greenhouse effect.doc

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Greenhouse Effecthttp://www.pasco.com/file_downloads/experiments/pdf-files/glx/earth/15-Greenhouse-Effect-la.pdf

PurposeMeasure the effect on temperature of a greenhouse gas (carbondioxideCO2) on a simulated atmosphere and compare this data against an

atmosphere with lower levels of CO2.

BackgroundWhat is the greenhouse effect?

The greenhouse effect was an expression first created by French mathematicianJean Fourier in 1822. Fourier suggested the Earths atmosphere acts like a glassgreenhouse, which lets through the rays from the Sun, but traps the re-radiatedrays from the ground. Fourier was correct, and later it was discovered thatatmospheric gases are transparent to shortwave radiation and absorb infrared(long-wave) radiation emitted from the surface of Earth. This prevents much ofthe Earths re-radiated thermal energy from escaping into space. This was an

important observation because it led to the understanding that most of theheating of our atmosphere comes indirectly from the Sun (shortwave radiation)and directly from the Earths surface (long-wave radiation). Without the presenceof the atmosphere and the greenhouse effect, the average temperature on Earthwould be approximately 30C lower (the temperature would be about 15Cinstead of +15C).

Fouriers analogy however, was somewhat skewed. The greenhouse effect, orthe warming effect of Earths atmosphere, was compared to glass buildings(greenhouses) built to protect and warm plants through the winter. The physics ofgreenhouse glass and Earths atmosphere are very different. Greenhouses

function largely through the suppression of air circulation and less via thetrapping of solar radiation by glass. Conversely, the atmosphere encourages aircirculation, and the source of atmospheric heating is not the trapping of warm airbut the air molecules actually absorbing radiant heat energy. The mechanism ofthe greenhouse effect (Fig. 1) stems from Earths intricate atmosphere, which iscomposed of:

molecular nitrogen (N2), 77%;

molecular oxygen (O2), 21%;

water vapor (H2O), 1%;

argon (Ar), 0.93%;

carbon dioxide (CO2), 0.035%;

methane (CH4), traces;

inert gases (Ne, He, Kr, Xe), traces, and;

particulates (silicate dust, sulfates, sea salt)


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Fig. 1. Greenhouse Effect

Table 1: Global Energy Balance

Space Atmosphere Land & Ocean

Origin Percent

(%)incoming

Interaction/

Component

Percent

(%)

Interaction/

Component

Percent

(%)

Sun 100

Absorbed byatmosphericH2O, dust, O3

16

Absorbedby ground

51Absorbed inclouds

3

Backscatteredby air

6

Reflected byclouds

20

Reflected bysurface

4

Balance 100= +49 +51

Note: The percent of energy portions vary from author to author, depending uponthe literature cited.


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Fig. 2. Global Energy Balance

The global energy balanceTable 1 and Fig 21 illustrate the global energy balance. The solar radiation (51%)that reaches the surface by directly passing through the atmosphere is used to

melt ice and snow, to heat the ground, to evaporate water, and inphotosynthesis. When the ground is heated, the surface emits energy back intospace as infrared (IR) radiation (long-wave). Much of this radiated energy doesnot make it into space, but is absorbed by greenhouse gases in the atmosphere.These gases become warmed and radiate a slightly altered spectrum of long-wave energy back to Earth's surface in a perpetual cycle, until the long-waveradiation is no longer available for absorption.

Effect of various gases on Earths temperatureMolecules of oxygen and nitrogen, which comprise 98% of atmospheric gases,are not able to absorb IR radiation; however, molecules like water and carbondioxide possess vibratory and rotational modes that facilitate energy absorptionin this spectrum. The natural greenhouse gases include water (H2O), carbondioxide (CO2), methane (CH4), and tropospheric ozone (O3). Anthropogenic(human produced) greenhouse gases include mainly CO2 but also nitrous oxide(N2O), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs),perfluorocarbons (PFCs), and sulphur hexafluoride (SF6).

Under clear conditions, void of clouds, H2O vapor is the predominant greenhousegas (60% to 70%). The second largest source of greenhouse gas is CO 2, which


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is often considered the most important Space Atmosphere Land & Oceancontributor to the intensity of the greenhouse effect and tropospheric warming.

Although the chlorofluorocarbons (e.g., CFC-12) contribution to the greenhouseeffect is relatively low, they are an environmental concern because they canabsorb IR 10,000 times better than CO2 due of their chemical structure. In

addition, SF6 appears to contribute little, but this potent gas has 24,000 times theIR absorption potential of CO2. Cloud cover creates a stronger greenhouse effectby absorbing radiation and emitting a portion back to the surface, keeping itwarm. (Note: clouds consist of water droplets and/or ice particles; clouds are notmerely water vapor.) At the same time, a considerable amount of solar radiationis reflected back to space when clouds are present. The net effect of cloud coveris a reduction of energy received by the Earth.

Understanding the difference between greenhouse effect and globalwarmingDo not confuse the term greenhouse effect with the term global warming.

Global warming is a highly debated topic focusing concern over the increasedconcentration of greenhouse gases (both natural and anthropogenic) in theatmosphere and the apparent gradual rise in the temperature of the Earth'ssurface over the past few centuries. The increased level of greenhouse gases(which have increased in concentration since about 1700 AD) is what precipitatesthe magnitude of the greenhouse effect, or the enhanced greenhouse effect,which leads to global warming. Scientists continue to debate the effects ofincreased greenhouse gases in the atmosphere and the issue of global warming.There are valid concerns regarding changes in cloud cover, CO 2 emissions,water vapor, and dust particles, which are capable of altering the energy balanceand climate on Earth. The challenge to scientists is to combine cross-functional

ideologies to analyze whether a global shift in temperature, precipitation, sealevel, and storm severity is a function of climate change, or simply climatevariability.

Materials and Equipment Required Vernier LabQuest beaker, 500-mL Temperature Probe 1/8 vinyl tubing (0.5 m) CO2 Sensor Erlenmeyer flask, 125-mL Small Tripod Base & Rod 1-hole stopper (for flask) Three Finger Clamp foam insulating lid black construction paper plastic tubing connector nib (2) clamp or clothes pin insulated mitt 150-W incandescent light source protective gear Make CO2 with either dry ice (50 g); Yeast, sugar, warm water; or alka seltzer

Safety Notes Wear protective gear at all times (gloves, goggles, etc.).

Avoid contact of dry ice with skin and eyes. Handle the dry ice with aninsulated mitt. Dry ice can burn your skin.


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Pre-Lab QuestionWhich test situation will cause heat from the lamp to be retained longerwith aironly or with air plus added CO2?

Equipment SetupNote: If you prefer to perform this experiment simultaneously, then construct twoof the devices and use two sets of sensors.

Air Without Added Carbon Dioxide Gas1. Cut a piece of black construction paper so it fits in the 1-L beaker.2. Place the foam insulating lid on the top of the beaker.3. Cut a hole in the top of the lid so the CO2 Sensor makes a snug fit.4. Press the Temperature Probe through the lid, creating another hole.5. Create a third hole in the foam insulating lid for the plastic tubing connector nib.6. Support the LabQuest with the Three Finger Clamp on the rod stand to

maintain the proper positioning of the LabQuest above the setup.

7. Using a ruler, place the light source 6 inches from the beaker.8. The CO2 Probe should be set to high


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Vernier LabQuest

Equipment SetupProcedureVernier LabQuest Setup1. Plug the Vernier CO2 Sensor and temperature probe into the VernierLabQuest.

Connect the CO2 Gas Sensor to the interface.

Start the data-collection software.

The software will identify the CO2 Gas Sensor and load a default data-

collection setup. You are now ready to collect data.

Note:Allow the CO2 Gas Sensor to warm up for about 90 seconds beforecollecting data.

CO2 Probe Temperature Probe


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Data

1. Turn on the light, wait for 30 seconds, and press the Start/Stop ( ) key tobegin recording data.

2. Collect data for 5 minutes. Turn off the light. Continue recording data for 20

minutes. Press the Start/Stop ( )key to stop recording data.

Air With Added Carbon Dioxide Gas

Equipment Setup1. Carefully take the rubber stopper out of the Erlenmeyer flask, put severalpieces of dry ice (may use yeast, sugar & warm water or alka seltzer and waterto generate CO2) into the flask, and put the stopper back into the flask.

Important: Use the insulated mitt to handle the dry ice.

Important: Do not move or bump the rest of the equipment setup.

Record Data

1. Turn on the light, wait for 30 seconds, and press the Start/Stop ( ) key tobegin recording data.

2. When the carbon dioxide concentration levels off, put the clamp on the tubingto prevent any further addition of CO2.

Note: The purpose of this step is to isolate the beaker from the cold flask.

3. Collect data for 5 minutes. Turn off the light. Continue recording data for 20

minutes. Press the Start/Stop ( )key to stop recording data.

4. Follow your instructors directions for cleaning up your work space.

Analyze1. Open the Graph display).Result: The Graph display opens displaying Temperature for 2 runs.

2. Press the select key, use the arrow keys to highlight the first Run #, select it,use the down arrow to highlight the run for the air-only test situation, and select it.Repeat for the second Run #, and select the run for the air plus CO2 testsituation.

Result: The Temperature vs. Time graphs for your 2 runs of data will bedisplayed.

3. Make a sketch of the graphed data and label your graph.


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4. Graph Temperature and CO2 Concentration on the x axis and time on the yaxis

5. Make a sketch of the graphed data and label your graph or use Excel.


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Table 1. CO2 & Temperature Data


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w/out added CO2 w/ added CO2Time

(sec)

CO2 ppm TempoF CO2 ppm Temp

oF

030

60

90

120

150

180

210

240

270

300

shut off light and record for 20 minutes @1 minute intervals

w/out added CO2 w/ added CO2Time

(minute)

CO2 ppm TempoF CO2 ppm Temp

oF

1

2

3

45

6

7

8

9

10

11

12

1314

15

16

17

18

19


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20


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Analysis/ Synthesis Questions

Analysis question1. Which system retained the heat longer?

Synthesis questions1. Based on your results, what can you assume about the effect of CO2 on

temperature in the atmosphere?2. Results can vary depending on the experimental design of the activity. List

the possible variables in your experiment.3. How would a loose seal with the lid affect your data? Describe what you

would expect the data to look like.4. A skeptic could argue that your results do not demonstrate that CO2 is

better than any other atmospheric gas in contributing to the greenhouseeffect. This individual may claim that the temperature difference wassimply due to an increased number of molecules (production of CO 2) in

the bottle. What is wrong with this claim?5. List three gases that contribute to the greenhouse effect.6. How does Earth benefit from the greenhouse effect?

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