251 Figure 5 - PM proportion and percentage of fall in PM levels at different vertical depths 3.2 Surface coal mine Vertical flights using sensor mounted UAV from the pit bottom to the pit top of the surface mine are shown in Figure 6. A significant variation in PM concentrations of three sizes was observed along vertical extent of the coal mine. Higher PM concentrations were recorded at the pit top and lower levels at the pit top, similar to those observed in surface iron ore mine. Mean PM levels recorded at the pit bottom (38-236 μg m-3) are 1.15-1.90 times the concentrations recorded at the pit top (33-124 μg m-3). Higher PM concentrations at the pit bottom can be attributed to the emissions from active mining operations accompanied by lower winds speeds compared to the pit top location. Pit bottom being an active working area with intense mining operations involving continuous movement and transfer of earthen soil and rock material causes particle to become airborne (Zafra-P´erez et al., 2023). Overall, a fall of 13-47 % was observed for a vertical depth of 130 m. Higher percentage of decrease happened for PM10 (47 %) compared to PM2.5 (15 %) and PM1 (13 %). Higher PM concentration fall in coarse
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