"1. Consider a coal fired power plant delivering an average of 1000 megawatts of electricity. Make the following assumptions:
i. It burns coal containing 2% sulfur by weight.
ii. Control technology results in the elimination of 90% of the emitted sulfur. The uncontrolled S is emitted as SO2.
iii. The coal contains 0.5% nitrogen by weight, all of which is emitted as NO2.
iv. The plants total nitrogen dioxide emissions are comprised of an equal amount of N from the fuel and N from the atmosphere.
v. The heat content of the coal is 30 MJ/kg and that heat is converted to electricity at an efficiency of 30%.
vi. The atmosphere downwind of the plant is rapidly mixed vertically below an inversion layer at a height of 500 meters.
vii. A wind averaging 15 km/h blows the plume in a wedge with an angle of 10o.
viii. Nearly all inhaled nitrogen dioxide is converted to nitrate (NO3-) in the human body. For every milligram of nitrate formed in, or taken in, the body, roughly 50 micrograms of nitrite (NO2-) are formed. For every milligram of nitrite formed or taken in, somewhere between 0.1 and 0.5 micrograms of nitrosamine (use dimethylnitrosamine, which is C2H6N2O) is formed in the body.
ix. The Brookhaven National Lab (BNL) estimate for excess deaths from exposure to sulfate in the air is 3.25 excess deaths per year per 106 persons exposed to each microgram(SO4)/m3.
a. Neglecting all removal processes in the plume, estimate the average concentrations of emitted S and N at a distance of 50 km downwind from the plant where a town is located. Express your answers in micrograms (of S or N) per cubic meter. (20 pts.)
b. The town contains 10,000 people. Assuming the BNL estimate of excess deaths from sulfate, and assuming 30% of the emitted SO2 is transformed to sulfate by the time the plume reaches the town, estimate how many excess deaths or fractions thereof will occur in the town each year due to the emitted SO2. (20 pts.)
c. Assuming the maximum conversion rate for nitrosamine formation, and assuming that 50% of the emitted NO2 from the power plant is converted to (respirable) nitrate before the plume reaches the town (note that both NO2 and nitrate inhalation are pathways for nitrosamine formation), estimate the daily contribution of the power plant to the townspeople’s nitrosamine burden. As with part a, neglect all processes that remove pollution from the plume before it reaches the town. (20 pts.)
d. Using your result above, and assuming the carcinogenic potency of nitrosamines in humans is 5.0, what is the lifetime probability of tumor induction associated with the daily nitrosamine formation from the power plant. Assume a linear dose-response relationship and recall that carcinogenic potency can be used to determine dE50 as described in class. (20 pts.)
e. Given your answer to b and d, which do you feel poses the greater threat to the health of the townspeople, the sulfur or the nitrogen emissions? Explain you answer. To answer this you will have to place the risk estimates for sulfate and for nitrosamines on a comparable basis. (20 pts.)
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