Size distribution of PM₂₀ observed to the north of the Tibetan Plateau

Abstract

The size distribution of airborne dust particles is an important parameter in the measurement of dust emissions due to wind erosion, and a quantitative and accurate description is necessary. Observations regarding the size distribution of airborne dust particles are currently lacking in Tibetan Plateau (TP). This study aims to obtain a dust particle size distribution and compare the difference in spatial distribution at a field site (FS) and two urban observation sites (Minfeng and Hetian), in the north of the TP, under the condition of the dust-days and clear-days. The observation data was collected from 5 July to 4 August, 2019. The mass concentration of dust (PM₂₀) was measured with a 10-stage quartz crystal microbalance cascade impactor. The results suggested that 91.9% of the particles were less than 1.4 µm on clear-days, and particles of d ≥ 1.4 µm increased to 27.2% with the occurrence of the dust events. More than 80% of the airborne dust particles were less than 1.4 µm for each friction velocity. The proportion of d < 0.7 µm was the greatest at 3.0 m (above the surface, similarly hereinafter) on dust-days, while the proportion of d > 0.7 μm was the greatest at 0.5 m on clear-days. During urban observation, with the occurrence of dust events, the concentration of a particle size greater than 2.5 µm increased most significantly in Minfeng, while the concentration of a particle size less than 0.7 µm increased most significantly in Hetian. Moreover, the proportion of particles with d < 0.7 μm had the smallest difference, while the proportion of particles with d > 1.4 µm had the most obvious difference among these three sites.