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The story of the development of automotive exhaust conversion catalysts is at once a simple and complex one. The major challenge is to keep it simple while remaining true to the complex interplay of technological achievements with political ideals and geographic, demographic, economic, and bureaucratic realities which culminated in the successful mass application of catalysts to the control of automotive exhaust pollution.Our study begins in California in the late forties, when the combination of the rapidly increasing population of humans and automobiles with geography and personal expectations focused political and scientific attention onto the photochemical reactions in the atmosphere between the hydrocarbons and nitrogen oxides which were being emitted in automobile exhaust, and on the effects of the reaction products on public health.Public demand for relief from the increasingly frequent smog incidents caused the California Legislature in 1947 to allow the formation of county or regional air pollution control districts; as these districts were formed they began to gather data on the air quality and sources of pollution, and to encourage scientific investigation into the origins of the periodic episodes of widespread eye irritation and respiratory discomfort. In 1952, Professor A. J. Haagen-Smit of the California Institute of Technology published his studies (1) which showed that some hydrocarbons and nitrogen oxides endemic to automobile exhaust reacted in sunlight to produce oxidants, including ozone, which were already known to, among other things, cause cracking of rubber and irritation of the eyes.[Cal-Tech is located in Pasadena, which is situated in the northwestern corner of the Los Angeles "basin", and which generally feels the full impact of auto exhaust-related smog.] This study, along with a concurrent investigation by the Los Angeles Air Pollution Control District (2) which showed that aerosols and mists could be produced photochemically by the polymerization of the photo-oxidation products of some of the exhaust hydrocarbons, laid the scientific basis for a serious

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