List of top Surface Environment Questions on Air, water and soil pollution: Causes

A rectangular face of 2.0 m x 2.5 m dimension is blasted with 20 kg explosive in a 1000 m long drive. One kilogram of explosive produces 2200 cm³ of nitrous fumes. The face is ventilated with a duct, located 10.0 m away from the face, to dilute the fumes. The quantity of air, in m³/s to be circulated for reducing the concentration of nitrous fumes to 5 ppm within a period of 5 minutes, is ____. (round off up to 2 decimals)
[Use the relation, t=2.303 $\frac{V_m}{Q}$ log $\frac{q}{v_mc}+\frac{v-v_m}{Q}$ where t=time, V_m=volume of the tunnel over which the mixing of the gases produced at the face, and air delivered by the fan occurs, c = concentration at time, t, V = volume of tunnel, Q = quantity of air flow, q = total volume of nitrous fumes produced]

Polluted air with particulate matters of diameter 50 μm enter with a horizontal velocity of 1.0 m/s at a height of 0.5 m from the bottom of a dry settling chamber. The density of the particle is 2000 kg/m³ and dynamic viscosity of the air is 1.8×10^-5 kg/m-s.
Assume streamline flow and the density of air is negligible as compared to particles and uniform horizontal velocity of 1.0 m/s of gas and particles within the chamber. 
Considering particle settling follows Stoke's law, the minimum length in m, of the chamber required for settling of the particle at its bottom, is____.(round off up to 2 decimals)