1503 3.3 Comparison between surface iron ore and coal mine Compared to the stationary-based ground monitoring methodology followed in the surface iron ore mine, UAV based monitoring in coal mine allowed for obtaining more continuous PM concentration data along the vertical depth. Although the mean PM concentration recorded at the pit bottom of both mines is similar, there existed a significant difference in the PM concentrations at the pit top. It is interesting to note that, the PM mass concentrations recorded at each vertical depth inside the coal mine is several times higher than those recoded in the iron ore mine. The material handled in terms of coal and overburden on day-to-day operations are significantly higher in coal mines compared to the iron ore mines, which causes the higher PM pollution in the coal mine. However, the fall in PM concentration observed at the immediate level above the pit bottom in the iron ore mine is higher compared to the coal mine. The percentage fall observed in the iron ore mine for a vertical depth of 100 m is higher compared to that of 130 m deep coal mine. This can be attributed to the high-density iron ore particle that settle faster, whereas the light weight coal particle with relatively lesser density tries to escape away from the source of generation under favorable conditions. 4. POSSIBLE APPLICATIONS OF LOW-COST SENSOR AND UAV 1. One of the important applications of low-cost sensors is for personal exposure monitoring of mine workers deployed at different mining operations. As these sensors are miniature in size and can be made portable, they offer minimal discomfort when attached to miner safety helmet. Sensor scan also be deployed inside the operators’ cabin of several HEMM, for real-time and continuous monitoring of pollution exposure of operators during the working shift. 2. Low-cost sensors are several times less expensive than the regulatory instruments, hence can be used for simultaneous monitoring of multiple working locations in and around the mines. Deploying a low-cost sensor network across the surface mine gives dense information of spatial and temporal variability of PM levels. Long term spatial monitoring allows for accurate identification of mining operations of potential emission strengths and other hotspots in the mining environment. 3. The integration of wireless connectivity in low-cost air sensors enables remote, real-time monitoring of particulate matter concentrations by mining authorities and other regulatory agencies, thereby enhancing surveillance efficiency and regulatory oversight. 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
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