250 Pit bottom, being the location with active mining operations involving development as well as production activities, generate more pollution. The recorded levels exceeded the safe limited recommended by both World Health Organization (WHO) guidelines and Indian National Ambient Air Quality Standards. These findings highlight the severity of occupational exposure risks faced by mine workers working in the mine. Temporal analysis of PM levels at different vertical depths exhibited peak concentrations at instances of mineral extraction. Direct correlation was observed between elevated PM levels for all three sizes during the loading and hauling activities. Handling of extracted mineral causes the loose soil along the unpaved haul roads to become airborne. Apart from resuspended dust particles, exhaust emission from the haul trucks and shovels contribute to fine PM. This pattern was consistent at all the sensors deployed along the vertical extent of the mine, indicating vertical transport of PM generated from the pit bottom mining operations. The current findings align with the results of several field-based sampling studies conducted across different surface mines (Gautam and Patra, 2015; Pradhan et al., 2025). To evaluate the percentage of PM escaped from the pit top with respect to that generated at the pit bottom due to in-pit mining operations, percentage of fall is calculated for all three particle sizes. Along with the fall, the variation in the proportion of PM1, PM2.5-1 and PM10-2.5 was investigated at different depths (Figure 5). From pit bottom to immediate level (526 mRL) above the pit bottom 9-78% of fall has been observed. Similarly, 31 to 83% of PM emitted at the pit bottom is retained with in the mine atmosphere of a 100 m depth iron ore mine. The rate of fall observed is higher for PM10-2.5 particles due to the reason that coarser particles have high settling tendency compared to the PM2.5-1 and PM1 particles. It can be noted that, most of coarser particles are retained with in the surface mining environment, and fine particles, especially PM1, escaped from the pit. The relative proportion of PM1, PM2.5-1, and PM10-2.5 at each vertical depth is presented using a pie chart (Figure 5). The proportion of coarser particles (PM10-2.5) at the pit bottom was found to be 63% and PM2.5-1 and PM1 was 21% and 15%, respectively. It is interesting to note that, PM2.5-1 proportion at each depth remained similar within a narrow range (18-21%). This can be attributed to the light weight nature of the fine particles that have tendency to stay airborne for considerable amount of time. Additionally, the proportions of PM1, PM1-2.5, and PM2.5-10 remained relatively constant at depths 542 mRL and above, indicating that the size distribution of particles in the air is very little affected beyond a height of 30 m from the source of emission.
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