# 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 NaNH4Data 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 ModelingBOARD: 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 ofthe 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 demonstrationmodeling 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.

### 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 contributorto light extinction in coastal areas. 4. The new algorithm reflects research finding that the mass concentration ofparticulate organic matter in rural areas is greater than represented by the old equation. 5. 

### The new algorithm includes a NO2term to represent times when light absorption by NO2is 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 orcold 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 ofthese 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 extinctionJ. 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

### 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 ofparticulate matter on light extinction than the old IMPROVE algorithm. Excellent justification ofthis conclusion is provided in theNovember 

### 2005 report ofthe IMPROVE Steering Committee, "Revised IMPROVE Algorithm for Estimating Light Extinction from Particle Speciation ~ata."' The new algorithm incorporates changes that represent much ofwhat has been learned about the relationship between particulate matter component concentrations and light extinction in the morethan 

### a decade since the old algorithm was developed. Themain reasons that justify using the new algorithm instead ofthe old one are the following: 1. The new algorithm overcomes the biases of the old algorithm on the haziest days (whenthe old algorithm underestimates light extinction) and on the clearest days (whenthe 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 orthe new IMPROVE equation. Figures 1- 

### 3 at the end ofthis summary illustrate the performance ofthe new and old equations comparedto nephelometer data for Great Smoky Mountains and Shenandoah National Parks and CapeRomain 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 eficienciesvary from location to location and timeto time as the sizedistribution ofthe aerosol changes, and it reflects this variation by increasingthe extinction efficiency 

### asthe concentrations of sulfates, nitrates, and organics increase. It also recognizes that thehumidityrelated growth rates ofparticles differ depending ontheir sizes. As a result, the new algorithm generally does 

### abetter job ofrepresenting light extinction at individual sitesthan does the old algorithm, as indicatedby the reduced fractional biases in each RPO region (see Tables 

### 3 and 5 compared to Tables 

### 2 and 4 

### as copied at the end ofthis summary from theIMPROVE 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 termthat 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 areasin the inter-mountain West (although incorporating sea salt into the calculation was already considered in a University ofCalifornia at Davis memo in 1995).

### 4. The new algorithm acknowledgesthat substantial recent research has shownthat the mass concentration ofparticulate organicmatter (oftendenoted 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 factorto a more-appropriate 1.8. 5. 

### The new algorithm recognizesthat there may be times (near urban areas or in some source emissionplumes) when light absorption by NO2gas is a meaningful contributor to light extinction,and thus includes a new term based on the NO2 concentration. 6. The new algorithmrecognizes that the assumption ofconstant Rayleigh scattering of 10~m-' (representative of an elevationofabout 

### 5000 feet) may have been adequatewhen only inter-mountain West siteswere considered,but is a distortion for sites close to sea level or with very hot or cold climates.It thus allows for sitespecific values ofthe Rayleigh scattering. At any given location, the net result of all these changes is typically small on average because some changesresult in increases in extinctionand some in decreases,but the apportionmentof that extinctionto the various components is more accurate with the new algorithm, especiallyon the haziest and clearest days. This is particularly important for the developmentof emissionmanagement strategies, because the benefits of control of concentrations of each specieswill be represented more correctly with the new algorithm.

### Enclosure 

### 2 Figure 1. 

### Aerosol Scattering vs Nephelometer Scattering ComparingNew and Old IMPROVE Algorithm and Daily 

### f(RH), Cape Romain Wildlife Refuge, 

### 2004.

Figure 

### 2.Aerosol Scattering

### vs.NephelometerScatteringUsingNewand Old IMPROVE Algorithm and Daily f(RH),Okefenokee, GA, 1993-1997


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0 50 100 150 200 250 300 ~NpMcrrnw4,(~') 0 50 100 150 200 250 300 24-hr Wphokmotmr b, (~m.')Figure 3.Aerosol Scattering vs.Nephelometer ScatteringUsing New and Old IMPROVE Algorithm and Daily f(RH), Shining Rock,NC 1995-1999


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### Figure 4.Aerosol Scatteringvs NephelometerScattering ComparingNew 

### and Old IMPROVEAlgorithm 

### and Daily 

### f(RH),Great Smoky Mountains National Park, 1995- 

### 2004.

... - 

### New IMPROVE Old IMPROVEFigure 5.Aerosol Scatteringvs.Nephelometer Scattering Using New and Old IMPROVEAlgorithm and Daily f(RH), Cohutta, GA 2004 only 

# I New IMPROVE 

# I I Old IMPROVE 

# I

24hrNrphelometar b., (urn") 0 50 100 150 200 250 300 24hr Nephelomrterb, (urn")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 concerningthe 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 ofthis new methodology to estimate visibility impacts from the SouthCarolina facilities to implement the Best Available Retrofit Technology requirement ofthe Regional Haze Rule. Thenew 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 CALPOSTmodels. The spreadsheet implements the new IMPROVE equation for calculating visibility impacts that was adopted by the IMPROVE Steering Committee inDecember 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 ofthe Code ofFederal Regulations (40 C.F.R), Part 51. 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 ofthe performance ofthe equation versus measured values, a submittal ofthe 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.,.., 

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## ..- ..--.., vv L C~~ILCLLL~.L JV~.. UC~~A) w LL~ PICICL .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 ofAir Quality Internet Address (URL) http Ilwww epa gov RecycledlRecyclable Prlntedw~th Vegetable 011 Based Inks on Recycled Paper (M~n~rnurn 30% Postconsurnerj