1

TEXAS 

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards 

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

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

NAAQS). In accordance with section 107(d) of the Clean Air Act, EPA must designate an area 

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

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

individual nonattainment areas are provided below. 

Intended Nonattainment Areas in Texas

Area Texas’ Recommended 

Nonattainment Counties 

EPA’s Intended 

Nonattainment Counties 

Dallas-Fort Worth, TX 

Collin 

Dallas 

Denton 

Ellis 

Johnson 

Kaufman 

Parker 

Rockwall 

Tarrant 

Collin 

Dallas 

Denton 

Ellis 

Hood 

Johnson 

Kaufman 

Parker 

Rockwall 

Tarrant 

Wise 

Houston-Galveston-Brazoria, 

TX 

Brazoria 

Chambers 

Fort Bend 

Galveston 

Harris 

Liberty 

Montgomery 

Waller 

Brazoria 

Chambers 

Fort Bend 

Galveston 

Harris 

Liberty 

Matagorda 

Montgomery 

Waller 

EPA intends to designate the remaining counties in Texas that are not listed in the table above as 

“unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analysis below provides the basis for intended nonattainment area boundaries. It relies on our 

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

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

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

analysis considering the factors identified below. EPA issued guidance on December 4, 2008 that 
2

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

recommended that states consider these factors in making their designations recommendations to EPA.1 

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

(FRM) or Federal Equivalent Method (FEM)2

 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. 

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) associated 

with 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 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. 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 

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

considering the nonattainment area’s boundary. 

Technical Analysis for Dallas-Fort Worth 

Figure 1 is a map of the Dallas-Fort Worth intended nonattainment area. 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 1997 

ozone NAAQS, and major transportation arteries.

Figure 1. Dallas-Fort Worth Intended Nonattainment Area 

 

1

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

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

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

2

 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 1970’s/early1980’s 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 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). 
3

For purposes of the 1997 8-hour ozone NAAQS, portions of this area were designated nonattainment. 

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. 

In March 2009,4 Texas recommended that the same counties be designated as nonattainment for the 

2008 ozone NAAQS based on air quality data from 2006-2008. Texas provided an update to the original 

recommendation in October 20115

 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.

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

intends to designate 11 counties in Texas (identified in Table 1 below) as “nonattainment” for the 2008 

ozone NAAQS as part of the Dallas/Fort Worth nonattainment area. 

Table 1. Texas's Recommended and EPA’s Intended Designated Nonattainment Counties for Dallas/Fort 

Worth.

 

4

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

Starfield, dated March 10, 2009. 5

 Updated 2008 ozone NAAQS designation recommendation letter from Governor Perry to Regional Administrator 

Armendariz, dated October 31, 2011. 
4

Dallas-Fort Worth Area State-Recommended 

Nonattainment Counties 

EPA Intended 

Nonattainment Counties 

Texas 

Collin 

Dallas 

Denton 

Ellis 

Johnson 

Kaufman 

Parker 

Rockwall 

Tarrant 

Collin 

Dallas 

Denton 

Ellis 

Hood 

Johnson 

Kaufman 

Parker 

Rockwall 

Tarrant 

Wise 

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 Dallas-Fort Worth 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 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 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 in Dallas-Fort Worth and nearby surrounding area are 

shown in Table 2. 
5

Table 2. Air Quality Data.

County State Recommended 

Nonattainment? 

2008-2010 Design Value 

(ppb) 

Collin County, TX Yes 77 

Cooke, TX No -- 

Dallas County, TX Yes 78 

Delta, TX No -- 

Denton County, TX Yes 80 

Ellis County, TX Yes 72 

Fannin, TX No -- 

Grayson, TX No -- 

Henderson, TX No -- 

Hood County, TX No 75 

Hunt, TX No 64 

Johnson County, TX Yes 80 

Kaufman County, TX Yes 67 

Palo Pinto, TX No -- 

Parker County, TX Yes 75 

Rockwall County, TX Yes 74 

Somervell, TX No -- 

Tarrant County, TX Yes 86 

Wise County, TX No -- 

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 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 or tpy) for violating and nearby 

counties that we considered for inclusion in the Dallas-Fort Worth CSA. 
6

Table 3. Total 2008 NOx and VOC Emissions from 2008 NEI. 

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy) 

Collin, TX Yes 10,322 14,503 

Cooke, TX No 3,853 5,790 

Dallas, TX Yes 51,023 63,473 

Delta, TX No 1,016 462 

Denton, TX Yes 17,421 24,932 

Ellis, TX Yes 15,768 6,543 

Fannin, TX No 2,165 1,207 

Grayson, TX No 5,919 7,401 

Henderson, TX No 3,573 6,067 

Hood, TX No 5,515 9,547 

Hunt, TX No 3,688 3,765 

Johnson, TX Yes 31,769 10,163 

Kaufman, TX Yes 5,868 3,510 

Palo Pinto, TX No 3,348 7,464 

Parker, TX Yes 9,550 11,708 

Rockwall, TX Yes 1,859 2,047 

Somervell, TX No 698 921 

Tarrant, TX Yes 56,408 49,021 

Wise, TX No 11,911 23,657 

Area-wide: 241,674 252,181 

Subsequent to development of the 2008 NEI, the Texas Commission on Environmental Quality (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 2009.6 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 Dallas-Fort Worth CSA counties. 

Table 4. TCEQ 2009 Barnett Shale Area Special Inventory. 

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy) 

Collin, TX Yes 

Cooke, TX No 76 490 

Dallas, TX Yes 0 5 

Delta, TX No 

Denton, TX Yes 429 3,523 

Ellis, TX Yes 120 49 

Fannin, TX No 

Grayson, TX No 

Henderson, TX No 

Hood, TX No 6,903 2,113 

 

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

Phase Two. 
7

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy) 

Hunt, TX No 

Johnson, TX Yes 1,101 1,614 

Kaufman, TX Yes 

Palo Pinto, TX No 1,226 833 

Parker, TX Yes 743 2,420 

Rockwall, TX Yes 

Somervell, TX No 1,119 221 

Tarrant, TX Yes 415 1,083 

Wise, TX No 2,520 6,032 

Area-wide: 14,652 18,383

The counties in the Dallas-Fort Worth 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 2008 NEI NOx emissions and 81 percent of the 2008 NEI VOC emissions of the entire 

area. 

Hood and Wise Counties also have comparatively high emissions of NOx and VOC. Based on just the 

2008 NEI data, Wise County’s emissions of VOC at 23,657 tpy are the 4th highest in the 19-county 

CSA, and Hood County’s 5,515 tpy of VOC emissions are the 8th highest in the 19-county CSA. Wise 

and Hood Counties also have comparatively high NOx emissions, which are 6th and 11th highest, 

respectively, in the CSA. 

Population density and degree of urbanization

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

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

from on-road and off-road vehicles and engines, consumer products, residential fuel combustion, and 

consumer services. Areas of dense population or commercial development are an indicator of area 

source and mobile source NOx and VOC emissions that may contribute to ozone formation that 

contributes to nonattainment in the area. Rapid population or VMT growth (see below) in a county on 

the urban perimeter signifies increasing integration with the core urban area, and indicates that it may be 

appropriate to include the area associated with area source and mobile source emissions as part of the 

nonattainment area. Table 5 shows the population, population density, and population growth 

information for each county in the area. 

Table 5. 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, TX Yes 782,341 0.88 282,143 18.5 

Cooke, TX No 38,734 0.04 1,979 0.4 

Dallas, TX Yes 2,368,139 2.6 142,691 2.2 

Delta, TX No 5,231 0.02 -106 -0.2 

Denton, TX Yes 662,614 0.69 223,647 18.7 

Ellis, TX Yes 149,610 0.16 37,228 13.5 

Fannin, TX No 33,915 0.04 2,575 3.8 

Grayson, TX No 120,877 0.12 9,891 4.6 

Henderson, TX No 78,532 0.08 4,990 0.09 
8

County 

State 

Recommended 

Nonattainment? 

2010 Population 

2010 Population 

Density 

(1000 pop/sq mi) 

Absolute change 

in population 

(2000-2010) 

Population % 

change 

(2000-2010) 

Hood, TX No 51,182 0.12 9,719 9.2 

Hunt, TX No 86,129 0.10 9,199 5.7 

Johnson, TX Yes 150,934 0.21 22,967 4.9 

Kaufman, TX Yes 103,350 0.13 31,268 17.6 

Palo Pinto, TX No 28,111 0.03 1,028 3.1 

Parker, TX Yes 116,927 0.13 27,690 15.4 

Rockwall, TX Yes 78,337 0.53 34,457 25.7 

Somervell, TX No 8,490 0.04 1,660 14.4 

Tarrant. TX Yes 1,809,034 2.01 354,603 12.2 

Wise, TX No 59,127 0.06 9,727 5.9 

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_GCTPL2.STO5&

prodType=table)

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

people. For the purposes of determining the boundary of the intended 2008 ozone nonattainment area, 

EPA evaluated 22 counties in the greater Dallas-Fort Worth area with a total population of 6,731,614 

people and an average population density of 460 people per square mile. 

Dallas and Tarrant Counties have by far 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 2,001 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 an additional eight 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 60,000 and 150,000 people and 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. Of these, 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 experienced population growth that ranged from approximately 10,000 to 40,000 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 contains Figure 3, Dallas-Fort Worth Ozone and Ozone Precursor 

Monitoring Network, and Figure 5, Population Density Change Percentage Between 2000 and 2010 

Census for Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network, which present 

graphical information on population density and growth for the Dallas-Fort Worth area. 
9

Traffic and commuting patterns

EPA evaluated the commuting patterns of residents in the area, as well as the total Vehicle Miles 

Traveled (VMT) for each county. In combination with the population/population density data and the 

location of main transportation arteries (see above), this information helps identify the probable location 

of non-point source emissions. A county with high VMT and/or a high number of commuters is 

generally an integral part of an urban area and indicates the presence of motor vehicle emissions that 

may contribute to ozone formation 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 the associated area source and mobile source emissions may be appropriate to 

include in the nonattainment area. Table 6 shows traffic and commuting pattern data, including total 

2008 VMT and 10-year VMT growth for each county. 

Table 6. Traffic and Commuting Patterns.

County State Recommended 

Nonattainment? 

2008 VMT* 

(million miles) 

% Change in VMT 

(2002 – 2008) 

Collin, TX Yes 6,198 +33 

Cooke, TX No 636 +16 

Dallas, TX Yes 26,625 +14 

Delta, TX No 72 -4 

Denton, TX Yes 5,507 +27 

Ellis, TX Yes 1,893 +49 

Fannin, TX No 334 +9 

Grayson, TX No 1,364 +3 

Henderson, TX No 768 +30 

Hood, TX No 443 +46 

Hunt, TX No 1,046 +26 

Johnson, TX Yes 1,432 +47 

Kaufman, TX Yes 1,548 +38 

Palo Pinto, TX No 397 +3 

Parker, TX Yes 1,280 +41 

Rockwall, TX Yes 676 +15 

Somervell, TX No 121 +27 

Tarrant. TX Yes 16,741 +17 

Wise, TX No 969 +16 

Area-wide: 68,050 ---- 

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

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

concentrations. Commuters in the Dallas-Fort Worth area traveled a total of approximately 68 billion 

miles during calendar year 2008. Four counties in the Dallas-Fort Worth area, Collin, Dallas, Denton, 

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

Tarrant Counties have particularly high total VMT counts at approximately 27 and 18 billion miles, 

respectively. An additional seven counties have 2008 VMT counts 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 Dallas-Fort Worth area have experienced high growth in VMT for the period 

from 2002 – 2008. The growth in VMT for 16 of these counties exceeds 14 percent, and for 10 of those 

counties the growth rate exceeded 25 percent. Four counties in particular have very high VMT growth 
10

for this period: Ellis County (+49%), Johnson County (+47%), Kaufman County (+38%), and Parker 

County (+41%). 

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. 

The attachment to this document contains Figure 3, Dallas-Fort Worth Ozone and Ozone Precursor 

Monitoring Network, including locations of major stationary sources, and locations of ambient monitors 

with their design values. 

EPA has performed 24-Hour wind back trajectories (which is an analysis of meteorological patterns) 

specifically on days when a number of the monitors in the Dallas-Fort Worth area have exceeded 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). The HYSPLIT model yields a centerline 

of where the air mass came from that makes up the air mass at a specific location and time. 

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 3 in the attachments as Figure 5. We 

also focused on this monitor and a number of other monitors in the Dallas-Fort Worth area, including the 

Eagle Mountain Lake monitor in Tarrant County and the Parker County monitor. 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 represents a good cross-section of the monitors in the Dallas-Fort Worth area 

that have had exceedances in the 2006-2010 period. 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. Normally when we are developing a conceptual model 

understanding of what yields ozone exceedances in an area we will evaluate 5 to 10 years worth of 

meteorological data. Therefore we decided to evaluate all days that had ozone exceedances at a number 

of monitors that give a representative data set for the 2006-2010 period. 

There are 3 additional figures in the attachment that include a zoom view for the Eagle Mountain Lake 

monitor and a large and a zoom view for the Parker County monitor. These figures are labeled Figures 

6a through 6c. These HYSLPIT trajectories are 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 includes the all nine counties included in the Dallas-Fort Worth 

nonattainment area for the 1997 8-hour standard and also Wise and Hood Counties. We note that there 

are some trajectories that pass over Hood County and continue to the Parker County monitor without 

traversing over the core Dallas-Fort Worth area. The 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. 

Overall, examination of the 24-hour back trajectories on high ozone days at select monitors in the 

existing Dallas-Fort Worth area indicates that air that originates or passes through the existing 9-county 
11

1997 nonattainment area and Hood and Wise counties prior to ozone exceedances being observed at 

existing monitors.

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 Dallas/Fort Worth area does not have 

any geographical or topographical barriers significantly limiting air pollution transport 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 should 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/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 Dallas-Fort Worth 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. 

Conclusion

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

counties should be included as part of the Dallas-Fort Worth nonattainment area because they are 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, Hood, Johnson, Kaufman, 

Parker, Rockwell, Tarrant, and Wise Counties. These are the same counties that were included in the 

Dallas-Fort Worth nonattainment area for the 1997 ozone NAAQS, with the addition of Hood and Wise 

Counties. 

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, Hood, Kaufman, Parker, Rockwell, 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). 
12

Collin, Dallas, Denton, Ellis, Hood, 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 and commuting patterns. 

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

monitored within the greater Dallas-Fort Worth 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. 

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

included. 

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

included. 

Denton County: Recommended for inclusion by Texas and has a violating monitor, so should 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 are often 

from the south so emissions from Ellis County often contribute to violations other counties. In addition, 

the number of commuters and growth rate indicate that Ellis County should be included in the 

nonattainment area. 

Hood County: Has 2008 NEI emissions of 5,515 tons of NOx and 9,547 tons of VOC, with TCEQ 2009 

Barnett Shale Special Inventory emissions of 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 

contribute to observed violations in other counties. This, in conjunction with high growth in population, 

indicates this county should be included in the nonattainment area. 

Johnson County: Recommended for inclusion by Texas and has a violating monitor, so should 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 are often 

from the east so emissions from Kaufman County often contribute to violations other counties. In 

addition, the VMT and growth rate indicate that Kaufman County should be included in the 

nonattainment area. 
13

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 rate all 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. 

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 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 indicate that this county should be included in the 

nonattainment area. 

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

included. 

Wise County: Has 2008 NEI emissions of 11,911 tons of NOx and 23,657 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. 

 
14

Technical Analysis for Houston-Galveston-Brazoria

Figure 2 is a map of the Houston-Galveston-Brazoria intended nonattainment area. 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 

1997 ozone NAAQS, and major transportation arteries. For purposes of the technical analysis, EPA 

evaluated all 12 twelve counties that comprise the Houston-Baytown-Huntsville CSA: Austin, Brazoria, 

Chambers, Fort Bend, Galveston, Harris, Liberty, Matagorda, Montgomery, San Jacinto, Walker, and 

Waller Counties.

 

For purposes of the 1997 8-hour ozone NAAQS, this area was designated nonattainment. The boundary 

for the nonattainment area for the 1997 ozone NAAQS included the entire counties of Brazoria, 

Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, and Waller. 

In March 2009,7 Texas recommended these same eight counties, Brazoria, Chambers, Fort Bend, 

Galveston, Harris, Liberty, Montgomery, and Waller, be designated as nonattainment for the 2008 

 

7

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

Starfield, dated March 10, 2009. 
15

ozone NAAQS based on air quality data from 2006-2008. Texas provided an update to the original 

recommendation in October 20118 based on air quality data from 2008-2010. The recommendations 

from the State are based on data from FEM monitors sited and operated in accordance with 40 CFR Part 

58. 

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

intends to designate 9 counties in Texas (identified in Table 7 below) as “nonattainment” for the 2008 

ozone NAAQS as part of the Houston nonattainment area. 

Table 7. Texas’s Recommended and EPA’s Intended Designated Nonattainment Counties for HoustonGalveston-Brazoria.

Houston-GalvestonBrazoria State-Recommended 

Nonattainment Counties 

EPA Intended 

Nonattainment Counties 

Texas 

Brazoria 

Chambers 

Fort Bend 

Galveston 

Harris 

Liberty 

Montgomery 

Waller 

Brazoria 

Chambers 

Fort Bend 

Galveston 

Harris 

Liberty 

Matagorda 

Montgomery 

Waller 

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 Houston-Baytown-Huntsville CSA 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 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 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 in the Houston and nearby surrounding area are 

shown in Table 8. 

 

8

 Updated 2008 ozone NAAQS designation recommendation letter from Governor Perry to Administrator Jackson, dated 

October 31, 2011. 
16

Table 8. Air Quality Data.

County State Recommended 

Nonattainment? 

2008-2010 Design Value 

(ppb) 

Austin, TX No -- 

Brazoria, TX Yes 84 

Chambers, TX Yes -- 

Fort Bend, TX Yes -- 

Galveston, TX Yes 75 

Harris, TX Yes 83 

Liberty, TX Yes -- 

Matagorda, TX No -- 

Montgomery, TX Yes 71 

San Jacinto, TX No -- 

Walker, TX No -- 

Waller, TX Yes -- 

Ambient monitors in Brazoria and Harris 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 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 9 shows emissions of NOx and VOC (given in tons per year or tpy) for violating and nearby 

counties that we considered for inclusion in the Houston area. 
17

Table 9. Total 2008 NOx and VOC Emissions. 

County State Recommended 

Nonattainment? NOx (tpy) VOC (tpy) 

Austin, TX No 3,829 3,422 

Brazoria, TX Yes 21,894 26,294 

Chambers, TX Yes 4,517 8,119 

Fort Bend, TX Yes 12,786 15,803 

Galveston, TX Yes 32,170 26,867 

Harris, TX Yes 165,610 135,931 

Liberty, TX Yes 3,345 24,137 

Matagorda, TX No 7,007 19,362 

Montgomery, TX Yes 8,434 14,012 

San Jacinto, TX No 1,361 6,064 

Walker, TX No 3,375 2,690 

Waller, TX Yes 2,080 3,993 

Area-wide: 266,408 286,694 

An area’s total emissions of ozone precursors is one of the most important factors to consider in 

determining its contribution to observed violations of the ozone standard. The counties in the core 

Houston area with the highest emissions of NOx are Brazoria, Fort Bend, Galveston, Harris, Matagorda, 

and Montgomery. More than 7,000 tpy of NOx emissions originates from each of these six counties, and 

collectively they represent approximately 248,000 tpy of NOx, or 93 percent of the total NOx emissions 

for the Houston area. Harris County, in particular, is characterized by high NOx emissions; the 166,000 

tpy of NOx originating from Harris County accounts for 62 percent of the total NOx inventory for the 

area. Significantly, each of these counties either has an air monitor that indicates a violation of the 2008 

ozone NAAQS or is adjacent to such a county. 

Likewise, the counties with the highest VOC emissions in this area are Brazoria, Chambers, Fort Bend, 

Galveston, Harris, Liberty, Matagorda, and Montgomery. More than 7,000 tpy of VOC emissions 

originates from each of these eight counties, and collectively they represent approximately 270,000 tpy 

of VOC, or 94 percent of the total VOC emissions for the Houston area. Harris County, in particular, is 

characterized by high VOC emissions; the 136,000 tpy of VOC originating from Harris County accounts 

for 47 percent of the total VOC inventory for the area. As with counties characterized by high NOx 

emissions, each of these counties either has an air monitor that indicates a violation of the 2008 ozone 

NAAQS or is adjacent to such a county. 

Population density and degree of urbanization

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

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

from on-road and off-road vehicles and engines, consumer products, residential fuel combustion, and 

consumer services. Areas of dense population or commercial development are an indicator of area 

source and mobile source NOx and VOC emissions that may contribute to ozone formation that 

contributes to nonattainment in the area. Rapid population or VMT growth (see below) in a county on 

the urban perimeter signifies increasing integration with the core urban area, and indicates that it may be 

appropriate to include the area associated with area source and mobile source emissions as part of the 

nonattainment area. Table 10 shows the population, population density, and population growth 

information for each county in the area. 
18

Table 10. 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) 

Austin, TX No 28,417 0.04 4,675 20 

Brazoria, TX Yes 313,166 0.21 70,036 29 

Chambers, TX Yes 35,096 0.04 8,931 34 

Fort Bend, TX Yes 585,375 0.66 226,617 63 

Galveston, TX Yes 291,309 0.44 40,601 16 

Harris, TX Yes 4,092,459 2.30 678,528 20 

Liberty, TX Yes 75,643 0.06 5,083 7 

Matagorda, TX No 36,702 0.03 -1,244 -3 

Montgomery, TX Yes 455,746 0.42 158,405 53 

San Jacinto, TX No 26,384 0.04 3,932 18 

Walker, TX No 67,861 0.08 6,117 10 

Waller, TX Yes 43,205 0.08 10,367 32 

Area-wide: 6,051,363 0.51 1,212,048 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)

The Houston area is a large metropolitan area with a total population of approximately 6 million people. 

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

evaluated all 12 counties in the Houston-Baytown-Huntsville CSA, which has a total population of 

6,051,363 people and an average population density of 510 people per square mile. 

Five counties in the CSA, Brazoria, Fort Bend, Galveston, Harris, and Montgomery, are densely 

populated; each has approximately 300,000 or more people and a population density exceeding 200 

people per square mile. These five counties account for 95 percent of the total population of the Houston 

area. Harris County stands out from the remaining counties in the region. Harris County has 

approximately 4.1 million people and a population density of 2,300 people per square mile. Fort Bend 

and Montgomery Counties have moderately high populations and population densities; the population of 

Fort Bend County is 585,000 with a density of 660 people per square mile, and the population of 

Montgomery County is 456,000 people with a density of 420 people per square mile. The remaining 

counties in the area are predominantly rural, with population densities at or below 80 people per square 

mile. 

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

70,000 people, which represents 94 percent of the total population growth for the area. Of these, the 

population of two of these counties grew by more than 200,000 people during the past decade: Fort 

Bend County (+226,617 people) and Harris County (+678,528 people). 

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, all but two of the counties in the area experienced 

double-digit growth in percent change in population. The counties of Fort Bend and Montgomery had 

particularly high values for percent change in population, at 63 and 53 percent, respectively. 

The attachments to this document contains Figure 6, Houston Ozone and Ozone Precursor Monitoring 

Network, and Figure 8, Population Density Change Percentage Between 2000 and 2010 Census for 

Houston Ozone and Ozone Precursor Monitoring Network, which present graphical information on 

population density and growth for the Houston area. 
19

Traffic and commuting patterns

EPA evaluated the commuting patterns of residents in the area, as well as the total Vehicle Miles 

Traveled (VMT) for each county. In combination with the population/population density data and the 

location of main transportation arteries (see above), this information helps identify the probable location 

of non-point source emissions. A county with high VMT and/or a high number of commuters is 

generally an integral part of an urban area and indicates the presence of motor vehicle emissions that 

may contribute to ozone formation 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 the associated area source and mobile source emissions may be appropriate to 

include in the nonattainment area. Table 11 shows traffic and commuting pattern data, including total 

2008 VMT and 10-year VMT growth for each county. 

Table 11. Traffic and Commuting Patterns.

County State Recommended 

Nonattainment? 

2008 VMT* 

(million miles) 

% Change in VMT 

(2002 – 2008) 

Austin, TX No 542 +18 

Brazoria, TX Yes 2,263 +16 

Chambers, TX Yes 935 +23 

Fort Bend, TX Yes 3,339 +23 

Galveston, TX Yes 2,210 +10 

Harris, TX Yes 40,379 +23 

Liberty, TX Yes 865 +12 

Matagorda, TX No 343 -1 

Montgomery, TX Yes 3,982 +22 

San Jacinto, TX No 317 +13 

Walker, TX No 944 +11 

Waller, TX Yes 759 +16 

Area-wide: 56,878 ----- 

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

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

concentrations. Commuters in the Houston area traveled a total of approximately 57 billion miles during 

calendar year 2008. Five counties in the Houston area, Brazoria, Fort Bend, Galveston, Harris, and 

Montgomery Counties, all have total VMT for calendar year 2008 in excess of 2 billion miles. These 

five counties have a combined VMT of 52 billion miles, or 92 percent of the total VMT for the area. 

Harris County has a particularly high total VMT count at approximately 40 billion miles, which is 71 

percent of the total VMT for the entire CMSA. 

All but one of the counties in the Houston area have experienced high growth in VMT for the period 

from 2002 – 2008. The growth in VMT for 11 of these counties exceeds 10 percent, and for 4 of those 

counties the growth rate exceeded 20 percent. The counties with the highest percent change in VMT for 

this period are Chambers County (+23%), Fort Bend County (+23%), Harris County (+23%), and 

Montgomery County (+22%). Austin, Brazoria, and Waller Counties each experienced growth in VMT 

exceeding 15 percent. 
20

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. The Houston-Baytown-Huntsville area is considered a subtropical coastal climate with normal recirculation occurring due to the land-sea breeze oscillation. This 

land-sea breeze oscillation results in transport of air among numerous counties along the gulf coast 

region in the Houston-Baytown-Huntsville area and this phenomena leads to air transport of emissions 

to monitors in the Houston-Baytown-Huntsville area that have previously monitored exceedances of the 

2008 ozone standard. 

The attachment to this document contains Figure 7, Houston Ozone and Ozone Precursor Monitoring 

Network, including locations of major stationary sources, and locations of ambient monitors with their 

design values. 

EPA has performed 24-Hour wind back trajectories (which is an analysis of meteorological patterns) 

specifically on days when a number of the monitors in the Houston-Baytown-Huntsville area have 

exceeded 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). The HYSPLIT model 

yields a centerline of where the air mass came from that makes up the air mass at a specific location and 

time. 

The HYSPLIT trajectories for 2008-2010 exceedance days at the Manvel monitor in Brazoria County 

were conducted and the resulting trajectories were overlaid on Figure 7 in the attachments as Figure 9. 

We also focused on this monitor and a number of other monitors in the Houston-Baytown-Huntsville 

area, including the NW Harris County and Wallisville Road monitors in Harris County, and the Texas 

City monitor in Galveston County. These monitors have recorded some of the highest ozone levels in 

the region and represent a good cross-section of the monitors in the Houston-Baytown-Huntsville area 

that have had exceedances in the 2006-2010 period. Since the 2008-2010 data is only for three years we 

evaluated more years to better understand the meteorological transport conditions that exist during 

ozone exceedances. Normally when we are developing a conceptual model understanding of what yields 

ozone exceedances in an area we will evaluate 5 to 10 years worth of meteorological data. Therefore, we 

decided to evaluate all days that had ozone exceedances at a number of monitors that give a 

representative data set for the 2006-2010 period. 

There are 8 figures in the attachment that include a large view and a zoom view for each of the four 

monitors (Manvel, NW Harris, Wallisville, and Texas City) labeled as Figures 10a through 10h. These 

HYSLPIT trajectories are 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 Manvel and NW Harris 

indicates that the areas upwind of the monitor prior to an ozone exceedance includes the 8 existing 

counties in the Houston-Galveston-Brazoria nonattainment area for the 1997 8-hour standard and also 

Matagorda county. We note that there are some trajectories that pass over Matagorda County and 

continue to the monitor without traversing over the Houston Ship Channel. The back trajectories for the 

Wallisville and Texas City monitors further support that air that is transported from Matagorda county 

ends up in the area of the monitor when ozone exceedances are monitored. 
21

Overall, examination of the 24-hour back trajectories on high ozone days at select monitors in the 

existing Houston-Galveston-Brazoria nonattainment area indicates that air originates or passes through 

the existing 8-county 1997 nonattainment area and Matagorda County prior to ozone exceedances being 

monitored at existing monitors. 

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 Houston area does not have any 

geographical or topographical barriers significantly limiting air pollution transport 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 should 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/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 Houston-Galveston-Brazoria area has previously established nonattainment boundaries associated 

with the 1-hour and 1997 8-hour ozone NAAQS. Texas has recommended that the boundary for the 

2008 ozone NAAQS be the same as for the 1997 ozone NAAQS. 

Conclusion

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

counties should be included as part of the Houston-Galveston-Brazoria nonattainment area because they 

are either violating the 2008 ozone NAAQS or contributing to a violation in a nearby area: Brazoria, 

Chambers, Fort Bend, Galveston, Harris, Liberty, Matagorda, Montgomery, and Waller Counties. These 

are the same counties that are included in the Houston-Galveston-Brazoria nonattainment area for the 

1997 ozone NAAQS, with the addition of Matagorda County. 

The air quality monitors in Brazoria and Harris Counties indicate violations of the 2008 ozone NAAQS 

based on the 2010 design values, therefore these counties are included in the nonattainment area. 

Chambers, Fort Bend, Galveston, Liberty, Matagorda, Montgomery, and Waller Counties are nearby 

counties that do not have monitors indicating concentrations of ozone in excess of 75 ppb, but EPA has 

concluded that these areas contribute to the ozone concentrations in violation of the 2008 ozone NAAQS 

through emissions from point sources and other, non-point sources (e.g., vehicles and other small area 

sources). 
22

The counties in the core Houston area with the highest emissions of NOx are Brazoria, Fort Bend, 

Galveston, Harris, Matagorda, and Montgomery. More than 7,000 tpy of NOx emissions originates from 

each of these six counties, and collectively they represent approximately 248,000 tpy of NOx, or 93 

percent of the total NOx emissions for the Houston area. Likewise, the counties with the highest VOC 

emissions in this area are Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Matagorda, and 

Montgomery. More than 7,000 tpy of VOC emissions originates from each of these eight counties, and 

collectively they represent approximately 270,000 tpy of VOC, or 94 percent of the total VOC emissions 

for the Houston area. 

Brazoria, Fort Bend, Galveston, Harris, and Montgomery Counties ranked comparatively high for 

factors related to population statistics, including total population, population density, and absolute and 

percent growth in population during the past decade. 

Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery and Waller Counties ranked 

comparatively high for factors related to traffic and commuting patterns, such as total VMT and percent 

growth in VMT. 

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

monitored within the greater Houston-Baytown-Huntsville area supports the consideration of inclusion 

of the existing 8-county nonattainment area (Harris, Galveston, Brazoria, Chambers, Fort Bend, Liberty, 

Montgomery, and Waller counties) and also Matagorda county. 

Brazoria County: Recommended for inclusion by Texas and has a violating monitor, so should be 

included. 

Chambers County: Recommended for inclusion by Texas; has 4,517 tons of NOx emissions and 8,119 

tons of VOC emissions annually; there are 40 people per square mile; has a 2010 population of 35,096 

with a growth rate of 34 percent between 2000 and 2010; total VMT is 935 million miles. The growth in 

population and VMT support the State’s recommendation to include this county as part of the 

nonattainment area. 

Fort Bend County: Recommended for inclusion by Texas; has 12,786 tons of NOx emissions and 

15,803 tons of VOC emissions annually; there are 660 people per square mile; has a 2010 population of 

585,375 with a growth rate of 63 percent between 2000 and 2010; total VMT is 3.3 billion miles. Its 

high ranking in emissions, population and commuting patterns all indicate it contributes to 

nonattainment and should be included in the Houston-Galveston-Brazoria nonattainment area. 

Galveston County: Recommended for inclusion by Texas; has 32,170 tons of NOx emissions and 

26,867 tons of VOC emissions annually; there are 440 people per square mile; has a 2010 population of 

291,309 with a growth rate of 16 percent between 2000 and 2010; total VMT is 2.2 billion miles. Its 

high ranking in emissions, population and commuting patterns all indicate it contributes to 

nonattainment and should be included in the Houston-Galveston-Brazoria nonattainment area.

Harris County: Recommended for inclusion by Texas and has a violating monitor, so should be 

included. 
23

Liberty County: Recommended for inclusion by Texas; has 3,345 tons of NOx emissions and 24,137 

tons of VOC emissions annually; there are 60 people per square mile; has a 2010 population of 75,643 

with a growth rate of 7 percent between 2000 and 2010; total VMT is 865 million miles. The growth in 

population and number and VMT indicate this county should be included in the Houston-GalvestonBrazoria nonattainment area. 

Matagorda County: Has 7,007 tons of NOx emissions and 19,362 tons of VOC emissions annually; 

there are 30 people per square mile; has a 2010 population of 36,702 with a negative growth rate of 3 

percent between 2000 and 2010; total VMT is 343 million miles. The high emissions in Matagorda 

argue that it should be included in the nonattainment area. Examination of back trajectories indicates 

these emissions could, at times, contribute to nonattainment in counties with violating monitors. Based 

on the combination of high emissions and examination of the meteorology through back trajectory 

analysis, EPA believes this county should be included in the Houston-Galveston-Brazoria nonattainment 

area. 

Montgomery County: Recommended for inclusion by Texas; has 8,434 tons of NOx emissions and 

14,012 tons of VOC emissions annually; there are 420 people per square mile; has a 2010 population of 

455,746 with a growth rate of 53 percent between 2000 and 2010; total VMT is 4 billion miles. Its high 

ranking in emissions, population and commuting patterns all indicate it contributes to nonattainment and 

should be included in the Houston-Galveston-Brazoria nonattainment area. 

Waller County: Recommended for inclusion by Texas; has 2,080 tons of NOx emissions and 3,993 tons 

of VOC emissions annually; there are 80 people per square mile; has a 2010 population of 43,205 with a 

growth rate of 32 percent between 2000 and 2010; total VMT is 759 million miles. The growth in 

population and VMT indicate this county should be included in the Houston-Galveston-Brazoria 

nonattainment area. 
24

ATTACHMENTS 

Figure 3. Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network, with Population Density. 

Figure 4. Population Density Change Percentage Between 2000 and 2010 Census for Dallas-Fort Worth 

Ozone and Ozone Precursor Monitoring Network. 

Figure 5. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Keller monitor 

for the 2008-2010 period. 

Figure 6a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Eagle Mtn. Lake Exceedances (2006-

10) (zoom view). 

Figure 6b. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10). 

Figure 6c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10) 

(zoom view). 

Figure 7. Houston Ozone and Ozone Precursor Monitoring Network, with Population Density. 

Figure 8. Population Density Change Percentage Between 2000 and 2010 Census for Houston Ozone 

and Ozone Precursor Monitoring Network 

Figure 9. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Manvel 

monitor for the 2008-2010 period. 

Figure 10a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Manvel Exceedances (2006-10). 

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

(zoom view). 

Figure 10c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory NW Harris Exceedances (2006-10). 

Figure 10d. NOAA HYSPLIT MODEL 24-Hour Back Trajectory NW Harris Exceedances (2006-10) 

(zoom view). 

Figure 10e. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Wallisville Exceedances (2006-10). 

Figure 10f. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Wallisville Exceedances (2006-10) 

(zoom view). 

Figure 10g. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Texas City Exceedances (2006-10). 

Figure 10h. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Texas City Exceedances (2006-10) 

(zoom view). 
25

Figure 3. Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network, with Populatio
26

Figure 4. Population Density Change Percentage Between 2000 and 2010 Census 

for Dallas-Fort Worth Ozone and Ozone Precursor Monitoring Network
27

Figure 5. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Keller monitor for t
28

Figure 6a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Eagle Mtn. Lake Exceedances (2006-10) (zoom vie
29

Figure 6b. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (200
30

Figure 6c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Parker County Exceedances (2006-10) 
31

Figure 7. Houston Ozone and Ozone Precursor Monitoring Network, with Population Den
32

Figure 8. Population Density Change Percentage Between 2000 and 2010 Census 

for Houston Ozone and Ozone Precursor Monitoring Network
33

Figure 9. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Manvel monitor fo
34

Figure 10a. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Manvel Exceedances (2006-
35

Figure 10b. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Manvel Exceedances (2006-10) (zo
36

Figure 10c. NOAA HYSPLIT MODEL 24-Hour Back Trajectory NWHarris Exceedances (2006
37

Figure 10d. NOAA HYSPLIT MODEL 24-Hour Back Trajectory NWHarris Exceedances (2006-10) (z
38

Figure 10e. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Wallisville Exceedances (200
39

Figure 10f. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Wallisville Exceedances (2006-10) (

Black Polygon is the approximate boundaries of Matagorda County 
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Figure 10g. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Texas City Exceedances (200