1 

### ARKANSAS Area Designations for the 2008 Ozone National Ambient Air Quality Standards

The table below identifies the areas and associated counties or parts of countie s in Arkansas that EPA intends to designate as nonattainment for the 200 8 ozone national ambient ai r quality standards (2008 NAAQS). In accordance with secti on 107(d) of the Clean Air Act, EPA must designate an area

“nonattainment” if it is violati ng the 2008 ozone NAAQS or if it is co ntributing to a violation of the 2008 ozone NAAQS in a nearby area. The techni cal analyses supporting the boundaries for the

individual nonattainment areas are provided below.

Intended Nonattainment Areas in Arkansas

Area Arkansas’ Recommended

Nonattainment Counties EPA’s Intended Nonattainment

Counties

Memphis, TN-MS-AR* Crittenden Crittenden

Little Rock, AR Pulaski None

*Memphis, TN-MS-AR is a multi-stat e nonattainment area. Table 1 belo w identifies the counties in the other states that EPA intends to design ate as part of the nonattainment area.

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

“unclassifiable/a ttainment” for the 2008 ozone NAAQS.

The analysis below provides the basis for inte nded nonattainment area bounda ries. It relies on our analysis of whether and which monitors are viol ating the 2008 ozone NAAQS, based on certified air quality monitoring data from 2008-2010 and an evalua tion 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 be low. EPA issued guidance on December 4, 2008 that

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

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

1. Air quality data (including the design value calculated for each FRM or FEM 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 ra nges or other basin boundaries);

1 The December 4, 2008 guidance memorandum “Area Designa tions for the 2008 Revised Ozone National Ambient Air Quality Standards” re fers 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 refers to Federal Reference Met hod, and FEM refers to Federal Equivale nt Method. FRM monitors utilize a chemiluminescent technique to measure ozone, while many FEM mon itors use a technique involving ultraviolet photometry. FEM methods began to be developed in the late 1970’s and ea rly1980’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/criteri a/reference-equivale nt-methods-list.pdf2 5. Jurisdictional boundaries (e.g., counties, air dist ricts, existing nonattainment areas, Indian country, metropolitan planni ng organizations (MPOs))

Ground-level ozone generally is not emitted directly in to the air, but is crea ted by chemical reactions between oxides of nitrogen (NOx) and volatile orga nic 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 wh ether 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 Sta tistical Area (CSA) or Core Based St atistical Area (CBSA) associated with the violating monitor(s). 3 All data and information used by EP A in this evaluation are the latest available to EPA and/or provide d to EPA by states or tribes.

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

CSA/CBSAs because certain f actors 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 c ontributing 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 th e county containing the violating monitor as the starting point for considering the nonattainment area’s boundary.

Technical Analysis for Memphis, TN-MS-AR

Figure 1 is a map of the Memphis, TN-MS-AR in tended nonattainment area. The map provides other relevant information including the locations and design values of ai r quality monitors, county and other jurisdictional boundaries, relevant statistical area boundaries, the nonattainment area boundary for 1997 ozone NAAQS, and major tr ansportation arteries.

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 mo st recent update, based on 2008 populatio n estimates, issued on December 1, 2009 (OMB Bulletin No. 10-02).3 Figure 1. Intended Memphis, 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 4

, Arkansas recommended that Crittenden County be designated as nonattainment for the 2008 ozone NAAQS based on validated air quality da ta from 2006 – 2008. These data are from Federal Equivalent Method (FEM) monitors sited and op erated in accordance with 40 CFR Part 58.

After considering these recommendations and based on EPA's technical analysis described below, EPA intends to designate two full counties, one each in Arkansas and Tennessee, and one partial county in Mississippi (identifie d in Table 1 below) as “nonattainment” for the 2008 ozone NAAQS as part of the Memphis, TN-MS-AR multi-state nonattainment area.

4 2008 ozone NAAQS designation recommendation letter from Governor Beebe to Acting Regional Administrator Starfield, dated March 10, 2009.4 Table 1. States’ Recommended and EPA’s Intended Designated Nonattainment Counties for Memphis,

TN-AR-MS

Memphis, TN-MS-AR State-Recommended

Nonattainment Counties EPA Intended

Nonattainment Counties

Arkansas Crittenden Crittenden Mississippi None DeSoto (partial) Tennessee None* Shelby *Recommendation based on preliminar y air quality data from 2009 – 2011.

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 Memphis, TN-MS-AR CBSA 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 speci fied air quality standard. The 2008 ozone NAAQS are met at a monitor when the annua l 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 A ppendix P. Where several m onitors are located in a county (or a designated nona ttainment 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, TN-MS-AR CBSA area are shown

in Table 2.

Table 2. Air Quality Data.

County State Recommended

Nonattainment? 2008-2010 Design Value (ppb)
Crittenden, AR Yes 74
DeSoto, MS No 73 Fayette, TN No -- Marshall, MS No -- Shelby, TN No* 76
Tate, MS No -- Tipton, TN No --
Tunica, MS No -- *Recommendation based on preliminary air quality da ta from 2009 – 2011; Tennesse e intends to certify data early for EPA to consider for final designation decisions.

Air quality monitoring in Shelby County, Tennessee indicates a violation of the 2008 ozone NAAQS, therefore this county is included in the nonattainment area. A county (o r partial county) must also be designated nonattainment if it cont ributes to a violation in a n earby area. Each county without a violating monitor that is located ne ar a county with a violating monito r has been evaluated, as discussed below, based on the five factors and other relevant information to determine whether it contributes to the nearby violation.5 

### Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions of ozone precursors (NO

x and VOC) and other emissions-related data that provide information on areas cont ributing to violating monitors.

Emissions Data

EPA evaluated county-level emission data for NO

x and VOC derived from the 2008 National Emissions Inventory (NEI), version 1.5. This is th e most recently available NEI. (See http://www.epa.gov/ttn/chie f/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 th at 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 designati ons are issued and emissions increases due to new

sources.

Table 3 shows emissions of NO

x and VOC (given in tons per year) for violating and nearby counties that

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

Table 3. Total 2008 NO

x and VOC Emissions.

County State Recommended

Nonattainment? NO

x (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
Area-wide: 59,619 44,628 *Recommendation based on preliminary air quality da ta from 2009 – 2011; Tennesse e intends to certify data early for EPA to consider for final designation decisions.

Of the eight counties evaluated fo r inclusion in the nonattainment area, the emissions from Shelby County, Tennessee eclipse those of the surrounding counties and account for about 66 percent of the NOx and 63 percent of the VOC precursor emissions in the CBSA. Of the county’s 39,519 tons per year of NOx emissions, 35 percent are from point and mobile emissions and 20 percent from area source emissions. Of the county’s 27, 929 tons per year of VOC emissions, 36 percent are from mobile sources and 32 percent are from 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 comprise d of 45 percent area sour ces, 35 percent mobile sources. DeSoto County’s total VOC emissions include 44 percent area sources and 34 percent mobile

sources.

Crittenden County contributes less th an 10 percent of the precursor CBSA emissions. Of the county’s total NOx emissions listed in Table 1, 45 percent are mobile sources and 34 percent from area sources.6 The county’s total VOC emissions in clude 35 percent area sources and 31 percent mobile sources. Only 5 percent of the County’s NOx emissions are from poi nt sources. Both Crittenden and DeSoto Counties have less than 1 percent of the entire area’s NOx and VOC point source emissions

Fayette and Tipton Counties in Tenn essee and Marshall, Tate, and T unica counties in Mississippi all contribute 5 percent or less NOx and VOC precursor emissions in the CBSA.

Together, Crittenden, DeSoto and Shelby Counties acc ount 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 significantly to the violations of the 2008 ozone NAAQS that have been observed by monitors in Shelby County, Tennessee and Critt enden County, Arkansas.

Population density and degree of urbanization

EPA evaluated the population and vehicle use characterist ics 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 co mmercial development are an indicator of area

source and mobile source NO

x and VOC emissions that may cont ribute to ozone formation that

contributes to nonattainment in th e area. Rapid population or VMT grow th (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 asso ciated with area source and mobile source emissions as part of the nonattainment area. Table 4 shows the populatio n, 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 0
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
Area-wide: 1,316,100 0.28 107,854 9 *Recommendation based on preliminary air quality da ta from 2009 – 2011; Tennesse e intends to certify data early for EPA to consider for final designation decisions.

Sources: U.S. Census Bureau populati on estimates for 2010 as of August 4, 2011 ( http://factfinder2.census .gov/faces/tableservices/js f/pages/productview.xhtml?pi d=DEC_10_PL_GCTPL2.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 po rtion of the county and mostly rural in the remaining portion of the County. DeSoto County c ontains 12 percent of the CBSA7 population, but experienced 48 per cent growth from 2000-2010. Tate, Tuni ca 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 per cent 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 Fi gure 2, Memphis Area Ozone and Ozone Precursor Monitoring Network, and Figure 3, Population Density Change Percentage Between 2000 and 2010 Census for Memphis Ozone and Ozone Precursor Monitoring Network, which present graphical information on population density an d growth for the Memphis area.

Traffic and commuting patterns

EPA evaluated the commuting patt erns 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 arte ries (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 contribute s to nonattainment in the area. Rapid population or VMT growth in a county on the urban perimeter signi fies increasing integrati on 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 tr affic and commuting pattern data, including total 2008 VMT and 10-year VMT growth for each county.

Table 5. Traffic and Commuting Patterns

. County State Recommended

Nonattainment? 2008 VMT* (million miles) % Change in VMT (2002 – 2008) Crittenden, AR Yes 903 8.0
DeSoto, MS No 1,629 20.0 Fayette, TN No 573 6.0
Marshall, MS No 725 20.0 Shelby, TN No** 8,789 1.0
Tate, MS No 376 20.0 Tipton, TN No 401 0
Tunica, MS No 337 20.0

Area-wide : 13,733 -- * MOBILE model VMT are those inputs into the NEI version 1.5. **Recommendation based on preliminary air quality data from 2009 – 2011; Tennessee intends to certify data early for EPA to cons ider for final designation decisions.

Shelby County is the only count y in the Memphis CBSA violati ng the 2008 ozone NAAQS with 2008- 2010 air quality data and is considered the core CBSA county. The County accounts for 64 percent of the VMT in the CBSA; and approximately 35 pe rcent of Shelby County’s NOx emissions and 34 percent VOC emissions are from mobile sources.

In DeSoto County accounts for 12 percent of the CBSA VMT (which is the second highest in the CBSA). Additionally, DeSoto County has a 48 per cent growth in population from 2000-2010 with approximately 35 and 34 percent of the County’s NOx and VOC emissi ons, respectively, deriving from

mobile sources.8 In Crittenden County accounts for less than 10 per cent of the CBSA VMT. From 2000-2010, Crittenden County had less than 1 percent popul ation growth with 45 percent a nd 31 percent of the County’s NOx and VOC emissions, respectively, deriving from mobile sources.

Of the 8-county area, Crittenden County, Arkans as, DeSoto County, Mississippi, and Shelby County, Tennessee are all characterized by comparatively hi gh VMT that exceed 900 million miles. Collectively,

these counties account for 82 percent of the total VMT in the eight-county area.



### Factor 3: Meteorology ( weather/transport patterns)

For this factor, EPA analyzed 30-years of Na tional 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 Me mphis CBSA as well as on days when area ozone monitors exceeded the 2008 ozone NAAQS. Additiona lly, 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) ex ceeded the 2008 NAAQS. These analyses were

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

formation.

EPA’s analysis of the NWS data indicate a predom inant south and south-southwest component for the Memphis CBSA, which means the winds blow most often from the south and south-southwest. However, an examination on days when monitors in DeSoto County (Her nando) exceeded the 2008 ozone NAAQS suggested a northerly component. Additionally, on days when monitors in Shelby County exceeded the 2008 NAAQS, the data indicate d a southerly wind component. The attachment to this document contains Figure 4, Memphis Area Ozone and Ozone Precursor Monitoring Network, which presents graphical information on 24-hour back trajectories for exc eedances in 2008-2010 at the Frayser monitor, locations of major stationary sour ces, and locations of ambi ent monitors with their design values. An examination of the meteorological data indicates that, fo r 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 traj ectories going back thro ugh Crittenden County, AR on only 1 out of 10 days.

Since the 2008-2010 data is only for three years a nd has only 10 exceedance days, we evaluated more years to better understand the meteorological transpor t 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 me teorological data. Therefore we decided to evaluate all days that had ozone exceedances at the Desi gn 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 th is document includes 72- hour back trajectories

for 2006-2010 ozone exceedances at th e Frayser monitor using the Na tional 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 evaluated 24-hour back trajectories fo r the 2006-2010 time period using the NOAA HYSPLIT model. The results of these back trajectories are incl uded in the attachment to this document as Figure 6 with a further zoom in view in Figure 7.9 Evaluation of Figures 6 and 7 fu rther support our previous conclu sions based on the 2008-2010 back trajectories when the Memphis area Frayser monito r has ozone exceedances. The 2006-2010 data further supports that most of the center lines of the back trajectories passes through Shelby County TN, and many of the back trajectory cente rlines pass through Desoto county in northern Mississippi with a comparatively smaller percentage passing through Crittenden C ounty, Arkansas.

EPA’s meteorological assessment of the areas’ emi ssions, the area monitors’ ozone exceedances, and specifically the wind back trajectory analysis at the Frayser monitor in dicate that these areas should be considered for potential inclusion in th e Memphis, TN-MS-AR nonattainment area.



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

The geography/topography analys is evaluates the physical features of the land that might affect the airshed and, therefore, the distri bution of ozone ove r the area. The Memphis, TN-MS-AR area does not have any geographical or topographical barriers signi ficantly limiting air pollution transport within its air shed. Therefore, this fact or did not play a significan t role in this evaluation.



### Factor 5: Jurisdictional boundaries

Once we identified the general areas we anticipated we would recommend to be included in the nonattainment area, we then considered existing ju risdictional boundaries for the purposes of providing a clearly defined legal boundary and to help identify the ar eas appropriate for carry ing out the air quality planning and enforcement functions for nonattainme nt areas. Examples of jurisdictional boundaries include existing/prior nonattainment area boundaries for ozone or other urban-scale pollutants, county lines, air district boundaries, township boundari es, areas covered by a metropolitan planning organization, state lines, Reservation boundaries , and urban growth boundaries. Where existing jurisdictional boundaries were not ad equate or appropriate to descri be the nonattainment area, other clearly defined and permanent landmarks or geographic coordinate s were considered.

The Memphis Area MPO is comprised to 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 transp ortation planning and esta blishing transportation conformity infrastructure within their resp ective boundaries. The Memphis Urban Area MPO jurisdiction is comprised of all of Shelby County, TN, the western four miles of Fayette County, TN and the northern twelve miles of DeSoto County. The portion of the Memphis Urban Area MPO in DeSoto County captures the more urbanized portion of the count y that has experience cont inuous 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 al ong 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 a nd 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 ri ght of way line to the intersection of eastern right of way line of State Highway 147; th en north along said right of way to the10 intersection of the southern ri ght of way line of State Highw ay 131; then west along said right of way line to the west ern right of way line of Count y 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 norther n right of way line of County Road 12 (Buck Lake Road); then eas t along said northern right of way line to State Road 306; then conti nuing east along the northern righ t of way line of State Road 306 to the western right of wa y 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 right of way line to the intersection of the northern righ t 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 ri ght of way line to th e 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 establis hed 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 enti rety. Whereas the Memphis nonattainment boundary for the 1997 8-hour ozone NAAQ S included Crittenden County, Arkansas and Shelby County, Tennessee in their en tireties. 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. With the ex ception of those counties that comprise the 1997 8- hour ozone boundary for this Area and the portion of Desoto County, Miss issippi discussed in this TSD for inclusion, we believe that the remainder of the counties in the CBSA do not contribute to the

violations at the monitors in this Area and theref ore are not necessary be c onsidered as part of the

nonattainment area. There is current infrastruc ture for meeting the tr ansportation conformity requirements in Shelby County and the urbanized por tions for Desoto County and Crittenden County since both the Memphis Urban Area and West Me mphis 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, our analysis suggest that bo th are likely contributing to the vi olation in Shelby County due to potential population-based emissions from mobile sources (commuting patte rns) and area source, meteorology and population growth.

The remaining Tennessee and Mississi ppi counties all have relative ly low population and urbanization, and precursor emission contribution and transport s uggesting negligible contri bution to the violating

county.



### Conclusion

Based on the assessment of the factors described above, EPA has preliminarily concluded that the following counties, or parts of counties, should be included as part of the Memphis, TN-MS-AR nonattainment area because they are either viol ating 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 Urban Area MPO boundary. Two of these counties, Shelby and Critte nden, are included in the Memphis, TN-MS-AR nonattainment area for the 1997 ozone NAAQS. One of the air quality mon itors in Shelby County

indicates a violation of the 2008 ozone NAAQS based on the 2010 DVs ; therefore this county is11 preliminarily included in the nonattainment area . Crittenden County, Arkansas, and Desoto County, Mississippi are nearby counties that do not have monitors indicating a vi olation of the standard based on 2008 – 2010 data. However, EPA has preliminarily conc luded that these counties (or portions thereof)

contribute to the ozone concentrations in viol ation of the 2008 ozone NAAQS through population-based emissions from mobile and non-point sources (e .g., vehicles and other small area sources).

Source category emissions data i ndicate that mobile sources and area sources are the primary contributors to ozone formation in the Memphis CBSA. Thus, population-based emissions such as significant total population or popula tion growth and precursor emissi on transport would indicate a county with contribution in the Memphis Area.

Shelby County, TN dominates the CBSA in terms of urbanization, precursor emission contribution and transport (through commuting patterns) which indicat e significant population- based emission (mobile and area sources) contribution to its own violating monitor. Alt hough the County population growth was less than 5 percent from 2000-2010, it is densely popul ated with 70 percent of the CBSA population and five times DeSoto County’s population. Shelby Count y makes up over 60 percent of the Area’s NOx and VOC emissions. More than 30 percent of the C ounty’s NOx and VOC emission derives from mobile sources and point sources.

DeSoto County, Mississippi has steadily grown in population from 2000-2010(particularly the northern portion) with a 48 percent increase, even though it only makes up 12 percent of the population. The County has the area’s second highest VMT. More than 30 percent of the County’s NOx and VOC emissions are from mobile sources and over 40 per cent from area sources. In addition, meteorology suggests that DeSoto County is li kely contributing to the violati on in Shelby County due to potential southerly transport of mobile and area emissions.

Crittenden County, Arkansas makes up less than 5 pe rcent of the CBSA populat ion with less than a 1 percent population growth from 2000-2010. Critte nden County is mostly rural with the least urbanization compared to Shelby and DeSoto Countie s. The County contributes less than 10 percent of the CBSA NOx and VOC precursor emissions. However, analysis of the meteor ological data indicates that emissions from Crittenden County do occasiona lly contribute to violations of the 2008 ozone NAAQS in Shelby County. EPA is proposing to in clude all of Crittenden County in the 2008 ozone Memphis, TN-MS-AR nonattainment area because the county was included in its entirety in the 1997 ozone Memphis, TN-MS-AR nonattainment area and because Arkansas recommended inclusion of the county in its entirety.

Technical Analysis for Little Rock, AR

In its March 2009 initial 2008 ozone NAAQS designati on recommendation letter to EPA, Arkansas recommended that Pulaski County be designated as nonattainment. This recommendation was based on ambient air quality monitoring data for the period from 2006 – 2008, which indicated a design value of 0.080 ppm. More recent validated ambient air quality m onitoring data indicates th at the Little Rock area is meeting the 2008 ozone NAAQS, and there are curren tly no monitors in the Little Rock area that

indicate a violation of the standard.

Although Arkansas has not submitted an updated 2008 ozone recommendation letter to rescind its initial

recommendation of nonattainment for Pulaski Count y, EPA is basing its desi gnation regarding Pulaski County and other counties in the Little Rock area on the most recently available validated ambient air12 quality monitoring data. The 2008-2010 8-hour ozone de sign value for Little Rock is 0.070 ppm (0.070 ppm at two sites and 0.0 67 ppm at one site).



### Conclusion

Based on the most recently available validated ambient air quality monitoring data, EPA has preliminarily concluded that no coun ties or portions of counties compri sing the Little Rock, Arkansas metropolitan statistical area should be designa ted as nonattainment for the 2008 ozone NAAQS.13 

### 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 traject ories of all 75 ppb exceed ances 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 Traj ectory Frayser Exceedances (2006-10) - Zoom

View.14Figure 2. Memphis Ozone and Ozone Precursor Monitoring Network, with Population Density15Figure 3. Population Density Change Percentage Between 2000 and 2010 Censusfor Memphis Ozone and Ozone Precursor Monitoring Network16Figure 4. Overlay of 24-hour HYSPLIT back trajectories of all 75 ppb exceedances at the Frayser monitor for the 2008-2010 period.17 Figure 5. NOAA HYSPLIT MODEL 72-Hour Back Trajectory Frayser Exceedances (2006-10)18 Figure 6. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Frayser Exceedances (2006-10)19 Figure 7. NOAA HYSPLIT MODEL 24-Hour Back Trajectory Frayser Exceedances (2006-10) -

Zoom View