Nevada Regional Haze 5-Year Progress Report, November 2014 4-1

4

Chapter Four – Jarbidge: Assessment of 

Visibility Conditions 

(40 CFR 51.308(g)(3))

Table of Contents

4.1 Status Summary................................................................................................................ 2

4.2 Visibility Conditions........................................................................................................ 3

4.3 Current Visibility Conditions........................................................................................... 3

4.4 Differences between Current and Baseline Conditions.................................................... 4

4.5 Changes in Visibility Impairment .................................................................................. 13

4.6 Visibility Trends............................................................................................................. 15

4.7 Effects of Outliers .......................................................................................................... 19
Nevada Regional Haze 5-Year Progress Report, November 2014 4-2

51.308(g)(3) For each mandatory Class 

I Federal area within the State, the 

State must assess the following visibility 

conditions and changes, with values for 

most impaired and least impaired days 

expressed in terms of 5-year averages 

of these annual values. 

(i) The current visibility conditions for 

the most impaired and least impaired 

days;

(ii) The difference between current 

visibility conditions for the most 

impaired and least impaired days and 

baseline conditions;

(iii) The change in visibility impairment 

for the most impaired and least 

impaired days over the past 5 years.

4.1 Status Summary

Current visibility conditions measured at JARB1, the IMPROVE monitor representing Nevada’s 

only mandatory Class I area (the Jarbidge WA), are shown in Table 4-1. On the worst days,

visibility impairment is strongly influenced by light extinction due to particulate organic matter, 

followed by coarse mass and sulfate. For the best days, visibility impairment is dominated by 

light extinction due to sulfate, followed by particulate organic matter and coarse mass. Annual 

conditions for the worst days show considerable variation from year to year, while the best days 

show much less variability. 

The dominant source categories for sulfur dioxide (precursor of sulfate) are anthropogenic. In 

contrast, the dominant source 

categories for the particulate 

organic matter precursors, VOCs

and primary organic aerosols, are 

natural. For coarse mass, the 

source categories are roughly 

equally divided between 

anthropogenic and natural sources

in the WestJump2008 inventory.

Section 5.5 of Chapter Five 

details the source categories for 

the emitted visibility impairing 

pollutants. 

Visibility conditions based on the 

rolling 5-year annual average haze 

index (in units of deciviews) have

improved slightly for the worst 

days. Progress for the worst days 

is impeded by large contributions 

to visibility impairment by 

particulate organic matter. This is well illustrated by the huge contribution to visibility 

impairment from wildfires in 2012, which caused a corresponding spike in the 2008-2012 period 

for worst days. See Section 4.4. Better progress is shown for the best days. It is noteworthy that 

on the best days in both 2002 and 2018 source areas outside the jurisdiction of state or federal 

regulation and/or control (i.e., Outside Domain, Canada, Mexico and Pacific Offshore) 

contribute more than two thirds to the sulfate concentration at JARB1. 2009 RH SIP, Section 

4.3.1.

Trend analyses of the period 2000 to 2012 show that visibility impairment due to sulfate and 

nitrate light extinction is decreasing through time for both the worst and best days. The trend 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-3

lines fitted to the annual data have slopes comparable or better than, i.e., showing greater 

improvement, the respective speciated glide slopes for the Jarbidge WA. See Section 4.6 for 

additional discussion. 

4.2 Visibility Conditions

40 CFR 51.308(g)(3) requires the state to assess the visibility conditions for the 20 percent most 

impaired (worst) and least impaired (best) days expressed in terms of the 5-year averages. The 

visibility conditions that must be reviewed include: 1) the current visibility conditions, 2) the 

difference between current visibility conditions compared to the baseline, and 3) the change in 

visibility impairment for the most and least impaired days over the past 5 years.

4.3 Current Visibility Conditions

This section addresses the requirement to report the current visibility conditions for the most 

impaired and least impaired days. 40 CFR 51.308 (g)(3)(i). The following sections discuss the 

differences between the most impaired and least impaired days, current versus baseline visibility 

conditions and trends.

Table 4-1 presents the annual visibility conditions at JARB1, the IMPROVE monitor 

representing Nevada’s Class I area (the Jarbidge WA), for the current planning period 

represented by the 5-year period 2008 to 2012 as well as the 5-year annual averages for the haze 

index and light extinction by species (inverse megameters1or Mm-1). In its discussion of 

visibility conditions, the NDEP is using the period 2008 through 2012 to define visibility 

conditions for the current progress period. The term “current planning period” refers to this 

current, most-recent planning period. The WRAP TSD (WRAP 2013) also assessed Nevada’s 

visibility conditions for the planning period 2005 through 2009. See Appendix A, Sections 

6.8.1.1 and 6.8.1.2. 

Table 4-1. Current Planning Period Annual Visibility Conditions and 5-Year Annual 

Averages for the Worst and Best Days Measured at JARB1

Year

Haze 

Index 

(dv)

Sulfate 

(Mm-1)

Nitrate 

(Mm-1)

POM 

(Mm-1)

EC 

(Mm-1)

Soil 

(Mm-1)

Coarse 

Mass 

(Mm-1)

Sea Salt 

(Mm-1)

Worst Days

2008 12.5 3.72 1.12 12.06 1.48 2.61 4.84 0.04

2009 11.1 4.43 0.53 7.32 1.12 2.31 5.66 0.30

2010 10.0 3.30 1.04 4.33 0.77 2.49 5.66 0.06

2011 11.7 4.16 0.67 7.71 1.21 2.49 6.85 0.40

2012 14.9 3.87 1.18 23.97 3.11 2.63 5.17 0.21

 

1 An inverse megameter is a unit of light extinction that can be directly related to gaseous and aerosol 

concentrations, while a deciview is a metric of haze proportional to the logarithm of the light extinction.
Nevada Regional Haze 5-Year Progress Report, November 2014 4-4

Year

Haze 

Index 

(dv)

Sulfate 

(Mm-1)

Nitrate 

(Mm-1)

POM 

(Mm-1)

EC 

(Mm-1)

Soil 

(Mm-1)

Coarse 

Mass 

(Mm-1)

Sea Salt 

(Mm-1)

Average 12.0 3.9 0.9 11.1 1.5 2.5 5.6 0.2

Best Days

2008 1.9 1.14 0.22 0.23 0.09 0.12 0.27 0.05

2009 1.8 0.95 0.16 0.31 0.11 0.12 0.28 0.03

2010 1.8 1.09 0.15 0.30 0.12 0.06 0.24 0.03

2011 2.1 1.21 0.19 0.39 0.13 0.10 0.26 0.07

2012 2.0 0.95 0.18 0.37 0.18 0.10 0.37 0.04

Average 1.9 1.1 0.2 0.3 0.1 0.1 0.3 0.0

4.4 Differences between Current and Baseline Conditions

This section addresses the difference between current visibility conditions for the most impaired 

and least impaired days and baseline visibility conditions. 40 CFR 51.308 (g)(3)(ii).

Table 4-2 presents the five-year annual average baseline and successive five-year planning 

period visibility conditions measured at JARB1 and the differences between the baseline and 

current conditions represented by the period 2008 to 2012 in units of haze index and speciated

light extinction. A negative difference indicates a reduction in haze, i.e., improved visibility. 

The haze index declined slightly for the worst days, but showed a much greater reduction for the 

best days. Monitored light extinction due to sulfate, nitrate, and elemental carbon has decreased 

between the baseline and progress periods for the worst days, while light extinction resulting 

from all the monitored species has remained the same or decreased for the best days. Recall that

the baseline period is represented by the years 2000 to 2004. Note the emissions sources for 

VOCs and primary organic aerosols, particulate organic matter precursors, are predominantly 

natural, while emissions sources for fine soil and coarse mass are approximately equally split 

between natural and anthropogenic sources in the WestJump2008 inventory. See Chapter Five.

Table 4-2. 5-Year Annual Average Baseline and Visibility Conditions for Successive 5-

Year Planning Periods for the Worst and Best Days Measured at JARB1

Planning 

Period

Haze 

Index 

(dv)

Sulfate 

(Mm-1)

Nitrate 

(Mm-1)

POM 

(Mm-1)

EC 

(Mm-1)

Soil 

(Mm-1)

Coarse 

Mass 

(Mm-1)

Sea Salt 

(Mm-1)

Worst Days

Baseline 12.1 4.0 1.1 10.0 1.6 2.4 5.5 0.1

2005-2009 12.4 4.4 1.4 10.0 1.7 2.6 5.9 0.2

2006-2010 12.2 4.0 1.1 9.6 1.6 2.7 6.1 0.1

2007-2011 11.7 3.9 1.0 8.4 1.2 2.7 6.2 0.2

2008-2012 12.0 3.9 0.9 11.1 1.5 2.5 5.6 0.2
Nevada Regional Haze 5-Year Progress Report, November 2014 4-5

Planning 

Period

Haze 

Index 

(dv)

Sulfate 

(Mm-1)

Nitrate 

(Mm-1)

POM 

(Mm-1)

EC 

(Mm-1)

Soil 

(Mm-1)

Coarse 

Mass 

(Mm-1)

Sea Salt 

(Mm-1)

Difference*-0.1 -0.1 -0.2 1.1 -0.1 0.1 0.1 0.1

Best Days

Baseline 2.6 1.2 0.3 0.8 0.3 0.1 0.3 0.0

2005-2009 2.2 1.1 0.2 0.5 0.2 0.1 0.3 0.0

2006-2010 2.0 1.1 0.2 0.4 0.1 0.1 0.3 0.0

2007-2011 2.0 1.1 0.2 0.3 0.1 0.1 0.3 0.0

2008-2012 1.9 1.1 0.2 0.3 0.1 0.1 0.3 0.0

Difference*-0.7 -0.1 -0.1 -0.5 -0.2 0.0 0.0 0.0

* Calculated as the difference between the baseline period and current conditions represented by the 2008-2012

period. A negative difference indicates a reduction in haze, i.e., improved visibility.

USEPA guidance (USEPA 2013) suggests states consider a chart of rolling 5-year averages of 

the annual averages to avoid any confusion or discussion regarding whether the proper current 

planning period has been identified. Table 4-3 presents the current visibility conditions as 

rolling 5-year averages of the annual conditions in deciviews. Figure 4-1 and Figure 4-2 present 

the 5-year baseline average visibility conditions, average annual visibility conditions, and the 5-

year rolling averages for the 20 percent worst days and 20 percent best days, respectively.

USEPA also suggests it may be useful to include additional monitoring data such as organic 

species. Figure 4-3 and Figure 4-4 present the annual speciated light extinction for the 20 

percent worst and 20 percent best days, respectively, and also show the annual haze index 

(deciviews) for the period spanning the baseline to the current planning period. These figures 

show the large variability from year to year in light extinction by species. For the worst days, the 

variability between years ranges from 0.4 Mm-1for Sea Salt (sea salt) to more than 18 Mm-1for 

particulate organic matter, and are two to three Mm-1for the remaining species: sulfate, nitrate, 

elemental carbon, soil, and coarse mass. The strong influence of particulate organic matter on 

the year-to-year variability in visibility conditions on the worst days is clearly shown on Figure 

4-3 by the visibility trend mimicking the particulate organic matter trends. Levels of particulate 

organic matter spiked in 2012 as a result of huge fire emissions that year, causing a 

corresponding spike in the 2008-2012 period for worst days. As can be seen in Figure 4-4,

visibility on the best days is generally improving with time with little variability from year to 

year.
Nevada Regional Haze 5-Year Progress Report, November 2014 4-6

Table 4-3. Five-Year Rolling Annual Average Haze Index for Baseline and Successive 

Planning Periods Measured at JARB1 (deciview)

2000 - 2004

(baseline) 2005 - 2009 2006 - 2010 2007 - 2011 2008 - 2012 Natural 

Conditions

20% Worst Days

12.1 12.4 12.2 11.7 12.0 7.9

20% Best Days

2.6 2.2 2.0 2.0 1.9 1.1

Figure 4-1. Worst Days: Annual Haze Index with 5-Year Baseline Average and 5-Year 

Rolling Averages (deciview)

Figure 4-2. Best Days: Annual Haze Index with 5-Year Baseline Average and 5-Year 

Rolling Averages (deciview)
Nevada Regional Haze 5-Year Progress Report, November 2014 4-7

Figure 4-3. Worst Days: Average Annual Visibility Conditions at JARB1 Expressed in 

Deciviews and Speciated Light Extinction (Mm-1)

Figure 4-4. Best Days: Average Annual Visibility Conditions at JARB1 Expressed in 

Deciviews and Speciated Light Extinction (Mm-1)

Figure 4-5 shows the differences between the 5-year average baseline speciated light extinction 

and the 5-year average speciated light extinction for each of the four successive progress periods

on the worst days. Figure 4-6 presents the same information for the best days. For the worst 

days, the bars generally show the same contribution and magnitude for both the baseline and the 

current planning periods, although there are noticeable variations in visibility impairment due to 

particulate organic matter. For the best days, there is a noticeable reduction in visibility 

impairment due to sulfate, nitrate, particulate organic matter, and elemental carbon from the 

baseline to the current planning period with an overall reduction in visibility impairment on the 

best days.
Nevada Regional Haze 5-Year Progress Report, November 2014 4-8

Figure 4-5. Worst Days: Five-Year Average Speciated Light Extinction for Baseline and 

Successive 5-Year Planning Periods Measured at JARB1

Figure 4-6. Best Days: Five-Year Average Speciated Light Extinction for Baseline and 

Successive 5-Year Planning Periods Measured at JARB1

Table 4-4 presents the relative percentage contribution and rank of each species to worst and best 

day visibility impairment for the baseline and four subsequent planning periods as well as the 5-

year average visibility impairment expressed in deciviews. The top three contributing species for 

each planning period are indicated on Table 4-4 by bold text. 

0

5

10

15

20

25

30

2000-2004

Baseline

2005-2009 2006-2010 2007-2011 2008-2012

Light Extinction, Bext (Mm-1)

Sea Salt

Coarse Mass

Soil

Elemental Carbon

Particulate Organic Mass

Ammonium Nitrate

Ammonium Sulfate

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

2000-2004

Baseline

2005-2009 2006-2010 2007-2011 2008-2012

Light Extinction, Bext (Mm-1)

Planning Period

Sea Salt

Coarse Mass

Soil

Elemental Carbon

Particulate Organic Mass

Ammonium Nitrate

Ammonium Sulfate
Nevada Regional Haze 5-Year Progress Report, November 2014 4-9

For the worst days, particulate organic matter is by far the dominate contributor to visibility 

impairment for the baseline as well as all the subsequent planning periods, contributing between 

35 and 43 percent of the visibility impairment. Particulate organic matter is followed by coarse 

mass, contributing between 22 and 26 percent of the impairment, and sulfate, contributing 

between 15 and 17 percent. Soil, elemental carbon, nitrate, and sea salt each contribute less to 

visibility impairment with contributions of roughly 10 percent for soil decreasing to less than one 

percent for sea salt. 

For the best days, sulfate is the dominant contributor, contributing roughly 40 to 50 percent of 

the visibility impairment at JARB1. The sulfate contribution is most likely high because best 

days represent times when there are few emissions from natural sources, so emissions from 

anthropogenic source categories become more dominant. Although the percent contribution 

from sulfate increases from the baseline period to the progress period, Table 4-2 shows that 

monitored concentrations are in fact decreasing. Source apportionment modeling accessed in the 

TSS2indicates that Nevada emissions contribute only 12.4 percent to 15.4 percent to modeled 

sulfate concentrations at JARB1 on the best days for 2002 and 2018, respectively. 2009 RH SIP, 

Figures 4-10 and 4-11.

Particulate organic matter is the second largest contributor on best days with roughly a 25 

percent contribution in the baseline period decreasing to 15 percent in the progress period. For 

the baseline period, nitrate is the third largest contributor with a contribution of roughly 10 

percent, although elemental carbon and coarse mass also contribute roughly 10 percent each to

baseline visibility impairment. Soil has a contribution of roughly three percent and sea salt 

roughly two percent during the baseline period. For the successive planning periods, the third 

largest contributor is coarse mass, contributing between 12 and 13 percent, followed by nitrate,

contributing roughly eight to nine percent. Elemental carbon and soil contribute roughly six to 

seven percent and four to five percent, respectively. Sea salt contributes roughly two percent. 

Although the ranking changes from worst days to best days, particulate organic matter, coarse 

mass, and sulfate are the three largest contributors to visibility impairment at JARB1 for the 

successive planning periods set forth in Figure 4-5 and Figure 4-6. As discussed in Chapter Five, 

emissions of VOCs and primary organic aerosols are primarily from non-anthropogenic sources. 

Gaseous VOCs are converted to particulate organic matter through chemical reactions in the 

atmosphere, while primary organic aerosols are emitted as particulate, both of these particulates 

are monitored as particulate organic matter. Roughly 40 percent of coarse mass emissions come 

from non-anthropogenic sources in the baseline period, while in the WestJump2008 inventory 

the source categories are roughly equally divided between anthropogenic and natural sources. 

SO2, which combines with ammonia (NH3) in the atmosphere to form ammonium sulfate, is the 

only one of the three largest contributors to visibility impairment at JARB1 that is dominantly 

 

2

http://vista.cira.colostate.edu/tss/, last viewed 8/25/2014.
Nevada Regional Haze 5-Year Progress Report, November 2014 4-10

emitted from anthropogenic sources; however, approximately two thirds of the sulfate monitored 

at JARB1 is attributed to sources out of Nevada’s control (2009 RH SIP, Section 4.3.1). 

Table 4-4. Average Visibility Conditions by Species for the Successive 5-Year Progress 

Periods at JARB1

Planning 

Period

Haze 

Index

(dv)

Percent Contribution to Aerosol Extinction by Species (Excludes 

Rayleigh) Expressed as % of Mm-1and [Rank]*

Sulfate*

(%)

Nitrate

(%)

POM*

(%)

EC

(%)

Soil

(%)

Coarse 

Mass*

(%)

Sea Salt

(%)

20% Worst Days

2000 -

2004 12.1 16.2

[3]

4.4

[6]

40.6

[1]

6.7

[5]

9.7

[4]

22.1

[2]

0.2

[7]

2005 -

2009 12.4 17.0

[3]

5.3

[6]

38.2

[1]

6.6

[5]

9.8

[4]

22.5

[2]

0.6

[7]

2006 -

2010 12.2 15.9

[3]

4.2

[6]

38.0

[1]

6.4

[5]

10.8

[4]

24.1

[2]

0.4

[7]

2007 -

2011 11.7 16.6

[3]

4.2

[6]

35.5

[1]

5.3

[5]

11.6

[4]

26.1

[2]

0.7

[7]

2008 -

2012 12.0 15.1

[3]

3.5

[6]

43.0

[1]

6.0

[5]

9.7

[4]

21.9

[2]

0.8

[7]

20% Best Days

2000 -

2004 2.6 41.0

[1]

9.8

[3]

26.1

[2]

9.5

[4]

2.7

[6]

9.2

[5]

1.7

[7]

2005 -

2009 2.2 46.7

[1]

8.2

[4]

19.3

[2]

6.6

[5]

4.5

[6]

12.7

[3]

2.0

[7]

2006 -

2010 2.0 48.9

[1]

8.6

[4]

16.6

[2]

6.1

[5]

4.6

[6]

13.1

[3]

2.1

[7]

2007 -

2011 2.0 50.5

[1]

9.2

[4]

15.6

[2]

5.5

[5]

4.6

[6]

12.4

[3]

2.3

[7]

2008 -

2012 1.9 50.5

[1]

8.5

[4]

15.1

[2]

5.7

[5]

4.7

[6]

13.2

[3]

2.4

[7]

*Highest three aerosol species contributions per planning period are presented in bold font. 

Table 4-5, drawing from the data in Table 4-2, presents the change in haze index as well as 

speciated light extinction from the baseline to the successive planning periods for both the worst 

and best days measured at JARB1. The change in light extinction is calculated as the planning

period average minus the baseline period average. A negative difference indicates a reduction in 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-11

haze, i.e., improved visibility. Figure 4-7 and Figure 4-8 portray these same data graphically for 

the worst and best days, respectively.

Table 4-5. Change in Aerosol Light Extinction by Species from 2000-2004 Baseline Period 

to Each Successive 5-Year Progress Period Measured at JARB1.*

Planning 

Period

Change in 

Haze 

Index (dv)

Change in Light Extinction by Species (Mm-1)

Sulfate Nitrate POM EC Soil CM Sea 

Salt

Worst Days

2005 -

2009 0.3 0.44 0.30 -0.04 0.07 0.16 0.42 0.10

2006 –

2010 0.1 0.02 -0.04 -0.43 -0.02 0.33 0.63 0.04

2007 –

2011 -0.4 -0.08 -0.10 -1.67 -0.41 0.32 0.70 0.11

2008 -

2012 -0.1 -0.10 -0.19 1.04 -0.11 0.10 0.17 0.14

Best Days

2005 -

2009 -0.4 -0.07 -0.09 -0.30 -0.12 0.03 0.04 0.00

2006 –

2010 -0.6 -0.10 -0.10 -0.39 -0.14 0.02 0.03 0.00

2007 –

2011 -0.6 -0.11 -0.09 -0.43 -0.16 0.02 0.00 0.00

2008 -

2012 -0.7 -0.14 -0.11 -0.45 -0.16 0.02 0.01 0.00

*Change in light extinction is calculated as the planning period average minus the baseline period average. 

Italicized, negative values indicate decreases in light extinction or improvement in visibility.

Table 4-5 shows that for the best days, visibility impairment decreases from baseline to planning 

period for the haze index, as well as light extinction due to sulfate, nitrate, particulate organic 

matter, and elemental carbon with 5-year each period, demonstrating continued improvements in 

visibility impairment with each successive 5-year planning period. Light extinction due to soil, 

coarse mass, and sea salt show little change between the baseline and planning periods. 

Similarly, for the worst days, sulfate and nitrate show continued improvement beginning with the 

2007 to 2010 and 2006 to 2010 planning periods, respectively. Sulfate and nitrate monitoring 

data measured at JARB1 during 2005 have some interesting characteristics that affect the 5-year 

averages and are discussed further in Section 4.5. Also noteworthy for the worst days is the 

large variability of impairment due to particulate organic matter light extinction, which 

demonstrates that one year of data can result in a difference of more than 2.5 Mm-1in extinction 

from one 5-year planning period to the next (2007-2011 and 2008-2012). The haze index does

not show any clear trends for the worst days due to the significant contributions to visibility 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-12

impairment from particulate organic matter. Changes in light extinction due to elemental carbon, 

soil, coarse mass and sea salt varies from planning period to planning period. 

Figure 4-7 presents the changes in speciated light extinction between 5-year planning periods 

and very clearly shows the variability between planning periods discussed above for worst days, 

particularly for particulate organic matter extinction. It also shows the reduction in sulfate and 

nitrate extinction for the most recent 5-year planning periods. Figure 4-8 shows the steady 

reduction of sulfate, nitrate, particulate organic matter, and elemental carbon contributions to 

light extinction with each successive planning period for the best days. 

Figure 4-7. Worst Days: Change in 5-Year Average Light Extinction between Baseline and 

Successive Planning Periods Measured at JARB1

-3.0

-2.0

-1.0

0.0

1.0

2.0

2005-2009 2006-2010 2007-2011 2008-2012

Change in Light Extinction, Bext (Mm-1)

Successive Planning Period

Sea Salt

Coarse Mass

Soil

Elemental Carbon

Particulate Organic Mass

Ammonium Nitrate

Ammonium Sulfate
Nevada Regional Haze 5-Year Progress Report, November 2014 4-13

Figure 4-8. Best Days: Change in 5-Year Average Light Extinction between Baseline and 

Successive Planning Periods Measured at JARB1

4.5 Changes in Visibility Impairment

This section addresses the change in visibility impairment for the most impaired and least 

impaired days over the past 5 years. 40 CFR 51.308 (g)(3)(iii).

The uniform rate of progress glidepath for Jarbidge WA is shown in Figure 4-9. The glidepath is 

one of the indicators used to set reasonable progress goals and is simply a graph portraying a 

straight line drawn from the level of visibility impairment for the worst days baseline period to 

the natural background level with 2064 as the attainment date. The glidepath in Figure 4-9 is 

represented by the sloping line with the open triangles identifying the uniform rate of progress at 

five year intervals. The uniform rate of progress value at Jarbidge in 2018 is 11.09 deciviews. 

The 2018 reasonable progress goal for Jarbidge WA is 11.05 deciviews.

3

 

3

See the discussion in Chapter One of the correction to the 2018 visibility projection for Jarbidge WA conducted by 

the Regional Modeling Center. Nevada concludes that it is reasonable to retain the reasonable progress goal of 

11.05 deciviews, which aligns closely with the 2018 uniform rate of progress value for Jarbidge WA.

-1.0

0.0

1.0

2005-2009 2006 - 2010 2007-2011 2008-2012

Change in Light Extinction, Bext (Mm-1)

Successive Planning Period

Sea Salt

Coarse Mass

Soil

Elemental Carbon

Particulate Organic Mass

Ammonium Nitrate

Ammonium Sulfate
Nevada Regional Haze 5-Year Progress Report, November 2014 4-14

Figure 4-9. Uniform Rate of Progress Glidepath for the Jarbidge Wilderness Area

Table 4-6 presents the visibility change between the current and baseline worst days and best 

days, including the visibility changes as required by the RHR. It also compares worst days 

current conditions with the 2018 reasonable progress goal to show the percent progress achieved 

since the baseline using the 2008-2012 five-year average. Visibility impairment on the best days 

shows substantial improvement, while only modest progress is shown for the worst days due to 

significant contribution of particulate organic matter extinction, which results from emissions of 

VOCs and primary organic aerosols from natural sources.

Table 4-6. 2018 Reasonable Progress Goal Summary for JARB1

Best 

Days 

Baseline 

(dv)

Best 

Days 

2008-

2012

(dv)

Visibility 

Improve

ment 

(dv)

Worst 

Days 

Baseline 

(dv)

Worst 

Days 

2008-

2012 

(dv)

Visibility 

Improve

ment 

(dv)

2018 

RPG 

(dv)

Worst

Days

Progress 

to 2018 

RPG by 

2012

2.6 1.9 0.7 12.1 12.0 0.1 11.05 9.5%

Figure 4-10 and Figure 4-11 present the annual visibility conditions for the current planning 

period. Figure 4-10 shows the large year-to-year variability of particulate organic matter

extinction for the worst days and its influence on the haze index as measured in deciviews. The 

Uniform Rate of Progress Glidepath

Jarbidge Wilderness Area - 20 Percent Best and Worst Days

12.07 11.79 11.44 11.09 10.74 10.39 10.04 9.69 9.34 8.99 8.64 8.29 7.87

0

2

4

6

8

10

12

14

16

2000 2004 2008 2012 2016 2020 2024 2028 2032 2036 2040 2044 2048 2052 2056 2060 2064

Year

Baseline Obs 20% W 2000-2004 Baseline 20% W Glide Path

Baseline Obs 20% B 2000-2004 Baseline 20% B Natural Conditions

2018 - End of 1st Planning Period Haze Index (Deciview) 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-15

large variability in particulate organic matter extinction during the 2008-2012 period

overwhelms the relatively flat trends in all of the other species extinction for the 2008-2012 

period when calculating the haze index. The annual extinction values for all of the monitored 

species other than particulate organic matter vary by 2.34 Mm-1or less, whereas particulate 

organic matter varies by almost 20 Mm-1. See Figure 4-1. The timelines representing the best 

days show much less year-to-year variability. See Figure 4-11.

Figure 4-10. Worst Days: Annual Visibility Conditions Measured at JARB1 for the 

Current Progress Period

Figure 4-11. Best Days: Annual Visibility Conditions Measured at JARB1 for the Current 

Progress Period

4.6 Visibility Trends

This section discusses changes in visibility impairment as characterized by annual average trend 

statistics as well as rolling 5-year average trend statistics for sulfate and nitrate. The regulatory 

requirement calls for an analysis of change over the past 5-year period, but does not preclude 

looking at a longer time frame. Since trend analysis is better suited to longer periods of time, 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-16

trends for the entire 13-year period, 2000 to 2012, are presented here. The trend lines represent 

linear regressions generated in Excel©.

Figure 4-12 presents the annual average sulfate light extinction trends for the worst days, all 

IMPROVE sampled days (all days), and the best days. The annual trends for the worst and best 

days are downward, indicating improvement in visibility impairment from light extinction due to 

sulfate. There is a slight upward trend for all days. The slope of the worst days trend line is 

-0.0187 Mm-1/yr, comparable to the slope of the sulfate glideslope for Jarbidge WA from 

baseline conditions to natural conditions (-0.0533 Mm-1/yr).

Figure 4-12. Annual Average Sulfate Light Extinction and Trends

Figure 4-13 presents the light extinction trends due to sulfate for the worst days, all days, and 

best days based on rolling 5-year averages. The 5-year trends for the worst and best days are 

downward, again indicating improvements in visibility impairment resulting from sulfate 

extinction, while the all days data show variability with a slight upward slope. Thus, both the 

annual and the 5-year average data demonstrate improvement in visibility impairment due to 

sulfate light extinction on the worst and best days.

0

1

2

3

4

5

6

Annual Average Sulfate Light 

Extinction, Bext (Mm-1)

Year

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)
Nevada Regional Haze 5-Year Progress Report, November 2014 4-17

Figure 4-13. Rolling Five-Year Average Sulfate Light Extinction and Trends

Figure 4-14 and Figure 4-15 present similar data for nitrate extinction. These data all show 

downward trends, clearly demonstrating improvement in annual visibility impairment resulting 

from light extinction due to nitrate for the worst, best, and all days. If the December 18, 2005 

nitrate spike discussed in the next section were omitted from the data set, the downward slope on 

the worst days would be even stronger. The slope of both the annual average worst days trend 

line (-0.0373 Mm-1/yr) and the 5-year average worst days trend line are an order of magnitude 

better than the slope of the nitrate glideslope for Jarbidge WA from baseline conditions to natural 

conditions (-0.0033 Mm-1/yr).

0

1

2

3

4

5

5-Year Annual Average Sulfate Light 

Extinction, Bext (Mm-1)

Planning Period

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)
Nevada Regional Haze 5-Year Progress Report, November 2014 4-18

Figure 4-14. Annual Average Nitrate Light Extinction and Trends

Figure 4-15. Rolling Five-Year Average Nitrate Light Extinction and Trends

Figure 4-11 through Figure 4-15 all demonstrate that JARB1 worst and best days visibility 

impairment resulting from light extinction due to sulfate and nitrate is improving over time, both 

on an annual basis as well as for the 5-year planning period averages. The slopes of the annual 

trend lines for the worst days are comparable or better than the respective glideslopes for sulfate 

and nitrate light extinction. Sulfate and nitrate form from SO2 and NOx emissions, which are 

0

1

2

3

Annual Average Nitrate Light 

Extinction, Bext (Mm-1)

Year

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)

0

1

2

5-Year Annual Average Nitrate Light 

Extinction, Bext (Mm-1)

Planning Period

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)
Nevada Regional Haze 5-Year Progress Report, November 2014 4-19

dominated by anthropogenic sources. Emission sources contributing to light extinction due to 

sulfate and nitrate at the Jarbidge WA are discussed in Chapter Six.

4.7 Effects of Outliers

As mentioned above, the 2005 monitor data from JARB1 has some interesting characteristics,

especially in late December when a large spike (40+ Mm-1, which is twice the next highest value 

recorded from 2000 to 2012) in monitored nitrate extinction occurred, corresponding to a smaller 

but distinct sulfate spike, as shown on Figure 4-16. The event that produced these spikes is not 

known to the NDEP, but similar spikes were seen across a wide-ranging geographic extent in the 

western United States, from Mount Hood Wilderness Area (WA) in Oregon (Figure 4-17) to 

Great Sand Dunes National Monument in Colorado (Figure 4-18). These figures present the 

nitrate and sulfate light extinction for all IMPROVE sample days in 2005 and show a consistent 

pattern of monitored nitrate light extinction during the December 2005 event although the values 

vary from site to site. Other IMPROVE monitoring sites across this vast region of the western 

United States record similar patterns of monitored nitrate light extinction for this event including,

but not limited to, Mount Jefferson WA/Mount Washington WA/Three Sisters WA in Oregon; 

Great Basin National Park in Nevada; Zion Canyon National Park and Capital Reef National 

Park in Utah; Grand Canyon National Park and Petrified Forest National Park in Arizona; Rocky 

Mountain National Park in Colorado; and Bandelier National Monument in New Mexico. 

Figure 4-16. 2005 Nitrate and Sulfate Monitor Data for the Jarbidge WA, Nevada
Nevada Regional Haze 5-Year Progress Report, November 2014 4-20

Figure 4-17. 2005 Nitrate and Sulfate Monitor Data for the Mount Hood WA, Washington

Figure 4-18. 2005 Nitrate and Sulfate Monitor Data for Great Sand Dunes NM, Colorado

The NDEP evaluated the impact of the December 18th nitrate extinction value on the annual 

average as well as the 5-year annual averages that include 2005 data. The 2005 41.88 Mm-1

extinction value was replaced with the average worst days nitrate light extinction (with the spike 

included in the average) from 2005, which is 2.72 Mm-1. The worst days were re-identified and 

the substituted December 18th data remained as one of the worst days (2.72 Mm-1is still the 

second highest nitrate light extinction for the 2005 worst days). The substituted data was used to 

re-calculate the worst days and all days annual light extinction and haze index, and the annual 

averages were then used to calculate the 5-year averages. This substitution lowered the average 

annual nitrate light extinction from 2.72 Mm-1to 1.09 Mm-1and lowered the annual average haze 

index from 11.3 deciviews to 10.9 deciviews. These are significant revisions based on 

conservative substitution of a single data point. 

Figure 4-19 presents the annual nitrate light extinction for the worst, all, and best days using the 

substituted data for comparison with Figure 4-14, which presents the original data. Note the 
Nevada Regional Haze 5-Year Progress Report, November 2014 4-21

slope for both the worst days and all sample days decreased slightly from the original data. The 

best days data remain unchanged by the substitution. The slope of the worst days nitrate light 

extinction trend line still exceeds the glideslope by an order of magnitude. 

Figure 4-19. Annual Average Nitrate Light Extinction and Trends, Substituted Data

Figure 4-20 presents the 5-year average nitrate light extinction for the worst, all, and best days 

using the substituted data for comparison with Figure 4-15. Note on Figure 4-15 how the 

inclusion of the December 18th event increases all the 5-year averages that include data from 

2005 (beginning with 2001-2005) and how quickly the 5-year averages drop when 2005 data is 

no longer included in the average (2006-2010). In addition, all the 5-year averages that include 

2005 data exceed 1.4 Mm-1 with a high of 1.52 Mm-1, while the high 5-year average of the 

substituted data is 1.2 Mm-1. 

0

1

2

3

Annual Average Sulfate Light 

Extinction, Bext (Mm-1)

Year

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)
Nevada Regional Haze 5-Year Progress Report, November 2014 4-22

Figure 4-20. Rolling Five-Year Annual Average Nitrate Light Extinction and Trends, 

Substituted Data

This data substitution exercise demonstrates the influence of one outlier data point on the annual 

average as well as the 5-year averages that incorporate the outlier data and how demonstration of 

progress can be stymied by a single data point. A more refined data substitution mechanism 

could be developed and may further reduce the annual nitrate extinction and haze index as well 

as the 5-year average nitrate extinction and haze index. Nevada urges the USEPA to 

acknowledge the influence of outliers and develop an acceptable regulatory mechanism to 

minimize the impact of outlier data on the evaluation of a state’s status in meeting its reasonable 

progress goal. 

0

1

2

5-Year Annual Average Nitrate 

Light Extinction, Bext (Mm-1)

Planning Period

Worst Days

All Days

Best Days

Linear (Worst Days)

Linear (All Days)

Linear (Best Days)