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 greater than 2 micrometer diameter size fraction. Successive sputtering and analysis below the first few adsorbed monolayers of all particles shows the presence of a thin (less than 150A) sulfur layer. These sulfur regions probably formed by surface reaction of sulfurâ€rich aerosols with each particle within the stratosphere. Settling rate calculations show that a typical sphere (10 micrometer diameter) may reside within the aerosol layer for around 20 days and thus, provide a qualitative guide to surface sulfur reaction rates.
