Consider the air over a city to be a box 100 km wide, 100 km long and 1 km high. Clean air is blowing into the box along one of its sides with a speed of 4 m/s. A reactive air pollutant is emitted into the box at a rate of 10 kg/s and decays with a decay rate constant k = 0.20 h-1.

a)Find the steady-state concentration of the air pollutant if the air is assumed to be completely mixed.

b) If the wind speed suddenly drops to 1 m/s, and all other conditions remain the same, estimate the air pollutant concentration 2 hours later.