CHEMISTRY of the ENVIRONMENT（环境化学课件2 ）.pptVIP

The SO2 from all sources in subsequently oxidized to sulfuric acid (under some conditions, the reduced sulfur compounds may be oxidized directly to H2SO4, without intermediate SO2 stage). The sulfur cycle is completed by rainout（雨除） (see Figure 6.8). This natural cycle is now being strongly perturbed by human activity. Large quantities of SO2 are emitted into the atmosphere by the burning of fossil fuels, especially coal and by the smelting of sulfur minerals. Since sulfuric acid is the main contributor to acid rain, the lower sulfate means less acid deposition. International shipping may play a significant role in the global sulfate aerosol. Satellite photographs show aerosol plumes(羽毛) hundreds of kilometers long in the wake of large ships. Their diesel engines burn the cheap “residual oil” that is left over at the refinery after the lighter hydrocarbons have been removed. This residual has a sulfur content of around 3 percent, and marine vessels are estimated to contribute 5 percent of the global sulfur emissions from all fuel combustion sources. The contribution can be much higher (up to 30 percent of an ambient levels) in regions with heavy coastal traffic. In Northern Hemisphere oceans, the sulfur emission from ships is comparable to the biogenic flux from planktonic dimethylsulfoxide(二甲基亚砜). In order to burn the residual oil, marine diesels operate at high temperatures, and also produce large quantities of NOx, contributing further to the global aerosol. In any event, it seems that fossil fuel burning has opposite effects on Earth’s climate: greenhouse warming due to the emitted CO2, and albedo cooling due to the emitted SO2. Ironically, the international effort to improve air quality by reducing emissions of sulfur may have the unintended consequence of augmenting(增加) the greenhouse warming. However, reducing soot from fuel burning could ameliorate warming since the black carbon particles (see Figure 6.11) absorb sunlight. SECTION 3 GREEN