The air shed over a city can be considered by a completely stirred tank reactor (cstr) model with two sides of 105 m in length and a mixing depth of 1000 m. 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 (coho) 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.

(a) what is the highest possible benzene concentration in the atmosphere?
(b) benzene is a known human carcinogen with a chronic potency factor of 2.9x102 (mg/kg/day) through inhalation. assume that a 70-kg person who breaths 20-m3 air a day has lived in the city all his life. what is the upper-bound lifetime incremental risk for inhaling benzene from air? according to the incremental risk, how many extra annual cancer deaths would be expected from the city if the city has a population of 1,000,000 and people living in the city have a life expectancy of 70 years?