大学化学课件6气溶胶化学及酸沉降化学英文精编整理.ppt

* SECTION 7 Chemistry of aerosol Definition and sort of aerosol (1) Definition A dispersion of microscopic solid or liquid particles in gaseous medium is called aerosol. Particulate matter in the atmosphere can be natural or man-made. For example, sulfate aerosol is from volcano eruption, fuel combustion and microbial activities. Sea salt aerosol is from sea spray and bubble bursting. Soot is from fuel combustion. Secondary organic aerosol is from volatile organic compounds. (2) Sort of aerosol According to cause of formation of aerosol, aerosol is divided into decentralization aerosol and agglomeration aerosol. According to diameter of aerosol, aerosol is divided into total suspended particulates (TSP), precipitated particles, floating particles, and inhalable particles. Dynamics diameter of particle is about 0.001～100μm. Large particles can settle out of the atmosphere by sedimentation in the earth’s gravitational field. The particle, more than 10μm, is called precipitated particles. The smaller solid particles have a maximum concentration about 18 km above the earth’s surface. The particle, less than 10μm, is called floating particles. Table 1 Conformation and main characteristic of aerosol 2. Source and collection of aerosol Table 2 Emissions and source of aerosol in the globe The particles in the atmosphere are known collectively as the atmospheric aerosol. Their size distribution is very wide, but as seen in Figure3, the aerosol is dominated by the smallest particles. Dust and sea spray are blown about by the wind in great quantity, but these particles are large and settle out rapidly. 3. Size distribution of aerosol Figure1 size distribution of aerosol The submicrometer particles are formed mainly by oxidation of sulfur-, nitrogen-, and carbon-containing gases in the atmosphere. These particles stay aloft much longer, with lifetimes of days or weeks. Gradually, they grow to larger ones via collisions and aggrega