Atmospheric Chemistry

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Atmospheric Chemistry
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• Stratospheric Ozone
• 1) Absorbs solar radiation (200-315nm)
• 2) Three types of UV
• UV-A (320-400 )
• UV-B (280-320nm)
• UV-C (200-280 nm)

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• 3) The greatest concentration of O3 is from 15-30
  km above Earth
• 4) The amount of Ozone varies
• 5) Quantified by the Dobson Unit (DU)
• 100 DU 1 mm of Ozone
• The Earth averages about 300 DU
• Antarctic 150 DU

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• Ozone Formation
• Oxygen molecules are hit with UV light and split
  into energized atoms that combine with an oxygen
  molecule to form ozone (O3).
• 1. O2 UV ? 2 O
• 2. O O2 M ? O3
• - this second reaction requires a third party
  molecule (M) to help absorb the extra energy
  usually another atmospheric gas

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• Processes of Ozone destruction
• Free Radicals atoms or molecules with a free
  (non-bonded) electron
• - highly unstable and reactive
• - Most responsible for non-oxygen destruction of
  ozone
• These include
• HOx, NOx, ClOx gases

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• Basic Process
• molecules float to the stratosphere and are
  bombarded by UV light
• molecules are broken apart forming free radicals
• free radicals attack ozone molecules causing them
  to break down and form more free radicals
• process continues until the free radicals bind to
  a sequestering molecule to become stable

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Generalized Reaction

• X2 UV ? X X
• X O3 ? XO O2
• XO O ? O2 X

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Overall Process

• X is not consumed by the reaction but remains
  to continue the breakdown of O3.
• O3 O ? 2 O2

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• Hydroxyl Radicals and the HOX Cycle
• Methods of Hydroxyl Generation
• 1. O (energized oxygen) H2O ? 2 OH
• 2. H2O UV ? H OH
• 3. H O3 ? OH O2

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• Decomposition of ozone by hydroxyl radical
• 1. OH O3 ? HOO O2
• 2. HOO O ? OH O2

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• NOX Cycle
• NO2 UV ? NO O
• This photodissociation makes possible
• NO O3 ?NO2 O2
• NO2 O ? NO O2 - note the free O is there
  because it is in the stratosphere where atomic
  density is low

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• The ClOx cycle
• Cl are mostly anthropogenic (man made) in
  source
• CH3Cl UV ? CH3 Cl

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MEMORIZE THESE!

• The main reaction with ozone
• CFCl3 UV (lt290 nm) ? CFCl2 Cl
• Cl O3 ? ClO O2
• ClO O ? Cl O2
• Net Reaction O3 O ? O2 O2

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• Anthropogenic sources of chlorine
• Mostly chlorinated fluorocarbons
• Refrigerants, solvents, propellants
• Chemically and biologically inert
• CFCs do not react in the troposphere but do in
  stratosphere

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• Properties of CFCs
• Can last 60 522 years in troposphere
• The ODP (ozone depletion potential) is correlated
  with the of Cl

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The Ozone Hole - Antarctica

• - Results from climatic factors and accumulation
  of pollutants
• Process
• Sun sets for the season dark and very cold
• Air currents form a circumpolar vortex that
  channels pollutants to form stratospheric clouds

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• Clouds form ice crystals of nitric acid, chlorine
  compounds and water
• The sunlight returns to photolyse and create free
  radicals of chlorine and nitrogen compounds
• Rapid degradation of ozone
• VIDEO Video 2
• Video3

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• End Result
• Ozone thickness decreases to 150 DU
• Free radicals spread north to South America, New
  Zealand and Australia
• Increases UV damage by allowing more UV-B
  radiation into troposphere

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• Health Effects
• - damage to plants
• - increased damage to skin and DNA (thymine
  dymers) ? skin cancer just like going to the
  Death Boxes known as tanning bed.

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• Montreal Protocol International agreement to
  limit/ban CFC use.

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• Tropospheric Chemistry
• To form photochemical smog, three main
  ingredients are needed
• nitrogen oxides (NOx)
• hydrocarbons (VOCs)
• energy from the sun in the form of ultraviolet
  light (UV).

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• Process
• Generation of NO, hydrocarbons (VOCs) and carbon
  monoxide (CO) from combustion in cars
• N2 O2?2 NO
• 2. In the air, nitrogen monoxide (nitric oxide)
  combines with molecular oxygen to form nitrogen
  dioxide within a few hours.
• 2NO O2?2 NO2

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• 3. Nitrogen dioxide absorbs light energy and
  splits to form nitrogen monoxide and atomic
  oxygen
• NO2?NO O
• 4. Then, in sunlight, the atomic oxygen combines
  with oxygen gas to form ozone
• O O2?O3

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• - If no other factors are involved, ozone and
  nitric oxide then react to form nitrogen dioxide
  and oxygen gas.
• O3 NO ?? NO2 O2
• - This last reaction is reversible and moves in
  one direction based on the temperature and the
  amount of sunlight.
• - If there is a lot of sunlight, the equation
  moves to the left, and more ozone is produced.
  If nothing else gets in the way, an equilibrium
  is reached, and the ozone level stabilizes.

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• 5. VOCs react with nitric oxide to produce PAN
  (peroxyacetyl nitrate).
• NO hydrocarbons?PAN

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• Two Results
• Volatile, reactive organic compounds are
  generated directly.
• Nitric oxide (NO) reacts with hydrocarbons
  instead of ozone increasing the amount of ozone
  in the troposphere to damaging levels.
• End Product
• - an accumulation of ozone and volatile organic
  compounds such as PAN, which are secondary
  pollutants
• - the sun moves the reactions along forming
  photochemical smog

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• Health Effects of Photochemical Smog
• eye irritation and poor visibility
• Strong oxidants such as ozone can damage the
  lungs.
• Damage to the lungs may stress the heart.
• loss of immune system function, increased
  susceptibility to infections, and fatigue.
• kill plant cells, causing leaves to develop
  brown spots or drop off the plant, reduce plant
  growth, and make plants more susceptible to
  damage from other causes.
• corrode and destroy many materials such as
  rubber, nylon, fabric, and paint.

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Greenhouse Effect, Enhanced Greenhouse Effect,
Global Warming Climate Change

• Greenhouse glass of greenhouse allows light into
  the plants and soil. Light is converted to heat
  (infrared radiation (IR)). The glass traps the
  heat making the greenhouse warm.

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• Greenhouse Effect on Earth Atmospheric gases act
  as the glass. Allow light in but absorb and
  redirect the IR back to the Earth.
• Not all gases do this. Some gases do this more
  than others. The ability to absorb IR and release
  it is called the Global Warming Potential. Carbon
  dioxide has a GWP value of 1 (base measurement)
  while CFCs can be hundreds or thousands of times
  greater than CO2.

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• THIS IS GOOD otherwise the Earth would be about
  -18 C.

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• Enhanced Greenhouse Effect (aka Global Warming)
  is the idea that increased amounts of Greenhouse
  gases will cause the global temperature to
  increase.

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• Effects
• Change of ocean temperature.
• changes ocean currents change in climate
• changes weather patterns change in climate
  loss of biodiversity. Also a change in
  agriculture.
• change in upwelling of nutrients loss of
  biodiversity
• decreases oxygen content loss of biodiversity

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• Increased CO2 in water
• Loss of Biodiversity
• increases acidity of water
• decreases productivity
• kills coral reefs

Loss of Biodiversity
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Competing Theories
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