Terrestrial Dust Samples
Although our primary reason for collecting dust in the stratosphere has been to supply researchers with interplanetary dust, we have always recognized that we also collect a significant amount of terrestrial dust. While this terrestrial material, principally wind-blown dust, volcanic ash and aerosols, and re-entering spacecraft debris particulates, has held little interest for most interplanetary dust workers, we realize that to other scientists this material is an important resource. We therefore invite requests for terrestrial dust from qualified workers, employing the same request guidelines as for stratospheric dust samples.
NASA has been collecting dust in the stratosphere since the beginning of 1981, employing U-2, ER-2 and WB-57 aircraft. These flights have ranged over most of the USA (as far north as Alaska) and Central America. We typically fly several collectors at a time on any particular aircraft. However, in the succeeding years full-scale particle collection has been suspended during periods of heavy volcanic particulate and aerosol content of the stratosphere. During these latter periods we have flown only one or two collectors at a time on the aircraft. Nevertheless, these particular collectors carry a record of the volcanic emissions present in the stratosphere following major eruptions.
Since 1981 the following volcanic eruptions are known to have placed material directly into the stratosphere: El Chichon (March 1982), Nevado del Ruiz (Nov. 1985), Mt. Augustine (March 1986), and Mt. Pinatubo (June 1991). After each of these eruptions we have noted the presence of (generally) submicrometer-sized ash particles and aerosol droplets on collectors, although we cannot always be certain of the identity of the volcano responsible for the material. For example, collectors from March 1981 contain abundant silicic volcanic ash although no volcanic eruption was known to have directly penetrated the stratosphere (Zolensky and Mackinnon, J. Geophysical Research 90, No. D3, pp 5801-5808, 1985). In addition, we have noted the presence of coarse-grained (less than or equal to 25 microns) volcanic ash on collectors with samples from August 1989 to April 1990, which cannot have been derived from any of the aforementioned eruptions.
At present volcanic materials are still contained within silicone oil (polydimethylsiloxane) on the original collectors. We have noted a tendency for the liquid aerosols (presumably sulfuric acid, predominantly) to crystallize over time in the oil.