Weekly aerosol samples have been collected and analyzed consistently at Mauna Loa Observatory from February 1979 through June of 1991. Previous studies reported data through April of 1985. This paper focuses mainly on the data from May 1985 to June 1991. However, previous data have been included when appropriate to examine the entire data record. Elemental concentrations, enrichment factors, principal component analysis and chemical mass balancing have been used to examine this 12 year data record. Yearly Asian dust episodes are the major contributor to trace metal concentrations and variance. Marine material contributes only a third of the trace metal mass compared to the crustal contribution. Anthropogenic and biogenic material usually contribute less than 5% of the trace element mass (excluding carbon and sulfate). Sulfate, which was measured by ion chromatography for part of the period, contributes a mass similar to crustal mineral; however, it does not have a strong seasonal pattern. A pollution episode in 1989 increased the budget of several elements by an order of magnitude or more. The trace acidic gas data support the conclusion that marine material in the free troposphere has been weathered, leading to a chlorine depletion in marine particles.¿ 1997 American Geophysical Union