This paper analyzes the political dimension of Miguel Masriera's (1901-1981) science popularization program. In the 1920s, Masriera worked at the Swiss Federal Institute of Technology (ETH) in Zurich - with Hermann Staudinger, the luminary of polymer chemistry - to later become a lecturer of theoretical and physical chemistry at the University of Barcelona. After living in exile in Paris, at the end of the Civil War he returned to Spain but never recovered his position. Instead, Masriera became an active popular science writer and adapted to the severe constraints of General Franco's military dictatorship (1939-1975). Inspired by the astronomer Arthur Eddington's world view, Masriera wrote and translated popular science books, and published articles in daily newspapers and journals. By examining Masriera's popular works, in particular his program for spreading "atomic culture" in Spain during the Cold War, this paper aims to contribute to the assessment of the role of science popularization in the domestic legitimization of that dictatorial regime and also its use as a vehicle for international recognition abroad. Copyright © Cambridge University Press.