APPENDIX C

Interstate Transport Analysis for the 2010 Sulfur Dioxide

Primary National Ambient Air Quality Standard
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APPENDIX C

Interstate Transport Analysis for the 2010 Sulfur Dioxide

Primary National Ambient Air Quality Standard

C.1 INTRODUCTION

Section 110(a)(2)(D)(i)(I) of the Clean Air Act (CAA) requires each state to prohibit emissions 

that contribute significantly to nonattainment in, or interfere with maintenance by, any other state 

with respect to any primary or secondary national ambient air quality standard (NAAQS). The 

Nevada Division of Environmental Protection (NDEP) evaluated the impact of transport of sulfur 

dioxide (SO2) emissions from Nevada sources to sensitive receptor areas in nearby states, other 

western states and eastern states. The NDEP used the U.S. Environmental Protection Agency 

(USEPA) map of preliminary nonattainment areas for the 2012 SO2 NAAQS 

(http://www.epa.gov/airquality/sulfurdioxide/designations/prelimmap.html) and the USEPA

2011 Design Value Report for Sulfur Dioxide (http://www.epa.gov/airtrends/values.html) to 

identify receptor areas, i.e., air quality planning areas that are nonattainment or maintenance for 

the 2010 or previous SO2 NAAQS or areas that have monitored values approaching the NAAQS. 

In evaluating the possible impact of SO2 transport from Nevada sources, the NDEP reviewed 

other states’ state implementation plan (SIP) submittals, 2010 SO2 NAAQS designation requests 

and responses and associated technical support documents, wind rose plots, 2008 National 

Emissions Inventory (NEI) data, and Clean Air Status and Trends Network (CASTNET, 

http://epa.gov/castnet/javaweb/index.html) monitoring data. CASTNET sites are located in areas 

where urban influences are minimal; they are considered representative of regional background 

SO2 levels. The NDEP reviewed five years (2007-2012) of CASTNET data collected at six 

national parks and one national monument: Nevada (Great Basin National Park), Utah 

(Canyonlands National Park), Montana (Glacier National Park), Colorado (Mesa Verde National 

Park), and Arizona (Grand Canyon National Park, Petrified Forest National Park, Chiricahua 

National Monument) (http://java.epa.gov/castnet/clearsession.do). The SO2 data for each of the 

seven CASTNET monitoring sites examined show low background SO2 levels throughout the 

year. Both average weekly and seasonal SO2 concentrations from the CASTNET sites were low,

below 2 ppb, indicating that the regional SO2 background concentrations are relatively low, 

which in turn implies that the bulk of the SO2 in the urban receptor areas is locally generated and 

not a regional or transport phenomenon.

 

C.2 TRANSPORT TO NONATTAINMENT RECEPTORS IN NEARBY STATES

The NDEP identified nonattainment receptors in two adjacent states: Arizona and Utah.

C.2.1 Arizona

The nearest nonattainment receptors to Nevada are the Hayden and Miami SO2 planning areas 

located in portions of Gila and Pinal Counties, Arizona. USEPA indicated in its February 6, 2013

120-day letter to the Governor of Arizona that it intends to designate Hayden and Miami 

nonattainment for the 2010 SO2 standard, in accordance with the Governor’s recommendation. In 
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the 2002 Hayden SO2 Nonattainment Area State Implementation and Maintenance Plan Arizona 

states, “Emissions inventories from all sources in the Hayden nonattainment area indicate that

although there are other sources of SO2 emissions, the ASARCO smelter is the primary source 

for SO2 emissions and comprises more than 99 percent of total SO2 emissions in the area.”

(http://www.azdeq.gov/environ/air/plan/download/haydensip.pdf, p.27). Similarly, the 2002

Miami SO2 Nonattainment Area State Implementation and Maintenance Plan notes, “Emissions 

inventories from all sources in the Miami nonattainment area indicate that although there are 

other sources of SO2 emissions, the Miami smelter is the primary source for SO2 emissions and 

comprises more than 99 percent of total SO2 emissions in the area.”

(http://www.azdeq.gov/environ/air/plan/download/miamisip.pdf, p.25). The emissions 

inventories for Hayden and Miami support the position that the elevated SO2 levels in Hayden 

and Miami are predominantly caused by local emission sources and not transport. 

The Hayden SO2 planning area is situated in part of Gila and Pinal Counties, while the Miami 

SO2 planning area is located within Gila County. These air quality planning areas are less than 

50 kilometers apart. USEPA’s 2008 National Emission Inventory shows emissions from the Gila 

and Pinal Counties total 29,470 tons (http://www.epa.gov/air/emissions/index.htm). The closest 

SO2 source in Nevada to the Hayden/Miami area is the Reid Gardner Generating Station (RGGS)

in Las Vegas. RGGS is approximately 330 miles from Hayden and 305 miles away from Miami

and emitted 940.69 tons of SO2 in 2008 or about three percent of the emissions from the receptor 

areas.

Meteorological data at the McCarran International Airport in Las Vegas for 2003 through 2011 

indicate that the prevailing winds in Las Vegas are from the south-southwest (Figure C.1). We 

can assume that winds leaving the Las Vegas area would blow mainly north-northeast, and not 

toward the Hayden/Miami area, which lies southeast of Las Vegas. Wind data from the Phoenix 

Sky Harbor International Airport for 2003 through 2011 show that the prevailing winds in 

Phoenix come mainly from the east and to a lesser degree from the west (Figure C.2). Thus, it is 

reasonable to conclude that locations southeast of the Phoenix area such as Hayden and Miami

are not significantly influenced by winds from Nevada. 

With respect to Arizona, the NDEP finds that emissions from Nevada do not significantly 

contribute to nonattainment of the 2010 SO2 NAAQS, based on the following evidence: (1) 

technical information indicating that elevated SO2 levels in Hayden/Miami were predominantly 

cause by local emission sources, (2) insignificant SO2 emissions from RGGS compared to local 

sources, (3) CASTNET data indicating that regional background levels of SO2 are generally 

low, and (4) meteorological data showing that the prevailing winds do not blow from Nevada 

toward the Hayden and Miami receptors.
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FIGURE C.1

LAS VEGAS, NEVADA WIND ROSE PLOT, 2003-2011
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FIGURE C.2

PHOENIX, ARIZONA WIND ROSE PLOT, 2003-2011
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C.2.1 Utah

Although Salt Lake County and Tooele County, Utah are still designated nonattainment for the 

24-hour and annual 1971 SO2 standard, there have been no recorded violations of the SO2

NAAQS since 1981 (http://www.airquality.utah.gov/Planning/SIP/SIPPDF/Secixb6.pdf). Utah’s 

October 25, 2011 letter to USEPA with area designation recommendations for the 2010 SO2

NAAQS confirms Utah’s long history of clean data: “Because Salt Lake County remains a 

nonattainment area for the initial 1971 SO2 NAAQS, Utah has a long-standing and robust SO2

monitoring network in Salt Lake County, extending into neighboring Davis County. For the past 

29 years, at none of those monitoring stations has the ambient SO2 concentration ever violated 

either the initial or revised standard.”

(http://www.epa.gov/so2designations/recletters/R8_UT_rev_rec.pdf). USEPA’s 120-day letter to 

Utah regarding responding to the Governor’s letter confirms continued clean data throughout 

Utah through 2011 (http://www.epa.gov/so2designations/eparesp/08_UT_resp.pd). The NDEP 

concludes that no areas in Utah are in danger of exceeding the 2010 SO2 NAAQS. 

The NDEP concludes that emissions from Nevada do not significantly contribute to 

nonattainment of the 2010 SO2 NAAQS in Utah, based on the following evidence: (1) 

monitoring data indicating that elevated SO2 levels in the Salt Lake-Tooele Counties 

nonattainment area ceased decades ago, and (2) CASTNET data demonstrating that regional 

background levels of SO2 are even lower than the low SO2 levels at identified receptors.

C.3 TRANSPORT TO NONATTAINMENT RECEPTORS IN WESTERN STATES

The NDEP identified two nonattainment receptors in one distant western state: Montana.

C.3.1 Billings and Laurel Area, Montana

In its February 6, 2013 120-day letter, the USEPA notified the Governor of Montana of its intent 

to designate Yellowstone County nonattainment for the 2010 SO2 NAAQS. Within Yellowstone 

County, all of the facilities that emit SO2 are located in the Billings and Laurel areas. Billings 

and Laurel are 15 miles apart. There are seven industrial point sources that are significant 

emitters of SO2 in the Billings/Laurel area: three petroleum refineries; a sugar beet processing 

plant; a coal-fired electrical generating station; a sulfur recovery plant; and a petroleum cokefired electrical/steam co-generation facility. Total emissions from these seven sources averaged 

about 8000 tpy during 2008, 2009 and 2010. 

(http://www.epa.gov/airquality/sulfurdioxide/designations/recletters/R8_MT_rec.pdf)

The closest SO2 source in Nevada to the Billings/Laurel receptor area is the North Valmy

Generating Station, which is jointly owned by NV Energy and Idaho Power. Valmy is over 540 

miles from the receptor area. In 2008, Valmy emitted 8130 tons of SO2. The NDEP reviewed 

meteorological data for Reno International Airport from 2003 through 2011 to indicate the 

prevailing wind direction for potential transport to the Montana nonattainment receptors (Figure 

C.3). The data indicate that the prevailing winds at Reno are mainly from the west-northwest. 

We can assume winds leaving the Reno area would blow east or southeast, not toward the 

Montana SO2 nonattainment receptors which lie northeast of Reno and Valmy.
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FIGURE C.3

RENO, NEVADA WIND ROSE PLOT, 2003-2011

Nevada relies on the following evidence to support a finding that emissions from Nevada do not 

significantly contribute to nonattainment of the 2010 SO2 NAAQS at the Billings/Laurel receptor 

area: (1) the overwhelming contribution of seven significant local emission sources to high SO2
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levels in the Billings/Laurel area, (2) CASTNET data indicating that regional background levels 

of SO2 are generally low during the time periods of elevated SO2 at the receptors, (3) the 

significant distance from the state of Nevada to the nonattainment receptors in Montana, and (4) 

the prevailing winds at Nevada emission sources not blowing toward the receptor area.

C.3.2 East Helena, Montana

In 1978, East Helena (in Lewis and Clark County), Montana was designated nonattainment for 

the 1971 SO2 standard. In 1995, USEPA approved Montana’s SO2 attainment demonstration SIP 

for East Helena. The SIP was developed in consultation with the ASARCO primary lead smelter, 

the only significant source of SO2 emissions in the East Helena nonattainment area (60 FR 5313, 

January 27, 1995). The ASARCO smelter shut down in 2001. According to the 2008 NEI, Lewis 

and Clark County emitted only 28 tons of SO2 from all source sectors combined in 2008 

(http://www.epa.gov/air/emissions/index.htm). USEPA has not proposed to designate East 

Helena nonattainment for the 2010 SO2 standard. 

Nevada’s closest significant source to the receptor area is the North Valmy Generation Station, 

which is approximately 480 miles away. Valmy emitted 8130 tons of SO2 in 2008. The NDEP 

reviewed meteorological data for Reno International Airport from 2003 through 2011 as a 

general indication of the prevailing wind direction for potential transport to the East Helena

receptor (Figure C.3). The data indicate that the prevailing winds at Reno are mainly from the 

west-northwest. We can assume winds leaving the Reno area would blow east or southeast, not 

toward East Helena, which is northeast of Reno and Valmy.

Nevada relies on the following evidence to support a finding that emissions from Nevada do not 

significantly contribute to nonattainment or maintenance of the SO2 NAAQS in East Helena: (1) 

information indicating that SO2 levels were predominantly caused by a local emission source that 

has since been shut down, (2) CASTNET data indicating that regional background levels of SO2

are even lower than concentrations currently monitored in Helena, Montana, (3) the significant 

distance from the state of Nevada to the nonattainment receptor in Montana, and (4) the 

prevailing winds at Nevada emission sources not blowing toward the receptor area.

C.4 TRANSPORT TO MAINTENANCE RECEPTORS IN NEARBY STATES

The NDEP identified maintenance receptors in one adjacent state: Arizona.

C.4.1 Arizona

There are four maintenance areas for the 1971 SO2 NAAQS in Arizona: the Ajo, Douglas, 

Morenci, and San Manuel SO2 planning areas. In 2001-2002, Arizona submitted redesignation 

requests and maintenance plans for all four areas. The emission inventories in those plans show 

that nearly all of the SO2 emissions in those areas came from the various copper smelters located 

these maintenance areas (http://www.azdeq.gov/environ/air/plan/). Only one smelter remains 

operational and is located in the San Manuel SO2 planning area. There have been no recorded 

monitoring violations of the SO2 NAAQS in any of these areas since the mid-1980s.

Furthermore, USEPA has not proposed to designate San Manuel nonattainment for the 2010 SO2

standard. 
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The RGGS in Las Vegas is the closest SO2 source in Nevada to the receptor areas. RGGS is 

approximately 300 miles from Arizona’s nearest maintenance receptor. Meteorological data at 

the McCarran International Airport in Las Vegas for 2003 through 2011 indicate that the 

prevailing winds in Las Vegas are from the south-southwest (Figure C.1). We can assume that 

winds leaving the Las Vegas area would blow mainly north-northeast, and not toward the 

maintenance areas, which lie south-southeast of Las Vegas. Meteorological data from the 

Phoenix Sky Harbor International Airport for 2003 through 2011 show that the prevailing winds 

in Phoenix come mainly from the east and to a lesser degree from the west (Figure C.2). Thus, it 

is reasonable to conclude that the maintenance areas southeast of the Phoenix area are not 

significantly influenced by emissions from Nevada. 

Based on the following evidence, the NDEP concludes that emissions from Nevada do not 

significantly interfere with the maintenance of the SO2 NAAQS in Ajo, Douglas, Morenci, or 

San Manuel: (1) technical information indicating that elevated SO2 levels in the maintenance 

areas were predominantly caused by local emission sources, (2) CASTNET data indicating that 

regional background levels of SO2 are generally low, (3) the significant distance from the state of 

Nevada to the receptors, and (4) meteorological data showing that the prevailing winds do not 

blow from Nevada toward the maintenance receptors.

C.5 TRANSPORT TO MAINTENANCE RECEPTORS IN WESTERN STATES

The NDEP identified maintenance receptors in one distant western state: New Mexico.

C.5.1 New Mexico

Grant County, New Mexico was designated nonattainment in 1978 and redesignated attainment 

in 2003. There have been no monitored violations of the SO2 NAAQS since 1975. New Mexico

attributes past violations to the Hurley smelter located directly outside the town of Hurley

(http://www.nmenv.state.nm.us/aqb/Control_Strat/sip/Grant_Text.pdf). As a consequence of 

emission controls placed on the smelter, Grant County had only 18 tons of SO2 emissions in 

2008 (http://www.epa.gov/air/emissions/index.htm). USEPA has not proposed to designate Grant 

County nonattainment for the 2010 SO2 standard 

(http://www.epa.gov/so2designations/eparesp/06_NM_resp.pdf).

The RGGS in Las Vegas is the closest SO2 source in Nevada to the Grant County maintenance 

area, approximately 570 miles away. RGGS emitted 940.69 tons of SO2 in 2008. Meteorological 

data at the McCarran International Airport in Las Vegas indicate that the prevailing winds in Las 

Vegas are from the south-southwest (Figure C.1). We can assume that winds leaving the Las 

Vegas area would blow mainly north-northeast and not southeasterly toward Grant County.

Absent CASTNET data for New Mexico, the NDEP reviewed five years (2007-2012) of data 

from four national parks between Nevada and New Mexico to determine SO2 background in New 

Mexico. These sites include the Mesa Verde National Park in Colorado, and the Grand Canyon 

National Park, Petrified Forest National Park, and Chiricahua National Monument in Arizona.

Both average weekly and seasonal SO2 concentrations from these National Park Service sites 

were low, below 2 ppb, indicating that the regional SO2 background concentrations are relatively 
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low, which in turn implies that the bulk of the SO2 in the urban receptor areas is locally 

generated and not a regional or transport phenomenon. 

Nevada relies on the following evidence to support a finding that emissions from Nevada do not 

significantly interfere with the maintenance of the 2010 SO2 NAAQS in Grant County, New 

Mexico: (1) technical information indicating that elevated SO2 levels in maintenance area were

predominantly caused by the Hurley smelter, (2) the significant distance from the state of 

Nevada to the receptor area, and (3) representative air quality data indicating that regional 

background levels of SO2 are generally low. 

C.6 TRANSPORT TO NONATTAINMENT/MAINTENANCE RECEPTORS IN 

EASTERN STATES 

The NDEP also considered potential SO2 transport from Nevada emission sources to the nearest 

nonattainment or maintenance receptors located in the eastern, midwestern, and southern states.

The nonattainment receptor nearest to Nevada is Jackson County, Missouri. The USEPA has 

proposed to designate Jackson County, Missouri nonattainment for the 2010 SO2 NAAQS

(http://www.epa.gov/airquality/sulfurdioxide/designations/eparesp/07_MO_resp.pdf). Jackson 

County is over 1000 miles away from the border of Nevada.

The NDEP evaluated the relative magnitude of SO2 emissions in Nevada to SO2 emissions in 

Missouri. The 2008 NEI indicates that SO2 emissions in Nevada are less than 5 percent of the 

SO2 emissions in Missouri (http://www.epa.gov/air/emissions/index.htm). Specifically, the 2008 

NEI shows 16,813 tons of SO2 from Nevada sources, compared to 415,204 tons of SO2 from 

Missouri sources (34,693 tons SO2 in Jackson County).

The NDEP believes the following factors support a finding that emissions from Nevada do not 

significantly contribute to nonattainment of the 2010 SO2 NAAQS at the Jackson County

receptor: (1) the relatively small magnitude of the emissions inventory of SO2 in Nevada

compared to Missouri, combined with (2) the relatively long distance of the state of Nevada from 

the receptor. These factors also support a qualitative conclusion that emissions from Nevada 

sources do not significantly contribute to nonattainment or interfere with the maintenance of

these NAAQS at any of the other receptors farther east. 

C.7 CONCLUSION

The preceding analysis indicates that sulfur dioxide nonattainment (current, and impending for 

the 2010 NAAQS) and maintenance areas in adjacent and nearby states, as well as other western 

and eastern states are generally the result of documented local emission sources, which in some 

cases have ceased operation since the time of designation. Furthermore, the receptor areas the 

NDEP identified for the 2010 SO2 NAAQS are a considerable distance from Nevada sources. 

Based on these factors and the above evaluation, the State of Nevada concludes that sulfur 

dioxide emissions from Nevada do not contribute to nonattainment or interfere with maintenance 

of the 2010 SO2 standard or the previous SO2 standards in any other state. Nevada commits to 

continue to review new air quality information as it becomes available to ensure that this 

negative declaration is still supported by such information.