Atmospheric particles were collected in them midlatitude upper troposphere (UT) and lower stratosphere (LS) by inertial impaction for subsequent electron microscopy and individual particle elemental analysis. More than 97% of particles analyzed on impactor substrates exposed in the LS contained an O and S in detectable quantities; these particles are believed to be acidic sulfate. Nonsulfate materials seen in the remaining particles included soot, other c-rich substances and crustal materials. Although not predominantly sulfate, usually carried a sulfur-rich coating in the LS. Samples collected very near and just below the tropopause were also dominated by sulfates. The fraction of sulfate particles analyzed on impactor substrates exposed in the UT was 91-94% of the total particle concentration. Nonsulfate substances observed in the UT samples included crustal-type materials, hydrated marine salts, carbon-rich materials of several types, and metal-containing substances of uncertain origin. Most of these UT particles were not coated with detectable quantities of sulfate. ¿ American Geophysical Union 1994