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. That

recommendation was based on 2008-2010 data and preliminary 2009-2011 data. On February 

29, 2012, Delaware submitted comments on EPA’s preliminary nonattainment area boundary 

decisions. In that letter, Delaware commented on EPA’s intended nonattainment area boundaries 

as well as EPA’s methodology for determining those boundaries. Delaware also commented on

EPA’s rejection of the large multi-state nonattainment area. 

EPA has addressed Delaware’s comments in the Responses to Significant Comments on the State 

and Tribal Designation Recommendations for the 2008 Ozone National Ambient Air Quality 

Standards document in the docket for these designations. In section 3.1.2 of this document, EPA 

addresses the concept of a large, multi-state nonattainment area and states that we do not believe 

that creation of a super-regional nonattainment area to address pollution transport is the 

appropriate approach. As an initial matter, Clean Air Act (CAA) section 107(d)(1) provides that 

areas designated nonattainment should include any “nearby” area contributing to a violation of 

the NAAQS. We believe that broad super-regional areas go beyond this by including areas that 

are not necessarily “nearby” but contribute to nonattainment through long-range transport. The 

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

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

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

to establish additional transport regions, as appropriate. Finally, we note that the approach taken 

by EPA is consistent with the approach Congress specified for serious and above areas for the 1-

hour NAAQS, where in section 107(d)(4)A), Congress set the Consolidated Metropolitan 

Statistical Area (CMSA) boundaries as the presumptive boundaries of the nonattainment area. In 

Catawba Co. v. EPA1

, the Court upheld that “contribute” under §107(a)(1)(A) of the CAA does 

not necessarily mean “any contribution” to nonattainment but rather a degree of contribution 

sufficient to deem an area nonattainment, that is, sufficient enough to warrant designation as 

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

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

EPA, 571 F.3d 20, 39 (D.C. Cir. 2009) (Internal citation omitted but with emphasis added). 

“Thus, reasonably exercising the discretion that Congress delegated to it, EPA interpreted 

“contribute” to mean “sufficiently contribute,” and then applied the CMSA presumption and 

nine-factor test precisely to identify those areas that meet that definition.” Id.

 1 Catawba County v. EPA, 571 F.3d 20, (D.C. Cir. 2009)
2

For the reasons stated above, EPA does 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 is designating as nonattainment for the 2008 ozone national ambient air quality standards 

(2008 ozone 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.

Nonattainment Areas in Delaware

Area

Delaware Recommended 

Nonattainment Counties

EPA’s Designated 

Nonattainment Counties

Philadelphia-WilmingtonAtlantic City, PA-NJ-MDDE

none New Castle

Seaford, DE none Sussex

The Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE Area is a multi-state nonattainment 

area. Table 1 in the Technical Analysis for the Philadelphia-Wilmington-Atlantic City, PA-NJMD-DE Area, below, identifies the counties in the other states that EPA is designating as part of 

the nonattainment area.

EPA is designating the remaining county in Delaware that is not listed in the table above, Kent 

County, as “unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analysis below provides the basis for the 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 ozone 

nonattainment area boundaries and recommended that states consider these factors in making 

their designation recommendations to EPA.2 

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);

 2 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.
3

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).3 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 (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.

 3 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).
4

Technical Analysis for the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD Area

Figure 1 is a map of the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD nonattainment 

area. The map provides other relevant information including the locations and 2010 design 

values of air quality monitors, county and other jurisdictional boundaries. The map shows the 

boundaries of the Philadelphia-Camden-Vineland, PA-NJ-DE-MD CSA, the existing 

nonattainment area boundary for the 1997 ozone NAAQS, and EPA’s nonattainment boundary 

for the 2008 ozone NAAQS.

Figure 1.

For purposes of the 1997 8-hour ozone NAAQS, much of this area was designated 

nonattainment. The Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area 

at that time 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-Wilmington-Atlantic City, PA-NJ-DE-MD 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, 
5

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 was based on 2008-2010 data and continues to be true based on preliminary 

2009-2011 data. The data are 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-Wilmington-Atlantic City, PA-NJ-DE-MD 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.) EPA has confirmed that 

the area is still nonattainment, based on the design value for 2010, which uses data from 2008 

through 2010.

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-Wilmington-Atlantic City, 

PA-NJ-DE-MD 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.) EPA has confirmed that the area is still 

nonattainment, based on the design value for 2010, which uses data from 2008 through 2010.

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 PhiladelphiaWilmington-Atlantic City, PA-NJ-DE-MD 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-Wilmington-Atlantic City, PA-NJ-DE-MD, 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 is designating 16 counties in Delaware, Maryland, New Jersey, and Pennsylvania 
6

(identified in Table 1 below) as “nonattainment” for the 2008 ozone NAAQS as the 

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD nonattainment area. 

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

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE Area.

Philadelphia State-Recommended 

Nonattainment Counties

Counties Designated by EPA

as Nonattainment

Delaware None New Castle

Maryland Cecil Cecil

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-CamdenVineland, PA-NJ-MD-DE CSA plus the counties outside the CSA that were included in the 

Philadelphia-Wilmington-Atlantic City nonattainment area for the 1997 ozone NAAQS. A more 

detailed meteorological assessment is included in a factor assessment for New Jersey’s request 

for Ocean and Mercer Counties is attached.

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-Wilmington-Atlantic City, PA-NJ-DE-MD 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 for the entire area. 

However, Pennsylvania submitted certified 2011 air quality data to EPA in November 2011. The 

only effect of using 2011 data is a slight change in the highest design value for the nonattainment 

area and the location of the highest design value. Since none of the other states in the 

nonattainment area submitted certified 2011 data to EPA while EPA was in the process of 

evaluating the states submittal, that is, though March 2011, EPA is using 2010 ozone data as the 

last year of data for evaluation of these requests. In ordinary circumstances, EPA does not use 

data from different years in different parts of nonattainment areas. The effects of using 2011 data 

from Pennsylvania are noted in Appendix C. 

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.
7

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-Wilmington-Atlantic City, 

PA-NJ-DE-MD CSA and several nearby surrounding counties 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

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 Camden, Cumberland, Gloucester, Mercer, and Ocean 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 
8

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 counties in the area of 

analysis.

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

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
9

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; Delaware and 

Montgomery Counties in Pennsylvania and Ocean and Burlington Counties in New Jersey. 

Counties with comparatively low emissions are Kent County, Delaware; Cecil County, 

Maryland; and Salem County 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 ozonecreating 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% 

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)
10

Philadelphia County, Pennsylvania has the highest population and population density in the area 

of analysis. Bucks, Chester, Montgomery, and Delaware Counties, in Pennsylvania; New Castle 

County in Delaware; and Ocean County in New Jersey also have comparatively large 

populations compared to Kent County, Delaware and Salem County 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

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. 
11

New Castle County, Delaware; and Bucks, Montgomery, and Philadelphia Counties in 

Pennsylvania; and Burlington County in New Jersey 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 PA-NJMD-DE 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 PA-NJ-MD-DE 

CSA, have the fewest commuters into the CSA. More about Ocean and Mercer Counties in 

Appendix A.

Factor 3: Meteorology (weather/transport patterns)

EPA evaluated available meteorological data, consisting of 30-year average summertime wind 

directions from the National Weather Service, and trajectories on high ozone days 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 
12

Pennsylvania, and Ocean County in New Jersey. Bucks County had the highest 2010 DV in the 

Philadelphia area, while Philadelphia County has the highest 2011 DV. Wind rose and trajectory 

analyses for Bucks and Philadelphia Counties provide data on the influence of weather on the 

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD nonattainment area in general. An 

analysis for Ocean County, the third highest site, is in Appendix A, where the wind and 

trajectories analyses are used to determine if Ocean (and nearby Mercer) Counties are better 

suited to be in the Philadelphia-Wilmington-Atlantic City area or the New York – Northern New 

Jersey-Long Island area.

The NWS 30-year average summertime wind directions are shown in Figure 2 for both Bucks 

and Philadelphia Counties. As can be seen from Figure 2, 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,

Philadelphia and Ocean 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 less likely to contribute to downwind violations during 

most of the ozone season, and Ocean and Mercer are more likely to be affected by emissions in 

the core of the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area than the core of the 

New York City area.

This is supported by two more detailed analyses for wind flows affecting monitors in 

Philadelphia and Bucks Counties (below) and Ocean and Mercer Counties (in Appendix A).

Detailed Analysis of Meteorological Transport Conditions for the Philadelphia 

Nonattainment Area

Figure 1. 30-Year Average Summertime Wind Directions in the Philadelphia Area
13

To further understand the meteorological transport conditions within the area around the 

Philadelphia area, we also evaluated 24-hour back trajectories for the 2007-2011 time period, 

using the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle 

Lagrangian Integrated Trajectory (HYSPLIT) model. The model uses the monitoring location 

as a starting point, and goes back in time using meteorological data to determine how a parcel of 

air would have traveled on a given day. EPA evaluated three separate elevations for each 

exceedance day to better characterize the wind pattern and pollution transport to the monitor. 

EPA used monitor 42-101-0024 in Bucks County as the starting point for the HYSPLIT back 

trajectories, as it currently has the highest DV in the Philadelphia-Wilmington-Atlantic City, PANJ-DE-MD area. The air quality monitoring data and HYSPLIT results for those exceedance 

days are available in the docket for this action. 

Table 1. 2007 to 2011 Exceedance-Day 8-Hour Ozone Values at Monitor 42-101-0024

Exceedance 

Day

8-hour 

average

(ppm ozone)

Exceedance

Day

8-hour 

average

(ppm ozone )

Exceedance

Day

8-hour 

average

(ppm ozone )

5/29/2006 0.077 7/28/2007 0.079 6/26/2010 0.084

5/30/2006 0.086 8/2/2007 0.104 7/5/2010 0.082

6/1/2006 0.084 8/3/2007 0.082 7/6/2010 0.084

6/17/2006 0.082 8/4/2007 0.08 7/7/2010 0.077

6/18/2006 0.096 8/17/2007 0.079 7/16/2010 0.08

6/19/2006 0.077 8/29/2007 0.077 7/19/2010 0.076

6/22/2006 0.081 8/30/2007 0.087 7/23/2010 0.088

7/11/2006 0.078 9/21/2007 0.083 7/28/2010 0.076

7/17/2006 0.085 4/19/2008 0.087 8/10/2010 0.088

7/18/2006 0.087 6/7/2008 0.079 8/19/2010 0.094

7/19/2006 0.077 6/10/2008 0.099 8/20/2010 0.062

7/31/2006 0.079 6/13/2008 0.08 8/29/2010 0.076

8/1/2006 0.08 6/14/2008 0.082 8/30/2010 0.079

8/2/2006 0.077 6/21/2008 0.079 9/1/2010 0.092

8/3/2006 0.077 7/3/2008 0.083 9/22/2010 0.079

8/6/2006 0.077 7/11/2008 0.082 6/1/2011 0.094

5/15/2007 0.076 7/12/2008 0.077 6/7/2011 0.089

5/25/2007 0.084 7/17/2008 0.078 6/8/2011 0.092

5/27/2007 0.087 7/18/2008 0.088 6/9/2011 0.093

5/30/2007 0.076 7/22/2008 0.085 6/10/2011 0.081

5/31/2007 0.095 7/29/2008 0.08 7/6/2011 0.076

6/1/2007 0.079 7/30/2008 0.087 7/7/2011 0.082

6/8/2007 0.097 9/4/2008 0.079 7/10/2011 0.077

6/19/2007 0.087 8/15/2009 0.084 7/18/2011 0.087

6/26/2007 0.095 5/1/2010 0.078 7/21/2011 0.085

7/9/2007 0.106 6/2/2010 0.08 7/22/2011 0.086
14

Exceedance 

Day

8-hour 

average

(ppm ozone)

Exceedance

Day

8-hour 

average

(ppm ozone )

Exceedance

Day

8-hour 

average

(ppm ozone )

7/14/2007 0.076 6/4/2010 0.079 7/29/2011 0.079

7/15/2007 0.076 6/19/2010 0.078

7/17/2007 0.081 6/22/2010 0.082

Figure 2 overlays HYSPLIT 24-hour back trajectories for all the 2007-2011 ozone exceedances 

at monitor 42-101-0024 on a Google Earth map of the northeastern United States. It gives an 

overview of long-range transport to the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD

area. As seen in Figure 2, the 24-hour back trajectories indicate regional transport from many 

directions and over several states.

Figure 2. NOAA HYSPLIT 24-Hour Back Trajectories for 2007-2011 Exceedances Days -

Overview

In Figure 3, below, these EPA has zoomed in on these same 24-hour HYSPLIT back trajectories, 

showing more of the nearby transport on high ozone days. This zoomed in perspective shows 

that on exceedance days, winds are predominantly from the south and southwest. This correlates 
15

reasonably well with the NWS 30-year average wind directly given above, which gave prevailing 

winds as from the west-southwest and south-southwest. Figure 3 also shows a large percent of 

exceedance days with winds coming from the northwest, and several exceedance days with 

winds coming from the east.

Figure 3. NOAA HYSPLIT 24-Hour Back Trajectories for 2006-2010 Exceedances Days -

Zoom View

To further illustrate the local transport situation in the Philadelphia-Wilmington-Atlantic City, 

PA-NJ-DE-MD area, EPA has selected specific trajectories for two “ozone episodes,” periods 

when the ozone levels are high for several consecutive days. As shown in Table 1, the 8-hour 

average ozone value at monitor 42-101-0024 was above the standard for three days in a row in 

2011 (June 7-9) and 2007 (May 30-June 1). Figure 4 shows that at the start of the 2011 episode, 

winds came from the predominant southwesterly direction. Figures 5 and 6 show that during the 

second and third days of the 2011 episode, wins were mainly from the west. Figures 7 through 9

depict the HYSPLIT back trajectories for the 2007 episode. These figures show that the while 

winds can start out northwest of at monitor 42-101-0024, throughout most of the 2007 episode 

winds were from the southwest.
16

Figures 4, 5 & 6, NOAA HYSPLIT 24-Hour Back Trajectories June 7-9, 2011
17

Figures 7, 8, & 9 NOAA HYSPLIT 24-Hour Back Trajectories May 30-June 1, 2007
18

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-Wilmington-Atlantic City, PA-NJ-DE-MD 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, 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 City, PA-NJ-DEMD 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-NJCT-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. 

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). 
19

Delaware

New Castle County has historically been part of the Philadelphia-Wilmington-Atlantic City, PANJ-DE-MD 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 PhiladelphiaCamden-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-Wilmington-Atlantic City, PANJ-DE-MD 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-Wilmington-Atlantic City, PA-NJDE-MD 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-Wilmington-Atlantic City, PA-NJ-DE-MD 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 the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD 

nonattainment area. While it was added to the Philadelphia-Camden-Vineland 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 been 

designated separately as the Reading area. Berks County was designated 
20

attainment/unclassifiable for 1-hour ozone. In addition, Berks County is covered by a separate 

MPO, the Berks County Planning Commission.

See Appendix B for EPA’s response to comments on the boundaries of the PhiladelphiaWilmington-Atlantic City, PA-NJ-DE-MD area in Pennsylvania.

New Jersey

Southern New Jersey, from Mercer and Ocean Counties southward, are part of the PhiladelphiaWilmington-Atlantic City, PA-NJ-DE-MD ozone nonattainment area since EPA’s previous 

eight-hour ozone standard designations in 2004, which were upheld by the US Court. Ocean 

County is part of the NYC transportation planning area and Mercer County is part of the 

Philadelphia planning area. We note that New Jersey’s desire to continue to include Ocean and 

Mercer Counties in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area is important 

to this factor, since New Jersey has to balance inconveniences due to transportation planning 

areas that are different from the nonattainment areas with benefits of including Ocean and 

Mercer Counties in the Philadelphia nonattainment area.

New Jersey also requested that EPA designate all of the counties from New Jersey that were 

designated as nonattainment for Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area for 

the 2008 ozone standard be designated as nonattainment for the 2011 ozone standard, even those 

counties that are not in the Philadelphia-Canden-Vineland CSA. 

Conclusion

Based on the assessment of factors described above, and with additional details in the enclosed 

Appendices, EPA concluded that the following counties meet the CAA criteria for inclusion in 

the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD nonattainment area for the 2008 

eight-hour ozone standard: 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, PA-NJ-DE-MD 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; Berks, Bucks, Montgomery and

Philadelphia Counties in Pennsylvania and Camden, Cumberland, Gloucester, Mercer and Ocean 

Counties in New Jersey show violations of the 2008 ozone NAAQS based on 2010 design 

values. Maryland and Pennsylvania have requested that these violating counties in their 

respective States be included as part of the Philadelphia-Wilmington-Atlantic City, PA-NJ-DEMD 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. New Jersey requested that its violating counties 

listed above be included in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area, as 
21

they were for the 1997 8-hour NAAQS. The factors above support inclusion of these counties 

and neighboring counties recommended by the states in that nonattainment area. Therefore, we 

will include them as part of the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD

nonattainment area for the 2008 ozone NAAQS. 

We have made a further analysis of the other counties in the area that Delaware and 

Pennsylvania did not include in their request for the Philadelphia-Wilmington-Atlantic City, PANJ-DE-MD nonattainment area, as well as further analysis of New Jersey’s request for Ocean 

and Mercer Counties to be included in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DEMD area, summarized as follows.

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-Wilmington-Atlantic City, PA-NJ-DE-MD

Area. Furthermore, New Castle County is part of the Philadelphia-Wilmington-Atlantic City 8-

hour ozone nonattainment area for the 1997 ozone standard 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 will designate New Castle County as nonattainment as 

part of the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD 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-Wilmington-Atlantic City, 

PA-NJ-DE-MD 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 are included in the Philadelphia-WilmingtonAtlantic City, PA-NJ-DE-MD 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.

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 
22

Berks County are not upwind of those monitors in the Philadelphia-Wilmington-Atlantic City, 

PA-NJ-DE-MD Area and thus we believe emissions from Berks County do not significantly 

contribute to nonattainment at those monitors. Therefore, EPA has concluded that Berks County 

should not be included in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD Area, and 

should be designated as nonattainment in a separate area4.

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-Wilmington-Atlantic City, PA-NJ-DE-MD Area, it is not likely that Sussex County 

is contributing significantly to the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area. 

Therefore, EPA has concluded that Sussex County should not be included in the PhiladelphiaWilmington-Atlantic City, PA-NJ-DE-MD area, and should be designated as nonattainment in a 

separate area5.

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 PhiladelphiaCamden-Vineland CSA. Therefore, EPA has concluded that Kent County should not be 

included in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area, and should be 

designated as unclassifiable/attainment.

Ocean and Mercer Counties are more affected by emissions from counties in the Philadelphia 

metropolitan area than emissions from counties in the New York City metropolitan area and EPA 

concludes that Ocean and Mercer Counties should be included in the Philadelphia-WilmingtonAtlantic City, PA-NJ-DE-MD area, as they were for the 1997 8-hour ozone NAAQS.

New Jersey requested all of the counties in the Philadelphia-Wilmington-Atlantic City, PA-NJDE-MD nonattainment area for the 1997 ozone NAAQS designations should be included in the 

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD nonattainment area for the 2008 ozone 

NAAQS designations. As noted in the beginning of this TSD, the issue placing Ocean and 

Mercer Counties in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD area when they 

are in the New York CSA is decided on the basis of the factor analysis. However, the other 

counties recommended by New Jersey for inclusion in the Philadelphia-Wilmington-Atlantic 

City, PA-NJ-DE-MD area that were in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DEMD area for the 1997 ozone NAAQS designations are approved by EPA, since New Jersey’s 

counties that are outside the Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD CSA are 

not in a metropolitan area shared by another state. Thus, EPA concurs with New Jersey’s 

recommendation for Atlantic, Burlington, Camden, Cape May, Cumberland, Gloucester, 

and Salem Counties to be included in the Philadelphia-Wilmington-Atlantic City, PA-NJ-DEMD nonattainment area for the 2008 ozone NAAQS.

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

III.

5 See EPA’s Technical Analysis for the Seaford Area, sent to the State of Delaware by EPA Region III.
23

Appendix A. 

Factor Analysis for New Jersey’s Request to Include Ocean and Mercer Counties in the 

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD Nonattainment Area

New Jersey proposes that the entire state be designated as nonattainment for the 2008 ozone 

NAAQS6

, but requested that the boundary between the New York City nonattainment area and 

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD (Philadelphia nonattainment area) be 

different from the CSA boundaries. 

EPA has determined that several factors are relevant to determining if the boundaries of the New 

York City and Philadelphia areas proposed by the State of New Jersey are approvable. The 

following sections provide additional information, as available and relevant. 

Factor 1: Air Quality Data 

Air quality data is based on the 8-hour ozone design values (in ppb) for air quality monitors in 

New Jersey, based on data for the 2008-2010 period (i.e., the 2010 design value, or DV). These

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 (75ppb) 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.

The 2010 DVs for the ozone NAAQS for counties New Jersey are 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

 6

 New Jersey (as well as Maryland, Delaware and Connecticut) requested a large, regional nonattainment area, with 

local designations if EPA did not approve the larger area designation. See EPA’s separate response to the states, 

elsewhere in these Technical Support Documents.
24

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

The highest design value in NJ is 81ppb in Ocean and Gloucester Counties. The highest design 

value in the Philadelphia nonattainment area is 83ppb in Bucks Co., PA. The highest design 

value in the New York City nonattainment area is 84 ppb in Suffolk County, Long Island, NY.

The elevated design values in Ocean County is a reason for including Ocean in the PhiladelphiaWilmington-Atlantic City nonattainment area, as other factors show its ozone is mostly from 

Philadelphia, not New York.

The air quality monitoring data are included in the docket for this action.

As shown in Figures 1 and 2, design values decrease further north and east from Ocean County, 

until the next set of peak design values occur downwind of New York City on Long Island and in 

Connecticut. This is an indication that Ocean County is affected strongly and mostly by sources 

to the south and west, which includes the Philadelphia area. This is typical of the northeastern 

United States, since most of peak ozone design values are found north and east of the centers of 

major urban areas.

Factor 2: Emissions and Emissions-Related Data

This factor does not provide much information related to New Jersey’s request for Ocean and 

Mercer Counties to be included in the prospective Philadelphia nonattainment area.

Emissions Data

Not evaluated because New Jersey has proposed that every county in New Jersey is proposed to 

be nonattainment. There are no counties proposed to be attainment in New Jersey.

The only issue, whether Mercer and Ocean Counties should continue to be included with the 

Philadelphia area as opposed to the New York area, does not use this factor as a deciding factor. 

The question that needs a multi-factor analysis is about whose emissions affect Ocean and 

Mercer Counties the most, which is best determined by analysis of transport of ozone and ozoneforming emissions. 
25

Population density and degree of urbanization

Not evaluated since the question is the impact of urban ozone on Ocean and Mercer County and 

less so about whether Ocean and Mercer Counties affect other areas. 

Traffic and commuting patterns

EPA evaluated the commuting patterns of residents in the area. A neighboring county with high 

VMT and/or a high number of commuters coming into the county with a violating monitor 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. The attached spreadsheet shows traffic and commuting pattern data, 

including total 2008 VMT* and 10-year VMT growth, number of commuters in each county who 

drive to another county within the area, the percent of total commuters in each county who 

commute to other counties within the area**, and the total vehicle miles traveled (VMT) for each 

county.

* 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.

The County-to-County Worker Flow data from 2000 was used in the previous 2004 analysis for 

the 1997 ozone standard. 

Based on 2000 data, the 2004 analysis noted that more commuters either stay in Ocean County 

or Mercer Counties or go to the Philadelphia area than go to the New York City area. 

The data are included in the docket for this action.

Commuting from Ocean and Mercer Counties into central Philadelphia is much lower than the 

counties with the highest numbers of commuters heading into Philadelphia. For Ocean County, 

most of the top-ranked counties for its commuters are in the New York-Newark-Bridgeport, NYNJ-CT-PA CSA. Mercer County’s second-ranked destination is New York County (Manhattan). 

However, the reason for including Ocean and Mercer Counties in the Philadelphia-WilimingtonAtlantic City nonattanment area is due to the impact that the Philadelphia area has on Ocean and 

Mercer Counties, not their impact on Philadelphia. 

Factor 3: Meteorology (weather/transport patterns)

EPA evaluated available meteorological data 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. 
26

Wind rose for 1988-1992

.

Figure 3-1. Daytime wind rose during ozone season, Philadelphia, PA.

The 1997 designation assessment showed, via wind roses (see above), trajectory analysis and 

contribution assessments, that Ocean County (and by extension, Mercer County) are downwind 

of the Philadelphia metropolitan area and are not as strongly affected by emissions from the New 

York City metropolitan area. More recent trajectory analyses continue to support New Jersey’s 

request. 

EPA produced trajectories from NOAA’s HYSPLIT program for days when monitoring sites in 

Mercer and Ocean Counties had the highest ozone concentrations from 2008 through 2011. 

Trajectories were run backwards from the monitoring site with the arrival time at the monitoring 

site at 1400 local standard time. Three trajectories were run for each day – starting at different 

altitudes that are climatologically within the mixed layer during the afternoon, when peak ozone 

typically occurs and thermal mixing from sunshine is at a maximum. These trajectories 

predominantly come through eastern Pennsylvania and less frequently from southeastern New 

York. Thus, emissions from the Philadelphia metropolitan area are more likely to affect Ocean 

and Mercer Counties than the New York City metropolitan area. 
27

In summary, these trajectories show when the air comes from on high ozone days at these 

monitoring sites in recent years.

Figure 3-2. Trajectories for high ozone days at monitors in Ocean and Mercer Counties.

Figure 3-2, with all of the trajectories for the three monitoring sites in Ocean and Mercer 

Counties, is too busy to examine closely. However, it shows that the thicket of trajectories is 

thickest over eastern Pennsylvania, and markedly less so over New York. This is not surprising, 

since the basic conceptual model for ozone formation in the metropolises of the northeastern 

corridor of the United States is for ozone to form on sunny days with surface winds from the 

southwest and winds aloft from the west. 

Here’s the classic example of the conceptual model from the University of Maryland:
28

Figure 3-3. Conceptual model of ozone transport

Here are composite graphics of the trajectories for each site in Ocean and Mercer Counties, as 

well as for each of the three altitudes:

 Figure 3-4. Trajectories to the ozone monitor in Ocean County, ending at 100 meters above 

ground level in mid-afternoon on high ozone days.
29

Figure 3-5. Trajectories to the ozone monitor in Ocean County, ending at 500 meters above 

ground level in mid-afternoon on high ozone days.

Figure 3-6. Trajectories to the ozone monitor in Ocean County, ending at 1000 meters above 

ground level in mid-afternoon on high ozone days.
30

Figure 3-7. Trajectories to the Rider University ozone monitor in Mercer County, ending at 100 

meters above ground level in mid-afternoon on high ozone days.

Figure 3-8. Trajectories to the Rider University ozone monitor in Mercer County, ending at 500 

meters above ground level in mid-afternoon on high ozone days.
31

Figure 3-9. Trajectories to the Rider University ozone monitor in Mercer County, ending at 

1000 meters above ground level in mid-afternoon on high ozone days.

Figure 3-10. Trajectories to the Washington Crossing ozone monitor in Mercer County, ending 

at 100 meters above ground level in mid-afternoon on high ozone days.
32

Figure 3-11. Trajectories to the Washington Crossing ozone monitor in Mercer County, ending 

at 500 meters above ground level in mid-afternoon on high ozone days.

Figure 3-12. Trajectories to the Washington Crossing ozone monitor in Mercer County, ending 

at 1000 meters above ground level in mid-afternoon on high ozone days.
33

The original mapping file for the trajectory analysis is included in the docket for this action.

Factor 4: Geography/topography (mountain ranges or other air basin 

boundaries)

New Jersey’s division of its nonattainment areas into two areas is not based on, nor affected by, 

topographic barriers. 

Factor 5: Jurisdictional boundaries

Once the general areas to be included in the nonattainment area were determined, EPA 

considered 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, 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 were considered.

EPA approved the inclusion of Ocean and Mercer Counties into the Philadelphia nonattainment 

area for the 2004 ozone nonattainment designations. 

Ocean County is in the New York City metropolitan transportation planning organization. 

Mercer County is in the Philadelphia metropolitan transportation planning organization. Since 

2004, New Jersey has worked with Ocean County being within the Philadelphia nonattainment 

area and in the New York City-centered transportation planning organization. If New Jersey 

requests that Ocean County should be included with the Philadelphia nonattainment area despite 

the possible difficulties of this situation, this factor should not be a reason for declining New 

Jersey’s request. 

Summary

EPA has determined that ozone concentrations in Mercer and Ocean Counties are more strongly 

affected by emissions from the Philadelphia metro area in eastern Pennsylvania than the New 

York City metro area in southeastern New York. Ocean and Mercer Counties should be in the 

Philadelphia ozone nonattainment area as they were for designations for the previous 1997 eighthour ozone standard. 

EPA uses five types of factors when we consider how to determine the boundaries of a 

nonattainment area:

1. Air quality data (including the design value calculated for each FRM or FEM monitor in 

the area); 
34

Both Ocean and Mercer Counties violate the air quality standard; with Ocean County 

having a higher design value than any monitors further downwind of Ocean County, 

except the peak monitors downwind of New York City. 

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

amount of emissions and emissions controls, and urban growth patterns);

This factor has a limited relevance to this issue, as the issue is whether the Ocean and 

Mercer Counties are more affected by the Philadelphia nonattainment area than the New 

York City area. However, one factor from the 2004 analysis noted that more commuters 

stay in Ocean County or go to the Philadelphia area than go to the New York City area.7

3. Meteorology (weather/transport patterns);

The 2004 analyses of the evaluation of boundaries for the 1997 ozone NAAQS8 show 

that Ocean County is much more likely to be impacted by winds from the Philadelphia 

area than winds from the New York City area. However, more recent wind rose data and 

trajectory analyses support New Jersey’s recommendation that Mercer and Ocean County 

are affected more strongly by the Philadelphia area than the New York area.

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

Not much of a factor, since there are no major topographic features affecting conclusions 

from the wind flow analyses.

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

country, metropolitan planning organizations (MPOs)) 

Ocean County is part of the NYC transportation planning area and Mercer County is part 

of the Philadelphia planning area. However, Ocean and Mercer Counties have been in 

the Philadelphia nonattainment area since 2004. New Jersey’s desire to continue to 

include Ocean and Mercer Counties in the Philadelphia area prevails, since New Jersey 

has to deal with any inconveniences due to transportation planning areas that are different 

from the nonattainment areas.

EPA received no negative comments during the comment period about the assignment of Ocean 

and Mercer Counties to the Philadelphia nonattainment area. 

 7

 This factor uses Census Bureau data from 2000, which will be updated if newer data are available. 8 http://www.epa.gov/ozonedesignations/1997standards/documents/tsd/ch3.pdf
35

Appendix B: Response to Comments on Berks County and the Philadelphia 

Nonattainment Area

In Pennsylvania’s February 28, 2012 response to EPA’s December 9, 2011 “120-day letter”, the 

Commonwealth provided information to respond to public comments on EPA’s preliminary 

recommendations. Comments were submitted to EPA, recommending that the agency include 

Reading (Berks County) in Philadelphia area because Reading is part of the PhiladelphiaCamden-Vineland Consolidated Statistical Area (CSA). The Commonwealth disagreed with this 

suggestion and supported EPA’s proposal to designate Berks County as a single county 

nonattainment area for the following reasons:

• The Commonwealth’s recommendation and EPA’s preliminary response are consistent with 

the Office of Management and Budget (OMB) definition. The OMB defines the Reading 

metropolitan statistical area as an area that consists of only Berks County. Although the 

OMB added Berks County to the Philadelphia CSA in 2006 because of increasing 

commuting ties to the larger area, Berks County traditionally has its own planning functions, 

including its own countywide transportation planning organization. 

• EPA designated Berks County as a single-county nonattainment area for the 1-hour ozone 

standard, the 1997 8-hour ozone standard and the 1997 fine particulate matter standard.

• Analysis of the most current work destination data for Berks County’ indicates that in 2009, 

57.7 percent of the employment of Berks County residents was in Berks County.

• The Reading Air Basin, defined in 25 Pa. Code § 121,1 and codified in 40 CFR 52.2020,

covers portions of Berks County and no other county.

• Based on the 2008 National Emissions Inventory shown below, VOC and NOx emissions 

(tons per year) in Berks County are low compared to emissions in the 5-county Philadelphia 

Area. The five Pennsylvania counties (Bucks, Chester, Delaware, Montgomery and 

Philadelphia) are part of a much larger CSA, which in turn is only part of the proposed fourstate Philadelphia-Wilmington-Atlantic City nonattainment area. Therefore, the inclusion of 

Berks County in the Philadelphia-Wilmington-Atlantic City area is unlikely to have a 

significant effect on the area attaining the standard.
36

Appendix C. Ozone Design Values in Pennsylvania Calculated Including 2011 Ozone Data

Pennsylvania submitted certified ozone data for 2011 to EPA in November 2011. Since no other 

states in the Philadelphia Area submitted certified ozone data for 2011 during EPA’s review 

process, EPA will not include Pennsylvania’s 2011 ozone data in calculating design values for 

designations. The effect of using 2011 data from Pennsylvania is listed below for information 

purposes, with the 2011 design value being calculated with air quality data from 2009, 2010 and 

2011.

County

State Recommended 

Nonattainment?

2010 8-hour Ozone 

DV (ppb)

2011 8-hour Ozone 

DV (ppb)

Atlantic, NJ Yes 74

Berks, PA Yes, other area 79 77

Bucks, PA Yes 83 80

Burlington, NJ Yes --

Camden, NJ Yes 80

Cape May, NJ Yes --

Cecil, MD Yes 80

Chester, PA No 76 74

Cumberland, NJ Yes 76

Delaware, PA No 74 73

Gloucester, NJ Yes 81

Kent, DE No 74

Mercer, NJ Yes 78

Montgomery, PA Yes 78 77

New Castle, DE Yes, other area 76

Ocean, NJ Yes 81

Philadelphia, PA Yes 82 83

Salem, NJ Yes --

Sussex, DE Yes, other area 77

Notes: Counties with no ozone monitor are identified with “--“ in the 2010 8-hour Ozone DV column.

2001 DVs are included for Pennsylvania counties because Pennsylvania submitted certified 2011 data to EPA in 

November 2011.

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

Pennsylvania, and Ocean County in New Jersey. Buck County had the highest 2010 DV in the 

Philadelphia area, while Philadelphia County has the highest 2011 DV.
37

Technical Analysis for the Seaford Area

Figure 1 is a map of the Seaford, DE 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 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, PA-NJ-MD-DE 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 
38

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) 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 is designating a new nonattainment area, the Seaford area, which consists of one 

county in Delaware, Sussex County (identified in Table 1 below) as “nonattainment” for the 

2008 ozone NAAQS.

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

Area.

Seaford State-Recommended 

Nonattainment Counties

EPA Designated

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, except for Cape May and Cumberland Counties, New 

Jersey. Based on EPA’s five-factor analyses, EPA has determined that Cape May and 

Cumberland Counties should be designated as nonattainment in the Philadelphia-WilmingtonAtlantic City Area for the 2008 ozone NAAQS. See EPA’s technical analyses for the 

Philadelphia-Wilmington-Atlantic City Area for EPA’s rationale supporting our nonattainment 

designation for these counties. To the extent that emissions from the Cape May and Cumberland 

Counties may contribute ozone concentrations in the Seaford nonattainment area, that 

contribution will be lessened by emission controls put in place in those separate nonattainment 

areas. Therefore, EPA is not including Cape May and Cumberland Counties in this analysis for 

the Seaford nonattainment area.

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 (75 ppb) or less. A DV is only valid if 

minimum data completeness criteria are met. See 40 CFR part 50 Appendix P. Where several 
39

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. 

Table 2. Air Quality Data.

County

State Recommended 

Nonattainment?

2010 8-hour Ozone DV 

(ppb)

Caroline, MD No --

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 shows a 

violation of the 2008 ozone NAAQS. Therefore, this county must be included in a 

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 
40

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. For this factor, we 

also considered 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 are in place before final designations are issued and 

emissions increases due to new sources. EPA received no such additional emissions data for the 

Seaford Area.

Table 3 shows emissions of NOx and VOC (in tons per year (tpy)) for violating and potentially 

contributing counties in the Seaford Area. 

Table 3. Total 2008 NOx and VOC Emissions.

County

State Recommended 

Nonattainment? NOx (tpy) VOC (tpy)

Caroline, MD No 983 1,324

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 has the next highest emissions, but those emissions are about half that of 

Sussex County’s. Caroline and Talbot Counties, Maryland, have the lowest emissions. Thus, 

the most likely source of ozone precursors for the Seaford Area is 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 offroad 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.
41

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)

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

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&p

rodType=table)

Sussex and Kent Counties, Delaware have the largest populations. Caroline, Dorchester, Talbot, 

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

populated in the area of analysis. All counties in the area of analysis have 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 VMT for each county in 2008.

Table 5. Traffic (VMT) Data.

County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

Caroline, MD No 371

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. 
42

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. 

Table 6. County to County Worker Flow.

Residence County Kent, 

DE

Sussex, 

DE

Caroline, 

MD

Dorchester,

MD

Talbot, 

MD

Wicomico, 

MD

Worcester, 

MD

Workplace County 

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

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

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

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

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

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

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

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.
43

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

To further understand the meteorological transport conditions within the area around Seaford, we 

also evaluated 24-hour back trajectories for the 2006-2010 time period, using the National 

Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle Lagrangian Integrated 

Trajectory (HYSPLIT) model. The model uses the monitoring location as a starting point, and 

goes back in time using meteorological data to determine how a parcel of air would have traveled 

on a given day. EPA evaluated three separate elevations for each exceedance day to better 

characterize the wind pattern and pollution transport to the monitor.

For this analysis, EPA used monitor 10-005-1002 as the starting point for the HYSPLIT back 

trajectories. EPA selected monitor 10-005-1002 because, of the two violating monitors in the 

Seaford Area, this monitor has the highest 2010 DV, 77.3 ppb versus 77.0 ppb at monitor 10-

005-1003. EPA used HYSPILT to evaluated wind patterns at the violating monitor for all days 

where the 8-hour average was above the 0.075 ppm standard (exceedance days) at monitor 10-

005-1002. The air quality monitoring data and HYSPLIT results for those exceedance days are 

available in the docket for this action. Table 7 lists the exceedance days and corresponding 8-

hour average ozone values for each exceedance day. Please note that there were no exceedance 

days in the Seaford Area in 2009.

Table 7. 2006 to 2010 Exceedance-Day 8-Hour Ozone Values at Monitor 10-005-1002

Exceedance 

Day

8-hour average

(ppm ozone)

Exceedance

Day

8-hour average

(ppm ozone )

5/30/2006 0.083 6/12/2008 0.081

6/20/2006 0.081 6/26/2008 0.078

6/21/2006 0.079 7/12/2008 0.077

7/18/2006 0.076 7/16/2008 0.081

8/2/2006 0.082 7/17/2008 0.091

8/3/2006 0.089 7/18/2008 0.085
44

Exceedance 

Day

8-hour average

(ppm ozone)

Exceedance

Day

8-hour average

(ppm ozone )

8/23/2006 0.083 8/1/2008 0.079

8/25/2006 0.078 5/6/2010 0.079

5/26/2007 0.084 6/23/2010 0.084

6/18/2007 0.081 7/5/2010 0.087

6/21/2007 0.076 7/6/2010 0.078

7/7/2007 0.078 7/7/2010 0.091

8/4/2007 0.081 8/10/2010 0.08

8/8/2007 0.084 8/11/2010 0.086

8/30/2007 0.077 8/30/2010 0.078

8/31/2007 0.078 9/24/2010 0.077

4/18/2008 0.079

Figure 3 overlays HYSPLIT 24-hour back trajectories for all the 2006-2010 ozone exceedances 

at monitor 10-005-1002 on a Google Earth map of the northeastern United States. It gives an 

overview of long-range transport to the Seaford Area. As seen in Figure 3, the 24-hour back 

trajectories indicate regional transport from many directions and over several states.

Figure 3. NOAA HYSPLIT 24-Hour Back Trajectories for 2006-2010 Exceedances Days -

Overview

In Figure 4, below, these EPA has zoomed in on these same 24-hour HYSPLIT back trajectories, 

showing more of the nearby transport on high ozone days. This zoomed in perspective shows 
45

that on exceedance days, there is no one dominant wind direction. However, on exceedance 

days, winds from the north, northwest, west, and southwest are more likely than winds from the 

east, southeast, and south.

Figure 4. NOAA HYSPLIT 24-Hour Back Trajectories for 2006-2010 Exceedances Days -

Zoom View

To further illustrate the local transport situation in the Seaford Area, EPA has selected specific 

trajectories for two “ozone episodes,” periods when the ozone levels are high for several 

consecutive days. As shown in Table 7, the 8-hour average ozone value at monitor 10-005-1002

was above the standard for three days in a row in 2008 (July 16-18) and 2010 (July 5-7). As 

shown in Figures 5 through 7, during the ozone episode in 2008, winds passed through almost all 

of the counties surrounding Sussex County. In Figure 5, the back trajectories pass through Kent 

County, Delaware, and Cape May and Cumberland Counties in New Jersey. In Figure 6, back 

trajectories pass through Caroline and Talbot Counties in Maryland, and Kent County, Delaware. 

In Figure 7, back trajectories pass through Dorchester, Wicomico, and Worcester Counties in 

Maryland, and Cape May County, New Jersey. Although emissions from those counties might 

contribute to violations in downwind Sussex County, Delaware, the emissions levels from those 

counties are relatively low, and relatively little actual contribution is expected, compared to the 

contribution of ozone precursors from Sussex County.
46

Figures 5, 6 & 7, NOAA HYSPLIT 24-Hour Back Trajectories July 16 - 18, 2008
47

Figures 8, 9 & 10, NOAA HYSPLIT 24-Hour Back Trajectories July 5 -7, 2010
48

The ozone episode in 2010 shows winds coming to Sussex County from the north, the west via 

Baltimore and Washington, DC, and the east via the Atlantic Ocean and New York City. This 

episode illustrates the regional nature of ozone. While this goes beyond the scope of the 

designation process, which focuses on nearby contribution to attainment, this highlights the need 

for rules to address transport ozone precursors, such as the Cross State Air Pollution Rule

(currently stayed by the court).

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 the 1997 ozone NAAQS. However, EPA is not including them in 

that area for the 2008 ozone NAAQS, as supported by EPA’s five-factor analysis for the 

Philadelphia-Wilmington-Atlantic City area9

. 

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 

 9 See EPA’s Technical Analysis for the Philadelphia-Wilmington-Atlantic City nonattainment area.
49

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 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 inclusion of the other counties in this 

analysis in the Seaford Area is not warranted. 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. 

Furthermore, Cape May County is being designated in the Philadelphia-Wilmington-Atlantic 

City nonattainment area. To the extent that emissions from the Cape May County may 

contribute ozone concentrations in the Seaford nonattainment area, that contribution will be 

lessened by emission controls put in place in that separate nonattainment area. Wind directions 

on ozone exceedance days show potential impacts from all counties in the area of analysis. 

Although emissions from those counties might contribute to violations in downwind Sussex 

County, Delaware, the emissions levels from those counties are relatively low, and relatively 

little actual contribution is expected, compared to the contribution of ozone precursors from 

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.