1

Technical Support Document— Area Designations for the Washington-BaltimoreNorthern Virginia, DC-MD-VA-WV Combined Statistical Area (CSA)

2008 Ozone National Ambient Air Quality Standards

Scope:

This Technical Support Document (TSD) is for designation of the final nonattainment and 

“unclassifiable/attainment” areas and the establishment of the boundaries thereof within the 

Washington-Baltimore-Northern Virginia, DC-MD-VA-WV CSA (hereafter the Washington-BaltimoreNV CSA or just “this/the CSA”).

Summary:

Maps of Final Nonattainment Areas:

Washington, DC-MD-VA area

Figure 1a is a map of the Washington, DC-MD-VA nonattainment area under the 2008 ozone NAAQS. 

The map provides other relevant information including the locations and design values of air quality 

monitors, county and other jurisdictional boundaries, the CSA boundary, prior nonattainment area 

boundaries for 1997 ozone NAAQS, and major transportation arteries. It also shows the 

attaining/violating status for 2008-2010 for the remainder to the remainder of the WashingtonBaltimore-Northern Virginia, DC-MD-VA-WV CSA as well as all or parts of the York-Hanover, PA 

CBSA, Lancaster, PA CBSA, Chambersburg, PA CBSA, Hagerstown-Martinsburg MD-WV CBSA, 

Richmond, VA CBSA, Philadelphia-Camden-Vineland CSA as well as other counties in Pennsylvania, 

Maryland, and Virginia.
2

Figure 1a. The Washington, DC-MD-VA Nonattainment Area

The boundary for the Washington, DC-MD-VA nonattainment area under the 2008 ozone NAAQS for 

the 2008 ozone NAAQS consists of:

(1) The Counties of Arlington, Fairfax, Loudoun, and Prince William, and the Cities of Alexandria, 

Fairfax, Falls Church, Manassas, and Manassas Park in Virginia; 

(2) The entire District of Columbia; and

(3) The Counties of Calvert, Charles, Frederick, Montgomery, and Prince George’s in Maryland.

Figure 1b is a map of the Baltimore MD nonattainment area under the 2008 ozone NAAQS. The map 

provides other relevant information including the locations and design values of air quality monitors,

county and other jurisdictional boundaries, the CSA boundary, prior nonattainment area boundaries for 

1997 ozone NAAQS, and major transportation arteries. It also shows the attaining/violating status for 

2008-2010 for the remainder to the remainder of the Washington-Baltimore-Northern Virginia, DC-MDVA-WV CSA as well as all or parts of the York-Hanover, PA CBSA, Lancaster, PA CBSA, 

Chambersburg, PA CBSA, Hagerstown-Martinsburg MD-WV CBSA, Richmond, VA CBSA,

Philadelphia-Camden-Vineland CSA as well as other counties in Pennsylvania, Maryland, and Virginia.
3

Baltimore Area

Figure 1b. The Baltimore, MD Nonattainment Area

The boundary for the Baltimore, MD nonattainment area under the 2008 ozone NAAQS consists of 

Anne Arundel, Baltimore, Carroll, Harford, and Howard Counties and Baltimore City.

Tables

Tables 1a to 1c below identifies the areas and associated counties or parts of counties in the District of 

Columbia, State of Maryland and Commonwealth of Virginia that EPA has determined must be 

designated as nonattainment for the 2008 ozone national ambient air quality standards (“2008 ozone 

NAAQS” or “2008 NAAQS”) and the nonattainment areas in which each will be placed. In accordance 

with section 107(d) of the Clean Air Act (CAA), EPA designates an area (county or a part of a county) 

“nonattainment” if it is violating the 2008 ozone NAAQS or if it is contributing to a violation of the 

2008 ozone NAAQS in a nearby area. The technical analyses supporting the boundaries for the 

individual nonattainment areas are provided below.

Table 1a. Nonattainment Areas in District of Columbia.

Area 

The District of Columbia’s 

Recommended Nonattainment EPA’s Nonattainment Counties
4

Counties

Washington, DC-MD-VA* District of Columbia: District of Columbia:

Table 1b. Nonattainment Areas in Maryland.

Area 

Maryland’s Recommended 

Nonattainment Counties EPA’s Nonattainment Counties

Washington, DC-MD-VA*

Calvert County 

Charles County 

Frederick County 

Montgomery County 

Prince George’s County

Calvert County 

Charles County 

Frederick County 

Montgomery County 

Prince George’s County

Baltimore, MD

Anne Arundel County

Baltimore City

Baltimore County

Carroll County

Harford County

Howard County

Anne Arundel County

Baltimore City

Baltimore County

Carroll County

Harford County

Howard County

Table 1c. Nonattainment Areas in Virginia.

Area 

Virginia’s Recommended 

Nonattainment Counties EPA’s Nonattainment Counties

Washington, DC-MD-VA*

Alexandria City 

Arlington County 

Fairfax City 

Fairfax County 

Falls Church City

Loudoun County 

Manassas City 

Manassas Park City 

Prince William County 

Alexandria City 

Arlington County 

Fairfax City 

Fairfax County 

Falls Church City

Loudoun County 

Manassas City 

Manassas Park City 

Prince William County 

*The Washington, DC-MD-VA nonattainment area is a multi-state nonattainment area.

Remainder of the Washington-Baltimore-NV CSA:

The remaining Counties and Cities in the Maryland, Virginia and West Virginia that are part of the 

Washington-Baltimore-NV CSA are designated “unclassifiable/attainment.”

Background – State Recommendations, EPA’s Proposed Modifications and State 

Responses:

The District of Columbia’s Recommendations:
5

March 2009:

On March 11, 2009, the District of Columbia recommended the entire District of Columbia be 

designated nonattainment as part of a nonattainment area which includes at a minimum the entire 

“Washington DC-MD-VA MSA” but the District also supported using larger combined statistical areas 

based upon sound science. The District supported its recommendation with air quality data that showed 

monitors in the District were violating the 2008 ozone NAAQS and an analysis of emissions showing 

that the District itself contributed less than 10 percent of 2002ozone precursor emissions within the 

“Metropolitan Washington Area” and thus would need reductions in a broader area than just the District to 

attain the 2008 ozone NAAQS.1

In response to EPA’s December 9, 2011, letter to the Mayor of the District of Columbia2regarding 

EPA’s proposed modifications to the District’s recommendations, on March 12, 2012, the District 

replied to EPA’s December 9, 2012 letter.3 

Maryland’s Recommendations:

The March 2009 recommendations:

On March 10, 20094, Maryland recommended retention of the current nonattainment boundaries “if EPA 

is confident that strong national rules would be in place three years in advance of attainment dates for 

nonattainment areas in Maryland.” These nonattainment areas included the current Baltimore 

nonattainment area and boundaries, the Maryland portions of the current Washington DC-MD-VA 

nonattainment area, and Cecil County as part of a Philadelphia based nonattainment area. With these 

recommendations, Maryland also recommended that Washington County be part of a nonattainment area 

based upon Hagerstown, Maryland, and an “Eastern Shore” nonattainment area comprising Kent and 

Queen Anne’s Counties. 

In the alternative, Maryland supports the “implementation of a large regional nonattainment area 

encompassing a significant portion of the U.S. East Coast” “if EPA is not confident that strong national 

rules will be in place” in order to “force regional controls and reductions in transported pollution” in an 

time frame appropriately related to the dates by which areas in Maryland are required to attain the 2008 

NAAQS. Under this alternative, Maryland would support a nonattainment designation for all counties 

and cities in the State.

Maryland noted that most of the State is already heavily regulated due to existing ozone and fine particle 

requirements. Maryland stated that its scientific research, which uses airplanes, ozone-measuring 

balloons, and laser measuring techniques, shows that air transported into Maryland often carries levels 

of ozone already exceeding the standard. Maryland concluded that it will need to rely heavily on 

reductions in transported pollution to meet the 2008 NAAQS. Maryland concluded that because of

“incoming” ozone levels above the standard, strong national rules will be needed for areas like Maryland 

to attain the 2008 NAAQS. Maryland provided a map which represented the spatial extent of 2008 

 

1

 The District cited the 2002 emissions inventory contained within its State Implementation Plan (SIP) revision dated May

23, 2007 for the Washington DC-MD-VA Nonattainment Area. This 2002 emissions inventory was for the Washington DCMD-VA nonattainment area under the 1997 ozone NAAQS (of 40 CFR 50.9) and thus covered an area smaller than the 

current Washington-Arlington-Alexandria Metropolitan Statistical Area. Refer to 76 FR 58116, September 20, 2011.

2

 Letter dated December 9, 2011, from Shawn M. Garvin, Regional Administrator, EPA Region III, to the Honorable 

Vincent C. Gray, Mayor of the District of Columbia. 

3

 Refer to Letter dated March 12, 2012, from Christophe A. G. Tulou, Director District department of the Environment, to 

Shawn M. Garvin, Regional Administrator, EPA Region III.

4

 March 10, 2009 Letter from the Honorable Martin J. O’Malley, Governor of Maryland, to William T. Wisniewski, 

Acting Regional Administrator, EPA Region III.
6

ozone levels in Maryland, Delaware, New Jersey and southeastern Pennsylvania to show that large areas 

outside of Maryland have levels above the 2008 NAAQS.

Maryland also provided a summary table of modeled 2009 design values for Delaware and Maryland 

based upon work performed by the Bureau of Air Quality Analysis and Research, Division of Air 

Resources, New York State Department of Environmental Conservation. 

In a December 9, 2011 letter to the State of Maryland,5EPA proposed to modify and respond to 

Maryland’s recommendations as follows:

(1) EPA would not designate Kent, Queen Anne’s and Washington Counties as nonattainment for the 

reasons provided in our cover letter.

(2) EPA would retain the current nonattainment area boundaries for portions of Maryland currently

designated nonattainment under the 1997 ozone NAAQS for the reasons provided in Parts I and II to the 

“Technical Analysis” below. 

(3) EPA intended to modify Maryland’s recommendations for Anne Arundel, Baltimore, Calvert, 

Carroll, Cecil, Charles, Frederick, Harford, Howard, Montgomery, and Prince George’s Counties and 

Baltimore City insofar as EPA declined to base its decisions upon the likelihood that additional “strong 

national rules” will be in-place at some time in the future. 

(4) EPA believed it cannot concur with a recommendation to designate as nonattainment a large portion 

of the East Coast of the U.S. due to transport from such an area and that EPA did not intend to designate 

a large nonattainment area as suggested by Maryland.

EPA noted that Maryland’s support of its recommendations is dated (as a recommendation made two 

years ago will be) because it relied upon 2008 and 2009 design value data and projections. As EPA 

noted previously, EPA must consider the best information available at the time EPA promulgates 

designations. Because the 2010 design values are available, EPA must consider this information and 

based upon this information believes that the extent of areas still violating the 2008 NAAQS is less than 

it was two years ago. 

March 7, 2012:

In response to EPA’s December 9, 2011, letter to the Governor of Maryland regarding EPA’s proposed 

modifications to Maryland’s recommendations, on March 7, 2012, Maryland reaffirmed as its 

recommendation for a multi-state nonattainment area.6 Maryland specifically recommended the 

following 17 States for inclusion in such an area: The District of Columbia7, Maryland, Delaware, New 

Jersey, New York, Pennsylvania, Virginia, West Virginia, Ohio, North Carolina, Tennessee, Missouri, 

Illinois, Indiana, Kentucky, Michigan and Wisconsin. Maryland provided a “5-factor analysis” in 

support of this recommendation. As an alternative to the 17-State nonattainment area, Maryland 

recommended that at a minimum the entire Washington-Baltimore-NV, DC-MD-VA-WV CSA be 

designated nonattainment. Maryland provided a “5-factor analysis” in support of this recommendation. 

After March 7, 2012:

 

5

 Letter dated December 1, 2011 from the Honorable Martin J. O'Malley, Governor of Maryland, to Shawn M. Garvin, 

Regional Administrator USEPA Region 3, Recommending Revised area Designations for Maryland for the 2008 Ozone 

NAAQS, item number EPA-HQ-OAR-2008-0476-0492 in the docket for this action.

6

 Letter dated March 7, 2012, from Robert M. Summers, Ph.D., Secretary, Maryland Department of the Environment to 

Shawn M. Garvin, Regional Administrator, EPA Region III. 

7

 Under CAA section 302(d) the District of Columbia is considered a “State” for the purposes of Title I and other Titles of 

the CAA. Hereafter in these responses to Maryland’s submittal, the term “State(s)” will refer to any “State” or the District

generically whereas the term “District of Columbia” or just “the District” will refer to the District of Columbia itself.
7

Subsequent to March 7, 2012, the Maryland Department of the Environment provided materials to 

supplement its “5-factor analyses” supporting its March 7, 2012 recommendations. These were:

(1) “Where does the air pollution in the OTR come from and what do we need to do to fix it?,” Tad 

Aburn, Director, Air and Radiation management Administration, presented at the OTC Annual meeting 

June 9 and 10, 2010.8 This document discussed the “elevated reservoir,” the NLLV, long-range 

transport, the correlation between ozone reductions and the number of EGUs installing controls due to 

the NOx SIP call, the “leeside” trough, linkage between all emissions in the 1997 Washington DC-MDVA Nonattainment area, and a call for controls throughout the eastern part of the country. 

(2) “Moving Forward to Address Regional Transport,” Tad Aburn, Air Director, MDE, 

February 8, 2012, MARAMA Science Meeting.

9

 This document discussed recent ozone data for the ten 

monitors in the OTR (2011 data), remaining possible local controls, the relative ratio of Baltimore 

emissions to other areas, emissions of top four States contributing to Maryland ozone, the “elevated 

reservoir,” the NLLV, long-range transport, Washington DC-MD-VA Nonattainment area contribution 

and the “bay breeze,” city to city transport, aloft measurements of up to 0.070 to 0.080 ppm after 2004, 

local emissions estimated to contribute 10 to 20 percent, the need for “super-regional” NOx controls, 

results of OTC scenario 4 modeling and with 5 percent additional beyond scenario 4 controls result in 

little ozone reductions, a call for Federal NOx measures on six source categories that represent 75 

percent of the NOx left to regulate.10 

(3) “Making Progress on Cleaner Air, What We’ve Achieved Under the Clean Air Act Amendments of 

1990, and Where We Need to Go, Getting to the New Ozone Standards, A Pathway Forward,” 

November 10th, 2010.

11

 This November 10th, 2010 presentation: discussed trends in regulatory

measures and ozone levels since 1990; predicted probable nonattainment areas under the 2008 ozone 

NAAQS, concluded that additional controls within the OTR are still critical but may only reduce about 

1/3 of the ozone problem in most OTC cities; and concluded that national/super-regional controls are 

now essential because incoming ozone is already measured at levels above a 60-70 ppb standard and 

thus contribution from outside the OTR represents approximately 2/3 of the ozone problem in most OTC 

cities. OTC identified priority source categories from the June 2010 OTC Resolution urging EPA to 

adopt national rules to reduce interstate NOx emissions from EGUs, from more stringent On-Road 

Vehicle Standards, from ICI Boilers, Cement Kilns, Marine Engines and Locomotives because these 

categories represent 75 percent of the NOx left to regulate, models of transport westerly and NLLJ, the 

“elevated reservoir,” the NLLJ, long-range transport, and reductions in ozone concentrations in both the 

“elevation reservoir” and at ground level attributable to the NOx SIP call. 

(4) “Modeling Committee Update,” OTC Air Directors’ Meeting, April 24th, 2012.” This document 

discussed 8-hour ozone trends, how design values changed (based upon 2011 preliminary data), 

potential nonattainment areas under the 2008 ozone NAAQS, hypothetical 2012 design values 

discounting 2009 data, and schedules for OTC air quality modeling. 

 

8

 Also available on-line at 

http://www.otcair.org/upload/Documents/Meeting%20Materials/ConceptualModel_20090602%20TAD%20FOR%20OTC%

20Final.pdf.

9

 Also available on line at http://www.marama.org/presentations/2012_Science/Aburn_Science2012#542,1,Slide.

10

 Subsequent to the State’s March 7, 2012 letter Maryland also submitted in a separate 4-page document which consisted 

solely of pages 33 through 36 of this document. 

11 Also available on line at 

http://www.otcair.org/upload/Documents/Meeting%20Materials/OTC%20Overall%20Progress%20Report%20-

%20Fall%202010.pdf.
8

EPA considered these documents as they related to elements of Maryland’s March 7, 2012 response to 

EPA.

Most of the salient points of these presentations were also discussed in Maryland’s March 7, 2012 letter. 

Maryland also submitted a document estimating reasonable further progress reductions in a 

nonattainment area with the borders of the 1997 Baltimore nonattainment area (that under the 1997 

ozone NAAQS) and a nonattainment area comprised of the entire Washington-Baltimore-NV CSA and a 

document of a “Aspirational Conformity Regulation.” EPA did not base its decisions on the former but 

rather used the 5-factor analysis to determine which portions of this CSA should be designated 

nonattainment. As to the latter, EPA did not base its decision on it because it represents a control 

regulation not yet implemented whereas the CAA requires EPA to base its decisions on current 

contribution.

Regarding a 17-State Nonattainment area:

In letters discussed previously in this document, Maryland and the District of Columbia recommended 

that EPA designate the entire State as part of a large multi-state nonattainment area including all or 

portions of 17 other states, and the District of Columbia. EPA does not believe that creation of a superregional nonattainment area to address pollution transport is the appropriate approach. As an initial 

matter, section 107(d)(1) provides that areas designated nonattainment should include any “nearby” area 

contributing to a violation of the NAAQS. We believe that broad super-regional areas go beyond this by

including areas that are not necessarily “nearby” but contribute to nonattainment through long-range 

transport. The CAA has separate provisions to address this phenomenon. Section 110(a)(2)(D) requires 

states to address ozone transport that contributes to a violation of the NAAQS in another State. In 

addition, section 184, creates the northeast ozone transport region and also grants EPA authority to 

establish additional transport regions, as appropriate. Finally, we note that the approach taken by EPA is 

consistent with the approach Congress specified for serious and above areas for the 1-hour NAAQS, 

where in section 107(d)(4)A), Congress set the CMSA boundaries as the presumptive boundaries of the 

nonattainment area. In Catawba Co. v. EPA12[1], the Court upheld that “contribute” under 

§107(a)(1)(A) of the CAA does not necessarily mean “any contribution” to nonattainment but rather a 

degree of contribution sufficient to deem an area nonattainment, that is, sufficient enough to warrant 

designation as nonattainment. “Section 107(d) is ambiguous as to how EPA should measure contribution 

and what degree of contribution is sufficient to deem an area nonattainment...” Catawba County v. 

EPA, 571 F.3d 20 (D.C. Cir. 2009) (Internal citation omitted but with emphasis added). “Thus, 

reasonably exercising the discretion that Congress delegated to it, EPA interpreted “contribute” to mean 

“sufficiently contribute,” and then applied the C/MSA presumption and nine-factor test precisely to 

identify those areas that meet that definition.”

Virginia’s Recommendations:

March 2009:

 
9

On March 11, 200913, Virginia recommended the four areas in Virginia for nonattainment. These were a 

Hampton Roads area, a Fredericksburg area, a Richmond area and a Northern Virginia area consisting of 

only a portion of Virginia within the “Washington DC-MD-VA” Metropolitan Statistical Area (MSA). 

Virginia supplied a “5-factor analysis” in support of its recommendations. 

November 2011 and later:

On November 21, 201114, Virginia updated its prior recommendations. Virginia specifically noted that 

of the four areas Virginia recommended for a nonattainment designation in 2009 two – the Hampton 

Roads and Fredericksburg areas – had come into attainment based upon 2008 to 2010 air quality

monitoring data. In addition, Virginia noted that the Richmond area was in attainment of the 2008 

ozone NAAQS based upon 2009-2011 air quality data and requested that the Richmond area not be 

designated nonattainment. 

Virginia did not send a reply in response to EPAs December 9, 2011, letter to the Governor of Virginia15

which did not propose to modify any of Virginia’s recommendations,

Subsequent to EPAs December 9, 2011 letter, the Virginia Department of Environmental Quality

provided a supplemental analysis in response other States’ revised recommendations for a combined 

Washington-Baltimore-NV CSA. 

Common elements of Recommendations:

All the recommendations are based upon 2008 to 2010 air quality data to identify the violating 

monitors.16 These data are from FRM monitors or FEM monitors sited and operated in accordance with 

40 CFR part 58. 

Technical Analysis for the Washington-Baltimore-Northern Virginia CSA –the 

Washington, DC-MD-VA and Baltimore Areas:

Factor Assessment

EPA’s analyses below provide the basis for the final nonattainment area boundaries. It relies on our 

analysis of whether and which monitors are violating the 2008 ozone NAAQS, based on certified air 

quality monitoring data from 2008-2010, and an evaluation of whether nearby areas are contributing to 

such violations. EPA has evaluated contributions from nearby areas based on a weight of evidence 

analysis considering the 5-factors identified below. EPA issued guidance on December 4, 2008 that 

 

13

 A letter dated March 11, 2009 from David K. Paylor, Director, Virginia Department of Environmental Quality, to William 

T. Wisneiwski, Acting Regional Administrator, EPA region III. 

14

 Letter dated November 21, 2011, from Michael G. Dowd, Air Quality Division Director, Virginia Department of 

Environmental Quality, to Diaina Esher, Director, Air Protection Division, EPA Region III.

15

 Letter dated December 9, 2011, from Shawn M. Garvin, Regional Administrator, EPA Region III, to the The Honorable 

Robert McDonnell, Governor of Virginia. 

16

 Although Virginia certified air quality data for all their monitors for the 2011 ozone season, Virginia’s November 21, 

2011 revised recommendation referred to use of the 2011 data with respect to the Richmond VA area. With respect to the 

Virginia’s portion of the Washington-Baltimore-NV CSA, the 2011 data does not alter the numbers of monitors violating of 

attaining the 2008 ozone NAAQS and therefore does not materially affect the decisions regarding the baoundaries of 

nonattainment areas within this CSA.
10

identified these factors as ones EPA would consider in determining nonattainment area boundaries and 

recommended that states consider these factors in making their designations recommendations to EPA.17 

1. Air quality data (including the design value calculated for each Federal Reference Method 

(FRM) monitor or Federal Equivalent Method (FEM) monitor in the area);

2. Emissions and emissions-related data (including location of sources and population, amount of 

emissions and emissions control, and urban growth patterns);

3. Meteorology (weather/transport patterns);

4. Geography and topography (mountain ranges or other basin boundaries);

5. Jurisdictional boundaries (e.g., counties, air districts, existing nonattainment areas, Indian 

country, metropolitan planning organizations (MPOs)).

Ground-level ozone is not emitted directly into the air, but is created by chemical reactions between 

oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Because 

NOx and VOC emissions from a broad range of sources over a wide area typically contribute to 

violations of the ozone standards, EPA believes it is important to consider whether there are contributing 

emissions from geographic areas near the violating monitor. 

In EPA’s designations guidance for the 2008 ozone NAAQS EPA recommended examining 

CSA/CBSAs because certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

using in this technical analysis to determine if a nearby area is contributing to a violation of the 2008 

ozone NAAQS. EPA used the same basic approach in the designation process for the 1997 ozone 

NAAQS. Where a violating monitor is not located in a CSA or CBSA, EPA’s guidance recommended 

using the boundary of the county containing the violating monitor as the starting point for considering 

the nonattainment area’s boundary. 

The Composition of the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV CSA:

The Washington, DC-MD-VA and Baltimore nonattainment areas are part of the WashingtonBaltimore-Northern Virginia, DC-MD-VA-WV CSA. This consists of the following CBSAs:18

 

(1) The Baltimore-Towson, MD Metropolitan Statistical Area (MSA)19,20- Anne Arundel, Baltimore, 

Carroll, Harford, Howard, and Queen Anne’s Counties and Baltimore City in Maryland;

(2) The Culpeper, VA Micropolitan Statistical Area (Culpeper, VA CBSA) – Culpeper County in 

Virginia;

(3) The Lexington Park, MD Micropolitan Statistical Area (Lexington Park, MD CBSA) - St. Mary’s 

County in Maryland;

(4) The Washington-Arlington-Alexandria, DC-VA-MD-WV MSA (Washington DC-MD-VA-WV

CBSA): The Maryland Portion: the Counties of Frederick, Montgomery, Calvert, Charles, and Prince 

George’s; the entire District of Columbia; the Virginia Portion: the Counties of Arlington, Clarke,

Fairfax, Fauquier, Loudoun, Prince William, Spotsylvania, Stafford, and Warren, and the Cities of 

 

17 The December 4, 2008 guidance memorandum “Area Designations for the 2008 Revised Ozone National Ambient Air 

Quality Standards” refers to 9 factors. In this technical support document we have grouped the emissions-related factors 

together under the heading of “Emissions and Emissions-Related Data,” which results in 5 categories of factors.

18

 Source: OMB Bulletin No. 10-02, December 1, 2009. 

19

 Metropolitan and Mircopolitan Statistical Areas are each types of CBSAs. Hereafter, MSA will refer to only to a 

Metropolitan Statistical Area, and, CBSA will refer to both Mircopolitan and Metropolitan Statistical Areas generally and 

also be used in lieu of Mircopolitan Statistical Area and Metropolitan Statistical Area when referring to a specific area.. 

20

 Generally hereafter the “Baltimore-Towson, MD CBSA.”
11

Alexandria, Fairfax, Falls Church, Fredericksburg, Manassas, and Manassas Park; and the West 

Virginia Portion: Jefferson County.

(5) The Winchester, VA-WV MSA - Frederick County and Winchester City in Virginia and Hampshire 

County in West Virginia.

Core Cities/Counties in this CSA:

Under OMB’s December 27, 2000 (65 FR 82228), Notice of decision “Standards for Defining 

Metropolitan and Micropolitan Statistical Areas” a CBSA is built around either an urbanized area or 

urbanized cluster with central counties and outlying counties. A central county is associated with the 

urbanized area or urban cluster that accounts for the largest portion of the county’s population. The 

central counties associated with a particular urbanized area or urban cluster are grouped to form a single 

cluster of central counties for purposes of measuring commuting to and from potentially qualifying 

outlying counties. A county qualifies as an outlying county of a CBSA if it meets the following 

commuting requirements: (a) at least 25 percent of the employed residents of the county work in the 

central county or counties of the CBSA; or (b) at least 25 percent of the employment in the county is 

accounted for by workers who reside in the central county or counties of the CBSA. The counties 

included in a CBSA must be contiguous. Two adjacent CBSAs will merge to form one CBSA if the 

central county or counties (as a group) of one CBSA qualify as outlying to the central county or counties 

(as a group) of the other CBSA using the measures that define an outlying county of a CBSA. Any two 

adjacent CBSAs will form a Combined Statistical Area (CSA) if the employment interchange measure21

between the two areas is at least 25; or, if the adjacent CBSAs that have an employment interchange 

measure of at least 15 and less than 25 they will combine if local opinion, as reported by the 

congressional delegations in both areas, favors combination. See, 65 FR 82228 at 82236-82237. 

In this TSD the following central city/counties in the Baltimore-Towson MD CBSA will be considered 

to be “core counties/city” of the 1997 Baltimore Nonattainment area: Anne Arundel, Baltimore, Howard 

Counties and Baltimore City.

Likewise, the following central cities/counties of the Washington-Arlington-Alexandria, DC-VA-MDWV CBSA will be considered to be the ”core cities/counties” in the 1997 Washington DC-MD-VA 

Nonattainment area: the District of Columbia, DC; Prince George’s County, MD; Arlington County, 

VA; Fairfax County, VA; Loudoun County, VA; Prince William County, VA; Alexandria City, VA; 

Fairfax City, VA; Falls Church City, VA; Manassas City, VA; and Manassas Park City, VA.

22

EPA Guidance and Historical Approaches:

The December 4, 2008 guidance memorandum “Area Designations for the 2008 Revised Ozone 

National Ambient Air Quality Standards” recommended for CSAs that the analysis should start with the 

CSA boundary associated with violating monitors. The Washington-Baltimore-NV CSA consists of five 

CBSAs comprising 34 counties and independent cities plus the District of Columbia.23 

As will be discussed under Factor 1 in a following section of this document, the monitors violating the 

2008 NAAQS are located in two areas still designated nonattainment under the 1997 ozone NAAQS –

 

21

 The employment interchange measure is a measure of ties between two adjacent entities. The employment interchange 

measure is the sum of the percentage of employed residents of the smaller entity who work in the larger entity and the 

percentage of employment in the smaller entity that is accounted for by workers who reside in the larger entity. 65 FR 82228 

at 82238.

22

 This is the CBSA core less Stafford County, VA.

23 Under section 302(d) of the CAA, the District of Columbia is considered a state. In this analysis the terms “state,” a 

“county” and/or an “independent city” when used in a broad sense may also refer to the District of Columbia when required 

by context.
12

the current Baltimore nonattainment area and the current Washington DC-MD-VA nonattainment area. 

(Further details of the designation of areas under the 1997 ozone NAAQS are discussed under Factor 5 

“Jurisdictional boundaries.”)

EPA used the same basic approach in the designation process for the 1997 ozone NAAQS as EPA is 

using for the 2008 ozone NAAQS. Therefore, EPA has previously considered the same factors for 

setting the boundaries of the current Baltimore and Washington DC-MD-VA nonattainment areas. For 

purposes of analysis, a reasonable step is to break the area into smaller pieces that reflect the boundaries 

used to designate areas under the 1997 ozone NAAQS. In other words, start with a presumption that the 

boundaries of the current Baltimore and Washington DC-MD-VA nonattainment areas include the 

counties and independent cities which contribute to the currently violating monitors, and then apply the 

five factors to see if the current Baltimore and Washington DC-MD-VA nonattainment areas should be

contracted, expanded, realigned, or even merged based upon differences in current conditions as 

opposed to conditions as of 2004 when areas were designated for the 1997 ozone NAAQS.

Grouping of Areas for Presentation:

For the purposes of the presentation of this analysis, the Washington-Baltimore-NV CSA will be 

broken into the following subcomponents: 

(1) The Baltimore Nonattainment Area as it was defined under the 1997 ozone NAAQS24 (1997 

Baltimore nonattainment area) consisting of Anne Arundel, Baltimore, Carroll, Harford, and Howard 

Counties and Baltimore City in Maryland.25 This is the Baltimore-Towson, MD CBSA less Queen 

Anne’s County in Maryland.

(2) The Washington DC-MD-VA Nonattainment Area as it was defined under the 1997 ozone NAAQS 

(1997 Washington DC-MD-VA nonattainment area)26 consisting of: the Maryland Portion: Frederick, 

Montgomery, Calvert, Charles, and Prince George’s Counties; the entire District of Columbia; and the 

Virginia Portion: Arlington, Fairfax, Loudoun, Prince William Counties, and the Cities of Alexandria, 

Fairfax, Falls Church, Manassas, and Manassas Park. 

(3) Fredericksburg, VA Area consisting of Fredericksburg City and Spotsylvania and Stafford Counties 

in Virginia.27

(4) The Frederick County, VA Area consisting of Frederick County and Winchester City in Virginia.28

(5) Eight other counties: Queen Anne’s County in Maryland (which was a portion of the Kent County

and Queen Anne’s County Area under the 1997 ozone NAAQS)

29; St. Mary’s County in Maryland; 

Clarke, Culpeper, Fauquier, and Warren Counties in Virginia; and Hampshire and Jefferson Counties in 

West Virginia.

As will discussed under the Factor 1 – Air Quality Data section of this TSD below, the 1997 Baltimore 

area and the 1997 Washington DC-MD-VA nonattainment area contain all the monitors within the entire 

CSA that area violating the 2008 ozone NAAQS.

 

24

 Codified at 40 CFR 50.9.

25

 Sources: 40 CFR 81.321 and to 69 FR 23838, April 30, 2004.

26

 Sources: 40 CFR 81.09, 81.321 and 81.347and to 69 FR 23838, April 30, 2004.

27

 This was a separately defined nonattainment and later maintenance area under the 1997 ozone NAAQS. Sources: 40 CFR 

81.347 and 69 FR 23838, April 30, 2004.

28

 This was a separately defined attainment/unclassifiable area under the 1997 ozone NAAQS. Sources: 40 CFR 81.347 and 

69 FR 23838, April 30, 2004.

29

 Sources: 40 CFR 81.321 and to 69 FR 23838, April 30, 2004.
13

EPA’s overall assessment of the factors for the Washington-Baltimore-NV CSA is as 

follows:

Factor Assessment

Factor 1: Air Quality Data 

For this factor, EPA considered 8-hour ozone design values in parts per million (ppm) for air quality 

monitors in counties in the Washington-Baltimore-NV CSA area based on data for the 2008-2010 

period, that is, based upon a monitor’s 2010 design value, which are the most recent years with fullycertified air quality data. A monitor’s design value is the metric or statistic that indicates whether that 

monitor attains a specified air quality standard. The 2008 ozone NAAQS are met when the annual 

fourth-highest daily maximum 8-hour average concentration, averaged over 3 years is 0.075 ppm, or 

less. A design value is only valid if minimum data completeness criteria are met. See, 40 CFR part 50 

Appendix P. Where several monitors are located in a county (or a designated nonattainment area or 

maintenance area), the design value for the county or for an area (which in general can be any grouping 

of counties or be some currently defined area such as a CBSA, CSA or current or former nonattainment 

area) is determined by the monitor in that county/area with the highest design value.

The 2010 design values for the ozone NAAQS for counties in the Washington-Baltimore-NV CSA are 

shown in Tables 2. The “AQS ID No.” is the identification number assigned to the monitor in EPA’s 

Air Quality System (AQS). The “short name” is a semi-descriptive name often used in various State 

and/or EPA records. Note that only counties in the Washington-Baltimore-NV CSA that have ozone 

monitors are included in Table 2.

Table 2. Monitor data for the Washington-Baltimore-NV CSA.

County (Co.)/City, 

State

Monitor AQS 

ID No. Short Name

State 

Recommended 

Nonattainment?

1997 

Nonattainment 

(NA)/attainment 

Area

8-hr Ozone 

Design Values, 

2008-2010 (ppm)

District of Columbia Monitors in the Washington-Baltimore-NV CSA:

District of Columbia 110010025

110010041

110010043

Takoma

River Terrace

McMillan 

Reservoir

Yes Washington NA

Washington NA

Washington NA

0.075

0.077

0.079

Maryland Monitors in the Washington-Baltimore-NV CSA:

Anne Arundel Co., 

MD

240030014 Davidsonville Yes Baltimore NA 0.079

Baltimore Co., MD 240051007

240053001

Padonia

Essex

Yes Baltimore NA

Baltimore NA

0.077

0.078

Calvert Co., MD 240090011 Calvert Co. Yes Washington 0.077

Carroll Co., MD 240130001 South Carroll Yes Baltimore NA 0.076

Charles Co., MD 240170010 Southern 

Maryland

Yes Washington NA 0.075

Frederick Co., MD 240210037 Frederick Co. Yes Washington NA 0.075

Harford Co., MD 240251001

240259001

Edgewood

Aldino

Yes Baltimore NA

Baltimore NA

0.089

0.078
14

Montgomery Co., MD 240313001 Rockville Yes Washington NA 0.074

Prince George’s Co., 

MD

240330030

240338003

Howard 

University –

Beltsville

Prince George’s

County

Equestrian 

Center30

Yes Washington NA 

Washington NA

0.078

0.077

Baltimore City, MD 245100054 Furley E.S.Rec 

Center

Yes Baltimore NA 0.067

Virginia Monitors in the portion of the Washington-Baltimore-NV CSA:

Arlington Co., VA 510130020 Arlington Yes Washington NA 0.079

Fairfax Co., VA 510590030 Franconia Yes Washington NA 0.081

Fauquier Co., VA 510610002 Sumerduck No Fauquier Co. 

Attainment

0.065

Frederick Co., VA 510690010 Butler Manuf. 

Co Near Rest

No Frederick Co. 

(VA) Attainment

0.068

Loudoun Co., VA 511071005 Ashburn Yes Washington NA 0.075

Prince William Co., 

VA

511530009 James S. Long 

Park

Yes Washington NA 0.070

Stafford Co., VA 511790001 Widewater No Fredericksburg 

NA/maintenance

0.070

Alexandria City, VA 515100009 Alexandria Yes Washington NA 0.074

West Virginia has no monitors in this CSA.

Note: Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 from 

http://www.epa.gov/airtrends/values.html).

A county or city that shows a violation of the 2008 ozone NAAQS must be included in a nonattainment 

area. See, section 107(d)(1)(A) of the CAA which requires designation of nonattainment for any area 

that does not meet a NAAQS. A county (or partial county) must also be designated nonattainment if it 

contributes to a violation in a nearby area. Each county without a violating monitor that is located near a 

county with a violating monitor has been evaluated based on the weight of evidence of the five factors

and other relevant information to determine whether it sufficiently contributes to a nearby violation.

Identification of Violating Monitors:

Nine counties within the Washington-Baltimore-NV CSA contain a monitor violating the 2008 Ozone 

NAAQS. These monitors are contained solely within the boundaries of those areas designated 

nonattainment under the 1997 Ozone NAAQS; these are the 1997 Washington, DC-MD-VA 

nonattainment area and the 1997 Baltimore nonattainment area. (See, 40 CFR 81.309, 81.321 and 

81.347.) All other monitors within the CSA, but outside the boundaries of designated nonattainment 

areas under the 1997 ozone NAAQS are attaining the 2008 Ozone NAAQS. Therefore, the following 

jurisdictions must be designated by operation of law as nonattainment,

31 within one or more 

nonattainment area(s) within the Washington-Baltimore-NV CSA: (1) The District of Columbia; (2) 

 

30

 Due to the length, may be shortened to “Pr. George’s Co Eq Ctr” at time hereafter.

31 EPA would expand the boundaries of nonattainment to include the whole county or the District of Columbia containing a 

violating monitor because the States or the District of Columbia so recommended.
15

Anne Arundel, Baltimore, Calvert, Carroll, Harford, Prince George’s Counties in Maryland; and (3) 

Arlington and Fairfax Counties in Virginia.

Analysis of the Concentrations as indicated by Design Values within the Washington-Baltimore-NV

CSA:

The highest concentrations within the Washington-Baltimore-NV CSA are found at the Edgewood site 

(or Edgewood monitor) in Harford County, MD and the Franconia site in Fairfax County, VA which 

have design values of 0.089 and 0.081 ppm, respectively. The fact that the Edgewood site has a high 

value is not surprising because this monitor was located for the objective of measuring highest 

concentrations on an urban scale. One can reasonably infer that this monitor was sited to be downwind 

of Baltimore City and other parts of the Baltimore-Towson, MD CBSA. See, Table 3-2a. in “Ambient 

Air Monitoring Network Plan For Calendar Year 2011,” by the Ambient Air Monitoring Program, Air 

and Radiation Administration Management, Maryland Department of the Environment, May 27, 2010.

32

 

Appendix 1 of this analysis contains a summary of relevant regulatory and guidance documents related 

to selection of sites for ozone monitors and to monitoring objectives.

In the 1997 Washington DC-MD-VA nonattainment area, the Howard University -Beltsville site has a 

dual monitoring objective of population exposure and highest concentration. This site would fulfill the 

requirement that the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area 

have such a site. Refer to Appendix 1 of this analysis. See, Table 3-2a. in “Ambient Air Monitoring 

Network Plan For Calendar Year 2011,” by the Ambient Air Monitoring Program, Air and Radiation 

Administration Management, Maryland Department of the Environment, May 27, 2010. One can 

reasonably infer that that this monitor was sited to monitor the expected highest concentrations 

downwind of the densely populated urban core surrounding the District of Columbia. 

In their 5-factor analyses submitted with the State’s March 7, 2012 letter,33 Maryland supplied extensive

information and data to show why the Edgewood monitor had a higher design value than other monitors 

in the CSA. This information related to transport of ozone and its precursors on various scale and the 

effect that the Appalachian Mountains and the Chesapeake Bay have on transport or on the 

concentration of ozone at monitors in Maryland and in particular at the Edgewood monitor. 

Generally, within the Washington-Baltimore-NV CSA the highest design values occur in two separate 

areas: (1) the first of these areas of peak design values is centered on the monitors in Fairfax County, the 

District of Columbia and Anne Arundel County with design values of 0.079 to 0.081 ppm; (2) the 

second areas of peak ozone concentrations is northeast of Baltimore City and centered on the Edgewood 

monitor in Harford County with a design value of 0.089 ppm. These two areas are “circled” with a red, 

solid line in Figure 2a below.

Near each of these areas of peak ozone concentrations are monitors each with a design value of 0.077 

ppm or 0.078 ppm. Near the Fairfax County-District of Columbia-Anne Arundel County group are the 

two monitoring sites in Prince George’s County, MD. In close proximity to and northeast of the 

Edgewood site are the Aldino monitor site in Harford County and the two monitoring sites (Essex and 

Padonia) in Baltimore County. Outside these areas, the design values fall off to attaining monitors. 

Monitors attaining the 2008 ozone NAAQS are found north, northwest, west, southwest and south of the 

curve formed by the Calvert County, MD—Fairfax County, VA—Carroll—Baltimore (Padonia) —

Harford Counties, MD monitors. (The curve of the Calvert County, MD—Fairfax County, VA—

 

32 Source: MDPlan2010.pdf (Downloaded 12/9/2011 from http://www.epa.gov/ttn/amtic/plans.html).

33

 Letter dated March 7, 2012, from Robert M. Summers, Ph.D., Secretary, Maryland Department of the Environment to 

Shawn M. Garvin, Regional Administrator, EPA Region III.
16

Carroll—Baltimore (Padonia) —Harford Counties, MD monitors is shown in Figure 2b below with a 

solid, pink line.) 

Just outside this curve of violating monitors are three monitors each with a design value of 0.075 ppm 

(just attaining the 2008 NAAQS) – the ones in Charles County, MD, Loudoun County, VA and 

Frederick County, MD. These attaining monitors are joined by a red, dashed line in Figure 2b. 

Adjacent States:

South, southwest, west, and northwest of these three monitors are a number of monitors generally 0.005 

ppm below the 2008 NAAQS. These are the monitors in Fauquier, Frederick, Prince William and 

Stafford Counties in Virginia. (These three are joined by a dotted, green line in Figure 2b.) There are 

also attaining monitors in the northern tip of Caroline County, VA, Berkeley County, WV and 

Washington County, MD. Table 3 provides basic data for these other monitors:

Table 3. Three Attaining Monitors Outside the Washington-Baltimore-NV CSA.

County/City, State

Monitor AQS ID 

No. Short Name

State 

Recommended 

Nonattainment?

8-hr Ozone 

Design Values, 

2008-2010 (ppm)

EPA final 

designation

Caroline County, 

VA

510330001 Corbin No 0.073 Attainment

Berkeley County, 

WV

540030003 Martinsburg Ball 

Field

No 0.070 Attainment

Washington 

County, MD

240430009 Hagerstown Yes or no34 0.072 Attainment

Note: Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 from 

http://www.epa.gov/airtrends/values.html).

The District of Columbia and Maryland both recommended a very large, 17-State nonattainment area. 

Maryland in particular questioned why States immediately adjacent to the Washington-Baltimore-NV 

CSA did not meet the geographic close proximity prong of CAA section 107(d)(1)(A). While EPA 

believes that the entire States of Delaware, Pennsylvania, Virginia and West Virginia do not meet 

section 107(d)’s requirements to be considered areas “contributing” to nonattainment in “nearby areas,” 

EPA’s reasoning for entire States does not necessarily suffice for adjacent CBSAs or counties not in a 

CBSA. EPA therefore considered ozone design value concentrations in other adjacent counties and 

CBSAs. The basic air quality data for such areas is provided in Table 4 below:

Table 4. Other Monitors in Adjacent Areas Outside the Washington-Baltimore-NV CSA.

CBSA or 

County/City, State

Monitor AQS ID 

No. 

8-hr Ozone 

Design Values, 

2008-2010 

(ppm)

EPA final 

designation

New Castle 

County, DE

1000-1007 or 

100031013

0.075 NonattainmentNote 4-2

Chester County, 

PA

420290100 0.076 Nonattainment Note 4-2

Cecil County, MD 240150003 0.080 Nonattainment Note 4-2

Dover CBSA (Kent 

Co.), DE

100010002 0.074 Attainment

Chambersburg 

(Franklin Co.), PA 

CBSA

420550001 Attainment

 

34

 Only if all of Maryland was part of a 17 State nonattainment area did Maryland recommend nonattainment.
17

York-Hanover 

CBSA (Adams and 

York Cos.),PA

421330008

421330011

420010002

0.071

0.074

0.073

Attainment

Lancaster 

County/CBSA, PA

420710007

420710012

0.077

0.075 

Nonattainment

Kent County, MD 240290002 0.075 Attainment

Page County, VA 511390004 0.066 Attainment

Madison County, 

VA

511130003 0.073 Attainment

Hanover County, 

VANote 4-1

510850003 0.075 Attainment

Notes:

Sources: Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 

from http://www.epa.gov/airtrends/values.html).

4-1: Part of the Richmond, VA CBSA.

4-2: As part of the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE 

nonattainment area

These patterns of ozone design values suggest that there could be two separate areas with a linkage 

between high emissions of ozone precursors in within some geographic region such as the core of the 

Baltimore-Towson CBSA or Washington CBSA and peak ozone design values in that geographic region

such as at the Edgewood monitor or the Franconia. One such geographic region might be the area 

northwest of Baltimore City centered on the Edgewood monitoring site in Harford County, MD. The 

Edgewood monitoring site is circled (in red) in Figure 2a below, the north-easternmost county in the 

Washington-Baltimore-NV CSA. The peak ozone area for the second such geographic region might be

the group of monitors consisting of the monitors in Fairfax County, VA, the District of Columbia, and 

possibly the monitor in Anne Arundel County, MD. These are also “circled” in Figure 2a below with a 

surrounding red solid line.
18
19

Design Value Changes – 2003 to 2010:

Table 5 shows the 2003 design values used to designate and classify areas under the 1997 ozone 

NAAQS, the 2008 design values used by the States to make their 2009 recommendations for the 2008

ozone NAAQS and the 2010 design values. The first and second highest design values in the 

Washington-Baltimore-NV CSA are emphasized in bold, underlined type; design values within 0.002 

ppm of the second highest value are emphasized in bold type.

Table 5. Air Quality Data – Design Values for 2003, 2008 and 2010.

County

State 

Recommended 

Nonattainment for 

2008 NAAQS?

2003 8-hour 

ozone 

design value

(ppm)

35

2008 8-hour 

Ozone 

design value

(ppm)

36

2010 8-hour 

Ozone 

design value

(ppm)

37

Baltimore nonattainment area:

Anne Arundel Co., MD Yes 0.098 0.087 0.079

Baltimore Co., MD Yes 0.093 0.085 0.078

Carroll Co., MD No 0.089 0.083 0.076

Harford Co., MD Yes 0.103 0.091 0.089

Baltimore City, MD Yes 0.082 Inc. D 0.067

Washington DC-MD-VA nonattainment area

District of Columbia, DC Yes 0.094 0.087 0.079

Calvert Co., MD No N/D 0.079 0.077

Charles Co., MD No 0.094 0.082 0.075

Frederick Co., MD No 0.088 0.082 0.075

Montgomery Co., MD No 0.088 Inc. D 0.074

Prince George’s Co., 

MD Yes 0.093 0.087 0.078

Arlington Co., VA Yes 0.099 0.085 0.079

Fairfax Co., VA Yes 0.097 0.087 0.081

Loudoun Co., VA Yes 0.092 0.083 0.075

Prince William Co., VA Yes 0.087 0.078 0.070

Alexandria City, VA Yes 0.092 0.081 0.074

Frederick Co., VA Area

Frederick, VA No 0.085 0.073 0.068

Fredericksburg, VA Area

Stafford, VA No 0.088 0.081 0.070

Other Counties

Fauquier, VA No <0.085 0.071 0.065

 

35 “Chapter 2 8-Hour Ozone Nonattainment Designations and Classifications” docket item EPA-HQ-OAR-2003-0083-1812 

in docket EPA-HQ-OAR-2003-0083 (downloaded November 15, 2011) and available on-line at Regulations.gov.

36 Data Source: dv_ozone_2006_2008.xls (downloaded on 11/29/2011 from http://www.epa.gov/airtrends/values.html.

37 Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 from http://www.epa.gov/airtrends/values.html.
20

Note: “N/D” means no data; “Inc. D” means there was incomplete data to calculate a design value; 

“<0.085” means the design value was under the 1997 ozone NAAQS and the county was designated 

attainment.

For designations under the 1997 ozone NAAQS, the Edgewood site in Harford County had a design 

value (for the period 2000-2002) of 0.103 ppm, and all other monitored counties in the 1997 Baltimore 

nonattainment area except that in Baltimore City violated the 1997 ozone NAAQS with a design value 

of 0.085 ppm or more.38 Likewise, for designations under the 1997 ozone NAAQS, Arlington County, 

VA had the highest design value of 0.099 ppm for the period 2001-2003; for the 2001-2003 period, all 

other counties currently having monitors in the current Washington DC-MD-VA nonattainment area 

except Calvert County (which did not have a monitor with 3 years of valid data for 2000-2002) violated 

the 1997 ozone NAAQS with a design value of 0.085 ppm or more.39 For the designations under the 

1997 ozone NAAQS, the design value for the 1997 Baltimore nonattainment area was 0.004 ppm greater 

than the design value for the 1997 Washington DC-MD-VA nonattainment area. Both areas were 

classified as moderate nonattainment areas.40

For their 2009 recommendations, the States generally relied upon 2008 design values. Three monitors 

in the 1997 Washington DC-MD-VA nonattainment area had a design value of 0.087 ppm (for 2006-

2008) which set the design value within the 1997 Washington DC-MD-VA nonattainment area at 0.087 

ppm. The Edgewood site in Harford County, MD had a design value for the same period of 0.091 ppm 

which set the design value within the 1997 Baltimore nonattainment area at 0.091 ppm. The difference 

in 2008 design values between these two nonattainment areas designated under the 1997 ozone NAAQS 

was still 0.004 ppm. 

Currently, for the period 2008-2010, the difference in design values for these two monitors has grown to 

0.008 ppm. 

The trend in design values has been downward since 2003. In 2008, no monitor in the current Baltimore 

and Washington DC-MD-VA nonattainment areas were attaining the 2008 NAAQS of 0.075 ppm; nor 

was the monitor in the Fredericksburg, VA Area. Now some of the counties and cities on the edge are 

attaining the 2008 NAAQS, and some interior areas, such Alexandria City, VA and Montgomery

County, MD, are as well. Admittedly, due to year to year fluctuations in weather from one ozone season 

to the next, the design values will also fluctuate in response, but over longer periods of time a definite 

overall trend will be apparent if there is progress. The counties and cities in the Washington-BaltimoreNV CSA saw a decrease in design values of 0.006 to 0.014 ppm over the period 2003 to 2008. Most

counties and cities in the Washington-Baltimore-NV CSA over the last two years (2008 to 2010) saw 

design value decreases of 0.006 to 0.011 ppm; however, during the last two years, two saw decreases of 

only 0.002 ppm. These were the monitors in Harford and Charles Counties in Maryland.

Of particular note are the design values in Frederick and Charles Counties in Maryland. These are 

within 0.002 ppm of attaining the 2008 NAAQS. As such, these counties might be classified as 

marginal nonattainment areas if each were a separate nonattainment area. The CAA contains a 

presumption that marginal areas are expected to attain the relevant ozone NAAQS without any

additional controls beyond those already promulgated; currently promulgated federal mobile source 

measures are one source of reductions available for marginal areas to attain the 2008 NAAQS and 

continue to occur as the fleet of older highway motor vehicles and other mobile source engines are 

 

38 “Chapter 2 8-Hour Ozone Nonattainment Designations and Classifications” docket item EPA-HQ-OAR-2003-0083-1812 

in docket EPA-HQ-OAR-2003-0083 (downloaded November 15, 2011) and available on-line at Regulations.gov

(http://www.regulations.gov).

39

 Ibid.

40

 Ibid. See also, 69 FR 23858, April 30, 2004.
21

replaced by new highway motor vehicles and other mobile source engines required to meet newer, more 

stringent emission standards. 

Also of note is the apparent trend at the Davidsonville monitoring site in Anne Arundel County, MD. 

The trend at this monitor seems to track that of the current Washington DC-MD-VA nonattainment area. 

In 2003, this monitor’s design value was 0.001 ppm less than the design value of 0.099 ppm for 

Arlington County, VA and 0.005 ppm of that in Harford County, MD (which established the design 

value for the 1997 Baltimore nonattainment area). In 2008 this monitor’s design value was equal to that 

for the 1997 Washington DC-MD-VA nonattainment area and 0.004 ppm less than that of Harford 

County. For 2010, this monitor’s design value was 0.002 ppm less than the design value of 0.081 ppm 

in Fairfax County, VA,

41 and 0.010 ppm of that in Harford County, MD. This monitor seems to track 

(that is, is always equal or less than) the peak in the current Washington DC-MD-VA nonattainment 

area and, as with the peak in the current Washington DC-MD-VA nonattainment area, has diverged 

from the trend in the Harford County, MD. Such a result might suggest that the air quality data at the 

monitor in Anne Arundel County is more influenced by emissions in the current Washington DC-MDVA nonattainment area than emissions in the rest of the current Baltimore nonattainment area.42

The 2008 to 2010 air quality data strongly suggest that there are two main peak points of ozone 

concentrations in the Washington-Baltimore-NV CSA. The first is in Harford County, Maryland in the 

northeast of the Washington-Baltimore-NV CSA. The second peak area is located at the Fairfax County

monitor in Virginia and this peak extends into Arlington County, VA, the District of Columbia and 

possibly into Anne Arundel County Maryland. 

A similar situation existed in 2004 when EPA designated areas for the 1997 ozone NAAQS. Harford 

County had the highest design value (0.103 ppm) of any monitor in the current CSA. Arlington County

had the highest design value (0.099 ppm) in the 1997 Washington DC-MD-VA nonattainment area; 

Fairfax County, VA and Anne Arundel County, MD both had design values close (0.097 and 0.098 ppm, 

respectively) to that in Arlington County, VA.

For 2008, the pattern was repeated. Harford County had the highest design value (0.091 ppm) of any 

monitor in the current CSA. Fairfax County, VA, the District of Columbia and Prince George’s County, 

MD all had the highest design (0.087 and 0.098 ppm, respectively) in the 1997 Washington DC-MD-VA 

nonattainment area and Anne Arundel County, MD had the same design value. All monitors in the 1997

Washington DC-MD-VA nonattainment area are showing currently attainment of the 1997 ozone 

NAAQS. Except for the monitors in Harford County, MD all other monitors (including that in Anne 

Arundel County, MD) in the 1997 Baltimore MD nonattainment area are currently showing attainment 

of the 1997 ozone NAAQS. 

The design values in this CSA over the last 7 years suggested that there are two central peak areas of 

nonattainment within the Washington-Baltimore-NV CSA. The first is in Harford County, MD in the 

far northeast portion of the Washington-Baltimore-NV CSA. The second is in the vicinity of Fairfax 

and Arlington Counties in Virginia and extends into the District of Columbia, and into Anne Arundel 

and Prince George’s Counties in Maryland. See Figure 2a.

 

41

 The Preliminary TSD for the December 9, 2011 letters sent to the States incorrectly stated this Davidsonville monitor was 

0.002 ppm less than the design value in Arlington County.

42

 As will be discussed under Factor 3 – Meteorology – consideration of prevailing winds on exceedance days support a 

conclusion that this monitor is more closely tied to the rest of the Baltimore area but also in part to Montgomery and Prince

George’s Counties in Maryland.
22

Detailed Analysis based Upon Exceedance Day Values:

EPA received comments from Maryland, the public and others regarding the adequacy of surface wind 

roses to represent wind patterns on days the 2008 ozone NAAQS is exceeded.

43

 As a result of such 

comments, EPA re-evaluated the five-factors for this CSA in light of meteorology data resulting from 

use of the National Oceanic and Atmospheric Administration’s (NOAA) Hybrid Single Particle 

Lagrangian Integrated Trajectory (HYSPLIT) Model to supplement the Factor 3 Meteorology portion of 

the analysis of the Preliminary TSD.44 

To allow consideration of air movement above the surface layer we ran the HYSPLIT model to obtain 

trajectories for three heights – 100 meters, 500 meters and 1,000 meters. We ran the HYSPLIT to obtain 

1,000 meter runs in order to better understand aloft movement of air that can be expected to mix down 

as the night-time inversion breaks-up. EPA considered 5 years, 2006 through 2010 inclusive, of 

exceedance day data of complete, certified data for the current monitors in the CSA. Due to the number 

of monitors and exceedance days (over 980 monitor-day combinations) EPA did not (and could not due 

to time constraints) run trajectories for each exceedance day at each monitor in the CSA. 

To narrow down the level of effort, EPA examined the air quality data (Factor 1) in more detail. 

We examined the 2006 to 2010 8-hour ozone concentrations for the monitors in the “violating center”45

of the CSA and grouped the data by days when the 2008 ozone NAAQS was exceeded. When selecting 

monitors for which to run the HYSPLIT model EPA had to consider the density of the monitoring 

network and the following issues: 

(1) a needed decision to designate all or a substantial portion of this CSA as one nonattainment area as 

recommended by two States or split the CSA into more than one nonattainment and attainment areas 

as recommended by two States;

(2) the need to develop a conceptual model of the relationship between meteorology (wind directions on 

exceedance days) and ozone concentrations within the CSA in light of Maryland’s (and other 

parties’) comments on meteorology;

(3) the observation that the design value for the current Washington DC-MD-VA nonattainment area by

the Davidsonville monitor in Anne Arundel County “tracks” that in the 1997 Washington DC-MDVA nonattainment area indicating this county may be linked to emission in this area;

(4) comment by the States that EPA’s preliminary analysis46 appeared to indicate that counties forming 

the borders between the Baltimore-Towson and the Washington DC-MD-VA-WV CBSAs, such as, 

Anne Arundel County, Prince George’s County and others could be placed in more than one 

nonattainment area and thus the CSA should contain one nonattainment area;

47

(5) Maryland’s comment that the uniformity of design values across the CSA for all monitors except the 

Edgewood monitor demonstrates that the two regions should be designated as one nonattainment 

area; and,

 

43 For example, refer to documents EPA-HQ-OAR-2008-0476-0405 and EPA-HQ-OAR-2008-0476-0456 and to the 

Response to Public Comments Document] in the docket for this action.

44

 “Preliminary Technical Support Document, December 2011, entitled, Maryland Area Designations for the 2008 Ozone 

National Ambient Air Quality Standards, prepared by the Region 3 USEPA” document number EPA-HQ-OAR-2008-0476-

0235 in the docket for this action.

45

 Basically all monitors in the CSA were considered except the monitor in Frederick County, VA.

46

 For example, refer to Preliminary Technical Support Document, December 2011, entitled, “Maryland Area Designations 

for the 2008 Ozone National Ambient Air Quality Standards,” prepared by US EPA Region 3 which is document number 

EPA-HQ-OAR-2008-0476-0235 in the docket for this action. Similar TSDs were prepared for EPA’s December 9, 2011 

responses to the District of Columbia and to Virginia – refer to document numbers EPA-HQ-OAR-2008-0476-0231 and 

EPA-HQ-OAR-2008-0476-0237.
23

(6) Maryland’s extensive information on meteorological and related geographical factors regarding 

transport in general and frequency and severity of exceedances at the Edgewood monitor. 

To consider these issues and State submitted data, EPA therefore needed to examine the air quality 

data in vastly more detail than in the case of many other areas in the country where perhaps there is 

only one violating monitor, perhaps the relationship between a few counties’ emissions and one or 

only one or two monitors are at issue, or where substantial geographic barriers constrain air 

movement. 

EPA obtained the 2006 through 2010 (inclusive) air quality monitoring data for each monitor by day for 

the Baltimore CBSA and for the Washington DC-MD-VA-WV CBSA. This data provides the 2006 

through 2010 data for all the violating monitors currently in the CSA. This data was downloaded on 

February 1, 2012, from http://www.epa.gov/airdata/ad_data_daily.html by selecting “Ozone” for the 

“Pollutant,” “2006, 2007, 2008, 2009 or 2010” (as applicable) for the “Year,” “Baltimore-Towson, MD” 

or “Washington-Arlington-Alexandria DC-MD-VA-WV” for “Select a City (defined as a CBSA),” and 

“All Sites” for the “Monitor Site” (with exceptional events data). A copy of the downloaded 

spreadsheet files has been placed in the docket for this action. This 2006 through 2010 (inclusive) data 

also includes daily 8-hour maximum ozone concentrations for the monitors in the CSA close to 

exceeding the 2008 ozone NAAQS such as those in Charles, Frederick and Montgomery Counties in 

Maryland, Loudoun County and Alexandria City in Virginia, the Takoma monitor in the District as well 

as many monitors with design values at or below 0.070 ppm. The only monitor within the CSA for 

which EPA did not obtain daily 8-hour maximum ozone concentrations for 2006 through 2010 was that 

in Frederick County, VA.

48

 In the 2006 to 2010 (inclusive) period for the monitors examined, EPA 

identified over 980 distinct instances of monitor-days.

Extraction and Grouping by Episodes:

EPA extracted for each monitor the date and the maximum 8-hour ozone concentration and grouped 

these by “episode.” In this document an “exceedance day” is for a monitor a day or date on which that 

monitor recorded a maximum 8-hour ozone concentration at or above 0.076 ppm. For the CSA or a 

CBSA, an exceedance day is a day or date on which at least one monitor in that CSA or CBSA, 

respectively, recorded a maximum 8-hour ozone concentration at or above 0.076 ppm. An “episode” is 

a period of at least one day or more than one consecutive days on which at least one monitor in the CSA 

or a CBSA recorded a maximum 8-hour ozone concentration at or above 0.076 ppm. 

Summary data for each episode in the years 2006, 2007, 2008, 2009 and 2010 is provided in Table A2-1 

of Appendix 2 of this document. For each exceedance day for the CSA, the maximum 8-hour ozone 

concentration is provided for each monitor exceeding the 2008 ozone NAAQS (that is, a value of 0.076 

ppm or more) for each monitor EPA has provided the following subset of data: the date, the AQS ID No. 

(expressed with hyphens, e.g., 24-025-1001 versus 240251001), the maximum 8-hour ozone 

concentration, the units of measure (ppm), the corresponding daily Air Quality Index (AQI) value the 

number of daily 1-hour ozone readings (“Daily Obs Count”) and percent completeness (“Percent 

Complete”) for that day, the AQS parameter code and description (“Descript”), the name of the State 

and the name of the County or City in which the monitor is located. The data is arranged by year, by

date and grouped by episode. The data in this Table A2-1 is only for those monitors in place as of 2008 

 

48

 EPA did not obtain this due to the parameters EPA used to filter the data; EPA filtered the AQS data by specifying by 

“Select a City (defined as a CBSA).” EPA did not intend to examine the air quality on a day by day basis for monitors with a 

design value at or below 0.070 ppm because these were well below the NAAQS and because EPA obtained the day by day 

data for the purpose of identifying the days the ozone NAAQS was exceeded for those monitors violating the 2008 ozone 

NAAQS. Therefore, EPA did not exclude the data for Frederick County, VA but rather incidentally obtained the day by day 

data for the other monitors with a design value well below the 2008 ozone NAAQS. 
24

to 2010 because these are the monitors the design values of which were used to determine which 

monitors and counties contained a violating monitor.

Table A2-2 in Appendix 2 to this document contains a subset of the episode days listed in Table A2-1 

for the three year period 2008 to 2010. EPA chose episodes from 2008 to 2010 because this was the 

most recent three year period of certified data available. Unlike Table A2-1 which provides data for 

only monitors that exceeded 0.075 ppm on a day, Table A2-2 also has the maximum 8-hour ozone 

concentration for all monitors in the Baltimore-Towson and Washington DC-MD-VA-WV CBSAs. 

For each monitor EPA has provided the following subset of data: the date, the AQS ID No. (expressed 

with hyphens, e.g., 24-025-1001 versus 240251001), the maximum 8-hour ozone concentration, the 

units of measure (ppm), the corresponding daily Air Quality Index (AQI) value, the number of daily 1-

hour ozone readings (“Daily Obs Count”) and percent completeness (“Percent Complete”) for that day, 

the AQS parameter code and description (“Descript”), the name of the State and the name of the County

or City in which the monitor is located. The data is arranged by year, by date and grouped by episode. 

EPA chose episodes that represented a variety of wind patterns as predicted by the HYSPLIT model and 

chose episodes that represented the worst conditions based upon length of the episodes in days, the 

number of different monitors recording an exceedance on at least one day of the episode, and the 

maximum concentrations recorded by monitors.

49

 EPA also chose other episodes during which the 

Edgewood monitor recorded an exceedance because Maryland presented extensive data regarding 

meteorological-topographical factors that disproportionately affect that monitor. EPA therefore 

obtained HYSPLIT model back-trajectories predictions for virtually all (if not all) exceedance days for 

this monitor. The purpose of examining a subset of all the episodes was to examine the concentration 

gradients occurring within the CSA and the concentrations measured on the ground at the monitors 

predicted to be on the up-wind boundary of the CSA. EPA examined these to see if the Edgewood 

monitor was atypical in that it might record higher concentrations than other monitors in close proximity

and to see how ozone concentrations waxed and waned in relation to the more densely populated/higher 

emissions counties and cities within the CSA and in relation to upwind-edge and downwind-edges of the 

CSA. EPA performed these analyses because a simple design value plot across the CSA does not 

represent daily, peak, 8-hour ozone concentration gradients except only on a very gross level of 

resolution as a design value represents a three-year average of only one value per year for each monitor. 

Maryland also submitted its analysis of transport of ozone across various boundaries – CBSA and, State 

– and scales – city-to-city and from Missouri to Maryland (discussed further under Factor 3 –

Meteorology). Maryland provided its analysis of the “elevated reservoir” and cited three monitors in 

close proximity that are located at high-elevations (relatively to monitors within the CSA).50 These 

monitors are the “Piney Run” monitor (AQS ID No. 24-023-0002) in Garrett County, MD, the “Big 

Meadows” monitor (AQS ID No. 51-113-0003) within the Madison County portion of Shenandoah 

National Park (SNP), and the “Methodist Hill” monitor (AQS ID No. 42-055-0001) in Franklin County, 

PA. EPA therefore examined 2008 to 2010 data for these monitors and placed the entire 2008 to 2010 

monitoring data in the docket for this action. A subset of this data is provided in Table A2-3 in 

Appendix 2 of this document. This subset is for the episode days of the 2008 to 2010 episodes listed in 

Table A2-1 and in cases for the day before the start of the episode. For each monitor EPA has provided 

the following subset of data: the date, the AQS ID No. (expressed with hyphens, e.g., 24-025-1001 

 

49

 In some respects these criteria are all inclusive in that examination of the episode data in Table A2-1 will show that the 

largest number of different monitors exceeding 0.075 ppm and the higher concentrations are found on days during multi-day 

episodes. Extra weight was given to an episode if a monitor recorded a concentration that was among the four-highest for 

that monitor during that year. 

50

 For example, refer to page 17 of “Moving Forward to Address Regional Transport,” Tad Aburn - Air Director, MDE, 

February 8, 2012 - MARAMA Science Meeting, a copy of which has been placed in the docket.
25

versus 240251001), the maximum 8-hour ozone concentration, the units of measure (ppm), the AQS 

parameter code and description (“Descript”), the name of the State and the name of the County or City 

in which the monitor is located. The data is arranged by date. 

In past designations, EPA has rarely considered this level of detail for every designation decision, but 

to reiterate, the decisions for this CSA are not typical due to: the State submitted information 

regarding meteorology and its effects on the Edgewood monitor; the differing recommendations by 

two States seeking a single nonattainment area for the CSA and another two seeking retention of the 

1997 Washington DC-MD-VA nonattainment boundaries. 

Design value and exceedance day trends for the 2006 to 2010 period:

As noted in Tables 2 and 5, the highest design value for the Washington-Baltimore-NV CSA is and has 

been set by the Edgewood monitor in Harford County, MD. The same monitor sets the design value

(DV) for the 1997 Baltimore nonattainment area. For the 1997 Washington DC-MD-VA nonattainment 

area, the location of the design value monitor has shifted over time. For 2008-2010, the Franconia 

monitor in Fairfax County, VA has a DV of 0.081 ppm. Based upon the 2008-2010 DVs, other monitors 

in this CSA with a DV close to the Franconia monitor are the Davidsonville, McMillan Reservoir and 

Arlington monitors, each with a DV of 0.079 ppm. Close behind are the Aldino, Howard U.–Beltsville 

and Essex monitors each with a DV of 0.078 ppm. 

Table 6 provides the DVs for these monitors and a few others since the 2006 to 2008 period:

Table 6. Design Values for Select Monitors

 Design value (ppm)

State Monitor

AQS ID

No.

2006-

2008

2007-

2009

2008-

2010

District of 

Columbia

McMillan 

Res 110010043 0.087 0.080 0.079

Anne Arundel Davidsonville 240030014 0.087 0.080 0.079

Baltimore Essex 240053001 0.085 0.078 0.078

Harford Edgewood 240251001 0.091 0.087 0.089

Harford Aldino 240259001 0.089 0.082 0.078

Prince 

George’s HU-Beltsville 240330030 0.083 0.078 0.078

Prince 

George’s

Pr Geo. Eq. 

Ctr. 240338003 0.087 0.078 0.077

Arlington Arlington 510130020 0.085 0.079 0.079

Fairfax Franconia 510590030 0.085 0.080 0.081

Data Sources:

dv_ozone_2006_2008.xls (downloaded on 11/29/2011 from http://www.epa.gov/airtrends/values.html). 

Ozone_DesignValues_20072009_FINALr03dec10.xls (downloaded on 3/30/2012 from 

http://www.epa.gov/airtrends/values.html)

ozone_dv75_20082010.xls (downloaded on 9/22/2011 from http://www.epa.gov/airtrends/values.html.

For the same set of monitors, Table 7 provides the approximate number of exceedances of the 0.075 

ppm standard per year.
26

Table 7. Approximate Number of Exceedance Days per Year for Select 

Monitors51

Monitor AQS ID No. 2006 2007 2008 2009 2010

McMillan 

Res. 11-001-0043 22 14 8 2 16

Davidsonville 24-003-0014 14 20 13 0 12

Essex 24-005-3001 19 13 11 1 15

Edgewood 24-025-1001 21 24 15 9 27

Aldino 24-025-9001 17 22 13 2 8

HUBeltsville52 24-033-0030 22 14 9 1 16

Pr Geo. Co. 

Eq. Ctr. 24-033-8003 16 17 10 0 9

Arlington 51-013-0020 17 19 8 2 13

Franconia 51-059-0030 18 14 6 1 13

Table 8 provides the approximate number of exceedances for the 3-year periods 2006 to 2008, 2007 to 

2009, 2008 to 2010 and grand total for 2006 to 2010: 

Table 8. Approximate Number of Exceedances for Select 

Monitors53

 Approximate Number of 

Exceedances

Monitor AQS ID No.

2006-

2008

2007-

2009

2008-

2010

2006-

2010

McMillan 

Res. 11-001-0043 44 24 26 62

Davidsonville 24-003-0014 47 33 25 59

Essex 24-005-3001 43 25 27 59

Edgewood 24-025-1001 60 48 51 96

Aldino 24-025-9001 52 37 23 62

HU-Beltsville 24-033-0030 45 24 26 62

Pr Geo. Co. 

Eq. Ctr. 24-033-8003 43 27 19 52

Arlington 51-013-0020 44 29 23 59

Franconia 51-059-0030 38 21 20 52

Data Sources: 

 

51

 Derived by manual sorting and compiling of the data in Table A2-1 in Appendix 2 to this document. Numbers may 

therefore be approximate only.

52

 Short for Howard University – Beltsville.

53

 Derived by manual sorting and compiling of the data in Table A2-1 in Appendix 2 to this document. Numbers may 

therefore be approximate only.
27

(1) Files Balt-Tow CBSA 2006 ad_viz_plotval_data.csv, Balt-Tow CBSA 2007 ad_viz_plotval_data.csv, Balt-Tow CBSA 2008 

ad_viz_plotval_data.csv, Balt-Tow CBSA 2009 ad_viz_plotval_data.csv and Balt-towson CBSA 2010 ad_viz_plotval_data.csv 

downloaded from http://www.epa.gov/airdata/ad_data_daily.html by selecting “Ozone” for the “Pollutant,” “2006, 2007, 2008, 2009 

or 2010” for the “Year,” “Baltimore-Towson, MD” for “Select a City (defined as a CBSA),” and “All Sites” for the “Monitor Site” 

(with exceptional events data). 

(2) Files Wash-AADC CBSA 2008 ad_viz_plotval_data.csv, Wash-AADC CBSA 2007 ad_viz_plotval_data.csv, Wash-AADC CBSA 

2008 ad_viz_plotval_data.csv, Wash-AADC CBSA 2009 ad_viz_plotval_data.csv and Wash-AADC CBSA 2010 

ad_viz_plotval_data.csv downloaded from http://www.epa.gov/airdata/ad_data_daily.html by selecting “Ozone” for the “Pollutant,” 

“2006, 2007, 2008, 2009 or 2010” for the “Year,” “Washington-Arlington-Alexandria DC-MD-VA-WV” for “Select a City (defined 

as a CBSA),” and “All Sites” for the “Monitor Site” (with exceptional events data). 

(3) All files downloaded February 1, 2012.

A few conclusions that can be drawn from Tables 6, 7 and 8 are:

(1) From Table 7 – 2009 had an atypically low number of exceedances. 

(2) From Table 6 – As a result of the 2009 ozone season data the design values dropped at all monitors 

for the period 2007 to 2009 from those in 2006-2008.

(3) From Table 6 – The difference between the Edgewood monitor and the highest design values in the 

Washington DC-MD-VA-WV CBSA grew from 0.004 ppm (0.091 – 0.087) for the 2006 to 2008 

period to 0.008 ppm (0.087 – 0.080) for the 2007 to 2009 period.

(4) From table 7 – The number of exceedances per monitor in 2010 returned to levels somewhere 

between the levels of 2007 and 2008 except for the Edgewood monitor which had more exceedances 

in 2010 than any other year in the period before 2009.

(5) From Table 6 – Except for the Franconia and Edgewood two monitors, in spite of the increase in 

number of exceedances in 2010, design values for the period 2008 to 2010 remained stable or 

dropped in comparison to the period for 2007 to 2009. The Franconia monitor saw an increase of 

0.001 ppm; for the Edgewood monitor the increase was 0.002 ppm.

(6) From Table 6 – The difference between the Edgewood monitor and the highest design value(s) in the 

Washington DC-MD-VA-WV CBSA grew from 0.007 ppm (0.087 – 0.080) for the 2007 to 2009 

period to 0.008 ppm for the 2008 to 2010 period.

(7) From Table 7 – Prior to 2009, the Edgewood monitor was ranked first or second in number of 

exceedances per year and had a comparable number of exceedances per year to the next lower or 

higher ranked monitor (21 versus 22; 24 versus 22, and 15 versus 13).

(8) From Table 7 – For 2009 and after, the Edgewood monitor had far more exceedances by a factor of 

4.5 (9 versus 2) times for 2009 and 1.6 times (27 versus 16) of the next highest monitor. 

(8) From Table 8 – For any three-year period during 2006 through 2010, the Edgewood monitor has 

always had the most exceedances over any three-year period; one might expect the monitor with the 

higher design values to have more exceedances but this does not always hold up. For the 2007 to 

2009 period, all the monitors within the Washington DC-MD-VA-WV CBSA listed in Tables 6 

through 8 and the Davidsonville monitor had more exceedances in this period but had equal or lower 

design values for 2007 to 2009 than the Franconia monitor. For 2008 to 2010, the Franconia 

monitor had fewer aggregate exceedances than all but one54 of the monitors within the Washington 

DC-MD-VA-WV CBSA and the Davidsonville monitor but still had a higher design value.

(9) The Edgewood monitor did not respond the same to whatever affected the design values and number 

of exceedances in 2009 and 2010 at other monitors.

By all accounts 2009 was a mild year insofar as conditions for ozone formation as shown by the number 

of exceedances recorded at various monitors. But the Edgewood monitor is the only one which 

recorded over four concentrations over 0.075 ppm during the 2009 ozone season. 

 

54

 That being the Prince George’s County Equestrian Center monitor.
28

In the current Baltimore-Towson CBSA as well as the CSA, the Edgewood monitor stands apart in both 

its current design value and number of exceedances in any three year period It has one and one-half 

times as many exceedances over the five-year period 2006 to 2010. 

In the current Washington DC-MD-VA-WV CBSA, the Franconia monitor currently sets the DV for this 

area but has not always done so as shown in Table 6 and has not had the most exceedance days in any

year nor any 3- or 5-year period.

Basic Statistics for the Edgewood monitor in Harford County, MD:

The number of exceedance days for the Edgewood monitor was counted to be 96 for the 5-year period 

2006 through 2010. EPA decided that these should be grouped somehow to make displaying the backtrajectories for more than one day easier to understand because for the 5-year period 2006 through 2010

there would be 288 (96 x 3) back-trajectories if all three altitudes for all days were displayed in one 

overlay. One way to analyze the exceedance data is to perform some basic statistical analyses on the data. 

Using the five years of data for the Edgewood monitor the mean, the median and the standard deviation were 

determined. The mean value of the exceedances is 0.0858 ppm, the median 0.085 ppm and the standard 

deviation is 0.008066 ppm55 (8 ppb). The distribution is somewhat skewed in that 50 values are below the 

mean and 46 are above the mean. The highest value, 0.113 ppm, is over 3 standard deviations from the mean 

whereas the lowest values, 0.076 ppm, lay only about 1.2 standard deviations off the mean.56 However, 14 

values are greater than the mean value plus 1 standard deviation (a value of 0.0939 ppm), and, 14 values are 

less than the mean value minus 1 standard deviation (a value of 0.077 ppm). Placing the data into quintiles57, 

the values would be as follows:

Table 9. Quintiles for the Edgewood monitor.

Group Ozone concentration range

1. Bottom Quintile 0.076-0.078 ppm

2. Lower Quintile 0.079 to 0.082 ppm

3. Middle Quintile 0.082 to 0.087 ppm

4. Upper Quintile 0.087 to 0.090 ppm

5. Top Quintile 0.091 ppm or more

Because several quintiles would contain concentrations of 0.082 and 0.087 ppm, the data was split into 

the following five groups such that each group was defined by a unique range of concentrations. The 

final grouping selected was as follows:

Table 10. Quintiles for the Edgewood monitor.

Group Number Ozone concentration range Number of values in Group

1. Bottom Quintile 0.076-0.078 ppm 19

2. Lower Quintile 0.079 to 0.082 ppm 16

3. Middle Quintile 0.082 to 0.087 ppm 21

 

55

 Using the Microsoft® Office Excel® “STDEV()” function.

56

 No doubt this fact could be due wholly or in part to fact that the mean and standard deviation were computed for only 

those values above the fixed value of 0.075 ppm of the entire set of ozone concentration readings.

57

 When distributed in groups of 19, 19, 20, 19 and 19.
29

4. Upper Quintile 0.087 to 0.090 ppm 21

5. Top Quintile 0.091 ppm or more 19

The data for this section was manually extracted from the data in Table A2-1 of Appendix 2 to this 

document. The full listing of Edgewood exceedance days upon which the statistics were based can be 

found in Tables A2-4 in Appendix 2 to this document. Numbers may therefore be approximate only. 

Episodes per Year and Length of Episodes

As defined earlier in this document, an exceedance day is any day during which at least one monitor in 

the CSA recorded an 8-hour ozone concentration of 0.076 ppm or more. An ozone episode is a period 

of one or more consecutive days during which at least one exceedance was recorded in the CSA. The 

following table provides some summary statistics for exceedance days and episodes for the CSA for the 

period 2006-2010 (all data approximate). 

Table 11. Episodes and Exceedance Days per Year 2006 to 201058

Year Number of 

Episodes

Number of 

Exceedance days

Length of 

Longest 

Episode(s) 

Dates of Longest 

Episode(s)

2006 15 38 5 days 5/28-6/1; 7/17 to 

7/21 and 8/22 to 

8/26

2007 16 51 8 days 7/31 to 8/7

2008 16 25 4 days 7/15 to 7/18

2009 8 10 2 days 6/25 to 6/26

2010 20 42 7 days 8/28 to 9/3

Totals 2006 to 

2010

65 166 8 days - - - -

Severity of Episodes:

If exceedances of or greater than 0.095 ppm (the mean plus more than one standard deviation for the 

Edgewood data) are considered to be “especially high,” then the monitors in the CSA recorded the 

following during the period 2006 to 2008: 

Table 12. Episodes with Any Exceedance Day over 0.094 ppm59

Year Dates Peak 

Concentration

At Monitor 

(AQS ID #)

Number of 

exceedances 

> 0.095 ppm 

during the 

year

Number of 

Different 

Monitors 

recording 

Value > 0.095 

ppm

 

58

 Derived by manual sorting and compiling of the data in Table 2A-1 of Appendix 2 of this document. Numbers may 

therefore be approximate only.

59 Derived by manual sorting and compiling of the data in Table 2A-1 of Appendix 2 of this document. Numbers may 

therefore be approximate only.
30

2006 5/28-6/1 0.116 Widewater

(511790001)

12 11

2006 6/21-6/22 0.096 Pr. Geo. Co. 

Eq. Ctr60

(240338003)

2 2

2006 7/17-7/21 0.118 Alexandria

(515100009)

16 10

2006 8/22-8/26 0.098 Essex

(240053001)

2 2

Totals for 2006 32 ----

2007 5/29-6/1 0.100 Aldino

(240259001)

1 1

2007 6/7-6/8 0.108 Aldino

(240259001)

2 2

2007 6/18-6/19 0.103 Davidsonville

(240030014)

3 3

2007 7/7-7/10 0.113 (2 

monitors)

Aldino & 

Edgewood

(240259001 

&240251001)

2 2

2007 7/14-7/17 0.095 Arlington 

(510130020)

1 1

2007 7/31-8/7 0.118 Davidsonville 

(240030014)

4 4

Totals for 2007 13

2008 6/10 0.099 Padonia

(240051007)

1 1

2008 6/12-6/14 0.097 Padonia

(240051007)

3 3

2008 7/11-7/12 0.100 Edgewood

(240051001)

1 1

2008 7/15-7/18 0.104 Arlington

(510130020)

6 6

Totals for 2008 11

2009 6/25-6/26 0.109 Edgewood 

(240051001)

1 1

Totals for 2009

2010 7/3-7/8 0.100 McMillan 

Reservoir

(110010043)

4 4

2010 7/23 0.101 Edgewood 

(240051001)

1 1

2010 8/9-8/11 0.115 Essex

(240053001)

6 5

 

60

 Short for Pr. Georges Co. Equestrian Ctr. 
31

2010 8/28-9/3 0.098 Calvert Co.

(240090011)

2 2

Totals for 2010 13

Totals 2006 to 2010 70 19 different 

monitors

Of these 70 exceedances over 0.094 ppm, Edgewood monitor recorded 14 (20%). Prince George’s Co. 

Equestrian Center and Davidsonville each recorded 6; McMillan, Essex and Arlington each recorded 5; 

Aldino and Fairfax each recorded 4; Howard U.–Beltsville and Widewater61 each recorded 3; nine other 

monitors each recorded 2 or 1.62 

Comparing Tables 11 and 12 the highest recorded value often occurs during the longest episode of the 

year. The longer episodes often have the largest number of monitors recording “especially high” 

concentrations. Once again, based upon the Tables 11 and 12, 2009 would seem to have been a mild 

year insofar as conditions for ozone formation. 

Conversely, there were around 17 single day episodes where only one monitor within the entire CSA 

recorded an exceedance of the 0.075 ppm standard. The highest concentration recorded on such days 

was 0.083 ppm with most recorded exceedances at or below 0.079 ppm. Eight of such days were at the 

Edgewood monitor.63 In addition there were around five single day episodes where only a pair of 

monitors “close” to each other each recorded an exceedance. Such parings are Edgewood-Padonia, 

Edgewood-Aldino, Edgewood-Essex, Southern Maryland-Calvert Co. and Davidsonville-Prince 

George’s Co. Equestrian Center. 

The air quality data shows that the CSA averages 13 episodes per year and 33.2 exceedance days per 

year for the period 2006 to 2010. The maximal length of the episodes ranges from 4 to 8 days (2009 

excluded) and around four episodes per year where concentrations in excess of 0.094 ppm can be 

expected (2009 excluded). 

The air quality data also shows that the Edgewood monitor is atypical; while it may not record the 

highest value in any given episode or year it is more likely to record an “especially high” value as 

reflected by its 2008-2010 DV of 0.089 ppm and its 20% share of “excessively high” values. This 

monitor also is more likely to record an exceedance and more likely to be the only monitor to record an 

exceedance during a single day episode. 

Episode Days and Extent of Exceedances:

Examination of this data suggests that the CSA is subject to various regimes that result in varying 

patterns of ozone levels within the CSA: 

On some days only one or a few monitors exceeded 0.075 ppm; on other days, the extent of exceedances 

was more widespread or extremely widespread with higher levels across most if not all of the CSA. On 

some days the highest readings were found at one end – either the North easternmost portion clustered 

around the monitors North and East of Baltimore City or around the District of Columbia’s and 

Arlington and Fairfax Counties’ monitors. 

 

61

 None in 2008 or later.

62

 These were: South Carroll, Rockville, Southern Maryland, Alexandria, Padonia, Calvert Co., James S. Long Park, Asburn 

and Furley E.S. Rec Center.

63

 The only pother monitors with two such days were Aldino and Rockville; the Franconia, River Terrace, Howard U—

Beltsville, Frederick County and Widewater monitors each had one. 
32

Some other conclusions can be reached: generally, especially high concentrations (in this case using 

Edgewood monitors’ “top quintile” threshold those over 0.091 ppm64) are often recorded on days which 

are part of a multi-day episode (that is, two or more consecutive days with at least one exceedance 

recorded at least one monitor within the CSA); there are exceptions such as on July 23, 2010 where 

“Edgewood” recorded a concentration of 0.101 ppm, and July 10, 2008, (0.099 ppm at the “Padonia” 

monitor in Baltimore County), 

The Edgewood Monitor May be Atypical

The “Edgewood” monitor does appear to be out of the ordinary besides in other ways besides its design 

value: This monitor does not necessarily record the highest 8-hour concentration of any CSA monitor 

for an ozone season but clearly has had a 4th high value each season that is greater than on average than 

other nearby monitors. For the period 2006 to 2008, this monitor did not have a number of exceedance 

days that stood apart from other monitors – in 2006 “Edgewood” recorded 21 exceedances versus the 

maximum of 22 elsewhere,65 in 2007 Edgewood recorded 24 exceedances versus the next highest 

number of 22, and in 2008 “Edgewood” recorded 15 exceedances versus the next highest number of 

1366.

67

 After 2008, the “Edgewood” monitor did start to record a higher number of exceedances – 9 in 

200968 versus a maximum of 2 at three other monitors and in 2010 “Edgewood” recorded 27 

exceedances versus a maximum of 16 elsewhere.69 This monitor represented about 20% of the days 

where only one monitor within the CSA exceeded 0.075 ppm. There are many days where this monitor 

recorded a peak 8-hour concentration 10, 20 or even 30 ppb (0.010, 0.020 and 0.030 ppm) higher than 

other close monitors such as the “Essex,” “Aldino” and “Padonia” monitors in Harford and Baltimore 

Counties. Maryland in their March 7, 20102 five-factor analyses presented evidence that a related 

topographical-meteorological phenomenon combine at the Edgewood location to result in higher levels 

of daily ozone concentrations at the Edgewood monitor than otherwise might occur. These 

phenomenons are discussed under Factor 3 Meteorology below. The results presented in this paragraph 

would suggest that Maryland’s conclusion could be is correct under certain conditions.

However, as stated previously in this document, a county/independent city (or partial county) must also 

be designated nonattainment if it contributes to a violation in a nearby area. Each county without a 

violating monitor that is located near a county with a violating monitor has been evaluated based on the 

weight of evidence of the five factors and other relevant information to determine whether it contributes 

to the nearby violation. In a CSA where counties with violating monitors are adjacent to each other and 

where EPA in the past concluded that there were two separate nonattainment areas, even a county with a 

violating monitor needs to be evaluated to see if that county sufficiently contributes to violations at 

another nearby, violating county. Such an evaluation can guide a decision on grouping counties with 

violating monitors to set the boundaries of a nonattainment area (or areas) containing more than one 

violating monitor.

Factor 2: Emissions and Emissions-Related Data

 

64

 In the aggregate, all monitors in the CSA recorded around 986 exceedances during 2006-2010 with the top 197 

(essentially the top quintile) concentrations being 0.088 ppm or higher.

65

 At the “McMillan Reservoir” monitor in the District of Columbia and the “Howard University-Beltsville” monitor in 

Prince George’s County, MD.

66

 At the “Davidsonville” and “Aldino” monitors in Anne Arundel and Harford Counties, Maryland, respectively.

67

 At the “Aldino” monitor also in Harford County, MD. 

68

 2009 was a year where a low number of exceedances were generally seen. 

69

 At the “McMillan Reservoir” and the “Howard University-Beltsville” monitors.
33

EPA evaluated emissions of ozone precursors (NOx and VOC) and other emissions-related data that 

provide information on areas contributing to violating monitors.

Emissions Data

All Emissions Aggregated at the County/City Level: 

EPA evaluated county-level emission data for NOx and VOC derived from the 2008 National Emissions 

Inventory (NEI), version 1.5. This is the most recently available NEI. (See,

http://www.epa.gov/ttn/chief/net/2008inventory.html). Sufficiently high emissions levels in a nearby

area indicate the potential for the area to contribute to monitored violations. We will also consider any

additional information we receive on changes to emissions levels that are not reflected in recent 

inventories. These changes include emissions reductions due to permanent and enforceable emissions 

controls that will be in place before final designations are issued and emissions increases due to new 

sources.

Table 13 shows emissions of NOx and VOC given in tons per year (tpy) for violating and potentially 

contributing counties in the 1997 Baltimore MD and Washington DC-MD-VA nonattainment areas and 

other portions of the Washington-Baltimore-NV CSA. 

Table 13. Total 2008 NOx and VOC Emissions.

County/City

State 

Recommended 

Nonattainment?

NOx

(tpy)

VOC 

(tpy)

Baltimore MD Nonattainment Area:

Anne Arundel County Co., MD Yes 30,541 14,423 

Baltimore City, MD Yes 18,621 11,397 

Carroll County, MD Yes 6,617 3,948 

Harford County, MD Yes 5,854 6,396 

Howard County, MD Yes 9,219 7,848 

Baltimore County, MD Yes 29,392 16,807 

Baltimore Subtotal:

 

100,244 60,819 

Washington DC-MD-VA Nonattainment Area:

District of Columbia, DC Yes 11,332 11,362 

Calvert County, MD Yes 2,797 2,406 

Charles County, MD Yes 5,823 3,939 

Frederick County, MD Yes 9,389 6,460 

Montgomery County, MD Yes 21,097 20,426 

Prince George’s County, MD Yes 24,043 18,882 

Arlington County, VA Yes 5,264 4,329 

Fairfax County, VA Yes 21,403 25,603 

Loudoun County, VA Yes 6,948 7,331

Prince William County, VA Yes 7,698 8,603

Alexandria City, VA Yes 3,349 2,625

Fairfax City, VA Yes 326 794 
34

Falls Church City, VA Yes 138 324 

Manassas City, VA Yes 553 1,020

Manassas Park City, VA Yes 92 285 

Washington DC-MD-VA Subtotal: 120,252 114,389

Table 13 (continued). Total 2008 NOx and VOC Emissions.

County

State 

Recommended 

Nonattainment?

NOx

(tpy)

VOC 

(tpy)

Fredericksburg, VA Area:

Spotsylvania County, VA No 3,539 4,226 

Stafford County, VA No 3,377 3,516 

Fredericksburg City, VA No 859 1,007 

Fredericksburg, VA Subtotal: 7,775 8,749 

Frederick County, VA Area:

Frederick County, VA No 2,838 4,714 

Winchester City, VA No 508 1,006 

Frederick Co., VA Area Subtotal: 3,346 5,720 

Other counties:

Queen Anne’s County, MD No 2,725 2,402 

St. Mary’s County, MD No 3,475 4,038 

Clarke County, VA No 941 949 

Culpeper County, VA No 1,726 2,109 

Fauquier County, VA No 3,383 3,389 

Warren County, VA No 1,463 1,773 

Hampshire County, WV No 734 2,078 

Jefferson County, WV No 1,566 1,481 

All other counties subtotal: 16,013 18,218 

CSA Total: 247,630 207,894 

Data sources: 

(1) NOx emissions (tpy)-NEI08v1.5 – Total NOx emissions include Nonpoint, Nonroad, Onroad and 

Facility NOx emissions from ftp://ftp.epa.gov/EmisInventory/2008_nei/v1.5_GPR (May 19, 2011).

(2) VOC emissions (tpy)-NEI08v1.5 –Total VOC emissions include Nonpoint, Nonroad, Onroad and 

Facility VOC emissions from ftp://ftp.epa.gov/EmisInventory/2008_nei/v1.5_GPR (May 19, 2011)
35

In their March 7, 2012 submittal, Maryland supplied an amended inventory for certain Maryland 

counties to reflect the 2009 EGU emission caps imposed under the Maryland Healthy Air Act and 

implementing regulation.70 The following Table 14 shows the effects that Maryland claimed.

Table 14. Total 2008 NOx and VOC Emissions.

County/City

State 

Recommended 

Nonattainment?

NOx

(tpy)

VOC 

(tpy)

Baltimore MD Nonattainment Area:

Anne Arundel County Co., MD Yes 22,110 14,423 

Baltimore City, MD Yes 18,621 11,397 

Carroll County, MD Yes 6,617 3,948 

Harford County, MD Yes 5,854 6,396 

Howard County, MD Yes 9,219 7,848 

Baltimore County, MD Yes 25,736 16,807 

Baltimore Subtotal: 88,157 60,819 

Washington DC-MD-VA Nonattainment Area:

District of Columbia, DC Yes 11,332 11,362 

Calvert County, MD Yes 2,797 2,406 

Charles County, MD Yes 5,823 3,939 

Frederick County, MD Yes 9,389 6,460 

Montgomery County, MD Yes 18,415 20,426 

Prince George’s County, MD Yes 19,793 18,882 

Arlington County, VA Yes 5,264 4,329 

Fairfax County, VA Yes 21,403 25,603 

Loudoun County, VA Yes 6,948 7,331 

Prince William County, VA Yes 7,698 8,603 

Alexandria City, VA Yes 3,349 2,625 

Fairfax City, VA Yes 326 794 

Falls Church City, VA Yes 138 324 

Manassas City, VA Yes 553 1,020 

Manassas Park City, VA Yes 92 285 

Washington DC-MD-VA Subtotal: 113,320 114,389 

Fredericksburg, VA Subtotal: 7,775 8,749 

Frederick Co., VA Area Subtotal: 3,346 5,720 

All other counties subtotal: 16,013 18,218 

CSA Total: 228,611 207,894

 

70

 Refer to regulation COMAR 26.11.27.01 through .04, and .06 “Emission Limitations for Power Plants” in the 

codification of the Maryland SIP at 40 CFR 52.1070(c) and also to 73 FR 51599, September 4, 2008.
36

The net overall effect is minimal in that the rankings by NOx overall emissions drop Montgomery

County out of the top five and raises Baltimore City, MD from sixth to fifth as shown in Table 15. 

Table 15. Ranking and NOx emissions of the Top Six NOx Emissions Counties

Area

Maryland

Adjusted

Value (tpy)

New 

Rank

2008 

NEI 

Value

(tpy)

Prior 

Rank

Baltimore County, MD 25,736 1 29,392 2

Anne Arundel County Co., 

MD 22,110 2 30,541 1

Fairfax County, VA 21,403 3 21,403 4

Prince George’s County, MD 19,793 4 24,043 3

Baltimore City, MD 18,621 5 18,621 6

Montgomery County, MD 18,415 6 21,097 5

For NOx emissions, in the following discussion the 2008 NEI value or ranking will be in braces “{}”. 

The 1997 Washington DC-MD-VA nonattainment area contains 49.6 % {48.5%} of the WashingtonBaltimore-NV CSA’s total NOx emissions and 55% of the Washington-Baltimore-NV CSA‘s total VOC 

emissions.

The 1997 Baltimore nonattainment area contains 38.6% {40.5%} of the Washington-Baltimore-NV 

CSA’s total NOx emissions and 29% of the Washington-Baltimore-NV CSA’s total VOC emissions.

Together the 1997 Washington DC-MD-VA and Baltimore nonattainment areas contain 88.1% {89%}

of the Washington-Baltimore-NV CSA’s total NOx emissions and 84% of the Washington-BaltimoreNV CSA’s total VOC emissions.

In the Washington-Baltimore-NV CSA, Anne Arundel, Baltimore, Prince George’s and Montgomery

Counties in Maryland, Baltimore City, MD and Fairfax County in Virginia comprise the “top six”

71

when ranking by VOC or by NOx emissions (with first being highest). Using the 2008 NEI data an area 

was in the “top five” within the Washington-Baltimore-NV CSA if it has NOx emissions of more than 

20,000 tpy or VOC emissions of more than 14,000 tpy. Using Maryland’s revised values, the difference 

between fifth and sixth for NOx emissions is insubstantial – only 1.1% of 18,415 tons per year. All of 

these areas contain a violating monitoring or are adjacent to at least one county with at least one monitor

violating the 2008 ozone NAAQS.

The following comprise the next five highest ranked (that is, numbers 7 through 11 within the 

Washington-Baltimore-NV CSA) for VOC or NOx emissions (not listed in order of ranking): Frederick 

 

71 The groupings by ranking were set to divide the 34 jurisdictions into four groups. To some extent the groups fell out 

naturally and are composed as follows: The same five jurisdictions ranked first to fifth for both NOx and VOC emissions and 

thus defined the “top five.” The same six jurisdictions fell within a rank of sixth through eleventh for both NOx and VOC 

emissions and thus defined the second group of sixth through eleventh. A “middle group” of those ranked between 12th and 

23rd inclusive included the same twelve jurisdictions where: Calvert County, MD ranked at 22nd for both NOx and VOC 

emissions; and Queen Anne’s County, MD ranked at 23rd for both NOx and VOC emissions. Jurisdictions with less than 

approximately 2,500 tpy NOx or 2,200 tpy VOC represent less than one per of the CSA total emissions and comprise those 

areas ranked 24th or lower.
37

and Howard Counties in Maryland, the District of Columbia, and, Loudoun and Prince William 

Counties in Virginia. An area ranking 7

th through 11th within the Washington-Baltimore-NV CSA 

needed to have NOx emissions of between 6,900 and 11,332 tpy or VOC emissions of between 6,400 

and 14,000 tpy. Of these, only the District of Columbia has two of three monitors violating the 2008 

ozone NAAQS. Loudoun County, VA and Frederick County each has a monitor with a design value of 

0.075 ppm which is only one ppm from violating the 2008 ozone NAAQS. All are adjacent to one or 

more counties or the District of Columbia which contain at least one monitor violating the 2008 ozone 

NAAQS. 

Of these “top 11” counties for emissions, Frederick, Montgomery, Prince George’s Counties in 

Maryland, the District of Columbia, and, Fairfax and Loudoun Counties in Virginia are clustered around 

the Fairfax County monitor which has a design value of 0.081 ppm. 

Of the top eleven, only Baltimore County, MD is adjacent to Harford County, MD which contains the 

Edgewood monitor which has a design value of 0.089 ppm. 

The low emissions of the Cities of Fairfax, Falls Church, Manassas and Manassas Park in Virginia result 

in low ranking for emissions when the jurisdictions in the Washington-Baltimore-NV CSA are ranked 

by emissions from highest to lowest. The Cities of Fairfax, Falls Church, and Manassas Park rank 32nd, 

33rd, and 34th (of 34) in the Washington-Baltimore-NV CSA. Manassas City ranks 28th for VOC and 

30th for NOx within the Washington-Baltimore-NV CSA. However, these are cities with very small 

land areas and are entirely surrounded or wedged in between larger counties. Table 16 compares the 

emissions and emission density of these cities with those jurisdictions that entirely surround these cities. 

Data for Alexandria City and with the District of Columbia are also presented to provide emissions 

densities for other highly urbanized areas.

Table 16. Total 2008 NOx and VOC Emissions Densities of Selected Cities and Counties.

County

State 

Recommended 

Nonattainment?

NOx

(tpy)

VOC 

(tpy)

Land 

Area (sq. 

mi.)

Emissions 

Density 

NOx

(tpy/sq. 

mi.)

Emissions 

Density 

VOC 

(tpy/sq. 

mi.)

District of Columbia Yes 11,332 11,362 67.9 166.89 167.34

Fairfax Co., VA Yes 21,403 25,603 405.9 52.73 63.08 

Fairfax City, VA Yes 326 794 6.1 53.37 130.21 

Falls Church City, VA Yes 138 324 2.0 68.80 162.14 

Arlington Co., VA Yes 5,264 4,329 25.8 204.04 167.78 

Prince William Co., VA Yes 7,698 8,603 348.9 22.06 24.66 

Manassas City, VA Yes 553 1,020 10.1 54.74 100.98 

Manassas Park City, VA Yes 92 285 1.5 61.25 190.25 

Alexandria City, VA Yes 3,349 2,625 15.2 220.35 172.70 

Notes: “sq. mi.” means square miles.

As can be seen from this table, the Cities of Fairfax, Falls Church, Manassas and Manassas Park have 

emissions densities in tons per year per square mile equal to or greater than the surrounding county in 

the cases of the Cities of Fairfax, Manassas and Manassas Park. In the case of Falls Church City, Falls 

Church has emissions densities greater than Fairfax County but less than Arlington County. Due to 
38

Virginia’s system of governance, these cities are inventoried separately; in most other states (Baltimore 

City in Maryland being one exception), such high density areas such as cities are not. The Cities of 

Fairfax, Falls Church, Manassas and Manassas Park can be considered to be high emissions areas on the 

basis of their emissions densities as opposed to their absolute emissions. 

As for Arlington County and Alexandria City in Virginia, these rank, respectively, 14th and 21st for VOC 

emissions and 15th and 20th for NOx, respectively. These jurisdictions are small in absolute land area 

but the emissions densities are the highest in the both the DC-MD-VA nonattainment area and the 

Washington-Baltimore-NV CSA. Both are adjacent to other areas containing a monitor violating the 

2008 NAAQS. 

Of the remaining two counties, Charles and Calvert in the 1997 Washington DC nonattainment area, 

these two rank in the “middle group” (between 12th and 23rd inclusive): Calvert County, MD ranks low 

in this “middle group” – 22nd within the Washington-Baltimore-NV CSA for both NOx and VOC, 

respectively; Charles County, MD ranks higher than Calvert in this “middling” group – 18th and 14th for 

VOC and NOx emissions, respectively. Both are adjacent to counties with violating monitors. Of the 

two, Charles is more likely to be upwind of a violating monitor because it is southeast of the Fairfax 

County, VA monitor, west-southwest of the monitor in Calvert County, MD and south-southwest of the 

Equestrian Center monitor in Prince George’s County, MD; Calvert County is due south of the monitor 

in Anne Arundel County, MD and south-southeast of the Equestrian Center monitor in Prince George’s 

County, MD. 

Of the remaining two counties, Harford and Carroll in the 1997 Baltimore nonattainment area, these two 

rank in the middle (between 12th and 23rd inclusive): Carroll County, MD ranks in the middle or high in 

this “middling” group – 17th and 12th for VOC and NOx emissions, respectively; Harford County, MD 

ranks higher than Carroll in this “middling” group – 12

th and 13th for VOC and NOx emissions, 

respectively. Both are adjacent to counties with violating monitors. Of the two, Carroll County is more 

likely to be upwind of a violating monitor because it is west-southwest to west of the Padonia monitor in 

Baltimore County, MD. Harford County, MD is adjacent to Baltimore County, MD but one can expect 

that it is unlikely to be upwind of either violating monitor in Baltimore County because both monitors in 

Harford County were sited to be downwind of the urbanized core of both Baltimore City and County. 

In general, the counties and cities in the 1997 Baltimore and Washington areas likely sufficiently 

contribute to nonattainment at one or more monitors in at least one of these two nonattainment areas 

because the County has a violating monitor, because the county or city is adjacent to a county with a 

violating monitor or the small city has emissions densities comparable to or higher than surrounding or 

adjacent areas. 

Of the other areas or the counties listed under “other counties” in the preceding table most have low 

emissions and are remote from areas containing a monitor violating the 2008 NAAQS: 

(1) The Frederick County, VA Area contains 1.5% {1.4%} and 2.8% of the Washington-Baltimore-NV 

CSA NOx and VOC emissions, respectively. As a whole this area would rank 18th for NOx emissions 

and 13th (the actual rank for Frederick County, VA alone) for VOC emissions. If the Frederick County, 

VA Area was included with the 1997 Washington DC-MD-VA nonattainment area, the emissions of the 

Frederick County, VA Area would be about 2.9 {2.7} and 4.8 percent of such an area’s NOx and VOC 

emissions, respectively. (For example, for VOC emissions, 2.7% = 3,346/(3346+120,252) * 100.) This 

area is remote from any counties with violating monitors and is separated from the 1997 Washington 

DC-MD-VA nonattainment area by the sparsely populated Clarke and Warren Counties in Virginia. 

(2) Hampshire County (emissions rankings within CSA: 25th for VOC & 29th for NOx) is remote from 

any violating monitor in the Washington-Baltimore-NV CSA and likewise has low emissions (1 percent 
39

or less of the Washington-Baltimore-NV CSA’s total for either NOx or VOC) in spite of its size (644 

square miles). If included with the 1997 Washington DC-MD-VA nonattainment area, its emissions 

would be about 1.8 percent or less of such an area’s NOx or VOC emissions, respectively. The nearest 

monitors in the Washington-Baltimore-NV CSA or elsewhere are those in Frederick County, VA and 

Berkeley County, WV. These have a design value well less than the 2008 NAAQS of 0.075 ppm. The 

design values are 0.068 ppm for Frederick County, VA and 0.070 ppm for Berkeley County, WV (Data 

source: Table 5 to ozone_dv75_20082010.xls (downloaded on 9/22/2011 from 

http://www.epa.gov/airtrends/values.html). 

(3) Clarke (emissions rankings within CSA: 27th for VOC & 31st for NOx) and Warren (emissions 

rankings within CSA: 26th for both VOC for NOx) Counties in Virginia each comprise less than one 

percent of CSA total for either NOx or VOC emissions. If either were included with the 1997

Washington DC-MD-VA nonattainment area, the emissions of either would be less than 1.6 percent of 

such an area’s NOx or VOC emissions, respectively. The nearest monitors within the CSA are attaining 

the 2008 NAAQS. 

(4) Queen Anne’s County MD (emissions rankings within CSA: 23th for both VOC & NOx) is at the 

bottom of the “middling” group (12th through 23rd inclusive) in the Washington-Baltimore-NV CSA. Its 

emissions are 1.1 to 1.2 percent of the Washington-Baltimore-NV CSA’s total for NOx or VOC. If 

included with the 1997 Baltimore nonattainment area, its emissions would be about 3.0 {2.9} and 3.5 

percent of such an area’s NOx and VOC emissions, respectively. Its emissions would add about 2.7 to 

3.8 percent. Queen Anne’s County is in close proximity (that is separated from adjacent counties in the 

Washington-Baltimore-NV CSA by stretches of the Chesapeake Bay) to several violating monitors, 

namely the Essex monitor in Baltimore County and the monitor in Anne Arundel County. Because 

Queen Anne’s County is in the Ozone Transport Region (OTR), section 184 of the CAA requires many

sources of VOC and major stationary sources of NOx be controlled by reasonably available control 

technology (RACT) pursuant to sections 182(b)(2) and 182(f) and requires major stationary sources of 

VOC and NOx be subject to nonattainment new source review (NSR) requirements at the OTR major 

stationary source thresholds. Also motor vehicles in Queen Anne’s County are subject to enhanced 

inspection and maintenance program (enhanced I/M) as required by section 184 of the CAA.72 

(5) Jefferson County, WV (emissions rankings within CSA: 27

th for VOC & 25th for NOx), if included 

with the 1997 Washington DC-MD-VA nonattainment area, would comprise about 1.4 {1.3} percent of 

such an area’s NOx or VOC emissions, respectively. 

(6) Fauquier County, VA emissions rankings within CSA: 20th for VOC & 18st for NOx is in the 

“middling” group (ranks 12th through 23rd inclusive) of the Washington-Baltimore-NV CSA. If 

included with the 1997 Washington DC-MD-VA nonattainment area, its emissions would be about 2.9 

{2.7} and 2.9 percent of such an area’s NOx and VOC emissions, respectively. However, Fauquier 

County is not adjacent to a county containing a monitor violating the 2008 NAAQS. Both the 

geographically nearest monitors (in Stafford and Prince William Counties, VA) have a design value of 

0.070 ppm well below the 2008 NAAQS.

(7) Culpeper County, VA (emissions rankings within CSA: 24th for both VOC & NOx) is just below the 

“middling” group. If included with the 1997 Washington DC-MD-VA nonattainment area, its emissions 

would be about 1.5 {1.4 } and 1.8 percent of such an area’s NOx and VOC emissions, respectively. 

 

72 See, 61 FR 56183 at 56185, October 31, 1996 for details on the OTR enhanced I/M requirements in Maryland. The 

relevant provisions that define the geographic scope of Maryland’s enhanced I/M program can be found in Code of Maryland 

Regulations (COMAR) 11.14.08.02B (19) and 11.14.08.03 in the approved Maryland SIP – see 40 CFR 51.1070(c). Copies 

of COMAR 11.14.08.02B(19) and 11.14.08.03 are available on-line via 

http://yosemite.epa.gov/r3/r3sips.nsf/SIPIndex!OpenForm
40

Culpeper County is even more remote than the adjacent Fauquier County from any county containing a 

monitor violating the 2008 NAAQS.

. 

(8) St. Mary’s County, MD ranks in the “middle” within the Washington-Baltimore-NV CSA (17th for 

NOx and 16th for VOC) for NOx and VOC emissions. If included with the 1997 Washington DC-MDVA nonattainment area, its emissions would be about 3.0 {2.8} and 3.4 percent of such an area’s NOx 

and VOC emissions, respectively. St. Mary’s County is adjacent to Calvert County which does contain 

a monitor violating the 2008 NAAQS.

(9) The Fredericksburg, VA Area contains the following areas: Stafford County (emissions rankings 

within CSA: 19th for both VOC & NOx); Spotsylvania County (emissions rankings within CSA: 16th for 

NOx and 15th for VOC); and Fredericksburg City (emissions rankings within CSA: 28th for NOx and 

29th for VOC). The total emissions in the Fredericksburg, VA Area are about 6.5 and 7.7 percent of the 

1997 Washington DC-MD-VA nonattainment area’s NOx and VOC emissions, respectively. Alone, 

Spotsylvania County’s emissions are about 3.4 {2.8} and 3.1 percent of the 1997 Washington DC-MDVA nonattainment area’s NOx and VOC emissions, respectively; the nearest monitors to Spotsylvania 

County are those in Fauquier and Stafford Counties in Virginia and Charles County in Maryland. The 

former two monitors are easily attaining the 2008 NAAQS. All of these three monitors are interposed 

between Spotsylvania County and violating monitors in the Washington-Baltimore-NV CSA. (Another 

monitor in an adjacent county is that in Caroline County, VA which is attaining the 2008 NAAQS with a 

design value of 0.073 ppm [Data source: Table 5 to ozone_dv75_20082010.xls (downloaded on 

9/22/2011 from http://www.epa.gov/airtrends/values.html)]). If Spotsylvania County contributes to 

ozone levels in other counties its highest contribution is likely to any one of these three counties. If 

Spotsylvania and Stafford Counties were included in a nonattainment area encompassing the 1997

Washington DC-MD-VA nonattainment area or one consisting of both the 1997 Baltimore and 

Washington DC-MD-VA nonattainment areas, then Fredericksburg City should also be included

because although its absolute emissions are low its emissions densities exceed that of each of the two 

surrounding counties. 

If added to the 1997 Washington DC-MD-VA nonattainment area, the total emissions of Stafford 

County alone would be about 2.9 {2.8} and 3.0 percent of the combined area’s NOx and VOC 

emissions, respectively. For the case where a combination of Stafford County and Fredericksburg City

are included in such an expanded nonattainment area, their combined emissions would be about 3.7 

{3.4} and 3.8 percent of such an area’s NOx and VOC emissions, respectively. The monitor in Stafford 

County is in the northeast corner of the county and is interposed between much of the county’s (or the 

combined emissions of the county plus Fredericksburg City) and the violating monitor in Fairfax 

County. The attaining monitor in Charles County, MD is interposed between Stafford County and the

violating monitor in Calvert County, MD. Likewise, the attaining monitors in Stafford and Fauquier 

Counties in Virginia and the attaining monitor in Charles County Maryland are interposed between 

Spotsylvania County and Fredericksburg City and the violating monitors in Calvert County, MD and 

Fairfax County, VA. 

Finally, of the city and two counties in the Fredericksburg Area only Stafford County is in the OTR.73 

Section 184 of the CAA requires that in attainment areas within the OTR many sources of VOC and 

 

73

 The OTR was defined in 1990 by section 184 of the CAA to include the statistical area that included the District of 

Columbia. In 1990, only Stafford County was part of the statistical area that included the District of Columbia. EPA has 

always interpreted the scope of section 184(a) to include only those states specified by name, the District of Columbia and 
41

major stationary sources in the OTR of NOx be controlled by reasonably available control technology

(RACT) pursuant to sections 182(b)(2) and 182(f) and requires major stationary sources of VOC and 

NOx be subject to nonattainment NSR requirements at the OTR major stationary source thresholds. 

Also motor vehicles in Stafford County are subject to enhanced I/M as required by section 184 of the 

CAA.74

Mobile Source Emissions:

Both Maryland and the District expressed concern about the effects of mobile source emissions on 

nonattainment within the CSA in their March 7, 2012, and March 12, 2012, responses to EPA’s 

December 9, 2011 letters,. Maryland’s comment was that the mobile source NOx emissions become the 

largest source of NOx emissions “post Maryland’s Healthy Air Act.” Maryland commented that the 

split between the Baltimore and Washington “areas” is approximately 40% and 60%, respectively. The 

District urged EPA to weight mobile source emissions more heavily than was done in the Preliminary

TSDs. 

EPA examined the 2008 emissions data used for the analysis for EPA’s preliminary TSD. EPA broke 

out the on-road mobile sources NOx emissions data for the CSA and found that the split between the 

aggregate on-road mobile source emissions of the current Washington and Baltimore Nonattainment 

areas is 61.6% in the current Washington DC-MD-VA Nonattainment area and 38.4% in the current 

Baltimore Nonattainment area. For the CSA, Table 17 provides a summary of the on-road mobile 

sources VOC and NOx emissions broken down by areas. 

Table 17. Mobile Source Emissions in the Washington-Baltimore-NV CSA:

NOx VOC

Area NOx (tpy) Percent of 

CSA Total

Area VOC (tpy) Percent of 

CSA Total

Baltimore Area 37,192 32.9% Baltimore Area 20,836.7 30.9%

Washington 

Area

Washington 

Area

Maryland 

Portion

29,960 26.5% Maryland 

Portion

18,418.2 27.3%

Virginia 

portion

23,476 20.8% Virginia 

portion

14,464.6 21.5%

DC Portion 6,333 5.6% DC Portion 4,041.3 6.0%

Washington 

Area sub-total

59,768 52.9% Washington 

Area sub-total

36,924.2 54.8%

Fredericksburg, 

VA CBSA

5,431 4.8% Fredericksburg, 

VA CBSA

3,387.0 5.0%

Frederick Co., 

VA area

1,675 1.5% Frederick Co., 

VA area

921.1 1.4%

 

those portions of other States which shared the same statistical area as the District as of November 15, 1990. See for 

example, 40 CFR 51.120 (60 FR 4712, Jan. 24, 1995) which related to a SIP call on all the OTR States. 

74 See 61 FR 57343 at 57346, November 6, 1996 for details on the OTR enhanced I/M requirements for Virginia. The 

relevant provisions that define the geographic scope of Virginia’s enhanced I/M program can be found in 9 VAC 5-91-20 

and 9 VAC 5-91-30 in the approved Virginia SIP – see 40 CFR 51.2420(c). Copies of 9 VAC 5-91-20 and 9 VAC 5-91-30 

are available on-line via http://yosemite.epa.gov/r3/r3sips.nsf/SIPIndex!OpenForm. 
42

Other Virginia

CSA Counties

4,978 4.4% Other Virginia

CSA Counties

2,918.4 4.3%

Other 

Maryland 

CSA Counties

3,101 2.7% Other 

Maryland 

CSA Counties

1,728.8 2.6%

West Virginia

Counties

918 0.8% West Virginia

Counties

714.3 1.4%

CSA Total 113,063 100.0% CSA Total 67,430.4 100.0%

A full listing is provided in Table 3-1 of Appendix 3 to this TSD. It provides county/city specific values 

for the CSA counties as well as some outside counties.

Maryland’s on-road NOx emissions are 62.1% of the CSA total and 69.3% of the aggregate on-road 

mobile source NOx emissions in the current Washington and Baltimore nonattainment areas. 

The two nonattainment areas under the 1997 ozone NAAQS account for 85.8 % of the NOx emissions 

and 85.7 % of the VOC emissions. On March 1, 2012, Virginia Department of Environmental Quality

(VA DEQ) submitted a presentation75 regarding the CSA. One slide shows how mobile source 

emissions declined since 2002; another slide noted that mobile source emissions are projected to 

continue to decline by 2017 with federal and state measures already in place. On one slide VA DEQ 

claimed that an analysis of transportation control measures undertaken for the Washington, DC 

transportation planning estimated that an expenditure of $85 million (annually) would reduce NOx 

emissions by only 220 tons per year.

EPA does not disagree that highway, mobile source emissions in the Washington DC-MD-VA 

nonattainment area (under the 1997 ozone standard) could well be 1.5 times those in the 1997 Baltimore 

ozone nonattainment area. However, mobile source emissions are well controlled by federal and state 

programs. Significant reductions can be expected in the coming years. 

Population density and degree of urbanization

EPA evaluated the population and vehicle use characteristics and trends of the area as indicators of the 

probable location and magnitude of non-point source emissions. These include ozone-creating 

emissions from on-road and off-road vehicles and engines, consumer products, residential fuel 

combustion, and consumer services. Areas of dense population or commercial development are an 

indicator of area source and mobile source NOx and VOC emissions that may contribute to ozone 

formation. Tables 18 and 19 show the population, land area, population density (in thousands of persons 

per square mile), and population growth information for each county/city in the Washington-BaltimoreNV CSA.

Table 18. Population and Growth in the Baltimore and Washington DC-MD-VA Nonattainment 

Area Portions of the Washington-Baltimore-NV CSA.

County

State Recommended 

Nonattainment?

2010 

Population

Land Area 

(sq. mi.)*

2010 

Population 

Density 

(1000 

pop/sq mi)

Absolute 

change in 

population 

(2000-

2010)

Population 

% change 

(2000-

2010)

Baltimore MD Nonattainment Area:

Anne Arundel Co., MD Yes 537,656 452 1.19 46,325 +9% 

 

75 A copy of which has been placed in the docket.
43

Baltimore City, MD Yes 620,961 87 7.14 (27,626) -4% 

Carroll Co., MD Yes 167,134 453 0.37 15,557 +10% 

Harford Co., MD Yes 244,826 460 0.53 25,362 +12% 

Howard Co., MD Yes 287,085 253 1.13 37,565 +15% 

Baltimore Co., MD Yes 805,029 624 1.29 49,037 +6% 

Baltimore Subtotals: 2,662,691 2,330 1.14 146,220 +6% 

Washington DC-MD-VA Nonattainment Area:

District of Columbia, DC Yes 601,723 68 8.86 30,000 +5% 

Calvert Co., MD Yes 88,737 237 0.37 13,573 +18% 

Charles Co., MD Yes 146,551 473 0.31 25,347 +21% 

Frederick Co., MD Yes 233,385 666 0.35 36,884 +19% 

Montgomery Co., MD Yes 971,777 506 1.92 94,282 +11% 

Prince George’s Co., MD Yes 863,420 493 1.75 60,213 +7% 

Arlington Co., VA Yes 207,627 26 8.05 18,045 +10% 

Fairfax Co., VA Yes 1,081,726 406 2.67 106,808 +11% 

Loudoun Co., VA Yes 312,311 521 0.60 138,440 +80% 

Prince William Co., VA Yes 402,002 349 1.15 118,206 +42% 

Alexandria City, VA Yes 139,966 15 9.21 10,626 +8% 

Fairfax City, VA Yes 22,565 6 3.70 929 +4% 

Falls Church City, VA Yes 12,332 2 6.17 1,940 +19% 

Manassas City, VA Yes 37,821 10 3.74 2,466 +7% 

Manassas Park City, VA Yes 14,273 2 9.52 3,934 +38% 

Washington DC-MD-VA Subtotals: 5,136,216 3,779 1.36 661,693 +15% 

Table 19. Population and Growth in Other Portions of the Washington-Baltimore-NV CSA.

County

State Recommended 

Nonattainment?

2010 

Population

Land 

Area 

(sq. 

mi.)*

2010 

Population 

Density 

(1000 

pop/sq mi)

Absolute 

change in 

population 

(2000-

2010)

Population 

% change 

(2000-

2010)

Fredericksburg, VA Area:

Spotsylvania Co., VA No 122,397 412 0.30 30,891 +34% 

Stafford Co., VA No 128,961 280 0.46 35,437 +38% 

Fredericksburg City, VA No 24,286 11 2.29 4,922 +25% 

Fredericksburg, VA Subtotals: 275,644 702 0.39 71,250 +35% 

Frederick County, VA Area:

Frederick Co., VA No 78,305 415 0.19 18,725 +31% 

Winchester City, VA No 26,203 9 2.82 2,510 +11% 

Frederick Co., VA Area Subtotals: 104,508 425 0.25 21,235 +26% 

Other counties:

Queen Anne’s Co., MD No 47,798 395 0.12 7,031 +17% 

St. Mary’s Co., MD No 105,151 402 0.26 18,631 +22% 
44

Culpeper Co., VA No 46,689 382 0.12 12,215 +35% 

Clarke Co., VA No 14,034 178 0.08 1,333 +10% 

Fauquier Co., VA No 65,203 651 0.10 9,615 +17% 

Warren Co., VA No 37,575 216 0.17 6,025 +19% 

Hampshire Co., WV No 23,964 644 0.04 3,673 +18% 

Jefferson Co., WV No 53,498 212 0.25 11,059 +26% 

All other counties subtotals: 393,912 3,080 0.13 69,582 +21% 

CSA Totals: 8,572,971 10,315 0.83 969,980 +13% 

* Values are rounded to nearest whole number; sub-totals and CSA total may not add-up due to rounding.

Sources: U.S. Census Bureau population estimates for 2010 as of August 4, 2011 

(http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=DEC_10_PL_GCTPL2.STO5&prodType

=table).

Subsequent to its March 7, 2012 letter Maryland supplied growth data for counties and cities in the 

CSA. A copy of this data has been appended to this TSD as Appendix 4. For the most part Maryland’s 

data compared 2000 against 2007 or 2009 to compute the population change. These data were from 

either Maryland’s MD Statistical Handbook or from a Virginia government sources. The exceptions 

were for Fairfax, King George’s and Loudoun Counties in Virginia for which Maryland cited U.S. 

Census Bureau as the source. For Fauquier County, VA Maryland submitted data posted on-line at 

“http://www.fauquiercounty.gov/government/departments/commdev/ index.cfm?action =demographics”

which provided a July 1, 2010 population estimate. The differences between Maryland’s values for 

Fairfax, Frederick (VA) and Loudoun Counties and those in Tables 18 and 19 are apparently revised 

Census Bureau values for 2000. 

Table 20. Maryland’s data for four Virginia Counties:

County

Population Data

2010 2000 Change 2000-

2010

Percent change, 2000 

to 2010

King George’s Co. 

VA

23,584 16,803 6,781 40.4%

Fairfax County, VA 1,081,726 969,749 111,977 11.5%

Frederick County, 

VA

78,305 59,209 19,096 32.3%

Loudoun Not provided Not 

provided

142,712 84.1%

EPA notes Maryland’s submission but is not going to use Maryland’s data for most areas because EPA 

would like to compare like periods to like periods (2000 to 2010) and use the most recent data (2010). 

EPA does note Maryland’s data for Fairfax, Frederick (VA) and Loudoun Counties but notes the 

differences really do not change the comparisons: for instance, whether Loudoun County’s growth rate 

was 80% or over 84% still makes its growth rate far larger than any other county or city in the CSA. 

Fairfax County’s rate is still between 11 and 12 % which is also well above the average growth rate for 

the entire CSA. Frederick County’s rate is still well over the CSA average and is essentially unchanged 

when in relation to other counties as it retains its relative ranking in relation to other counties – that is, it 

is still ahead of Jefferson County, WV and behind Spotsylvania County, VA. For the Fauquier County

data, the population given by Maryland is apparently a July 1, 2010 estimate. 
45

The following discussion will therefore use the data from Tables 18 and 19 to allow “like to like” 

comparisons.

The 1997 Washington DC-MD-VA nonattainment area contains 59.9% of the Washington-BaltimoreNV CSA’s total population and 68.2% of the Washington-Baltimore-NV CSA’s total absolute change in 

population. The Cities of Fairfax, Falls Church, Manassas and Manassas Park once again have lower 

absolute populations and change in population but these areas are generally more densely populated than 

the surrounding county or nearby counties. The exception is Falls Church City which has a density less 

than Arlington County on one side (6.17 versus 8.05) but twice as high as Fairfax County (6.17 versus 

2.67) on its other side. Some densely populated cities had low growth rates less than the area’s overall 

rate while others such as Falls Church were slightly greater than the area’s overall rate while Manassas 

Park’s was over twice the area’s overall rate. Of the other portions, those with the highest population 

densities grew at a rate less than the area’s overall rate, and, conversely those with population densities 

less than the area’s overall average grew more quickly. The fastest growing areas are in Virginia 

(Loudoun and Prince William Counties) both of which border Fairfax County which has a monitor

violating the 2008 NAAQS. Just over half (55%) of the population live in the areas – the District of 

Columbia and Fairfax, Arlington Charles, Prince George’s and Calvert Counties – that contain one or 

more monitors violating the 2008 NAAQS. Adding in those who live in areas adjacent to these areas 

with violating monitors (that is the entire 1997 Washington DC-MD-VA nonattainment area less 

Frederick County Maryland) encompasses 95 percent of the 1997 nonattainment area’s population; 

Frederick County however is adjacent to Carroll County, MD that contains a monitor violating the 2008 

NAAQS.

The 1997 Baltimore nonattainment area contains 38.1% of the Washington-Baltimore-NV CSA’s total 

population and 15.1% of the Washington-Baltimore-NV CSA’s total absolute change in population. Of 

the areas in the 1997 Baltimore nonattainment area, Howard and Harford Counties had growth rates 

appreciably higher than the area’s overall rate. Carroll County is the least densely populated area in the 

nonattainment area and had a growth rate greater than the area’s overall rate. Well over half (63%) the 

area’s population lives in Harford and Baltimore Counties, and, Baltimore City and thus are in close 

proximity to the Edgewood monitor with the highest design value in the Washington-Baltimore-NV 

CSA’s and the 1997 Baltimore nonattainment area. Well over half (64%) the area’s population lives in 

Howard and Baltimore Counties and Baltimore City, and thus are in close proximity to the monitors in 

Baltimore County. Anne Arundel County is adjacent to the heavily populated Prince George’s County, 

MD and Howard County, MD the latter of which had the highest growth rate in the Baltimore 

nonattainment area and had a growth rate comparable to the faster growing 1997 Washington DC-MDVA nonattainment area.

Together the 1997 Washington DC-MD-VA and Baltimore nonattainment areas contain 91.0% of the 

Washington-Baltimore-NV CSA’s total population and 83.3% of the overall change within the 

Washington-Baltimore-NV CSA. Most of the areas within these two 1997 nonattainment areas are 

moderately to very densely populated. In general, the counties and cities in the 1997 Baltimore and 

Washington nonattainment areas likely sufficiently contribute to nonattainment at one or more monitors 

in at least one of these two areas because the County has a violating monitor, because the county or city

is adjacent to a county with a violating monitor or the small city has a population density comparable to 

or higher than surrounding or adjacent areas. 

Of the other areas or the counties listed under “other counties” in the preceding table most are relatively

sparsely populated or remote from areas containing a monitor violating the 2008 NAAQS: 
46

(1) The Frederick County, VA Area still contains only 1.2% of the Washington-Baltimore-NV CSA’s 

population in spite of its growth rate of twice the overall rate in the Washington-Baltimore-NV CSA. 

This area is remote from any counties with violating monitors and is separated from the 1997

Washington DC-MD-VA nonattainment area by the sparsely populated Clarke and Warren Counties in 

Virginia. This area’s total population is less than the absolute population change in Fairfax County, 

Loudoun County or Prince William County in Virginia. 

(2) Hampshire County is remote from any violating monitor in the Washington-Baltimore-NV CSA and 

is likewise sparsely populated. It growth rate is not appreciably greater than that of the WashingtonBaltimore-NV CSA as a whole and its absolute population change is one-tenth that of Frederick County, 

MD which has a similar land area and growth rate.

(3) Clarke and Warren Counties in Virginia are sparsely populated and their absolute change in 

population is small in comparison to areas within the 1997 Washington DC-MD-VA nonattainment area. 

Clarke County has a population that is less than all other areas in the Washington-Baltimore-NV CSA 

except the very small Falls Church City. 

(4) Queen Anne’s County MD has a growth rate nearly three times that of the 1997 Baltimore 

nonattainment area but both the absolute change and the absolute population are small. It is still 

sparsely populated. 

(5) Jefferson County, WV had a growth rate twice the overall rate in the Washington-Baltimore-NV 

CSA. It is still sparsely populated and is not adjacent to a county containing a monitor violating the 

2008 NAAQS. In addition, Jefferson County’s total population is half the absolute population change

in the adjacent Loudoun County, VA.

(6) Fauquier County, VA had a growth rate comparable to that of the 1997 Washington DC-MD-VA 

nonattainment area (17% versus 15%) but its absolute change was small – around 9,600 which is one 

one-hundredth of the Washington-Baltimore-NV CSA’s overall change or 1.5% of that for the 1997

Washington DC-MD-VA nonattainment area. Fauquier County is still sparely populated and is not 

adjacent to a county containing a monitor violating the 2008 NAAQS.

(7) The situation for Culpeper County, VA is similar to that for Fauquier County, VA. Culpeper had a 

growth rate of 35 percent. In addition, it is still sparely populated and has a smaller population than 

Fauquier County. However, Culpeper County is even more remote from any county containing a 

monitor violating the 2008 NAAQS.

. 

(8) St. Mary’s County, MD is the most populous and most densely populated of the “other counties.” 

Even so, its total population is less than the absolute population change in Fairfax County, Loudoun 

County or Prince William County in Virginia. St. Mary’s County is less densely populated than any

county or city in either the Washington DC-MD-VA or Baltimore nonattainment areas. Its absolute 

population is greater than Calvert County, MD which is smaller in size. St. Mary’s County is adjacent 

to Calvert County which does contain a monitor violating the 2008 NAAQS.

(9) The Fredericksburg, VA Area had not insubstantial growth. Its individual jurisdictions grew at a rate 

from about two to three times faster than the Washington-Baltimore-NV CSA’s overall rate and overall 

at a rate twice that of the 1997 Washington DC-MD-VA nonattainment area. In terms of land area and 

population density it is somewhat comparable to Frederick County, MD, but it had an absolute change in 

population almost twice Frederick County. Unlike Fredrick County, MD, the Fredericksburg, VA Area 

is not adjacent to any county with a monitor violating the 2008 NAAQS. 
47

Traffic and commuting patterns

EPA evaluated the commuting patterns of residents in the area, as well as the total Vehicle Miles 

Traveled (VMT) for each county. In combination with the population/population density data and the 

location of main transportation arteries (see Figure 1a or 1b above); this information helps identify the 

probable location of non-point source emissions. A county with high VMT and/or a high number of 

commuters is generally an integral part of an urban area and indicates the presence of motor vehicle 

emissions that may contribute to ozone formation. Table 20 shows the total vehicle miles traveled 

(VMT) and total number of commuters for each county within the Washington-Baltimore-NV CSA.

Table 21. Traffic and Commuting Patterns.

County

State 

Recommended 

Nonattainment?

2008 VMT (million 

miles)

Total 

Commuters

Baltimore MD Nonattainment Area:

Anne Arundel Co., MD Yes 5,759 255,425 

Baltimore City, MD Yes 3,619 249,125 

Carroll Co., MD Yes 1,272 77,394 

Harford Co., MD Yes 2,324 111,398 

Howard Co., MD Yes 3,793 134,596 

Baltimore Co., MD Yes 8,227 373,013 

Baltimore 

Subtotals: 24,994 1,200,951 

Washington DC-MD-VA Nonattainment Area:

District of Columbia, DC Yes 3,685 260,296 

Calvert Co., MD Yes 764 37,355 

Charles Co., MD Yes 1,260 61,504 

Frederick Co., MD Yes 2,932 102,033 

Montgomery Co., MD Yes 7,443 454,680 

Prince George’s Co., MD Yes 8,718 396,948 

Arlington Co., VA Yes 1,634 115,614 

Fairfax Co., VA Yes 10,484 526,655 

Loudoun Co., VA Yes 1,567 92,040 

Prince William Co., VA Yes 3,094 150,274 

Alexandria City, VA Yes 793 76,811 

Fairfax City, VA Yes 177 11,753 

Falls Church City, VA Yes 62 5,803 

Manassas City, VA Yes 290 18,077 

Manassas Park City, VA Yes 27 5,415 

Washington DC-MD-VA Subtotals: 42,929 2,315,258 

Fredericksburg, VA Area:

Spotsylvania Co., VA No 1,256 45,132 

Stafford Co., VA No 1,698 48,202 

Fredericksburg City, VA No 363 9,564 

Fredericksburg, VA Subtotals: 3,317 102,898 

Frederick County, VA Area:
48

Frederick Co., VA No 542 30,167 

Winchester City, VA No 135 11,865 

Frederick Co., VA Area Subtotals: 677 42,032 

Other counties:

Queen Anne’s Co., MD No 923 20,736 

St. Mary’s Co., MD No 822 43,101 

Clarke Co., VA No 300 6,438 

Culpeper Co., VA No 520 15,951 

Fauquier Co., VA No 1,055 28,103 

Warren Co., VA No 435 15,286 

Hampshire Co., WV No 216 8,255 

Jefferson Co., WV No 388 20,937 

All other counties 

subtotals: 4,659 158,807 

CSA Totals: 76,576 3,819,946 

* MOBILE model VMTs are those inputs into the NEI version 1.5. 

** U.S. Census Bureau estimates for 2000 County-to-County Worker Flow 

http://www.census.gov/hhes/commuting/data/commuting.html.

Together the 1997 Washington DC-MD-VA and Baltimore nonattainment areas contain 88.7 percent of 

total VMT and 92 percent of the total commuters within the Washington-Baltimore-NV CSA. 

As stated previously in this document, EPA recommended examining CSA/CBSAs because certain 

factors used to establish CSAs and CBSAs are similar to the factors EPA is using in this technical 

analysis to determine if a nearby area is contributing to a violation of the 2008 ozone NAAQS. These 

similar factors include degree of urbanization which is used to define a “central county (or counties)” in 

a CBSA and certain employment related commuting indices which are used to join “outlying counties” 

to “central county (or counties)” to form a CBSA. One or more CBSAs are always joined if the 

“employment interchange rate” 76 is 25 percent and may be joined to form a CSA if the “employment 

interchange rate” is at least 15 percent between these two CBSAs. 77 Therefore, there is some degree of 

urbanization and commuting within the CBSAs comprising the Washington-Baltimore-NV CSA and 

some degree of commuting between CBSAs within this CSA. However, when a county’s number of 

commuters or VMT are a significant fraction of another county’s, such a county cannot indicate the 

presence of as much motor vehicle emissions that may contribute to ozone formation as the county with 

the higher VMT or number of commuters.

The 1997 Washington DC-MD-VA nonattainment area contains 56.1% of the total VMT and 60.6% of 

total commuters within the Washington-Baltimore-NV CSA. There is a vast disparity in the absolute 

VMT values within the 1997 Washington DC-MD-VA nonattainment area: excluding such physically

small areas as the Cities of Fairfax, Falls Church, Manassas and Manassas Park, the VMT of Fairfax 

County, VA is over 13 times that of Calvert County, MD. The top three in terms of absolute VMT are 

 

76 The “employment interchange rate” between two areas is defined as the sum of the percentage of employed residents of the 

area with the smaller total population who work in the area with the larger total population and the percentage of employment 

in the area with the smaller total population that is accounted for by workers residing in the area with the larger total 

population. See, 64 FR 56628 at 56643, October 20, 1999. 

77 See “Section 8. Combining Adjacent Core Based Statistical Areas,” 65 FR 82228 at 82237, December 27, 2000. These 

current standards came into use starting 2003 (65 FR 82228 at 82235-82236) and will be replaced in 2013 when the 2010 

standards come into force (75 FR 37246 at 37249, June 28, 2010). 
49

Fairfax County, VA and Montgomery and Prince George’s Counties in Maryland. Together they

comprise 26,644 million (62%) of 42,929 million VMT for the 1997 Washington DC-MD-VA 

nonattainment area. Together they contain or enclose all the violating monitors within the 1997

Washington DC-MD-VA nonattainment area except that in Calvert County, MD. The next three areas 

in terms of VMT are the District of Columbia, Prince William County, VA and Frederick County, MD 

which comprise 9,711 million (22.6%) of 42,929 million VMT for this 1997 nonattainment area. Filling 

out 95 percent of the VMT in the 1997 Washington DC-MD-VA nonattainment area are the combined 

VMT of Loudoun and Arlington Counties in Virginia and Charles County, MD with 4,461 million 

(10.4%) of 42,929 million. With respect to the Cities of Alexandria, Fairfax and Falls Church, these are 

all adjacent to an area that contains a violating monitor. With respect to the Cities of Manassas and 

Manassas Park, these two cities under this factor might or might not sufficiently contribute to 

nonattainment within the Washington-Baltimore-NV CSA but should be included in a nonattainment 

area if the surrounding county of Prince William County is. As far as VMT is concerned, Calvert 

County is on the edge of the Washington-Baltimore-NV CSA and has the lowest VMT of any area 

within the 1997 Washington DC-MD-VA nonattainment area exclusive of the smaller independent cities 

in Virginia. Calvert County is adjacent to two counties (Prince George’s and Anne Arundel) in 

Maryland containing a violating monitor. 

The 1997 Baltimore nonattainment area contains 32.6% of the Washington-Baltimore-NV CSA’s total 

VMT and 31.4% of the Washington-Baltimore-NV CSA’s total commuters. Of the areas in the 1997

Baltimore nonattainment area, all except Baltimore City and Howard contain a violating monitor. 

Baltimore and Anne Arundel Counties rank one and two for total VMT and for total number of 

commuters within the 1997 Baltimore nonattainment area. Carroll County has the lowest VMT and 

number of commuters within the 1997 Baltimore nonattainment area. As far as absolute VMT, the ratio 

of the highest to the smallest value is about 6.5 to 1. Carroll and Harford Counties are at the bottom. 

Carroll County’s VMT comprises about 5% of 1997 Baltimore nonattainment area’s VMT. Harford 

County likely contributes to the ozone violation at the two monitors located within Harford County. 

Because these monitors were located to be downwind of the main urbanized core surrounding Baltimore 

City, Harford County might not be a contributor to violations at other monitors in the WashingtonBaltimore-NV CSA but rather more a receptor of ozone and precursor emissions from within the 

Washington-Baltimore-NV CSA.

In general, the counties and cities in the 1997 Baltimore and Washington nonattainment areas likely 

sufficiently contribute to nonattainment at one or more monitors in at least one of these two areas 

because in most cases commuting patterns and VMT favor inclusion and most are adjacent to a county

containing a violating monitor. 

Of the other areas or counties listed under “Other counties” in the preceding table, all but one has less 

than 1,000 million VMT. Together these eight “other” counties comprise 6.1 percent of the 

Washington-Baltimore-NV CSA’s total VMT and comprise 4.2 percent of the Washington-BaltimoreNV CSA’s total commuters. Of these “Other counties,” St. Mary’s and Queen Anne’s in Maryland, and 

Fauquier in Virginia, comprise most of the VMT and total commuters of these eight “other” counties. 

Table 13 shows the share (as a percentage of the Washington-Baltimore-NV CSA’s total) of Fauquier, 

Queen Anne’s, and St. Mary’s Counties of the VMT and total commuters and compares these three with 

the remaining five “Other” counties:

Table 22. Traffic and Commuting Patterns – Fauquier, Queen Anne’s and St. Mary’s Counties as 

a Percentage of CSA Totals.
50

County, State 

2008 VMT 

(% of CSA 

total)

Number 

commuting to 

any violating 

counties (% of 

CSA total)

Total Commuters 

(% of CSA total)

Fauquier Co., VA 1.4% 0.3% 1.1%

St. Mary’s Co., MD 1.1% 0.3% 1.1%

Queen Anne’s Co., MD 1.2% 0.3% 0.5%

Subtotal: 3.7% 0.9% 2.8%

Subtotal for Clarke, 

Culpeper, & Warren 

Counties, VA and 

Hampshire & Jefferson 

Counties, WV 2.4% 0.4% 1.4%

Total eight “other” 

counties 6.1% 1.3% 4.2%

Share of Fauquier, Queen 

Anne’s, and St. Mary’s 

Counties 60.1% 72.1% 67.3%

(1) The Frederick County, VA Area contains less than 1 percent of the Washington-Baltimore-NV 

CSA’s VMT or those “commuting to or within any violating counties.” The area’s VMT (677 million) 

is less than any other area within the 1997 Washington nonattainment area (independent cities 

excepted). The total number of commuters is 1.1 percent of the total number of commuters in the 

Washington-Baltimore-NV CSA. This area is remote from any counties with violating monitors and is 

separated from the 1997 Washington DC-MD-VA nonattainment area by Clarke and Warren Counties in 

Virginia. 

(2) Hampshire County is remote from any violating monitor in the Washington-Baltimore-NV CSA and 

likewise has low VMT (216 million). The VMT is less than all but the three smallest independent cities 

in the 1997 Washington nonattainment area. 

(3) Clarke and Warren Counties in Virginia have low VMT which is only greater than some of the small 

independent cities of comparable population (Manassas Park City and Manassas City, respectively) in 

the Washington-Baltimore-NV CSA. 

(4) Queen Anne’s County MD has 20,576 total commuters which is less than one-third the number of 

the next lowest county (Carroll County with 77,394) in the Baltimore-Towson, MD CBSA but only onehalf percent (0.5%) of the Washington-Baltimore-NV CSA’s total or 1.7 percent of the total for the 1997

Baltimore nonattainment area. Queen Anne’s County is only connected to the rest of the CBSA by the 

Chesapeake Bay Bridge (U.S. Routes 50 and 301) across the Chesapeake Bay to Anne Arundel County

(see Figure 1a or 1b which shows a road crossing the Chesapeake Bay from Queen Anne’s to Anne 

Arundel). Queen Anne’s has 923 million VMT (1.2% of the Washington-Baltimore-NV CSA’s total or 

3.7% of the 1997 Baltimore nonattainment area) which is comparable to that of Carroll County ((1,272 

million) even though Queen Anne’s population is roughly one third of Carroll’s (47,798 versus 

167,134). 
51

(5) Jefferson County, WV has low VMT (388 million) which is only greater than some of the small 

independent cities of comparable population (Manassas Park City and Manassas City combined).

Jefferson County is not adjacent to a county containing a monitor violating the 2008 NAAQS. 

(6) Fauquier County, VA has the most VMT of these “other counties” at 1,055 million (1.4% of the 

Washington-Baltimore-NV CSA’s total or 2.5% of the total for the 1997 Washington-DC-MD-VA 

nonattainment area). Fauquier is comparable to Charles County, MD (1,260 million) which has twice 

the population (146,551 versus 65,203) but is greater than that of Calvert County, MD (764 million 

VMT), which has a slightly greater population. Fauquier County has fewer commuters than either 

Charles or Calvert Counties. Fauquier County is separated from the nearest counties with violating 

monitors by Loudoun and Prince William Counties in Virginia. 

(7) The situation for Culpeper County, VA is similar to that for Warren County, VA. Its VMT is 

slightly greater at 520 million (versus 435) than Warren’s. The numbers of commuters are similar, at 

15,951 versus 15,286, respectively. However, Culpeper County is even more remote from any county

containing a monitor violating the 2008 NAAQS. Culpeper County is separated from the nearest 

counties with violating monitors by Fauquier, Loudoun and Prince William Counties in Virginia.

. 

(8) St. Mary’s County, MD has a VMT of 822 million (1.1% of the Washington-Baltimore-NV CSA’s 

total or 1.9% of the total for the 1997 Washington-DC-MD-VA nonattainment area). This is more than 

Calvert County, MD. The total number of commuters at 43,101 (1.1% of the Washington-BaltimoreNV CSA’s total or 1.9% of the total for the 1997 Washington-DC-MD-VA nonattainment area) is 

between that of Calvert and Charles Counties, which is not surprising because St. Mary’s population 

falls between that of these other two. St. Mary’s comprises the CBSA of the Lexington Park MD 

micropolitan statistical area, whereas Charles County is part of the 1997 Washington DC-MD-VA 

nonattainment area; the 1997 Washington DC-MD-VA nonattainment area is within a different CBSA –

the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area – than St. 

Mary’s. Because St. Mary’s County is in a separate CBSA from the 1997 Washington DC-MD-VA 

nonattainment area, that is, is not part of the Washington-Arlington-Alexandria, DC-VA-MD-WV 

Metropolitan Statistical Area, one can infer that the degree of integration between St. Mary’s County

and the 1997 Washington DC-MD-VA nonattainment area is likely less than that of either Charles or 

Calvert County. St. Mary’s County is adjacent to Calvert County which does contain a monitor 

violating the 2008 NAAQS. 

(9) The Fredericksburg, VA Area as a whole has 3,317 million VMT which is 4.3% of the WashingtonBaltimore-NV CSA’s total or 7.7% of the total for the 1997 Washington-DC-MD-VA nonattainment 

area. The total number of commuters is 22,124; this is 2.7 percent of the Washington-Baltimore-NV 

CSA’s total or 4.4 percent of the total for the 1997 Washington-DC-MD-VA nonattainment area. The 

total VMT and total number of commuters for the Fredericksburg, VA Area are comparable to that of 

Prince William County, VA. Unlike Prince William County, VA, the Fredericksburg, VA Area is not 

adjacent to any county with a monitor violating the 2008 NAAQS. The Fredericksburg, VA Area is 

within the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area which 

contains the 1997 Washington DC-MD-VA nonattainment area. Of the three jurisdictions within the 

Fredericksburg, VA Area, Stafford County has the largest VMT and total number of commuters. 

With Regards to Counties in the CSA and Mobile Source Emissions:

Counties included as part of any CSA indicates ties to the core urban area. As discussed under “Core 

Cities/Counties in this CSA” elsewhere in this document, inclusion in a CBSA or combination of two or 

more CBSAs indicates commuting linkages above various thresholds. 
52

Just because a county is located in a CSA, this fact does not fully reflect the amount of VMT and hence 

emissions commuting puts within any particular counties of a CSA. The obvious factors are: whether 

or not the county or city is a core city or county within its parent CBSA or is an outlying county or city 

of a CBSA; its proximity to the core county/counties of its parent CBSA; its proximity to core counties 

and cities of an adjacent CBSA, and so on. 

The Washington-Baltimore-NV CSA consists of: the Baltimore-Towson CBSA; the Culpeper, VA 

Micropolitan Statistical Area (Culpeper CBSA); the Lexington Park MD (St. Mary’s County), 

Micropolitan Statistical Area (Lexington Park CBSA); the Washington-Arlington-Alexandria, DC-VAMD-WV Metropolitan Statistical Area (Washington CBSA); and the Winchester, VA-WV Metropolitan 

Statistical Area (Winchester CBSA). 

Anne Arundel and Prince George’s Counties are core counties (see “Core Cities/Counties in this CSA” 

elsewhere in this document) of their respective “parent” CBSAs – the Baltimore-Towson CBSA and the 

Washington CBSA. They are adjacent to each other. EPA does not doubt that there is cross-commuting 

between the two. Likewise, as Maryland noted, Washington Beltway facilitates travel in the 

Washington CBSA; this roadway as well as other such as Interstate-95 and its offshoots facilitate 

commuting among the core counties/cities of the Washington CBSA such as the District of Columbia, 

Fairfax Co., VA, and Montgomery and Prince George’s Counties in Maryland. 

Conversely, Hampshire County, WV is an outlying county in the Winchester CBSA. The Winchester 

CBSA is part of the Washington-Baltimore-NV CSA. For the Winchester CBSA to be part of the CSA, 

the percentage of workers in the Winchester CBSA commute to the Washington CBSA plus of the 

percentage of the employment in the Winchester CBSA is of residents from the Washington CBSA that 

is at least 15 percent but might be at least 25 percent.78 By virtue of its status as an outlying county, one 

knows at least 25 percent of the employment in Hampshire is from residents of Winchester City and 

Frederick County, VA or 15 percent of the commuters in Hampshire County reside in Virginia. That the 

Winchester CBSA is part of the Washington-Baltimore-NV CSA only means there is employment 

related commuting interchange between it and the larger Washington CBSA. Warren and Clarke 

Counties in Virginia are outlying counties in the Washington CBSA and adjacent to the Winchester 

CBSA (namely Frederick County, VA). It would seem that the commuting ties among these counties 

alone could tie the Winchester area to the Washington CBSA and hence to the greater WashingtonBaltimore-NV CSA. 

Likewise, Warren and Clarke Counties in Virginia are each an outlying county in the Washington 

CBSA. This means at least 25 percent of those workers of either work in the central counties and cities 

of the Washington CBSA or 25 percent of the employment in either is from persons from the central 

counties and cities: the nearest central county to Clarke County is the adjacent Loudoun County; in the 

case of Warren County the nearest adjacent central county is Prince William with part of the outlying 

county of Fauquier in between; however, Interstate 66 runs through Warren County into Prince William 

County and to Fairfax County and no doubt facilitates commuting. 

The CSA delineation does not necessarily connote on-road vehicular travel, only the interchange of 

employment. Thus, a portion of the commuting within some of the CBSAs or between CBSAs 

constituting the Washington-Baltimore-NV CSA could be by rail using the various subway and light rail 

systems within the CSA.

 

78

 Refer to OMB’s December 27, 2000 (65 FR 82228), Notice of decision “Standards for Defining Metropolitan and 

Micropolitan Statistical Areas” for how OMB determines CBSAs and CSAs and refer to the discussion under the heading 

“The Composition of the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV CSA” elsewhere in this document.
53

EPA recommended starting the boundary determination process at the boundaries of a CSA/CBSA 

because the factors used to establish the CBSAs and CSAs are similar to some of the factors EPA 

considers in determining whether a nearby area is contributing to the violation(s) of the standard. But 

EPA determines whether an area is contributing to the violation(s) of the standard at a nearby monitor 

only after consideration of all five factors. Conversely, EPA believes the fact that a county or city is not 

in a CBSA/CSA is noteworthy because the level of employment interchange and hence commuting is 

usually less than the criteria levels used by OMB. 

Factor 3: Meteorology (weather/transport patterns)

Background:

EPA received comments that surface wind roses are not the best technical tool to assess prevailing winds 

because surface wind roses do not represent the three-dimensional flow of air in the atmosphere; 

transport patterns based solely on surface wind speed and direction ignores aloft winds and regular 

vertical mixing such as occurs daily; three-dimensional wind fields provide a more realistic presentation 

of the origins of air during ozone exceedance days.79 As a result of such comments, EPA re-evaluated 

the five-factors for this CSA in light of meteorology data resulting from use of the National Oceanic and 

Atmospheric Administration’s (NOAA) Hybrid Single Particle Lagrangian Integrated Trajectory

(HYSPLIT) Model for this Factor 3 Meteorology portion of this document.80 This analysis supplements 

and to a great extent supplants the Factor 3 analysis in “Technical Analysis for the Washington, DCMD-VA and Baltimore Areas81” by improving EPA’s understanding of prevailing winds. 

To allow consideration of air movement above the surface layer, we ran the HYSPLIT model to obtain 

trajectories for three heights – 100 meters, 500 meters and 1,000 meters. We ran the HYSPLIT to obtain 

1,000 meter runs in order to better understand aloft movement of air that can be expected to mix down 

as the night-time inversion breaks-up. Due to the number of monitors and exceedance days EPA did not 

(and could not due to time constraints) run trajectories for each exceedance day at each monitor in the 

CSA. 

To narrow down the level of effort, EPA examined the air quality data (Factor 1) in more detail. 

We examined the 2006 to 2010 8-hour ozone concentrations for the monitors in the “violating center”82

of the CSA and grouped the data by days when the 2008 ozone NAAQS was exceeded. When selecting 

monitors for which to run the HYSPLIT model EPA had to consider the density of the monitoring 

network, the need to decide whether to designate all or a substantial portion of this CSA as one 

nonattainment area or split the CSA into more than one nonattainment area, and the need to develop a 

conceptual model of the relationship between meteorology (wind directions on exceedance days) and 

ozone concentrations within the CSA in light of Maryland’s (and other parties’) comments on 

meteorology, and comments noting that the “tracking” of the design value for the 1997 Washington DCMD-VA nonattainment area by the Davidsonville monitor in Anne Arundel County indicates there 

should be only one nonattainment area within the CSA.

 

79 For example, refer to documents EPA-HQ-OAR-2008-0476-0405 and EPA-HQ-OAR-2008-0476-0456.

80

 “Preliminary Technical Support Document, December 2011, entitled, Maryland Area Designations for the 2008 Ozone 

National Ambient Air Quality Standards, prepared by the Region 3 USEPA” document number EPA-HQ-OAR-2008-0476-

0235 in the docket for this action.

81

 Refer to in docket item numbers EPA-HQ-OAR-2008-0476-0235, EPA-HQ-OAR-2008-0476-0405 and EPA-HQ-OAR2008-0476-0456 in the docket for this action.

82

 Basically all monitors in the CSA were considered except the monitor in Frederick County, VA.
54

Normally when we are developing a conceptual model understanding of what yields ozone exceedances 

in an area we will evaluate 5 to 10 years worth of meteorological data. In some areas where the 

meteorology is well known, where the design value monitor statistically dominates the data in terms of 

design value and number of exceedances, or where there is only one violating monitor in the area, we 

might need to examine the wind patterns on days the 0.075 ppm standard was exceeded at that violating

monitor. However, in the case of the Washington-Baltimore-NV CSA, there were several determinations 

to be made or factors to consider: First EPA had to determine whether the CSA should contain one 

nonattainment area enclosing all the violating monitors within the CSA as recommended by two States or be 

split into two nonattainment areas (and some attainment areas) as recommended by two States. Second, the 

patterns of exceeding monitors on exceedance days shows that parts of the area might be exceeding on 

certain days while other parts not recording exceedances on the same days. Third, especially high values can 

occur at different monitors. Fourth, on multi-episode days portions of the area record exceedances or 

especially high values on some days while other parts record exceedances or especially high values on other 

days of the same episode. There is also the need to examine ozone concentration gradients and the need to 

correlate concentration levels across the CSA with model predicted wind directions. These determinations 

and factors would support performance of a more extensive meteorology analysis than most areas in the 

country. 

In past designations, EPA has rarely considered this level of detail for every designation decision, but 

to reiterate, the decisions for this CSA are not typical due to: the State submitted information 

regarding meteorology and its effects on the Edgewood monitor and the differing recommendations 

of two States seeking a single nonattainment area for the CSA and another two States seeking 

retention of the 1997 Washington DC-MD-VA nonattainment boundaries. 

About HYSPLIT generally:

We used the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian 

Integrated Trajectory Model (NOAA HYSPLIT or just “HYSPLIT”) to develop a conceptual model of 

the meteorological transport conditions within the regional area within and around the CSA. We 

evaluated 24-hour back trajectories for the 2006-2010 time period using the NOAA HYSPLIT model. 

We evaluated trajectories for 100, 500 and 1000 meter heights to gain an understanding of where air 

may “mix down” as the nighttime inversion breaks-up. 

Several factors need to be kept in mind:

HYSPLIT back-trajectories are depicted as a relatively thin line, which can be taken to represent the 

center of an air parcel of some width. An area traversed by the line is considered traversed by the air 

parcel. 

HYSPLIT back-trajectories used in ozone designations are based upon meteorological fields at a 40 

km (about 24.8 miles) resolution. 

HYSPLIT back-trajectories are produced at various end heights to capture the behavior of air parcels 

at various heights within the mixed layer of the atmosphere. Lower-level trajectories may be affected by

terrain.

HYSPLIT back-trajectories end at the monitoring site in question; therefore, if one starts at the 

monitor the further a point is on the curve is away from the monitor (the end point), the location of the 

air mass is further back in time. 

Selection of Monitors:

We aimed to develop an understanding of what wind patterns were conducive to ozone formation 

throughout the area. However, to develop three (100, 500 & 1000 m) back trajectories for every

exceedance day for every monitor would produce hundreds of results that might not materially provide 

more information than a fewer number. Clearly, data for the Edgewood monitor in Harford County, MD 
55

is critical because this monitor has the highest design value of any monitor in the CSA and by far 

experiences more exceedance days. 

The Franconia monitor in Fairfax County, VA is also important because it is the current design value 

monitor in the Washington DC-MD-VA nonattainment area and is the violating monitor furthest from 

the Edgewood monitor. (Franconia is in the far southwest of the CSA, and, Edgewood is in the far 

northeast.) However, the Franconia monitor did not have as many exceedance days as several other 

monitors in the southwest, being surpassed by the McMillan Reservoir monitor in the District of 

Columbia and the Arlington monitor in Arlington County, VA. See Tables 6, 7 and 8 elsewhere in this 

document. For this reason, the Arlington and McMillan Reservoir monitors were also considered. 

The Davidsonville monitor in Anne Arundel County was selected based upon its design value history (at 

times equal to that in the current Washington DC-MD-VA Nonattainment area), number of “especially

high” exceedances over the 2006 to 2010 period and its location close to the border of the two 

nonattainment areas designated under the 1997 ozone NAAQS. 

Initially, the Howard U—Beltsville monitor was likewise selected over the monitor at Prince George’s 

Equestrian Center because Howard U—Beltsville monitor is closer to the border of the two 

nonattainment areas designated under the 1997 ozone NAAQS, currently has a higher design value and 

has recorded more exceedance days over the 2006-2010 period. By using the data for the Davidsonville 

and Howard U—Beltsville monitors EPA could correlate the ground level ozone concentrations with the 

back-trajectory results to gain an understanding of air movement patterns and measured ozone values in 

that portion of the two current nonattainment area’s common border. 

Finally, HYSPLIT back-trajectories for certain other monitors were considered when necessary to gain 

an understanding of wind directions on those days for which the main monitors did not exceed the 2008 

ozone NAAQS. For other monitors, we examined the back-trajectories for some monitors as surrogates

for other close monitors. For example, the McMillan, Arlington and Fairfax monitors are close to the 

Takoma and River Terrace monitors in the District. Therefore, on days for which we had backtrajectories for one or more of the three former monitors we inferred that these represented the 

prevailing winds at the other two monitors in the District. Likewise, comparing the trajectories available 

for an episode day, we could gain an overall sense of the prevailing winds for that day. For 2006 and 

2007, certain other monitors were examined as well. These were certain days for outlying monitors such 

as those in Carroll (South Carroll), Calvert (Calvert Co.) and Charles (Southern Maryland) Counties in 

Maryland and Stafford County (Widewater) in Virginia. 

Grouping:

EPA categorized the back-trajectory results into roughly five quintiles by the concentration measured at 

the monitor. The concentration ranges for these “quintiles” were based upon the results of the analysis 

for the Edgewood monitor. Refer to Table 10 elsewhere in this document for the ranges of each 

“Group.” 

Some General Observations:

Review of the HYSPLIT predicted trajectories actually occurred in two batches. Our first review looked 

at the 2008-2010 predictions. Our second review considered the 2007 and 2008 predictions. Our 

evaluation considered all the 2006 to 2010 predicted back-trajectories. The back-trajectories for 

different monitors suggest that 2006 and 2007 featured more episodes featuring southerly or 

southwesterly winds than 2008 and 2010 (2009 had so few episodes no general conclusion would seem 

warranted). Even so, 2006 to 2010 contained a considerable number of exceedance days featuring 
56

winds from the northeast, north and northwest which corresponded to higher concentrations (say in 

Group 4 or higher – that is, over 0.087 ppm) or “especially high” concentrations (that is, 0.095 ppm ---

see under Factor 1 under “Severity of Episodes” and Table 12 elsewhere in this document) recorded at 

the Edgewood monitor.

Sample Results:

Figures on the following pages provide examples of the HYSPLIT results. An electronic copy of all the 

HYSPLIT results has been placed in the docket for this action due to the voluminous nature of all the 

outputs (1807 single pages in Adobe® Acrobat®83 portable data file (PDF) format which when zipped are 

over 50 megabytes in size). 

Figures 4a through 4d show sample 100, 500 and 1000 meter Results for the Edgewood Monitor for July

6, 2010. Figures 5a through 5d show sample 100, 500 and 1000 meter Results for the Edgewood 

Monitor for August 10, 2010.

 

83

 Trademarks of Adobe Systems Incorporated.
57

Figure 4a All Levels – 100, 500, 1000 meters
58

Figure 4b -- 100 Meters (Above) Figure 4c – 500 meters (above)

Figure 4d. 1000 meter Results (above)
59

Figure 5a. All Levels – 100, 500 and 1000 meters
60

Figure 5b 100 meters (above) Figure 4c 500 meters (above)

F

Figure 5d 1000 meter Results (Above)
61

Analyses:

1. Does the current Washington DC-MD-VA Nonattainment area contribute to nonattainment in the 

current Baltimore MD Nonattainment area?

For the 2008 to 2010 time period, the HYSPLIT trajectories support the conclusion that the Edgewood 

monitor is downwind of the 1997 Washington DC-MD-VA Nonattainment area. The trajectories for 

just the 100 and 500 meter heights suggest the Edgewood monitor is downwind of the 1997 Washington 

DC-MD-VA Nonattainment area on the following days when the Edgewood monitor exceeded 0.075 

ppm:

Table 23. Days by Year the Edgewood Monitor is Downwind of the 1997 Washington DC-MDVA Nonattainment area:

YEAR

Trajectory Height 2008 2009 2010

100 meters 6/7, 6/13-14, 7/3, 

7/12, 7/29, & 9/4

6/26, 7/15-7/16, 8/16 

& 8/18

5/21, 6/22, 6/26-6/27, 

7/3-7/4, 7/16, 7/23, 

8/9, 8/29, 9/1-9/2, 

9/24

500 meters 4/19, 6/13; 7/3, 7/18, 

7/29, & 9/4

7/15 6/22, 6/26-6/27, 7/16, 

7/23, 7/31, 8/9, 9/1, 

9/2 & 9/24.

The air at 100 and 500 meters height are likely the first to mix when the night-time inversion breaks up. 

These days represent 25 of the 51 2008-2010 exceedance days for the 100 meter height and 17 of 51 

days for the 500 meter height.

The HYSPLIT back-trajectories indicate that many other areas are also upwind of this monitor on many

days. On some days the winds come from the east or northeast. On other days the winds come from the 

south but the trajectory does not cross the core of the Washington CBSA84 but does cross outlying 

counties (such as Calvert or Charles) of the 1997 Washington DC-MD-VA nonattainment area. 

Likewise, on some days when the predicted directions are from the northwest, the trajectories might

only cross an outlying Frederick County, MD and not the core of the Washington CBSA. When the 

predicted winds are from the west, northwest, southwest and south-southwest, the trajectories almost 

always cross the core of the Baltimore nonattainment area.85 

Figures 5A-1 to 5A-1086 of Appendix 5 “Appendix 5: HYSPLIT Trajectories for Edgewood by Group 

and Exceedance Days Over 0.100 ppm” show the HYSPLIT results overlaid on a map. They are 

 

84

 Refer to “The Composition of the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV CSA” elsewhere in this 

document.

85

 The Baltimore-Towson CBSA and Baltimore nonattainment area share the same “core” as discussed in “The Composition 

of the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV CSA” elsewhere in this document.

86

 The following nomenclature is used for the figures in the appendices to this document: The first number is the appendix 

number, the “A” indicates that the figure is in an appendix, and the number after the hyphen is the figure number within that 

appendix. Thus Figure 5A-1 refers to the first figure in Appendix 5 of this document. 
62

grouped by the “Groups” defined in Table 10 elsewhere in this document. For each “Group” there is a 

map for 2008 to 2010 exceedance days and one for 2006 to 2007 exceedance days. 

Analysis of the full set of data for the Edgewood monitor counted the back-trajectory for each altitude 

for each day. Thus each exceedance day would contribute three to the aggregate sum. The trajectories 

were placed in one of three exclusive categories: “Not any part of the Washington CBSA,” “Only the 

Charles, Frederick or Calvert Counties portion of the Washington CBSA” or the “Washington CBSA 

except Calvert/Charles/Frederick Counties in MD.” A trajectory was counted under the “Not any part of 

the Washington CBSA” only when the trajectory never crossed any area in the. A trajectory was counted 

under the “Only the Charles, Frederick (MD) or Calvert Counties portion of the Washington CBSA” if 

the only portion of the CBSA it crossed was in Charles, Frederick and/or Calvert counties. Likewise if 

the trajectory crossed anywhere in the Washington CBSA it was counted under the “Washington CBSA 

except Calvert/Charles/Frederick Counties in MD” unless it only crossed Charles, Frederick (MD) or 

Calvert Counties. The gross results of this analysis are found in Table 24:

Table 24. Trajectory Counts for Edgewood Monitor:

Geographic area Number of Trajectories 

Counted87

Percent of Total

Not Washington CBSA 126 46.32%

Only Frederick (MD), Calvert, 

and/or Charles Co. of 1997 

Washington DC-MD-VA 

nonattainment area

56 20.59%

Washington CBSA except 

Calvert/Charles/Frederick 

Counties in MD

90 33.09%

272

EPA does agree that air masses arriving at the Edgewood monitor on exceedance days can arrive from 

the West-Northwest, from the Northwest, from the Southwest and even from the North and Northeast as 

well as days where the air mass stayed locally – essentially circulated within the CSA boundaries – for a 

24-hour period. 

EPA acknowledges that there are exceedance days when the Edgewood monitor records concentrations 

of 0.087 ppm and higher (as well as days when the concentration is less than 0.087 ppm) and the air 

masses came to Edgewood via the core CBSA counties and cities of the Washington CBSA and the 

southern outer counties/CBSAs (such Calvert, Charles and St. Mary’s), or the westerly outer 

counties/CBSAs (such as the Winchester, VA area or Clarke (VA), Warren (VA) or Jefferson (WV)). 

For instance, on July 3, 2008 (a single day episode), the trajectories at all three levels were from the 

Southwest and arrived via the core CBSA counties and cities of the Washington CBSA and passed 

through Baltimore City before arriving at Edgewood. Yet, he only two monitors in the CSA that 

recorded exceedances were at Edgewood at 0.089 ppm and at Aldino at 0.079 ppm. Likewise, on July

18, 2008 (the second day of a 2-day episode) the back-trajectories suggest Edgewood was directly 

downwind of much of the core CBSA counties and cities of the Washington CBSA and recorded an

 

87

 These counts were made off Figures 4A-1 to 4A-10. Some trajectories may have been missed. Even so, a general sense 

of exceedance day prevailing winds can be inferred overall.
63

exceedance of 0.102 ppm.88 Similarly, on July 23, 2010 (a single day episode), the back-trajectories 

from Edgewood were similar to those on July 3, 2008. The Edgewood monitor recorded an exceedance 

of 0.101 ppm as did the Aldino (at 0.086 ppm) and Essex (at 0.082 ppm) monitors.89 

Examining the back-trajectory results for the Edgewood monitor, EPA does not dispute that the “core 

CBSA counties and cities” of the 1997 Washington DC-MD-VA Nonattainment area is upwind of the 

Baltimore CBSA on many days the 2008 ozone NAAQS is exceeded.90 Likewise, based upon the backtrajectories, EPA cannot exclude the outlying counties of the Baltimore and Washington CBSAs and the 

adjacent CBSAs of Culpeper and Winchester in Virginia and Lexington Park, MD, from further 

consideration regarding contribution. However, based upon the back-trajectories for some days when 

the concentration recorded at the Edgewood monitor was 0.087 ppm or higher, the back-trajectories 

predicted that the bulk of the air did not travel over most portions of the Washington CBSA (excepting 

at times Frederick County, MD) but came from the Northwest, the North-northwest, the North and even 

from the Northeast. Table 25 provides a listing of such days for just 2008 to 2010 alone.

Table 25. Days by Year the Edgewood Monitor is Not Downwind of the 1997 Washington 

DC-MD-VA Nonattainment area:

YEAR

Trajectory Height 2008 2009 2010

Edgewood Monitor: 

100 meters – 22 of 51 

days

4/18, 6/12, 7/16-17 & 

7/28/ 

4/26, 6/25, 7/13 & 

8/27/

5/5, 5/27, 6/2, 6/23, 

6/25, 7/17, 7/31, 7/5-

7/7, 8/19 & 8/30-31

500 meters – 27 of 51 

days

4/18, 6/12, 7/11-12, 

7/16-17 & 7/28 

4/26, 6/5, 6/25-6/26, 

7/13, 8/16 & 

8/27/2009

5/5, 5/21, 5/27, 6/2, 

6/23, 6/25, 7/31, 7/5-

7/7, 8/10, 8/19 & 

8/30-31

At the Edgewood monitor on some of the days with higher ozone readings (“Groups 4 & 5” – measured 

concentration > 0.087 ppm) the HYSPLIT trajectories suggest the winds came from the 1997 

Washington DC-MD-VA Nonattainment area on some days but came from elsewhere on other days. 

Refer to Figures 4A-1 to 4A-5 in Appendix 4. On the “Group 2 and 3” days (between 0.079 through 

0.086 ppm inclusive), the predominant directions seem to be from the South to Southwest, that is, often 

through the Washington CBSA. For other days (“Group 1” < 0.078 ppm) the winds come from a variety

of directions. 

When trajectories end at the Edgewood monitor, these trajectories pass through the “core” (say Fairfax 

County, VA, the District, Prince George’s and Montgomery Counties in Maryland) of the 1997 

Washington DC-MD-VA Nonattainment area, and they also cross Anne Arundel County, Maryland and 

 

88

 The back-trajectories suggest that the Howard University-Beltsville monitor in Prince George’s County, MD was directly 

downwind of the Arlington (VA), Fairfax (VA) and Montgomery (MD) and Prince George’s (MD) Counties as well as the 

District of Columbia; this monitor had an exceedance of 0.097 ppm. 

89

 The difference between the values at Aldino and Essex might be due to Aldino likely being immediately downwind of the 

high emissions areas of Baltimore City and Baltimore County as well as the ore of the Washington CBSA and Howard and/or 

Anne Arundel Counties in Maryland.

90

 As defined by OMB these would be: Montgomery and Prince George's Counties in Maryland; the District of Columbia; 

and, Arlington, Fairfax County, Loudoun, Prince William and (to a lesser extent) Stafford Counties plus the Cities of 

Alexandria, Fairfax, Falls Church, Manassas, and Manassas Park in Virginia. Refer to OMB Bulletin No. 10-02, “Update of 

Statistical Area Definitions and Guidance on Their Uses,” December 1, 2009.
64

skirt the Southeastern fringes of Baltimore City and County or pass through Baltimore City and parts of 

Baltimore County and through Howard County. 

So while the 1997 Washington DC-MD-VA Nonattainment area is often upwind of the Edgewood 

monitor, there are a considerable number of days were this monitor recorded an ozone concentration 

considerably over the NAAQS (say 0.087 ppm or more, i.e., “Groups 4 and 5” days) when the 

trajectories (of any height) did not pass through the 1997 Washington DC-MD-VA Nonattainment area. 

This happened on the following dates: June 7, June 14, July 11 and July 17, 2008; May 5, June 2, June 

25 and 26, July 5 through 7, August 10, August 19 and the period August 29 and 30, 2010. 

For instance, on July 11, 2008 (the first day of a two day episode), the trajectories of the air masses 

arriving at Edgewood did not cross the core CBSA counties/cities of the Washington CBSA but came 

from the Northwest via Washington, Frederick (MD), Carroll, Howard and Baltimore Counties. The 

concentration at Edgewood was 0.100 ppm as well as 0.084 ppm at Essex to the Southwest and 0.079 

ppm at Aldino to the Northeast of Edgewood.

91

 On June 25, 2009 (the first day of 2-day episode), the 

back-trajectories from Edgewood came from the North, and this monitor recorded an exceedance of 

0.109 ppm. The only other exceedances observed that day were 0.079 ppm at Aldino, 0.086 ppm at 

Essex and 0.076 ppm in Calvert County, MD.92 Likewise, on May 27, 2010 (single day episode), the 

back-trajectories from Edgewood came from the Northeast; Edgewood recorded an exceedance of .089 

ppm. For the period July 3 through 7, 2010 (the first 5 days of a 6-day episode), the 100 meter level 

back-trajectories passed through the core CBSA counties and cities of the Washington CBSA before 

arriving at Edgewood on the first two days. On these first two days, the 500 and 1000 meter backtrajectories did not pass through the core CBSA counties and cities of the Washington CBSA because 

they arrived via Harford and/or Baltimore County or via Baltimore City only. For the next three days all 

back-trajectories passed through Harford, Cecil and/or Baltimore Counties before arriving at Edgewood. 

Edgewood recorded the following exceedances (by date from the 3rd to the 7th): 0.082 ppm, 0.090 ppm, 

0.097 ppm, 0.092 ppm and 0.088 pm. EPA believes that it is quite possible or likely that the readings on 

the 5th to the 7th were affected by the return of the ozone precursors emitted at ground level (from under 

100 meters) in the Washington CBSA on the 3rd and the 4th, but higher level winds apparently never 

passed through much of the Washington CBSA on these days. 

These results suggest that the 1997 Washington DC-MD-VA nonattainment area and even the 

Washington CBSA as a whole are upwind of the Edgewood monitor on some days the 2008 ozone 

NAAQS is exceeded at the Edgewood monitor. However, there are a considerable number of days when 

the HYSPLIT back-trajectories crossed no part of the Washington CBSA or just a portion of Fredrick 

County, MD only. This latter result says the Washington CBSA is not the only cause of high levels of 

ozone at the Edgewood monitor.

2. Placement of Anne Arundel and Prince George’s Counties

EPA also examined in some detail back-trajectories for the Davidsonville (AQS ID No. 24-003-0014) 

and Howard University-Beltsville (Howard U-B – AQS ID No 24-033-0030) monitors in Anne Arundel 

and Prince George’s Counties, respectively, in Maryland. 

 

91

 The only other monitor in the CSA recording an exccedance was Davidsonville at 0.076 ppm. The back-trajectories to 

Davidsonville passed through the core of the Washington CBSA.

92

 On June 26, 2009, the back-trajectories ending at Edgewood” were from the west crossing the West Virginia “panhandle”, 

northern Loudoun County, VA, Washington, Frederick, and/or Carroll Counties (MD) and finally as they must Baltimore 

City and/or County. The Edgewood monitor recorded an exceedance of 0.091 ppm while the Aldino monitor recorded an 

exceedance of 0.081 ppm. The only other exceedances recorded in the CSA were at Arlington, VA and the District of 

Columbia each with a maximum of 0.080 ppm.
65

Anne Arundel County:

Figures 6A-1 to 6A-10 of Appendix 6 “HYSPLIT Trajectories for the Davidsonville, Prince George’s 

Equestrian Center and Howard University—Beltsville by Group” show the HYSPLIT results overlaid on 

a map. They are grouped by the “Groups” defined in Table 10 elsewhere in this document. For each 

“Group” there is a map for 2008 to 2010 exceedance days and one for 2006 to 2007 exceedance days. 

The Davidsonville monitor likewise can receive air from many directions on episode days. Given the 

close proximity of Prince George’s, Calvert and Charles Counties to the Davidsonville site, many

trajectories from the Northwest cannot help but graze the northern portion of Prince George’s; likewise, 

when the trajectories are from the South or Southwest, the trajectory may not cross the core of the 1997 

Washington DC-MD-VA nonattainment area but only cross the outlying Calvert and/or Charles 

Counties. Maryland has full ability to regulate these 3 counties regardless of what nonattainment area 

they are placed.

On some days the trajectories could not only skim Prince George’s, Calvert and Charles Counties, but 

they also crossed a portion of the 1997 Baltimore nonattainment area and later the Washington area and 

vice versa.

Analysis of the full set of data for the Davidsonville monitor counted the back-trajectory for each 

altitude for each day. Unlike the analysis for the Edgewood monitor for which a trajectory was placed 

in an exclusive category, a trajectory that passes through both the Washington CBSA and the 1997 

Baltimore nonattainment area was counted twice since both areas were implicated. Thus each 

exceedance day would contribute three or in some case six to the aggregate sum. The categories used 

were “1997 Baltimore nonattainment area” which means no part of the Washington CBSA was crossed 

and some other portion of the 1997 Baltimore nonattainment area except Anne Arundel County was 

crossed;

93 the “Washington CBSA excluding Charles and/or Calvert Counties only” which means that 

no part of the Washington CBSA was crossed except Charles and/or Calvert Counties, “Charles or 

Calvert County only” which means no other part of the Washington CBSA was crossed except one or 

both of these counties, “Prince George’s County only” which means the only portion of the Washington 

CBSA crossed was Prince George’s County and then into the rest of the 1997 Baltimore nonattainment 

area, and “Other” which means no part of a trajectory passes through any portion of the 1997 Baltimore 

nonattainment area (except Anne Arundel County) or the Washington CBSA. The gross results of this 

analysis are found in Table 26.

Table 26. Trajectory Counts for Davidsonville Monitor:94

2008 to 2010 2006 to 2010

Geographic area

Number of 

Trajectories 

Counted

Percent of 

Total

Number of 

Trajectories 

Counted

Percent of 

Total

Washington CBSA excluding 

Charles and/or Calvert Counties 

only

14 19.7% 58 38.6%

 

93

 Given the location of the Davidsonville monitor all trajectories must pass through some portion no matter how short.

94

 These counts were made off Figures 5A-1 to 5A-10. Some trajectories may have been missed. Even so, a general sense 

of exceedance day prevailing winds can be inferred overall.
66

Calvert and/or Charles County

only

2 2.8% 16 10.5%

Prince George’s County only 13 18.3% 7 4.6%

1997 Baltimore nonattainment 

area

40 56.3% 64 42.1%

Other 2 2.8% 11 7.2%

Total 71 166

Over the five years, the data slightly favors the Washington CBSA as being predominantly upwind of 

the Davidsonville monitor though trajectories through Calvert and/or Charles only are passing through 

lower emissions area. Over the last three years, the data more heavily favors the 1997 Baltimore 

nonattainment area as being predominantly upwind of the Davidsonville monitor. 

Of the days with exceedances above 0.078 ppm, the counts are:

Table 27. Trajectory Counts for Davidsonville Monitor – Exceedance Days over 0.078 ppm:95

2008 to 2010 2006 to 2010

Geographic area

Number of 

Trajectories 

Counted

Percent of 

Total

Number of 

Trajectories 

Counted

Percent of 

Total

Washington CBSA excluding 

Charles and/or Calvert Counties 

only

8 18.2% 32 36.4%

Calvert and/or Charles County

only

0 0.0% 11 9.3%

Prince George’s County only 9 20.5% 7 5.9%

1997 Baltimore nonattainment 

area

27 61.4% 44 43.2%

Other 0 0.0% 6 5.1%

Total 118

Review of Figures 6A-4 through 6A-5, and 6A-9 through 6A-10, corresponding to exceedance days of 

0.087 ppm or higher – substantially over 0.075 ppm by over 15 percent – suggest that the Davidsonville 

monitor records its highest exceedances when it is downwind of the 1997 Washington and Baltimore 

nonattainment areas. 

Over the five years, the data slightly favors placement of the Davidsonville monitor with the core of the 

Washington CBSA though trajectories through Calvert and/or Charles only are passing through lower 

emissions area. 

Prince George’s County – Howard-University-Beltsville (Howard U-Beltsville):

For the Howard U-Beltsville monitor the reverse is true. For a preponderance of the days where an 

exceedance of 0.079 ppm or more was recorded, the back-trajectories passed through the core CBSA 

 

95

 These counts were made off Figures 5A-1 to 5A-10. Some trajectories may have been missed. Even so, a general sense 

of exceedance day prevailing winds can be inferred overall.
67

counties and cities of the Washington CBSA as well as at times Calvert, Charles, Frederick and St. 

Mary’s County in Maryland and through Fauquier and other outlying Counties in Virginia. For days 

with an exceedance of 0.078 ppm of less, there was no clear pattern; the trajectories were from various 

directions though none passed through the Baltimore CBSA other than Carroll County. For these 

reasons, based upon reception of ozone and ozone precursors, EPA believes that the Howard University

– Beltsville monitor should be placed in a nonattainment area that includes the core CBSA counties and

city of the Baltimore CBSA. 

Naturally all trajectories must pass through Prince George’s County and thus would count as passing 

through the Washington CBSA. However, some trajectories at some point looped into Prince George’s 

County before traversing the 1997 Baltimore nonattainment area. Some also skimmed the border of 

Montgomery and Howard Counties. The categories used were: (1) “Washington CBSA (except Prince 

George’s County and skims)” which means the trajectory crossed some portion of the Washington 

CBSA (except Prince George’s), did not skim the Montgomery-Howard border, and crossed no portion 

of the 1997 Baltimore nonattainment area; (2) “Direct to 1997 Baltimore nonattainment area” which 

means the trajectory crossed from Prince George’s County into the 1997 Baltimore nonattainment area 

without a loop within Prince George’s; (3) “Loop Prince George’s and Howard;” (4) “Washington plus 

Baltimore” which means the trajectory at some point crossed both the Washington CBSA (except only a 

crossing of Prince George’s County) and the 1997 Baltimore nonattainment area: and (5) “Skimmed 

Montgomery and Howard” which counted those skimming the border of Montgomery and Howard 

Counties and did not cross any other portion of the Washington CBSA (excepting Prince George’s).

The gross results of this analysis are found in Tables 28 and 29.

Table 28. Trajectory Counts for Howard U-Beltsville Monitor:96

2008 to 2010 2006 to 2010

Geographic area

Number of 

Trajectories 

Counted

Percent of 

Total

Number of 

Trajectories

Counted

Percent of 

Total

Washington CBSA (except 

Prince George’s County and 

skims)

35 59.3% 66 65.4%

Loop Prince George’s and 

Howard

3 5.1% 3 2.9%

Skimmed Montgomery and 

Howard

6 10.2% 6 5.9%

Direct to 1997 Baltimore 

nonattainment area

15 25.4% 23 22.8%

Washington plus Baltimore 0 0.0% 3 2.9%

Total 59 101

Table 29. Trajectory Counts for Howard U-Beltsville Monitor – Exceedance Days over 0.078 

ppm:97

2008 to 2010 2006 to 2010

Geographic area Number of Percent of Number of Percent of 

 

96

 These counts were made off Figures 5A-1 to 5A-10. Some trajectories may have been missed. Even so, a general sense 

of exceedance day prevailing winds can be inferred overall.

97

 These counts were made off Figures 5A-1 to 5A-10. Some trajectories may have been missed. Even so, a general sense

of exceedance day prevailing winds can be inferred overall.
68

Trajectories 

Counted

Total Trajectories 

Counted

Total

Washington CBSA (except 

Prince George’s County and 

skims)

34 63.2% 49 69.0%

Loop Prince George’s and 

Howard

3 5.9% 3 4.2%

Skimmed Montgomery and 

Howard

2 5.3% 2 2.8%

Direct to 1997 Baltimore 

nonattainment area

9 23.7% 23 22.8%

Washington plus Baltimore 0 0.0% 3 4.2%

Total 38 71

This monitor is located such that air masses have to pass through the “core” counties and cities of both 

the 1997 Baltimore and Washington nonattainment areas. Most of Prince George’s County lies to the 

south and Southeast, Anne Arundel and/or Howard Counties are immediately east, north and northnorthwest, Montgomery County is northwest, the District is directly to the southwest. 

 For the Howard U-B monitor, for a preponderance of the days where an exceedance of 0.079 ppm or 

more or, of less than 0.078 ppm was recorded, the back-trajectories passed through the Washington 

CBSA. For these reasons, based upon reception of ozone and ozone precursors, EPA believes that the 

Howard University – Beltsville monitor should be placed in a nonattainment area that includes the core 

CBSA counties and city of the Washington CBSA. 

Prince George’s County – Prince George’s Equestrian Center:

For the Prince George’s Equestrian Center (Pr. G. Eq. Ctr.) monitor, the pattern ought to be a mix 

between the situations found at Davidsonville and Howard-U—Beltsville monitors for 2008-2010. 

Because 2006 to 2007 exhibited a different bias towards winds from the south than 2008 to 2010, we 

examined some trajectories for 2006 and 2007, particularly to capture days where Anne Arundel and 

Howard U-Beltsville did not exceed 0.075 ppm. These are displayed on Figures 6A-11 through 6A-14. 

These suggest that the monitor exceeds on days when the winds pass through Prince George’s County

form the Northwest, West, Southwest and then pass through other portions of the 1997 Washington DCMD-VA nonattainment area and other core counties and cities of the Washington CBSA. However, on 

days where it recorded an exceedance of 0.087 ppm or more (“Groups” 4 and 5 days – refer to Figure 

6A-14 in Appendix 6) many trajectories pass through the Baltimore CBSA before turning back and 

passing through either the core of the 1997 Washington Nonattainment area (including the northwest 

portion of Prince George’s itself) or through Charles County. 

Prince George’s County- Conclusion:

The meteorology assessment strongly favors placement of the Howard U-Beltsville monitor in the 

nonattainment area containing the core the Washington CBSA which is the core of the 1997 Washington 

nonattainment area. 

To a lesser extent, the meteorology assessment favors placement of the Prince George’s Equestrian 

Center monitor in the nonattainment area containing the core the Washington CBSA which is the core of 

the 1997 Washington nonattainment area. 
69

Because the Howard U-Beltsville monitor is so strongly linked to the Washington CBSA and because 

the Prince George’s Equestrian Center monitor is also linked to this CBSA more than the 1997 

Baltimore Nonattainment area, the meteorology assessment strongly favors placement of Prince 

George’s County in the nonattainment area containing the core of the Washington CBSA which is also

the core of the 1997 Washington nonattainment area. 

2. Does the current Baltimore MD Nonattainment area contribute to nonattainment in the current 

Washington DC-MD-VA Nonattainment area?

EPA also investigated if the Baltimore CBSA or 1997 nonattainment area also may contribute to the 

monitors in the Washington CBSA namely the McMillan Reservoir (DC), Arlington and Franconia 

(VA) monitors – “the 3-central monitors” in this CBSA. In the previous part of this document, we 

looked at the two monitors in Prince George’s County, MD and concluded that meteorology favors 

placement with the nonattainment area containing the core of the Washington CBSA which is also the 

core of the 1997 Washington nonattainment area. 

Figures 7A-1 to 7A-10 of Appendix 7 “Appendix 7: HYSPLIT Trajectories for Arlington, Franconia & 

McMillan Res. Monitors by Group” show the HYSPLIT results overlaid on a map. They are grouped by

the “Groups” defined in Table 10 elsewhere in this document. For each “Group” there is a map for 2008 

to 2010 exceedance days and one for 2006 to 2007 exceedance days. 

Once again geographic location dictates the sort of trajectories that are possible. The trajectories can be 

placed into 5 categories: (1) on some exceedance days are pretty much straight from the north or 

northeast into Montgomery of Prince George’s Counties before ending at one of the three monitors; (2) 

some sweep through only Anne Arundel County of the 1997 Baltimore Nonattainment area; (3) some 

cross only Howard and/or Carroll Counties in the 1997 Baltimore Nonattainment area; (4) some cross 

over both portions of both the 1997 Baltimore Nonattainment area as well as the 1997 Washington area; 

and, finally, (5) some pass over no part of the Baltimore nonattainment area. Due to the geographic 

location of these monitors, most trajectories that cross some portion of the 1997 Baltimore 

Nonattainment area must also cross the core CBSA counties of Montgomery and Prince George’s in 

Maryland and Fairfax in Virginia as well as the District of Columbia on days where the trajectories run 

straight from Baltimore City to the Arlington and Franconia monitors. 

Note that each of these three monitors did not necessarily record a value in the range for the same group 

on the same days as the others; for example, on “Group 5” days (values >0.091 ppm) all three recorded a

value over 0.092 ppm on 7/17/2008 (0.095, 0.100 and 0.104 ppm) and 7/7/2010 (0.092, 0.095 and 0.100 

ppm) but only two recorded values over 0.092 ppm on 6/12/2008 (0.093 & 0.096 ppm with the 3rd at 

0.085 ppm) and only Franconia recorded a value of 0.091 ppm or more on 8/30/2010 (but the other 

exceeded 0.075 ppm). And note that one monitor might have an exceedance on a day that falls within 

one “Group” while another has an exceedance on the same day that falls into another group. For 

example, on 8/10/2010, Arlington recorded a concentration of 0.088 ppm (in “Group 4”) while 

Franconia recorded a concentration of 0.082 ppm (within “Group 3”). Refer to Table 2A-1. These 

trajectories are presented in Figures 7A-3 and 7A-4 in Appendix7. 

The gross results of this analysis are found in Table 30. Because these monitors may exceed on the 

same days, the gross counts overstate the results. Therefore because there are three monitors the gross 
70

results are divided by three to allow some sort of absolute numbers to numbers comparison with the 

Edgewood monitor and the others discussed in the preceding part of this document.

Table 30. Trajectory Counts for the Franconia, McMillan Res. And Arlington Monitors:98

Category Gross Count Adjusted (Gross/3) Percentage

2006-2010 Data

(1) Straight – Baltimore 80 26.7 18.2%

(2) Anne Arundel County only 28 9.3 6.4%

(3) Howard and Carroll 47 15.7 10.7%

(4) Baltimore and Washington 11 3.7 2.5%

(5) No part of 1997 Baltimore area 266 86.7 60.6%

439 146.3

2008-2010 Data only

(1) Straight – Baltimore 54 18.0 23.8%

(2) Anne Arundel County only 2 0.7 0.9%

(3) Howard and Carroll 38 12.7 16.7%

(4) Baltimore and Washington 8 2.7 3.5%

(5) No part of 1997 Baltimore area 108 36.0 47.6%

227 75.7

Examination of the back-trajectory results for these three monitors in the Washington CBSA, EPA also 

concludes that the “core CBSA counties and city” of the Baltimore CBSA are upwind of these three 

violating monitors in the Washington CBSA. Many of the days for which an exceedance of 0.087 ppm 

or more was recorded at any one (or more) of the monitors in Arlington and Fairfax Counties (VA) and 

the District of Columba, the back-trajectories implicate some portion of the core CBSA counties and city

of the Baltimore CBSA. Of course, air from the core CBSA counties and city of the Baltimore CBSA to 

one of these monitors has to pass through Prince George’s and/or Montgomery Counties in Maryland as 

well.99 

4. Monitors and Counties

Generally:

Examination of available data has shown that every county, the District, and Baltimore City are likely

upwind of one or more violating monitors at times. Examination of the figures in Appendices 5, 6 and 

7, also show that on average the closer a county/city is to a monitor the more likely it has more 

trajectories to that monitor crossing it. 

As for the county or city containing a violating monitor, it has to be designated nonattainment but all 

back-trajectories from that monitor must pass over the county in which a violating monitor is located. 

Of course, size is a factor. Classic examples are those in Prince George’s County, MD: The Howard UBeltsville monitor sees many trajectories from the south cross its north-south axis. Likewise, the Prince 

 

98

 These counts were made off Figures 5A-1 to 5A-10. Some trajectories may have been missed. Even so, a general sense 

of exceedance day prevailing winds can be inferred overall.

99

 And through the District of Columbia most time as well in the case of monitors in Arlington and Fairfax Counties in 

Virginia.
71

George’s Equestrian Center monitor sees many trajectories cross its southern half and many cross its 

north-south axis. 

Some relatively small areas with violating monitors such as that in Arlington County or perhaps even the 

District of Columbia are hard to analyze in this respect. At most the air mass spends a brief period of 

time in the small entity during the period immediately before the air mass reaches the monitor. These 

two monitors are located in a region of high emissions and emissions density. Contribution to ozone at 

these monitors may result from emissions from the larger adjacent areas as well as from mixing from the 

layers of air above the nocturnal inversion and from other long-range transported ozone and precursors.

Carroll Co., MD and Calvert County Maryland:

Examination of the trajectories for surrogate monitors on specific days when either of the Calvert 

County or the South Carroll monitors recorded an exceedance for the period 2008 to 2010 suggest these 

two monitors record exceedances when downwind of the urbanized cores of the 1997 nonattainment 

areas. We ran the HYPLIT for these monitors for 2006 and 2007 once we discerned that the 2006 and 

2007 wind patterns for other monitors showed that the wind patterns for 2008 and 2010 might not 

represent a good sampling of exceedance patterns. The back-trajectories for 2006 and 2007 also suggest 

these two monitors record exceedances when downwind of the urbanized cores of the 1997 

nonattainment areas. For the South Carroll monitor, the principal local upwind areas are the District, 

Montgomery, Howard, Prince George’s, Fairfax, Prince William, Anne Arundel and Charles Counties,

with Frederick and Baltimore Counties plus Baltimore City being occasionally upwind. There can be 

days when the back-trajectories suggest Carroll County is upwind of the CSA; examples included

September 4, 2008. 

For Calvert County, the principal local upwind areas are the Anne Arundel, Howard, Prince George’s, 

Baltimore Counties plus Baltimore City, and to a lesser extent, Carroll County, with the District, 

Harford and Montgomery Counties being occasionally upwind. There can be days when the backtrajectories suggest Calvert County is upwind of the CSA; examples include September 4, 2008. . 

The 2006 and 2007 trajectories are found in Figures 9A-1 and 9A-2 of Appendix 9 to this document.

Outlying Counties:

Figures 9A-3 to 9A-11 show the trajectories crossing counties in various areas. The areas are: (1) the 

western CSA counties and areas of Clarke, Culpeper, Fauquier, Warren in Virginia, of Jefferson and 

Hampshire in West Virginia, and the Frederick County Area in Virginia; (2) Queen Anne’s County, 

MD, (3) St. Mary’s County, MD, and (4) the Fredericksburg area in Virginia. For the first three, there 

are two figures – one with trajectories to violating monitors in the 1997 Washington area and one to 

violating monitors in the 1997 Baltimore area. For the last, the 1997 Washington area has been broken 

into two slides – one for violating monitors in Virginia and one for violating monitors in the District and 

Maryland.

Western CSA counties and areas of Clarke, Culpeper, Fauquier, Warren in Virginia, of Jefferson and 

Hampshire in West Virginia, and the Frederick County Area

Figures 9A-3 to 9A-4 show the trajectories crossing these areas. One cannot directly compare the 

figures directly in that the back-trajectories from the 1997 Washington area represent 5 monitors versus 

two in the 1997 Baltimore area. Figures 9A-3 to 9A-4 suggest that these areas are upwind of both the 

1997 Baltimore and Washington nonattainment areas. However, Figure 9A-3 suggests that Culpeper, 

Fauquier, Warren and Jefferson Counties are more often upwind of monitors in the 1997 Washington 
72

nonattainment area than Clarke and Hampshire Counties and the Frederick County Area in Virginia. 

Figures 9A-1 and 9A-2 suggest these areas are rarely upwind of the monitors in Carroll and Calvert 

Counties.

Queen Anne’s County, MD

Figures 9A-5 to 9A-6 show the trajectories crossing Queen Anne’s. One cannot directly compare the 

figures in that the back-trajectories from the 1997 Washington area represent 5 monitors versus two in 

the 1997 Baltimore area. Figures 9A-5 and 9A-6 suggests that Queen Anne’s County is upwind of 

violating monitors in both the 1997 Baltimore and Washington nonattainment areas. Figures 9A-1 and 

9A-2 suggest Queen Anne’s is rarely upwind of the monitors in Carroll and Calvert Counties.

St. Mary’s County, MD

Figures 9A-5 to 9A-6 show the trajectories crossing St. Mary’s. Comparing Figures 9A-5 and 9A-6 

suggests that St. Mary’s County is more often upwind of violating monitors in the 1997 Baltimore

Nonattainment area because many more trajectories from the two monitors cross the county than those 

from the five monitors in the 1997 Washington Nonattainment area. Figures 9A-1 and 9A-2 suggest St. 

Mary’s is rarely upwind of the monitor in Carroll County; on days when Calvert County receives winds 

from the south, St. Mary’s is likely upwind of Calvert County.

The Fredericksburg area in Virginia

Figures 9A-7 to 9A-9 show the trajectories crossing the Fredericksburg area in Virginia. 

One cannot directly compare Figure 9A-8 to the other two because it represents 3 monitors in the 

District’s and Maryland’s portions of the 1997 Washington area, whereas the other two figures results 

from only two other monitors. Figure 9A-9 is for the Davidsonville and Edgewood monitors the latter 

of which had far more exceedances than any other monitor in the CSA. The other four are comparable 

in number of exceedance days – in the range of 52 to 62. That Figure 9A-9 shows fewer trajectories 

than the other two suggests the Fredericksburg Area is more often upwind of the 1997 Washington 

Nonattainment area. Figures 9A-7 and 9A-8 suggest that when the Fredericksburg Area is upwind of 

these monitors the air mass moves through this area and then to the northwest over the Arlington,

Franconia, McMillan and Howard U-Beltsville monitors in turn. Figures 6A-11 to 6A-14 suggest this 

area is at times upwind of the Prince George’s Equestrian Center monitor as well. Figures 9A-1 and 9A2 suggest this area is rarely upwind of the monitor in Calvert County but is upwind of Carroll County’s 

monitor about one-third of the time. 

Linkage Table for Violating Counties:

Examining the available information, EPA has updated the linkage tables over those used previously.

Table 31. Meteorological Linkages

Location of Violating 

Downwind Receptor 

Monitor

Adjacent Upwind Possible 

Contributing Area(s

Close Upwind Possible Contributing 

Area(s) – Counties, Cities or CBSAs

Harford County Baltimore County, adjacent 

CBSAs in Maryland and 

Pennsylvania.

Baltimore City, Anne Arundel, Howard, 

Montgomery, Prince George’s, 

Fairfax100, Arlington101, Frederick (MD), 

 

100 Wherever Fairfax County is indicated also includes at times Fairfax City and Alexandra City.

101

 Wherever Arlington County is indicated also includes at times Falls Church City
73

The District102, and CBSAs in Delaware, 

Maryland and Pennsylvania adjacent to 

the Washington-Baltimore-NV CSA and 

to a lesser extent, Calvert, Charles, Prince 

William,

103 Loudoun.

Baltimore County Anne Arundel, Carroll, Harford, & 

Howard Counties; Baltimore City; 

and adjacent CBSAs in 

Pennsylvania.

Frederick (MD), Prince George’s and 

Montgomery, Fairfax, Arlington, the 

District, CBSAs in Delaware, Maryland 

and Pennsylvania adjacent to the 

Washington-Baltimore-NV CSA a and to 

a lesser extent, the Calvert, Charles, 

Prince William, Loudoun.

Carroll County Howard and Montgomery

Counties; to a lesser extent,

Baltimore and Frederick, (MD) 

Cos. And Baltimore City.

Arlington, Anne Arundel and Prince 

George’s, Fairfax, the District, County, 

VA. Prince George’s, Fairfax, and 

Charles, and to a lesser extent Loudoun, 

Calvert, Frederick (MD), Prince William, 

and Baltimore Counties plus Baltimore 

City.

Anne Arundel County Baltimore Co., Calvert, Prince 

George's, and Howard.

Fairfax, Charles, the District, Baltimore 

City, Montgomery, and to a lesser extent, 

Loudoun, Prince William, Arlington, and 

Frederick (MD).

Fairfax County, VA Arlington, Charles, Loudoun, 

Montgomery, Prince George’s, the 

District, Alexandria and Fairfax 

Cities and to a lesser extent Prince 

William.

Anne Arundel, Howard, Calvert, Carroll, 

plus Baltimore Co. and City and to a 

lesser extent Frederick (MD), Prince 

William and the Fredericksburg area.

Arlington County, VA Fairfax, the District, and Falls 

Church City.

Anne Arundel, Charles, Howard, 

Loudoun, Montgomery, Calvert, Prince 

George’s, Prince William, Alexandria 

and Fairfax Cities plus Baltimore Co. and 

City and to a lesser extent: Prince 

William, Frederick (MD), and the 

Fredericksburg area.

District of Columbia Montgomery, Prince George's 

Arlington, Fairfax, and, 

Alexandria and Falls Church 

Cities.

Charles, Howard, plus Baltimore Co. and 

City, the Fredericksburg area and to a 

lesser extent: Calvert, Carroll, Prince 

William Loudoun, Frederick (MD)

Prince George’s 

County, MD

District of Columbia, Anne 

Arundel, Charles Fairfax, 

Montgomery, Howard; and to a 

lesser extent:

Calvert.

Arlington, Prince William, Baltimore Co. 

and City, and to a lesser extent: the 

Fredericksburg area, Loudoun, and 

Frederick (MD).

 

102

 Wherever the District is indicated also includes at times Alexandra City.

103 Wherever Prince William County is indicated also includes at times also Manassas and Manassas Park Cities.
74

Calvert County, MD Prince George’s and Anne 

Arundel, and possibly to a lesser 

extent: Saint Mary’s, and Charles.

Baltimore Co. and City, Howard, and to a 

lesser extent: Fairfax, Montgomery, 

Frederick (MD), Carroll, and Harford.

5. Other Meteorological Analyses

Regarding Transport on Larger Scales, the Nocturnal Low Level Jet (NLLJ) the “Bay Breeze” and “Leeside” trough104:

EPA does not disagree with Maryland that transport of ozone and its precursors from other States such 

as those of the Ohio River Valley and Pennsylvania, Virginia, North Carolina and others affects ozone 

levels at monitors in Maryland. As discussed elsewhere in this document, EPA believes that large scale 

transport is to be addressed under other provisions of the CAA and not section 107(d)(1)(A) 

designations. For the reasons discussed in section 3.1.2 of “Responses to Significant Comments on the 

State and Tribal Designation Recommendations for the 2008 Ozone National Ambient Air Quality

Standards (NAAQS),” Docket Number EPA-HQ-OAR-2008-0476, U.S. Environmental Protection 

Agency, April 2012, EPA believes that the CAA requires the nonattainment designation process under 

section 107(d)(1)(A) requires contribution to be of a level sufficient to warrant a nonattainment 

designation and such contribution must be to violating areas that are “nearby;” the longer range transport 

that is not addressed under section 107(a)(1)(A), the CAA prohibits “significant” contribution, not any

contribution.

EPA does not dispute Maryland’s data regarding aloft levels of ozone entering Maryland. However, 

EPA notes that these aloft levels do not seem to be causing violations at ground level ozone monitors 

between Maryland’s borders and most of the States that Maryland has identified: Kentucky, North 

Carolina, Ohio, Michigan, Indiana, West Virginia and others. All monitors in West Virginia are 

currently attaining the 2008 ozone NAAQs. This is based upon the fact that many of these are attaining 

the 2008 ozone NAAQS at this time. Of note are those closest to Maryland such as that in Monongalia, 

Greenbrier and Berkeley Counties as well as those along the Pennsylvania-West Virginia border. The 

monitors in Virginia south of the Washington-Baltimore-NV CSA, in particular those in Frederick, 

Caroline, Loudoun, Fauquier, Stafford, Albemarle, Page, Madison and all in the Richmond, VA CBSA 

are currently attaining the 2008 ozone NAAQS.105 The monitor in Madison County, VA is located on a 

ridge of the mountains within the border of Shenandoah National Park. So are the monitors in Garrett 

and Washington Counties in Maryland. The same is true for all monitors save a couple in Pennsylvania 

located west of the Lancaster, Reading, Allentown-Bethlehem-Easton and Philadelphia-CamdenWilmington CBSAs in Pennsylvania. Most are attaining with the only exceptions are in the Pittsburgh 

area; so are many in Eastern Ohio along the Pennsylvania-Ohio border.106 

Also, on many days that EPA examined by comparing the HYSPLIT back-trajectories and monitored 

ozone concentrations for particular episode days. In addition to the monitors in the CSA, EPA examined 

measured ozone concentrations at three higher elevation monitors near the CSA for 2008-2010 episode 

 

104

 Maryland’s March 7, 2012, letter in response to EPA’s December 9, 2011, letter discussed portions of these topics under 

various factors; EPA is consolidating the responses here.

105

 Richmond had a design value of 0.076 ppm based upon 2008 to 2010 data but because Virginia certified its 2011 data 

early, EPA considered the 2009 to 2011 design value of 0.075 ppm as the most current design value upon which to base a 

attainment/unclassifiable-nonattainment decision. 

106

 Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 from http://www.epa.gov/airtrends/values.html).
75

days. These monitors were the Shenandoah National Park (SNP) monitor (“SNP”) (AQS ID No. 51-

113-0003) located in Madison County, VA, the monitor in Garrett County, Maryland (“Piney Run,” 

AQS ID No. 24-023-0002) and the monitor in Franklin County, PA (“Methodist Hill,” AQS ID No. 42-

055-0001).107 Refer to the data in Table A2-3: Air Quality Data – “Three ‘Higher Elevation Monitors’ 

Episode Days for 2008 through 2010” in Appendix 2. In some cases where our HYSPLIT results 

suggested one or more of these monitors could be upwind of the CSA, EPA did indeed find one of these 

monitors recording an ozone concentration above the 0.075 ppm NAAQS.108 These days were often on 

the second or later day of a multi-day episode. However, EPA found that on other days the measured 

ozone concentrations at one or more of these monitors was 0.010 ppm (10 ppb) below the NAAQS and 

more days where the measured ozone concentrations at one or more of these monitors was well below 

0.065 ppm. 

For instance, on April 18, 2008, the Methodist Hill monitor recorded a 0.074 ppm while both the 

Davidsonville and Edgewood monitors recorded 0.087 and 0.086 ppm, respectively. The SNP monitor 

recorded a concentration of 0.071 ppm on September 2, 2010 and the Methodist Hill monitor a 0.077 

ppm while the Padonia (North of Baltimore) and Edgewood monitors recorded 0.092 and 0.82 ppm, 

respectively.

109

 On the previous day, the Edgewood monitor recorded a 0.090 ppm while the SNP 

monitor recorded only a 0.062 ppm.110 

High levels of ozone at these three higher elevation monitors did not always correspond to the worst 

levels of ozone measured within the CSA. For example, on June 26, 2009, the Edgewood monitor 

recorded a 0.091 ppm; on the same day, the Piney Run and Methodist Hill monitors recorded 0.059 and 

0.047 ppm, respectively. Likewise, on July 23, 2010, the Piney Run monitor recorded a 0.047 ppm 

while the Edgewood monitor recorded 0.101 ppm. Finally, on June 14, 2008, the Piney Run, Methodist 

Hill and SNP monitors recorded 0.041, 0.052 and 0.069 ppm, respectively, while the Edgewood monitor 

recorded 0.093 ppm. 

This data set to correlate the possible “aloft reservoir” with the back-trajectories is limited by the 

number of higher- elevation monitors in close proximity to the CSA. EPA did not attempt to identify

one of these three higher elevation monitors as a good surrogate for each ozone exceedance day within 

the CSA and on a number of days could not do so because the back-trajectories predicted the prevailing 

winds blew from the Northeast for which none of these three higher-elevation monitors could be 

considered an adequate surrogate. Instead, EPA could only examine back-trajectories for a number of 

episodes focusing on those with higher concentrations measured within the CSA or those with higher 

concentrations measured at one of these three higher elevation monitors to gain a sample of what this 

data might reveal. 

 

107

 Maryland identified these three as examples of higher elevation monitors which might provide an indication of the levels 

in an elevated reservoir. Refer to 

http://www.otcair.org/upload/Documents/Meeting%20Materials/ConceptualModel_20090602%20TAD%20FOR%20OTC%

20Final.pdf which Maryland sent to EPA subsequent to their March 7, 2012, response and copy of which has been placed in 

the docket.

108

 EPA did not necessarily require the back-trajectory to cross the county; if one of these three higher elevation monitors 

was between back-trajectories at different elevations or close enough to be a reasonable indicator, EPA considered the data. 

109 The HYSPLIT back-trajectories for the 500 and 1000 meter levels were geographically offset; the 1000 meter trajectory 

was more northerly than the 500 meter one. That the Padonia monitor recorded a higher concentration than Edgewood could 

be due to its location downwind of the heavy emissions areas of Baltimore CBSA core. The Back-trajectories for the 100 

meter level for bth the Howard-University-Beltsville and Edgewood sites indicated a southerly wind in the CSA.

110

 These two days in September 2010 were near the end of a seven-day (8/28 to 9/3/2010) episode.
76

Gradients within the Washington-Baltimore-NV CSA:

EPA examined a number of episodes to determine what sorts of ozone gradients are observed within the 

CSA. EPA examined the back-trajectories to gain some understanding of the prevailing winds on the 

particular episode day and considered the ozone concentrations at all monitors within the violating 

center of the CSA. EPA considered a variety of episodes with emphasis on the longer episodes, those 

with highest ozone readings, and those with the most widespread extent of measured exceedances.111 

Some single day episodes were considered as well, such as July 23, 2010 on which the Edgewood 

monitor recorded 0.101 ppm with only two other monitors in the CSA exceeding at 0.082 ppm. 

EPA considered the peak ozone concentrations at monitors for which the HYSPLIT back-trajectories 

predicted were on the upwind edge of the CSA for that day of the episode and examined the ozone 

concentrations across the CSA. In most instances the monitors on the predicted upwind edge were 

below the 0.075 ppm NAAQS. Sometimes the values were below 0.060 ppm (60 ppb) but at other times 

often between 0.070 and 0.074 ppm (70 to 74 ppb). Lower upwind values often correlated with lower 

peak values and vice versa. For some episodes the HYSPLIT predicted trajectories showed that the 

prevailing winds drastically shifted direct by around 180 degrees. Examples included September 3 and 

4, 2008 and April 18 and 19, 2008 where the winds on the first day were northerly and on the second 

day were predicted to be southerly. On the first day the northern, upwind monitors for the Washington 

CBSA were generally below 0.075 ppm – sometimes well below at 0.053 to 0.068 ppm – and the peak 

values occurred downwind of the core CBSA counties and cities of the Washington CBSA. On the 

second day, the southern monitors were now predicted to be on the upwind edge; these recorded 

exceedances in the 0.076 to 0.081 ppm range. In the Baltimore CBSA, on April 18, 2008, both the 

Aldino and Edgewood monitors recorded values of 0.085-0.086 ppm when on the predicted upwind 

edge; on the second day they recorded lower values – 0.082 ppm at Edgewood and less than 0.075 ppm 

at Aldino. The high values on April 18th when both the Aldino and Edgewood monitors were on the 

predicted upwind edge could be due to these monitors being downwind of the Lancaster and York 

CBSAs. In the September 2008 episode, both were less than 0.065 ppm when on the predicted upwind 

edge, and only Edgewood recorded an exceedance of 0.080 ppm on September 4th. Based upon

examination of the predicted upwind, ground level concentrations, EPA can conclude that incoming 

aloft ozone levels do not seem to cause appreciable numbers of exceedances at monitors located at the 

predicted, upwind edges of the CSA. 

EPA found that often the monitor at the Equestrian Center in Prince George’s County,

112

 the monitors 

in Anne Arundel (Davidsonville), Charles and Calvert Counties record their highest concentrations 

when these monitors are downwind of the core CBSA counties and cities of the Washington and/or 

Baltimore CBSAs. However, on other days, these monitors recorded exceedances when they seemed to 

be on the upwind edge of the CSA, but on these days the exceedances were generally low in the 0.076 to 

0.079 ppm range. The Howard University-Beltsville monitor in Prince George’s County, MD is located 

between the core CBSA counties and cities of the Washington CBSA and the Baltimore CBSA. As 

noted elsewhere, EPA found that for a preponderance of the days where an exceedance of 0.079 ppm or 

more was recorded at the Howard University-Beltsville monitor that trajectories passed through the core 

 

111

 Needless to say, quite often the longest episodes produce the highest concentrations and the widest extent of measured 

exceedances. 

112

 this is located essentially east of the District of Columbia as opposed to the Howard U-Beltsville Monitor in the same 

county which is essentially on a line between Baltimore City and the District; the latter monitor is located near Beltsville,

MD between Interstate 95 and the Baltimore-Washington Parkway.
77

CBSA counties and cities of the Washington CBSA as well as at time Calvert, Charles, Frederick and St. 

Mary’s County in Maryland and through Fauquier and other outlying Counties in Virginia. 

EPA did not expend much effort to determine when the monitors in Fauquier, Prince William and 

Stafford Counties in Virginia recorded high values because the design value at these monitors is 

comfortably below (0.070 ppm or less) the 2008 NAAQS. Likewise, EPA could not discern definitive 

trends for the monitors Frederick and Carroll Counties in Maryland because these monitors did not have 

many exceedances – 10 and 12, respectively, -- in the time period examined. Also, the design values of 

these monitors are barely above the 2008 ozone NAAQS at 0.075 or 0.076 ppm. 

EPA did note that the gradients around the Edgewood monitoring site in Harford County, MD might 

well be steeper on some days than elsewhere in the CSA on high exceedance days. In the Washington 

CBSA plus the Davidsonville monitor in Anne Arundel County that is close to the border of the 

Washington CBSA, steep gradients can also occur. EPA considered these two groups separately for 

several reasons: (1) These two sets of monitors sets are separated by considerable distance between 

being literally at opposite ends of the region of violating monitors in the CSA; (2) Maryland’s 

persuasive evidence that the Edgewood monitor is affected by meteorological-topographical factors in a 

manner different from other monitors in the CSA. These observations were made by comparing the 

concentration of one monitor with those close to the first and computing the difference. The minimum 

difference for each exceedance day examined was noted. The monitors in Harford (Aldino) and 

Baltimore (Essex and Padonia) Counties were considered to be close to the Edgewood monitor. For the 

Washington CBSA plus Davidsonville site, close monitors might include those in the District, Fairfax 

and Arlington Counties in Virginia, those in Prince George’s County, MD plus the Davidsonville 

monitor in Anne Arundel County, MD. For both sets, the difference could be as low as zero or often as 

high as 0.010 to 0.011 ppm. For the Washington CBSA/Davidsonville case, the highest values were 

0.014 ppm. One such day was August 20, 2010; monitors in the District and Arlington County, VA 

recorded concentrations in the range of 0.077 to 0.081 ppm and the Howard university-Beltsville 

monitor, for which the HYSPLIT back-trajectories predicted was immediately upwind, recorded a 

concentration of 0.066 ppm. This value differs from the other two close monitors’ concentrations by

0.011 to 0.015 ppm. Another case was August 30, 2010; The Franconia monitor recorded 0.091 ppm 

while one in the District recorded 0.077 ppm for a difference of 0.014 ppm; on the same day the 

monitors in Calvert and Charles Counties in Maryland recorded 0.098 and 0.087 ppm, respectively. In 

contrast, the Edgewood monitor and on occasion the Essex monitor in Baltimore County, MD record 

similar concentrations that are appreciably higher than other nearby monitors. The highest differences 

are shown in Table 32.

Table 32. Edgewood and Essex Exceptional Gradients 

Date High Monitor Concentration 

(ppm)

Next highest 

Concentration 

(ppm)

At location Difference 

(ppm)

7/11/2008 Edgewood 0.100 0.084 Essex 0.016

6/25/2009 Edgewood 0.109 0.086 Aldino 0.023 

7/6/2010 Edgewood 0.092 0.072 Padonia 0.020

7/6/2010 Essex 0.090 0.072 Padonia 0.018

8/10/2010 Edgewood 0.110 0.086 Padonia 0.024

8/10/2010 Essex 0.115 0.086 Padonia 0.029

8/29/2010 Edgewood 0.096 0.066 Aldino 0.030

On July 6th and August 10, 2010, the HYSPLIT back-trajectories predicted the prevailing winds were 

from the Northwest. Refer to Figures 4a to 4d and 5a to 5d. In which case, any “bay breeze” effect 
78

might well affect the concentrations recorded at the Essex monitor in a manner similar to the Edgewood 

monitor. The Essex monitor is similarly sited to the Edgewood monitor in that it is on a peninsula and 

close to the Chesapeake Bay; however, for winds from the Northwest, the Essex monitor is likely

downwind of more local emissions because it is closer to Baltimore City within the core of the 

Baltimore CBSA. EPA concludes that the greater extremes in concentration gradients around the 

Edgewood monitor than that found in other parts of the CSA could well be an indication that the “Bay 

Breeze” and/or convergence of southwest and the lee-side winds do in fact result in more extreme 

exceedances at the Edgewood monitor (and perhaps the Essex monitor at times) than would be 

otherwise seen.

Maryland’s Modeling Results:

Subsequent to the State’s March 7, 2012 letter Maryland also provided various summaries of the results 

of the OTC modeling, or of Maryland modeling including the results summarized in the State’s March 7, 

2012 letter. These were: 

“Using CMAQ to Evaluate the Impact of the Washington DC Area on the Baltimore Area, 

A Series of Sensitivity Runs to look at Contribution and Culpability, Additional Information for EPA” 

MDE and the UMCP, April 7, 2012

And its attachment “Attachment Baltimore NAA and Maryland Zero Emissions Modeling, and 

Washington DC NAA Only Emissions Modeling Results, Modeling Completed by University of 

Maryland College Park (UMD) for the Maryland Department of the Environment (MDE)”

This document included the same summary information as that in Appendix C of the State’s March 7, 

2012 letter but also included sensitivity analysis for the emissions in the 1997 Washington DC-MD-VA 

Nonattainment area. A copy of these documents have been placed in the docket for this final action.

EPA does not dispute that the 1997 Washington DC-MD-VA Nonattainment area may contribute to 

ozone concentrations in the 1997 Baltimore Nonattainment area. EPA’s own meteorological assessment 

resulted in the same conclusion that the prevailing winds on some ozone exceedance days in Baltimore 

are such that emissions in the 1997 Washington DC-MD-VA Nonattainment area contribute to ozone 

levels in the 1997 Baltimore Nonattainment area. However, the issue is, when considered in light of all 

five factors, whether the 1997 Washington DC-MD-VA and Baltimore nonattainment areas should be 

one area under the 2008 ozone NAAQS. 

Generally, the “Washington DC Area” case, predicts maximum concentrations that are compatible with 

EPA’s HYPLT back-trajectories. EPA and Maryland’s data sets do not match up perfectly; EPA did not 

run the HYSPLIT model for August 5th and 8th due to the low number of exceedances on these two days 

(two at 0.079 ppm on the 5th at an attaining monitor and an outside monitor and none on the 8th). 

Likewise, Maryland did not submit a summary of the results for August 13th, 16th and 17th which were 

likewise days with few exceeding monitors (one at 0.076 ppm on the 13th, one at 0.076 ppm on the 15th, 

and three exceedances (0.080, 0.086 and 0.086 ppm) on the 17th. On August 1st and 4th, the HYSPLIT 

model predicted the prevailing winds were from the Northeast to the Northwest (depending on day and 

altitude). The Maryland “Washington DC NAA” runs predicted the maximum effects south of the 

District in roughly the Southeastern portion of Fairfax County, VA, the Southwest portion of Prince 
79

George’s County, MD and Northern Charles County. Likewise on August 2nd, 3rd, 6th, 12th and 15th, 

which were days when the HYSPLIT model predicted the prevailing winds were from the southwest to 

west-southwest at lower levels (100 and 500 meters), the Maryland model predicted the maximum 

effects for the Washington DC Area (identified as the “only DC” case in Maryland’s submittal) were 

northeast of the District of Columbia along a line between the District and Baltimore City. 

EPA reviewed the information and only has a few comments. On some days the base case modeling 

results suggest widespread non-attainment through the 1997 Washington DC-MD-VA and Baltimore 

Nonattainment areas when in fact the monitors recorded few exceedances. For example, on August 14, 

2007, the results suggested the area of highest concentration was centered on Charles County, MD 

which in fact was where the only exceedance was recorded (a 0.077 ppm). However, for areas just north 

and west of the Charles County’s two Peninsulas, mainly in Fairfax County, VA and Prince George’s 

County, MD the base case results suggest values well above 0.076 ppm (colored red on the map in 

Maryland’s submittal), but the Franconia monitor recorded an 8-hour concentration of 0.071 ppm, and, 

the Prince George’s Equestrian Center monitor recorded a 0.069 ppm. Similarly, on August 3, 2007, the 

base case results predicted high values on a line between roughly the District through northern Prince 

George’s County (near the Howard University-Beltsville site)/Montgomery County, MD (home of the 

Rockville monitor) to Baltimore City and central and North Baltimore County with values much closer 

to 0.095 ppm than 0.076 ppm (colored red to dark red on the map in Maryland’s submittal). In fact, a 

monitor in the District and the one at Rockville, MD both recorded a 0.084 ppm (highest in the CSA); 

the Edgewood and Aldino monitors in Harford County recorded 0.078 and 0.081 ppm, respectively; the 

Howard-University-Beltsville monitor recorded a 0.077 ppm; and, the Padonia and Essex monitors in 

Baltimore County recorded a 0.062 ppm and 0.072 ppm respectively. However, for August 4, 2007, a 

day on which 19 of the current monitors in the CSA recorded exceedances, the base case results 

predicted a wide area of high values. On that day, the Davidsonville and Prince George Equestrian 

Center recorded the highest concentrations at 0.118 and 0.110 ppm, respectively. About 12 monitors 

recorded concentrations at or more than 0.085 ppm. Likewise on 7/7/2007, the base case predicted 

exceedances over a wide portion of the CSA when in fact 12 of the current monitors recorded 

exceedances. EPA acknowledges Maryland noted that for such sensitivity runs the exact ppb 

projections are much less important than the relative (small, medium, large) size and directions of the 

ozone benefit or disbenefit. 

Regarding Maryland’s Modeling Results for July 9, 2007:

Maryland cited research and modeling performed by the University of Maryland (UMD). This includes 

high resolution (0.5 kilometer (km) domain) WRF (meteorological) and CMAQ (photochemical) 

modeling in an effort to learn how the bay breeze dynamics work and if pollution from the Washington 

area is transported towards the Edgewood monitor. This high resolution meteorological modeling shows 

westerly winds transport ozone and ozone precursors from the Washington region to over the bay 

starting in the early morning hours (7 AM). Refer to Figure 3-3 (of the Maryland submittal) for these 

meteorological modeling results of the Maryland submittal. Later in the morning, at around 9 AM 

(EST) meteorological modeling shows winds over the bay become northerly and stagnation in the 

northern end of the Chesapeake Bay causes pollutants to accumulate. Refer to Figure 3-4 (of the 

Maryland submittal) for these meteorological modeling results. High resolution CMAQ modeling 

illustrates how early morning stagnation over the Chesapeake Bay allows high pollution concentrations 

at the bay breeze convergence zone to buildup and then be lofted and transported downwind towards the 

Edgewood monitor. Maryland provided summary results in form of map overlays for the 0.5 km grid 

and coarser grids for July 9, 2007. One such result compared the model-predicted ozone concentrations 
80

to the actual measured values for July 9th for 0.5, 1.5, 4.5 and 13.5 km grid resolutions. The higher the 

resolution (that is, the smaller the grid size) the better the model-predicted values matched the measured 

value near the Edgewood monitor.

EPA acknowledges that Maryland has investigated use of a finer grid around the Edgewood monitoring 

site for modeling ozone concentrations. EPA does not dispute that such modeling shows that emissions 

from the Washington CBSA or portions thereof contribute to concentrations in excess of the 2008 ozone 

NAAQS at the Edgewood monitor. However, using the HYSPLIT model generated back-trajectories, 

EPA has identified around 15 days in the last three years where the HYSPLIT predicted prevailing 

winds did not arrive via the 1997 Washington DC-MD-VA Nonattainment area or even from the 

Washington CBSA at large yet the Edgewood monitor recorded exceedances of 0.082 ppm or higher. 

On around 11 of those days the recorded concentration was 0.087 ppm or higher. The HYSPLIT results 

predict that Chester, Lancaster and York Counties in Pennsylvania, Cecil and Washington Counties in 

Maryland, and New Castle County, DE are upwind on some of such days. All of these counties are part 

of other CBSAs and most are designated nonattainment under the 2008 ozone NAAQS. 

EPA compared the back-trajectories predicted by the HYSPLIT model to the results Maryland submitted 

for July 9, 2007. Refer to Figure 5A-11 in Appendix 5 of this TSD; the July 9, 2007 trajectories are 

specially indicated. The HYSPLIT back-trajectories showed the winds turning from a northwesterly

flow to a flow running to the northeast parallel to the shore of the bay between Anne Arundel County

and the Edgewood monitoring site. The 100 meter back trajectory was closest to the bay and the 1000 

meter trajectory was furthest away with the 500 meter trajectory in between. The recorded 

concentration at the Edgewood monitor on July 9th was 0.0113 ppm which was the highest concentration 

recorded at this monitor in the 5 years 2006 through 2010, inclusive. In the 5 year period 2006 through 

2010, inclusive, the Edgewood monitor has recorded five additional concentrations in excess of 0.100 

ppm. These occurred on August 10, 2010 (0.110 ppm), June 25, 2009 (0.109 ppm), May 30, 2006 

(0.103 ppm), July 18, 2008 (0.102 ppm) and July 23, 2010 (0.101 ppm). The HYSPLIT predicted 15 

back-trajectories for these days of which eight do not pass anywhere near the 1997 Washington-DCMD-VA nonattainment area or the Washington DC-MD-VA-WV CBSA at all. Refer to Figures 5A-11 

and 5A-12 in Appendix 5 of this document. Of the remaining seven back-trajectories, three pass 

through the core CBSA counties and cities of the Washington DC-MD-VA_WV CBSA; two graze 

either the extreme corner of Montgomery or Prince George’s Counties in Maryland and pass through the 

outer counties of either Calvert or Frederick (MD); one starts in Pennsylvania then heads southeast 

through Frederick, Carroll, Howard and Anne Arundel Counties before looping abruptly through Prince 

George’s and finishes in a northeasterly direction via Anne Arundel towards Edgewood, and, the last 

passes in a northeasterly direction through the Winchester Virginia CBSA and the HagerstownMartinsburg MD-WV CBSA and grazes the northwest corner of Frederick County, MD, then arches 

through Adams County, PA, and finishes in a southeasterly direction through Carroll and Baltimore 

Counties. EPA does not dispute that such modeling shows that emissions from the Washington CBSA 

or portions thereof could contribute to concentrations in excess of the 2008 ozone NAAQS at the 

Edgewood monitor. However, EPA’s analyses implicate areas other than portions of the Washington 

DC-MD-VA-WV CBSA or 1997 Washington DC-MD-VA ozone nonattainment area on days when 

particularly high ozone concentrations have been recorded at the Edgewood monitor. EPA cannot 

concur with Maryland’s conclusion that mobile source emissions in the 1997 Washington DC-MD-VA 

ozone nonattainment area or even the Washington DC-MD-VA-WV CBSA are the sole cause of the 

higher ozone concentrations measured at Edgewood based upon the results of a single episode day.
81

4. Notes on Fredericksburg, VA Area, Frederick County, VA Area, and the “other counties:”

The closest monitors to the “outer rim” Virginia and West Virginia counties in the WashingtonBaltimore-NV CSA are attaining the 2008 ozone NAAQS. These “outer rim” counties are the Counties 

of Frederick, Warren, Clarke, and Culpeper and Winchester City in Virginia, and Jefferson County, WV. 

The most relevant attaining monitors are those in Frederick County, MD and in Loudoun, Prince 

William, Fauquier, and Stafford Counties in Virginia. Of these “outer rim” counties, Clarke County, 

VA and Jefferson County, WV are adjacent to Frederick County, MD or Loudoun County, VA, both of 

which contain a monitor with a design value of 0.075 ppm. The monitors attaining the 2008 ozone 

NAAAQS in Frederick County, MD or Loudoun County, VA are located between Clarke County, VA 

and/or Jefferson County, WV, and the violating monitors in Carroll County, MD and/or Fairfax County, 

VA. In contrast, Culpeper County, VA is adjacent to Fauquier County which contains a monitor with a 

design value of 0.070 ppm or lower. Prince William County, VA is interposed between Fauquier, and 

Stafford Counties, and thus between Culpeper County and the violating monitor in Fairfax County. To 

the extent Clarke County, VA and Jefferson County, WV are upwind of the monitors in Frederick 

County, MD or Loudoun County, VA their contribution to air quality in Frederick County, MD or 

Loudoun County, VA does not result in a violation of the 2008 NAAQS. In the case of Culpeper 

County, VA, to the extent it is upwind of the monitors in to Fauquier, Prince William , and Stafford 

Counties Culpeper County’s contribution to air quality in the latter three counties does not result in a 

violation of the 2008 NAAQS. The case of Frederick or Warren Counties and Winchester City in 

Virginia is the same as the case for Clarke County, VA and Jefferson County, WV.

5. Original Wind Roses:

The original wind roses in Factor 3 analysis in “Technical Analysis for the Washington, DC-MD-VA 

and Baltimore Areas” in Docket item numbers EPA-HQ-OAR-2008-0476-0235 are reproduced in 

Appendix 8.

Factor 4: Geography/topography (mountain ranges or other air basin boundaries)

The geography/topography analysis evaluates the physical features of the land that might affect the 

airshed and, therefore, the distribution of ozone over the area.

Warren and Clarke Counties are separated from the rest of the Washington-Baltimore-NV CSA by the 

easternmost portion of the Appalachian Mountains.113 The Frederick County, VA area is west of these 

two counties and thus is also separated from the major, urbanized portions of this CSA by the 

easternmost portion of the Appalachian Mountains. Jefferson County, WV is adjacent to Clarke County, 

VA and also is so separated. 

Other than Warren and Clarke Counties discussed in the preceding paragraph, the WashingtonBaltimore-NV CSA area generally does not have any geographical or topographical barriers appreciably

 

113 Page 3-593 of “Chapter 3 Justifications in Support of EPA's 8-hour Ozone Designations & Classifications” docket item 

EPA-HQ-OAR-2003-0083-1813 in docket EPA-HQ-OAR-2003-0083 (downloaded May 27, 2011) and available on-line at 

Regulations.gov (http://www.regulations.gov/#!home;oldLink=false).
82

limiting air pollution transport within its air shed. Therefore, there are no barriers to transport elsewhere 

in this CSA.

Maryland agreed with the EPA conclusion that the Washington-Baltimore-NV CSA generally does not 

have any barriers appreciably limiting air pollution within its air shed. The Appalachian Mountains are a

barrier to surface transport but not to aloft transport of ozone and ozone precursors.

Maryland states that the following geographical features create meteorological phenomenon that 

function in a role similar to geographical barriers:

(1) The Chesapeake Bay “breeze” plays a role similar to a geographical barrier by preventing pollution 

from blowing out to sea and channeling it back toward the Baltimore area, and especially at the 

Edgewood monitor.

(2) Maryland also said that the position of the Appalachian Mountains enables formation of a 

meteorological phenomenon called a “leeside trough.” According to the American Meteorological 

Association Glossary (2010), a leeside trough is “a pressure trough formed on the lee side [opposite the 

wind] of a mountain range in situations where the wind is blowing with a substantial component across 

the mountain ridge; often seen on United States weather maps east of the Rocky Mountains, and 

sometimes east of the Appalachians.” Maryland said that the leeside trough usually develops over 

Maryland, this phenomenon results in pollutants from the Ohio River Valley and Western PA veering 

(or turning northward) into Maryland and at the same time allows ozone and ozone precursors to be 

transported from Virginia and North Carolina into Maryland too.

(3) Another meteorological phenomenon that results from the location of the Appalachian

Mountains to the west and the Atlantic Ocean to the east is the nocturnal low level jet (NLLJ).

The NNLJ is a fast moving stream of air that is typically observed between the Appalachian Mountains 

and the Atlantic Ocean during the late night and early morning hours. This fast moving stream of air can 

reach speeds of 40 mph and stretches from North Carolina to Maryland and further. 

EPA has considered certain geographical-topological related phenomenon which affects air movements 

under the Factor 3 Meteorology response. EPA acknowledges that the “leeside” trough and the “bay 

breeze” could well act as barriers to air movement and tend to concentrate ozone levels at the Edgewood 

monitor site more than elsewhere. To the extent the “leeside” trough and NLLJ relate to transport from 

other States beyond the scale of intra-CSA or transport from adjacent CBSAs, EPA considers such 

transport to be within the scope of the prohibitions of sections 110(a)(2)(D) and/or 176A. EPA has 

addressed Maryland’s comments in sections 3.1.2 and 3.2.3.1 of “Responses to Significant Comments 

on the State and Tribal Designation Recommendations for the 2008 Ozone National Ambient Air 

Quality Standards (NAAQS),” Docket Number EPA-HQ-OAR-2008-0476, U.S. Environmental 

Protection Agency, April 2012.

EPA has reviewed Maryland’s information on the NLLJ and concludes that by Maryland’s own data –

winds travelling 200 miles overnight – the NLLJ is indicative of long-range transport not to be 

addressed when designating nonattainment areas under section 107(d). 

Factor 5: Jurisdictional boundaries

EPA considers existing jurisdictional boundaries for the purposes of providing a clearly defined legal 

boundary and carrying out the air quality planning and enforcement functions for nonattainment areas. 
83

Examples of jurisdictional boundaries include existing/prior nonattainment areas for ozone or other 

urban-scale pollutants, counties, air districts, townships, metropolitan planning organizations (MPOs), 

state lines, Reservations, urban growth boundary, etc. Where existing jurisdictional boundaries are not 

adequate to describe the nonattainment area, other clearly defined and permanent landmarks or 

geographic coordinates are used. 

For the 1997 ozone NAAQS, the Washington-Baltimore-NV CSA is was broken down as shown in 

Table 33:
84

Table 33. Breakdown of the Washington-Baltimore-NV CSA by Area under the 1997 Ozone 

NAAQS.

Area Name Constituent Counties and Cities: Status (as of November 22, 

2011) (40 CFR 81.309, 81.321, 

81.347 and 81.349)

1997 Baltimore Nonattainment 

Area:

Anne Arundel, Baltimore, 

Carroll, Harford, and Howard 

Counties and Baltimore City in 

Maryland.

Nonattainment - Serious114

1997 Washington DC-MD-VA 

Nonattainment Area:

Maryland Portion: Frederick, 

Montgomery, Calvert, Charles 

and Prince George’s Counties.

The entire District of Columbia.

Virginia Portion: Arlington, 

Fairfax, Loudoun, Prince 

William Counties, and, the Cities 

of Alexandria, Fairfax, Falls 

Church, Manassas, and 

Manassas Park.

Nonattainment - Moderate115

Frederick County, VA Area: Frederick County and 

Winchester City in Virginia.

Attainment

Fredericksburg, VA Area: City of Fredericksburg and 

Spotsylvania and Stafford 

Counties in Virginia.

Attainment (Maintenance)

Queen Anne’s County portion of 

the Kent County and Queen 

Anne’s County Area: 

Queen Anne’s County in 

Maryland

Attainment (Maintenance)

Other Attainment Counties: In Maryland: St. Mary’s County

In Virginia: Clarke, Culpeper, 

Fauquier, and Warren Counties.

In West Virginia: Hampshire 

and Jefferson Counties.

Attainment

Attainment

Attainment

“Attainment (Maintenance)”signifies an area initially designated nonattainment effective June 15, 2004 

(69 FR 23858, April 30, 2004) and later redesignated to attainment subject to a maintenance plan under 

section 175A of the CAA.

“Attainment” signifies an area initially designated attainment effective June 15, 2004 (69 FR 23858, 

April 30, 2004) or April 15, 2008 (73 FR 17897).

 

114

 EPA reclassified the area on February 1, 2012. Refer to 77 FR 4901.

115

 EPA determined that the area attained by its statutory, applicable attainment date and remains in attainment. Refer to 77 

FR 11739, Feb. 28, 2012.
85

The boundaries of the Baltimore severe nonattainment area under the 1-hour ozone NAAQS were the 

same as those for the 1997 ozone NAAQS shown in the preceding table. (56 FR 56694, November 6, 

1991)

The boundaries of the Washington DC-MD-VA severe nonattainment area under the 1-hour ozone 

NAAQS included those shown for the 1997 ozone NAAQS shown in the preceding table plus Stafford 

County, VA (56 FR 56694, November 6, 1991).

Queen Anne’s County in Maryland was part of the Kent County and Queen Anne’s County 1-hour 

attainment (maintenance) area under the 1-hour ozone NAAQS.

All other portions of the Washington-Baltimore-NV CSA were designated attainment for the 1-hour 

ozone NAAQS (56 FR 56694, November 6, 1991).

As far as transportation planning is concerned, the Baltimore and Washington DC-MD-VA 

nonattainment areas are served by different MPOs. The National Capital Region Transportation 

Planning Board (TPB) is the MPO for much of the Washington-Arlington- current Washington DC-MDVA nonattainment area. TPB’s planning area covers the District of Columbia and surrounding 

jurisdictions. In Maryland these jurisdictions include Frederick County, Montgomery County, and 

Prince George’s County and the St. Charles urbanized area of Charles County, plus the cities of Bowie, 

College Park, Frederick, Gaithersburg, Greenbelt, Rockville, and Takoma Park. In Virginia, the 

planning area includes Alexandria, Arlington County, the City of Fairfax, Fairfax County, Falls Church, 

Loudoun County, and the Cities of Manassas and Manassas Park, and Prince William County.

116

The Baltimore Regional Transportation Board consists of 11 members of the Baltimore Regional 

Transportation Board are made up of elected officials from the cities of Annapolis and Baltimore, the 

counties of Anne Arundel, Baltimore, Carroll, Harford and Howard .

117

 

Likewise, the Fredericksburg VA Area is covered by its own MPO – the Fredericksburg Area 

Metropolitan Planning Organization (FAMPO). FAMPO’s region includes the City of Fredericksburg 

and counties of Spotsylvania and Stafford.118

The air quality planning for the Washington DC-MD-VA area has been a multi-jurisdictional area since 

before 1990. Section 107(d)(4)(A) of the CAA set the presumptive boundaries for serious and higher 

classified ozone nonattainment areas at the larger of the CBSA or Consolidated Metropolitan Statistical 

Area (CMSA) area subject to certain alterations allowed by section 107(d)(4)(A). In addition, the 

Metropolitan Washington Air Quality Committee (MWAQC), a multi-state air quality planning 

organization comprised of: (1) elected officials of the Council of Governments (COG) member 

jurisdictions plus members from Charles, Calvert, and Stafford counties; (2) the air management and 

transportation directors of the District of Columbia, Maryland, and Virginia; (3) members of the 

Maryland and Virginia General Assemblies; and (4) the chair of the TPB.

119

 The principal mandates of 

MWAQC are to prepare plans demonstrating attainment of the federal ozone standards and “rate of 

progress” reductions in criteria pollutants and prepare inventories and budgets of emissions for the 

current Washington DC-MD-VA nonattainment area. No other area (nonattainment or otherwise) has 

such a group. Past practice dictates against splitting the relevant portions of the current Washington 

DC-MD-VA nonattainment area along state lines.

 

116 http://www.mwcog.org/transportation/tpb/, last checked November 28, 2011.

117

 “BRTB Members,” http://www.baltometro.org/transportation-planning/brtb-members last checked November 28, 2011.

118

 “About FAMPO,” http://www.fampo.gwregion.org/ last checked November 28, 2011.

119 "BYLAWS of the Metropolitan Washington Air Quality Committee" as amended through October 27, 2004. 

http://www.mwcog.org/environment/air/downloads/MWAQC_bylaws.PDF downloaded November 28, 2011.
86

Summary of the 5-Factor Analysis:

Individual County/City Summaries:

Harford County: Harford County must be designated nonattainment due to the presence of two 

monitors violating the 2008 ozone NAAQS. It contains the monitor with the highest design value within 

the Washington-Baltimore-NV CSA as well as the 1997 Baltimore nonattainment area. Harford County

has total emissions which are neither at the low or high end – it ranks in the middle (that is between 12th

through 23rd inclusive when ranked from largest to smallest) within the Washington-Baltimore-NV 

CSA; likewise, its mobile source emissions are also ranked 11th for both VOC and NOx; its population 

is one tenth of that in the 1997 Baltimore nonattainment area and not exceptionally large or small; its 

population density is half the overall average for the 1997 Baltimore nonattainment area; commuting 

patterns indicate it is linked to the Baltimore CBSA as an outlying county; traffic patterns merit no 

special attention one way or another; meteorology indicates its total emissions may contribute to 

nonattainment in Baltimore County (as well as to its own nonattainment). Meteorology indicates it is 

downwind of Baltimore County, adjacent CBSAs in Maryland and Pennsylvania, Baltimore City, the 

Counties/Cities/States of Anne Arundel, Howard, Montgomery, Prince George’s, Fairfax120, 

Arlington121, Frederick (MD), The District122, and to a lesser extent, the Counties of Calvert, Charles, 

Prince William, Loudoun.

Factors that favor placement of this county in a nonattainment area containing Baltimore County and 

hence as part of a Baltimore Area with the same or similar boundaries as for the 1997 Baltimore 

nonattainment area are jurisdictional boundaries and meteorology which indicates it is often downwind 

of all the other counties in the Baltimore CBSA. It is upwind of other many violating monitors in the 

CSA though rarely that in Carroll county. It is also often downwind of CBSAs in Delaware, Maryland 

and/or Pennsylvania adjacent to the Washington-Baltimore-NV CSA.

Baltimore County: Baltimore County must be designated nonattainment due to the presence of two 

monitors violating the 2008 ozone NAAQS. Baltimore County is among “top six” counties for total 

emissions in the Washington-Baltimore-NV CSA. Its mobile source emissions are ranked 3rd for VOC 

and 2nd for NOx. It is adjacent to Harford County which has the highest design value in the 

Washington-Baltimore-NV CSA and the 1997 Baltimore nonattainment area. It has the highest 

population in the 1997 Baltimore nonattainment area. Its growth rate is well below the WashingtonBaltimore-NV CSA’s average, but equal to the 1997 Baltimore nonattainment area average rate. It has 

the highest VMT within the 1997 Baltimore nonattainment area and third highest within the 

Washington-Baltimore-NV CSA. Its VMT is about one-third the total for the 1997 Baltimore 

nonattainment area and about one-ninth of the total for the Washington-Baltimore-NV CSA. 

Commuting patterns link it to the Baltimore CBSA as a core county. Meteorology indicates it is upwind 

of Harford County’s Edgewood and Anne Arundel’s Davidsonville monitors much of the time and is 

upwind of other monitors in the CSA though rarely that in Carroll County. Meteorology indicates it is 

downwind of Harford County, Baltimore City, and the Counties/Cities/States of Anne Arundel, Howard, 

Montgomery, Prince George’s, Fairfax123, Arlington124, Frederick (MD), The District125, and to a lesser 

 

120 Wherever Fairfax County is indicated also includes at times Fairfax City and Alexandra City.

121

 Wherever Arlington County is indicated also includes at times Falls Church City

122

 Wherever the District is indicated also includes at times Alexandra City.

123 Wherever Fairfax County is indicated also includes at times Fairfax City and Alexandra City.

124

 Wherever Arlington County is indicated also includes at times Falls Church City

125

 Wherever the District is indicated also includes at times Alexandra City.
87

extent, the Counties/Cities/States of Calvert, Charles, Prince William, Loudoun. It is also likely 

downwind of CBSAs in Delaware, Maryland and/or Pennsylvania adjacent to the WashingtonBaltimore-NV CSA. 

Factors that favor placement of Baltimore County in a nonattainment area containing Harford and Anne 

Arundel Counties, that is, as part of the Baltimore Area with the same or similar boundaries as the 1997 

Baltimore nonattainment area, are its total emissions, jurisdictional boundaries, commuting patterns, and 

meteorology which indicates it is upwind of a violating monitors in Harford and Anne Arundel 

Counties. We weigh the factors as supporting placement in a Baltimore Area with the same or similar 

boundaries as the 1997 Baltimore nonattainment area. 

Baltimore City: This city does not have violating monitor. It ranks in the “top six” counties for total 

emissions within the Washington-Baltimore-NV CSA and third (of six) in the 1997 Baltimore 

nonattainment area. Its mobile source emissions are ranked 7th for VOC and 8th for NOx. It is densely

populated, but experienced a population decline over the past 10 years. Its VMT is about one-eighth 

that of the 1997 Baltimore nonattainment area. Meteorology indicates it is upwind of Harford County’s 

Edgewood monitor and likely those in Baltimore County at times and of Anne Arundel’s Davidsonville 

monitor much of the time and is upwind of other monitors in the CSA though rarely that in Carroll 

County. Commuting patterns link it to the Baltimore CBSA as a core county.

Factors that favor designation of Baltimore City as nonattainment based upon contribution are total 

emissions, commuting patterns, jurisdictional boundaries, and possible contribution to Anne Arundel, 

Harford and Baltimore Counties. These factors support placement in a Baltimore Area with the same or 

similar boundaries as the 1997 Baltimore nonattainment area. 

Howard County: Howard County does not have a violating monitor. It ranks in the “top 11” counties 

for total emissions within the Washington-Baltimore-NV CSA and fourth (of six) in the 1997 Baltimore 

nonattainment area. Its mobile source emissions are ranked 8th for VOC and 7th for NOx. It is densely

populated. Its growth rate is about equal to the Washington-Baltimore-NV CSA’s average but over 

twice that for the 1997 Baltimore nonattainment area average. Its VMT is not exceptional. Commuting 

patterns link it to the Baltimore CBSA as a core county.

Meteorology indicates it is upwind of violating monitors throughout the CSA especially those around 

the District-Arlington-Fairfax-Prince George’s Counties/States, those in Anne Arundel, Baltimore and 

Harford Counties and that in Carroll County. 

Meteorology suggests it has about equal influence on nonattainment in the 1997 Baltimore 

nonattainment area and in the 1997 Washington DC-MD-VA nonattainment area. Factors that favor 

designation of Howard County as nonattainment based upon contribution are its total emissions, 

jurisdictional boundaries, and meteorology indicating contribution to violating monitors in Harford, 

Baltimore and Carroll Counties. Factors that favor placement with Prince George’s County and other 

1997 Washington area monitors are its possible contribution. That it is part of the Baltimore-Towson 

CBSA and not the Washington CBSA suggests that it is more linked to the former by commuting and 

hence mobile source emissions. Factors that favor designation of Howard County as nonattainment

based upon contribution are total emissions, commuting patterns, jurisdictional boundaries, and possible 

contribution to Anne Arundel, Harford and Baltimore Counties. These factors support placement in a 

Baltimore Area with the same or similar boundaries as the 1997 Baltimore nonattainment area.
88

Carroll County: Carroll County must be designated nonattainment due to the presence of a monitor 

violating the 2008 ozone NAAQS. It is adjacent to one other county with a violating monitor –

Baltimore County. It has total emissions which are neither at the low or high end – it ranks in the 

middle (12th through 23rd inclusive) within the Washington-Baltimore-NV CSA. Its mobile source 

emissions are ranked 17th for VOC and 18th for NOx. It has the lowest population and population 

density within the 1997 Baltimore nonattainment area with a growth rate less than the WashingtonBaltimore-NV CSA’s average but twice that for the 1997 Baltimore nonattainment area. Likewise, its 

VMT and number of commuters are at the lower end for the Washington-Baltimore-NV CSA and the 

1997 Baltimore nonattainment area. Commuting patterns link it to the Baltimore CBSA as an outlying 

county. That it is part of the Baltimore-Towson CBSA and not the Washington CBSA suggests that it 

is more linked to the former by commuting and hence mobile source emissions. 

Meteorology indicates that it is upwind of the violating monitors in Harford and Baltimore Counties as 

well as violating monitors throughout the CSA, especially those around the Arlington-Fairfax-Prince 

George’s Counties/States, those in Anne Arundel, Baltimore and Harford Counties and to a lesser extent 

the District. It is downwind of the Counties/Cities/States of Howard, Montgomery, Arlington, Anne 

Arundel, Prince George’s, Fairfax, the District of Columbia, and Charles, and, to a lesser extent

Loudoun, Calvert, Frederick (MD), Prince William, and Baltimore Counties plus Baltimore City. 

Its monitor has a design value within 0.001 parts per million (ppm) of attaining the 2008 ozone NAAQS. 

This air quality consideration suggests that the monitor in Carroll County will likely be attaining the 

2008 NAAQS within a few years without further controls and will not be the key monitor needed for 

attainment within the Washington-Baltimore-NV CSA or in an area containing Harford County. Factors 

favoring including it as part of a Baltimore Area with the same or similar boundaries as for the 1997 

NAAQS: (1) jurisdictional boundaries; (2) possible contribution to monitors in the Baltimore CBSA, (3) 

contribution from the Baltimore area; and (4) commuting patterns. Factors favoring inclusion with the 

1997 Washington DC-MD-VA nonattainment area counties are meteorology supporting contribution 

from this area to Carroll County and vice versa. 

The possible contribution to the violating monitor in Carroll County from Anne Arundel, Frederick

(MD), Prince George’s and Montgomery Counties in Maryland is likely more than the possible 

contribution from the closest areas in other States – the District plus Arlington, Fairfax, and Loudoun 

Counties because the total (NOx plus VOC) emissions from these Maryland counties (53,000 – 69,000) 

are somewhat greater that of the out-of-State areas (44,000 – 48,000) and because the Maryland

counties are more proximate. EPA has determined that these out-of-State areas should be designated 

nonattainment, and, to the extent that emissions from these out-of-State areas may contribute ozone 

concentrations in Carroll County, that contribution will be lessened by emission controls already in 

place in those out-of-State areas. Overall the factors support placement in a Baltimore Area with the 

same or similar boundaries as the 1997 Baltimore nonattainment area since placement of Carroll County

will not affect the probable needed controls for attainment at the South Carroll monitor. 

Anne Arundel County: Anne Arundel County must be designated nonattainment due to the presence 

of a monitor violating the 2008 ozone NAAQS. It is among the “top six” in total emissions in the 

Washington-Baltimore-NV CSA and the top two in the 1997 Baltimore nonattainment area. Its mobile 

source emissions are ranked 5th for VOC and 5th for NOx. It is more densely populated than the either 

the average for the Washington-Baltimore-NV CSA or the 1997 Baltimore nonattainment area. Its 

growth rate is less than the Washington-Baltimore-NV CSA’s average but higher than that for the 1997 

Baltimore nonattainment area. Its VMT is about one-fifth the total for the 1997 Baltimore 
89

nonattainment area and about one-thirteenth of the total for the Washington-Baltimore-NV CSA. 

Commuting patterns link it to the Baltimore CBSA as a core county. That it is part of the BaltimoreTowson CBSA and not the Washington CBSA suggests that it is more linked to the former CBSA by

commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of many monitors in the CSA but in particular Edgewood in Harford 

County. Meteorology indicates it is downwind of the Counties/Cities/States of Baltimore Co., Calvert, 

Prince George's, Howard, Fairfax, Charles, the District, Baltimore City, Montgomery, and to a lesser 

extent, Loudoun, Arlington, Prince William, and Frederick (MD). 

Factors that favor inclusion of Anne Arundel County in a nonattainment area based upon contribution 

are its total emissions, jurisdictional boundaries, commuting patterns and meteorology in that it is 

proximate to and a possible contributor to Edgewood in Harford County. Factors that favor inclusion 

with a nonattainment area including the District, Fairfax, Calvert, Arlington and Prince George’s 

Counties are meteorology and total emissions. 

Factors that favor inclusion with Baltimore City and County and Harford County are jurisdictional 

boundaries. Air quality considerations suggest that the monitor in Anne Arundel County might likely be 

attaining the 2008 NAAQS within a few years without further controls and will not be the key monitor 

needed for attainment within the Washington-Baltimore-NV CSA or in an area containing Harford 

County. 

For these reasons, the factors weigh in favor of grouping Anne Arundel County with the rest the 

Baltimore nonattainment area. 

Fairfax County, VA: Fairfax County must be designated nonattainment due to the presence of a 

monitor violating the 2008 ozone NAAQS. It contains the monitor with the second highest design value 

within the Washington-Baltimore-NV CSA as well as the 1997 Washington DC-MD-VA nonattainment 

area. However, its design value is only 0.002 ppm more than other monitors in the District of Columbia 

and Arlington County. The monitors in Arlington and Fairfax Counties and in the District of Columbia 

are clustered in a relatively small area at the core of the Washington-Arlington-Alexandria, DC-VAMD-WV MSA. Fairfax County is among the “top six” counties for total emissions in the WashingtonBaltimore-NV CSA. Its mobile source emissions are ranked 1st for VOC and 1st for NOx. It has the 

highest population in the Washington-Baltimore-NV CSA. Its growth rate is slightly below the 

Washington-Baltimore-NV CSA’s average rate and the 1997 Washington DC-MD-VA nonattainment 

area’s average rate. It has the highest VMT and number of commuters within the 1997 Washington DCMD-VA nonattainment area and highest within the Washington-Baltimore-NV CSA. Its VMT is about 

one-fourth the total for the 1997 Washington DC-MD-VA nonattainment area and one-seventh of the 

total for the Washington-Baltimore-NV CSA. Commuting patterns link it to the Washington CBSA as a 

core county. 

Meteorology indicates it is upwind of violating monitors in Arlington County, VA and the District of 

Columbia and in Prince George’s County as well as those in Anne Arundel, Prince George’s, Baltimore 

and Harford Counties. Meteorology indicates it is downwind of the Counties/Cities/States of 

Arlington, Fairfax City, Loudoun, Alexandria City, Prince George's, Charles, the District, Montgomery, 

Baltimore Co., Calvert, Howard, Baltimore City, and to a lesser extent Frederick (MD), Prince William 

and the Fredericksburg area.
90

Factors that favor inclusion in a nonattainment that includes Arlington County and the District of 

Columbia, that is, as part of a Washington-DC-MD-VA nonattainment area with the same or similar 

boundaries as for the 1997 ozone NAAQS are its total emissions, meteorology, commuting patterns, the 

close proximity of Arlington and Fairfax Counties’ and the District of Columbia’s monitors with design 

values of 0.079 to 0.081 ppm at the Arlington-Fairfax-District core, jurisdictional boundaries and 

Virginia’s recommendation. 

Factors that favor inclusion in a nonattainment that includes Anne Arundel, Harford, and Baltimore 

Counties, that is, as part of a Baltimore nonattainment area with the same or similar boundaries as for 

the 1997 ozone NAAQS, are its total emissions, meteorology,

For these reasons, the factors weigh in favor of inclusion of Fairfax County in a nonattainment area that 

includes Arlington County and the District of Columbia, that is, as part of a Washington-DC-MD-VA 

nonattainment area with the same or similar boundaries as for the 1997 ozone NAAQS

Prince George’s County, MD: Prince George’s County must be designated nonattainment due to the 

presence of two monitors violating the 2008 NAAQS. It is among the “top six” counties for total 

emissions in the Washington-Baltimore-NV CSA and essentially tied for second with Montgomery

County, MD within the 1997 Washington DC-MD-VA nonattainment area. Its mobile source emissions 

are ranked 2nd for VOC and 3rd for NOx. It is more densely populated the either the average for the 

Washington-Baltimore-NV CSA or the 1997 Washington DC-MD-VA nonattainment area. Its growth 

rate is slightly less than that in the Washington-Baltimore-NV CSA and 1997 Washington DC-MD-VA 

nonattainment area averages. It is the third most populous area in the Washington-Baltimore-NV CSA 

and 1997 Washington DC-MD-VA nonattainment area. It has the second highest VMT and third 

highest number of commuters within the Washington-Baltimore-NV CSA. Commuting patterns link it 

to the Washington CBSA as a core county. That it is part of the Washington CBSA and not the 

Baltimore-Towson CBSA suggests that it is more linked to the former CBSA by commuting and hence 

mobile source emissions. Its VMT is about one-fifth the total for the 1997 Washington DC-MD-VA 

nonattainment area and about one-ninth of the total for the Washington-Baltimore-NV CSA. 

Meteorology indicates it is upwind of violating monitors in Calvert, Arlington and Fairfax Counties and 

the District of Columbia as well as those in Anne Arundel, Baltimore and Harford Counties and to a 

lesser extent, Carroll County. 

Meteorology indicates it is downwind of the Counties/Cities/States of Arlington, District of Columbia, 

Anne Arundel, Charles, Fairfax, Montgomery, Howard, Prince William, Baltimore Co. and City, and to 

a lesser extent: Loudoun, Calvert, and Frederick (MD) and the Fredericksburg area.

Meteorology favors including Prince George’s County as part of a nonattainment area with either Anne 

Arundel County or with Fairfax and Arlington Counties plus the District

Factors that favor inclusion in a nonattainment that includes Arlington County and the District of 

Columbia, that is, as part of a Washington-DC-MD-VA nonattainment area with the same or similar 

boundaries as for the 1997 ozone NAAQS, are its jurisdictional boundaries, commuting patterns, total 

emissions, meteorology, and commuting patterns. 
91

Factors that favor inclusion in a nonattainment area that includes Anne Arundel, Harford, and Baltimore 

Counties, that is, as part of a Baltimore nonattainment area with the same or similar boundaries as for 

the 1997 ozone NAAQS are its total emissions, and meteorology.

Therefore, the factors favor grouping Prince George’s County with the Fairfax County, VA and the 

District of Columbia monitors as part of a Washington-DC-MD-VA Area with the same or similar 

boundaries as for the 1997 ozone NAAQS. 

Montgomery County, MD: Montgomery County does not have a violating monitor, but has a monitor 

with a design value of 0.074 ppm. It is among the “top six” counties for total emissions in the 

Washington-Baltimore-NV CSA and essentially tied for second with Prince George’s County, MD 

within the 1997 Washington DC-MD-VA nonattainment area. Its mobile source emissions are ranked 

4th for VOC and 4th for NOx. It is more densely populated the either the average for the WashingtonBaltimore-NV CSA or the 1997 Washington DC-MD-VA nonattainment area. Its growth rate is slightly 

less than the Washington-Baltimore-NV CSA and 1997 Washington DC-MD-VA nonattainment area 

averages. It is the second most populous area in the Washington-Baltimore-NV CSA and 1997 

Washington DC-MD-VA nonattainment area. It has the fourth highest VMT within the WashingtonBaltimore-NV CSA and third highest number of commuters within the Washington-Baltimore-NV CSA. 

Its VMT is about one-sixth the total for the 1997 Washington DC-MD-VA nonattainment area and about 

one-tenth of the total for the Washington-Baltimore-NV CSA. Commuting patterns link it to the 

Washington CBSA as a core county. That it is part of the Washington CBSA and not the BaltimoreTowson CBSA suggests that it is more linked to the former CBSA by commuting and hence mobile 

source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Baltimore, 

Harford, Arlington Fairfax, Calvert, Prince George’s, and Anne Arundel Counties and the District of 

Columbia and to a lesser extent Carroll. The monitor in Carroll County has a design value is within 

0.001 ppm of attaining the 2008 ozone NAAQS. This air quality consideration suggests that the monitor 

in Carroll County will likely be attaining the 2008 NAAQS within a few years without further controls 

and will not be the key monitor needed for attainment within the Washington-Baltimore-NV CSA or in 

an area containing Harford County. 

Factors that favor inclusion in a nonattainment area that includes Arlington County and the District of 

Columbia, that is, as part of a Washington-DC-MD-VA nonattainment area with the same or similar 

boundaries as for the 1997 ozone NAAQS are its jurisdictional boundaries, commuting patterns, total 

emissions, meteorology to some extent, and commuting patterns. 

Factors that favor inclusion in a nonattainment area that includes Anne Arundel, Harford, and Baltimore 

Counties, that is, as part of a Baltimore nonattainment area with the same or similar boundaries as for 

the 1997 ozone NAAQS are its total emissions, and meteorology to a fair extent.

Therefore, the factors favor grouping Prince George’s County with the Fairfax County, VA and the 

District of Columbia monitors as part of a Washington-DC-MD-VA Area with the same or similar 

boundaries as for the 1997 ozone NAAQS. 

Frederick County, MD: Frederick County does not have a violating monitor, but has a monitor with a 

design value of 0.074 ppm. It ranks in the “top 11” counties for total emissions within the WashingtonBaltimore-NV CSA and fifth in the 1997 Washington DC-MD-VA nonattainment area. It is sparsely
92

populated. Its mobile source emissions are ranked 10th for VOC and 9th for NOx. Its growth rate is a 

little more than the 1997 Washington DC-MD-VA nonattainment area average but over 1.5 times that of 

the Washington-Baltimore-NV CSA’s average. Its VMT is not exceptional. Commuting patterns link 

it to the Washington CBSA as an outlying county. That it is part of the Washington CBSA and not the 

Baltimore-Towson CBSA suggests that it is more linked to the former CBSA by commuting and hence 

mobile source emissions.

Meteorology indicates it is upwind of violating monitors in Baltimore and Harford Counties and to a 

lesser extent the Counties/Cities/States of Arlington, Fairfax, Calvert, Prince George’s, Carroll and Anne 

Arundel Counties and the District of Columbia. Meteorology slightly favors for including Frederick 

County as part of a nonattainment area with Baltimore and Harford Counties.

Factors that favor inclusion in a nonattainment area containing Baltimore and Harford Counties are

meteorology and emissions. Factors that favor inclusion with a Washington-DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area are jurisdictional 

boundaries as part of the 1997 Washington DC-MD-VA nonattainment area, and commuting patterns.

Therefore, the factors favor grouping Frederick County, MD with the Fairfax County, VA and the 

District of Columbia monitors as part of a Washington-DC-MD-VA Area with the same or similar 

boundaries as for the 1997 ozone NAAQS. 

Calvert County, MD: Calvert County must be designated nonattainment due to the presence of a 

monitor violating the 2008 ozone NAAQS. It ranks in the “middle group” (between 12th and 23rd

inclusive) for NOx and VOC total emissions within the Washington-Baltimore-NV CSA. Its mobile 

source emissions are ranked 23rd for VOC and 24th for NOx. It has the smallest population of any 

county (and even less than Alexandria City, VA) in the 1997 Washington DC-MD-VA nonattainment 

area (some cities in Virginia are smaller). It has the lowest VMT of any county (but those of most cities 

in Virginia are smaller) within the 1997 Washington DC-MD-VA nonattainment area. Its growth rate is 

one and one half times the Washington-Baltimore-NV CSA’s average but the overall change is low. Its 

population density is low at less than one third that of the 1997 Washington DC-MD-VA nonattainment 

area. Commuting patterns link it to the Washington CBSA as an outlying county. That it is part of the 

Washington CBSA and not the Baltimore-Towson CBSA suggests that it is more linked to the former 

CBSA by commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Arlington, 

Fairfax, and Anne Arundel Counties and to a lesser extent the Counties/Cities/States of Prince 

George’s, Baltimore, Harford, Carroll and the District of Columbia. Meteorology indicates it is 

downwind of the Counties/Cities/States of Prince George’s, Anne Arundel, Baltimore Co. and City, 

Howard, and to a lesser extent: Fairfax, Montgomery, Frederick (MD), Carroll, Harford plus possibly

Saint Mary’s, and Charles. 

Air quality considerations suggest that Calvert and Prince George’s and Anne Arundel Counties will 

attain the 2008 NAAQS within about the same time period without further controls and that none of the 

monitors in these counties will be the key monitor needed for attainment within the WashingtonBaltimore-NV CSA or in an area containing Fairfax County. 
93

Factors that favor inclusion in a nonattainment area containing Anne Arundel or Harford County as part 

of a Baltimore Area with the same or similar boundaries as the 1997 Baltimore nonattainment area are 

meteorology which indicates that at times Calvert County is upwind of Anne Arundel and Harford at 

times. 

Factors that favor inclusion in a nonattainment area containing Prince George’s and Fairfax Counties 

are: meteorology which indicates Calvert County could contribute to and could receive contribution 

from counties which are part of the 1997 Washington-DC-MD-VA nonattainment area, commuting 

patterns and jurisdictional boundaries. 

Therefore, the factors favor grouping Calvert County with the Fairfax County, VA and the District of 

Columbia monitors as part of a Washington-DC-MD-VA Area with the same or similar boundaries as 

for the 1997 ozone NAAQS. 

Charles County, MD: Charles County does not have violating monitor but has a monitor with a 

design value of 0.075 ppm. It ranks in the “middle group” (between 12th and 23rd inclusive) for NOx 

and VOC total emissions within the Washington-Baltimore-NV CSA. Its mobile source emissions are 

ranked 18th for VOC and 19th for NOx. Its population is smaller than any county in the 1997 

Washington DC-MD-VA nonattainment area except Calvert County (but those of cities in Virginia are 

smaller). Its growth rate is around one and one half times both the Washington-Baltimore-NV CSA and 

1997 Washington DC-MD-VA nonattainment area averages but the overall change is lower than any 

other county except Calvert County within the 1997 Washington DC-MD-VA nonattainment area. Its 

population density is low at less than one third that of the 1997 Washington DC-MD-VA nonattainment 

area. It has the lowest VMT of any county except Calvert County (but those of the cities in Virginia are 

smaller) within the 1997 Washington DC-MD-VA nonattainment area. The overall number of 

commuters is but a tiny fraction of that for the 1997 Washington DC-MD-VA nonattainment area. 

Commuting patterns link it to the Washington CBSA as an outlying county. That it is part of the 

Washington CBSA and not the Baltimore-Towson CBSA suggests that it is more linked to the former 

CBSA by commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Arlington, 

Fairfax, Prince George’s, Carroll, and Anne Arundel Counties and the District of Columbia, and, to a 

lesser extent the Counties/Cities/States of Baltimore, and Harford plus possibly Calvert. Air quality

considerations suggest that Calvert, Anne Arundel and Carroll Counties will attain the 2008 NAAQS 

within about the same time period without further controls and that none of the monitors in these 

counties will be the key monitor needed for attainment within the Washington-Baltimore-NV CSA or in 

an area containing Fairfax or Prince George’s County, or, the District. 

Factors that favor inclusion in a nonattainment area containing Anne Arundel, Baltimore and Harford 

Counties are meteorology. Factors that favor inclusion with a Washington-DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area are jurisdictional 

boundaries, and commuting patterns.

Therefore, the factors favor grouping Charles County with a Washington-DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area. 
94

Loudoun County, VA: Loudoun County does not have a violating monitor but has a monitor with a 

design value of 0.075 ppm. It ranks in the “top 11” counties (10th for VOC and 11th for NOx) for total 

emissions within the Washington-Baltimore-NV CSA and ties for sixth (with Frederick County, MD) in 

the 1997 Washington DC-MD-VA nonattainment area. Its mobile source emissions are ranked 15th for 

VOC and 16th for NOx. Its population is near the median for counties in the 1997 Washington DCMD-VA nonattainment area and its density is one-half that of the 1997 Washington DC-MD-VA 

nonattainment area. Its growth rate was 80 percent and the absolute change in population was greater 

than the entire population of all the cities in Virginia except Alexandria and even some of the counties in 

the 1997 Washington DC-MD-VA nonattainment area. Its growth rate is around one and one half times 

both the Washington-Baltimore-NV CSA and 1997 Washington DC-MD-VA nonattainment area 

averages but the overall change is lower than any other county except Calvert County within the 1997 

Washington DC-MD-VA nonattainment area. Commuting patterns link it to the Washington CBSA as a 

core county. That it is part of the Washington CBSA and not the Baltimore-Towson CBSA suggests 

that it is more linked to the former CBSA by commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Arlington and 

Fairfax, and, to a lesser extent the Counties/Cities/States of Baltimore, Prince George’s, Anne Arundel, 

Carroll, and Harford and the District of Columbia. Air quality considerations suggest that Anne Arundel

and Carroll Counties will attain the 2008 NAAQS within about the same time period without further 

controls, and, that none of these monitors in these counties will be the key monitor needed for 

attainment within the Washington-Baltimore-NV CSA or in an area containing Fairfax or Prince 

George’s County, or, the District. 

Factors that favor placement of Loudoun County in a nonattainment area Fairfax and Arlington Counties 

as part of a Washington-DC-MD-VA Area with the same or similar boundaries as the 1997 WashingtonDC-MD-VA nonattainment area are its closer proximity to Fairfax and Arlington Counties, emissions, 

growth rate, commuting patterns, and jurisdictional boundaries.

Factors that favor inclusion of Loudoun County in a nonattainment area containing Anne Arundel, 

Baltimore and Harford Counties are meteorology, emissions, and growth rates. Factors that favor 

inclusion with a Washington-DC-MD-VA Area with the same or similar boundaries as the 1997

Washington-DC-MD-VA nonattainment area are meteorology, are its closer proximity to Fairfax and 

Arlington Counties emissions, Virginia’s recommendation, jurisdictional boundaries, and commuting 

patterns.

Therefore, the factors favor grouping Loudoun County with a Washington DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area. 

Arlington County, VA: Arlington County must be designated nonattainment due to the presence of a 

monitor violating the 2008 ozone NAAQS. Its design value is similar to those in part of the District of 

Columbia and only 0.002 ppm less than that in Fairfax County. These monitors are clustered in a 

relatively small area at the core of the Washington-Arlington-Alexandria, DC-VA-MD-WV MSA. It

ranks high in the “middle group” for total emissions within the Washington-Baltimore-NV CSA. Its 

mobile source emissions are ranked 14th for VOC and 13th for NOx. While its absolute total emissions

and population are not exceptional, its total emissions and population densities are both high which is 

indicative of an urban core area. Population growth was slightly less than the averages for the 

Washington-Baltimore-NV CSA and the 1997 Washington DC-MD-VA nonattainment area. Its VMT 
95

is less than one-twenty-fifth of that even for the 1997 Washington DC-MD-VA nonattainment area. 

Commuting patterns link it to the Washington CBSA as a core county. That it is part of the Washington 

CBSA and not the Baltimore-Towson CBSA suggests that it is more linked to the former CBSA by 

commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Baltimore, 

Prince George’s, Harford, Fairfax and Carroll and the District of Columbia, and, to a lesser extent the 

Counties/Cities/States of Anne Arundel. Meteorology indicates it is downwind of the 

Counties/Cities/States of Fairfax, the District, Falls Church City, Anne Arundel, Charles, Howard, 

Loudoun, Montgomery, Calvert, Prince George’s, Prince William, Alexandria and Fairfax Cities plus 

Baltimore Co. and City and to a lesser extent: Prince William, Frederick (MD), and the Fredericksburg 

area.

The factors somewhat favor a designation of nonattainment based upon contribution: these are its total 

emissions and population densities, meteorological indications of possible interstate contribution to and 

from the District of Columbia, and jurisdictional boundaries.

Factors that favor inclusion of Arlington County in a nonattainment area containing Anne Arundel, 

Baltimore and Harford Counties are meteorology and emissions. 

Factors that favor placement of Arlington County in a nonattainment area with Fairfax County and the 

District as part of a Washington-DC-MD-VA Area with the same or similar boundaries as the 1997

Washington-DC-MD-VA nonattainment area are its closer proximity to Fairfax and Arlington Counties, 

emissions, Virginia’s recommendation, commuting patterns, and jurisdictional boundaries.

Therefore, the factors favor grouping Arlington County with the Washington-DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area. 

Prince William County, VA: Prince William County does not have violating monitor. It ranks in the 

“top 11” counties (8th for VOC and 10th for NOx) for total emissions within the Washington-BaltimoreNV CSA and ties for fourth (VOC) and fifth (NOx) in the 1997 Washington DC-MD-VA nonattainment 

area. Its mobile source emissions are ranked 9th for VOC and 10th for NOx. Its population is fifth 

within the 1997 Washington DC-MD-VA nonattainment area and its population density is a little less 

than that of the 1997 Washington DC-MD-VA nonattainment area. Its growth rate was 42 percent, and, 

the absolute change in population was second highest in the 1997 Washington DC-MD-VA 

nonattainment area. Its VMT is not exceptional. Commuting patterns link it to the Washington CBSA 

as a core county. That it is part of the Washington CBSA and not the Baltimore-Towson CBSA 

suggests that it is more linked to the former CBSA by commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Prince 

George’s, and, to a lesser extent the Counties/Cities/States of Baltimore, Anne Arundel, Harford, 

Fairfax and Carroll and the District of Columbia. 

Factors that favor inclusion of Prince William County in a nonattainment area containing Anne Arundel, 

Baltimore and Harford Counties are meteorology, and emissions. 
96

Factors that favor placement of Prince William County in a nonattainment area with Arlington and 

Fairfax Counties and the District as part of a Washington-DC-MD-VA Area with the same or similar 

boundaries as the 1997 Washington-DC-MD-VA nonattainment area are its closer proximity to Fairfax 

and Arlington Counties, emissions, Virginia’s recommendation, commuting patterns, growth and 

jurisdictional boundaries.

Therefore, the factors favor grouping Prince William County with the Washington-DC-MD-VA Area 

with the same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area. 

Alexandria City, VA: Alexandra City does not have violating monitor. It has total emissions which 

are neither at the low or high end – it ranks in low end (21st VOC and 20th NOx) of the middle (12th

through 23rd inclusive) within the Washington-Baltimore-NV CSA. Its mobile source emissions are 

ranked 25th for VOC and 25th for NOx. Its population is not exceptional, but it is densely populated –

about 7 times the 1997 Washington DC-MD-VA nonattainment area average. Its growth was less than 

the 1997 Washington DC-MD-VA nonattainment area average. Its VMT is not exceptional. Its 

emission densities are high. Commuting patterns link it to the Washington CBSA as a core city. That it 

is part of the Washington CBSA and not the Baltimore-Towson CBSA suggests that it is more linked to 

the former CBSA by commuting and hence mobile source emissions. 

Meteorology indicates this city is likely upwind of violating monitors in the same counties and the 

District as the District of Columbia Arlington County and perhaps Fairfax County.

The factors favor a designation of nonattainment based upon contribution: these are possible 

contribution to the monitors in Arlington, Fairfax and Prince George’s Counties and the District of 

Columbia, total emissions and population densities, commuting patterns, Virginia’s recommendation 

and jurisdictional boundaries. While it may possibly contribute to monitors in Anne Arundel, Harford 

and other Counties, its close proximity and high emissions densities favor merging for boundaries 

purposes with the surrounding jurisdictions of Fairfax County and the District of Columbia.

The factors favor placing this county in the same nonattainment area as Fairfax and Arlington Counties 

and the District of Columbia. Factors favoring this placement are jurisdictional boundaries, commuting 

patterns, possible contribution to Fairfax and Arlington Counties, and Virginia’s recommendation. No 

factors compel placement in a different nonattainment area. 

Fairfax, Manassas, Manassas Park, and Falls Church Cities, VA: Fairfax, Manassas, Manassas 

Park, and Falls Church Cities do not have a monitor. Fairfax and Falls Church Cities are in close 

proximity to the violating monitors in Fairfax and Arlington Counties. All are small – ten square miles 

or less (for comparison: Alexandria City is 26, the District of Columbia is over 60 and Frederick 

County, MD the largest is over 650 square miles). Generally all have low absolute total emissions, 

VMT, and number of commuters. All are ranked 29th or lower for mobile source emissions. All are 

densely populated with a density just under 3 to 7 times the overall CSA density. The total emissions

densities are high which is likely typical for urban core areas. Their total emissions and population 

densities are comparable to or higher than the adjacent/surrounding counties and thus these cities are 

indistinguishable from these adjacent/surrounding counties. Commuting patterns link it to the 

Washington CBSA as a core city. That it is part of the Washington CBSA and not the BaltimoreTowson CBSA suggests that it is more linked to the former CBSA by commuting and hence mobile 

source emissions. 
97

Meteorology indicates these cities are likely upwind of violating monitors in the same counties and the 

District as the applicable adjacent/enclosing jurisdictions – the District of Columbia, Arlington, Fairfax 

and/or Prince George’s Counties. While each of these may possibly contribute to many monitors in the 

CSA, their close proximities and high emissions densities favor merging for boundaries purposes with 

the enclosing/adjacent jurisdictions of the District of Columbia, Arlington, Fairfax and/or Prince 

George’s Counties.

The factors that favor designation of nonattainment for contribution are mainly their total emissions

densities, commuting patterns, jurisdictional boundaries, Virginia’s recommendations and population 

densities which are comparable to or higher than the adjacent/surrounding counties. Fairfax City should 

be in a nonattainment area that includes Fairfax and Arlington Counties and the District of Columbia as 

part of a Washington-DC-MD-VA Area with the same or similar boundaries as the 1997 WashingtonDC-MD-VA nonattainment area. Falls Church City should be in a nonattainment area that includes 

Fairfax and Arlington Counties and the District of Columbia, for the same reasons as for Arlington and 

Fairfax Counties between which Falls Church is located. Manassas and Manassas Park Cities should be 

in the same nonattainment area as Fairfax and Arlington Counties for the same reasons as for Prince 

William County, which encloses both.

The District of Columbia: The District of Columbia must be designated nonattainment due to the 

presence of monitors violating the 2008 ozone NAAQS. Its design value is similar to those in part of the 

Arlington County and only 0.002 ppm less than that in Fairfax County. These monitors are clustered in 

a relatively small area at the core of the Washington-Arlington-Alexandria, DC-VA-MD-WV MSA. It 

ranks in the “top 11” counties (at 7th for both NOx and VOC) for total emissions within the WashingtonBaltimore-NV CSA and fourth in the 1997 Washington DC-MD-VA nonattainment area. Its mobile 

source emissions are ranked 6th for VOC and 6th for NOx. It is densely populated (8 times the average 

for the 1997 Washington DC-MD-VA nonattainment area) and has the sixth highest population within 

the Washington-Baltimore-NV CSA and the fourth within the 1997 Washington DC-MD-VA 

nonattainment area. Its growth rate is well less than – about one-third – of the 1997 Washington DCMD-VA nonattainment area and CSA averages. Its VMT is not exceptional at one-twelfth that of the 

1997 Washington DC-MD-VA nonattainment area. Commuting patterns link it to the Washington 

CBSA as a core city. That it is part of the Washington CBSA and not the Baltimore-Towson CBSA 

suggests that it is more linked to the former CBSA by commuting and hence mobile source emissions. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Prince 

George’s, Baltimore, Anne Arundel, Harford, Fairfax and Carroll. Meteorology indicates it is

downwind of the Counties/Cities/States of Montgomery, Prince George's Arlington, Fairfax, Charles, 

Howard, plus Baltimore Co. and City, the Fredericksburg area and Alexandria and Falls Church Cities,

and, to a lesser extent: Calvert, Carroll, Prince William Loudoun, and Frederick (MD).

The District of Columbia’s initial recommendation was for nonattainment. The District of Columbia’s 

analysis suggested that its total emissions were a small (7% NOx and 9% VOC) part of those in the 1997 

Washington DC-MD-VA nonattainment area and suggested the need for additional controls on on-road 

and off-road mobile and disperse area sources and stricter controls on large industrial sources and power 

plants to curtail transported pollution. At this point in the designation process, EPA does not disagree 

with the District of Columbia that an appreciable part of the air quality problem within the District of 

Columbia is due to total emissions outside its borders. This decision is based in part upon the District of 

Columbia’s evaluation and in part upon EPA’s evaluation contained within this document. The District 

of Columbia is surrounded by three of the “top six” counties for total emissions in the Washington-
98

Baltimore-NV CSA. These are: Fairfax County, VA (4th NOx, 1st VOC); Montgomery County, MD (5th

NOX, 2nd VOC); and Prince George’s County, MD (3rd for NOx and VOC). These three counties 

comprise the top three within the 1997 Washington DC-MD-VA nonattainment area. The District is a 

densely populated area at the core of the Washington-Arlington-Alexandria, DC-VA-MD-WV CBSA. 

The District’s mobile source emissions rank 6th (for both NOx and VOC) overall in the CSA. Around 

the District are three of the top five jurisdictions in the CSA for mobile source emissions – Fairfax, 

Montgomery and Prince George’s Counties. 

The factors that favor the placement of the District of Columbia in the same nonattainment area as 

Prince George’s, Fairfax and Arlington Counties as part of a Washington-DC-MD-VA Area with the 

same or similar boundaries as the 1997 Washington-DC-MD-VA nonattainment area are: jurisdictional 

boundaries; commuting patterns; meteorological indications of possible contribution to and from the 

District of Columbia and counties in the 1997 Washington-DC-MD-VA nonattainment area; and the 

close proximity of violating monitors in Arlington, Prince George’s and Fairfax Counties as well as the 

District of Columbia’s monitors with design values of 0.079 to 0.081 ppm at the Arlington-FairfaxDistrict core. Likewise, the high emissions in surrounding areas favor the placement of the District of 

Columbia in the same nonattainment area as Prince George’s, Fairfax and Arlington Counties as part of 

a Washington-DC-MD-VA Area with the same or similar boundaries as the 1997 Washington-DC-MDVA nonattainment area. No factors compel placement in a different nonattainment area. 

The Frederick County, VA Area (Frederick County and Winchester City in Virginia)

This area does not have a violating monitor, but has a monitor with a design value of 0.070 ppm. In 

total, this area has aggregate total emissions about equal to Arlington County, VA for NOx and less than 

Frederick County, MD for VOC. As such, the area would rank 13th VOC and 15th NOx within the 

Washington-Baltimore-NV CSA. Likewise, the total area’s mobile source emissions would rank 13

th for 

VOC and 18th for NOx. Individually each city/county in this area ranks lower. The total population is 

less than Alexandria City and would exceed only Calvert County, MD (and the other cities in Virginia). 

The growth rate was not quite twice the Washington-Baltimore-NV CSA average but the absolute 

change is less than most counties in the Washington-Baltimore-NV CSA. Total VMT is less than 

Alexandria City. The area is separated from the main parts of the Washington-Baltimore-NV CSA by

the easternmost portion of the Appalachian Mountains. The area is not adjacent to any county with a 

violating monitor. Meteorology suggest this area is upwind of violating monitors within the CSA but 

the closest monitors are attaining the 2008 ozone NAAQS. Available meteorological information does 

not favor 1997 Baltimore or 1997 Washington nonattainment areas. Commuting patterns indicate that 

this area is a separate CBSA thus has less interchange with the Washington CBSA than adjacent 

counties within the Washington CBSA have with the core of the Washington CBSA. The geographic 

remoteness, middling emissions, jurisdictional boundaries and Virginia’s recommendation are factors 

favoring a designation as “unclassifiable/attainment” due to the remoteness of this area from violating 

monitors and its low population density, and the presence of a monitor attaining the 2008 ozone 

NAAQS. 

Fredericksburg, VA Area (City of Fredericksburg, Spotsylvania and Stafford Counties) 

Stafford County does not have violating monitor but has a monitor with a design value of 0.070 ppm. 

For total emissions, Spotsylvania and Stafford Counties rank between 15th and 19th for total emissions –

within the “middle group” (between 12th and 23rd inclusive) – within the Washington-Baltimore-NV 

CSA. As for mobile source emissions, Spotsylvania is ranked 12th for VOC and 12th for NOx, and, 

Stafford is ranked 13th for VOC and 14th for NOx. Their populations, VMT and number of commuters 

are not exceptional. They are relatively sparely populated, having a population density less than even 
99

the Washington-Baltimore-NV CSA average. In total the Fredericksburg, VA Area would have total 

emissions about equal to Prince William County, VA, a population less than Loudoun County, VA, an 

absolute population growth between Montgomery and Prince George's Counties in Maryland, VMT 

about 110 percent of Prince William’s. Commuting patterns link it to the Washington CBSA as: a core 

county n the case of Stafford County; and as outlying city/county in the case of Spotsylvania and 

Fredericksburg City. 

Meteorology indicates it is upwind of violating monitors in the Counties/Cities/States of Fairfax, 

Arlington and the District of Columbia as well as the Counties/Cities/States of Prince George’s 

Baltimore, Anne Arundel, and, Harford,. 

Meteorology indicates that the Fredericksburg, VA Area is upwind of violating monitors in Arlington 

County, VA about 22 percent of the time and of the monitor in Prince George’s County, MD about 18 

percent of the time. Meteorology and total emissions indicate the possibility of contribution to 

Arlington and Prince George’s Counties. However, as the tip of the Fredericksburg, VA Area closest to 

violating monitors in the Washington-Baltimore-NV CSA, Stafford County is more remote from these 

violating monitors than Charles County, MD or Prince William County, VA over which total emissions

from Stafford County have to travel to reach a violating monitor. Charles County, MD or Prince 

William County, VA are adjacent to Stafford County and are attaining the 2008 ozone NAAQS. 

The factors that favor designation of “unclassifiable/attainment” would seem to outweigh those for 

another designation are: the better than the NAAQS air quality in Stafford County, this area’s lack of 

close proximity to areas with a violating monitor, jurisdictional boundaries and Virginia’s 

recommendations. 

Queen Anne’s County, MD: Queen Anne’s County does not have violating monitor. For total 

emissions it ranks at the bottom (23rd for both NOx and VOC) within the “middle group” (between 12th

and 23rd inclusive) within the Washington-Baltimore-NV CSA. Its mobile source emissions are ranked 

20th for VOC and 17th for NOx. Its population is low – about one fourth of the county within the 1997 

Baltimore MD nonattainment area (Carroll Co.) with the lowest population. Its growth rate is about 

three times that of the 1997 Baltimore MD nonattainment area, but the absolute change is less than half 

that of Carroll County, MD. Its VMT is low and less than that of even Carroll County, MD. 

Commuting patterns link it to the Baltimore CBSA as an outlying county. 

Meteorology indicates it is upwind of violating monitors in both the 1997 Baltimore and Washington 

nonattainment areas. 

This county is in the OTR and is subject to Maryland’s enhanced I/M program. 

The meteorology favors designation as nonattainment based upon contribution, and, the total emissions

related factors are not compelling for a nonattainment designation given that the county is in the OTR, 

the low emissions related factors and given the limited access for commuting to the rest of the 

Washington-Baltimore-NV CSA. The jurisdictional boundaries factor would seem to favor designation 

of “unclassifiable/attainment” and outweigh factors favoring a nonattainment designation. The factors 

favor a designation of “attainment/unclassifiable” would seem to outweigh those for another 

designation.
100

St. Mary’s County: St. Mary’s County does not have violating monitor. For total emissions it ranks 

16th VOC and 17th NOx– within the “middle group” (between 12th and 23rd inclusive) of the 

Washington-Baltimore-NV CSA. Its mobile source emissions are ranked 19th for VOC and 21st for 

NOx. Its population is lower than all other jurisdictions within the 1997 Washington DC-MD-VA 

nonattainment area. Its growth rate is about one and one-half times that of the 1997 Washington DCMD-VA nonattainment area, but the absolute change is less than half that of Carroll County, MD. Its 

VMT is low and less than that of Alexandria City and less than one and one-half times that of Calvert 

County. Commuting patterns indicate that this area is a separate CBSA thus has less interchange with 

the Washington CBSA than adjacent counties within the Washington CBSA have with the core of the 

Washington CBSA. 

Meteorology indicates St. Mary’s County is upwind of violating monitors in both the 1997 Baltimore 

and Washington nonattainment areas and suggests that it is more often upwind of violating monitors in 

the 1997 Baltimore nonattainment area. 

St. Mary’s County is in the OTR. Its total emissions related factors are not compelling for a 

nonattainment designation given that the county is in the OTR. Its possible contributions to 

nonattainment at the Edgewood monitor are solely intrastate. Because this possible contribution to 

violating monitors involves only intrastate contribution, Maryland will primarily be responsible for 

mitigating any such intrastate contribution. 

The low emissions-related factors and that of jurisdictional boundaries favor an “unclassifiable

/attainment” designation. 

Fauquier County, VA: Fauquier County does not have violating monitor but has a monitor with a 

design value of 0.065 ppm. For total emissions it ranks 15th VOC and 20th NOx within the WashingtonBaltimore-NV CSA – within the “middle group” (between 12th and 23rd inclusive). Its mobile source 

emissions are ranked 16th for VOC and 15th for NOx. Its population is low, and, it is sparely populated. 

Its growth rate was about one and one-half times that of the Washington-Baltimore-NV CSA as a whole, 

but the absolute change is low. Its VMT is low in comparison to most other areas within the 1997 

Washington DC-MD-VA nonattainment area. Only 27 percent of its commuters travel into an area with 

a violating monitor. 

Meteorology indicates it is upwind of violating monitors in both the 1997 Baltimore and Washington 

nonattainment areas. 

Factors that favor designation as nonattainment for contribution are possible contribution to Fairfax and 

Arlington Counties. Factors that favor designation as “unclassifiable/attainment” are Virginia’s 

recommendation (possible contribution to the closest violating monitors is intrastate), low population, 

jurisdictional boundaries, and the presence of a monitor attaining the 2008 NAAQS in Fauquier, 

Stafford and Prince William Counties. The factors that favor designation as “unclassifiable/attainment” 

seem to outweigh factors for a nonattainment designation.

Culpeper, Clarke, and Warren Counties in Virginia and Hampshire and Jefferson Counties in 

West Virginia: None of these counties have a violating monitor. Both states recommended that these 

counties within their State be designated attainment. For total emissions, each ranks 24th or lower in the 

Washington-Baltimore-NV CSA. Culpeper’s mobile source emissions are ranked 21st for VOC and 

23rd for NOx AND Warren’s rank 24th and 22nd. The West Virginia Counties each rank far lower 27th
101

or less. The population of each is low, and, each is sparely populated. The VMT of each is low. For all 

but Jefferson County, the total number of commuters is less than that of Manassas City. The total 

number of commuters in Jefferson County is not appreciably greater than that of Manassas City (20,937 

versus 18,077, respectively). The total emissions of each are 1 percent or less than the total for the 

Washington-Baltimore-NV CSA. Commuting patterns link Culpeper, Clarke, Jefferson and Warren 

Counties to the Washington CBSA as outlying counties. Commuting patterns link Hampshire County to 

the Winchester VA, CBSA as an outlying county. Because the Winchester , VA CBSA is a separate 

CBSA form the Washington and Baltimore-Towson CBSAs Hampshire has less interchange with the 

Washington CBSA than adjacent counties within the Washington CBSA have with the core of the 

Washington CBSA. Some of these counties separated from the main parts of the WashingtonBaltimore-NV CSA by the easternmost portion of the Appalachian Mountains.

These “outer rim” counties in the Washington-Baltimore-NV CSA in Virginia and West Virginia are 

closest to attaining monitors to the extent they are upwind of any monitors in the WashingtonBaltimore-NV CSA. These “outer rim” areas are the Counties of Frederick, Warren, Clarke, and 

Culpeper and Winchester City in Virginia, Jefferson County, WV. The relevant attaining monitors are 

those in Frederick County, MD and in Loudoun, Prince William, Fauquier, and Stafford Counties in 

Virginia. Of these “outer rim” counties, Clarke County, VA and Jefferson County, WV are the ones 

more likely to sufficient contribute to a violating monitor because the closest monitors within the 

Washington-Baltimore-NV CSA just attain the 2008 ozone NAAQS. No factors would seem to support 

designation as nonattainment; the factors that favor designation as “attainment/unclassifiable” are the 

States’ recommendations, remoteness from violating monitors, low total emissions related factors, and 

jurisdictional boundaries.

Nonattainment Areas:

As discussed above, EPA has determined that certain counties/cities can be formed into a Baltimore, 

MD nonattainment area consisting of Anne Arundel, Baltimore, Carroll, Harford, and Howard Counties 

and Baltimore City in Maryland and, that certain counties/cities can be formed into a Washington, DCMD-VA nonattainment area consisting of: 

The Counties of Frederick, Montgomery, Calvert, Charles, and Prince George’s in Maryland; 

The entire District of Columbia; and,

The Counties of Arlington, Fairfax, Loudoun, and Prince William and the Cities of Alexandria, 

Fairfax, Falls Church, Manassas, and Manassas Park in Virginia.

One area or two:

As discussed under Factor 3, EPA believes that the Edgewood monitor could well be affected on a 

substantial number of days by emissions in CBSAs adjacent to the Washington-Baltimore-NV CSA in 

Pennsylvania, Delaware and even Maryland as well as by emissions in the Washington, DC-MA-VA 

nonattainment area under the 2008 ozone NAAQS. Likewise, EPA does not discount the effects of 

mobile source emissions throughout the Washington-Baltimore-NV CSA but can conclude that the 

majority of these are in Maryland and that the mobile source emissions in the Washington, DC-MD-VA 

nonattainment area are not the sole cause of high exceedances at the Edgewood monitor. Mobile source 

emissions will decline throughout the CSA and the other nonattainment and attainment areas 

surrounding this CSA. Numerous EPA regulations for new motor vehicles and other on-road and non-
102

road mobile source engines will continue to produce reductions in ozone and ozone precursors before 

the Baltimore area’s attainment date. See, 77 FR 8197 at 8202, February 14, 2012. As Maryland noted, 

States have limited ability to regulate mobile source emissions.126 EPA sees little reason to designate 

areas nonattainment due solely to emissions sources which will decline substantially due to already 

promulgated Federal rules and which the States involved will have little ability to regulate. 

As for the CBSAs adjacent to the Washington-Baltimore-NV CSA in Pennsylvania, Delaware and even 

Maryland, these are in the ozone transport region (OTR) formed under section 184 of the CAA. The 

Washington, DC-MD-VA ozone nonattainment area and Stafford County, VA is also in the OTR and 

thus is subject to the same minimum section 184 requirements which include reasonably available 

control technology requirements, enhanced vehicle inspection and maintenance programs, and major 

source permitting requirements at least as stringent as an area classified as moderate nonattainment as 

these other CBSAs. 

EPA therefore concludes that there would be limited benefit in combining Baltimore, MD nonattainment 

area and the Washington, DC-MD-VA nonattainment area to address mobile source emissions in the 

Washington CBSA that would not offset consideration of jurisdictional boundaries by involving 

additional MPOs in the Baltimore, ND area planning process.

EPA has determined that it is appropriate to keep two nonattainment areas in this CSA. 

Conclusions:

Based on the assessment of factors described above, EPA has concluded that the following counties and 

independent cities listed below meet the CAA criteria for inclusion in the two nonattainment areas 

indicated below:

A Baltimore, MD nonattainment area consisting of Anne Arundel, Baltimore, Carroll, Harford, and 

Howard Counties and Baltimore City in Maryland.

A Washington, DC-MD-VA nonattainment area consisting of: 

The Counties of Frederick, Montgomery, Calvert, Charles, and Prince George’s in Maryland; 

The entire District of Columbia; and,

The Counties of Arlington, Fairfax, Loudoun, and Prince William and the Cities of Alexandria, 

Fairfax, Falls Church, Manassas, and Manassas Park in Virginia.

 

126

 “Emissions from mobile sources, including onroad, nonroad, marine, air, and rail, also continue to contribute 

significantly to NOx and VOC emissions levels, but the setting of mobile emissions standards is outside the authority of most 

states to regulate. “ Refr to “APPENDIX A 5 (9) – FACTOR ANALYSIS FOR THE 16 STATE NONATTAINMENT 

AREA,” to a Letter dated March 7, 2012, from Robert M. Summers, Ph.D., Secretary, Maryland Department of the 

Environment to Shawn M. Garvin, Regional Administrator, EPA Region III. 
103

Appendix 1: Pertinent Background on Monitoring Objectives and Scales

Objectives:

EPA has identified three major objectives for air quality monitoring:

(1) Provide air pollution data to the general public in a timely manner. 

(2) Support compliance with ambient air quality standards and emissions strategy development. EPA 

and others will be used data from monitors for NAAQS pollutants to compare an area’s air pollution 

levels against the NAAQS. 

(3) Support for air pollution research studies. 

EPA has specified that to support these three basic air quality monitoring objectives, a network must be 

designed with a variety of types of monitoring sites. Monitoring sites must be capable of determining 

among other things the peak air pollution levels, typical levels in populated areas, air pollution 

transported into and outside of a city or region, and air pollution levels near specific sources. The six 

general site types are:

(1) Sites located to determine the highest or maximum concentrations expected to occur in the area 

covered by the network.

(2) Sites located to measure “population exposure,” that is, typical concentrations in areas of high 

population density.

(3) Sites located to determine the impact of substantial sources or source categories on air quality.

(4) Sites located to determine general background concentration levels.

(5) Sites located to determine the extent of regional pollutant transport among populated areas; and in 

support of secondary standards.

(6) Sites located to measure air pollution impacts on visibility, vegetation damage, or other welfarebased impacts.

See, section 1.1 of Appendix D to 40 CFR Part 58 “Ambient Air Quality Surveillance” (Appendix D 

hereafter).

Regarding Regulatory Compliance and Maximum Concentration Sites:

For regulatory compliance, the principle objective is to measure the ozone concentration in the high 

population density areas and the maximum downwind concentration from the urban region. It is 

important to be careful when selecting the high population sites because, particularly in dense urban 

areas, the greatest concentration of people may be in an area with heavy automobile traffic, which may

result in low ozone concentration due to nitric oxide titration. See, section 4.2 of Guideline On Ozone 

Monitoring Site Selection, EPA-454/R-98-002, August 1998 (1998 Guideline hereafter). 

Within an ozone monitoring network, at least one ozone site for each CBSA, or CSA if multiple CBSAs 

are involved, must be designed to record the maximum concentration for that particular metropolitan 

area (section 4.1(b) of Appendix D to 40 CFR Part 58). Based upon a review of meteorological and air 

quality data, the prospective maximum concentration monitor site should be selected in a direction from 

the city that is most likely to observe the highest ozone concentrations, more specifically, downwind 

during periods of photochemical activity. In many cases, these maximum concentration ozone sites will 

be located 10 to 30 miles or more downwind from the urban area where maximum ozone precursor

emissions originate (see, section 4.1(f) of Appendix D). 
104

Regarding Scales:

Section 4.1(c) of Appendix D defines “urban scale” as “an area of city-like dimensions, on the order of 

several kilometers to 50 or more kilometers or more.” “Urban-scale sites can also be used to measure 

high concentrations downwind of the area having the highest precursor emissions.” See, section 4.2 of 

Guideline On Ozone Monitoring Site Selection, EPA-454/R-98-002, August 1998 (1998 Guideline). 

Section 4.1(c) of Appendix D to 40 CFR Part 58 (“Ambient Air Quality Surveillance”) defines 

“Neighborhood scale” as some reasonably homogeneous urban sub-region, with dimensions of a few 

kilometers. Homogeneity refers to pollutant concentrations. Neighborhood scale data will provide 

valuable information for developing, testing, and revising concepts and models that describe 

urban/regional concentration patterns. These data will be useful to the understanding and definition of 

processes that take periods of hours to occur and hence involve considerable mixing and transport. 

Under stagnation conditions, a site located in the neighborhood scale may also experience peak 

concentration levels within a metropolitan area.

Section 4.1(c) of Appendix D to 40 CFR Part 58 (“Ambient Air Quality Surveillance”) defines 

“Regional scale” as a scale of measurement will be used to typify concentrations over large portions of a 

metropolitan area and even larger areas with dimensions of as much as hundreds of kilometers. Such 

measurements will be useful for assessing the O3 that is transported to and from a metropolitan area, as 

well as background concentrations. In some situations, particularly when considering very large 

metropolitan areas with complex source mixtures, regional scale sites can be the maximum 

concentration location.
105

Appendix 3 to Technical Support Document—

Area Designations for the Washington-Baltimore-Northern Virginia, DC-MD-VAWV Combined Statistical Area (CSA) 2008 Ozone National Ambient Air Quality 

Standards
106

Population growth rates

From 2000 to 2010, Loudoun County VA grew at a rate of 84.1%, the 5th highest growth rate in the 

US127. There were no Maryland counties in the top 10 US growth rates for counties of 10,000 or more. 

Virginia statewide population increases were also higher than Maryland’s increases from 1980 to 

2010128. The Virginia County data are located in the footnoted web page129. Maryland county data are 

from MDP’s Maryland Statistical Handbook130.

State % chg 1980-1990 % chg 1990-2000 % chg 2000-2010

Maryland 13.4 10.8 9.0

Virginia 15.8 14.4 13.0

Northern VA 16.3 (2000-2007)

County (Baltimore, DC 

and Ex-urban)

Growth Rate in 

Percent

Growth in 

absolute pop.

change

Data Years

Virginia counties

Washington DC region

Loudoun 84.1 142,712 2000-2010

Loudoun 62.5 105,997 2000-2007

Fairfax 11.5131 42,763 2000-2007

Prince William 32.5 91,126 2000-2007

Fauquier132 18.3 65,460 2010

Fredericksburg area

Spotsylvania 32.6 29,512 2000-2007

Stafford 30.2 27,941 2000-2007

King George133 40.4 2000-2010

Winchester area

Frederick 32.3134 13,740 2000-2007

Maryland counties GR > 15% in bold

Baltimore region

Anne Arundel 6.4 31,545 2000-2009

Baltimore County 4.7 35,506 2000-2009

Baltimore City -2.1 -13,736 2000-2009

Carroll 12.7 19,192 2000-2009

Harford 10.9 23,924 2000-2009

Howard 13.7 34,035 2000-2009

 

127 US Census link to a PDF for Population Distribution and Change: 2000 to 2010 (page 9), 

http://2010.census.gov/2010census/

128 http://www.census.gov/compendia/statab/cats/population.html--#14: State Population--Rank, Percent Change, And 

Population Density (link to a PDF document)

129 http://vaperforms.virginia.gov/extras/profileSummary.php--links to a PDF report

130 MD Statistical Handbook linked from the following web page: http://planning.maryland.gov/msdc/S2_Estimate.shtml

131 http://quickfacts.census.gov/qfd/states/51/51059.html

132 http://www.fauquiercounty.gov/government/departments/commdev/index.cfm?action=demographics

133 http://quickfacts.census.gov/qfd/states/51/51099.html

134 http://quickfacts.census.gov/qfd/states/51/51069.html
107

Washington DC region

Montgomery 11.3 98,254 2000-2009

Prince George’s 4.1 33,044 2000-2009

Frederick 16.7 32,704 2000-2009

Calvert 19.6 14,649 2000-2009

Charles 18.0 21,680 2000-2009

Washington County EAC

Washington 10.6 13,987 2000-2009

Attainment/exurban

St. Mary’s 19.4 16,767 2000-2009

Kent/Queen Anne’s 

Maintenance Area

Queen Anne’s 18.2 7,398 2000-2009

Kent 5.5 1,047 2000-2009

Philadelphia region

Cecil 17.3 14,845 2000-2009
108

Appendix 8 to Technical Support Document—

Area Designations for the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV Combined 

Statistical Area (CSA) 

2008 Ozone National Ambient Air Quality Standards

30 Year Average Wind Rose Data

This is reprinted from “Technical Analysis for the Washington, DC-MD-VA and Baltimore Areas” in

Docket item numbers EPA-HQ-OAR-2008-0476-0235, EPA-HQ-OAR-2008-0476-0405 and EPA-HQOAR-2008-0476-0456.

The analysis in “Factor 3: Meteorology (weather/transport patterns)” elsewhere in this document 

supplements and to great extent supersedes this data.

The 30-year average summer surface-level wind directions for the design value county in each of the 

areas is shown in Figures 3a through 3 d. 

For Harford County (Figure 3a), MD in the in the Baltimore nonattainment area the winds are from the 

west-northwest through the south-southeast about 62 percent of the time.

Map Legend: WNW means from the west-northwest; NNW means from the north-northwest; NNE 

means from the north-northeast; ENE means from the east-northeast; ESE means from the eastsoutheast; SSE means from the south-southeast; SSW means from the south-southwest; and, WSW 

means from the west-southwest.

For Fairfax County (Figure 3b), VA in the Washington DC-MD-VA nonattainment area the winds are 

from the west-northwest through the southeast about 64 percent of the time.

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

NNE

ENE

ESE

SSE

SSW

WSW

WNW

NNW

Figure 3a. Harford Co., MD

Harford Co., MD
109

For Stafford County (Figure 3c) in the Fredericksburg, VA Area the winds are from the south-southwest 

through the south-southeast about 39 percent of the time and from other directions more or less equally.

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

NNE

ENE

ESE

SSE

SSW

WSW

WNW

NNW

Figure 3b. Fairfax County, VA

Fairfax County, VA

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

NNE

ENE

ESE

SSE

SSW

WSW

WNW

NNW

Figure 3c. Stafford County, VA

Stafford County, VA
110

For Frederick County (Figure 3d) in the Frederick County, VA Area the winds are from the southsouthwest through the south-southeast about 37 percent of the time and from other directions more or 

less equally with the exception of west-northwest which occurs a little over 15 percent of the time. 

Figures 3e and f show the data for all the counties in the Baltimore and Washington DC-MD-VA 

nonattainment areas, respectively. The patterns are essentially the same for all counties and cities in the 

Washington DC-MD-VA nonattainment area and the same for all counties and cities in the current 

Baltimore nonattainment area. 

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

NNE

ENE

ESE

SSE

SSW

WSW

WNW

NNW

Figure 3d. Frederick County, VA

Frederick County, VA
111

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

NNE

ENE

ESE

SSE

SSW

WSW

WN

W

NNW

Anne Arundel Co., MD

Baltimore Co., MD

Carroll Co., MD

Harford Co., MD

Howard Co., MD

Baltimore City, MD

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

NNE

ENE

ESE

SSE

SSW

WSW

WN

W

NNW

Arlington Co., VA

District of Columbia

Fairfax Co., VA

Fauquier Co., VA

Loudoun Co., VA

Prince William Co., VA

Calvert Co., MD

Charles Co., MD

Frederick Co., MD

Montgomery Co., MD

Prince George's Co., MD

Figure 3f. Washington DC-MD-VA NA Area

Figure 3e. Baltimore Nonattainment Area