Chapter One – Overview 

1.1 NEVADA’S CLASS I AREA – JARBIDGE WILDERNESS AREA 

1.1.1 Geographic and Physiographic Setting 

1.1.2 Visibility Impairment 

1.1.3 Observed Haze Events 

 1.1.3.1 Windblown Dust Events 

 1.1.3.2 Natural Fire Events 

1.2 THE WESTERN REGIONAL AIR PARTNERSHIP AND NEVADA 

1.3 TECHNICAL SUPPORT BACKGROUND 

1.3.1 Regional Haze Monitoring Network 

1.3.1.1 Overview of the IMPROVE Monitoring Network 

 1.3.1.2 IMPROVE Monitor JARB1

1.3.2 Emissions Analyses and Projections 

1.3.2.1 Preparation of Baseline Emissions Inventories 

1.3.2.2 Projected 2018 Emissions Inventories 

1.3.2.3 WRAP’s Technical Support System

1.3.3 Air Quality Modeling 

1.3.3.1 Visibility Modeling 

1.3.3.2 Source Apportionment Modeling 

1.4 REFERENCES 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-1 
1.1 NEVADA’S CLASS I AREA – JARBIDGE WILDERNESS AREA 

Nevada has one mandatory Class I Area, the 113,167 acre Jarbidge Wilderness Area (Jarbidge 

WA), located within the Humboldt National Forest in the northeastern portion of Nevada, as 

shown on Figure 1-1. 

FIGURE 1-1 

LOCATION MAP SHOWING MANDATORY CLASS I AREAS 

IN THE WRAP REGION

1.1.1 Geographic and Physiographic Setting 

Much of the following discussion regarding the physiographic and geologic setting of Nevada is 

paraphrased from Stewart (1980). Nevada lies almost entirely within the Great Basin portion of 

the Basin and Range physiographic province. The Basin and Range is characterized by a series 

of generally north-trending mountain ranges separated by alluvial valleys as shown on Figure 1-

2. A small portion along the western part of the state lies within the mountainous Sierra Nevada 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-2 
province, and an area of moderate elevation and low relief along the northern border of the state 

is part of the Owyhee Upland adjacent to the Snake River Plain of Idaho. 

FIGURE 1-2 

LOCATION MAP OF NEVADA AND PORTIONS OF ADJACENT STATES

The mountain ranges in Nevada are generally 5 to 15 miles wide and rise 1,000 to 5,000 feet 

above the adjoining valleys, which are about as wide as the mountain ranges. The mountain 

ranges are typically elongate with many extending more than 50 miles in a north or north-east 

direction. The Basin and Range topography is the result of extension block faulting and the 

basins have trapped continental sediments derived from the adjacent highlands. 

Much of Nevada is an area of internal drainage. The largest river within the Great Basin, the 

Humboldt, heads in the northeastern part of the state, traverses westward and then southward to 

terminate in the Humboldt and Carson Sinks in the western part of the state. Many of the basins 

in Nevada are floored by flat mud-surfaced playas that are flooded by runoff from the mountains 

during times of high precipitation. Playas are shown on Figure 1-2 by the whitish areas in the 

western and southern portions of the state. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-3 
Most of the unconsolidated sedimentary material less than six million years old forms 

widespread alluvial fan, stream terrace, flood plain, valley flat and playa deposits. These units 

grade from coarse gravel near the mountains or ranges to fine silt and clay in the valley and on 

the playas. Other sedimentary material in this age span forms landslide, morainal, lacustrine, 

shoreline and eolian (i.e., carried, deposited or eroded by the wind) sand dune deposits. 

During the Pleistocene, large inland lakes occupied many of the present day broad valleys of 

Nevada as shown on Figure 1-3 by the blue tint. Most of the playa deposits of Nevada represent 

part of the little-modified bottom sediments of these lakes. Wave-cut terraces and sand and 

gravel beach and bar deposits occur along what were the shores of these lakes. The sandy lake 

margin deposits provided sand for many of the dune areas of the state. 

FIGURE 1-3 

EXTENT OF PLEISTOCENE LAKES IN THE GREAT BASIN

Map from Ken Adams, Desert Research Institute, 2008 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-4 
The Snake River Plain, a section of the Columbia Plateau, follows the Snake River across Idaho, 

stretching roughly 400 miles from the Wyoming border to eastern Oregon (see Figure 1-4). The 

Snake River Plain is characterized by plains and low hills considerably lower and less rugged 

than surrounding physiographic regions. Agriculture is the main land use of the Snake River 

Plain, with irrigated croplands, widespread livestock grazing and locally important feedlot and 

dairy operations. Note the proximity of this vast agricultural area to the Jarbidge WA, shown by 

the yellow symbol in Figure 1-2. 

FIGURE 1-4 

LOCATION MAP OF SNAKE RIVER PLAIN

The following discussion of Nevada’s climate is paraphrased from NOAA (1985). Nevada’s 

principal climatic features are bright sunshine, small annual precipitation, (averaging nine inches 

in the valleys and deserts) heavy snowfall in the higher mountains, clean, dry air, and 

exceptionally large daily ranges of temperature Wide local variations of temperature and rainfall 

are common. The average annual number of days with precipitation of 0.01 inch or more varies 

considerably; Las Vegas averages 23, Reno 49, Winnemucca 67, Ely 72 and Elko 78. 

Nevada lies on the eastern, lee side of the Sierra Nevada Range, a massive mountain barrier that 

markedly influences the climate of the state. The prevailing winds are from the west, and as the 

warm moist air from the Pacific Ocean ascends the western slopes of the Sierra Range, the air 

cools, condensation takes place and most of the moisture falls as precipitation. As the air 

descends the eastern slope, it is warmed by compression, and very little precipitation occurs. 

The effects of this mountain barrier are felt not only in the west but throughout the state, with the 

result that the lowlands of Nevada are largely desert or steppes. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-5 
Jarbidge WA lies near the Idaho border just north of the physical geographic boundary 

separating the Columbia Plateau region, including the Snake River Plain, and the Great Basin 

region to the south. It consists of the headwaters basin of the Jarbidge River East Fork that flows 

north from the center of the wilderness area, and the headwaters basin of Marys River that flows 

south from the center of the wilderness area, part of the Columbia River/Great Basin 

hydrographic divide. The terrain encompassed by the wilderness area consists of deep canyons 

with steep slopes. The Jarbidge River Canyon, which comprises the upper main headwaters of 

the Jarbidge River proper, is oriented south to north, with its mouth several miles to the north 

where it drains into the Bruneau River. 

The area illustrates Nevada’s typical basin and range topography (see Figure 1-5) with elevations 

ranging from 2,100 m (6,900 ft) where the Jarbidge River East Fork exits the wilderness into 

Idaho’s Snake River Plains to eight peaks over 3,000 m (~10,000 ft) high along the Jarbidge 

Mountain crest, which includes the highest peak, Marys River Peak at 3,170 m (10,398 ft). The 

varied terrain is cut by deep canyons with steep slopes and supports a range of vegetation zones 

from sagebrush flats to glaciated alpine basins. 

FIGURE 1-5 

JARBIDGE WILDERNESS AREA AND VICINITY

1.1.2 Visibility Impairment

Regional haze is pollution from disparate sources that impairs visibility over a large region, 

including national parks, forests and wilderness areas. Of all the federal Class I areas, visibility 

was determined to be an important value at 156. These 156 mandatory class I areas are the 

subject of the Regional Haze Rule (RHR). Regional haze is caused by sources and activities 

emitting fine particles and their precursors. Those emissions are often transported over large 

regions. Particles affect visibility through the scattering and absorption of light, and fine 

particles – particles similar in size to the wavelength of light – are most efficient, per unit of 

mass, at reducing visibility. Fine particles may either be emitted directly or formed from 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-6 
emissions of precursors, the most important of which are sulfur dioxide (SO2) and nitrogen 

oxides (NOx). Reducing fine particles in the atmosphere is generally considered to be an 

effective method of reducing regional haze, and thus improving visibility. It is also generally 

considered that fine particles also adversely impact human health, especially respiratory and 

cardiovascular systems. 

Most visibility impairment occurs when pollution in the form of small particles scatter or absorb 

light. Air pollutants come from a variety of natural and anthropogenic sources. Natural sources 

include windblown dust and smoke from wildfires. Anthropogenic sources include motor 

vehicles, electric utility and industrial fuel burning, and manufacturing operations. Higher 

concentrations of pollutants result in more absorption and scattering of light, which reduce the 

clarity and color of a scene. Some types of particles, such as sulfates, are more effective at 

scattering light, particularly during humid conditions. Other particles like elemental carbon from 

combustion processes are highly efficient at absorbing light. Commonly, the receptor is the 

human eye and the object may be a single viewing target or a scene. 

In the 156 mandatory Class I areas across the country, visual range has been substantially 

reduced by air pollution. In the West, visual range has decreased from an average of 140 miles 

to 35-90 miles. Much of the visibility impairment in the West can be attributed to natural 

emissions of smoke and dust with significant contributions resulting from international emissions 

from beyond the boundaries of the United States, including Canada and Mexico. 

Some haze-causing particles are directly emitted to the air. Others are formed when gases 

emitted to the air form particles as they are carried many miles from the source of the pollutants. 

Some haze forming pollutants are also linked to human health problems and other environmental 

damage. In addition, particles such as nitrates and sulfates contribute to acid deposition 

potentially making lakes, rivers and streams unsuitable for some forms of aquatic life and 

impacting flora in the ecosystem. These same acid particles can also erode materials such as 

paint, buildings or other natural and manmade structures. 

1.1.3 Observed Haze Events 

Nevada regularly experiences regional haze events due to natural emissions of smoke and dust. 

The Nevada Division of Environmental Protection (NDEP) staff has witnessed numerous haze 

events due to fire and wind. The text below provides some anecdotal evidence and images of the 

significance of these haze events. 

1.1.3.1 Windblown Dust Events 

Observed windblown dust events occur during at least two different meteorological conditions: 

unstable, well-mixed atmosphere with high winds; and unstable, highly-convective atmosphere 

with very low winds. Examples are provided below. 

Both of these windblown dust events occurred in the vicinity of Mill City, Nevada in Humboldt 

County along the Humboldt River. Mill City is roughly mid-way between Lovelock and 

Winnemucca on I-80, or approximately 30 miles southwest of Winnemucca. The upper image of 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-7 
Figure 1-6 (looking northeast) shows a large plume of dust originating at the surface with a truck 

stop in the near background, while the lower image shows the plume mixing higher into the 

atmosphere. This truck stop is shown near the lower center of Figure 1-7 (i.e., adjacent to the 

Highway 95 marker shown on the image). Note the textured area extending to the north and 

west of the highway across the Humboldt River valley. This is an area of active to semi-active 

sand dunes demonstrating eolian transport of sediments parallel to the highway and is the source 

of the windblown dust shown in the figure. Figure 1-6 was taken on August 8, 2008 in the early 

evening. 

 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-8 
FIGURE 1-6 

AUGUST 2008 DUST EVENT NEAR MILL CITY, NEVADA

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-9 
FIGURE 1-7 

SOURCE AREA FOR OBSERVED DUST EVENT

Figure 1-8 looks west and was taken midday August 17, 2008. This image shows a group of dust 

devils originating from an area of sand dunes adjacent to the Humboldt River approximately 10 

miles north of the truck stop shown in the previous figure. The larger of these dust devils 

appears to be transporting dust some distance into the atmosphere. The relative significance of 

the contributions from this type of event to visibility impairment is not well documented or 

understood. 

The dune fields supplying material to these two dust events are an extensive mosaic of active, 

semi-active and stabilized sand dunes extending much of the distance between Lovelock and 

Winnemucca along the sandy margins of a large Pleistocene inland lake (see Figure 1-3). 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-10 
FIGURE 1-8 

AUGUST 2008 CONVECTIVE DUST EVENT NEAR MILL CITY, NEVADA

In addition to the dust events described above, NDEP staff also observed a regional dust event 

while driving from Twin Falls, Idaho to Wells, Nevada on the morning of May 28, 2007. During 

this event strong northwest winds across the Snake River Plain resulted in regional transport of 

particulate matter, possibly from local sources as well as the Bureau Dune Field (Smith, 1982), 

located approximately 80 miles north of the Jarbidge WA near Mountain Home, Idaho. As the 

winds picked up during the morning, visibility progressively and noticeably deteriorated over the 

Jarbidge Mountains and the area of the Jarbidge WA visible from Highway 93 until the 

mountains were no longer visible. The distance from the highway to the Jarbidge WA is 

approximately 35 miles. 

These anecdotal examples of dust events suggest the importance of natural emissions 

contributions to visibility impairment in the West. 

1.1.3.2 Natural Fire Events 

Emissions from natural fire events are common contributors to visibility impairment at Class I 

areas throughout the West. The summer of 2008 was a particularly bad fire year in northern 

California, when lightning storms started numerous fires in early summer. The upper image on 

Figure 1-9 is a smoke-obscured view of Lake Tahoe from Mount Tallac, located within the 

Desolation Wilderness Area just over four miles from the mouth of Emerald Bay and 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-11 
approximately 6 miles from the BLIS1 Interagency Monitoring of Protected Visual 

Environments (IMPROVE) monitor representing the Desolation Wilderness Area. 

The lower image presents a similar view of Lake Tahoe from Mount Tallac created using Google 

Earth technology. Note the top of Mount Tallac in the lower left corner, the location of Cascade 

Lake in the near foreground, with Lake Tahoe and Emerald Bay in the mid-background. 

The BLIS1 monitor is located approximately two miles north of Emerald Bay near the shore of 

Lake Tahoe. The image was captured midday July 27, 2008, one of many smoke-obscured days 

experienced during the summer of 2008 on the east slope of the Sierra due to California 

wildfires. This haze event was attributed to wild fires near Yosemite National Park 

approximately 100 miles to the south southeast.

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-12 
FIGURE 1-9 

OBSERVED JULY 2008 LAKE TAHOE SMOKE EVENT

A similarly intense smoke event was also observed near the Nevada/Utah border while driving 

west between Delta, Utah and Ely, Nevada on Highway 50 in the vicinity of Great Basin 

National Park. While approaching the Nevada border from the east on September 17, 2007, the 

Snake Range, approximately 30 miles distant, was partially obscured by smoke as shown by the 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-13 
upper image in Figure 1-10, which was taken from inside a vehicle. The lower image was 

recreated using Google Earth technology. The highest point visible in the lower image is 

Wheeler Peak, which is barely visible in the upper image. 

FIGURE 1-10 

SEPTEMBER 2007 REGIONAL SMOKE EVENT EASTERN NEVADA 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-14 
At Sacramento Pass, where Highway 50 crosses the Snake Range, visibility across Spring Valley 

was completely obscured and there was a strong smell of wood smoke. This event was related to 

wildfires in southern California approximately 350 miles to the southwest. 

This anecdotal evidence of visibility impairment from wildfires emphasizes the role of natural 

fire in visibility impairment, both from local and distant sources. 

1.2 THE WESTERN REGIONAL AIR PARTNERSHIP AND NEVADA 

USEPA funded five Regional Planning Organizations throughout the country to coordinate 

regional haze rule-related activities between states in each region. Nevada participates in the 

Western Regional Air Partnership (WRAP), the consensus organization of western states, tribes, 

and federal agencies, which oversees analyses of monitoring data and preparation of technical 

reports regarding regional haze in the western United States. 

The WRAP was formed in September 1997 as the successor organization to the Grand Canyon 

Visibility Transport Commission. It is administered jointly by the Western Governors 

Association (WGA) and the National Tribal Environmental Council (NTEC). The mission of the 

WRAP is to identify regional or common air management issues and to develop and implement 

strategies to address these issues. The WRAP is a partnership of states and tribes as well as 

federal agencies and was designated by USEPA to assist western states in the development of

regional haze plans. It provides a coordination mechanism with regard to science and 

technology support for policy and programmatic uses in the western United States. 

WRAP member states include Alaska, Arizona, California, Colorado, Idaho, Montana, New 

Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming. Federal 

participants are the Department of the Interior (National Park Service and Fish & Wildlife 

Service,) the Department of Agriculture (Forest Service) and USEPA. Although Nevada is not a 

formal member, Nevada has been an active, cooperative participant in the WRAP and in the 

forums, workgroups and committees that were formed to address many elements of this Regional 

Haze State Implementation Plan (RH SIP). 

Work by WRAP committees, forums and workgroups is accomplished by the staff time 

contributed by state, tribal, Federal Land Manager (FLM), USEPA and environmental, industry 

and public representatives, with the support of WRAP staffing through WGA and NTEC. 

WRAP work is also handled through contracts to environmental consulting firms, to analyze air 

pollution data collected by states and tribes in their regulatory programs as well as to prepare 

data and analyses for natural and/or uncontrollable air pollution sources. 

The WRAP established stakeholder-based technical and policy oversight committees to assist in 

managing the development of regional haze work products. Working groups and forums were 

established to develop technical tools and work products the states and tribes needed to develop 

their implementation plans. Much of the WRAP’s effort focused on regional technical analysis, 

which is the basis for developing strategies to meet the RHR requirement to demonstrate 

reasonable progress towards natural visibility conditions in Class I areas. This includes the 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-15 
compilation of emission inventories, air quality modeling and ambient monitoring and data 

analysis. 

The WRAP has developed a regionally-consistent and comparable body of technical data and 

analysis tools that has been invaluable in addressing regional haze in west. These data and tools 

are provided for use and evaluation through a transparent and open network of interrelated data 

support web systems and a technical decision support system: 

WRAP Technical Data Support Centers 

• Visibility Information Exchange Web System (http://vista.cira.colostate.edu/views/): 

VIEWS provides on-line access to monitoring data, research results and special studies 

related to visibility. 

• Causes of Haze Assessment (http://www.coha.dri.edu/): COHA provides a detailed 

analysis of ambient monitoring data for regional haze in the WRAP region. 

• Fire Emissions Tracking System (http://www.wrapfets.org/): FETS is a database with a 

web interface for tracking and managing planned and unplanned fire events. Users can 

view fire data on-screen with a mapping tool and query the database for downloads of 

data. 

• Regional Modeling Center (http://pah.cert.ucr.edu/aqm/308/): The WRAP’s RMC at the 

University of California Riverside provides state and tribal agencies with sophisticated 

modeling of regional haze and other air quality parameters in the western United States. 

• Emissions Data Management System (http://wrapedms.org/default_login.asp): EDMS is 

an emission inventory data warehouse for states and tribes. The system provides a 

consistent, complete and regional approach to emissions data management and tracking. 

WRAP Technical Decision Support System 

• Technical Support System (http://vista.cira.colostate.edu/tss/): TSS integrates a number 

of different data support resources under one web-based decision support umbrella for 

regional haze planning and implementation. 

In addition to these technical tools and work products, the WRAP has provided a forum for 

coordination and consultation with other states, tribes and FLMs. The major amount of interstate 

consultation in the development of this SIP was through the Implementation Work Group (IWG) 

of the WRAP. Nevada participated in the IWG, which took the products of the WRAP technical 

analysis and consultation process and developed a process for establishing reasonable progress 

goals in the western Class I areas. Chapter Nine of this document discusses the process that 

Nevada participated in to address the consultation requirements with FLMs, tribes and other 

WRAP states during the development of this plan and Nevada’s commitments for future 

consultation. 

1.3 TECHNICAL SUPPORT BACKGROUND 

1.3.1 Regional Haze Monitoring Network 

In response to the 1977 Clean Air Act Amendments, the IMPROVE program was established in 

1985 to aid the creation of federal and state implementation plans for the protection of visibility 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-16 
in Class I areas. Air monitoring devices at these locations are operated and maintained through a 

formal cooperative relationship between the USEPA and the National Park Service, U.S. Fish 

and Wildlife Service, Bureau of Land Management and U.S. Forest Service, collectively called 

the FLMs. In 1991, several additional organizations joined the effort: State and Territorial Air 

Pollution Program Administrators/Association of Local Air Pollution Control Officials (recently 

renamed National Association of Clean Air Agencies), Western States Air Resources Council, 

Mid-Atlantic Regional Air Management Association and Northeast States for Coordinated Air 

Use Management. 

The IMPROVE program implemented an extensive long-term monitoring program to establish 

the current visibility conditions, track changes in visibility and determine causal mechanism for 

the visibility impairment in the national parks and wilderness areas. The data collected at the 

IMPROVE monitoring sites are used by land managers, industry planners, scientists, consultants, 

public interest groups and air quality regulators to better understand and protect the visual air 

quality resource in Class I areas. IMPROVE documents the visual air quality in wilderness areas 

and national parks throughout the United States. 

1.3.1.1 Overview of the IMPROVE Monitoring Network 

The IMPROVE network focuses on rural areas in the western Unites States. Other visibility and 

aerosol monitoring networks, such as that of the National Weather Service Airport Visibility 

Data, may focus on different air sheds and have different data collection objectives. In 1988, 

IMPROVE began with 20 monitoring sites. After publication of the regional haze rule in 1999, 

the first step in the implementation process was the upgrade and expansion of the IMPROVE 

network to 110 sites nationally. Figure 1-11 shows the current IMPROVE monitoring network 

throughout the United States. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-17 
FIGURE 1-11 

MAP OF IMPROVE MONITORING NETWORK IN THE UNITED STATES

The IMPROVE network consists of aerosol and optical samplers. Every IMPROVE site deploys 

an aerosol sampler to measure speciated fine aerosols and coarse mass. Select sites also deploy a 

transmissometer and nephelometers to measure light extinction and scattering respectively, as 

well as automatic camera systems to visually measure the scene. Particulate concentration data 

are obtained every third day over a 24-hour collection period and converted into reconstructed 

light extinction through a complex calculation using the IMPROVE equation that may be viewed 

at: http://vista.cira.colostate.edu/improve/Tools/ReconBext/reconBext.htm. Light extinction, the 

impairment of visibility, occurs due to particles and gases that reflect and absorb light. 

Reconstructed light extinction (denoted as bext) is expressed in units of inverse megameters 

(1/Mm or Mm-1). The RHR requires the tracking of visibility conditions in terms of the Haze 

Index (HI) metric expressed in the deciview unit (40 CFR 51.308(d)(2)). The relationship 

between light extinction in Mm-1, Haze Index in dv and visual range in km is indicated by the 

scale in Figure 1-12. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-18 
FIGURE 1-12 

LIGHT EXTINCTION-HAZE INDEX-VISUAL RANGE SCALE

The deciview is a unit of measurement of haze that is designed so that uniform changes in 

haziness correspond approximately to uniform incremental changes in perception across the 

entire range of conditions, from pristine to highly impaired. More information regarding 

tracking visibility conditions is found in USEPA’s Guidance for Tracking Progress Under the 

Regional Haze Rule at: http://www.epa.gov/ttn/oarpg/t1/memoranda/rh_tpurhr_gd.pdf. 

The IMPROVE data undergo extensive quality assurance and control procedures and analyses by 

its contractors and the National Park Service before it is released. The aerosol and optical data 

are made publicly available approximately nine months after collection. In addition, seasonal 

and annual data reports, special study data reports, technical publications and other data and 

analysis reports are prepared. IMPROVE program resources are available at: 

http://vista.cira.colostate.edu/Improve. 

1.3.1.2 IMPROVE Monitor JARB1 

Two operating IMPROVE monitoring sites are located in Nevada, one at Great Basin National 

Park and the other at the Jarbidge WA. The Walker River Paiute Tribe, a third monitoring site in 

Nevada, operated from June 2003 to November 2005. The IMPROVE monitor representing the 

air quality at the Jarbidge WA is identified as JARB1.

JARB1 was among the first 20 IMPROVE sites to start operation in 1988 and is sponsored by 

the U. S. Forest Service. Generally, JARB1 is expected to be representative of aerosol 

characteristics in the Jarbidge WA especially when the atmosphere is well mixed and regionally 

homogeneous. However, the site is at a low elevation in the Jarbidge River Canyon that is 

separate from the Jarbidge WA and upper East Fork of the Jarbidge River. Consequently, the 

monitoring site may at times be isolated from wilderness locations and potentially impacted by 

different local emission sources. Figure 1-4 shows the location of the JARB1 monitoring site by 

a bright green dot. 

As does every IMPROVE site, JARB1 deploys an aerosol sampler to measure speciated aerosols 

and coarse mass. Along with other selected sites, JARB1 also has an automatic camera system

to obtain a visual record, a transmissometer to measure light extinction, and a nephelometer to 

measure light scattering. Data from these sampling devices are used to determine the visibility 

status at the Jarbidge WA. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-19 
1.3.2 Emissions Analyses and Projections 

USEPA’s RHR requires statewide emission inventories of pollutants that are reasonably 

anticipated to cause or contribute to visibility impairment in any mandatory Class I area. 

Nevada’s inventories are presented in Chapter Three. These emissions inventories are available 

from the WRAP TSS (http://vista.cira.colostate.edu/TSS/Results/Emissions.aspx). The TSS 

webpage has links to many references that describe in detail the emissions methods used in 

developing the point, area, mobile, dust, offshore and fire emission inventories. 

Emissions scenarios used in the development of this SIP represent actual baseline emissions 

(Base02), typical baseline emissions (Plan02), and projected emissions (Base18 and PRP18). 

The baseline period includes 2000 through 2004, represented by 2002, while the projected 

inventories denote 2018 emissions, as discussed below. The projected inventories take into 

account growth, “on-the-books” and “on-the-way” controls and regulations and the application 

of regional haze strategies. The year 2018 was selected as it represents the first milestone date 

for demonstrating reasonable progress. These inventories were used for visibility and source 

apportionment modeling. 

The pollutants examined are SO2, sulfur oxides (SOx), NOx, volatile organic compound (VOC), 

primary organic aerosol (POA), elemental carbon (EC), fine particulate (PM fine), coarse 

particulate (PM coarse) and ammonia (NH3). It is important to note that each of these pollutants 

have characteristics that differ in terms of ability to affect visibility. Assuming one emission unit 

of PM fine, for example, the same unit of SO2 or NOx would be about three times more effective 

at impairing visibility. Organic carbon is about four times more effective and elemental carbon 

about ten times more effective at impairing visibility. (Organic carbon is discussed in Chapter 

Four as part of the weighted emissions potential analysis.) Conversely, PM coarse is about half 

as effective as PM fine. Both VOC and NH3 affect visibility only after certain chemical 

reactions occur and, therefore, cannot be compared in this manner. 

1.3.2.1 Preparation of Baseline Emissions Inventories 

2002 Base Case (Base02) Inventory

The Base02 inventory used actual data reported by states, locals, tribes and USEPA databases, 

which evolved from states’ actual emissions data submitted to USEPA for the 2002 National 

Emission Inventory. The WRAP Stationary Sources Joint Forum contracted with Eastern 

Research Group (ERG) and subcontractors ENVIRON International Corporation and Alpine 

Geophysics to improve upon the 2002 WRAP emissions inventory, particularly for oil and gas 

area sources and for large point sources on selected tribal lands. The documents describing this 

project can be reviewed in detail by selecting the following links: 

• http://www.wrapair.org/forums/ssjf/documents/Pivot_Tables/2006-

01_REPORT_QA_of_the_2002_WRAP_Stationary_Sources%20EI.pdf

• http://wrapair.org/forums/ssjf/documents/eictts/OilGas/WRAP_Oil&Gas_Final_Report.1

22805.pdf

• http://www.wrapair.org/forums/fejf/documents/WRAP_2002_PhII_EI_Report_20050722

.pdf. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-20 
The purpose of the Base02 scenario is to represent the actual conditions in calendar year 2002 

with respect to ambient air quality and the associated sources of visibility-impairing air 

pollutants. The Base02 emissions inventories were used to validate the air quality model and 

associated databases and to demonstrate acceptable model performance with respect to 

replicating observed particulate matter air quality. Version “a” of the 2002 base case inventory, 

Base02a, was developed based on preliminary 2002 modeling which can be reviewed in detail at

http://pah.cert.ucr.edu/aqm/308/reports/final/2002_MPE_report_main_body_FINAL.pdf. 

Improved 2002 emissions data for the United States, Mexico and Canada were used to create a 

final base 2002 annual emissions database, Base02b, for use in the Community Multi-Scale Air 

Quality (CMAQ) model and the Comprehensive Air Quality Model with Extensions (CAMx) 

model performance evaluations. Actual 2002 fire emissions data were included in this Base02b 

inventory. 

2000 Through 2004 Baseline-Period (Plan02) Inventory

The 2000 through 2004 baseline period planning case emissions scenario is referred to as 

“Plan02”. As with the Base02 inventories, Plan02 has undergone a number of revisions and 

enhancements to arrive at the final versions used in visibility and source apportionment 

modeling. The Plan02 series of inventories was developed to represent baseline period 

emissions patterns based on average, or “typical” conditions. The Plan02 inventory was 

developed from the Base02 emissions modeling scenarios by incorporating: 

1. Replacement of actual 2002 fire emissions inventories with the baseline typical fire 

emissions inventories; 

2. Replacement of the temporal profiles for large stationary point sources with profiles 

developed from an average of several years surrounding 2002; and 

3. Corrections to the off-road mobile, on-road mobile, offshore Pacific shipping lane and 

WRAP oil and gas inventories. 

The inventory series Plan02a, Plan02b and Plan02c provided a basis for comparison with the 

future year 2018 projected emissions, as well as for gauging reasonable progress with respect to 

future year visibility. The Plan02d emission inventory was based on the minor changes to the 

Plan02c emission inventory. These revisions to the Plan02c emission inventory included: 

1. Updating the current status of point sources related to the BART requirements under the 

regional haze rule; and 

2. Correcting erroneous or missing Standard Industrial Classification and/or source 

classification codes (SCC). 

The Plan02c inventory was used for source apportionment modeling, whereas the Plan02d 

inventory was used for visibility modeling and weighted emission potential (WEP) analyses, as 

discussed in section 1.3.3.1 below. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-21 
1.3.2.2 Projected 2018 Emissions Inventories 

2018 Base Case (Base18) Inventory

The 2018 future-year base case emissions scenario is referred to as “2018 Base Case” or 

“Base18”. The Base18 emissions scenario is used to represent conditions in 2018 with respect to 

sources of visibility-impairing air pollutants, taking into consideration growth and controls. The 

Base18b inventory contained summaries of 2018 stationary point and area source emission 

inventories projected from the Plan02c inventory and was initially completed by ERG in January 

2006. ERG’s report is available at 

http://www.wrapair.org/forums/ssjf/documents/eictts/docs/WRAP_2018_EI-Version_1-

Report_Jan2006.pdf. 

This inventory was used for source apportionment modeling. Modeling results based on this 

emission inventory are used to define the future year ambient air quality and visibility metrics. 

The projection methodology included the following steps: 

1. Permit Limits: Adjusting projected emissions downward in cases where the projected 

emissions may have inadvertently exceeded an enforceable emission limit. 

2. Section §309 Flags: Point sources in the Grand Canyon Visibility Transport states whose 

2002 facility-level SO2 emissions were at least 100 tons/year were assigned section §309 

flags. 

3. Retirement and Replacement Rates: Effects of retirement were estimated using annual 

retirement rates based on expected equipment lifetimes. Retired equipment was replaced 

by lower-emitting new equipment. Unit lifetimes were examined for natural gas-fired 

electric generating units (EGUs). No retirements were assumed for coal-fired EGUs. 

4. Control factors: Emission reductions due to known (on-the-books) controls, consent 

decree reductions, SIP control measures and other relevant regulations that have gone 

into effect since 2002, or will go into effect before the end of 2018 (on-the-way). These 

controls do not include impacts from any future control scenarios that have yet to be 

determined. 

5. Growth Factors: SCC-specific growth factors developed from the Economic Growth 

Analysis System (EGAS) projection factor model were included. 

6. Adjustments:

(a) Emissions for new facilities that have come on-line since 2002, 

(b) Corrections for facilities that retired in 2003 or 2004 and will not return to operation in 

the future, and 

(c) Other (i.e., ratios to correct certain PM10 and PM2.5 emission factors/SCCs for 

combustion of natural gas) 

2018 Preliminary Reasonable Progress (PRP18) Inventory

Several enhancements and corrections were subsequently made to the 2018 Base18b inventory 

resulting in the PRP18a inventory. The WRAP region 2018 point and area source inventory 

projections were updated from the 2018 Base18b inventory with information from individual 

state air agencies. The PRP18a inventory was created to establish the most representative 

source-specific emissions projections data as the basis for preparing regional haze plans. The 

PRP18a inventory was used for visibility modeling. Development of the PRP18a inventory is 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-22 
documented in a technical memo available at 

http://www.wrapair.org/forums/ssjf/documents/eictts/Projections/PRP18_EI_tech%20memo_061

607.pdf. 

The PRP18a inventory revisions included the following elements: 

1. Presumptive BART emission limits were applied to BART-eligible coal-fired EGUs for 

SO2 only and not for NOx. 

2. Specific BART limits for all coal-fired EGU sources subject to BART in Colorado, North 

Dakota and Utah, as well as one facility in Oregon. 

2. Based on state and local agency comments, SCC codes were corrected and source 

information was updated based on new sources, inactive sources and facility name

changes. 

3. For EGU facilities reporting to USEPA’s Clean Air Markets Division’s acid rain database, 

EGU facility IDs were corrected and missing EGU source records were added. 

4. Revised EGU projections of future coal-fired EGU construction: used Energy Information 

Administration projections of 2018 energy requirements; determined existing WRAP 

region capacity to identify total new requirements; added existing state and local agency 

EGU permits; added 11 new “Model” 500MW EGU units operating at BACT levels. Of 

the 11 proposed future coal-fired EGU plants, one is in Nevada. 

5. Revisions to the WRAP Oil and Gas point and area source emission inventory were 

incorporated based on work done by ENVIRON in 2007 

(http://www.wrapair.org/forums/ogwg/documents/2007-

10_Phase_II_O&G_Final)Report(v10-07%20rev.s).pdf). 

6. Updates to the 2018 SO2 emission projections for Non-Utility Point sources were 

incorporated based on work done by Pechan and Associates in 2006 

(http://wrapair.org/forums/ssjf/documents/eictts/Projections/Report-WRAP_SO2-

oct11_Final.pdf). 

The Base18b inventory was used for source apportionment modeling, whereas the PRP18a 

inventory was used for visibility modeling and weighted emission potential (WEP) analyses, as 

discussed in section 1.3.3.1 below. 

1.3.2.3 WRAP’s Technical Support System 

Air quality and visibility modeling in support of regional haze planning in the WRAP region is 

the responsibility of the WRAP Modeling Forum’s RMC. The RMC uses the air pollution 

emissions data as described and displayed in the TSS Emissions Section to simulate historic air 

quality conditions and estimate the benefit of emissions reductions programs in the future. The 

RMC uses regional gridded dispersion models for these simulations. The RMC website 

(http://pah.cert.ucr.edu/aqm/308/) provides modeling inputs and data results for review and 

download, using pre-set data processing, visualization and download capabilities. The TSS 

provides key summary air quality and visibility modeling data through enhanced analysis and 

display tools. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-23 
1.3.3 Air Quality Modeling 

The sources of PM2.5 are difficult to quantify because of the complex nature of their formation, 

transport and removal from the atmosphere. This makes it difficult to simply use emissions data 

to determine which pollutants should be controlled to most effectively improve visibility. 

Photochemical air quality models offer opportunity to better understand the sources of PM2.5 by 

simulating the emissions of pollutants and the formation, transport and deposition of PM2.5. If an 

air quality model performs well for an historical episode, the model may then be useful for 

identifying the sources of PM2.5 and helping to select the most effective emissions reduction 

strategies for attaining visibility goals. Although several types of air quality modeling systems 

are available, the gridded, three-dimensional, Eulerian models provide the most complete spatial 

representation and the most comprehensive representation of processes affecting PM2.5, 

especially for situations in which multiple pollutant sources interact to form PM2.5. 

The WRAP RMC utilized two regulatory air quality modeling systems to conduct all regional 

haze modeling. A brief discussion of each of these models is provided below. 

Community Multi-Scale Air Quality Model

USEPA initially developed the CMAQ modeling system in the late 1990s. The model source 

code and supporting data can be downloaded from the Community Modeling and Analysis 

System Center (http://www.cmascenter.org/), which is funded by USEPA to distribute and 

provide limited support for CMAQ users. CMAQ was designed as a “one atmosphere” modeling 

system to encompass modeling of multiple pollutants and issues, including ozone, PM, visibility 

and air toxics. This is in contrast to many earlier air quality models that focused on singlepollutant issues (e.g., ozone modeling by the Urban Airshed Model). CMAQ is a Eulerian model 

-- that is, it is a grid-based model in which the frame of reference is a fixed, three-dimensional 

grid with uniformly sized horizontal grid cells and variable vertical layer thicknesses. The 

number and size of grid cells and the number and thicknesses of layers are defined by the user, 

based in part on the size of the modeling domain to be used for each modeling project. The key 

science processes included in CMAQ are emissions, advection and dispersion, photochemical 

transformation, aerosol thermodynamics and phase transfer, aqueous chemistry, and wet and dry 

deposition of trace species. CMAQ offers a variety of choices in the numerical algorithms for 

treating many of these processes, and it is designed so that new algorithms can be included in the 

model. CMAQ offers a choice of three photochemical mechanisms for solving gas-phase 

chemistry: the Regional Acid Deposition Mechanism version 2 (RADM2); a fixed coefficient 

version of the SAPRC90 mechanism; and the Carbon Bond IV mechanism (CB-IV). 

Comprehensive Air Quality Model with Extensions 

The CAMx model was initially developed by ENVIRON in the late 1990s as a nested-grid, gasphase, Eulerian photochemical grid model. ENVIRON later revised CAMx to treat PM, visibility 

and air toxics. While there are many similarities between the CMAQ and CAMx systems, there 

are also some significant differences in their treatment of advection, dispersion, aerosol 

formation, and dry and wet deposition. 

In support of the WRAP regional haze air quality modeling efforts, the RMC developed air 

quality modeling inputs including annual meteorology and emissions inventories for a 2002 

actual emissions base case, a planning case to represent the 2000 through 2004 regional haze 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-24 
baseline period using averages for key emissions categories, and a 2018 base case of projected 

emissions determined using factors known at the end of 2005. All emission inventories were 

developed using the Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system. Each 

of these inventories has undergone a number of revisions throughout the development process to 

arrive at the final versions used in CMAQ and CAMx air quality modeling. The development of

each of these emission scenarios is documented under the emissions inventory sections of the 

TSS. In addition to various sensitivities scenarios, the WRAP performed air quality model 

simulations for each of the emissions scenarios. 

Initial conditions are specified by the user for the first day of a model simulation. For 

continental-scale modeling using the Regional Planning Organization (RPO) Unified 36-km

domain, the initial conditions can affect model results for as many as 15 days, although the effect 

typically becomes very small after about 7 days. A model spin-up period is included in each 

simulation to eliminate any effects from the initial conditions. For the WRAP modeling, the 

annual simulation is divided into four quarters, and included a 15-day spin-up period for the 

quarters beginning in April, July and October. For the quarter beginning in January 2002, a spinup period covering December 16-31, 2001, using meteorology and emissions data developed for 

Central Regional Air Planning Association (CENRAP) were used. 

Boundary conditions specify the concentrations of gas and PM species at the four lateral 

boundaries of the model domain. Boundary conditions determine the amounts of gas and PM 

species that are transported into the model domain when wind flow is into the domain. Boundary 

conditions have a much larger effect on model simulations than do initial conditions. For some

areas in the WRAP region and for clean conditions, the boundary conditions can be a substantial 

contributor to visibility impairment. 

For this study, boundary conditions data generated in an annual simulation of the global-scale 

GEOS-Chem model that was completed by Jacob et al. (http://wwwas.harvard.edu/chemistry/trop/geos/) for calendar year 2002 were applied. Additional data 

processing of the GEOS-Chem data was required before using them in CMAQ and CAMx. The 

data first had to be mapped to the boundaries of the WRAP domain, and the gas and PM species 

had to be remapped to a set of species used in the CMAQ and CAMx models. This work was 

completed by Byun and coworkers (http://wwwas.harvard.edu/chemistry/trop/geos/meetings/2005/ppt/Expanding_Model_Capabilities/GEOSCMAQ_april_4_Byun.ppt). 

The CMAQ model options and configuration used for the WRAP 36-km model simulations are 

described in Tonnesen et al. (2006) 

(http://pah.cert.ucr.edu/aqm/308/reports/final/2002_MPE_report_main_body_FINAL.pdf). The 

RMC prepared a white paper describing the air quality modeling preformed for WRAP, available 

at http://vista.cira.colostate.edu/docs/wrap/Modeling/AirQualityModeling.doc. The white paper 

provides detailed information regarding the modeling software, data sources, development and 

results of various model simulations, model performance evaluation, visibility projections, PM 

source apportionment using Particulate Matter Source Attribution Tracking (PSAT) and model 

sensitivity simulations. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-25 
1.3.3.1 Visibility Modeling 

The RHR goals include achieving natural visibility conditions at 156 federally mandated Class I 

areas by 2064. In more specific terms, that goal is defined as visibility improvement toward 

natural conditions for the 20 percent of days that have the worst visibility (termed “20 percent 

worst” visibility days), and no worsening in visibility for the 20 percent of days that have the 

best visibility (“20 percent best” visibility days). One component of the states’ demonstration to 

USEPA that they are making reasonable progress toward this 2064 goal is the comparison of 

modeled visibility projections for 2018 with what is termed a uniform rate of progress (URP) 

from baseline to natural conditions by 2064. 

Preliminary 2018 visibility projections have been made using the Plan02d and PRP18a CMAQ 

36-km modeling results, following USEPA guidance that recommends applying the modeling 

results in a relative sense to project future-year visibility conditions (U.S. EPA, 2001, 2003a, 

2006). Projections are made using relative response factors (RRFs), which are defined as the 

ratio of the future-year modeling results to the current-year modeling results. The calculated 

RRFs are applied to the baseline observed visibility conditions to project future-year observed 

visibility. These projections can then be used to assess the effectiveness of the simulated 

emission control strategies that were included in the future-year modeling. The major features of 

USEPA’s recommended visibility projections are as follows (U.S. EPA, 2003a,b, 2006): 

• Monitoring data should be used to define current air quality. 

• Monitored concentrations of PM10 are divided into six major components; the first five 

are assumed to be PM2.5 and the sixth is PM2.5-10. 

o SO4 (sulfate) 

o NO3 (particulate nitrate)

o OC (organic carbon) 

o EC (elemental carbon) 

o OF (other fine particulate or soil) 

o CM (coarse matter). 

• Models are used in a relative sense to develop RRFs between future and current predicted 

concentrations of each component. 

• Component-specific RRFs are multiplied by current monitored values to estimate future 

component concentrations. 

• Estimates of future component concentrations are consolidated to provide an estimate of 

future air quality. 

• Future estimated air quality is compared with the goal for regional haze to see whether 

the simulated control strategy would result in the goal being met. 

• It is acceptable to assume that all measured sulfate is in the form of ammonium sulfate 

[(NH4)2SO4] and all particulate nitrate is in the form of ammonium nitrate [NH4NO3]. 

RRFs calculated from modeling results can be used to project future-year visibility. For the 

current modeling efforts, RRFs are the ratio of the 2018 modeling results to the 2002 modeling 

results and are specific to each Class I area and each PM species. RRFs are applied to the 

Baseline Condition observed PM species levels to project future-year PM levels, which are then 

used with the IMPROVE extinction equation listed above to assess visibility. The following six 

steps are used to project future-year visibility for the 20 percent best and 20 percent worst 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-26 
visibility days (the discussion below is for 20 percent worst days but also applies to 20 percent 

best days): 

1. For each Class I area and each monitored day, daily visibility is ranked using IMPROVE 

data and IMPROVE extinction equation for each year from the five-year baseline period

(2000-2004) to identify the 20 percent worst visibility days for each year. 

2. Use an air quality model to simulate a base-year period (ideally 2000-2004, but in reality 

just 2002) and a future year (e.g., 2018), then apply the resulting information to develop 

Class-I-area-specific RRFs for each of the six components of light extinction in the 

IMPROVE aerosol extinction equation. 

3. Multiply the RRFs by the measured 24-h PM data for each day from the 20 percent worst 

days for each year from the five-year baseline period to obtain projected future-year 

(2018) 24-h PM concentrations for the 20 percent worst days. 

4. Compute the future-year daily extinction using the IMPROVE aerosol extinction equation and the projected PM concentrations for each of the 20 percent worst days in the 

five-year baseline from Step 3. 

5. For each of the 20 percent worst days within each year of the five-year baseline, convert 

the future-year daily extinction to units of deciview and average the daily deciview 

values within each of the five years separately to obtain five years of average deciview 

visibility for the 20 percent worst days. 

6. Average the five years of average deciview visibility to obtain the future-year visibility

Haze Index estimate that is compared with the 2018 progress goal. 

For all of the WRAP Class I areas, the RMC performed preliminary 2018 visibility projections 

and compared them to the 2018 URP using the Plan02d and PRP18a CMAQ modeling results 

and the old and new IMPROVE equations. 

1.3.3.2 Source Apportionment Modeling 

Impairment of visibility in Class I areas is caused by a combination of local air pollutants and 

regional pollutants that are transported long distances. To develop effective visibility 

improvement strategies, the WRAP member states and tribes need to know the relative 

contributions of local and transported pollutants, and which emissions sources are significant 

contributors to visibility impairment at a given Class I area. 

A variety of modeling and data analysis methods can be used to perform source apportionment 

of the PM observed at a given receptor site. One method is to implement a mass-tracking 

algorithm in the air quality model to explicitly track for a given emissions source the chemical 

transformations, transport and removal of the PM that was formed from that source. Masstracking methods have been implemented in the CAMx air quality model as PSAT. 

Source apportionment for regional haze planning was conducted using various modeling 

techniques. The SOx/NOx Tracer and Organic Aerosol Tracer were performed using the regional 

PSAT air quality model. The WEP analysis included the synthesis of emissions data and 

meteorological back trajectories. The PMF Receptor Modeling and Causes of Dust analysis were

complex statistical exercises involving IMPROVE monitoring data. Not all source 

apportionment techniques were applied to all pollutants. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-27 
Particle Source Apportionment Tracking

The main objective of applying CAMx/PSAT is to evaluate the regional haze air quality for 

conditions typical of the 2000 through 2004 baseline period (Plan02c) and future-year 2018 

(Base18b) conditions. These results are used: 

• To assess the contributions of different geographic source regions (e.g., states) and source 

categories to current (2000-2004) and future (2018) visibility impairment at Class I areas, in 

order to obtain improved understanding of the causes of the impairment and which states 

are included in the area of influence of a given Class I area. 

• To determine which source categories contributing to the area of influence for each Class I 

area are changing, and by how much, between the 2000 through 2004 and 2018 base cases. 

by varying only controllable anthropogenic emissions between the 2 PSAT simulations; and 

• To identify the source regions and emissions categories that, if controlled to lower 

emissions rates than the 2018 base case levels, would produce the greatest visibility 

improvements at a Class I area. 

The PSAT performs source apportionment based on user-defined source groups. A source group 

is the combination of a geographic source region and an emissions source category. Examples of 

source regions include states, nonattainment areas and counties. Examples of source categories 

include mobile sources, biogenic sources and elevated point sources; PSAT can even focus on 

individual sources. The user defines a geographic source region map to specify the source 

regions of interest. He or she then inputs each source category as separate, gridded low-level 

emissions and/or elevated-point-source emissions. The model then determines each source group 

by overlaying the source categories on the source region map. PM source apportionment 

modeling was performed for aerosol SO4 and aerosol NO3 and their related species (e.g., SO2, 

NO, NO2, HNO3, NH3, and NH4). The PSAT simulations include 9 tracers, 18 source regions 

(see Table 1-1) and 6 source groups (see Table 1-2). 

TABLE 1-1

WRAP CAMx/PSAT SOURCE REGIONS

Source 

Region ID Source Region Description

1 Source Region 

ID Source Region Description

1

1 Arizona (AZ) 10 South Dakota (SD) 

2 California (CA) 11 Utah (UT) 

3 Colorado (CO) 12 Washington (WA) 

4 Idaho (ID) 13 Wyoming (WY) 

5 Montana (MT) 14 Pacific off-shore & Sea of 

Cortez (OF) 

6 Nevada (NV) 15 CENRAP states (CE) 

7 New Mexico (NM) 16 Eastern U.S., Gulf of Mexico, 

& Atlantic Ocean (EA) 

8 North Dakota (ND) 17 Mexico (MX) 

9 Oregon (OR) 18 Canada (CN) 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-28 
1

The abbreviations in parentheses are used to identify source regions in PSAT receptor bar plots.

TABLE 1-2

WRAP CAMx/PSAT EMISSIONS SOURCE GROUPS

Emissions 

Source Groups 

Low-level Sources Elevated Sources 

1 Low-level point sources (including stationary 

off-shore) 

Elevated point sources 

(including stationary offshore) 

2 Anthropogenic wildfires (WRAP only) Anthropogenic wild fires 

(WRAP only) 

3 Total mobile (on-road, off-road, including 

planes, trains, ships in/near port, off-shore 

shipping) 

4 Natural emissions (natural fire, WRAP only, 

biogenics) 

Natural emissions (natural 

fire, WRAP only, biogenics) 

5 Non-WRAP wildfires (elevated fire sources in 

other RPOs) 

Non-WRAP wild fires 

(elevated fire sources in 

other RPOs) 

6 Everything else (area sources, all dust, 

fugitive ammonia, non-elevated fire sources 

in other RPOs) 

The source apportionment model results are typically presented in two ways: 

• Spatial plots showing the area of influence of a source group’s PM species contributions 

throughout the model domain, either at a given hourly-average point in time or averaged 

over some time interval (e.g., monthly average). 

• Receptor bar plots showing the rank order of source groupings that contribute to PM 

species at any given receptor site. These plots also can be at a particular point in time or 

averaged over selected time intervals—for example, the average source contributions for 

the 20 percent worst visibility days. 

The primary products of the WRAP PSAT modeling were receptor bar plots showing the 

emission source groups that contribute the most to the model grid cells containing each 

IMPROVE monitoring site and other receptor sites identified by WRAP. 

Two annual 36-km CAMx/PSAT model simulations were performed: one with the Plan02c 

typical-year baseline case and the other with the Base18b future-year case. It is expected that the 

states and tribes will use these results to assess the sources that contribute to visibility 

impairment at each Class I Area and to guide the choice of emission control strategies. The RMC 

web site includes a full set of source apportionment spatial plots and receptor bar plots for both 

Plan02b and Base18b. These graphical displays of the PSAT results, as well as additional 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-29 
analyses of these results are available on the TSS under 

http://vista.cira.colostate.edu/TSS/Results/SA.aspx. 

Additional information related to the CAMx air quality model and PSAT apportionment 

algorithm can be found at

http://vista.cira.colostate.edu/docs/wrap/attribution/PSATMethods.doc. 

Weighted Emissions Potential

The WEP was developed as a screening tool for states to decide which source regions have the 

potential to contribute to haze formation at specific Class I areas, based on both the 2002 and 

2018 emissions inventories. This method does not produce highly accurate results because, 

unlike the air quality model and associated PSAT analysis, it does not account for chemistry and 

removal processes. Instead, it relies on an integration of gridded emissions data, back trajectory 

residence time data, a one-over-distance factor to approximate deposition and a normalization of

the final results. Residence time over an area is indicative of general flow patterns, but does not 

necessarily imply the area contributed significantly to haze at a given receptor. Therefore, users 

are cautioned to view the WEP as one piece of a larger, more comprehensive weight of evidence 

analysis. 

The emissions data used were the annual, 36km grid SMOKE-processed, model-ready emissions 

inventories provided by the WRAP RMC. The analysis was performed for nine pollutants (maps 

were generated for all but the last three): 

• Sulfur oxides 

• Nitrogen oxides 

• Organic carbon 

• Elemental carbon 

• Fine particulate matter 

• Coarse particulate matter 

• Ammonia 

• Volatile organic carbon 

• Carbon monoxide 

The following source categories for each pollutant were identified and preserved through the

analysis: 

• Biogenic 

• Natural fire 

• Point 

• Area 

• WRAP oil and gas 

• Off-shore 

• On-road mobile 

• Off-road mobile 

• Road dust 

• Fugitive dust 

• Windblown dust 

• Anthropogenic fires. 

The back trajectory residence times were provided by the WRAP COHA. The COHA project 

used NOAA’s HYSPLIT model to generate eight back trajectories daily for each WRAP Class I 

area for the entire five-year baseline period (2000 through 2004). From these individual 

trajectories, residence time fields were generated for one-degree latitude by one-degree longitude 

grid cells. Residence time analysis computes the amount of time (e.g., number of hours) or 

percent of time an air parcel is in a horizontal grid cell. Plotted on a map, residence time is 

shown as percent of total hours in each grid cell across the domain, thus allowing an 

interpretation of general air flow patterns for a given Class I area. The residence time fields for 

the 20 percent worst and best IMPROVE-monitored extinction days were selected for the WEP 

analysis to highlight the potential emissions sources during those specific periods. Additional 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-30 
information regarding back trajectory modeling can be found at 

http://vista.cira.colostate.edu/docs/wrap/Modeling/BackTrajectoryModeling.doc. 

The WEP analysis consisted of weighting the annual gridded emissions (by pollutant and source 

category) by the worst and best extinction days residence times for the five-year baseline period. 

To account for deposition along the trajectories, the result was further weighted by a one-overdistance factor, measured as the distance in km between the centroid of each emissions grid cell 

and the centroid of the grid cell containing the Class I area monitoring site under investigation. 

(The “home” grid cell of the monitoring site was weighted by one fourth of the 36km grid cell 

distance, or one-over-9km, to avoid a large response in that grid cell.) The resulting weighted 

emissions field was normalized by the highest grid cell to ease interpretation. 

The WEP is not a rigorous, stand-alone analysis, but a simple, straightforward use of existing 

data. As such, there are several caveats to keep in mind when using WEP results as part of a 

comprehensive weight of evidence analysis: 

• This analysis does not take into account any emissions chemistry. 

• While actual emissions may vary considerably throughout the year, this analysis pairs up 

annual emissions data with 20 percent worst/best extinction days residence times – this is 

likely most problematic for carbon and dust emissions, which can be highly episodic. 

• Coarse particle and some fine particle dust emissions tend not to be transported long 

distances due to their large mass. 

• The WEP results are unitless numbers, normalized to the largest-valued grid cell. 

Effective use of these results requires an understanding of actual emissions values and 

their relative contribution to haze at a given Class I area. 

Additional information regarding WEP analysis can be found at 

http://vista.cira.colostate.edu/docs/wrap/attribution/WEPMethods.doc. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-31 
1.4 REFERENCES 

NOAA, 1985. Climate Narrative of the States-Volume 1. Gale Research Company. 

R.S.U. Smith, “Sand Dunes in the North American Deserts.” in G. Bender(ed.), Reference 

Handbook of the Deserts of North America, Greenwood Press, Westport, Conn., 1982. pp. 481-

554. 

J.H. Stewart, Geology of Nevada: Special Publication 4. Nevada Bureau of Mines and Geology, 

1980. 

WRAP 2002. Visibility Model Performance Evaluation-Final Report. Western Regional Air 

Partnership, February 24, 2006. 

NEVADA REGIONAL HAZE STATE IMPLEMENTATION PLAN, October 2009 1-32