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Executive Summary
Pages 1-18

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From page 1... ... has reported that visibility impairment caused by air pollution occurs in varying degrees at many park monitoring stations virtually all the time. Today, the average visual range in most of Me western United States, including national parks and wilderness areas, is 100-150 km (about 60-100 miles) Read the entire page →
From page 2... ... The Clean Air Act includes two emissions control programs specif~cally concerned with visibility in national parks and wilderness areas. One of these, the Prevention of Significant Deterioration (PSD) Read the entire page →
From page 3... ... Moreover, many sources of visibility impairment in national parks and wilderness areas are exempt from PSD requirements, because they are considered minor sources, or because they existed before the PSD program took effect in the 1970s. The other visibility protection program under the Clean Air Act requires states to establish measures to achieve "reasonable progress" towards the national visibility goal and to require the installation of the "best available retrofit technology" on large sources contributing to visibility impairment in mandatory Class ~ areas. Read the entire page →
From page 4... ... Emission-contro} measures already adopted or planned will not solve the nation's visibility problems. The acid rain control program established by the 1990 Clean Air Act Amendments has been predicted to reduce SO2 emissions in the East by about 36% by 2010. Read the entire page →
From page 5... ... It considers the regulatory and institutional frameworks for efforts to improve and protect visibility, including the Clean Air Act (Chapter 3~. This report also reviews the scientific understanding of haze formation and visibility impairment, including the meteorological and chemical processes responsible for the transport and Read the entire page →
From page 6... ... In discussing control techniques, the report describes the emissions reduction potential of various control measures and illustrates the translation of control measures into a rough prediction of effects on visibility (Chapter 6~. The report also considers policy implications of scientific knowledge about visibility and recommends approaches to remedy scientific and technical gaps that limit present understanding of source effects on visibility and the ability to evaluate control measures (Chapter 74. Read the entire page →
From page 7... ... Because haze is caused by the combined effects of the emissions of many sources, it would be an extremely time-consuming and expensive undertaking to try to determine, one source at a time, the percent contribution of each source to haze. For instance, the efforts to trace the contribution of the Navajo Generating Station to haze in the Grand Canyon National Park took several years and cost millions of dollars without leading to quantitatively definitive answers. Read the entire page →
From page 8... ... � Hybrid combinations of chemical mass balance receptor models with a different source-oriented secondary particulate mass formation model, and used with empirical data for pollutant scattering and absorption efficiencies. Receptor models are models that infer source contributions by characterizing atmospheric aerosol samples, often using chemical elements or compounds in those samples to identify emissions from particular source types. Read the entire page →
From page 9... ... For complex applications that require the greatest sophistication, the most advanced reactive plume models available should be used with measured data on particle properties in such plumes and should be accompanied by an adequate treatment of background pollutants. To assess new single sources, the most advanced reactive plume models available should be used with measured data on particle properties in the plumes of similar sources and accompanied by an adequate treatment of background pollutants. Read the entire page →
From page 10... ... In We East, sulfates derived from SO2 emissions from coal-fired power plants account for about one-half of all anthropogenic light extinction. Reductions in these emissions are expected to occur in the next two decades as a result of the 1990 Clean Air Act Amendments' acid rain control program. Read the entire page →
From page 11... ... RECOMMENDED RESEARCH The committee addressed the need to alleviate scientific and technical gaps in He areas of visibility and aerosol monitoring and measurement, source apportionment, and emissions control technology. The committee considered what measures might be taken to understand beKer the sources of haze, possible means of reducing emissions from those sources, and alternative ways of preventing future visibility impairment in Class areas. Read the entire page →
From page 12... ... In particular, information is needed about the potential of new sources to reduce visibility in Class ~ areas and about the effects on such areas of the new emissions trading programs of the 1990 Clean Air Act Amendments. EPA's current visibility-screening mode! Read the entire page →
From page 13... ... Measurement Methods Current measurement methods permit reasonable estimates of the average contributions of major aerosol constituents to atmospheric visibility impairment. However, several aerosol measurement methods need to be developed or improved for the following: � Accurate measurement of organic and elemental carbon particles, especially at low concentrations; � Routine measurement of the water content of airborne particles; � Measuring particle size distributions; � Continuous measurement of sulfates, organics, elemental carbon, nitrates, and elemental composition; � Solar- and battery-powered measurement for use in remote areas. Read the entire page →
From page 14... ... Instrumentation for continuous measurements of particle absorption coeff~cients should be developed. Source-Apportionment Modeling Source-apportionment models require better input data on source emissions, along with unified procedures for testing individual sources. Read the entire page →
From page 15... ... FUTURE DIRECTIONS FOR PROTECTING AND IMPROVING VISIBILITY Present scientific knowledge has important implications for the design of programs to protect and improve visibility. What is needed, overall, is the recognition that any effective visibility protection program must be Read the entire page →
From page 16... ... Such a program would mark a considerable break from the present approach of focusing on visible plumes from nearby sources and of attempting to determine the effects of individual sources on visibility impairment. Although visibility impairment is as well understood as any other air pollution effect, gaps in knowledge remain. Read the entire page →
From page 17... ... Proto~1ng V1s~1 N~1on~ Pa~ slid ~ldemess gems Read the entire page →

From page 1...

... has reported that visibility impairment caused by air pollution occurs in varying degrees at many park monitoring stations virtually all the time. Today, the average visual range in most of Me western United States, including national parks and wilderness areas, is 100-150 km (about 60-100 miles)

Executive Summary Pages 1-18

Executive Summary
Pages 1-18