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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION III

1650 Arch Street

Philadelphia, Pennsylvania 19103

DATE: September 22, 2011

SUBJECT: Technical Support Document for Determinations of Attainment of the 1997 Fine 

Particle Standard for the Metropolitan Washington, District of ColumbiaMaryland-Virginia (DC-MD-VA) and Martinsburg-Hagerstown, West VirginiaMaryland (WV-MD) Areas

/s/

FROM: Irene Shandruk, Physical Scientist 

Office of Air Program Planning 

TO: File

/s/

THRU: Cristina Fernandez, Associate Director 

Office of Air Program Planning

A. BACKGROUND

In 1997, EPA revised the health-based National Ambient Air Quality Standard (NAAQS) for 

fine particulate matter (PM2.5) , setting it at 15.0 micrograms per cubic meter (ug/m3) based on a 

3-year average of annual mean PM2.5 concentrations, and a 24-hour standard of 65 ug/m3based 

on a 3-year average of the 98th percentile of 24-hour concentrations. EPA established the 

standards based on significant evidence and numerous health studies demonstrating that serious 

health effects are associated with exposures to particulate matter. 

On January 5, 2005 (70 FR 944), EPA finalized its air quality designations and classifications 

across the country with respect to the 1997 PM2.5 standard. These designations became effective 

on April 5, 2005. The Metropolitan Washington, DC-MD-VA and the Martinsburg-Hagerstown, 

WV-MD nonattainment areas were designated nonattainment for the 1997 annual PM2.5

NAAQS. See, 40 CFR part 81.309 (the District), 40 CFR 81.321 (Maryland), 40 CFR 81.347 

(Virginia), and 40 CFR 81.349 (West Virginia). 

The Metropolitan Washington 1997 annual PM2.5 nonattainment area consists of the District of 

Columbia (the District), a Northern Virginia portion (Arlington, Fairfax, Loudoun, and Prince 

William Counties and the cities of Alexandria, Falls Church, Fairfax, Manassas, and Manassas 

Park), and Charles, Frederick, Montgomery, and Prince George’s Counties in Maryland. The 

Martinsburg-Hagerstown 1997 annual PM2.5 nonattainment area consists of Washington County

in Maryland and Berkley County in West Virginia. 

On October 17, 2006 (71 FR 61144), EPA retained the 1997 annual PM2.5 NAAQS at 15 μg/m3
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based on a 3-year average of annual mean PM2.5 concentrations, and promulgated a 24-hour 

standard of 35 μg/m3based on a 3-year average of the 98th percentile of 24-hour concentrations 

(the “2006 24-hour standard”). On November 13, 2009, EPA designated the MartinsburgHagerstown, WV-MD and Metropolitan Washington, DC-MD-VA areas as attainment for the 

2006 24-hour standard (74 FR 58688). In that action, EPA also clarified the designations for the 

NAAQS promulgated in 1997, stating that these geographical Areas were designated as 

nonattainment for the annual standard, but attainment for the 1997 24-hour standard (40 CFR 

part 81.309 for the District, 40 CFR part 81.321 for Maryland, 40 CFR part 81.347 for Virginia,

and 40 CFR part 81.349 for West Virginia). Today’s action, however, does not address 

attainment designations of either the 1997 or the 2006 24-hour standard.

In response to legal challenges of the annual standard promulgated in 2006, the U.S. Court of 

Appeals for the District of Columbia Circuit (D.C. Circuit) remanded this standard to EPA for 

further consideration. See American Farm Bureau Federation and National Pork Producers 

Council, et al. v. EPA, 559 F.3d 512 (D.C. Cir. 2009). However, given that the 1997 and 2006 

annual standards are essentially identical, attainment of the 1997 annual standard would also 

indicate attainment of the remanded 2006 annual standard.

EPA previously made clean data determinations related to the 1997 annual PM2.5 NAAQS for 

each of these Areas pursuant to 40 CFR 51.1004(c). Determinations were made for the 

Metropolitan Washington Area on January 12, 2009 (74 FR 1146) and for the MartinsburgHagerstown Area on November 20, 2009 (74 FR 60199). These clean data determinations

remain in effect.

Under CAA section 179(c), EPA is required to make a determination that a nonattainment area 

has attained by its attainment date, and publish that determination in the Federal Register. The 

determination of attainment is not equivalent to a redesignation, and the states must still meet the 

statutory requirements for redesignation in order for the Areas to be redesignated to attainment. 

Complete, quality-assured, and certified PM2.5 air quality monitoring data recorded in the EPA 

Air Quality System (AQS) database for 2007 through 2009, show that the Metropolitan 

Washington, DC-MD-VA and the Martinsburg-Hagerstown, WV-MD nonattainment areas 

attained the 1997 annual PM2.5 NAAQS by their applicable attainment date of April 5, 2010.

B. EPA EVALUATION

EPA has reviewed the ambient air monitoring data for PM2.5, consistent with the requirements 

contained in 40 CFR part 50 and recorded in the data in the EPA AQS database for the 

Metropolitan Washington, DC-MD-VA and the Martinsburg-Hagerstown, WV-MD 

nonattainment areas for the monitoring period from 2007 through 2009. On the basis of that 

review, EPA has concluded that the area attained the 1997 annual PM2.5 NAAQS based on data 

for the 2007-2009 monitoring period. 

Under EPA regulations at 40 CFR 50.7, the annual primary and secondary PM2.5 standards are 

met when the annual arithmetic mean concentrations, as determined in accordance with 40 CFR 

part 50, appendix N, is less than or equal to 15.0 μg/m3, at all relevant monitoring sites. The 
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values calculated in accordance with 40 CFR part 50, appendix N, are referred to as design 

values, and these values are used to determine if an area is attaining the PM2.5 NAAQS. 

According to the PM2.5 implementation rule, the attainment date for these Areas is April 5, 2010

and the monitoring data from 2007 through 2009 is used to determine if the Areas attained by 

April 5, 2010. 

Data Completeness

A complete year of air quality data comprises four calendar quarters, with each quarter 

containing data from at least 75% capture of the scheduled sampling days. Data that does not 

meet the 75% capture has been analyzed by EPA with substitution of conservative values to 

determine that some sites not meeting capture rates are still sufficient to show attainment. The 

Metropolitan Washington Area contained one such site which had incomplete data: Fairfax 

County Virginia Annandale Site.

As discussed in greater detail below, the Annandale monitor (AQS ID 510591005) was the only 

monitor in the Metropolitan Washington Area without a valid attaining design value for 2007-

2009 due to incomplete data. This monitor has never had a violating design value (DV) but was 

incomplete for 2007-2009 because it had to be removed temporarily from the end of April 2008 

to the middle of June 2008. This temporary removal was due to the roof on which the monitor

was stationed needing replacement.

EPA has reviewed the ambient air monitoring data for PM2.5, consistent with the requirements 

contained in 40 CFR part 50 and recorded in the EPA Air Quality System database for the 

Metropolitan Washington Area from 2007 through the present time. Currently all monitors are 

measuring concentrations averaging well below the annual standard of 15.0 ug/m3. The highest 

DV for the most recent 3 years, 2007-2009, for the Metropolitan Washington Area is 12.4 ug/m3, 

based on monitoring data collected in Maryland at the Bladensburg monitor. All 3-year averages 

of the annual mean PM2.5 concentrations are below the NAAQS from 2007-2009.

In order to determine whether the NAAQS has been attained for the Annandale monitor, AQS ID 

510591005, EPA has applied a recently developed procedure to address the missing data, and 

determine valid design values for the monitor for the annual standard for 2007-2009. EPA’s 

procedure is described in the following section.

Addressing Missing Data

An objective statistical method was developed to determine if monitors that lack complete data 

would have met the NAAQS in subsequent time periods. The Annandale monitor in the 

Metropolitan Washington nonattainment area lacked complete data due to a siting issue.

The general concept behind the statistical method to determine whether an incomplete monitor 

(target) would have met the NAAQS is to establish a linear regression relationship between the 

target monitor and another monitor in the nonattainment area (candidate). The linear regression 

would then be used to fill in the missing data for the target monitor. The results are checked with 

an additional statistical technique, known as bootstrapping, to verify if the conclusion of 
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attainment is correct. The Metropolitan Washington nonattainment area has 16 monitoring 

locations which provide an ample number of monitors to compare to the target monitor.

The monitor of interest in this analysis is the Annandale monitor. This site was temporarily 

removed from April 2008 to June 2008 due to a roof replacement causing an incomplete design 

value of 11.3 μg/m3 for 2007-2009. The goal of this methodology is to appropriately fill in the 

missing data from the second quarter of 2008 to judge whether this location would likely have 

monitored attainment of the NAAQS had the monitor had complete data. The Metroplitan 

Washington Area has a monitoring location with complete data for 2007-2009, which is similar 

enough to warrant comparison to the Annandale monitor.

Concept for Determining Design Values

The concept behind the method for determining a design value for a monitor with incomplete 

data is to establish a linear regression relationship between a target site with incomplete data and 

another site in the Washington, D.C. PM2.5 nonattainment area which has more complete data in 

the period in which the target site is data deficient. The linear regression relationship would be 

based on time periods in which both the target and candidate monitor was operating. The linear 

regression equation developed from the relationship between the target and candidate monitor 

was used to fill in missing data for the target site in any quarter in the most recent three-year 

period that did not have 75 percent completeness based on actual observations, so that the normal 

data completeness requirement of 75 percent of data in each quarter of the three years is met. 

After the missing data for the sites was filled in, the results were verified through an additional 

statistical test. The additional statistical test used, referred to as bootstrapping, examines the 

differences between the predicted fill in concentrations and the actual observed concentrations to 

determine if the design values for the monitors with incomplete data meet the annual NAAQS 

for PM2.5. 

EPA established criteria to assure that the DV for the Annandale monitor in the Metropolitan 

Washington Area, as estimated by the method, was robust enough to allow consideration of the 

results in a weight of evidence decision. EPA established criteria both for the operating period 

of the comparison monitor and for the number of days of samples that the comparison monitor 

and the Annandale monitor have in common. EPA has not established bright lines or specific 

requirements for determining DVs for monitors with less than complete data.

The candidate monitor would have operated during the 3-year period (2007-2009) in the 

Metropolitan Washington PM2.5 nonattainment area in which the target monitor has incomplete 

data in order to establish a significant relationship between the monitors. The candidate monitor 

does not necessarily have to have complete data in all 12 quarters of the 3-year period, but the 

candidate monitor would have enough observations to allow it to be used to fill in enough 

missing days for the target monitor so that the target monitor will end up with at least 75 percent 

completeness in all 12 quarters. 

Pairs of sample data for the target monitor and candidate monitor from the most recent 20-

quarter period of operation of the target monitor was used. The “period of operation” of the 

target monitor was based on the date of the last reported sample from the monitor. The candidate 
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monitor had at least 100 historical sample pairs in common with target monitor during this 

period. When there were more than 100 pairs in the 20-quarter period all available pairs were 

used. In addition to the 100 pairs over the 20-quarters, candidate monitors had at least 20 paired 

days of data in common with the target monitor for each calendar quarter (adding together the 

number of days in a given calendar quarter [Q1, Q2, Q3, or Q4] across the 20-quarter period).

Several candidate sites met the eligibility criteria of 100 pairs over the 20 quarters, and at least 

20 paired days of data in common with the target monitors for each calendar quarter. 

Method for Determining Design Values

Step 1: Organize data and perform linear regression(s) between target monitor and candidate 

monitors.

All the available paired data within the period limit described above was used to develop a linear 

regression to predict target concentrations from candidate concentrations. A regression was 

performed for each possible pairing that met the criteria utilized for 100 data points and 20 data 

points per calendar quarter (across all years) in the most recent 20 quarters for each candidate 

monitor in the Metropolitan Washington PM2.5 nonattainment area. 

Step 2: Select Candidate site

The Metropolitan Washington PM2.5 nonattainment area has a large number of monitors which 

could have been used as candidate sites. Only one candidate monitor (Mclean, AQS ID

51059500) was selected for the Annandale monitor. The follow steps were used to select the 

candidate monitor. 

1) Candidate monitors were placed into order of highest correlation (highest r-squared in 

the linear regression) with the Target. 

2) Using the regression equation relating concentrations at the Target monitor and the 

Candidate monitor, estimates of the 24-hour average concentrations were made at the Target 

monitor for all missing scheduled days in the initially incomplete quarter, in the most recent 

three-year period at the Target. Estimates were only made for days on which a concentration is 

available at the Candidate monitor. Estimates were not made for any days in the quarter for 

which the Target monitor had 75 percent or more complete data initially. The estimates were 

combined with any reported data at the Target monitor in the recent 3-year period and the data 

capture rates were computed for the originally incomplete quarter. The computation of data 

capture rates required an assumption that the required sampling frequency for the Target monitor 

was recorded. If the Candidate monitor had a lower sampling frequency than the Target 

monitor, some missing scheduled days for the Target were not substituted for the regressionbased estimates. When the Candidate monitor had a lower sampling frequency than the Target 

monitor, the Target monitor sampling schedule was assumed to be a combination of the Target 

and Candidate monitors schedules, weighted by the number of originally present and originally 

missing scheduled days at the Target monitor. 
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3) If after performing the process in step 2, the results produce all 12 quarters at the 

Target monitor having at least 75 percent of scheduled values, the Candidate monitor was 

selected as the Candidate for the remaining steps. If 75 percent of the scheduled values for the 

Target monitor were not obtained, step 2 was repeated for the next best correlated site. This 

process was repeated until the Target monitor had 75 percent of its scheduled values.

Step 3: Design Value Computed

The three-year design value was calculated using the actual observations of the Target monitor 

and the regression-based estimates of daily concentrations. The design value for the Annandale 

monitor in the Metropolitan Washington PM2.5 nonattainment area was below the NAAQS.

Step 4: Statistical confidence of a design value below the NAAQS checked

The results of Step 3 showed the design value for the Annandale monitor in the Metropolitan 

Washington PM2.5 nonattainment area to be below the NAAQS. In order to show that there is at 

most a 10 percent probability that the actual design value (had the Annandale monitor operated 

more days) was above the NAAQS, further analysis was performed as follows:

(a) Residuals were calculated from the regression.

(b) A bootstrap analysis was performed, repeating the regression-based substitution in 

Step 2 but adding to each estimated 24-hour value that substitutes for a missing scheduled 

monitored value a plus or minus residual that has been randomly drawn (with 

replacement) from the pool of regression residuals. This step randomly applies real 

residuals from the linear regression to the imputed current-period Target values.

(c) Repeat (b) for a total of 1000 runs. 

(d) For each of the 1000 bootstrap trials, the 3-year design value was calculated. This 

will provide a pseudo confidence interval for the partially imputed current-period design 

value for the Target.

(e) Since none of the 1000 runs resulted in a design value above the NAAQS, the 

Annandale was considered to have met the NAAQS. 

Determining the design value for Annandale monitor AQS ID: 510591005

Steps 1 and 2 were performed with Annandale (AQS ID: 510591005) as the Target monitor. The 

results of the regressions can be found in Figure 2. On Figure 2, the Target monitor is listed as 

Site A. The Candidate site that was used is listed as Site B. The monitor Mclean, (AQS ID: 

510595001), had the highest correlation with Annandale and met the operating period and paired 

data eligibility criteria for being a Candidate site. The results of the regression between the 

Annandale and Mclean monitors is shown in Figure 3. Estimates for the missing data for second 

quarter 2008, were made. As a result of filling in the missing data, the Annandale monitor now 

had 30 days of data for second quarter 2008. A design value of 11.4 g/m3 was calculated for 

the Annandale monitor when the missing data was filled in Figure 4. The statistical confidence 

of the design value was checked using the method outlined in Step 4. The results of the 1000 

bootstrap trials provided the following results: 21 DVs of 11.2 μg/m3, 716 DVs of 11.3 μg/m3, 

260 DVs of 11.4 μg/m3, and 3 DVs of 11.5 μg/m3. None of the 1000 bootstrapping trials 
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resulted in a violating DV, which provides statistical confidence that the Annandale monitor is 

attaining the annual PM2.5 NAAQS.

Metropolitan Washington Annual De si gn Value History

• Two sites ha ve registe red (valid) viola ting DVs since designations.

• Bot h si tes have subsequently posted valid “mee ting NAAQS” DVs.

• A third site (510591005) that ne ver has ha d a violating DV but has had previous valid

“me eting NAAQS” DVs wa s incomplete in 2007-2009. 510591005 isthe Site A.

Figure 1

 Annual desi gnations base d

on 2001-2003 da ta

? Site A

Dist rict Of Co lDi umbst riact o f Colu mbia 110010041 16.5 NA 16.4 NA 15.8 NA 15.1 NA 14.8 in c-a 14.4 A 14.0 A 13 .0 A 12.0 A

Dist rict Of Co lDi umbst riact o f Colu mbia 110010042 15.2 inc-n a 15.3 NA 14.7 inc- a 14.5 A 14.5 A 14.5 A 14.2 A 13 .1 A 12.1 A

Dist rict Of Co lDi umbst riact o f Colu mbia 110010043 15.7 NA 15.6 NA 15.2 NA 14.7 A 14.4 A 14.0 A 13.5 A 12 .5 A 11.6 A

M ar yland M o ntg omery 240313001 13.5 inc-a 13.4 A 12.6 A 12.5 A 12.7 A 12.5 A 12.2 A 11 .4 A 10.7 A

M ar yland P rince Geor ge's 240330001 17.3 NA 17.1 NA 17.2 inc- na 18.5 inc-n a

M ar yland P rince Geor ge's 240330002 12.1 in c-a 11.8 inc- a 11.1 inc-a 10.6 in c-a 9.8 inc- a

M ar yland P rince Geor ge's 240330025 14.1 inc-a 13 .3 in c-a 12.4 A

M ar yland P rince Geor ge's 240330030 12.6 inc-a 13.0 in c-a 12.5 inc- a 12.2 A 11 .4 A 10.5 A

M ar yland P rince Geor ge's 240338001 14.4 inc-a 14.0 in c-a 13.5 inc- a

M ar yland P rince Geor ge's 240338003 15.5 in c-na 14.1 inc- a 13.8 inc-a 13.2 A 13.1 A 12.8 A 11 .9 A 10.8 A

Virg inia A rling ton 510130020 14.5 inc-a 14.8 A 14.6 A 14.5 A 14.6 A 14.2 A 14.0 A 12 .9 A 11.9 A

Virg inia F airfax 510590030 14.0 inc-a 13.9 A 13.6 A 13.4 A 13.6 A 13.4 A 13.0 A 12 .1 A 11.1 A

Virg inia F airfax 510591004 14.6 inc-a 14.6 in c-a 13.9 inc- a

Virg inia F airfax 510591005 13.7 in c-a 13.4 inc- a 13.5 inc-a 13.8 A 13.6 A 13.5 A 12 .4 in c-a 11.3 inc- a

Virg inia F airfax 510595001 14.6 inc-a 14.5 A 14.0 A 13.9 A 14.1 A 13.9 A 13.7 A 12 .7 A 11.7 A

Virg inia L oud oun 511071005 13.6 inc-a 13.8 A 13.6 A 13.5 A 13.9 A 13.6 A 13.2 A 12 .2 A 11.2 A

2002-2004 2004- 2006 2005-2007 200 6-2008

An nua l Design Valu es

2 003-2005 2007- 2009

s tate_ name c oun ty_ name

2000-2002 2001- 2003

site

1999-2001
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Washington Sites and 2007-2009 DVs & Data Capture

•Site 510595001 has the highest correlation with Site A (~ 0.98) and has sufficient paired data to establish a good 

relationship and it does have data available in 2008-Q2 to produce Site A estimates for that quarter. This site is

used as the site B. Both sites are classified as a ‘neighborhood’ measurement scale.

npairsQ1 npairsQ2 npairsQ3 npairsQ4 corr

Washington, D510591005 C-MD-VA510591005 11.3 inc-a 11.3 inc-a 140 133 143 145 1

Washington, D510595001 C-MD-VA510591005 11.3 inc-a 11.7 A 121 119 127 135 0.979208

Washington, D510130020 C-MD-VA510591005 11.3 inc-a 11.9 A 136 130 140 140 0.978532

Washington, D510590030 C-MD-VA510591005 11.3 inc-a 11.1 A 126 124 129 139 0.974824

Washington, D511071005 C-MD-VA510591005 11.3 inc-a 11.2 A 131 128 134 136 0.955308

Washington, D240330030 C-MD-VA510591005 11.3 inc-a 10.5 A 117 113 131 108 0.95002

Washington, D240313001 C-MD-VA510591005 11.3 inc-a 10.7 A 131 127 140 139 0.949089

Washington, D110010043 C-MD-VA510591005 11.3 inc-a 11.6 A 130 129 138 139 0.948051

Washington, D240330025 C-MD-VA510591005 11.3 inc-a 12.4 A 61 71 78 76 0.946811

Washington, D110010041 C-MD-VA510591005 11.3 inc-a 12 A 130 127 140 138 0.939266

Washington, D240338003 C-MD-VA510591005 11.3 inc-a 10.8 A 128 126 127 138 0.938246

Washington, D110010042 C-MD-VA510591005 11.3 inc-a 12.1 A 132 127 140 134 0.919068

Area Site A Site B

DV Site 

A

DV

status

Site A

DV Site 

B

DV

status

Site B

20-quarter look (2005-Q1 - 2009-Q4)

2007 Q1 2007 Q2 2007 Q3 2007 Q4 2008 Q1 2008 Q2 2008 Q3 2008 Q4 2009 Q1 2009 Q2 2009 Q3 2009 Q4

510591005 90% 100% 100% 87% 87% 43% 87% 97% 90% 100% 97% 100%

510595001 87% 87% 90% 97% 90% 97% 94% 100% 97% 100% 93% 94%

510130020 100% 100% 97% 100% 100% 100% 97% 93% 97% 94% 100% 97%

510590030 82% 92% 91% 96% 95% 95% 98% 92% 97% 98% 88% 98%

511071005 90% 97% 90% 87% 97% 100% 97% 93% 100% 100% 93% 100%

240330030 90% 93% 100% 80% 94% 100% 94% 93% 90% 90% 93% 94%

240313001 100% 93% 100% 97% 100% 97% 97% 100% 93% 100% 100% 90%

110010043 86% 96% 96% 93% 96% 92% 97% 91% 92% 97% 99% 93%

240330025 100% 100% 97% 93% 87% 100% 97% 90% 83% 100% 97% 100%

110010041 84% 93% 92% 97% 95% 93% 99% 100% 98% 100% 100% 99%

240338003 100% 100% 90% 100% 97% 97% 100% 97% 100% 97% 93% 100%

110010042 93% 93% 100% 97% 100% 93% 100% 93% 100% 97% 93% 90%

Quarterly Data Capture, 2007-2009

Site B

Site A 

Site B 

Figure 2
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Linear Regression Results

• The computed 510591005 (Site A) – 510595001 (Site B) linear relationship is:

Site A concentration = 0.2826 + 0.9519 * Site B concentration

•The linear regression is 

based on the most recent 5 

years of paired (Site A: Site 

B) data 

•The residuals from this 

model are used in the 

subsequent bootstrapping

v_a

0

10

20

30

40

50

v_b

0 10 20 30 40 50

Figure 3
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Imputation and Resulting Data Capture and DV Recalculation

Before

2008-Q2 is deficient

Incomplete DV is 11.3

After

2008-Q2 is now complete

“Complete” DV is 11.4

Figure 4

After accounting for the data completeness issue in the Metropolitan Washington Area, Table 1 

shows the annual PM2.5 design values for each monitor in the Metropolitan Washington, DCMD-VA and the Martinsburg-Hagerstown, WV-MD areas for the years 2007-2009. All 2007-

2009 design values are below 15.0 μg/m3.
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Table 1. Design Values for the Metropolitan Washington, DC-MD-VA and MartinsburgHagerstown, WV-MD Areas*

State County Monitor ID

2007 

Annual 

Mean

2008 

Annual 

Mean

2009 

Annual 

Mean

Certified

Design 

Value

2007-2009 

(μg/m3)

Metropolitan Washington, DC-VA-MD

DC District of 

Columbia 110010041 13.6 12.0 10.5 12.0

District of 

Columbia 110010042 13.7 12.3 10.1 12.1

District of 

Columbia 110010043 13.0 11.6 10.2 11.6

VA Alexandria No monitor

Arlington 510130020 13.8 12.0 10.1 11.9

Fairfax 510590030 12.5 11.1 9.8 11.1

Farifax County 510591005 13.3 11.2 9.5 11.3

Fairfax 510595001 13.5 11.8 9.7 11.7

Falls Church No monitor

Loudon 511071005 12.8 11.5 9.2 11.2

Manassas No monitor

Manassas Park No monitor

MD Charles No monitor

Frederick No monitor

Montgomery 240313001 11.7 10.8 9.4 10.7

Prince George 240330025 14.1 12.4 10.7 12.4

Prince George 240330030 11.8 10.9 8.7 10.5

Prince George 240338003 12.4 11.2 8.8 10.8

Martinsburg-Hagerstown, WV-MD

WV Berkley 240430009 12.9 11.8 9.7 11.5

MD Washington 540030003 15.6 14.2 12.1 14.0

* The data presented in Table 1 are available at http://www.epa.gov/air/airtrends/values.html.

C. CONCLUSIONS AND RECOMMENDED AGENCY ACTION

Based on data for the 2007-2009 monitoring period, the Metropolitan Washington, DC-MD-VA 

and the Martinsburg-Hagerstown, WV-MD areas have attained the 1997 annual PM2.5 NAAQS 

by the attainment date of April 5, 2010.