Stratospheric and tropospheric components of ⁷Be in surface air

Abstract

7Be and 90Sr concentrations were measured simultaneously in samples from NASA's Global Atmospheric Sampling Program. The samples were collected from January 1978 through June 1979 at 9 to 12 km and between 11° and 60°N. 7Be concentrations ranged from 150 to 6900 fCi/m3, while 90Sr correspondingly varied from 10 to 320 fCi/m3. The average 7Be concentration in the samples collected in the lower stratosphere was 4500 fCi/m3. In the upper troposphere, 7Be concentrations were generally less than 1000 and often only a few hundred fCi/m3. In situ production of 7Be in the upper troposphere at ∼11 km was estimated at 340 fCi/m3. Since 90Sr is only present in the atmosphere because of nuclear testing, except immediately after such tests, 90Sr in the troposphere is due only to the subsidence of stratospheric air. Since atmospheric processes are not expected to alter 7Be/90Sr ratios during transport, surface 90Sr and stratospheric 7Be/90Sr ratios can be used to estimate 7Be transported from the stratosphere. Our analyses show that on an annual basis the stratosphere contributed ∼25% of the observed 7Be concentration. During spring and summer months, the stratospheric component can approach 40%, while on a daily basis this can be even larger.

Seasonality of ⁷Be concentrations in Europe and influence of tropopause height

“…Be from the upper troposphere to the middle and lower troposphere in the summer months (e.g. Feely et al, 1982Feely et al, , 1989. In addition, similarly to the findings for the annual means, the influence of latitude on 7…”

“…In fact, the exchange between stratosphere and troposphere is only about the 20 % of the total amount of 7 Be measured at surface level (Dutkiewicz and Husain, 1985). The analysis also highlighted the importance of local/regional/synoptic surface conditions on 7 Be activity concentrations.…”

Atmospheric Deposition of 7Be in the Southeast of China: A Case Study in Xiamen

“…Its deposition to the ground is usually influenced by latitude, sunspot numbers, and the intensity of geomagnetic field (Masarik et al, 1999;Nagai et al, 2000;Usoskin et al, 2008;Chao et al, 2012). Since the residence time of 7 Be in the stratosphere is much longer than its half-life (Turekian et al, 1983), 7 Be usually maintains in a nearly steady state with respect to its production and removal, resulting in a nearly constant content of 7 Be in the stratosphere (Dutkiewicz et al, 1985). 7 Be enters into the troposphere either through Brewer-Dobson circulation or through air mass exchange mainly in the mid-latitude regions during spring when the troposphere becomes thin (Kim et al, 1998).…”

Using beryllium-7 to assess cross-tropopause transport in global models

“…We examined the observational constraint from Dutkiewicz and Husain (1985) (DH85) on the stratospheric contribution to tropospheric 7 Be using the GMI modeling framework. DH85 analyzed the observed 7 Be / 90 Sr ratio, which suggests that 23-27 % of the 7 Be in surface air at northern mid-latitudes is of stratospheric origin.…”