Variation des concentrations et caracteristiques physiques des noyaux d'aitken dans un site non pollue

Advantages of the use of radioactive tracers222Rn and212Pb for the study of aitken nuclei within the lower troposphere

“…Sources that are very intense and localized (e.g., industrial or urban polluted areas) but few in number would show distribution profiles that differ from those of 2•2pb. This find complies with what we have observed by comparing at ground level on a nonpolluted site the variations of nucleus and radon concentrations [Lopez et al, 1973]. This will be defined further in a separate work in which the relative importance of the various sources of Aitken nuclei in our sample areas will be discussed [Lopez et al.…”

“…This hypothesis is probably true within the lower layers, since it corresponds, to a large extent, to coagulation. In the case of the profiles obtained at a distance of l O0 km from the coast, that is to say, profiles whose vertical concentration gradients in the mixing layer are low, it may be said that the ratio of the mean concentrations ( [Lopez et at., 1973[Lopez et at., , 1974.…”

“…In fact the phenomenon of disappearance is more complex than the one represented by (1), the granulometric spectrum being polydispersed. The mean radius of these particles increases during the night [Lopez et al, 1973], and models indicate that polydispersion. should decrease during the same time period [Whitby et al, 1972].…”

“…•x•Pb, the intensity of the nocturnal source at near ground level being weaker at night[Lopez et al, 1973].At 1200 m the flux of nuclei into free atmosphere can be expressed in the form= where K•z• is the vertical exchange coefficient at 1200 m of the order of I m • s -x, determined with the aid of the ThB, and dC/dz is the concentration gradient at 1200 m.At this level the mean nucleus flux measured at nighttime is less than 1000 particles cm -• s -x, i.e., a maximum of 4.3 X 107 nuclei cm -• passing into free atmosphere during the night. This value corresponds to 1/10 of the total quantity contained in the layer 400-1200 m (4.6 X 108 nuclei for a cross-sectional column area of I cm•).…”