1

Tennessee

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 Tennessee that EPA 

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

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

(county or part of a county) “nonattainment” if it is violating the 2008 ozone NAAQS or if it is 

contributing to a violation of the 2008 ozone NAAQS in a nearby area. The technical analyses 

supporting the boundaries for the individual nonattainment areas are provided below.

Intended Nonattainment Areas in Tennessee

Area 

Tennessee’s Recommended 

Nonattainment Counties

EPA’s Intended Nonattainment 

Counties

Knoxville-Sevierville-La 

Follette, TN

Blount (partial)

Cocke (partial)

Sevier (partial)

Anderson

Blount

Cocke (partial)

Knox

Loudon

Sevier

Memphis, TN-MS-AR* None Shelby

*Memphis, TN-MS-AR is a multi-state nonattainment area. Table 1 below identifies the counties in the 

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

EPA intends to designate the remaining counties in Tennessee 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 

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 

monitor or Federal Equivalent Method (FEM) monitor in the area);

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

emissions and emissions controls, and urban growth patterns);

3. Meteorology (weather/transport patterns);

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

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

country, metropolitan planning organizations (MPOs))

 

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

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).

2 All data and information used by EPA in this evaluation are the latest 

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

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

CSA/CBSAs because certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

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

ozone NAAQS. 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. 

 

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

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

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

2009 (OMB Bulletin No. 10-02).
3

Technical Analysis for Knoxville-Sevierville-La Follette

Figure 1 is a map of the Knoxville-Sevierville-La Follette intended nonattainment area. The map also 

shows locations and design values of air quality monitors, county and other jurisdictional boundaries, 

the nonattainment area boundary for 1997 ozone NAAQS, and major transportation arteries.

Figure 1. Knoxville-Sevierville-La Follette CSA

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 Anderson, Blount, 

Jefferson, Knox, Loudon, and Sevier in Tennessee, and a portion of Cocke County, Tennessee. 

In March 2009, Tennessee recommended that Anderson, Blount, Knox, Loudon, and Sevier Counties in 

their entireties, and a portion of Cocke County be designated as the “Knoxville” nonattainment area for 

the 2008 8-hour ozone standard based on air quality data from 2006-2008. In March 2009, Tennessee 

also recommended that Jefferson County be designated as the “Morristown” nonattainment area, 

separate from a Knoxville nonattainment area, for the 2008 8-hour ozone standard based on air quality 

data from 2006-2008. Letter from James H. Fyke, Commissioner, State of Tennessee Department of 

Environment and Conservation to A. Stanley Meiburg, Acting Regional Administrator, US EPA Region

4 (March 10, 2009) (on file with US EPA Region 4). In November 2011, Tennessee provided an update 

to their 2009 original recommendation based on preliminary air quality data from 2009-2011. In its 

updated recommendation, Tennessee recommended that the portions of Blount, Cocke and Sevier 

Counties that comprise the Tennessee portion of the Great Smoky Mountains National Park be 
4

designated “nonattainment” for the 2008 ozone NAAQS. Letter from Robert J. Martineau Jr, 

Commissioner, State of Tennessee Department of Environment and Conservation to Gwen Keyes 

Fleming, Regional Administrator, US EPA Region 4 (Nov. 8, 2011) (on file with US EPA Region 4). 

The March 2009 and November 2011 recommendations were 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 five entire counties and one partial county in Tennessee (identified in Table 1 

below) as “nonattainment” for the 2008 ozone NAAQS as part of the Knoxville-Sevierville-La Follette 

nonattainment area. 

Table 1. State's Recommended and EPA’s Intended Designated Nonattainment Counties for KnoxvilleSevierville-La Follette.

Knoxville-SeviervilleLa FolletteState-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Tennessee Blount (partial)

Cocke (partial)

Sevier (partial)

Anderson

Blount

Cocke (partial)

Knox

Loudon

Sevier

Factor Assessment

Factor 1: Air Quality Data 

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

monitors in counties in the Knoxville-Sevierville-La Follette 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 fourthhighest daily maximum 8-hour average concentration, averaged over 3 years is 75 ppb or less. A DV is 

only valid if minimum data completeness criteria are met. See 40 CFR part 50 Appendix P. Where 

several 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 Knoxville-Sevierville-La Follette and nearby 

surrounding area are shown in Table 2. 

Table 2. Air Quality Data.

County*

State Recommended 

Nonattainment?

2008-2010 Design Value 

(ppb)

Anderson, TN No 70

Blount, TN Yes (Partial) 77

Cocke, TN Yes (Partial) N/A

Jefferson, TN No 74

Knox, TN No 76

Loudon, TN No 73
5

Sevier, TN Yes (Partial) 76

*Counties with violating monitors are shown in bold.

Blount, Knox and Sevier Counties show violations 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. The precursor emission source-category percentages used below and throughout the document 

were derived from emissions data from the 2008 NEI version 1.5 referenced above.

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

counties in the Knoxville-Sevierville-La Follette, TN CSA that we considered for inclusion in the 

Knoxville-Sevierville-La Follette area. 

Table 3. Total 2008 NOx and VOC Emissions.

County* State Recommended

Nonattainment? NOx (tpy) VOC (tpy)

Anderson, TN No 12,475 3,569

Blount, TN Yes (Partial) 3,593 6,749

Campbell, TN No 2,964 1,773

Cocke, TN Yes (Partial) 1,761 2,273

Grainger, TN No 687 1,216

Hamblen, TN No 6,612 4,719

Jefferson, TN No 3,148 3,329

Knox, TN No 15,169 16,182

Loudon, TN No 3,751 3,340

Roane, TN No 10,711 3,006

Sevier, TN Yes (Partial) 2,602 5,399

Union, TN No 432 959

Areawide: 63,905 52,514

*Counties that EPA intends to designate as nonattainment are shown in bold.
6

Knox County is leading all counties with 24 percent of NOx and 31 percent VOC of the CSA’s 

emissions. Anderson County emitted 19 percent of the CSA’s NOx emissions with 77 percent from 

point sources. It is worth noting that the Bull Run Facility Electric Generating Unit (EGU) in Anderson 

County generated 1,086 tons of NOx with Selective Catalytic Reduction (SCR) control during the 2008 

ozone season. Blount County was the second highest VOC contributor at 6,749 tons, 13 percent of the 

CSA total. Sevier County had the third highest VOC levels with 5,400 tons, about 10 percent of the CSA

total. In addition, 18 percent of all VOC emissions from mobile sources originated from Blount and 

Sevier Counties.

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. Rapid population or vehicle miles travelled (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 the area source and mobile source emissions as part of

the nonattainment area. Table 4 shows the population, population density, and population growth 

information for each county in the area.

Table 4. Population and Growth.

County*

State 

Recommended 

Nonattainment?

2010 Population

2010 Population 

Density

(1000 pop/sq mi)

Absolute change 

in population

(2000-2010)

Population % 

change

(2000-2010)

Anderson No 75,129 0.22 3,897 +5%

Blount Yes (Partial) 123,010 0.22 16,793 +16%

Campbell No 40,716 0.08 853 +2%

Cocke Yes (Partial) 35,662 0.08 2,035 +6%

Grainger No 22,657 0.07 1,920 +9%

Hamblen No 62,544 0.36 4,301 +7%

Jefferson No 51,407 0.16 6,825 +15%

Knox No 432,226 0.82 49,198 +13%

Loudon No 48,556 0.20 9,342 +24%

Roane No 54,181 0.14 2,238 +4%

Sevier Yes (Partial) 89,889 0.15 18,190 +25%

Union No 19,109 0.08 1,250 +7%

Areawide: 1,055,086 0.23 116,842 12%

*Counties that EPA intends to designate as nonattainment are shown in bold.

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)

In terms of population growth, Sevier, Loudon and Blount Counties experienced the largest with 25 

percent, 24 percent and 16 percent, respectively. Sevier County has the second highest absolute change 

in population with 18,190. Most of the urban area is in the center (Sevierville) with sparsely populated 

communities on the northwest side of the county adjacent to Knoxville. Loudon is mostly rural with 
7

sparsely populated areas along the US Highway 11 corridor. Blount County’s population grew 16 

percent and is home to 11 percent of the CSA’s population making it second to Knox County. Blount 

County’s urban and agriculture development is in the northwestern half of the County. Knox County 

has highest population density, the largest absolute change in population, and, the largest population in 

the 12-county CSA. Anderson County has intermittent urbanization in Oak Ridge and Clifton on the 

southwestern part of the county, adjacent to Knoxville. Jefferson County is mostly rural with the center 

of the urban density in Jefferson City, and in closer proximity (compared to Knoxville) to the more 

urbanized area of Morristown in Hamblen County. 

Traffic VMT data and commuting patterns

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 the 

associated area source and mobile source emissions may be appropriate to include in the nonattainment 

area. Table 5 shows the total 2008 VMT for each county.

Table 5. Traffic and VMT Data.

County* State Recommended Nonattainment? 2008 VMT**

(million miles)

Anderson No 831

Blount Yes (Partial) 1,105

Campbell No 656

Cocke Yes (Partial) 455

Grainger No 232

Hamblen No 656

Jefferson No 819

Knox No 5,304

Loudon No 782

Roane No 743

Sevier Yes (Partial) 1,164

Union No 134

Areawide: 12,881

*Counties that EPA intends to designate as nonattainment are shown in bold.

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

Knox County leads the CSA with the highest VMT followed by Sevier and Blount counties.

Factor 3: Meteorology (weather/transport patterns)

For this factor, EPA analyzed 30-years of National Weather Service (NWS) wind speed and wind 

direction data collected at the Knoxville/McGhee Tyson Airport (Station #13891) to help determine 

transport patterns and source contributions. EPA assessed wind direction and speed for the 2008-2010 

“ozone season” (March through October) in the Knoxville-Sevierville-La Follette, TN CSA. The 

analysis was conducted to better understand the fate and transport of precursor emissions contributing to 
8

ozone formation. EPA’s analysis of the NWS data indicate predominate southwest, west-southwest and 

northern component for the Knoxville-Sevierville-La Follette, TN CSA

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.

Regional topography consists of linear ridge and parallel lowland valleys. The Area has predominantly 

high elevations in the northern regions and lower elevations further south ranging from 700 to 1,500 

feet. The Knoxville-Sevierville-La Follette, TN area includes the Tennessee portion of the Great Smoky 

Mountains National Park (GSMNP). This area consists of densely forested high peaks and valleys. The 

highest point in the state is at Clingman’s Dome with an elevation of 6,643 feet. There are three 

violating monitors in the Knoxville area that are at the higher elevations and within the GSMNP. These 

monitors are Look Rock (AQS ID: 47-009-0101, 2008-2010 DV of 77 ppb) in Blount County, Cove 

Mountain (AQS ID: 47-155-0101, 2008-2010 DV of 76 ppb) in Sevier County, and Clingman's Dome 

(AQS ID: 47-155-0102, 2008-2010 DV of 76 ppb), also in Sevier County.

Figure 2 shows a topographical map of Knoxville and the National Park. These two monitors are 

located at a significantly higher elevation than the Knox County monitors. High elevation ozone sites 

often measure elevated ozone levels overnight due to regional transport of tropospheric ozone formed 

during the daytime. The regional transport mechanisms that cause these events are related to downward 

transport by vertical mixing that concentrates the tropospheric ozone or by horizontal transport from 

surrounding areas (Eliasson et al, 2003). The long duration of these nocturnal events can also be 

attributed to a lack of local Nitric Oxide (NO) emissions which act to titrate the ozone and reduce the 

ambient ozone concentration as occurs in urban areas overnight (Eliasson et al, 2003) 3.

Figure 3 compares the hourly distribution of daily maximum hourly ozone values over 65 ppb for four 

sites: Look Rock, two urban Knox County Sites, and Blue Ridge Parkway, another high elevation site in 

North Carolina in the GSMNP that is further removed from urban areas. The Knoxville sites show a 

typical urban pattern of ozone events in the afternoon (approximately 12:00 pm to 6:00 pm). The Blue 

Ridge Parkway site is impacted primarily by regional transport and shows a typical high elevation site 

pattern of ozone events overnight (approximately 9:00 pm to 3:00 am). This site is not in the Knoxville 

Sevierville-La Follette CBSA and is only included as an example of another high elevation site. The 

Look Rock site shows a combination of these two signals, indicating that the site is impacted by both 

downwind afternoon ozone formation from Knoxville and high elevation ozone transport. In some 

cases, these two processes could be affecting the Look Rock monitor simultaneously. 

Figure 4 shows the frequency of ozone hourly values greater than 75 ppb by wind direction and time of 

day for the Look Rock site. This figure illustrates two distinct groups of high ozone events: afternoon 

ozone from the south to southeast (Knoxville) and overnight ozone from the north to northwest (regional 

transport). The Cove Mountain site in Sevier County shows a similar pattern as the Look Rock, 

although with a slightly less pronounced urban signal.

 

3

Ingegärd Eliasson, Sofia Thorsson, Yvonne Andersson-Sköld, Summer nocturnal ozone maxima in Göteborg, Sweden, 

Atmospheric Environment, Volume 37, Issue 19, June 2003, Pages 2615-2627.
9

As a result of these analyses, EPA has preliminarily concluded that both downwind urban ozone 

formation from Knoxville Knox County and high elevation regional transport of ozone contribute to the 

NAAQS violations at the Look Rock and Cove Mountain monitors.

Figure 2. Topographical map of Knoxville and the Great Smoky Mountains National Park
10

Figure 3. 2007-2010 Count of Daily Max Values > 65 ppb

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0 Count

2007-2010 Count of Daily Max Hourly Values > 65 ppb

GREAT SMOKY MOUNTAINS NP LOOK ROCK

TOWER BLUE RIDGE PKWY MILE MARKER 410

9315 RUTLEDGE PIKE MASCOT TN 37806

4625 MILDRED DRIVE

Overlap of 

downwind

and high 

elevation 

ozone

Urban/DownwindO3 profile

High elevation/transport O3 profile
11

Figure 4. Frequency of Look Rock Ozone Hourly Values >75 ppb

Factor 5: Jurisdictional boundaries

Once we identified the general areas we anticipate recommending as nonattainment areas, 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, area covered by a MPOs, state lines, areas of Indian Country,

and urban growth boundary. 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 Knoxville-Sevierville-La Follette area has previously established nonattainment boundaries 

associated with the both the 1-hour ozone and 1997 8-hour ozone NAAQS. The Knoxville-SeviervilleLa Follette nonattainment boundary for the 1-hour ozone NAAQS included Knox County, Tennessee in 

its entirety. Whereas the Knoxville-Sevierville-La Follette nonattainment boundary for the 1997 8-hour 
12

ozone NAAQS included Anderson, Blount, Jefferson, Knox, Loudon, and Sevier Counties in Tennessee 

in their entireties, and a portion of Cocke County, Tennessee. 

The Knoxville-Sevierville-La Follette CSA is composed of two MPOs, the Knoxville Regional 

Transportation Planning Organization (TPO) and Lakeway Area Metropolitan Transportation Planning

Organization (MTPO). The Knoxville TPO includes Loudon, Blount, Knox and Sevier Counties. The 

Lakeway MTPO includes Jefferson and Hamblen Counties. 

Jefferson County had a violating monitor based on air quality data used for the 2004 designation for the 

1997 ozone NAAQS. It was included within the nonattainment area boundary based on the violation, 

not based on a determination that emissions from the county were contributing to a violation in a nearby 

area violating the standard. Current monitor reading shows Jefferson as attaining. In addition, a portion 

of Jefferson County (Jefferson City) falls under the Lakeway MTPO. 

Conclusion

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

counties should be included as part of the Knoxville-Sevierville-La Follette nonattainment area because 

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

Anderson, Blount, Knox, Loudon and Sevier Counties, in their entireties. A portion of Cocke County is 

brought in since it comprises the GSMNP. All of these counties are included in the Knoxville 

nonattainment area for the 1997 ozone NAAQS. The air quality monitors in Blount, Knox and Sevier 

Counties indicate violations of the 2008 ozone NAAQS based on 2010 DVs, therefore these counties are 

preliminarily included in the nonattainment area. Anderson and Loudon Counties, in their entireties, 

and a portion of Cocke County in Tennessee are nearby counties that do not have a violating monitor, 

but EPA has preliminarily concluded that these counties contribute to the ozone concentrations in 

violation of the 2008 ozone NAAQS through emissions from point sources and non-point sources (e.g., 

vehicles and other small area sources). Knox County, Tennessee has among the highest NOx and VOC 

emissions in the area. Anderson County ranked relatively high for large NOx emissions, contributing 19 

percent of the CSA’s total NOx. Given the prevalent wind (southwest, west-southwest and northern), 

Anderson County, which is adjacent to Knox County, is contributing to the violating monitor to Knox 

County and therefore is being brought in for contribution. While SCR controls were installed at the 

plant, there has been a steady increase in NOx emission levels since 2006. 
13

Technical Analysis for Memphis, TN-MS-AR

Figure 1 is a map of the Memphis, TN-MS-AR 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. TN-MS-AR Nonattainment Area

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 

Crittenden County, Arkansas, and Shelby County, Tennessee.

In March 2009, Tennessee recommended that Shelby County be designated “nonattainment” for the

2008 8-hour ozone standard based on air quality data from 2006-2008. Letter from James H. Fyke, 

Commissioner, State of Tennessee Department of Environment and Conservation to A. Stanley 

Meiburg, Acting Regional Administrator, US EPA Region 4 (March 10, 2009) (on file with US EPA 

Region 4). Tennessee provided an update to its original recommendation in November 2011 based on 

preliminary 2009-2011 air quality data. In Tennessee’s updated recommendation, the state did not 

provide a specific update to its 2009 recommendation for the Memphis TN-MS-AR but stated that all 
14

other counties (with the exception of those recommended for Knoxville) should be designated 

unclassifiable/attainment. Letter from Robert J. Martineau Jr, Commissioner, State of Tennessee 

Department of Environment and Conservation to Gwendolyn Keyes Fleming, Regional Administrator, 

US EPA Region 4 (November 8, 2011) (on file with US EPA Region 4).

Also, in March 2009, Mississippi recommended that DeSoto County, Mississippi be designated as a 

nonattainment area separate from the Memphis nonattainment area for the 2008 ozone NAAQS based 

on air quality data from 2006-2008. Mississippi provided an update to the original recommendation in 

October 2011 based on air quality data from 2008-2010, and preliminary data from 2009-2011. In its 

updated recommendation, Mississippi recommended that all counties in the State be designated 

attainment for the 2008 ozone NAAQS. Letter from Haley Barbour, Governor of the State of 

Mississippi to A. Stanley Meiburg, Acting Regional Administrator, US EPA Region 4 (March 3, 2009) 

and Gwendolyn Keyes Fleming, Regional Administrator US EPA Region 4 (October 27, 2011) (on file 

with US EPA Region 4). Additionally, in March 2009, Arkansas recommended that Crittenden County, 

Arkansas be designated nonattainment based on 2006-2008 air quality data. Arkansas did not update its 

2009 ozone recommendation. These data are from FEM monitors sited and operated in accordance with 

40 CFR Part 58. Letter from Mike Beebe, Governor of the State of Arkansas to Lawrence E. Starfield, 

Acting Regional Administrator, US EPA Region 6 (March 10, 2009) (on file with US EPA Region 6).

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

intends to designate one county in Arkansas, one county (partial) in Mississippi, and one county in 

Tennessee (identified in Table 1 below) as nonattainment for the 2008 ozone NAAQS as part of the 

Memphis, TN-MS-AR multi-state nonattainment area. 

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

TN-MS-AR.

Memphis, TN-MS-AR State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Arkansas Crittenden Crittenden

Mississippi None DeSoto (partial)

Tennessee None Shelby

Factor Assessment

Factor 1: Air Quality Data 

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

monitors in counties in the Memphis, TN-MS-AR 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 75 ppb or less. A DV is only valid if minimum 

data completeness criteria are met. See 40 CFR part 50 Appendix P. Where several 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 Memphis and nearby surrounding area are 

shown in Table 2. 
15

Table 2. Air Quality Data4.

County State Recommended 

Nonattainment?

2008-2010 Design Value 

(ppb)

Crittenden, AR Yes 74

DeSoto, MS No 73

Shelby, TN No 76

Shelby County, Tennessee shows a violation of the 2008 ozone NAAQS, therefore this county is

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. The precursor emission source-category percentages used below and throughout the document 

were derived from emissions data from the 2008 NEI version 1.5 referenced above.

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

counties that we considered for inclusion in the Memphis, TN-MS-AR area. 

 

4 Only counties in the Memphis CBSA that have ozone monitors are included in this table.
16

Table 3. Total 2008 NOx and VOC Emissions.

County

State Recommended 

Nonattainment NOx (tpy) VOC (tpy)

Crittenden, AR Yes 4,047 3,805

DeSoto, MS No 5,080 5,222

Fayette, TN No 2,385 1,406

Marshall, MS No 1,769 1,527

Shelby, TN No 39,519 27,929

Tate, MS No 3,102 1,392

Tipton, TN No 2,119 2,251

Tunica, MS No 1,598 1,096

Areawide: 59,619 44,628

*Counties that EPA intends to designate as nonattainment are shown in bold.

Shelby County contributes about 66 percent of the NOx and 63 percent of the VOC precursor emissions 

in the CBSA. Shelby makes up 23 percent of the entire CBSA NOx emissions and 22 percent of the 

area’s VOC emissions. Of the county’s 39,519 NOx emissions, 35 percent are from point and mobile 

emissions and 20 percent from area source emissions. The County’s 27, 929 VOC emissions include 36 

percent mobile sources and 32 percent area sources.

DeSoto County contributes about 9 percent NOx and 12 percent VOC precursor emissions in the CBSA. 

The County’s 5,080 NOx emissions are mostly comprised of 45 percent area sources, 35 percent mobile 

sources. DeSoto County’s total VOC emissions include 44 percent area sources and 34 percent mobile 

sources.

Crittenden County contributes less than 10 percent of the precursor CBSA emissions. Of the County’s 

total NOx emissions listed in Table 1, 45 percent are from mobile sources and 34 percent from area 

sources. The County’s total VOC emissions include 35 percent from area sources and 31 percent from

mobile sources. Only 5 percent of the County’s NOx emissions are from point sources. Both Crittenden 

and DeSoto Counties represent less than 1 percent of the entire area’s NOx and VOC point source 

emissions

Fayette and Tipton Counties in Tennessee and Marshall, Tate, and Tunica counties in Mississippi all 

contribute 5 percent or less NOx and VOC precursor emissions in the CBSA. 

Together, Crittenden, DeSoto and Shelby Counties account for 82 percent of the NOx emissions and 83 

percent of the VOC emissions for the 8-county area. The emissions from Fayette and Tipton Counties in 

Tennessee and Marshall, Tate and Tunica Counties in Mississippi are not thought to contribute to the 

violations of the 2008 ozone NAAQS that have been observed by monitors in Shelby County, Tennessee 

and Crittenden County, Arkansas.
17

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. 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 the area source and mobile source emissions as part of the nonattainment area. 

Table 4 shows the population, population density, and population growth information for each county in 

the area.

Table 4. Population and Growth.

County

State 

Recommended 

Nonattainment?

2010 

Population

2010 

Population 

Density 

(1000 pop/sq 

mi)

Absolute 

change in 

population 

(2000-2010)

Population 

% change 

(2000-

2010)

Crittenden, 

AR Yes 50,902 0.08 (75) <1%

DeSoto, MS No 161,252 0.32 52,584 +48%

Fayette, TN No 38,413 0.05 9,313 +32%

Marshall, MS No 37,144 0.05 2,093 +6%

Shelby, TN No 927,644 1.18 29,393 +3%

Tate, MS No 28,886 0.07 3,444 +14%

Tipton, TN No 61,081 0.13 9,545 +19%

Tunica, MS No 10,778 0.02 1,557 +17%

Areawide: 1,316,100 0.28 107,854 +9%

*Counties that EPA intends to designate as nonattainment are shown in bold.

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)

Shelby County, Tennessee is densely populated containing 70 percent of the CBSA population. From 

2000-2010, the County only had 3 percent growth in population. Fayette and Tipton County in 

Tennessee had moderate growth from 2000-2010 but are sparsely populated. 

DeSoto County, Mississippi is moderately populated in the northern portion of the county and mostly 

rural in the remaining portion of the County. DeSoto County contains 12 percent of the CBSA 

population, but experienced 48 percent growth from 2000-2010. Tate, Tunica and Marshall Counties in 

Mississippi all make up 3 percent or less of the CBSA population and are sparsely populated. 

Crittenden County, Arkansas had less than 1 percent population growth from 2000-2010 and contains 

only 4 percent of the CBSA population. The County is mostly rural with little urbanization. 

The attachment to this document contains Figure 2, Memphis Area Ozone and Ozone Precursor 

Monitoring Network, and Figure 3, Population Density Change Percentage Between 2000 and 2010 
18

Census for Memphis Ozone and Ozone Precursor Monitoring Network, which present graphical 

information on population density and growth for the Memphis area.

Traffic VMT data and commuting patterns

EPA evaluated the total VMT for each county in the Memphis CBSA. 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 the associated area source and mobile source emissions may be appropriate to 

include in the nonattainment area. Table 5 shows total 2008 VMT for each county.

Table 5. Traffic and VMT Data.

County

State Recommended 

Nonattainment?

2008 VMT** (million 

miles)

Crittenden, AR Yes 903

DeSoto, MS No 1,629

Fayette, TN No 573

Marshall, MS No 725

Shelby, TN No 8,789

Tate, MS No 376

Tipton, TN No 401

Tunica, MS No 337

Areawide: 13,733

*Counties that EPA intends to designate as nonattainment are shown in bold.

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

Shelby County is the only county in the Memphis CBSA violating the 2008 ozone NAAQS with 2008-

2010 air quality data and is considered the core CBSA county, with 64 percent of the VMT in the 

Memphis CBSA; Approximately 35 percent of Shelby County’s NOx emissions and 34 percent VOC 

emissions are from mobile sources. 

DeSoto County has the second highest VMT in the Memphis CBSA (12% of the total Memphis CBSA). 

Additionally, DeSoto County has a 48 percent growth in population from 2000-2010 with approximately 

35 and 34 percent of the County’s NOx and VOC emissions (respectively) deriving from mobile 

sources.

Crittenden County, has less than 10 percent of the CBSA VMT (third highest in the Memphis CBSA). 

From 2000-2010, Crittenden County had less than 1 percent population growth with 45 percent and 31 

percent of the County’s NOx and VOC emissions(respectively) deriving from mobile sources.

The remaining counties in the Memphis CBSA all have low total population and population growth with 

little urbanization and low precursor emission contribution suggesting negligible contribution of 

population-based emissions.
19

Factor 3: Meteorology (weather/transport patterns)

For this factor, EPA analyzed 30-years of National Weather Service (NWS) wind speed and wind 

direction data collected at the Memphis International Airport (NWS Station 13893) to help determine 

transport patterns and source contributions. EPA assessed wind direction and speed for the 2008-2010 

“ozone season” (March through October) in the Memphis CBSA as well as on days when area ozone 

monitors exceeded the 2008 ozone NAAQS. Additionally, EPA evaluated wind back trajectories (which 

are an analysis of meteorological patterns) specifically on days when the current ozone design value 

monitor in Shelby County (Frayser monitor) exceeded the 2008 NAAQS. These analyses were 

conducted to better understand the fate and transport of precursor emissions contributing to ozone 

formation. 

 

EPA’s analysis of the NWS data indicate predominate south and south-southwest component for the 

Memphis CBSA. However, an examination on days when monitors in DeSoto County (Hernando) 

exceeded the 2008 ozone NAAQS suggested a northerly component. Additionally, on days when 

monitors in Shelby County exceeded the 2008 NAAQS, the data indicated a southerly wind component. 

Figure 2, Memphis Area Ozone and Ozone Precursor Monitoring Network, and Figure 4 present 

graphical information on 24-hour back trajectories for exceedances in 2008-2010 at the Frayser monitor, 

locations of major stationary sources, and locations of ambient monitors with their design values. An 

examination of the meteorological data indicates that, for the 2008-2010 days with ozone concentrations 

above 75 ppb at the Memphis 2008-2010 Design Value site (Frayser monitor), the wind back trajectories 

primarily go back through Shelby County, TN (on 10 out of 10 days) and DeSoto County, MS (on 7 out 

of 10 days), with back trajectories going back through Crittenden County, AR on only 1 out of 10 days. 

As mentioned in Factor 1, the Shelby County monitor is the only monitor in the Memphis CBSA with a 

2008-2010 violation of the 2008 ozone NAAQS.

Since the 2008-2010 data is only for three years and has only 10 exceedance days, 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 the Design Value monitor (Frayser) for the 2006-2010 period. 

The 2006 and 2007 years had more meteorology that was conducive for ozone formation than the years 

of 2008, 2009, and 2010. Figure 5 in the attachment to this document includes 72-hour back trajectories 

for 2006-2010 ozone exceedances at the Frayser monitor using the National Oceanic and Atmospheric 

Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model (NOAA HYSPLIT). To 

further understand the meteorological transport conditions within the regional area around Memphis, we 

also evaluated24-hour back trajectories for the 2006-2010 time-periods using the NOAA HYSPLIT 

model. The results of these back trajectories are included in the attachment to this document as Figure 6 

with a further zoom in view in Figure 7.

Evaluation of Figures 6 and 7 further supports our previous conclusions based on the 2008-2010 back 

trajectories when the Memphis area Frayser monitor has ozone exceedances. The 2006-2010 data further 

supports that most of the centerlines of the back trajectories passes through Shelby County TN, and 

many of the back trajectory centerlines pass through DeSoto county in northern Mississippi with smaller 

percentage passing through Crittenden County, Arkansas. 

EPA’s meteorological assessment of the area monitors ozone exceedances and specifically the wind 

back trajectory analysis at the Frayser monitor indicate that Shelby County is likely an emission 
20

contributor to exceedances of the 2008 NAAQS at the Frayser monitor. Furthermore, the assessment 

also suggests that DeSoto and Crittenden Counties should be considered for potential inclusion in the 

intended Memphis nonattainment area. 

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 Memphis area does not have any geographical or topographical barriers 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 for nonattainment, 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, area covered by an MPO, 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 Memphis Area MPO is comprised of two study areas; the Memphis Urban Area MPO and the West 

Memphis MPO. Both organizations are considered multi-jurisdictional agencies responsible for the 

implementation and coordination of urban transportation planning and establishing transportation 

conformity infrastructure within their respective boundaries. The Memphis Urban jurisdiction is 

comprised of all of Shelby County, Tennessee, the western four miles of Fayette County, Tennessee and 

the northern twelve miles of DeSoto County. The portion of the Memphis Urban MPO in DeSoto 

County captures the more urbanized portion of the county that has experience continuous growth as well 

as the ozone air quality monitor. The West Memphis jurisdiction is comprised of the current and 

potential future urbanized portion of Crittenden County (including the ozone air quality monitor) with 

the following legal description:

That area west from the Mississippi River along the southern right of way line of County Road 

18 (Miller Road and Caldwell Road) to the western right of way line of County Road 205 

(Hinkley Road); then north along said right of way line and continuing north to the intersection 

of the southern right of way line of the St. Louis-Southwestern Railroad; then in a southwesterly 

direction along said right of way line to the intersection of eastern right of way line of State 

Highway 147; then north along said right of way to the intersection of the southern right of way 

line of State Highway 131; then west along said right of way line to the western right of way line 

of County Road 51(Eubank Road); then north along said right of way line to U.S. 70; then 

continuing north along the western right of way line of County Road 25 (Katie Goodhope) to the 

northern right of way line of County Road 12 (Buck Lake Road); then east along said northern 

right of way line to State Road 306; then continuing east along the northern right of way line of 

State Road 306 to the western right of way line of County Road 165; then north along said right 

of way line to the northern right of way line of County Road 168; then northeasterly along said 
21

right of way line to the intersection of the northern right of way of County Road 172; then east 

along said right of way line to the intersection of the western right of way line of County Road 5; 

then north along said right of way line to the intersection of the northern right of way line of 

James Mill Road; then east along said northern right of way line to the Mississippi River being 

the eastern boundary of the study area.

Memphis, TN-MS-AR Area has previously established nonattainment boundaries associated with both 

the 1-hour ozone and 1997 8-hour ozone NAAQS. The Memphis nonattainment boundary for the 1-

hour ozone NAAQS included Shelby County, Tennessee in its entirety. Whereas the Memphis 

nonattainment boundary for the 1997 8-hour ozone NAAQS included Crittenden County, Arkansas and 

Shelby County, Tennessee in their entireties. Tennessee has recommended a different boundary for the 

2008 ozone NAAQS for their portion of this Area. Arkansas recommended the same as the previous 

boundary for their portion of this Area. In addition, there is current infrastructure for meeting the 

transportation conformity requirements in Shelby County and the urbanized portions of DeSoto County 

and Crittenden County since both the Memphis Urban area and West Memphis MPO are currently 

implementing these requirements for the 1997 8-hour ozone standard.

Even though, DeSoto and Crittenden Counties do not have violating monitors for the 2008 ozone 

NAAQS based on air quality data from 2008-2010, our analysis suggest that both are likely contributing 

to the violation in Shelby County due to potential population-based emissions from mobile sources 

(VMT) and area source, meteorology and population growth.

Conclusion

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

following counties should be included as part of the intended Memphis nonattainment area because they 

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

County, Arkansas, and Shelby County, Tennessee in their entireties, and the portion of DeSoto County 

that is included in the Memphis MPO boundary. Two of these counties (i.e., Crittenden County,

Arkansas and Shelby County, Tennessee) are included in the Memphis nonattainment area for the 1997 

ozone NAAQS. One of the air quality monitors in Shelby County indicates violation of the 2008 ozone

NAAQS based on 2010 DVs, therefore this county is preliminarily included in the nonattainment area. 

Crittenden County, Arkansas, and DeSoto County, Mississippi are nearby counties that do not have

monitors indicating a violation of the standard based on 2010 DVs. However, EPA has preliminarily 

concluded that these counties (or portions thereof) contribute to the ozone concentrations in violation of 

the 2008 ozone NAAQS through population-based emissions from mobile and area sources (e.g., 

vehicles and other small area sources) and county VMT. 

Source category emissions data indicate that mobile sources and area sources are the primary 

contributors to ozone formation in the Memphis CBSA. Thus, population-based emissions such as total 

population or population growth, and precursor emission transport would indicate a county with 

contribution in the Memphis Area.

Shelby County, Tennessee dominates the CBSA in terms of urbanization, precursor emission 

contribution and transport which indicate population-based emission (mobile and area sources) 

contribution to its own violating monitor. Although the County population growth was less than 5 

percent from 2000-2010, it is densely populated with 70 percent of the CBSA population and five times 

DeSoto County’s population. Shelby County makes up over 60 percent of the Area’s NOx and VOC 
22

emissions. The County’s has over 30 percent of the County’s NOx and VOC emission coming from 

mobile sources and point sources. Meteorological analysis also indicates that Shelby County is 

contributing to its own violation as well as other monitors in the Memphis CBSA.

The population in DeSoto County, Mississippi has grown steadily from 2000-2010 (particularly the 

northern portion) with a 48 percent increase, even though it only makes up 12 percent of the total 

population in the CBSA. The County also has the CBSA’s second highest VMT. More than 30 percent 

of the County’s NOx and VOC emissions are from mobile sources and over 40 percent from area 

sources. In addition, meteorology suggests that DeSoto County is likely contributing to the violation in 

Shelby County due to potential southerly transport of mobile and area emissions. 

Crittenden County, Arkansas makes up less than 5 percent of the CBSA population with less than a 1 

percent population growth from 2000-2010. Crittenden County is mostly rural with the least 

urbanization compared to Shelby and DeSoto Counties. The County contributes less than 10 percent of 

the CBSA NOx and VOC precursor emissions. However, Crittenden County has over 40 percent of its 

NOx emission deriving from area sources which is considered a primary contributor to the formation of 

ozone in the Memphis area. EPA is proposing to include all of Crittenden County in the 2008 ozone 

Memphis nonattainment area because the county was included in its entirety in the 1997 ozone Memphis 

nonattainment area and because Arkansas recommended inclusion of the county in its entirety.

The remaining Tennessee (Tipton, Fayette) and Mississippi (Marshal, Tate, and Tunica) counties all 

have low population and urbanization, and precursor emission contribution and transport suggesting 

negligible contribution to the violating county. With the exception of those counties that comprise the 

Memphis, TN-MS-AR 1997 8-hour ozone boundary and the portion of DeSoto County, Mississippi 

discussed in this TSD for inclusion, EPA preliminarily concludes that the remainder of the counties in 

the CBSA do not contribute to the violations at the monitors in the CBSA and therefore are not being

considered as part of the nonattainment area. 
23

ATTACHMENTS

Figure 2. Memphis Ozone and Ozone Precursor Monitoring Network, with Population Density.

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

and Ozone Precursor Monitoring Network.

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

monitor for the 2008-2010 period.

Figure 5. NOAA HYSPLIT MODEL 72-Hour Back Trajectory Frayser Exceedances (2006-10).

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

Figure 7. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Frayser Exceedances (2006-10) - Zoom 

View.
24

Figure 2. Memphis Ozone and Ozone Precursor Monitoring Network, with Population Density
25

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

for Memphis Ozone and Ozone Precursor Monitoring Network
26

Figure 4 - Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances 

at the Frayser monitor for the 2008-2010 period.
27

Figure 5. NOAA HYSPLIT MODEL 72-Hour Back Trajectory Frayser Exceedances (2006-10)
28

Figure 6. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Frayser Exceedances (2006-10)
29

Figure 7. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Frayser 

Exceedances (2006-10) - Zoom View