The nature of particulate matter.

The origin and the nature of particulate matter which is found in the earth's atmosphere, and which is measured to evaluate air pollution, are discussed. The importance of defining particulate matter in terms of its physical structure and its chemical composition is emphasized. Attention is drawn to the surface activity of particulate matter and it is shown that, because of its micropore fine structure and its content of metals, particulate matter may act as a catalyst for some reactions, and also as a carrier for any vapour and gas. Ammonia, hydrocarbons and nitrogen oxides, adsorbed on particulates, have been detected and determined. The compositions of both inorganic and organic fractions of particulates are discussed and a procedure for the systematic analysis of various classes of organic compounds is outlined. The results obtained by thin layer and gas chromatography to elucidate the composition of the organic fraction are