Appendix O 

New IMPROVE Algorithm 
Table of Contents 

Appendix O.1 South Carolina’s Request for Approval and Approval to Use the New 

IMPROVE Equation for BART Modeling 

Appendix O.2 EPA Request for Additional Information: Sea Salt 

Appendix O.3 South Carolina’s Responses to EPA: Sea Salt 

Appendix O.3.a Cape Romain Sea Salt Analysis 

Appendix O.3.b VISTAS NaNH4 Data 

Appendix O.3.c VISTAS Sodium Chloride Comparisons 
Appendix O.1 

South Carolina’s Request for Approval to 

Use the New IMPROVE Equation for 

BART Modeling 
Appendix O.1 - 1
BOARD: 

I'aul C. Aughrry, Ill 

Chairman 

Edwin H. Cooper. 111 

\'ice (:h.~irman 

BOARD: 

Henry C. Scorr 

M. [)avid Mitchell. MI) 

Sreven C;. li~sner 

Secrerary C. Fdrl Hunter. C:ornm~ss~oncr 

/'YoI)I,II!I~,~ ,~II,/!'Y~)~/~ IJI~,~ !/I(, /~~w,'ri~ ,of.i/)( /II,IJ!';, ,it/(! !;I( II.OIIJI/(.II~ 

September 10,2007 

Glenn A ,UcCall 

Coleman F. Buckhouse. ,U[) 

Mr. J. I. Palmer. Regional Administrator 

U.S. EPA, Region 4 

Atlanta Federal Center 

61 Forsyth Street, SW 

Atlanta, Georgia 30303-8909 - 

Subject: Request for Approval to Use New IMPROVE Equation for BART Modeling 

Dear Mr. Palmer: 

The South Carolina Department of Health and Environmental Control Bureau of Air Quality (SC 

DHEC BAQ) has been working with Visibility Improvement States and Tribal Association of the 

Southeast (VISTAS) and U.S. Environmental Protection Agency (EPA) Region 4 staff to implement 

the Best Available Retrofit Technology (BART) requirements of the Regional Haze Rule. As part of 

this process, the need for a methodology to post-process CALPUFFICALPOST modeling data to 

implement the new IMPROVE equation was identified. VISTAS tasked Dr. Ivar Tombach to 

develop such a methodology. The resulting spreadsheet and supporting information was submitted 

by the state of North Carolina to EPA and the Federal Land Managers (FLMs) for review. EPA 

Region 4 staff commented that they consider this post-processing methodology a non-regulatory 

modeling application requiring compliance with section 3.2 of Appendix W Part 51: Guideline on 

Air Qualily Models and that SC DHEC BAQ must obtain approval for its use from the EPA 

Regional Administrator. In response to these comments and for the reasons discussed below, the 

following additional information is provided and formal approval of use of this alternative by the 

affected South Carolina sources for BART exemption and demonstration modeling is requested. 

Rationale of Need for Use of New IMPROVE Equation 

The new IMPROVE equation, which is a much better representation of the effects of particulate 

matter on light extinction than the old equation, takes into account the latest scientific understanding 

of several parameters: 

1. The new algorithm overcomes biases of the old algorithm on the haziest days and the clearest 

days as demonstrated by comparing the measured light extinction from nephelometers at 

Class I areas to light extinction calculated using each of the equations. 

2. The new algorithm recognizes spatial and temporal variation in light extinction as size 

distribution of the aerosol changes by increasing extinction efficiency as sulfate, nitrate and 

organics concentrations increase. 

Appendix O.1 - 2
J. I. Palmer 

September 10,2007 

Page 2 

3. The new algorithm incorporates a term to reflect the contribution of fine sea salt and its 

hygroscopic growth with increasing relative humidity recognizing research findings showing 

that fine sea salt can be an important contributor to light extinction in coastal areas. 

4. The new algorithm reflects research finding that the mass concentration of particulate organic 

matter in rural areas is greater than represented by the old equation. 

5. The new algorithm includes a NO2 term to represent times when light absorption by NO2 is a 

meaningful contributor to light extinction. 

6. The new algorithm incorporates site-specific Rayleigh scattering values to better represent 

sites close to sea level or with very hot or cold climates. 

With this combination of revisions to the IMPROVE equation, the resulting apportionment of 

extinction to various components is more accurate on the haziest and clearest days. This is 

important for development of emission control strategies since the benefits of control of 

concentrations of each species will be represented more correctly with the new algorithm. Further 

discussion of these reasons is included in Enclosure 1. 

South Carolina's only Class I area, Cape Romain, is located on the coast. The ability to 

appropriately represent the contribution of sea salt for sources affecting visibility at Cape Romain is 

important in determining these sources contribution to haze and evaluating the benefit of potential 

control strategies. U.S. EPA Region 4, National Park Seyvice, and the US Fish & Wildlife Service 

determined that adding site-specific data to account for the impact of sea salt and Rayleigh scattering 

to the old IMPROVE equation is not recommended, but rather that the entire new IMPROVE 

equation should be used. A spreadsheet was developed for VISTAS by Dr. Tombach to implement 

the entire new IMPROVE equation for use with CALPUFF and contains a modification of 

CALPOST that calculates the light extinction from the CALPUFF output. In their review of .the 

spreadsheet and supporting documentation, EPA Region 4 staff commented that the VISTAS 

methodology contained in the spreadsheet appropriately implements the features of the new 

IMPROVE equation, with the exception of the nitrogen dioxide term. EPA Region 4 fiuther stated 

that it would be acceptable to use the total NOx concentration from the CALPOST output as a 

conservative surrogate for NOz in order to address the NO2 term in the new IMPROVE equation. 

EPA Region 4 indicated that the VISTAS methodology to incorporate the new IMPROVE equation 

would be acceptable on a case-by-case basis upon consultation with the EPA Regional Office once 

the NO2 term was addressed. Since the initial EPA review of the methodology, Dr. Tombach has 

modified the spreadsheet to address the NOz contribution. A copy of the modified spreadsheet and 

instructions is provided as Enclosure 3 for your review. 

Eauation Performance versus Measured Values 

Comparison of the old versus new IMPROVE equation and nephelometer data at several Class I 

areas, including Cape Romain, are included in Enclosure 2. The old IMPROVE equation tends to 

show a low bias on high extinction days. The new equation shows a better match on high extinction 

Appendix O.1 - 3
J. I. Palmer 

September 10,2007 

Page 3 

days with a slight high bias. The correlation coefficients are often slightly lower for the new 

equation than the old equation because there is slightly more scatter at the low end of the equation. 

Since only one year of data is available for Cape Romain, data and equation comparisons are also 

included for the nearby Class I areas of Okefenokee and Cohutta in Georgia and Shining Rock and 

Great Smoky Mountains in North Carolina. This data indicates that the new equation is a much 

better overall tool for converting mass data into visibility data than the old equation. 

We look forward to your response to this request for approval to use the VISTAS methodology for 

purposes of determining BART eligibility. Should you have any questions regarding this matter, 

please contact John Glass of my staff at (803) 898-4074. 

Robert W. King, Jr., P.E. 

Deputy Commissioner 

Environmental Quality Control 

Enclosures 

cc: Myra C. Reece, SCDHEC Bureau of Air Quality 

Kay Prince, EPA Region 4 

Brenda Johnson, EPA Region 4 

Appendix O.1 - 4
Enclosure 1 

Why Use the New IMPROVE Algorithm? 

The new IMPROVE algorithm, which has been approved by the IMPROVE Steering 

Committee, is a much better representation of the effects of particulate matter on light 

extinction than the old IMPROVE algorithm. Excellent justification of this conclusion is 

provided in the November 2005 report of the IMPROVE Steering Committee, "Revised 

IMPROVE Algorithm for Estimating Light Extinction from Particle Speciation ~ata."' 

The new algorithm incorporates changes that represent much of what has been learned 

about the relationship between particulate matter component concentrations and light 

extinction in the more than a decade since the old algorithm was developed. The main 

reasons that justify using the new algorithm instead of the old one are the following: 

1. The new algorithm overcomes the biases of the old algorithm on the haziest days 

(when the old algorithm underestimates light extinction) and on the clearest days 

(when the old algorithm overestimates extinction). This improvement can be seen 

by comparing measured light scattering from nephelometers with light scattering 

calculated using either the original IMPROVE equation or the new IMPROVE 

equation. Figures 1- 3 at the end of this summary illustrate the performance of the 

new and old equations compared to nephelometer data for Great Smoky 

Mountains and Shenandoah National Parks and Cape Romain Wildlife Refuge. 

Additional examples are available on the Air Resource Specialists ftp site2 and in 

the IMPROVE report referenced above. 

2. The new algorithm recognizes that light extinction eficiencies vary from location 

to location and time to time as the size distribution of the aerosol changes, and it 

reflects this variation by increasing the extinction efficiency as the concentrations 

of sulfates, nitrates, and organics increase. It also recognizes that the humidityrelated growth rates of particles differ depending on their sizes. As a result, the 

new algorithm generally does a better job of representing light extinction at 

individual sites than does the old algorithm, as indicated by the reduced fractional 

biases in each RPO region (see Tables 3 and 5 compared to Tables 2 and 4 as 

copied at the end of this summary from the IMPROVE report.) 

3. The new algorithm recognizes research findings that show that fine sea salt can be 

an important contributor to light extinction in coastal areas, and thus includes a 

new term that reflects its contribution and its hygroscopic growth with increasing 

relative humidity. The old algorithm ignores sea salt, probably because it was 

originally developed mainly for inland Class I areas in the inter-mountain West 

(although incorporating sea salt into the calculation was already considered in a 

University of California at Davis memo in 1995). 

Appendix O.1 - 5
4. The new algorithm acknowledges that substantial recent research has shown that 

the mass concentration of particulate organic matter (often denoted by OMC in 

IMPROVE publications) in rural areas is a greater multiple of the measured OC 

concentration than the 1.4 value used in the old algorithm. The new algorithm 

updates the factor to a more-appropriate 1.8. 

5. The new algorithm recognizes that there may be times (near urban areas or in 

some source emission plumes) when light absorption by NO2 gas is a meaningful 

contributor to light extinction, and thus includes a new term based on the NO2 

concentration. 

6. The new algorithm recognizes that the assumption of constant Rayleigh scattering 

of 10 ~m-' (representative of an elevation of about 5000 feet) may have been 

adequate when only inter-mountain West sites were considered, but is a distortion 

for sites close to sea level or with very hot or cold climates. It thus allows for sitespecific values of the Rayleigh scattering. 

At any given location, the net result of all these changes is typically small on average 

because some changes result in increases in extinction and some in decreases, but the 

apportionment of that extinction to the various components is more accurate with the new 

algorithm, especially on the haziest and clearest days. This is particularly important for 

the development of emission management strategies, because the benefits of control of 

concentrations of each species will be represented more correctly with the new algorithm. 

Appendix O.1 - 6
Enclosure 2 

Figure 1. Aerosol Scattering vs Nephelometer Scattering Comparing New and Old 

IMPROVE Algorithm and Daily f(RH), Cape Romain Wildlife Refuge, 2004. 

Figure 2. Aerosol Scattering vs. Nephelometer Scattering Using New and Old 

IMPROVE Algorithm and Daily f(RH), Okefenokee, GA, 1993-1997 

New IMPROVE 

300 :a I 

y = 0.072 + 0.00 , . ,' 

,' rP = 0.78 ,. ., 

250 ....... i ......... ........ 

E 

b 200 .......... ........ ..... : 

0 - 150 ...................... . 

e 

: 100 ....... .................... b 

f .... I H - 

50 ................................... 

I 

0 Y' 

0 50 100 150 200 250 300 

2Chr Wlphrlomrtrr b, [Mm*) 

New IMPROVE 

300 

r 

Old IMPROVE 

300 - 

y = 0.721 + 18.46 j 

7 250 ........ @=O.M ..-..; ................. <.. ..... 

E , ,I . 

r_ a 200 ..................... L ................. .............. ;:. , , 

- . 0 150 ... 

.) 

............... 

........................... 

I 

0 1" 1 -A 

0 50 100 150 200 250 300 

2Chr Mephrlomrtrr b,,(Mm") 

Old IMPROVE 

- 250 

E 

E. 2yJ 

r 

300 

- 250 - 

E 

E. 200.. 

r 

0 

3 lW. E 

z la, f 

N 

0 

-- y=l.lax+o.n 

#=ow ., . -. -- - ............................. 5 

, , 

......... , ...................... ..,. :. ...-.. , .---... 1 

, ~ . ~ ~ . 

y = 1.00~ + 5.80 

R' = 0.91 ---~- ...................... ,-I. ...... 

' ,' 

.................................. :: .......... 

,I 

.. .....................I ...... : ............... 

................. /,.': ,. -, ................................... . ,' 

.i 

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9' I 

n 

0 I' 7 

0 50 100 150 200 250 300 

~NpMcrrnw4,(~') 

0 50 100 150 200 250 300 

24-hr Wphokmotmr b, (~m.') 

Appendix O.1 - 7
Figure 3. Aerosol Scattering vs. Nephelometer Scattering Using New and Old 

IMPROVE Algorithm and Daily f(RH), Shining Rock, NC 1995-1999 

New IMPROVE 

2.50 ..... ............ 

....... : ................. > ...... ; < ,::1. ........... 

0 50 100 150 200 250 300 

24-hr Nrphrbmrbr b., (Mm") 

Old IMPROVE 

24-hr Nrphrbmrbr b, (Mm") 

Figure 4. Aerosol Scattering vs Nephelometer Scattering Comparing New and Old 

IMPROVE Algorithm and Daily f(RH), Great Smoky Mountains National Park, 1995- 

2004. 

... - 

New IMPROVE Old IMPROVE 

Appendix O.1 - 8
Figure 5. Aerosol Scattering vs. Nephelometer Scattering Using New and Old 

IMPROVE Algorithm and Daily f(RH), Cohutta, GA 2004 only 

I New IMPROVE I I Old IMPROVE I 

24hr Nrphelometar b., (urn") 

0 50 100 150 200 250 300 

24hr Nephelomrter b, (urn") 

Appendix O.1 - 9
UNITED STATES ENVIRONMENTAL PROTECTION AGENC 

REGION 4 

ATLANTAFEDERALCENTER 

61 FORSYTH STREET 

ATLANTA, GEORGIA 30303-8960 

Robert W. King, Jr., P.E. 

Deputy Commissioner 

South Carolina Department of 

Health and Environmental Control 

2600 Bull Street 

Columbia, South Carolina 2920 1 

Dear p";a& Mr. 

Thank you for your September 10,2007, letter and the September 24, 2007, email 

concerning the application of the new Interagency Monitoring of Protected Visual Environments 

(IMPROVE) equation. The September 24,2007, email provided revised documentation to 

replace the enclosures in your letter. You requested the use of this new methodology to estimate 

visibility impacts from the South Carolina facilities to implement the Best Available Retrofit 

Technology requirement of the Regional Haze Rule. 

The new methodology uses a spreadsheet developed by the Visibility Improvement - 

State and Tribal Association of the Southeast to post-process the visibility modeling output from 

the CALPUFF and CALPOST models. The spreadsheet implements the new IMPROVE 

equation for calculating visibility impacts that was adopted by the IMPROVE Steering 

Committee in December 2005. The U. S. Environmental Protection Agency (EPA), Region 4 

has previously provided comments indicating that new methodology is an alternative modeling 

approach and should meet the requirements in Section 3.2 of Appendix W, Guideline on Air 

Quali~ Models contained in title 40 of the Code of Federal Regulations (40 C.F.R), Part 5 1. We 

have reviewed your rationale for using the new methodology. This demonstration included a 

rationale for the need to use the new IMPROVE equation, a discussion of the performance of the 

equation versus measured values, a submittal of the modified post-processing methodology and 

documentation to support the development of concentrations for the different terms in the 

equation. Based on the demonstration provided in your letter, we are approving your request. 

xar, ,, -:,*, r.,.., :,,:,,. -c '..."tnCt i-7"-"",,- to-, 7 ..- ..--.., vv L C~~ILCLLL~.L JV~.. UC~~A) w LL~ PI CICL .L~WL , LllCl .;I\ ilCIIuLILILt. If KT EL: be ~f 

further assistance, please contact me or Beverly Banister. Director of the Air, Pesticides and 

Toxics Management Division, at (404) 562-9077. 

Regional Administrator 

cc: Myra C. Reece 

SCDHEC Bureau 

of Air Quality 

Internet Address (URL) http Ilwww epa gov 

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