sit anywhere today! today: topic # 8 atmospheric structure & chemical composition tuesday sep...

SIT ANYWHERE TODAY!

TODAY: TOPIC # 8 Atmospheric Structure & Chemical

Composition

Tuesday Sep 28th

ASSIGNMENT I-2 on Tree-Ring Skeleton Plotting & Crossdating is due TONIGHT by 11:59 pm in the D2L DROPBOX NOTE: “Turnitin” will be activated to identify

plagiarism – use your own words please

RQ-4 on Thermodynamics is due THURSDAY (30 minutes before our next class)

TEST # 2 is a week from today! The “Top 10 Things to Study” is posted under Study Guides.

Fire up your CLICKERS for some review questions from last week’s classes:

CHANNEL 40

Clicker Participation Points will be compiled STARTING TODAY!

NOTE: I’ve downloaded the Clicker Registration Roster and several of you have still not registered your device at all and many of you have not properly entered your UANetId *sigh*

Linking to life . . . . .

While we're on the subject, here's a tip for would-be job-seekers: Follow the instructions. If, say, an employment ad says to "send a cover letter, a resume and links to work samples," it's best to send a cover letter, a resume and links to work samples. I promise you that other applicants are following those instructions, and if you're not ... well, you look like a doofus. Just sayin'.

To start off, some clicker review questions from last week’s classes . . . . .

Q-1 Which of the following absorption curves represents a hypothetical atmosphere that has a “perfect” greenhouse effect ?

1.

2.

3.

4.

p 38

Nitrous Oxide N2O

Ozone O3

Carbon Dioxide CO2

Water Vapor H2O

All gases in the atmosphere together!

Q2 – Which of the following absorption curves is for a GAS that is NOT a greenhouse gas!

1: W 2: X 3: Y 4: Z 5: NONE of THEM

W

X

Y

Z

Absorption in this part of the absorption curve (IR wavelengths) indicates that OZONE is a greenhouse gas . . . .

. . . even though OZONE also absorbs radiation in the UV part of the spectrum!

Q3 - Here’s the absorption curve for ALL the gases in the atmosphere put together, i.e. curve for the “Whole Atmosphere”

Last week we talked about two “windows” in the curve that indicate at what wavelengths radiation easily comes IN to the surface of the Earth or escapes OUT to Space. Where are these two windows?

A B C D E1: A + B 2: B + E 3: C & D 4: D + E

Absorption by ALL the gases in the atmosphere put together –

i.e. curve for the “Whole Atmosphere”

UV Visible

Far IRNIR

Outgoing LW

Incoming SW

thru IR atmospheri

c window

thru UV / Vis atmospheric

window

Bottom row p 38

KEY CONCEPTS TO GET OUT OF ALL OF THIS:

1. Solar radiation is mostly in shortwave (SW) form (visible and UV).

Most visible & UV wavelengths are TRANSMITTED through the atmosphere but some (esp. harmful UV) are absorbed on their way to Earth's surface by O2 and O3.

2. Most of the incoming solar energy absorbed by the Earth and the atmosphere is absorbed at the EARTH'S SURFACE which then radiates IR outward to heat up the atmosphere.

Hence, the ATMOSPHERE is HEATED primarily from BELOW(i.e. from terrestrial radiation)

3. Terrestrial radiation is mostly in longwave (LW) form (IR).

Much of the outgoing terrestrial radiation is ABSORBED by H2O and CO2 (and other GH gases) before it escapes to space, and it is re-radiated back to the Earth's surface

This is the "Greenhouse Effect".

4. The re-radiation of LW (IR) energy to the Earth’s surface by GH gases is what keeps the Earth in the "just right" temperature range for water to be present in all 3 phases and just right for US too!

Without the "Greenhouse Effect," the Earth would be too COLD for life as we know it!

Topic # 8ATMOSPHERIC STRUCTURE &

CHEMICAL COMPOSITION All about the GASES IN THE ATMOSPHERE, esp. GREENHOUSE GASES!

Class Notes pp 39- 43

OBJECTIVES: To understand:

-- the VERTICALSTRUCTURE of the atmosphere & its relationship to temperature

-- which GASES are in the atmosphere

-- where they are concentrated, and

-- why gases at different levels are linked to the Greenhouse Effect

& Ozone Depletion

Things you’ve seen before that will all come together under this topic:

LESS DENSE

DENSE AIR

E = T 4

m = a / T

R-O-Y-G-B-V

E = h c / λ

We travel together, passengers in a little space-ship, dependent on its vulnerable supplies of air

and soil. ~ Adlai Stevenson

(4) Some IR radiation is absorbed by GH gases in the atmosphere and emitted back to Earth

Modified Cartoon of Solar (SW) & Terrestrial (LW) wavelengths of radiation:(3) Some IR

radiation is emitted from the Earth’s surface right out to space through “IR window”

(2) The Earth absorbs SW

(1) Some Incoming SW radiation from the SUN goes right through the atmosphere to Earth (w/o being absorbed)

(5) Some IR radiation is absorbed by GH gases in the atmosphere, but is emitted out to space (not back to Earth)

review

BUT WHAT ABOUT INCOMING SOLAR SW?

IS IT DEPICTEDCORRECTLY?

Sun’s peak at 0.5 m

Earth’s peak at 10 m

Wein’s is the law behind this cartoon

Review p 36

Shortwave SOLAR radiation

(SW) = UV + VIS + Near IR Solar SW

wavelengths:

Visible light : 44% UV : 7%Near IR: 37%

TERRESTRIAL radiation (LW) = Far IR

Terrestrial (Earth) radiation wavelengths:

Review p 36

Earth absorbs SW

How do we correct the depiction of incoming

SW?

Some SW gets absorbed on its way down to the surface!

(in addition to terrestrial LW (IR) radiation being absorbed in the GHE)

Some SW absorbed

http://earthguide.ucsd.edu/earthguide/diagrams/atmosphere/index.html



~1700 C at 600 km (~370 mi)

The Vertical Structure

of the AtmosphereKEY CONCEPT: The atmosphere’s vertical structure is defined by CHANGES in the trend of TEMPERATURE with height.

Mesopause

Stratopause

Tropopause

p 40 top

“TRy Sally’s Maroon THermals”

. . . or think up your own!

MA

RO

ON S

Atmospheric Pressure &

Mass Vary with Height

(on p 45 In SGC-I)

99% of mass lies below ~ 50 km (top of Stratosphere)50% of mass lies below ~ 6 km (middle Troposphere)

Atmospheric Pressure = weight of the air column above

The Vertical Structure of the Atmosphere

Why the zig-zags

in the

temperature / height graph?

Mesopause

Stratopause

Tropopause

p 40

The changes in temperature with height are the result of:

differential absorption of shortwave (SW)& longwave (LW) radiation

by atmospheric GASES concentrated at various altitudes.

p 39

Outgoing terrestrial LW (Far IR) radiated from Earth’s surface

Incoming solar SW (mostly visible & near IR + UV)

p 39

Here’s why these

changes in temperatur

e occur

p 39

KEY CONCEPT:

On its way to the Earth’s surface, several things can happen to incoming SOLAR RADIATION:

• TRANSMITTED (to Earth’s surface)

• ABSORBED (by gases, dust, clouds)

• SCATTERED / REFLECTED

• Reflected back to space

• Scattered (and indirectly transmitted to Earth’s surface)

Let’s look closer at the incoming shortwave (SW) radiation (UV, Visible & “near IR”)

REVIEW: The pattern of electromagnetic wavelengths that are absorbed & emitted by a particular atom (or combination of atoms)

is called its ABSORPTION SPECTRUM or its ABSORPTION CURVE

%UV

C-B-A

The Absorption curve for Ozone / Oxygen

How incoming SOLAR radiation of different wavelengths gets TRANSMITTED or ABSORBED by different gaseson its way to the Earth’s surface

absorbed by N2 & O2

absorbedby O2

absorbed by O3

Thermosphere

Mesosphere

Stratosphere

Troposphere

UVUV

C + BNear UV A

+ VisibleNear IR

Transmitted nearly undiminishedw/ some scattering

Some absorbed slightly by O2

Some absorbed

by H2 O

UVUV rays < .32 μm very harmful to

life on Earth arrows 1, 2 + 3

p 40

Q 4. The GREATEST amount of incoming solar energy (represented by the width of the arrows) is transferred to Earth via which wavelengths of electromagnetic radiation?

1. UV < 0.12 2. UV 0.12 – 0.18 3.UVC + UVB4.UVA + Visible5.Near IR6.BOTH 4 + 5

Q 5. Why does ARROW #5’s radiation get attenuated below 10 km?

1.Because ozone (O3) is abundant below 10 km and absorbs large amounts of incoming IR

2.Because this is the area of the troposphere where water vapor (H2O) is abundant and (as a GHG) it absorbs IR

3.Because clouds in the troposphere block out some of the incoming visible light rays

Q 5. Why does ARROW #3’s radiation get attenuated below 50 km?1. Because this is the area of the

mesosphere and there is very little absorption of radiation in this layer

2. Because nitrogen (N2) and oxygen (O2) are abundant at 50 km and act as GHG’s to absorb the UVC + UVB rays

3. Because this is the area of the stratosphere where ozone (O3) is concentrated and absorbs harmful UVC + UVB rays

Q 6. Why does ARROW #3’s radiation get attenuated below 50 km?1. Because this is the area of the

mesosphere and there is very little absorption of radiation in this layer

2. Because nitrogen (N2) and oxygen (O2) are abundant at 50 km and act as GHG’s to absorb the UVC + UVB rays

3. Because this is the area of the stratosphere where ozone (O3) is concentrated and absorbs harmful UVC + UVB rays


REVIEW . . .



Q 7 - The atmospheric layer of the troposphere is important to global climate change because:

1. it is the layer closest to the sun, which is the source of the Earth’s energy

2. it is the layer in which temperature INCREASES with altitude in the atmosphere and where most of the atmosphere’s ozone occurs

3. it is the layer in which most of our weather, heat transfer, & greenhouse gases occur

Q8 – Here are 3 graphs showing “something” varying with altitude in the atmosphere. Which is which?

1. A = water vaporB = pressureC = temperature

2. A = temperatureB = pressureC = ozone concentration

3. A = ozone concentrationB = temperature in the troposphereC =temperature in the stratosphere

A B C

Q9 – Here is the graph of atmospheric pressure vs. altitude, with “parcels of air” shown to depict the density of the atmosphere’s gases at 3 different altitudes. If the air in Parcel X is forced to subside (sink) to the altitude of Parcel Z, what will happen to the air in Parcel X?

1. it will get more dense and get cooler

2. it will get more dense and warm up

3. it will get more dense, and no change in temperature will occur

x

y

z

ZOMBIE BREAK !

The end of:

http://www.pbs.org/wgbh/nova/solar/



ATMOSPHERIC COMPOSITION

Which gases? What concentration?

Which ones are Greenhouse Gases (GHG)?Where do the GHG’s come

from?

Which GHG’s are changing in concentration due to HUMAN ACTIVITIES?

GAS Symbol

% by volum

e

% in ppm

Nitrogen N2 78.08 780,000

Oxygen O2 20.95 209,500

Argon Ar 0.93 9,300

Most Abundant Gases in the Atmosphere

Total = 99.96% p 41

GAS Symbol

% by volume

% in ppm

Water VaporH2O

0.00001

(South

Pole) to 4.0

(Tropics)

0.1 - 40,000

Carbon Dioxide CO2

0.0390(and

rising!)

360(in 1997)

390 !(in May 2009)

Next Most Abundant Gases:

Greenhouse Gases ! p 41

GAS Symbol

% by volume

% in ppm

Methane CH4 0.00017 1.7

Nitrous Oxide N2 O 0.00003 0.3

Ozone O3 0.0000004 0.01

CFCs (Freon-11)

CCl3F 0.000000026

0.00026

CFCs(Freon-12)

CCl2F2 0.000000047

0.00047

Other Important Greenhouse Gases:

Greenhouse Gases! p 41

Absorption by ALL the gases in the atmosphere put together –

i.e. curve for the “Whole Atmosphere”

UV Visible

Far IRNIR

Outgoing LW

Incoming SW

thru IR atmospheri

c window

thru UV / Vis atmospheric

window

Review bottom of p 38

WATER VAPOR

* Arrives in atmosphere naturally through evaporation & transpiration

* Due to unique quantum rotation frequency, H2O molecules are excellent absorbers of IR wavelengths of 12 μm and longer; Just listen!

This info is in Table on p 41

H2 O

WHOLEATMOSPHERE

IR at 12 μm absorbed

Virtually 100% of IR longer than 12 μm is absorbed by H2O vapor and CO2

(12 μm close to the radiation wavelength of 10 μm, at which most of Earth’s terrestrial radiation is emitted.)

Graphs on p 38 Class Notes

Just listen!

* H2O has variable concentrationand residence time in the atmosphere depending on location and atmospheric circulation

WATER VAPOR (cont):

Blue = wettest climates, lots of humidity & water vapor

Yellow = driest climates, less atmospheric water vapor

Equator

Just listen!

At higher air temperatures, H2O molecules collide & rebound more

frequently, leading to expansion of the air & the water vapor in the air.

Hence hot climates can hold more

water vapor in the air

At lower air temperatures as air gets more dense, H2O molecules are more likely to bond so that a phase change to liquid water or even solid ice can occur.

Hence in cooler climates, more of the available H2O is likely to be in

the liquid or solid state on the Earth’s surface

* H2O is NOT globally increasing in direct response to human-induced factors, but if global temperatures get warmer, H2O vapor in the atmosphere will increase . . . .

Why???

WATER VAPOR (cont):

. . . due to more evaporation in the warmer climate!

THINK ABOUT THIS!

CARBON DIOXIDE:

* Arrives in atmosphere naturally through the natural carbon cycle

* Due to unique quantum bending mode vibration behavior, CO2 molecules are excellent absorbers of electromagnetic radiation of about 15 μm

Just listen!This info is in Table on p 41

CO2

WHOLEATMOSPHERE

IR at 15 μm absorbed

CO2 is excellent absorber of radiation of about 15 μm

(15 μm close to the radiation wavelength of 10 μm, at which most of Earth’s terrestrial radiation is emitted.) See figure on p

38

CARBON DIOXIDE (cont.):* Has increased dramatically

since the 1800s due to:

(1) fossil fuel combustion: oil, coal, gas -- especially coal, and

(2) deforestation -- which has the effect of increasing the amount of carbon in the atmospheric “reservoir” by reducing the photosynthesis outflow and increasing the respiration inflow.

(Deforestation also accelerates forest decomposition, burning, etc. adding to the overall respiration inflow.)


CARBON DIOXIDE: Trends

Data from ice cores

CARBON DIOXIDE --- Trends:

The Keeling Curve

Annual fluctuations due to seasonal photosynthesis / respiration cycle in forests

(mostly deforestation)

CARBON emissions into the atmosphere are increasing:

(deforestation)

CARBON DIOXIDE (cont.):

* RESIDENCE TIME in the atmosphere of CARBON ATOMS in the carbon cycle = ~ 12.7 years;

but residence time of CO2 GAS MOLECULES is estimated at about 100 years

Plus it takes 50 to 100 years for atmospheric CO2 to adjust to changes in sources or sinks.If we make changes now, it will still be many, many years before the effect will be felt!


METHANE (CH4): Sources

* Produced naturally in anaerobic processes (e.g., decomposition of plant material in swamps & bogs)

* Has increased due to the following activities: raising cattle / livestock, rice production, landfill decomposition, pipeline leaks

* Has relatively short atmospheric residence time because it reacts with OH (~10 years) This info is in Table on p 41

METHANE: Trends

NITROUS OXIDE (N2O): Sources

* Produced naturally in soils

* Has increased due to fossil fuel combustion (esp. diesel), forest burning, use of nitrogen fertilizers

* Has long atmospheric residence time (~ 150 years)


NITROUS OXIDE: Trends

NITROUS OXIDE: Trends

www.ipcc.ch

The grey bars show the reconstructed ranges of natural variability for the past 650 kyr

CO2

N2O

CH4

Radiative Forcing

AnotherZOMBIE BREAK !

CFCs (Freon-11 & Freon-12)* Human-made CFCs (didn’t exist in

atmosphere prior to 1950s)

* Have increased at rates faster than any other greenhouse gas; used in refrigerants, fire retardants, some aerosol propellants & foam blowing agents

* Absorb at different wavelengths than H2O and CO2 (in 8 –12 μm “WINDOW” part of spectrum), hence a single molecule can have great effect

MONTREAL (and subsequent) PROTOCOLS have reduced CFCs!


CFCs: Trends

FREON-11

FREON-12

Human-made -- didn’t exist before 1950!

Montreal Protocol signed in 1987

ES p 219

Q10 – Why do you think the concentration of CFC’s didn’t begin dropping immediately after the Montreal Protocol in 1987?

1. Because it was an international “agreement only” and the nations of the world never followed through.

2. Because it called for only a 50% reduction of CFC’s over 10 years and had to be followed by more stringent protocols later.

3. Because CFC’s are very stable molecules and don’t break down easily once they are in the atmosphere.

OZONE: Sources

Produced naturally in photochemical reactions in STRATOSPHERIC ozone layer --“good ozone”Has increased in

TROPOSPHERE due to photochemical smog reactions -- “bad ozone”

Fig 3-11SGC-I p 46


O3 absorbs IR radiation of 9.6 μm, close to wavelength of maximum terrestrial radiation

(10 μm)

Bottom of p 34 (also see pp 38 in SGC-I)

IR

UV / VIS

OZONE: Trends

Stratospheric ozone varies by latitude and season -- is affected by solar radiation, volcanic eruptions & chemical reactions due to CFCs.

Overall, O3 is decreasing in the STRATOSPHERE

Solar effects

Volcanic effects

More on OZONE later on in the semester

Two Important Global Change Terms Related

to Atmospheric Composition(They are being introduced now, but we’ll discuss them in more detail

later)

Radiative Forcing (RF) – Change in incoming minus outgoing radiation at the tropopause due to some factor.

For example, a change in the concentration of carbon dioxide or the output of the Sun.

In the IPCC report, radiative forcing is further defined as the change relative to the year 1750 as a global average. p 42

Global warming potential (GWP) - An index that measures how much a given mass of greenhouse gas is estimated to contribute to global warming.

p 42

1. Four gases N2, O2, Ar, & CO2 comprise about 99% of the volume of the atmosphere. These are the major gases.

However, even the "minor" gases by % volume can be extremely important to us, especially H2O, CH4 , and O3 which -- together with CO2 -- are the main GREENHOUSE EFFECT gases.

SUMMARY OF KEY CONCEPTS

p 43

Even smaller amounts of other trace gases such as CFC's and halons can play an important role by disrupting stratospheric ozone.

ALSO:

p 43

2. Most of the MASS of the atmosphere is in the bottom few kilometers.

Traces of the Earth's atmospheric gases can be detected up to 60,000 km above the earth's surface, but:

* 99% of the mass of the atmosphere lies below 50 km (near top of stratosphere) and

* 50% of the mass lies below about 6 km (middle troposphere).

p 43

3. Different gases are abundant at certain levels in the atmosphere.

Because gases absorb and emit only certain wavelengths of radiation, different wavelengths are absorbed at different altitudes, depending on which gas is abundant at that level . . . .

p 43

. . . Wherever radiation is absorbed by these gases, the atmosphere heats up, leading to VARIATIONS IN THE VERTICAL TEMPERATURE PROFILE of the atmosphere. . . .

p 43

. . . N2, N, O and O2 are very effective in absorbing very short wave radiation that is HARMFUL (e.g. x-rays and the shorter ultraviolet wavelengths).

Since these gases are abundant at high altitudes, much of this harmful radiation never reaches the earth's surface. . . .

p 43

. . . Similarly, O3 in the concentrated ozone layer (at about 25 - 35 km in the mid-stratosphere) absorbs additional amounts of the HARMFUL ultraviolet shortwave radiation. . . .

p 43

. . . H2O and CO2 are most abundant close to the earth's surface in the lower troposphere.

Being greenhouse gases, they are transparent to incoming solar shortwave radiation, but they absorb terrestrial longwave radiation emitted from the earth's surface. . . . .

p 43

Thanks, Greenhouse Effect!

They then re-radiate much of this energy back to the surface, keeping the earth comfortably warmer than it would be without a "Greenhouse Effect."

p 43

4. The differential absorption of wavelengths of radiation by atmospheric gases at various elevations leads to the "vertical structure" of the atmosphere:

Troposphere, Stratosphere, Mesosphere, Thermosphere.

The boundaries separating these layers of the atmosphere are defined by temperature changes and are referred to as “pauses” i.e., tropopause, stratopause, and mesospause. p 43

ANNOUNCEMENTS -- Sep 28th

ASSIGNMENT I-2 on Tree-Ring Skeleton Plotting & Crossdating is due TONIGHT by 11:59 pm in the D2L DROPBOX NOTE: “Turnitin” will be activated to identify

plagiarism – use your own words please

RQ-4 on Thermodynamics is due THURSDAY (30 minutes before our next class)

TEST # 2 is a week from today! The “Top 10 Things to Study” is posted under Study Guides.

sit anywhere today! today: topic # 8 atmospheric structure & chemical composition tuesday sep...

Documents

hypothetical atmosphere

following absorption

d e absorption

greenhouse gas

wavelengths radiation

visible uv wavelengths

d e q3 heres

harmful uv