The atmospheric compartmentHow much does it weigh?

Temperature and pressure

Circulation and mixing

Where did Oxygen come from

Particle emissions

Emissions of other pollutants

The total atmosphere weights5.13x1018 kg

Assume that an average car weighs 1000 kg or one metric tonne

how many cars are equal to the weight of the atmosphere?

if you could cover the earth in cars how high would the stack be? Assume the average car has a “foot print” of 4x2 meters and is 2 meters high?

atmosphere weighs 5.13E+18 kilograms

car weighs 1000 kilograms

# cars = to atmosphere= 5.13E+15 cars

radius of the earth = 4000 miles

radius of earth = 6437.376 kilometers

surface area of earth= 5.20E+08 square kilometersarea= 4 pi xr 2̂area of a car = 0.000008 square kilokometer

# cars/surface 6.50605E+13

weight of one surface 6.50605E+16of cars

# of layers of cars= 78.8

height of cars = 158 meters

Two important features the atmosphericCompartment aretemperature and pressure

The atmosphere is usually divided into the following:

• Troposphere 0-10 km

• tropopause ~10km

• Stratosphere 10-50km

• stratopause ~50 km

• mesosphere 50-80kn

• Thermosphere 80 + km

These divisions come about because of temperature differences as one increases in altitude:

The troposphere contains about 80% of the atmospheric mass.

Air cools with altitude in the troposphere. The top; 10-15 km is at ~-60oC; which means very little water vapor.

In the stratosphere, temp. increases with height because O3 absorbs uv radiation.

Thermal mixing of air (heat) is responsible for global circulation in the lower atmosphere.

The atmosphere is held to earth’s surface by the gravitational attraction of the earth

At a given altitude the downward force (F) is related to the mass (M) of the atmosphere above that point.

F= M (g); where g is the gravitational acceleration constant

The pressure or force per unit area

decreases with increasing altitude

The decline in pressure (P) with altitude is approximately = to

log P= - 0.06 (z); where z is thealtitude in km and P is bars

How thin is the air at the top of Mt. Everest?Mt. Everest is 8882 meters high or 8.88 km high

log P = -0.06 x 8.88

P = 10-0.06x 8.88 = 0. 293 bars

Assume there are 1.01bars/atm.

This means there is < 1/3 of the air

Where does log p = - 0.06 (z) come from;

Force = mass x accelerationacceleration = g

The mass of air over a surface, A, equals height x

A x mass/volume; the mass / volume = density, ;

So Force = -z x A x x g

The change in force at any altitude

dF = -dz x A x x g; F/A = pressure, p

So the change in pressure with height isdp= -dz x x g

dp = -dz x x g

What is the ideal gas law

pV = nRT

Show that = Mw x p/RT

Substituting for in dp = -dz x x g

dp = -dz x Mw x p/RT x g

So dp/p = -dz x Mw /RT x g Integrating

So p = po exp {-Mw g z /RT}

p = po exp {-Mw g z /RT}

If we set H = (Mw g /RT)-1 it has the units of length

and we get a simple expression p= po exp {-z /H}

Solving for H at 290K; R = 8.3 joules/(K mole) one joule = 1kg meter2/sec2

average Mw of air = 28.9 g/mole g = 9.8 meter/sec2

H = 8.5 km; people actually find that 7km works best; when 7 km is used we end up with

log p = - 0.06 (z);

Is it possible in the troposphere to calculate the rate that temperature of the air decreases with altitude?

The first law of thermo says that the change internal energy of a system is the sum of its changes in heat content and work that is done.

dU = dq - dw

A change in work can only occur if a force moves through a distance; dw = d (fxz) = d (pV) for work there must be movement

Hence dw = Vdp and dU = dq - Vdp

Another form of energy is call enthalpy (H) which is the sum of the internal energy and pV from pV=nRT

so H = U + PV or dH = dq –Vdp + Vdp +pdV = Vdp (dq is assumed to be zero for a process that does not have a heat loss)

The change in the heat of a mass, per change in a degree centigrade, is called its specific heat Cp and Cp = dH/dT

To do this we need to start with simple thermodynamics

we said the enthalpy dH = Vdp

specific heat capacity; Cp = dH/dT

So Cp dT= dH = Vdp

Before we said that the change in pressure with height, z was dp= -dz x x g

So substituting for dp we get

Cp dT= - V x dz x x g

So the change in temp with height is dT/dz = - V x x g/ Cp

Density is mass/V; so for an air mass of one gram, = 1/V

This puts Cp in units of energy gram-1 deg-1; for dry air this is 0.24 cal gram-1 o K-1 and we will call it cp

So - dT/dz = g/ cp where g = 9.8 m sec-2

1 cal = 4.1 joules so cp = ~1 joule gram-1 o K-1

One joule = 1 kg m2sec-2

So - dT/dz = g/ cp = 0.0098 oK/meter or 9.8 oK/kilometer

The fact that - dT/dz = g/ cp = 9.8 oK/kilometer is constant is consistent with observations

And this is called the dry adiabatic lapse rate so that - dT/dz = d

When - dT/dz > d the atmosphere will be unstable and air will move (convection) to re-establish a stability

Air that contains water is not as heavy and has a smaller lapse rate and this will vary with the amount of water

If the air is saturated with water the lapse rate is often called s

Near the surface sis ~ -4 oK/km and at 6 km and –5oK/km it is ~-6K/km at 7km high

The quantity d is called the dry adiabatic lapse rate

At midday, there is generally a reasonably well-mixed layer lying above the surface layer into which the direct emissions are injected.

As the sun goes down, radiative cooling results in the formation of a stable nocturnal boundary layer, corresponding to a radiation inversion.

alt

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temp

midday

alt

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temp

Sun-down earth cools

Inversion layera

ltit

ud

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temp

more cooling at surface at night

}

What happens to the material above the inversion layer??

These materials are in a residual layer that contains the species that were well-mixed in the boundary layer during the daytime. These species are trapped above and do not mix rapidly during the night with either the inversion boundary layer below or the free troposphere above.

Inversion layeralt

itu

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temp

more cooling at surface at night

residual layer

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When the sun comes up the next day it heats the earth an the air close to the earth.

Inversion layeralt

itu

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temp

more cooling at surface at night

}

During the next day heating of the earth's surface results in mixing of the contents of the nocturnal boundary layer and the residual layer above it

Inversion layer

alt

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temp

Heating at surface during the next day

}

Mixing height in the morning

• We will start with the balloon temperature curve that is taken at the airport each morning.

• In the morning the temperature usually increases with height for a few hundred meters and then starts to decrease with height (see the green curve) according to the temperature sensor on the balloon

• The the break in the curve usually defines the inversion height in the early morning

Mixing height in the morning

Balloon temperature

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Temp in oC

Inversion height}

Mixing height in the morning• There are another set of lines called the dry adiabatic lines, which are

thermodynamically calculated, and represent the ideal decrease in temperature with height for dry air starting from the ground.

• In the morning, the mixing height is estimated by taking the lowest temperature just before sunrise and adding 5oC to it, and then moving up the dry adiabatic line at that temperature until it intersects the balloon temperature line or the green curve.

• Let’s say the lowest temperature just before sunrise was 20oC. We would add 5oC to it and get 25oC. We then move up the 25oC dry adiabatic line. We then go straight across to the right, to the height in kilometers and get a morning mixing height of ~350 meters (0.35 km). This is illustrated in the next slide. It is animated so you can see it more easily

Mixing height in the morning

Balloon temperature

Temp in oC

20 25 30 35

Dry adiabaticlines

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0.00.10.20.30.4

1.1

1.5

Mixing height in the afternoon

• To get the mixing height in the afternoon, you just take the highest temperature between 12:00pm and 15:00 pm

• Do not add anything to it, but as before run up the dry adiabatic curve and intersect the morning balloon temperature curve.

• Let say the highest afternoon temperature is 35oC, we would estimate an afternoon mixing height of ~1.67 km

Afternoon Mixing height

Balloon temperature

Temp in oC

20 25 30 35

Dry adiabaticlines

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0.00.10.20.30.4

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1.5

At the equator air is heated and rises and water is evaporated.

As the air rises it cools producing large amounts of precipitation in equatorial regions.

Having lost its moisture the air mass moves north and south.

It then sinks and compresses (~30oN and S latitude) causing deserts

How does air circulate

Circulation currents

equator

30oN

Hadleycell

A similar system at the poles occurs where cold air sinks and flows south (in the northern hemisphere.

These sinking columns of air create a circulation system called Hadley cells

Circulation currents

equator

30oN

Hadleycell

Hadleycellindirect

cells

In between the Hadley cells, north and south of the equator, and at the poles, counter current or indirect cells are set up.

These drive circulation between 40-60o latitude, producing westerly winds and storms

Circulation currents

equator

30oN

Hadleycell

Hadleycellindirect

cell

The air in each hemisphere mixes with a time constant , , of a few months.

The air between the north and south hemispheres completely mix on the order of one year.

Air mixes into the stratosphere from rising Hadley cells in the tropics, storms and eddy diffusion.

exchange between the troposphere and the stratosphere can be thought of in terms of mean residence times (MRT)

The mean residence time (MRT) can be expressed as:

MRT = mass / flux

where flux is mass/time

If 75% of the mass/year in the stratosphere comes from the troposphere

1

MRT = ----------------- = 1.3 years– 0.75/year

Mt. Pinatubo in the Philippines erupted in June 1991, and added a huge amount of

SO2 and particulate matter the stratosphere. After one year how much

SO2 was left?

For a 1st order process C= Coe -1 year/ MRT

C/Co= e -1 year/ MRT = e -1/1.3= 0.47 or ~ 50%

in 4 years, C/Co= e -4 years/1.3 years = ~5%

What happened to global temperatures after the Pinatubo eruption

A lot of SO2 was injected into the atmosphere

What we will learn later that SO2 forms fine sulfate particles that reflect light back into the atmosphere and this cools the upper troposphere

Three gases, O2, N2, and argon make up 99% of the atmosphere mass of 5.14x1021 g

These gases are relatively un-reactive and their mean residence times are much longer than the rate of atmospheric mixing. Hence the conc. of N2, O2, and the Nobel gases (He, Ne, Ar, Kr, and Xe) are relatively uniform.

Atmospheric Composition

N2 78.084% 3.87x1021 grams

O2 20.946 1.19x1021

Ar 0.934 6.59x1021

CO2 0.036 2.80x1018

Ne 18.2 ppm 6.49x1016

H2 510 ppb 1.82x1014

CFC 11 280 ppt 6.79x1012

MeBr 11 ppt 1.84x1011

Atmospheric Composition

Where does oxygen come from in our atmosphere?

~3.8 billion years ago the earliest bacteria were able to take acetic acid and metabolize it to CO2 and water.

CH3COOH CO2+ H2O

A later form of bacteria could obtain energy from the reduction of H2S to S

CO2 +2H2SCH2 O+ 2S + H2O

As supplies of H2S were consumed in the oceans other energy generating metabolic processes became more competitive

one was photosynthesis

H2O +CO2CH2O + O2

A good summary of the “Rise of Life on Earth”

is given in National Geographic, vol 193, p 54, March 1998

Experiments in the early 1950’s (Dr. Stanley Miller, U. Cal. San Diego) showed that is is

possible to generate amino acids in an atmosphere of CH4, NH3 and H2 over a pool of water with an electrical discharge

This gave rise to the theory that “life” could have originated in warm tidal pools of the oceans,

since amino acids are the building blocks of “life”.

It is now thought that the atmosphere 4-3.5 billion years ago consisted of CO2 and N2

sparking CO2 and N2 does not generate large amounts of organics

A more recent theory is that “life” could have originated in deep hot pools of water heated by volcanic rock.

Some of the most primitive live forms, called thermophil bacteria, can live at 190oC and consume iron and sulfur (3.8 billion years ago).

Another theory involves ice. Trapped H2C=O, NH3, HCN and water--->glycine (amino acid) followed by meteorite impact

Photosynthetic cyanobacteria (blue green algae) may go back 3.46 billion years. They were recently found in a rock from NW Australia.

It is felt these types of bacteria invaded other cells and their chloroplasts“stayed” there.

Some bacteria were also invaded by mitochondria which burn sugar

These photosynthetic cells gave off huge amounts of oxygen.

Oxygen did not really start to build up in the earth's atmosphere until ~2 billion years ago. Why??

The oceans contained much dissolved iron. It had to be oxidized before O2 could persist in the atmosphere.

The atmosphere contains particles which are known as aerosols. These come from a number of different sources

Soil minerals are dispersed by wind erosion from arid (dry) and semi-arid regions

Particles with a diameter of 1.0 m (the smallest we can see is 20 m) are held aloft by turbulent motion and can be transported long distances

Aerosols

It is estimated that 1x1015grams/year of soil particles enter the atmosphere and 20% are involved in long range transport.

Dust from the deserts of central Asia falls on the Pacific ocean where it contributes much of the iron (Fe) needed by oceanic phytoplankton

Dust from the Sahara desert supplies nutrients to phytoplankton in the Atlantic ocean and phosphorous to the Amazon rain forest.

The oceans create bubbles which burst and provide a huge quantity of large and small aerosols.

About 200x1012 grams of sea salt are carried to land each year

Forest fires in the Amazon are thought to produce 1x1013 grams of fine aerosols.

These aerosols affect regional rain fall patterns and influence global warming

Volcanoes emit particles into the atmosphere which contribute to soil development down wind of major eruptions.

Small particles are also produced by reactions of gases in the atmosphere

SO2 ----> H2SO4

H2SO4 + NH3 --> [NH4]2SO4 aerosols

These aerosols and others from the sea (dimethylsulfoxide) influence global warming

Natural sourcesPrimary aerosols

Soil dust 1500x 1012 g/yearsea salt 1300volcanic dust 33organic particles 50

Secondary aerosolssulfates from organics 90sulfates from SO2 12organic condensates 55nitrates from NOx 22

sum of natural sources 3070 x1012g/year

Anthropogenic sourcesPrimary aerosol

Industrial particles 100x 1012 g/yearsoot 20forest fires 80

Secondary aerosolssulfates from SO2 140organic condensates 10nitrates from NOx 36

sum of Anthropogenic 390 x1012g/year

sum of natural sources 3070 x1012g/year

If more particles are emitted from natural sources, why are we worried about man made or anthropogenic sources; they are 10 times less????

sum of Anthropogenic 390 x1012g/year

sum of natural sources 3070 x1012g/year

Primary pollutants emitted into the atmosphere- sources

Oxides of nitrogen (NOx = NO + NO2)

Sulfur dioxide (SO2)

Carbon monoxide (CO)

Volatile hydrocarbonds (VOCs)

Approximately 72 Tg (1Tg = 1x1012grams ) of NOx emitted into the atmosphere

The US emits ~30% of this

On the next slide we will look at global trends in emissions of NOx

NOx Emissions Trends

Much of the NOx comes from

Cars

Power plans

Off the road vehicles

The same emitted mass of NOx from different sources can have different atmospheric chemistry effects.

NOx

dilution aloft

NOx emitted near the ground

NOx Emissions in the US

SO2 Emissions trends

SO2 Emissions in the US

VOC Emissions in the US

CO Emissions in the US

Lead Emissions in the US

Lead Emissions in the US