The surface chemistries of three particulate samples collected from the lower stratosphere have been determined using a Scanning Auger Microprobe (SAM). These samples are typical of the most abundant natural and anthropogenic particles observed within the stratosphere in the >2&mgr;m diameter size fraction. Successive sputtering and analysis below the first few adsorbed monolayers of all particles shows the presence of a thin (<150A) sulfur layer. These sulfur regions probably formed by surface reaction of sulfur-rich aerosols with each particle within the stratosphere. Settling rate calculations show that a typical sphere (10&mgr;m diameter) may reside within a aerosol layer for ~20 days and thus, provide a qualitative guide to surface sulfur reaction rates.