Pinatubo

Similar heterogeneous reactions also can occur, but somewhat less efticientiy, in the lower stratosphere on global sulfate clouds (ie, aerosols of sulfuric acid), which are formed by oxidation of SO2 and COS from volcanic and biological activity, respectively (80). The effect is most pronounced in the colder regions of the stratosphere at high latitudes. Indeed, the sulfate aerosols resulting from emptions of El Chicon in 1982 and Mt. Pinatubo in 1991 have been impHcated in subsequent reduced ozone concentrations (85). 

Hansen, J., Ruedy, R., Sato, M. and Reynolds, R. (1996). Global surface air temperature in 1995 Return to pre-Pinatubo level, Geophys. Res. Lett. 23, 1665-1668. 

Solomon S, Sanders RW, Garcia RR, et al. 1993. Increased chlorine dioxide over Antarctica caused by volcanic aerosols from Mount Pinatubo. Nature 363 245-248. 

There are several reasons for the dramatic ozone destruction (see Fig. 2.17) low temperatures may have prolonged the presence of polar stratospheric clouds, which play a key role in the ozone destruction, the polar vortex was very stable, there were increased sulfate aerosols from the 1991 Mount Pinatubo volcanic eruption, which also contribute to heterogeneous chemistry, and chlorine levels had continued to increase. These issues are treated in more detail shortly. 

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. 

Figure 12.28 shows the particle surface area size distribution before the Mount Pinatubo eruption (Fig. 12.28a), inside the main aerosol layer several months after the eruption (Fig. 12.28b), and almost two years after the eruption (Fig. 12.28c). (See Chapter 9.A.2 for a description of how particle size distributions are normally characterized.) Prior to the eruption, the surface area distribution is unimodal, with typical radii of 0.05-0.09 /xrn and a number concentration of l-20 particles cm 1. In the main stratospheric aerosol layer formed after the eruption, the distribution is bimodal...

Figure 12.29 shows the ratio of the particle surface area at an altitude of 20 km and 45°N latitude to that in 1978-1979 for the period from 1979 to 1995 based on satellite measurements (Solomon et al., 1996). The increases due to volcanic eruptions are evident, particularly the Mount Pinatubo eruption. 

Laboratory studies of the uptake of CIO into sulfuric acid (Martin et al., 1979, 1980), taken in light of a deficit in the inorganic chlorine budget at 17 km after the Mount Pinatubo eruption, led Jaegle et al. (1996) to propose that a heterogeneous reaction of CIO on sulfuric acid aerosols to form perchloric acid, HC104, may also occur. 

FIGURE 12.28 Particle surface area distributions in the stratosphere (a) before Mount Pinatubo eruption, (b) August 20, 1991, over California, and (c) May 7, 1993, over California (adapted from Russell et al. (1996) and Goodman et al. (1994)). 

There are a number of measurements documenting changes in NO and NO. in the stratosphere after the Mount Pinatubo eruption and which have been attributed to the removal of oxides of nitrogen due to reactions on aerosol particles. For example, a decrease in stratospheric NOz after the eruption followed by a return to normal levels has been reported (e.g., see Van Roozendael et al., 1997 and De Maziere et al., 1998). Similarly, NO decreases of up to 70% were reported, as well as increases in gaseous HN03 (much of that produced on the sulfate particles is released to the gas phase) (e.g., see Coffey and Mankin, 1993 Koike et al., 1993, 1994 David et al., 1994 Webster et al., 1994 and Rinsland et al., 1994). 

A similar relationship was observed in Germany. Figure 12.36, for example, shows the deviation of the monthly mean ozone concentration after corrections for seasonal variations, long-term trends, the QBO and vortex effects, and the associated particle surface area concentration from 1991 to 1994 (Ansmann et al., 1996). The increase in the particle surface area due to Mount Pinatubo is clear associated with this increase in aerosol particles are negative monthly mean deviations in ozone that persist until fall 1993, when the surface area approaches the preeruption values. Similarly, the decrease in the total column ozone from 1980-1982 to 1993 observed at Edmonton, Alberta, Canada, and shown at the beginning of this chapter in Fig. 12.1 has been attributed to the effects of the Mount Pinatubo eruption (Kerr et al., 1993). 

Anderson, J., and V. K. Saxena, Temporal Changes of Mount Pinatubo Aerosol Characteristics over Northern Midlatitudes Derived from SAGE II Extinction Measurements, J. Geophys. Res., 101, 19455-19463 (1996). 

Angel I, J. K Comparison of Stratospheric Warming Following Agung, El Chichon, and Pinatubo Volcanic Eruptions, Geophys. Res. Lett., 20, 715-718 (1993a). 

Ansmann, A., F. Wagner, U. Wandinger, and I. Mattis, Pinatubo Aerosol and Stratospheric Ozone Reduction Observations over Central Europe, J. Geophys. Res., 101, 18775-18785 (1996). 

De Maziere, M M. Van Roozendael, C. Hermans, P. C. Simon, P. Demoulin, G. Roland, and R. Zander, Quantitative Evaluation of the Post-Mount Pinatubo N02 Reduction and Recovery, Based on 10 Years of Fourier Transform Infrared and UV-Visi-ble Spectroscopic Measurements at Jungfraujoch, J. Geophys. Res., 103, 10849-10858 (1998). 

Deshler, T D. J. Hofmann, B. J. Johnson, and W. R. Rozier, Balloonborne Measurements of the Pinatubo Aerosol Size Distribution and Volatility at Laramie, Wyoming during the Summer of 1991, Geophys. Res. Lett., 19, 199-202 (1992). 

Dutton, E. G., and J. R. Christy, Solar Radiative Forcing at Selected Locations and Evidence for Global Lower Tropospheric Cooling Following the Eruptions of El Chichon and Pinatubo, Geophys. Res. Lett., 19, 2313-2316 (1992). 

Fiocco, G., D. Fua, and G. Visconti, Eds., The Effects of Mt. Pinatubo Eruption on the Atmosphere and Climate, NATO ASI Series Volume 42, Subseries I, Global Environmental Change, Springer-Verlag, Berlin/New York, 1996. 

S. Verma, Evolution of Pinatubo Aerosol near 19 km Altitude over Western North America, Geophys. Res. Lett., 21, 1129-1132... 

D. Nganga, A. Minga, B. Cros, C. F. Butler, M. A. Fenn, C. S. Long, and L. L. Stowe, Aerosol-Associated Changes in Tropical Stratospheric Ozone Following the Eruption of Mount Pinatubo, J. Geophys. Res., 99, 8197-8211 (1994). 

Hofmann, D. J., and S. J. Oltmans, Anomalous Antarctic Ozone during 1992 Evidence for Pinatubo Volcanic Aerosol Effects, J. Geophys. Res., 98, 18555-18561 (1993). 

Hofmann, D. J S. J. Oltmans, W. D. Komhyr, J. M. Harris, J. A. Lathrop, A. O. Langford, T. Deshler, B. J. Johnson, A. Torres, and W. A. Matthews, Ozone Loss in the Lower Stratosphere over the United States in 1992-1993 Evidence for Heterogeneous Chemistry on the Pinatubo Aerosol, Geophys. Res. Lett, 21, 65-68 (1994b). 

Mickley, L. J., J. P. D. Abbatt, J. E. Frederick, and J. M. Russell III, Response of Summertime Odd Nitrogen and Ozone at 17 mbar to Mount Pinatubo Aerosol over the Southern Midlatitudes Observations from the Halogen Occultation Experiment, J. Geophys. Res., 102, 23573-23582 (1997a). 

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