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

Abstract

Radioactive elements of various origins (⁷Be, ³²P, ⁹⁰Sr, ²¹⁰Pb, ²¹⁰Po) 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 ⁹⁰Sr, the periodical variation connected with the exchanges between the stratosphere and the troposphere is confirmed, but it is shown that the increase recorded for ⁷Be and ³²P 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. In the case of 210Pb, moreover, the origin of the air mass must be taken into account. The ⁹⁰Sr/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 ⁷Be/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 210Po/210Pb 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 A1 (air-layer between 2 and 6 km), to values of about 1/30 to 1/40 d?1. Lastly, studies by simulation on models confirm the influence of the processes of precipitation scavenging and vertical exchanges.DOI: 10.1111/j.2153-3490.1974.tb01616.x