6.24. In Problem 6.6, what is the maximum downwind distance at which the ground level con- centration, directly under the plume centerline, is greater than or equal to 30 µg/m³, (a) If the mixing height L = 1000 m? (b) If the mixing height L is infinite?

The air shed over a city can be considered by a completely stirred tank reactor (CSTR) model with two sides of 2×10° m in length and a mixing depth of 500 m. Horizontal wind blows at 4 m/s from one side of the box and exits from the opposite side. Assume that within the box, the air is well mixed all the time. Within the air shed, benzene (C6H6) is emitted by automobiles, power plants, and factories at a rate of 0.4 kg/s. No benzene is brought to the city by wind. When equilibrated, what is the benzene concentration in the atmosphere? Please sketch the model first. Pay attention to the units.

9. Consider the NOx emissions from two rural sources. The second source is located 500 m south and 500 m east of the first source. Source 1 emits 20.5 g/s and has an effective height of 100 m. Source 2 emits 35 g/s and has an effective height of 150 m. Sketch the locations of the stacks and the receptor site. Determine the concentration at a receptor located 4 km east and 200 m south of source one. Atmospheric conditions are neutral with a westerly wind of 5 m/s measured at 10 m.

A paper plant is proposed for a location 1 km upwind from a town.  It will emit 40 g/s of hydrogen sulfide, which has an odor threshold of about 0.1 mg/m3.  Assume that winds at 10 m above ground are 2.5 m/s, and at the effective stack height they typically vary from 4 – 10 m/s blowing toward the town.  If it is summer day with a few broken clouds, What stack height should be used to assure concentrations are no more than 0.1 times the odor threshold at the near edge of town (1 km away)? To be conservative, the stack will be designed assuming no plume rise. Will any buildings (e.g., the country cabin or the doghouse on the far edge of town) experience higher concentrations than a residence at the 1 km boundary? Briefly explain your answer.