A coal-fired power plant emits 143000 kg/day of SO ₂ from a stack of effective height equal to 128 m. On an overcast summer afternoon, when the wind speed at the 10-m height is 2.4 m/s, what will be the ground-level SO ₂ concentration in μg/m ³ ) at a location 3 km downwind and 1.5 km perpendicular to the wind direction?