1. (4 pts) You are asked to evaluate a stack that is emitting PM2.5 at a rate of 220 g/s. The stack is located in an urban area where the surface wind speed is 3 m/s. The stack has an effective stack height of 80 m, and an actual stack height of 50 m. Calculate the ground-level concentration of the pollutant (µg/m³) on a cloudy summer day: a) 800 m directly downwind b) 5,000 m directly downwind