1

MARYLAND

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

The table below identifies the areas and associated counties or parts of counties in the State of Maryland

that EPA intends to designate as nonattainment for the 2008 ozone national ambient air quality standards 

(“2008 ozone NAAQS” or “2008 NAAQS”). In accordance with section 107(d) of the Clean Air Act 

(CAA), EPA must designate 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.

Intended Nonattainment Areas in Maryland:

Area 

Maryland’s Recommended 

Nonattainment Counties

EPA’s Intended 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

Philadelphia** Cecil County Cecil County

*The Washington, DC-MD-VA area is a multi-state nonattainment area. Table 3 in Part I of this 

document identifies the counties in the other states that EPA intends to designate as part of the 

nonattainment area.

** The Philadelphia area is a multi-state nonattainment area. Table 16 in Part II of this document 

identifies the counties in the other states that EPA intends to designate as part of the nonattainment area.

EPA intends to designate the remaining counties, cities and areas in Maryland that are not listed in the 

table above as “unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analyses below provide the basis for intended 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 factors identified below. EPA issued guidance on December 4, 2008 that 
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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.1 

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

(FRM) monitors 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 controls, 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 a broad geographic area. Accordingly, EPA chose to examine the 5 factors with respect 

to the larger of the Combined Statistical Area (CSA) or Core Based Statistical Area (CBSA) within 

which the violating monitor(s) are located.2 All data and information used by EPA in this evaluation are 

the latest available to EPA and/or provided to EPA by states or tribes.

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. 

Maryland’s Recommendations:

On March 10, 2009, 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 

 

1 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.

2

 Lists of CBSAs and CSAs and their geographic components are provided at 

www.census.gov/population/www/metroareas/metrodef.html . The lists are periodically updated by the Office of 

Management and Budget. EPA used the most recent update, based on 2008 population estimates, issued on December 1, 

2009 (OMB Bulletin No. 10-02).
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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 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. 

EPA proposes 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 for State of Maryland” below. 

(3) EPA intends 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 declines to base its decisions upon the likelihood that additional “strong national 

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

First, EPA believes that EPA cannot base decisions regarding nonattainment area boundaries upon the 

likelihood of additional national rules being promulgated in the future. EPA believes the CAA places 

limits upon the sort of factors EPA can consider when designating areas nonattainment and setting 

boundaries for those areas. Section 107(d)(1)(A) sets forth the requirements for designating areas:

“...the Governor of each State shall (and at any other time the Governor of a State deems 

appropriate the Governor may) submit to the Administrator a list of all areas (or portions 

thereof) in the State, designating as—

(i) nonattainment, any area that does not meet (or that contributes to ambient air 

quality in a nearby area that does not meet) the national primary or secondary ambient air 

quality standard for the pollutant,

(ii) attainment, any area (other than an area identified in clause (i)) that meets the national 

primary or secondary ambient air quality standard for the pollutant ...”

EPA interprets this provision to require States and EPA to designate as “nonattainment” any area 

containing a monitor violating a NAAQS as long as the monitor meets the requirements for a FRM 

monitor or FEM monitor, the monitor is properly sited, and the data meets minimum data quality 
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requirements.3 Then, starting with the monitor, the States and EPA are to build nonattainment areas 

outward from the violating monitor with the “contributes to nonattainment” provision – “contributes to 

ambient air quality in a nearby area that does not meet” a NAAQS. Section 107(d)(1)(A)(i) uses the 

present tense – “contributes” and not some other tense such as the past tense “contributed” or some other 

conditional tense such as “would still contribute.” Therefore, EPA believes section 107(d)(1)(A)(i) 

places certain limits regarding the factors which can be considered when setting boundaries under the 

“contributes to nonattainment” provision. One natural reading is that an area must be designated 

nonattainment if it “contributes to nonattainment” in a “nearby area” at the time EPA promulgates the 

final designations pursuant to section 107. Because the CAA sets statutory deadlines for EPA to 

promulgate designations, EPA must base its decision upon the best available information at the time the 

Administrator makes the final decisions. 

EPA’s designation and boundary guidance such as the December 4, 2008 guidance memorandum “Area 

Designations for the 2008 Revised Ozone National Ambient Air Quality Standards,” reflect this view. 

This provided nine factors (consolidated into five for this document) for the States to consider and that 

EPA intends to consider. One factor is emissions-related data. EPA interprets emissions-related data to 

include actual and estimated emissions of VOC and NOx from sources, such as the data available in the 

latest National Emissions Inventory available, and to include the latest information and trends for 

Vehicle Miles Traveled (VMT) and commuting, and population characteristics and trends of the area. 

As far as control levels, EPA will consider any additional information received on enforceable emissions 

controls that are not reflected in recent inventories, but which will be in place before final designations 

are issued. 

Maryland’s recommendation of March 10, 2009 would exclude an area which “contributes to 

nonattainment” in a “nearby area” at the time EPA makes nonattainment decisions but would not 

“contribute to nonattainment” at some time in the future if some rule or rules are promulgated. EPA 

believes that such an action would contravene section 107(d)(1)(A)(i) because if the rules are not 

promulgated the contributing area would still “contribute to nonattainment” to the same “nearby area” 

and not be designated “nonattainment.” Thus EPA concludes that the recommendation would have EPA 

base a nonattainment area boundary decision upon a criterion which does not comport with the CAA. 

(4) EPA believes 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. 

Maryland recommended that EPA designate the entire State as part of a large multi-state nonattainment 

area including a significant portion of the U.S. East Coast. Section 107(d) of the CAA requires EPA to 

designate as nonattainment all areas violating the ozone NAAQS and any nearby areas that are 

contributing to a violation in another area. Under the designation provision, only "nearby" areas that 

contribute to the violation must be included as part of the nonattainment area. There are other 

provisions of the CAA that address longer range transport of ozone pollutions, such as sections 

110(a)(2)(D), 126, and 184. The phenomenon of ozone transport must be balanced against the need to 

have smaller areas that can focus on local control measures. We note that most of the States that 

Maryland seeks to include as part of this large nonattainment area did not make a similar request. While 

a few other states did request that EPA designate a broad area in the eastern part of the United States as 

nonattainment, each of those recommendations varied from the others. In the absence of broad 

 

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If a monitor meets the FER or FEM and siting requirements but has insufficient data EPA can use other provisions of the 

CAA such as an “unclassifiable” designation or delay designation under the one-year extension provisions of section 

107(d)(1)(B)(i) when this provisions is available.
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agreement among a large group of states to create such a large nonattainment area, demonstrating a 

commitment to work together to address both long-range and local transport of emissions, EPA does not 

intend to designate a large nonattainment area as suggested by Maryland.

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

years ago will be) because it relies 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. 

Technical Analysis for State of Maryland:

Part I. Technical Analysis for the Washington, DC-MD-VA and Baltimore Areas.

The Washington, DC-MD-VA and Baltimore areas are part of the Washington-Baltimore-Northern 

Virginia, DC-MD-VA-WV Combined Statistical Area (Washington-Baltimore-NV CSA). This consists 

of the following CBSAs:4 

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

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

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

(3) The Lexington Park, MD Micropolitan Statistical Area - St. Mary's County in Maryland;

(4) The Washington-Arlington-Alexandria, DC-VA-MD-WV MSA: 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 Alexandria, Fairfax, Falls Church, 

Fredericksburg, Manassas, and Manassas Park; and the West Virginia Portion: Jefferson County.

(5) The Winchester, VA-WV Metropolitan Statistical Area - Frederick County and Winchester City in 

Virginia and Hampshire County in West Virginia.

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.5 

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 –

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.”)

 

4 OMB Bulletin No. 10-02, December 1, 2009.

5 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.
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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.

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 is currently defined under the 1997 ozone NAAQS (current 

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

Counties and Baltimore City in Maryland. 

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

NAAQS (current Washington DC-MD-VA nonattainment area) 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) The Frederick County, VA Area consisting of Frederick County and Winchester City in Virginia.

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

in Virginia.

(5) Eight other counties: Queen Anne's County in Maryland (which is a portion of the Kent County and 

Queen Anne's County Area); St. Mary's County in Maryland; Clarke, Culpeper, Fauquier, and Warren 

Counties in Virginia; and Hampshire and Jefferson Counties in West Virginia.

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

(1) The Current Baltimore Nonattainment Area

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 current Baltimore nonattainment area. Harford 

County has 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; its population is one tenth of that in the current Baltimore nonattainment area and not 

exceptionally large or small; its population density is half the overall average for the current Baltimore

nonattainment area; traffic and commuting patterns merit no special attention one way or another; 

meteorology indicates its emissions may contribute to nonattainment in Baltimore County (as well as to 

its own nonattainment). 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 

current Baltimore nonattainment area are jurisdictional boundaries, and meteorology which indicates it 
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is both upwind and downwind of Baltimore County. Therefore, we do not believe that there is a strong 

reason to modify Maryland’s recommendation to include this County as part of a Baltimore Area with 

the same boundaries as for the current Baltimore nonattainment area.

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 five” counties for 

emissions in the Washington-Baltimore-NV CSA. It is adjacent to Harford County which has the 

highest design value in the Washington-Baltimore-NV CSA and the current Baltimore nonattainment 

area. It has the highest population in the current Baltimore nonattainment area. Its growth rate is well 

below the Washington-Baltimore-NV CSA’s average, but equal to the current Baltimore nonattainment 

area average rate. It has the highest VMT within the current Baltimore nonattainment area and third 

highest within the Washington-Baltimore-NV CSA. Its VMT is about one-third the total for the current 

Baltimore nonattainment area and about one-ninth of the total for the Washington-Baltimore-NV CSA. 

Meteorology indicates it is upwind Harford County’s Edgewood monitor over 60 percent of the time. 

Factors that favor placement of Baltimore County in a nonattainment area containing Harford County, 

that is, as part of a Baltimore Area with the same or similar boundaries as the current Baltimore 

nonattainment area, are its emissions, jurisdictional boundaries and meteorology which indicates it is 

both upwind and downwind of a violating monitor in Harford County. We weigh Maryland’s 

recommendations as supporting placement in a Baltimore Area with the same or similar boundaries as 

the current Baltimore nonattainment area. No factors favor any other grouping. 

Baltimore City: This city does not have violating monitor. It ranks in the “top 11” counties for 

emissions within the Washington-Baltimore-NV CSA and third (of six) in the current Baltimore 

nonattainment area. It is densely populated, but experienced a population decline over the past 10 years. 

Its VMT is about one-eighth that of the current Baltimore nonattainment area. Meteorology indicates it 

is upwind of Harford County’s violating Edgewood monitor over 30 percent of the time and upwind of 

violating monitors in Baltimore County. Factors that favor designation of Baltimore City as 

nonattainment based upon contribution are emissions, Maryland’s recommendations, jurisdictional 

boundaries, and possible contribution to Harford and Baltimore Counties. These factors support 

placement in a Baltimore Area with the same or similar boundaries as the current Baltimore 

nonattainment area. Therefore, we do not believe that there is a strong reason to modify Maryland’s 

recommendation to include this County as part of a Baltimore Area with the same boundaries as for the 

current Baltimore nonattainment area. No factors favor any other grouping. 

Howard County: Howard County does not have a violating monitor. It ranks in the “top 11” counties

for emissions within the Washington-Baltimore-NV CSA and fourth (of six) in the current Baltimore 

nonattainment area. It is densely populated. Its growth rate is about equal the Washington-BaltimoreNV CSA’s average but over twice that for the current Baltimore nonattainment area average. Its VMT 

is not exceptional. Meteorology indicates it is upwind of both violating monitors in Baltimore County 

21 and 18 percent of the time and of the violating monitor in Carroll County 16 percent of the time. It is 

also upwind of a violating monitor in Prince George’s County up to 11 percent of the time. 

Meteorology indicates it has more influence on nonattainment in the current Baltimore nonattainment 

area than in the current Washington DC-MD-VA nonattainment area. Factors that favor designation of 

Howard County as nonattainment based upon contribution are its emissions, are jurisdictional 

boundaries, Maryland’s recommendations and meteorology indicating contribution to violating monitors 

in Baltimore and Carroll Counties. Factors that favor placement with Prince George’s County are its

possible contribution to that county. Howard County’s possible contribution is to a greater number of 

monitors in the current Baltimore nonattainment area and such possible contribution likely is more 
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frequent than to monitors in the current Washington DC-MD-VA nonattainment area. Overall the 

former factors would outweigh the latter, and, therefore support placement of Howard County in a 

Baltimore Area with the same or similar boundaries as the current Baltimore nonattainment area.

Therefore, we do not believe that there is a strong reason to modify Maryland’s recommendation to 

include this County as part of a Baltimore Area with the same boundaries as for the current Baltimore 

nonattainment area.

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 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. It has the lowest population 

and population density within the current Baltimore nonattainment area with a growth rate less than the 

Washington-Baltimore-NV CSA’s average but twice that for the current Baltimore nonattainment area. 

Likewise, its VMT and number of commuters are at the lower end for the Washington-Baltimore-NV 

CSA and the current Baltimore nonattainment area. Meteorology indicates that it is upwind of the 

violating Padonia monitor in Baltimore County 52 percent of the time and also indicates that Carroll 

County is downwind from some counties (Frederick and Montgomery Counties in Maryland and 

probably to a lesser extent Loudoun County, VA) in the current Washington DC-MD-VA nonattainment 

area some 31 to 32 percent of the time. 

Its monitor has a design value is 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; and (2) meteorology indicates that emissions from 

the county impact violating monitors in Baltimore County approximately 50 percent of the time, which 

is significantly more than emissions impact other monitors in the CSA. Factors favoring inclusion with 

the current Washington DC-MD-VA nonattainment area counties are meteorology supporting 

contribution from these approximately 30 percent of the time when its monitor is showing exceedances. 

The possible contribution to the violating monitor in Carroll County from Frederick and Montgomery 

Counties in Maryland is likely much more than the possible contribution from Loudoun County because 

the total (NOx plus VOC) emissions from these two counties are four times that of Loudoun County and

because the Maryland counties are more proximate. While Loudoun County, VA does not have a 

violating monitor but is intended to be designated nonattainment. Overall the factors support placement 

in a Baltimore Area with the same or similar boundaries as the current Baltimore nonattainment area. 

Therefore, we do not believe that there is a strong reason to modify Maryland’s recommendation to 

include this County as part of a Baltimore Area with the same boundaries as for the current Baltimore 

nonattainment area.

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 five” in emissions in the 

Washington-Baltimore-NV CSA and the top two in the current Baltimore nonattainment area. It is more 

densely populated than the either the average for the Washington-Baltimore-NV CSA or the current 

Baltimore nonattainment area. Its growth rate is less than the Washington-Baltimore-NV CSA’s 

average but higher than that for the current Baltimore nonattainment area. Its VMT is about one-fifth 

the total for the current Baltimore nonattainment area and about one-thirteenth of the total for the 

Washington-Baltimore-NV CSA. Meteorology indicates it is upwind of a violating monitor in Prince 
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George’s County which is part of the current Washington DC-MD-VA nonattainment area and has a 

more frequent impact on that monitor than it does on violating monitors in other portions of the current 

Baltimore nonattainment area; likewise, meteorology indicates that the monitor in this county is 

downwind of two adjacent counties (Calvert and Prince George’s) in the current Washington DC-MDVA nonattainment area and that emissions from those counties likely impact that monitor more 

frequently than emissions from other counties in the current Baltimore nonattainment area. Factors that 

favor inclusion of Anne Arundel County in a nonattainment area based upon contribution are its 

emissions, jurisdictional boundaries, and meteorology. Factors that favor inclusion with a 

nonattainment area including Calvert and Prince George’s Counties are meteorology. Factors that favor 

inclusion with Baltimore City and County and Harford County are jurisdictional boundaries and 

Maryland’s recommendation to retain current nonattainment area boundaries. Because Anne Arundel’s 

possible contribution involves only intrastate contribution Maryland’s recommendation deserves extra 

weight because Maryland will be responsible for mitigating any such intrastate contribution. Air quality 

considerations suggest that the monitor in Anne Arundel 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. 

Therefore, we do not believe that there is a strong reason to modify Maryland’s recommendation to 

include this County as part of a nonattainment area with the same boundaries as the current Baltimore 

nonattainment area. For these reasons, the factors weigh in favor of grouping Anne Arundel County 

with the rest the current Baltimore nonattainment area. 

(2) The Current Washington DC-MD-VA 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 current 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-ArlingtonAlexandria, DC-VA-MD-WV MSA. Fairfax County is among the “top five” counties for emissions in 

the Washington-Baltimore-NV CSA. 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 

current Washington DC-MD-VA nonattainment area’s average rate. It has the highest VMT and 

number of commuters within the current Washington DC-MD-VA nonattainment area and highest 

within the Washington-Baltimore-NV CSA. Its VMT is about one-fourth the total for the current 

Washington DC-MD-VA nonattainment area and one-seventh of the total for the WashingtonBaltimore-NV CSA. Meteorology indicates it is upwind of violating monitors in Arlington County, VA 

and the District of Columbia about 50 percent of the time. 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 emissions, meteorology, 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-FairfaxDistrict core of 0.079 to 0.081 ppm at the Arlington-Fairfax-District core, jurisdictional boundaries and 

Virginia’s recommendation. No factors support inclusion in a different nonattainment area.

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 five” counties for emissions

in the Washington-Baltimore-NV CSA and essentially tied for second with Montgomery County, MD 

within the current Washington DC-MD-VA nonattainment area. It is more densely populated the either 
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the average for the Washington-Baltimore-NV CSA or the current Washington DC-MD-VA 

nonattainment area. Its growth rate is slightly less than that in the Washington-Baltimore-NV CSA and 

current Washington DC-MD-VA nonattainment area averages. It is the third most populous area in the 

Washington-Baltimore-NV CSA and current Washington DC-MD-VA nonattainment area. It has the 

second highest VMT and third highest number of commuters within the Washington-Baltimore-NV 

CSA. Its VMT is about one-fifth the total for the current 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 the violating monitor in Anne Arundel County which is part of the current Baltimore 

nonattainment area more frequently than it is upwind of any violating monitors in other portions of the 

current Washington DC-MD-VA nonattainment area; meteorology indicates it is upwind of the violating 

monitor in Anne Arundel County 66 percent of the time; and meteorology indicates it is upwind of 

violating monitors in Fairfax County and the District of Columbia about 27 and 38 percent of the time 

and suggests it is upwind of the Calvert County’s violating monitor (which is part of the current 

Washington DC-MD-VA nonattainment area for the 1997 NAAQS), about 27 percent of the time. In 

addition, meteorology indicates that the monitors in this county are downwind of Anne Arundel and 

Montgomery Counties in Maryland (29% and 15%, respectively) and the District of Columbia and 

Fairfax County, VA (18 and 16%, respectively). Meteorology indicates this county could be included in 

a nonattainment area containing Anne Arundel County or in a nonattainment area including Fairfax 

County, Calvert County and the District of Columbia. While meteorology more strongly favors for 

including Prince George’s County as part of a nonattainment area with Anne Arundel County, we weigh 

Maryland’s recommendation as to which nonattainment area to include the county in when all counties 

at issue will be designated as nonattainment. Moreover, because Prince George’s County receives 

possible contribution from counties in other States and possibly contributes to violations at monitors in 

other states, this consideration weighs heavily in grouping this county those other counties. 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 five” counties for emissions in the WashingtonBaltimore-NV CSA and essentially tied for second with Prince George’s County, MD within the current 

Washington DC-MD-VA nonattainment area. It is more densely populated the either the average for the

Washington-Baltimore-NV CSA or the current Washington DC-MD-VA nonattainment area. Its growth 

rate is slightly less than the Washington-Baltimore-NV CSA and current Washington DC-MD-VA 

nonattainment area averages. It is the second most populous area in the Washington-Baltimore-NV 

CSA and current Washington DC-MD-VA nonattainment area. It has the fourth highest VMT within 

the Washington-Baltimore-NV CSA and third highest number of commuters within the WashingtonBaltimore-NV CSA. Its VMT is about one-sixth the total for the current Washington DC-MD-VA 

nonattainment area and about one-tenth of the total for the Washington-Baltimore-NV CSA. 

Meteorology indicates it is upwind of the violating monitor in Carroll County 32 percent of the time; 

and meteorology indicates it is upwind of violating monitors in Prince George’s County and the District 

of Columbia about 15 and 13 percent of the time, respectively. Meteorology indicates this county could 

be included in a nonattainment area containing Carroll County (that is, as part of a Baltimore Area with 

the same or similar boundaries as the current Baltimore nonattainment area) or in a nonattainment area 

including Prince George’s County and the District of Columbia (that is, as part of a Washington-DCMD-VA Area with the same or similar boundaries as the current Washington-DC-MD-VA 

nonattainment area). The possible effects on Prince George’s County and the District of Columbia 

deserve more weight because the design value of Carroll County is less than those of Prince George’s 
11

County and the District of Columbia and because this grouping places it with monitors in other States to 

which it may contribute. 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. We give weight to Maryland’s recommendation as to which nonattainment 

area to include the county in when we intend to designate as nonattainment all counties at issue. 

Factors that favor inclusion of this county in a nonattainment area based upon contribution are its 

emissions, jurisdictional boundaries, and meteorology. Factors that favor inclusion in a nonattainment 

area containing Carroll County are its emissions and meteorology. Factors that favor inclusion with 

Prince George’s County and the District of Columbia as part of a Washington-DC-MD-VA Area with 

the same or similar boundaries as the current Washington-DC-MD-VA nonattainment area are its 

emissions, meteorology, placement in an interstate area and jurisdictional boundaries. Therefore, we do 

not believe that there is a strong reason to modify Maryland’s recommendation to include this County as 

part of a Washington-DC-MD-VA Area with the same or similar boundaries as the current WashingtonDC-MD-VA nonattainment area.

Frederick County, MD: Frederick County does not have violating monitor, but has a monitor with a 

design value of 0.074 ppm. It ranks in the “top 11” counties for emissions within the WashingtonBaltimore-NV CSA and fifth in the current Washington DC-MD-VA nonattainment area. It is sparsely 

populated. Its growth rate is a little more than the current 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. Meteorology indicates it is upwind of the violating monitor in Carroll County 31 percent of 

the time. Meteorology supports inclusion in a nonattainment area containing Carroll County. Air 

quality considerations suggest that Carroll County will attain the 2008 NAAQS within a few years 

without further controls and will not be the key monitor needed for attainment within the WashingtonBaltimore-NV CSA or in a smaller area only containing Harford County. Frederick County is in the 

Washington-Arlington-Alexandria, DC-VA-MD-WV MSA and thus has commuting ties to the rest of 

this MSA which includes the current Washington DC-MD-VA nonattainment area. The WashingtonArlington-Alexandria, DC-VA-MD-WV MSA is part of the Washington Baltimore-NV CSA which 

means there are some commuting ties between this MSA and other CBSAs within this CSA. In the case 

of Frederick County, the adjacent CBSA is the Baltimore-Towson MSA which includes the current 

Baltimore nonattainment area. Because Frederick County’s possible contribution involves only 

intrastate contribution either of Maryland’s recommendations are valid because Maryland will be 

responsible for mitigating any such intrastate contribution. Emissions and meteorology support 

inclusion of Frederick County in a nonattainment area based upon possible contribution. While 

meteorology more strongly favors for including Frederick County as part of a nonattainment area with 

Carroll County, we give great weight Maryland’s recommendation as to which nonattainment area to 

include the county in when we intend to designate as nonattainment all counties at issue and when the 

possible contribution is only intrastate. Factors that favor inclusion in a nonattainment area containing 

Carroll County are meteorology. Factors that favor inclusion with a Washington-DC-MD-VA Area with 

the same or similar boundaries as the current Washington-DC-MD-VA nonattainment area are

jurisdictional boundaries, and Maryland’s one recommendation 

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 emissions within the Washington-Baltimore-NV CSA. It has the smallest 

population of any county (and even less than Alexandria City, VA) in the current Washington DC-MD-
12

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 current 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 current Washington 

DC-MD-VA nonattainment area. Meteorology indicates it is upwind of violating monitors in Prince 

George’s County (in the current Washington-DC-MD-VA nonattainment area) and in Anne Arundel 

County (in the current Baltimore nonattainment area) about 18 and 20 percent of the time. Meteorology 

indicates that at times Anne Arundel is upwind of Prince George’s and, at other times, vice versa. 

The effect which Calvert County can have on either Anne Arundel or Prince George’s is far less than 

Anne Arundel and Prince George’s have on each other because Calvert County’s emissions are far less 

than that of either Anne Arundel or Prince George’s Counties. Meteorology also indicates that at times 

Prince George’s is upwind of Calvert County about 22 percent of the time. However, the emissions in 

Prince George’s County are around 8 times that of Calvert County and thus the effects of Prince 

George’s County’s emissions on Calvert County are much greater than vice versa. Furthermore, 

meteorology indicates that Charles County, MD is upwind of Calvert County about 29 percent of the 

time and thus more frequently than Calvert County is upwind of Anne Arundel County. Overall, 

meteorology and the ratio of Prince George’s County’s emissions to Calvert County’s emissions favors 

grouping Calvert County with Charles Prince George’s Counties. Because possible contribution across 

current nonattainment area boundaries involves only intrastate contribution Maryland’s 

recommendations are valid; Maryland will be responsible for mitigating any such intrastate contribution. 

Air quality considerations suggest that Anne Arundel County will attain the 2008 NAAQS within a few 

years without further controls and its monitor will not be the key monitor needed for attainment within 

the Washington-Baltimore-NV CSA or in an area containing Fairfax County. Air quality considerations 

suggest that the same is true for Calvert and Prince George’s Counties in that attainment within a few 

years is possible without further controls and neither will be the key monitor needed for attainment 

within the Washington-Baltimore-NV CSA or in an area containing Harford County. Therefore, it does 

not matter whether this county is grouped with the Harford County monitor or the Fairfax County 

monitor. Factors that favor inclusion in a nonattainment area containing Anne Arundel County as part 

of a Baltimore Area with the same or similar boundaries as the current Baltimore nonattainment area are 

meteorology which indicates that at times Calvert County is upwind of Anne Arundel County at times

but less strongly than it favors inclusion in a nonattainment area containing Charles and Prince George’s 

Counties. We heavily weigh Maryland’s recommendation to retain the current nonattainment area 

boundaries when we intend to designate all counties at issue as nonattainment. Factors that favor 

inclusion in a nonattainment area containing Charles and Prince George’s Counties are: meteorology 

which indicates Calvert County could contribute to and could receive contribution from counties which 

are part of the current Washington-DC-MD-VA nonattainment area and jurisdictional boundaries. 

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 emissions within the Washington-Baltimore-NV CSA. Its population is smaller than any 

county in the current 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 WashingtonBaltimore-NV CSA and current Washington DC-MD-VA nonattainment area averages but the overall 

change is lower than any other county except Calvert County within the current Washington DC-MDVA nonattainment area. Its population density is low at less than one third that of the current 

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 current Washington DC-MD-VA 

nonattainment area. The overall number of commuters is but a tiny fraction of that for the current 
13

Washington DC-MD-VA nonattainment area. Meteorology indicates it is upwind of violating monitors 

in Fairfax County, VA about 39 percent of the time and of violating monitors in Prince George’s County 

and Calvert County about 35 and 29 percent of the time, respectively. Factors that favor inclusion in a 

nonattainment area are meteorology with possible interstate contribution to Fairfax County, VA, 

Maryland’s recommendations and jurisdictional boundaries. Factors that favor inclusion with Prince 

George’s County, Calvert County and Fairfax Country as part of a Washington-DC-MD-VA Area with 

the same or similar boundaries as the current Washington-DC-MD-VA nonattainment area are: 

meteorology and jurisdictional boundaries. Therefore, we do not believe that there is a strong reason to 

modify Maryland’s recommendation to include this County as part of a nonattainment area with the 

same boundaries as for the 1997 ozone NAAQS.

Loudoun County, VA: Loudoun County does not have 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 

emissions within the Washington-Baltimore-NV CSA and ties for sixth (with Frederick County, MD) in 

the current Washington DC-MD-VA nonattainment area. Its population is near the median for counties 

in the current Washington DC-MD-VA nonattainment area and its density is one-half that of the current 

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 current Washington DC-MD-VA nonattainment area. Its growth rate is 

around one and one half times both the Washington-Baltimore-NV CSA and current Washington DCMD-VA nonattainment area averages but the overall change is lower than any other county except 

Calvert County within the current Washington DC-MD-VA nonattainment area. Meteorology indicates

it is upwind of violating monitors in Fairfax and Arlington Counties, VA in the current Washington-DCMD-VA nonattainment area about 16 percent of the time and Carroll County, MD in the current 

Baltimore nonattainment area in Maryland about 15 percent of the time. Air quality considerations 

suggest that Carroll County with a design value of 0.0076 ppm counties will attain 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. Carroll County likely will attain sooner than Fairfax and 

Arlington Counties with design vales of 0.081 and 0.079 ppm respectively. Loudoun County is adjacent 

to Fairfax County, VA; in contrast, the shortest path for transport of ozone and its precursors from 

Loudoun County to Carroll has to pass through Frederick or Montgomery Counties in Maryland. 

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 current 

Washington-DC-MD-VA nonattainment area are its closer proximity to Fairfax and Arlington Counties, 

the higher design values of the monitors in Fairfax and Arlington Counties, air quality considerations 

and jurisdictional boundaries.

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 emissions within the Washington-Baltimore-NV CSA. While its 

absolute emissions and population are not exceptional, its 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 current Washington DC-MD-VA nonattainment area. Its 

VMT is less than one-twenty-fifth of that even for the current Washington DC-MD-VA nonattainment 

area. Meteorology indicates this county is upwind of violating monitors in Fairfax County, VA and the 
14

District of Columbia about 10 and 15 percent of the time, respectively. It is downwind of Fairfax 

County about 50 percent of the time and the District of Columbia about 10 percent of the time. The 

factors somewhat favor a designation of nonattainment based upon contribution: these are its emissions 

and population densities, meteorological indications of possible interstate contribution to and from the 

District of Columbia and jurisdictional boundaries. The factors favor placing Arlington County in the 

same nonattainment area as Fairfax County and the District of Columbia as part of a Washington-DCMD-VA Area with the same or similar boundaries as the current Washington-DC-MD-VA 

nonattainment area. Factors favoring this placement are jurisdictional boundaries, meteorological 

indications of possible interstate contribution among Arlington and Fairfax Counties and the District of 

Columbia, the close proximity of these three counties monitors with design values of 0.079 to 0.081 

ppm at the Arlington-Fairfax-District core and Virginia’s recommendation. No factors compel 

placement in a different nonattainment area. 

Prince William County, VA: Prince William County does not have violating monitor. It ranks in the 

“top 11” counties (8thfor VOC and 10th for NOx) for emissions within the Washington-Baltimore-NV 

CSA and ties for fourth (VOC) and fifth (NOx) in the current Washington DC-MD-VA nonattainment 

area. Its population is fifth within the current Washington DC-MD-VA nonattainment area and its 

population density is a little less than that of the current Washington DC-MD-VA nonattainment area. 

Its growth rate was 42 percent, and, the absolute change in population was second highest in the current 

Washington DC-MD-VA nonattainment area. Its VMT is not exceptional. Meteorology indicates this 

county is upwind of violating monitors in Fairfax and Arlington Counties in Virginia about 36 percent of 

the time and of the monitor in Loudoun County about 39 percent of the time. The factors favor a 

designation of nonattainment based upon contribution: these are possible contribution to the monitors in 

Fairfax and Arlington Counties and jurisdictional boundaries. Factors that strongly favor inclusion in a 

nonattainment area based upon contribution are its possible contribution to violating monitors in 

Virginia and other states and to the possible design value monitor for a nonattainment area in Fairfax 

County, VA, Virginia’s recommendation, its emissions, its, and jurisdictional boundaries. The factors 

favor placing this county in the same nonattainment area as Fairfax and Arlington Counties. Factors 

favoring this placement are jurisdictional boundaries, possible contribution to Fairfax and Arlington 

Counties, and Virginia’s recommendation. No factors compel placement in a different nonattainment 

area. 

Alexandria City, VA: Alexandra City does not have violating monitor. It has emissions which are 

neither at the low or high end – it ranks in low end (21st VOC and 20th VOC) of the middle (12th through 

23rd inclusive) within the Washington-Baltimore-NV CSA. Its population is not exceptional, but it is 

densely populated – about 7 times the current Washington DC-MD-VA nonattainment area average. Its 

growth was less than the current Washington DC-MD-VA nonattainment area average. Its VMT is not 

exceptional. Its emission densities are high. Meteorology indicates this county is upwind of violating 

monitors in both Arlington County, VA and the District of Columbia about 25 percent of the time and of 

that in Fairfax County, VA about 10 percent of the time. The factors favor a designation of 

nonattainment based upon contribution: these are possible contribution to the monitors in Fairfax and 

Arlington Counties and the District of Columbia, emissions and population densities, Virginia’s 

recommendation and jurisdictional boundaries. 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, possible contribution to Fairfax and Arlington Counties, 

and Virginia’s recommendation. No factors compel placement in a different nonattainment area. 
15

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 between the 

violating monitors in Arlington Fairfax and Arlington Counties and the attaining monitor in Loudoun 

County. 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 emissions, VMT, and number of commuters. All are densely populated with a density just 

under 3 to 7 times the overall CSA density. The emissions densities are high which is likely typical for 

urban core areas. Their 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. The factors that favor designation of nonattainment for contribution are 

mainly their emissions and population densities which are comparable to or higher than the 

adjacent/surrounding counties and Virginia’s recommendations. 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 current Washington-DCMD-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 emissions within the WashingtonBaltimore-NV CSA and fourth in the current Washington DC-MD-VA nonattainment area. It is densely 

populated (8 times the average for the current Washington DC-MD-VA nonattainment area) and has the 

sixth highest population within the Washington-Baltimore-NV CSA and the fourth within the current 

Washington DC-MD-VA nonattainment area. Its growth rate is well less than – about one-third – of the 

current Washington DC-MD-VA nonattainment area and CSA averages. Its VMT is not exceptional at 

one-twelfth that of the current Washington DC-MD-VA nonattainment area. Meteorology indicates this 

county is upwind of violating monitors in Prince George’s County, MD about 18 percent of the time and 

the Arlington and Fairfax monitors about 10 and 5 percent of the time, respectively. Meteorology 

indicates it is downwind of Arlington County, VA and Montgomery County, MD about 15 and 13 

percent of the time respectively. Meteorology indicates it is downwind of Prince George’s County, MD 

about 28 percent of the time. Meteorology indicates that Fairfax County, VA is likely upwind of the 

violating monitors in the District of Columbia about 50 percent of the time and has higher emissions 

than the District of Columbia. The District of Columbia’s recommendation was for nonattainment. The 

District of Columbia’s analysis suggested that its emissions were a small (7% NOx and 9% VOC) part 

of those in the current 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 preliminarily agrees with the District of Columbia that an appreciable part of the air 

quality problem within the District of Columbia is due to emissions outside its borders. This 

preliminary decision is based in part upon the District of Columbia’s evaluation and in part upon EPA’s 

evaluation to date contained within this document. The District of Columbia is surrounded by three of 

the “top five” counties for emissions in the Washington-Baltimore-NV CSA. These are: Fairfax County, 

VA (4th NOx, 1st VOC); Montgomery County, MD (5th NOX, 2nd VOC); and Prince George’s County, 
16

MD (3rd for NOx and VOC). These three counties comprise the top three within the current Washington 

DC-MD-VA nonattainment area. The District is a densely populated area at the core of the WashingtonArlington-Alexandria, DC-VA-MD-WV MSA. The factors that favor the placement of the District of 

Columbia in the same nonattainment area as Fairfax and Arlington Counties as part of a WashingtonDC-MD-VA Area with the same or similar boundaries as the current Washington-DC-MD-VA 

nonattainment area are: jurisdictional boundaries; meteorological indications of possible contribution to 

and from the District of Columbia and counties in the current Washington-DC-MD-VA nonattainment 

area; and 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. No factors 

compel placement in a different nonattainment area.

(3) 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 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. 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. The factors would seem to 

favor a designation as “attainment/unclassifiable” 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.

(4) 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 emissions, Spotsylvania and Stafford Counties rank between 15th and 19th for emissions – within the 

“middle group” (between 12th and 23rd inclusive) – within the Washington-Baltimore-NV CSA. Their 

populations, VMT and number of commuters are not exceptional. They are relatively sparely populated 

having a population density less than even the Washington-Baltimore-NV CSA average. In total the 

Fredericksburg, VA Area would have 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. 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 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 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 “attainment/unclassifiable” 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. 
17

(5) Eight Other Counties: Queen Anne's County in Maryland; St. Mary's County in Maryland; 

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

Counties in West Virginia.

Queen Anne’s County, MD: Queen Anne’s County does not have violating monitor. For 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 population is low – about one fourth of the 

county within the current Baltimore MD nonattainment area (Carroll Co.) with the lowest population. 

Its growth rate is about three times that of the current 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. Meteorology indicates it is upwind of the violating Edgewood monitor about 25 

percent of the time, is upwind of the violating Essex monitor about 24 percent of the time and is upwind 

of the violating monitor in Anne Arundel County about 23 percent of the time. 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 emissions related factors are not compelling for a 

nonattainment designation given that the county is in the OTR and given the limited access for 

commuting to the rest of the Washington-Baltimore-NV CSA. It is possible contributions to 

nonattainment are solely intrastate. Because its possible contribution involves only intrastate counties 

either of the Maryland’s recommendations are valid; Maryland will be responsible for mitigating any 

such intrastate contribution. Maryland’s recommendation and the jurisdictional boundaries factor would 

seem to favor designation as attainment/unclassifiable and outweigh factors favoring a nonattainment 

designation. Therefore, we do not believe that there is a strong reason to modify Maryland’s 

recommendation to include this County as part of a Baltimore Area with the same boundaries as for the 

current Baltimore area.

St. Mary’s County: St. Mary’s County does not have violating monitor. For emissions it ranks 16th

VOC and 17th NOx– within the “middle group” (between 12th and 23rd inclusive) of the WashingtonBaltimore-NV CSA. Its population is lower than all other jurisdictions within the current Washington 

DC-MD-VA nonattainment area. Its growth rate is about one and one-half times that of the current 

Washington DC-MD-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. Meteorology indicates it is upwind of the violating monitor in Calvert County 

about 36 percent of the time. However, the violating monitor in Calvert 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 Calvert 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 St. Mary’s County is in the OTR. Its emissions related factors are not compelling for a 

nonattainment designation given that the county is in the OTR. Its possible contributions to 

nonattainment are solely intrastate. Because its possible contribution to violating monitors involves only 

intrastate counties Maryland will primarily be responsible for mitigating any such intrastate 

contribution. We will give Maryland’s recommendation great weight and conclude that the factors of 

jurisdictional boundaries and air quality considerations favor designation as “attainment/unclassifiable”

and outweigh factors favoring a nonattainment designation. 

Fauquier County, VA: Fauquier County does not have violating monitor but has a monitor with a 

design value of 0.065 ppm. For emissions it ranks 15th VOC and 20th NOx within the WashingtonBaltimore-NV CSA – within the “middle group” (between 12th and 23rd inclusive). Its population is 

low, and, it is sparely populated. Its growth rate was about one and one-half times that of the 
18

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 current Washington DC-MD-VA nonattainment area. Only 

27 percent of its commuters travel into an area with a violating monitor. Meteorology indicates this 

county is upwind of violating monitors in Fairfax and Arlington Counties in Virginia about 10 percent of 

the time. Factors that favor designation as nonattainment for contribution are possible contribution to 

Fairfax and Arlington Counties. Factors that favor designation as attainment/unclassifiable 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. The 

factors that favor designation as attainment/unclassifiable 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 emissions, each ranks 24th or lower in the 

Washington-Baltimore-NV CSA. 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 emissions of each are 1 percent or less than 

the total for the Washington-Baltimore-NV CSA. These “outer rim” counties in the WashingtonBaltimore-NV CSA in Virginia and West Virginia are closest to attaining monitors to the extent they are 

upwind of any monitors in the Washington-Baltimore-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 emissions related factors, and jurisdictional boundaries.

Two Separate Nonattainment Areas: Baltimore and Washington DC-MD-VA 

Baltimore-Towson, MD MSA:

The Edgewood monitor in Harford County has the highest design value in the current Baltimore 

nonattainment area and Washington-Baltimore-NV CSA at 0.089 ppm. Building from this monitor, 

meteorology and emissions-related factors suggest the existence of the following relationships between 

possible contributing area(s) and receptor monitors shown in Table 1: 

Table 1. Upwind-Downwind Linkages current Baltimore MD nonattainment area.

Location of Downwind Receptor 

Monitor

Close Upwind Possible 

Contributing Area(s) in 

Maryland

Close Upwind Possible 

Contributing Area(s) in other 

States

Harford County Baltimore and Queen Anne’s 

County; Baltimore City.

Baltimore County Anne Arundel, Carroll, Harford, 

Howard and Queen Anne’s 

Counties; Baltimore City.

Carroll County Baltimore, Frederick, Howard (Loudoun County, VA.)
19

and Montgomery Counties.

Anne Arundel County Calvert, Prince George's and 

Queen Anne’s Counties.

Note: A county in parentheses is not adjacent to the downwind receptor monitor.

The current Baltimore MD nonattainment area forms an area with progression of possible upwind 

contributing areas and possible downwind receptor monitors. The farthest of these upwind counties 

however have a possible contribution-receptor relationship with counties in the current Washington DCMD-VA nonattainment area. Harford County’s high design value is no doubt influenced by the close 

proximity of Baltimore County and Baltimore City and to a lesser extent by Anne Arundel County. 

Baltimore and Anne Arundel Counties both rank in the “top five” counties for emissions in the 

Washington-Baltimore-NV CSA for both NOx and VOC emissions. Baltimore City is ranked sixth in 

the Washington-Baltimore-NV CSA for both NOx and VOC emissions.

Washington-Arlington-Alexandria, DC-VA-MD-WV MSA, Winchester, VA-WV MSA, Culpeper, 

VA and Lexington Park, MD Micropolitan Statistical Areas:

These areas are summarized together because the smaller statistical areas of Winchester, Culpeper and 

Lexington Park are adjacent to the Washington-Arlington-Alexandria, DC-VA-MD-WV MSA and not 

adjacent to the Baltimore-Towson, MD MSA. The monitor in Fairfax County, VA has a design value of 

0.081 ppm which is the second highest within the Washington-Baltimore-NV CSA. In close proximity 

are the monitors in Arlington County, VA and the District of Columbia all of which have a design value 

of 0.079 ppm. Surrounding these monitors are counties with monitors that have lower design values of 

0.078 or 0.077 ppm in Prince George’s and Calvert Counties in Maryland or of 0.075 ppm or less –

Charles, Frederick and Montgomery Counties in Maryland, and Loudoun and Prince William Counties 

(plus Alexandria City) in Virginia. This suggests a core of peak nonattainment surrounded by declining 

ozone concentrations on the predominantly upwind or downwind sides. Building from these “core” 

monitors in Arlington and Fairfax Counties and the District of Columbia, meteorology and emissionsrelated factors suggest the existence of the following relationships between possible contributing area 

and receptor monitors shown in Table 2: 

Table 2. Upwind-Downwind Linkages current Washington DC-MD-VA nonattainment area and 

Adjacent Areas.

Location of Downwind Receptor 

Monitor

Close Upwind Possible

Contributing Area(s) in State 

with Downwind Receptor

Close Upwind Possible 

Contributing Area(s) in another 

State

Fairfax County, VA Arlington, Fauquier, Loudoun 

and Prince William6 Counties, 

VA, and, Alexandria and Falls 

Church Cities in Virginia.

Charles and Prince George's 

Counties in Maryland.

Arlington County, VA Fairfax,7(Fauquier,) Loudoun, 

Prince William, and Stafford 

Counties in Virginia, and, 

Alexandria and Falls Church 

Cities in Virginia in Virginia.

District of Columbia Arlington, Fairfax, (Fauquier.) 

 

6 Wherever Prince William County is indicated also includes at times also Manassas and Manassas Park Cities.

7 Wherever Fairfax County is indicated also includes at times also Fairfax City.
20

Loudoun and Prince William 

Counties, and, Alexandria and 

Falls Church Cities in Virginia.

Montgomery and Prince 

George's Counties in Maryland.

Prince George’s County, MD Calvert, Charles and Howard 

Counties in Maryland.

District of Columbia.

Fairfax and Stafford William 

Counties in Virginia.

Calvert County, MD Charles, Prince George’s and St. 

Mary’s Counties in Maryland.

Note: A county in parentheses is not adjacent to the downwind receptor monitor.

The monitors in the District of Columbia, Arlington County and Fairfax County (and at time in Prince 

George’s County, MD) apparently form a “central core of nonattainment monitors” in the current 

Washington DC-MD-VA nonattainment area. This result is not surprising because Montgomery and 

Prince George's Counties in Maryland and Fairfax County, VA are all rank in the “top five” for 

emissions in the Washington-Baltimore-NV CSA. In addition, the District of Columbia and Loudoun 

and Prince William Counties in Virginia rank between 6th and 11th for emissions. 

Overall, the 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 often into Anne 

Arundel and Prince George’s Counties in Maryland. 

Consideration of emissions and meteorological related factors suggest that the monitor in Harford 

County, MD is primarily influenced by the current Baltimore nonattainment area as shown in the 

summary in Table 1 above.

Harford County’s high design value is no doubt influenced by the close proximity of Baltimore County 

and Baltimore City and to a lesser extent by Anne Arundel County. Baltimore and Anne Arundel 

Counties both rank in the “top five” counties in the Washington-Baltimore-NV CSA for both NOx and 

VOC emissions. Baltimore City is ranked sixth in the Washington-Baltimore-NV CSA for both NOx 

and VOC emissions. 

Consideration of emissions and meteorological related factors suggest that the “central core of 

nonattainment monitors” in the current Washington DC-MD-VA nonattainment area are primarily 

influenced by possible contribution from the current Washington DC-MD-VA nonattainment area. See 

Table 2. These monitors in the District of Columbia, Arlington County and Fairfax County, and, to a 

lesser extent, Prince George’s County form a “central core of nonattainment monitors” because they are 

within or surrounded by high emissions counties of: Montgomery and Prince George's Counties in 

Maryland and Fairfax, Loudoun and Prince William Counties in Virginia and the District of Columbia. 

Table 1 suggests that the monitor in Anne Arundel County, MD is an extension of this “central core of 

nonattainment monitors” because two counties in the current Washington DC-MD-VA nonattainment 

area – Calvert and Prince George’s Counties – are upwind of this monitor at times. 
21

Tables 1 and 2 suggest that these counties– Anne Arundel, Carroll and Howard Counties in Maryland –

in the current Baltimore nonattainment area could contribute to, could receive contribution from, or 

could both contribute and receive contribution from counties in the current Washington DC-MD-VA 

nonattainment the current Baltimore nonattainment area. Likewise, Tables 1 and 2 suggest that the 

following counties – Calvert, Frederick, Montgomery and Prince George’s in Maryland and to a lesser 

extent Loudoun County, VA in the current Washington DC-MD-VA nonattainment area could

contribute, could receive contribution, or could both contribute and receive contribution from counties 

in the current Baltimore nonattainment area. However, consideration of all the factors including 

jurisdictional boundaries and including the States’ recommendations the current nonattainment 

boundaries should be maintained.

With regards to Howard County, MD, it can be kept with the rest of the current Baltimore nonattainment 

area because overall consideration of the five factors including the State’s recommendations favor this 

result as previously discussed in this document under “Analysis and Assessment of Factors” for the 

“Current Baltimore Nonattainment Area.” With regards to Carroll County, MD, it can be kept with the 

rest of the current Baltimore nonattainment area because overall consideration of the five factors 

including the State’s recommendations favor this result as previously discussed in this document under 

“Analysis and Assessment of Factors” for the “Current Baltimore Nonattainment Area.” With regards to 

Anne Arundel County, MD, it can be kept with the rest of the current Baltimore nonattainment area 

because overall consideration of the five factors including the State’s recommendations favor this result 

as previously discussed in this document under “Analysis and Assessment of Factors” for the “Current 

Baltimore Nonattainment Area.” With regards to Fredrick County, MD, it can be kept with the rest of 

the current Washington DC-MD-VA nonattainment area because overall consideration of the five 

factors including the State’s recommendations favor this result as previously discussed in this document 

under “Analysis and Assessment of Factors” for the “Current Washington DC- MD-VA Nonattainment 

Area.” With regards to Calvert County, MD, it can be kept with the rest of the current Washington DCMD-VA nonattainment area because overall consideration of the five factors including the State’s 

recommendations favor this result as previously discussed in this document under “Analysis and 

Assessment of Factors” for the “Current Washington DC- MD-VA Nonattainment Area.” With regards 

to Montgomery County, MD, it can be kept with the rest of the current Washington DC-MD-VA 

nonattainment area because overall consideration of the five factors including the State’s 

recommendations favor this result as previously discussed in this document under “Analysis and 

Assessment of Factors” for the “Current Washington DC- MD-VA Nonattainment Area.” With regards 

to Prince George’s County, MD, it can be kept with the rest of the current Washington DC-MD-VA 

nonattainment area because overall consideration of the five factors including the State’s 

recommendations favor this result as previously discussed in this document under “Analysis and 

Assessment of Factors” for the “Current Washington DC- MD-VA Nonattainment Area.” 

Figure 1 is a map of the intended Washington, DC-MD-VA nonattainment area. The map provides 

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

other jurisdictional boundaries, the CSA boundary, the current existing nonattainment area boundaries 

for 1997 ozone NAAQS, and major transportation arteries.
22

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

For the 1997 ozone NAAQS, this identical area was designated nonattainment. The boundary for the 

current Washington DC-MD-VA nonattainment area for the 1997 ozone NAAQS includes:

(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.
23

Figure 1b. The Intended Baltimore MD Area

For purposes of the 1997 ozone NAAQS, this identical area was designated nonattainment. The 

boundary for the current Baltimore nonattainment area for the 1997 ozone NAAQS included Anne 

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

On March 10, 2009, Maryland recommended that the same counties in both areas be designated as 

nonattainment for the 2008 ozone NAAQS based on air quality data from 2006-2008. These data are 

from FRM monitors or FEM monitors sited and operated in accordance with 40 CFR part 58. 

After considering these recommendations and based on EPA's technical analysis described below, EPA 

intends to designate the counties and independent cities in the States identified in Table 3 below as 

“nonattainment” for the 2008 ozone NAAQS as part of the Washington, DC-MD-VA Area multi-state 

nonattainment area and the Baltimore area intrastate nonattainment area. Table A includes Maryland’s 

portion of an intended nonattainment area was well as the counties/independent cities in the other states 

that EPA intends to designate as part of an intended nonattainment area. 
24

Table 3. State's Recommended and EPA’s Intended Designated Nonattainment Counties for the 

Washington, DC-MD-VA Area and the Baltimore MD Area.

Washington, DC-MDVAState-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

District of Columbia Entire District of Columbia Entire District of Columbia

Maryland

Calvert County 

Charles County 

Frederick County 

Montgomery County 

Prince George's County

Calvert County 

Charles County 

Frederick County 

Montgomery County 

Prince George's County

Virginia

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 

Baltimore State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Maryland

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
25

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 4 and 5. Note that only counties in the Washington-Baltimore-NV CSA that have 

ozone monitors are included in Tables 4 and 5.

Table 4. Monitor data for Maryland’s Portions of the Washington-Baltimore-NV CSA.

County/City, State Monitor AQS 

ID#

Short Name State 

Recommended 

Nonattainment?

8-hr Ozone Design Values, 2008-2010 

(ppm)

Anne Arundel Co., 

MD

240030014 Davidsonville Yes 0.079

Baltimore Co., MD 240051007

240053001

Padonia

Essex

Yes 0.077

0.078

Calvert Co., MD 240090011 Calvert Co. Yes 0.077

Carroll Co., MD 240130001 South Carroll Yes 0.076

Charles Co., MD 240170010 Southern 

Maryland

Yes 0.075

Frederick Co., MD 240210037 Frederick Co. Yes 0.075

Harford Co., MD 240251001

240259001

Edgewood

Aldino

Yes 0.089

0.078

Montgomery Co., MD 240313001 Rockville Yes 0.074

Prince George's Co., 

MD

240330030

240338003

Howard U. –

Beltsville

Pr. Georges 

Co. 

Equestrian Ctr

Yes 0.078

0.077

Baltimore City, MD 245100054 Furley 

E.S.Rec 

Center

Yes 0.067

Table 5. Monitor data for Portions of the Washington-Baltimore-NV CSA in Other States.
26

County/City, State Monitor AQS 

ID#

Short Name State 

Recommended 

Nonattainment?

8-hr Ozone Design Values, 2008-2010 

(ppm)

District of Columbia 110010025

110010041

110010043

Takoma

River Terrace

McMillan 

Reservoir

Yes 0.075

0.077

0.079

Virginia portion of the Washington-Baltimore CSA:

Arlington Co., VA 510130020 Arlington Yes 0.079

Fairfax Co., VA 510590030 Franconia Yes 0.081

Fauquier Co., VA 510610002 Sumerduck No 0.065

Frederick Co., VA 510690010 Butler Manuf. 

Co Near Rest

No 0.068

Loudoun Co., VA 511071005 Ashburn Yes 0.075

Prince William Co., 

VA

511530009 James S. 

Long Park

Yes 0.070

Stafford Co., VA 511790001 Widewater No 0.070

Alexandria City, VA 515100009 Alexandria Yes 0.074

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 currently designated 

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

nonattainment area and the current 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,

8

either within one or more 

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

 

8 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.
27

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

Arlington and Fairfax Counties in Virginia.

Analysis of the Concentrations within the Washington-Baltimore-NV CSA:

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

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 MSA. 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.

9

 Appendix 1 to Part I 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 current Washington DC-MD-VA nonattainment area, the Howard University (HU)-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 to Part I 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. 

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

areas of peak ozone concentrations: (1) the first of these areas of peak ozone concentrations 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 site in Harford County and the two monitoring sites 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—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. 

 

9

Source: MDPlan2010.pdf (Downloaded 12/9/2011 from http://www.epa.gov/ttn/amtic/plans.html).
28

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 6 provides basic data for these other monitors:

Table 6. Three Attaining Monitors Outside the Washington-Baltimore-NV CSA.

County/City, State Monitor AQS 

ID#

Short Name State 

Recommended 

Nonattainment?

8-hr Ozone Design 

Values, 2008-2010 

(ppm)

Caroline County, VA 510330001 Corbin No 0.073

Berkeley County, WV 540030003 Martinsburg 

Ball Field

No 0.070

Washington County, 

MD

240430009 Hagerstown No 0.072

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

between high emissions of ozone precursors in within some geographic region and peak ozone design 

values in that geographic region: 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 and is in Harford County, MD, the north-easternmost county in the 

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

monitors comprised of the monitors in Fairfax County, VA, in the District of Columbia and possibly of 

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

surrounding red solid line. 
29
30

Design Value Changes – 2003 to 2010:

Table 7 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 

NAAQS and the 2010 design values. The first and second highest design values in the WashingtonBaltimore-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 7. Air Quality Data – Design Values for 2003, 2008 and 2010.

County

State 

Recommended 

Nonattainment for 

2008 NAAQS?

2003 8-hour 

ozone 

design value

(ppm)10

2008 8-hour 

Ozone 

design value

(ppm)11

2010 8-hour 

Ozone 

design value

(ppm)12

Current 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

Current 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

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.

 

10 “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.

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

12 Data Source: ozone_dv75_20082010.xls (downloaded on 9/22/2011 from http://www.epa.gov/airtrends/values.html.
31

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 current 

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

design value of 0.085 ppm or more.13 Likewise, for designations under the 1997 ozone NAAQS, 

Arlington County, VA had the highest design value of 0.099 ppm (2000-2002); for the 2000-2002 

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.14 For the 

designations under the 1997 ozone NAAQS, the design value for the current Baltimore nonattainment 

area was 0.004 ppm greater than the design value for the current Washington DC-MD-VA 

nonattainment area. Both areas were classified as moderate nonattainment areas.15

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

in the current Washington DC-MD-VA nonattainment area had a design value of 0.087 ppm which set 

the design value for the current Washington DC-MD-VA nonattainment area at 0.087 ppm. The 

Edgewood site in Harford County, MD had a design value of 0.091 ppm which set the design value for 

the current Baltimore nonattainment area at 0.087 ppm. The difference in 2008 design values between 

these two current nonattainment areas was still 0.004 ppm. 

Currently, for the period 2008-2010, the difference in design values for these two current nonattainment 

areas has grown to 0.008 ppm. Whether or not this difference would cause these two current 

nonattainment areas to have a different classification in the event they remain separate areas will only be 

known once EPA promulgates a final rule that sets the classification scheme for the 2008 NAAQS.

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 would likely 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 

 

13 “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).

14

 Ibid.

15

 Ibid. See also, 69 FR 23858, April 30, 2004.
32

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 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 establishes the design value for the current Baltimore 

nonattainment area). In 2008 this monitor’s design value was equal to that for the current 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 for Arlington County, 

VA 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. This result suggest that the air quality data at the monitor in Anne Arundel 

County is more related to activity in the current Washington DC-MD-VA nonattainment area than the 

rest of the current Baltimore nonattainment area.

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 current 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 current Washington DC-MDVA nonattainment area and Anne Arundel County, MD had the same design value. All monitors in the 

current 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 current Baltimore MD nonattainment area are currently showing 

attainment of the 1997 ozone NAAQS. 

The air quality data over the last 7 years indicates 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. 

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 
33

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

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

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 8 shows emissions of NOx and VOC given in tons per year (tpy) for violating and potentially 

contributing counties in the current Baltimore MD and Washington DC-MD-VA nonattainment areas 

and other portions of the Washington-Baltimore-NV CSA. 

Table 8. Total 2008 NOx and VOC Emissions.

County/City

State 

Recommended 

Nonattainment?

NOx

(tpy)

VOC 

(tpy)

Current 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 
34

Table 8 (continued). Total 2008 NOx and VOC Emissions.

County/City

State 

Recommended 

Nonattainment?

NOx 

(tpy)

VOC 

(tpy)

Current 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 

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 
35

Table 8 (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)

The current Washington DC-MD-VA nonattainment area contains 48.5% of the Washington-BaltimoreNV CSA’s total NOx emissions and 55% of the Washington-Baltimore-NV CSA‘s total VOC 

emissions.

The current Baltimore nonattainment area contains 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 current Washington DC-MD-VA and Baltimore nonattainment areas contain 89% of the 

Washington-Baltimore-NV CSA’s total NOx emissions and 84% of the Washington-Baltimore-NV 

CSA’s total VOC emissions.
36

In the Washington-Baltimore-NV CSA, Anne Arundel, Baltimore, Prince George's and Montgomery 

Counties in Maryland and Fairfax County in Virginia comprise the “top five”

16 when ranking by VOC 

or by NOx emissions (with first being highest). An area in the “top five” within the WashingtonBaltimore-NV CSA needed to have NOx emissions of more than 20,000 tpy or VOC emissions of more 

than 14,000 tpy. With the exception of Montgomery County, MD, all of these areas contain monitors

violating the 2008 ozone NAAQS. Montgomery County, MD is adjacent to two counties that contain

monitors violating the 2008 ozone NAAQS. Likewise, Anne Arundel, Baltimore, and Prince George's 

Counties in Maryland and Fairfax County are adjacent to one or more counties or the District of 

Columbia which contain a monitor violating the 2008 ozone NAAQS. 

The following comprise the next six highest ranked (that is, numbers 6 through 11 within the 

Washington-Baltimore-NV CSA) for VOC or NOx emissions (not listed in order of ranking): Baltimore 

City and Frederick and Howard Counties in Maryland, the District of Columbia, and, Loudoun and 

Prince William Counties in Virginia. An area ranking 6th through 11th within the WashingtonBaltimore-NV CSA needed to have NOx emissions of between 6,900 and 20,000 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 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 9 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.

 

 

16 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

Table 9. 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 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 

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 current 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 current 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 
38

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 current 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 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 1.4% 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 current Washington DC-MD-VA nonattainment area, the emissions of the 

Frederick County, VA Area would be about 2.7and 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 current 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 

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 current 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 Current 

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 current Baltimore nonattainment area, its emissions would be about 2.9 and 3.5 

percent of such an area’s NOx and VOC emissions, respectively. Its emissions would add about 2.7 to 
39

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.17 

(5) Jefferson County, WV (emissions rankings within CSA: 27th for VOC & 25th for NOx), if included 

with the current Washington DC-MD-VA nonattainment area, would comprise about 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 current Washington DC-MD-VA nonattainment area, its emissions would be about 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 current Washington DC-MD-VA nonattainment area, its 

emissions would be about 1.4 and 1.8 percent of such an area’s NOx and VOC emissions, respectively. 

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 current Washington DCMD-VA nonattainment area, its emissions would be about 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 

current Washington DC-MD-VA nonattainment area’s NOx and VOC emissions, respectively. Alone, 

Spotsylvania County’s emissions are about 2.8 and 3.1 percent of the current Washington DC-MD-VA 

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 

 

17 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

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 current 

Washington DC-MD-VA nonattainment area or one consisting of both the current 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 current Washington DC-MD-VA nonattainment area, the total emissions of Stafford 

County alone would be about 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 3.4 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, Stafford County is in the OTR. Section 184 of the CAA requires that in attainment areas within 

the OTR many sources of VOC and 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.18

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 10 and 11 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.

 

18 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. 
41

Table 10. Population and Growth in the Current 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)

Current Baltimore MD Nonattainment Area:

Anne Arundel Co., MD Yes 537,656 452 1.19 46,325 +9% 

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% 

Current 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 11. 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% 
42

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% 

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).

The current 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 current Washington DC-MD-VA nonattainment area less 

Frederick County Maryland) encompasses 95 percent of the current nonattainment area’s population; 

Frederick County is however adjacent to Carroll County, MD that contains a monitor violating the 2008 

NAAQS.

The current 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 current Baltimore NAA, 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 
43

proximity to the Edgewood monitor with the highest design value in the Washington-Baltimore-NV 

CSA’s and the current 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 which had the highest growth rate in the Baltimore nonattainment area 

and had a growth rate comparable to the faster growing current Washington DC-MD-VA nonattainment 

area.

Together the current 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 current nonattainment areas are 

moderately to very densely populated. In general, the counties and cities in the current 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: 

(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 current 

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 current 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 current 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 current Washington DC-MD-VA 

nonattainment area (17% versus 15%) but its absolute change was small – around 9,600 which is one 
44

one-hundredth of the Washington-Baltimore-NV CSA’s overall change or 1.5% of that for the current 

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 current 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. 

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 1 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 12 shows the total vehicle miles traveled (VMT) and total 

number of commuters for each county within the Washington-Baltimore-NV CSA.

Table 12. Traffic and Commuting Patterns.

County

State 

Recommended 

Nonattainment?

2008 VMT (million 

miles)

Total 

Commuters

Current 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 

Current Washington DC-MD-VA Nonattainment Area:

District of Columbia, DC Yes 3,685 260,296 
45

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:

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 current 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. 
46

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” 19 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. 20 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 current 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 current 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 

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 current Washington DC-MD-VA 

nonattainment area. Together they contain or enclose all the violating monitors within the current 

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 current nonattainment area. 

Filling out 95 percent of the VMT in the current 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 current 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 current 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 current 

Baltimore NAA, 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 

current Baltimore nonattainment area. Carroll County has the lowest VMT and number of commuters

 

19 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. 

20 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). 
47

within the current 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 current 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 Washington-Baltimore-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 current 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 the counties listed under “Other counties” in the preceding table, all but one have 

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 with 

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 13. Traffic and Commuting Patterns – Fauquier, Queen Anne’s and St. Mary’s Counties as 

a Percentage of CSA Totals.

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 current Washington nonattainment area (independent cities 
48

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 current 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 current 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 MSA but only onehalf percent (0.5%) of the Washington-Baltimore-NV CSA’s total or 1.7 percent of the total for the 

current Baltimore nonattainment area. Queen Anne’s County is only connected to the rest of the MSA 

by the Chesapeake Bay Bridge (U.S. Routes 50 and 301) across the Chesapeake Bay to Anne Arundel 

County (see Figure 1 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 current 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). 

(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 current Washington-DC-MD-VA 

nonattainment area) which 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) 

of 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 current 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 WashingtonBaltimore-NV CSA’s total or 1.9% of the total for the current Washington-DC-MD-VA nonattainment 

area) is between that of Calvert and Charles Counties which is not surprising because St. Mary’s 

population is between that of these other two. St. Mary’s comprises the CBSA of the Lexington Park 
49

MD micropolitan statistical area whereas Charles County is part of the current Washington DC-MD-VA 

nonattainment area; the current 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 current 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 current 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 current 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 current 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 current 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. 

Factor 3: Meteorology (weather/transport patterns)

The data:

The 30-year average summer surface-level wind directions for the design value county in each of the 

current areas is shown in Figures 3a through 3 d. 

For Harford County (Figure 3a), MD in the in the current 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 east0.0%

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
50

southeast; 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 current Washington DC-MD-VA nonattainment area the 

winds are from the west-northwest through the southeast about 64 percent of the time.

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
51

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. 

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
52

Figures 3e and f show the data for all the counties in the current Baltimore and Washington DC-MD-VA 

nonattainment areas, respectively. The patterns are essentially the same for all counties and cities in the 

current 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

WN

W

NNW

Anne Arundel Co., MD

Baltimore Co., MD

Carroll Co., MD

Harford Co., MD

Howard Co., MD

Baltimore City, MD

Figure 3e. Current Baltimore Nonattainment Area
53

Analyses:

In general, a county with a violating monitor or monitors will be presumed to be “upwind” of its 

monitor or those monitors at least some of the time because Figures 3a through 3f suggest summertime 

winds can come from any direction some of the time. 

The analysis for each county or city (or sometimes a county and any enclosed or adjacent city) will 

estimate the percent of time that county or city is upwind of the nearest violating monitors. At times the 

monitors in Frederick, Loudoun and Charles counties will be considered to see if a county not in either 

the current Baltimore or Washington nonattainment areas could be having an effect on these monitors 

which are close to violating the 2008 NAAQS. 

The effects counties in the current Washington nonattainment area might be having on the violating 

monitors in Anne Arundel and Carroll Counties will be considered see if the current Baltimore and 

Washington nonattainment areas might be sufficiently linked by contribution. Likewise, the effects that 

counties in the current Baltimore nonattainment area might be having on the violating monitors in Prince 

George’s County, MD will be considered for the same purpose. Also, the Frederick County, MD 

monitor will be considered with respect to possible impacts from nearby counties in the current 

Baltimore nonattainment for the purpose to see if the current Baltimore and Washington nonattainment 

areas might be sufficiently linked here by contribution from Baltimore to Washington. 

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. Current Washington DC-MD-VA NA Area
54

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. 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. Frederick County, MD or Loudoun County, VA is 

interposed 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, and Stafford Counties both of which contain 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.

Parts of Fauquier County, VA could be at times upwind of the Loudoun County monitor (roughly 

WSW) of the monitor and hence not upwind more than roughly 10 percent of the time; and at times, 

Fauquier County could not upwind more than roughly 10 percent of the time from the monitors in 

Fairfax County, Arlington County or the District of Columbia because Fauquier County is roughly 

WSW of these monitors.

Of the Fredericksburg, VA Area, Stafford County is closest to the Fairfax County-Arlington-District of 

Columbia monitors. Stafford County’s monitor may not fully represent the effects of the emissions from 

the northwestern half of this county upon the monitor in Arlington County. This portion of Stafford is 

roughly south-southwest of Arlington County and hence upwind about 22 percent of the time. Likewise, 

Stafford is roughly southwest of Prince George’s County, MD and would be upwind less than 18 percent 

of the time (average of the SSW and WSW values). Spotsylvania County and Fredericksburg City have 

the attaining monitors in Stafford and Fauquier Counties in Virginia and the attaining monitor in Charles 

County, MD between these portions of the Fredericksburg, VA Area and the nearest violating monitor in 

the Washington-Baltimore-NV CSA. With respect to the Stafford County monitor, Spotsylvania County 

and Fredericksburg City are essentially SW and thus would be upwind about 19 percent of the time 

(average of SSW and WSW). 

St. Mary’s County, MD is adjacent to Calvert County, MD and roughly SSW to west-southwest of the 

monitor and hence upwind approximately 36 percent of the time. Likewise, St. Mary’s County is SSE 

of the Monitor in Charles County, MD and hence upwind about 15 percent of the time. 

Queen Anne’s County is closest to the violating Edgewood monitor in Harford County, the monitor in 

Anne Arundel County and the Essex monitor in Baltimore County. It is roughly south to SE of 

Edgewood and hence upwind about 25 (average of SSW and SSE plus average of SSE and ESE) percent 

of the time.
55

It is roughly south to SE of Essex and hence upwind about 24 (average of SSW and SSE plus average of 

SSE and ESE) percent of the time. It is roughly east to ESE of Anne Arundel and hence upwind about 

23 (average of ESE and ENE plus ESE) percent of the time.

Current Washington DC-MD-VA Nonattainment Area:

Within the current Washington DC-MD-VA nonattainment area the situation is as follows:

The violating monitors closest to Prince William County, VA and the two associated cities (Manassas 

and Manassas Park) are those in Loudoun County, Fairfax County, Arlington County and the District of 

Columbia. 21 Prince William County and the two associated cities are generally south-southwest to due 

west-southwest of the Fairfax County-Arlington County-District of Columbia monitors. They would be 

upwind around 36 percent of the time. With respect to Loudoun County, VA they are essentially southsoutheast to south-southwest of the monitor and are at upwind about 39 percent of the time. 

The violating monitors closest to Loudoun County are those in Fairfax County, Arlington County and 

the District of Columbia. Loudoun County is essentially northwest of these monitors. It would be 

upwind around 16 percent of the time (average of north-northwest and west-northwest). With respect to 

the monitors in Frederick County, MD and Carroll County, MD, Loudoun County is south-southwest of 

Frederick County and west-southwest of Carroll County. It would be upwind of Frederick County, MD 

about 24 percent of the time and of Carroll County, MD less than 15 percent of the time.

The violating monitors closest to Fairfax County, VA (plus the enclosed Fairfax City) are those in

Loudoun County, Arlington County and District of Columbia. With respect to the Arlington County and 

District of Columbia monitors22 the “Fairfaxes” (county and city) are west-northwest to north-northwest 

and thus would be upwind over 50 percent of the time. With respect to the Loudoun County monitor, 

this county and city are essentially southwest and thus would be upwind roughly 17 percent of the time 

(average of south-southwest and west-southwest). Parts of Fairfax County are west of the easternmost 

monitor (Pr. Georges Co. Equestrian Ctr) in Prince George’s County, MD and would be upwind roughly 

16 percent of the time (average of west-southwest and west-northwest). 

Falls Church City23 and Arlington County are closest to the monitors in Fairfax County, VA and those in 

the District of Columbia. With respect to the Fairfax County monitor, this county and city are 

essentially north-northeast and thus would be upwind about 10 percent of the time. With respect to the 

Arlington County monitor, Falls Church City is roughly northwest and thus would be upwind at most 15 

percent of the time (average of west-northwest and north-northwest). With respect to the District of 

Columbia monitors, this county and city are roughly west-southwest and thus would be upwind at most 

15 percent of the time. 

 

21 With respect to this county these monitors are so close to ether that they will be considered as a group for the determination 

of percent of time the county is upwind.

22 With respect to this county these monitors are so close to ether that they will be considered as a group for the determination 

of percent of time the county is upwind.

23

 Falls Church City is small geographically and will be considered as an appendage of Arlington County for any monitor 

except that in Arlington County, in which case Fall Church City will be considered on its own.
56

Alexandria City is closest to the monitors in Arlington and Fairfax Counties in Virginia and those in the 

District of Columbia. With respect to the Arlington County and District of Columbia monitors, this city 

is essentially south-southwest and thus would be upwind less than 25 percent of the time. With respect 

to the Fairfax County monitor, this city is essentially north and thus would be upwind less than 13 

percent of the time. 

Frederick County, MD is closest to the violating monitor in Carroll County, MD. With respect to the 

Carroll County monitor, this county is essentially west-northwest to west-southwest and thus would be 

upwind about 31 percent of the time. 

Montgomery County, MD is closest to the violating monitors in Prince George’s and Carroll Counties in 

Maryland and those in the District of Columbia. With respect to the Carroll County monitor, this county 

is essentially west-southwest to south-southwest and thus would be upwind about 32 percent of the time. 

With respect to the monitor (Howard U.–Beltsville) in the north of Prince George’s County, this county 

is essentially northwest and thus would be upwind about 15 percent of the time (average of westnorthwest and north-northwest). With respect to the monitors in the District of Columbia, this county is 

north-northwest to north-northeast and thus would be upwind at most 13 percent of the time. 

Prince George’s County, MD is close to the violating monitors in Anne Arundel and Calvert Counties in 

MD, Fairfax Co. VA, and the District of Columbia. With respect to the monitors in the District of 

Columbia, this county is south-southeast to north-northeast and thus would be upwind at most 38 

percent of the time. With respect to the Anne Arundel County monitor, this county is south-southwest 

to north-northwest and thus would be upwind about 66 percent of the time. With respect to the Calvert 

County monitor, this county is north-northwest to west-northwest and thus would be upwind about 22 

percent of the time. With respect to the Fairfax County monitor, this county is south-southeast to eastnortheast and thus would be upwind about 27 percent of the time.

Charles County, MD is close to the violating monitors in Prince George’s and Calvert Counties in 

Maryland and the violating monitor in Fairfax County, VA. With respect to the monitor (Pr. Georges

Co. Equestrian Ctr) in the eastern part of Prince George’s County, this county is essentially SSW to 

WSW and thus would be upwind about 35 percent of the time. With respect to the Calvert County 

monitor, this county is essentially WNW to WSW and thus would be upwind about 25 percent of the 

time. With respect to the Fairfax County monitor, this county is essentially SSW to SSE and thus would 

be upwind about 39 percent of the time. 

Calvert County, MD is close to violating monitors in that it is adjacent to Prince George’s and Anne 

Arundel Counties in Maryland. With respect to the monitor (Pr. Georges Co. Equestrian Ctr) in the 

eastern part of Prince George’s County, this county is essentially southeast and thus would be upwind 

about 18 percent of the time (average of SSE and SSW). With respect to the Anne Arundel County 

monitor, this county is essentially SSW and thus would be upwind about 20 percent of the time. 
57

The District of Columbia is close to the violating monitors in Prince George’s County, MD, Arlington

and Fairfax Counties in Virginia in that it is adjacent to these two counties. With respect to the 

Arlington County monitor, the District of Columbia is essentially ENE and thus would be upwind well 

less than 10 percent of the time. With respect to the Prince George’s County monitors, the District of 

Columbia is essentially SW of the northernmost monitor (Howard U. –Beltsville) in Prince George’s 

County and thus would be upwind about 18 percent of the time (average of WSW and SSW), and, the 

District of Columbia is essentially NNW of the monitor (Pr. Georges Co. Equestrian Ctr) in the east of 

Prince George’s County and thus would be upwind no more than 7 percent of the time. With respect to 

the Fairfax County monitor, the District of Columbia is essentially NNE and thus would be upwind 

about 5 percent of the time. 

Current Baltimore Nonattainment Area:

Harford County, MD is close to the violating monitors in Baltimore County in Maryland. With respect 

to the southernmost monitor (Essex) in Baltimore County, this county is essentially NNE to ESE and 

thus would be upwind about 8 percent of the time. With respect to the northernmost monitor (Padonia) 

in Baltimore County, this county is essentially ENE to NNE and thus would be upwind about 22 percent 

of the time. 

Baltimore City, MD is close to the violating monitors in Harford and Baltimore Counties in Maryland. 

With respect to either monitor (Edgewood or Aldino) in Harford County, this city is essentially SW and 

thus would be upwind about 33 percent of the time (average of WSW and SSW). With respect to the 

southernmost monitor (Essex) in Baltimore County, this city is essentially west and thus would be 

upwind about 21 percent of the time (average of WSW and WNW). With respect to the northernmost 

monitor (Padonia) in Baltimore County, this city is essentially to the south and thus would be upwind 

about 14 percent of the time. 

Baltimore County, MD is closest to the violating monitors in Harford and Carroll Counties in Maryland. 

With respect to the respect to the southernmost monitor (Edgewood) in Harford County, this county is 

essentially NNW to SSW and thus would be upwind about 61 percent of the time. With respect to the 

respect to the northernmost monitor (Aldino) in Harford County, this county is primarily WNW to SSW

and thus would be upwind about 56 percent of the time. With respect to the Carroll County monitor, 

this county is essentially ENE to ESE and thus would be upwind about 14 percent of the time. 

Howard County, MD is closest to the violating monitor in Carroll County, the northernmost monitor 

(Howard U. –Beltsville) in Prince George’s County and somewhat proximate to the monitors in 

Baltimore County. With respect to the Carroll County monitor, this county is essentially southwest and 

thus would be upwind about 16 percent of the time (average of SSW and SSE). With respect to the

Howard U. –Beltsville monitor, this county is essentially to the north and thus would be upwind about 

11 percent of the time (average of NNW and NNE). With respect to the northernmost monitor (Padonia) 

in Baltimore County, this county is essentially SW and thus would be upwind about 18 percent of the 

time (average of SSW to WSW). With respect to the southernmost monitor (Essex) in Baltimore 

County, this county is essentially west and thus would be upwind about 21 percent of the time (average 

of WSW and WNW). With respect to the Frederick County, MD monitor, this county is essentially ESE 

to ENE and thus would be upwind about 14 percent of the time. 
58

Anne Arundel County, MD is closest to the violating monitors in Prince George’s County and somewhat 

proximate to the southernmost monitor (Essex) in Baltimore County. With respect to the respect to the 

southernmost monitor (Essex) in Baltimore County, this county is primarily SW and thus would be 

upwind about 17 percent of the time (average of SSW to WSW). With respect to the monitor (Pr. 

Georges Co. Equestrian Ctr) in the eastern part of Prince George’s County, this county is essentially 

NNE to ESE and thus would be upwind about 18 percent of the time. With respect to the northernmost 

monitor (Howard U. –Beltsville) in Prince George’s County, this county is essentially SSE to ENE and 

thus would be upwind about 29 percent of the time. 

Carroll County, MD is closest to the northernmost monitor (Padonia) in Baltimore County. With respect 

to the Padonia monitor, this county is essentially NNW to WSW and thus would be upwind about 52

percent of the time. With respect to the Frederick County, MD monitor, this county is essentially NE

and thus would be upwind about 8 percent of the time (average of NNE to ENE). 

Discussion and summary for the current Baltimore nonattainment Area:

For the most part, the counties and cities in the current Baltimore nonattainment area mainly affect each 

other. With the exception of Anne Arundel County, the remainder of the current Baltimore 

nonattainment area seems to have the most frequent possible impacts on violating monitors within this 

nonattainment area: 

Baltimore Area:

For the most part, the counties and cities in the current Baltimore nonattainment area mainly affect each 

other. With the exception of Anne Arundel County, the other areas have the most impact on violating 

monitors within this nonattainment area: 

Highest percentages at a close violating monitor:

o Baltimore County is upwind of the Edgewood monitor in Harford County some 61 

percent of the time.

o Baltimore City is upwind of the Edgewood and Aldino, Harford County monitors some 

33 percent of the time.

o Carroll and Harford Counties upwind of the Padonia Baltimore County monitor monitors 

some 52 and 22 percent of the time, respectively.

Second highest percentages at a close violating monitor:

o Baltimore and Howard Counties upwind of the Carroll County monitor some 14 and 16 

percent of the time, respectively.

o Baltimore City upwind of the Padonia, Baltimore County monitors some 14 percent of 

the time.
59

There appear to be some clear upwind-downwind effects across the boundaries of the current Baltimore 

and Washington DC-MD-VA nonattainment areas:

Anne Arundel County is likely upwind of the northernmost violating monitor (Howard U.–

Beltsville) in Prince George’s County 29 percent of the time but is upwind of the violating Essex 

monitor in Baltimore County 18 percent of the time. 

Howard County is likely upwind of the northernmost violating monitor (Howard U.–Beltsville) 

in Prince George’s County 29 percent 11 percent of the time.

Discussion and summary for the current Washington DC-MD_VA nonattainment Area

In the current Washington DC-MD-VA nonattainment area, the violating monitors in Fairfax and 

Arlington Counties in Virginia, and those in the District of Columbia are downwind of close-by counties 

and cities in Virginia. Loudoun and Prince William Counties in Virginia are most often upwind of the 

closest violating monitors in Fairfax and Arlington Counties in Virginia and those in the District of 

Columbia some 36 and 16 percent of the time. Fairfax County, VA is most often upwind of the 

Arlington County and District of Columbia monitors some 50 percent of the time. Charles County, MD 

is more often upwind of the Fairfax County, VA monitor (perhaps 39 percent of the time) than other 

monitors in this current nonattainment area. 

That adjacent and geographically close counties and cities in Virginia are so often upwind of the District 

of Columbia is salient because such potential contributions cross state lines. For instance, Prince 

George’s County, MD is likely upwind of the monitor in Anne Arundel County, MD (some 66 % of the 

time) than upwind of the monitor in Fairfax County (some 27 percent of the time). The same cross-state 

situation is true for the relationship between Charles and Prince George’s Counties and Fairfax County, 

VA. 

Several Maryland counties in the current Washington DC-MD-VA nonattainment area are most 

frequently upwind of and most proximate to a violating monitor in the current Baltimore nonattainment 

area. The Carroll County monitor is downwind of Frederick and Montgomery counties in Maryland 

some 31 to 32% of the time. Likewise the Anne Arundel County monitor is downwind of Prince 

George's and Calvert Counties in Maryland some 66 and 20 percent of the time, respectively. 

Montgomery, Calvert and Charles Counties in Maryland are upwind of one or more violating monitors 

in Prince George’s County, MD some 15, 18 and 35 percent of the time, respectively. 

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.24 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 

 

24 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).
60

easternmost portion of the Appalachian Mountains. Jefferson Count, 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

limiting air pollution transport within its air shed. Therefore, there are no barriers to transport elsewhere 

in this CSA.

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. 

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 currently broken down as shown in 

Table 14:
61

Table 14. 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)

Current Baltimore 

Nonattainment Area:

Anne Arundel, Baltimore, 

Carroll, Harford, and Howard 

Counties and Baltimore City in 

Maryland.

Nonattainment - Moderate

Current Washington DC-MDVA 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 - Moderate

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).
62

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 current Baltimore nonattainment area and the current

Washington DC-MD-VA nonattainment area are served by different MPOs. The National Capital 

Region Transportation Planning Board (TPB) is the MPO for the much of the Washington-Arlingtoncurrent Washington DC-MD-VA 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.

25

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 .

26

 

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.27

The Washington DC-MD-VA air quality planning 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 Metropolitan Statistical Area (MSA) 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 multistate 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.

28

 The 

principal mandates of MWAQC are to prepare plans demonstrating attainment of the federal ozone 

 

25 http://www.mwcog.org/transportation/tpb/, last checked November 28, 2011.

26

 “BRTB Members,” http://www.baltometro.org/transportation-planning/brtb-members last checked November 28, 2011.

27

 “About FAMPO,” http://www.fampo.gwregion.org/ last checked November 28, 2011.

28 "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.
63

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.

Conclusions:

Based on the assessment of factors described above, EPA has preliminarily concluded that the following 

counties and independent cities listed in Tables 15 below meet the CAA criteria for inclusion in the 

nonattainment areas indicated therein:

Table 15. EPA’s Intended Designated Nonattainment Counties and Independent Cities in the 

Washington-Baltimore-NV CSA.

Washington, DC-MD-VA Area

EPA Intended Nonattainment Counties 

District of Columbia Entire District of Columbia

Maryland

Calvert County 

Charles County 

Frederick County 

Montgomery County 

Prince George's County

Virginia

Alexandria City 

Arlington County 

Fairfax City 

Fairfax County 

Falls Church City 

Loudoun County 

Manassas City 

Manassas Park City 

Prince William County 

Baltimore Area

EPA Intended Nonattainment Counties

Maryland

Anne Arundel, Maryland

Carroll, Maryland

Harford, Maryland

Howard, Maryland

Baltimore, Maryland

Baltimore City, Maryland
64

Appendix 1 to Part I: 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 MSA, or CSA if multiple MSAs 

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 
65

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). 

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.
66

Part II. Technical Analysis for the Philadelphia-Wilmington-Atlantic City Area

Note: Part II contains a new sequence of figure and table numbering that starts anew with figure 

1and table 1. 

Figure 1 is a map of the Philadelphia-Wilmington-Atlantic City intended nonattainment area (the 

Philadelphia Area). The map provides other relevant information including the locations and design 

values of air quality monitors, county and other jurisdictional boundaries. The map shows the 

boundaries of the Philadelphia-Camden-Vineland CSA, the existing nonattainment area boundary for the 

1997 ozone NAAQS, and EPA’s intended nonattainment boundary for the 2008 ozone NAAQS.

Figure 1.

For purposes of the 1997 8-hour ozone NAAQS, this area was designated nonattainment. The 

Philadelphia-Wilmington-Atlantic City nonattainment area included the entire counties of Kent, New 

Castle, and Sussex in Delaware; Cecil in Maryland; Atlantic, Burlington, Camden, Cape May, 

Cumberland, Gloucester, Mercer, Ocean, and Salem in New Jersey; and Bucks, Chester, Delaware, 

Montgomery, and Philadelphia in Pennsylvania.

In March 2009, the State of Delaware recommended that no counties in Delaware be included in the 

Philadelphia Area for the 2008 ozone NAAQS based on air quality data from 2006-2008. Instead, 

Delaware recommend a large, multi-state nonattainment area, covering the entire States of Delaware, 
67

Maryland, Michigan, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Virginia, and West 

Virginia, and the District of Columbia. Alternatively, Delaware recommended that the entire State of 

Delaware be designated as a stand-alone nonattainment area. In October 2011, Delaware updated its 

recommendations. In that letter, Delaware expanded its recommended large multi-state nonattainment 

area to include the States of Kentucky, Indiana, Illinois, Missouri, Tennessee, and Wisconsin. In 

addition, in its October 2011 letter, the State of Delaware specified that if EPA did not accept either of its 

designation options, then Kent County should not be designated nonattainment. This recommendation is 

based on 2008-2010 data and preliminary 2009-2011 data. The recommendations were based on data from

Federal Reference Method (FRM) monitors or Federal Equivalent Method (FEM) monitors sited and 

operated in accordance with 40 CFR Part 58. (See the March 18, 2009 letter from Governor Jack A. 

Markell to EPA, received on April 3, 2009; and the October 28, 2011 letter from the Delaware

Department of Natural Resources and Environmental Control.)

In March 2009, the State of Maryland recommended that Cecil County be designated as nonattainment 

as part of the Philadelphia Area for the 2008 ozone NAAQS based on air quality data from 2006-2008. 

This is the same Maryland County that was included in the Philadelphia-Wilmington-Atlantic City

nonattainment area for the 1997 ozone NAAQS. This recommendation was based on data from FRM 

monitors or FEM monitors sited and operated in accordance with 40 CFR Part 58. (See the March 10,

2009 letter from Governor Martin O’Malley to EPA, received on March 16, 2009.)

In April 2009, the State of New Jersey recommended that the same nine counties in New Jersey that 

were included in the Philadelphia-Wilmington-Atlantic City nonattainment area for the 1997 ozone 

NAAQS be designated as nonattainment in the Philadelphia Area for the 2008 ozone NAAQS based on 

air quality data from 2006-2008. This recommendation was based on data from FRM monitors or FEM 

monitors sited and operated in accordance with 40 CFR Part 58. (See the April 1, 2009 letter from the

New Jersey Department of Environmental Protection to EPA.)

In March 2009, the Commonwealth of Pennsylvania recommended that the same five counties in 

Pennsylvania that were included in the Philadelphia-Wilmington-Atlantic City nonattainment area for 

the 1997 ozone NAAQS be designated as nonattainment in the Philadelphia Area for the 2008 ozone 

NAAQS based on air quality data from 2006-2008. Pennsylvania provided an update to the original 

recommendation in November 2011 based on air quality data from 2009-2011. That recommendation 

was to remove Chester and Delaware Counties from the Philadelphia Area, and designate those counties 

as attainment. This recommendation was based on data from FRM monitors or FEM monitors sited and 

operated in accordance with 40 CFR Part 58. (See the March 17, 2009 and November 22, 2011 letters

from the Pennsylvania Department of Environmental Protection to EPA.) 

After considering these recommendations and based on EPA's technical analysis described below, EPA 

intends to designate 16 counties in Delaware, Maryland, New Jersey, and Pennsylvania (identified in 

Table 1 below) as “nonattainment” for the 2008 ozone NAAQS as the Philadelphia Area nonattainment 

area. 

Table 1. State's Recommended and EPA’s Intended Designated Nonattainment Counties for the 

Philadelphia Area.

Philadelphia State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Delaware None New Castle

Maryland Cecil Cecil
68

New Jersey

Atlantic, Burlington, Camden, Cape 

May, Cumberland, Gloucester, 

Mercer, Ocean, and Salem

Atlantic, Burlington, Camden, Cape 

May, Cumberland, Gloucester, 

Mercer, Ocean, and Salem

Pennsylvania Bucks, Montgomery, and 

Philadelphia

Bucks, Chester, Delaware, 

Montgomery, and Philadelphia

Factor Assessment

The counties evaluated in this analysis include all counties in the Philadelphia-Camden-Vineland CSA 

plus the counties outside the CSA that were included in the Philadelphia-Wilmington-Atlantic City 

nonattainment area for the 1997 ozone NAAQS.

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values (in parts per billion (ppb)) for air quality 

monitors in counties in the Philadelphia Area based on data for the 2008-2010 period (i.e., the 2010 

design value, or DV), which are the most recent years with fully-certified air quality data. A monitor’s 

DV 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 DV 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 DV for the county or area is 

determined by the monitor with the highest level.

Note: Monitors that are eligible for providing design value data generally include State and Local Air 

Monitoring Stations (SLAMS) that are sited in accordance with 40 CFR Part 58, Appendix D (Section 

4.1) and operating with a federal reference method (FRM) or federal equivalent method (FEM) monitor 

that meets the requirements of 40 CFR part 58, appendix A. All data from a special purpose monitor 

(SPM) using an FRM or FEM which has operated for more than 24 months is eligible for comparison to 

the NAAQS unless the monitoring agency demonstrates that the data came from a particular period 

during which the requirements of appendix A (quality assurance requirements) or appendix E (probe and 

monitoring path siting criteria) were not met.

The 2010 DVs for the ozone NAAQS for counties in the Philadelphia-Camden-Vineland CBSA and 

several nearby surrounding area are shown in Table 2. 

Table 2. Air Quality Data.

County

State Recommended 

Nonattainment?

2010 8-hour Ozone 

DV (ppb)

Atlantic, NJ Yes 74

Berks, PA Yes, other area 79

Bucks, PA Yes 83

Burlington, NJ Yes --

Camden, NJ Yes 80

Cape May, NJ Yes --

Cecil, MD Yes 80

Chester, PA No 76
69

Cumberland, NJ Yes 76

Delaware, PA No 74

Gloucester, NJ Yes 81

Kent, DE No 74

Mercer, NJ Yes 78

Montgomery, PA Yes 78

New Castle, DE Yes, other area 76

Ocean, NJ Yes 81

Philadelphia, PA Yes 82

Salem, NJ Yes --

Sussex, DE Yes, other area 77

Note: Counties with no ozone monitor are identified with “--“ in the 2010 8-hour Ozone DV column.

In accordance with section 107(d) of the Clean Air Act, EPA must designate an area nonattainment if it 

is violating the 2008 ozone NAAQS. New Castle and Sussex Counties in Delaware, Cecil County, 

Maryland; Berks, Bucks, Montgomery, and Philadelphia Counties in Pennsylvania; and several counties 

in New Jersey show violations of the 2008 ozone NAAQS. Therefore, these counties must be included 

in a nonattainment area. 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 contributes to the nearby violation. 

Factor 2: Emissions and Emissions-Related Data

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

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) Significant emissions levels in a nearby area 

indicate the potential for the area to contribute to observed 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 3 shows emissions of NOx and VOC (given in tons per year) for violating and potentially 

contributing counties in the Philadelphia Area. 

Table 3. Total 2008 NOx and VOC Emissions.

County

State Recommended 

Nonattainment? NOx (tpy) VOC (tpy)

Atlantic, NJ Yes 6,143 10,713

Berks, PA Yes, other area 18,908 15,918
70

Bucks, PA Yes 17,736 21,160

Burlington, NJ Yes 10,919 12,909

Camden, NJ Yes 12,725 10,731

Cape May, NJ Yes 6,407 7,774

Cecil, MD Yes 4,763 3,715

Chester, PA No 16,806 16,351

Cumberland, NJ Yes 4,916 5,727

Delaware, PA No 28,118 15,881

Gloucester, NJ Yes 18,335 11,756

Kent, DE No 7,667 5,381

Mercer, NJ Yes 9,909 8,160

Montgomery, PA Yes 22,741 26,372

New Castle, DE Yes, other area 22,633 14,133

Ocean, NJ Yes 9,909 19,572

Philadelphia, PA Yes 33,176 32,021

Salem, NJ Yes 6,106 3,308

Sussex, DE Yes, other area 14,870 9,972

Philadelphia County, PA has the highest NOx and VOC emissions in the area of analysis. Other 

counties with comparatively high emissions are New Castle County in Delaware; and Delaware and 

Montgomery Counties in Pennsylvania. Counties with comparatively low emissions are Kent County, 

Delaware; Cecil County, Maryland; and several counties in New Jersey.

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. Table 4 shows the population, population density, and population growth information for 

each county in the area.

Table 4. Population and Growth.

County

State 

Recommended 

Nonattainment?

2010 

Population

2010 Population 

Density (1000 

pop/sq mi)

Absolute change 

in population 

(2000-2010)

Population % 

change 

(2000-2010)

Atlantic, NJ Yes 274,549 0.45 21,569 +9% 

Berks, PA Yes, other area 411,442 0.48 36,945 +10% 

Bucks, PA Yes 625,249 1.01 25,841 +4% 

Burlington, NJ Yes 448,734 0.55 24,255 +6% 

Camden, NJ Yes 513,657 2.26 6,064 +1% 

Cape May, NJ Yes 97,265 0.34 (5,043) -5% 

Cecil, MD Yes 101,108 0.27 14,643 +17% 

Chester, PA No 498,886 0.66 63,107 +14% 

Cumberland, NJ Yes 156,898 0.31 10,547 +7% 

Delaware, PA No 558,979 2.93 6,938 +1% 
71

Gloucester, NJ Yes 288,288 0.86 31,962 +12% 

Kent, DE No 162,310 0.27 35,200 +28% 

Mercer, NJ Yes 366,513 1.60 14,979 +4% 

Montgomery, PA Yes 799,874 1.64 48,936 +7% 

New Castle, DE Yes, other area 538,479 1.11 36,620 +7% 

Ocean, NJ Yes 576,567 0.76 62,913 +12% 

Philadelphia, PA Yes 1,526,006 10.71 12,194 +1% 

Salem, NJ Yes 66,083 0.19 1,867 +3% 

Sussex, DE Yes, other area 197,145 0.20 39,710 +25% 

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)

Philadelphia County, Pennsylvania has the highest population and population density in the area of 

analysis. Bucks, Chester, Montgomery, and Delaware Counties, in Pennsylvania and New Castle 

County in Delaware also have comparatively large populations compared to Kent County, Delaware and 

several counties in New Jersey with comparatively small populations and population densities. Most 

counties in the analysis have experienced some population growth.

Traffic and commuting patterns

EPA evaluated the total Vehicle Miles Traveled (VMT) for each county in the area. In combination 

with the population/population density data and the location of main transportation arteries (see Figure 

1, above), this information helps identify the probable location of non-point source emissions. A county 

with high VMT is generally an integral part of an urban area and indicates the presence of motor vehicle 

emissions that may contribute to ozone formation. Rapid population or VMT growth in a county on the 

urban perimeter signifies increasing integration with the core urban area, and indicates that the 

associated area source and mobile source emissions may be appropriate to include in the nonattainment 

area. Table 5 shows total 2008 VMT for each county.

Table 5. Traffic (VMT) Data.

County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

Atlantic, NJ Yes 2,863

Berks, PA Yes, other area 3,335

Bucks, PA Yes 5,021

Burlington, NJ Yes 4,524

Camden, NJ Yes 3,923

Cape May, NJ Yes 1,040

Cecil, MD Yes 1,350

Chester, PA No 4,410

Cumberland, NJ Yes 1,163

Delaware, PA No 3,782

Gloucester, NJ Yes 2,645

Kent, DE No 1,565

Mercer, NJ Yes 3,306
72

Montgomery, PA Yes 6,883

New Castle, DE Yes, other area 5,266

Ocean, NJ Yes 3,834

Philadelphia, PA Yes 5,955

Salem, NJ Yes 992

Sussex, DE Yes, other area 2,122

* MOBILE model VMT are those inputs into the NEI version 1.5. 

New Castle County, Delaware; and Bucks, Montgomery, and Philadelphia Counties in Pennsylvania 

have the highest VMT in the area of analysis. Kent County, Delaware; Cecil County, Maryland; and 

several counties in New Jersey have relatively low VMT.

Table 6. County to County Worker Flow.

Residence County Kent, 

DE

New Castle, 

DE

Sussex, 

DE

Cecil, 

MD

Berks, 

PA

Bucks, 

PA

Chester, 

PA

Delaware, 

PA

Montgomery,

PA

Philadelphia,

PA

Workplace County 

Kent, DE 47,455 3,927 5,704 186 157 18 131 112 41 65

New Castle, DE 6,058 209,742 1,119 14,059 493 12,976 9,002 1,201 1,856

Sussex, DE 3,779 319 52,073 33 29 15 6 39

Cecil, MD 243 3,379 42 18,446 18 557 192 52

Atlantic, NJ 11 142 31 4 172 73 231 181 831

Burlington, NJ 40 475 25 27 40 4,250 426 1,306 1,559 5,087

Camden, NJ 55 434 10 72 27 2,039 539 2,287 1,844 7,196

Cape May, NJ 27 20 13 54 81 118 95 324

Cumberland, NJ 26 164 5 19 42 24 103 66 140

Gloucester, NJ 750 19 82 16 362 411 1,251 405 1,502

Mercer, NJ 10 78 12 7 37 20,812 222 345 1,298 1,676

Ocean, NJ 13 30 8 5 220 23 10 13 86

Salem, NJ 32 1,841 11 139 37 155 245 59 84

Berks, PA 4 48 5 140,819 410 1,916 187 4,231 243

Bucks, PA 12 261 12 22 675 168,090 1,133 2,060 23,722 23,248

Chester, PA 37 4,738 33 941 5,596 3,036 137,678 18,504 25,006 7,810

Delaware, PA 125 8,150 61 373 505 2,754 17,870 137,988 11,758 21,802

Montgomery, PA 27 1,851 53 176 12,727 48,414 25,673 28,144 245,619 59,970

Philadelphia, PA 83 5,386 131 254 702 31,892 10,568 48,151 54,576 429,667

Source: US Census Bureau County-To-County Worker Flow Files 

http://www.census.gov/population/www/cen2000/commuting/index.html

Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties in Pennsylvania have the highest 

numbers of commuters to other counties in the Philadelphia-Camden-Vineland CSA. New Castle 

County, Delaware, Cecil County, Maryland, and Berks County, Pennsylvania have moderate numbers of 

commuters into other counties in the CSA. Sussex and Kent Counties in Delaware, which are not in the 

Philadelphia-Camden-Vineland CSA, have the fewest commuters into the CSA.

Factor 3: Meteorology (weather/transport patterns)

EPA evaluated available meteorological data, consisting of 30-year average summertime wind directions

from the National Weather Service, to help determine how meteorological conditions, such as weather, 

transport patterns and stagnation conditions, would affect the fate and transport of precursor emissions 

contributing to ozone formation. 
73

The highest ozone design values, over 80 ppb, are in Bucks and Philadelphia Counties, in Pennsylvania, 

and Ocean County in New Jersey. The winds during the ozone season come predominantly from the 

southwest. This indicates that emissions from Chester and Delaware Counties in Pennsylvania; New 

Castle County, Delaware; Cecil County, Maryland; and counties in southwest New Jersey contribute to 

the downwind violations in Bucks and Philadelphia Counties during most of the ozone season. 

Considering prevailing wind patterns and the location of the highest violating monitors, Berks County, 

Pennsylvania and Kent and Sussex Counties in Delaware are unlikely to contribute to downwind 

violations during most of the ozone season.

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.

The Philadelphia Area does not have any geographical or topographical barriers significantly limiting air

pollution transport within its air shed. Therefore, there are no barriers to contribution from upwind 

areas.

Factor 5: Jurisdictional boundaries

EPA considers existing jurisdictional boundaries for the purposes of providing a clearly defined legal 

boundary and so that areas designated nonattainment have the legal authority and cooperative planning 

necessary to carrying out the air quality planning and enforcement functions for nonattainment areas. 

Examples of jurisdictional boundaries include existing/prior nonattainment areas for ozone or other 

urban-scale pollutants, counties, air districts, townships, metropolitan planning organizations, 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.

The major jurisdictional boundaries in the Philadelphia-Wilmington-Atlantic area are the state lines 

between Pennsylvania, Delaware, and New Jersey. Air-quality monitors that violate the 2008 8-hour 

ozone NAAQS in the Philadelphia Area are located in Delaware, Maryland, New Jersey, and 

Pennsylvania. 

The Philadelphia-Camden-Vineland CSA consists of New Castle County, Delaware; Cecil County, 

Maryland; Burlington, Camden, Cumberland, Gloucester, and Salem Counties in New Jersey, and 

Berks, Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties in Pennsylvania. All those 

counties, except for Berks County, Pennsylvania are included in the Philadelphia-Wilmington-Atlantic 

City nonattainment area for the 1997 8-hour ozone NAAQS. The nonattainment area also includes Kent 

and Sussex Counties, Delaware and Atlantic, Cape May, Mercer, and Ocean Counties, New Jersey. 

Mercer and Ocean Counties, New Jersey are part of the New York-Newark-Bridgeport, NY-NJ-CT-PA

CSA. Atlantic County makes up the Atlantic City-Hammonton, NJ MSA. Cape May County makes up 

the Ocean City, NJ MSA. In Delaware, Kent County, Delaware makes up the Dover MSA and Sussex 

County makes up the Seaford Micropolitan Statistical Area. 
74

The Delaware Valley Regional Planning Commission (DVRPC), the metropolitan planning organization 

(MPO) in the Philadelphia Area, serves Bucks, Chester, Delaware, Montgomery, and Philadelphia 

Counties in Pennsylvania, and Burlington, Camden, Gloucester, and Mercer Counties in New Jersey. 

New Castle County, DE and Cecil County, Maryland are in a separate MPO, the Wilmington Area 

Planning Council (WILMAPCO). 

Delaware

New Castle County has historically been part of the Philadelphia nonattainment area for ozone (1-hour 

and 8-hour) and fine particulate matter (PM2.5). New Castle County is part of the Wilmington, DE-MDNJ Metropolitan Division of the Philadelphia-Camden-Wilmington Metropolitan Statistical Area (MSA)

in the Philadelphia-Camden-Vineland CSA. Being part of a statistical area indicates that counties are 

linked through employment and commuting. According to the Office of Management and Budget’s 

“Standards for Defining Metropolitan and Micropolitan Statistical Areas,” published in the Federal 

Register on December 27, 2000 (65 FR 82228), the “general concept of a Metropolitan Statistical Area 

or a Micropolitan Statistical Area is that of an area containing a recognized population nucleus and 

adjacent communities that have a high degree of integration with that nucleus.” Delaware,

Pennsylvania, Maryland and New Jersey have a long history of working cooperatively through the 

Ozone Transport Commission (OTC) and the Mid-Atlantic Northeast Visibility Union (MANE-VU)

with ozone attainment planning. Furthermore, the two local MPOs, DVRPC and WILMAPCO, have 

worked together for decades.

Kent and Sussex Counties are less connected to the Philadelphia Area. They are not part of the 

Philadelphia-Camden-Vineland CSA. Kent County makes up the Dover MSA, and Sussex County 

makes up the Seaford Micropolitan Statistical Area. The Dover/Kent County MPO is the planning 

organization for Kent County, Delaware. This MPO covers 20 municipalities including all of Smyrna, 

which is also in New Castle County and all of Milford, which is also in Sussex County. Planning for 

Sussex County is done by the Sussex County Planning and Zoning Commission While Kent County was 

part of the Philadelphia-Wilmington-Trenton nonattainment area for the 1-hour ozone NAAQS, Sussex 

County was a separate nonattainment area. 

Maryland

Cecil County has historically been part of the Philadelphia nonattainment area for ozone (1-hour and 8-

hour) and PM2.5. Cecil County is part of the Wilmington, DE-MD-NJ Metropolitan Division of the 

Philadelphia-Camden-Wilmington MSA in the Philadelphia-Camden-Vineland CSA. Maryland, 

Delaware, Pennsylvania, and New Jersey have a long history of working cooperatively through the OTC 

and MANE-VU and with ozone attainment planning. Furthermore, the two local MPOs, DVRPC and 

WILMAPCO, have worked together for decades. 

Pennsylvania

Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties have historically been part of the 

Philadelphia nonattainment area for ozone (1-hour and 8-hour) and PM2.5. These five counties are part 

of the Philadelphia, PA Metropolitan Division of the Philadelphia-Camden-Wilmington MSA in the 

Philadelphia-Camden-Vineland CSA. These counties are part of DVRPC, the main MPO for the 

Philadelphia Area.

Berks County is less connected to Philadelphia. While it was added to the Philadelphia-CamdenVineland CSA in December 2005, it’s in a separate MSA, the Reading, PA MSA. Berks County has 
75

historically not been part of the Philadelphia nonattainment area for 8-hour ozone and PM2.5, but has 

been designated separately as the Reading area. Berks County was designated attainment/unclassifiable 

for 1-hour ozone. In addition, Berks County is covered by a separate MPO, the Berks County 

Planning Commission. 

Conclusion

Based on the assessment of factors described above, EPA has preliminarily concluded that the following 

counties meet the CAA criteria for inclusion in the Philadelphia-Camden-Atlantic City nonattainment 

area: New Castle County, Delaware; Cecil County, Maryland; Atlantic, Burlington, Camden, Cape 

May, Cumberland, Gloucester, Mercer, Ocean, and Salem Counties in New Jersey; and Bucks, Chester, 

Delaware, Montgomery, and Philadelphia Counties in Pennsylvania. The Philadelphia-WilmingtonAtlantic City nonattainment area for the 1997 8-hour ozone NAAQS included these same counties, plus 

Kent and Sussex Counties in Delaware. New Castle County in Delaware; Cecil County in Maryland; and 

Berks, Bucks, Montgomery, and Philadelphia Counties in Pennsylvania show violations of the 2008 

ozone NAAQS.29 Maryland and Pennsylvania have requested that these violating counties in their 

respective States be included as part of the Philadelphia nonattainment area, which is consistent with 

their inclusion of that area for the 1-hour and 1997 8-hour NAAQS and the PM2.5 NAAQS. 

Additionally, we think the factors above support inclusion of these counties in that nonattainment area. 

Therefore, we intend to include them as part of the Philadelphia nonattainment area for the 2008 ozone 

NAAQS. 

New Castle County, Delaware has relatively high emissions, high population, and high VMT. 

Considering prevailing winds from the southwest, this county likely contributes to downwind violations 

of the ozone NAAQS in the Philadelphia Area. Furthermore, New Castle County is part of the 

Philadelphia-Wilmington-Atlantic City 8-hour ozone nonattainment area and the Philadelphia-CamdenVineland CSA. New Castle County has a moderate degree of commuting into the other counties in the 

CSA, including over 24,000 commuters into Cecil, Chester, Delaware, Montgomery, and Philadelphia 

Counties. Therefore, EPA intends to designate New Castle County as nonattainment as part of the 

Philadelphia Area.

Chester and Delaware Counties in Pennsylvania are part of the Philadelphia, PA Metropolitan Division 

of the Philadelphia-Camden-Wilmington MSA in the Philadelphia-Camden-Vineland CSA. These 

counties have been historically part of the Philadelphia nonattainment areas for ozone (8-hour and 1-

hour) and PM2.5 and are linked together with significant commuting throughout the 5 counties. These

counties have relatively high populations and population densities. Delaware County has the second 

highest NOx emissions in the areas of analysis and among the highest VOC emissions. Taking into 

account the prevailing winds during the ozone season are predominantly from the southwest, emissions 

from Chester and Delaware Counties likely contribute to downwind violations in Bucks and 

Philadelphia Counties during most of the ozone season. Considering all these factors, EPA has 

concluded that Chester and Delaware Counties should be included in the Philadelphia Area.

In addition, monitors in Sussex County, Delaware and Berks County, Pennsylvania show violations of 

the 2008 ozone NAAQS and must be designated nonattainment. We believe that Sussex County, 

 

29 We discuss our conclusions as to the New Jersey counties in a Technical Analysis for the Philadelphia-WilmingtonAtlantic City Area sent to the State of New Jersey from EPA Region II.
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Delaware and Berks County, Pennsylvania should be designated as in separate nonattainment areas, and 

explained below.

Berks County, Pennsylvania has a violating monitor, but relatively moderate emissions, population, and 

VMT. There is some commuting from Berks County to the other counties in the Philadelphia Area, and 

Berks County is part of the Philadelphia-Camden-Vineland CSA. However, Berks County has 

historically been a separate ozone and PM2.5 nonattainment area. The County’s MPO, the Berks 

County Planning Commission, is separate from the Philadelphia Area’s MPO, DVRPC. Furthermore, 

meteorology indicates that on typical summer days when the violating monitors are experiencing 

exceedances of the ozone NAAQS, emissions from Berks County are not upwind of those monitors in 

the Philadelphia Area and thus we believe emissions from Berks County do not significantly contribute 

to nonattainment at those monitors. Therefore, EPA has preliminarily concluded that Berks County 

should not be included in the Philadelphia Area, and should be designated as nonattainment in a separate 

area30.

Sussex County, Delaware has a monitor that is violating the 2008 ozone NAAQS. It has moderate

emissions and population in the area as compared with the other counties in the area of analysis. It is 

not part of the Philadelphia-Camden-Vineland CSA. Furthermore, considering prevailing winds from 

the southwest and the location of the highest violating monitors in the Philadelphia Area, it is not likely 

that Sussex County is contributing significantly to the Philadelphia Area. Therefore, EPA has 

preliminarily concluded that Sussex County should not be included in the Philadelphia Area, and should 

be designated as nonattainment in a separate area31.

Kent County, Delaware has a monitor that meets the 2008 8-hour ozone NAAQS. This county has 

comparatively low emissions, population and VMT, and is not part of the Philadelphia-CamdenVineland CSA. Therefore, EPA has preliminarily concluded that Kent County should not be included in 

the Philadelphia Area, and should be designated as unclassifiable/attainment.

 

30 See EPA’s Technical Analysis for the Reading Area, sent to the Commonwealth of Pennsylvania by EPA Region III.

31 See EPA’s Technical Analysis for the Seaford Area, sent to the State of Delaware by EPA Region III.