A person may demonstrate observable effects on the central nervous system when exposed to carbon monoxide at a concentration of 50 ppm, may lose consciousness at a concentration of 250 ppm, and may die at a concentration of 750 ppm. A "typical" urban environment produces carbon monoxide at a rate of 1.2 L/m2-hr. If a temperature inversion forms over the city at a height of 0.70 km, how long will it take the carbon monoxide concentration to reach 50 ppm if the wind velocity is zero? If the wind velocity is 1 m/s, what steady-state concentration of CO will be observed? Assume that the city is approximately square, 20 km on each side.