1499 Table 1 – Performance evaluation of OPC N3 sensor with respect to the reference instrument. Performance metrics Target value Dust type OPC N3 Linearity Coefficient of determination (R2) ≥ 0.70 Coal 0.97a Iron ore 0.77a Bias Slope 1.0 ± 0.35 Coal 0.51 Iron ore 0.82a Intercept (b) -5 ≤ b ≤ 5 µg m3 Coal 9.8 Iron ore -7 Error Normalized root mean square error (NRMSE) ≤ 30% Coal 60 Iron ore 34 aMeets US EPA criterion 3. RESULTS AND DISCUSSION 3.1 Surface iron ore mine A significant variability in PM levels was observed at different depth in iron ore mine, with higher variability in PM10 compared to PM2.5 ad PM1. Higher PM levels (PM10: 228 μg m-3, PM2.5: 84 μg m-3, PM1: 35 μg m-3) were recorded at the pit bottom location and lowest was found to be at the pit top (Figure 4). Figure 4 – PM concentration at different vertical depth in surface iron ore mine 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
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