Atmospheric trace chemistry in the American humid tropics

Numerous attempts have been made to define global mean concentrations of trace substances and to incorporate these into global models of net source and sink strengths of the various natural and anthropogenic atmospheric con-taminants. One of the most extensive was certainly the work of Robinson & Robbins (1967). However, it now appears with increasing clarity that such models are a t best mathemati-cal abstractions. Many substances really do not become a part of the global atmosphere, in the sense that they are mixed meridionally through-out the atmosphere. Their lifetimes are rather short compared with such mixing times. The concept is discussed a t rather more length by Kellogg et al. (1972). It therefore seems more meaningful to discuss zonal mean values, and perhaps to distinguish variations on a still smaller scale. The authors and their collaborators have conducted extensive studies in the American tropics to determine trace substance concentra-tions in a variety of tropical environments. The details of these studies are being reported extensively elsewhere (Hutton & Rasmussen,