Atmospheric ChemistryAtmospheric Chemistry

Stratospheric OzoneStratospheric Ozone

1) Absorbs 1) Absorbs solar radiation (200-solar radiation (200-315nm)315nm)

2) Three types of 2) Three types of UVUV

UV-A (320-400 )UV-A (320-400 )

UV-B (280-320nm)UV-B (280-320nm)

UV-C (200-280 nm)UV-C (200-280 nm)

3) The greatest concentration of 3) The greatest concentration of OO33 is is from 15-30 km above Earthfrom 15-30 km above Earth

4) The amount of Ozone 4) The amount of Ozone variesvaries

5) Quantified by the 5) Quantified by the Dobson Unit Dobson Unit (DU)(DU)

100 DU100 DU = = 1 mm of Ozone1 mm of Ozone

The Earth averages about The Earth averages about 300 DU300 DU

Antarctic = Antarctic = 150 DU150 DU

Ozone Formation:Ozone Formation:

Oxygen molecules are Oxygen molecules are hit with UV hit with UV lightlight and and split into energized split into energized atomsatoms that combine with an that combine with an oxygen oxygen molecule to form ozone (Omolecule to form ozone (O33).).

1. 1. OO22 + UV + UV 2 O• 2 O•

2. 2. O• + OO• + O22 + M + M O O33

- this second reaction requires a third - this second reaction requires a third party molecule (M) to help absorb party molecule (M) to help absorb the extra energy – usually another the extra energy – usually another atmospheric gasatmospheric gas

Processes of Ozone destructionProcesses of Ozone destruction

Free RadicalsFree Radicals: : atoms or molecules atoms or molecules with a with a free (non-bonded) electronfree (non-bonded) electron

- highly - highly unstable and reactiveunstable and reactive

- Most responsible for - Most responsible for non-oxygen non-oxygen destruction of ozonedestruction of ozone

These include:These include:

HOx•, NOx•, ClOx• gasesHOx•, NOx•, ClOx• gases

Basic ProcessBasic Process:: molecules float to the molecules float to the stratospherestratosphere

and are bombarded by and are bombarded by UV lightUV light molecules are molecules are broken apartbroken apart forming forming

free radicalsfree radicals free radicals free radicals attack ozone attack ozone

moleculesmolecules causing them to causing them to break break downdown and and form more free radicalsform more free radicals

process continues until the process continues until the free free radicals bind to a sequestering radicals bind to a sequestering moleculemolecule to become stable to become stable

Generalized ReactionGeneralized Reaction

XX22 + UV + UV X X• +• + X X• • X• + OX• + O33 XO + O XO + O22 XO + O• XO + O• O O22 + X• + X•

Overall Process:Overall Process:

X• is not consumed by the X• is not consumed by the reaction but remains to continue reaction but remains to continue the breakdown of Othe breakdown of O33..

OO33 + O + O 2 O 2 O22

Hydroxyl Radicals and the HOX Hydroxyl Radicals and the HOX CycleCycle

Methods of Hydroxyl Generation:Methods of Hydroxyl Generation:

11. O• (energized oxygen) + H. O• (energized oxygen) + H22O O 2 •OH2 •OH

2. 2. HH22O + UV O + UV •H + •OH •H + •OH

3. 3. H • + OH • + O33 •OH + O •OH + O22

Decomposition of ozone by Decomposition of ozone by hydroxyl radical:hydroxyl radical:

1. 1. •OH + O•OH + O33 HOO• + O HOO• + O22

2. 2. HOO• + O• HOO• + O• •OH + O •OH + O22

NOX CycleNOX Cycle

NONO22 + UV + UV NO• + O• NO• + O• This photodissociation makes This photodissociation makes

possible:possible:

NO• + ONO• + O33 NONO22 + O + O22

NONO22 + O• + O• NO• + O NO• + O22 - note the free - note the free “O” is there because it is in the “O” is there because it is in the stratosphere where atomic density stratosphere where atomic density is lowis low

The ClOx cycleThe ClOx cycle

Cl• are Cl• are mostly anthropogenic (man mostly anthropogenic (man made) in sourcemade) in source

CHCH33Cl + UV Cl + UV •CH •CH33 + •Cl + •Cl

MEMORIZE THESE!MEMORIZE THESE!

The main reaction with ozoneThe main reaction with ozone

CFClCFCl33 + UV (<290 nm) + UV (<290 nm) •CFCl •CFCl22 + + Cl•Cl•

Cl• +OCl• +O33 ClO• + O ClO• + O22

ClO• + O• ClO• + O• Cl• + O Cl• + O22

Net Reaction = Net Reaction = OO33 + O + O O O22 + O + O22

Anthropogenic sources of chlorineAnthropogenic sources of chlorine

1.1. Mostly Mostly chlorinated fluorocarbonschlorinated fluorocarbons

2.2. Refrigerants, solvents, propellantsRefrigerants, solvents, propellants

3.3. Chemically and biologically inertChemically and biologically inert

4.4. CFCs CFCs do not react in the do not react in the troposphere but do in stratospheretroposphere but do in stratosphere

Properties of CFCsProperties of CFCs

1.1. Can last 60 – 522 years in Can last 60 – 522 years in tropospheretroposphere

2.2. The The ODP (ozone depletion ODP (ozone depletion potential) is correlated with the potential) is correlated with the # of Cl# of Cl

The Ozone Hole - The Ozone Hole - AntarcticaAntarctica

- Results from - Results from climatic factors and climatic factors and accumulation of pollutantsaccumulation of pollutants

ProcessProcess::1)1) Sun sets for the season – Sun sets for the season – dark and dark and

very coldvery cold 2)2) Air currents Air currents form a circumpolar form a circumpolar

vortexvortex that channels pollutants to that channels pollutants to form form stratospheric cloudsstratospheric clouds

3)3) Clouds form Clouds form ice crystals of nitric acid, ice crystals of nitric acid, chlorine compounds and waterchlorine compounds and water

4)4) The sunlight returns to The sunlight returns to photolyse and photolyse and create free radicals of chlorine andcreate free radicals of chlorine and nitrogennitrogen compounds compounds

5)5) Rapid Rapid degradation of ozonedegradation of ozoneVIDEO Video #2Video#3

End Result:End Result:

1.1. Ozone thickness decreases to Ozone thickness decreases to 150 DU150 DU

2.2. Free radicals Free radicals spread north to South spread north to South America, New Zealand and America, New Zealand and AustraliaAustralia

3.3. Increases Increases UV damageUV damage by allowing by allowing more more UV-B radiationUV-B radiation into troposphere into troposphere

Health EffectsHealth Effects::

- damage to - damage to plantsplants

- increased damage to - increased damage to skin and DNA skin and DNA (thymine dymers)(thymine dymers) skin cancerskin cancer – – just like going to the Death Boxes just like going to the Death Boxes known as tanning bed. known as tanning bed.

Montreal Protocol: InternationalMontreal Protocol: International agreement to limit/ban CFC use.agreement to limit/ban CFC use.

Tropospheric ChemistryTropospheric Chemistry

To form To form photochemical smogphotochemical smog, three , three main ingredients are needed:main ingredients are needed:

1.1. nitrogen oxides (NOx)nitrogen oxides (NOx)

2.2. hydrocarbons (VOCs)hydrocarbons (VOCs)

3.3. energy from the energy from the sun in the form of sun in the form of ultraviolet light (UV).ultraviolet light (UV).

ProcessProcess: :

1.1. Generation of Generation of NO, hydrocarbons NO, hydrocarbons (VOCs) and carbon monoxide (VOCs) and carbon monoxide (CO) from combustion in cars(CO) from combustion in cars

NN22 + O + O222 NO2 NO

2. In the air, 2. In the air, nitrogen monoxide nitrogen monoxide (nitric oxide) combines with (nitric oxide) combines with molecular oxygenmolecular oxygen to form to form nitrogen dioxidenitrogen dioxide within a few within a few hours.hours.

2NO + O2NO + O222 NO2 NO22

3. Nitrogen dioxide 3. Nitrogen dioxide absorbs light absorbs light energy and splits to form energy and splits to form nitrogen monoxidenitrogen monoxide and atomic and atomic oxygen:oxygen:

NONO22NO + O•NO + O•

4. Then, in sunlight, the 4. Then, in sunlight, the atomic atomic oxygen combines with oxygen oxygen combines with oxygen gas to form ozonegas to form ozone

O• + OO• + O22OO33

- If no other factors are involved, - If no other factors are involved, ozone and ozone and nitric oxide then react to form nitric oxide then react to form nitrogen dioxide and oxygen gas.nitrogen dioxide and oxygen gas.

OO33 + NO + NO NO NO22 + O + O22

- This last reaction is - This last reaction is reversiblereversible and and moves in moves in one direction basedone direction based on the on the temperature and the amount of temperature and the amount of sunlightsunlight. .

- If there is a lot of - If there is a lot of sunlight, the sunlight, the equation moves to the leftequation moves to the left, and more , and more ozone is producedozone is produced. If nothing else gets . If nothing else gets in the way, an in the way, an equilibriumequilibrium is reached, is reached, and the and the ozone level stabilizesozone level stabilizes. .

5. 5. VOCs react with nitric oxide to VOCs react with nitric oxide to produce PANproduce PAN (peroxyacetyl nitrate). (peroxyacetyl nitrate).

NO + hydrocarbonsNO + hydrocarbonsPANPAN

Two ResultsTwo Results::1.1. Volatile, reactive organic compounds Volatile, reactive organic compounds

are generated directlyare generated directly. . 2.2. Nitric oxide (NO) reacts with Nitric oxide (NO) reacts with

hydrocarbons instead of ozone hydrocarbons instead of ozone increasing the amount of ozone in increasing the amount of ozone in the troposphere to damaging levelsthe troposphere to damaging levels..

End ProductEnd Product::- an - an accumulation of ozoneaccumulation of ozone and and volatile volatile

organic compoundsorganic compounds such as PAN, which such as PAN, which are secondary pollutantsare secondary pollutants

- the sun moves the reactions along forming - the sun moves the reactions along forming photochemical smogphotochemical smog

Health Effects of Photochemical SmogHealth Effects of Photochemical Smog eye irritationeye irritation and poor visibility and poor visibility Strong oxidants such as ozone can Strong oxidants such as ozone can

damage the lungsdamage the lungs. . Damage to the lungs may Damage to the lungs may stress the stress the

heartheart. . loss of loss of immune system functionimmune system function, ,

increased susceptibility to infections, and increased susceptibility to infections, and fatigue. fatigue.

kill kill plant cellsplant cells, causing leaves to develop , causing leaves to develop brown spots or drop off the plant, reduce brown spots or drop off the plant, reduce plant growth, and make plants more plant growth, and make plants more susceptible to damage from other causes. susceptible to damage from other causes.

corrode and destroy many materialscorrode and destroy many materials such as rubber, nylon, fabric, and paint.such as rubber, nylon, fabric, and paint.

Greenhouse Effect, Enhanced Greenhouse Greenhouse Effect, Enhanced Greenhouse Effect, Effect,

Global Warming & Climate ChangeGlobal Warming & Climate Change

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

Greenhouse Effect on EarthGreenhouse Effect on Earth: : Atmospheric Atmospheric gases act as the glassgases act as the glass. Allow light in but . Allow light in but absorb and absorb and redirect the IR back to the redirect the IR back to the EarthEarth. .

Not all gases do this. Some gases do Not all gases do this. Some gases do this more than others. The ability to this more than others. The ability to absorb IR and release it is called the absorb IR and release it is called the Global Warming PotentialGlobal Warming Potential. Carbon . Carbon dioxide has a GWP value of 1 (base dioxide has a GWP value of 1 (base measurement) while CFC’s can be measurement) while CFC’s can be hundreds or thousands of times greater hundreds or thousands of times greater than CO2. than CO2.

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

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

EffectsEffects:: Change of Change of ocean temperatureocean temperature.. changes changes ocean currents = change ocean currents = change

in climatein climate changes changes weather patterns = weather patterns =

change in climate = loss of change in climate = loss of biodiversity. Also a change in biodiversity. Also a change in agricultureagriculture. .

change in change in upwelling of nutrients = upwelling of nutrients = loss of biodiversityloss of biodiversity

decreases decreases oxygen content = loss of oxygen content = loss of biodiversitybiodiversity

Increased Increased COCO22 in water in water Loss of BiodiversityLoss of Biodiversity increases increases acidity of wateracidity of water decreases decreases productivityproductivity kills kills coral reefscoral reefs

Loss of Biodiversity

Competing TheoriesCompeting Theories