Quiz #1 - The Stratosphere & Its Pollution

Only need flashcard 34 and over.

planetary accretion

• physical properties brought particles together forming planetesimals

• gravitational pull attracts additional objects, forming a protoplanet

• proto-Earth continues growing over a very long period of time

protoplanet collision

• small protoplanet Theia collides into the young proto-Earth

• protoplanet Theia mixed with proto-Earth while some debris was held in orbit

• disk of debris from Theia and proto-Earth aggregates to form the Moon

asteroid bombardment

• asteroids and comets struck the Earth and Moon (as well as other planets in the inner solar system)

• constant bombardment caused the Earth to remain molten with episodes of volcanic eruptions
  

stratification & cooling

• materials comprising the Earth begin to separate with respect to density

• denser materials sank to the core

• lighter materials formed moved to the outer reaches of the Earth

• Earth begins to cool

stratification

• layering is found in the abiotic (non-living ) spheres of the Earth

• density (d) = mass (m) / volume (v)

• mass= amount of matter comprising an object

• matter=the stuff that makes up everything

• volume=the amount of space an object occupies

atom

• the basic building block of matter comprised of subatomic particles including proton(s), neutron(s), and electron(s)

three subatomic particles

• proton (p): positively charged particle

• electron (e-): negatively charged particle

• neutrons (n): neutral particles

nucleus

• positively charged center of an atom comprised of proton(s) and neutron(s)

orbitals

• sites where electrons (e-) could be

cation

• positively charged atoms or molecules

anion

• negatively charged atoms or molecules

dipole

• molecule with positive and negative  charges; partial charges on molecules

volume

• the amount of space that a substance occupies

• solid: definite

• liquid: definite

• gas: indefinite

shape

• the structure or form that a substance occupies in 3D space 

• solid: definite

• liquid: indefinite

• gas: definite

intermolecular forces

• the electrostatic forces between molecules usually due to charged or partially charged species

• solid: strong

• liquid: moderate

• gas: weak

intramolecular forces

• forces within the molecule keeping it together, specifically the bonds between the atoms

density

• a measure of compactness or closeness of the molecules, atoms, etc.

• solid: high

• liquid: moderate

• gas: low

compressibility

• ability to be reduced in volume

• solid: incompressible

• liquid: incompressible

• gas: compressible

particle motion

• movement of the molecules, atoms, etc.

• solid: low

• liquid: moderate

• gas: high

kinetic energy

• energy of a substance due to motion

• solid: low

• liquid: moderate

• gas: high

geosphere (1/4)

• the solid Earth

• “geo” means earth

• outer layers solidified, the crust began to form while maintaining molten layers below

• large cracks created plates and landmasses (eventually creating the continents we know today)

• all metals, rocks, minerals, soils, landforms, etc. from the core to the crust

• solid and liquid particles comprising Earth itself

atmosphere (2/4)

• “atmo” means air

• the air above Earth’s surface

• early atmosphere consisted of gases from volcanic eruptions: water vapor (H₂O_(g)) and carbon dioxide (CO₂)

• as the biosphere evolved, carbon dioxide (CO₂) was converted to oxygen (O₂)

• mixtures of gaseous particles that surround Earth

• no definite shape nor volume as it flows into space

• protects life from incoming radiation

• provides warming effect to maintain life

• has undergone and will continue to undergo changes

• gases found in the outer edges slowly leave Earth's atmosphere into outer space (less massive)

• the molecules within this sphere will probably not collide

• as altitude increases, gravity and molecules decrease; less particles, less collisions, less reactions

• as altitude decreases, gravity and molecules increase; more particles, more collisions, more reactions

• other factors, such as temperature & water vapor, are important to atmospheric pressure 

hydrosphere (3/4)

• “hydro” means water

• all water on Earth’s surface

• comets and asteroids brought water (H₂O)

• volcanic eruptions released water vapor (H₂O_(g)) into the atmosphere

• as the Earth cooled, water (H₂O_(g)) began to condense forming bodies of water (H₂O_(l)) and eventually ice (H₂O_(s))

• solid=snow/ice

• liquid=water

• properties of water are crucial for life on Earth

• freshwater = 2.5% of total global water

biosphere (4/4)

• “bio” means life

• the living things on Earth

• organisms that could survive without oxygen (O₂) were first to appear on Earth

• some organisms evolved photosynthetic abilities, producing oxygen (O₂)

• change in the atmosphere supported new life forms that relied on oxygen (O₂)

• all biotic (living) organisms, such as plants, animals, fungi, and microorganisms, on Earth

• have self-sustaining processes or functions to external stimuli

• ability to grow, reproduce, move, metabolize, breathe, excrete, etc.

lithosphere

• part of the lithosphere

• “litho” means stone

• all metals, rocks, minerals, soils, landforms, etc. from the crust to the upper mantle

• rigid and brittle

• mostly solid until seismic triggers force magma towards the surface as lava

• provides important minerals (serving as nutrients) for plants and animals

• provides resources (metals, fossil fuels, ores, etc.) needed for human activities

• provides habitats/homes

cryosphere

• “cryo” means icy cold or frost

• all water on Earth in its solid form (H₂O_(s))

• different parts of the cryosphere experience changes on different timescales

exosphere

• temperature is independent of altitude & varies with solar activity

thermosphere

• higher temperature (hotter) with increasing altitude

mesosphere

• lower temperature (colder) with increasing altitude

stratosphere

• “strat” means layer

• higher temperature (hotter) with increasing altitude

• lacks the turbulence and updrafts from troposphere

troposphere

• “tropos” means change

• lower temperature (colder) with increasing altitude

• 75% of the mass of the entire atmosphere

• warmer air below will rise and cool air above will sink

• 99% of all water vapor ( H₂O_(g) ) in the atmosphere is found in the troposphere

• 3 main circulations between due to the Earth's rotation: Hadley Cells (closest to equator), Ferrel Cells (middle cells), Polar Cells (closest to poles)

Earth in & out of balance

• equilibrium: a state of balance in which external and/or internal influences cancel each other to maintain that same state

• systems maintaining the balance can be static (remaining the same over long periods of time) or dynamic (constantly changing)

• humanity disturbs the exchange, impacting the other spheres, as well as other living organisms within the biosphere itself

technosphere

• all technological objects (machines, factories, cars, buildings, internet, AI, agriculture, etc.) made or modified by humans for human activities and/or habits; the built environment

• “biosphere is extremely good at recycling the material it is made of … the technosphere, by contrast, is poor at recycling” – UNESCO 2024

• primary source of modern pollution

atmospheric chemistry

• understanding the composition of the atmosphere and relevant photochemical reactions before applying the science to the stratosphere

heterogeneous

• no uniformity in the composition

homogeneous

• uniform composition throughout

main atmospheric gases

• Nitrogen (N₂)

• Oxygen (O₂)

• Argon (Ar) (inert/noble gas; do not react with other molecules)

trace atmospheric gases

• very low concentration but still has significant impact on the planet

• Carbon Dioxide (CO₂)

• Ozone (O₃)

• Methane (CH₄)

• Nitrous Oxide (N₂O)

• Water Vapor (H₂O_(g))

• Neon (Ne) (inert/noble gas; do not react with other molecules)

• Helium (He) (inert/noble gas; do not react with other molecules)

• Krypton (Kr) (inert/noble gas; do not react with other molecules)

• Xenon (Xe) (inert/noble gas; do not react with other molecules)

photochemistry

• chemical reactions and/or physical processes that occur when light interacts with a molecule

• when photons excite molecules to higher energy (vibrational and/or electronic) levels, leading to chemical transformations

• transformations can include chemical reactions, rearrangements, or emission of energy as heat or light

electromagnetic spectrum

• the range of electromagnetic radiation (electric and magnetic fields) from the sun

• the particles that make up electromagnetic radiation are referred to as photons or “energy packets”; they exhibit particle-wave duality

• wavelength (λ) is the distance from peak to peak

• frequency (ν) is the number of waves that pass through a point in a second

• increasing frequency from right to left (700nm=low v, long λ, low E to 400nm=high v, short λ, high E)

atmospheric photochemistry

• the study of gaseous molecules that react with “light” within the atmosphere

• M + photon → M* → Ʌ• •Ʌ (where “M” represents a molecule and “*” denotes an excited state for M) { vibrational relaxation, fluorescence, photodissociation }

Jablonski Energy Diagram

• a diagram that shows the electronic states of a molecule and the various radiative (light-emitting) and non-radiative (heat-releasing) transitions between them

• shows how a molecule returns to its ground state after absorbing electromagnetic radiation (light)

• only two electrons can occupy each orbital

• singlet ground state (S₀): most stable, lowest-energy electronic state of a molecule where all electrons are paired

• singlet excited state (S_1…): promoted electron has the same spin orientation as it had in the ground state (paired)

• triplet excited state (T_1…): promoted electron has the same spin orientation (parallel) as the other unpaired electron

vibrational relaxation

• photon with low energy can cause the greenhouse effect

• traps heat, specifically the sun’s radiation, in a planet’s lower atmosphere

• greenhouse gases (GHGs) prevent the Earth from losing heat to space

fluorescence

• the right amount of energy causes electrons to jump from a normal, low energy “ground state” to an unstable higher energy “excited state”

• molecule cannot remain in an unstable state for long

• electrons immediately falls to its ground state giving off light

photodissociation

• photon with high enough energy can break chemical bonds within the molecule

• creating radicals (highly reactive fragments) that can then undergo further reactions

• can lead to chain reactions

• M + photon → M* → Ʌ• •Ʌ; ex. A-B (molecule = M) + photon → A-B* → A• + B•

applying atmospheric chemistry

• using what we have learned about the relevant reactions, we will now look at photodissociation in the stratosphere and understand its importance

oxygen photodissociation

• O₂ +  photon (λ ≤ 240 nm)  → O₂* → 2 O•
  

ozone formation

• O• + O₂ → O₃ + heat

• O• + O₂ + M → O₃ + M + heat
  

oxygen recombination

• O• + O• → O₂

• however, two oxygen atoms (O•) can recombine to form a molecule of oxygen (O₂)

importance of ozone (O₃)

• absorption spectrum = a plot of wavelength versus the extent of absorption

• “obtained by measuring the amount of electromagnetic radiation absorbed by a sample at various wavelengths” – Advances in Nanotech, 2022

• high energy photons that do reach the earth are caught in the stratosphere

• ozone (O₃) filters most of the ultraviolet (UV) range

solar radiation spectrum

ozone photodissociation

• O₃ +  photon (λ ≤ 320 nm)  → O₂ + O•

ozone conversion

• O₃ +  O• → 2 O₂

• collisions with insufficient energy to result in a reaction

Chapman Cycle

• the photochemical reactions conducted in the stratosphere that describe the formation and destruction of ozone (O₃)

molecular oxygen reactivity

• a photon with a wavelength of 240 nm has the right amount of energy (E) to excite oxygen (O₂) which then breaks apart to monoatomic oxygen radical (O•)

• radical: unpaired valence electron

ozone layer

• ozone (O₃) in the stratosphere that protects life on earth from ultraviolet (UV) radiation

• not a “layer” since the gas is dispersed throughout stratosphere

• a region in the stratosphere with higher concentration (or presence) of ozone (O₃)

ozone holes

• thinning of the ozone (O₃) layer in the stratosphere, typically found above the North and/or South Pole(s)

• less than 200 Dobson Units (DU)

• average ozone globally: 300 DU; anthropogenic ozone loss: < 200 DU; average ozone hole: 100 DU

• 1 DU = 0.01 mm thickness of ozone (O₃) at STP if compressed into a layer at sea level.

when ozone holes occur

• Antarctic (South Pole): September to November; first observed 1979; ideal conditions makes it larger

• Arctic (North Pole): January to March; more of an ozone “dip”; first ozone hole appeared in 2011 

• generally, ozone (O₃) holes have recovered but still exist and relevant reactions must be considered

ozone depleting substances (ODSs)

• cfcs, hcfcs, and halons

NAMING HALONS

1^st = # of C atoms

2^nd = # of F atoms

3^rd = # of Cl atoms

4^th = # of Br atoms

• ex. CBrF₃ = halon-1301; CBrClF₂ = halon-1211

products containing ODSs

• refrigerators, air conditioners, foam, aerosol propellants, fire suppressant, chemical manufacturing, solvent in degreaser lubricants, paint stripping, pesticide

catalysts destroying ozone

• radical species of chlorine (Cl•) and bromine (Br•) broken off from ozone-depleting substances (ODSs)

• chlorine (Cl•) and bromine (Br•) radicals are the products from the interaction of ultraviolet (UV) radiation with ODSs within the stratosphere

• CFCl₃ + photon → CFCl₂• + Cl•

simplifying the radicals

• X = Cl• or Br•

• X' = the “partner” halogen radical in a reaction

• if X is Cl•, then X’ is Br•, and vice versa

deactivating the radicals

• chlorine (Cl•) and bromine (Br•) radicals could react with other molecules in the stratosphere resulting in deactivation of the reactive species

• reservoir species are relatively stable, non-radical compounds that temporarily store radical chlorine (Cl•) and bromine (Br•) preventing them from destroying ozone (O₃)

• these reservoirs act like “holding tanks” for radicals until released under the right conditions

• X and X’ will be used to represent chlorine (Cl•) or bromine (Br•) radicals trapped within the reservoir species… when “X” is bromine (Br) … hypobromous acid (HOBr) = HOX; bromine nitrate (BrONO₂) = XONO₂; hydrogen bromide (HBr) = HX

activating the catalyst

• cold temperature +

  North & South Poles; the South Pole has the colder temperatures; hence, the size difference

• no “light” +

  stops light-driven atmospheric reactions; therefore, inactive molecules accumulate

• pressure drop +

  creates a vortex; reservoir species are trapped in an area

• = polar stratospheric clouds

  tiny ice crystals that “catch” the inactive molecules; H₂O(g) → H₂O(s)

polar stratospheric clouds (PSCs)

• polar Stratospheric Clouds (PSCs) give the inactive molecules surfaces to become active molecules for ozone (O₃) destruction

• Cl₂, Br₂, and BrCl are released as gases

• when ultraviolet (UV) light returns, these molecules photodissociate:

  Cl₂ + hv → 2 Cl•

  Br₂​ + hv → 2 Br•

  BrCl + hv → Br• + Cl•

catalytic ozone destruction: Mechanism 1

• occurs when [O•] is high (upper stratosphere)

• in the upper stratosphere there is enough high-energy UV-C radiation that can effectively photodissociate molecular oxygen (O₂), generating a high concentration of monoatomic oxygen radicals (O•)

• reaction #1: X• + O₃ → XO• + O₂

• reaction #2: XO• + O• → X• + O₂

• O₃ + X• + XO• + O• → XO• + O₂ + X• + O₂

• overall reaction: O₃ + O• → O₂ + O₂ = O₃ + O• → 2 O₂

• X• is recycled; therefore, it is a catalyst for ozone (O₃) destruction
  

catalytic ozone destruction: Mechanism 2

• occurs when [O•] is low (lower stratosphere)

• by the time solar radiation penetrates down into the lower stratosphere, most of the high-energy UV-C photons capable of splitting molecular oxygen (O₂) have already been absorbed at higher altitudes

• reaction #1: X• + O₃→ XO• + O₂

• reaction #2: X’• + O₃ → X’O• + O₂

• reaction #3: XO• + X’O• → → X• + X’• + O₂

• 2 O₃ + X• + X’• + XO• + X’O• → XO• + X’O• + X• + X’• + 3 O₂

• 2 O₃ + X• + X’• + XO• + X’O• → XO• + X’O• + X• + X’• + 3 O₂

• overall reaction: 2 O₃ → 3 O₂

• X• is recycled; therefore, it is a catalyst for ozone (O₃) destruction

a world avoided

• between 1970 and 1980, scientists discovered that chlorofluorocarbons (CFCs) and related chemicals destroyed ozone (O₃)

• in 1987, the Montreal Protocol, an international treaty was designed to protect the ozone (O₃) layer by  phasing out the production and consumption of ozone-depleting substances (ODSs)

• the protocol went into effect in 1989, after being ratified by all 198 United Nations (UN) member states

the ban on ODSs

• developed countries – stricter/earlier phaseout deadlines

• developing countries – delayed phaseout timelines to allow for economic adjustment

• scope: developed countries under Montreal Protocol; source: EPA or UNEP

• while this is critical for protecting the ozone (O₃) layer, their replacements, hydrofluorocarbons (HFCs) do not harm ozone (O₃) but are powerful greenhouse gases

other catalysts for ozone holes

• chlorine (Cl•) and bromine (Br•) radicals but also, radicals of…nitrogen oxides (NO_x); nitrogen monoxide radical (NO•); nitrogen dioxide radical (NO₂•) and hydrogen oxides (HO_x); hydroxyl radical (HO•); hydroperoxyl radical (HO₂•)

• NOₓ and HOₓ are mostly made in the troposphere, and only a fraction of these radicals or their precursors is transported into the stratosphere.

why it matters

Why should we be concerned about stratospheric ozone (O₃) if ozone-depleting substances (ODSs) are banned and the other catalysts (NO_x and HO_x) are only transported in fractions from the troposphere?

• rockets (and other high-altitude combustion sources) directly inject nitrogen oxides (NO_x) into the stratosphere, bypassing slow transport

• even small amounts of nitrogen oxides (NO_x) can participate in catalytic ozone (O₃) destruction cycles, locally depleting ozone (O₃)

• human activities can still influence stratospheric chemistry, even after reducing long-lived pollutants like chlorofluorocarbons (CFCs)

rockets & nitrogen oxides (NO_x)

• high-temperature combustion of rocket fuels produces nitrogen monoxide (NO•) via thermal excitation

• temperatures are high enough to break the strong triple bond in molecular nitrogen (N₂), and double bond in molecular oxygen (O₂)

• nitrogen monoxide radical (NO•) can react with ozone (O₃) via Mechanism 1 or 2

• these reactions catalytically destroy ozone