BASELINE AND 

NATURAL BACKGROUND 

VISIBILITY CONDITIONS 

CONSIDERATIONS AND PROPOSED APPROACH 

TO THE CALCULATION OF BASELINE AND 

NATURAL BACKGROUND VISIBILITY 

CONDITIONS AT MANE-VU CLASS I AREAS

Prepared by NESCAUM 

December, 2006 
ii

Members of NESCAUM 

Anne Gobin, Bureau Chief 

Connecticut Department of Environmental Protection, Bureau of Air Management 

James P. Brooks, Bureau Director 

Maine Department of Environmental Protection, Bureau of Air Quality 

Barbara Kwetz, Director 

Massachusetts Department of Environmental Protection, Bureau of Waste Prevention 

Robert Scott, Director 

New Hampshire Department of Environmental Services, Air Resources Division 

William O’Sullivan, Director 

New Jersey Department of Environmental Protection, Office of Air Quality Management 

David Shaw, Director 

New York Department of Environmental Conservation, Division of Air Recourses 

Stephen Majkut, Chief 

Rhode Island Department of Environmental Management, Office of Air Resources 

Richard A. Valentinetti, Director 

Vermont Department of Environmental Conservation, Air Pollution Control Division 

Arthur Marin, Executive Director 

NESCAUM 
iii

BASELINE AND 

NATURAL BACKGROUND 

VISIBILITY CONDITIONS 

CONSIDERATIONS AND PROPOSED APPROACH 

TO THE CALCULATION OF BASELINE AND 

NATURAL BACKGROUND VISIBILITY 

CONDITIONS AT MANE-VU CLASS I AREAS

Prepared by NESCAUM 

December, 2006 
iv

BASELINE AND NATURAL 

BACKGROUND VISIBILITY CONDITIONS 

Considerations and Proposed Approach to the 

Calculation of Baseline and Natural Background Visibility 

Conditions at MANE-VU Class I Areas 

Project Manager

Gary Kleiman, NESCAUM 

 

Principal Contributors

Gary Kleiman, John Graham, NESCAUM 
v

Acknowledgements 

NESCAUM acknowledges the funding support for this work through U.S. EPA 

agreement number XA-97318101-0 to the Ozone Transport Commission in support of the

MANE-VU Regional Planning Organization. 

Printed: January, 2007
vi

TABLE OF CONTENTS 

1. Introduction................................................................................................................. 1 

2. The Default Method.................................................................................................... 2 

2.1. Application of the Default Methods ............................................................... 4 

3. The Alternative Method.............................................................................................. 6 

3.1. Application of the Alternative Method........................................................... 9

4. Recommendations..................................................................................................... 12 
Baseline and Natural Background Visibility Conditions Page 1

1. INTRODUCTION 

The long-term visibility conditions that would exist in absence of human-caused 

impairment are referred to as natural background visibility conditions. Accurate 

assessment of these conditions is important due to their role in determining the uniform 

rate of progress that states must consider when setting reasonable progress goals for each 

mandatory Federal Class I area subject to the Regional Haze Rule. Baseline visibility 

conditions – based on monitored visibility during the five year baseline period (2000-

2004) – and estimated natural background visibility conditions will determine the 

uniform rate of progress states will consider when setting reasonable progress goals for 

any Class I site. 

In September 2001, the U.S. Environmental Protection Agency (EPA) issued draft 

methodological guidelines for the calculation of natural background and baseline 

visibility conditions as well as methods for tracking progress relative to the derived 

uniform rate of progress. EPA subsequently finalized this draft guidance in September 

2003. The final guidance recommends a default method and allows for certain 

refinements that states may wish to pursue in order to make these estimates more 

representative of a specific Class I area if it is poorly represented by the default method. 

In the spring of 2006, the IMPROVE Steering Committee adopted an alternative 

formulation of the reconstructed extinction equation to address certain aspects of the 

default calculation method. These aspects were well understood from a scientific 

perspective and were felt to improve the performance of the equation at reproducing 

observed visibility at Class I sites. This alternative formulation of the reconstructed 

extinction equation was not adopted as a replacement to the default method, but as an 

alternative to the default method for states and RPOs to consider as they proceed with the 

regional haze planning process. It seems likely that most, if not all, RPOs are considering 

this alternative formulation as the means by which they will calculate baseline conditions, 

natural background conditions, and track progress toward the national visibility goals 

under the Regional Haze Rule. 

In this report, MANE-VU reviews the default and alternative approaches to the 

calculation of baseline and natural background conditions and presents a discussion of the 

principle differences between the methods. In addition, the default and alternative 

methods are applied to each Class I area in or near the MANE-VU region in order to 

establish differences in baseline conditions, natural background conditions, and 2018 

uniform progress goals under each approach. 

The prior MANE-VU position on natural background conditions was issued in 

June, 2004 and stated that, “Refinements to other aspects of the default method (e.g., 

refinements to the assumed distribution or treatment of Rayleigh extinction, inclusion of 

sea salt, and improved assumptions about the chemical composition of the organic 

fraction) may be warranted prior to submissions of SIPs depending on the degree to 

which scientific consensus is formed around a specific approach...” Based upon the 

subsequent reviews conducted by the IMPROVE Steering Committee, as well as internal 

Technical Steering Committee deliberations, MANE-VU is now ready to adopt the 

alternative reconstructed extinction algorithm for the reasons described in this report. 
Baseline and Natural Background Visibility Conditions Page 2

2. THE DEFAULT METHOD 

The default method is explained in detail in Estimating Natural Background 

Visibility Conditions (U.S.EPA, 2003a) and Guidance for Tracking Progress under the 

Regional Haze Rule (U.S. EPA, 2003b). Summary information is provided here but the 

reader should consult the original guidance documents for any question on how to apply 

this method. 

Estimates of natural visibility impairment due to fine and coarse particles were 

derived using the 1990 National Acid Precipitation Assessment Program reported average 

ambient concentrations of naturally present particles (Trijonis, 1990). Separate 

concentration values were given for the eastern and western United States; no finer 

spatial resolution is available. Average natural background light extinction due to 

particles was then calculated using the IMPROVE methodology and site specific 

ANNUAL f(RH) values. Worst visibility levels are derived using the work of Ames and 

Malm (2001), who estimated the standard deviation of visibility in deciviews in the 

eastern U.S. as 3 dv. By assuming a roughly normal distribution of data, the default 

method adds (subtracts) 1.28*(3 dv) to the average estimated natural background to 

calculate the 90th (10th) percentile level, which is taken by EPA to be representative of the 

mean of the 20 percent worst (best) conditions. 

In the East, the default method for calculating best and worst natural background 

visibility conditions (in dv) for any area in the eastern U.S. uses the following formulae: 

P90 = HI +1.28 sd 

P10 = HI – 1.28 sd 

P90 and P10 represent the 90th and 10th percentile, respectively, the Haze Index 

(HI) represents annual average visibility in units of deciview, and sd is the standard 

deviation of daily average visibility values throughout a year, defined by the guidance as 

3.0 for the eastern U.S. The Haze Index is calculated as shown: 

HI =10 ln (bext/10) 

The atmospheric extinction, bext, is given by the familiar IMPROVE equation 

(IMPROVE, 2000) in inverse megameters: 

bext = (3)f(RH)[sulfate] + (3)f(RH)[nitrate] + (4)[OMC] + (10)[LAC] 

+(1)[SOIL] + (0.6)[CM] + 10

Table 2-1 below provides the default values to be applied at all eastern U.S. Class 

I areas. The result of using these default values in the above equation with an assumed 

annual average f(RH) value of 3.17 in the northeastern U.S. (the average of 11 

northeastern U.S. sites) is approximately 3.6 dv on the 20 percent best days and 11.3 dv 

on the 20 percent worst days.
Baseline and Natural Background Visibility Conditions Page 3

The methods for calculating baseline conditions on the 20 percent best or worst 

days start by repeating the calculation of the Haze Index (HI) as shown above with the 

individual species mass concentrations replaced by the actual monitored values for each 

day during the baseline period. These values should be sorted from highest to lowest for 

each year in the baseline period. Averages (in dv) for each year can be calculated for HI 

values associated with the 20 percent most impaired and 20 percent least impaired days. 

The average HI values for the 20 percent most impaired and 20 percent least impaired 

days in each year should then be averaged for the five consecutive years 2000-2004 to 

define baseline conditions. One important distinction between the natural conditions and 

baseline HI calculations is that the f(RH) values shown in Table 2-2 for natural 

conditions estimates are annual averages. EPA has also estimated site-specific 

Table 2-1. Default parameters used in calculating 

natural background visibility for sites in the eastern U.S. 

Parameter Value Fractional 

Uncertainty

Reference/Comments 

[SULFATE] 0.23 μg/m3 200% Trijonis, 1990 

[NITRATE] 0.10 μg/m3 200% Trijonis, 1990 

[OC] 1.0 μg/m3 200% Trijonis, 1990 

[LAC] 0.02 μg/m3 250% Trijonis, 1990 

[SOIL] 0.50 μg/m3 200% Trijonis, 1990 

[CM] 3.0 μg/m3 200% Trijonis, 1990 

f(RH) ~3.2 15% Varies by site (see Table 2-2) 

Organic multiplier 1.4 50% [OMC]=1.4*[OC] 

σS/N 3.0 m2

/g 33% Hegg, 1997; IMPROVE, 2000; 

Malm, 2000 

σOC 4.0 m2

/g 30% Hegg 1997; Trijonis 1990 

σEC 10.0 m2

/g 40% Malm, 1996 

σsoil 1.0 m2

/g 25% Trijonis, 1990 

σcoarse 0.6 m2

/g 33% IMPROVE, 2000 

Rayleigh 10 Mm-1 20 % Varies with altitude/season 

sd (standard deviation 

of daily visibility) 

3.0 dv 16% Ames and Malm, 2001 

10th, 90th percentile 

adjustment 

1.28 15% Regulation calls for mean of top 

twenty percent, not 90th percentile 

Parameters used in 

potential refinements 

 

[NaCl] ~0.5 50% Varies by site, IMPROVE 

σNaCl 2.5 m2

/s 16% Haywood, 1999 

f(RH)NaCl ~3.2 33% Assumed same as S, N 

Note: The mass estimates presented above are based on estimates of fine particulate concentrations that would exist in 

absence of any manmade pollution (including Mexican and Canadian emissions) consistent with planning requirements of 

the Regional Haze Rule. MANE-VU accepts this as an appropriate planning goal and intends to consider the contribution 

of international transport in deciding what controls are “reasonable” under the regional haze program. 
Baseline and Natural Background Visibility Conditions Page 4

climatological mean monthly average values of f(RH) that are provided in an appendix to 

its guidance (EPA, 2003b) and used for the individual HI calculations for baseline 

conditions. 

2.1. Application of the Default Methods 

The Class I areas in the MANE-VU region that are subject to the requirements of 

the Regional Haze Rule are: Acadia National Park, Maine; Brigantine Wilderness (within 

the Edwin B. Forsythe National Wildlife Refuge), New Jersey; Great Gulf Wilderness, 

New Hampshire; Lye Brook Wilderness, Vermont; Moosehorn Wilderness (within the 

Moosehorn National Wildlife Refuge), Maine; Presidential Range – Dry River 

Wilderness, New Hampshire; and Roosevelt Campobello International Park, New 

Brunswick. In addition to these Class I areas, we consider several nearby Class I areas 

where MANE-VU states may be contributing to visibility impairment. These Class I 

areas include: Dolly Sods Wilderness and the Otter Creek Wilderness in West Virginia as 

well as Shenandoah National Park and the James River Face Wilderness in Virginia. 

MANE-VU understands that it is the responsibility of the appropriate VISTAS states to 

establish estimates of natural visibility conditions and reasonable progress goals for these 

areas. It is anticipated, however, that subsequent consultations will occur with those 

MANE-VU states that may be affecting visibility in these areas. MANE-VU has 

therefore calculated estimates of natural background visibility conditions at the nearby 

sites using MANE-VU approved methods in order to facilitate future consultations. 

The only factor in the default method that varies by site is the climatological 

annual mean relative humidity adjustment factor. Table 2-2 lists this value for the Class I 

sites of interest and the resulting best 20 percent and worst 20 percent estimates of natural 

visibility conditions. The variation among sites using the default method is purely a 

function of differences in climatological annual mean relative humidity, with southern 

and coastal sites being more humid than inland or elevated sites. 
Baseline and Natural Background Visibility Conditions Page 5

Table 2-2. Site-specific relative humidity adjustment factors, best and worst 

(default) estimates of natural background visibility conditions. 

MANE-VU Mandatory Federal Class I Area 

f(RH) 

Best 

Visibility

(dv) 

Worst 

Visibility

(dv) 

Maine 

Acadia National Park 3.34 3.77 11.45 

Moosehorn Wilderness 3.15 3.68 11.36 

Roosevelt Campobello International Park, New 

Brunswick 

3.16 3.68 11.37 

New Hampshire 

Great Gulf Wilderness 3.01 3.63 11.30 

Presidential Range – Dry River Wilderness 3.02 3.65 11.30 

New Jersey 

Brigantine Wilderness 2.97 3.60 11.28 

Vermont 

Lye Brook Wilderness 2.91 3.57 11.25 

Nearby Mandatory Federal Class I Area 

 

Virginia 

James River Face Wilderness 2.93 3.56 11.26 

Shenandoah National Park 2.95 3.57 11.27 

West Virginia 

Dolly Sods Wilderness 3.06 3.64 11.32 

Otter Creek Wilderness 3.06 3.65 11.32 
Baseline and Natural Background Visibility Conditions Page 6

3. THE ALTERNATIVE METHOD 

According to EPA guidance, “[T]he default approach to estimating natural 

visibility conditions presented in this document is adequate for the development of 

progress goals for the first implementation period under the regional haze rule” (U.S. 

EPA, 2003a). However, the guidance does leave the door open for individual states or 

RPOs to adopt their own methods for calculating natural background (or baseline 

conditions) if they can demonstrate that the change from the default represents a 

significant refinement that better characterizes natural visibility (or baseline) conditions 

at a specific Class I site. 

Table 2-3. Site-specific best and worst (default) estimates of 

baseline visibility conditions (2000-2004). 

MANE-VU Mandatory Federal Class I Area Best 

Visibility

(dv) 

Worst 

Visibility

(dv) 

Maine 

 Acadia National Park 8.06 22.34 

 Moosehorn Wilderness 8.48 21.18 

 Roosevelt Campobello International Park, New 

Brunswick 

8.48 21.18 

New Hampshire 

 Great Gulf Wilderness 7.50 22.25 

 Presidential Range – Dry River Wilderness 7.50 22.25 

New Jersey 

 Brigantine Wilderness 13.72 27.60 

Vermont 

 Lye Brook Wilderness 6.20 23.70 

Nearby Mandatory Federal Class I Area 

 

Virginia 

 James River Face Wilderness 14.35 27.72 

 Shenandoah National Park 11.34 27.88 

West Virginia 

 Dolly Sods Wilderness 12.70 27.64 

 Otter Creek Wilderness 12.70 27.64 
Baseline and Natural Background Visibility Conditions Page 7

In response to a number of concerns raised with respect to the use of the default 

methods for Regional Haze Rule compliance (Lowenthal and Kumar, 2003; Ryan et al., 

2005), the IMPROVE Steering Committee established a subcommittee to review the 

default approach and recommend refinements to address criticisms and improve the 

performance for tracking progress under the Haze Rule. The details presented below 

come from that subcommittee’s summary report and a review of potential refinements by 

Hand and Malm (2005). 

The recommended revised algorithm is shown in the equation below with revised 

terms in bold font. The total sulfate, nitrate, and organic carbon compound concentrations 

are each split into two fractions, representing small and large size distributions of those 

components. Although not explicitly shown in the equation, the organic mass 

concentration used in this new algorithm is 1.8 times the organic carbon mass 

concentration, which is changed from 1.4 times the carbon mass concentration as used for 

input in the current IMPROVE algorithm. New terms have been added for sea salt 

(important for coastal locations) and for absorption by NO2 (only used where NO2 data 

are available). Site-specific Rayleigh scattering is calculated for the elevation and annual 

average temperature of each of the IMPROVE monitoring sites. 

Bext ≈ 2.2 x fS(RH) x [Small Sulfate] + 4.8 x fL(RH) x [Large Sulfate] + 

 2.4 x fS(RH) x [Small Nitrate] + 5.1 x fL(RH) x [Large Nitrate] + 

 2.8 x [Small Organic Mass] + 6.1 x [Large Organic Mass] + 

 10 x [Elemental Carbon Mass] + 1 x [Fine Soil Mass] + 

 1.7 x fSS(RH) x [Sea Salt Mass] + 0.6 x [Coarse Mass] + 

 Rayleigh Scattering (site specific) + 0.33 x [NO2 (ppb)] 

 The apportionment of the total concentration of sulfate compounds into the 

concentrations of the small and large size fractions is accomplished using the following 

equations. 

 

 

 

 

The same equations are used to apportion total nitrate and total organic mass 

concentrations into the small and large size fractions. 

Sea salt is calculated as 1.8 x [Chloride], or 1.8 x [Chlorine] if the chloride 

measurement is below detection limits, missing, or invalid. The algorithm uses three 

water growth adjustment terms as shown in Figure 3-1 and Table 3-1. They are for use 

[ ] [ ] [ ]

3

L rga e Sultate = Total Sulfate , for Total Sulfate ≥ 20 μg / m

[ ] [ ][ ] [ ] 3

3

, 20 /

20 /

arg Total Sulfate for Total Sulfate g m

g m

Total Sulfate L e Sulfate μ

μ

= × <

[Small Sulfate] = [Total Sulfate]−[Large Sulfate]
Baseline and Natural Background Visibility Conditions Page 8

with the small size distribution and the large size distribution sulfate and nitrate 

compounds and for sea salt (fS(RH), fL(RH), and fSS(RH), respectively). 

Figure 3-1. Water growth curves for small and large size distribution sulfate and 

nitrate, sea salt, and the original IMPROVE algorithm sulfate and nitrate. 

Water Growth Curves

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100

Relative Humidity (%)

f(RH)

fS(RH)

fL(RH)

Original

fSS(RH)

Table 3-1. f(RH) for small and large size distribution sulfate and nitrate, and 

sea salt. 

RH (%) fS(RH) fL(RH) fSS(RH) RH (%) fS(RH) fL(RH) fSS(RH) RH (%) fS(RH) fL(RH) fSS(RH) 

0 to 36 1.00 1.00 1.00 56 1.78 1.61 2.58 76 2.60 2.18 3.35 

37 1.38 1.31 1.00 57 1.81 1.63 2.59 77 2.67 2.22 3.42 

38 1.40 1.32 1.00 58 1.83 1.65 2.62 78 2.75 2.27 3.52 

39 1.42 1.34 1.00 59 1.86 1.67 2.66 79 2.84 2.33 3.57 

40 1.44 1.35 1.00 60 1.89 1.69 2.69 80 2.93 2.39 3.63 

41 1.46 1.36 1.00 61 1.92 1.71 2.73 81 3.03 2.45 3.69 

42 1.48 1.38 1.00 62 1.95 1.73 2.78 82 3.15 2.52 3.81 

43 1.49 1.39 1.00 63 1.99 1.75 2.83 83 3.27 2.60 3.95 

44 1.51 1.41 1.00 64 2.02 1.78 2.83 84 3.42 2.69 4.04 

45 1.53 1.42 1.00 65 2.06 1.80 2.86 85 3.58 2.79 4.11 

46 1.55 1.44 1.00 66 2.09 1.83 2.89 86 3.76 2.90 4.28 

47 1.57 1.45 2.36 67 2.13 1.86 2.91 87 3.98 3.02 4.49 

48 1.59 1.47 2.38 68 2.17 1.89 2.95 88 4.23 3.16 4.61 

49 1.62 1.49 2.42 69 2.22 1.92 3.01 89 4.53 3.33 4.86 

50 1.64 1.50 2.45 70 2.26 1.95 3.05 90 4.90 3.53 5.12 

51 1.66 1.52 2.48 71 2.31 1.98 3.13 91 5.35 3.77 5.38 

52 1.68 1.54 2.50 72 2.36 2.01 3.17 92 5.93 4.06 5.75 

53 1.71 1.55 2.51 73 2.41 2.05 3.21 93 6.71 4.43 6.17 

54 1.73 1.57 2.53 74 2.47 2.09 3.25 94 7.78 4.92 6.72 

55 1.76 1.59 2.56 75 2.54 2.13 3.27 95 9.34 5.57 7.35 
Baseline and Natural Background Visibility Conditions Page 9

The proposed new algorithm for estimating haze reduces the biases compared to 

measurements at the high and low extremes. This is most apparent for the hazier eastern 

sites. The composition of days selected as best and worst by the current and the new 

algorithm are very similar, and similar to days selected by measurements. Most of the 

reduction of bias associated with the new algorithm is attributed to the use of the split 

component extinction efficiency method for sulfate, nitrate, and organic components that 

permitted variable extinction efficiency depending on the component mass concentration. 

Although not subject to explicit performance testing, the proposed new algorithm also 

contains specific changes from the current algorithm that reflect a better understanding of 

the atmosphere as reflected in the more recent scientific literature (e.g., change to 1.8 

from 1.4 for organic compound mass to carbon mass ratio) and a more complete 

accounting for contributors to haze (e.g., sea salt and NO2 terms), and use of site specific 

Rayleigh scattering terms to reduce elevation-related bias. 

Unlike the default approach, which directly uses the Trijonis natural species 

concentration estimates to calculate natural haze levels, the Alternative Approach uses 

the baseline data (current species concentrations) with a multiplier applied to each species 

measurement in order to give the Trijonis estimate for that species. The ratio of the 

Trijonis estimates for each species divided by the annual mean values for the species is 

used to transform the entire data set to what is then assumed to be the natural species 

concentration levels for that site and year. This process is applied to each of the complete 

years of data (as defined by the EPA tracking progress guidance) in the baseline period 

(2000 through 2004). Sites with three complete years of data are treated as having 

sufficient data for this assessment. If any of the current annual means for any species is 

less than the Trijonis estimate for that species, the unadjusted species data are used. 

Trijonis estimates did not include sea salt, which is only significant at a few coastal sites. 

Estimates of current sea salt concentrations determined from Cl-

 ion data (described as 

part of the new IMPROVE algorithm) are taken to be natural contributors to haze. 

3.1. Application of the Alternative Method 

Here we present a comparison of the background and natural visibility conditions 

calculated using the default and the alternative methods (see Table 3-2 and Table 3-3). 

Corresponding visibility improvement targets for 2018 using each approach are also 

presented (see Table 3-3). Results suggest that the alternative approach leads to very 

similar uniform rates of progress in New England with slightly greater visibility 

improvement required in the Mid-Atlantic region relative to the default approach. 
Baseline and Natural Background Visibility Conditions Page 10

Table 3-2. Comparison of default and alternative approaches for estimating the 20 percent 

worst natural background visibility conditions at MANE-VU and nearby sites (2000-2004). 

MANE-VU Mandatory 

Federal Class I Area 

Default 

Baseline

dv 

Alternative 

Baseline 

dv 

Default 

Natural

dv 

Alternative 

Natural 

dv 

Maine 

 

Acadia National Park 22.34 22.89 11.45 12.43 

Moosehorn Wilderness 21.18 21.72 11.36 12.01 

Roosevelt Campobello 

International Park, New 

Brunswick 

21.18 21.72 11.37 12.01 

New Hampshire 

Great Gulf Wilderness 22.25 22.82 11.30 11.99 

Presidential Range – Dry 

River Wilderness 

22.25 22.82 11.30 11.99 

New Jersey 

Brigantine Wilderness 27.60 29.01 11.28 12.24 

Vermont 

Lye Brook Wilderness 23.70 24.45 11.25 11.73 

Nearby Mandatory Federal 

Class I Areas 

 

Virginia 

James River Face Wilderness 27.72 29.12 11.26 11.13 

Shenandoah National Park 27.88 29.31 11.27 11.35 

West Virginia 

Dolly Sods Wilderness 27.64 29.04 11.32 10.39 

Otter Creek Wilderness 27.64 29.04 11.32 10.39 
Baseline and Natural Background Visibility Conditions Page 11

 

Table 3-3. Estimated uniform rates of progress (ROP) (to be considered for worst 20 percent 

days) and Best Day Baseline Conditions (not to be degraded on best 20 percent days) for first 

implementation period. 

MANE-VU Mandatory Federal Class I 

Area 

Default 

ROP 

Worst day 

(dv/14 yrs)

Alternative 

ROP 

Worst day 

(dv/14 yrs) 

Default 

Baseline 

Visibility 

Best Day (dv) 

Alternative 

Baseline 

Visibility 

Best Day (dv) 

Maine 

Acadia National Park 2.54 2.44 8.06 8.77 

Moosehorn Wilderness 2.29 2.27 8.48 9.15 

Roosevelt Campobello 

International Park, New 

Brunswick 

2.29 2.27 8.48 9.15 

New Hampshire 

Great Gulf Wilderness†

2.56 2.53 7.50 7.66 

Presidential Range – Dry River 

Wilderness† 2.56 2.53 7.50 7.66 

New Jersey 

Brigantine Wilderness‡

3.81 3.91 13.72 14.33 

Vermont 

Lye Brook Wilderness 2.91 2.97 6.20 6.36 

Nearby Mandatory Federal Class I Area 

Virginia 

James River Face Wildernessп

3.84 4.20 14.35 14.21 

Shenandoah National Park‡

3.88 4.19 11.34 10.93 

West Virginia 

 

Dolly Sods Wilderness 3.81 4.35 12.70 12.28 

Otter Creek Wilderness 3.81 4.35 12.70 12.28 

 Note: The values are presented for the default and alternative approaches at MANE-VU and nearby sites (2000-2004). 
Baseline and Natural Background Visibility Conditions Page 12

The default estimates provide a sound, nationally consistent framework on which 

to base the regulatory structure of the Haze Rule that is justified by the current state of 

scientific understanding of these issues. However, an alternative approach for the 

calculation of reconstructed extinction under the Regional Haze Rule has been developed 

that provides all of the same advantages. EPA recommendations on potential refinements 

to the default approach (Pitchford, personal communication, 2004) suggest that, if used, 

any refinements should be broadly accepted by the scientific community, substantial, 

practical to implement, and not create arbitrary inconsistencies. The alternative approach 

endorsed by the IMPROVE Steering Committee for baseline and natural background 

conditions meet these requirements. 

4. RECOMMENDATIONS 

This document reviews EPA guidelines and an IMPROVE Steering Committeeendorsed alternative for calculating baseline and natural background visibility conditions 

under the Regional Haze Rule. It also explores how adoption of the alternative approach 

would affect calculated rates of progress and other regulatory drivers under the Haze 

Rule. 

The alternative approach attempts to incorporate better science for several 

components of the equation to calculate reconstructed extinction that reflects the latest 

scientific research. MANE-VU recognizes the time and effort that has been invested in 

the development of this alternative. We also recognize the high likelihood that other 

RPOs will adopt and use the alternative approach and consider it desirable to use a 

similar approach to other RPOs with which MANE-VU will consult on visibility goals. 

Given the large uncertainties that remain in our ability to estimate the concentrations of 

organic carbon and other species that would be present in the absence of anthropogenic 

influences, we are not certain that the alternative approach significantly improves the 

overall accuracy of the estimated natural background conditions, but it certainly does not 

diminish the accuracy and is likely to improve our estimates of baseline conditions. 

Finally, MANE-VU has considered the fact that the uniform rate of progress that 

results from these calculations is a relatively arbitrary baseline against which progress is 

measured. This Haze Rule requires states to consider this uniform rate, but control 

decisions are to be based on a four-factor analysis that is independent of the uniform rate 

of progress. The relatively small differences in the uniform rate that are introduced as a 

result of using the alternative approach further diminish the significance of this decision. 

Based on all of the considerations above, MANE-VU recommends adoption of the 

alternative approach for use in 2008 MANE-VU SIP submittals, active participation in 

further research efforts on this topic, and future reconsideration of natural background 

visibility conditions as evolving scientific understanding warrants. 
Baseline and Natural Background Visibility Conditions Page 13

References 

Ames, R. B., and Malm, W. C., Recommendations for Natural Condition Deciview 

Variability: An Examination of IMPROVE Data Frequency Distributions. Proceedings 

(CDROM) of A&WMA/AGU Specialty Conference on Regional Haze and Global 

Radiation Balance -- Aerosol Measurements and Models: Closure, Reconciliation and 

Evaluation, Bend, Oregon, 2-5 October, 2001. 

Hand, J.L. and W.C. Malm, Review of the IMPROVE Equation for Estimating Ambient 

Light Extinction Coefficients, on the IMPROVE web site at 

http://vista.cira.colostate.edu/improve/Publications/GrayLit/gray_literature.htm, 2005. 

Haywood, Ramaswamy, and Soden, Tropospheric aerosol climate forcing in Clear-Sky 

Satellite Observations over the oceans, Science, V283, pg. 1299-1303, 26 February, 

1999. 

Hegg, Livingston, Hobbs, Novakov and Russell, Chemical Apportionment of aerosol 

column optical depth off the Mid-Atlantic coast of the United States, Journal of 

Geophysical Research, vol. 102, No. D21, pg. 25,293-25,303, 1997. 

IMPROVE, Malm, W. C., Principal Author, Spatial and Seasonal Patterns and Temporal 

Variability of Haze and Its Constituents in the United States: Report III, Cooperative 

Institute for Research in the Atmosphere, Colorado State University, Ft. Collins, CO, 

May, 2000. 

Kumar, N. Recommendations for Natural Background Conditions and Potential 

Refinements, Proceedings (CDROM) of MANE-VU/MARAMA Science Meeting on 

Regional Haze – Organic Aerosols and Natural Background Conditions, MARAMA 

Baltimore, MD, 27-29 January, 2004. 

Lowenthal, D. H., and Kumar, N. PM2.5 Mass and Light Extinction Reconstruction in 

IMPROVE. Journal of the Air and Waste Management Association, Vol. 53, pp. 1109-

1120, 2003. 

Malm, Molenar, Eldred and Sisler, Examining the relationship among atmospheric 

aerosols and light scattering and extinction in the Grand Canyon area, Journal of 

Geophysical Research, vol. 101, No. D14, pg. 19,251-19,265, 1996. 

Malm, Day, Kreidenweis, Light Scattering Characteristics of Aerosols as a function of 

Relative Humidity: Part 1- A comparison of Measured Scattering and Aerosol 

Concentrations Using the Theoretical Models, Journal of the Air and Waste Management 

Association, Vol. 50, pg. 686-700, May 2000. 

U.S. EPA, Guidance for Estimating Natural Visibility Conditions under the Regional 

Haze Rule, EPA-454/B-03-005, September, 2003a. 
Baseline and Natural Background Visibility Conditions Page 14

U.S. EPA, Guidance for Tracking Progress under the Regional Haze Rule, EPA-454/B03-004, September, 2003b. 

Ryan, P.A., Lowenthal, D., and Kumar, N., Improved light extinction reconstruction in 

Interagency Monitoring of Protected Visual Environments, J. Air & Waste Manage. 

Assoc. 55, 1751-1759, 2005. 

Trijonis, J. C., Characterization of Natural Background Aerosol Concentrations, 

Appendix A in Acidic Deposition: State of Science and Technology. Report 24. Visibility: 

Existing and Historical Conditions -- Causes and Effects, J. C. Trijonis, lead author, 

National Acid Precipitation Assessment Program, Washington, DC, 1990.