overview of global warming, ozone depletion, and...

Overview of Global Warming, Ozone Depletion, and Air Quality

AOSC 434/658R & CHEM 434/678A

Ross Salawitch

Class Web Site: http://www.atmos.umd.edu/~rjs/class/spr2011

Lecture 2

Notes:

• Tim and Ross co-teach this class; please include both on any class related email

• Lectures are the “glue” that hold this class together:

therefore, attendance is strongly encouraged

• We like to “ask questions” for many reasons: to get to know you, to keep you

engaged, etc. Please participate at your own level of comfort

• Problem sets tend to quantitative and exams tend to be qualitative:

problem set #1, due 2 weeks from today, has been posted.

We strongly encourage students to not wait until

the night before the P. Set is due to get started

1Copyright © 2011 University of Maryland.

This material may not be reproduced or redistributed, in whole or in part, without written permission from Ross Salawitch or Tim Canty.

1 February 2011

Overview of Global Warming, Ozone Depletion, and Air Quality

• Course theme: effect of human activity on atmospheric composition

– climate change

– air quality

– stratospheric ozone depletion and recovery

Today’s goals:

1) Overview of climate change, air quality, and ozone depletion

2) We’ll provide lots of “detail” today … we do not expect all of these

details to “stick”, but we do expect, when you review this lecture

at the end of this semester, for these details to be understandable

3) Linkages between these topics, which are often thought of as

“disparate”, but actually are linked in profoundly important manners



http://www.atmos.umd.edu/~rjs/class/spr2011

Greenhouse Effect



Radiative Forcing of Climate, 1750 to 2005

Question 2.1, IPCC, 2007



Change in Radiative Forcing


Change in Surface Radiative Forcing ≡ Change in Energy reaching the

Surface as GHGs Rise, due to variations in magnitude of terms pictured

above once equilibrium is re-established (“Back Radiation” most important)



Modern CO2 Record

Legacy of Charles Keeling, Scripps Institution of Oceanography, La Jolla, CA

http://www.esrl.noaa.gov/gmd/ccgg/trends



http://www.esrl.noaa.gov/gmd/ccgg/trends

GHG Record Over Last Several Millennium




GWP − Global Warming Potential

time final

CH4 4

time initial4 time final

CO2 2

time initial

[CH (t)] dt

GWP (CH )

[CO (t) dt]

a

a

×=

×

where:

aCH4 = Radiative Efficiency (W m−2 kg−1) due to an increase in CH4

aCO2 = Radiative Efficiency (W m−2 kg−1) due to an increase in CO2

CH4 (t) = time-dependent response to an instantaneous release of a pulse of CH4

CO2 (t) = time-dependent response to an instantaneous release of a pulse of CO2






from IPCC 2007 “Physical Science Basis”


Over the time horizon of ~1750 to 2005:

RF CH4 relative to CO2 ≈ 26.4 × 1250 ppb / 100 ppm = 26.4 × 0.0125 = 0.33

RF N2O relative to CO2 ≈ 216 × 50 ppb / 100 ppm = 216 × 5×10−4 = 0.11

Total RF CH4 + N2O relative to CO2 ≈ 0.44

This rough estimate is not too different than the RF of CH4 + N2O

relative to RF of CO2, ~38%, from FAQ 2.1, Figure 2



Solar and Volcanic Forcings

(Model Inputs)

IPCC 2001

Climate Change: Scientific Basis



GHGs, Aerosols, & O3 Forcings

(Model Inputs)

IPCC 2001




All Forcings

(Model Inputs)

IPCC 2001




Modeling Climate ChangeAre humans responsible?

Orbital variations: too slow

Volcanoes: no sustained forcing

Solar variability:

Perhaps dominant forcing of Medieval Warming and Little Ice Age

Small effect since ~1860Recent Data

1860 2000YEAR

Medieval Max

Maunder Min

Modern Max

Medieval Max

Maunder Min

Modern Max

Reconstructed

Temperature

Historic Data

YEAR



Modeling Climate Change



Are humans responsible?



Solar variability:


Small effect since ~1860

Internal variability (eg, El Niño / La Niña) :

Climate record from 1000 to 1850 shows nothing like sustained,

present rate of warming

1000 2000Year

0.8

0

Modeling Climate ChangeAre humans responsible?



Solar variability:


Small effect since ~1860

Internal variability (eg, El Niño / La Niña) :

Climate record from 1000 to 1850 shows nothing like sustained,

present rate of warming

IPCC Climate Change 2007: The Physical Science Basis concludes:

Very high confidence* the globally averaged net effect of human

activities since 1750 has been one of warming

* At least a 9 out of 10 chance of being correct

IPCC Intergovernmental Panel on Climate Change

Note: IPCC models do not include climate-carbon cycle feedbacknor do they include the realistic effects ice sheet dynamics



Earth’s Atmosphere – Effect of Humans

Stratospheric Ozone – shields surface from solar UV radiation

Update

After Farman et al., Large losses of total ozone in Antarctica reveal

Seasonal ClOx/NOx interaction, Nature, 315, 207, 1985.Rising chlorine due

to industrial activity



Ozone Depletion and Halocarbons

ODP (species " ") =i

3

3

global loss of O due to unit mass emission of " "

global loss of O due to unit mass emission of CFC-11

i

CFC-11

Br Cl

CFC-11

1( + )

3

i

i

MWn n

MW

τατ

≈

where :is the global atmospheric lifetimeτ

is the molecular weightMW

is the number of chlorine or bromine atomsn

is the effectiveness of ozone loss by bromineαrelative to ozone loss by chlorine

α changed from 45 (WMO, 2002) to 65 (WMO,2006)



CFC Usage Prior to the Montreal Protocol

Refrigeration

Solvents

Foams

Aerosols

Others

The uses of CFCs in various sectors before the 1987 Montreal Protocol,

which required countries to phase out their production to protect the ozone layer.

From: http://www.ace.mmu.ac.uk/Resources/Fact_Sheets/Key_Stage_4/Ozone_Depletion/05.html



What is this compound?

••

Cl••

••

FC

Cl

F••

••

•••••• ••

••

••

••

How is it eventually removed from the atmosphere ?

What does it produce upon its removal ?



http://www.ace.mmu.ac.uk/Resources/Fact_Sheets/Key_Stage_4/Ozone_Depletion/05.html

Radicals

• Odd number of electrons - unpaired electron in outer valence shell

• Go to great lengths to pair off lone electron

• Exceptionally reactive

When CFCs Decompose (in the stratosphere)

They Produce Chlorine Radicals

Cl

O••

Cl

•• •

••

••

••• •

••••

••

••

O••

•

ClO : Chlorine monoxide

See pages 57 to 68, Ch 2, Chemistry in Context, for description of

Lewis Dot Structures of atmospherically important species



Chlorine Radicals Lead to Ozone Loss

ClO + ClO + M → ClOOCl + M

Cl + O3 → ClO + O2

Cl + O3 → ClO + O2

ClOOCl + hν → ClOO + Cl

ClOO + heat → Cl + O2



Montreal Protocol Has Banned Most Industrial Production

of CFCs and Halons

Rising chlorine due

to industrial activityTwenty Questions and Answers About The

Ozone Layer: 2006 Update (WMO, 2006)

and the ozone layer is perhaps in initial phase of “recovery”



Link Between Ozone Depletion and Climate Change

Most ozone depleting

substances have a

significant “GWP”

GWP weighted emissions of CO2

GWP weighted emissions of CFCs,

without early aerosol propellant ban

(i.e., no ban on CFCs)

GWP weighted emissions of CFCs,

without Montreal Protocol

Velders et al., PNAS, 2007

Twenty Questions and Answers About The Ozone Layer: 2006 Update (WMO, 2006)



NO & NO2 : Emitted by fossil fuel combustion & biomass burning

N2 + O2 2 NO

CO: Emitted by fossil fuel combustion & biomass burning

Complete combustion:

2 C8H18 + 25 O2 16 CO2 + 18 H2O

Extreme, incomplete combustion:

2 C8H18 + 17 O2 16 CO + 18 H2O

Tropospheric Ozone Production

OH + CO → CO2 + H

H + O2 + M → HO2 + M

HO2 + NO → OH + NO2

NO2 + hν → NO + O

O + O2 + M → O3 + M

High T



Tropospheric Pollutants (The Air We Breathe)

Criteria Pollutants

From Chapter 1

Chemistry in Context

Criteria pollutant: identified as being common-

place and detrimental to human welfare (i.e.,

ubiquitous pollutant)

Primary pollutant: emitted directly into the

atmosphere and retains same chemical form

following emission

Secondary pollutant: formed by atmospheric

reactions involving chemical precursors. Control

generally more challenging than that of primary

pollutants because mitigation of secondary

pollutants requires identification of the precursor

compounds, quantification of sources, and detailed

understanding of the chemical reactions that form

the secondary pollutant (chemical mechanism)



Significant Improvements in Air Quality since early 1980s

Chapter 1

Chemistry in Context



Significant Improvements in Local Air Quality since early 1980s

http://www.mde.state.md.us/programs/ResearchCenter/ReportsandPublications/

eMDE/Pages/researchcenter/publications/general/eMDE/vol4no8/Article4_phot

o1.aspx



http://www.mde.state.md.us/programs/ResearchCenter/ReportsandPublications/

Significant Improvements in Local Air Quality since early 1980s

http://www.mde.state.md.us/programs/ResearchCenter/

ReportsandPublications/eMDE/Pages/researchcenter/pu

blications/general/eMDE/vol4no8/Article4_photo1.aspx



Air Quality Standards and Why We Care

YearAveraging

Period

EPA Surface

Ozone

Standard

1979 1 hr 125 ppb

1997 8 hr 80 ppb

2008 8 hr * 75 ppb

2011# ??? ???

* The 8 hr standard is met when the 3-yr average of

the annual 4th highest daily maximum 8 hr O3

is less than 75 ppb.

Increased risk of premature mortality

for even low levels of surface O3; further

reductions will benefit public health

Bell et al., 2006http://www.ncbi.nlm.nih.gov/sites/ppmc/articles/PMC1440776

# The EPA will release a new surface ozone standard summer of 2011

Wall Street Journal article:

http://online.wsj.com/article/SB10001424052748703493504576007622632878748.html



http://www.mde.state.md.us/programs/ResearchCenter/

http://www.ncbi.nlm.nih.gov/sites/ppmc/articles/PMC1440776

http://online.wsj.com/article/SB10001424052748703493504576007622632878748.html

Next Lecture: Fundamentals of Earth’s Atmosphere (Tim)

Reading:

Chemistry in Context, Sections 1.1, 1.2, and 1.5

Jacobson: pages 50 to 64

Admission Ticket for Lecture 3 is now posted at:

http://www.atmos.umd.edu/~rjs/class/spr2011/admission_tickets/Air_Pollution_2011_admis_ticket_lecture_03.pdf



Naming Convention for CFCs & HalonsPlease note: you will not be tested on this information!

It is provided in case anyone is interested Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of Chlorine, Fluorine, and

Carbon. They had been used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as

solvents, and as refrigerants. CFCs are classified as halocarbons, a class of compounds that contain atoms of carbon

and halogen atoms. Hydrochlorofluorocarbons (HCFCs) contain Hydrogen, Chlorine, Fluorine, and Carbon and, due

to their H atom, are reactive in the troposphere (the H reacts with OH to form H2O).

Individual CFC and HCFC molecules are labeled with an archaic numbering system consisting of three integers: i, j,

and k. If only two integers are given, the value of the first integer is zero. The digits correspond to:

i : number of carbon atoms minus 1

j : number of hydrogen atoms plus 1

k : number of fluorine atoms

The number of chlorine atoms is found by Cl = 2(C+1) − H − F, where C, H, & F represent the number of Carbon,

Hydrogen, and Fluorine atoms.

Hence:

CFC-11 (CFCl3) has i + 1 = 1 Carbon atom, j − 1 = 0 Hydrogen atoms, k = 1 Fluorine atom, and 2 (1+1) − 0 − 1

= 3 Chlorine atoms.

CFC-12 (CF2Cl2) has i + 1 = 1 Carbon atom, j − 1 = 0 Hydrogen atoms, k = 2 Fluorine atom, and 2 (1+1) − 0 − 2

= 2 Chlorine atoms.

HCFC-142 (C2H3F2Cl) has i + 1 = 2 Carbon atoms, j − 1 = 3 Hydrogen atoms, k = 2 Fluorine atom, and 2 (2+1)

− 3 − 2 = 1 Chlorine atom.

Halons are fluorocarbons that contain at least one bromine and no hydrogen. The nomenclature for naming halons is

simpler than CFCs, because halons use i j k l, where i = number of carbon atoms, j = number of fluorine atoms, k =

number of chlorine atoms, and l = number of bromine. For example, Halon-2402 is C2F4Br2 and Halon-1211 is

CF2ClBr.



http://www.atmos.umd.edu/~rjs/class/spr2011/admission_tickets/Air_Pollution_2011_admis_ticket_lecture_03.pdf

overview of global warming, ozone depletion, and...

Documents