Problems due to air pollution are not limited to the territory of one country, but affect or may affect other neighbouring countries. In Spain, the concern about environmental pollution as a consequence of emissions from cars and industries officially began in 1972 with Law 38/1972 on the protection of the atmospheric environment; as a result of this Law, the "characteristics, qualities and conditions of use of fuels" were officially defined and limited for the first time: Decree 2204/1975. Translated with www.DeepL.com/Translator