1

Delaware

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

In March 2009, the State of Delaware recommended a large, multi-state nonattainment area, 

covering the entire States of Delaware, Maryland, Michigan, New Jersey, New York, North 

Carolina, Ohio, Pennsylvania, Virginia, and West Virginia, plus the District of Columbia. 

Alternatively, Delaware recommended that the entire State of Delaware be designated as a standalone 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. 

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 Delaware 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 

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, we do not intend to designate a large nonattainment area as suggested by Delaware.

The table below identifies the areas and associated counties or parts of counties in Delaware that 

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

standards (2008 NAAQS). 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 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 Delaware

Area

Delaware Recommended 

Nonattainment Counties

EPA’s Intended 

Nonattainment Counties

Philadelphia-WilmingtonAtlantic City none New Castle

Seaford none Sussex

The Philadelphia- Wilmington-Atlantic City Area is a multi-state nonattainment area. Table 1 in 

the Technical Analysis for the Philadelphia- Wilmington-Atlantic City Area, below, identifies 

the counties in the other states that EPA intends to designate as part of the nonattainment area.
2

EPA intends to designate the remaining county in Delaware that is not listed in the table above as 

“unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analysis below provides the basis for the 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 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 FRM or 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 is located the violating monitor(s).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 NAAQS3EPA recommended examining 

CSA/CBSAs because certain factors (such as population) 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.

 

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 emissionsrelated 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).
3

Technical Analysis for the Philadelphia-Wilmington-Atlantic City Area

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, 

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 
4

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 PhiladelphiaWilmington-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

New Jersey Atlantic, Burlington, Camden, Cape May, 

Cumberland, Gloucester, Mercer, Ocean, 

Atlantic, Burlington, Camden, Cape 

May, Cumberland, Gloucester, 
5

and Salem 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

Cumberland, NJ Yes 76

Delaware, PA No 74
6

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

Bucks, PA Yes 17,736 21,160
7

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% 

Gloucester, NJ Yes 288,288 0.86 31,962 +12% 
8

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&prod

Type=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

Montgomery, PA Yes 6,883
9

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. 

The highest ozone design values, over 80 ppb, are in Bucks and Philadelphia Counties, in 
10

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-WilmingtonAtlantic 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-CTPA 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. 
11

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-MD-NJ 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 MidAtlantic 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 

historically not been part of the Philadelphia nonattainment area for 8-hour ozone and PM2.5, but has 
12

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-Wilmington-Atlantic 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.4 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 PhiladelphiaCamden-Vineland 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, 

Delaware and Berks County, Pennsylvania should be designated as in separate nonattainment areas, 

and explained below.

 

4 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.
13

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 area5.

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 area6.

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.

 

5

See EPA’s Technical Analysis for the Reading Area, sent to the Commonwealth of Pennsylvania by EPA Region III.

6

See EPA’s Technical Analysis for the Seaford Area, sent to the State of Delaware by EPA Region III.
14

Technical Analysis for the Seaford Area

Figure 1 is a map of the intended Seaford nonattainment 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 Seaford Micropolitan Statistical 

Area (Sussex County, Delaware), the Dover Metropolitan Statistical Area (MSA) (Kent County, 

Delaware), 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 ozone NAAQS, the entire State of Delaware, including the Seaford Area, 

was designated nonattainment and was included in the Philadelphia-Wilmington-Atlantic City 

nonattainment area.

In March 2009, the State of Delaware recommended a large, multi-state nonattainment area, 

covering the entire States of Delaware, 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 standalone 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 
15

and preliminary 2009-2011 data. The recommendations were based on data from Federal Reference 

Method (FRM) monitors or Federal Equivalent Method (FEM) 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.)

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

EPA intends to designate one county in Delaware, Sussex County (identified in Table 1 below) as 

“nonattainment” for the 2008 ozone NAAQS as part of a newly designated Seaford nonattainment 

area. 

Table 1. State's Recommended and EPA’s Intended Designated Nonattainment Counties for the 

Seaford Area.

Seaford State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Delaware None Sussex

Factor Assessment

The area covered by this analysis is the Seaford Micropolitan Statistical Area (Sussex County, 

Delaware) and surrounding counties.

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values (DV) (in parts per billion (ppb)) for air 

quality monitors in the county in the Seaford Area (Sussex County, Delaware) and counties in the 

nearby surrounding 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 DV.

Note: Eligible monitors for providing design value data generally include State and Local Air 

Monitoring Stations (SLAMS) at population-oriented locations with an FRM or FEM monitor. All 

data from Special Purpose Monitors (SPM) using an FRM or FEM are eligible for comparison to the 

relevant NAAQS, subject to the requirements given in the October 17, 2006 Revision to Ambient 

Air Monitoring Regulations (71 FR 61236). All monitors used to provide data must meet the 

monitor siting and eligibility requirements given in 71 FR 61236 to 61328 in order to be acceptable 

for comparison to 2008 ozone NAAQS for designation purposes.

The 2010 DVs for the ozone NAAQS for counties in the Seaford Area (Sussex County, Delaware) 

and nearby surrounding area are shown in Table 2. 
16

Table 2. Air Quality Data.

County

State Recommended 

Nonattainment?

2010 8-hour Ozone DV 

(ppb)

Cape May, NJ Yes, other area --

Caroline, MD No --

Cumberland, NJ Yes, other area 76

Dorchester, MD No --

Kent, DE No 74

Sussex, DE Yes, other area 77

Talbot, MD No --

Wicomico, MD No --

Worcester, MD No --

Note: Counties with no ozone monitor are indicated 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. Sussex County, Delaware and Cumberland County, New 

Jersey show violations of the 2008 ozone NAAQS. Therefore, these counties must be included in a 

nonattainment area. EPA’s preliminary recommendation is to designate Cumberland County, New 

Jersey nonattainment in another nonattainment area, the Philadelphia-Wilmington-Atlantic City 

nonattainment area.

 

Note that the absence of a violating monitor is not a sufficient reason to eliminate counties as 

candidates for nonattainment status based upon contribution to violations in other nearby areas. 

Each county is evaluated based on the weight of evidence of the five factors. 

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 (in tons per year (tpy)) for violating and potentially 

contributing counties in the Seaford Area. 
17

Table 3. Total 2008 NOx and VOC Emissions.

County

State Recommended 

Nonattainment? NOx (tpy) VOC (tpy)

Cape May, NJ Yes, other area 6,407 7,774

Caroline, MD No 983 1,324

Cumberland, NJ Yes, other area 4,916 5,727

Dorchester, MD No 1,666 3,516

Kent, DE No 7,667 5,381

Sussex, DE Yes, other area 14,870 9,972

Talbot, MD No 1,822 2,869

Wicomico, MD No 2,391 3,669

Worcester, MD No 2,154 4,860

Sussex County, Delaware has the highest NOx and VOC emissions in the area of analysis. Kent 

County, Delaware; and Cape May County, New Jersey have the next highest emissions, but those 

counties emissions are about half that of Sussex County’s. Caroline and Talbot Counties, Maryland, 

have the lowest emissions suggesting that these counties may not be contributors to ozone 

nonattainment in the Seaford Area (Sussex County, Delaware).

Population density and degree of urbanization

EPA evaluated the population and vehicle use characteristics and trends in the Seaford Area and the 

nearby surrounding area as indicators of the probable location and magnitude of non-point source 

emissions. These include ozone-creating emissions from sources such as 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)

Cape May, NJ Yes, other area 97,265 0.34 (5,043) -5%

Caroline, MD No 33,066 0.10 3,241 +11%

Cumberland, NJ Yes, other area 156,898 0.31 10,547 +7%

Dorchester, MD No 32,618 0.05 35,200 +28

Kent, DE No 162,310 0.27 35,200 +28%

Sussex, DE Yes, other area 197,145 0.20 39,710 +25%

Talbot, MD No 37,782 0.12 3,890 +11%

Wicomico, MD No 98,733 0.25 13,872 +16%

Worcester, MD No 51,454 0.09 4,678 +10%

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&prod

Type=table)

Sussex and Kent Counties, Delaware and Cumberland County, New Jersey have the largest

populations and are the most densely populated in the area of analysis. Caroline, Dorchester, Talbot, 
18

and Worcester Counties in Maryland have the smallest population and are the least densely 

populated in the area of analysis. All but once county in the area of analysis has experienced 

population growth from 2000 to 2010. Note that the eastern coast of Sussex County, Delaware has 

several popular beaches, including Lewes and Rehoboth. The population of these beach areas 

increases substantially in the summertime (i.e., in the ozone season). Thus, non-point source 

emissions in Sussex County are higher in the ozone season than the rest of the year.

Traffic and commuting patterns

EPA evaluated the total Vehicle Miles Traveled (VMT) for each county in the Seaford Area and 

nearby surrounding 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 the 

total vehicle miles traveled (VMT) for each county in 2008.

Table 5. Traffic (VMT) Data.

County

State 

Recommended 

Nonattainment?

2008 VMT*

(million miles)

Cape May, NJ Yes, other area 1,040

Caroline, MD No 371

Cumberland, NJ Yes, other area 1,163

Dorchester, MD No 395

Kent, DE No 1,565

Sussex, DE Yes, other area 2,122

Talbot, MD No 614

Wicomico, MD No 1,008

Worcester, MD No 645

* MOBILE model VMT are those inputs into the NEI version 1.5. 

Sussex County, Delaware has the highest VMT in the area of analysis. Furthermore, as stated above, 

the eastern coast of Sussex County, Delaware has several popular beaches, including Lewes and 

Rehoboth. The traffic through Sussex County to the beach areas increases substantially in the 

summertime (i.e., in the ozone season). Thus, VMT and mobile source emissions in Sussex County

are higher in the ozone season than the rest of the year. Caroline and Dorchester Counties, Maryland 

have the lowest VMT. 
19

Table 6. County to County Worker Flow.

Residence County Kent, 

DE

Sussex, 

DE

Caroline, 

MD

Dorchester, 

MD

Talbot, 

MD

Wicomico, 

MD

Worcester, 

MD

Cape May, 

NJ

Cumberland, 

NJ

Workplace County 

Kent, DE 47,455 5,704 731 55 51 109 28 9 0

Sussex, DE 3,779 52,073 504 416 43 2,422 1,112 0 0

Caroline, MD 297 607 6,219 734 598 104 13 0 0

Dorchester, MD 68 373 566 9,391 774 844 20 0 0

Talbot, MD 121 371 3,221 1,955 12,194 274 21 0 0

Wicomico, MD 112 3,518 120 646 74 32,576 2,896 0 0

Worcester, MD 29 1,869 8 43 2 2,954 15,463 0 0

Cape May, NJ 0 20 0 0 4 10 28 31,782 1,162

Cumberland, NJ 26 5 0 0 0 0 0 1,129 43,866

Source: US Census Bureau County-To-County Worker Flow Files 

http://www.census.gov/population/www/cen2000/commuting/index.html

As shown in Table 6, above, Kent County, Delaware; and Wicomico and Worcester Counties, 

Maryland have the most commuting to and from Sussex County, Delaware. Caroline, Dorchester, 

and Talbot Counties, Maryland have comparatively little commuting to and from Sussex County, 

Delaware. The counties in New Jersey have no commuters to and from Sussex County, Delaware.

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 weather, transport patterns and 

stagnation conditions, would affect the fate and transport of precursor emissions contributing to 

ozone formation in the Seaford Area. 

As shown in Figure 2 below, in Sussex County, Delaware, the prevailing winds during the ozone 

season come predominantly from the south-southwest. This indicates that emissions from Kent 

County, Delaware and the counties in New Jersey are not expected to contribute to violations at the 

Sussex County, Delaware monitors. Dorchester, Wicomico, and Worcester Counties in Maryland 

are upwind of the violating monitors. Although emissions from those counties might contribute to 

violations in downwind Sussex County, Delaware, the emissions levels from those counties are so 

low that little actual contribution is expected.
20

Figure 2. 30-Year Average Summertime Wind Directions in Sussex County, Delaware.

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 Seaford 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.

Kent and Sussex Counties, Delaware were included in the Philadelphia-Wilmington-Atlantic City 

nonattainment area for 1997 ozone NAAQS. However, EPA’s preliminary recommendation is to 

not include them in that area for the 2008 ozone NAAQS, as supported by EPA’s five-factor analysis 

for the Philadelphia-Wilmington-Atlantic City area7. 

 

7

See EPA’s Technical Analysis for the Philadelphia-Wilmington-Atlantic City nonattainment area.
21

Sussex and Kent Counties in Delaware are in separate statistical areas. 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.” Sussex County makes up the Seaford Micropolitan Statistical Area,

while Kent County, Delaware makes up the Dover MSA. The Dover/Kent County MPO is the 

planning organization for Kent County. 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. 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. 

The main jurisdiction boundaries that separate Caroline, Dorchester, Talbot, Wicomico, and 

Worcester Counties, Maryland; and Cape May and Cumberland Counties, New Jersey from the 

Seaford area are state boundaries. Furthermore, these counties are not part of the Seaford 

Micropolitan Statistical Area. Cape May County, New Jersey is in the Ocean City, NJ MSA. 

Cumberland County, New Jersey is in the Vineland-Millville-Bridgeton, NJ MSA, which is part of 

the Philadelphia-Camden-Vineland, DE-MD-NJ-PA CSA. Dorchester County, Maryland is in the 

Cambridge, MD Micropolitan Statistical Area. Talbot County, Maryland makes up the Easton, MD 

Micropolitan Statistical Area. Worcester County, Maryland makes up the Ocean Pines, MD 

micropolitan statistical area and Wicomico County, Maryland is in the Salisbury, MD MSA, which 

are both part of the Salisbury-Ocean Pines, MD CSA. Therefore, the Seaford Area is generally 

unconnected with these other counties.

Conclusion

Based on the assessment of factors described above, EPA has preliminarily concluded that Sussex 

County, Delaware meets the Clean Air Act criteria for inclusion in its own nonattainment area, the 

Seaford nonattainment area.

Sussex County, Delaware has violating monitors and the highest emissions, population, and VMT in 

the area of analysis. EPA has concluded that the other counties in this analysis are not likely to 

contribute to ozone violations in Sussex County. These counties have comparatively low emissions, 

populations, and VMT. Kent County, Delaware; and Cape May County, New Jersey have the next 

highest emissions, but those counties emissions are about half that of Sussex County’s. Dominant 

ozone season winds are from the south-south west. This indicates that emissions from Kent County 

and the counties in New Jersey are not expected to contribute to violations at the Sussex County, 

Delaware monitors. Dorchester, Wicomico, and Worcester Counties in Maryland are upwind of the 

violating monitors. However, emissions from those counties are comparatively low suggesting that 

emissions from those counties would contribute little to violations in downwind Sussex County. 

Furthermore, the other counties in the area of analysis are not linked jurisdictionally to Sussex 

County and are not part of the Seaford Microplitan Statistical Area.