“The Principles of Sustainable Development and the Possibilities of Limiting the Global Effects of Smog by Medium-Sized Cities Located in the European Union on the Example of Mikołów (Poland) and Żylina (Slovakia)”. Problemy Ekorozwoju , vol. 15, no. 2, July 2020, pp. 111-9, https://doi.org/10.35784/pe.2020.2.12.