Atmospheric Chemistry

Question 1

Atmospheric profiles

Answer 1

Exosphere, thermosphere, mesosphere, stratosphere, and troposphere

Question 2

Composition of gases in the atmosphere

Answer 2

70% O2, 20% N2, 10% others

Question 3

Purpose of the atmosphere

Answer 3

Protects the earth’s surface from cosmic and solar radiation.

Question 4

Why are altitudes of atmospheric profiles slightly variable?

Answer 4

As the earth isn’t fully spherical, some areas are closer to the sun as it rotates, thus causing gas particles to expand with increased temperature.

Question 5

Why do most chemical reactions occur in the mesosphere?

Answer 5

Because it experiences solar emissions from above and thermal/chemical emmisions from the surface.

Question 6

Absorption

Answer 6

The conversion of electromagnetic radiation into atomic or molecular internal energy

Question 7

Photoionisation

Answer 7

Removal of an electron from an atom or molecule, requires high levels of energy

Question 8

Photodissociation

Answer 8

Photon-induced decomposition of a molecular species, breaking bonds.

Question 9

Fluorescence

Answer 9

Emission of a photon when excited molecules return to their normal state. The wavelength of the admitted light is the same or longer than the absorbed wavelength.

Question 10

Collisional quenching

Answer 10

Where the internal energy of an excited molecule that could be released as light is translated into other forms (usually heat) through collisions with other molecules.

Question 11

Intermolecular energy transfer

Answer 11

Where collisions cause an excited molecule to transfer its energy to another molecule, however, it is not translated into other forms; the other molecule can now potentially fluoresce instead.

Question 12

Black body radiation

Answer 12

The emission of electromagnetic radiation by an opaque, non-reflective object that has a constant temperature and is held in equilibrium with its surroundings.

Question 13

Thermosphere

Answer 13

Absorbs the harshest radiation from the sun, being the furthest out.

Question 14

Thermosphere: distance from earth

Answer 14

over 80km

Question 15

Thermosphere: chemical comosition

Answer 15

N2 and O2

Question 16

Thermosphere: temperature change and pressure

Answer 16

-92 to 1200 degrees from down to up, lowest pressure of all layers due to few molecular collisions.

Question 17

Thermosphere: temperature gradient explanation

Answer 17

Caused by the absorption of short wavelength radiation. When gases absorb photons with energy that exceeds the ionisation energy, the gases become ionised and gain energy, and therefore temperature increases. Higher up in the thermosphere, where there are higher levels of radiation, it is warmer as a result.

Question 18

Thermosphere: radiation

Answer 18

Due to few molecular collisions, energy is mainly dissipated by radiative loss. In lower layers where molecular collisions are more frequent, energy becomes translated and passed on to other molecules, keeping energy moving and temperature generally constant across the region. In the thermosphere, however, where energy cannot be easily passed around, it tends to get released directly as radiation. As a result, there are sharp temperature changes between day and night due to lack of solar radiation and very little air flow, which increases the contrast further.

Question 19

Solar wind

Answer 19

Charged particles are emitted from the sun, interacting with the outer edges of the atmosphere

Question 20

Cosmic rays

Answer 20

High-energy charged particles that come from outside the solar system, often distant stars, supernovae and cosmic events.

Question 21

Van Allen belts

Answer 21

Regions (inner and outer ring) around the earth that are filled with charged particles, mainly from solar wind. They trap the charged particles to stop them hitting the earth directly and prevent harm. They are stronger when there are higher levels of solar activity. The earth’s magnetic field keeps these charged particles in place

Question 22

Inner and outer Van Allen belts

Answer 22

The inner belt is filled with protons, and the outer belt is filled with electrons.

Question 23

Example: Aurora Borealis

Answer 23

Charged particles in the thermosphere collide with gases, causing excitation of electrons. This leads to fluorescence, thus forming the aurora. The colour relates to the energy involved in the collision and the nature of the gas involved (N2, O2)

Question 24

Example: Radio signals

Answer 24

The thermosphere has the important quality of bouncing radio signals transmitted from the earth.

Question 25

Why is Aurora most visible near the poles?

Answer 25

The earth's magnetic field lines converge at the geomagnetic north and south poles. Magnetospheric electrons can be accelerated by various processes and hit the atmosphere as they flow along magnetic field lines in polar regions.

Question 26

Mesosphere

Answer 26

The second-highest atmospheric profile; not many chemical reactions here due to a lack of ions. The concentration of molecules is slightly increased.

Question 27

Mesosphere: distance from earth

Answer 27

50-80 km

Question 28

Mesosphere: chemical composition

Answer 28

N2 and O2

Question 29

Mesosphere: temperature change and pressure

Answer 29

-2 - -92 at the top, low pressure

Question 30

Mesosphere: Temperature gradient implications

Answer 30

The warmest temperature is at the bottom of the mesosphere. Due to this inversion air currents (wind) are formed.

Question 31

Mesosphere: Gases

Answer 31

The gases are thick enough to slow down meteors hurtling towards the atmosphere, where they burn up.

Question 32

Stratopause

Answer 32

The divide between the mesosphere and the stratosphere

Question 33

Stratosphere

Answer 33

The chemistry in this region is mainly ozone photochemistry

Question 34

Stratosphere: distance from earth

Answer 34

15-50 km

Question 35

Stratosphere: chemical composition

Answer 35

mostly N2, O2, O3, CFCs and trace gases

Question 36

Stratosphere: temperature gradient and pressure

Answer 36

-56 to -2 degrees, reasonable pressure

Question 37

Stratosphere: temperature gradient implications

Answer 37

Indicates that there is photochemistry occuring in the region e.g., O2 related chemisrty, in particular absorption of UV light by the stratospheric ozone.

Question 38

Stratosphere: radiation

Answer 38

exceeds 220 nm (UV radiation)

Question 39

Mesosphere: radiation

Answer 39

Though the amount of high-energy radiation is reduced, chemical composition is similar, so little heating in this region from solar absorption. Some radiation is absorbed in this region.

Question 40

Mesosphere: temperature gradient implications

Answer 40

Due to the temperature inversions in this atmospheric profile, wind occurs

Question 41

Stratosphere: photochemical pathways

Answer 41

N2, H2O, CH4: no photochemistry when the wavelength > 180 nm O2: O + O when wavelength > 240 nm 0* + O for higher wavelengths O3: O2 + O O2 + O*

Question 42

Photochemical pathways

Answer 42

A chemical reaction that is triggered when light energy is absorbed by molecules. In the ozone layer, ozone particles split into O2 and O when hit by UV light, which can then react with one another to form ozone particles again. Dynamic balance: ozone-oxygen cycle.

Question 43

Ozone chemistry

Answer 43

When ozone molecules absorb photons, their internal energy increases and must release/translate this energy.

Question 44

Ozone chemistry: the Chapman Cycle

Answer 44

Where ozone dissociates into oxygen and diatomic oxygen. Clearly a destructive process, means that the ozone in the stratosphere would rapidly disappear. The process is constantly in a state of dynamic equilibrium.

Question 45

Ozone chemistry: ozone layer

Answer 45

Assuming the destructive processes are constant, ozone concentrations will be highest where the formation processes are most frequent. [O2] decreases with increased altitude and pressure whereas UV-C levels increase. This means that there is a layer of ozone that is created in the lower stratosphere.

Question 46

Ozone chemistry: Catalytic destruction

Answer 46

It is suggested that there are other mechanisms for ozone destruction because the chapman cycle alone would result in too-high a concentration of ozone. Other mechanisms for ozone destruction are described as catalytic as the concentration of whatever reacts does not change. They convert either O3 or O into O2.

Question 47

Stratospheric OH radicals

Answer 47

Formed via the reaction between UV and ozone, highly unpredictable and reactive species. They then react with other species e.g., H2O, CH4, NO2 through free radical substitution.

Question 48

Stratospheric halogen radicals

Answer 48

There are a few natural sources of Cl or Br radicals in the atmosphere, however some form from oceanic emissions. Most halogen radicals are caused by human activity.

Question 49

CFCs

Answer 49

Chlorofluorocarbons: long atmospheric lifetimes, chemically and biologically inert, low bp, non toxic/flammable. Only forms of loss are deposition and transport.

Question 50

Implications of CFCs in the stratosphere

Answer 50

In the stratosphere, CFCs can be photolysed to produce Cl* which can catalytically destroy ozone.

Question 51

Antarctica: CFC timeline

Answer 51

In the early 1980s, there was little knowledge of stratospheric ozone destruction. 1982: first noticed a decrease in ozone concentrations. 1989: large hole burnt in the ozone layer at 14-22 km altitude, caused 98% reduction of ozone. This hole has since spread over the entire continent towards Australia and New Zealand.

Question 52

Abnormal Antarctic chemistry

Answer 52

In the polar vortex temperatures (-80) freezing chemicals are formed containing (HCl, ClONO2, NO2, CH4) These species react readily on cloud surfaces, converting cast amounts of reservoir species into atmospherically hazardous halogenated compounds.

Question 53

Polar stratospheric clouds (PSCs)

Answer 53

ClONO2 + HCl = Cl2 + HNO3 ClONO2 + H20 = HOCl + HNO3 HNO3 will be rained out from these PSCs, however Cl2 and HOCl are stored within the clouds. With the nitrogen removed through rain, the chlorine species are now free to react with the ozone. When temperatures rise, the chemistry of these regions return to normal.

Question 54

Dimerisation and its importance

Answer 54

???

Question 55

Antarctic vs Arctic.

Answer 55

Arctic only found minor ozone loss in the atmosphere as it isn't cool enough. The arctic vortex is much weaker with more mixing, which leads to fewer PSCs and less ozone depletion overall.

Question 56

Troposphere

Answer 56

The atmospheric profile closest to the earth.

Question 57

Troposphere: distance

Answer 57

0-10 km at the poles, 16km at the tropics

Question 58

Troposphere: chemical composition

Answer 58

Broad composition including 85% of total atmospheric mass.

Question 59

Troposphere: temperature gradient and pressure

Answer 59

15 - -56 degrees from bottom to top. 1 bar of pressure.

Question 60

Troposphere: radiation

Answer 60

UV-A, visible light, some infrared radiation.

Question 61

Troposphere: temperature gradient implications

Answer 61

Inverted temperature profile causes wind, low temperature in the tropopause means that many tropospheric species e.g., water, are frozen out and cannot enter the stratosphere.

Question 62

Tropopause

Answer 62

An effective temperature barrier between the troposphere and stratosphere.

Question 63

Troposphere: Human impact

Answer 63

Tropospheric chemistry is heavily influenced by humans and land features (land/sea). Humans don't induce new chemistry, however tend to push equilibriums too far in one direction.

Question 64

Key species in tropospheric chemistry

Answer 64

HOx, NOx, SOx, terpenes, aerosols

Question 65

Terpenes

Question 66

Acid rain

Answer 66

Caused by a fine balance of CO2 in the troposphere. Equilibrium in gaseous CO2 is maintained by CO2 dissolving into water masses, which can lead to the production of carbonic acid (H2CO3, pH 5.6)

Question 67

Effects of acid rain

Answer 67

Destruction of marble or limestone buildings. Leach minerals out of soil, which are essential for growth Al3+ can poison trees SO2 attacks foliage Al3+ and SO42- are toxic to fish and many lakes cannot regulate the pH of their water under 6.

Question 68

Working out if an ion is hard or soft

Answer 68

charge/radius, hard = high number, soft = low number

Question 69

Photochemical smog

Answer 69

Formed by SO2, killed 4000 of the London population in 1952. Made up from UV light, hydrocarbons and NOx. Causes eyes/nasal/throat irritation and severely reduced visibility.

Question 70

The origins of smog

Answer 70

Combustion engines produce hydrocarbons and NOx, which are key to the formation of smog. Piston engines also tend to emit unoxidised hydrocarbons, caused by the incomplete combustion near the walls of the engine.

Question 71

Smog mitigation efforts

Answer 71

Since 2008, emissions for light duty motor vehicles in the USA have been capped at 0.41 g/mile HCs, 0.4 g/mile NO, 3.4 g/mile CO. Catalytic converters have also helped to reduce pollutant emissions.

Question 72

Indicators of smog formation

Answer 72

Production of tropospheric ozone and peroxyacetylnitrate (PAN).

Question 73

Degree of toxicity of smog

Answer 73

Unknown as a whole, but O3 is toxic to humans, causing irritation to the respiratory mucous system, and PAN can cause eye irritation, phytotoxicity and mutagenicity.

Question 74

Source of O3

Answer 74

Tropospheric source: NO2 reacting with UV light.

Question 75

Source of peroxy radicals

Answer 75

Many exist as a result of photolytic processes between O3/UV or NO*/NO2/H2O (more likely) Non-photolytic sources include: HONO/UV and alkene/O3

Question 76

Criegee intermediates

Question 77

Global warming

Answer 77

Temperature of the earth on aerage is increasing, sea levels are rising and ice caps are melting.

Question 78

Global warming: effects on earth

Answer 78

Assuming the earth is a black body emitter, the earth could become an emitter with a temperature of 256K, however the earth would become uninhabitable.

Question 79

Radiative absorption

Answer 79

Real surface temp of the earth is 288K, 32K discrepancy is due to absorption of solar flux. The earth mainly emits long-wavelength infrared radiation.

Question 80

Greenhouse gases

Answer 80

Absorb emissions from the earth's surface - effectively trapping it and preventing it from being passed into space. Creates a net warming effect.