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hh  dd  D zN #c P7P#SYSTEMS APPLICATIONS INTERNATIONAL`t"t"Jă   yd0dddy ]]C  ydhdddy #,< P7 ,P#  zN #O P7{P#9560r1ap.wp5`kt"6#c P7P#Final " October 1996ă] %Appendix A  Y_ } BIBLIOGRAPHY OF RELEVANT VISIBILITY PUBLICATIONS ă_0,0h 0,0h  hhhh  dddd @A-@Pt zN #c P7P#SYSTEMS APPLICATIONS INTERNATIONAL`!!t"FA-ă   yd0dddyQt zN #c P7P#A-`%t"(SYSTEMS APPLICATIONS INTERNATIONALă   yd0dddy]]]R  ydhdddy #,< P7 ,P#  zN #O P7{P#9560r1ap.wp5`kt"6#c P7P#Final " October 1996ă]]_S  ydhdddy #,< P7 ,P#  zP #c P7P#Final " October 1996`dt">#O P7{P#9560r1ap.wp5]  Y % Appendix A ă  Y` } BIBLIOGRAPHY OF RELEVANT VISIBILITY PUBLICATIONS ă A review of the literature has been conducted to identify existing information concerning the effects of air pollutants on visibility in the Southern Appalachian Mountain Initiative (SAMI) region, particularly in Class I (park and wilderness) areas. This review was conducted to establish (1) the current status and historical trends of visibility impairment in the Southern Appalachians, (2) the contribution of anthropogenic activity to visibility impairment, (3) the relationships between visibility impairment and pollutant concentrations, and (4) models that can be used to estimate the effects on future visibility conditions due to various emission management options. The results of the literature review were used to: (1)Xestablish a foundation of current knowledge concerning visibility impairment in the Southern Appalachian mountainous region, comprising eight states (West Virginia, Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, and Alabama),t" (2)Xidentify critical gaps that limit our understanding of the relationships between pollutant exposures and visibility impairment, and recommend how those gaps could be filled, andt" (3)Xrecommend methodologies and tools to employ in the design of the effects component of a technical assessment linking emissions, exposures, effects, and socioeconomic consequences.t" The first task in this effort was to perform an objective assessment of all relevant research, including the likely application of the work to the current assessment objectives. As part of that assessment, the technical and scientific literature has been examined to identify existing publications, studies and data pertaining to historical visibility trends, current visibility conditions, contributions of anthropogenic emissions to current and historic conditions, and the relationships between pollutant concentrations and visibility impairment. With increased regulatory activity in recent years, specialty conferences on visibility, and the Clean Air Act directives toward addressing visibility issues, the recent literature on visibility is expansive. A number of prominent visibility modeling and characterization studies have been conducted, and to a large extent, these represent a consolidation of much of the information obtained in many other studies and reports. *0,, The following bibliography contains, for each significant visibility study, the study title, date of publication, authors (or agency) responsible for preparation of the study or report, for whom the study or report was prepared, the purpose of the study, data and models (if any) that were used in the study, and a brief description of the major findings and conclusions generated by the study. Studies were sought in two general areas: (1) those that characterized visibility conditions (particularly in the SAMI region), and (2) those that addressed visibility modeling issues. In pursuing these objectives, a number of notable reports were encountered that summarized previous study results, and/or made recommendations regarding data analysis and modeling. Therefore, the major reports obtained were divided into three groups: (1)Xsummary and recommendation studies,t" (2)Xvisibility characterization studies, andt" (3)Xvisibility modeling studies.t" Many of the studies included below could have been placed in more than one group (e.g., a study that provided a characterization of visibility and also addressed the modeling relationships between pollutant concentrations and visibility impairment). To develop recommendations for visibility characterization and modeling for SAMI, a large number of reports were considered in addition to the major studies described below. The databases, modeling results, and findings of many of these reports were incorporated into and cited by the major visibility studies. Numerous journal articles, conference papers, government documents, and other reports, that provided evidence of existing visibility conditions (and trends) in the SAMI region, and/or addressed visibility monitoring, regulatory, or modeling issues, were reviewed in the course of this study. A number of these reports are cited throughout this report to support the findings, conclusions and recommendations presented. A complete bibliography of relevant literature may be found in the reference list following Section 6. N0,,  X  A.1 SUMMARY AND RECOMMENDATION STUDIES  Y  Study: Interim Findings on the Status of Visibility Research  Y  Date: February 1995  Ya  Prepared by: Office of Research and Development, U.S. EPA  Y4  Prepared for: Required under provisions of Clean Air Act  Y  Purpose of study: Report summarizes the results of visibility research published since 1990 that relate to CAA provisions. The report also discusses visibility research in progress. This report provides a comprehensive review of recent reports and publications on visibility.  Y  Data used: N/A  Yh  Models used: N/A  Y;  Conclusions: The concluding remarks summarize the direction federal visibility research is likely to take as well as a statement of the status of global visibility research. 0,,  Y  Study: Protecting Visibility in National Parks and Wilderness Areas  Y  Date: 1993  Y  Prepared by: National Research Council, NAS  Yb  Prepared for: USDI, USDOE, USDA, Arizona Salt River Project, Chevron Corp.  Y5  Purpose of study: This report outlines working principles for assessing the relative importance of anthropogenic emissions contributing to haze in Class I areas and considers various alternative source control measures. The report recommends strategies for filling scientific and technical gaps in current methods and databases. The models and data presented in the report are recommended or use.  Y  Data used: Empirical pollutant scattering and absorption efficiencies; measured particle size distribution data. Recommended monitoring measurements: highsensitivity nephelometry; continuous particle absorption coefficient measurements; measured particle concentrations; accurate concentration measurements of organic and elemental carbon particles; measurement of water content of particles; particle size distribution measurements; continuous measurement of sulfates, organics, carbon, nitrates and elemental composition.  Y  Models used: Speciated rollback models. Recommended models: hybrid combinations of chemical mass balance receptor models with empirical data for pollutant scattering and absorption efficiencies; Recommended model development: advanced reactive model for analysis of plumes from single sources; gridbased multiplesource regional model for analysis of regional haze; hybrid combinations of mechanistic models for transport and secondary particle formation with measured particle size distribution data.  Y  Conclusions: The concluding remarks state that an effective visibility program must be aimed at preventing and reducing regional haze and would represent a considerably different approach than is currently employed, which is to focus on visible plumes from nearby individual sources. #0,,  Y  Study: A Clean Air Act Exposure and Effects Assessment 19931994  Y  Date: June 1994  Y  Prepared by: Atmospheric Research and Exposure Assessment Laboratory, U.S. Environmental Protection Agency, with contributions from U.S. EPA, Man Tech Environmental Technology, U.S. Forest Service, others  Y4  Prepared for: EPA managers, congressional staff, general public  Y  Purpose of study: Present the most current, validated information on the status and trends in air quality and the effects of air pollution on U.S. nonurban ecosystems, including deposition and visibility. The report also outlines an ecological benefits integrated assessment approach to be incorporated into future reports.  Y  Data used: The report discusses the IMPROVE, EFPVN, CASTNET and GCVTC monitoring programs.  YQ  Models used: N/A  Y$  Findings: The visibility chapter of the report presents a brief summary of visibility characteristics for regions of the U.S., taken from previous published research. Some ongoing and future monitoring efforts are presented in a section on future visibility assessments. 0,,  Y  Study: NAPAP State of Science and Technology Report 24; Visibility: Existing and Historical Conditions Causes and Effects  Y  Date: October 1990  Yx  Prepared by: Trijonis et al., National Acid Precipitation Assessment Program (NAPAP)  Y4  Purpose of study: The NAPAP State of Science and Technology Report 24 is a review and analysis of the known scientific information, as of 1990, on visibility and the relationship of visibility to air quality. The report reviews visibility conditions (existing and historical) and visibility models. The report also makes recommendations for future research.  Y  Data used: National Weather Service Airport Visibility Data (since 1918); IMPROVE data (since 1987); Eastern Fine Particle Visibility Network (19881989); NPS data (since 1978); Sulfate Regional Experiment (19771978) and other data.  YP  Models used: The report presents results from previous visibility analyses. However, the report discusses the theories involved in describing (and modeling) visibility, including radiation scattering, extinction coefficients and particle contributions to total extinction (extinction budgets); visual range and contrast definitions; Visibility Image Processing System (VIPS).  Y  Findings: Historical trend evaluation indicates that haziness over the eastern United States since the late 1940's has been dominated by sulfur emission sources. Fine particle scattering in the East accounts for more than 3/4 of the nonRayleigh light extinction. Sulfates account for the majority of fine particle mass.  YU  Conclusions: Measurements should be improved to reduce particle sampling artifacts  Y? (particularly organics). In situ techniques are needed for liquid water monitoring. Nephelometers need to be improved so as not to modify the aerosols. Visibility and aerosol monitoring should be geographically extended to allow pattern and cause/effect relationship assessments. There is a lack of comprehensive data for the southern part of the East and for the wintertime throughout the East. Data should be collected to formulate light extinction budgets for worstcase and bestcase conditions in addition to average conditions. Further work is needed to characterize the nonlinear relationships between light scattering and concentrations of aerosol components. Comparisons of light extinction budgets with total visibility budgets, including consideration of path radiance, should be performed. D&0,,  X  A.2 VISIBILITY CHARACTERIZATION STUDIES  Y  Study: Interagency Monitoring of Protected Visual Environments (IMPROVE) 1993 Report  Yw  Date: February 1993  YJ  Prepared by: J.F. Sisler, D. Huffman and D.A. Latimer  Y  Purpose of study: The objectives of the IMPROVE program are to: establish current background visibility in Class I areas; identify chemical species and emission sources responsible for existing anthropogenic visibility impairment; and document longterm trends. The study presents results from measurements made at IMPROVE sites and makes recommendations for future research.  Y  Data used: IMPROVE consists of aerosol monitoring and scene monitoring (automated cameras) at 36 sites, and optical monitoring (transmissometers) to measure light  Yg extinction at 20 sites. The aerosol monitoring consists of one PM10 and three PM2.5 samplers (using teflon, nylon and quartz filters). Two 24hour duration aerosol samples are collected per week. Chemical compositions are determined, including elements, ions, organic and light absorbing carbon. Relative humidity is measured continuously at the transmissometer sites. Elemental sulfur and sulfate concentrations are also measured simultaneously with the transmissometers.  Y  Models used: N/A  Y  Findings: The light absorption coefficient to elemental carbon mass ratio was twice as large as expected. The difference may be due to other substances or uncertainties in measurements. The IMPROVE data confirmed that fine aerosols are more efficient at light scattering than coarse aerosols. The highest fine aerosol concentrations are in Washington D.C., in the Appalachian Mountains, and southern California. Fine aerosol composition varies with geographic location and season. Of the 19 regions in the IMPROVE network, sulfate is the largest single component of fine aerosol in six regions, primarily in the East. Fine mass aerosol concentrations are highest generally in summer. Acidity of sulfate aerosol was estimated statistically from hydrogen, sulfate and organic carbon concentrations. The Shenandoah site is identified as acidic. Sulfate accounts for 2/3 of the total aerosol light extinction annually and 3/4 in summer in the Appalachian Mountains. Measured light extinction is generally within ten percent of the reconstructed values calculated from the measured concentrations of the major aerosol species. However, the* 0,, average reconstructed extinction is about 80 percent of the average measured light extinction in the Appalachian Mountains during summer. Deciview measures of human perception are used to classify areas as having good or bad visibility. The Appalachian region has noticeably worse (than average) visibility. Peak visibility impairment occurs in summer.  Y_  Conclusions: IMPROVE recommendations for future research are: better understand organic carbon light absorption and develop an adjustment to current light absorption calculation; determine the composition of lightabsorbing carbon particulate matter; reevaluate the sulfate and nitrate relative humidity corrections; investigate the hygroscopicity of organics; determine the causes of the underestimation of the calculated light extinction from aerosol concentrations.  0,,  Y  Study: Shenandoah Visibility Study  Y  Date: 1991  Y  Prepared by: UC Davis  Yb  Purpose of study: Assess visibility impairment in Shenandoah National Park.  Y5  Data used: 12 hour (6 am 6 pm) samples collected daily between July and August, 1991 at one site, and between July and September, 1991 at a second site in VA.  Y Measurements: PM2.5 and PM10 aerosol samples collected on Teflon, nylon and quarts substrates; analyzed for mass, light absorption, hydrogen, Na through Pb elemental analysis, Cl, NO3, SO4=, NH3 and carbon.  Y  Models used: N/A h 0,,  Y  Study: NAPAP 1992 Report to Congress  Y  Date: June 1993 (Chapter 4, "Ambient Air Concentrations, Deposition, and Visibility")  Y  Prepared by: National Acid Precipitation Assessment Program (NAPAP)  Yb  Prepared for: U.S. Congress  Y5  Purpose of study: The NAPAP report addresses research applicable to the assessment of current sources of visibility impairing pollution and clean air corridors.  Y  Data used: Measurements from the IMPROVE network. The data from IMPROVE are compared with earlier data and evaluated for consistency.  Y  Models used: Visibility trends are estimated based upon emission reductions achieved in the past and projected for the future.  Yi  Findings: Concentrations and deposition of pollutants are higher in the vicinity of major point sources and in urban areas than at regionally representative sites; seasonal and meteorological conditions affect the influence of specific sources/source regions on specific receptors; except for areas impacted by local sources, air concentrations and deposition of pollutants are highest at higher elevations in the Appalachians.  Y  Conclusions: Adequate information exists to justify new visibility protection rules; targeting singlepoint sources may not be the best approach, since a wide variety of sources can contribute to regional haze.  0,,  Y  Study: Southern Appalachian Assessment (SAA)  Y  Date: 1996  Y  Prepared by: Federal and State Agencies; coordinated through Southern Appalachian Man and the Biosphere (SAMAB) Cooperative  YK  Purpose of study: The Southern Appalachian Assessment is an integrated ecological assessment of the Southern Appalachian region, including reports on atmospheric, social, cultural, economic, terrestrial and aquatic resources. The atmospheric technical report includes a broadscale assessment of visibility in the region. The report summarizes visibility conditions primarily from camera monitoring data. The data are analyzed to obtain monthly estimates of visibility conditions over a period of 4 to 5 years. The SAA report also addresses effects of the 1990 CAAA on visibility (projections were taken from EPA's 1993 Report to Congress) and makes recommendations for improving the data.  Yf  Data used: 35mm camera monitoring from eight sites in the Appalachians (AL, AR, GA, VA, WV, TN, and NC) established by the Southern Region of the U.S. Forest Service. The first site (James River Face Wilderness, VA) began collecting data in 1987. The seven other sites began collecting data in 1989. Some sites had single targets, other sites multiple targets. Slides were recorded at 09:00, 12:00 and 15:00 daily until 1993. Slides were analyzed using densitometric analysis to determine scene contrast. Standard Visual Range (SVR) was determined from scene contrast, sight path distance, Rayleigh coefficient and inherent contrast of the target.  Y  Models used: No models were used in this study.  Yk  Findings: Very large seasonal differences were observed in SVR, with winter having approximately four times longer visual ranges than summer. The median historic annual visual range estimates are between 48 and 98 km. The monitoring site areas can be placed into two groups: Dolly Sods W, James River Face W, Caney Creek W, and Shenandoah NP have generally poorer visibility (median SVR 4858 km, worst SVR < 20 km, best SVR 140190 km) than Cohutta W, Linville Gorge W, Shining Rock W, Upper Buffalo W, and Joyce KilmerSlickrock W (median SVR 6090 km, worst SVR 2040 km, best SVR > 200 km). The photographic data are also analyzed for uniform haze, layered haze and weather conditions. The worst visibility conditions occur within the northern and southern portions of the Southern Appalachians (West Virginia and Virginia in the north; northern Georgia and Alabama in the south). Visibility in the Southern Appalachians has deteriorated considerably since the 1950s. Sulfates are the largest single contributor to haziness in the region. Sulfate concentrations increased 2 to 3 percent each year between 1982 and 1992.  Y(  Conclusions: Visibility can be improved in the region by reducing sulfur dioxide emissions from humancaused sources. * 0,,  Y  Study: Historical Data Summaries and Permanent Photographic Archive for James River Face Wilderness, Virginia; 19871992  Y  Date:  January 1995  Yx  Prepared by: Air Resource Specialists, Inc.  YK  Prepared for: U.S. Forest Service  Y  Purpose of study: Review and summarize all James River Face Wilderness photographic data collected from November 1987 through November 1992.  Y  Data used: The USFS automatic photographic monitoring system produced 35mm slides taken at 0900, 1200 and 1500 daily from 1987 through 1992. Due to vandalism in 1988, the camera was moved to a different site. Each photographic slide was reviewed and assigned a code based on target and sky illumination conditions, weather conditions, visible hazes or plumes, and unusable/missing observations. The data were analyzed by periods: Winter, Spring, Summer, Fall, Annual, Monthly and Historical. Standard Visual Range and Deciview values were estimated from a series of slides, chosen to represent the range of visibility conditions that occurred during the period. Slidederived scene contrast was estimated based on densitometric analysis, and then the contrast was used to estimate the Standard Visual Range for each slide.  Y  Models used: N/A  Y  Findings: Cumulative frequency summaries for the SVR, deciview and total extinction were computed and ranked into Clean (visibility is better 10% of the time), Median, and Dirty (visibility is better 90% of the time, and poorer 10% of the time) episodes. Historical trend analysis indicates that during the period 1987 to 1992, visibility improved at all levels. As expected, the best visibility occurs in winter and the poorest visibility observed in summer.  Y  Conclusions: N/A 0,,  Y  Study: Southeastern Aerosol and Visibility Study (SEAVS)  Y  Date: 1995 (study plan)  Y  Prepared by: EPRI, NPS, others  Yb  Prepared for: SEAVS is a collaboration among universities, consulting firms, electric utilities, the National Park Service (NPS), and Electric Power Research Institute (EPRI)  Y  Purpose of study: The SEAVS partnership seeks to fill gaps in the knowledge of atmospheric fine particle characteristics and visibility under the humid conditions of the southeastern U.S. The study is to produce instruments, data, and methodologies to improve the ability to predict changes in airborne particle characteristics and visibility resulting from changes in emissions. The regional SAMI assessment is envisioned to benefit from the results of the SEAVS research program. The study is to run for 2 and 1/2 years. The SEAVS Study intends to reduce uncertainties about the role of water and organics in particles in order to ensure proper allocation of particle components and haze to appropriate sources. The overall objectives of the study are to (1) determine the contributions of the major constituents to particle mass and light extinction for a representative location in the southeastern U.S., and (2) produce a field data set under humid conditions to test and improve models that simulate aerosol composition and light scattering.  Y  Data used: Instrumentation development for measuring aerosol properties under humid eastern conditions, based on technologies previously used in the Southwest, has already been completed. Beginning in July 1995, the instruments are to be tested and data  Yk collected over a 6 week period. The data to be collected are: PM2.5 properties with emphasis on the contribution of water and organics to aerosols; trace substance concentrations; and human perceptions of visibility. The collected data are to be used to characterize the air quality and to test simulation methods.  Y  Models used: A code for simulating the composition and water content of inorganic and organic aerosols is being developed. Mie scattering theory will be used to relate aerosol composition to atmospheric optical properties, and to estimate the contributions of different aerosol components to the total light extinction. The Hunt model for color appearance will be used with human observers to measure perceived colors.  Yo$  Findings: Work in Progress; data were collected during summer 1995  YB&  Conclusions: Work in Progress (0,,  X  A.3 VISIBILITY MODELING STUDIES  Y  Study: SAMI Evaluation of Existing Information and Specifying Models  Y  Date: May 1995 (draft report)  Yx  Prepared by: EARTH TECH (formerly Sigma)  YK  Prepared for: Southern Appalachian Mountains Initiative (SAMI)  Y  Purpose of study: Provide a catalog of models available for air quality assessment of SAMI region and provide information to assist other elements of SAMI in assessing spatial and temporal distributions of emissions.  Y  Data used: N/A  Y  Models used: Report discusses and evaluates many air quality modeling approaches. Shortterm reducedform air quality models, such as RADMRPM and VARED, are recommended for use on a regional scale. For visibility, postprocessor analysis of air quality species concentrations is discussed. Models reviewed include CALPOST, VASM, MESOPUFF II, PLUVUE II, ERT and ROME. It is recommended that SAMI follow the protocol of the GCVTC for evaluating visibility impacts.  Y  Conclusions: Recommendations developed for modeling of SAMI region (see Models used). 0,,  Y  Study: Assessment of the Effects of the 1990 Clean Air Act Amendments (CAAA) on Visibility in Class I Areas  Y  Date: October 1993  Yx  Prepared by: Systems Applications International (SAI)  YK  Prepared for: U.S. EPA  Y  Purpose of study: Provide estimates of the expected improvements of visibility in Class I areas due to emission reductions required by 1990 CAAA.  Y  Data used: 1985 NAPAP emission inventory, IMPROVE data, MOUDI impactor data.  Y  Models used: (1) NPSAQMS (RTMII) air quality model for Southwest U.S. to generate pollutant species concentrations. Postprocessing to estimate scattering coefficients from pollutant concentrations and scattering efficiencies from MOUDI impactor data (Mie theory). (2) Emission rollback calculations to estimate CAAA effects on particulate concentrations for entire U.S. Postprocessing to estimate atmospheric optical parameters (extinction and deciviews).  Y   Conclusions: (1) Little change expected in temporal distribution of visual range or deciview at most Class I areas in the Southwest U.S. (2) Rollback analysis indicated larger change expected in Southeast U.S. (average extinction in SAMI Class I areas is predicted to be reduced by approximately 25 percent due to 1990 CAAA). 0,,  Y  Study: Effects of the Clean Air Act Amendments on Visibility in Class I Areas  Y  Date: 1993  Y  Prepared by: U.S. EPA, Office of Air Quality, Planning and Standards  Yb  Prepared for: U.S. Congress  Y5  Purpose of study: Assess the progress and improvements expected on visibility in Class I areas due to implementation of the 1990 CAAA.  Y  Data used: N/A. Report incorporates previous SAI results of rollback calculations for entire U.S. and regional dispersion modeling for Southwest (Gray et al., 1993). IMPROVE and NPS data from NAPAP (Trijonis et al., 1990) are used to characterize current visibility conditions.  Y  Models used: (1) Simple emissionsdriven air quality analysis to estimate areas likely to see changes in the distribution of anthropogenic visibility impairing pollutants; empirical extinction efficiencies and simple sulfate and nitrate humidity dependent extinction efficiencies incorporated. (2) RADM with post processor EMVIS for sulfate impact in Southeast. (3) RTMII model for estimating visibility impacts in Southwest.  Y  Findings: Significant improvements are expected for Class I areas along the central and southern portions of the Appalachian Mountains. RADM modeling for the Southeast predicts annual average visibility (visual range) improvements at Great Smoky Mountains National Park (+13 km, 4 dV), Shenandoah National Park (+13km, 4 dV), and Sipsey Wilderness (+9 km, 2 dV). There is considerable uncertainty in the analysis (due largely to uncertainties in predicting future emissions).  YV  Conclusions: Visibility is improving and will continue to improve due to the 1990 CAAA but there will still remain perceptible manmade regional visibility impairment in all Class I areas nationwide. 0,,  Y  Study: A Study of Visibility Improvements in the Southern Appalachians  Y  Date: 1995  Y  Prepared by: University of North Carolina, School of Public Health (student project)  Yb  Prepared for: The Southern Appalachian Mountain Initiative (unsolicited)  Y5  Purpose of study: Evaluate the contribution of sulfur dioxide emissions from coalfired power plants to visibility impairment in the Great Smoky Mountains National Park (GSMNP).  Y  Data used: Emission data from Air Quality Divisions of North Carolina and Alabama and TVA. Sulfur particle, light scattering and relative humidity data from the IMPROVE Look Rock monitoring site (winter 1991 data).  Y  Models used: SourceReceptor: meteorological wind data were used to estimate formation and transport of sulfate particles from power plants to monitoring site. Visibility: observed the correlation between RHadjusted particulate sulfur concentrations and scattering coefficient (obtained from photographic records). Used particulate sulfur as a surrogate for visibility impairment.  Y  Conclusions: Recommends use of MESOPUFF Lagrangian model to estimate concentrations of sulfate in the GSMNP from sources within the eight state boundaries of the SAMI region. Recommends investigation of emissions from sources other than power plants and industrial sites. Report also contains economic cost analysis study. 0,,  Y  Study: Mt. Zirkel Wilderness Area Reasonable Attribution Study of Visibility Impairment  Y  Date: January 1995 (study plan)  Yx  Prepared by: Desert Research Institute, Sonoma Technology, Inc., and Air Resource Specialists, Inc.  Y4  Prepared for: Colorado Department of Public Health and Environment  Y  Purpose of study: The goal of the Mt. Zirkel Visibility Study is to explain the nature and causes of visibility impairment in the Mt. Zirkel Wilderness (northwestern Colorado), and to determine the extent to which episodes of impairment can reasonably be attributed to a single source. Specific objectives are the characterization of haze in the Mt. Zirkel Wilderness, including the frequency and intensity and the relationship of haze to meteorological conditions; characterizing the behavior of power plant plumes in the Yampa Valley; determining the light extinction budget; comparing results from different modeling and data analysis methods and assigning confidence levels to source contribution estimates. The study is to run from Fall 1994 through June 1996.  Y"  Data used: Annual and intensive air quality, aerosol, visibility, and meteorological measurements are proposed. The annual measurements are to include photographic and time lapse video measurements. Light absorption of aerosol deposits, surface, and upperair meteorologic measurements will also be taken. Aerosol samples are to be taken during daylight hours at two sites throughout the study year (Dec. 1994 through 1995). Three onemonth intensive study periods will supplement the annual measurements, when additional measurements will be made.  Yk  Models used: Multiple linear regression analysis of scattering and absorption on chemical concentrations; ELSIE visibility model to estimate extinction efficiencies; source and receptor models (including CALPUFF) to estimate source apportionment.  Y' An aerosol evolution model is to be developed to estimate upper and lower limits on SO2 conversion to particulate sulfate using plume aging times.  Y  Findings: Work in Progress  Y!  Conclusions: Work in Progress "0,,  Y  Study: Grand Canyon Visibility Transport Commission (GCVTC)  Y  Date: established November 1991  Y  Prepared by: numerous researchers are involved in study  Yb  Prepared for: GCVTC consists of governors of ninestate western region; U.S. EPA and Southern California Edison are partners in the project.  Y  Purpose of study: GCVTC was created in response to CAAA provision establishing transport regions for regional haze analysis. GCVTC study objectives are to use existing studies and data to determine the impact of current and projected emissions on visibility on the Colorado Plateau, and to evaluate and recommend control strategies for addressing regional haze. Commission's report is due (to EPA Administrator) November 1995.  Y~  Data used: Base year emission inventory, routine and special study air quality and visibility measurements  Y:  Models used: Five air quality models (for assessing changes in concentrations due to emission changes) will be evaluated: VARED, CAPITA, ASTRAP, a statistical trajectory model, and RAMS. The visibility (extinction) model has been constructed using simple extinction efficiency relationships selected by consensus (however, recent data were used to augment efficiencies developed by Trijonis et al., 1990).  Y  Findings: Work in Progress  Y  Conclusions: Work in Progress