*Coal often contains sulfur as an impurity that is released as gaseous SO2 during
combustion. SO2 is one of six primary air pollutants monitored by the U.S. EPA. The
Clean Air Act limits sulfur emissions from large coal-fired boilers to 0.54 kg (1.2 lbs)
of sulfur per million Btus of heat generated. (1 metric ton=1,000 kg=2,200 lbs=1.1
tons; 1 kg=2.20lbs).
1. Given that coal used by electric power plants has a heating value of 27.5 million
Btus per metric ton, determine the number of kg of coal needed to produce 1
million Btus of heat.
(106 BTU)
æ 27.5 ´106 BTU ö
ç
÷
ç
÷
1000
kg
è
ø
= 36.36 kg
2. Assuming that all the sulfur in the coal is released to the atmosphere during
combustion, what is the maximum percentage of sulfur the coal can contain and still
allow the utility to comply with the Clean Air Act?
The EPA allows 0.54 kg of sulfur per 36.36 kg of coal, so the percentage of sulfur
must be no more than
0.54
´100% = 1.49% .
36.36
*Under normal driving conditions, an internal combustion engine produces
approximately 200 grams (0.2 kilograms or 0.44 pounds) of CO2 per kilometer
driven. In one large city, there are 7 million cars, and each car is driven an average
of 20,000 kilometers (12, 400 miles) per year.
3. Calculate the carbon footprint per car, the number of metric tons of CO2
produced by a typical car in one year.
æ
öæ
kg CO2 ö æ
ç0.2
÷ ç2 ´104 km/yr ÷ ç10-3 mt
ç
֍
ç
÷
km ø è
car ø è
kg
è
ö
mt
÷÷ = 4
car yr
ø
4. Calculate the total carbon footprint for all cars in the city, the metric tons of CO2
produced by all cars in one year. (1 metric ton=1,000 kg=1.1 tons). Worth 10
points.
æ
mt ö
÷÷ = 28 million mt/yr
7 ´106 cars çç4
è car yr ø
(
)
*This information from an EPA report shows the typical composition of U.S.
municipal solid waste (MSW) in 2006.FE 11
Yard trimmings 14%
Food Scraps 13%
Other 4%
Paper 36%
Glass Plastics 6%
Rubber, leather and textiles 8%
Wood 6%
The average daily MSW production per person in the US in 2006 was 2.10 kilograms
(4.60 pounds).
5. Use the data in the figure above to understand what makes up the annual MSW
ecological footprint for a typical American. For each category in the pie chart,
calculate the total weight in kilograms (and pounds) generated in 2006 by the
average American. (1 kilogram = 2.20 pounds)
æ
kg ö æ
days ö
kg
çç2.1
÷÷ çç365.25
÷÷ = 767
day
yr
yr
è
øè
ø
Per capita annual MSW
Category of waste
%
kg/yr
lb/yr
Paper
36
276.1
125.5
Yard Trimmings
14
107.4
48.8
Food Scraps
13
99.7
45.3
Plastic
13
99.7
45.3
Rubber, Leather, Textiles
8
61.4
27.9
Glass
6
46.0
20.9
Wood
6
46.0
20.9
Other
4
30.7
13.9
Total
100
767.03
348.65
per capita annual MSW (kg)
46.0
30.7
Paper
46.0
276.1
61.4
Yard Trimmings
Food Scraps
99.7
Plastic
99.7
107.4
Rubber, Leather,
Textiles