Sulfurous acid formation from atmospheric sulfur

Ga.s-to-particie conversion may result from homogeneous gas-phase processes, or it may be controlled by processes in the particulate phase. Gas-phase processes, either physical or chemical, can produce a supersaturated state which then collapses by aero,s ol formation. Physical processes producing supersaturation include adiabatic expansion or mixing with coo air—-discussed in the last chapter—or radiative or conductive cooling. Gas-phase chemical reactions such as the oxidation of SO2 to sulfuric acid in the atmosphere or the oxidation of SiCU to SiOi in industry also generate condensable products. 

Sulfur-oxidising bacteria convert inorganic sulfur compounds to sulfuric acid that can cause severe damage to mineral material. Thiobacillus species have been implicated with concrete corrosion in the Melbourne and Hamburg sewer systems due to sulfuric acid formation. However, a role in stone decay is less certain since sulfuric acid and calcium sulfate in stone can originate from the direct action of atmospheric pollution and acid rain. 

Current processes for the manufacture of trinitrotoluene (TNT) produce atmospheric and water pollution that is only partly relieved by mechanical clean-up methods. TNT is currently produced from toluene by successive mono-, di-, and trinitrations with mixed aqueous nitric and sulfuric acids in the first two steps and anhydrous mixed acid in the last. Each stage in the current process is conducted at elevated temperatures, and side reactions in the overall process directly produce thousands of pounds of oxides of nitrogen, sulfuric acid aerosols, and volatile nitro organic products (such as tetranitromethane and nitroaro-matics). These pollutants derive from the thermal decomposition of the aqueous nitric acid solutions, from oxidative side reactions that produce as many as 40 by-product compounds, and from formation of unsymmetrlcal "meta" Isomers. Since symmetrical TNT is inevitably accompanied by meta isomers as well as oxidation products, the crude material is treated with sodium sulfite solutions to remove the undesirable Isomers and nitroaromatics by derivatization. The spent sulfite solution, known as "red water, is then disposed of by combustion to an inorganic ash. Itself a disposal problem. 

Carmichael, G. R., D. G. Streets, G. Calori, M. Amman, M. Z. Jacobson, J. Hansen and H. Ueda (2002) Changing trends in sulfur emissions in Asia Implications for acid deposition, air pollution, and climate. Environmental Sciences and Technology 356, 4707-4713 Carroll, J. J. and A. E. Mather (1992) The system carbon dioxide-water and the Krichevsky-Kasarnovsky equation. Journal of Solution Chemistry 21, 607-621 Carlton, A. G., C. Wiedinnyer and J. H. Kroll (2009) A review of secondary organic aerosol (SOA) formation from isoprene. Atmospheric Chemistry and Physics 9, 4987-5005 Carslaw, K. S., O. Boucher, D. V Spracklen, G. W. Mann, J. G. L. Rae, S. Woodward and M. Kulmala (2010) A review of natural aerosol interactions and feedbacks within the Earth system. Atmospheric Chemistry and Physics 10, 1701-1737... 

The equihbrium shown in equation 3 normally ties far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is compHcated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequently, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

Similarly, SO2 and SO3 (SOJ compounds are produced in combustion by the oxidation of sulfur compounds within the fuel source. SO , emitted into the atmosphere can be incorporated into aerosol particles and wet-deposited as corrosive sulfuric acid. Both NO , and SO , emissions contribute to acid rain content from wet deposition, due to their participation in the formation of nitric and sulfuric acid, respectively. 

In simple terms, the global sulfur cycle has two components. One is biochemical involving the conversion of sulfate to sulfide and the formation of DMS the other is atmospheric photochemical oxidation of DMS to sulfur oxyacids. DMS is formed mainly in the oceans by microorganisms and to a lesser extent in plants. About 38M0 Tg year-1 of DMS are released to the atmosphere from the oceans. The major precursor for DMS formation is the sulfonium salt, dimethylsulfoniopropionate, (CH3)2 S+ CH2 CH2 COOH, DMSP. DMSP lyase enzymes catalyze an elimination of acrylic acid from DMSP (Equation 12) with the release of DMS ... 

Adsorption of nitric and sulfuric acids on ice particles provides the sol of the nitrating mixture. An important catalyst of aromatic nitration, nitrous acid, is typical for polluted atmospheres. Combustion sources contribute to air pollution via soot and NO emissions. The observed formation of HNO2 results from the reduction of nitrogen oxides in the presence of water by C—O and C—H groups in soot (Ammann et al. 1998). As seen, gas-phase nitration is important ecologically. 

It is known from studies carried out over many decades that oxides of nitrogen at high concentrations dissolve in aqueous solution and react to form species such as nitrate and nitrite. With the focus on acid deposition and the chemistry leading to the formation of nitric and sulfuric acids during the 1970s and 1980s, a great deal of research was carried out on these reactions at much lower concentrations relevant to atmospheric conditions (for reviews, see Schwartz and White, 1981, 1983 and Schwartz, 1984). 

The term binary homogeneous nucleation is used to describe the formation of particles from two different gas-phase compounds such as sulfuric acid and water such nucleation can occur when their individual concentrations are significantly smaller than the saturation concentrations needed for nucleation of the pure compounds. It is believed that in the atmosphere, formation of particles from low-volatility gases occurs not by condensation of a single species but rather by the formation and growth of molecular clusters involving at least two, and as described shortly, probably three or more different species. 

A few comments Sulfur dioxide (S02) is a gas produced by volcanoes and from many industrial processes. It is sometimes used as a preservative in alcoholic drinks, or dried apricots and other fruits. Generally, the combustion of fossil fuels containing sulfur compounds such as coal and petroleum results in sulfur dioxide being emitted into the atmosphere. Beyond its irritating effect on the lungs, sulfur dioxide is also a threat to the environment, since it is well known to contribute to acid-rain formation. 

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