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Aerosol samples were collected during 2007 on the Urumqi Glacier No. 1. Size, morphology, and elemental compositions of more than 38,000 particles were determined by scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDX). Based on the morphology and elemental compositions, particles were classed into 5 groups: Si-rich particles; Ca-rich particles; Fe-rich particles; K-rich particles and S-rich particles. Most of the particles were irregular shaped mineral particles smaller than 2.5 mu m (PM 2.5); only 1.7% of the particles (small Fe-rich particles and S-rich particles) may be emitted by anthropogenic activities, which suggested that natural processes are the primary source of PM 2.5. Backward air mass trajectory analysis suggests that the arid and semi-arid regions of central Asia are the primary source of PM 2.5 to the region. (C) 2010 Elsevier B.V. All rights reserved.