环境化学之大气.ppt

54 ? 云内清除过程（雨除） 在云滴上和云滴间的碰撞，并使云滴不断生长， 与此同时，各种污染气体溶于云滴中并发生各种 化学反应；当云滴成熟后即变成雨从云基下落。 ? 云下清除过程(冲刷) 雨滴离开云基，在其下落过程中有可能继续吸收和 捕获大气中的污染气体和气溶胶，这就是污染物的 云下清除或降水的冲刷作用。 降水的酸化过程 雨滴下降时吸收SO2(g)在液相氧化成SO42- 冲刷 云滴成为雨滴降落时清除了含SO42-气溶胶 云滴吸收了SO2(g)在液相氧化成SO42- 雨除 云形成时含SO42-的粒子以凝结核形式参与降水 过程 由源排放的SO2(g)经气相反应→H2SO4、SO42- 55 降水具体酸化过程 平流 扩 散 沉 降 雨水酸化过程示意 56 气溶胶和微量的气体的云内清除 化学反应 除 气溶胶和微量的气体的云下清除 干 SO2(aq) 云内清除 H2SO4 云 SO2(aq) 下 清 H2SO4 SO2(g) SO42- SO42- 57 58 酸雨的形成必须具备以下几个条件 ? 污染源条件,即酸性污染物的排放以及转 化条件。 ? 大气中的气态碱性物质浓度较低，对酸 性降水的缓冲能力很弱 ? 大气中颗粒物的酸碱度及其缓冲能力。 ? 天气形式的影响。 59 酸雨的危害 对土壤生态系统的影响 水生生态系统 对植物的影响 对材料和古迹的影响 对人体健康的影响 Climate-Greenhouse Effect Greenhouse Glass, the material that greenhouse is made of, 1) transmit short-wavelength visible light, 2) absorbs and redirects the longer wavelengths of energy. These two aspects make the greenhouse warmer than outside air temperature. Greenhouse effect of the atmosphere ? Light from the sun includes the entire visible region and smaller portions of the adjacent UV and infrared regions. ? Sunlight penetrates the atmosphere and warms the earth’s surface. ? Longer wavelength infrared radiation(IR) is radiated from the earth’s surface. ? A considerable amount of the outgoing IR radiation is absorbed by gases in the atmosphere and reradiated back to earth. The gases in the atmosphere that act like glass in a greenhouse are called greenhouse gases. Natural Greenhouse effect The natural greenhouse effect causes the mean temperature of the Earths surface to be about 33oC warmer than it would be if natural greenhouse gases were not present. Enhanced greenhouse effect When concentrations of greenhouse gases increase, more infrared radiation is returned toward the earth and the surface temperature rises. What makes a gas greenhouse gas? Able to absorb infrared light ? Must have molecular vibration(s)(分子振动) – This excludes monoatomic(单原子) gases as greenhouse gases. (That is why argon, the third most abundant atmospheric constituent