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Global Environmental Processes > Atmosphere I + II > Flashcards

Atmosphere I + II Flashcards

1
Q

What’s the first key process in the atmosphere? what was the early atmosphere made of mainly? Why is this process so important?

A

Loss:

The early atmosphere was mainly H2 and He ( the most common elements in the universe)

These molecules have mainly been lost to space because they are light Nd have speeds high enough to escape ( Escape velocity) from the earths gravitational field

Loss or hydrogen of helium is what Is responsible for turning the atmosphere from
Anoxic to oxic.

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2
Q

What is the great oxidation event?

A

2.5 billion years ago. Loss of hydrogen of helium. Anoxic to oxic. Gives rise to multicellular organisms

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3
Q

What is the key process number two? Give an external example of it

A

Supply
The early earth was continually supplied with volatile gases attached to planetesimals.

These gases were volatilised into the atmosphere. Main gases are methane ( CH4), nitrogen, ammonia and water (vapour)

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4
Q

What did we the internal supply for the early atmosphere? What is the typical gas composition of this early supply?

A

Volcanoes continue to emit gases into the atmosphere. Typical composition of volcano gases is 70% water, 20% CO2 2% SO2 etc

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5
Q

Does the amount of gas emitted by volcanoes make a significant part of the atmosphere ?

A

The present mass of the atmosphere is only about 1 percent of the total outgassed material - the rest has been re-cycled e.g as carbonate rocks and sea water

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6
Q

What is the key process number 3?

A

Removal

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7
Q

What is a lot of key process driven by

A

It’s driven by gaseous solubility in water

Nitrogen - 0.02/litre
Oxygen 0.06g/litre
HCl 700g/litre

HCL good that it’s very soluble as very toxic

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8
Q

What is key process number 4?

A

Biogeochemical modifications

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9
Q

How was moon formed? Talk about graphs

A

Known as Theia, the Mars-sized body collided with Earth, throwing vaporized chunks of the young planet’s crust into space. Gravity bound the ejected particles together, creating a moon that is the largest in the solar system in relation to its host planet.1

In proto earth high amount of co2 but low solar luminosity both act to create conditions for life

Loads of co2 greenhouse effect runs away we need co2 so loads of energy gets to earth

Lots of helium and hydrogen in protoearth almost no oxygen. All oxygen produced being rapidly used by oxidative chemical processes. Only after we have had enough helium loss cab oxygen start to build off.

Build up of oxygen linked with first instances of photosynthesis

With oxygen in atmosphere through Chapman reactions you develop a stratospheric ozone column this shields earth surface from UVB and totally screens out UVC and you get development of a habitable earth.

Rock record 4.2 billion years ago that allows us to get an idea of these large scale processes

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10
Q

How is stratospheric ozone formed?

A

O2 In the atmosphere reacts with uvc ( short wavelength, high energy) . You split the molecular oxygen in half to get O + O

O2 + UV-C -> O + O

O2 + O -> O3

This tends to absorb and block uvc and block it out as a thicker stratospheric ozone column . Totally blocks out UVB and this makes it possible for multicellular live to live on land surface ( oceans)

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11
Q

Discuss oxygen cycling over millions of years

A

Oxygen in early protoatmosphere linked to photosynthesis

Once you have photosynthesis occurring got potential of oxygen to build up. Decomposition uses up oxygen the leaf generated. So for oxygen to build up can’t just have photosynthesis

So you have carbon burial. So you bury lots of photosynthetic carbon and this turns into coal. A lot of this carbon doesn’t decay. So drives increase in o2

So really as a result of the carbon doesn’t use up oxygen decaying and oxygen generated as a byproduct of photosynthesis is stored in the atmosphere

However rock weathering or combustion ( carbon oxidation) draws down atmospheric Oxygen

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12
Q

What is key process 4.i

A

Phanerozoic O2 : the rise of land plants

Get from smaller to larger plants and more carbon being locked up in coal deposits

Rise of massive dragonfly meganeura monyi

and arthopleura (millipede )

Gigantism is driven by atmospheric oxygen?

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13
Q

What is the experimental evidence for the link between large insect side and high amounts of atmospheric oxygen?

A

Fruit fly ( drosophila ) was examined at 21 percent o2 ( current day oxygen conditions) and did generational growth experiments. 5 generations of growth at 35 percent oxygen and you got + 20 percent increase in mass of females and 12 percent increase in mass of males

  • this fruit fly useful as can keep in lab and goes through generations quickly
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14
Q

Describe the variability is dissolved oxygen concentration?

A

Tropical oceans contain low dissolved oxygen concentration

Antarctic oceans have high dissolved oxygen content

Would expect crustaceans in Antarctic to be larger than the tropics

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15
Q

What’s key process 4.ii

A

Phanerozoic CO2

Early atmosphere has a high amount of CO2 that’s driven by volcanic outgassing

410 ppm co2 now

Evolution of Plants - atmospheric co2 decreases

Weathering sucks co2 from atmosphere. Plants with extensive root system

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16
Q

What is the chemical composition of clean dry air?

A 
Nitrogen - 78 %
Oxygen - 21 %
Argon - 0.9 % .  2 Ns low key abunfany
Neon - 18 ppm
Helium - 5 ppm
Carbon dioxide - 410 ppm Oct 2019
Pre industrial level - 280
Methane - 1.85 ppm ( and rising)
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17
Q

Is N2O a greenhouse gas?

A

Yes

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18
Q

What has the natural variability of co2 over the last 650 kyrs been?

A

120 ppm

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19
Q

What had the natural variability of CH4 been over the last 650 kyrs been?

A

400 ppb

Parts per billion

Human activity is close to pushing the atmosphere Beyond this background response for CH4 and surpassed it for CO2

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20
Q

What is the unique property of water?

How much liquid water is in green plants and many animals ?

What percentage of water covers the earths surface?

A

It is the only material present in the earth in all three phases : solid, liquid and gas

It moves between the 3 phases, mainly influenced by temperature and the concentration of the gas phase (water)

But because it can exist in these 3 phases the % composition is highly variable, from 0.1 % in cold dry air to 4% in moist warm air. Not like the other gases

Liquid water covers 70 percent of the earths surface and green plants are 90 percent water and many animals are 70 percent water

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21
Q

Talk about the composition of air ie the lifetime of its components

A

All the components listed in the composition of air are well mixed

We expect their concentrations to be similar at all places and times ( on average)

This tells us that they are relatively unreactive and have long lifetimes in the atmosphere

As a consequence, people talk about air as though there is one gas called “air”, consisting of ‘air molecules’ that

22
Q

What is the molecular weight of air?

A

Because composition is dominated by N2, O2 and Ar ( total 99.9 %) And because their proportions are quite constant

Mair = ,f of molecular weight of the components = 28.9 g/mol

Where 1 mol = 1 Avagadro No. of molecules = 6.02 x 10^23 molecules

23
Q

Why is there atmospheric pressure?

A

Pressure is the force per unit of area

Gas pressure is the force generated on a surface by all the gas molecules colliding with the surface

24
Q

What are the units of atmospheric pressure?

A

Pressure = force per unit of area, so the SI unit of pressure will be Newton m-2 = N m-2

1 Nm^-2 = 1 Pa

In practice millibars ( mbar) are also widely used

1 mbar = 100 Pa ( = 1 hPa)

25
Q

What is the value for the standard atmospheric pressure?

A

101.325 kPa = 1013.25 mb

Range

Lowest low - 93 kPa ( 930 mb)

Highest high. 107 kPa ( 1070 mb)

14 difference
average is like 7 more (jhalf)

26
Q

Talk about variation of pressure with height

A

Gravitational force acts on every molecule, towards the centre of the Earth

Molecules at any height exert enough pressure ( by collisions) to oppose the gravitational force due to all the molecules above them

Therefore pressure is greatest at the bottom of the atmosphere ( more molecules above them) and decreases with height

27
Q

Talk about the equation related to the variation of pressure with height

A

Pressure falls exponentially with height

P(z) = P0 exp ( -z/H)

Where

P(z) = the pressure at height z ( in Pa)
P(0) = the pressure at sea level
= 101.325

H= the scale height of the atmosphere
= 8434m

28
Q

What is scale height?

A

Scale height is the height at which pressure has decreased to 1/e of surface value = 8434m

29
Q

What is the global average temperature

A

15 degrees

K= degrees Celsius + 273.2 . = 288.2

30
Q

What are the 3 main causes for temperature variation ?

A

Input of heat from the ground or sea surface

Cooling of the air as it rises and pressure falls ( or warming as it sinks)

Absorption of solar radiation by the ozone layer by the ozone layer at 20-50 km

31
Q

What are the 5 regions of the atmosphere?

Slide 36

A

Exosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

Temperature decreases with height from ground level ( global average 15 degrees) up to 12 km ( -average -55 degrees). This is the well mixed troposphere

Temperature increases from 12 km to 50 km ( average back up to 0 degrees). This is the poorly mixed stratosphere.

Temperature decreases again above 50 km and this is the mesosphere

32
Q

Describe key facts about the atmosphere and height

A

Almost all clouds and weather are below 15 km

Almost all of the atmosphere is below 100 km

33
Q

Why is water wonderful but an anomalous liquid

A

The only material people from present on the earth in all 3 phases: solid, liquid and gas

34
Q

Describe more special features of water

A

Maximum density is at 4 degrees ( only for pure water and not seawater)

Influence glacier, iceberg and ice sheet development

Highest surface tension of all common liquids - controls the properties o water droplets, and the string of soil. Affects how rain moves through dry soil

Highest heat capacity of all liquids except ammonia

Highest latent heat of vaporisation of all liquids

Highest latent heat of fusion of all liquids

Highest dissolving power of all common liquids

35
Q

Describe the water molecule

A

Very simple atomic structure

Two hydrogen atoms bonded to one oxygen atom with covalent bonds

The hydrogen side of the water molecule has a slight positive charge and on the oxygen side there is a negative charge ( dipolar)

A covalent bond is a chemical bond between two atoms in which electrons are shared - in water each of the covalent bond contains 2 electrons - one from the hydrogen and one from the oxygen atom. Both atoms share electrons

36
Q

Describe bonding in water molecules

A

There is local bonding between clusters of molecules

The bonding is due to electrostatic atttacfion ( hydrogen bonding) between the positive and negative poles of individual molecules.

The bonds are continually breaking and reforming, so that molecules are free to move around in the liquid

If you apply higher energy into system bond strength breaks down - water vapour

If you take more and more energy out of the system you get ice

37
Q

How is ice formed?

A

When sufficient heat energy is removed from liquid water, the molecules align in a hexagonal fixed structure - ice

( open Lattice structure

Ordered, molecular structure

38
Q

How is water vapour formed?

A

When sufficient heat energy is added to liquid water, the molecules break free from the attraction of their neighbours and become independent gas molecules - water vapour

Randomness

39
Q

What does lattice like structure mean for oxygen?

A

They trap more oxygen within the “net” of water. So that’s why you have higher dissolved oxygen concentration in colder water. The molecular structure how it’s order enables more oxygen to be trapped. When you hear that up more space and less trapped oxygen. But smaller crustaceans

links to the antartic and tropic why there’s more dissolced osygen

40
Q

What is the latent heat of fusion?

A

The energy required to melt solid ice to liquid water is called the latent heat of fusion

The energy required to evaporate liquid water to gaseous water vapour is called the latent heat of vaporisation

41
Q

How many MJ does it take to evaporate 1 kg of water

A

Latent heat of vaporisation = 2.4 MJ kg-1

High latent heat of vaporisation

If the water condenses back to liquid 2.4 MJ is recovered

42
Q

Talk about saturated vapour pressure

A

Air at any temperature will only hold a certain amount of water as vapour once you reach the saturated stage it rains out and falls to the earths surface

The air is then said to be saturated with water vapour

The amount held increases rapidly with temperature

Hot air holds a lot more water volume ( humid in tropics )

43
Q

What is condensation?

A

When moist air is cooled, the air eventually becomes saturated with water vapour.

When cooled further, the excess water vapour has to condense out as liquids ( raindrops) or solid ( hailstones and snowflakes)

Cool air holds less water vapour

44
Q

What is evaporation driven by?

A

Evaporation of water is driven by solar radiation

Almost constant 1370 W m-2 ( solar constant) available at the top of the Earth’s atmosphere

Amount at the ground depends on time of day, season of the year and location on the planet

45
Q

How does solar radiation vary and what is it affected by?

A

On average, the amount of solar radiation increase from Poles to the equator

It is heavily affected by cloud amount, which depends on nearest to coat

46
Q

Shit on UV-B radiation

A

High amounts of solar radiation in tropics and that drives ozone formation and that ozone is exported to higher altitudes

47
Q

How many stable isotopes does oxygen have?

A

3 stable isotopes and each isotope has a slightly different mass due to different number of neutrons ( 8 9 10 respectively)

016 + O17 O18

Their relative natural abundances are 99.76, 0.04 and 0.20

This slight difference in mass results in the different oxygen atoms and hence water molecules responding differently

( move differently through atmosphere )

16 has highest abudnace

Oxygen 18 is heavy
Oxygen 16 is light

48
Q

Talk about about evaporation of water and oxygen isotopes?

A

As H2O^16 is lighter it is evaporated with greater ease than the heavier H2O^18

All to do with energy

As H2O^18 is heavier these water molecules are the first to condense out

These creates a gradient in the ratio of O^16 and O^18 and this gradient is driven by temperature

With high latitude ( polar) sites having less of these heavy H2O^18 compared to standards

The ratio of O^16 to O^18is effectively controlled by temperature

49
Q

Talk about temperature of atmosphere or water and oxygen isotopes

A

Hot: more negative more 16O

Cold: More positive more 18O

50
Q

Talk about the hydrological cycle

A

Solar radiation evaporates water from soil, vegetation and water surfaces

The water and latent heat are stored in the atmosphere

The air containing the water moves from warmer regions to cooler regions

When the air cools, the water condenses ad rain, snow, hail and returns to the surface

The latent heat energy is recovered as sensible heat

Global Environmental Processes (8 decks)

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