MANE-VU SIP Template Natural Background Visibility

APPENDIX XX June 10, 2004

-1- 

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### I AREASMANE-VU SIP Template Natural Background Visibility

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-2- NATURAL BACKGROUND VISIBILITY CONDITIONS

1. INTRODUCTION
The long-term visibility conditions that would exis t 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 must be considered when setting reasonable pro gress goals for each mandatory Federal Class I area subject to the Regional Haze Rule. Ba seline 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 to be considered when setting reasonable progress goals for any Clas s I site.

The U.S. Environmental Protection Agency (EPA) issu ed draft methodological guidelines for the calculation of natural backgroun d and baseline visibility conditions at each site as well as methods for tracking progress relat ive to the uniform rate of progress that these values determine. This draft guidance, issued in September 2001 was subsequently finalized in September 2003. The final guidance re commends a default method and allows for certain refinements that states may wish to pur sue in order to make these estimates more representative of a specific Class I area that may be poorly represented by the default method.

This appendix provides a description of the default method for calculation of natural background conditions. In addition, the default me thod is applied to each Class I area in or near the MANE-VU region in order to establish default natural background conditions on the twenty percent best and worst days. A discussion o f potential refinements to the default method is presented along with rationale for their consideration. The uncertainty associated with each potential refinement is then considered i n the context of the overall uncertainty of the default estimates. Finally, a recommendation fo r estimating natural visibility conditions to be included in this SIP is provided.

Based upon these analyses, as well as comments rece ived on the draft MANE-VU proposal, it appears that while some aspects of the default calculation method are understood well enough that they could be considere d as potential refinements, MANE-VU does not feel these refinements are warranted in li ght of the very large uncertainties associated with the most basic elements of the defa ult estimates (naturally occurring ambient concentrations). The identified refinements would result in substantial differences relative to default estimates without significantly improving t he accuracy of our estimate relative to the default. Rather, MANE-VU advocates a proposed appr oach that is based on use of the default estimates while a program of research is un dertaken to refine those elements which are most uncertain (natural concentrations) in orde r to reduce the overall uncertainty as better scientific understanding of these issues evo lves. Refinements to other aspects of the default method (e.g. refinements to the assumed dis tribution or treatment of RayleighMANE-VU SIP Template Natural Background Visibility

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-3- extinction, inclusion of sea salt, and improved ass umptions 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 arou nd a specific approach and will be reconsidered at a later point.

2. THE DEFAULT METHOD
The default method is explained in detail in Estimating Natural Background Visibility Conditions (U.S.EPA, 2003). Summary information is provided here but the reader should consult the original guidance documents for any que stion as to how this method is applied.

Estimates of natural visibility impairment due to f ine and coarse particles were derived using the 1990 National Acid Precipitation Assessme nt Program reported average ambient concentrations of naturally present particles (Trij onis, 1990). Separate concentration values were given for the Eastern and Western United State s, 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 US as 3 dv. By assuming a roughly normal distribution of data, the default method adds (subtracts) 1.28*(3 d v) to the average estimated natural background to calculate the 90 th (10 th ) percentile level which is taken by EPA to be representative of the mean of the twenty percent wo rst (best) conditions.

Thus in the East, the default method for calculatin g best and worst natural background visibility conditions (in deciviews) for any area i n the Eastern U.S. would use the following formulae:

P90 = HI +1.28 sd

P10 = HI – 1.28 sd

Where The Haze Index (HI) represents annual average visibility in units of deciview and sd is the standard deviation of daily average visib ility 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)

where the atmospheric extinction, bext, is given by the familiar IMPROVE equation (IMPROVE, 2000) in inverse megameters:MANE-VU SIP Template Natural Background Visibility

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

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

Thus with respect to potential refinements to the d efault method, three primary approaches can be considered: refinements to the ma ss estimates (including spatial and temporal allocation as well as addition of other im portant species), refinement to the relative humidity adjustment factors (including averaging ti mes and addition of adjustment factors Table 1. Default Parameters Used in Calculating Nat ural Background Visibility for Sites in the Eastern U.S.

Parameter Value Fractional Uncertainty Reference/Comments

[SULFATE] 0.23 μg/m 3 200% Trijonis, 1990 [NITRATE] 0.10 μg/m 3 200% Trijonis, 1990 [OC] 1.0 μg/m 3 200% Trijonis, 1990 [LAC] 0.02 μg/m 3 250% Trijonis, 1990 [SOIL] 0.50 μg/m 3 200% Trijonis, 1990 [CM] 3.0 μg/m 3 200% Trijonis, 1990 f(RH) ~3.2 15% Varies by site (see Table 2) Organic multiplier 1.4 50% [OCM]=1.4*[OC]



### σ S/N 3.0 m 2 /g 33% Hegg, 1997; IMPROVE, 2000; Malm, 2000



### σ OC 4.0 m 2 /g 30% Hegg 1997; Trijonis 1990



### σ EC 10.0 m 2 /g 40% Malm, 1996



### σ soil 1.0 m 2 /g 25% Trijonis, 1990



### σ coarse 0.6 m 2 /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

10 th , 90 th percentile adjustment 1.28 15% Regulation calls for mean of top twenty percent, not 90 th percentile Parameters used in potential refinements [NaCl] ~0.5 50% Varies by site, IMPROVE



### σ NaCl 2.5 m 2 /s 16% Haywood, 1999 f(RH) NaCl ~3.2 33% Assumed same as S, N Note: the mass estimates presented above are based are on estimates of fine particulate concentrations that would exist in absence of any m anmade pollution (including Mexican and Canadian emissions) consistent with planning requir ements of the regional haze rule. MANE-VU accepts this as an appropriate planning goal and in tends to consider the contribution of international transport in deciding what controls are “reasonable ” under the regional haze program. Table 1. Default Parameters Used in Calculating Nat ural Background Visibility for Sites in the Eastern U.S.

Parameter Value Fractional Uncertainty Reference/Comments

[SULFATE] 0.23 μg/m 3 200% Trijonis, 1990 [NITRATE] 0.10 μg/m 3 200% Trijonis, 1990 [OC] 1.0 μg/m 3 200% Trijonis, 1990 [LAC] 0.02 μg/m 3 250% Trijonis, 1990 [SOIL] 0.50 μg/m 3 200% Trijonis, 1990 [CM] 3.0 μg/m 3 200% Trijonis, 1990 f(RH) ~3.2 15% Varies by site (see Table 2) Organic multiplier 1.4 50% [OCM]=1.4*[OC]



### σ S/N 3.0 m 2 /g 33% Hegg, 1997; IMPROVE, 2000; Malm, 2000



### σ OC 4.0 m 2 /g 30% Hegg 1997; Trijonis 1990



### σ EC 10.0 m 2 /g 40% Malm, 1996



### σ soil 1.0 m 2 /g 25% Trijonis, 1990



### σ coarse 0.6 m 2 /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

10 th , 90 th percentile adjustment 1.28 15% Regulation calls for mean of top twenty percent, not 90 th percentile Parameters used in potential refinements [NaCl] ~0.5 50% Varies by site, IMPROVE



### σ NaCl 2.5 m 2 /s 16% Haywood, 1999 f(RH) NaCl ~3.2 33% Assumed same as S, N Note: the mass estimates presented above are based are on estimates of fine particulate concentrations that would exist in absence of any m anmade pollution (including Mexican and Canadian emissions) consistent with planning requir ements of the regional haze rule. MANE-VU accepts this as an appropriate planning goal and in tends to consider the contribution of international transport in deciding what controls are “reasonable ” under the regional haze program.MANE-VU SIP Template Natural Background Visibility

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-5- for species assumed to be non-hydroscopic), and ref inement to the assumed distribution of visibility conditions throughout the year (includin g the width, amplitude and potentially shape of the distribution). Potential refinements are considered in section 4.

Table 1 below provides the default values to be app lied at all Eastern U.S. Class I areas. The result of using these default values in the abo ve equation with an assumed annual average f(RH) value of 3.17 (the average of 11 Nort heastern U.S. sites) default estimated visibility in the Northeastern U.S. is approximatel y 3.6 dv on the twenty percent best days and 11.3 dv on the twenty percent worst days.

3. APPLICATION OF THE DEFAULT METHOD
The Class I areas in the MANE-VU region that are su bject to the requirements of the regional haze rule are: Acadia National Park, Maine ; Brigantine Wilderness (within the Edwin B. Forsythe National Wildlife Refuge), New Je rsey; Great Gulf Wilderness, New Hampshire; Lye Brook Wilderness, Vermont; Moosehorn Wilderness (within the Moosehorn National Wildlife Refuge), Maine; Preside ntial Range – Dry River Wilderness, New Hampshire; and Roosevelt Campobello Internation al Park, New Brunswick. In addition to these Class I areas, we consider severa l 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 V irginia as well as Shenandoah National Park and the James River Face Wilderness in Virgini a. 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 which may be affecting visibility in these areas. MANE-VU has therefore c alculated estimates of natural background visibility conditions at the nearby sites using MAN E-VU approved methods in order to facilitate future consultations.

The only factor in the default method that varies b y site is the climatological annual mean relative humidity adjustment factor. Table 2 lists this value for the Class I sites of interest and the resulting best 20 percent and worst 20 perc ent estimates of natural visibility conditions. The variation among sites using the de fault 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.MANE-VU SIP Template Natural Background Visibility

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-6- 4. POTENTIAL REFINEMENTS
According to the guidance (U.S. EPA, 2003), “... the default approach to estimating natural visibility conditions presented in this doc ument is adequate for the development of progress goals for the first implementation period under the regional haze rule.” However, the guidance does leave the door open for individua l states or RPOs to adopt their own methods for calculating natural background if they can demonstrate that the change from Table 2. Site Specific Relative Humidity Adjustment Factors, Best and Worst (Default) Estimates of Natural Background Visibility Conditio ns

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 Br unswick 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 11.32MANE-VU SIP Template Natural Background Visibility

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-7- the default represents a significant refinement tha t better characterizes natural visibility conditions at a specific Class I site.

The five Regional Planning Organizations have ident ified a number of areas for potential improvement and have hired a contractor to refine t he understanding of natural background levels of particulates. The statement of work for this project (managed by the WRAP) includes the following text: “There are three broad ly different ways to refine the default natural aerosol concentrations that are briefly dis cussed in the guidance document. The default annual estimates of species concentrations for the best and worst 20% haze conditions can be replaced by better annual estimat es, by seasonally varying estimates, or by event-specific estimates (e.g. in the case of fores t fire and dust storm impacts). Any technically defensible combination of these differe nt ways to refine the natural aerosol concentration is acceptable. It is likely that ref inement will be a multi-step process over a period of many years as the information required to justify changes are developed and reviewed.” The three methods of refinement noted i n this statement of work, mirror those listed in the guidance, however, the guidance also states that, “states may identify other[ refined approaches] that are more appropriate to th eir own situations.”

As noted in section 2, in addition to different way s to adjust ambient concentration estimates, the relative humidity adjustment factor and the shape of the distribution would also affect the resulting estimates of naturally oc curring visibility. The VISTAS RPO has commissioned a consultant to investigate potential refinements to natural background (Tombach, 2003). In addition, a white paper develop ed by EPRI on this topic and a recent presentation by Bill Malm of CIRA (a principal inve stigator of the IMPROVE program) all serve to inform the multitude of ways that calculat ions for natural background conditions could be refined (Malm, 2004; Kumar, 2004). A syno psis of several potential refinements and the rationale for their consideration are prese nted here. For more detailed discussion of the scientific merit of each potential refinement, the original references cited above (or those contained in the brief explanations below) should b e consulted.

1. Increase the value of the organic multiplier

The estimates of organic carbon mass that are used in the guidance are derived from Trijonis (1990), however his original estimate (1.5 ) has been adjusted to be consistent with the ratio of organic carbon mass/organic carbo n that is used in the IMPROVE program. This value, 1.4, is uncertain and several review articles and studies (Watson 2002, Turpin and Lim 2001, Malm 2004) have suggeste d higher values between 1.8 and 2.1 are more appropriate values. If a higher v alue were to be used for the organic carbon multiplier, the estimate of natural background organic carbon mass would be similarly affected since the original Trij onis estimate was based on organic carbon, [OC], and a multiplicative factor which re lates [OC] to organic carbon mass, [OCM].

2. Adjust the factor used to translate average visibilit y conditions into twenty percent worst or best conditions

The guidance recommendation for calculating the twe nty percent worst and best visibility conditions by multiplying the average by 1.28 times the standard deviationMANE-VU SIP Template Natural Background Visibility

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-8- of 3.0 assumes a normal distribution and is designe d to return the 90 th percentile value in that distribution. The Regional Haze Rule requires improvement on the average of the twenty percent worst days. This val ue is not equivalent to the 90 th percentile of a normal distribution. The 92 nd percentile is closer to the simple average of the top twenty percent of values, if you assume a normal distribution (Lowenthal et al., 2003). In this case, a factor o f 1.40 is more appropriate for calculation of the 92 nd percentile, or the mean of the top twenty percent of values. However, it is clear that the distributions of visi bility conditions at most Class I sites are not perfectly normal. In fact, the 90 th percentile may be closer to the average of the top twenty percent of visibility conditions at sites that do not experience as many extreme visibility conditions as a normal distribut ion would predict (Malm, 2004).

3. Account for visibility impairment due to sea salt at c oastal sites

Many Class I sites are located along the coast and are significantly affected by coarse mode sea salt particles. The tail of the coarse mo de sea salt particle size distribution is within the sub-2.5 micron size fraction and shou ld properly be included the IMPROVE equation. This would be a straightforward refinement if we assume that all sea salt is in the form of sodium chloride (NaC l). However, significant evidence suggests that a substantial portion of the sodium a long the Gulf Coast is associated with sodium nitrate (NaNO 3 ) (Malm, 2004). As sea salt particles age, atmosph eric chemical processes appear to replace chloride with other ions, altering both the chemical composition and the scattering efficiency.

4. Account for hygroscopicity of sea salt

Research to date reflects a substantial degree of u ncertainty regarding the appropriate scattering efficiency and hygroscopic growth of sea salt particles. Refined estimates hold the potential to significantly change natural background estimates depending on assumed composition and concentrations.

5. Account for organic PM of oceanic origin

Observational evidence exists to support the hypoth esis that significant levels of organic precursor gases are emitted over the open o cean which could potentially increase the natural background levels of organics, particularly at coastal sites.

6. Review soil concentrations

Tombach (2003) suggests that fine soil contribution s in the Southeast U.S. are underpredicted by the Trijonis estimate of 0.5 ug/m 3. He bases this on the estimated impact of Saharan dust and Asian dust tha t are subject to inter-continental transport. The contribution of these sources to No rtheast and Mid-Atlantic sites is estimated to be significantly less than for Southea st and Western U.S.

7. Account for episodic inter-continental dust contribution sMANE-VU SIP Template Natural Background Visibility

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-9- In addition to contributing on an annual average ba sis, the Saharan and Asian dust impacts are likely to be highly variable in time an d should not necessarily be applied on an annual average basis. Given the extreme unce rtainty in predicting the frequency of occurrence at any specific site, there is no reliable means of estimating the temporal frequency for these effects.

8. Review organic and sulfur emissions from forests

Observational evidence exists for the tropics (most ly the Amazon River Basin) to suggest that the estimated natural background conce ntrations of organics and sulfur compounds may be significantly higher than the Trij onis values in those areas. Application of these data to U.S. areas remains hig hly uncertain and requires further research.

9. Improve estimates of organic and elemental carbon rele ased by natural fires

Global modeling studies have produced estimates for organic and elemental carbon released by natural fires that are consistent with the Trijonis estimates used by EPA. Nonetheless, these studies as well as the Trijonis estimates remain uncertain and could be refined through further research efforts.

10. Account for inter-continental sulfate and nitrate contr ibutions

Techniques to account for the fraction of light sca ttering and absorbing PM that results from extra-jurisdictional anthropogenic emi ssions (i.e. Canada, Mexico, Asia) could be developed with the same rough level of unc ertainty that is used in the current default method for calculating natural visi bility conditions. This is less a refinement of natural background, however and more of a policy decision as to how natural background conditions are defined and what is an appropriate planning goal. The definition in statute and planning goal support ed by the courts should remain as described in EPA guidance. MANE-VU feels that inte rnational contributions to Class I fine particulate burdens should be consider ed in setting reasonable progress goals, not natural condition estimates.

11. Use global chemical transport models to refine estimat es of natural ambient concentrations

The use of global models will certainly prove to be a useful tool for future research into the topic of natural background conditions, bu t MANE-VU does not feel that these tools provide a consistent framework to serve as the basis for a national program. The uncertainties within the model struct ure mirror the uncertainties in observational evidence for deducing ambient emissio n levels of specific PM components.

12. Refine temporal resolution of relative humidity adjustm ent factors/consider observed relative humidity data inst ead of climatological average data.MANE-VU SIP Template Natural Background Visibility

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-10- The use of different averaging periods and differen t relative humidity data certainly does affect the resulting estimates of visibility c onditions. Climatologically average data serves to remove inter-annual variability of h umidity from the process of tracking progress. This ensures that measured prog ress is based on changes in pollution, rather than meteorological variability. Further research into the most appropriate averaging period is still warranted.

In addition to the many potential refinements liste d above, NESCAUM has considered one other possible refinement to the default method ; the use of a higher Rayleigh scattering estimates for coastal sites (12Mm -1 are approximate Rayleigh conditions at sea level; 10 Mm -1 is used for all

sites in the IMPROVE equation).

Of the multitude of ways that natural background vi sibility conditions could be refined, MANE-VU believes that very few can be justified as significantly improving the accuracy on the basis of current scientific understanding. Tha t is not to say that MANE-VU feels that the default estimates of natural conditions are tru ly representative of natural conditions at each site or that each of the potential refinements listed above does not bear further investigation, but rather that alternative methods or values for use in calculating more precise values for most of the refinements listed a bove are not readily available at this time.

Research into many of the potential refinements abo ve should be continued and MANEVU intends to continue research on many of these qu estions. However, MANE-VU feels that only a very few of these potential refinements can justifiably be considered at this time. These include an alternative value for the carbon m ultiplier, the calculation of the 92 nd percentile of a normal distribution to represent th e mean of the top twenty percent worst visibility conditions, and the inclusion of sea sal t at coastal locations and refined estimates of Rayleigh scattering. Calculations were performed t o evaluate the effect of these potential refinements to better understand the effect of such changes on resulting rates of progress and are shown in Tables 3 and 4.MANE-VU SIP Template Natural Background Visibility

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-11- Table 3. Default and Refined Estimates of the Twent y Percent Worst Natural Background Visibility Conditions at MANE-VU and Nearby Sites. Default val ues are provided for comparison, estimates labeled “[OMC]=[OC]*1.8” are calculated using 1.8 a s the organic multiplier, “P90=HI+1.40*sd” values are calculated using the 92 nd percentile instead of the 90 th percentile of the visibility distribution, “w/seasalt” values show the effect of adding the me asured value of sea salt mass at coastal sites, and “Rayleigh 12Mm -1 ” values show the effect of using alternate Rayleig h scattering at coastal sites.

Assumption tested at MANE-VU Mandatory Federal Class I Area Default Visibility

dv [OMC]= [OC]*1.8

dv P90=HI +1.40*sd

dv w/ sea salt

dv Rayleigh 12 Mm -1

dv

Maine Acadia National Park 11.45 12.17 11.81 12.87 12.34

Moosehorn Wilderness 11.36 12.09 11.72 12.88 12.26

Roosevelt Campobello International Park, New Brunswick 11.37 12.09 11.73 12.88 12.27

New Hampshire Great Gulf Wilderness 11.30 12.03 11.66

Presidential Range – Dry River Wilderness 11.30 12.03 11.66

New Jersey Brigantine Wilderness 11.28 12.01 11.64 13.40 12.19

Vermont Lye Brook Wilderness 11.25 11.99 11.61

Nearby Mandatory Federal Class I

Areas

Virginia James River Face Wilderness 11.26 11.99 11.62

Shenandoah National Park 11.27 12.00 11.63

West Virginia Dolly Sods Wilderness 11.32 12.05 11.68

Otter Creek Wilderness 11.32 12.05 11.68MANE-VU SIP Template Natural Background Visibility

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-12- Table 4. Estimated baseline visibility conditions, † Uniform Rates of Progress (ROP) to be considered for first implementation period, and Effect of Natu ral Background Refinements on ROP at MANE-VU and Nearby Sites. “1.8*OC” values are the percent change in uniform progress (relative to the default ROP) resulting from the substitution of the 1.8 car bon multiplier, “1.4*sd” values are the percent change in uniform progress when the 92 nd percentiles are used to represent the average of t he worst twenty percent visibility conditions, “sea salt” va lues are the percent change in uniform progress whe n extinction due to measured sea salt at coastal site s is included and “Rayleigh” values are the percent change in uniform progress when 12Mm -1 of Rayleigh extinction is used at sea-level sites.

MANE-VU Mandatory Federal Class I

Area Baseline Visibility

dv Default

ROP dv/14 yrs 1.8*[OC]

%change 1.40*sd

%change sea salt

%change Rayleigh

%change

Maine Acadia National Park 22.86 2.66 -3.9% -3.2% -6.7% -6.0%

Moosehorn Wilderness 21.53 2.37 -3.8% -3.5% -8.9% -6.5%

Roosevelt Campobello International Park, New Brunswick 21.53 2.37 -3.8% -3.5% -8.9% -6.5%

New Hampshire Great Gulf Wilderness †

Presidential Range – Dry River Wilderness †

New Jersey Brigantine Wilderness ‡ 27.92 3.88 -2.5% -2.2% -10.5% -4.7%

Vermont Lye Brook Wilderness 24.24 3.03 -4.1% -2.8%

Nearby Mandatory Federal Class I Area

Virginia James River Face Wilderness п 28.41 4.00 -2.4% -2.1%

Shenandoah National Park ‡ 27.55 3.80 -2.8% -2.2%

West Virginia

Dolly Sods Wilderness 27.72 3.83 -3.1% -2.2%

Otter Creek Wilderness 27.72 3.83 -3.1% -2.2%

† Note that EPA guidance requires at least 3 complet e years out of 5 to calculate baseline conditions. Routine year-round monitoring did not begin at Camp Dodge (IMPROVE site for Great Gul f/Presidential Range) until June 2000 so estimates o f baseline conditions (and thus a uniform rate of progress) will not be possib le for these sites until data are available through June 2003. ‡ Only 4 years of data was used in the calculation o f estimated baseline conditions and uniform rates o f progress at these sites since 1998 did not meet completeness criteria at these sites.

п Only 3 years of data was used in the calculation o f estimated baseline conditions and uniform rates o f progress at this site since 1998MANE-VU SIP Template Natural Background Visibility

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-13- The uniform rate of progress as determined by basel ine and natural background conditions is most sensitive to absolute changes in natural background estimates (as opposed to baseline conditions), given the logarithmic stru cture of the haze index. For example, using data from Brigantine Wilderness Area 1999-2002 (a f our year period that overlaps, but does not correspond to the baseline period as described by EPA guidance) the default estimate for baseline visibility conditions is 27.92 dv. If sea salt is included in the reconstructed extinction calculation, the baseline estimate incre ases by 0.24 dv to 28.16 dv. Changes in natural background resulting from the addition to s ea salt at Brigantine are from 11.28 to 13.40 dv, a difference of 2.12 dv. The end result is a decrease of approximately 10.5 percent in the required rate of progress slope during the i nitial period. Although the annual rate decreases by less than 0.03 dv/year, the change ove r the course of 14 years is 4 tenths of a deciview which is a substantial difference. The es timated impact of adding sea salt to Brigantine has the largest effect of any of the ref inements considered here, thus all refinements considered (on an individual basis) hav e less than 10.5 percent impact on the 1 st period progress goal.

While the changes in the rate of progress resulting from these refinements are substantial, the decision to refine baseline condit ions must be based on whether the refinements are statistically

significant. In order to meet that test, a potent ial refinement must alter the rate of progress to the point that the re fined value lies outside the range of uncertainty of the default value. To implement ref inements that do not meet this test would result in new values that are substantially differe nt, but not significantly more accurate.

Very large uncertainties are associated with most o f the parameters that go into the default natural background calculation and many of the potential refinements. For example, In the case of a change to the organic multiplier, different values ranging from 1.4 to 2.1 or higher have been proposed, however the uncertainty bounds of these estimates are large and overlapping (i.e. most estimates are within the uncertainty bounds of the others and thus

are not statistically

different).

In the case of sea salt, it certainly represents an improvement in accuracy to include a term for sea salt scattering when we know it to exi st. Given the potential for complex chemical interaction of sodium and chlorine with ot her components of particulate matter, estimates of uncertainty are difficult to quantify and large (on the order of 50 percent). While estimated values that would be appropriate fo r MANE-VU coastal Class I sites are statistically different from zero, the resulting im provement in the overall accuracy of the final natural visibility estimates relative to the defaul t estimates must be calculated using standard error propagation techniques.

Following standard error propagation techniques (Ta ylor, 1982), estimates of the contribution of each parameter (see table 1) to the overall accuracy of natural extinction estimates have been derived. The fractional contri bution of each parameter to total extinction is presented in Figure 1 for coastal and inland sites in the MANE-VU region. As this figure demonstrates, the overwhelming, dominan t contributor to the accuracy of the estimate of total extinction is the uncertainty in organic carbon mass.MANE-VU SIP Template Natural Background Visibility

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-14- Because of the logarithmic relationship between ext inction and deciview, the standard error propagation techniques do not apply simply to the resulting estimate of natural background deciview. The high and low error bounds for the extinction estimate do not translate into an equivalent fractional uncertainty of the resulting deciview estimate. To account for this, Figure 2 presents a range of cont ributions to the final natural background visibility in units of deciview. The two estimates of fractional contribution are based on estimates of extinction that correspond to the high and low error estimates of the extinction calculation. Following standard error propagation techniques again, (Taylor, 1982) these two distinct estimates of uncertainty associated with t he extinction calculation are then compared to the uncertainty in assumptions regarding the sha pe of the distribution of natural visibility conditions in units of deciview. Figure 2 presents the relative contribution of each component for both the high and low estimates of ex tinction. A reasonable estimate for the contribution of each component would, therefore, li e somewhere between these two estimates, but we have no reliable way to determine exactly where. Due to the nature of the logarithmic relationship, the lower estimate is mor e sensitive to small changes than the upper range of uncertainty, so the true contribution is p robably closer to the “high” estimate than the “low” estimate, but cannot be quantitatively de termined in an easy way.

Figure 1. Relative contribution to overall uncerta inty of natural background visibility extinction at MANE-VU Class I Areas. Several potential refinemen ts that have been proposed are highlighted in red in the legend.

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Coastal Inland EC dry extinction soil dry extinction f(RH) EC mass NaCl dry extinction coarse dry extinction S/N dry extinction soil mass NaCl f(RH) OC dry extinction NaCl Mass Rayleigh N mass OCM factor

coarse mass S mass OC MassMANE-VU SIP Template Natural Background Visibility

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-15- Based on this general review of uncertainties assoc iated with the refinements and the potentially substantial effect on rate of progress slopes that could result from implementing such changes, it is appropriate to accept the defau lt natural background visibility estimates as provided in U.S. EPA guidance. The default estimat es provide a sound, nationally consistent framework on which to base the regulatory structure of the haze rule that is justified based upon the current state of scientific understanding of these issues.

Further, EPA recommendations on potential refinemen ts (Pitchford, personal communication, 2004) suggest that such refinements be broadly accepted by the scientific community, substantial, practical to implement and not create arbitrary inconsistencies. In addition, these recommendations request that state efforts to refine the default estimates should not side-track technical efforts on other as pects of the regional haze program. Hence, it is appropriate to adopt the default natur al background conditions at present time until broad consensus on refined estimates of the i ndividual species concentrations (in particular, organic carbon) is established. Figure 2. Range of relative contribution to overall uncertainty in natural background deciview estimat es (high and low extremes derived using extreme values of extinction range)



### 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

high extreme low extreme Standard deviation 92nd vs 90th percentile Uncertainty in extinctionMANE-VU SIP Template Natural Background Visibility

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-16- 5. RECOMMENDATION
This document reviews potential refinements to EPA guidelines for calculating natural background visibility conditions and explores how s uch refinements are likely to affect calculated rates of progress. Based on the curren tly available literature on naturally occurring fine particulate matter over the coastal and continental U.S. and a detailed analysis of the error propagation of such refinements on the resulting estimates of natural visibility conditions, changes to the default methods for calc ulating these conditions will not be undertaken by MANE-VU at this time.

MANE-VU recognizes the simplicity of the default ap proach and supports future adjustments which better reflect true natural backg round visibility levels as the science surrounding this issue evolves and more accurate in formation is available to support such changes. In particular, efforts to reduce the uncer tainties associated with estimates of organic carbon, sulfate and coarse mass are most important to pursue through future research activities aimed at improving estimates of natural visibility conditions. Potential refinements investigated in this document including the additio n of sea salt, revision of the organic carbon multiplier and improved understanding of the distribution of naturally occurring visibility conditions rank as a second tier set of priorities to be addressed through future research.

Based on this review, MANE-VU proposes to adopt the default estimates at this time, to actively participate in further research efforts on this topic, and to reconsider our position with respect to natural background visibility condi tions as future scientific understanding

warrants.

References

Ames, R. B., and Malm, W. C. (2001). Recommendation s for Natural Condition Deciview Variability: An Examination of IMPROVE Data Frequen cy Distributions. Proceedings (CDROM) of A&WMA/AGU Specialty Conference on Region al Haze and Global Radiation Balance -- Aerosol Measurements and Model s: Closure, Reconciliation and Evaluation, Bend, Oregon, 2-5 October.

Day, Malm, Kreidenweis Aerosol Light Scattering Me asurements as a Function of Relative Humidity JAWMA 50: 710-716 May 2000

Eldred, Feeney, Wakabayashi The Major Components o f PM2.5 at Remote Sites across the United States V1 of AWMA Proceedings of an Intern ational Specialty Conference Jan 1998 Long Beach CA pp13-26

Haywood Ramaswamy and Soden SCIENCE V283 26Feb99 1299-1303 Tropospheric aerosol climate forcing in Clear-Sky Satellite Obse rvations over the oceans.

Hegg, Livingston, Hobbs, Novakov and Russell JGR v ol. 102 D21 P25293-303 1997 Chemical Apportionment of aerosol column optical de pth off the Mid-Atlantic coast of theMANE-VU SIP Template Natural Background Visibility

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-17- United States

IMPROVE, (2000), Malm, W. C., Principal Author, Spa tial and Seasonal Patterns and Temporal Variability of Haze and Its Constituents i n the United States: Report III. Cooperative Institute for Research in the Atmospher e, Colorado State university, Ft. Collins, CO. May.

Kumar, N. (2004). Recommendations for Natural Backg round Conditions and Potential Refinements. Proceedings (CDROM) of MANE-VU/MARAMA Science Meeting on Regional Haze – Organic Aerosols and Natural Backgr ound Conditions, Baltimore, MD, 27- 29 January.

Lowenthal, D. H., and Kumar, N. (2003). PM2.5 Mass and Light Extinction Reconstruction in IMPROVE. Journal of the Air and Waste Management Association , Vol. 53, pp. 1109-1120.

Malm, Molenar, Eldred and Sisler Examining the rel ationship among atmospheric aerosols and light scattering and extinction in the Grand Ca nyon area JGR V101 D14 pg19251-65 1996

Malm, Day, Kreidenweis, Light Scattering Character istics of Aerosols as a function of Relative Humidity: Part 1- A comparison of Measured Scattering and Aerosol Concentrations Using the Theoretical Models. JAWMA 50:686-700 May 2000

Malm, W. C. (2004). Recommendations for Natural Bac kground Conditions and Potential Refinements. Proceedings (CDROM) of MANE-VU/MARAMA Science Meeting on Regional Haze – Organic Aerosols and Natural Backgr ound Conditions, Baltimore, MD, 27- 29 January.

U.S. EPA (2003). Guidance for Estimating Natural Vi sibility Conditions under the Regional Haze Rule. EPA-454/B-03-005 . September.

Taylor, J. R. (1982). An Introduction to Error Anal ysis, University Science Books, Oxford University Press, Mill Valley, CA.

Tombach, I., 2003. On Refining Estimates of Natural Background Light Extinction in the VISTAS Region, A report prepared for VISTAS, Decemb er 04.

Trijonis, J. C. (1990). Characterization of Natural Background Aerosol Concentrations. Appendix A in Acidic Deposition: State of Science a nd Technology. Report 24. Visibility: Existing and Historical Conditions -- Causes and Ef fects. J. C. Trijonis, lead author. National Acid Precipitation Assessment Program, Washington, DC.

Turpin, B. J., and Lim, H-J. (2001). Species Contri butions to PM2.5 Mass Concentrations: Revisiting Common Assumptions for Estimating Organi c Mass. Aerosol Science and Technology

, Vol. 35, pp. 602-610.MANE-VU SIP Template Natural Background Visibility

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-18- Watson, J.G. (2002). Visibility: Science and Regula tion. J. Air Waste Manag. Assoc., 52 , 628- 713.