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8/13/2019 Stratospheric Chemistry
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StratosphericChemistryFrances Pauline U. Onting
Ma. Jedil R. Esteba
Why should we care
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Why should we care Stratospheric ozone levels are declining.
6 - 10% decline in stratospheric ozone levelsduring the past three decades
Some degree of stratospheric ozone loss hasaffected all latitudes
Every time even a small amount of
the ozone layer is lost, more ultraviolet lightfrom the sun can reach the Earth.
By 2075 about 60 million will have skin
cancer
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Flashback on Stratospheric Chemistry1923
Gordon Dobson developed the first spectrometer to
measure ozone in the atmosphere and characterizedits latitudinal seasonal variability
1928
Thomas Midgley develops CFC, replacing ammoniaand SO2
1930
Sydney Chapman published several theoretical paperson upper-atmospheric ozonenow known as theChapman Cycle
1950
The atmosphere was viewed as largely a chemical inertfluid
that moves heat, momentum and moisture
that transports pollutants away from cities
Photochemistry limited to the upper atmosphere(ionosphere)
Urban Photochemistry (LA smog)
1960
CFCs become popular in industry
air conditioning
spray cans
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1970
The atmosphere started to be seen as a chemicallydynamic system
New analytic instrumentation
New measurements of chemical rate constant
Simple atmospheric model
Stratospheric ozone became a major scientific issue
Aircraft NOxIndustrially manufactured CFCs
Photochemistry of tropospheric ozone started to beinvestigated at the global scale.
1980
Discovery of the stratosphericozone hole and role ofheterogeneous chemistry
Recognition that air pollution isbecoming a global issue
Potential importance ofgreenhouse gases other thanCO2 in the climate system
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1990
Role of the biosphere for the chemistry of thetroposphere (e.g., biogenic hydrocarbons)
Role of chemical compounds in the climate system
Aerosols and cloud microphysics
New research infrastructure and approaches for
tropospheric studies
Spacecraft
Surface networks
Large airborne campaigns
Comprehensive chemical-transport models
International efforts (e.g., IGAC)
OZONEozein -to smell
Officially named as a chemical in 1840, afternoted that it had similar smell to phosphorus whenexposed to air Electric discharges in air "
Ozone was realized to be a good disinfectant
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UV shield
Greenhouse gas
Precursor of OH,
main atmospheric oxidant
Toxic to humans and
vegetation
10%
Troposphere
Stratosphere:
90% of total
Consequences of less Ozone
CONSEQUENCE CAUSE
Increase in skin cancerUV light penetrate more deeply andmutate skin DNA
Increase in cataract Energetic UV light damages eyes
Decline in Plant Productivity UV light easily damages plant tissue
Decline in Animal Productivity
Reduces plankton population
Reduces penguin population
Reduces the percentage ofhatching of frog eggs
UV light easily damages animal tissue
Lowered White Blood Cell sunburn from UV exposure
Global WarmingGreen House Effect
lower plant productivity, less CO2removedthe more CO2. more radiated heat canbe absorbed
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UV Absorption of Ozone
UV Absorption of Ozone
AGING
BURNING
DANGER
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Dobson Unit
Measurement for total column ozone
Production of OzoneThe Chapman mechanism
O2+ h O + O (< 240nm)
O + O2 + M O3+ M
O3+ h O2 + O
O + O3 O2O + O + M O2 + M
Smogchemistry
(CH4, CO, HC) + OH HO2
HO2+ NO OH + NO2
NO2+ h NO + O
O + O2+ M O3+ M
O O3O2slow
slow
fast
Odd oxygen fam ily
[Ox] = [O3] + [O]
R2
R3
R4
R1
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Steady state ozone
1. Ozone is formed in one step and consumed in twosteps
d[O3]/dt= -d[O3]/dt]
rate b= rate c+ rated
2. Atomic oxygen is formed in two steps, consumedin two steps.
d[O]/dt = -d [O]/dt
2 (rate a + rate c) = rate b+rated
Steady state ozone
1. kb (O)(O2)(M)= kc (O3) + kd (O)(O3)
2. 2ka (O2) + kc (O3)+ kb (O)(O2)(m) + kd (O)(O3)
Through Addition:2ka (O2) + 2kd (O)(O3)
Through Subtraction:
kb (O)(O2)(M) = ka (O2) +kc (O3)
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Steady state ozoneSince ka (O2)
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Hydroxyl RadicalO3+ OHHO2 + O2
O + HO2OH + O2
Net: O3+ O2 O2
Chlorine and Bromine
O3+ ClClO + O2
O + ClOCl + O2
Net: O3+ O2 O2
Nitric Oxide
O3+ NONO2 + O2
O + NO2NO + O2
Net: O3+ O2 O2
WATER VAPOR IN STRATOSPHERE
Source:transport from troposphere, oxidation of methane (CH4)
http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003101/h2o-movie.m2v8/13/2019 Stratospheric Chemistry
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HOx-CATALYZED OZONE LOSS
HOx H + OH + HO2family
Initiation: 12HO+O( ) 2D
Propagation: 3 2 2
2 3
3
2
2
OH+O HO
HO+
Net:
O OH+
2O
2
3O
Termination:2 2
OH+HO HO+
OH HO2H2O
slow
slow
fast
Termination RecyclingNO2+ OH + M HNO3+ M HNO3 + hNO2+ OHNO2+ O3NO3 + O2 HNO3+ OHNO3 + H2ONO3+ NO2+ MN2O5+ M NO3+ hNO2+ ON2O5+ H2O2HNO3 N2O5+ hNO2+ NO3
Propagation
NO + O3 NO2+ O NO + O3NO2+ O2
NO2 + hNO + O NO2+ ONO + O2O + O2+ MO3+ M
Null cycle Net O3+ O2O2
Initiation N2O + O(1D) 2NO
NOx-CATALYZED OZONE LOSS(NOxNO + NO2)
Day
Night
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STRATOSPHERIC DISTRIBUTION OF CFC-12
Initiation: Cl radical generation from non-radical precursorsCF2Cl2+ hCF2Cl + Cl
Propagation:
Cl + O3ClO + O2
ClO + OCl + O2
Net: O3+ O2O2
ClOx-CATALYZED OZONE LOSS(ClOxCl + ClO)
Termination: Recycling:Cl + CH4HCl + CH3 HCl + OHCl + H2O
ClO + NO2+ MClNO3+ M ClNO3+ hvCl + NO3
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By the simulated year 2020, 17 %of ozone is depletedglobally
By 2040, global ozone concentrations is the same levelthe "hole" over Antarctica. The UV index in mid-latitudecities reaches 15, giving a sunburn in about 10 minutes
In 2050, Ozone levels in the stratosphere over the tropicscollapse to near zero
By 2065, global ozone drops to 110 DU, a 67% drop. Year-round polar values hover between 50 and 100 DU. Theintensity of UV radiation doubles; at certain shorterwavelengths, intensity rises by 10,000 times.
WORLD WITHOUT CONTROL
The polar winter leads to the formation of the polarvortex which isolates the air within it.
Cold temperatures form inside the vortex; cold enoughfor the formation of Polar Stratospheric Clouds (PSCs).
As the vortex air is isolated, the cold temperatures andthe PSCs persist.
Polar Stratospheric Clouds
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UV Light breaks CFCapart.
Resulting Cl existseither as ClO or as freeCl.
Gases in atmospherereact with ClO and Clto trap in inert
reservoirs of ClONO2and HCl
How PSC Help Chlorine Destroy OzoneWithout With
PSC free Cl2from reservoirs.
ClO-ClO cycle begins oncesunlight breaks Cl2 apart.
Cl atoms react with O3,forming ClO and O2.
ClO forms dimer and breaks
down to Cl and O2. Cl attacksozone again
PSC prevent reservoirs fromforming by removing nitrogenfrom atmosphere throughprecipitation of HNO3.
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No ozone loss occurs until sunlightreturns to the air
inside the polar vortex and allows the production ofactive chlorine and initiates the catalytic ozonedestruction cycles.
Ozone loss is rapid. The ozone hole currently covers ageographic region a little bigger than Antarctica andextends nearly 10km in altitude in the lowerstratosphere.
MT. PINATUB0 ERUPTION
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Ozone reduction of 6-30%.Pinatubo aerosols may beresponsible for the a lossof 10%of Antarctic ozone"before" the Antarcticozone hole formed in1992.
Over the Antarctic ozonewas 50%lower thannormal between 13-16 km
altitude and was totallyabsent between 16-18 km. Ozone hole appeared
over Europe for the 1sttime.
Eruption caused low ozone record
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Measurements of Stratospheric Ozone
What has been done?
Montreal protocol
Ban of production of CFCs
Substitutes for CFCs
x
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About the Montreal ProtocolTOO LATE
NO COUNTRY TOOK IMMEDIATE ACTION
No practical action done by those signed!
CHEMICALS ALREADY IN ATMOSPHERE AND ATTACK OZONE
Chemicals were already produced!
MANY REFUSED TO SIGN
(China / India) unless they get some financial help intheir demand!
DEVELOPING COUNTRIES EXEMPTED- do not have technology to switch alternatives
There are TWO SUBSTITUTES FOR CFCs
reactive in Earthslower atmosphere
lesser chance of their Cl and F components ever
reaching the stratosphere
Not ENTIRELY SAFER
react to form another type of acid rain detrimentalto
wetlands
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UPDATES ON
STRATOSPHERIC OZONE
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Important points from article: WARM Antarctic temperature = HELPUV-protecting
layer Seasonal hole is at smallest maximum extent,
SECONDsmallest average in 20 years The average size of 2012 ozone hole at 17.7 million
square kilometers COLDTEMPERATURES = DESTROYOZONE LAYER
Natural weather fluctuations led to warmer Antartictemperature LIMITEDdamage
Stratospheric ozonelevels increases duringthe next 30-50 years
The Montreal Protocolprovisions lower ozone-depleting chemicals inthe upper atmosphere