### Analysis of Environmental Protectio n Agency Technical Support Document

Arkansas Area Designations for the 2008 Ozone National Ambient Air Quality Standards

Arkansas Department of Environmental Quality

Air Division – Planning Branch

February 2012

### Analysis of Environmental Protectio n Agency Technical Support Document

Arkansas Area Designations for the 2008 Ozone National Ambient Air Quality Standards

On December 9, 2011, the federal Environmental Pr otection Agency (EPA) sent a letter to the

Honorable Mike Beebe, Governor of the State of Arkansas, de scribing a proposal to designate

the attainment status of Arkansas counties wi th regard to the National Ambient Air Quality

Standards (NAAQS) for ozone. Incl uded with the letter as an enclosure, the EPA provided a

Technical Support Document (TSD) 1 

### that describes the reasoning it us ed to arrive at preliminary

designations. In that letter, the EPA stated its intent to designa te Crittenden County, AR as being

in nonattainment of the 2008 ozone NAAQS an d all other counties in the State as

unclassifiable/attainment. This document is prepar ed in response to the EPA TSD. It contains

information intended to rebut the EPA propos al to designate Critt enden County, AR as

nonattainment for the 2008 ozone NAAQS.

According to an EPA guidance memorandum (A rea Designations for the 2008 Revised Ozone

National Ambient Air Quality Standards – R. J. Meyers, Principal Assistant Administrator –

12/04/08), during its review of the State’s recommended nonattain ment designations, EPA is to

consider / evaluate 9 factors when determin ing nonattainment area boundaries. The designation

process for the 2008 ozone NAAQS has, by nece ssity, been altered somewhat from the

traditionally followed process due to the reconsideration announced by EPA Administrator Lisa

P. Jackson on 9/16/09, the proposal for an altern ate “2008” standard and the ultimate decision on

09/22/11 to withdraw the proposed alternate standard and implemen t the original 2008 Standard.

In the above-referenced letter to Governor Mike Beebe, EPA stated that it would make its

preliminary designations decisions based on previously submitted State recommendations,

modified as necessary, by the use of the most cu rrent certified quality as sured/quality controlled

data for the 2008 – 2010 time frame (unless the Stat e “early certified” monitor data for 2011 and

request the use of 2009 – 2011 data). Arkansas has not yet certified the 2011 ozone monitor

data; therefore the monitor data for the year s 2008-2010 must be utilized for attainment

designation purposes.

Crittenden County, Arkansas is currently design ated as a maintenance area for the 1997 ozone

NAAQS. In 2009, Arkansas Governor Mike Beebe submitted a letter to EPA that included a

designation recommendation of nonattainme nt for the 2008 ozone NAAQS for Crittenden

County, AR. This recommendation was based on monito ring data that was recorded at the ozone

monitoring station that is located in Marion, Ar kansas for the years 2006 - 2008. Due to delays

in implementation of the 2008 ozone NAAQS, as referenced above, this recommendation has

become outdated. Based on ozone monitoring data collected at the Marion monitor site through

2010 (the last year for which qua lity-assured data has been provi ded to the EPA), Arkansas is

now recommending that Crittenden County, Arkans as be designated as attainment for the 2008

ozone NAAQS. The 2010 Design Value (DV) for the Marion monitor is 74 ppb.

EPA states on page 11 of the TSD that it “... is proposing to include all of Crittenden County in

the 2008 ozone Memphis, TN-MS-AR nonattainment area because the county was included in its

1 ARKANSAS

– Area Designations for the 2008 Ozone National Ambient Air Quality Standards (Dec. 2011)2 

### entirety in the 1997 ozone Memphis, TN-MS-AR nonattainment area and because Arkansas

recommended inclusion of th e county in its entirety.”

It should be noted that there is no regulatory justification for recommending the inclusion of a

county in a nonattainment area based on its classification unde r a previous NAAQS.

Additionally, the rationale for in clusion of Crittenden County based on the previously submitted

(2009) State recommendations significantly depa rts from EPA’s publically announced procedure

for making preliminary designation determina tions. The 2009 State recommendation should be

considered only to the extent that the use of the 2008-2010 monito r data still indicates that a

monitor show levels above the 2008 NAAQS.

As noted above, Arkansas is revising its recommendation based on the 2010 DV and is not

recommending that Crittenden County, AR be designated as nonattainment.

Based on 2010 DVs for all ozone monitors locate d in the Memphis, TN-MS-AR CBSA, the only

monitoring station that had a DV higher than the NAAQS was the Frayser monitor site in

Memphis, Tennessee. ADEQ agrees that the EPA’s stated intent to use 2010 DVs as the basis for

designations is appropriate, especially since the 2010 DV wo uld best represent the ozone

concentrations experienced by the majority of the population in the densely urbanized portion of

the Memphis area. Using 2010 DVs would also best represent monitoring in the vicinity of most

of the major industrial and mob ile sources of ozone precursor emissions in the Memphis area.

Promulgated and proposed federal rules have proj ected near–future attain ment in the Memphis

area. Delays in implementation of the 2008 ozone NAAQS and other federally mandated

programs have significantly impacted the ability of States to make progress in demonstrating

regional attainment. Designati ng the area nonattainment for th e 2008 standard would serve no

useful purpose since it is likely, based on current trends further di scussed herein, that the entire

area will be attaining the sta ndard in the near future.

In the TSD, EPA states that preliminary designations are based on:

Whether and which monitors are viol ating the 2008 ozone NAAQS with 2010 DVs.

and

Evaluation of whether nearby areas are contributing to violations.

Based on the above, Crittenden County, AR shoul d not be designated nonattainment for the 2008

Ozone NAAQS nor included in the nonattainment designation due to contribution to NAAQS

violation. The 2010 DV for the ozone monitor lo cated in Marion, AR di d not violate the 2008

ozone NAAQS. Of the four ozone monitors loca ted in the Memphis, TN-MS-AR Core Based

Statistical Area (CBSA), only the Frayser monitor site, located in Memphis, TN, had a DV that

exceeded the 2008 NAAQS.

The EPA TSD does not provide a scientifically defensible basis for its presumption that

Crittenden County, AR contributes significantly to violations at the Frayser monitor site. While3 

### the TSD attempts to assert that emissions, popul ation and traffic patterns in Crittenden County,

AR contribute to the DV of the Frayser monito r, the only indication of potential contributions

that the EPA has asserted with any meaningf ul documentation is that prevailing winds

occasionally pass through Crittenden County, AR. The TSD failed to docum ent or elaborate in

any way to show a correlation between winds pa tterns from Crittenden County, AR toward the

violating monitor (Frayse r) that establishes significant pollutant distribution that could be viewed

as contributing to the exceedance of the NAAQS.

ICF International, a meteorolog ical consulting firm, has provide d ADEQ with an analysis that

refutes the contention presente d in the TSD by showing that Crittenden County, AR has only a

marginal and infrequent influence on ozone concen trations recorded at the Frayser monitor site.

The ICF memorandum is included as an Appendix herein.

The following discussion of the EPA TSD follows the structure of that document. Headings in

bold type highlight the elements of the “5 factor analysis” that the EPA used to make preliminary

determinations.4 

### Weight of Evidence (WOE) analysis

Factor 1: Air Quality Data

EPA’s Table 2 shows that Arkansas has r ecommended nonattainment for Crittenden County.

While Arkansas originally recommended nonatt ainment when recommendations were first

required, Arkansas is revising it s recommendation to attainment/ unclassifiable based on the 2010

DV of 74 ppb for the Marion monitor.

Tennessee has requested that EPA use its 2011 DVs (74 ppb) for designation purposes. The 2011

monitoring data for Arkansas monitors has yet to be certified as meeti ng quality assurance and

control protocols and th erefore, cannot be used for attain ment designation purposes within

Arkansas. Using 2011 DVs would cause the Marion monitor in Crittenden County, AR to have

the highest estimated DV (77 ppb) in the CBSA. This would still result in nonattainment but

would result in a higher DV being used for cl assification purposes. Basing a nonattainment

designation on the DV of a primarily “downwind” m onitor in an adjacent State in a CBSA where

all other monitors are showing attainment would not be repres entative of the regional ozone

formation and concentration dynamics.5 

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

location of sources

Memphis/Shelby County Tennessee emission s ources dominate the area-wide emissions

inventory. Arkansas has no control over th e numerous emission sources in the Tennessee

inventory. Sources in Tennessee account for 74 percent of the NO

x 

### emissions and 71 percent of

the VOC emissions in the CBSA.

A significant portion of the emissi ons inventory for Crittenden Count y, AR consists of emissions

from agricultural activities. Many of these em issions sources are operated intermittently and

should not be considered as contributing to typi cal ozone season daily emissions. Emissions from

agricultural equipment are being reduced throug h federal programs requiring cleaner fuels and

more efficient engines. Emissions from agricult ural equipment in Crittenden County, Arkansas

should continue to decline as new federal sta ndards regulating non-road engines and fuels are

implemented.

As evidenced by the information provided on Pgs. 5 – 8 and in Fig. 2 of the EPA TSD,

Memphis/Shelby County, TN has the most pot ential for effective emission reductions.

location of population

Based on EPA analysis, 70 percent of the CBSA population resides in Shelby County, TN. The

population of Crittenden County represents only 4 percent of the CBSA population. Crittenden

County, Arkansas is primarily rural croplands and wetlands. As shown in Table 4 of the EPA

TSD, the population of Crittenden County, Arka nsas has actually decreased between 2000 and

2010. With the exception of West Memphis a nd Marion, the population density of Crittenden

County is extremely low.

amount of emissions

On P. 5, EPA’s TSD states that “Crittenden C ounty contributes less th an 10 percent of the

precursor CBSA emissions.” The actual contributi on, based on the values in EPA’s Table 3 is 7.5

percent. By generalizing, EPA’s analysis overs tates Crittenden County em issions by 2.5 percent.

P. 6 of EPA’s TSD states that “Both Crittenden County and DeSo to Counties have less than 1

percent of the entire area’s NOx and VOC emissi ons.” Crittenden County, Arkansas continues to

be subject to federal requirements for Preven tion of Significant Deteri oration (PSD). It is

apparent that any Crittenden County point sour ce emission reductions th at would be mandated

under a new nonattainment designation w ould have limited effectiveness.

Crittenden County NOx and VOC emissions from all anthropogenic sour ce categories (point,

area, mobile and non-road) for 2008 have decreased from 2005 levels. This may well be a factor

in the downward trend in ozone DVs that is described in Appendix A herein.6 

### The statement on P. 6 that “The emissions from Fayette and Tipton Counties in Tennessee and

Marshall, Tate and Tunica Counties in Mississipp i 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 Crittenden County Arkansas.” is un supported by analysis and misrepresents areawide contributions.

While county-by-county emission totals and percentage s show emissions in a relative sense, they

do not, of themselves, indicate a significant cont ribution to nonattainment in an adjacent or

nearby county.

emissions controls

Due to its previous nonattainment designation, most practically available emission controls are

already in place in Crittenden County. Exampl es of programs already in place include:

Prevention of Significant Deterior ation (PSD) New Source Review

Stage I Vapor Recovery

municipal fleet diesel retrofits

private-sector Truck Stop Electrification

Intelligent Transportation Systems

federal fuel and engine st andards have reduced Crittenden County mobile emissions

federal fuel and engine st andards have reduced Crittenden County non-road emissions

Transportation Conformity in the West Memphis Area Transportation Study area.

urban growth patterns

Column 6 of EPA’s Table 4 represents the populat ion change in Crittende n County as 0 percent.

On P. 7 EPA states that Critt enden County “... had less than 1 percent population growth from

2000 – 2010 and contains only 4 percent of the CBSA population.” Using the numbers in Table

4, the population of Crittenden County ha s actually declined by 1 percent.

Table 4 also indicates th at there has been population growth in all other coun ties in the CBSA.

DeSoto County, Mississippi has the highest actual population grow th in the CBSA.

Ozone DVs in the CBSA have shown a downwar d trend, despite an overall increase in

population of 107,854 in the period from 2000 – 2010.

On P. 7, EPA states that it has evaluated “... th e commuting patterns of re sidents in the area...”

but the TSD provides no documentation of any analysis of commuting activity that would

support this statement. The title of EPA’s Table 5 is labeled “Traffic and Commuting Patterns”7 

### but is mislabeled since it c ontains no information regarding commuting patterns. The latest

available data from the U.S. Census Bureau (1980) shows that only a bout 10 percent of the

population of Crittenden County, AR (~5000 - 6000 people) commutes to work in Shelby

County, TN.

EPA states on P. 7 that “Crittenden County acco unts for less than 10 percent of the CBSA VMT.

The values in Table 5 show that Crittenden C ounty accounts for less than 7 percent of the CBSA

VMT. As can be visualized from the data contained in Figure 1, Mobile source NO

x 

### emissions in

Crittenden County, Arkansas are dominated by comme rcial vehicles and passenger vehicles that

are passing through the county on the two in terstate roadways that traverse it.

Figure 1



### The Arkansas Highway and Transportation Depa rtment has provided an analysis comparing

Daily Vehicle Miles Traveled (DMVT) in Critte nden County, AR to statewide totals for the

years 2000 – 2010. Crittenden County DMVT peak ed in 2007 at 2,500,000 and dropped to

2,250,000 in 2010. The 2010 DVMT for Crittenden County, AR is at the lowest level since 2001.

Over the same period, the statewide DVMT trend has continued to rise. When compared to

statewide trends, this regional decline in traffic may be indicative of fact ors that are influencing 

# Crittenden County Mobile Source NOX (TONS)

Rural Interstate

Urban Interstate

Urban Minor Arterial

Rural Minor Arterial

Rural Major Collector

Rural Local

Urban Other Principal Arterial

Urban Local

Urban Collector

Rural Other Principal Arterial

Rural Minor Collector8 

### driving behavior in Crittenden County. Factors c ontributing to the declin e in Crittenden County

DVMT might include reduced commercial activity caused by a sluggish economy and a

reduction in driving influenced by rising fuel prices. Charts 1 and 2 depict Crittenden County,

Arkansas and state-wide VMT trends for the years 2000 – 2010.910 

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

With respect to monitored concentrations at the Frayser site, EPA has provided insufficient

evidence of a significant contribution from Critt enden County. The analysis provided herein as

an Appendix (Analysis of 8-Hour Ozone Design Value Trends – ICF International – Jan, 2011)

describes how emissions from Crittenden County are unlikely to have a significant impact on the

DV for the Frayser monitor. Note that Crittenden C ounty lies to the west of the rest of the CBSA.

As stated in the ICF memorandum:

For both periods considered, there is no apparently causal relationship between

winds from the SW to the W and high ozone at the Frayser monitor. In fact, low

wind speeds, easterly wind components (E to SSE winds), and/or northerly winds

are more likely on ozone exceedance days compared to all days and appear to be a

determining factor for ozone exceedances at this site.

The EPA TSD describes the use of historic me teorological data, primarily wind patterns, as a

means of representing current contributions to n onattainment at the Frasier monitor. It does not

consider the air quality of the air mass that might influence ozone concentr ations at a particular

monitoring site and does not acc ount for emission reductions r ealized in the latest years

analyzed.

The fact that an air mass passed through a por tion of Crittenden County, AR prior to it arriving

in the vicinity of the Frayser monitor site do es not constitute a demonstration of significant

contribution to a monitored exceedance. HYSPLIT modeling alone is insufficient evidence of a

significant contribution. The EP A TSD acknowledges “back trajec tories going back through

Crittenden County, AR on only one out of 10 da ys” for the years 2008 – 2010. The ICF analysis

provides additional analysis indicating that Cr ittenden County would influence Frayser monitor

site ozone concentrations only infrequently and marginally.11 

### Factor 4: Geography and topography (mount ain ranges or other basin boundaries)

EPA asserts that this factor “did not play a significant role in this evaluation.” ADEQ has

identified no relevant issues with respect to this factor.12 

### Factor 5: Jurisdictional boundaries

Crittenden County, Arkansas was previously de signated as a Targeted Economic Development

Zone (TEDZ). At that time , ADEQ was required to demons trate through photochemical

modeling that the emissions from any new major fac ilities would not cause or contribute to either

reattainment or maintenance of the 1997 ozone standard. Since then, no new major sources have

been sited in Cr ittenden County, AR.

Also since that time, total annual emissions of ozone precursor polluta nts have decreased and

ozone concentrations at the Marion monitor site , and all other sites in the CBSA, have been

trending downward (see Fig. 2). It is apparent that emission reduc tions already being realized in

Crittenden County, AR are resulting in improved air quality in the region.

Figure 2



### The major sources of ozone precursor emissions within the CBSA are located in the State of

Tennessee. Table 3 in the EPA TSD clearly dem onstrates this. The Stat e of Arkansas has no

authority to require either the State of Te nnessee or Memphis/Shelby County, Tennessee, a

jurisdiction with a local air quality control pr ogram, to implement any control measures that

might be required to assure attainment and maintenance of the ozone NAAQS.

It is appropriate that Crittende n County, Arkansas be treated as a separate jurisdiction when

considering its attainment status and any im plications of nonattainment implementation. Its

previous designation as a TEDZ and the fact that it was required to conduct its own

Transportation Conformity demonstr ations are examples of how it ha s been previously treated as

a separate jurisdiction when required to address regional air quality issues.

Since Crittenden County, Arkansas is currently designated as a maintenance area for the 1997

ozone standard and has already been require d to implement emission reduction and control 0 25 50 75 100 125

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010ppb 

### 8

‐ Hr Ozone Design Values

Marion Hernando Frayser Orgill13 

### measures, there are no additional benefits to be achieved by a new nonattainment designation.

Designating Crittenden County, Ar kansas as a nonattainment area for the 2008 NAAQS would

serve no useful purpose.

### Appendix – Analysis of 8-hour Ozone Design Value Trends

## MEMORANDUM

To: Kelly Jobe, Mark McCorkle, and Tony Davis, Arkansas DEQ

From: Sharon Douglas, Jay Haney, and Belle Hudischewskyj, ICF

Date: January 24, 2012

Re: 8-Hour Ozone Related Analyses



## Analysis of 8-hour Ozone Design Value Trends

The 2008

‐ 2010 8

‐ hour ozone design values for monitoring sites within the greater Memphis area are

very close to the current National Ambient Air Quality Standard (NAAQS) of 75 ppb. The design values

are 76 ppb for the Frayser monitoring site in Shelby County (TN), 74 ppb for the Marion monitoring site

in Crittenden County (AR), and 73 ppb for both the Edmund Orgill Park monitoring site in Shelby County

and the Hernando monitoring site in DeSoto County (MS). The design value for a given monitor is the

three

‐ year average of the fourth highest daily maximum 8

‐ hour average concentration for each of the

three years. This metric was formulated to limit the effects of year

‐ to

‐ year variations in meteorology as

well as unusual or infrequent meteorological or emissions conditions on attainment designations and

attainment status.

With values so close to the NAAQS, however, year

‐ to

‐ year variations in meteorology can influence the

designation of attainment. As an example, preliminary data indicate that the design values for 2009

‐

2011 are 74, 77, 73, and 74 ppb for the Frayser, Marion, Orgill, and Hernando monitors, respectively

(with the values for the Frayser and Marion sites giving a different outcome relative to attainment just

one year later). In this case, given the potential confounding effects of year

‐ to year

‐ variations in

meteorology, it is important to consider both current design values and longer

‐ term trends in the

determination of attainment/nonattainment.

The following analysis examines recent trends in design values for each of the monitors in the Memphis

area and attempts to reconcile the trends in 8

‐ hour ozone with known changes in emissions, both locally

and regionally. This analysis focuses on the 15

‐ year period 1996

‐ 2010.

Figure 1 displays the 8

‐ hour ozone design values for each of the four monitoring sites in the Memphis

area. The sites and counties are as follows: Marion (Crittenden County, AR), Hernando (DeSoto County,

MS), Frayser and Edmond Orgill Park (Shelby County, TN). Note that the design value for the Frayser

monitor is the higher of the two values for Shelby County. The year indicated on the plot is the end year

of the three

‐ year design

‐ value period.Figure 1. 8-Hour Ozone Design Values for Sites within the Greater Memphis Area for the Period 1996-2010.

All four sites show a clear downward trend in design value for the period, culminating with values near

75 ppb in 2010.

Previous studies such as the Arkansas

‐ Tennessee

‐ Mississippi Ozone Study (ATMOS) (Douglas et al.,

2004) and the Crittenden County Ozone Study (CCOS) (Douglas et al., 2005), have indicated that the site

with the maximum design value for the area varies from year to year based on the frequency of

occurrence of meteorological conditions (primarily wind directions) that are conducive to high ozone at

the specific sites. The CCOS study found that:

 High ozone days at the Frayser site are char acterized, on average, by southerly or

northwesterly surface winds (depending on the concentration level), and easterly to

southwesterly winds aloft.

 High ozone days for Edmund Orgill Park have southerly wind components at all

levels, and, on average, southerly to southwesterly winds at the surface and

southeasterly to southwesterly winds aloft.

 High ozone days for the Marion site are characterized, on average, by southeasterly

winds both near the surface and aloft. Certain of the high ozone days have easterly

winds near the surface. Winds aloft also va ry from southeasterly (to southwesterly or

westerly) on certain of the higher ozone days.

 High ozone days for Hernando are clearly di stinguished by northerly and easterly

wind components. Surface winds range from northwesterly to northeasterly, while

winds aloft are primarily from these same directions, but occasionally (especially on

the highest ozone days) from the east or southeast.

Considering two consecutive design

‐ value periods, a large percentage of days with wind from the

northwest might result in the regional maximum value at the Frayser site for the first period, while a

shift to more southwesterly winds during the next design value period might cause the location of 0 25 50 75 100 125

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010ppb 

### 8

‐ Hr Ozone Design Values

Marion Hernando Frayser Orgillmaximum design value to shift to the Marion site. This finding indicates that it is important to consider

the sites as a group (as well as individually) in determining attainment.

Figure 2 shows the average 8

‐ hour ozone design value, where the average is taken over all four sites.

Figure 2. Four-Site Average 8-Hour Ozone Design Values for the Greater Memphis Area for the Period 1996-2010.

Figure 3 shows the maximum 8

‐ hour ozone design value, where the maximum is taken over all four

sites.

Figure 3. Four-Site Maximum 8-Hour Ozone Design Values for the Greater Memphis Area for the Period 1996-2010.

Linear trend lines indicate that, on average, both the regional

‐ average design value (based on all four

sites) and the regional

‐ maximum design value (based on all four sites) decrease by approximately 1.25

ppb per year during this period. The confirms the overall downward trend despite that year

‐ to

‐ year

differences in meteorology (and specifically prevailing wind directions) cause the location of the regional

maximum value to vary from year to year. y = ‐ 1.2545x + 95.969

0 25 50 75 100 125

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010ppb 

### Regional

‐ Average 8

‐ Hr Ozone Design Values

Average Linear (Average)

y = ‐ 1.2786x + 99.429

0 25 50 75 100 125

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010ppb 

### Regional

‐ Maximum 8

‐ Hr Ozone Design Values

Max Linear (Max)It follows that the decrease in ozone design values between 1996 and 2010 is attributable to emissions

reductions during that period. Many of these reductions are associated with the Clean Air Act

Amendments (CAAA) of 1990, which has led to reductions in emissions of volatile organic compounds

(VOCs), oxides of nitrogen (NO

x ), and carbon monoxide (CO) from a variety of sources including electric

generating units (EGUs), industrial point sources, non

‐ point industrial and area sources, and on

‐ road and

non

‐ road motor vehicles and other equipment. National

‐ scale emissions reductions associated with the

CAAA during the period 1996

‐ 2010 have affected national, regional, and local pollutant concentrations.

General emission reduction programs associated with the CAAA include the following:

• Title I VOC and NO

x reasonably available control technology (RACT) requirements in ozone

nonattainment areas (NAAs);

• Title II on-road motor vehicle and non-road engine/vehicle provisions (NO

x , VOC, and CO);

• Title III National Emissions Standards for Hazardous Air Pollutants (NESHAPS), and

• Title IV emissions programs for electric generation units (EGUs), primarily for SO 2.

In 1999, EPA promulgated the Regional Haze Rule to help protect visibility in national parks and

wilderness areas. The rule mandated that states develop programs to identify short and long

‐ term

strategies to reduce precursor emissions (primarily NO

x and SO 2 ) in an effort to reduce the formation of

secondary fine particulates (PM

2.5 ). The program included the identification of best available retrofit

technology (BART) for older industrial sources and expanded visibility monitoring of Class I areas.

Regional haze program plans were to be finalized by the states by 2008 with the initial phase of the

program reductions completed by 2018. In addition, specific emission reduction programs targeting

interstate transport of ozone and precursor emissions, primarily NO

x , that were expected to affect air

quality somewhat in the Greater Memphis area include the NO

x SIP Call and the Clean Air Interstate Rule

(CAIR). The NO

x SIP Call (Phase I) was promulgated in September 1998 and mandated that 22 eastern

states implement programs to decrease NO

x emissions, primarily from EGUs, to lessen the effects of the

regional transport of ground

‐ level ozone. Phase I reductions were to begin in 2003. Phase II of the NO

x

SIP call rule was promulgated in April 2004 and required that reductions be in place by 2007. Reductions

in emissions from the NO

x SIP call were required in Tennessee and Missouri, but not Arkansas,

Mississippi, Texas, or Louisiana, so the effect on Greater Memphis may have been limited.

The Clean Air Interstate Rule (CAIR) was promulgated in March 2005 and mandated significant

reductions in SO 2 and NO

x emissions primarily from EGUs in 28 eastern states. Concurrent with this

legislation, EPA also issued the Clean Air Mercury Rule (CAMR) targeting mercury emissions from coal

‐

fired EGUs. Together, the CAIR and CAMR programs were intended to reduce regional emissions in the

eastern U.S., with Phase I reductions originally slated to start in 2010, and Phase II reductions in 2015.

The CAIR and CAMR rules mandated reductions in Tennessee, Mississippi, Arkansas (ozone season only),

Texas, and Louisiana, but not Missouri. The effects of emission reductions from CAIR may have only

been realized somewhat in 2009 and more fully in 2010 when control equipment was supposed to be in

place.

In July 2008, the U.S. Court of Appeals for the D.C. Circuit remanded the CAIR rule back to EPA for review

and possible revisions but kept in place the original emission reduction requirements of CAIR. In July

2011, EPA issued the Cross

‐ State Air Pollution Rule (CSAPR), also referred to as the Transport Rule,

which was intended to replace CAIR. The CSAPR rule mandated emission reductions in Tennessee,

Mississippi, Arkansas, Texas, Louisiana, Missouri, and Nebraska. However, in December 2011, the rule

was stayed by the D.C. Circuit court for further review, keeping in place the original provisions of CAIR.In addition to programs primarily targeting EGUs and other large industrial sources, regional emissions

reductions during this period have likely been realized in the on

‐ road mobile source sector due to the

fleet turnover of older vehicles, the use of cleaner fuels, and the introduction of cleaner, more efficient

engines resulting from compliance with the applicable Corporate Average Fuel Economy Standards

(CAFE) for cars and trucks, despite increases in vehicle miles traveled. Other programs promulgated by

EPA in this period include new regulations and emission standards resulting from the Clean Air Nonroad

Diesel rule of 2004 for diesel fuels, and engines (including locomotives and marine diesel engines), and

updated performance standards/rules for spark

‐ ignition engines affecting various off road equipment

promulgated in 2008, with emission reductions expected from equipment turnover primarily after 2010.

EPA recently conducted an analysis to assess the effects of the Clean Air Act (CAA) on air quality, the

environment, public health, and the economy (EPA, 2011a). This work was performed in accordance

with Section 812 of the CAAA of 1990 that requires the EPA to periodically assess the effects of the

Clean Air Act (CAA) on air quality, the environment, public health, and the economy. As part of this

analysis, EPA prepared emissions estimates for 1990, 2000, 2010, and 2020. Emissions for the historical

years (1990 and 2000) were based on the best available emission inventories for these years. Projection

to the future years was based on economic growth projections, future

‐ year control requirements (for

attainment of NAAQS), and control efficiencies.

Figures 4 and 5 display the emissions data from the Section 812 EPA study (EPA, 2011a) for the years

1996

‐ 2010, for two different geographical regions. Figure 4 displays VOC and NO

x emission totals for the

three states for which a portion of the state is a part of the greater Memphis area (Arkansas, Tennessee,

and Mississippi) as well as ten additional states surrounding the three

‐ state area: Alabama, Georgia,

Illinois, Indiana, Kansas, Kentucky, Louisiana, Missouri, Oklahoma, and Texas. Figure 5 displays emission

totals for Arkansas, Tennessee, and Mississippi only. Estimates for the interim years are based on

interpolation.

Figure 4. Estimated Emissions Totals for the 13- State Region Surrounding Mem phis for the Period 1996-

2010.

Figure 5. Estimated Emissions Totals for the 3-Stat e Region Surrounding Memphis for the Period 1996-2010. 0 2,000 4,000 6,000 8,000 10,000

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010thousandtons/yr 

### 13

‐ State VOC & NOx Emissions

VOC NOxThe emissions trends for both the 13

‐ state and 3

‐ state regions indicate a reduction in both VOC and NO

x

emissions between 1996 and 2010. NO

x emission decrease at a faster rate than VOC emissions. These

reductions are consistent with the expected reductions in EGUs, area sources, and on

‐ road and non

‐

road sources resulting fleet turnover, equipment replacement, and other controls mandated by CAAA

programs as well as the special rules targeting ozone transport in the eastern U.S. An examination of the

trends in local emissions in recent years also shows a reduction in emissions. Figure 6 provides annual

anthropogenic emission totals for Crittenden County, AR; Shelby County, TN; and DeSoto County, MS for

2005 and 2008. This information was extracted from EPA’s National Emission Inventory (NEI). (Note the

difference in scale for Shelby County). The percent reductions in NOx and VOC are very consistent for

each of the counties and, with a few exceptions, emissions for nearly all source categories are less in

2008 compared to 2005.

Figure 6. Anthropogenic Emissions Totals (tons/year) for the Greater Memphis Area for 2005 and 2008 0 400 800 1,200 1,600 2,000

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010thousandtons/yr 

### 3

‐ State VOC & NOx Emissions

VOC NOx

0 5000 10000 15000 20000 25000 30000 35000 40000 45000



### NOX VOC CO 

### 2005 and 2008 Emissions (tons/yr) for Crittenden

County, AR

2005

2008The regional

‐ scale emissions trends are consistent with the reduction in 8

‐ hour ozone design values

during this period. The local

‐ scale emissions in recent years also show a reduction in ozone precursor

emissions. This indicates that national/regional air quality improvement programs, including those

realized on the local scale, are contributing to the observed ozone reductions in the Memphis area.

Beyond 2010, in addition to the emission reductions expected to be realized by the Regional Haze Rule

and the final version and full implementation of the Cross

‐ State rule for EGUs, other new or updated

standards and regulations to take full effect include those for recreational equipment, lawn & garden

equipment, and gasoline

‐ powered boats and personal watercraft. For the on

‐ road mobile sector, further

emission reductions are expected from fleet turnover and the introduction of cleaner and more fuel

efficient engines mandated by the applicable CAFE standards that are currently in place for cars and

trucks.

It follows that these anticipated future emissions reductions associated with national, regional, and local

air quality improvement programs will lead to further reductions in ozone and design values that are

sufficiently below the standard to achieve sustained attainment of the NAAQS in the near future. 0 5000 10000 15000 20000 25000 30000 35000 40000 45000



### NOX VOC CO 

### 2005 and 2008 Emissions (tons/yr) for DeSoto County, MS

2005

2008

0 50000 100000 150000 200000 250000



### NOX VOC CO 

### 2005 and 2008 Emissions (tons/yr) for Shelby County, TN

2005

2008

## Freque n

Ozone a

A key fac t

nonattai n

County d o

its conclu

in part o n

more det a

conduciv e

County. T

the Natio

Figure 7 i l

October) f

highest o z

the direct

indicates t

of wind s p

Figure 7. S u Season Day s

Winds fr o

season, b u

Figure 8 i l

daily max i

ppb. Aga i

Distinguis

ozone

‐ se a 

## n c y

Anal y s

a t the Fras e

t or in EPA’s r e

n ment area is

o occasionall y

sion that em i

n backward tr

a il and exami

e to transpor t

T his analysis f o

nal Weather

l lustrates the

f or the perio d

z one concent r

ion from whi c

t he frequenc y

p eeds.

u rface Wind Dire c

s (April–Octobe r

m the north,

u t all wind di r

l lustrates the

i mum 8

‐ hour

i n the data ar

hing feature s

a son days, ca n 

## is of Contr

e r Monitor

e commendat

an analysis o

y contribute t

i ssions from C

ajectories de

nes the freq u

t of precurso r

o cusses on t h

Service (NW S

frequency o f

d 1996

‐ 2010.

r ation 6 am ‐

c h the wind i s

y of occurren c

c

tions and Wind

r 1996–2010).

south, and s o

r ections are r e

frequency o f

ozone conce

e for 6 am

– 6

in the wind p

n help to defi n 

## ibutions fr o

ion (EPA, 20 1

o f meteorolo g

t o violations o

C rittenden C o

rived using t h

u ency of occ u

r emissions f r

h e 15

‐ year p e

S ) monitorin g

f wind directi o

Wind data fo

6 pm CST are

s blowing. Th e

c e of a partic u

Speeds at the M e

o uthwest are

e presented.

f wind directi o

ntration at th

6 pm and rep r

p lots for the o

n e the wind a 

## o m Critten d

1 1b) to inclu d

g ical data tha t

o f the 2008 o

o unty contrib

h e HYSPLIT m

u rrence of wi n

r om Crittend e

e riod 1996

‐ 2 0

g site at the M

o ns and spee d

r the hours p r

shown. In th

e length of th e

u lar wind dir e

e mphis NWS St a

most comm o

o ns and spee d

e Frayser mo

r esent the pe

o zone exceed a

a nd/or transp o 

## d en Count y

d e Crittenden

t “indicates t

o zone NAAQS

ute to excee d

m odel. This an

n d directions

e n County to

0 10 and uses h

M emphis Inte r

d s for all ozo n

r ior to and d u

is diagram, t h

e bar within t

e ction. The sh

a tion for the Hou r

o n during the d

d s for all ozo n

nitoring site w

riod April thr o

a nce days, w h

o rt patterns l e 

## y

Emissio n

County in th

hat emission

in Shelby Co

d ances at th e

alysis explor e

(and wind s p

the Frayser m

hourly surfa c

r national Air p

n e season da y

u ring the nor m

h e indicated w

t hat wind

‐ dir e

ading indicat e

r s 6 am – 6 pm C

daytime hou r

n e season da y

w as greater t h

o ugh Octobe r

h en contrast e

eading to hig h 

## n s to High

e Memphis

s from Critte n

unty.” EPA b a

e Frayser mo n

e s this findin g

p eeds) that a r

m onitor in Sh

c e wind data f

p ort.

y s (April thro u

m al period of

w ind directio n

e ction sector

e s the distrib u

C ST for All Ozon e

r s during the o

y s for which t h

h an or equal t

r

, 1996

‐ 2010.

e d to those fo

h ozone. n den

a sed

n itor

g in

r e

elby

f rom

u gh

n is

u tion

e

o zone

h e

t o 75

r allFigure 8. S u

Exceedanc e

In this ca s

from SS W

on high o z

different o

more like l

a westerl y

emission s

county is

and alon g

Most (m o

monitor a

percent) o

pm. To fo

direction s

wind spe e

ozone se a u rface Wind Dire c

Days for the Fr a

s e, wind spee d

W to NNW) ar e

z one days. Th

o n high ozon e

l y to occur an

y component

s from Critte n

considered, t

g I

‐ 70 all of w h

o re than 55 p e

a re based on

o f the daily m

cus on the h o

s and wind s p

e ds leading u

a son days an d c

tions and Wind

a yser Monitoring

d s are lower f

e less frequen

ese results in

e days compa

d are possibl y

(specifically

n den County t

t he range is S

h ich are with

e rcent) of th e

hourly data f o

m aximum 1

‐ h o

o urs leading u

p eeds for the

p to the hou r

d days with m Speeds at the M e Site (April–Octo

f or the high o z

t and easterl y

dicate that t h

red to all ozo

y a contributi n

SW to NW) a

t o the Frayse

W to W, sinc e

in this range

e daily maxi m

o r the hours o

o ur ozone co n

u p to the pea

hours 8 am t o

r s of maximu m

m aximum ozo e mphis NWS St a ber 1996–2010).

z one days. I n

y wind comp o

h e distributio n

ne season da y

n g factor for s

re conducive

r monitor. If t

e most emiss

of direction.

m um 8

‐ hour o z

o f 10 am to 6

n centrations

k ozone con c

o noon was a

m ozone (8 a m

ne concentr a a tion for the Hou r

n addition, w e

o nents (from N

n of wind dir e

ys and that e a

s ome high oz o

to transport

t he location o

s ions are loca t

zone concen t

6 pm. In addi t

occur betwe e

c entrations, t

a lso examine d

m

– noon) ar e

a tions at the F r s 6 am – 6 pm C

e sterly wind c o

N NE to SSE) a

e ctions and w

a sterly wind c

o ne days. No t

of ozone an d

o f emissions s

ted in West M

t rations for t h

t ion, most (m

en the hours

he distributi o

d

. The wind d

e shown in Fi

F rayser moni t C ST for Ozone

o mponents ( w

a re more freq

ind speeds is

c omponents a

t e that wind s

d precursor

s ources withi

M emphis, M a

h e Frayser

ore than 70

of 11 am an d

o n of wind

d irections an d

gure 9 for b o

t oring site. w inds

uent

a re

s with

i n the

a rion,

d 2

d

o th allFigure 9. S u Season Day s

The resul t

there is a

For both p

the W an d

SSE wind s

appear t o

Further e x

reveals t h

or more h

hours of S

during th i

to excee d

consider e

This pote n

relative t o

presente d

in Table 1 u rface Wind Dire c

s and Ozone Ex c

t s for 8 am

–

shift from w e

p eriods consi

d high ozone

s ), and/or no r

o be a determ

x amination o

h at up to 19. 2

h ours of SW t

S W to W win d

i s period, it f o

d ances at the

e d and at mo s

n tial for cont

o other coun t

d by EPA in t h

1

. c tions and Wind

c

eedance Days f o

noon are si m

e sterly to ea s

dered, there

at the Frays e

r therly winds

ining factor f

f the wind di r

2 percent of t h

o NW winds a

d s. Consideri n

o llows that e m

Frayser site o

s t 2.2 days p e

r ibution, ho w

t ies. The 200 8

h e technical s Speeds at the M e

o r the Frayser M o

m ilar to those

s terly wind c o

is no appare n

e r monitor. In

are more lik e

f or ozone exc

r ections on t h

h e exceedan c

a nd that up t o

n g that there

m issions fro m

o n at most 2. 8

e r year if the S

w ever, should

8 emissions f o

upport docu m e mphis NWS St a

o nitoring Site (A p

for all dayti m

o mponents f o

n tly causal r e

fact, low wi n

e ly on ozone

eedances at t

h e exceedan c

c e days that o

o 15.6 perce n

were an ave r

m all of Critte n

8 days per ye

S W to W ran g

also conside

o r Crittenden

m ent for the d a tion for the Hou r

p ril–October 199 6

m e hours in t h

o r high ozone

e lationship b e

n d speeds, e a

exceedance d

t his site.

c e days at th e

o ccurred bet w

n t of the exc e

r age of 14.3 e

n den County

e ar if the SW t

g e is conside r

r the total e m

n

, DeSoto, an d

designation ( r s 8 am – Noon C

6–2010).

h at wind spe e

days at the F

e tween wind s

a sterly wind c

d ays compar e

e Frayser mo n

w een 1996 a n

e edance day s

e xceedance d

had the pot e

t o NW wind d

r ed.

m issions for C

d Shelby Cou n

( EPA, 2011b) ) C ST for All Ozon e

e ds are lower

F rayser moni t

s from the S W

c omponents (

e d to all days

n itoring site

n d 2010 had o

s had one or m

d ays per year

e ntial to cont r

d irection ran g

C rittenden Co

n ties (as

) are summar e

and

t or.

W to

( E to

s and

o ne

m ore

r ibute

g e is

unty

r izedTable 1. 2008 VOC and NO

x Emissions.

Emissions (tpy) % of 3-County Emissions Total

County VOC NO

x VOC NO

x

Crittenden 3,805 4,047 10.3 8.3

DeSoto 5,222 5,080 14.1 10.4

Shelby 27,929 39,519 75.6 81.2

3

‐ County 36,956 48,646

VOC emissions from Crittenden County account for about 10 percent of the emissions for the 3

‐ county

area. NO

x emissions from Crittenden County account for about 8 percent of the total emissions for the

3

‐ county area.

The simple probability analysis in Table 2, couples the wind direction frequency and emissions data. The

analysis estimates the number of exceedance days per year at the Frayser monitoring site with a

potential contribution from emissions from Crittenden County based on wind direction alone, as well as

an adjusted value that accounts for the emissions relative to the overall emissions totals for the area.

The analysis considers two periods: 1996

‐ 2010 and 2001

‐ 2010 and the wind direction range from SW to

NW. The overall percentage of days with SW to NW winds assumes one hour per day with winds from

this direction and is thus a high estimate. The larger of the two emissions fractions comparing emissions

for Crittenden County to the 3

‐ county area (the VOC fraction) is used.

Table 2. Summary of Number of Exceedance Days at the Frayser Monitoring Site with a Potential for Contribution from Emissions

from Crittenden County, Based on Wind Direction Alone and Adjusted for Emissions: Based on SW to NW Winds.

(A) (B) ( C) (D) (E) (F) (G) (H) (I) (J)

Period #

Exceedance

Days # Yrs #

Exceedance

Days/Yr % of

Exceedance

Days with

SW to NW

Wind

Directions

(%) # of

Exceedance

Days/Yr

with a

Potential for

Contribution Fraction of

Exceedance

Days on

Which

Contribution

is Possible Fraction of

Emissions

Represented

by Crittenden

Co Joint

Probability

of

Contribution

Based on

Wind

Direction &

Emissions EmissionsAdjusted #

of

Exceedance

Days/Yr

with a

Potential for

Contribution

1996-

2010 215 15 14.33 19.20 2.75 0.19 0.10 0.02 0.28

2001-

2010 89 10 8.90 19.10 1.70 0.19 0.10 0.02 0.18

Calculated values by column are as follows:

D = B/C (Number of exceedance days per year)

F = D • E/100 (Number of exceedance days with SW to NW winds for at least one daytime hour)

I = G • H (Joint probability defined as fraction of days with SW to NW wind directions multiplied by the emissions fraction for

Crittenden County)

J = D • I (Adjusted number of exceedance days per year with a potential for contribution that accounts for both SW to NW wind

direction frequency and the emission fraction)Considering only wind directions as an indicator of potential contribution, emissions from Crittenden

County may have contributed to exceedances at the Frayser monitor on fewer than three days per year

during the period 1996

‐ 2010 and on fewer than 2 days per year during the period 2001

‐ 2010. As noted

above, the calculated values are conservatively high estimates since they are based on the maximum

number of exceedance days with transport

‐ conducive winds. In both cases, this contribution is not likely

to influence the fourth highest ozone concentration at the Frayser monitor in any given year. Since the

emissions for Crittenden County are small compared to the total emissions for Shelby County and the

three

‐ county area, an adjusted potential for contribution is also calculated based on the joint probability

of 1) wind directions from SW to NW and 2) the likelihood of emissions from Crittenden County being

involved in the ozone formation (based on the relative amount of emissions compared to the entire

area). The adjusted potential for contribution is very small and is estimated to have occurred on less

than one day per year for both periods.

As noted earlier, a majority of the emissions in Crittenden County are located to the west and southwest

of the Frayser monitoring site. Table 3 estimates the number of exceedance days per year at the Frayser

monitoring site with a potential contribution from emissions from Crittenden County for the wind

direction range from SW to W.

Table 3. Summary of Number of Exceedance Days at the Frayser Monitoring Site with a Potential for Contribution from Emissions

from Crittenden County, Based on Wind Direction Alone and Adjusted for Emissions: Based on SW to W Winds.

(A) (B) ( C) (D) (E) (F) (G) (H) (I) (J)

Period #

Exceedance

Days # Yrs #

Exceedance

Days/Yr % of

Exceedance

Days with

SW to NW

Wind

Directions

(%) # of

Exceedance

Days/Yr

with a

Potential for

Contribution Fraction of

Exceedance

Days on

Which

Contribution

is Possible Fraction of

Emissions

Represented

by Crittenden

Co Joint

Probability

of

Contribution

Based on

Wind

Direction &

Emissions EmissionsAdjusted #

of

Exceedance

Days/Yr

with a

Potential for

Contribution

1996-

2010 215 15 14.33 15.60 2.24 0.16 0.10 0.02 0.23

2001-

2010 89 10 8.90 15.40 1.37 0.15 0.10 0.02 0.14

Calculated values by column are as follows:

D = B/C (Number of exceedance days per year)

F = D • E/100 (Number of exceedance days with SW to NW winds for at least one daytime hour)

I = G • H (Joint probability defined as fraction of days with SW to NW wind directions multiplied by the emissions fraction for

Crittenden County)

J = D • I (Adjusted number of exceedance days per year with a potential for contribution that accounts for both SW to NW wind

direction frequency and the emission fraction)

Considering only wind directions as an indicator of potential contribution, emissions from Crittenden

County may have contributed to exceedances at the Frayser monitor on approximately two days per

year during the period 1996

‐ 2010 and approximately one day per year during the period 2001

‐ 2010.

Again, this contribution is not likely to influence the fourth highest ozone concentration at the Frayser

monitor in any given year. For this range of wind directions, the adjusted potential for contribution is

very small and is estimated to have occurred on less than one day per year for both periods.These results are generally consistent with EPA findings (EPA, 2011b) which are based on the use of

HYSPLIT and 2006

‐ 2010 meteorological data. EPA found that most of back trajectories for ozone

exceedance days at the Frayser monitor pass “through Shelby County TN, and many of the back

trajectory centerlines pass through Desoto County in northern Mississippi with a comparatively smaller

percentage passing through Crittenden County, Arkansas.” The current analysis considers a longer

period and quantifies this potential for contribution based on both wind direction and emissions. The

results suggest that the potential for contribution is very small (with a frequency equivalent to much less

than one exceedance day per year).



## Summary

Meteorological conditions on episode days for the Frayser monitor show that Crittenden County

emissions are unlikely to significantly influence ozone concentrations at the Frayser site. Considering

only wind directions as an indicator of potential contribution, emissions from Crittenden County may

have contributed to exceedances at the Frayser monitor on approximately two days per year during the

period 1996

‐ 2010 and approximately one day per year during the period 2001

‐ 2010. The current

analysis considers a longer period and quantifies this potential for contribution based on both wind

direction and emissions. The results suggest that the potential for contribution is very small (with a

frequency equivalent to much less than one exceedance day per year).

All four monitoring sites in the greater Memphis area sites show a clear downward trend in 8

‐ hour

ozone design value for the period 1996

‐ 2010, culminating with values near 75 ppb in 2010. Both the

regional

‐ average design value (based on all four sites) and the regional

‐ maximum design value (based

on all four sites) also indicate a clear downward trend and both values decrease by approximately 1.25

ppb per year during the period. This trend is consistent with a reduction in national, regional, and local

ozone precursor emissions during this same time period. This indicates that national/regional air quality

improvement programs, including those realized on the local scale, are contributing to the observed

ozone reductions in the Memphis area.

Current design values and trends indicate that emission reductions being realized from current and

planned federal measures should result in near

‐ term air quality improvements. The resulting emissions

reductions will lead to further reductions in ozone and design values that are sufficiently below the

standard to achieve sustained attainment of the NAAQS in the near future. The emission reductions

include those expected to be realized by the final version and full implementation of the Cross

‐ State rule

for EGUs, the Regional Haze Rule, as well as new or updated standards and regulations for recreational

equipment, lawn & garden equipment, and gasoline

‐ powered boats and personal watercraft. For the on

‐

road mobile sector, further emission reductions are expected from fleet turnover and the introduction

of cleaner and more fuel efficient engines mandated by the applicable CAFE standards that are currently

in place for cars and trucks.



## References

Douglas, S. G., Y. Wei, J. Mangahas, B. Hudischewskyj, A. Alvarez, G. Glass, S. Hartley, and J. L. Haney.

2004. “Early Action Compact Ozone Modeling Analysis for the State of Tennessee and Adjacent

Areas of Arkansas and Mississippi.” Technical Support Document. ICF International, San Rafael,

California (04

‐ 012).Douglas, S. G., S. Beckmann, B. Hudischewskyj, and J. L. Haney. 2005. “Conceptual Description for 8

‐ Hour

for the Memphis Metropolitan Area.” Prepared for the Arkansas Department of Environmental

Quality. Prepared by ICF International, San Rafael, California (05

‐ 057).

EPA. 2011a. “The Benefits and Costs of the Clean Air Act from 1990 to 2020.”

http://www.epa.gov/oar/sect812/feb11/fullreport.pdf

.

EPA. 2011b. “Arkansas: Area Designations for the 2008 Ozone National Ambient Air Quality Standards.”

http://www.epa.gov/ozonedesignations/2008standards/state.htm

.