Residence time of tropospheric aerosols in association with radioactive nuclides.

The residence time of atmospheric aerosol particles is a function of various removal processes, such as dry deposition by impaction, diffusion, sedimentation and resuspension as well as wet deposition by rain drops (precipitation scavenging). Estimation of the mean-residence time of atmospheric aerosols could be based on measurements of the activities and ratios of activities of cosmic-ray produced radionuclides, such as (7)Be and the radioactive decay products of radon-222 emanated from soil into the atmosphere, such as (210)Pb, (210)Bi and (210)Po. It was found that a mean value of about 8 days could be applied to aerosol particles in the lower atmosphere below precipitation cloud levels as resulted by the application of two different methods, i.e. the (7)Be-associated atmospheric aerosols and the radon decay product aerosols at two different locations, i.e. at Thessaloniki, Greece 40 degrees 38'N 22 degrees 58'E with dry (precipitation free) climate and at Oak Ridge, Tennessee, USA 35 degrees 58'N 84 degrees 17'W with high precipitation (wet climate), roughly at similar temperate latitudes, but the first one at East longitude and the other at West longitude, respectively.