K. G. Snetsinger

Physical and optical properties of the Pinatubo volcanic aerosol: Aircraft observations with impactors and a Sun-tracking photometer

As determined in situ by impactor samplers flown on an ER-2 at 16.5- to 20.7-km pressure altitude and on a DC-8 at 9.5- to 12.6-km pressure altitudes, the 1991 Pinatubo volcanic eruption increased the particle surface area of stratospheric aerosols up to 50-fold and the particle volume up to 2 orders of magnitude. Particle composition was typical of a sulfuric acid-water mixture at ER-2 altitudes. Ash particles coated with sulfuric acid comprised a significant fraction of aerosol at DC-8 altitudes. Mie-computed light extinction increased up to 20-fold at midvisible and greater than 100-fold at near-IR wavelengths. The optical thickness measured through the aerosol layer by an autotracking Sun photometer aboard a DC-8 aircraft at 10.7- to 11.3-km pressure altitudes shows a spectral shape that is similar to the Mie-calculated spectral extinction at ER-2 altitudes. Surface area distributions calculated by inversion of spectral optical depth measurements show characteristics that are similar to the mean surface area distribution resulting from 35 in situ measurements.

Black carbon (soot) aerosol in the lower stratosphere and upper troposphere

As determined by impactor samplers flown on ER-2 and DC-8 aircraft, black carbon aerosol (BCA) mass loadings in the stratosphere average 0.6 nanograms per standard cubic meter, or 0.01% of the total aerosol. Upper tropospheric BCA increases to 0.3%. Low stratospheric concentration is commensurate with present commercial air traffic fuel consumption, given the following assumptions: the BCA emissions are 0.1 grams per kilogram of fuel consumed, 10% of route mileage is above the tropopause, and average BCA stratospheric residence time is about one year. Taking BCA into account, the stratospheric single scatter albedo is ≈0.99. Using parameters for planned supersonic commercial aircraft, whose emissions will be predominantly in the stratosphere, we show that such traffic will double stratospheric BCA concentration. This would reduce the aerosol single scattering albedo by one percent, and double the BCA surface area that is available for heterogeneous chemistry.

Evolution of Pinatubo aerosol near 19 km altitude over western North America

Stratospheric aerosols, collected near 19 km altitude on wire impactors over western North America from August 20, 1991 to May 11, 1993, show strong influence of the June 1991 Mt. Pinatubo eruption. Lognormal size distributions are bimodal; each of the mode radii increases and reaches maximum value at about 15 months after eruption. The second (large particle) mode becomes well developed then, and about 40% of the droplets are larger than 0.4 {mu} radius. The eruption of Mt. Spurr (Alaska) may also have contributed to this. Sulfate mass loading decays exponentially (e-folding 216 days), similar to El Chichon. Silicates are present in samples only immediately after eruptions. Two years after eruption, sulfate mass loading is about 0.4 {mu}g/m{sup 3}, about an order of magnitude higher than background pre-volcanic values. Aerosol size distributions are still bimodal with a very well-defined large droplet mode. 25 refs., 3 figs., 1 tab.

A case of Type I polar stratospheric cloud formation by heterogeneous nucleation

The NASA ER-2 aircraft flew on January 24, 1989, from Stavanger to Spitsbergen, Norway, at the 430–440 K potential temperature surface (19.2–19.8 km pressure altitude). Aerosols were sampled continuously by an optical particle counter (PMS-FSSP300) for concentration and size analyses, and during five 10-min intervals by four wire and one replicator impactor for concentration, size, composition, and phase analyses. During sampling, the air saturation of H2O with respect to ice changed from 20% to 100%, and of HNO3 with respect to nitric acid trihydrate (NAT) from subaturation to supersaturation. Data from both instruments indicate a condensation of hydrochloric acid and, later, nitric acid on the background aerosol particles as the ambient temperature decreases along the flight track. This heterogeneous nucleation mechanism generates type I polar stratospheric cloud particles of 10-fold enhanced optical depth, which could play a role in stratospheric ozone depletion.

Niningerite: A New Meteoritic Sulfide

Niningerite, a new meteoritic sulfide ranging in composition from (Fe0.19Mg0.66Mn0.14Ca0.007Cr0.002)S to (Fe0.52Mg0.33Mn0.06Ca0.06Cr0.03Zn0.004)S, from the type-I enstatite chondrites Abee, Saint Sauveur, Adhi-Kot, Indarch, St. Marks, and Kota-Kota, is described. It is named in honor of H. H. Nininger.

Calibration correction of an active scattering spectrometer probe to account for refractive index of stratospheric aerosols : comparison of results with inertial impaction

Real-time particle size spectra are being acquired on our research aircraft with relative ease and speed by techniques that make use of the real-time interaction of laser light with aerosols and cloud droplets. The results are, however, sometimes ambiguous, because the optical “signatures” of the particles depend on their refractive indices in addition to physical dimensions. The calibration supplied by the manufacturer is based on instrument response to a specific test aerosol, e.g., latex spheres (refractive index = 1.59). Such a calibration is strictly valid only for sample aerosols of refractive index and shape similar to the test aerosol. Whenever the sample aerosol differs from the test aerosol, a calibration correction is in order. Of concern here is the use of an active scattering spectrometer probe (ASAS-X), to measure sulfuric acid aerosols on high-flying U-2 and ER-2 research aircraft. Correcting the calibration of the ASAS-X for dilute sulfuric acid droplets (refractive index = 1.44) that pred...

Soot in the stratosphere: The impact of current and HSCT aircraft emissions

One of the trace components of emissions from aircraft engines and other combustion sources are soot particles. These particles are strongly absorbing in the visible and IR spectra, may act as condensation nuclei, and may provide a large surface area for the catalytic promotion of gas-phase chemical reactions. Soot if found throughout the troposphere, even at remote locations, and also in the stratosphere. Present techniques do not allow an unambiguous identification of the sources. This paper discusses the emission of soot from existing and proposed aircraft and the contribution of this soot to concentrations observed in the troposphere and stratosphere. We consider the implications of these emissions for issues in stratospheric physics and chemistry. 11 refs.

Effects of El Chichon volcanic effluents on stratospheric aerosol dynamics

The effects of El Chichons April 1982 eruption on stratospheric aerosol dynamics are presently discussed in terms of log-normal size distributions over 15-20 km sample altitudes between 30 and 45 deg N over the contiguous U.S. After collection, samples were studied by SEM, and log-normal size distributions were fitted to the data-points obtained. It is found that stratospheric aerosol behavior is explainable by the laws of aerosol mechanics more easily than has been the case for tropospheric aerosol, for which the source-sink relationship is much more complex.