Atmospheric depositional fluxes of ⁷Be and ²¹⁰Pb at Galveston and College Station, Texas

The bulk depositional fluxes of 210 Pb and 7 Be were measured at a coastal (Galveston) and an inland (College Station) station for about 3 years, between 1989 and 1991. The annual depositional fluxes of 7 Be and 210 Pb at Galveston during this period varied by a factor of about 2.5, between 8.9 and 23.2 disintegrations per minute (dpm) cm −2 yr −1 , with a mean of 14.7 dpm cm −2 yr −1 for 7 Be, and 0.67 and 1.71 dpm cm −2 yr −1 , with a mean of 1.03 dpm cm −2 yr −1 for 210 Pb, respectively. The precipitation‐normalized 7 Be flux increases with increasing amount of precipitation. There is no systematic and consistent seasonal trend in the depositional fluxes for 7 Be or for 210 Pb. The volume‐weighted 210 Pb concentrations, when normalized to the amount of precipitation, seem to be constant over the time period of this study. Four to six heavy rain events (> 5 cm) in a single day account for 20–30% of the annual deposition of 7 Be and 210 Pb. Such events account, however, for only about 4–6% of the total number of rainy days in a year. The dry depositional fluxes of these nuclides appear to be a significant fraction of the bulk depositional flux only during the months when there is very little rain. The fraction of dry to total depositional flux of 210 Pb appears to be higher than that of 7 Be. The strong positive correlation between 7 Be and 210 Pb depositional fluxes indicates that the flux of both nuclides is controlled by scavenging processes by local precipitation. This correlation also indicates that a major portion of the air masses that brings precipitation to Galveston and College Station is of continental origin. Our data therefore suggest that 7 Be and 210 Pb cannot be used as independent atmospheric tracers in our coastal station. This observation is consistent with those observed at many other continental and coastal stations.