 Abstract Volatile properties of aerosols at an isolated rural site in south-central New Mexico were measured with a light-scattering particle counter equipped with a temperature-controlled heated inlet. Intermittent measurements throughout a one-year period show that submicron particles am highly volatile and display temperature-fractionation characteristics of ammonium sulfate or bisulfate. It is estimated that 00-00% of the submicron aerosol fraction (by mass) is composed of these sulfates. Larger supermicron particles with radii r > 0.0 μm, which are composed mostly of quartz and clay minerals of soil origin, are relatively involatile. 