Imagine that you drove your car to school/work today. When you arrive, you reali
ID: 282984 • Letter: I
Question
Imagine that you drove your car to school/work today. When you arrive, you realize that you accidentally left a lightbulb on in your apartment. In terms of CO2 emissions, is it worth making a trip home from work to turn off the lightbulb?
Make the following assumptions:
The lightbulb uses 100W, and would be on for an extra 8 hours if you don’t drive back home to turn it off.
Electricity has an emissions intensity of 0.6 kg CO2e/kWh.
The drive would be very short, just 5 km round trip in a Prius that uses 5 L of gasoline per 100 km (the U.S. average is 45 km or about 28 miles).
You can use a lifecycle emissions factor of 3.2 kg CO2e per liter of gasoline (this is a bit higher than what you find in the Conversion Sheet).
a) How much CO2 will the electricity for the light bulb release?
b) How much CO2 will the car release?
c) What if you walked home to do this? Your round trip would be a 6.5 km walk, burning about 200 kcal in total. You estimate that your diet has an emissions intensity of 2 g CO2e/kcal, a bit below the American average. How much CO2 would you release in this walk?
Explanation / Answer
Given light bulb usage = 100W
It would be on for extra 8hrs if it is on.
given Electricity has an emissions intensity = 0.6 kg CO2e /kWh
a) how much CO2 will the electricity for the light bulb release: =?
Given light emission intensity = 0.6kgCO2e/kWh
100w for 8h = 800Wh
0.6kg CO2 emission for 1000 Wh
then how many Kg of CO2 for 800Wh =
= (0.6 *800) / 1000
=0.48kg CO2e / Wh for 8hrs.
b)how much CO2 the car release =
given distance = 5km
5 L f gasoline / 100km
how many liters for 5km=
=(5*5)/100
=0.25lit for 5 km
and given 3.2kg CO2 emission for 1 litre
then how many kg of CO2 emission for 0.25litres =
(3.2*0.25)/1
= 0.8kgCO2 for 0.25litres
= 0.8kgCO2 emitted.
So it would be better to left the bulb instead of going back in order to reduce CO2 emission.
[0.48kg is less than 0.8kg]
c)given 6.5km of walk burns 200kCal
given emission intensity = 2gCO2 e /kcal
2g of CO2 emission in 1 KCal
howmany grams of CO2 for 200kCal
= (200*2)/1
= 400g/kcal
1kg = 1000g
? = 400g
= (400*1)/1000
=0.4kg of CO2e / kCal