247 the vertical extent of the mine. Most of the active mining operations using heavy earth moving machinery were at the pit bottom during the sampling. The selection of benches was based on the active mining operations, accessibility and safety. Along with OPC N3 sensor, portable weather stations were installed at the pit bottom and the pit top for monitoring the prevailing meteorological parameters inside the mine and in the ambient atmosphere (Figure 2). Sampling was conducted during the working shift of the mine. All the sensors were calibrated at the pit top of the mine for 4 hours before deploying them inside the mine. Collected sensor data was multiplied by the correction factor derived from the calibration experiment. Figure 2 – Sampling protocol using low-cost OPC N3 sensors deployed at multiple benches of iron ore mine Surface coal mine (operated by Mahanadi Coalfields Limited, India) is 130 m deep and employs dumper and shovel combination method for extraction of coal and removal of over burden. For measuring the vertical PM profile, OPC N3 sensor was mounted on to an unnamed aerial vehicle (UAV) (Figure 3). Vertical flights with a constant ascent speed of 1 m s-1 were conducted staring from the pit bottom up to the pit top level. To understand the influence of diurnal variation on PM mass concentration distribution along vertical depth of the surface coal mines, vertical flights were conducted during morning, afternoon and evening time. Overall, 30 vertical flights were conducted out which valid data was obtained from 22 vertical flights. Meteorological parameters such as temperature and relative humidity prevailing along the vertical extent of the mine were monitored using a portable weather station deployed on the UAV.
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