Etude des variations des ⁷Be, ³²P, ⁹⁰Sr, ²¹⁰Pb et ²¹⁰Po dans la troposphére

Abstract

Radioactive elements of various origins (?Be, 32P, SOSr, ZlOPb, W?o) have been measured at Toulouse in South-Western France, for several years (1965 to 1969) in ground-level air with samplings of short duration (1 to 4 days), as well as in precipitations and air in altitude. The study of results shows the very important influence of precipitation scavenging processes upon the variations of activity. As concerns QOSr, the periodical variation connected with the exchanges between the stratosphere and the troposphere is confirmed, but it is shown that the increase recorded for ?Be and szP in spring and summer, in ground-level air, is due to the variation in the precipitation scavenging processes and not to contributions from the stratosphere. I n the case of *lOPb, moreover, the origin of the air mass must be taken into account. The QoSr/7Be ratio, allowing to eliminate the influence of scavenging, is quite suitable to characterize the air coming from the stratosphere, but no evidence is found, in ground-level air, of any relation with the possibilities of downward influx from the stratosphere. As concerns the ?Be/32P ratio, the results show the existence of a seasonal variation (maximum in winter) likely due to vertical exchange processes. An important discrepancy is noticed between the theoretical and experimental values of this ratio. The results obtained at Toulouse are in good accordance with those found at the same latitude, but a comparison between the measurements obtained in various stations tends to prove that the vertical exchanges are decreasing in summer above the oceans. The vertical distribution of the zlOPo/zlOPb ratio, deduced from the measurements in precipitations, leads, for the vertical exchange coefficient Kz, to values of about 3 to 6 m2/s, and for the scavenging coefficient hl (air-layer between 2 and 6 km), to values of about 1/30 to 1/40 d-l. Lastly, studies by simuIation on models confirm the influence of the processes of precipitation scavenging and vertical exchanges.

Reconstruction of 137Cs signal in Cuba using 7Be as tracer of vertical transport processes in the atmosphere

“…5). The estimated 137 Cs values in aerosols for Cienfuegos are in agreement with those reported (Larsen et al, 1995) in Puerto Rico (1970-1974), the Bahamas (1968-1972), Panama (1965-1967) and Hawaii (1970-1994. The highest levels, 3.7 mBq m -3 , were estimated for 1963, coinciding with the period of most intense atmospheric deposition from nuclear weapon tests.…”

“…The seasonal behavior of 7 Be depends on many factors, not fully studied yet, the transfer mechanism in the tropopause and the regional weather conditions being the most important ones for its variability (Marenco and Fontan, 1974).…”

Climatology of tropospheric ozone in southern Europe and its relation to potential vorticity

“…The authors analyzed tropopause foldings, considered by them to be the most effective mechanism of stratosphere-troposphere exchange, and the deposition of radioactive debris of stratospheric origin at the ground. It was pointed out that surface Sr 9ø concentrations depend partly also on scavenging processes in water droplets, removing Sr 9ø from the atmosphere [Staley, 1982;Marenco and Fontan, 1974]. Compared to the seasonal variation of the high PV-class, Danielsen and Mohnen's estimation shows a phase shift toward earlier in spring.…”

“…To compare the seasonal variation of the high PV-class at the 500-hPa level with that of the cross-troposphere ozone flux, no phase shift was accounted for, as stratospheric intrusions descend often down to the middle troposphere, [e.g., Viezee et al, 1983;Ancellet et al, 1991]. This ratio is maximum in May/June [Marenco and Fontan, 1974] I I I I I I I I I I I I I [Levy et al, 1985]. The seasonal variation of Sr 9ø concentrations at ground recorded in southwestern France during 1967-1969 (Figure 7) [Marenco, 1986] should be more representative for the OHP than Danielsen and Mohnen's [1977] hemispheric estimation and shows a seasonal maximum in June.…”

The relative concentrations of radon daughter products in surface air and the significance of their ratios

“…We h. ave applied these models to the case of stable elements prod?ed continuously at various altitudes in the troposphere an4 also to the case o• the radioactive elements generally considered. It is possibl• to assess the global conditions for largerscale scavenging and vertical exchanges by comparing the theo,retical and experimental results of the vertical distributions of activities and activity ratios [Marerico and Fortran, 1974a;Marenco, 1974]. We find that, under these conditions, the residence time of stable aerosols (0.3 •t) produced continuously in the troposphere varies, theoretically, between 18 and 96 days according to their production altitude between the ground and the tropopause.…”