ATTACHMENT A 

AIR QUALITY IN THE DISTRICT OF COLUMBIA 

1) District of Columbia’s Ambient Air Monitoring Network 

District Department of the Environment’s Air Quality Division (AQD) operates and maintains the 

ambient air quality monitoring network for the District as mandated by the federal Clean Air Act. The 

network consists of five air monitoring stations. Ambient measurements are made for all criteria air 

pollutants, urban air toxics, and various pollutants including ground-level ozone and fine particulate 

matter (PM2.5) precursor compounds. Of the five stations in the District, three stations measure groundlevel ozone (ozone) and report air quality levels every hour. Figure 1 below shows the ambient ozone 

network on a DC map, and the Table 1 gives the monitor type and related information for the ozone 

measurement stations. 

Table 1: District of Columbia’s Ground-level Ozone Air Quality Monitoring Stations 

Site Name Site ID Address Monitor Type 

Takoma Park 11-001-0025 Dahlia St. & Piney Branch 

Road N.W. 

NAMS/ SLAMS 

NAMS/ SLAMS 

River Terrace 11-001-0041 34th & Dix Streets, N.E. SLAMS 

McMillan 

Reservoir 11-001-0043 2500 First Street, N.W 

PAMS Type 2 

Air Quality Index 

National Air Toxics Trends 

PM25 Chemical Speciation 

Network (CSN) 

NCore Network (candidate site) 

Figure 1: District of Columbia’s Ground-level Ozone Air Quality Monitoring Network 

Monitored air quality data from these three stations are used to track the District’s progress towards 

achieving its air quality goals for meeting the national ambient air quality standards (NAAQS) and for 

verifying attainment status for ozone. 

Takoma School 

11-001-0025 McMillan

11-001-0043 

River Terrace 

11-001-0041 

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2) Ozone Air Quality Design Concentrations 

Presented below in Table 2 and Figure 2 are the design concentration values, in parts per million (ppm), 

for 8-hour ozone air quality for recent years from the District’s ambient stations network. The design 

concentrations were determined by following EPA’s guidance. Note that the data for calendar year 2008 

are yet to be certified by the state air agency, and AQD will transmit official certification to EPA Region 

III by the July 1, 2009 deadline. 

Table 2: Ozone design value concentrations in the District of Columbia 

2006 2007 2008*

Takoma Park 

11-001-0025 0.080 0.081 0.080

River Terrace 

11-001-0041 0.079 0.085 0.086

McMillan Reservoir 

11-001-0043 0.085 0.087 0.087

District of Columbia 0.085 0.087 0.087

*Data for calendar year 2008 are yet to be certified

Design Concentration (ppm) Station Name/Id

The design concentrations at the District’s monitoring stations varied between 0.079 ppm and 0.087 ppm 

during the evaluation period and recorded violations of the ozone 8-hour new NAAQS (0.075 ppm). 

Figure 2: Ozone design value concentrations at District’s monitoring stations

0.045

0.055

0.065

0.075

0.085

0.095

2006 2007 2008*

YEAR

Ozone Design Concentration (ppm)

Takoma Park 

11-001-0025

River Terrace 

11-001-0041

McMillan Reservoir 

11-001-0043

Also, based on EPA’s guidance, the highest concentration value among the three stations will determine 

the District’s design concentration for a given evaluation year. The 8-hour ozone design concentrations 

in the District for 2006, 2007 and 2008 are 0.085 ppm, 0.087 ppm, and 0.087 ppm, respectively. The 

District’s ozone design concentrations were in violation of the 0.075 ppm 8-hour NAAQS, and the level 

of violation in 2008 was 0.012 ppm above the ozone air quality standard. 

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3) Ozone Precursor Pollutant Emissions in the District and the Metropolitan Areas 

Volatile organic compounds (VOCs) and nitrogen oxides (NOx) are the primary precursor pollutants 

that lead to ground-level ozone air quality issues during warmer months of the year. Presented in Table 

3 and Figure 3 below are the jurisdiction-level air pollution emissions for the metropolitan Washington, 

DC-MD-VA area for a typical summer day in 2002. The Metro area includes the District of Columbia; 

Charles, Calvert, Frederick, Montgomery and Prince George’s counties in Maryland; the cities of 

Bowie, College Park, Gaithersburg, Greenbelt, Frederick, Rockville, and Takoma Park in suburban 

Maryland; and Arlington, Fairfax, Loudoun, Prince William counties and the cities of Alexandria, Falls 

Church, Fairfax, Manassas, and Manassas Park in northern Virginia. 

Table 3: Pollution Emissions for Ozone Precursors in the Metropolitan Washington Area for 2002 

(Data source: Washington DC-MD-VA Nonattainment Area’s Ground-level Ozone SIPs, May 23, 2007)

Jurisdiction Volatile Organic 

Compounds (VOCs) 

Nitrogen Oxides 

(NOx) 

District of Columbia 39.1 41.3 

Suburban Maryland 217.0 329.0 

Northern Virginia 192.2 226.9 

Metropolitan Area Total 

Emissions (Tons/Day) 448.3 597.2 

Being a non-industrial jurisdiction, District is home to a small number of sources that contribute to its 

ozone air quality problem and precursor pollution emissions in the metropolitan area. 

Figure 3: Pollution Emissions for Ozone Precursors in the Metropolitan Washington Area in 2002 

(Data source: Washington DC-MD-VA Nonattainment Area’s Ground-level Ozone SIPs, May 23, 2007)

48%

43%

9%

MD VA DC

Metro Area's VOC Emissions: 448 tons/day

38% 55%

7%

MD VA DC

Metro Area's NOx Emissions: 597 tons/day

The air pollution sources in the metropolitan area emitted 448.3 tons/day VOCs and 597.2 tons/day NOx 

during the year 2002. Contribution from the District’s sources was 39.1 tons of VOCs and 41.3 tons of 

NOx per day, which represents seven to nine percent of the ozone precursor emissions in the 

Washington DC-MD-VA metropolitan area. 

The District has implemented stricter controls on its sources since the early nineties and continues its 

pursuit to further reduce its contribution. The District’s local controls include an inspection and 

maintenance program to curtail pollution from vehicles, NOx budget programs on stationary point 

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sources, and VOC controls for solvents, industrial and auto maintenance products, gasoline handling, 

and other diverse area sources. Table 4 below shows the projected air pollution emissions for 2009 for 

the metropolitan Washington, DC-MD-VA area for a typical summer day. 

Table 4: Projected Emissions for Ozone Precursors in the Metropolitan Washington Area for 2009 

(Data source: Washington DC-MD-VA Nonattainment Area’s Ground-level Ozone SIPs, May 23, 2007)

Jurisdiction Volatile Organic 

Compounds (VOCs) 

Nitrogen Oxides 

(NOx) 

District of Columbia 31.5 27.6 

Suburban Maryland 168.5 179.6 

Northern Virginia 148.8 154.9 

Metropolitan Area Total 

Emissions (Tons/Day) 348.8 362.1 

A comparison of the ozone precursor pollution emissions between 2002 and 2009 in the District 

indicates a 19% reduction in VOC emissions and a 33% drop in NOx emissions. Despite its significant 

efforts to reduce ozone precursor pollution from its sources, the monitors in the District did not show 

proportionate improvement in ambient air quality, and the District’s air monitors continue to record 

violations of the 8-hour ozone NAAQS. 

Analyses by the Ozone Transport Commission (OTC) since the 1990s point to transported pollution as 

having a significant contribution for the ozone air quality in OTC member states including the District. 

Mitigating pollution transport is critical for a non-industrial urban jurisdiction with air quality issues 

such as the District. National efforts to impose additional controls on on-road and off-road mobile and 

disperse area sources and stricter controls on large industrial sources and power plants to curtail 

transported pollution are needed to assist the District and other nonattainment areas in the nation to 

achieve the new 8-hour ozone NAAQS. 

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