This article analyzes the ways in which identical and divergent perceptions of the carcinogenicity of diesel-engine emissions emerged in the United States and West Germany between 1970 and 1990. Therefore, it reviews how automakers, policymakers, experts, and the media negotiated which exhaust emissions were either eco-friendly or hazardous. Communicating complex technological and scientific facts to the public, these actors translated the information into easily comprehensible terms. In the United States, this simplification forged the perception that diesel cars’ particulate emissions were cancer-causing between 1977 and 1981; a similar change occurred in Germany between 1984 and 1987. Consumers reacted and shied away from purchasing diesel vehicles. While Americans continued to stigmatize diesel cars, Germans re-embraced the technology by the late 1980s. Consequently, new “clean” diesels were introduced, and the discourse on exhaust emissions shifted from health-hazardous particulates to the ecological problem of the greenhouse effect, casting the fuel-efficient diesel in an entirely new light.

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This article traces the different classifications of diesel emissions either as “safe” or as “hazardous” in the US and in West Germany between 1977 and 1995. It argues that the environmental regulation of diesel emissions was a political threshold. It contributes to our general understanding of how politicians, environmental lobbyists, scientists, and engineers constructed the standards and norms that defined the “safe” limit of environmental pollutants. After discussing how diesel emissions came under review as a potential carcinogen, I will show that the coding as “safe” or as “hazardous” resulted from negotiations that were entirely dependent on the temporal, geographical, and intellectual contexts in which diesel technology, scientific research on their emissions, and political regulation were embedded. In particular, I trace the differences in German and US regulatory policy. While US regulation relied more on epidemiology that provided only weak data on the carcinogenicity of diesel particulates in the early 1980s, German government agencies tended to base their policy around the mid-1980s more on the results of animal tests and shortly afterwards also on epidemiology. Furthermore, the article reveals how US and German automakers tried to foster doubt on the carcinogenicity of diesel emissions and how their approaches differed and shifted. Thereby, it sheds light on the triangular relationship between technology, science, and politics in regulatory processes by analyzing the different roles of the state, automakers, scientists, and environmental agencies in Germany and in the United States.

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