This thesis reinterprets the history of railways and steam traction through the lens of air pollution between the 1820s and 1960s, using a comparative approach between France and Great Britain. By shifting the focus from steam to smoke, it not only provides a new example of the social and environmental damages caused by industrialization in the 19th and 20th centuries, but also demonstrates how air pollution can influence the development of a technical system. Drawing on the sensitivities expressed by local residents, passengers, and workers, the study explores how this pollution perceivable by sight and smell shaped the representations of railways and the railway environment itself. These perceptions were subject to various biases that led to the underestimation of locomotive smoke and delayed the evolution of its framing from the local to the national level and from a local nuisance to a public health problem. Among these biases were the familiarity of smoke, its dispersion, and its seemingly mobile nature, despite its concentration around stationary industrial facilities. The comparative approach reveals both common patterns and cultural differences in attitudes toward coal, steam, and smoke in France and Great Britain. It shows that the British context was more conducive to recognizing the railways' contribution to air pollution and framing it as a public issue. Following a chronological and thematic structure, the thesis first examines how negative perceptions of coal smoke immediately constrained the integration of mobile engines into the living environment during industrialization. Railway operators responded with a strategy of acclimatisation to the technology, based, on the one hand, on the enchantment of steam traction and the discredit of critics and, on the other hand, on various technical and environmental compromises and adjustments. However, the increasing use of smoky coal fuels in order to achieve economies of scale undermined this strategy, leading to an increase in tensions on and around railways, and to the image of the "smoke locomotive". By the late 19th century, the development of alternatives to steam traction in urban areas challenged the steam locomotive's status as a symbol of modernity and contributed to its disenchantment. In particular, the advent of electricity intensified demands for railway smoke abatement. In the 20th century, amid growing competition, railway operators and decision-makers became increasingly aware of public demand for cleaner transport and the economic costs of pollution. This awareness drove the transition from steam to oil and electricity. Finally, the thesis analyzes how the rail industry reframed its image by embracing modernization and promoting itself as a clean and environmentally friendly mode of transport, transforming the stigma of dirtiness into a narrative of ecological responsibility.