UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION III

1650 Arch Street

Philadelphia, Pennsylvania 19103-2029

SUBJECT: Supplement to Technical Support Document 

for Approval and Promulgation of Air Quality 

Implementation Plans; District of Columbia, 

Maryland and Virginia; Attainment 

Demonstration for the 1997 8-Hour Ozone 

National Ambient Air Quality Standard for 

the Washington, DC-MD-VA Moderate 

Nonattainment Area (Docket ID#: EPA-R03-

OAR-2013-0132).

February 12, 2015

FROM: Christopher Cripps /s/

Environmental Engineer (3AP30)

TO: Docket ID#: EPA-R03-OAR-2013-0132

THRU: Marilyn Powers /s/

Acting Associate Director, 

Office of Air Program Planning 

This technical support document (TSD)1is a supplement to the “Technical Support 

Document for Approval and Promulgation of Air Quality Implementation Plans; District of 

Columbia, Maryland and Virginia; Attainment Demonstration for the 1997 8-Hour Ozone 

National Ambient Air Quality Standard for the Washington, DC-MD-VA Moderate 

Nonattainment Area (Docket ID#: EPA-R03-OAR-2013-0132)” dated February 26, 2013

docketed at www.rgeulations.gov as document number EPA-R03- EPA-R03-OAR-2013-0132-

0006 in docket number EPA-R03-OAR-2013-0132. 

I. Background & Scope

A. Background

 

1 This document is called the “Attainment TSD” in the notice of proposed rulemaking for which this document was 

prepared. 
2

In a March 20, 2013 (78 FR 17161) notice of proposed rulemaking (the “March 20, 2013 

NPR”), EPA proposed to approve SIP revisions submitted during June 2007 by the District of 

Columbia, the State of Maryland and the Commonwealth of Virginia. 

The Washington DC-MD-VA ozone nonattainment area (the Washington Area) is 

classified as Moderate nonattainment under the 1997 ozone national ambient air quality standard 

(1997 NAAQS) found in 40 CFR 50.10. 

In the rulemaking docket for this action was the “Technical Support Document for 

Approval and Promulgation of Air Quality Implementation Plans; District of Columbia, 

Maryland and Virginia; Attainment Demonstration for the 1997 8-Hour Ozone National Ambient 

Air Quality Standard for the Washington, DC-MD-VA Moderate Nonattainment Area,” dated 

February 26, 2013 (February 26, 2013 TSD). 

Further details on the content of these June 2007 SIP revisions and the March 20, 2013

NPR can be found in the docket for this action. Refer to item numbers EPA-R03-OAR-2013-

0132-0001 (the March 20, 2013 NPR) and EPA-R03-OAR-2013-0132-0006 (the February 26, 

2013 TSD) in docket EPA-R03-OAR-2013-0132.

B. Scope

This TSD is to:

(1) Update the actual monitored design values for the presented in the February 26, 2013 

TSD. EPA has concluded that air quality (AQ) monitoring data beyond the attainment date is 

less important in considering trends for purposes of determining whether the area would attain by 

the attainment date. However, while EPA did note air quality monitoring data and the associated 

design values beyond 2008-2010, we did so only for informative purposes, and this data cannot 

play a role in EPA’s determination that the modeled attainment demonstration supported 

attainment of the NAAQS by June 2010. For the same reason, that is, for informational purposes 

only, EPA has examined certified ambient AQ monitoring data from EPA’s Air Quality System 

(AQS) ambient AQ monitoring database and computed design values through the 2012-2014 

period.

(2) Compare the differences between modeled 2009 design values versus actual 

monitored 2010-2012 design values for the purposes of responding to certain comments.

II. Design Values for 2010 through 2013

A. Design Values

For the 1997 ozone NAAQS, the primary and secondary ozone ambient air quality 

standards are met at an ambient air quality monitoring site when the 3-year average of the annual 

fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.084

ppm.2

 

2 See 40 CFR Part 50.9 and Appendix I thereto.
3

For the 2008 ozone NAAQS, the primary and secondary O3 ambient air quality standards 

are met at an ambient air quality monitoring site when the 3-year average of the annual fourthhighest daily maximum 8-hour average O3 concentration is less than or equal to 0.075 ppm.3

 

The design value for either the 1997 or 2008 ozone NAAQS is the 3-year average of the 

annual fourth-highest daily maximum 8-hour average ozone concentration at an ambient air 

quality monitoring site and therefore is used to determine compliance with the NAAQS.

EPA chose to set the form of the 1997 ozone NAAQS as a three year average to 

minimize year-to-year impacts of extreme meteorological events that are conducive to ozone 

formation and vice versa. The Administrator adopted the Clean Air Scientific Advisory 

Committee’s recommendation that “a more robust, concentration-based form would minimize 

such instability and provide some insulation from the impacts of extreme meteorological events 

that are conducive to [ozone] formation.” See 62 FR 38856, 38868 (July 18, 1997). The form of 

the 1997 ozone NAAQS is intended to minimize the effect of not only those years with more 

extreme meteorological events conducive to ozone formation but also those years with more 

meteorological events not conducive to ozone formation. 

B. Design Values used in the March 20, 2013 NPR:

The latest design values available for the March 20, 2013 NPR were for the 2009 to 2011 

period. These were tabulated in Section III C. “Actual Ozone Design Values” of the February 

26, 2013 TSD.

4

 

C. Actual Ozone Design Values After 2009 to 2011.

The recent actual design values based upon AQ monitoring data for the Washington Area 

have been below the 84 ppb (0.08 ppm) 1997 ozone NAAQS. This AQ monitoring data is from 

EPA’s AQS and are those certified by the states. These values are shown in Table 1:

Table 1. Actual Monitored Design Values 2010 to 2013.

Site Data

Actual Monitored Design 

Values (ppb)

AIRS ID Site Name Jurisdiction State 

2008-

2010

2009-

2011

2010-

2012

2011-

2013

11-001-0025 Takoma * District of Columbia --- 75 I I I

11-001-0041 River Terrace District of Columbia --- 77 76 80 72

11-001-0043 McMillan * District of Columbia --- 79 79 84 79

11-001-0050 Takoma Rec. 

Center* 

District of Columbia --- ND ND ND I

 

3 See 40 CFR Part 50.15 and Appendix P thereto.

4 The February 26, 2013 TSD apparently had two parts of Section III identified as sub-section “C.” The citation here 

is to the second.
4

24-009-0010 Calvert Calvert MD 77 79 83 77

24-017-0010 Southern MD Charles MD 75 77 83 77

24-021-0037 Frederick 

Municipal Airport

Frederick MD 76 76 79 74

24-031-3001 Rockville Montgomery MD 74 76 77 74

24-033-0030 HU-Beltsville Prince George's MD 79 79 82 76

24-033-8003 PG Equestrian 

Center 

Prince George's MD 77 79 87 81

51-013-0020 Aurora Hills Arlington County VA 79 80 86 79

51-059-0005 Chantilly Fairfax County VA I I I I

51-059-0018 Mount Vernon Fairfax County VA I I I I

51-059-0030 Franconia Fairfax County VA 81 82 86 79

51-059-1005 Annandale Fairfax County VA I I I I

51-059-5001 McLean Fairfax County VA I I I I

51-107-1005 Ashburn Loudoun County VA 75 73 75 71

51-153-0009 Long Park Prince William 

County

VA 70 69 72 69

51-510-0009 Alexandria Alexandria City VA 74 77 83 I

Notes:

An “I” in a design value column means there was not 3 years of complete AQ monitoring data which is required to 

compute a design value according to 40 CFR Part 50.10 and Appendix I thereto. 

An “ND” in a design value column means that because the monitor was not in operation during this period there was 

not 3 years of complete AQ monitoring data which is required to compute a design value according to 40 CFR Part 

50.10 and Appendix I thereto.

An underlined value indicates the highest actual monitored value which represents the “Design Value” for the entire 

Washington Area.

Sources:

The 2008 to 2010 design values are from Table 1 or 2 from the notice of proposed rulemaking (76 FR 58206 at 

58208-58209, September 20, 2011) for the February 28, 2012 (77 FR 11739) final rule regarding two determinations 

about the status of the Washington Area under 1997 ozone NAAQS.

The 2009-2011 and later period design values are from:

“Ozone Detailed Information (excel file Ozone_DesignValues_20112013_FINAL_08_01_14, 560k) - Last 

Updated: 8/1/2014, AQS Data Retrieval: 6/24/2014 downloaded from http://www.epa.gov/airtrends/values.html on 

August 21, 2014. 

All design values in the original sources have been converted from ppm to ppb by multiplying the design value in 

ppm by the conversion factor 1000 ppb/ppm.

* Takoma Recreation Center monitoring station (located at 301 Van Buren Street) has been in operation since 

January 2013. This station was established as a replacement site for Takoma School station (11-001-0025) which 

had ceased operations in 2011 because of a fire incident. 

In January 2011, the McMillan site has expanded into an NCore network monitoring station.

Source: District of Columbia, 2013 Annual Ambient Air Monitoring Network Plan May 13, 2013 (Draft). A copy 

is attached to this document. This document is also available on-line at 

http://www.epa.gov/ttn/amtic/files/networkplans/DC2013Plan.pdf. 
5

D. Preliminary AQ Monitoring Data for the 2014 Ozone Season:

EPA has also examined available 2014 ozone season AQ monitoring data. EPA notes 

that this AQ monitoring data is preliminary, that is, it has not undergone all the quality 

assurance/quality control review and certification necessary to be used for regulatory purposes 

and does not cover the entire 2014 ozone season for the Washington Area which ends October 

31, 2014. See Table D-3 “Ozone Monitoring Season by State” in Appendix D to 40 CFR Part 

58. EPA examined the AQ monitoring data entered into EPA’s AQS to date. 

The following tables present: (1) the 2012 and 2013 ozone season 4th maximum seasonal 

values that have been already certified and for the 2014 ozone season the values entered into 

AQS as of February 10, 2015; and, (2) the percentage of valid days for each year as of February 

10, 2015. 

The design value is the computed 3-year average of the annual fourth-highest daily 

maximum 8-hour average ozone concentrations (Season 4th Maximum in the following table) 

shall be expressed to three decimal places (the remaining digits to the right are truncated). See

sections 2.2 and 3.0 of Appendix I to 40 CFR 50.10.

Table 2. Preliminary Monitored Design Values for the Period 2012 to 2014.

Site Data Season 4th Maximum Design 

Value**

AIRS ID Site Name Jurisdiction State 2012* 2013* 2014** 2012-

2014

11-001-0025 Takoma District of 

Columbia --- ND ND ND ND

11-001-0041 River Terrace District of 

Columbia --- 76 62 ND I

11-001-0043 McMillan NCORE District of 

Columbia --- 87 66 68 73

11-001-0050

Takoma Recreation 

Center (301 Van Buren 

Street)

District of 

Columbia --- ND 66 69 I

24-009-0010 Calvert Calvert MD 82 67 70 73

24-017-0010 Southern MD Charles MD 84 64 67 71

24-021-0037 Frederick Municipal 

Airpt. Frederick MD 78 69 63 70

24-031-3001 Rockville Montgomery MD 73 69 64 68

24-033-0030 HU-Beltsville Prince George's MD 79 68 65 70

24-033-8003 PG Equestrian Center Prince George's MD 90 69 69 76

24-033-9991 Powder Mill Rd, Laurel Prince George's MD 84 72 69 75 (ID)

51-013-0020 Aurora Hills Arlington County VA 84 67 71 74

51-059-0030 Franconia Fairfax County VA 84 67 69 73

51-107-1005 Ashburn Loudoun County VA 73 66 63 67

51-153-0009 Long Park Prince William 

County VA 72 66 62 66

51-510-0009 Alexandria Alexandria City VA 86 ND ND ND
6

51-510-0021 3200 Colvin Street*** Alexandria VA 56 63 ND ND

Notes:

An “I” in a design value column means there was not 3 years of complete AQ monitoring data which is 

required to compute a design value according to 40 CFR Part 5010 and Appendix I thereto. 

An “ND” in a design value column means that because the monitor was not in operation during this period 

there was not 3 years of complete AQ monitoring data which is required to compute a design value according 

to 40 CFR Part 5010 and Appendix I thereto.

An “ID” in a cell indicates that the seasonal AQ monitoring data and/or the 3 years of AQ monitoring data do 

not meet the minimum data requirements of 40 CFR 50.10, Appendix I.

* Certified AQ monitoring data.

** Preliminary AQ monitoring data which may not be final before May 1, 2015. Therefore the 2012-2014 Design Values 

are preliminary.

*** The Alexandria City monitor (ID# 51-510-0009 at 517 N Saint Asaph St.) in Virginia ceased operations on August 21, 

2012 due to closure of the building in which it was located. The ozone monitors (and other monitors for other pollutants) 

were relocated to 3200 Colvin Street (as ID # 51-510-0021). But, the ozone monitor has been designated a special purpose 

monitor (SPM) due to numerous interferences at this location. Source: Letter dated June 14, 2013 from David K. Paylor, 

Director, re: Virginia Annual Air Quality Network review (copy attached to this document) Also available on-line at 

http://www.epa.gov/ttn/amtic/files/networkplans/VA2013Plan.pdf. EPA Administrator will not base a NAAQS violation 

determination for ozone NAAQS solely the on AQ monitoring data from the SPM when the SPM is discontinued within 24 

months of start-up (See 40 CFR 58.20(d). 

Sources:

The 2012, 2013 and (preliminary) 2014 AQ monitoring data are from http://www.epa.gov/airdata/ad_rep_mon.html:

Selecting Ozone under 1. Pollutant

Selecting “Washington-Arlington-Alexandria, DC-VA-MD-WV” as a Select a City (defined as a CBSA) under 3. 

Geographic Area

Selecting 2011, 2012, 2013 or 2014, as appropriate, under 2. Year.

Selecting “Include exceptional events data” under 4. Exceptional Events.

Files were downloaded as using “Download PDF (printable page)” in the format 

“Ozone_monitor_report_20YY.pdf” where “YY” is the year (11, 12, 13 or 14). These data files downloaded on August 22, 

2014 for the 2011 through 2013 AQ monitoring data and on February 10, 2015 for the 2014 ([preliminary) AQ monitoring 

data (as file Ozone_monitor_report_2014 2-10-2015.pdf). 

This selection of CBSA will also return AQ monitoring data for two monitors that are NOT in the Washington Area: (1) 

That in Fauquier County, VA (ID # 51-061-0002); and, that in Stafford County, VA (ID # 51-179-0001).

Table 3. Seasonal and 3-year Average AQ Monitoring Data Completeness 2012 to 

2014.

Site Data Percent Valid days Average 

%

AIRS ID Site Name Jurisdiction State 2012* 2013* 2014** 2012-

2014

11-001-0025 Takoma District of 

Columbia --- ND ND ND ND

11-001-0041 River Terrace District of 

Columbia --- 98% 99% ND I

11-001-0043 McMillan NCORE District of 

Columbia --- 100% 99% 99% 99%
7

11-001-0050

Takoma Recreation 

Center (301 Van Buren 

Street)

District of 

Columbia --- ND 42% 98% I

24-009-0010 Calvert Calvert MD 98% 99% 100% 99%

24-017-0010 Southern MD Charles MD 90% 90% 97% 92%

24-021-0037 Frederick Municipal 

Airpt. Frederick MD 92% 97% 82% 90%

24-031-3001 Rockville Montgomery MD 98% 98% 99% 98%

24-033-0030 HU-Beltsville Prince George's MD 100% 100% 99% 100%

24-033-8003 PG Equestrian Center Prince George's MD 97% 100% 98% 98%

24-033-9991 Powder Mill Rd, 

Laurel*** Prince George's MD 88% 82% 86% 85%

51-013-0020 Aurora Hills Arlington County VA 99% 99% 85% 94%

51-059-0030 Franconia Fairfax County VA 98% 99% 85% 94%

51-107-

1005 Ashburn Loudoun County VA 99% 100% 85% 95%

51-153-

0009 Long Park Prince William County VA 99% 100% 86% 95%

51-510-

0009 Alexandria Alexandria City VA 64% ND ND I

51-510-

0021 3200 Colvin Street Alexandria VA 29% 91% ND I

An “I” or “ND” is the same as in the preceding table.

* Certified AQ monitoring data.

** Preliminary AQ monitoring data which may not be final before May 1, 2015 and may not reflect all monitored values. 

States are not required to report AQ monitoring data to AQS before 90 days after the end of the quarterly reporting period. 

Thus the August through September 2014 (3rd quarter) and October 2014 (4th quarter of 2014 is October 1st to December 

31st) AQ monitoring data may not have been reported to date because this AQ monitoring data are due not before 

December 31, 2014 and before March 31, 2015, respectively. Therefore the 2012-2014 percent valid day averages are 

preliminary. See 40 CFR 58.16(b).

*** Also known as the “Beltsville” site. This is a “CASTNET” (Clean Air Status and Trends Network) site operated by 

EPA. See http://www.epa.gov/castnet/javaweb/site_pages/BEL116.html In 2011 EPA upgraded all ozone monitoring 

equipment at CASTNET sites to comply with the requirements in 40 Code of Federal Regulations (CFR) Part 58. Each 

CASTNET site that measures hourly ozone meets the additional audit requirements and complies with the data reporting 

deadlines set forth in the CFR (http://epa.gov/castnet/javaweb/ozone.html). 

Sources: See preceding table.

The highlighted5data in Tables 2 and 3 above indicate data periods which do not meet 

the minimum AQ monitoring data requirements of 40 CFR 50.9 and Appendix I thereto. 

Sections 2.3 (b) and (c) set forth the minimum requirements for AQ monitoring data

completeness in order to make a valid comparison with the 1997 ozone NAAQS (of 40 CFR 

50.9):

 

5 The highlighting is yellow if the table are printed or copied using a device capable of printing/copying in color; 

otherwise, the highlighting will be grey.
8

§2.3 “(b) This comparison shall be based on three consecutive, complete calendar years 

of air quality monitoring data. This requirement is met for the three year period at a monitoring 

site if daily maximum 8-hour average concentrations are available for at least 90%, on average, 

of the days during the designated ozone monitoring season, with a minimum data completeness 

in any one year of at least 75% of the designated sampling days. When computing whether the 

minimum data completeness requirements have been met, meteorological or ambient data may 

be sufficient to demonstrate that meteorological conditions on missing days were not conducive 

to concentrations above the level of the standard. Missing days assumed less than the level of the 

standard are counted for the purpose of meeting the data completeness requirement, subject to 

the approval of the appropriate Regional Administrator.”

§2.3 “(c) Years with concentrations greater than the level of the standard shall not be 

ignored on the ground that they have less than complete data. Thus, in computing the 3-year 

average fourth maximum concentration, calendar years with less than 75% data completeness 

shall be included in the computation if the average annual fourth maximum 8-hour concentration 

is greater than the level of the standard.”

The monitor at Powder Mill Rd, Laurel, MD does not meet the three-year average of 90%

requirement. 

E. Conclusions on Recent Air Quality Monitoring Data:

1. AQ Monitoring Data Through 2013

As the commenters on the March 20, 2013 NPR noted, dropping the 2009 AQ monitoring 

data and adding the 2012 ozone season AQ monitoring data had the effect of raising ozone 

design values. This raised some design values above the 84 ppb effective level of the 1997 

ozone NAAQS. As shown in Table 1 above, the increases ranged between 1 to 8 ppb. 

However, the 2011-2013 design values dropped nearly as dramatically as the 2010-2012 

rose. At the monitors violating the 1997 ozone NAAQS based upon 2010-2012 AQ monitoring 

data, their 2011-2013 design values fell 6 to 7 ppb. Of the other monitors not violating the 1997 

ozone NAAQS based upon 2010-2012 AQ monitoring data, their 2011-2013 design values fell 3 

to 8 ppb. Only one monitor, that at the Prince George's (PG) Equestrian Center in Prince 

George's County, Maryland had a design value over 80 ppb at 81 ppb. 

Air quality data beyond the attainment date is less important in considering trends for 

purposes of determining whether the area would attain by the attainment date. EPA notes that air 

quality data for years after the applicable attainment date is not determinative of, nor relevant to, 

whether the Area attained by its applicable attainment date, which is the requirement against 

which we evaluate attainment demonstrations for compliance with requirements in CAA sections 

172 and 182. In the March 20, 2013 NPR, EPA summarized the reasons for approving the 

attainment demonstrations in the June 2007 SIP revisions, including recent ozone design value 

trends and the Washington Area’s attainment of the standard by 2010. However, while EPA did 

note air quality monitoring data and the associated design values beyond 2008-2010, we did so 

only for informative purposes, and this data cannot play a role in EPA’s determination that the 
9

modeled attainment demonstration supported attainment of the NAAQS by June 2010. For the 

same reason, that is, for informational purposes only, EPA has examined certified AQ 

monitoring data from AQS and computed design values through the 2012-2013 period.

2. 2014 Air Quality Monitoring Data Conclusions:

Until the 2014 AQ monitoring data is fully entered into AQS and certified, final

comparisons with the 1997 ozone NAAQS cannot be made. However, the available AQ 

monitoring data indicates that design values will drop further. Based upon 2011-2013 AQ 

monitoring data, seven monitors violated the 2008 ozone NAAQS of 0.075 ppm (= 75 ppb) with 

design values of 77 to 81 ppb. 

Based upon preliminary 2014 AQ monitoring data, the number of monitors violating the 

more stringent 2008 ozone NAAQS is expected to drop to 1 monitor; that monitor is located at 

the Prince George's (PG) Equestrian Center in Prince George's County, Maryland which a 

projected 2014 design value of just 76 ppb. Overall, decreases on the order of 3 to 6 ppb can be 

expected.6 For informational purposes only, EPA has examined certified AQ monitoring data 

from AQS and computed a preliminary design value for the 2012-2013 period.

III. Other tables

A. Comparison of Modeled Design Values to Actual Design Values for 2009, 2012 and 2013

EPA did compare the modeled design values to the actual design values based upon AQ 

monitoring data. This comparison is found in Table 2 “Modeled Predicted 2009 Design Values 

versus Actual Monitored Design Values” in the February 26, 2013 TSD. The model-predicted 

design values were those obtained by the modeled attainment test using EPA’s preferred method 

for computing a modeling baseline design value and for a modeled relative reduction factor for 

each monitor. The model-predicted design values indicated only two monitors will be at or 

slightly above 84 parts per billion (ppb). These monitors were those at the Aurora Hills and 

Mount Vernon sites. A comparison of actual monitored design values and model-predicted 

design values for only four sites was presented in Table 2. These four sites were those with the 

four highest 2009 model-predicted design values. At the very least, this comparison showed that 

the actual attainment year design values were below the model-predicted values but, more 

significantly, were below the 1997 ozone NAAQS of 84 ppb. 

At the time EPA issued the March 20, 2012 NPR, EPA did not have certified 2012 or 2013 AQ 

monitoring data. Therefore, at the time EPA proposed to approve the June 2007 SIP revisions, 

the ozone air quality as expressed as design values, did show a downward trend at least through 

the attainment year period of 2007-2009, during which the Washington Area attained the 1997 

ozone NAAQS by the attainment date applicable under section 181 of the CAA. (As the 

commenters point out the trends for the 2008-2009 and 2009-2011 periods show gradual creep 

 

6 This assumes a 73 ppb design value for the McMillan NCORE monitor assuming the COG 4th daily maxima of 68 

ppb versus the AQS value of 43 ppb.
10

upwards.) Now that the 2012 and 2013 AQ monitoring data is available, the 2012 air quality design values show a sharp spike and

indeed are close to some of the maximum predicted values in the WOE analyses but not necessarily at the same monitors. In Table A4 “Minimum and Maximum predicted 2009 design values” of Appendix A to the February 26, 2014 TSD, the highest possible design

values predicted by modeling after consideration of alternative base line design values and variations in determining RRFs were 88.4 

ppb for the Aurora Hills monitor and 85.7 ppb or slightly less for 3 other monitors (Mount Vernon, Fairfax County, VA (ID #51-059-

0018); Franconia, Fairfax County, VA (ID# 51-059-0030) and McMillan Reservoir (NCORE),District of Columbia (ID# 11-001-

0043).7 However, based upon the 2011-2013 AQ monitoring data (and the 2012-2014 AQ monitoring data based upon the 

preliminary 2014 AQ monitoring data), the Washington Area is once again attaining the 1997 ozone NAAQS.

Table 4 below shows a comparison of model-predicted design values and actual design values based upon monitored AQ 

monitoring data for all monitors in the Washington Area. The model-predicted values are the “EPA preferred method” 2009 modelpredicted design values and the maximum predicted design value using alternative base line design values and RRFs.

Table 4. Modeled 2009 Design Values versus Actual Monitored Design Values 2009 to 2013.

Site Data 2009 

Preferred 

Modeled 

DV #1

2009 

Max 

Modeled 

DV #2

Actual Monitored Design Values (ppb)

AIRS ID Site Name Jurisdiction State 2007-

2009

2008-

2010

2009-

2011

2010-

2012

2011-

2013

11-001-

0025 Takoma District of Columbia DC 79.1 79.1 77 75 I I I

11-001-

0041 River Terrace District of Columbia DC 78.6 83.6 78 77 76 80 72

11-001-

0043 McMillan District of Columbia DC 81.9 85.4 80 79 79 84 79

24-009-

0010 Calvert Calvert County MD ND ND 74 77 79 83 77

24-017-

0010 Southern MD Charles County MD 75.1 76 75 75 77 83 77

24-021-

0037 

Frederick Municipal 

Airport Frederick County MD 73.9 74.4 76 76 76 79 74

 

7 This “maximum” model-predicted design value resulted from the method for determining base line design values and RRFs which yielded the highest modelpredicted design value discussed in section 10.5.9 “Alternative Design Value Calculation Techniques” in document ID# EPA-R03-OAR-2013-0132-0005 in the 

docket for this action. 
11

24-031-

3001 Rockville Montgomery County MD 76.4 77.5 78 74 76 77 74

24-033-

0002 Greenbelt Prince George's County MD 81.7 81.7 78 79 79 82 76

24-033-

8003 

PG Equestrian 

Center 

Prince George's 

County MD 81.3 81.9 78 77 79 87 81

51-013-

0020 Aurora Hills Arlington County VA 86.2 88.4 79 79 80 86 79

51-059-

0005 Chantilly Fairfax County VA 75.4 79 73 I I I I

51-059-

0018 Mount Vernon Fairfax County VA 85.4 85.7 80 I I I I

51-059-

0030 Franconia Fairfax County VA 83.6 85.4 80 81 82 86 79

51-059-

1005 Annandale Fairfax County VA 82.7 82.7 78 I I I I

51-059-

5001 McLean Fairfax County VA 77.7 77.7 77 I I I I

51-107-

1005 Ashburn Loudoun County VA 78.2 80.4 77 75 73 75 71

51-153-

0009 Long Park Prince William County VA 74 75.8 71 70 69 72 69

51-510-

0009 Alexandria Alexandria City VA 79.5 81.2 75 74 77 83 I

Notes: #1. 2009 Model-predicted design value (DV) using EPA Methods: DVB times EPA RRF from Table 10-5. Modeling Attainment Test Using EPA 

Preferred Methodology in PLAN TO IMPROVE AIR QUALITY IN THE WASHINGTON, DC-MD-VA REGION dated May 23, 2007 (Page 10-11) Column 

labeled "DVF." Document number EPA-R03-OAR-2013-0132-0005 in the docket for this action available at www.regulations.gov. 

#2. From far right hand column labeled "N Maximum" Table A-4 "Minimum and Maximum predicted 2009 design values from Table A-3" in Appendix A to 

the February 26, 2013 TSD.

Of note are the three monitors which violated the 1997 ozone NAAQS based upon 2010-2012 AQ monitoring data and the McMillian 

NCORE monitor which was the only other current monitor for which a maximum predicted design value was 85 ppb or higher. As can 

be seen in Table 6, for the Aurora Hills and Franconia monitors the actual 2010-2012 design values are within 1 ppb of the EPA 

preferred method design value and the maximum predicted design vale, respectively. The same is essentially true for the McMillian 

NCORE site because actual 2010-2012 design value is between the EPA preferred method and maximum predicted design values. In 
12

contrast, the model-predicted design value for the PG Equestrian Center monitor does not match 

well with the 2010-2012 actual monitored design value. The actual 2012 design value is much 

higher.

B. Differences between Modeled 2009 Design Values versus Actual Monitored 2010-2012 

Design Values

Table 5 compares the differences between modeled 2009 design values versus actual 

monitored 2010-2012 design values. The differences are shown in columns 8 and 9. The 

difference in column 8 is the difference between the actual 2010-2012 design value and the 

model-predicted design value using the EPA preferred method for determining base line design 

values and RRFs. The difference in column 9 is the difference between the actual 2010-2012 

design value and the model-predicted design value using the method for determining base line 

design values and RRFs which yielded the highest model-predicted design value. In both 

columns 8 and 9, a positive value means the model-predicted DV was less than the actual 2010-

2012 DV (an “under-prediction”), and a negative value means that the model-predicted DV was 

greater than the actual 2010-2012 DV (an “over-prediction”).

Table 5. Difference Between Modeled 2009 Design Values versus Actual Monitored 2010-2012 Design Value 

1 2 3 4 5 6 7 8 9

Site Data

2009 Preferred

Modeled DV 1

2009 

Max 

Modeled 

DV 2

Actual 

DV 

2010-

2012

Column 

7 minus 

column 

5

Column 

7 minus 

column 

6

AIRS ID Site Name Jurisdiction State 

11-001-

0041 River Terrace District of Columbia DC 78.6 83.6 80 1.4 -3.6

11-001-

0043 McMillan District of Columbia DC 81.9 85.4 84 2.1 -1.4

24-017-

0010 Southern MD Charles Co. MD 75.1 76 83 7.9 7

24-021-

0037 

Frederick 

Municipal 

Airport

Frederick Co. MD 73.9 74.4 79 5.1 4.6

24-031-

3001 Rockville Montgomery Co. MD 76.4 77.5 77 0.6 -0.5

24-033-

0002 Greenbelt Prince George'sCo. MD 81.7 81.7 82 0.3 0.3

24-033-

8003 

PG Equestrian 

Center 

Prince George's 

Co. MD 81.3 81.9 87 5.7 5.1

51-013-

0020 Aurora Hills Arlington Co. VA 86.2 88.4 86 -0.2 -2.4

51-059-

0030 Franconia Fairfax Co. VA 83.6 85.4 86 2.4 0.6

51-107-

1005 Ashburn Loudoun Co. VA 78.2 80.4 75 -3.2 -5.4
13

51-153-

0009 Long Park Prince William Co. VA 74 75.8 72 -2 -3.8

51-510-

0009 Alexandria Alexandria City VA 79.5 81.2 83 3.5 1.8

As can be seen in Table 5, there is a vast spread of predictions versus 2010-2012 actual 

design values. The three worst “under-predictions” were at the Southern MD, Frederick 

Municipal Airport and the PG Equestrian Center sites. Of these, the first two did not violate the 

1997 ozone NAAQS based upon 2010-2012 AQ monitoring data. The two worst “overpredictions” were for the Ashburn and Long Park sites and these two sites did not violate the 

1997 ozone NAAQS based upon 2010-2012 AQ monitoring data. The rest of the monitoring 

sites fall somewhere in between.

EPA does not dispute that weather plays an important role in the severity of ozone 

formation. Certainly, the 2010-2012 period was more conducive to ozone formation that prior 

periods after 2007-2009 and the later 2011-2013 period (and the current 2012-2014 period based 

upon the preliminary 2014 AQ monitoring data). However, EPA cannot say 2012 weather 

conditions are more typical of the 2002 year than other periods because in part the commenters 

did not provide any weather related statistics such as number of days during which the 

temperature exceeded some threshold such as 90 degrees Fahrenheit for comparison to other 

periods or years. And in any case, whether or not 2012 meteorology are more similar to 2002 

meteorology as opposed to 2009 meteorology or whether or not 2012 meteorology is more 

conducive to ozone formation than 2009 meteorology, EPA believes that these considerations do 

not bar EPA approval of the June 2007 SIPs. 

While the 2010-2012 air quality design value does show an increase over the design 

values EPA previously considered, EPA continues to believe the AQ monitoring data for the 

Washington Area supports our approval of the June 2007 SIP revisions as the 2011-2013 design 

value (and the 2012-2014 design value based upon the preliminary 2014 AQ monitoring data) 

shows the Washington Area is attaining the 1997 ozone NAAQS. EPA has examined ozone 

design values for the Washington Area for 2011 – 2013 and has examined preliminary AQ 

monitoring data for 2014 which demonstrate the Washington Area continues to attain the 1997 

ozone NAAQS and demonstrate the overall ozone design value trend is decreasing from 2003 to 

2014. 

V. List of Appendices 

A. Appendix A:

Ozone_monitor_report_2011.pdf

Ozone_monitor_report_2012.pdf

Ozone_monitor_report_2013.pdf

Ozone_monitor_report_2014 2-10-2015.pdf
14

Ozone_DesignValues_20112013_FINAL_08_01_14.xlsx, (560k) - Last Updated: 8/1/2014, 

AQS Data Retrieval: 6/24/2014 downloaded from http://www.epa.gov/airtrends/values.html on 

August 21, 2014.

B. Appendix B – Monitor Values Reports:

Geographic Area: Washington-Arlington-Alexandria, DC-VA-MD-WV

Pollutant: Ozone

Source: U.S. EPA AirData http://www.epa.gov/airdata

Attachment B-1: Year: 2011 – Generated: August 22, 2014. 

(Ozone_monitor_report_2011.pdf)

Attachment B-2: Year: 2012 – Generated: August 22, 2014. 

(Ozone_monitor_report_2012.pdf)

Attachment B-3: Year: 2013 – Generated: August 22, 2014. 

(Ozone_monitor_report_2013.pdf)

Attachment B-4: Year: 2014 (Annual statistics for 2014 are not final until May 1, 2015)

Generated: February 10, 2015. Ozone_monitor_report_2014 2-10-2015.pdf) 

C. Appendix C - Annual Ambient Air Monitoring Network Plans and 5 Year Assessments 

and Monitoring Location Map:

Attachment C-1: District of Columbia, 2013 Annual Ambient Air Monitoring Network Plan 

May 13, 2013 (Draft). A copy is attached to this document. This document is also available online at http://www.epa.gov/ttn/amtic/files/networkplans/DC2013Plan.pdf. 

Attachment C-2: Letter dated June 14, 2013 from David K. Paylor, Director, re: Virginia 

Annual Air Quality Network Review (copy attached to this document). Also available on-line at 

http://www.epa.gov/ttn/amtic/files/networkplans/VA2013Plan.pdf. 

Attachment C-3: Five-Year Assessment of District of Columbia’s Ambient Air Monitoring 

Network, July 1, 2010(copy attached to this document). This document is also available on-line 

at

http://www.epa.gov/ttn/amtic/files/networkplans/ DCassess2010.pdf.

Attachment C-4: Department of The Environment, Maryland 5-Year Network Assessment, 

September 15, 2010, (copy attached to this document). Also available on-line at 

http://www.epa.gov/ttn/amtic/files/networkplans/MDassess2010.pdf.

Attachment C-5: Letter dated July 1, 2010 from David K. Paylor, Director, re: Virginia 2010 

Air Quality Monitoring Network Assessment (copy attached to this document). Also available 

on-line at http://www.epa.gov/ttn/amtic/files/networkplans/VAassess2010.pdf.

Attachment C-6: Location of Ozone Monitors in the Washington, D.C. Area 
15

Supplement to Technical Support Document for Approval and Promulgation of Air

Quality Implementation Plans; District of Columbia, Maryland and Virginia; Attainment

Demonstration for the 1997 8-Hour Ozone National Ambient Air Quality Standard for the

Washington, DC-MD-VA Moderate Nonattainment Area (Docket ID#: EPA-R03-OAR2013-0132).

Appendix A. Electronic Files on Attached CD Only:

Ozone_monitor_report_2011.pdf

Ozone_monitor_report_2012.pdf

Ozone_monitor_report_2013.pdf

Ozone_monitor_report_2014 2-10-2015.pdf

Ozone_DesignValues_20112013_FINAL_08_01_14.xlsx, (560k) - Last Updated: 8/1/2014,

AQS Data Retrieval: 6/24/2014 downloaded from http://www.epa.gov/airtrends/values.html

on August 21, 2014.
16