market for chemicals based on coal is not likely to develop until it becomes practical to produce gaseous and liquid fuels from coal.

Coals have a variety of other specialized uses, most of them low-volume applications. For example, anthracites can be used as filter material for tertiary water treatment processes. Lignites have some ion-exchange behavior and can be used in some cases as inexpensive ion-exchange ''resins." These applications include wastewater treatment (e.g., the removal of chromium from electroplating wastes) and the concentration of ions, such as gold, in hydrometallurgy. Lignites can also be converted into so-called humic acids, which are useful soil amendments and can be nitrated to form fertilizers. There is also interest in converting coals, particularly those of high carbon content, into carbon-based materials, such as graphites. Most of the R&D on these niche applications is taking place outside the United States. At the present time, no significant domestic markets for these applications are anticipated during the period addressed in this study.

Environmental concerns will have the greatest influence on future coal use for power generation in the industrialized countries (IEA, 1993b). In the United States, coal-fired power plants are already subject to a range of emission controls that will likely become increasingly stringent and wide ranging over the periods addressed by this study. Current and possible regulations governing emissions from coal-fired power plants are summarized below, along with information on the current status of control technologies. Appendix D reviews recent trends in U.S. regulatory policy and technology approaches to address environmental issues. Emissions control technologies are discussed in more detail in Chapter 7.

National ambient air quality standards for particulate matter, sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and photochemical ozone were promulgated under the 1970 Clean Air Act to protect human health and welfare throughout the country.¹¹ The primary drivers of technology innovation to control air quality over the past two decades have been pollutant-specific emission standards for new and existing air pollution sources, together with the ambient air quality standards, both promulgated by federal and state governments.

In contrast to ambient air quality standards, aimed at protecting human health, acid deposition regulations guard against cultural and ecological concerns, including damage to aquatic systems, forests, visibility, and materials. Anticipation of acid rain controls was the main factor motivating SO₂ and nitrogen oxides