The Ozone Layer“Good Up High, Bad Nearby”

Matt KirchnerCbE 562Wednesday October 5th, 2005

Ozone Layer Introduction

What does it do?• Absorbs ultraviolet light from

the sun• Uses absorbed energy to

generate oxygen radicals• Oxygen radicals both build up

and breakdown ozone• Protects Earthlings from

cancer- causing UV rays• Protects crops, seas,

amphibious populations

The Ozone Layer: Where is it?

Ozone Chemistry

+

hν2

1/v <~240 nm

+ 2

Chapman Reactions (occur naturally)

Ozone Layer Measurement•Dobson Unit:

–Ozone over area evaluated at STP–Thickness of area measured–1 DU (Dobson Unit) = 0.01 mm thick / area–Named after G.M.B Dobson, Oxford, Eng (1889-1976)

e.g. over Labrador, Canada

Dobson Spectrophotometer•Compares UV light intensity at different wavelengths absorbed by ozone•16 Climate Monitoring and Diagnostics Laboratory (CMDL) stations•Over 80 stations worldwide

Ozone Layer Depletion

Ozone Hole vs. Global Warming

•Ozone Hole–Hole passes UV light–UV light damages DNA causing cancer–Localized damage under areas of weakened layer–Hole exists over Antarctica–Caused by CFCs, bromine, NOx compounds, VOCs

•Global Warming–Traps heat in atmosphere–Heat elevates global temperature–Raises average temperature across globe–Covers entire globe

–Caused by CO2 buildup from burning fossil fuels

What about Ozone Action Days?• “Good up high…”

– Absorbs harmful UV light from Sun– Natural protection

• “Bad nearby…”– VOCs, NOx create ozone in

troposphere (atmosphere closest to Earth’s surface)

– Primarily responsible for smog in cities

Ozone Depletion Chemistry-Polar Vortex

• Cold Antarctic air during winter isolates air over landmass

• Winds cause cyclone effect• Lack of sunlight keeps air cold

(< -80°C)

• Clouds of HNO3 form at this T

• HNO3 reacts with CFCs to from Cl2

• Cl2 breaks down ozone

Detailed Reaction PathwayChlorine Breakdown

ClO + ClO + M -> Cl2O2 + M

Cl2O2 + hv -> Cl + ClO2

ClO2 + M -> Cl + O2 + M

2 x (Cl + O3) -> 2 x (ClO + O2) ________________________

net: 2 O3 -> 3 O2

Bromine Breakdown

ClO + BrO -> Br + Cl + O2

Cl + O3 -> ClO + O2

Br + O3 -> BrO + O2 ________________________

Net: 2 O3 -> 3 O2

Notes:

•Chlorine forms during winter in polar vortex

•Bromine exists in atmosphere from man

•Sunlight (hv) activates chlorine / bromine radicals in spring

•Produces as many halogens as consumes

Common ozone depletion gases

CFC Number

Chemical Name

GWP / ODP

Uses

CFC-11 Trichlorofluro-methane

4680 / 1 Propellant

CFC-12 Dichloro-difluoromethane

10720 / 1 Refrigerant

HCFC-22(aka R22)

Monochloro-difluoromethane

1780 / 0.05 Refrigerant

CCl4 Carbon Tetrachloride

1380 / 0.73 Industrial Solvent

Space filling models of some CFCs

CFC-11: Trichlorofluoromethane CCl3F

CFC-12: Dichlorodifluoromethane CCl2F2

HCFC-22 (R22): Chlorodifluoromethane CHClF2

Carbon Tetrachloride:CCl4

Roadmap for Rebuilding• Stop use of CFCs

– Laws– Behavior changes

• Develop replacement materials– Science– Engineering

• Generate more ozone in upper atmosphere– Remove existing free radicals– Ionize upper atmosphere

Montreal Protocol (1987)• CFCs, halons, carbon tet,

methyl chloroform phased out by 2005.

• Exceptions– MDIs for asthma (CFCs -11, -12, -

114)– Methyl Chloroform in Space

Shuttle and Titan rockets– Other class 1 substances in lab

use

Rhinocort pulled from shelves• Contained:

trichloromonofluoromethane, dichlorotetrafluoroethane, and dichlorodifluoromethane

• (CFC-11, Halon-242, CFC-12 respectively)

Individual contributions• What can you do to reduce

CFCs– Keep A/C units (car, home) in good

condition– Purchase units w/o CFCs– Make sure technician is EPA

certified

Replacement Materials (R-22)• Evaporative Cooling

– Doesn’t use chemicals at all– Only good in warm, arid climates

• HFC-134a (1,1,1,2-Tetrafluoroethane)– Used in new installations– Can’t be used in existing

• NU-22– Can be used in existing

installations– Physical properties like R-22

Radical Solutions• Remove Cl* with ion curtains• Alfred Wong (UCLA): charge Cl*

to -, attract to curtains

It’s Shocking• O3 is created from electrical

current passing through O2

• Theoretically, zap enough O2 to generate O3

ReferencesEPA. "Ozone Science: The Facts Behind the Phaseout." 21 June 2004 <http://www.epa.gov/ozone/science/sc_fact.html>. 5 October 2005.

Folger, Tim. "Blimps to the Rescue." Discover Magazine October 1994.

Gleason, Karin L. "The Dobson Spectrophotometer." . 19 September 2005 <http://www.ozonelayer.noaa.gov/action/dobson.htm>.

Kitayamay, J., and M. Kuzumotoyz. "Theoretical and Experimental Study on Ozone Generation Characteristics of an Oxygen-Fed Ozone Generator in Silent Discharge." Journal of Physics D: Applied Physics. 30: 2453.

Pulmonary - Critical Care Associates of East Texas. "Rhinocort Nasal Inhaler.“ <http://www.pcca.net/images/Medication_Images/Rhinocort.GIF>. 5 October 2005