Concentration measurements of 7Be and 137Cs in ground level air in the Belgrade City area

Concentrations of 7Be and 137Cs in ground level air in the city area (Belgrade, central Serbia) were determined in the period from 1991–1996. The average monthly concentrations of 7Be in ground level air were in the range of 2–7 mBq/m3 with pronounced one or two maxima in summer or early fall and a minimum in winter. The average air concentrations for 137Cs were from 0.5–8.5 × 10−5 Bq/m3, with a spread maximum in the spring-summer period and a pronounced maximum during the winter. A general increase in 7Be and 137Cs concentrations during 1993 was recorded. The maximum seasonal indices were 1.3 for 7Be (summers) and 2.7 (late springs and early summers) and 3.4 (winters) for 137Cs. No correlation with the amount of precipitation and 137Cs concentrations in air was determined, while the washout effect of rainfalls seems to be more closely related with variations in 7Be concentrations