Stratospheric particles

At the end of the fifties a program was started in the U.S. A. to study stratospheric aerosol particles. The results of the program were analyzed by Junge and his associates (see Junge, 1963). The most important achievement of this study was the discovery of an aerosol layer between 15-20 km consisting mostly of large particles (see Subsection 4.3.3). 

To investigate their chemical composition, stratospheric particles were collected by aircraft- and balloon-borne impactors. Elements with atomic numbers of 12-30 were identified in the samples by electron microprobe and X-ray fluorescence techniques. Table 24 summarizes the results obtained (Junge, 1963). In this table the sulfur is given as sulfate since further wet chemical analyses showed that the sulfur occurred as sulfate particles. In can be seen from the data tabulated that 89 % of the mass of the components identified is sulfate. Data also indicate that the quantity of NH4 is sufficient only to neutralize about one third of the sulfate ions. Further flights carried out over a wide range of latitudes (60° S-70° N) demonstrated that this sulfate layer can be observed everywhere in the stratosphere. 

About ten years later a new stratospheric aerosol program was performed. In this case, particles were collected between 17 and 28 km by absolute filters having a collection efficiency of virtually 100 % in all size ranges. Table 25 gives the results of a sampling day when particles were collected at an altitude of 18 km. It the last column of the table the percentage of sulfate ions possibly neutralized by NH4 is also presented. It can be seen that the concentrations measured by this more recent 

16 According to Jaenicke (1978) in the Aitken size range 25 % of particles consists of organic materials under tropospheric background conditions. 

Chemical composition of stratospheric aerosol particles (Junge, 1963) 

---

For example, modeling studies by Weisenstein et al. (1996) predict that the surface area of stratospheric particles could increase by as much as 75%, if 10% of the S02 is rapidly converted to H2S04. Yu and Turco... 

Injection of species into the stratosphere associated with these launches includes emissions not only from the rocket exhaust but also from ablation of the solid rocket motors, the paint on the outer hulls, and hardware from satellites and discarded portions of rockets in the atmosphere (Zolensky et al., 1989). The increase in launches of such vehicles has led to a significant increase in particles associated with solid rocket use. Figure 12.10, for example, shows the concentration of large (>l-/xm diameter) solid stratospheric particles in the 17- to 19-km altitude region from 1976 to 1984,... 

FIGURE 12.10 Concentration of stratospheric particles with >1 /cm at altitudes of 17-19 km from 1976 to 1984 (adapted from Zolensky et al., 1989). 

Similarly, the reaction of HC1 with N205 is slow in the gas phase, but was shown in the late 1980s to occur rapidly on ice surfaces or in the solutions found in stratospheric particles (Tolbert et al., 1988b Leu, 1988b) ... 

Another method of probing sulfuric acid aerosols is to heat the sample intake sufficiently to vaporize sulfuric acid-water aerosols but not other particles such as those containing ash minerals the difference between the measured particles with and without intake heating provides a measure of the contribution of sulfuric acid-water. Using this technique, Deshler et al. (1992), for example, have shown that more than 90% of the stratospheric particles above Laramie, Wyoming, after the Mount Pinatubo eruption were composed of sulfuric acid-water mixtures. 

Prenni, A. J T. B. Onasch, R. T. Tisdale, R. L. Siefert, and M. A. Tolbert, Composition-Dependent Freezing Nucleation Rates for HNO,-H20 Aerosols Resembling Gravity-Wave-Perturbed Stratospheric Particles, J. Geophys. Res., 103, 28439-28450 (1998). 

Flynn, G. J. and Sutton, S. R. (1992) Trace elements in chondritic stratospheric particles zinc depletion as a possible indicator of atmospheric entry heating. Proceedings of the Lunar and Planetary Science Conference, 22, 171-184. 

Nier, A. O., Schlutter, D. J. (1990) Helium and neon isotopes in stratospheric particles. Meteoritics, 25, 263-7. 

Gooding J.L., Clanton U.S., Gabel E.M. and Warren J.L., El Chichon volcanic ash in the stratosphere particle abundances and size distributions after the El Chichon eruption. Geophys. Res. Lett. , 10, 1033-1036 (1983). 

Rajan R. S., Brownlee D. E., Tomandl D., Hodge P. W., Farrar H., and Britten R. A. (1977) Detection of He in stratospheric particles gives evidence of extraterrestrial origin. Nature 267, 133-134. 

We can conclude that the origin of stratospheric particles is not well established. It is proposed, however, that volcanic activity is at least one of the most important factors governing the aerosol cycle in the stratosphere. It is obvious that much work remains to be done in measuring not only particulate, but also gaseous sulfur compounds in the stratosphere (see Georgii, 1978). 

Mossop, S. C., 1965 Stratospheric particles at 20 km altitude. Geochim. et Cosmochim. Acta 29,201-207. 

The chemical composition of stratospheric particles at a given altitude is governed by local thermodynamic conditions, and specifically is a complex function of temperature and water vapor concentration. The solubility of gas-phase compounds into liquid aerosol particles... 

Carslaw, K.S., and T. Peter, Uncertainties in reactive uptake coefficients for solid stratospheric particles-1. Surface chemistry. Geophys Res Lett 24, 1743, 1997. 

Fan TW-M, Teh SJ, Hinton DE, Higashi RM (2002) Selenium biotransformations into proteinaceous forms by foodweb organisms of selenium-laden drainage waters in California. Aquatic Toxicology 57 65-84 Flynn GJ, Sutton SR (1992) Trace Elements in Chondritic Stratospheric Particles Zinc Depletion as a Possible Indicator of Atmospheric Entry Heating. Proc. Of Lunar and Planetary Science 22, Lunar and Planetary Institute, Houston, 171-184... 

Mackinnon IDR, Mogk DW (1985) Surface sulfur measurements on stratospheric particles. Geophys Res Lett 12 93-96... 

Figure 4 shows the stratospheric particle zoo with all currently known or speculated transitions between diflTerent particles . Phases shown are either marked as liquid (1) or as a sulfuric acid hydrate (SAX, with X = M, T, H, etc., including the mixed hydrate MIX) or nitric acid hydrate (NAX, with X = T, D, P etc.). On the left hand side the diagram shows the stability regions of the solid phases under typical stratospheric conditions at 50 mbar (5 ppmv H2O, 10 ppbv HNO3). The right hand side of Fig. 4 shows transitions relating these phases. Thermodynamically allowed transitions that are also kinetically feasible are marked by an arrow (-+), while transitions which are thermodynamically allowed but kinetically so slow that they will not occur in the stratosphere are marked by crossed arrows ). 

This review has shown that proper diagnosis and prognosis of the depletion of polar ozone depends crucially on our understanding of stratospheric particles. In particular we need to ... 

---