satisfied if the monitoring data show that the area is meeting the air 

quality criteria for limited maintenance area, 7.65 ppm. The design value requirement is 

expected to provide adequate assurance of maintenance over the 10-year period. The 

maintenance demonstration does not require to project emissions over the maintenance 

period. 

(3) Monitoring Network and Verification of Continued Attainment: In an LMP, to 

verify the attainment status of the area over the maintenance period, the state must show 

continuous operation of an appropriate EPA-approved air quality monitoring network, in 

accordance with 40 CFR part 58.

(4) Contingency measures: The same requirement continues to apply.

(5) Conformity determination: While EPA’s LMP option does not exempt an area from 

the need to affirm conformity, the area may demonstrate conformity without submitting an 

emissions budget. Under the LMP option, the emissions budgets are essentially not 

constraining for the length of the maintenance period, because it is unreasonable to expect 

that the qualifying area will experience so much growth in that period that a violation of the 

CO NAAQS would result. For this reason, any Federal actions requiring conformity 

determinations under the transportation conformity rules could be considered to satisfy the 

“budget test,” required in 40 CFR 93.158(a)(5)(i)(A), 93.118, 93.119, and 93.120. While 

not subject to the budget test, the limited maintenance areas remain subject to other 

transportation conformity requirements of 40 CFR part 93, subpart A.
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IV. STATE SUBMITTAL

On July 18, 2011, PADEP submitted, on behalf of ACHD, a SIP revision, that was supplemented 

on November 26, 2013. The SIP revision consists of the second 10-year update to the CO 

NAAQS maintenance plan for the Pittsburgh Area, as required by CAA section 175A(b). The 

July 18, 2011 submission included a maintenance demonstration, a verification of continued 

attainment, and a contingency plan. The November 26, 2013 supplemental SIP revision included 

the attainment emissions inventory and clarified the July 18, 2011 submittal’s maintenance 

demonstration.

V. EPA’S EVALUATION

This section presents a detailed discussion of EPA’s evaluation of the Pittsburgh Area’s CO 

second maintenance plan provided on the July 18, 2011 and November 26, 2013 submittals.

A. LMP Eligibility

The last violation of the 8-hour CO NAAQS in the Pittsburgh Area was in 1987. The second 

highest non-overlapping 8-hour CO average concentration level (“second highest 8-hour average) 

is used for comparison to the 8-hour CO NAAQS. Table 1 shows the historic CO 8-hour design 

values (i.e., the second highest 8-hour average CO levels) for the CO monitoring sites in the Area

over the 1988-2013 period, as recorded in EPA’s Air Quality System (AQS) and included in the 

submittal. See Appendixes A-1 thru A-4 of this document for the AQS Reports (AMP450NC) 

with 2010-2013 air quality data. 

Monitoring data shows that the Pittsburgh Area continues to attain the CO NAAQS. As shown 

in Table 1, the second highest 8-hour CO average concentrations recorded at all monitoring 

stations in the Pittsburgh Area have remained below 7.65 ppm since 1994. In addition, ACHD 

reported that the 1-hour CO NAAQS has not been violated in the Pittsburgh Area since 1980, 

and has been below 15 ppm since 1988. Thus, monitoring data show that Pittsburgh Area 

continues to be eligible for the LMP option. 
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Table 1. Pittsburgh Area’s CO Second Highest 8-Hour Average Concentrations during 

1988-2013, in ppm 

Year

Oakland a

(42-003-0026)

Forbes Avenue 

at Grant Street 

(Courthouse)

(42-003-0038)

Gateway 

Center Subway 

Entrance 

(Point) b

(42-003-0052)

Flag Plaza 

(Bedford 

Avenue) b

(42-003-0031)

1988 8.4 6.6 6.5 -

1989 6.5 7.8 6.7 -

1990 6.9 8.1 6.5 -

1991 5.0 6.2 6.6 -

1992 7.7 7.8 6.7 -

1993 4.8 6.2 5.2 -

1994 5.6 7.5 6.8 -

1995 4.3 5.9 3.8 -

1996 5.0 4.8 3.9 -

1997 2.5 3.9 2.9 -

1998 - 4.9 3.1 -

1999 - 4.0 3.1 -

2000 - 3.5 2.6 -

2001 - 3.4 - -

2002 - 2.9 - -

2003 - 3.5 - 2.2

2004 - 2.5 - 1.9

2005 - 2.3 - 1.8

2006 - 2.1 - 1.8

2007 - 3.5 - 1.3

2008 - 1.6 - 1.3

2009 - 1.5 - 1.3

2010 - 1.7 - 1.2

2011 - 1.6 - 1.4

2012 - 1.7 - 1.5

2013c

1.5 1.4

Source: Pennsylvania’s July 18, 2011 SIP submittal and EPA’s January 9, 2014 AQS Reports AMP450. 

a The CO monitor at the Oakland site (AQS ID: 42-003-0026) was terminated in October 1997, as approved by 

EPA.

b EPA approved the removal of the CO monitor at the Gateway Center Subway Entrance (Point) (AQS ID: 42-003-

0052) in May 2000 and its relocation to the Flag Plaza (AQS ID: 42-003-0031) near the Civic Arena, which started 

operating in 2003. 

c

 Air quality monitoring data for 2013 is preliminary. 
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B. Attainment Emissions Inventory

For the CO maintenance plan, ACHD developed a 2008 attainment emissions inventory to 

identify the level of actual emissions in the Pittsburgh Area that is sufficient for the Area to 

continue to attain the CO NAAQS. The Pittsburgh Area’s CO attainment inventory is based on 

the latest available planning assumptions for the 2008, reflecting typical winter day CO 

emissions for the Area. ACHD selected the 2008 year for its attainment emissions inventory 

because it contained at the time of submittal the most current and comprehensive emissions 

estimates that were representative of actual emissions in Allegheny County, and because during 

this time the air quality was showing maintenance of the CO NAAQS in the Area. 

The 2008 emissions inventory was taken from EPA’s 2008 National Emissions Inventory (NEI) 

(Version 2, April 10, 2012) for the months of January, February, and December, and was 

adjusted as necessary to reflect typical winter day CO emissions. The submitted 2008 attainment 

inventory contains emissions estimates of point, area, mobile onroad and mobile nonroad road 

sources in the Area. The primary source of CO emissions in the Allegheny Area is the onroad 

(highway) sources, contributing to 54% of total CO emissions of the Area. Table 2 provides a 

summary of the 2008 attainment inventory submitted with the maintenance plan. Table 2 

presents the 2008 attainment inventory in annual CO emissions and CO emissions for a typical 

winter day. For a more detailed evaluation of the 2008 emissions inventory, see EPA’s 

Technical Support Document (TSD) dated February 4, 2014 for this rulemaking action, which is 

available online at www.regulations.gov, Docket number EPA-R03-OAR-2012-0248.

Table 2. Pittsburgh Area’s CO 2008 Attainment Emissions Inventory (tons per day)

Source Category CO Annual Emissions CO Typical Winter Day Emissions

Point 25.28 22.76

Area 43.12 57.65

Onroad 265.48 396.38

Nonroad 155.11 96.99

TOTAL 488.99 573.78

C. Maintenance Demonstration 

Under the LMP option, there is no requirement to project emissions over the 10-year 

maintenance period for the Pittsburgh Area, as long as the Area continues to have a CO air 

quality at or below 7.65 ppm. The monitoring data presented in Table 1 show that the Pittsburgh 

Area has historically measured and continues to measure concentrations below 7.65 ppm. The 

continuous downward trend in CO monitoring data in the Area has demonstrated that air quality 

improvements can be attributed to permanent, enforceable reductions of CO emissions. These 

reductions are largely achieved through more stringent Federal controls on vehicles and fuels, 

and state and local measures implemented in the Area and approved in the Pennsylvania SIP. In 

addition, EPA acknowledges that Allegheny County has a SIP-approved PSD permitting program 
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(78 FR 13493, February 18, 2013), which prevents increase of CO emissions from construction

or modification of major stationary sources. EPA believes that the LMP eligibility together with 

the continuation of existing CO emissions control programs, sufficiently and adequately 

demonstrate that the Pittsburgh Area will maintain the CO NAAQS through the second 10-year 

maintenance period and beyond. 

Although not required, ACHD included a demonstration as part of its second maintenance plan 

to show maintenance of the CO NAAQS during the second 10-year period for the Pittsburgh 

Area. For a maintenance demonstration, emissions inventories are required to be projected to 

future dates to assess the influence of future growth and controls; however, the demonstration 

need not be based on modeling. See Wall v. EPA, supra; Sierra Club v. EPA, supra. See also 66 

FR 53099-53100 and 68 FR 25430-32. ACHD used projected inventories to show that the 

Pittsburgh Area continues to remain in attainment and developed projected inventories for an 

interim year of 2013 and a maintenance end year of 2022. Where the emissions inventory 

method of showing maintenance of the NAAQS is used, a state may demonstrate maintenance by 

showing that the future emissions of a pollutant or its precursors will not exceed the level of the 

attainment inventory. The demonstration should project emissions for a period of 10 years 

following the redesignation or the initial 10-year maintenance period. The projected inventory 

should consider future growth, should be consistent with the attainment inventory, and should 

document data inputs and assumptions. 

Evaluation of Projected Emissions Inventories

The projected 2013 and 2022 emissions inventories include typical winter day CO emissions 

estimates only for the onroad sources in the Pittsburgh Area. As mentioned earlier, this sector 

constitutes the primary emissions source category in the Pittsburgh Area and emissions 

reductions from this source category should be sufficient to demonstrate maintenance of the CO 

NAAQS for the Area. EPA has evaluated the accuracy of the projected emissions inventories 

based on the thorough review of the methodology and data assumptions used by ACHD for 

modeling the CO emissions in the Allegheny County. 

The 2013 and 2022 onroad emissions inventories were developed with EPA’s latest highway 

emissions model at the time of submittal, MOVES2010a.1 When using MOVES2010a for 

developing SIP inventories, the methodologies used should conform to the recommendations 

provided by EPA in the “Technical Guidance on the Use of MOVES2010a for Emission 

Inventory Preparation in State Implementation Plans and Transportation Conformity.” ACHD 

used a pre- and post- processing software, PPSUITE, to assist in processing traffic data and VMT 

 

1 MOVES2010 is a computer model designed by EPA to estimate air pollution emissions and emissions inventories 

of various pollutants and precursors from on-road mobile sources for SIP and transportation conformity purposes. 

MOVES2010 was designed to replace the previous emissions model, MOBILE6.2, which was released in 2004 (69 

FR 28830). MOVES2010 was released on March 2, 2010 (75 FR 9411), while MOVES2010a, a minor revision to 

enhance model performance, was released subsequently on September 8, 2010. ACHD used MOVES 2010a in 

developing the projected emissions inventories.
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and the results produced by MOVES2010a. ACHD also used CENTRAL software system as the 

process controller to assist running MOVES2010a. 

ACHD used a combination of local data and national default data (internal to MOVES2010a) to 

estimate CO emissions for a typical winter day during 2013 and 2022. As recommended by 

EPA’s guidance, ACHD used local data for primary modeling input parameters which have a 

significant impact in mobile source emissions, including: Temperature, humidity, gasoline fuel 

formulations, vehicle source type population and age distribution based on vehicle registration 

data from the Pennsylvania Department of Transportation (PennDOT), Department of Motor 

Vehicles (DMV), traffic volumes and VMT estimates from PennDOT Roadway Management 

System, and inspection and maintenance (I/M) parameters. Most local data inputs reflect the 

latest planning assumptions based on 2008 data, with the exception of I/ M programs and fuel 

characteristics inputs which are based on the most current assumptions.

To develop the 2013 and 2022 traffic parameters as input data for MOVES2010a, ACHD used 

growth rates based on 2008 local traffic data and socioeconomic forecasts developed following 

the methodology from the 2005 PennDOT’s Final Report “Statistical Evaluation of Projected 

Traffic Growth, Traffic Growth Forecasting System” (March 14, 2005). Daily and monthly 

seasonal factors, developed from PennDOT’s Bureau of Planning and Research “2008 

Pennsylvania Traffic Data,” were used to adjust traffic data to a typical winter day. The 

projected inventories take into account control measures which were in place in 2008 and are 

expected to be in place by 2022 for Allegheny County. These vehicle control measures include: 

The National Low Emission Vehicle Program (NLEV) and Federal Tier II Low Sulfur Program, 

emissions standards for medium and heavy duty vehicles in 2002, 2004, 2007, and 2011, Stage II 

and Onboard Refueling Vapor Recovert (ORVR), and the Pennsylvania Clean Vehicles (PCV) 

Program (PaCode, Title 25, Chapter 126) that incorporates the California Low Emission Vehicle 

Program (CA LEVII). 

EPA finds that the 2011 and 2013 emissions inventories were developed in conformance with 

EPA’s guidance, and therefore, are approvable as part of the maintenance demonstration. A 

summary of the projected onroad CO emissions inventories for the Pittsburgh Area is provided in 

Table 3. 

Table 3. Pittsburgh Area’s CO Projected 2013 and 2022 Vehicle Miles Traveled (VMT) 

and Typical Winter Day Emissions for Onroad Sources, in tons per day (tpd) 

2013 2022

VMT

CO Typical 

Winter Day 

Emissions

VMT

CO Typical 

Winter Day 

Emissions

25,727,530 394.53 28,377,731 336.27

Evaluation of Maintenance Demonstration
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The purpose of the maintenance demonstration is to show that future CO emissions will remain 

at or below the 2008 attainment emissions levels for the Pittsburgh Area through the 2022. 

Tables 4 provides a comparison of the CO emissions inventories for the Pittsburgh Area for the 

2008 attainment year, the 2013 interim year, and the 2022 maintenance plan end year. Despite of 

the projected increase in VMT (see Table 3) in the Area, the inventories show that the CO 

emissions between 2008 and 2022 for the Area are projected to be reduced by 15 percent, due to 

the implementation of the vehicle control measures in Allegheny County. EPA finds that 

maintenance demonstration shows that the Pittsburgh Area will continue to maintain the CO 

NAAQS during the second maintenance period, throughout 2022. 

Table 3. Comparison of the 2008, 2013, and 2022 CO Typical Winter Day Emissions for 

Onroad Sources in the Pittsburgh Area, in tpd

Emissions of Onroad Sources Emissions Reductions

2008 2013 2022 2008-2013 2008-2022

396.38 394.53 336.27 1.85 60.11

D. Monitoring Network and Verification of Continued Attainment

In accordance with 40 CFR part 58, ACHD operates and maintains an EPA-approved CO 

monitoring network in the Pittsburgh Area, in order to verify attainment of the CO NAAQS and 

ensure the need to trigger contingency measures. Currently, the monitoring network consists of 2 

monitoring sites, the Forbes Avenue and Grant Street site (AQS ID: 42-003-0038) and the Flag 

Plaza site (AQS ID: 42-003-0031), whose data is eligible for comparison to the CO NAAQS.

ACHD operated a CO monitoring site in Oakland (42-003-0026) until its termination on October 

1997. The monitor at the Gateway Center Subway Entrance (42-003-0052) was shut down in 

May 2000 to accommodate local construction work and, as approved by EPA, was permanently 

relocated to the Flag Plaza site (42-003-0031) in 2003. 

EPA previously determined that the CO monitoring network for the Pittsburgh Area is adequate. 

EPA found that the number of monitors in the Area meets the minimum regulatory requirements 

given in 40 CFR part 58, appendix D, section 4.2, and that the monitoring network in place is in 

accordance with ACHD’s most recent annual monitoring network plans approved by EPA, as 

required by 40 CFR 58.10. ACHD’s 2013 annual ambient monitoring network plan was 

approved by EPA in a December 10, 2013 letter from Shawn M. Garvin, Regional Administrator

of EPA Region III, to James Thompson, Air Quality Program Manager of ACHD. In addition, 

ACHD has committed to continue maintaining a CO monitoring network in accordance with 

EPA requirements. EPA believes ACHD’s current CO monitoring network is adequate to verify 

continued attainment of the CO NAAQS in the Pittsburgh Area. 
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E. Contingency Plan

The Pittsburgh Area’s second CO maintenance plan carries forward the same contingency 

provisions that were included in the first maintenance plan and previously approved by EPA. 

The plan relies on quality-assured air quality monitoring data in the Pittsburgh Area to identify 

the triggering indicator necessary to implement contingency measures. As a triggering event, a 

verified ambient CO concentration for an 8-hour period over the 8-hour CO NAAQS, or 9.00 

ppm, must be recorded at least twice at one monitor station from November to February. In the 

event of a violation of the 8-hour CO NAAQS, a “vehicle idling restriction” will be implemented

as a contingency measure. The vehicle idling restriction is applicable from November to 

February throughout the Allegheny County and consists of limiting to five minutes the amount of 

time that a gasoline engine vehicle is permitted to idle. This restriction will have the following 

exceptions: The need for heating and powering of refrigeration systems on trucks, operation of 

emergency vehicles and vehicles that are motionless due to traffic conditions beyond operator’s 

control. Three (3) months after ACHD records a violation or once EPA notifies ACHD that this 

contingency measure must be implemented, ACHD will adopt within 12 months the vehicle 

idling restriction as a regulation. The regulation will be implemented within 8 months after 

adoption. In the future, ACHD may request EPA to consider the approval of alternative 

contingency measures by providing a demonstration that the alternative measures will provide an 

air quality and public health benefit equal to or greater than that resulting from the 

implementation of the idling restriction.

F. Transportation Conformity

While EPA’s LMP option does not exempt the Pittsburgh Area from the need to affirm 

conformity, under this option the Area may demonstrate transportation conformity without 

submitting MVEBs. ACHD did not submit any MVEBs with the Pittsburgh Area’s CO second 

maintenance plan. However, EPA believes that the second maintenance plan demonstrates that it 

is unreasonable to expect that the Area would experience enough growth in motor vehicle 

(onroad) emissions for a violation of the CO NAAQS to occur, and on that basis, EPA is 

proposing to approve this plan for transportation conformity purposes. 

Evaluation of transportation conformity for transportation projects in Allegheny County is 

usually performed by the Southwestern Pennsylvania Commission and other agencies. This 

determination waives the need for CO MVEB, although it does not relieve the Pittsburgh Area of 

the other transportation conformity requirements. After EPA’s approval of this finding, there 

will be no requirement for ACHD to satisfy the regional emissions analysis with respect to CO 

under 40 CFR 93.118 and/or 40 CFR 93.119 in determining the conformity of transportation 

plans, programs and projects in the Pittsburgh Area. See 40 CFR 93.109(j).
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VI. RECOMMENDED AGENCY ACTION

EPA finds that the second CO maintenance plan for the Pittsburgh Area, submitted by the 

Commonwealth as a SIP revision on July 18, 2011 and supplemented on November 26, 2013, 

provides an acceptable update of the various elements of the initial EPA-approved CO 

maintenance plan, and essentially carries forward all of the control measures and contingency 

provisions relied upon in the earlier plan. EPA concludes that the Pittsburgh Area’s second CO 

maintenance plan concurs with EPA’s guidance for limited maintenance plans and thus, satisfies 

the requirements of CAA section 175A.