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Appendix C – Maintenance Receptors 

1. EPA Region 9 States – California and Nevada 

1. Eastern California – Inyo County 

2. Southern California – Riverside and San Bernardino Counties 

3. Northern California – Butte, Sacramento, and Sutter Counties 

4. California/Mexico Border – Imperial County 

5. Nevada – Washoe County 

2. EPA Region 8 States – Montana and Utah 

 1. Montana – Lewis and Clark County (Helena) 

2. Montana –Silver Bow County (Butte) 

3. Utah – Utah County (Provo-Orem) 

4. Utah – Davis, Salt Lake and Weber Counties (Greater Salt Lake Area) 

3. EPA Region 10 States –Washington 

1. Washington – Pierce County (Tacoma) 

 2. Washington – Yakima County (Yakima) 

 
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1.1. Eastern California – Inyo County 

County Site Name Description 

Inyo Keeler This site is affected primarily is by local crustal sources. 

Massive erosion from Owens dry lake; in Owens Valley. 

Elevated levels of PM2.5 in Inyo County are measured at a single monitor, the Keeler monitor, which is 

located adjacent to the Owens Lake Bed. (See Figures 1.1.A and 1.1.B, below). The Owens Lake Bed is 

surrounded by steep terrain. EPA believes that because of the proximity of the monitor to a large local 

source of particulate matter, and the steep nearby terrain. It is therefore reasonable to conclude that 

emissions from Oregon do not interfere with the maintenance of the 24-hour PM2.5 standard at this 

receptor. 

The Owens Valley Planning Area (OVPA) is located in Inyo County in eastern-central California. It is 

situated at the south end of the deep, long, narrow Owens Valley with the Sierra Nevada to the west 

(maximum elevation 14,495 feet), the Inyo Mountains to the east (maximum elevation 14,246 feet), and 

the Coso Range to the south (maximum elevation 8,160 feet). The predominantly dry, alkaline Owens 

Lake bed is approximately eight miles south of the community of Lone Pine on U.S. Highway 395, 60 

miles north of the city of Ridgecrest, and 35 miles west of Death Valley. The bed of Owens Lake is 

defined as the area below 3,600 feet above mean sea level (all elevations will be given in feet above 

mean sea level). The lake bed extends about seventeen miles north and south and ten miles east and west 

and covers an area of approximately 110 square miles (70,000 acres). 

Table 1: PM2.5 Levels at the Keeler Monitor 

Year PM2.5 Level (μg/m3) 

2008 -2010 36 

2009 -2011 36 

2010 -2012 33 

Owens Lake is the largest single source of PM-10 in the United States.1 Water was first diverted from 

the Owens River to the City of Los Angeles in 1913, and by 1926 Owens Lake was dry. Today, the 

Owens lakebed produces enormous amounts of windblown dust in exceedance of federal air pollution 

standards for particulate matter. 

                                                            

1 http://www.gbuapcd.org/owenslake.htm
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Monitoring and research conducted for more than 20 years, as well as three previous State 

Implementation Plans (SIPs), has determined that wind-blown dust from the dry bed of Owens Lake is 

the dominant cause of NAAQS violations for PM10 in the nonattainment area. 2

Figure 1.1.A: Keeler Dunes 3

                                                            

2

 Final 2008 Owens Valley PM10 Planning Area Demonstration of Attainment State Implementation Plan, January 28, 2008. 

http://www.gbuapcd.org/ovpm10sip.htm

3 http://www.gbuapcd.org/owenslake/dustID/20120516CurrentSites.
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Figure 1.1.B: Owens Lake Dust ID Network Map 
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1.2. Southern California –Riverside, Los Angeles, and San Bernardino Counties 

County Site Number 2008-2010 2009-2011 2010-2012

Riverside 060658001 38 35 34 

San Bernardino 060710025 37 34 32 

San Bernardino 060712002 37 31 32 

Los Angeles 060370002 38 36 31 

The high PM2.5 concentrations in the South Coast Air Basin are mainly due to the secondary formation 

of smaller particulates resulting from mobile, stationary and area source emissions of precursor gases 

(i.e., NOx, SOx, NH4, and VOC) that are converted to PM in the atmosphere. 

Speciated PM2.5 data at the Central Los Angeles Site (CELA) and the Rubidoux site (RIVR) indicate 

that organic carbon, ammonium nitrate, and ammonium sulfate constitute the major components at each 

site (shown in Figures 1.2.A and 1.2.B, below). 24-hour PM2.5 design value trends show strong 

downward trend at all sites in the South Coast Basin (shown in Figure 1.2.C, below).4

PM2.5 is essentially a combustion generated pollutant due to the volume of traffic flow and numbers of 

sources (both point and area) located in the region. It is important to note that the areas with the highest 

concentrations are directly downwind of an area with major ammonia sources associated with dairies 

and poultry farming.5

The South Coast Air Quality DRAFT 2012 Air Quality Management Plan6 air quality projections show 

that the emission control strategy outlined in the plan will result in air quality improvement at each of 

the receptors (see Figure 1.2.D: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 

Baseline, 2014 and 2014 Controlled). 

The air quality trends and projections indicate that the emission strategy is effective in reducing PM2.5. 

It is therefore reasonable to conclude that emissions from Oregon do not interfere with the maintenance 

of the 24-hour PM2.5 standard at these receptors. 

                                                            

4

 Joe Cassmassi, Scientific, Technical & Modeling Peer Review (STMPR) Advisory Group Meeting, September 22, 2011. 

5

 Final 2007 Air Quality Management Plan (AQMP), Appendix V – Modeling and Attainment Demonstrations June, V-2-10. 6 http://www.aqmd.gov/aqmp/2012aqmp/draft/Chapters/Ch5.pdf
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Figure 1.2.A: Speciated data for Central Los Angeles7

                                                            

7

 STMPR Item # 5 - 2008 PM2.5 Air Quality Characterization, January 19, 2012. Bong-Mann Kim. 
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Figure 1.2.B: Speciated PM2.5 data for the Rubidoux site in Riverside County 8

                                                            

8

 STMPR Item # 5 - 2008 PM2.5 Air Quality Characterization, January 19, 2012. Bong-Mann Kim. 
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Figure 1.2.C: 24-hour PM2.5 Design Value Trends 

 
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Figure 1.2.D: Maximum 24-Hour Average PM2.5 Design Concentrations: 

2008 Baseline, 2014 and 2014 Controlled9

                                                            

9 http://www.aqmd.gov/aqmp/2012aqmp/draft/Chapters/Ch5.pdf
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1.3. Northern California – Butte, Sacramento, and Sutter Counties 

County Site Name Description 

Butte Chico This receptor is in the Chico nonattainment area. 

The monitored exceedances likely reflect localized sources occurring 

during wintertime temperature inversions with low winds that persist 

for several days in an area that trap emissions together with complex 

topography. The speciation data from high concentration days 

indicates that as much as 75% of the concentrations are due to organic 

carbon, which also indicates that residential wood burning emissions 

are the dominant source. Also, about 70% of the emissions are 

estimated to be from area sources, of which residential wood burning is 

the dominant source, contributing 2.65 of the 6.4 tons per day (ARB 

Almanac website (2006) 

http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm) 

Sacramento SacramentoDel Paso 

Manor 

This receptor is in the Sacramento Metro nonattainment area. 

The monitored exceedances likely reflect localized sources occurring 

during wintertime temperature inversions with low winds that persist 

for several days. The speciation data on days during cold seasons in 

2004-2006 with the highest 5 percentile of PM2.5 concentrations show 

that the mass is 47-60% total carbon mass (TCM), which indicates 

residential wood burning as a significantly contributing source 

(http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_F_li

mited_2004-06_speciation_data_report.pdf). 

The largest single source of Sacramento's wintertime PM2.5 emissions 

is wood and other solid fuel burning in fireplaces, wood inserts, wood 

stoves and pellet stoves. 

There is a strong downward trend in this area in recent years 

(http://www.epa.gov/region9/air/trends/pm25.html). 

Sutter Yuba City Yuba City-Marysville 

The monitored exceedances likely reflect localized sources occurring 

during wintertime temperature inversions with low winds that persist 

for several days. 

There is a strong downward trend and preliminary 2009-2011 data 

indicates the area may be attaining the standard. 

(http://www.epa.gov/region9/air/trends/pm25.html). 
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The Northern Sacramento Valley Air Basin is bounded on north and west by the Coastal Mountain 

Range and on the east by the southern portion of the Cascade Mountain Range and the northern portion 

of the Sierra Nevada Mountains. These mountain ranges reach heights in excess of 6,000 feet with peaks 

rising much higher. This provides a substantial physical barrier to locally created pollution. 

For the areas under consideration, high PM2.5 concentrations mostly occur during stagnant conditions 

during winter, with radiation inversions. The cooling of the ground, as heat is radiated away, creates an 

inversion, since air near the ground is cooler than that above. This inhibits mixing and confines 

pollutants to a relatively shallow layer near the ground. A typical value for maximum mixing height 

during high PM2.5 conditions is 300 meters (984 feet) AGL (above ground level). EPA recognizes that 

an inversion height is not a rigid boundary extending through a fixed elevation. In reality the inversion 

would be partly terrain-following, and the degree of stagnation would be subject to additional influences 

at the foothill edges, such as strong diurnal slope flows. In any case, mixing heights vary by site and 

date, so any single height can provide only a scale for comparison, not a definitive value. Nevertheless, 

the inversion height provides an indicator of the area over which inversions may be enhancing pollution 

concentrations, and of the extent of the area that may be contributing to NAAQS violations. 

Because these areas in Northern California have topographical features higher than the typical daytime 

height of the inversion layer, EPA considered the inversion height to estimate the size of the area likely 

to have similar pollution conditions and to contribute to NAAQS violations. For example, the eastern 

portion of Butte County extends into the foothills of the Sierra Nevada Mountains. For Chico, the 300 

meters AGL (984 feet) inversion layer thickness translates to an elevation contour of 375 meters (1221 

feet) MSL (above Mean Sea Level). Much of eastern portion Butte County is above this elevation, as 

shown in Figure 1.3.B below. 

In summary, topography is an important factor in these areas, given that the inversion layer, which can 

lead to winter PM2.5 exceedances in the Sacramento Valley, is blocked by the Sierra foothills. 

The steep terrain and speciated PM2.5 data at these Northern California receptors supports the fact that 

the PM2.5 is largely of local origin. It is therefore reasonable to conclude that emissions from Oregon do 

not interfere with maintenance of the 24-hour PM2.5 standard at these receptors. 
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Figure 1.3.A: Average Composition on 14 Exceedance Days - Chico 

Average Composition on

14 Exceedance Days- Chico

AmmNitrate

16%

AmmSulfate

2%

OC

75%

Other

2%

Geological

1%

Elements

2%

EC

2%

PM2.5 Mass= 52.2 ug/ m3

Sum of Species=51.4 ug/ m3
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Figure 1.3.B: Map of Butte County PM2.5 Nonattainment Area 
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1.4. California/Mexico Border – Imperial County 

Levels of PM2.5 in Imperial County that exceed the 2006 24-hour PM2.5 NAAQS are recorded at the 

Calexico – Ethel Street monitoring site, which is located near the Mexican Border (see Figure 1 below). 

The elevated levels of PM2.5 occur primarily in the wintertime, and seven of the nine values above the 

level of 35 μg/m3 in the years 2008-2010 occur in December or January (See table 1, below). 

The levels of PM2.5 measured at the Brawley and El Centro monitoring sites are always lower – usually 

much lower – than those measured at the Calexico Ethel Street monitor on days when the PM2.5 levels 

at the Calexico Ethel Street monitor exceed 35 μg/m3

 (see Figure 2, below). Because these nearby 

monitors do not show similar increases in monitored values, it appears that the cause of elevated PM2.5 

appears to be from a local source near the California/Mexico Border. It is therefore reasonable to 

conclude that emissions from Oregon do not interfere with maintenance of the 24-hour PM2.5 standard 

at this receptor. 

Figure 1: PM2.5 Monitoring Sites in Imperial County California 
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Table 1.1.A: Calexico-Ethel Street: Dates of PM2.5 Values Above 35μg/m3

for the Years 2006 through 2010 

Year Dates 

2008 January 4, and December 22, 25 

2009 September 4, and December 12, 21, 24 

2010 June 28, and December 4 

Figure 2: PM2.5 levels (μg/m3) at Imperial PM2.5 Monitoring Sites 

from 2006 to 2010, for days of elevated PM2.5 

 

0

10

20

30

40

50

60

70

Calexico ‐Ethel

El Centro

Brawley
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1.5 Nevada – Washoe County

Elevated PM2.5 levels at the Reno receptor generally occur during wintertime stagnation episodes, with 

lower levels of PM2.5 during the other times of the year (see Figures 1.6.A thru 1.6.D: PM2.5 24-hour 

Averages at the Reno PM2.5 Monitoring Site.) Low temperatures and strong inversions are the dominant 

contributing factors to the elevated PM2.5 levels: 

The year began with several consecutive days of stable atmospheric conditions and strong 

temperature inversions. The lowest temperature of the month (18 degrees) occurred on 

January 4. The low temperature and the strong inversions were contributing factors to a 24-hour 

PM2.5 concentration and NAAQS exceedance of 38.8 μg/m3 on January 5, 2010.10

The levels of PM2.5 measured in March through November in 2008 through 2011 are generally very 

low. The exception to this is in June and July of 2008 when wildfires had a large impact on PM2.5 

concentrations in this area, and the Washoe County Health District has flagged the affected data as 

exceptional events.11 An exceptional events request was submitted to EPA Region IX in October 2009. 

EPA has not yet taken action on the request.12

The wintertime PM2.5 exceedances occur during periods of strong inversions and are largely due to 

local emissions. . It is therefore reasonable to conclude that emissions from Oregon do not interfere with 

maintenance of the 24-hour PM2.5 standard at this receptor. 

                                                            

10 Washoe County, Nevada Air Quality Trends (2001-2010), May 2011. 

http://www.co.washoe.nv.us/repository/files/4/Washoe-County-Air-Quality-Trends-2001-2010.pdf 11 Washoe County, Nevada Air Quality Trends (2002-2011), May 24, 2012. 

http://www.co.washoe.nv.us/repository/files/4/Washoe-County-Air-QualityTrends-2002-2011.pdf 12 Id.
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Figure 1.6.A: PM2.5 24-hour Averages at the Reno PM2.5 Monitoring Site for 2008 
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Figure 1.6.B: PM2.5 24-hour Averages at the Reno PM2.5 Monitoring Site for 2009 
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Figure 1.6.C: PM2.5 24-hour Averages at the Reno PM2.5 Monitoring Site for 2010 

 
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Figure 1.6.D: PM2.5 24-hour Averages at the Reno PM2.5 Monitoring Site for 2011 
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Figure 1.6.E: Washoe County Ambient Air Monitoring Sites (2002-2011)13

                                                            

13 http://www.co.washoe.nv.us/repository/files/4/Washoe-County-Air-QualityTrends-2002-2011.pdf 
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2. Region 8 States – Montana and Utah 

2.1. Montana – Lewis and Clark (Helena) 

Elevated levels of PM2.5 in the Helena area occur primarily in the winter months.14 The Helena Valley 

is topographically prone to cold pool inversion conditions during the winter months.15 Speciation data 

indicates that emissions from wood smoke are the primary contributor to exceedances of the PM2.5 

standard in Helena.16 In the months when violations of the NAAQS occurred at the Helena receptor, the 

nearby Gate of the Mountains Wilderness Area monitor did not exceed 2 μg/m3.

17 All of these factors 

taken together indicate that high levels of PM2.5 in Helena are driven by local emissions, which become 

trapped and build during wintertime inversions. 

2.2. Montana – Silver Bow County (Butte) 

Elevated levels of PM2.5 in the Butte area occur primarily in the winter months.18 The Butte area is 

topographically prone to wintertime temperature inversions, as it is situated in a mountain valley. 

Speciation data indicates that emissions from wood smoke are the primary contributor to exceedances of 

the PM2.5 standard in Butte.19 These factors indicate that high levels of PM2.5 in Butte are driven by 

local emissions, which become trapped and build during wintertime inversions. 

Based on the above factors, we believe it is reasonable to conclude that emissions from Oregon do not 

interfere with maintenance of the 2006 24-hour PM2.5 standard at these Montana receptors. 

2.3. Utah – Utah County (Provo)

A large portion of Utah County is designated as the Provo 2006 24-hour PM2.5 nonattainment area 

(NAA). 

The Provo NAA is situated in the Utah Valley. Like the other low-lying valleys just west of the Wasatch 

Front, the topography of the Utah Valley makes it prone to temperature inversions. During inversions, 

the Provo NAA features stagnant air masses and calm to light winds. As the airshed is essentially 

capped, PM2.5 is formed in-situ (and trapped) via fresh locally derived emission sources and secondary 

                                                            

14 The maintenance receptor in Helena, MT violated the 2006 PM2.5 NAAQS only in 2010. Each of the exceedances of the

2006 PM2.5 standard at this receptor during 2010 occurred during the winter months, with all but one exceedance

occurring in December or January.  Monitor values are accessible on EPA’s AirData website,

http://www.epa.gov/airquality/airdata/.   15 Johnson, J. “Case Study of a Persistent Cold Pool in the Helena Valley.” NOAA. November 21, 2000.   16 Ward, T., Lange, T., “The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley communities.”

Environmental Pollution 158 (2010) 723–729. 17 The Gate of the Mountains IMRPOVE monitor is located roughly 17 miles from Helena, MT. The IMPROVE monitor data

can be found in Appendix D to this TSD, in the docket for this action. 18 In 2009 and 2010, the only recent years in which the Butte maintenance receptor violated the 2006 PM2.5 NAAQS, each

exceedance of the NAAQS occurred in either December or January. Monitor values are accessible on EPA’s AirData website,

http://www.epa.gov/airquality/airdata/.    19 Ward, T., Lange, T., “The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley communities.”

Environmental Pollution 158 (2010) 723–729.
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chemistry. Transport of air masses between the Salt Lake City and Provo NAAs can occur during 

inversions, as there is a 4.75-mile gap in the mountains separating these airsheds which is below the 

approximate average inversion height for these areas. 

Speciation data from exceedance days from 2004-2006 showed the average composition of PM2.5 in 

Provo is 71% ammonium nitrate, with 21% carbon and organic compounds, 8% ammonium sulfate, and 

2% crustal. 

Several factors, including significant mobile, point and area sources contribute to primary and 

secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 standard during stable weather events 

associated with strong inversions. Based on this information, we believe it is reasonable to conclude 

that emissions from Oregon do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at 

this receptor. 

2.4. Utah – Davis, Salt Lake and Weber Counties (Greater Salt Lake Area) 

All of Salt Lake and Davis Counties and a portion of Weber County are designated as part of the Salt 

Lake City (SLC) 2006 24-hour PM2.5 nonattainment area (NAA). 

The SLC NAA is situated in a valley bordered on the west by the Stansbury Mountains, Promontory 

Mountains and the Great Salt Lake, and on the east by the Wasatch Front. During inversions, the NAA 

becomes a closed airshed (save for potential transport between the Salt Lake City and Provo NAAs) 

featuring stagnant air masses and light winds which typically oscillate back and forth within the airshed. 

As the airshed is essentially capped during inversions, PM2.5 is formed in-situ (and trapped) via fresh 

locally derived emission sources and secondary chemistry. 

Speciation data from exceedance days from 2004-2006 showed the average composition of PM2.5 in 

Salt Lake City is 58% ammonium nitrate, 31% carbon and organic compounds, 8% ammonium sulfate, 

and 2% crustal. 

Several factors, including significant mobile, point and area sources contribute to primary and 

secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 standard during stable weather events 

associated with strong inversions. 

Based on the above-described factors, we believe it is reasonable to conclude that emissions from 

Oregon do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at these receptors. 

3. Region 10 States - Washington 

3.1 Washington – Pierce County (Tacoma) 

(Site name: Tacoma-South L Street) 

A portion of Pierce County (Tacoma) is designated nonattainment for the 2006 24-hour PM2.5 NAAQS.
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The state analysis indicates that wood smoke associated with home heating is the largest source of 

PM2.5 in the Tacoma-Pierce County nonattainment area. 

The state data asserts that the 24-hour PM2.5 problem is highly localized. Surface measurements at 

multiple sites suggest that the only design values which violate the 2006 24-hour PM2.5 NAAQS are in 

the core of the nonattainment area, within about 3 km of the South L Street monitor. Beyond about 3-

5km, the design values drop and are well below the NAAQS. 

On-site sonic anemometer and vertical temperature profile measurements revealed that exceedances 

only occurred: in winter; at night; when there was a surface inversion; below an ambient temperature of 

about 50F; when wind speeds were less than 1.5 mph. 

Within 3km of the South L Street monitor, during the season in which the violations occur, wood smoke 

is the largest source, on-road mobile is second but appears to be significantly smaller, industrial and 

other sources make up the remainder and are minor. 

EPA Region 10 PMF receptor modeling identified 10 factors contributing to elevated wintertime 24-

hour PM2.5 levels including wood smoke (60%), organic pyrolysis rich (10%), nitrate rich (7%), iron 

rich (7%), sulfate rich (5%) and smaller contributions from other identified factors (gasoline vehicles, 

sea salt, soil, aged sea salt, and a 2nd sulfate rich factor). 

3.2 Washington – Yakima County (Yakima) 

EPA Region 10 PMF receptor modeling identified 10 factors contributing to elevated wintertime PM2.5 

including wood smoke (24%), nitrate rich (24%), gasoline vehicles (16%), organic pyrolysis rich (9%), 

sulfate rich (7%) and smaller contributions from other identified factors (iron rich, sea salt, soil, zinc 

rich, and urban unidentified). 

Based on the above-described factors, we believe it is reasonable to conclude that emissions from 

Oregon do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at these Washington 

receptors.