SUBJECT: Technical Support Document Regarding Ozone Monitoring Data — District of

Columbia, Maryland, and Virginia; Determination of Attainment ofthe 1997 8-

Hour Ozone National Ambient Air Quality Standard and Clean Data

Determination for the Washington, DC-MD-VA 8-Hour Ozone Moderate

Nonattainment Area

FROM: ASenior Air Quality Planning Specialist

Office of Air Program Planning

TO: Fil /1

THRU: ‘Cfistina Fernandez, Associate irector

Office of Air Program Planning

This document provides a technical review of the air quality monitoring data used to support the

Environmental Protection Agency’s (EPA’s) proposed determination that the Washington, DCMD-VA 8-hour ozone moderate nonattainment area (the Washington Area) has attained the 1997

ozone national ambient air quality standard (NAAQS) by its statutory attainment date and EPA’s

proposed clean data determination for the Washington Area.

I. BACKGROUND

This Washington Area includes the District of Columbia; Arlington, Fairfax, Loudoun, and

Prince William Counties and the cities of Alexandria, Fairfax, Falls Church, Manassas, andManassas Park in Virginia; and Calvert, Charles, Frederick, Montgomery, and Prince George’s

Counties in Maryland. The Washington Area was classified as a moderate nonattainment area.

See 40 CFR 81.309, 81.321 and 81.347. Moderate areas are required to attain the 1997 8-hour

ozone NAAQS by no later than June 15, 2010. $c, 40 CFR 5 1.903.

II. EVALUATION OF AIR QUALITY MONITORING DATA

A. Data Requirements

The criteria for determining if an area is attaining the 1997 8-hour ozone NAAQS are set out in

40 CFR 50.10 and appendix I. The determination is based on the most recent three complete,

consecutive calendar years of quality-assured air quality monitoring data at all ozone monitoring
The data must be collected and quality-assured in accordance with 40 CFR part 58, and must be

recorded in EPA’s Air Quality System (AQS). The data supporting attainment ofthe standardmust be complete in accordance with 40 CFR part 50, appendix I. The data completeness

requirement is met when the percent of days with valid ambient monitoring data, averaged overthree years, is greater than 90%, and no single year has less than 75% data completeness. For the

Washington Area, the ozone season extends from the beginning of April through the end of

October. A complete ozone season consists of 214 monitoring days.

B. Certified Air Quality Monitoring Data, 2007-2009The District of Columbia, the State of Maryland, and the Commonwealth of Virginia (“the

States”) submitted complete, quality assured air quality monitoring data into AQS. The States

then certified that data. Attached are two AQS reports containing 8-hour ozone data for the

Washington Area for 2007 to 2009. Table 1, below, summarizes those reports.

Table 1: 2007-2009 Washington Area 8-Hour Ozone Design Values & Data Completeness

4th Highest Value 2007-2009 Percent Completeness

(ppm) Design (valid monitored days / required days) State County Site ID Value 2007-2009 2007 2008 2009 2007 2008 2009 (ppm) average

Calvert 240090011 0.079 0.077 0.068 0.074 93 88 94 92Charles 240170010 0.083 0.078 0.066 0.075 100 96 100 99

Maryland Frederick 240210037 0.086 0.075 0.069 0.076 100 98 97 98

Montgomery 240313001 0.088 0.076 0.070 0.078 64 89 98 84

240330030 0.084 0.081 0.070 0.078 100 97 88 95 Prince George’s 240338003 0.088 0.079 0.067 0.078 94 99 100 98

Arlington 510130020 0.088 0.084 0.067 0.079 100 100 100 100

510590005 0.078 0.078 0.065 0.073 100 98 100 99510590018 0.088 0.085 0.069 0.080 100 100 100 100

Fairfax 510590030 0.085 0.085 0.070 0.080 100 99 99 99

Virginia 510591005 0.084 0.082 0.070 0.078 99 81 100 93

510595001 0.083 0.080 0.068 0.077 99 100 100 100

Loudoun 511071005 0.086 0.079 0.068 0.077 100 97 100 99

PrinceWilliam 511530009 0.076 0.074 0.064 0.071 97 98 100 98Alexandria City 515100009 0.084 0.075 0.066 0.075 99 94 97 97

110010025 0.084 0.075 0.072 0.077 98 100 88 95

District of District of 110010041 0.089 0.082 0.064 0.078 100 100 99 100 Columbia Columbia

110010043 0.087 0.084 0.071 0.080 99 100 100 100

2
pp

75% data completeness, certain data substitution is allowed.

“When computing whether the minimum data completeness requirements have been met,

meteorological or ambient data may be sufficient to demonstrate that meteorologicalconditions on missing days were not conducive to concentrations above the level ofthe

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.”

On March 4, 2011, the Maryland Department ofthe Environment (MDE), submitted a data

substitution analysis for monitor 240313001 for the 2007 ozone season. The monitor was shut

down for 75 days (April 1 to June 14) due to replacement of a trailer at the monitoring location.

MDE’s analysis, dated January 11, 2011, uses the data substitution provisions of appendix Ito 40

CFR part 50 to determine that 75 days had metrological conditions that were not conducive to

ozone formation above the level of the 2008 ozone NAAQS, 0.075 ppm. MDE requested that

missing monitoring data for those 75 days be counted in determining data completeness for2007. In a letter dated May 4, 2011, EPA Deputy Regional Administrator William C. Early,acting on behalf of Regional Administrator Shawn M. Garvin, approved that MDE’s data

substitution analysis for 57 ofthe 75 days. MDE’s data substitution analysis and EPA’s approval

letter are attached.

2007-2009 Data Comparison to NAAQS

As shown in Table 1, all 2007-2009 8-hour ozone design values for the Washington Area are

0.084 ppm or less. The data substitution analysis, described above, for monitor 240313001

results in an additional 57 days of data, for a total of 195 valid days. With the approved data

substitution, data completeness for 2007 is 91%, with a 2007-2009 three-year average

completeness of 93%. Thus, when considering the data substitution analysis for monitor240313001, all monitors meet the completeness criteria. Therefore, the Washington Area meets

the 1997 8-hour ozone NAAQS, considering 2007-2009 data.

C. Certified Air Quality Monitoring Data, 2008-20 10

The States have all certified their 2010 data. Attached are two AQS reports containing 8-hour

ozone data for the Washington Area for 2008 to 2010. As shown in Table 2, below, 2008-20 10

8-hour ozone design values for the Washington Area are 0.084 ppm or less. However, four

monitors in Fairfax County, VA have low data completeness in 2010 because, as described inmore detail, below, these monitors were shut down.

3
Note: “SD” indicates that the monitor was shut down.

Monitor Shutdowns in Fairfax County, Virginia

Due to the decision by the Fairfax County government to no longer provide funding to theFairfax County Health Department (FCDH) for operating and maintaining the ambient air

monitoring stations in Fairfax County, FCHD ceased the operation and maintenance of their

county-wide ozone monitoring network. Monitors 510590005, 510591005, and 510595001 wereshut down at the end of 2009. Therefore, there is no 2010 data for these three monitors. Monitor

510590018 was shut down on July 1,2010.

Virginia Department of Environmental Quality (VADEQ) worked with EPA prior to FCHD

shutting down these monitors. Because the Washington Area has more ozone monitoring sites

than minimally required, and because VADEQ performed an analysis on the sites that werebeing shutdown showing a strong correlation between the ambient ozone data collected at the

Fairfax County ozone sites targeted for discontinuation and existing VADEQ ozone air

monitoring sites currently operating in proximity to the Fairfax County area, EPA approved the

shutdowns in VADEQ’s 2010 Annual Network Plan.

2008-20 10 Data Comparison to NAAQS

EPA approved the shutdown of four monitors in Fairfax County, monitors 510590005,

510591005, 510595001, and 510590018. Therefore, EPA will not consider these monitors for

comparison to the NAAQS in 2010. As shown in Table 2, all 2008-2010 8-hour ozone design

values for the remaining monitors in the Washington Area are 0.084 ppm or less. These

monitors all meet the completeness criteria. Therefore, the Washington Area continues to meet

Maryland Frederick 240210037 0.075 0.069 0.083 0.076 98 97 100 98

Montgomery 240313001 0.076 0.070 0.077 0.074 89 98 92 93

240330030 0081 0.070 0.085 0.079 97 88 95 93 Prince George’s 240338003 0.079 0.067 0.085 0.077 99 100 97 99

Arlington 510130020 0.084 0.067 0.087 0.079 100 100 84 95

5l0590005 0.078 0.065 98 100 0

5l05900l8 0.085 0.069 0.068 0.074 100 100 40 80

Fairfax 510590030 0.085 0.070 0.089 0.081 99 99 85 94

Virginia 5los9oos 0.082 0.070 81 100 0 60

510595001 SD 0.080 0.068 100 100 0 67

Loudoun 511071005 0.079 0.068 0.078 0.075 97 100 84 94PrinceWilliarn 511530009 0.074 0.064 0.073 0.070 98 100 85 94

Alexandria City 515100009 0.075 0.066 0.081 0.074 94 97 83 91

110010025 0.075 0.072 0.079 0.075 100 88 83 90

District of District of

Columbia Columbia 110010041 0.082 0.064 0.086 0.077 100 99 84

110010043 0.084 0.071 0.082 0.079 100 100 85 95

4
- EPA AQS Quick Look Report (AMP45O), dated December 29, 2010, containing 2007- 2009

ozone air quality data for the remaining part of the Virginia portion of the Washington Area.

- May 4, 2011 EPA letter to MDE approving MDE’s January 11, 2011 Data Substitution

Analysis, submitted to EPA by letter dated March 4, 2011.

- MDE’s January 11, 2011 Data Substitution Analysis for AQS Site ID: 240313001,

submitted via cover letter dated March 4, 2011.

- EPA AQS Quick Look Report (AMP45O), dated May 27, 2011, containing 2008 - 2010

ozone air quality data for District of Columbia and portions Virginia of the Washington

Area, and part ofthe Maryland portion of the Washington Area.

- EPA AQS Quick Look Report (AMP45O), dated May 27, 2011, containing 2008 -2010

ozone air quality data for the remaining part of the Maryland portion ofthe Washington

Area.

5