one type apparently arises when the air in the city becomes stagnant, while another type is clearly associated with unusually large industrial emissions. The Pb/Br ratio is not a practical tool for measuring the relative amounts of pollution from industrial and automotive sources-at least in an area with no strong industrial sources of Pb.
AcknowledgmentThe authors would like to acknowledge the assistance of D. Yesso in preparing standard solutions, and of W. Strang of the Allegheny County Air Pollution Bureau who provided data on carbon monoxide and fine particulates in the Pittsburgh area.
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