Sulfuric acid in the stratosphere

Arnold F. and Fabian R., First measurements of gas phase sulfuric acid in the stratosphere. Nature, 283, 55 (1980). 

The volcanoes in the Transantarctic Mountains and in Marie Byrd Land of West Antarctica erupted lava flows and pyroclastic ash that was deposited on the surface of the ice sheets. The ash was subsequently buried by snow and was thereby incorporated into the ice. The resulting ash layers now serve a useful purpose in the study of the ice sheets because they are unique event horizons whose age can be determined by isotopic methods (e.g., Folco et al. 2007). In addition, these horizons have preserved a record of the deformation of the ice sheets that is revealed by mapping their outcrop patterns on the bare-ice surfaces in the ablation zones. The chemical composition of the ash has been used to identify the volcanoes from which certain ash layers were erupted, while the sulfate concentration and the acidity (pH) of the ice above an ash layer provide clues to the amount of sulfuric acid that was injected into the stratosphere (Palais 1985). The volcanic dust and sulfuric acid in the stratosphere can cause temporary cooling of the global climate as demonstrated by the eruptions of Krakatau (Indonesia) in 1883, Mount St. Helens (Washington) in 1980, El Chichon (Mexico) in 1982, and Mount Pinatubo (Philippines) in 1992 (Holland and Petersen 1995 Thompson and Mosley-Thompson 1981 Kyle et al. 1981 Self etal. 1981). 

The fate of sulfuric acid in the upper stratosphere and mesosphere is key to understanding the role of sulfur in the upper atmosphere [10]. In this regard the photolysis of sulfuric acid (H2SO4) via the reaction... 

Fig. 3-13. Left Vertical distribution of carbonyl sulfide and sulfur dioxide in the stratosphere. [From data of Maroulis et al. (1977), Sandalls and Penkett (1977), Torres el al. (1980), Mankin et al. (1979), Inn et al. (1979, 1981) for COS, and from Jaeschke et al. (1976), Maroulis et al. (1980), Georgii and Meixner (1980), Inn et al. (1981) for S02.] Curves represent calculations of Turco et al. (1980, 1981a) for an assumed cutoff of COS photodissociation of 312 nm. Right Vertical distribution of gaseous and particulate sulfuric acid. Solid squares and circles are from mass spectrometric measurements of Arijs et al. (1982) and Viggiano and Arnold (1983), respectively. Open circles with error bars (one standard deviation) are from filter collections of Lazrus and Gandrud (1977). The range given by the thin lines indicates the seasonal variability of particulate sulfate. The solid line indicates the vapor pressure of H2S04 over a 75% H2S04/25% H20 mixture.

There are many different types of surfaces available for reactions in the atmosphere. In the stratosphere, these include ice crystals, some containing nitric acid, liquid sulfuric acid-water mixtures, and ternary solutions of nitric and sulfuric acids and water. In the troposphere, liquid particles containing sulfate, nitrate, organics, trace metals, and carbon are common. Sea... 

The concentration of sulfuric acid in SSA is typically 50-80 wt% under mid- and low-latitude stratosphere conditions. However, as the temperature drops, these particles take up increasing amounts of water, which dilutes the particles to as low as 30 wt% H2S04. Gaseous nitric acid is also absorbed by these solutions, forming ternary H2S04-H20-HN03 solutions with as much as 30 wt% in each acid. 

Hofmann, D. J., Increase in the Stratospheric Background Sulfuric Acid Aerosol Mass in the Past 10 Years, Science, 248, 996-1000 (1990). 

The uptake coefficient on liquid sulfuric acid is due to QONO, hydrolysis and has been shown to depend strongly on the composition. It was indicated that y depends on the HjO activity of the mixture [93]. A detailed model for applying the laboratory uptake coefficient for this reaction to the small aerosol composition found in the stratosphere has been developed [43,96]. 

In addition to ice formation, salts also precipitate as these solutions are lofted to higher altitudes. A consequence of the formation of these solid phases (ice and salts) and the low-temperature eutectics of strong acids (Fig. 3.5) is that the atmospheric solutions become more and more acidic with altitude (Fig. 5.8). For example, the final elevation (temperature) examined is 11.54 km (—50 °C). At this point, the calculated concentrations of the Hubbard Brook solution are H+ = 7.55m with acid anions (Cl-, NO3, SO4-, HSOJ) = 7.91m. Similarly, for the Mt. Sonnblick solution, H+ = 6.50 m and acid anions = 6.90 m. These acidic trends are in line with stratospheric chemistries, which are predominantly sulfuric/nitric acid aerosols (Carslaw et al. 1997). For example, the total acid concentration at 20.7km in the stratosphere is 10.17m (calculated from fig. 7 in Carslaw et al. 1997), which is in line with our lower atmospheric concentrations. 

While the sulfuric acid is key nucleation precursor in the low troposphere, its contribution to the polar stratospheric chemistry is a lot more modest. Another strong acid-nitric-plays a major role as the dominant reservoir for ozone destroying odd nitrogen radicals (NOj) in the lower and middle polar stratosphere. Nitric acid is an extremely detrimental component in the polar stratosphere clouds (PSCs), where nitric acid and water are the main constituents, whose presence significantly increases the rate of the ozone depletion by halogen radicals. Gas-phase hydrates of the nitric acid that condense and crystallize in the stratosphere play an important role in the physics and chemistry of polar stratospheric clouds (PSCs) related directly to the ozone depletion in Arctic and Antarctic. 

Arnold F., Fabian R. and Joos W., Measurements of the height variation of sulfuric acid vapor concentrations in the stratosphere. Geophys Res. Lett. , 8, 293 (1981). 

This scheme conserves HO c and results in a predicted e-folding lifetime of SO2 in the stratosphere of 38 days (i.e., the time taken for the abundance of SO2 to drop by 1/e of its starting amount), only slightly longer than the observed time of 33-35 days (Eigure 8 Read et al., 1993). The aerosol consisted of around 25% water and 75% sulfuric acid by weight. 

Sulfuric acid is an important component of upper planetary atmospheres. The background sulfur found in the Earth s stratosphere derives... 

Sulfur compounds are very important atmospheric constituents, since in clean tropospheric air as well as in the stratosphere the majority of aerosol particles are composed of ammonium sulfate or sulfuric acid (see Chapter 4). This finding is particularly interesting since with the exception of sea salt sulfur, a predominant portion of sulfur emission is in gaseous form. 

First of all, volcanic activity must be mentioned it introduces both gases (see Section 2.3 and Subsection 3.6.2) and particles into the atmosphere. The particles play an important temporary role in the control of atmospheric optical properties and radiation balance. Thus, after the eruption of Krakatoa in 1883 unusual darkness was observed over Batavia and the height of the volcanic cloud reached the altitude of nearly 30 km (18 miles). After the violent eruption of the Agung volcano in 1963 the optical effect of ash particles was identified at several points of the Earth and a temperature increase of 2 C was measured in the stratosphere (see Cadle, 1973)due to the radiation absorption of particles. While an important part of volcanic particulate matter consists of dispersed lava, sulfuric acid also was detected in volcanic fume (Cadle, 1973). 

Liquid and solid particles observed in the atmosphere are generally a mixture of water, sulfuric acid and nitric acid with potentially the presence of traces of other chemical compounds like HC1 (see Table 5.9 in Section 5.7). The determination of the pseudo first-order rate coefficient kx (see Eq. (2.65)) for uptake by such particles in the stratosphere requires an accurate estimate of the surface area density available and of the reaction probability involved. 

Steele, H.M., and P. Hamill, Effects of temperature and humidity on the growth and optical properties of sulfuric acid-water droplets in the stratosphere. J Atmos Set IS, 517, 1981. 

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