Abstract:

A series of investigations were performed to provide particle size signatures of urban dust near the ground in Changchun, China. A total of 34 samples of dust were collected along the north-south and the east-west axis using a systematic sampling strategy (about 1.5 m above the ground surface). The laser particle size instrument was employed to analyze the particle size. According to the analytical results, the mean median grain size and the arithmetic mean diameter of the near-surface urban dusts in Changchun was 21.58 μm and 24.24 μm, respectively. The coarse silt (10.00-80.00 μm) content in the urban dusts was higher relatively, which was 71.28% on average, while the clay particle (<5.00 μm) and fine silt (5.00-10.00 μm) was 14.75% and 13.05%, respectively. The distribution of grain size was characterized by skewed positively, bimodal and middling to narrow kurtosis, which was similar to the gain size distribution of modern dust storms and street dust and indicated that urban dust near the ground is a mixture of coarse grains derived from local area and fine grains transported over long distances, and was derived from aeolian processes. The gain size in urban dust near the ground was almost completely below 100.00 μm, which indicated that these particles were pick up and transported by suspension under proper aerodynamic conditions. Meanwhile, the average content of PM₁₀ and PM_2.5 in urban dust near the ground was 27.76% and 7.32%, respectively, which were much higher, showing the high potential hazards. There were no significant spatial variations of gain size distribution, however, the variation range of grain size in central urban area was small relatively, which indicated that the origination of urban dust near the ground was multiple and complicated in suburban compared with that of the central urban area.

Key words: urban, near surface, dust, particle size, Changchun, PM_2.5