1

4.0 Analyses of Individual Nonattainment Area 

4.10 Region 10 Nonattainment Areas 

4.10.4 Washington 

State of Washington Area Designations For the 

24-Hour Fine Particle National Ambient Air Quality Standard 

The table below identifies the counties in Washington State that EPA has designated as not 

attaining the 2006 24-hour fine particle (PM2.5) standard.1

 A county (or part thereof) is 

designated as nonattainment if it has an air quality monitor that is violating the standard or if the 

county is determined to be contributing to the violation of the standard. 

 

Area 

WA Recommended 

Nonattainment Counties 

EPA’s Designated 

Nonattainment Counties 

Wapato Hills-Puyallup 

River Valley (Tacoma) 

Pierce (partial) Pierce (partial) 

EPA has designated the remaining counties in the state as “attainment/unclassifiable.” 

EPA Technical Analysis for the Wapato Hills-Puyallup River Valley nonattainment area in 

Washington State

Introduction 

Pursuant to section 107(d) of the Clean Air Act, EPA must designate as nonattainment those 

areas that violate the NAAQS and those nearby areas that contribute to violations. This technical 

analysis for the Wapato Hills-Puyallup River Valley nonattainment area identifies the single 

county in Washington State with a monitor that violates the 24-hour PM2.5 standard (Pierce 

County) and evaluates nearby counties in the Seattle-Tacoma-Olympia area for contributions to 

fine particle concentrations in the area. EPA has evaluated these counties based on the weight of 

evidence of the following nine factors recommended in EPA guidance and any other relevant 

information: 

- pollutant emissions 

- air quality data 

- population density and degree of urbanization 

 

1 EPA designated nonattainment areas for the 1997 fine particle standards in 2005. In 2006, the 

24-hour PM2.5 standard was revised from 65 micrograms per cubic meter (average of 98th

percentile values for 3 consecutive years) to 35 micrograms per cubic meter; the level of the 

annual standard for PM2.5 remained unchanged at 15 micrograms per cubic meter (average of 

annual averages for 3 consecutive years). 
2

- traffic and commuting patterns 

- growth 

- meteorology 

- geography and topography 

- jurisdictional boundaries 

- level of control of emissions sources 

We also used analytical tools and data such as pollution roses, fine particle composition 

monitoring data, back trajectory analyses, and the contributing emission score (CES) to evaluate 

these areas. (See additional discussion of the CES under factor 1 below.) 

 

Figure 1 is a map of the counties in the Seattle-Tacoma-Olympia area and other relevant 

information such as the locations and design values of air quality monitors, and the metropolitan 

area boundary. 

Figure 1. Wapato Hills-Puyallup River Valley (partial Pierce County) nonattainment area and 

surrounding counties in Seattle Tacoma area 
3

The violating monitor in the Pierce County area is located at 7802 South L Street (South L Street 

monitor) in a suburban area of the City of Tacoma. The nonattainment area is referred to as the 

Wapato Hills-Puyallup River Valley (WHPRV) area. The City of Tacoma is a major urban 

center in the Southern Puget Sound Region. Situated on Commencement Bay, an inlet of Puget 

Sound, Tacoma lies at the foot of Mt. Rainier in the Puyallup River valley, bordered by 

mountains. Commencement Bay serves the Port of Tacoma, a major center of international 

trade. The Port handled more than $36.33 billion in annual trade and nearly 2 million TEUs 

(Twenty-foot Equivalent container Units) in 2007. Tacoma is situated in the Seattle-TacomaOlympia Consolidated Statistical Area, a highly urbanized area along the Interstate 5 corridor. 

To the east of Interstate 5, along the eastern portion of Pierce, King, Snohomish, and Thurston 

Counties the Cascade mountains rise to over 14,000 feet in elevation at Mt Rainier in Pierce 

County. Tacoma is about 36 miles south from the city of Seattle, the largest city in Washington 

State and 30 miles north of the City of Olympia, the Capitol of Washington State. See Figure 2. 

The Puyallup Indian Reservation is located in the Tacoma Area, about five miles northeast of the 

violating monitor and is located within in the Wapato Hills-Puyallup River Valley partial county 

nonattainment area boundary. See Figure 3. The nonattainment area boundary is the pink line 

and the Puyallup Indian Reservation is shown in cross hatch. 

Figure 2. Southern Puget Sound area topography 
4

 

Figure 3. Wapato Hills-Puyallup River Valley Nonattainment Area 

The boundary of the Wapato Hills-Puyallup River Valley nonattainment area is described as 

follows: 

• Starting from where an extension of Kennedy Road Northeast would intersect 

Commencement Bay, proceed north to the intersection of Marine View Drive (State 

Route 509) and Kennedy Road Northeast. 

• Proceed south on Marine View Drive to Hylebos Creek. 

• Proceed south along Hylebos Creek to 12th Street East. 

• Proceed east on 12th Street East to 70th Avenue East. 

• Proceed south on 70th Avenue East to State Route 99 (S.R. 99). 

• Proceed north on S.R. 99 0.1 mile north of Birch Street to a driveway to the east. 

• Proceed east along the driveway and continue east along the same alignment to the 

Pierce County Line/Comprehensive Urban Growth Area (CUGA) boundary. 

• Proceed east along the Pierce County Line/CUGA boundary to the eastern boundary of 

Edgewood. 

• Proceed south along the eastern boundary of Edgewood to eastern boundary of the 

Sumner Urban Service Area. 

• Proceed south along eastern boundary of the Sumner Urban Service Area to the 

eastern boundary of the Puyallup Urban Service Area. 
5

• Proceed south along the eastern boundary of the Puyallup Urban Service Area to the 

eastern boundary of Puyallup/CUGA boundary. 

• Proceed south and then west along the CUGA boundary to the eastern boundary of 

McChord Air Force Base. 

• Proceed north along the eastern boundary of McChord Air Force Base to the 

northernmost point on the eastern boundary. 

• Proceed from the northernmost point on the eastern boundary of McChord Air Force 

Base to the south right-of-way of S.R. 512. 

• Proceed west along the south right-of-way of S.R. 512 to the south right-of-way of I-5. 

• Proceed south along the south right-of-way to I-5 to the point opposite the boundary 

between Lakewood and Camp Murray. 

• Proceed north across I-5 to the boundary between Lakewood and Camp Murray. 

• Proceed north along the western boundary of Lakewood to the point where the western 

boundary coincides with the CUGA boundary. 

• Proceed north along the CUGA boundary to the southern boundary of Point Defiance 

Park. 

• Proceed east along the southern boundary of Point Defiance Park to Commencement 

Bay/CUGA boundary. 

• Proceed southeast, then northeast, and finally northwest along the CUGA boundary to 

the starting point. 
6

In December 2007, the State of Washington recommended that a portion of Pierce County (the 

Wapato Hills-Puyallup River Valley area) be designated as “nonattainment” for the 2006 24-

hour PM2.5 standard based on air quality data from 2004-2006. These data are from Federal 

Reference Method (FRM) monitors located in the State. See December 18, 2007 letter from Jay 

Manning, Director of the Washington Department of Ecology to Elin Miller, Regional 

Administrator EPA Region 10. On March 13, 2008, the State submitted to EPA the partial 

county boundary shown in Figure 27. The State also submitted the following information to 

supplement their recommendation in a letter to EPA on July 25, 20082

: 

• An analysis of speciation data for the South L Street monitor and monitors in the 

Duwamish area and Lake Forest Park area 

• An analysis of meteorological data from meteorological instrumentation colocated with the South L Street monitor 

• An analysis of continuous monitoring data including diurnal air quality trends for 

monitors in King and Pierce Counties 

Based on EPA's technical analysis and review of information provided by the State as described 

below, EPA has designated the Wapato Hills-Puyallup River Valley area (a portion of Pierce 

County) in State of Washington as nonattainment for the 24-hour PM2.5 air-quality standard, 

based upon currently available information (see table below). 

Wapato Hills-Puyallup 

River Valley nonattainment 

area 

WA Recommended 

Nonattainment Counties 

EPA’s-Final Designated 

Nonattainment Counties 

Washington State Pierce (partial) Pierce (partial) 

The following is a technical analysis for the Wapato Hills-Puyallup River Valley nonattainment 

area (a portion of Pierce County) in State of Washington. 

Factor 1: Emissions data 

For this factor, EPA evaluated county level emission data for the following PM2.5 components 

and precursor pollutants: “PM2.5 emissions total,” “PM2.5 emissions carbon,” “PM2.5 emissions 

other,” “SO2,” “NOx,” “VOCs,” and “NH3.” “PM2.5 emissions total” represents direct emissions 

of PM2.5 and includes: “PM2.5 emissions carbon,” “PM2.5 emissions other”, primary sulfate 

(SO4), and primary nitrate. (Although primary sulfate and primary nitrate, which are emitted 

directly from stacks rather than forming in atmospheric reactions with SO2 and NOx, are part of 

“PM2.5 emissions total,” they are not shown in Table 1 as separate items). “PM2.5 emissions 

 

2 See the following docket materials: 

• July 25 WA State letter attachment PS Diurnals_2005-2007 data.png 

• July 25 WA State letter attachment Presentation to OAQPS_as of25-Jul-08.pdf 

• July 25 WA State letter attachment Tacoma L Street characteristics.pdf 

• July 25 WA State letter attachment Tacoma L Street Speciation.pdf 

• July 25 WA State letter attachment Tacoma_PM2.5 episode_12-16-Jan-07.png 

• July 25 WA State letter attachment Duwamish_SO4_NO3_OC_ECvs_PM2.5_with_FRM.png 

• July 25 WA State letter attachment Lake Forest_Park_SO4_NO3_OC_ECvs_PM2.5_with_FRM.png 
7

carbon” represents the sum of organic carbon (OC) and elemental carbon (EC) emissions, and 

“PM2.5 emissions other” represents other inorganic particles (crustal). Emissions of SO2 and 

NOx, which are precursors of the secondary PM2.5 components sulfate and nitrate, are also 

considered. VOCs (volatile organic compounds) and NH3 (ammonia) are also potential PM2.5

precursors and are included for consideration. 

Emissions data were derived from the 2005 National Emissions Inventory (NEI), version 1. See 

http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html. 

EPA also considered the Contributing Emissions Score (CES) for each county. The CES is a 

metric that takes into consideration emissions data, meteorological data, and air quality 

monitoring information to provide a relative ranking of counties in and near an area. Note that 

this metric is not the exclusive manner for considering data for these factors. A summary of the 

CES is included in attachment 2, and a more detailed description can be found at 

http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html#C. 

Table 1 shows emissions of PM2.5 and precursor pollutants components (given in tons per year) 

and the CES for violating and potentially contributing counties in the Seattle-Tacoma-Olympia 

area. Counties are listed in descending order by CES. 

Table 1. PM2.5 Related Emissions and Contributing Emissions Score 

County State 

Recommended 

Nonattainment? 

CES 

Score 

(Rank) 

PM2.5 

emissions 

- total 

(tpy) 

PM2.5 

emissions - 

carbon (tpy) 

PM2.5 

emissions - 

other (tpy) 

SO2 

emissions 

(tpy) 

NOx 

emissions 

(tpy) 

VOC 

emissions 

(tpy) 

NH3 

emissions 

(tpy) 

King No 100 (1) 6,362 4,168 2,194 7,361 75,825 89,446 2,564 

Pierce Yes (partial) 60 (2) 3,766 2,255 1,511 3,200 31,905 32,097 1,410 

Thurston No 17 (3) 2,221 1,348 873 478 8,389 14,985 1,620 

Kitsap No 14 (4) 2,204 1,201 1,004 442 6,199 9,588 274 

Snohomish No 13 (5) 3,714 2,223 1,492 2,256 22,687 28,861 1,932 

Skagit No 11 1,605 819 786 10,345 12,417 11,173 1,809 

Island No 4 841 453 388 485 4,463 4,128 358 

Mason No 3 767 439 328 100 1,623 3,846 90 

Total PM2.5 emissions in King County as well as individual chemical precursor components of 

PM2.5 are generally two times the emissions in Pierce County, the county which contains the 

violating monitor. In addition, the CES score of 100 indicates potential contributing emissions 

from King County. The next highest CES score of 17 was for Thurston County, which contains 

the City of Olympia located 36 miles to the south of the violating monitor. Given the low CES 

scores and relatively low emissions in Thurston, Kitsap, Snohomish, Skagit, Island and Mason 

Counties these Counties are less likely to contribute to the exceedences at the South L Street 

monitor than King County and Pierce County which have higher emissions and CES scores. We 

note that in counties with large land areas and complex terrain such as King and Pierce Counties, 

the CES does not account for diurnal variation in hourly PM2.5 and sharp spatial gradients in 
8

emissions. 3 Those factors were separately considered and used in developing our designation 

rationale. 

 The State of Washington submitted seasonal emissions inventory data as part of its nine 

factors analysis attachment to its letter to EPA dated December 18, 2007. Figure 4 and Table 2 

display seasonal emissions in Pierce County, Washington for 2005 from the State’s submittal. 

As discussed below in factor 2 (air quality data), PM2.5 exceedences at the violating monitor in 

Pierce County have occurred in the months of November, December, January and February 

during the years 2004-2007. 

Winter season (December through February) air emissions of PM2.5 in Pierce County are 

balanced among: 

 (1) outdoor open burning (202 tons per season, 24%), 

 (2) mobile sources (230 tons per season, 27%), 

 (3) fireplaces and woodstoves (326 tons per season, 39%), and 

 (4) other sources (84 tons per season, 10%) 

Washington noted that these are estimates for a countywide emission inventory, and that 

outdoor open burning (with an estimated 24% contribution) is likely not occurring in the urban 

portion of the county near the violating monitor. Open burning is prohibited in these areas. 

Figure 4. 

 

3

 See supporting documentation section on limitations of the CES. Because of differences in county size, and 

topography across the country, the score may require careful interpretation for some areas, particularly in the 

western United States. 

Pierce County Winter PM2.5 Emissions in 2005

Mobile 

Sources

27%

Fireplaces 

and 

Woodstoves

39%

Other 

Source 

Categories

10%

Outdoor 

Open 

Burning

24%
9

Table 2. Pierce County Seasonal PM2.5 Emission Sources in 2005 

tpy tpy

Annual Summer Fall Winter Spring Annual Summer Fall Winter Spring

1,258 377 377 202 302 Outdoor Open Burning

Land clearing burning 941 282 282 151 226

Yard waste burning 185 56 56 30 44

Forest wildfires and managed burns 117 35 35 19 28

Structural fires 11 3 3 3 3

Agricultural waste burning 4 1 1 1 1

1,036 284 259 230 263 Mobile Sources

On-road gasoline vehicles 296 77 74 71 74

Non-road diesel engines 280 78 67 62 73

On-road diesel vehicles 201 52 50 48 50

Non-road gasoline engines 80 22 19 18 21

Ocean-going vessels 54 14 14 14 14

Harbor vessels 35 9 9 9 9

Railroad diesel engines 27 7 7 7 7

On-road CNG and LPG engines 4 1 1 1 1

Aircraft ground support engines 3 1 1 1 1

Aircraft 2 1 1 1 1

Non-road LPG engines 2 1 1 1 1

Recreational boats 52 22 17 0 13

679 34 95 326 224 Fireplaces and Woodstoves

Wood stove wood burning 430 22 60 206 142

Fireplace wood burning 165 8 23 79 54

Fireplace and wood stove firelog burning 78 4 11 37 26

Pellet stove wood burning 6 0 1 3 2

261 49 56 84 72 Other Source Categories

Industrial point sources 181 45 45 45 45

Natural gas burning 67 3 9 32 22

Boiler and furnace distillate oil burning 11 1 2 5 4

Propane furnaces and boilers 2 0 0 1 1

3,234 744 787 842 860 Totals 3,234 744 787 842 860

PM2.5 Emission Source Categories and 

Subcategories

2005 Category PM2.5 Emissions

tons/season

2005 Subcategory PM2.5 Emissions

tons/season

Fireplaces and woodstoves are the largest source of emissions in Pierce County (39%). The 

State conducted additional analyses to determine the spatial variation in wood burning activities. 

Figure 5 displays the number of people using wood as a primary source of heat in the immediate 

area of the South L monitor, per square mile. The information source is the 2000 census, and is 

presented at a block group level4

. This information does not capture those who use wood as a 

secondary heat source, or those who use fireplaces for ambiance. The highest density of 

woodstove/fireplace use occurs within the Tacoma urban growth boundary and in census blocks 

north of SR 512 in the vicinity of the monitor. See Figures 5 and 6.

Based on annual emissions inventory data for Pierce, King and surrounding counties, 

VOC and NOx emissions comprise the largest portion of total PM2.5 emissions. However, this 

data is annual data and exceedences of the 24-hour PM2.5 standard at the South L Street monitor 

occur exclusively in the late fall-winter seasons. Seasonal emissions inventory data submitted by 

the State indicates that emissions from woodstoves and fireplaces account for over 40% of the 

 

4

 US Census Bureau. http://factfinder.census.gov/home/saff/main.html
10

total emissions in Pierce County, while mobile sources account for 27% of total emissions in 

Pierce County during the winter season when exceedences of the 24-hour PM2.5 standard occur. 

 Based on emission levels and CES values, EPA considered King and Pierce Counties 

candidates for a 24-hour PM2.5 nonattainment designation for violations at the South L Street 

monitor in Pierce County. However, we have further evaluated potential contributions from 

surrounding counties in the Seattle-Tacoma-Olympia area in our analysis of the remaining ninefactors. 
11

Figure 5. 
12

Figure 6. 
13

Factor 2: Air quality data 

This factor considers the 24-hour PM2.5 design values (in μg/m3

) for air quality monitors in 

counties in the Seattle-Tacoma-Olympia based on data for the 2005-2007 period. A monitor’s 

design value indicates whether that monitor attains a specified air quality standard. The 24-hour 

PM2.5 standards are met when the 3-year average of a monitor’s 98th percentile values is 35 

μg/m3

 or less. A design value is only valid if minimum data completeness criteria are met. 

. 

The 24-hour PM2.5 design values for counties in the Seattle-Tacoma-Olympia area are shown in 

Table 3. 

Table 3. Air Quality Data for Seattle-Tacoma-Olympia Area 

County State 

Recommended 

 Nonattainment? 

Design Values

2004-06

(μg/m3

) 

Design Values

2005-07

(μg/m3

) 

Pierce, WA Yes 42 43 

King, WA No 29 31 

Snohomish, WA No 33 35 

Thurston, WA No N/A N/A 

Island, WA No N/A N/A 

Kitsap, WA No N/A N/A 

Mason, WA No N/A N/A 

In Washington State, the monitor at 7802 South L Street in Tacoma (Pierce County) is the only 

monitor that violates the 24-hour PM2.5 standard based on 2005-2007 data. King and Snohomish 

County do not violate based on 2004-2006 or 2005-2007 data. The remaining counties do not 

have Federal Reference Method monitor, therefore Federal Reference Method5

 data is not 

available for these counties. 

 Although the surrounding counties of King and Snohomish do not violate the standard, 

this alone was not sufficient information for EPA to eliminate King County or Snohomish 

County as candidates for inclusion in the nonattainment area. Nearby counties could be 

contributing to the violations at the South L Street monitor even though there are no violating 

monitors in those counties. 

 EPA analyzed data submitted by the State of Washington collected from monitoring 

several sites in addition to the Pierce County Tacoma South L Street Site to better characterize 

PM2.5 in Tacoma and in the surrounding counties. Since the high CES score for King County 

indicates a potential contribution to the exceedences at the South L Street monitor from King 

County, and since western King County is a highly urbanized area, this analysis focused in 

particular on examining additional air quality data for King County. 

 

5

 Design values are based on data collected at FRM or FEM monitors. The State operates other monitors in these counties but 

they are not FRM or FEM monitors. 
14

 Figure 7 shows the location of several monitors in the Puget Sound area. The following 

pages discuss air quality data from these sites located along the Interstate 5 corridor in Pierce and 

King Counties. These areas include Marysville, Lynnwood, Lake Forest Park and Tacoma, 

which are largely urban-suburban residential areas, and the Duwamish, Puyallup South and Kent 

Valley areas, which are more industrialized areas. 

 Table 4 displays the top 5% of concentrations at the South L Street Monitor from 2004-

2007 from EPA’s Air Quality System (AQS) repository of ambient air quality data. All of these 

concentrations occurred during the months of November, December, January or February with 

the exception of one which occurred in late October, 2007. The exceedences at the South L 

Street monitor occur during the winter as the State suggests in its nine factor analysis. 

Table 4. Top 5% values at Tacoma L Street Monitor from 2004-2007 
15

Figure 7. Puget Sound Area monitor locations 

Lake Forest

Maryswville 

Lake Forest Park

Mountlake Terrace

Queen Anne Hill 

Duwamish 

Kent

South L Street Monitor

Puyallup South
16

Speciation Profiles 

The State submitted chemical speciation monitoring data collected at the Tacoma South L Street 

monitoring site in the year 2006. Fifty nine (59) samples were collected (one sample every six 

days). Out of these 59 samples, four samples were for days above 30 μg/m3

, and 55 samples 

were for days that were below 20 μg/m3

. Figure 8 displays percentage of the speciated 

components of total PM2.5 for the two highest days in 2006 for which the speciation data was 

collected. On December 19th, 21.57 μg/m3 (74%) of the total PM2.5 was organic and elemental 

carbon. Sulfate and nitrate were .87 μg/m3 (3%) and 1.86 (6%) respectively of the total PM 2.5. 

On December 31, 37.67 μg/m3

 of PM2.5 (69%) was organic carbon, 2.86 μg/m3 was elemental 

carbon (5%), 1.94 (4%) was sulfate and 1.54 μg/m3

 (3%) was nitrate. 

Figure 8. Speciated components of Total PM2.5 from the Tacoma South L Street Monitor on 

high days in 2006 

Figure 9 is a plot of PM2.5 fraction components by season against PM2.5 concentration. The 

highest concentrations of PM2.5 occur at the L Street monitor in November and December. 

During the first (Jan- March) and fourth (Oct-Dec) quarters when the exceedences occur, the 

ratios of sulfate and nitrate with total PM2.5 are generally less than 0.2. The highest ratios of 

sulfate and nitrate to total PM2.5 (above 0.2) occur in the second (April-June) and third (JuneAugust) quarters when PM2.5 concentrations are less than 15 μg/m3

. The organic carbon fraction 

to total PM2.5 ratio is highest of any component at all times during the year ranging from 0.2-

0.5). In the fourth quarter, the OC/total PM reaches its highest levels when PM2.5 concentrations 

are greater than 30 μg/m3

. 
17

Figure 9. Seasonal PM2.5 components collected at the South L Street monitor in 2006. 

 
18

Positive Matrix Factorization analysis of chemical components on Pierce County filter 

Since an analysis of chemical speciation data for high PM2.5 days at the South L Street monitor 

in 2006 was an important part of the State’s submittal, EPA evaluated the State's submittal of 

speciation data for the South L Street site using the Positive Matrix Factorization (PMF) tool. 

PMF is one of the receptor models that EPA’s Office of Research and Development has 

developed to provide scientific support for current ambient air quality standards and for 

implementation of those standards by identifying and quantifying contributions for source 

apportionment. This model draws from ambient air quality data sets and receptor model 

algorithms to compute profiles and relative contributions from different source categories. See 

http://www.epa.gov/heasd/products/pmf/pmf.htm.6

 This evaluation using the PMF tool also 

supplements the speciation data and other information provided by the State on source 

contributions to the violations at the South L Street monitor by providing information on 

categories of sources and relative contributions from these sources to the violations at the South 

L Street Federal Reference Monitor. This analysis was particularly informative in our evaluation 

of the unique Tacoma area PM 2.5 pollution problem where the State's submittal suggests 

localized sources cause and contribute to the violations at the South L Street monitor and where, 

as explained above, and distinct from most other areas in the country we have evaluated, the CES 

tool had limitations for the area. Additionally, and as explained above, our final boundary 

determination for this area is based on a myriad of factors and various analyses, only one of 

which is a PMF analysis. Taken together with other data and facts analyzed and explained in 

detail elsewhere in this document, it helps us to better understand the types of source categories 

which cause or contribute to the PM2.5 pollution in the Tacoma area. 

The 2006-07 PMF data set included 111 data points (a sample every 6th day), most of which was 

the same period that the State used in their speciation monitoring study of the area. EPA's 

evaluation of this dataset using PMF indicates relative source contributions that support the 

State’s analysis of the chemical speciation and other air quality data which indicates that smoke 

from woodstoves and fireplaces is the major contributor to PM2.5 on high days at the South L 

Street monitor. PMF results indicate that wood smoke contributed 60-90% of the mass on 6 out 

of 7 days when total PM2.5 mass exceeded 30 μg/m3. See Table 5. More detailed information 

on the PMF analysis for the South L Street monitor is included in the docket for this action. 

 

6 Positive matrix factorization (PMF) (Footnoted: A. Reff et al, “Receptor Modeling of Ambient Particulate Matter 

Data Using Positive Matrix Factorization: Review of Existing Methods,” Journal of the Air and Waste Management 

Association, 57:146-154, February 2007.) is a recent development in the class of data analysis techniques called 

factor analysis, in which the fundamental problem is to resolve the identities and contributions of components in an 

unknown mixture. PMF has been used extensively for source apportionment of ambient particulate matter (PM), to 

resolve the mixture of sources that contributes to PM samples. PMF is especially applicable to working with 

environmental data because it incorporates the variable uncertainties often associated with measurements of 

environmental samples, and forces all of the values in the solution profiles and contributions to be nonnegative, 

which is more realistic than solutions from previously used methods like principal components analysis.
19

Table 5. Positive Matrix Factorization Results for L Street monitor for days over 30 in 2006 and 

2007 

Comparison with monitoring data from other sites in King County 

Figure 10 contains seasonal PM2.5 components from two monitors, one in an industrialized area 

the southern portion of King County (Duwamish) and the other in northern King County in a 

residential area, Lake Forest Park. The Lake Forest Park monitor is a neighborhood scale site 

and is representative of the Lake Forest Park general area.7

 Figure 11 shows the location of these 

monitors in relation to the South L Street Monitor in Tacoma. The Duwamish monitor is about 

30 miles north of the South L Street Monitor and the Lake Forest Park Monitor is about 50 miles 

north of the South L Street Monitor. 

 The Lake Forest Park monitor generally shows the same pattern observed at the South L 

Street monitor. Organic carbon dominates all fractions but the highest (>20 ug/m3 occur) 

fraction occurs in the first and fourth quarters. The highest fractions of sulfate and nitrate occur 

in the second and third quarters of the year when PM2.5 concentrations are lowest (generally 

below 10). The Duwamish monitor shows a shift upward of sulfate/ PM2.5 ratio for all quarters. 

Ratios of sulfate to total PM2.5 are more consistent throughout the year at the Duwamish monitor 

and generally range between .1-.3. The data points at this monitor are more tightly clustered 

showing less seasonal variation then at the Lake Forest Park and Tacoma monitor. 

 

7

 Washington State Department of Ecology 2008 Ambient Air Monitoring Network Report 
20

 Figure 10. Seasonal PM2.5 components at Lake Forest Park and Duwamish since 2005 
21

Figure 11. Location of monitors in the Southern Puget Sound Area 

Figure 9 Seasonal PM2.5 components at Duwamish since 2005 

Lake Forest Park 

Duwamish 

Tacoma S L. 

Kent Valley 

Queen Anne Hill 

Mountlake Terrace 

Marysville 

Puyallup South
22

Diurnal Profiles 

Figures 12-14 display diurnal PM2.5 concentrations at continuous monitors throughout the Puget 

Sound Area. Figure 12 shows diurnal PM2.5 concentrations at the South L Street monitor for the 

period 2001-2007. PM concentrations at the South L Street monitor rise sharply beginning in the 

late afternoon and then peak around midnight then tail off around mid day. Survey data from 

Washington State indicate that this profile is related to woodstove use8

. Surveys indicate that 

individuals ignite or add fresh fuel in the late afternoon or early evening and often add fuel 

before bedtime resulting in peak concentrations at night and lowest concentrations during the day 

while individuals are away from home. The diurnal profile for the Lake Forest Park monitor 

(Figure 13) shows a similar “V” shaped profile to the profile observed at the L Street monitor 

while the profile while the profile for the Duwamish monitor (Figure 14) is relatively flat. 

Figure 15 is a map of the monitors throughout the Puget Sound area with diurnal profiles. The 

“V” shaped profile is observed at monitors in the communities in Snohomish County to the 

North (Lynnwood, Lake Forest Park and Marysville). A flatter profile is observed at the 

monitors in central and southern King County; the Queen Anne monitor, the Seattle Duwamish 

Valley monitor and the Kent Valley monitor. 

Figure 12. 

Figure 13. 

 

8

 Puget Sound Clean Air Agency 2007 woodstove use survey 
23

Figure 14. 

Figure 15. Diurnal profiles at monitoring sites in Pierce, King and Snohomish Counties 
24

Figure 16 plots one hour averages from a co-located nephelometer at the Tacoma L Street 

monitor during an episode. On January 12, 2007 the 24-hour design value at the L Street 

monitor was 44.7 μg/m3 and on January 15, 2007, the 24-hour design value at the L Street 

monitor was 58.6 μg/m3. The red line indicates the 24-hour standard, 35 μg/m3. Peak PM2.5

during this episode occurred around midnight on January 13 and January 15. During the day of 

the 12th and the 13th PM2.5 levels dropped to less than 10 μg/m3

. The pattern repeats with 

nighttime highs climbing well above the standard and daytime lows. 

 When this pattern is observed at Tacoma, an identical pattern is noted at the other 

monitors throughout the Region with the V shaped profile. In between events, PM2.5 levels 

generally drop to very low levels (<10 μg/m3

) indicating that there is not significant transport of 

PM precursors from other areas (Figure 18). Days that do not drop to very low levels are days 

where inversions have not broken down completely. 

Figure 16. PM2.5Tacoma L Street January 11-16 2007 

 
25

Figure 17. Simultaneous PM2.5 peaks at Southern Puget Sound monitors 

Air Quality Data Discussion/Conclusions 

Concentrations of PM2.5 throughout the Southern Puget Sound area peak at night and in the 

winter. The diurnal patterns are observed at neighborhood scale monitors in Pierce and King 

County and show peaks consistent with use of woodstoves collected through woodstove surveys. 

Monitors in the more industrial areas in southern King County (Kent and Duwamish) between 

the neighborhood scale monitors to the north and the South L Street monitor to the south do not 

exhibit strong diurnal patterns consistent with woodstove use surveys. Seasonality of sulfate and 

nitrate concentrations at these monitors is also less variable than the seasonality of sulfate, nitrate 

and organic carbon observed at the South L Street monitor and other neighborhood monitors 

(Lake Forest Park). The diurnal profiles and seasonality of organic carbon (components that are 

associated with burning of wood) indicate that emissions from woodstoves and fireplaces 

contribute to elevated wintertime concentrations in residential areas such as the South L Street 

and Lake Forest Park areas. 

 Based on EPA’s PMF analysis, organic carbon/woodstoves contribute 60-90% of PM2.5

to the exceedences at the South L Street Monitor. Contributions of regional PM2.5 precursors 

(SOx and NOx) that dominate the King County emissions inventory contribute less than 20-30% 

of total PM2.5 to the Tacoma monitor. Based on speciation monitoring at the South L Street 

monitoring site, organic carbon and elemental carbon contribute over 70% of the PM2.5

concentration on the highest days in 2006 and sulfate and nitrate contribute less than 10% 

combined of the total PM2.5 concentration on these days. Based on speciation monitoring, 

emissions from King County (over 75,000 tpy NOx and 7500 tpy SOx) as well as emissions 

from the other counties in the CMSA potentially contribute less than 10 % of total PM2.5

concentrations on high days at the South L Street Monitor. 

 Based on the foregoing analyses, EPA concludes that sources contributing the violations 

of the PM2.5 exceedences at the South L Street monitor are predominantly local sources 

dominated by woodstove and fireplace emissions in the Tacoma area and not transport from 

King County or other counties in the Seattle-Tacoma-Olympia area. 

 This information along with the information discussed in the other factors, particularly 

factors 6 and 7 (meteorology and topography) was used to determine that the partial Pierce 

County boundary submitted by the State on March 13, 2008 is sufficiently large enough to 

contains sources contributing to the 24-hour PM2.5 violations at the South L Street monitor. 
26

Factor 3: Population density and degree of urbanization (including commercial 

development) 

Table 6 shows the 2005 population for each county in the Seattle-Tacoma-Olympia area being 

evaluated, as well as the population density for each County in that area. Population data give an 

indication of whether it is likely that population-based emissions might contribute to violations 

of the 24-hour PM2.5 standards. King County, Pierce County and Snohomish County contain 

large cities with large populations. Most of the areas in between are urban or suburban. The 

City of Everett is the largest city in Snohomish County. King County has the highest population 

(1.79 million) and the highest population density with 824 people/square mile. Pierce County 

has the next highest population at 753,209 with the third highest population density in the 

Seattle-Tacoma-Olympia area. Snohomish County has the third highest population in the area. 

King County and Pierce Counties have the highest CES scores at 100 and 60 respectively. The 

CES Score for Snohomish County is much lower at 13. 

Table 6. Population in the Puget Sound area 

County State 

Recommended 

Nonattainment? 

2005 Population 2005 

Population 

Density 

(people/sq mi) 

Percent Population 

Change (2000-05) 

King No 1,799,119 824 3 

Pierce Yes 753,209 445 7 

Thurston No 228,881 305 10 

Kitsap No 241,525 583 4 

Snohomish No 655,564 312 8 

Skagit No 113,181 65 9 

Island No 79,983 377 11 

Mason No 54,169 54 9 

The State addressed population density in its nine factor analysis. Figure 18 shows population 

density for the city of Tacoma and surrounding Pierce County areas, at the 2000 census block 

group level. In Pierce County, the highest population density occurs inside of the 

Comprehensive Urban Growth Area (CUGA) in the vicinity of the L Street monitor, and along 

the eastern shore of the Puget Sound to the north of the Port of Tacoma. 9

 Population density 

generally decreases to the south and the east of the Port of Tacoma and the CUGA. Figure 19 

shows the population of the recommended nonattainment area and the surrounding portions of 

Pierce County. 

Based on the air quality data we reviewed above and the additional factors that we review below 

which indicate that local sources cause the violations at the South L Street monitor, and based on 

population data which indicate that the highest population density in the Pierce County area is 

within the Tacoma CUGA, EPA concludes that a boundary that includes populations/potential 

sources in the Tacoma CUGA is appropriately large enough to include populations and sources 

contributing to the violations at the South L Street monitor. 

 

9

 See Chapter 36.70A RCW for more on the Washington State Growth Management Act which defines an urban 

growth area or areas within which urban growth shall be encouraged and outside of which growth can occur only if 

it is not urban in nature. 
27

Figure 18. 
28

Figure 19. Pierce County Population Density with recommended nonattainment area boundary 

Factor 4: Traffic and commuting patterns

This factor considers the number of commuters in each county who drive to another county 

within the Seattle-Tacoma-Olympia area, the percent of total commuters in each county who 

commute to other counties within the Seattle-Tacoma-Olympia area, as well as the total Vehicle 

Miles Traveled (VMT) for each county in millions of miles (see Table 7). A county with 

numerous commuters is generally an integral part of an urban area and could be an appropriate 
29

county for implementing mobile-source emission control strategies, thus warranting inclusion in 

the nonattainment area. 10

Table 7. Traffic and commuting patterns in the Puget Sound area 

County State 

recommend

ed 

Nonattainm

ent? 

 Vehicle 

Miles 

Traveled in 

2005 

(millions 

annually) 

 Percent 

VMT 

Growth 

(1996-

2005) 

Number 

commuting 

into any 

violating 

counties 

Percent 

commuting 

into any 

violating 

counties 

Number 

commuting into 

and w/in the 

statistical area 

Percent 

commuting 

into and w/in 

the statistical 

area 

King No 16,806 10 18,560 2 903,520 99 

Pierce Yes (P) 6,247 13 228,280 70 319,830 99 

Thurston No 2,146 7 14,350 14 96,030 95 

Kitsap No 1,633 (10) 5,120 5 104,640 98 

Snohomish No 5,225 9 1,240 0 296,750 99 

Skagit No 1,185 35 140 0 42,950 95 

Island No 397 (5) 50 0 31,510 97 

Mason No 438 13 860 5 18,310 97 

The listing of Counties on Table 7 reflects a ranking based on the number of people commuting 

to other counties. King County VMT in 2005 was the highest in the area with historic VMT 

growth of 10%. Two percent of commuters from King County commute into Pierce County, the 

County with the violating monitor. Seventy percent of commuters in Pierce County remain 

within Pierce County. VMT growth in Pierce County between 1996-2005 was 13%. Both King 

County and Pierce County contain major ports (the Port of Tacoma and the Port of Seattle), so 

there are increased levels of diesel traffic to move goods at the Ports. Interstate 5 is a major N-S 

corridor along the West Coast of the United States with significant diesel truck traffic. 

Washington looked at Pierce County VMT growth in its nine factors analysis. 

Washington obtained information from the Puget Sound Regional Council’s recently released 

draft Vision 2040 transportation plan for the region, incorporating known travel improvements 

and the preferred growth options emphasizing core centers for development. The output from 

PSRC's transportation demand model provides some travel growth estimates for the Pierce 

County area and is shown in Table 8.11

 

10 Note: The 2005 VMT data used for table 5 and 6 of the 9-factor analysis has been derived using methodology similar to that 

described in “Documentation for the final 2002 Mobile National Emissions Inventory, Version 3, September 2007, prepared for 

the Emission Inventory Group, U.S. EPA. This document may be found at: at 

ftp://ftp.epa.gov/EmisInventory/2002finalnei/documentation/mobile/2002_mobile_nei_version_3_report_092807.pdf

The 2005 VMT data were taken from documentation which is still draft, but which should be released in 2008. 

11 Puget Sound Regional Council. Draft Vision 2040 Supplemental Draft Environmental Impact Statement (SDEIS). July 2007. 

http://www.psrc.org/projects/vision/pubs/sdeis/index.htm and http://www.psrc.org/tpbgrowthandtrans2.pdf. 

Puget Sound Regional Council. Vision 2020 Update DEIS. Transportation Demand Model Output Data. Appendix D-5, 

pages D-18 to D-29. http://www.psrc.org/projects/vision/deis/appd.pdf.
30

Table 8. Pierce County Daily Travel Measures by Category in 2000 and 2040 

Daily Category of Travel 2000 Reference Data 2040 Units

Work Person Trips 293,886 535,330 Trips 

Non-work Person Trips 1,757,784 3,183,447 Trips 

Freeways Vehicle Miles Traveled 6,288,090 8,870,622 VMT

Arterials/Local Streets VMT 10,650,108 16,299,840 VMT

Freeways Vehicle Hours Traveled 129,929 191,106 VHT 

Arterials/Local Streets VHT 363,175 617,769 VHT 

Even with planned road and transit improvements, work and non-work person trips are estimated 

to increase by over 80%, while vehicle miles traveled and vehicle hours traveled are estimated to 

increase by 40% and 60%, respectively, from 2000 to 2040. Based on EPA’s PMF analysis of 

air quality data, mobile emissions likely do not contribute more than 5-10% of total PM2.5 at the 

L Street monitor on high days. The State’s boundary includes potential mobile source related 

contributions in the Tacoma area including the Port of Tacoma as well as sections of Interstate 5 

and State Highway 99 and EPA has concluded that the inclusion of these areas is sufficient to 

capture potential contributions from these sources. 

Note: The 2005 VMT data used for table 5 and 6 of the 9-factor analysis have been derived 

using methodology such as that described in "Documentation for the 2005 Mobile National 

Emissions Inventory, Version 2," December 2008, prepared for the Emission Inventory Group, 

U.S. EPA. This document may be found at: 

ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile_sector/documentation/2005_mobile_nei_versi

on_2_report.pdf 

Factor 5: Growth rates and patterns 

This factor looks at expected population and VMT for Counties in the Seattle-Tacoma-Olympia 

area from 2000 to 2005, as well as patterns of population and VMT growth. A county with rapid 

population or VMT growth is generally an integral part of an urban area and could be 

contributing to fine particle concentrations in the area. 

 Table 9 below shows population, population growth, VMT and VMT growth for counties 

that are included in the Seattle-Tacoma-Olympia area. Counties are listed in descending order 

based on VMT growth between 1996 and 2005. 
31

Table 9. Population and VMT Growth and Percent Change 

County 2005 

Population 

Percent Population 

Change (2000-05) 

 Vehicle Miles Traveled 

in 2005 (millions 

annually) 

 Percent VMT Growth 

(1996-2005) 

King, WA 1,799,119 3 16,806 10 

Pierce, WA 753,209 7 6,247 13 

Thurston, WA 228,881 10 2,146 7 

Kitsap, WA 241,525 4 1,633 (10) 

Snohomish, WA 655,564 8 5,225 9 

Skagit, WA 113,181 9 1,185 35 

Island, WA 79,983 11 397 (5) 

Mason,WA 54,169 9 438 13 

King County has the highest population but had the lowest population growth rate from 2000-

2005 (3%). Pierce County population growth was double that of King County for the same time 

period. Thurston County and Island Counties experienced the highest growth in population from 

2000-2005 at 10% and 11% respectively. However, the population of both of these areas is 1-2 

orders of magnitude lower than that of King County and 3-8 times lower than that of Pierce 

County. As stated above, based on air quality data, mobile emissions likely do not contribute 

more than 5-10% of total PM2.5 to L Street monitor PM2.5 concentrations on high days. EPA’s 

final boundary includes most of the Pierce County Growth area including the Port of Tacoma. 

Factor 6: Meteorology (weather/transport patterns) 

For this factor, EPA considered data from National Weather Service instruments in the area. 

Wind direction and wind speed data for 2005-2007 were analyzed, with an emphasis on “high 

PM2.5 days” for each of two seasons (an October-April “cold” season and a May-September 

“warm” season). These high days are defined as days where any FRM or FEM air quality 

monitors had 24-hour PM2.5 concentrations above 95% on a frequency distribution curve of 

PM2.5 24-hour values. 

 For each air quality monitoring site, EPA developed a “pollution rose” to understand the 

prevailing wind direction and wind speed on the days with highest fine particle concentrations. 

The figure identifies 24-hour PM2.5 values by color; days exceeding 35 ug/m3 are denoted with 

a red or black icon. A dot indicates the day occurred in the warm season; a triangle indicates the 

day occurred in the cool season. The center of the figure indicates the location of the air quality 

monitoring site, and the location of the icon in relation to the center indicates the direction from 

which the wind was blowing on that day. An icon that is close to the center indicates a low 

average wind speed on that day. Higher wind speeds are indicated when the icon is further away 

from the center. 

 Figure 20 is a pollution rose from instrumentation at Boeing Field, a King County airport 

which is located about 24 miles north of the violating monitor. Based on this pollution rose, the 

prevailing surface wind directions for the highest PM2.5 days in King County are from the 

southeast of the Lake Forest Park monitoring site in King County. 
32

 Given terrain influence and complex meteorology in King County and Pierce County, it 

was important to look at data from a meteorological station located closer to the violating 

monitor. As mentioned above, the Boeing Field monitor is located 24 miles away from the 

South L Street monitor. EPA, therefore, also created a pollution rose using data from the 

McChord Air Force Base which is located about 3 miles southwest of the violating monitor. 

Figure 21 is the pollution rose created with the McChord data. Based on this pollution rose, 

during high days at the Tacoma L Street monitor, wind speeds are less than 2 miles per hour. 

Because of these low wind speeds we could not draw a conclusion on an average prevailing 

surface wind direction for high PM2.5 days (exceeding 30 ug/m3). For days below 30 ug/m3 

average prevailing winds are from the southwest. The low wind speeds as well as the direction 

of the average prevailing winds at the McChord indicate that emissions from King County are 

not likely contributing to the violations at the South L Street monitor. 

Figure 20. Pollution Rose for King County WA (Source: Boeing Field) 
33

 

 Figure 21. Pollution rose for Pierce County WA (Source: McChord AFB) 
34

 

We note that the meteorology factor is also considered in each county’s Contributing Emissions 

Score because the method for deriving this metric included an analysis of trajectories of air 

masses for high PM2.5 days. The data used to create the CES for the Tacoma monitor was from 

the Seattle –Tacoma International Airport which is located 6 miles south of Boeing Field. Given 

the complex meteorology and topography of the area, and given that EPA’s pollution roses for 

the McChord Air Force Base meteorological site and the King County Boeing Field Airport 

show very different wind patterns, EPA considered the data from the McChord Air Force Base 

meteorological site in lieu of the CES for the meteorological factor analysis for the Wapato 

Hills-Puyallup River Valley area.

The wind rose from the McChord Air Force base demonstrates meteorological conditions 

in the Wapato Hills-Puyallup River Valley area during the fall and winter seasons when the 

exceedences occur at the South L Street monitor. During this time, regional air stagnations 

interrupt westerly wind flows and strong subsidence temperature inversions trap pollution levels 

and colder mean temperatures stimulate the use of residential heating devices. 

Temperature inversions vary in intensity and can persist over a period of days. These 

inversions change the mixing layer depth dramatically but generally lower the layer to less than 

800m. During persistent winter stagnations, mixing heights less than 300m are frequently 

observed typically these conditions occur when the duration of stable conditions extends beyond 

three days. 12 This occurs approximately 3-4 times during the fall and winter seasons. 

Puget Sound Clean Air Agency, in coordination with the National Weather Service office 

in Seattle operates a radar wind profiler at the Sand Point Laboratory of the NOAA. Figure 22 

displays the mixing height during the typical stagnation event in the Puget Sound area. Mixing 

heights at 600 meters or less are observed during the typical PM2.5 event. 

 

12 A Presentation to Northwest AirQuest on Analysis of Sand Point Wind Profiler and RASS system, included in the 

docket for this action. 
35

Figure 22. Typical inversion profile for the Southern Puget Sound Region stagnation 

Air movement in the area surrounding the South L Street monitoring station is influenced by 

these meteorological conditions. Figure 26 plots wind direction against hourly concentrations, 

wind direction against wind speed, wind speed against hourly concentrations and temperature 

against hourly concentration data gathered from a 2001-2008 Washington State temporary 

monitoring study13. This data indicates that meteorological conditions that are present at the L 

Street Monitoring site are typical of those observed in the area's fall and winter seasons including 

periods influenced by moderate temperatures, strong Pacific storms, and air stagnations. Highest 

hourly concentrations occur at temperatures below freezing, highest concentrations are 

associated with winds below 5 mph and often times less than 1 mph, and the highest winds from 

 

13 Study results are included in the State of Washington’s Nine Factors Analysis 
36

the south and the southwest quadrant correspond to lowest PM2.5 concentrations and the lowest 

winds from the east to southeast correspond to highest PM2.5 concentrations. 

EPA determined from this meterological data that transport from King County and other 

areas is not occurring during the periods of the highest concentrations and that a partial county 

boundary surrounding the South L Street monitor and capturing the sources in the Tacoma area 

within the CUGA is sufficiently large enough to sources of emissions that contribute to the 

violations at the South L Street monitor. 

Figure 23. Hourly concentrations and wind speed at Tacoma L Street Monitor from 2001-2008 

2004 

Factor 7: Geography/topography (mountain ranges or other air basin boundaries) 

The geography/topography analysis evaluates the physical features of the land that might have an 

effect on the air shed and therefore on the distribution of PM2.5 over the Wapato Hills-Puyallup 

River Valley/Tacoma area. Tacoma lies east of the Cascade Mountains, which act as a 

topographical barrier to pollution flow from east to west. The Olympic Mountains to the west 

result also influence pollution flow. Air flow from the west typically flows around the Olympics 

and converges in the Seattle Tacoma area. See Figure 24. This flow is interrupted during 

periods of stagnation during which low lying topographic features can influence the flow of 

pollution. 
37

 Local topography in the Tacoma area has an influence on pollutant transport. Figure 25 

displays topography in the Tacoma area. The Port area of Tacoma is surrounded by bowl like 

topography. Beyond the Port to the north, hills rise to 400 ft creating a topographical barrier 

between the north and the south. The northernmost boundary occurs at the foot of this bluff 

along SR 509. Based on our review of topographical information, as well as air quality data 

which shows that local sources contribute to the violations at the South L Street monitor and 

meteorology data which indicates that wind speeds are less than 5 mph during exceedences, 

EPA’s boundary follows the topographical bluff along SR 509 is sufficiently large enough to 

capture the sources in the area contributing to the violations at the South L Street monitor. 

Figure 24. Seattle-Tacoma-Olympia area topography 

Marysvill

Lake Forest 

Duwamish 

Tacoma L 

Lynnwoo

Queen 

Kent 

Puyallup South 
38

Figure 25. Tacoma area topography 

 

Factor 8: Jurisdictional boundaries (e.g., existing PM2.5 areas) 

In evaluating the jurisdictional boundary factor, EPA gave special consideration to areas that 

were already designated nonattainment in 2005 for violating the 1997 fine particle standards. 

Analysis of chemical composition data in these areas indicates that the same components that 

make up most of the PM2.5 mass in the area on an annual average basis (such as sulfate and 

direct PM2.5 carbon in many eastern areas) also are key contributors to the PM2.5 mass on days 

exceeding the 24-hour PM2.5 standard. These data indicate that in many cities, the same source 

categories that contribute to violations of the annual standard also contribute to exceedances of 

the 24-hour standard. 

Most areas that were originally designated nonattainment for the PM2.5 standards still have not 

attained the standards. Thus, EPA has generally concluded that counties that were designated as 

having emissions sources contributing to fine particle concentrations which continue to exceed 

the 1997 standards (all areas violated the annual standard, two also violated the previous 24-hour 

standard) also contribute to fine particle concentrations on the highest days. For this reason, 
39

EPA believes that for most existing nonattainment areas, the nonattainment area for the 2006 24-

hour standard should be the same. Consideration also should be given to existing boundaries and 

organizations as they may facilitate air quality planning and the implementation of control 

measures to attain the standard. Areas already designated as nonattainment represent important 

boundaries for state air quality planning. 

Given that no areas in Washington State violated the 1997 PM2.5 standards, our analysis of 

jurisdictional boundaries considered the planning and organizational structure of the SeattleTacoma-Olympia area to determine if the implementation of controls in a potential 

nonattainment area can be carried out in a cohesive manner. The boundary of King and Pierce 

County is less than 5 miles north of the Port of Tacoma and runs east-west along the top of the 

bluff north of the Port of Tacoma. 

Puyallup Tribal trust land parcels are located within 5-10 miles to the north and northwest of the 

L Street monitor and are contained within the boundary of the nonattainment area recommended 

by the State. To the south of the L Street monitor, Fort Lewis and the McChord Airforce base 

form a jurisdictional boundary (federal/state) land. (Figure 26). 

Figure 26. Wapato Hills-Puyallup River Valley nonattainment area and jurisdictional boundaries 

of surrounding areas 

EPA examined emissions from the two military jurisdictions to determine if sources in these 

areas are contributing to the violations at the South L Street Monitor. Emissions from the 
40

McChord Airforce base are less than 1.5 tons per year in 2006. On-base housing units include 

only 11 wood burning fireplaces and no woodstoves. Additionally, emissions at Fort Lewis are 5 

tons per year or less than 0.2% of the total PM2.5 for the PM2.5 inventory for Pierce County. 

Accordingly, EPA is excluding these military areas from the nonattainment area boundary. 

 The Wapato Hills-Puyallup River Valley nonattainment area contains the Puyallup Indian 

Reservation. Congress explicitly authorized the State of Washington and local agencies to 

administer environmental laws regulating activities on non-trust lands within the Puyallup Indian 

Reservation under the Puyallup Tribe of Indians Land Claims Settlement Act of 1989, 25 U.S.C. 

1773. Activities on trust and restricted lands within the boundary of the Puyallup Reservation 

are the responsibility of EPA and the Tribe. Given these separate jurisdictions, the Wapato 

Hills- Puyallup River Valley nonattainment area will be managed as a multi-jurisdictional 

nonattainment area with the EPA and the Puyallup Tribe responsible for nonattainment area air 

quality planning activities on trust and restricted lands within the Puyallup Reservation and the 

State responsible for nonattainment area air quality planning activities on all other portions of the 

nonattainment area including non-trust lands within the boundary of the Puyallup Reservation. 

 

 Given low potential contributions of the McChord Air Force Base, the Fort Lewis 

Military Base, and King County to the north (based on the air quality, topography and 

meteorology data discussed above), as well as low potential contributions from areas outside of 

the Tacoma CUGA, EPA’s boundary follows the Pierce-King County line, excluding King 

County to the north and along the boundaries of the military bases, to the south, excluding those 

boundaries as well as excluding areas to the east of the easternmost boundary of the Tacoma 

CUGA. 

Factor 9: Level of control of emission sources 

Under this factor, the existing level of control of emission sources is taken into consideration. 

The emissions data used by EPA in this technical analysis and provided in Table 1 (under Factor 

1) represent emissions levels taking into account any control strategies implemented in the 

Seattle-Tacoma-Olympia area before 2005 on stationary, mobile, and area sources. Data are 

presented for PM 2.5 components that are directly emitted (carbonaceous PM 2.5 and crustal PM 

2.5) and for pollutants which react in the atmosphere to form fine particles (e.g. SO2, NOx, VOC, 

and ammonia). 

 The State addressed the level of control of emission sources in the Seattle-TacomaOlympia area in their nine factors analysis noting a number of regulatory and non-regulatory 

programs in the area. 

However, given that EPA’s analysis of the other eight factors has shown that the State’s 

boundary is sufficient to capture sources contributing to the violations at the South L Street 

monitor, this information was not an important consideration in our decision on our intended 

boundary. 
41

 The following is a summary of the State’s submittal followed by a summary of EPA’s nine 

factor analysis. 

Summary of the State’s submittals 

The State submitted to EPA the partial county boundary shown in Figure 27 to EPA on March 

13, 2008. In its nine factors analysis included with this and its December 18, 2007 submittal, the 

State focused on local sources potentially contributing to the violating monitor at South L Street. 

The State explained that air quality data indicates that exceedences occur during the winter 

months (November-February), when meteorology is conducive to inversions that trap pollutants 

and people use wood to heat their homes. Continuous air quality monitors and woodstove survey 

data indicate that concentrations are highest during evening hours, and this corresponds to times 

when people burn in woodstoves and fireplaces. The State also reviewed PM2.5 speciation data 

from the South L Street monitor for the highest day in 2006 that indicates that carbonaceous 

PM2.5, which is an indicator of emissions from burning of wood, accounts for 74% or more of the 

total PM2.5 observed at the South L Street monitor. 

The State’s conclusion from this air quality data as well as the other data it analyzed in its 

nine factors analysis is that elevated concentrations at the South L Street monitor are due to local 

emissions (dominated by woodstove and fireplace emissions) occurring under meteorological 

conditions conducive to trapping those emissions locally. Accordingly, the State used the 

comprehensive urban growth area (CUGA) as a starting point for defining the nonattainment 

area because it encompasses woodstoves and other sources in Tacoma, its suburbs and the Urban 

Growth Area. They further excluded areas in the CUGA from inclusion in the boundary based on 

lack of population or sources of emissions. These areas include Port Defiance Park, Fort Lewis 

Base and McChord Air Force Base to the south and a topographic bluff to the northernmost edge 

of the (CUGA). See Figure 27. The State’s basis for excluding these areas is: 

1) The Fort Lewis and McChord Air Force Bases have minimal PM2.5 emissions, population 

density and forecasted growth. The State also argued that these areas are not upwind of 

the violating monitor when it experiences elevated PM2.5 concentrations. 

2) Throughout the area near the Pierce-King County line, sites are either on highlands or in 

valleys with little in between. The State’s analysis found that the highlands along the 

northern county line are in a different air shed from the land to the south and that the 

bluffs bordering Commencement Bay and the river valley to the south help trap fine 

particulates and increase pollutant concentrations during inversions that occur in the 

winter months. The State drew the northwestern boundary of the proposed nonattainment 

area to exclude these bluffs. They used surrogates of a road (S.R 509) and a stream to 

draw the boundary. This use of surrogates does not exclude any major sources from the 

nonattainment area. 

3) The State excluded Point Defiance Park from the proposed nonattainment area because 

the area does not contribute to nonattainment. Only 105 of the Park’s 702 acres are 

maintained. 

In focusing its initial analysis on the CUGA and local sources, the State did not directly address 

whether or not contributions from areas outside of the CUGA contribute to the violations at the L 
42

Street monitor. After EPA shared information with the states from contributing emissions score 

(CES) modeling which indicated a potential contribution from regional sources to the north, the 

State submitted additional analyses and data that focused on assessing regional contributions to 

the Tacoma L Street Monitor. This information included the following: 

1) Hourly monitoring data over 24-hour periods for the South L Street site and other sites in 

Puget Sound that show 24-hour patterns in PM2.5 levels at sites in the southern King 

County industrial areas (Duwamish and Kent), differ from those observed at monitors in 

N. King County (Lake Forest Park) and in Tacoma. In N. King County and in Tacoma, 

“v” shaped diurnal patterns are observed. These patterns indicate that peak PM2.5

concentrations occur at night and concentrations decrease during the day. These patterns 

generally correspond with periods of increased woodstove use in the evening hours noted 

on surveys conducted by the Puget Sound Clean Air Agency. 

2) Speciated PM2.5 data for the South L Street monitor compared with data for other sites 

indicating that carbonaceous PM impacts the Tacoma monitor predominantly in the 

winter when fractions of sulfate and nitrate compared with total PM2.5 are low. The 

Duwamish monitor shows ratios of sulfate/total PM that are more consistent throughout 

the year. 

3) Additional meteorological data for the L Street Monitor showing that exceedences occur 

in the winter during very low wind speeds (less than 5 mph) indicating stagnant 

conditions. 

The State concluded from this additional analysis that high Tacoma concentrations are due to 

local emissions dominated by emissions of carbonaceous PM2.5 occurring under conditions 

conducive to high concentrations (meteorology) and not transport. 

Conclusion: EPA’s review of the State’s submittal and summary of final decision

Based on monitoring data for the years 2005-2007, EPA’s nine factors analysis for the SeattleTacoma-Olympia area and other relevant factual and technical information as discussed above, 

EPA is designating the Wapato Hills-Puyallup River Valley (a portion of Pierce County) area in 

the State of Washington as “nonattainment” for the 24-Hour PM2.5 standard. See Figure 27. 

 EPA’s final designations for the State of Washington also included a review of 

information submitted by the State of Washington in determining the attainment status for the 

24-Hour PM2.5 standard areas in the State of Washington as well as the boundary for the Wapato 

Hills-Puyallup River Valley Nonattainment area14. 

 

14 On March 13, 2008, the State submitted a supplement to their initial designation recommendation letter and nine 

factors analysis dated December 18th letter and included a boundary recommendation for the area surrounding the 

monitor at 7802 South L Street (South L Street monitor). In addition to the March 13th letter, the State submitted a 

letter dated July 28, 2008 containing addition technical information for EPA’s consideration. 
43

We note that The Wapato Hills-Puyallup River Valley nonattainment area is a multijurisdictional nonattainment area, with the EPA and the Puyallup Tribe responsible for 

nonattainment area air quality planning activities on Puyallup tribal trust and restricted lands and 

the State responsible for nonattainment area air quality planning activities on all other portions of 

the nonattainment area including non-trust lands within the boundary of the Puyallup 

Reservation.15. 

EPA conducted a nine factors analysis of data for the Wapato Hills-Puyallup River Valley area 

and surrounding areas (counties in the Seattle-Tacoma-Olympia CMSA) and reviewed 

information that Washington State submitted on March 13, 2008 focused on the Tacoma CUGA 

as well as the information it later submitted on July 25, 2008. EPA’s nine factors analysis and 

review of the State’s submittals supports using the partial county boundary that the State of 

Washington submitted to EPA because: 

• Chemical speciation data indicates that there is a 74% or more contribution from 

carbonaceous PM2.5 PM which is associated with burning in woodstoves and 

fireplaces, and 10% or less contribution from PM2.5 components that are typically 

regional such as sulfate and nitrate. 

• EPA’s analysis of positive matrix factorization data indicates that 60-90% of total 

PM2.5 on exceeding days at the South L Street monitor is from wood smoke. 

There are no other sources of smoke during the winter season in the CUGA. By 

law outdoor burning is prohibited in this area. 

• Hourly PM2.5 levels at the South L Street monitor peak in the evenings and 

decrease dramatically during the day. These patterns are consistent with 

woodstove surveys conducted in Tacoma which show that on high PM2.5 days, 

woodstove use PM2.5 peaks in the late evening and is lowest around noon. 

• Meteorological data shows very low mixing heights during stagnation events 

when the exceedences are occurring, and low wind speeds (typically less than 5 

mph). Local topographical features in the area restrict pollution flow in the 

Tacoma area during stagnation events. 

• Population density in Pierce County is concentrated within the CUGA. The Fort 

Lewis and McChord Air Force Base military installations to the south are not 

included in the nonattainment area because emissions from the bases contribute 

less than 0.2% to the total inventory of PM2.5 emissions in the area. 

• The nonattainment area includes the Port of Tacoma because it has substantial 

PM2.5 emissions (estimated at 90 tons per year). This does not include offterminal emissions, which contribute additional PM2.5. The Port projects a 

 

15 Congress explicitly authorized state and local agencies to adminster activities only on non-trust lands within the 

Puyallup Indian Reservation under the Puyallup Tribe of Indians Land Claims Settlement Act of 1989, 25 U.S.C. 

1773. Activities on trust land restricted ands within the boundary of the Puyallup Reservation are the responsibility 

of EPA and the PuyallupTribe.
44

dramatic increase of its cargo handling capacity in the next two decades, with an 

estimated cargo growth factor of 4.8 from 1999 to 2015. 

 

• Analyses of speciated PM 2.5 data, diurnal patterns of PM 2.5 concentrations, and 

meteorological information from the Puget Sound region indicate that sources 

contributing the violations of the 24-hour PM2.5 standard at the South L Street 

monitor are predominantly local sources dominated by woodstove and fireplace 

emissions in the Tacoma area and not transport from King County or other 

counties in the Seattle-Tacoma-Olympia area. 

EPA has determined the boundary submitted by the State of Washington in March 2008 is 

appropriately sized to contain the sources that contribute to the violations at the South L Street 

monitor including populated areas in the Tacoma area where households operate woodstoves and 

fireplaces in the winter, and mobile sources and diesel traffic associated with good movements at 

the Port of Tacoma and sections of Interstate 5 and State Highway 99. The final boundary 

includes all land within the boundary of the Puyallup Indian Reservation. 

Additional information regarding responses to specific State comments can be found in EPA's 

Response to Comments document at 

http://www.epa.gov/pmdesignations/2006standards/tech.htm. 
45

Figure 27. Wapato Hills-Puyallup River Valley nonattainment area 
46

Attachment 2 

Description of the Contributing Emissions Score

The CES is a metric that takes into consideration emissions data, meteorological data, and air 

quality monitoring information to provide a relative ranking of counties in and near an area. 

Using this methodology, scores were developed for each county in and around the relevant metro 

area. The county with the highest contribution potential was assigned a score of 100, and other 

county scores were adjusted in relation to the highest county. The CES represents the relative 

maximum influence that emissions in that county have on a violating county. The CES, which 

reflects consideration of multiple factors, should be considered in evaluating the weight of 

evidence supporting designation decisions for each area. 

The CES for each county was derived by incorporating the following significant information and 

variables that impact PM2.5 transport: 

• Major PM2.5 components: total carbon (organic carbon (OC) and elemental carbon 

(EC)), SO2, NOx, and inorganic particles (crustal). 

• PM2.5 emissions for the highest (generally top 5%) PM2.5 emission days (herein called 

“high days”) for each of two seasons, cold (Oct-Apr) and warm (May-Sept) 

• Meteorology on high days using the NOAA HYSPLIT model for determining trajectories 

of air masses for specified days 

• The “urban increment” of a violating monitor, which is the urban PM2.5 concentration 

that is in addition to a regional background PM2.5 concentration, determined for each 

PM2.5 component 

• Distance from each potentially contributing county to a violating county or counties 

[A more detailed description of the CES can be found at 

http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html#C.]