Appendix C – Maintenance Receptors 

1

Technical Support Document for EPA’s Proposed Action on the 

State of Arizona’s 2009 Infrastructure State Implementation Plan (Transport Portion) for the 

2006 24-hour Fine Particulate (PM2.5) National Ambient Air Quality Standard 

Appendix C – Maintenance Receptors 

1. EPA Region 9 States – California 

1. California/Mexico Border – Imperial County 

2. Northern California/San Francisco Bay Area – Alameda, Santa Clara, and Solano Counties 

3. Northern California – Sacramento County 

4. Southern California – Orange, Los Angeles, Riverside, and San Bernardino Counties 

2. EPA Region 8 States – Utah 

1. Utah – Utah County (Provo-Orem) 

2. Utah – Salt Lake and Weber Counties (Greater Salt Lake Area) 

Note: See Appendix E for further technical data for Greater Salt Lake Area, Utah. 

 
Appendix C – Maintenance Receptors 

2

1.1. 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 fifteen of the eighteen values above 

the level of 35 μg/m3 in the years 2006-2010 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 Arizona will not interfere with the maintenance of the 24-hour PM2.5 

standard at this receptor. 

Figure 1: PM2.5 Monitoring Sites in Imperial County California 

 
Appendix C – Maintenance Receptors 

3

Table 1.1.A: Calexico-Ethel Street: Dates of PM2.5 Values Above 35μg/m3

for the Years 2006 through 2010

Year Date 

2006 January 8, 14, 17, 29 and December 22, 25 

2007 November 20, and December 5, 17 

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
Appendix C – Maintenance Receptors 

4

1.2. Northern California/San Francisco Bay Area – Alameda, Santa Clara, and Solano Counties 

Table 1.2.A: San Francisco Bay Area Maintenance Receptor Design Values 

County ID 

Design Value 

(μg/m3) 

2006-2008 

Design Value 

(μg/m3) 

2007-2009 

Design 

Value(μg/m3) 

2008-2010 

Alameda 060010007 36 34 30

Santa Clara 060850005 36 34 30

Solano 060950004 36 36 31

The maintenance receptors in the San Francisco Bay Area, shown in Table 1 and Figure 3, were only 

slightly above the standard (1 μg/m3) for the years 2006-2008 and 2007-2009. There is a downward 

trend in the 24-hour PM2.5 design value at each of the receptors. 

The monitored PM2.5 values above 35μg/m3likely reflect localized sources because they occur during 

wintertime temperature inversions with low winds that persist for several days, which allow directly 

emitted and secondary PM to build up over a few days.

1

Figures 4 and 5 illustrate the wind speed and 

direction for various levels of PM2.5, and show that elevated levels of PM2.5 occur during wintertime 

conditions with light wind speed. The Bay Area Air Quality Management District analyses show that 

during the winter peak season, wood burning can account for 33 to over 80 percent of the PM2.5 

concentrations. Ammonium nitrate and elemental carbon from diesel sources can also contribute to 

elevated PM2.5 concentrations. 

During summer, the Pacific high pressure system (Pacific High) typically strengthens and resides in the 

northeastern Pacific Ocean, pushing the jet stream and its attendant storm systems well to the north of 

California. In winter, the Pacific High weakens and shifts southward, which allows storm systems to 

come across central California. As a result, almost all of the Bay Area’s annual precipitation takes place 

in the November through April period. During the winter rainy periods, inversions are weak or 

nonexistent, winds are often moderate and air pollution potential is very low. However, during winter 

periods when high pressure systems become established over the Bay Area, inversions become strong, 

winds are light and pollution potential is high. These periods are characterized by winds that flow out of 

the Central Valley into the Bay Area and often include tule fog. 

The San Francisco Air Basin encompasses approximately 5,430 square miles and consists of all of 

Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo and Santa Clara counties, the southern 

half of Sonoma County and the southwestern portion of Solano County. The region is characterized by 

 

1 BAAQMD Reports: Sources of Bay Area Fine Particulates (2008); Fine Particulate Matter Data Analysis and Modeling in 

the Bay Area (2009); Evaluation of the Effectiveness and Benefits of the Wood Burning Rule in the San Francisco Bay Area 

for winter 2009-2010 (2010); Trends in Bay Area Ambient Particulates (2011). 
Appendix C – Maintenance Receptors 

5

complex terrain, consisting of coastal mountain ranges, rugged hillsides, and inland valleys and bays. 

Elevations range from sea level to 1,500 feet. 

EPA believes that, based on the local nature of the PM2.5 problem and the distance of the area from 

Arizona, it is reasonable to conclude that emissions from Arizona will not interfere with the maintenance 

of the 24-hour PM2.5 standard at these receptors. 
Appendix C – Maintenance Receptors 

6

Figure 3: San Francisco Bay Area 
Appendix C – Maintenance Receptors 

7

Figure 4: Alameda County Pollution Rose for 2005-2007 

S

W E

2 4 6 8 10 12+

Wind Speed (mph)

Site 060011001

San Francisco Bay Area, CA [Alameda County, CA]

Pollution Rose, 2005-2007

Year

2004

2005

2006

98th %-ile

27.6

30.4

33.3

# days > 35

.

2

2

Design

Value

30-A

2 exceedance(s) not plotted 

(due to missing or variable wind data) 

San Francisco Bay Area, CA

Meteorological data from 11.8 miles away

SAN_JOSE_INTL_AP (ID=23293)

2005

2006

2007

Concentration:

n > 40 μg/m3

n 35 - 40 μg/m3

n 30 - 35 μg/m3

n < 30 μg/m3

Season:

cool (Oct-Apr)

warm (May-Sep)
Appendix C – Maintenance Receptors 

8

Figure 5: Santa Clara County Pollution Rose for 2005-2007 

 
Appendix C – Maintenance Receptors 

9

1.3 Northern California – Sacramento County 

County Site Name Description 

Sacramento Site ID: 

060670010 

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 of 

emissions. 

(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). 

The Northern Sacramento Valley Air Basin is bounded on the 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. 

The maintenance receptor identified above likely reflects 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 the 

PM2.5 has a high carbon mass, which also indicates that residential wood burning emissions are the 

dominant source.

2 Also, as noted above, 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. 

For the area 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 m (984 ft) 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 

 

2 ARB Almanac website (2006) http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm)
Appendix C – Maintenance Receptors 

10

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 interfere with maintenance of the NAAQS. 

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 interfere with maintenance of the NAAQS. 

In summary, topography is an important factor for this area, 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 this Northern California receptor supports the fact that the 

PM2.5 is largely of local origin. Therefore, it is reasonable to conclude that transport from Arizona does 

not interfere with maintenance of the 2006 PM2.5 standard at this receptor. 

1.4. Southern California – Orange, Los Angeles, Riverside, and San Bernardino Counties 

Table 1.4.A: South Coast Air Basin Maintenance Receptor Design Values 

County Site Name Description 

Orange Anaheim The 2008-2010 design value for this site is 30 μg/m3. The 

previous design values were 38 μg/m3 in 2006-2008, and 37 

μg/m3 in 2007-2009. 

The current design value for the Anaheim site is 30 μg/m3, well below the 2006 24-hour PM2.5 

standard. The Anaheim site has shown a consistent downward trend over the last ten years. (see Figure 

6 : 24-Hour Average PM2.5 Design Concentrations 1999-2010). The South Coast Air Quality DRAFT 

2012 Air Quality Management Plan air quality projections show that the emission control strategy 

outlined in the plan will result in air quality improvement at this site. (see Figure 7: Maximum 24-Hour 

Average PM2.5 Design Concentrations: 2008 Baseline, 2014 and 2014 Controlled). Therefore, it is 

reasonable to conclude that emissions from Arizona will not interfere with the maintenance of the 24-

hour PM2.5 standard at this receptor. 

A more complete discussion of air quality in the South Coast Air Basin is included in Appendix B – 

Nonattainment Receptors at B.1.2.
Appendix C – Maintenance Receptors 

11

Figure 6 : 24-Hour Average PM2.5 Design Concentrations 1999-2010.3

Figure 7: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 Baseline, 2014 and 

2014 Controlled4

 

3

Joe Cassmassi, Item #2, Scientific, Technical & Modeling Peer Review (STMPR) Advisory Group Meeting #1 for 2012 Air 

Quality Management Plan (AQMP), September 22, 2011. 

http://aqmd.gov/gb_comit/stmpradvgrp/2012AQMP/meetings/2011/sept22/stmpr01.pdf 
Appendix C – Maintenance Receptors 

12

2.1 Utah – Utah County 

(Site ID: 490495008) 

A large portion of Utah County is designated as the Provo 2006 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 

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 standard during stable weather events associated with strong 

inversions. 

2.2 Utah – Salt Lake and Weber Counties (Greater Salt Lake Area) 

(Site IDs: 490353007 (Salt Lake County) and 490570007 (Weber County)) 

 

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

(SLC) 2006 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 standard during stable weather events associated with strong 

inversions. 

 

4

http://www.aqmd.gov/aqmp/2012aqmp/draft/Chapters/Ch5.pdf