A SEARCH FOR THE SEASONAL VARIABILITY ON THE DEPOSITIONAL FLUXES OF BE-7 AND PB-210

Investigations of the atmospheric fallout of Be-7 and Pb-210 in many p laces around the globe indicate that there are seasonal variations on the depositional fluxes of these nuclides: high in winter in a few pla ces, while in most places the high occurs in spring. However, these ea rlier studies did not address quantitatively the corresponding seasona l variations of the amount of precipitation during these periods. Data on the depositional fluxes of Be-7 and Pb-210 in Galveston, Texas, du ring the years 1989-1991 indicate that the seasonal variation is not u niform from year to year, and the amount of precipitation primarily co ntrols the depositional fluxes. All the recently published data on the depositional fluxes of these radionuclides to date are synthesized, A lso, the seasonal variations of the depositional fluxes of Be-7 and Pb -210 due to the variations in the amounts of precipitation during, the se seasons are discussed This study clearly shows that the depositiona l fluxes of Be-7 and Pb-210 during fall were minimum, and most of the time the fallout maxima were confined to either spring and/or summer. Interseasonal variations of the depositional fluxes of these nuclides do not remain the same. The data presented in this paper in conjunctio n with earlier published data seem to indicate that the observed seaso nal increase in the depositional fluxes of Be-7 during spring is not d ue to the troposphere-stratosphere exchange of air masses during that season. The Be-7/Pb-210 activity ratio values remain the highest in su mmer and this is attributed to the increased rate of vertical transpor t of Be-7 (from the upper troposphere to the middle and lower troposph ere) and Pb-210 (from the lower troposphere to upper troposphere) due to decreased stability of the troposphere during summer months.