Mathematics – Probability
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.583s&link_type=abstract
Meteoritics, vol. 30, no. 5, page 583
Mathematics
Probability
3
Bromine, Elements, Volatile, Interplanetary Dust Particles, Stratosphere, Tof-Sims
Scientific paper
Volatile element enrichments compared to CI abundances in stratospheric interplanetary dust particles especially for Br have been interpreted as due to atmospheric contamination processes [1] or, less substantiated, as being indicative for a new type of chondritic material [2, 3]. Although only little is known about the actual Br concentration in the stratosphere, it is well accepted that halogens play an important role in stratospheric chemistry and therefore contamination processes have to be excluded before a Br-rich chondritic parent body can be speculated on. The analysis of the lateral distribution of halogens in IDPs with high-resolution imaging TOF-SIMS (time-of-flight secondary-ion-mass-spectrometry) [4] may help to solve the controversy about the ubiquity of Br in stratospheric IDPs. Besides controversially discussed theoretical models which try to test correlations between Br-content and stratospheric residence time or surface areas [5, 6, 7], first observational hints for halogen contamination of at least two chondritic IDPs were found for W7029E5, where Br- salt nanocrystals of presumably atmospheric origin were observed [5], and for L2006G1, which showed a halogen-rich exterior rim [8]. TOF-SIMS with its extremely high surface sensitivity -- the information depth is in the order of a few atomic monolayers -- seems to be suitable for a systematic search for surface correlated halogens in IDPs. Although, in general, plane surfaces are required for TOF-SIMS measurements, particle analysis is possible with this technique [9], though quantification is highly complicated due to topographic effects on secondary ion production and detection probability. We analyzed five stratospheric particles from small area collector U2071 which were previously investigated with SEM-EDX [10]. Silicone oil on the surfaces of some particles could still be detected with TOF-SIMS, even after extensive hexane rinsing. In three cases (chondritic particles U2071B7a, F3, and H1a) this suppresses the detection of most elements including the halogens. For U2071B6, another chondritic particle, neither silicone oil nor halogens were detected. U2071D1, a non-chondritic, particle of so far unidentified origin with high Ca, Si, and C (22, 11, and 11 wt.-%, respectively), was selected for this analysis because on the dust collector several aerosol droplets were found to be attached to the particle. These droplets were removed during particle transfer and subsequent extensive hexane rinsing. Nevertheless, on the remaining surface of U2071D1 halogens were indubitably detected. Rough estimates show F:Cl:Br secondary ion ratios of 40:60:1, cum grano salis, comparable with stratospheric element ratios [4]. The results suggest that surface contamination with halogen-containing aerosols may cause at least in part the observed Br-enrichments for IDPs. Even the lack of evidence for surface correlated halogens for some IDPs does not imply an extraterrestrial origin of their Br [4]. Chemical reactions between fine-grained porous IDPs and aerosols can highly influence especially the trace element content not only on the outer surface but also of inner portions [4]. References: [1] Jessberger E. K. et al. (1992) EPSL, 112, 91-99. [2] Flynn G. J. and Sutton S. R. (1992) LPS XXIII, 373-374. [3] Flynn G. J. et al. (1993) LPS XXIV, 495-496. [4] Stephan T. et al. (1994) EPSL, 128, 453-467. [5] Rietmeijer F. J. M. (1993) JGR, 98, E7409-E7414. [6] Bohsung J. et al. (1994) LPS XXV, 139-140. [7] Bohsung J. et al. (1995) JGR, 100, E7549-E7550. [8] Stephan T. et al. (1994) LPS XXV, 1341-1342. [9] Zehnpfenning J. et al. (1994) SIMS IX, 453-456, Wiley. [10] Stephan T. et al. (1994) Meteoritics, 29, 536-537.
Jessberger Elmar K.
Rost Detlef
Stephan Thomas
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