Section IV - Chemical and Physical Reactions, Transport and Fate of Fine Particulate Pollutants

Abstract

This chapter discusses the chemical and physical reactions, transport and fate of fine particulate pollutants. Fine particulates can be formed after combustion through condensation of low-volatile substances during cooling of the flue gases in the stack. These particulates consist of either high molecular weight organic compounds or non-volatile inorganic compounds. Particulates in exhaust gases from gasoline-powered cars include lead compounds, carbon particulates, motor oil, and non-volatile reaction products formed from motor oil in the combustion zone. The reaction products include high molecular weight olefins, carbonyl compounds, and free acids. Lead particles in the exhaust gases include several different lead oxide or lead halide compounds. The emission of particulate matter from diesel oil-fueled motor vehicles is greater than that from gasoline-fueled vehicles. The organic content of the particulates is also higher. Much of the particulate matter in the atmosphere is not directly emitted from combustion or industrial sources, but is formed there from gaseous pollutants. The conversion of gas to particle is accelerated by the photochemistry of the atmosphere. Particles also grow by absorbing gases. The most important process is water condensation. However, the absorption of SO2, ammonia, and nitric acid are major reactions determining the size distribution of aged aerosols.