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Measurements of 22Na in the Atmosphere: Ground Level Activity Concentration Values from Wet and Dry Deposition Samples

“…One can argue that the comparison between the two methods should be made, more significantly, in terms of the activity concentrations C instead of the fluxes Φ. This is very easy to do: Taking into account Equation (3) the following equation (Equation (8)) can be obtained, allowing a direct calculation of the atmospheric activity concentration values fromhe deposition data: (8) in which for all data the average value v m = 0.04 m/s were used [16]. The activity concentration values calculated with Equation 8are then plotted for comparison in Figure 8.…”

“…The resulting water is then reduced by evaporation (90 • C) and brought to dryness. The residue is finally weighted, put in a little cylindrical jar (see Figure 2) and counted with hyperpure germanium detectors (HPGe) for 16 h. in which C is still the activity concentration, while vm is a mean deposition velocity experimentally evaluated after measuring simultaneously the deposition data (see Equation 2) and the corresponding activity concentration C in atmosphere [15,16]. In doing so we must bear in mind that the physical meaning of vm is quite different respect to that of vd: while vd is a mean velocity obtained averaging over the distribution of all the velocities of the settling particulate suspended in atmosphere, vm is not a real velocity, just an empirical parameter encompassing the effect of dry deposition and precipitation, and whose dimensions are those of a velocity.…”

“…In doing so we must bear in mind that the physical meaning of vm is quite different respect to that of vd: while vd is a mean velocity obtained averaging over the distribution of all the velocities of the settling particulate suspended in atmosphere, vm is not a real velocity, just an empirical parameter encompassing the effect of dry deposition and precipitation, and whose dimensions are those of a velocity. For that reason the numerical values of vm are much greater that those of vd, the latter being related only to the much slower dry deposition processes: experimental measurements performed on 137 Cs gave for vm a value around 0.04 m/s [16], while typical values of vd , strongly dependent on the particulate diameter and other factors as well [17], are typically in the range 0.1-0.001 cm/s. The experimental set up for the collection of the wet and dry deposition samples is a stainless steel tank placed on the roof of the laboratory building (see Figure 1).…”