Water droplet H2SO4 concentration

Fog droplets (10-50 m diameter) are formed in the water-saturated atmosphere (relative humidity = 100%) by condensation on aerosol particles (see Figure 5.2). The fog droplets absorb gases such as SO2, NH3, HCl, and NO. The water droplets are a favorable milieu for the oxidation of many reductants, above all, of SO2 to H2SO4. The liquid water content of a typical fog is often on the order of 10 liter water per m air. The concentrations of ions in fog droplets are often 10-50 times larger than those of rain (Figure 5.11). Clouds process substantial volumes of air and transfer gas and aerosols over large distances. On the other hand, fog droplets are important collectors of local pollutants in the proximity of the earth s surface. 

Many measurements have been made for the reaction of HOCl and HQ on sulfuric acid liquid droplets H2SO4 H20 (1). The uptake coefficient of this reaction is dependent on temperature, water vapor, and concentration ratio of H2SO4/ H2O. The reason is thought to be that the solubility of HOCl and HCl is affected largely by these parameters. The experimental results of the reaction of HCl with HOCl and with CIONO2 in sulfuric acid droplets described in Sect. 6.5.5 has been proposed to be explained by the following acid-catalyzed protonadon reaction pathways. 

The stratosphere contains a natural aerosol layer at altitudes of 12-30 km. This aerosol is composed of small sulfuric acid droplets with size on the order of 0.2 pm diameter and at number concentrations of 1-lOcm-3. In the midlatitude lower stratosphere (about 16 km) the temperature is about 220 K, and the particles in equilibrium with 5 ppm H20 have compositions of 70-75 wt% H2SO4. As temperature decreases, these particles absorb water to maintain equilibrium at 195 K, they are about 40 wt% H2S04. 

The role of the Kelvin effect on the composition of atmospheric H2SO4-H2O droplets is illustrated in Figure 9.16. If the effect were negligible the equilibrium aerosol composition would not be a function of its size. This is the case for particles larger than 0.1 /zm in diameter. For smaller particles the H2SO4 mole fraction in the droplet is highly dependent on particle size. Also notice that for a fixed droplet size, the water concentration increases as the relative humidity increases. 

Sulfuric acid (H2SO4), the most un)ortant industrial chemical in the world, is prepared by oxidizing sulfur to sulfur dioxide and then to sulfur trioxide. Although sulfur trioxide reacts with water to form sulfuric acid, it forms a mist of fine droplets of H2SO4 with water vapor that is hard to condense. Instead, sulfur trioxide is first dissolved in 98 pa-cent sulfuric acid to form oleum (H2S2O7). On treatment with water, concentrated sulfuric acid can be generated. Write equations for all the steps and draw Lewis structures of oleum based on the discussion in Example 9.11. 

Sulfuric acid, H2SO4, is one of the most important of all chemicals, finding use throughout the chemical industry and related industries. It is a heavy, oily liquid (density 1.838 g cm ), which fumes slightly in air, as the result of the liberation of traces of sulfur trioxide, which then combine with water vapor to form droplets of sulfuric acid. When heated, pure sulfuric acid yields a vapor rich in sulfur trioxide, and then boils, at 338°C, with the constant composition 98% H2SO4, 2% water. This is the ordinary concentrated sulfuric acid of commerce. 

The preceding reactions occur throughout the stratosphere and are responsible for depletion of ozone on a global scale. The extreme ozone depletion at the South Pole, however, did not at first seem to be consistent with the kinetics of the knovm ozone-destroying reactions and the known free chlorine concentrations. The discrepancy turned out to be due to heterogeneous chemistry (Fig. 4.47). Under wintertime conditions when polar stratospheric temperatures drop below approximately —78 °C, polar stratospheric clouds (PSCs) are formed. These clouds can form from H2SO4/H2O droplets, which take up HNO3 under cold temperatures from ice crystals formed from the condensation of water and from solid... 

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