254 4. Matching the size of water droplets to that of airborne particulate matter has been shown to enhance mitigation efficiency by increasing droplet–particle collision and adhesion, thereby promoting particle agglomeration and gravitational settling from the air. Few of the sensors are capable of measuring particle size distribution and hence can be used for effective suppression and prevention of airborne dust particles. 5. Due to their less weight compared to other bulky reference instruments, sensors can be easily mounted on the unmanned aerial vehicle for conducting vertical and horizontal flights. Vertical flights provide information on vertical distribution of pollution concentration, dispersion pattern and the influences of key meteorological factors in vertical direction. 6. Sensor mounted UAV can be used for measuring the pollution in several inaccessible locations, such a spontaneous combustion in both underground and surface mines. 7. For restricting the mining generated PM in reaching the surrounding communities, green cover around the mine periphery was considered to one of most important nature-based solution. Sensor mounted UAV can be used in investigating the efficiency of such mitigation measure. 5. CONCLUSIONS Low-cost air sensors have the potential to transform the real-time monitoring of pollution levels in the mining industry. Compared to the regulatory recommended continuous personal dust samplers, air sensors offer several advantages in term of cost, compactness, portability and wireless connectivity. However, to be used as reliable devices, the sensor data needs to be adjusted with a site-specific calibration factor to obtain reference equivalent measurements. The study compared two different methods of obtaining vertical PM concentration distribution in surface mines. Low-cost PM sensors were successfully deployed as stationary monitoring devices as well as non-stationary measuring device when attached to UAV. A clear indication of peak concentration during mineral extraction was visible. Sensor mounted UAV measurement in surface coal mine resulted in continuous profiles with dense information on diurnal variation along the vertical direction. The mean PM concentration recorded at the pit bottom of the surface iron ore and coal mine were higher compared to the corresponding pit top concentration levels. The levels were several times higher than the national standards and international guidelines. Decreasing concentration profiles has been observed, with higher rate of fall in PM10 concentrations compared to PM2.5 and PM1. A direct correlation between active mining operations and increased PM levels was observed, indicating the contribution of mining operations to different sizes PM. In both the surface mines, most of PM generated at the pit bottom retained inside the mine, particularly the coarse particles. Fine particles escaped from the pit top. Among the morning, afternoon and evening sessions, higher concentration was recorded during the evening flights for all three particle sizes, possibly due to lower mixing height. The findings of the current study show successful application of lowcost PM sensors in harsh and high concentration surface ming environments in obtaining reasonably accurate pollution concentration information in real-time. This pollution data combined with different active mining operations could lead to the development of more effective dust mitigation strategies, improved worker safety, and optimized operational schedules to minimize the environmental impact of surface mining.
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