Reactions Involved In Particle Formation And Growth

The formation of secondary particulate matter in various size ranges by chemical reactions in the atmosphere may occur by a number of mechanisms. These include (1) reactions of gases to form low-vapor-pressure products (e.g., the oxidation of S02 to H2S04 or the reaction of aromatics with OH to form multifunctional oxygenated products) followed by nucleation to form new particles or condensation on preexisting particles, along with some coagulation between particles, (2) reaction of gases on the surfaces of existing particles to form condensed-phase products (e.g., the reaction of gaseous HNO-, with sea salt particles to form NaN03), and (3) chemical reactions within the aqueous phase in fogs, cloud, or aerosol particles (e.g., S02 oxidation to sulfate; see Chapter 8).

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