A global assessment of natural sources of atmospheric trace metals

Abstract

A PROPER inventory of atmospheric emissions from natural sources is basic to our understanding of the atmospheric cycle of the trace metals (and metalloids), and is also needed for assessing the extent of regional and global pollution by toxic metals1. It is generally presumed that the principal natural sources of trace metals in the atmosphere are wind-borne soil particles, volcanoes, seasalt spray and wild forest fires2–6. Recent studies have shown, however, that particulate organic matter is the dominant component of atmospheric aerosols in non-urban areas7–10 and that over 60% of the airborne trace metals in forested regions can be attributed to aerosols of biogenic origin11,12. Here I estimate that biogenic sources can account for 30–50% of the global baseline emissions of trace metals. For most of the toxic metals, the natural fluxes are small compared with emissions from industrial activities, implying that mankind has become the key agent in the global atmospheric cycle of trace metals and metalloids.