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FIGURE 2-10 Comparison of growth areas and air pollution emissions, 1970-2004. US air quality has improved despite increases in gross domestic product, vehicle miles traveled, and energy consumption since the 1970s.

SOURCE: US Environmental Protection Agency. Air Emissions Trends—Continued Progress Through 2004. Available at:

have resulted in vastly reduced emissions and improved air quality (Figure 2-10). Parallel advances in petroleum refining and the adoption and improvement of catalytic converters increased engine efficiency and removed harmful byproducts from the combustion process. Those achievements have reduced overall automobile emissions by 31%, and carbon monoxide emissions per automobile are 85% lower than in the 1970s.29


In the early 1920s, scientists began working on nontoxic, nonflammable replacements for ammonia and other toxic refrigerants then in use. In 1928, Frigidaire synthesized the world’s first chlorofluorocarbon (CFC), trademarked as Freon. By the 1970s, however, it had become clear that CFCs contribute to losses in the atmosphere’s protective layer of ozone. In


National Energy Policy Development Group. National Energy Policy. Washington, DC: US Government Printing Office, May 2001.

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