Surface Environment, Mine Ventilation and Underground Hazards · Surface Environment · 2 marks · Numerical answer
A 20×40 km city has an inversion lid 100 m high. Wind enters perpendicular to the 20 km side at 4 m/s. PM₁ emission is 1 kg/s. Under a steady well-mixed box model, find concentration in μg/m³, to one decimal. Assume negligible incoming concentration.
The ventilation cross-section is the upwind width times mixing height:20000×100=2000000 m². Volume flow is 4×2000000=8000000 m³/s. Concentration is emission/flow=1/8000000 kg/m³. Convert kg to micrograms using 10⁹ to obtain 125.0 μg/m³. The downwind city length cancels from the steady mass balance.
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