Stratospheric Chemistry

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.m2v


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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

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Stratospheric Chemistry