SCE Report on
The Desert and InterMountain Air Transport Project

Publication Number: 600-00-015
Publication Date: September 1999

The executive summary, abstract and table of contents for this report are available below. This publication is available as an Adobe Acrobat Portable Document Format Files. In order to download, read and print PDF files, you will need a copy of the free Acrobat Reader software installed in and configured for your computer. The software can be downloaded from Adobe Systems Incorporated's website.

---

Executive Summary

The Desert and InterMountain Air Transport Project (DMAT) was approved for funding in late 1997 as a California Energy Commission (CEC) Public Interest Energy Research (PIER) Program transition program. The PIER funding allowed the completion of an ongoing Southern California Edison (SCE) environmental improvement program that had been underway since 1989 with funding from the California Public Utilities Commission and other co-sponsors. The goal of the PIER DMAT Program was to carry out fundamental research to characterize, quantify, and assess the fate and transport of air emissions and their impact on visibility from electric utility sources located principally in California to locations within California and beyond its borders. The by-products of this research have provided fundamental scientific and technical information useful to decision-makers in debating national and California visibility issues. Applying the best science available and applicable to California ensures that regulatory decisions are well founded. This report summarizes the research studies that were completed as part of the PIER DMAT Project.

The PIER DMAT Project was divided into two principal areas: completing a project on Measurements of Haze and Visual Effects (Project MOHAVE) and its supporting studies, and addressing visibility and fine particulate research issues related specifically to California.

Project MOHAVE

Project MOHAVE was designed to quantify the relative contribution of air emissions from SCEís Mohave Power Project (MPP) to visibility impairment at the Grand Canyon National Park (GCNP). Project MOHAVE was conceived in 1991 and completed in 1999 as a joint industry and government partnership involving SCE, the U.S. Environmental Protection Agency (USEPA), and the U.S. National Park Service. PIER transition funding permitted the completion of a number of Project MOHAVE research studies whose results were ultimately integrated into the Project MOHAVE Final Report.

Objectives

• Develop new methods for judging the adequacy of regional wind fields.
• Apply an advanced reactive plume chemistry model to quantify the conversion of plume sulfur dioxide to atmospheric particulate sulfate from MPP.
• Review the optical properties of fine particulates on visual impairment and quantify the impact of MPPís emissions on visibility.
• Complete and deliver the Project MOHAVE Final Report.

Outcomes

The PIER DMAT studies yielded information linkages important in meeting the goal of quantifying the visual impacts of emissions from MPP. For example, one of the wind fields evaluated during the PIER DMAT Project provided basic input data to the reactive plume chemistry model task. The output from the plume chemistry model task then provided information on particulate plume concentrations for various chemical constituents. These plume particulate values provided the necessary information to another PIER DMAT task to develop estimates of MPP plume impacts on visibility. These results, along with those from other Project MOHAVE investigators, formed the content for the Project MOHAVE Final Report, the final PIER DMAT task for the Project MOHAVE research area.

Conclusions

The key conclusion from Project MOHAVE was that there were no observational relationships linking emissions from MPP, as represented by a unique tracer, and visual impairment at locations within the GCNP. There was, however, clear observational evidence linking emissions from distant source regions such as southern and central California, northern Mexico, and nearby Las Vegas to visual impairment at the GCNP. Several different modeling methods were applied to understand the range of potential impacts from MPP. Significant differences were noted between the modeling results and are most likely due to different representations of sulfate formation chemistry in clouds assumed in each model. On average MPP was found to contribute between 0.2% to 0.6% of the total light extinction during summer at the western end of the GCNP. During "worst case" (at the 90^th percentile frequency) conditions, MPP was found to contribute between 1.3% and 2.8% of the total. These levels of impact are not perceptible to the human eye.

Recommendations

• Further research to increase knowledge of the three-dimensional patterns of wind speed and direction, as well as to gather information about the rate of formation of sulfur-containing particles in clouds, would decrease uncertainty in model predictions.
• This research identified the theoretical conditions that justify regression apportionment of light scattering, and showed how deviations from these conditions caused errors in the apportionment. It examined the degree to which these conditions were satisfied for one set of data from one location and season, but did not address how generally these results apply to other situations. Further application of this method to other settings is needed to establish whether the observations noted here are representative.
• Further work is necessary to understand the uncertainties of the Tracer Potential method for comparing wind fields.
• In performing complex plume chemistry simulations, it is extremely important to have available measurements of pollutant concentrations at plume heights consisting of ozone, nitrogen oxides, hydrogen peroxide, OH radical, water vapor, ammonia, and trace metals such as manganese and iron.
• To the extent possible within resource constraints, emission source attribution projects need to strive for hourly averaged air quality concentration data.

California-Specific Visibility and Particulate Research

The second component of the PIER DMAT Project examined a number of visibility issues relevant to California. This research area contained three sub-parts. One study examined the historical trends in emissions, visibility, and fine particulates at locations in California, including several visibility-protected national parks and monuments, to assess the extent of visual impairment in California.

Two additional efforts were coordinated under the direction of the Electric Power Research Institute. Several fundamental research activities were conducted to examine, characterize, compare, and estimate potential errors of various methods for the measurement of fine particulate matter and its chemical components. These activities included analyses of particulate measurement programs at Riverside and Bakersfield, California.

Finally, a new and advanced air quality model was developed, which can be used to simulate the formation of atmospheric aerosols and photochemical ozone from point sources such as power plants. This model has undergone preliminary testing but additional work needs to be done before the model can be applied on an operational basis.

Objectives

• Document the historical trends in atmospheric particulates, visibility, and visibility-impairing emissions in California.
• Relate these trends to emission trends from the energy sector in California.
• Compile a database consisting of the air quality/emission trend data.
• Evaluate the efficacy of the present generation of mathematical models for use in performing regional visibility assessments in California.
• Provide recommendations for improving the state-of-the-science for sampling PM₁₀ and PM_2.5.
• Develop and test an advanced point-source reactive chemistry dispersion model incorporating all of the best features (gas- and aqueous-phase chemistry, plume dynamics, aerosol dynamics, etc.) of existing models.
• Investigate the extent to which PM_2.5 measurements made with Teflon filter-based samplers differ in mass and chemical composition from aerosol particles at the point of sampling or inhalation.
• Test, compare, and quantify the sampling errors associated with several continuous and discrete samplers designed to quantify PM_2.5 mass or chemical composition.
• Compile onto a compact disc the Winhaze visual air quality modeler image software program and base images for several national parks in the United States, including the GCNP and Yosemite National Park in California.

Outcomes

The objectives for all tasks were met. Specifically:

• Emissions, optical and particulate matter data were acquired and compiled into databases for subsequent analysis. The California Air Resources Board (1998) estimated annual average daily emissions of PM₁₀, nitrogen oxides, sulfur oxides, carbon monoxide and volatile organic compounds at five-year intervals from 1985 through 2010, categorized by standard industrial classification code and source category code within each county and air basin.
• Several studies were completed to identify the state-of-the-science regional modeling techniques that may be useful for particulate and visibility modeling in California. Also, a review was completed identifying potential improvements to the monitoring of fine particulates (PM_2.5).
• The Second-order Closure Integrated Puff model with Chemistry (SCICHEM) development was completed, which simulates liquid-phase chemistry and gas-particle thermodynamic equilibrium. Existing modules for aqueous-phase chemistry and aerosol thermodynamics were compared and the most appropriate modules incorporated into SCICHEM. The enhanced model was then tested for a range of conditions to determine if model results were physically and chemically consistent. The results from these sensitivity studies showed that the model responded in a physically and chemically consistent and directionally correct manner to all the input parameter variations.

Conclusions

• Statistically significant decreases in concentrations occurred between 1989 and 1996 in several air basins. Most notable were decreases in the San Joaquin Valley during winter and at San Gorgonio Wilderness Area during spring, which are the times of year when concentrations are highest at these locations.
• Estimated emissions of PM_2.5, nitrogen oxides, and sulfur oxides decreased throughout the state between 1990 and 1995. These decreases are consistent with the observed decreases in concentrations. However, decreases in concentrations did not accompany decreases in emissions everywhere.
• Coupled with the decreasing trends in particulate concentrations and particulate-causing emissions, improving trends in visibility were noted in several visibility-protected areas of California including: Redwood National Park, Yosemite National Park, Point Reyes National Seashore, Pinnacles National Monument, and San Gorgonio Wilderness Area.
• Emissions from energy production are small percentages of PM_2.5, nitrogen oxide, and sulfur oxide emissions in California, so energy production likely does not contribute substantially to decreased visibility or increased PM_2.5 concentrations.
• Emissions from non-mobile source energy use are a larger percentage of total emissions than emissions from energy production. In particular, wood burning is a substantial contributor to PM_2.5 emissions in cooler locations, such as the Lake Tahoe and Mountain Counties Air Basins. Therefore, emissions from non-mobile source energy use may be important contributors to reduced visibility and increased PM_2.5 concentrations in some parts of the state.
• The highest fine particle concentrations in California are present in locations with surrounding topography that limits dispersion. These areas include the Central Valley, the South Coast Air Basin, the San Francisco Bay area, and the Lake Tahoe Air Basin. The highest concentrations at these locations generally occur during the fall or winter, when periods of low inversions and low wind speeds lead to the accumulation of emitted particulate matter.
• Carbon-containing materials and ammonium nitrate are the major constituents of PM_2.5 at the locations with the highest PM_2.5 mass concentrations. Wood burning may be a major source of the carbon-containing materials, particularly at locations with cooler fall and winter temperatures, while the ammonium nitrate is formed from atmospheric reactions that involve nitrogen oxides and ammonia.
• Our results indicate that USEPAís Federal Reference Method for PM_2.5 sampling does have significant limitations. It cannot assess the chemical composition of the collected aerosol, and it may be susceptible to sampling errors based on gas-particle partitioning of volatile organics and nitrate under certain conditions.
• Revision of our understanding of the composition of PM_2.5 has additional implications beyond accurate sampling of airborne aerosol mass. Because the various components of PM_2.5 have different dominant sources, accurate characterization of aerosol composition is necessary to design effective emission management strategies.
• The SCICHEM plume model is potentially an important tool for examining potential impacts on air quality from existing and proposed emission sources such as power plants.

Recommendations

• More effort needs to be employed in testing the SCICHEM model against actual field measurements to provide real-world tests of model performance.
• More extensive spatial coverage is needed to better understand the nature and causes of visibility and particulate matter concentrations in California. Implementation of the PM_2.5 monitoring network in conjunction with expansion of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network will help provide this information in the future.
• Our observations highlight the need for a more robust sampling system for carbon in airborne particles that measures the gas-particle partitioning as it exists in an unperturbed air parcel.

Abstract

Relationships between air emissions, airborne particulates, and visibility were examined through a series of research projects involving particulate and meteorological measurements, plume aerosol modeling, and historical trend analyses. Two principal research areas were pursued: completing Project MOHAVE (Measurements of Haze and Visual Effects) and initiating California-specific particulate and visibility research. Project MOHAVE was initiated in 1991 as part of a U.S. Congressional appropriation to the U.S. Environmental Protection Agency to study the relative effects of air emissions from the Mohave Power Project (MPP), a large coal-fired power plant located near Las Vegas, NV, on visibility levels at the Grand Canyon National Park. Using a variety of analysis techniques, two principal conclusions were derived for the Project MOHAVE research: 1) from observational data, analysts were unable to find any statistical relationships linking emissions from MPP and visual impairment at locations within the Grand Canyon National Park; and 2) using several plume models, MPP was found, on average, to contribute during summer between 0.2 to 0.6% of the total light extinction and during worst-case conditions (90^th percentile frequency) between 1.3 to 2.8% of the total. These percentage contributions are not perceptible to the human eye.

A second research area investigated the extent of visual impairment in California. This involved examining historical trends of emission-causing pollutants and visibility at several locations in California, evaluating the accuracy of particulate matter measurement methods, and developing new tools for examining plume impacts from point sources. Several conclusions were drawn from this work. The trend analysis showed that from 1989 to 1996, statewide trends in particulate concentrations exhibited statistically significant decreases in many air basins consistent with decreasing trends in emissions of oxides of nitrogen and sulfur, and volatile organic compounds. Improving trends in visibility were noted in several visibility-protected areas such as Yosemite National Park, Pinnacles National Monument, Redwood National Park, Point Reyes National Seashore, and San Gorgonio Wilderness Area. The particulate measurement studies found that the Federal Reference Method for measuring fine particulate matter has significant technical limitations stemming from sampling errors relating to gas-particle partitioning of volatile organics and nitrates. This finding is significant because such sampling errors may lead to underestimation of PM_2.5 concentrations and to an improper identification of the sources of airborne particulate matter in designing effective emission management control strategies. Finally, a new state-of-the-art air quality model was developed and tested that embodies current scientific thinking regarding dispersion and chemistry of point source emission plumes. Such a model can provide a useful tool for evaluating potential impacts from new and existing power plant emissions on air quality.

Table of Contents

Preface

Executive Summary

Abstract

1.0 Introduction

2.0 Research Results

3.0 Conclusions and Recommendations

4.0 Glossary

5.0 References

Appendices

Appendix A         Executive Summary, Project MOHAVE Final Report, submitted to the USEPA March 1999.

Appendix B          Mirabella, V. A. and R. J. Farber, 1999. Relating Summer Ambient Particulate Sulfur, Sulfur Dioxide, and Light Scattering to Gaseous Tracer Emissions from the Mohave Power Project, accepted for publication in the Journal of the Air & Waste Management Association.

Appendix C          Koracin, D., Frye, J., and V. Isakov, 1999. A Method of Evaluating Atmospheric Models Using Tracer Measurements, accepted for publication in the Journal Of Applied Meteorology.

Appendix D          Karamchandani, P., Zhang, Y., and C. Seigneur, 1999. Simulation of Sulfate Formation in the Mohave Power Plant Plume. Report prepared for the Electric Power Research Institute, January.

Appendix E          Lowenthal, D., J.G. Watson, and P. Saxena, 1999. Contributions to Light Extinction During Project MOHAVE, submitted to Atmospheric Environment, September.

Appendix F          Vasconcelos, L. A. de P., Macias, E., McMurray, P. H., Turpin, B. J., and W. White, 1999. A Closure Study of Extinction Apportionment by Multiple Regression, submitted to Atmospheric Environment, July.

Appendix G          Project MOHAVE Final Report Independent Peer Review Comments.

Appendix H          ENSR Corporation, 1999. "Extent of Visual Impairment in California." Report prepared for Southern California Edison Company, June.

Appendix I            Santos, L., Sykes, R. I., Karamchandani, P., Seigneur, C., Lurmann, F., and R. Arndt, 1999: Second-order Puff Model with Aqueous-Phase Chemistry and Aerosols, Draft Final Report prepared for EPRI, SCE, and California Energy Commission. Santos, L. and R. I. Sykes, 1999: File Formats (Model Technical Documentation). Draft Final Report prepared for EPRI, SCE, and California Energy Commission.

Appendix J            Babich, P., Wang, P-Y., Allen, G., Sioutas, C. and P. Koutrakis, 1999: Development and Evaluation of a Continuous PM _2.5 Mass Monitor, submitted to Aerosol Science and Technology, July. Van Loy, M., Saxena, P., and Allan, M. A., 1999: Characteristics of PM _2.5, Sampling Method Intercomparison and Fine Particulate Composition at Six Urban Sites, Draft Final Report prepared for EPRI, SCE, and California Energy Commission, September.

Appendix K           Winhaze Visual Modeling Program and Project MOHAVE Images

List of Figures

Figure 1. Class I Areas in California, Nevada, Utah, and Arizona

Figure 2. Project MOHAVE Air quality monitoring network for measurement of aerosol composition and gaseous species

Figure 3. Topography of the Colorado River Valley

List of Tables

Table 1. Contributors to Project MOHAVE

Table 2. Timeline of PIER DMAT Project/Project MOHAVE

Table 3. Transport/Chemistry Results for Meadview, ROME Model

Table 4. Transport/Chemistry Results for Hopi Point, ROME Model

Table 5. Example results for PTL external-mixture model of SCAQS aerosol data