Sulfur dioxide homogeneous oxidation

The other removal process, wet deposition, removes sulfur from the atmosphere as sulfates in rain. This would be the fate of sulfuric acid produced via the homogeneous oxidation of SO2, but oxidation also proceeds within droplets. Aqueous sulfur dioxide is oxidized only slowly by dissolved oxygen, but the production of sulfuric acid, which is much stronger, leads to acidification... 

Most sulfuric acid in the atmosphere is initially emitted as sulfur dioxide (SO2), which contains sulfur in the (-t-IV) oxidation state. The SO2 can dissolve in water droplets to form a relatively weak acid, sulfurous acid (H2SO3). In the presence of hydroxyl radicals in the atmosphere, however, sulfur dioxide is oxidized to sulfur trioxide (SO3), which contains sulfur in the (+VI) oxidation state. SO3 subsequently reacts with water to form the strong acid H2SO4 (sulfuric acid). This homogeneous oxidation of SO2 to H2SO4 has a daily-averaged rate of 0.01/hr (Luria and Sievering, 1991). 

Finally, atmospheric chemical transformations are classified in terms of whether they occur as a gas (homogeneous), on a surface, or in a liquid droplet (heterogeneous). An example of the last is the oxidation of dissolved sulfur dioxide in a liquid droplet. Thus, chemical transformations can occur in the gas phase, forming secondary products such as NO2 and O3 in the liquid phase, such as SO2 oxidation in liquid droplets or water films and as gas-to-particle conversion, in which the oxidized product condenses to form an aerosol. 

Preparation of Cellulose-Styrene-Sulfur Dioxide Graft Copolymer (Homogeneous Grafting). The procedure for preparation of cellulose-styrene copolymer in a S0 -diethylamine (DEA)-dimethylsulf-oxide (DMS0) medium was described in our previous paper (3). The grafting proceeds homogeneously throughout the reaction. 

Example 8.8 Entropy production in a homogeneous chemical system The oxidation of sulfur dioxide to trioxide over a vanadium pentoxide catalyst is... 

Sulfur dioxide can undergo homogeneous oxidation through attack by the OH radical ... 

Two processes are used commercially to produce sulfuric acid, the contact process, where the oxidation of sulfur dioxide to sulfur trioxide is accomplished with air heterogeneously using a solid catalyst, and the chamber process, where the oxidation step is accomplished homogeneously with a gaseous catalyst. Of the two, the contact process is used to produce more than 95% of the supply of sulfuric acid at present, both in Europe and in North America. 

Sulfur dioxide (SO ) and nitrogen oxides (NO ) are oxidized to sulfate and nitrate aerosols either homogeneously rn the gas phase or heterogeneously in atmospheric microdroplets and hydrometeors Gas-phase production of nitric acid appears to be the dominant source of aerosol nitrate because the aqueous phase reactions of NO (aq) are slow at the nitrogen oxide partial pressures typically encountered in the atmosphere (5,i5). Conversely, field studies indicate that the relative importance of homogeneous and heterogeneous SO2 oxidation processes depends on a variety of climatological factors such as relative humidity and the intensity of solar radiation (4, -1 ). 

Further studies pointed out that the homogeneous oxidation of S02 becomes faster when the air also contains nitrogen dioxide and ozone. Thus, N02 absorbs solar radiation in the visible spectrum and dissociates (see [3.32]) to give atomic oxygen. Oxygen atoms produce ozone or react with S02 to form sulfur trioxide (Cadle and Powers, 1966) ... 

A wide variety of interrelated homogenous gas-phase, solution-phase, and heterogenous chemistry may ultimately result in oxidation of SO2 to sulfuric acid in DUV exposure tools. The three main possible reaction pathways for the oxidation of sulfur dioxide to sulfuric acid in the exposure chamber may include (i) direct oxidation of sulfur dioxide by stable atmospheric oxygen, (ii) catalyzed oxidation of sulfur dioxide by metal ions, and (iii) photochemical oxidation of sulfur dioxide by ozone and hydroxyl radical. 

A thoroughly studied example of homogeneous catalysis in the gas phase was formerly used in sulfuric acid manufacture. The key step, the oxidation of sulfur dioxide to sulfur trioxide, occurs so slowly that it is not economical ... 

The oxidation of sulfur dioxide using nitric oxide as a catalyst is an example of homogeneous catalysis, which is the use of a catalyst in the same phase as the reacting species. The catalyst NO and the reacting species SO2 and O2 are all in the gas phase. Another example occurs in the oxidation of thallium(l) to thallium(lll) by cerium(TV) in aqneous solution. 

Sander, S. P., Seinfeld, J. H., "Chemical Kinetics of Homogeneous Atmospheric Oxidation of Sulfur Dioxide, Environ. 

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