Stoyanov, Stiliyan, and Margarita Filipova. “RESEARCH OF THE VARIATIONS OF THE ATMOSPHERIC OZONE AND CHANGE OF THE ULTRAVIOLET SUN RADIATION OVER NORTHEASTERN BULGARIA”. JOURNAL SCIENTIFIC AND APPLIED RESEARCH 2, no. 1 (March 4, 2023): 90–93. Accessed November 7, 2024. https://jsar.ftn.shu.bg/index.php/jsar/article/view/48.