The Earth’s Atmosphere

The primordial atmosphere

Venus Primordial Earth

Carbon Dioxide 98% 98%

Nitrogen 1.9% 1.9%

Oxygen trace trace

Atm. Pressure (bars)

90 60

Where is Earth’s CO2?

Rocks - like limestone(and some in plant life and in the ocean)

Water, Oxygen, Life

Venus Earth Then Earth Now

Carbon Dioxide 98% 98% 0.03%

Nitrogen 1.9% 1.9% 79%

Oxygen trace trace 21%

Atm. Pressure (bars)

90 60 1.0

Composition of the Atmosphere• Radiatively and chemically inactive gases

– Nitrogen (N2) – 78% of lower atmosphere by volume

• does not react with other substances• a neutral substance• Just a filler adding inert bulk to the atmosphere

– Argon (Ar) – just under 1% of surface atmosphere• Also largely inert

Composition of the Atmosphere• Radiatively and

chemically active gases– Oxygen (O2) - very reactive.

21.5% of atmosphere• Combines with other

substances easily in oxidation

– Water vapor (H2O↑) – very reactive.

• Can vary greatly in atmospheric concentration (< 1% to >2%)

• Important greenhouse gas

• Important to energy transfer and precipitation

Anything Special About 21% Oxygen?

By 2.5 Billion years ago plankton were altering the oxygen content of the atmosphere

• Radiatively and chemically active gases – Carbon dioxide (CO2) – important trace gas

• ~400 ppm• Consumed by plants for photosynthesis• Important, rapidly increasing greenhouse gas

– Methane (CH4) – important trace gas• Very low concentration ~1800 ppb, but very efficient

greenhouse gas• Also rapidly increasing concentration

Composition of the Atmosphere

The Greenhouse EffectThe Greenhouse Effect• What are

Greenhouse Gasses?

• Any gas molecule with two atoms of different elements.– Water vapor (H2O) 1-

3%

– Carbon dioxide (CO2) 0.04%

– Methane (CH4) 0.00018%

• What are Greenhouse Gasses?

• Any gas molecule with two atoms of different elements.– Water vapor (H2O) 1-

3%

– Carbon dioxide (CO2) 0.04%

– Methane (CH4) 0.00018%

• Aerosols – tiny airborne liquid or solid particles– Scatter or absorb solar radiation, cooling surface– Sources:

Composition of the Atmosphere

Dust

Salt

FuelBurning

Meteors

Smoke

Atmospheric Pressure & DensityAtmospheric Pressure & Density

• Atmosphere exerts constant pressure on Earth

• Atmospheric pressure is weight of air column over a unit of area on surface

• Atmosphere exerts constant pressure on Earth

• Atmospheric pressure is weight of air column over a unit of area on surface

Air Pressure

Metric:1 kg/cm2

English:15lb/in2

Air Pressure Change with Altitude• Air pressure decreases with

altitude– Near surface, air pressure drops

rapidly

– Higher in atmosphere, slower drop in pressure

• Air at higher altitude less dense, less oxygen– At altitudes > 3000 m, can cause

mountain sickness

– Symptoms include:• Shortness of breath

• Nausea

• Headache

• Nosebleed

Temperature Structure of Atmosphere

Temperature Structure of Atmosphere

• In lower atmosphere, temp drops with altitude

• Rate of decrease called Lapse Rate (ºC/1000m)

• Avg midlatitude lapse rate = 6.4ºC/1000m

• Value called Environmental Lapse Rate (ELR)

• ELR varies with atmospheric conditions

• In lower atmosphere, temp drops with altitude

• Rate of decrease called Lapse Rate (ºC/1000m)

• Avg midlatitude lapse rate = 6.4ºC/1000m

• Value called Environmental Lapse Rate (ELR)

• ELR varies with atmospheric conditions

Temperature Structure of AtmosphereTemperature Structure of Atmosphere

TroposphereTroposphere• Lowest atmospheric

layer – 8-16 km thick• All human activity and

most weather here• Thicker at Equator,

thinner near poles• Temp cools with altitude• Top of troposphere is

where temp stops cooling

• Lowest atmospheric layer – 8-16 km thick

• All human activity and most weather here

• Thicker at Equator, thinner near poles

• Temp cools with altitude• Top of troposphere is

where temp stops cooling

StratosphereStratosphere• Lies above the tropopause

(~12-50 km altitude)

• Contains ozone layer intercepting UV radiation– This causes stratosphere

to warm with altitude

• Little mixing with air in troposphere– Exception is volcanic

eruption– Can push aerosols into

stratosphere– Aerosols can cool Earth

for a year or more– e.g. Tambora → year

without a summer, 1816

• Lies above the tropopause (~12-50 km altitude)

• Contains ozone layer intercepting UV radiation– This causes stratosphere

to warm with altitude

• Little mixing with air in troposphere– Exception is volcanic

eruption– Can push aerosols into

stratosphere– Aerosols can cool Earth

for a year or more– e.g. Tambora → year

without a summer, 1816

Ozone in the Upper AtmosphereOzone in the Upper Atmosphere

• Ozone (O3) – form of oxygen

– Mostly in stratosphere, 14-50 km above surface

– Absorbs ultraviolet radiation, protecting Earth

– Normal reaction:

• UV radiation absorbed by O3

• O3 splits into O2 and O

• O2 and O reform into ozone (O3)

• Ozone (O3) – form of oxygen

– Mostly in stratosphere, 14-50 km above surface

– Absorbs ultraviolet radiation, protecting Earth

– Normal reaction:

• UV radiation absorbed by O3

• O3 splits into O2 and O

• O2 and O reform into ozone (O3)

– Ozone concentrations hurt by presence of CFCs• CFCs - synthetic chemicals used as refrigerant • They migrate from surface into upper atmosphere

• Deplete ozone as Chlorine (Cl) attacks O3 molecules

1. UV radiation strikes CFC molecule

2. Cl atom released, attacks O3 molecule

3. O2 and ClO are the result

4. ClO joins with free oxygen (O)

5. O2 and Cl are the result

6. O2 cannot stop UV radiation

7. Cl attacks another O3 (step 2)

8. One Cl can eliminate many O3 molecules

– Ozone concentrations hurt by presence of CFCs• CFCs - synthetic chemicals used as refrigerant • They migrate from surface into upper atmosphere

• Deplete ozone as Chlorine (Cl) attacks O3 molecules

1. UV radiation strikes CFC molecule

2. Cl atom released, attacks O3 molecule

3. O2 and ClO are the result

4. ClO joins with free oxygen (O)

5. O2 and Cl are the result

6. O2 cannot stop UV radiation

7. Cl attacks another O3 (step 2)

8. One Cl can eliminate many O3 molecules

Ozone in the Upper AtmosphereOzone in the Upper Atmosphere

• Obvious “hole” in ozone appeared in 1980s

• 1987 agreement to replace CFCs successful

• Most CFCs have been phased out• Highest CFC concentration in 1997• Since 1997 concentration has decreased• CFC molecules very stable, hard to

break down• Several decades for CFCs to disappear

• Obvious “hole” in ozone appeared in 1980s

• 1987 agreement to replace CFCs successful

• Most CFCs have been phased out• Highest CFC concentration in 1997• Since 1997 concentration has decreased• CFC molecules very stable, hard to

break down• Several decades for CFCs to disappear

Ozone in the Upper AtmosphereOzone in the Upper Atmosphere

• O3 is a pollutant near Earth’s surface

• Harmful to human lung tissue• Does not protect from UV radiation• Formed by:

– organic chemicals– nitrogen/oxygen molecules from

burning– sunlight

• So, most prevalent in cities during summer

• O3 is a pollutant near Earth’s surface

• Harmful to human lung tissue• Does not protect from UV radiation• Formed by:

– organic chemicals– nitrogen/oxygen molecules from

burning– sunlight

• So, most prevalent in cities during summer

Ozone in the Lower AtmosphereOzone in the Lower Atmosphere

A few more words about Aerosols – tiny airborne liquid or solid particles

Brown CloudsBrown Clouds

• These are essentially smog due to human activity– Stoves

– Cooking fires

• Two effects– Absorb solar radiation and

heat lower atm (2-3 km altitude)

– Blocks Sunlight producing ground cooling

• May effect the monsoons

• These are essentially smog due to human activity– Stoves

– Cooking fires

• Two effects– Absorb solar radiation and

heat lower atm (2-3 km altitude)

– Blocks Sunlight producing ground cooling

• May effect the monsoons

Brown CloudsBrown Clouds• This is not just a problem

in Asia or China• What do you know about

the 1952 London Smog?– December 5-9

– The fog there was so thick that people could not see their own feet!

– About 4,000 people died (maybe as many as 12,000)

• This is not just a problem in Asia or China

• What do you know about the 1952 London Smog?– December 5-9

– The fog there was so thick that people could not see their own feet!

– About 4,000 people died (maybe as many as 12,000)

Global DimmingGlobal Dimming• Because of aerosols

pollution, the brightness of the Earth's surface has dropped about 7%

• This probably represents a net cooling due to more sunlight being reflected by the increased particle load in the atmosphere

• Because of aerosols pollution, the brightness of the Earth's surface has dropped about 7%

• This probably represents a net cooling due to more sunlight being reflected by the increased particle load in the atmosphere

• The US embassy in Beijing posts hourly automated air quality measurements at @beijingair on Twitter. Another site: http://iphone.bjair.info/

‒ http://beijing.usembassy-china.org.cn/070109air.html

• On 18 November 2010, the feed described the PM2.5 measurement as "crazy bad" after registering a reading in excess of 500 for the first time.

• This description was later changed to "beyond index", a level which recurred in February, October, and December 2011 (also 1-19-2012 at 558)

• @BeijingAir 1/23/15 11:00pm local; PM2.5; 330; Hazardous

The Carbon Cycle

The Carbon Cycle

You can see the Earth “breathe” in the carbon cycle

http://www.esrl.noaa.gov/gmd/ccgg/trends/

http://www.esrl.noaa.gov/gmd/ccgg/trends/

Industrial Revolution

Current level 400 PPM

Discovery of America

• Remember, the whole pre-industrial atmosphere had about 600 gigatons of carbon.

• Right now we are adding about 9 gigatons/year, mostly from fossil fuels

• All volcanic sources contribute an average of ~0.2 gigatons of Carbon per year

• Mount Pinatubo eruption is estimated at ~0.0015-0.080 Gt of Carbon

How does the system maintain balance (without us)?

How does the system maintain balance (without us)?

• Chemical weathering removes CO2– Water and CO2 interact with silicate

rock….weathering into clays, calcium carbonate

• Volcanism puts it back in the atmosphere

• Chemical weathering removes CO2– Water and CO2 interact with silicate

rock….weathering into clays, calcium carbonate

• Volcanism puts it back in the atmosphere

Weathering Removes CO2Weathering Removes CO2

• The rate of weathering is controlled by a bunch of factors.– Temperature: Reactions

are quicker the hotter it is, so roughly double for every 10C of temp change.

– Precipitation: more water, more carbonic acid

– Vegetation: Planets enhance carbonic acid and break down rocks (increases rates 2-10 times)

• The rate of weathering is controlled by a bunch of factors.– Temperature: Reactions

are quicker the hotter it is, so roughly double for every 10C of temp change.

– Precipitation: more water, more carbonic acid

– Vegetation: Planets enhance carbonic acid and break down rocks (increases rates 2-10 times)

Tectonic Control of CO2: UpliftTectonic Control of CO2: Uplift• Tectonics (mountain

building) can also increase weathering

• Uplift causes all sorts of processes that increase weathering– Glaciers– Mass Wasting– Enhanced rainfall

• Tectonics (mountain building) can also increase weathering

• Uplift causes all sorts of processes that increase weathering– Glaciers– Mass Wasting– Enhanced rainfall

And things are actually a bit unusual right now….

• CO2 is part of a functional feedback loop.• Warm conditions speed the removal of

CO2 (by weathering) leading to reduced warming.

• Cool conditions slow weathering, leading to reducing cooling.

• CO2 is part of a functional feedback loop.• Warm conditions speed the removal of

CO2 (by weathering) leading to reduced warming.

• Cool conditions slow weathering, leading to reducing cooling.

Tectonic Control of CO2Tectonic Control of CO2

• The only (natural) way to get CO2 out of the ground is volcanism.

• The only (natural) way to get CO2 out of the ground is volcanism.

Volcanism is the flip side

of weathering

Volcanism is the flip side

of weathering

• But the rates of volcanism vary a lot• But the rates of volcanism vary a lot

• Again, CO2 acts as a planetary thermostat through tectonic feedback loops.

• Fast spreading increases CO2 with leads to greater weathering and faster CO2 removal.

• Slow spreading reduces CO2 input, but leads to cool conditions that reduce weathering, leading to reduced cooling.

But sometimes the thermostat breaksBut sometimes the thermostat breaks

• Around 650-800 Myr there is evidence of ice sheets near the equator

• Around 650-800 Myr there is evidence of ice sheets near the equator