# Georqia Department of Natural Resources Environmental Protection Division Air Protection Branch 4244 International Parkway Suite 120 Atlanta Georgia 30354 4041363-7000 Fax: 4041363-71 00 Noel Holcomb, Commissioner Carol A. Couch, PhD., Director Heather Abrams, Branch Chief 

### August 19,2008

Mr. J. I. 

### Palmer, Regional Administrator U.S. EPA: Region IV Atlanta Federal Center 61 

### Forsyth Street, SW Atlanta, Georgia 30303-8909 Subject: Request for Approval to Use New IMPROVE Equationfor BART Modeling Dear Mr. Palmer: The Georgia Environmental Protection Division (GA EPD) has been working with the Visibility Improvement States and Tribal Association of the Southeast (VISTAS) and the U.S. Environmental Protection Agency (EPA) Region IV 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. lvar Tombach to develop such a methodology. The resulting spreadsheet and supporting informationwas 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 Quality 

### iv7vdeis and 

### that i4CiiAG ~mst obtain approval for its use from the EPA Regional Administrator. On the basis of these comments and for the reasons discussed below, GA EPD is providing the following additional information and requests a formal approval of use of this alternative by the affected sources for BART exemption and BART determination modeling.

Rationalefor 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 understandingof 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.

### Mr. 

### J. I. Palmer August 19,2008 Page Two
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 organic concentrations increase. 

### 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 NO2is a meaningful contributor to light extinction.
6. 

### The new algorithm incorporates site-specific Rayleigh scattering values to better ~spresent sites c!ose 

### t:, 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. Two of Georgia's BART eligible sources, Georgia Pacific Cedar Springs and Georgia Power Company-Plant Bowen, have requested the use of the new IMPROVE equation. Specifically, the new IMPROVE equation will more accurately represent the spatial and temporal variation in light extinction caused by sulfate, nitrate, and organic carbon concentrations. As a result, these sources can better determine their contribution to haze and more accurately evaluate the benefits of potential control strategies. 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 the review of the spreadsheet and supporting documentation, EPA Region IV 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 

### further stated that it would be acceptable to use the total NOx concentration from the CALPOST output as a conservative surrogate for NO2in order to address the NO2term in the new IMPROVE equation. EPA Region IV indicated, that the

### Mr. J. I. Palmer August 19,2008 Page Three 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 NO2contribution. A copy of the modified spreadsheet and instructions is provided as Enclosure 3 

### for your review.



### Evaluation Performance versus Measured Values Comparison of the old versus new IMPROVE equation and nephelometer data at several Class 

### I areas, including Okefenokee and Cohutta, 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 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 m+ore scatter at the low end of the equation. Overall, this data indicates that the new equation is overall a much better 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 BART exemption modeling and BART determination modeling. Should you have any questions regarding this matter, please contact James Boylan at (404) 

### 362-4851. Sincerely,

Carol A. Couch Director CC:HA:JJ:JK:TV:klc

c: Jimmy Johnson, GA EPD Jim Boylan, GA EPD Jim Kelly, GA EPD Dick Schutt, EPA Region 4 

### Michele Notarianni, EPA Region 4 

### Brenda Johnson, EPA Region 

### 4

### Enclosure 1 

### DRAFT 10/26/06 Why 

### Use the New 

### IMPROVE Algorithm?

The new IMPROVE algorithm, which has been approvedby the IMPROVE Steering Committee,is a much better representationofthe effects ofparticulate matter on light extinction than the old IMPROVE algorithm. Excellent justification of this conclusion is provided in the November 2005 

### report ofthe WROVESteering Committee, "Revised IMPROVE Algorithm for EstimatingLight Extinction £?omParticle SpeciationData."
The new algorithm incorporateschanges that representmuch 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 thatjustify using the new algorithm instead ofthe old one are the following:


### 1. The new algorithm overcomes the biases ofthe old algorithm on the haziest days (when the old algorithmunderestimates light extinction) and on the clearest days (when the old algorithm overestimates extinction).
2. The new algorithm recognizes that light extinction efficienciesvary from location to location and time to time as the size distributionofthe aerosol changes, and it reflects this variationby increasing the extinctionefficiency as the concentrations of sulfates, nitrates, and organicsincrease. It also recognizes that the humidityrelated growth rates ofparticles differ dependingon their sizes.As a result, the new algorithm generally does a betterjob of representing light extinction at individual sites than does the old algorithm, as indicatedby the reduced fractional biases in each RPO region

3. 

### The new algorithm recognizesresearch findingsthat show that fine sea salt canbe an important contributorto light extinctionin 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 originallydeveloped mainly for inland Class 

### I areas in the inter-mountain West (although incorporating sea salt into the calculationwas already considered in a Universityof California at Davis memo in 1995).
4.



### . The new algorithm acknowledges that substantialrecent research has shown that the mass concentrationofparticulate organic matter (often denoted by OMC in IMPROVEpublications) in rural areas is a greater multiple ofthe measured OC concentration than the 1.4value used in the old algorithm. The new algorithm updates the factorto 

### a more-appropriatel.8.

### 5. The new algorithmrecognizes that there may be times (nearurban areas or in some source emissionplumes) when light absorption by NO2gas is a meaningfd contributorto light extinction, and thus includes a new term based on the NO2 concentration.
6. 

### The new algorithmrecognizes that the assumption of constant Rayleigh scattering of 10

### Mrn-' (representative of an elevation of about 5000 feet) may have been adequate when only inter-mountainWest sites were considered, but is a distortion for sites close to sea level or with very hot or cold climates. It thus allows for sitespecificvalues ofthe Rayleigh scattering.
At any given location, the net result of all these changes is typically small on average because some changes result in increasesin extinction and some in decreases, but the apportionment of that extinctionto the various components is more accurate with the new algorithm, especiallyon the haziest and clearest days. This is particularlyimportant for the development of emission management strategies,because the benefits ofcontrol of concentrationsof each specieswill be represented more correctly with the new algorithm.

### Enclosure2.



### Old IMPROVE

Figure 1. 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

0 SO Ion iw 266 2W 3Qa

Figure 2. Aerosol Scattering vs Nephelometer Scattering Comparing New and Old IMPROVE Algorithm and Daily f(RH), Cohutta WildernessArea, 2004

### New IMPROVE 

# 1

# 1 Old IMPROVE

Figure 3. Aerosol Scattering vs Nephelometer Scattering Comparing New and Old IMPROVE Algorithm and Daily fo, Cape Romain Wildlife Refuge, 2004



### Old IMPROVE

Figure 4. Aerosol Scattering vs Nephelometer Scattering ComparingNew and Old IMPROVE Algorithmand Daily f(RH), Okefenokee Wilderness Area, 1993-1997

### lvar Tombach, Ph.

## D. 

## 8&dV+ 753 Grada Ave. Camarillo, CA 93010 805 388-2341 805 445-9424 fax itornbach@aol.com



### Instructions: A Postprocessor for Recalculating CALPOST Visibility Outputs with the New IMPROVE Algorithm
Version 

### 2 14 October 2006

Introduction


### CALPOST can be used to processes outputs from CALPUFF modeling of a source's emissions to calculate the 24-hr average visibility impairmentscaused by primary and secondary particulate matter attributable to emissions from the modeled source. Those increments are presented in two tables,both labeled "Ranked Daily Visibility Change", in the CALPOST output (.LST) file. The table of interest to us has the subtitle "Modeled Extinction by Species" and lists the dates and locations of such incremental impacts in light extinction (bexJin ranked order, starting with the one that represents the largest percentage change in light extinction.' In addition, with a different setup of the control file CALPOST.INP, the CALPOST postprocessor can be used to calculate 24-hr averages ofNOxconcentrations. As described below, the outputsfrom that additional CALPOSTrun 

### can be used to assess the visibility impact ofthe NO2 gas in the source plume. Visibility effects due to particulatematter are calculated in CALPOST from CALPUFF-modeled particulatematter component concentrations using effectively the "traditional" IMPROVE algorithm. CALPOST allows for choice ofthe humidity scatteringenhancement function (f(RH)) to be used with the IMPROVE algorithm; for modeling in connection with the US EPA's Regional Haze Regulations (RHR),the appropriate form of f(RH) is the one described and tabulated in the EPA's 2003 guidance for tracking progress under the RHR. Visibility effects due to NO2 are not considered in the CALPOST visibility calculation. Recently, the IMPROVE Steering Committee developed a new algorithm for estimating light extinction fromparticulate matter component concentrations. This algorithm (the "new IMPROVE algorithm") provides a better correspondence between the measured visibility and

The other table in the CALPOSTvisibility output file, with the subtitle "% of Modeled Extinction by Species", provides equivalent results in terms of changes in the haze index, in deciviews. The two tables represent the same results, with identical ranking of events, while just using different (but mathematically related) metrics.that calculated from particulatematter component concentrations. The new algorithm differs in several substantiveways from the traditional one: The extinctionefficiencies of sulfates, nitrates, and organics have been changed and are now functions oftheir concentrations. The extinction efficienciesof sulfate and nitrate are no longer identical, although the new hygroscopic scatteringenhancement factors applied to them are the same. The concentration ofparticulate organicmatter (POM; variously also labeled OCM or OMC, and sometimes just called "organics") is now taken to be 1.8times that of the measured organic carbon (OC) concentration. (Confusingly, CALPOST labels the organics concentration as OC.)
The contribution of fine sea salt to light extinction has been added, and is accompanied by its own hygroscopic scattering enhancement factor, f,,(RH). The light scattering by air itself (Rayleigh scattering) now varies with site elevation and mean temperature. It is to be rounded offto the nearest one ~m-' when used with the new algorithm. The light absorption by NO2 gas has been added.
The new IMPROVE algorithm is represented by the followingformu~a:~
bat = 2.2fs(RH)*[smallsulfate] 

### + 4.8f~(')*[large sulfate] +2.4.fs(RH).[smallnitrate] 

### + 5.1$(RH)-[large nitrate] +2.8-[small organics] 

### + 6.1 *[large organics] +I0-[elemental carbon] +I-finesoil] +l.7.fss(M)-[seasalt] +O.6-[coarse matter] +Rayleighscattering (sitespec@) +O.33*[NO.&pb)]
The concentrationsof "large" and "small" sulfate particles are calculated as follows: [large sulfate] = {[totalsulfate]/20)-[totalsulfate] $[total sulfate] < 20 ,ug3 [large sulfate] = [total sulfate] $[total suljbte] 

### 120 ,ug/m3 (Eqs-2) [small sulfate] = [total sulfate] -[large sulfate].
Identical formulas, with changes in component names, are used for nitrate and organics. In effect, these formulas conclude that low concentrations of these components are mainly in the form of "small" particles with their own extinction efficiency and fs(RH), while high

Square brackets denote concentrations.concentrations (approaching 20 &m3) are mainly in the form of "large" particles with a different extinction efficiency and ~L(RH). The scaling factor [total sulfate]/20 sets the fractionof total sulfate that is small.
The sea salt concentration is taken to be 1.8*[Cl-]or, if chloride ion measurements are not available, the chlorine concentration can be used in its place. Site specific Rayleigh scattering values have been calculated for all IMPROVE sites.3Nitrogen dioxide concentrations are not measured at IMPROVE sites, but the ambientNO2 concentrations under natural conditions can be expectedto be negligibly small. The higher NO2 concentration in a source plume may be great enough to cause a change in visibility, however.


### In order to enable CALPOST to calculate CALPUFF-modeled source impacts on visibility using the new IMPROVE algorithm, it would have to be extensively reprogrammed. As an alternative, such a calculation could be done "off line" by adding another layer of post processing after CALPOST. To this end, I have developed a processor, in the form of an Excel workbook, that takes the CALPOST "Ranked Daily Visibility Change: Modeled Extinctionby Species" output table, referenced against default annual average natural conditions concentrations, and creates an equivalenttable of results based on the new algorithm. It can also incorporatethe visibility impact due to light absorptionby NO2 in the plume. The followingdescribesthe science behind the processor (which we'll call the CALPOSTIMPROVE Processor) and provides instructions for using it. Concepts


### In addition to the mechanical changesimposed by all the new terms in the new IMPROVE formula, applying the new algorithm also requires some conceptual changes. Thebiggest of these is that the extinction efficienciesof sulfates, nitrates, and organics now depend on the concentrations of those species. Thepractical implication ofthis is that extinction is no longer linearly additive. To calculate total extinction,you cannot take a background level of extinction and add to it CALPOST's calculation of extinctioncaused by the particulate matter coming from 

### a source, because when the two aerosols mix in the atmosphere their combined mass concentration results in increases in the extinction efficiencies of both the background and the source contribution. This means that combining background particulate matter with the particulate matter from a source gives an extinction result that is greater than the sum of the two separate extinctions.
With the nonlinear behavior resulting from applying the new IMPROVE algorithm,the extinction impact ofthe source (i.e., the increase in extinction resulting from introducing source emissionsinto the atmosphere)is the sum ofthree parts: 1. The source impact calculatedby the new IMPROVE algorithm using the CALPOST outputs for a plume in isolation;

Revised IMPROVE Algorithm for estimating Light Extinction from Particle SpeciationData. Report to IMPROVE Steering Committee, November 2005.

### 2. An 

### increase in that source impact because the extinction efficiency increaseswhen the source's aerosol combines with the background aerosol; and correspondingly,
3. An 

### increase in the extinction of the background aerosolbecause ofthat same mixing. The total new extinction is the sum ofthe above three components plus the original background extinction.The originalbackground extinction isjust that calculated by the new IMPROVE algorithm fiom background concentrations of the various components, without any consideration ofthe effects of theplume. For this application, the background is taken to be that describedby EPAYs defaultnatural conditions. The difference between the total extinction and the background is the impact of the source. More details about the calculation are given in the appendix. Description ofProcessor 

### The CALPOST-IMPROVE Processor is a Microsoft Excel workbook that consists of four worksheets. In Version 2 

### the worksheets are the following. Input & 

### Output -The output table from CALPOST is importedto here and user entries are made for the Rayleigh scattering coefficient and, if desired, for a sea salt concentration at the Class I area of interest. The NO, concentration on each day attributable to the emissions fiom the source can also be entered together with an assumption of what fi-actionoftheNOxis in the form ofNOz. A revised table, with extinction based on the new IMPROVE algorithmis then presented on the samepage. This is the only page on which user input takes place, and the results of the calculations appear on this page. Calculations 

### -- The calculations themselves are all done on this worksheet. There is no user input to this page. The variables are explained on the worksheet itself, so the user can find intermediate values if so inclined. F(RH) -

### This worksheet tabulates the traditional IMPROVE f(RH) against RH, and then also lists values for the three new humidity growth functions,fs(RH), fL(RH),and fss(RH). It serves as a lookup table for the "Ca1cu1ations" worksheet. Rayleigh & 

### Sea Salt -

### Thispage tabulates the IMPROVE-recommended Rayleigh scattering coefficients for all VISTAS Class I areas and for Class I areas in adjacent states. It also lists the average sea salt concentrationsfor the same locations, as tabulated on the VIEWS web site,based on chloride or chlorine measurements by IMPROVE monitors between 2000 and 2004. This sheet just provides information for the user; it is not linked to the rest of the workbook. The user can obtain Rayleigh and sea salt numbers for the Class I area of interest fiom this table and then manually enter them in the designated spaces in worksheet 1.Instructions for Using the CALPOST-IMPROVE Processor 

### These instructions apply to Version 2 

### of the processor. Version 2 

### includes the ability to calculate the light extinction effects ofNO2 resulting from the source's emissions. Step 1.Begin by opening the output (.LST) file from a CALPOST visibility calculation run 

### in a 

### text editor or word processing program.4In the second half ofthe file, locate the table "Ranked Daily Visibility Change" with the subheading "Modeled Extinction by Step 2. 

### Copy this table and paste it onto a new page. Save it as a text (.txt) file, not as a formatted (e.g., MS Word .doc or .rtf) file. The final table should contain only the column headings and the data. Delete all other captions, any additional data summariesat the end, and blank lines before or after the table. The processor can handle a maximum of 22 

### lines of data (i.e., the highest rank in the last,unlabeled, column shouldbe 22) plus a row of column captions. Delete any data that exceedthis limit. (Fewer than 22 

### lines of data are OK.) The result should look like the example in Figure 1, although the line wrapping may differ. Step 3. 

### Open the CALPOST-IMPROVEProcessor in Microsoft Excel. Savethe open file under a new name so that the original emptyprocessor willremain availablefor futureuse. The front worksheet, labeled "Input & 

### Output" looks like Figure 2. There is a large empty box, surrounded by double lines, into which the table created abovewill be imported, as described be10w.~ On the right is a box into which NOxconcentrationsmay be entered manually, and a smallbox below this box is provided for entry ofthe user's assumption ofwhat fraction of that NO, is in the form ofNO2.Two smaller boxes provide for user input ofthe Rayleigh scattering coefficient and, optionally, sea salt concentrationfor the Class I area, as described below. Results ofthe new IMPROVE algorithm calculations appear in blue in the lowerhalf ofthe worksheet and some additional results, that are also useful for quality control, appear in green to the right of the large box. At the moment, many results cells will display nonsensical numbers and errormessages, such as shown in Figure 2. 

### Step 4. 

### Selectthe upper left cell (A7) in the largebox. On the Excel menu bar, go toDataBGet External Data 

### and click onImport Text ~ile.~ 

### (Ifthe large box is not empty, click onEdit Text Import 

### instead.) Selectthe file that contains the table created in Step 2 and click on the GetData 

### button. Go through the Text Import Wizard steps, checkingthat all values appear correctly in separate columns. (The label "COORDINATES 

### (km)"willbe split over two columns; this is OK.) When everything appears in order, clickFinish.

4 The background concentrations that were entered into CALPOST must be the EPA-prescribed default annual average natural conditionsconcentrations for the East. The processor will not give correct answers if other concentrationswere used in CALPOST.

For future reference iil Step 7, this may also be a good time io locate the table wiih the same title but with the subtitle "% of Modeled Extinction by Species", which appears later in the output file.

Ifthe workbook has already been used, the boxes may not be empty. This does not matter. The exact wordingmay vary slightlybetween different versions of Microsoft Excel. The terminology used here is from Excel 2004 for Macintosh.YEAR DAY HR RECEPTOR COORDINATES (km) TYPE BEXT(Mode1) BEXT(BKG) BEXT(Tota1) %CHANGE F(RH1 bxS04 bxN03 bxOC bxEC bxPMC bxPMF

Figure 

### 1. Example of CALPOST Output Table, in Proper Format for Importing into the CALPOST-IMPROVEProcessor.


### Step 5.' The "Import Data" window will appear, with cell A7 indicated as the location at which data will be entered. Click on theProperties 

### button. In the window that appears, select "Overwrite existing cells with new data, clear unused cells" and uncheck "Adjust column width", then click on OK. Now click on the OKbutton in the "Import Data" window. Step 6. 

### Assuming that your Excel applicationis set up to automatically recalculate whenever any entries are changed, you should now have filledthe cells in the large box on the first worksheet,

Ifthe processor alreadyhad data in it andEdit TextImport was clicked in Step 4, then the "hpoi-tData" window will not appear and Step 5 can be skipped.. At cell A7, import "Ranked Daily Visibility Change" (bext) table, ~ncluding column headings, 2. Check calculated values below 5. (Optional) agalnst CALPOST% "Ranked Daily Enter 24hr -om CALPOST (22 days, nlax) V~siblh~ Chsltge" (dv) table NOx conc. EARDAY HR RECEPTOR COORDINATES (km) TYPE BEXT(Mode1) BEXT(BKG)BEXT(Total) %CHANGE F(RH) bxSO4 bxNO3 bxOC bxEC bxPMC bxPMF Rank NOx(ppb) dv!total\ dv(bk0' ' '-NUMl ' iNLlMl Nut41 ' "NUM1 " JNLINI * 4NUMI ' %NUMI ' 8NUMI * INCIM~ Adv 

# I

.(Optaonnl) Insert .tnnuat average sea salt concentration, from "Raylelgh Sea Salt" mrksheet. Leave blenk if not used, 1.e. default Is 0.

Figure 

### 2. Example of Appearance of Input & Output Worksheet before Data Entry.numbers should have appeared in the green columns to the right, and some numbers will have appeared in the output table in blue on the lower half ofthe worksheet. If the data import worked properly, none ofthe imported data should have spilled out ofthe large box. Check that all the column captions in bold outsidethe largebox are now duplicated on the fust line in the box. (There won't be a caption for Rank.) Step 

### 7. As a further check on whether everything is correct so far, the dv information in the three columns to the right ofthe largebox should be the same as that in the second CALPOSTtable "Ranked Daily Visibility Change: % of Modeled Extinctionby Species", which was mentioned in Footnote 1. Step 8. Beneath the large box that wasjust filledwith imported data, enter the Rayleigh scattering coefficient for the Class I area of interest into the top smallbox after red instruction 3. Also, if you wish, fill in the other small box, the one after red instruction4, with the annual average sea salt concentration. (The sea salt box may be left blank, but the Rayleigh scattering coefficient box must be filled in.) To help with filling in these two boxes, the fourth worksheet, "Rayleigh & Sea Salty', provides IMPROVE-calculated values ofthe Rayleigh coefficients for Class I areas in the VISTAS region and in adjacent states. Also, average sea salt concentrations for 2000-2004, calculated in accordancewith the new IMPROVE procedures, can be found there. Step 9.' Ifthe impact due to NO2 is to be considered, a second CALPOST run will be needed to provide the 24-hr averageNO, concentrations estimatedby CALPUFF. For this purpose, 

### run CALPOSTusing the ASPEC =NOX option in Input Group 1 ofthe CALPOST.INP control file. The NO, values to insert in the NO, input box on the Input & Output page oftheprocessor have to be extracted manually from the CALPOST output file for each date and receptor listed in the file that was imported in Steps 1through 

### 5 above and are displayed in the left hand columns in the largebox. Step 10. Select a value between 0 and 1to represent what fraction ofNOxis in the form ofNO2.Enter this value into the small box at red instruction 6 below the column where the NO, concentrationswere entered.'' Step 11. Theblue data table at the bottom ofthe page represents the new IMPROVE algorithm outputs. An exampleis shown in Figure 3. This table can be compared with the original CALPOST table at the top ofthe page. All of the columns in both tables show exactly the same variables, except that the F(RH) column in the top table is replaced by just the RH in the lower table (since the new procedure has three different f(RH) fimctions) and a new baNO2 column has been added to the bottom table to show the light absorption due to NO2 (in ~m-I). Although the events are listed in the same order in both tables, note that their rankings may have changed, as is the case for many of the lines in the blue output table in Figure 3.

Steps 8 and 9 are optional.If the impact due to NO2 is not of interest, just leave the entry fields mentioned in these stepsblank. loAn easy way to see the effect of the NO2 on the source's impact in the output table in the lower half ofthe page is to toggle this N02/NO, value between the selected value and zero.

### For those who are interested in more detail concerning the calculationsthat takeplace, values ofthe three f(RH) functions appear in columns M 

### through 0

### on the second, "Calculations" spreadsheet. The extinctionimpact ofthe source, including enhancement ofthe extinction efficiencies for sulfates, nitrates, and organics because of greater total mass concentrations, appears in 

### columns V through AC. 

### Extinction due to the annual average natural background appearsin Columns AJ through AN; 

### natural background extinctions for those components that are enhancedby greater total mass concentrations appear in columnsAU through AX.1. At cell A?, import "Ranked Dally Visibility Change" (bext) table, including column headings, 2. Check calculatedvalues below 5. (Opttonal) from CALPOST (22 days, max) against CALPOST's "Ranked Dally Enter 24hr Vlslblllty Change" (dv) table NO% conc. NWPW dv~lolal) dv(bkg) Aclv Q <I9 7 72 2 26 4.923 21.65 26.573 22.74 3.5 4.475 0 404 0.038 0.001 0.001 0.004 2 9 77 7 72 2 05 3.15 21.47 24.62 14.67 3.3 2.684 0.428 0.033 0.001 0.001 0.003 3 9 01 / 64 1 37 2.594 21.29 23.884 12 18 3.1 2.017 0.557 0.018 0,001 0 0.002 4 8 71 / 56 1 15 2.502 21.47 23.972 11.65 3.3 2.269 0.201 0.028 0,001 0,001 0.003 5 874 164 110 2.011 21.83 23.841 9.21 3.7 1.963 0.031 0.015 0,001 0 0.001 6 8 69 7 81 0 88 1.872 21.2 23.072 8.83 3 1.542 0.32 0.009 0 0 0.001 7 8 Po 7 51 0 8'1 1.649 21.65 23.299 7.62 3.5 1.625 0.012 0.01 0 0 0.001 S4U 7 12 U 13 1.524 22.19 23.714 6.87 4.1 1.482 0.0290.011 0 0 0,001 863 797 066 1.459 21.47 22.929 6.8 3.3 1.284 0.16 0.014 0.001 0 0.001 1 8 30 7.64 0.66 21.47 22.906 6.69 3.3 1.281 0.14 0.013 0 0 0,001 1 8 29 7 64 l 65 21.47 22.74 5.92 3.3 1.202 0.058 0.009 0 0 0.001 1 8 22 7 64 0 57 22.1 23.337 8 47 7.?3 0 54 8 45 7.03 0.52 8 0') 7 64 0 45 6 12 7 72 0 40 / 99 7 60 0.39 7 93 7.56 0.3s 7 94 7.60 0 34 8 06 7 72 0.3, 7 8s 7 56 0 32 8 22 7.93 0.29

Figure 3. Example of Appearance of Finished Input & Output Worksheet.

### Appendix Details of Calculation Approach As an example ofthe calculation steps, assumethat the sulfate concentrationresulting from emissions from a source is [SE]and the sulfate in the undisturbed natural background is [SN], for a total ambient sulfate concentration of [ST]. According to Equations 1 and 2 in the main body ofthis document, the total extinction due to sulfate for this combination is b,,(sulfate) =2.2.fs(RH)*[smallsulfate]+ 4.8.fL(RH)*[large sulfate], (Eq. A-1) where

(Eqs. A-2) [small sulfateT] =[ST]-[large sulfateT],
and the subscript T denotes total sulfate
For the original background, where there is no source impact, the corresponding formulas for the terms in EquationsA-2 are

[largesulfate^] = [SN]if[S~] 

## >20 ,ug/m3 (Eqs. A-3) [smallsulfate^] =[SN]-[large sulfate^], where the subscript N denotes natural sulfate.
Similar calculations need to be carried out for nitrates. Contributionsofthe other particulate components are linear and canjust be calculatedaccording to Equation 1.
If the impact due to NO2is also to be considered, then the source impact due to this component is, according to Equation 

### 1,

where PO2] is in ppb. It is reasonable to assume that the ambient NO2 concentrations under natural conditions would be so small as to cause negligible light absorption, so the correspondingterm is not needed in the natural conditionscalculation.
The contributions due to the various components are summed together as in Equation I to obtain the total extinction bext,T and the naturalbackground extinctionbext,N. Thefractional change in extinction is then calculated as the difference, normalized by the natural background extinction

a result that can also be expressed in deciviews.
These formulas are used in the CALPOST-IMPROVE Processor. Similarformulas apply for nitrates and organics. There is no nonlinearity in the remaining terms in Equation 

### 1.