1502 Figure 6 – Vertical profile of different sized PM concentration measured by the UAV Out of morning, afternoon, and evening sessions, higher PM concentrations were recorded during the evening session and lower during the afternoon session. Concentrations recorded during the morning session were significantly higher than the afternoon session but lower than the evening session. It is interesting to note that PM level along the vertical depth during the afternoon session were confined within a narrow range. Afternoons are usually hot with higher atmospheric boundary layer that cause unstable atmospheric conditions and favor particle dispersion. In contrast, higher PM concentration in the evening can be attributed to the gradual accumulation of particles emitted from continuous mining operations, accompanied by a decrease in the atmospheric boundary layer height and poor vertical mixing. The temperature difference between the pit bottom and the pit top during the afternoon is significantly higher compared to the morning and evening sessions. Therefore, limited dispersion happened in the morning and evening, leading to higher PM levels along the vertical extent of the mine.
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