Seaside is a city of 20 km x 10 km located between two parallel mountain ranges

Question

Seaside is a city of 20 km x 10 km located between two parallel mountain ranges 300 meters high -- other city borders are the ocean and an opening onto an uninhabited prairie (see Figure). The meteorology in the valley is such that conditions during the day are quite stagnant: the wind comes from the south at a slow 2 km/hr and the mixing height is only 50 meter over the top of the mountain tops, so the overall ‘basin’ can be considered to be 350 m high, but with air only flowing in the top 50 m. Vehicles in Seaside are in poor condition and driven heavily: they burn 2 million liters of gasoline over 24 hours at a constant rate. The vehicles are highly polluting and emit high levels of carbon monoxide (CO Emission factor of 900 gCO /kg fuel). Air from outside the valley has negligible levels of CO, and CO can be considered conservative inside the valley. The density of gasoline is 720 kg/m3.

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Problem 2 (30 points)

Seaside is a city of 20 km x 10 km located between two parallel mountain ranges 300 meters high -- other city borders are the ocean and an opening onto an uninhabited prairie (see Figure). The meteorology in the valley is such that conditions during the day are quite stagnant: the wind comes from the south at a slow 2 km/hr and the mixing height is only 50 meter over the top of the mountain tops, so the overall ‘basin’ can be considered to be 350 m high, but with air only flowing in the top 50 m. Vehicles in Seaside are in poor condition and driven heavily: they burn 2 million liters of gasoline over 24 hours at a constant rate. The vehicles are highly polluting and emit high levels of carbon monoxide (CO Emission factor of 900 gCO /kg fuel). Air from outside the valley has negligible levels of CO, and CO can be considered conservative inside the valley. The density of gasoline is 720 kg/m3.

(a) What is the steady state concentration of CO under daytime conditions?

(b) Seaside has a CO air quality standard of 20 ppm, will it meet the standard during the day? Seaside is always at 25 C and 1 atm.

(c) Name two symptoms or health impacts in humans due to excessive CO exposure.

(d) Name an emission control device that could limit CO emissions in these vehicles?

Explanation / Answer

(a)
Width, W = 20km, mixing height, H = 50m = 0.05km, Length, L = 10km
CO creation rate, Q =
900 gCO/kg fuel * 720 kg/m3 * 1e-3 m3/l *2E6 l/hr = 12.96E8 g/hr
wind velocity, u = 2km/hr

mass balance of   pollutants
Accumulation rate =   (flow rates in )-(flow rates out)   + (creation rate)   0 =

(f8low rates in, g/s) + (Q, creation rate, g/s) – (flow rates out, g/s)  
0w = 0 + Q – u*W*H*c
8
c = Q/(u*W*H) = 12.96E8/(2*20*0.05) = 6.48E8 g/km3 = 0.648 g/m3  

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