1

Dallas-Fort Worth, Texas

Final Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

This is the Technical Support Document (TSD) for the final area designations in the Dallas-Fort Worth 

(DFW) area for the 2008 ozone national ambient air quality standards (2008 ozone NAAQS).

1 Throughout this document “we,” “our,” and “us” means the United States Environmental Protection Agency 

(EPA).

Table 1 below identifies counties in Texas that EPA is designating as nonattainment for the 2008 ozone 

NAAQS as part of the DFW, Texas nonattainment area. 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. EPA is designating two 

nonattainment areas within the state of Texas, the DFW nonattainment area and the Houston-GalvestonBrazoria (HGB) nonattainment area. The technical analysis supporting the designation and boundaries 

for the DFW nonattainment area is provided below. This TSD includes our evaluation of information 

submitted by the State of Texas and the public. The formal responses to comments received are provided 

in the 2008 ozone designation response to comments document which can be found in the electronic 

docket for this action, identified as EPA-HQ-OAR-2008-0476 at www.regulations.gov.

Table 1. Counties in Texas Included in the Dallas-Fort Worth 2008 Ozone Nonattainment Area

Area Texas’ Recommended 

Nonattainment Counties

EPA’s Designated

Nonattainment Counties

Dallas-Fort Worth, TX

Collin

Dallas

Denton

Ellis

Johnson

Kaufman

Parker

Rockwall

Tarrant

Collin

Dallas

Denton

Ellis

Johnson

Kaufman

Parker

Rockwall

Tarrant

Wise

EPA is designating as “unclassifiable/attainment” for the 2008 ozone NAAQS the remaining counties in 

Texas that are not included in the table above or in the HGB nonattainment area (see the separate TSD

for the HGB area).

The analysis below provides the basis for designated 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 on 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 criteria EPA would consider in determining nonattainment area boundaries 

 1 The primary 8-hour ozone standard, set to protect human health, was revised on March 27, 2008 (73 FR 16436) from 0.08 

parts per million (ppm) to 0.075 ppm. The secondary ozone standard, set to protect human welfare and the environment, was 

revised to be consistent with the primary ozone standard.
2

and recommended that states consider these factors in making their designations recommendations to 

EPA.

2

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

(FRM) or Federal Equivalent Method (FEM)

3 monitor in the area);

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

emissions and emissions controls, and urban growth patterns);

3. Meteorology (weather/transport patterns);

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

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

country, metropolitan planning organizations (MPOs))

Ground-level ozone generally 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. 

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

violations of the ozone standards. 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) associated with 

the air monitors that are measuring violations of the 2008 ozone NAAQS (the “violating monitor(s)”).

4

All data and information used by EPA in this evaluation are the latest available to EPA and/or provided 

to EPA by the State of Texas.

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

boundaries, thus we consider the larger boundaries of CSAs/CBSAs to establish the initial geographic 

scope for counties to be evaluated for their potential to contribute to violations of the NAAQS in nearby 

areas. In addition, certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

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

ozone NAAQS. Each CSA/CBSA consists of counties containing at least one urban core plus adjacent 

counties that have a high degree of social and economic integration with the urban core(s) as measured 

by commuting ties. Congress required a similar approach in 1990 for areas classified as serious or above 

for the 1-hour ozone standard and 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 

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

considering the nonattainment area boundary.

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

Quality Standards” refers to nine factors. In this TSD we have grouped the emissions-related factors together under the 

heading of “Emissions and Emissions-Related Data,” which results in five categories of factors. 3 FRM monitors utilize a chemi-luminescent technique to measure ozone, while many FEM monitors use a technique 

involving ultraviolet photometry. FEM methods began to be developed in the late 1970s/early1980s and are now the most 

widely utilized methods for monitoring ozone levels. Refer to 40 CFR Part 53 for a more detailed description of FEM and 

FRM methods. http://www.epa.gov/ttnamti1/files/ambient/criteria/reference-equivalent-methods-list.pdf 4 Lists of CBSAs and CSAs and their geographic components are provided at 

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

and Budget. EPA used the most recent update, based on 2008 population estimates, issued on December 1, 2009 (OMB 

Bulletin No. 10-02).
3

Technical Analysis for Dallas-Fort Worth, TX

Figure 1 is a map of the DFW designated nonattainment area for the 2008 ozone standard. The map 

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

county and other jurisdictional boundaries, relevant statistical area boundaries, the nonattainment area 

boundary for the 1997 ozone NAAQS, and major transportation arteries. The DFW CSA is comprised of 

seven CBSAs, all within Texas: (1) the Athens Micropolitan Statistical Area (Henderson County), (2) 

the Bonham Micropolitan Statistical Area (Fannin County); (3) the Dallas-Fort Worth-Arlington 

Metropolitan Statistical Area (Collin, Dallas, Delta, Denton, Ellis, Hunt, Johnson, Kaufman, Parker, 

Rockwall, Tarrant and Wise Counties); (4) the Gainesville Micropolitan Statistical Area (Cooke 

County); (5) the Granbury Micropolitan Statistical Area (Hood and Somervell Counties); (6) the Mineral 

Wells Micropolitan Statistical Area (Palo Pinto County); and (7) the Sherman-Denison Metropolitan 

Statistical Area (Grayson County). For this technical analysis, EPA evaluated all 19 counties in the 

DFW CSA, as well as five counties outside (to the south/southeast) of the CSA: Freestone, Limestone, 

McLennan, Navarro and Robertson.

Figure 1. Dallas-Fort Worth Designated Nonattainment Area

The boundary for the nonattainment area for the 1997 ozone NAAQS included the entire counties of 

Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwell, and Tarrant.
4

In March 2009,

5 Texas recommended that the same counties as those designated nonattainment under 

the 1997 ozone standard, plus Hood County, be designated as nonattainment for the 2008 ozone 

NAAQS based on air quality data from 2005-2007 and uncertified data for 2008. Texas provided an 

update to the original recommendation in October 20116 based on air quality data from 2008-2010. The

State’s recommendations are based on data from FEM monitors sited and operated in accordance with 

40 CFR Part 58 and an analysis by the Texas Commission on Environmental Quality (TCEQ).

On December 9, 2011, EPA initiated the 120-day consultation process by notifying Texas that based on 

EPA’s technical analysis of the DFW CSA the EPA intended to add Hood and Wise Counties to the nine 

counties Texas recommended be designated as the DFW ozone nonattainment area and requesting that if

the State wished to provide additional information to EPA regarding the intended designations, it should 

do so by February 29, 2012. EPA also provided the public a 30-day opportunity to submit comments on 

EPA’s intended designations in a December 20, 2011, announcement in the Federal Register (76 FR 

78872). In January, EPA extended the public comment period to February 3, 2012 (January 19, 2012, 77 

FR 2677). The public comments we received are provided in the electronic docket, identified as EPAHQ-OAR-2008-0476 and located at www.regulations.gov. On February 29, 2012, Texas submitted 

comments and additional technical information to EPA.7 We also received comments from over 40 

organizations and individuals.

After considering the State’s original recommendations as well as additional information provided by 

the state of Texas and others during the public comment period, and based on EPA's technical analysis 

described below, EPA is designating ten counties in Texas (identified in Table 1 above) as

“nonattainment” for the 2008 ozone NAAQS as part of the DFW nonattainment area. The ten counties 

include the nine counties recommended by the State of Texas and Wise County. EPA is designating 

Hood County as “unclassifiable/attainment.”

Factor Assessment

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values (in ppm) for air quality monitors in counties 

in the DFW CSA based on data for the 2008-2010 period (i.e., the 2010 design value, or DV), which are

the most recent years with certified air quality data. A monitor’s DV is the metric or statistic that 

indicates whether that monitor meets or attains a specified air quality standard. The 2008 ozone NAAQS 

are met at a monitor when the annual fourth-highest daily maximum 8-hour average concentration, 

averaged over 3 years is 0.075 ppm or less. A DV is valid only if minimum data completeness criteria 

are met. See 40 CFR part 50 Appendix P. Where several monitors are located in a county (or a 

designated nonattainment area or maintenance area), the DV for the county or area is determined by the 

monitor with the highest DV.

The 2010 DVs for the ozone NAAQS for counties in the DFW CSA and five additional counties outside 

the CSA are provided in Table 2 below.

 5 Initial 2008 ozone NAAQS designation recommendation letter from Governor Perry to Acting Regional Administrator 

Starfield, dated March 10, 2009. 6 Updated 2008 ozone NAAQS designation recommendation letter from Governor Perry to Regional Administrator 

Armendariz, dated October 31, 2011. 7 Letter from Governor Perry to Regional Administrator Armendariz, dated February 29, 2012.
5

Table 2. Air Quality Data.

County State Recommended Nonattainment? 2008-2010 Design Value

(parts per million or ppm)

Collin Yes 0.077

Cooke No --

Dallas Yes 0.078

Delta No --

Denton Yes 0.080

Ellis Yes 0.072

Fannin No --

Grayson No --

Henderson No --

Hood No 0.075

Hunt No 0.064

Johnson Yes 0.080

Kaufman Yes 0.067

Palo Pinto No --

Parker Yes 0.075

Rockwall Yes 0.074

Somervell No --

Tarrant Yes 0.086

Wise No --

Counties outside 

of the DFW CSA

Freestone No --

Limestone No --

McLennan No 0.070

Navarro No --8

Robertson No --

Counties with design values exceeding the NAAQS are indicated in bold typeface.

Air quality monitors in Collin, Dallas, Denton, Johnson, and Tarrant Counties indicate a violation of the 

2008 ozone NAAQS, therefore these counties are included in the nonattainment area. A county (or 

partial county) must also be designated nonattainment if it contributes to a violation in a nearby area. 

Each county without a violating monitor that is located near a county with a violating monitor has been 

evaluated, as discussed below, based on the five factors.

The Eagle Mountain Lake ozone monitor (48-439-0075) in Tarrant County, which is less than 1⁄2 mile 

from Wise County, violates the 2008 ozone NAAQS with a 2008-2010 DV of 0.085 ppm. The 2008-

2010 DV for the Hood County ozone monitor (48-221-0001) was 10 parts per billion (ppb) lower, with a 

DV of 0.075 ppm, which meets the 2008 ozone NAAQS.

Freestone, Limestone, McLennan, Navarro and Robertson counties do not all have air quality monitors. 

Those that do however, are not showing a violation of the 2008 ozone standard. In addition, these five 

counties are not adjacent to, or nearby, a county with a violating monitor.

 8 The monitor in Navarro County began operation in June 2009 and thus does not have a design value for 2008-2010.
6

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. The emissions and emissions-related 

data we are evaluating include data from the 2008 National Emissions Inventory (NEI); the Barnett 

Shale Special Inventory provided by the TCEQ; population density and degree of urbanization; traffic 

data; and worker data. Each of these factors is described below.

Emissions Data

Significant emissions levels in a nearby area indicate the potential for the area to contribute to monitored

violations of the NAAQS. EPA evaluated county-level emission data for NOx and VOC derived from 

(1) the 2008 NEI, version 1.5, (2) a 2009 emissions inventory of oil and gas activities in the Barnett 

Shale, and (3) emissions inventory updates provided by Texas. (See the February 29, 2012, letter from 

Texas Governor Perry and http://www.epa.gov/ttn/chief/net/2008inventory.html). Based on information 

we received from Texas, we revised the 2008 VOC emissions inventory for Hood and Wise Counties. 

The revised 2008 VOC emissions inventory for Hood County is 8,739 tons per year (tpy), down from 

9,547 tpy reported in NEI version 1.5. The revised emissions inventory for Wise County is 17,609 tpy, 

down from the 23,657 tpy reported in NEI version 1.5. These reductions in the VOC emissions for Hood 

and Wise Counties are due to revised oil and gas sector pneumatic emissions for 2008 that Texas 

submitted to the NEI in October 2011. This revised data was not reflected in NEI version 1.5.

Table 3 indicates emissions of NOx and VOC (expressed in tpy) for violating and nearby counties that 

we considered for inclusion in the Dallas-Fort Worth CSA.
7

Table 3. Total 2008 NOx and VOC Emissions*

County State Recommended

Nonattainment?

NOx

(tpy)

VOC

(tpy)

Collin Yes 10,322 14,503

Cooke No 3,853 5,790

Dallas Yes 51,023 63,473

Delta No 1,016 462

Denton Yes 17,421 24,932

Ellis Yes 15,768 6,543

Fannin No 2,165 1,207

Grayson No 5,919 7,401

Henderson No 3,573 6,067

Hood No 5,515 8,739

Hunt No 3,688 3,765

Johnson Yes 31,769 10,163

Kaufman Yes 5,868 3,510

Palo Pinto No 3,348 7,464

Parker Yes 9,550 11,708

Rockwall Yes 1,859 2,047

Somervell No 698 921

Tarrant Yes 56,408 49,021

Wise No 11,911 17,609

Area-wide: 241,674 245,325

*With VOC emissions revisions for Hood and Wise Counties submitted by TCEQ.

Counties with monitors indicating a violation of the NAAQS are indicated in bold.

Subsequent to development of the 2008 NEI, the TCEQ prepared an emissions inventory of NOx and 

VOC emissions resulting from Barnett Shale oil and gas production, transmission, processing, and 

related activities during calendar year 2009.9 Table 4 below presents an updated Barnett Shale Area 

Special Inventory of NOx and VOC emissions from oil and gas production activities for the counties in 

the Dallas-Fort Worth CSA. EPA also considered the additional contribution of NOx and VOC 

emissions from Barnett Shale area oil and gas production activities in its evaluation of emissions for the 

DFW CSA counties.

 9 http://www.tceq.texas.gov/airquality/point-source-ei/psei.html#barnett2. Reference Barnett Shale Area Special Inventory, 

Phase Two.
8

Table 4. TCEQ 2009 Barnett Shale Area Special Inventory.

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy)

Collin Yes

Cooke No 76 490

Dallas Yes 0 5

Delta No

Denton Yes 429 3,523

Ellis Yes 120 49

Fannin No

Grayson No

Henderson No

Hood No 6,903 2,113

Hunt No

Johnson Yes 1,101 1,614

Kaufman Yes

Palo Pinto No 1,226 833

Parker Yes 743 2,420

Rockwall Yes

Somervell No 1,119 221

Tarrant Yes 415 1,083

Wise No 2,520 6,032

Area-wide: 14,652 18,383

Counties with monitors indicating a violation of the NAAQS are indicated in bold.

The counties in the DFW CSA with the highest emissions of NOx and VOC are Collin, Dallas, Denton, 

Ellis, Johnson, Parker, Tarrant, and Wise. Together, these counties account for 84 percent of the NOx 

emissions and 81 percent of the VOC emissions for the entire area for 2008.

Wise County also has comparatively high emissions of NOx and VOC. Based on just the adjusted 2008 

NEI data, Wise County’s emissions of VOC at 17,609 tpy are the 4th highest in the 19-county CSA, and 

Wise County’s NOx emissions are the 6th highest of the counties in the CSA.

In addition to providing updated 2008 emissions inventory data for Hood and Wise Counties, Texas 

provided information indicating that: Hood County NOx emissions from point sources decreased from 

5,964 tpy in 2002 to 1,178 tpy in 2010; and that Wise County NOx emissions from point sources 

decreased from 2,895 tpy in 2002 to 2,163 tpy in 2010.

EPA also received comments and information regarding current emissions from oil and gas activities 

from Hood County representatives.10 This information indicates that well exploration and development 

within Hood County has declined significantly since 2009, when TCEQ’s special inventory was 

conducted.

 10 These letters and all other comments received are in the docket for this action, identified as EPA-HQ-OAR-2008-0476 at 

www.regulations.gov.
9

Additionally, EPA received comments concerning the impact of emissions from five counties outside 

the DFW CSA, Freestone, Limestone, McLennan, Navarro, and Robertson Counties, on air quality in 

the core CSA counties. These counties are south and southeast of the DFW nonattainment area. The 

NOx and VOC emissions from these counties are presented in Table 5 below.

Table 5. Total 2008 NOx and VOC Emissions from the 2008 NEI, version 1.5 for five counties outside 

of the DFW CSA.

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy)

Freestone No 18,773 10,595

Limestone No 19,214 5,749

McLennan No 10,616 6,980

Navarro No 5,920 4,457

Robertson No 11,528 4,893

The five counties in Table 5 above have comparatively high levels of emissions of NOx and VOC and 

thus have the potential to contribute to monitored violations, but these counties are not in, or nearby, a 

county with a violating monitor. 

Population density and degree of urbanization

EPA evaluated the population and vehicle use characteristics and trends of the area as indicators of the 

probable location and magnitude of non-point source emissions. These include ozone precursor 

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 that contributes to nonattainment in the area. Rapid growth in population or vehicle miles 

traveled (VMT) in a county on the urban perimeter signifies increasing integration with the core urban 

area, and indicates that it may be appropriate to include such perimeter area(s) as part of the 

nonattainment area. Table 6 presents the population, population density, and population growth 

information for each county in the area.
10

Table 6. 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)

Collin Yes 782,341 0.88 282,143 56.4

Cooke No 38,734 0.04 1,979 5.4

Dallas Yes 2,368,139 2.6 142,691 6.4

Delta No 5,231 0.02 –106 –2.0

Denton Yes 662,614 0.69 223,647 50.9

Ellis Yes 149,610 0.16 37,228 33.1

Fannin No 33,915 0.04 2,575 8.2

Grayson No 120,877 0.12 9,891 8.9

Henderson No 78,532 0.08 4,990 6.8

Hood No 51,182 0.12 9,719 23.4

Hunt No 86,129 0.10 9,199 12.0

Johnson Yes 150,934 0.21 22,967 17.9

Kaufman Yes 103,350 0.13 31,268 43.4

Palo Pinto No 28,111 0.03 1,028 3.8

Parker Yes 116,927 0.13 27,690 31.0

Rockwall Yes 78,337 0.53 34,457 78.5

Somervell No 8,490 0.04 1,660 24.3

Tarrant Yes 1,809,034 2.01 354,603 24.4

Wise No 59,127 0.06 9,727 19.7

Area-wide: 6,731,614 0.46 1,207,356 21.9

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_GCTP

L2.STO5&prodType=table)

Counties with monitors indicating a violation of the NAAQS are indicated in bold.

The Dallas-Fort Worth area is a large metropolitan area with a population approaching 7 million people. 

For the purposes of determining the boundary of the 2008 ozone nonattainment area, EPA evaluated 22 

counties in the greater DFW area with a combined population of 6,731,614 people and an average 

population density of 460 people per square mile.

Dallas and Tarrant Counties have the highest and most dense populations. Dallas County has 

approximately 2.4 million people and a population density of 2,600 people per square mile, and Tarrant 

County has approximately 1.8 million people and a population density of 2,010 people per square mile. 

Two other counties, Collin and Denton are also densely populated; each has more than 500,000 people 

and a population density exceeding 500 people per square mile.

There are eight additional counties in this area with populations exceeding 50,000 people and/or 

population densities exceeding 100 people per square mile. These counties include: Ellis, Grayson, 

Hood, Johnson, Kaufman, Parker, and Rockwall. These counties are characterized by population counts 

that range between approximately 50,000 and 150,000 people and/or population densities that range 

from 120 to 530 people per square mile.

Ten of the counties in this area experienced population growth between 2000 and 2010 in excess of 

approximately 10,000 people. The population of four of these counties grew by more than 100,000 

people during the past decade: Collin County (+282,143 people), Dallas County (+142,000 people), 

Denton County (+223,647 people), and Tarrant County (+354,603 people). Six additional counties 
11

experienced population growth that ranged from approximately 10,000 to 50,000 people: Ellis, Johnson, 

Kaufman, Parker, Rockwall, and Wise Counties.

A final population and growth metric evaluated by EPA was the percent change in population during the 

period from 2000 to 2010. During this decade, eight of the 22 counties experienced a percent change in 

population that exceeded 10 percent: Collin (+18.5%), Denton (+18.7%), Ellis (+13.5%), Kaufman 

(+17.6%), Parker (+15.4%), Rockwall (+25.7%), Somervell (+14.4%), and Tarrant (+12.2%) Counties.

The attachment to this document includes Figure 2, Dallas-Fort Worth Ozone and Ozone Precursor 

Monitoring Network, with Population Density; and Figure 3, Population Density Change in Percentage 

Between the 2000 and 2010 Census for the Dallas-Fort Worth Ozone and Ozone Precursor Monitoring 

Network, which present graphical information on population density and growth for the DFW area.

Table 7 below presents population data for the five outlying counties that EPA also evaluated for 

inclusion in the DFW nonattainment area. 

Table 7. Population and Growth for the five counties outside of the DFW CSA

County

State 

Recommended 

Nonattainment?

2010

Population

2010 Population 

Density

(1000 pop/sq mi)

Absolute change 

in population

(2000-2010)

Population % 

change

(2000-2010)

Freestone No 19,816 0.02 1,949 10.9

Limestone No 23,384 0.02 1,333 6

McLennan No 234,906 0.22 21,389 10

Navarro No 47,735 0.04 2,611 5.8

Robertson No 16,622 0.01 622 3.9

McLennan County has a population greater than 50,000 and a population density greater than 100 

people per square mile; and Freestone and McLennan counties have experienced population growth of at 

least 10 percent, indicating the potential to contribute to violations. However, as indicated earlier in this 

TSD, the five counties listed in Table 7 do not have violating monitors, nor are they nearby violating 

monitors.

Traffic data

EPA evaluated the total VMT for each county. In combination with the population/population density 

data and the location of main transportation arteries (see 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 that contributes to nonattainment in the area. Rapid population or VMT growth in a county on 

the urban perimeter signifies increasing integration with the core urban area, and indicates that such 

perimeter area(s) may be appropriate to include in the nonattainment area. Table 8 shows traffic data, 

including 2008 VMT and VMT growth for each county in the DFW CSA.
12

Table 8. Traffic Data.

Texas County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

% Change in VMT

(2002 – 2008)

Collin Yes 6,198 +33

Cooke No 636 +16

Dallas Yes 26,625 +14

Delta No 72 -4

Denton Yes 5,507 +27

Ellis Yes 1,893 +49

Fannin No 334 +9

Grayson No 1,364 +3

Henderson No 768 +30

Hood No 443 +46

Hunt No 1,046 +26

Johnson Yes 1,432 +47

Kaufman Yes 1,548 +38

Palo Pinto No 397 +3

Parker Yes 1,280 +41

Rockwall Yes 676 +15

Somervell No 121 +27

Tarrant Yes 16,741 +17

Wise No 969 +16

Area-wide: 68,050 ----

* MOBILE model VMTs are those inputs into the 2008 NEI version 1.5.

Counties with monitors indicating a violation of the NAAQS are indicated in bold.

The VMT is an important metric as an indicator of potential contribution to ground level ozone 

concentrations. Commuters in the DFW area traveled a total of approximately 68 billion miles during 

calendar year 2008. Four counties in the DFW area, Collin, Dallas, Denton, and Tarrant Counties, each 

have total VMT for calendar year 2008 in excess of 5 billion miles. Dallas and Tarrant Counties have 

particularly high VMT of approximately 27 and 18 billion miles, respectively. An additional seven 

counties have 2008 VMT in the range of approximately 1 – 2 billion miles; these counties are Ellis, 

Grayson, Hunt, Johnson, Kaufman, Parker, and Wise Counties.

Most of the counties in the DFW area have experienced growth in VMT for the period from 2002 –

2008. The growth in VMT for 15 of these counties exceeds 10 percent, and for 10 of those counties the 

growth rate exceeded 25 percent. Five counties in particular have comparatively high VMT growth for 

this period: Ellis County (+49%), Hood (+46%), Johnson County (+47%), Kaufman County (+38%), 

and Parker County (+41%). However, of the 19 counties listed in Table 8, Ellis, Kaufman, Johnson and 

Parker counties rank 5th, 6th, 7th and 9th in absolute VMT, respectively, while Hood ranks 15th.

Table 9 below provides the VMT data for the five outlying counties that EPA evaluated for inclusion in 

the DFW nonattainment area. These counties have VMT that is comparatively lower than that of the 

counties recommended by Texas for inclusion in the nonattainment area, with the exception of Rockwall 

County.
13

Table 9. Traffic Data for the Five Counties Outside of the DFW CSA

Texas County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

% Change in VMT

(2002 – 2008)

Freestone No 650 +13

Limestone No 315 +18

McLennan No 275 +12

Navarro No 800 –37

Robertson No 345 +17

In addition to VMT, we have evaluated worker data collected by the US Census Bureau11 for the nine 

counties recommended by Texas for inclusion in the nonattainment area and two additional counties, 

Hood and Wise, that EPA considered for inclusion in the nonattainment area to inform our designations 

decisions. The data in Table 10 below are 2010 data and reflect an analysis of work destinations (all 

jobs) for residents in these 11 counties. 

Table 10. Worker Data

County

State

Recommended 

Nonattainment?

Number of 

County Residents 

who Work

Number of County 

Residents who Work in 

Counties with 

Violating Monitors

Percent of County 

Residents who Work in 

Counties with Violating 

Monitors

Collin Yes 364,301 320,714 88.0%

Dallas Yes 975,350 852,017 87.3%

Denton Yes 300,910 265,220 88.1%

Ellis Yes 63,773 37,071 58.1%

Hood No 18,133 6,932 38.2%

Johnson Yes 65,252 51,883 79.5%

Kaufman Yes 46,344 28,491 61.4%

Parker Yes 48,779 28,260 57.9%

Rockwall Yes 34,716 22,255 64.1%

Tarrant Yes 785,269 696,283 88.6%

Wise No 22,650 10,374 45.8%

Area-wide: 2,725,477 2,319,500 85.1%

Counties with monitors indicating a violation of the NAAQS are indicated in bold.

For each of the 11 counties shown in Table 10 above, a significant fraction of residents work in the 

counties with violating monitors, thus contributing to mobile source emissions. This high percentage of 

workforce interchange indicates integration with the urban core counties.

Table 11 below provides the worker data for the five outlying counties that EPA evaluated for inclusion 

in the DFW nonattainment area. 

 11 The worker data can be accessed on the internet at http://onthemap.ces.census.gov/. Please see Appendix 1 in the 

Attachment for instructions to access the worker data.
14

Table 11. Worker Data for the five counties outside of the DFW CSA

County

State

Recommended 

Nonattainment?

Number of 

County Residents 

who Work

Number of County 

Residents who Work in 

Counties with 

Violating Monitors

Percent of County 

Residents who Work in 

Counties with Violating 

Monitors

Freestone No 7,681 1,781 23.1%

Limestone No 8,720 1,805 20.6%

McLennan No 96,116 10,730 11.1%

Navarro No 19,865 5,174 26.0%

Robertson No 7,188 258 3.5%

For each of the five counties shown in Table 11 above, a smaller fraction of county residents work in the 

counties with violating monitors, which suggests that at this time there is little, if any integration with 

the urban core counties. 

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. Based on past research by EPA and TCEQ the DFW area is 

generally characterized as having ozone exceedances with lower wind speeds and winds from many 

directions but the more frequent directions are easterly through southwesterly winds. Light winds with 

weak frontal passages and conversion zones also are a common meteorological condition that often 

leads to high ozone in the DFW area. EPA’s analysis of meteorology is focused on the meteorology and 

transport phenomena that results in transport of air emissions to monitors in the DFW area that have 

monitored exceedances of the 2008 ozone standard. 

The attachment to this document includes Figure 2, Dallas-Fort Worth Ozone and Ozone Precursor 

Monitoring Network, with Population Density, which provides locations of major stationary sources and 

locations of ambient monitors with their design values.

EPA has performed 24-hour wind back trajectories (an analysis of meteorological/transport patterns) 

specifically on days when certain monitors (identified below) in the DFW area measured an exceedance 

of the 2008 NAAQS. These analyses were conducted to better understand the area’s meteorological 

transport conditions using the National Oceanic and Atmospheric Administration Hybrid Single Particle 

Lagrangian Integrated Trajectory Model (NOAA HYSPLIT or HYSPLIT). The HYSPLIT model yields 

an estimate of the path an air mass has traveled before reaching a monitor at a specific location and time. 

Specifically, the model provides the centerline of the probable path. By knowing where an air mass has 

traveled before reaching a monitor where an exceedance has occurred, one can consider what potential 

areas and emission sources could have contributed to the exceedance. 

The HYSPLIT trajectories for 2008-2010 exceedance days at the Keller monitor in Tarrant County were 

conducted and the resulting trajectories were overlaid on Figure 2 in the attachments and are shown in 

Figure 4. We focused on the Keller and Eagle Mountain Lake monitors in Tarrant County and the Parker 

County monitor because the Keller and Eagle Mountain Lake monitors have recorded some of the 

highest ozone levels in the region, and inclusion of the Parker County monitor provided a good crosssection of the monitors in the western DFW area that experienced exceedances in the 2006-2010 period. 
15

In analysis of the DFW conceptual model for ozone exceedances, these monitors also seemed to have 

the most potent to be impacted by emissions from Hood or Wise Counties. Since the 2008-2010 data for 

the Keller monitor is only for three years, we evaluated additional years to better understand the 

meteorological transport conditions that exist during ozone exceedances. When we are developing a 

conceptual model for understanding what types of meteorology are present when ozone exceedances 

occur in an area we evaluate 5 to 10 years worth of meteorological data. By considering a longer period 

of time, we have greater assurance that the most representative weather conditions are considered and 

control strategies and decision making are not driven by unusual meteorology.

There are three additional figures in the attachment that include a zoom view for each of the Keller, 

Eagle Mountain Lake and Parker County monitors. These are labeled as Figures 5a through 5c. These 

zoom views are HYSLPIT 24-hour back trajectories for each of these monitors on days when they had 

exceedances of the 75 ppb standard. Evaluation of the back trajectories for the Keller, Eagle Mountain 

Lake, and Parker County monitors indicates that the areas upwind of the monitors prior to an ozone 

exceedance include all the counties in the 1997 8- hour DFW nonattainment area (Collin, Dallas, 

Denton, Ellis, Johnson, Kaufman, Parker, Rockwall and Tarrant counties), and also Wise and Hood 

Counties. The additional back trajectories for the Eagle Mountain Lake and Parker County monitors 

further support that air that is transported from Hood and Wise counties ends up in the area of the 

monitor when ozone exceedances are observed.

We did receive comments that we should not consider potential impacts at the Parker monitor from 

Hood County emissions since the Parker monitor’s 2010 DV (2008-2010 data) is attaining the standard 

with a 75 ppb. We evaluated the Parker monitor because it is part of the existing 9-county DFW 

nonattainment area for the 1997 8-hour ozone NAAQS and Parker County was recommended by Texas 

to be part of the DFW nonattainment area for the 2008 8-hour ozone NAAQS. In review of the 2006-

2010 HYSPLIT back trajectories for the Parker County monitor ozone exceedances, some of the 

trajectories pass through the Hood County area. However, since the Parker monitor is attaining the 2008 

NAAQS, we did not put significant weight on the back trajectories for the Parker County monitor.

TCEQ SOURCE APPORTIONMENT MODELING

The TCEQ has developed CAMx photochemical modeling for previous ozone attainment 

demonstrations. The TCEQ did additional modeling using these CAMx databases to provide source 

apportionment modeling that assessed the potential contribution of Hood and Wise county emissions to 

modeled high ozone values in the DFW area. The TCEQ’s analysis was performed for a period of a 

month in early 2006 summer (May 31 to July 1) for three monitors that EPA had performed back 

trajectories. They also evaluated this base episode with a future year analysis of 2012 (2006 meteorology 

with 2012 emission estimates). In summarizing this work, they provided average and maximum impacts 

to daily 8-hour modeled exceedances in the base case (2006) and 2012. The TCEQ indicated the impacts 

were small and supported not including Hood or Wise counties.
16

EPA Assessment:

Source apportionment analysis can be a good tool to combine the meteorology/transport of air parcels 

during high ozone days with the emissions of specific areas to evaluate potential impact on ozone levels 

from emissions in specific source areas, Hood and Wise County emissions in this case. The EPA 

appreciates the efforts of TCEQ to provide the modeling to aid in decisions on designations. 

One of EPA’s observations regarding TCEQ’s Source Apportionment Modeling (SAM) is that the 

modeling is not inclusive of an entire ozone season. Evaluations of the conceptual model for high ozone 

in DFW by TCEQ, EPA and others indicates that high ozone in DFW is roughly a bimodal distribution 

with lower peaks in early summer (May-June) and the highest values in mid to late-summer (JulySeptember) and that the mid to late summer has some different meteorological/transport regimes than 

the early summer episodes. Therefore, TCEQ’s SAM does not include a large number of days and does 

not include all of the meteorology regimes conducive for ozone events in DFW and is missing the events 

that happen in mid to late-summer that often set the DFW area’s DV. As a result, it may be appropriate 

to place more weight on the maximum estimated impact and the number of days with sizeable impacts 

on violating monitors as compared to average impact. Another observation is that the evaluation used 

modeled exceedances for contribution and the modeling is underestimating exceedances on many days 

and therefore is underestimating the number of days of potential contribution. Modeling is significantly 

under predicting peaks by 5-20 ppb at critical monitors; therefore we also looked at contribution at lower 

modeled values (70 ppb). The EPA analyzed the 2006 and 2012 modeling information, but felt the 2012 

analysis took into account recent control measures that TCEQ has implemented to lower DFW ozone 

levels and the 2012 was closer to what emission levels are at the time we are making these designation 

decisions. We have summarized the information provided by TCEQ in the letter from Governor Rick 

Perry dated February 29, 2012. This summary of SAM estimates of impacts for Hood and Wise County 

emissions is included in Table 12.
17

Table 12. TCEQ Source Apportionment – Hood and Wise County Anthropogenic Emissions Impact (in 

ppb) on Modeled Ozone exceedances

HOOD WISE

Site Monitor Site AVG MAX AVG MAX

EMTL Eagle Mountain Lake 0.010 0.03 0.520 0.81

KELC Keller 0.010 0.02 0.010 0.03

WTFD Parker – Weatherford 0.030 0.16 0.670 1.29

In the course of our review, we requested and TCEQ provided additional modeling files that included 

SAM results at most of the monitors in DFW. EPA has reviewed this additional information and did 

discover some errors/discrepancies in TCEQ’s spreadsheets.12 EPA shared the errors/discrepancies with 

TCEQ. TCEQ had also used the average of the predicted ozone levels in the grid cells around the 

monitor, and EPA guidance is to use the maximum, so EPA reanalyzed the data using the maximum 

ozone levels in the grid cells around a monitor. 

In analyzing SAM for a specific area for designation we evaluated the average impact, maximum 

impact, and an additional metric, the number of days where impacts may be high enough that reductions 

might be beneficial in development of an attainment demonstration. Often in attainment demonstration 

modeling, controlling of sources is evaluated and results in only a few tenths of a ppb change, therefore 

we used a 1% of the standard cut point for days where we would consider Hood or Wise County’s 

impact to be significant. We determined the number of days an impact was over 1% (0.75 ppb) on a 

modeled exceedance of the 75 ppb standard and also model exceedances greater than 70 ppb. Also since 

this SAM misses the mid to late summer meteorology/transport that results in high ozone and is not a 

full picture of DFW ozone exceedances, we put more weight on peaks and # of days over 0.75 ppb at 

area monitors (NA and near NA 2008-2010). The corrected SAM and EPA’s assessment of TCEQ’s 

SAM is included in Table 13 and Table 14.

 12 Additional information has been included in the docket for this action and additional information is included in a zipped 

file “TCEQ back-up information.zip and EPA assessment of Matagorda.zip.”
18

Table 13. Corrected TCEQ Source Apportionment with EPA’s assessment – Hood County Anthropogenic Emissions

HOOD

Modeled days >75 

ppb (2012)

# of days >0.75 ppb

HOOD 

Modeled days >70 ppb 

(2012)

Site # of days >0.75 ppb

AVG 

(ppb)

MAX 

(ppb)

AVG 

(ppb)

MAX 

(ppb)

DENT Denton 0.06 0.48 0.06 0.48

EMTL Eagle Mtn. 0.10 0.46 0.19 1.12 1

KELC Keller 0.05 0.25 0.05 0.25

GRAP Grapevine 0.01 0.05 0.01 0.05

FWMC FW NW 0.03 0.17 0.07 0.45

FRIC Frisco 0.01 0.02 0.01 0.02

WTFD1 Parker - Weatherford 0.85 2.26 4 0.77 2.26 4

CLEB Cleburne 0.01 0.03 0.01 0.03

ARLA Arlington 0.01 0.02 0.00 0.02

PIPT Pilot Point 0.04 0.23 0.04 0.23

GRAN1 Granbury (Hood) 2.34 5.77 9 2.63 5.77 9

Total Occurrences

1

 Based on most recent certified monitoring data, the Parker and Hood County monitors have a DV of 75 ppb, which is in attainment of the 

2008 8-hour ozone NAAQS. 
19

Table 14. Corrected TCEQ Source Apportionment with EPA’s assessment – Wise County Anthropogenic Emissions

WISE 

Modeled days >75 

ppb (2012)

# of days >0.75 ppb

WISE 

Modeled days >70 ppb 

(2012)

Site # of days >0.75 ppb

AVG

(ppb)

MAX 

(ppb)

AVG 

(ppb)

MAX 

(ppb)

DENT Denton 0.13 1.15 1 0.128 1.15 1

EMTL Eagle Mtn. 0.36 0.86 1 0.677 5.03 2

KELC Keller 0.05 0.5 0.360 0.50

GRAP Grapevine 0.07 0.99 1 0.293 3.85 2

FWMC FW NW 0.09 1.08 1 0.104 1.08 1

FRIC Frisco 0.03 0.36 0.031 0.36

WTFD1 Parker - Weatherford 0.85 7.48 1 1.217 7.48 2

CLEB Cleburne 0.12 0.88 0.120 0.88 1

ARLA Arlington 0.17 1.72 1 0.124 1.72 1

PIPT Pilot Point 0.03 0.14 0.028 0.14

MDLO Midlothian 0.12 1.09 1 0.111 1.09 1

GRAN1 Granbury (Hood) 0.33 3.07 1 0.308 3.07 1

GRVL Greenville 0.01 0.03 0.007 0.01

Total Occurrences 6 occurrences over 4 days 9 occurrences over 5 days

1

 Based on most recent certified monitoring data, the Parker and Hood County monitors have a DV of 75 ppb, which is in attainment of the 

2008 8-hour ozone NAAQS
20

In both Table 13 and Table 14, the Parker and Hood County information is highlighted in green as these 

monitors are currently in attainment at the time of designation based on 2008-2010 data. As a result, we 

have put little weight on the impact of emissions on Hood and Parker monitors. Hood County emissions 

do not have a large contribution on any days using the 75 ppb modeled threshold and only one day 

above with a contribution over 0.75 ppb using the 70 ppb modeling threshold on current DFW monitors 

(not including Parker or Hood monitors). Some concerns were raised that the SAM may include higher 

emissions than are currently present for Hood County sources and thus the SAM may be overestimating 

Hood County emission impacts. Even without considering the potential uncertainty in the emissions for 

Hood County in the modeling, it does not appear that the modeling shows significant impacts on 

monitors that are currently violating the standard. SAM does show significant impact on Parker County 

from Hood at times but as mentioned previously, we did not put significant weight on these impacts 

because Parker County is currently attaining the standard.

In our evaluation of the Wise County SAM, Wise County emissions have a larger average and 

maximum contribution than Hood County emissions using the 75 ppb modeled exceedance threshold. 

Furthermore, when using this threshold, Wise County emissions resulted in 6 occurrences (over 4 days) 

of an impact of more than 0.75 ppb days on DFW monitors (not including Parker or Hood monitors). To 

take into account concerns that the modeled period is not inclusive of all conditions that lead to high 

ozone and the modeling underestimation concerns, we also evaluated contributions to all modeled values 

of greater than 70 ppb. This analysis indicated Wise County emissions had even larger impacts of up to 

5 ppb on the Eagle Mountain Lake monitor, which is one of the monitors in DFW that sets the DV for 

the DFW area. This analysis also indicated that Wise County emissions resulted in 9 occurrences (over 5 

days) that impacts of more than 0.75 ppb occurred at DFW area monitors (not including Parker or Hood 

county monitors). It does appear that the SAM provides evidence for inclusion of Wise County.

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 air

shed and, therefore, the distribution of ozone over the area. The DFW area does not have any 

geographical or topographical barriers significantly limiting air pollution transport into or within its air

shed. Therefore, this factor did not play a significant role in this evaluation.

Factor 5: Jurisdictional boundaries

Once we identified the general areas we anticipated we would recommend be included in the 

nonattainment area, we then considered existing jurisdictional boundaries for the purposes of providing 

a clearly defined legal boundary and to help identify the areas appropriate for carrying out the air quality 

planning and enforcement functions for nonattainment areas. Examples of jurisdictional boundaries 

include existing or prior nonattainment area boundaries for ozone or other urban-scale pollutants, county 

lines, air district boundaries, township boundaries, areas covered by a metropolitan planning 

organization, state lines, Reservation boundaries, and urban growth boundaries. Where existing 

jurisdictional boundaries were not adequate or appropriate to describe the nonattainment area, other 

clearly defined and permanent landmarks or geographic coordinates were considered.

The DFW area has previously established nonattainment boundaries associated with the 1-hour and 

1997 8-hour ozone NAAQS. Texas has recommended the boundary for the 2008 ozone NAAQS be the 

same as that for the 1997 ozone NAAQS.
21

In addition to the CSA boundary, an important boundary is that of the metropolitan planning 

organization (MPO). In the DFW area, the MPO is the North Central Texas Council of Governments, 

which is responsible for planning and implementing transportation programs and projects aimed at

reducing congestion, enhancing mobility, and improving air quality. The 10 counties in the DFW 2008 

ozone nonattainment area are in the same MPO boundary.

Freestone, Limestone, McLennan, Navarro and Robertson counties are outside of the DFW CSA. While 

Navarro County is inside the DFW MPO boundary, Freestone, Limestone, McLennan and Robertson 

counties are not. Furthermore, Freestone, Limestone and McLennan counties are in an MPO boundary 

that does not include Robertson County.

Conclusion

Based on the assessment of factors described above, EPA has concluded that the following counties will 

be included as part of the DFW ozone nonattainment area because they have air quality monitors that 

indicate a violation of the 2008 ozone NAAQS, or because they are contributing to a violation in a 

nearby area: Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwell, Tarrant, and Wise

Counties. These are the same counties that were included in the DFW nonattainment area for the 1997 

ozone NAAQS, with the addition of Wise County.

The air quality monitors in Collin, Dallas, Denton, Johnson, and Tarrant Counties indicate violations of 

the 2008 ozone NAAQS based on the 2010 DVs, therefore these counties are included in the 

nonattainment area.

Ellis, Kaufman, Parker, Rockwall, and Wise Counties are nearby counties that do not have monitors

indicating ambient ozone concentrations in excess of 75 ppb, but EPA has concluded that these areas 

contribute to observed violations of the 2008 ozone standard in nearby counties, through emissions from 

point sources and other, non-point sources (e.g., vehicles and other small area sources).

Collin, Dallas, Denton, Ellis, Johnson, Parker, Tarrant, and Wise Counties have among the highest NOx 

and VOC emissions in the area. Each of these counties either has a monitor indicating a violation of the 

2008 ozone NAAQS or is adjacent to one or more such counties.

Collin, Dallas, Denton, Ellis, Grayson, Hood, Johnson, Kaufman, Parker, Rockwall, Somervell, Tarrant, 

and Wise Counties ranked comparatively high for factors related to population statistics, and Collin, 

Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, Tarrant, and Wise Counties ranked 

comparatively high for factors related to traffic data.

EPA’s meteorological assessment when ozone exceedances of the 2008 ozone standard have been 

monitored within the DFW area supports the consideration of inclusion of the existing 9-county 

nonattainment area (Dallas, Tarrant, Collin, Denton, Ellis, Johnson, Parker, Rockwall, and Kaufman 

counties) and Hood and Wise counties.
22

Collin County: Recommended for inclusion by Texas and has a violating monitor, so will be included.

Dallas County: Recommended for inclusion by Texas and has a violating monitor, so will be included.

Denton County: Recommended for inclusion by Texas and has a violating monitor, so will be included.

Ellis County: Recommended for inclusion by Texas; has 2008 NEI emissions of 15,768 tons of NOx and 

6,543 tons of VOC; there are 160 people per square mile; has a 2010 population of 149,610 with a 

growth rate of 13.5 percent between 2000 and 2010; total VMT is 1.9 billion miles. Winds often flow 

from the south, southeast and east, so emissions from Ellis County often contribute to violations in other 

DFW counties. These factors, in conjunction with the number of commuters and growth rate support the 

inclusion of Ellis County in the nonattainment area.

Hood County: Has 2008 NEI emissions of 5,515 tons of NOx and 8,739 tons of VOC, with TCEQ 2009 

Barnett Shale Special Inventory emissions of an additional 6,903 tons of NOx and 2,113 tons of VOC; 

there are 120 people per square mile; has a 2010 population of 51,182 with a growth rate of 9.2 percent 

between 2000 and 2010; total VMT is 443 million miles. Emissions from this county have grown 

considerably, due primarily to oil and gas development. Back trajectories show that at times Hood 

County emissions could potentially contribute to observed violations in other counties. Much of the 

emissions from Hood County were based on oil and gas activities. We received information that 

exploration has dropped dramatically, calling into question whether current emissions are as high as 

estimated by TCEQ’s special inventory. As discussed, we are giving little weight to the fact that Hood 

County emissions contribute to exceedances in Parker County because Parker County is currently 

monitoring attainment. Hood County is some distance from monitors that are currently violating the 

2008 ozone standard. The SAM analysis conducted by TCEQ also does not indicate a significant impact 

from Hood County on currently violating monitors. Taken together, the amount of emissions, the 

distance from the monitor, the population and the VMT do not warrant inclusion of Hood County as part 

of the nonattainment area.

Johnson County: Recommended for inclusion by Texas and has a violating monitor, so will be included.

Kaufman County: Recommended for inclusion by Texas; has 2008 NEI emissions of 5,868 tons of NOx 

and 3,510 tons of VOC; there are 130 people per square mile; has a 2010 population of 103,350 with a 

growth rate of 17.6 percent between 2000 and 2010; total VMT is 1.5 billion miles. Winds often flow 

from the south, southeast and east, so emissions from Kaufman County often contribute to violations 

other counties. These factors, in conjunction with the VMT and growth rate support the inclusion of 

Kaufman County in the nonattainment area.

Parker County: Recommended for inclusion by Texas; has 2008 NEI emissions of 9,550 tons of NOx 

and 11,708 tons of VOC; there are 130 people per square mile; has a 2010 population of 116,927 with a 

growth rate of 15.4 percent between 2000 and 2010; total VMT is 1.3 billion miles. The comparatively 

high emissions and population growth rates indicate that Parker County should be included in the 

nonattainment area. In addition, at times back trajectories indicate that emissions from Parker County 

contribute to observed violations in the area. These factors support the inclusion of Parker County in the 

nonattainment area.

Rockwall County: Recommended for inclusion by Texas; has 2008 NEI emissions of 1,859 tons of NOx 

and 2,047 tons of VOC; there are 530 people per square mile; has a 2010 population of 78,337 with a 
23

growth rate of 25.7 percent between 2000 and 2010; total VMT is 676 million miles. While a small 

county, its population density and emissions support the inclusion of Rockwall County in the 

nonattainment area.

Tarrant County: Recommended for inclusion by Texas and has a violating monitor, so will be included.

Wise County: Has 2008 NEI emissions of 11,911 tons of NOx and 17,609 tons of VOC; there are 60

people per square mile; has a 2010 population of 59,127 with a growth rate of 5.9 percent between 2000 

and 2010; total VMT is 969 million. The close proximity of these comparatively high emissions to 

violating monitors indicates that this county should be included in the nonattainment area. The high 

growth in these emissions is due in large part to growth in emissions from Barnett Shale gas production 

development, but also due to growth in population. Examination of back trajectories indicates that at 

times emissions from Wise County contribute to observed violations in the area and also to observed 

violations that have helped set the DFW area DV in the past. Source apportionment modeling for a 

portion of an ozone season indicates that emissions from Wise County can contribute to observed 

violations in the DFW nonattainment area. These factors support the inclusion of Wise County in the 

nonattainment area.

McLennan and Navarro counties do not have violating monitors, and Freestone, Limestone, McLennan, 

Navarro and Robertson counties are not nearby a county with a violating monitor. Freestone, Limestone, 

McLennan, Navarro and Robertson counties have significant levels of emissions of NOx and VOC and 

thus have the potential to contribute to monitored violations, but are not in or nearby counties with a 

violating monitor. McLennan County has a population greater than 60,000 and a population density 

greater than 100 people per square mile; and Freestone and McLennan counties have experienced 

population growth of at least 10 percent, indicating the potential to contribute to violations, but are not 

in or nearby counties with a violating monitor. Freestone, Limestone, McLennan, Navarro and 

Robertson counties have a small fraction of residents that work in the counties with violating monitors, 

which suggests that at this time there is little, if any integration with the urban core counties. Finally, 

Freestone, Limestone, McLennan, Navarro and Robertson counties are outside of the DFW CSA, and all 

but Navarro County are outside of the MPO boundary.

Our evaluation of data for Freestone, Limestone, McLennan, Navarro and Robertson Counties does not 

support a nonattainment designation for the 2008 ozone standard at this time. We do not believe these 

five counties are contributing to violations of the 2008 ozone standard in a nearby area.

Our evaluation of data for Cooke, Delta, Fannin, Grayson, Henderson, Hunt and Somervell Counties 

does not support a nonattainment designation. We did not receive any comments that these counties 

should be included in the DFW nonattainment area.
24

ATTACHMENTS

Appendix 1. Accessing Worker Data from http://onthemap.ces.census.gov/.

Figure 2. Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network, with Population Density.

Figure 3. Population Density Change Percentage Between 2000 and 2010 Census for Dallas-Fort Worth 

Ozone and Ozone Precursor Monitoring Network.

Figure 4. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Keller monitor 

for the 2008-2010 period.

Figure 5a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Eagle Mtn. Lake Exceedances (2006-

10) (zoom view).

Figure 5b. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10).

Figure 5c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10)

(zoom view).
25

Appendix 1. Accessing Worker Data from http://onthemap.ces.census.gov/.

1. Open your internet browser to http://onthemap.ces.census.gov/.

2. Click on “Text-Only” in the upper right corner.

3. In the open search box, type the name of the county for which you seek information. Click on 

“Counties” in the drop-down box for “Search All Names” and then click the “Go” button. The search 

results will appear on your screen and click on the appropriate county, even if you are offered only one 

choice.

4. Analysis settings will appear next on your screen. To gather our worker data, under the Home/Work 

Area, we clicked on “Home.” Under the Analysis Type, we clicked on “Destination” and then under 

“Options for Destination: Destination Type” we used the drop-down box and clicked on “Counties.” We 

clicked on 2010 for the year, and “All Jobs” for the Job Type. Then scroll down to the bottom of the 

page and click the “Run Analysis” button.

5. The Work Destination Analysis will appear next on your screen. The default setting will show you the 

top 10 counties where workers are employed. To show additional counties, click on “Top 25” and then 

click the “Update” button.

6. To run analyses for additional counties, scroll to the top of the screen and click on “Return to search.” 
26

Figure 2. Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network, with Population Density
27

Figure 3. Population Density Change Percentage Between 2000 and 2010 Census

for Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network
28

Figure 4. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Keller monitor for the 2008-2010 period
29

Figure 5a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Eagle Mtn. Lake Exceedances (2006-10) (zoom view).
30

Figure 5b. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10).
31

Figure 5c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10) (zoom view).