Shape of atmospheric mineral particles collected in three Chinese arid-regions

The shape of atmospheric mineral particles of 0.1 - 6 mum radius was studied by electron microscopy applied to the samples collected in three and regions in China (Qira in the Taklamakan Desert, Zhangye near the southern border of the Badain-Jaran Desert and Hohhot in northern China). In all three regions, the mineral particles showed irregular shapes with a median aspect ratio b/a (ratio of the longest dimension b to the orthogonal width a) of 1.4. Although the aspect ratio exhibited no clear size dependence, the circularity factor (4 piS/l(2); S is surface area and l is periphery length) tended to decrease with increasing radius, suggesting the presence of aggregated mineral particles at larger sizes. The ratio of particle height-to-width h/a was also evaluated by measuring the shadow length. The median ratio h/a was 0.49 in Hohhot, 0.29 in Zhangye and 0.23 in Qira. Analytical functions were fitted to the grand total of the frequency distributions of aspect ratios, height-to-width ratios and circularity factors allowing parametric calculations of radiative effects and calculations of optical and sedimentation behavior of mineral particles.