2021
AP
®
Environmental
Science
Sample Student Responses
and Scoring Commentary
Set 2
Inside:
Free Response Question 3
•• Scoring Guideline
•• Student Samples
•• Scoring Commentary
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AP®EnvironmentalScience2021ScoringGuidelines
©2021CollegeBoard
Question3:AnalyzeanEnvironmentalProblemandProposeaSolution
DoingCalculations 10points
(a) Describewhycoalisconsideredanonrenewableenergysource. 1point
Acceptoneofthefollowing:
Nonrenewableenergysourceslikecoalexistinafixed/finite/limitedamount.
Theformationrateofcoalislessthantheconsumption/combustionrateofcoal.
(b) Describeonepotentialenvironmentaladvantageofreplacingacoal‐firedpowerplantwith
anatural‐gaspowerplant.
1point
Acceptoneofthefollowing:
Naturalgascombustionemitsfewergreenhousegases/lessCO
2
.
Naturalgascombustiondoesnotemitmercury/lead/cadmium/uranium.
NaturalgascombustionemitslessNO
x
/SO
x
/reducesacidprecipitation.
Naturalgascombustionproducesless/noparticulatematter/soot/smog.
Transportofnaturalgasdestroys/fragmentslesshabitatorrequireslessfossilfueluse
thantransportofcoal.
Habitatdestructionduetotheimpoundmentofcoalashorcoalslurryisnegated.
Coalextractiondestroyshabitatbystripminingormountaintopremoval.
(c) Describeoneeconomicadvantageofusingnaturalgas,ratherthancoal,inproducing
electricity.
1point
Acceptoneofthefollowing:
Transportofnaturalgas(inpipelines)costslessthantransportofcoal(byrail).
Naturalgas(methane)harvestedfromadecompositionreaction(landfills,wastewater
treatmentplants,biodigesters)costslessthancoal.
Therearefewerhealth‐relatedissueslinkedtotheburningofnaturalgasthanare
linked
toburningcoal,leadingtolowerhealthcarecostsforindividualsorsocietyasa
whole.
Therearefewerpollutioncontrolsneededforanaturalgaspowerplant,decreasing
thecostofo
peration/construction/permitting.
Therearelowercombustion‐residuedisposalcostsfromtheoperationofnaturalgas
burnin
gpowerplantsthanfromcoal‐burningpowerplants.
Natural‐gas‐burningpowerplantsaremuchmoreefficient(moreelectricityoutput
fromthe
sameenergyinput)thancoal‐burningpowerplantsleadingtolowerfuel
costs.
AP®EnvironmentalScience2021ScoringGuidelines
©2021CollegeBoard
(d) Whennaturalgasisusedtoheathomes,itcanproducecarbonmonoxidegas,whichcan
leadtocarbonmonoxidepoisoninginhumans.Proposeasolutiontoreducetheincidence
ofcarbonmonoxidepoisoninginhumans.
1point
Acceptoneofthefollowing:
Install/use/replace/updatecarbonmonoxidedetectors/alarms/sensorsorreplacethe
batterieswithinthesedevices.
Performregularmaintenanceonnaturalgasfurnacestoensurethatminimalcarbon
monoxideiscreatedorthatthecombustionproductsareproperlyvented/exhausted
tothebuildingexterior.
Createlawsorregulationsthatmandatethatcarbonmonoxidedetectorsmustbe
installedinallhomesofanytype.
UsePSA’s,billboards,orothermethodstoinform/educatethepublicaboutcarbon
monoxidepoisoning.
Changethehomeheatingsystemtoamethodthatdoesnotincludethecombustionof
afuelthatmayproducecarbonmonoxide.
(e) CalculatethepercentchangeintheaverageannualPM
2.5
concentrationintheairfrom
1990to2016.Showyourwork.
1point
Onepointforthecorrectsetup(mustincludeunitsandmultiplicationby100toyielda
truepercentage)tocalculatethepercentchange:
188 μg/m
33
85μg/m
100
85μg/m
3
Onepointforthecorrectcalculationofthepercentchange: 1point
121%
120%
121.2%
Totalforpart(e) 2points
(f) TreescanremovePM
2.5
fromtheatmospherewhenparticulatessettleontheleavesand
aresubsequentlywashedontosoilbyrain.TheaverageannualremovalofPM
2.5
is2.3
kilogramsperhectare.CalculatethedecreaseinPM
2.5
removalinkilogramsiflogging
reducedaforestedareafrom50,000hectaresto43,000hectares.Showyourwork.
1point
Onepointforthecorrectsetup(mustincludeunits)tocalculatethenumberofkilograms
ofPM
2.5
:

2.3 kg
50, 000 ha 43, 000 ha
hectare
50, 000ha 2.3 kg ha 115, 000kg;43, 000 ha 2.3 kg ha 98, 900 kg
115, 000 kg 98,900 kg
AP®EnvironmentalScience2021ScoringGuidelines
©2021CollegeBoard
OnepointforthecorrectcalculationofthenumberofkilogramsofPM
2.5
: 1point
16,100kilogramsofPM
2.5
16,000kilogramsofPM
2.5
Totalforpart(f) 2points
(g) Researchhasshownthathospitaladmissionsforcardiovascularproblemsincrease1%with
every10%increaseinPM
2.5
concentration.Acityexperienceda23%increaseinPM
2.5
concentrationandhad7,390hospitaladmissionsforcardiovascularissuesoveraone‐year
period.Calculatetheanticipatedincreaseinthenumberofhospitaladmissionsfor
cardiovascularissuesduringthenextyearifthePM
2.5
concentrationcontinuestoriseatan
identicalrate.Showyourwork.
1point
Onepointforthecorrectsetuptocalculatetheincreaseinhospitaladmissions:
0.23
0.01 7, 390 admissions
0.10
0.23 1
7,390 admissions
0.10 100
23%
1% 7, 390 admissions
10%
Onepointforthecorrectcalculationoftheincreaseinhospitaladmissions. 1point
Acceptoneofthefollowing:
169moreadmissions
170moreadmissions
Totalforpart(g) 2points
Totalforquestion3 10points
3A 1 of 1
3B 1 of 1
3C 1 of 1
AP
®
Environmental Science 2021 Scoring Commentary
Question 3
Note: Student samples are quoted verbatim and may contain grammatical errors.
Overview
The intent of this question was for students to demonstrate their ability to describe nonrenewable energy
s
ources and compare coal and natural gas electricity generation. Students were expected to show their work
and complete calculations related to air pollution/particulate pollution.
In part (a) students were expected to demonstrate an understanding of nonrenewable energy sources [Practice
1-Conecept Explanation, Topic 6.1 is Renewable and Nonrenewable Energy]. In parts (b) and (c) students were
asked to describe an environmental and an economic advantage of replacing a coal-fired powerplant with a
natural-gas power plant [Practice 7-Environmental Solutions, Topic 6.3 Fuel Types and Uses]. In part (d)
students were asked to propose a solution to reduce the incidence of carbon monoxide poisoning in humans. In
parts (e), (f), and (g), students were asked to calculate the percent change of an air pollutant over a particular
time period, the amount of particulate pollution reduction by leaf deposition, and the increase in the number of
hospital admissions due to an increase in particulate pollution. The calculation portions of the question
evaluated understanding and application of Science Practice 6 Mathematical Routines [Topic 7.1-Introduction
to Air Pollution].
Sample: 3A
Score: 8
One point was earned in part (a) for describing “coal … is being used faster than it can replenish.” One point was
earned in part (b) for describing an environmental advantage as “there will be less greenhouse gases in the air.”
No point was earned in part (c). One point was earned in part (d) for proposing the solution of “install … carbon
monoxide detectors.” One point was earned in part (e) for calculating the correct percent change of 121.176%. No
point was earned for the setup as units were not included. Two points were earned in part (f). One point was
earned for calculating the correct answer of 16,100 kg, and one point was earned for the correct setup, including
units. Two points were earned in part (g). One point was earned for calculating the correct answer of 170. One
point was earned for the correct setup.
Sample: 3B
Score: 5
One point was earned in part (a) for describing coal as nonrenewable because there “is not an infinite amount of
it.” One point was earned in part (b) for describing an environmental advantage as “less pollutants like carbon
dioxide are produced with natural gas power plants.” No point was earned in part (c). One point was earned in
part (d) for proposing the solution to carbon monoxide poisoning as “Homes could be required to have so many
carbon monoxide alarms.” One point was earned in part (e) for calculating the correct percent increase of
121.18%. No point was earned for the setup as no units are included. One point was earned in part (f) for
calculating the correct decrease of
PM
2.5
as 16,100 kg. No point was earned for the setup as no units are included,
and the “98,900” is converted to “989,000” in the subtraction pair. No points were earned in part (g).
Sample: 3C
Score: 2
One point was earned in part (a) for describing coal as “located on Earth in finite supply.” No point was earned in
pa
rt (b). No point was earned in part (c). No point was earned in part (d). One point was earned in part (e) for
calculating the correct answer of 121.176% increase. No point was earned for the setup as units are not included.
No points were earned in part (f). No points were earned in part (g).
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