Size distribution of dust aerosols observed over the Horqin Sandy Land in Inner Mongolia, China

Particle size distributions (psds) of airborne dust (PM20) during different dust emission events are investigated in this study, using data obtained from a dust-event monitoring station in the Horgin Sandy Land in Inner Mongolia, China. The results show that for a weak saltation-bombardment and aggregate-disintegration dust emission (SADE) event (0.44 < u(*) < 0.47 m s(-1)) on 7 April 2012, dust aerosols <= 1 mu m in diameter (d) accounted for 80% for all dusts measured. While for a strong SADE event (0.85 < u(*) < 0.89 m s(-1)) on the same day, large dust aerosols (d >= 2.5 mu m) increased significantly, with the largest proportion (40%) located in 4-7 mu m, which agreed with the airborne dust psds observed during another two strong SADE events (mean u(*) = 0.78 and 0.68 m s(-1)) on 13-14 April 2013. However, for a convective turbulent dust emission (CTDE) event (mean u(*) = 0.31 m s(-1)) on 17 April 2013, the mean proportion of dust aerosols <0.45 mu m reached 70%, which suggests that only fine dust particles loosely distributed at the surface could be easily uplifted into the atmosphere by convective turbulence. It found that the airborne dust psds at emission move to the larger sizes with the increasing u(*), but they remain unchanged when u(*) doesn't change too much. In addition, the dust psds for a non-local dust event on 19 April 2012 appeared smoother because of the mixing of dust aerosols through the processes of dust advection and deposition. (C) 2015 Elsevier B.V. All rights reserved.R&D Special Fund for Public Welfare Industry (meteorology); Ministry of Finance and Ministry of Science and Technology [GYHY201506001]; Public Welfare Projects for Environmental Protection [201409001, 201309009]; National Natural Science Foundation of China [41475007]; Basic Research Funds of Central Public Welfare Research Institutes [2014IAE-CMA-D]SCI(E)ARTICLEleexl.ouc@163.com; hsdq@pku.edu.cn231-2391