Investigations of Cloud Altering Effects of Atmospheric Aerosols using a New Mixed Eulerian ...

319 Pages·2004·2.4 MB·English

by  Henry Donnan Steele

Investigations of Cloud Altering Effects of
Atmospheric Aerosols using a New Mixed
Eulerian-Lagrangian Aerosol Model
Henry Donnan Steele
Center for Global Change Science
Department of Earth, Atmospheric and Planetary Sciences
MIT, Cambridge, MA 02139-4307 USA
M A S S ACHUSET
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Center for Global Change Science
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TUTEOF TE C H N
Report No. 74
September 2004
The Earth’s unique environment for life is determined by an interactive system comprising the
atmosphere, ocean, land, and the living organisms themselves. Scientists studying the Earth have long
known that this system is not static but changing. As scientific understanding of causal mechanisms for
environmental change has improved in recent years there has been a concomitant growth in public
awareness of the susceptibility of the present environment to significant regional and global change. Such
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century due to the continued rise in the atmospheric concentrations of carbon dioxide and other
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Investigations of Cloud Altering Effects of Atmospheric Aerosols
using a New Mixed Eulerian-Lagrangian Aerosol Model
by
Henry Donnan Steele
B.S. Physics and Computer Science
Yale University, 1998
Submitted to the Department of Earth, Atmospheric, and Planetary Sciences
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Atmospheric Chemistry
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
September 2004
(cid:1)c Massachusetts Institute of Technology 2004. All rights reserved.
Author...................................................................................
Department of Earth, Atmospheric, and Planetary Sciences
August 17, 2004
Certified by...............................................................................
Ronald G. Prinn
TEPCO Professor of Atmospheric Chemistry
Thesis Supervisor
Accepted by..............................................................................
Maria Zuber
E. A. Griswold Professor of Geophysics
Head of the Department
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Investigations of Cloud Altering Effects of Atmospheric Aerosols using a New
Mixed Eulerian-Lagrangian Aerosol Model
by
Henry Donnan Steele
Submitted to the Department of Earth, Atmospheric, and Planetary Sciences
on August 17, 2004, in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy in Atmospheric Chemistry
Abstract
Industry, urban development, and other anthropogenic influences have substantially altered the
composition and size-distribution of atmospheric aerosol particles over the last century. This, in
turn,hasalteredcloudalbedo, lifetime, andpatternswhichtogether arethoughttoexertanegative
radiative forcing on the climate; these are the indirect effects of atmospheric aerosols. Thespecifics
of the process by which aerosol particles seed cloud particles are complex and highly uncertain.
The goal of this thesis is to refine understanding of the role of various aerosol types in determining
cloudproperties. Weapproachthisgoal byconstructinganewhighlydetailed aerosol-cloud process
model that is designed to simulate condensation upon complex aerosol populations. We use this
model to investigate the microphysics of aerosol-cloud interactions, specifically considering the role
of cloud dynamics and of the ubiquitous mixed soot / sulfate aerosols.
We describe the Mixed Eulerian-Lagrangian Aerosol Model (MELAM). This new computer
model of aerosol microphysics is specifically tailored to simulate condensation and activation as
accurately as possible. It specifically calculates aerosol thermodynamics, condensation, coagula-
tion, gas and aqueous phase chemistry, and dissolution. The model is able to consider inorganic
aerosols and aerosols with both inorganics and insoluble cores; the specific chemical system to be
considered is specified by the user in text input files. Aerosol particles may be represented using
“sectional distributions” or using a “representative sample” distribution which tracks individual
particles. We also develop a constant updraft speed, adiabatic parcel model and a variable updraft
speed, episodically entraining parcel model to provide boundary conditions to MELAM and allow
simulations of aerosol activation in cloud updrafts.
Using MELAM and the parcel models, we demonstrate that aerosol activation depends on the
composition andsizedistributionofthesub-cloudaerosolpopulation,ontheupdraftspeedthrough
aparcel’sliftingcondensationlevel, ontheverticalprofileoftheupdraftspeed,andonentrainment.
We use a convective parameterization that was developed for use in global or regional models to
drive the episodically entraining, variable updraft speed parcel model. Ultimately, reducing the
uncertainty of the global impact of the indirect effects of aerosols will depend on successfully
linking cloud parameterizations to models of aerosol activation; our work represents a step in that
direction.
We also considertheactivation of mixed soot/sulfateparticles incloud updrafts. We constrain
for the first time a model of condensation onto these mixed particles that incorporates the contact
angle of the soot / solution interface and the size of the soot core. We find that as soot ages and
its contact angle with water decreases, mixed soot / sulfate aerosols activate more readily than
the equivalent sulfate aerosols that do not have soot inclusions. We use data from the Aerosol
Characterization Experiments (ACE) 1 and 2, and from the Indian Ocean Experiment (INDOEX)
to define representative aerosol distributions for clean, polluted, and very polluted marine environ-
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ments. Using these distributions, we argue that the trace levels of soot observed in clean marine
environments donotsubstantially impactaerosol activation, whilethepresenceof sootsignificantly
increases the number of aerosol that activate in polluted areas.
Thesis Supervisor: Ronald G. Prinn
Title: TEPCO Professor of Atmospheric Chemistry
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Acknowledgments
I am fortunate to have spent my graduate school years here at M.I.T.; I found everything here
that I had hoped to find, and oftentimes much more. This thesis is the culmination of many stages
of learning and discovery and marks the end of an important stage of my life. I did not make it
throughthese six years on my own. Throughoutthe pastsix years, I have leaned on many teachers,
advisors, colleagues, friends, and on my family; I am very grateful to each of them.
My advisor Ron Prinn provided countless lessons in the classroom and in his office, and showed
by example what it is to do science well. He was always generous with his time, advice, confidence,
and support. And he tolerated my pursuitof many non-scientific interests with patience and grace.
I am fortunate to have worked with him over these past several years. The other members of
my committee – Greg McRae, Mario Molina, and Kerry Emanuel – have each contributed time,
expertise, and encouragement. I very much appreciate their efforts. This thesis also benefited
enormously from discussions with Don Lucas, Yu-Han Chen, Chien Wang, Greg Lawson, Ico San
Martini, Bill Boos, Rob Korty, Zan Stine, Sam Arey, Gary Kleiman, and many others. I have
always appreciated the quality of the scientific community I found here, and will always appreciate
the collaborations I began here and the friendships I formed here.
I owe a great debt to my friends and family for their love, encouragement, and supportover the
past few years. I am blessed to have so many wonderful people in my life.
This thesis research was supported by the Federal and Industry Sponsors of the MIT Joint
Program on the Science and Policy of Global Change (U.S. Department of Energy, U.S. National
ScienceFoundation,AlstomPower (France), AmericanElectricPower (USA),BPp.l.c.(UK/USA),
ChevronTexaco Corporation (USA), DaimlerChrysler AG (Germany), Duke Energy (USA), J-
Power (Electric Power Development Co., Ltd.) (Japan), Electric Power Research Institute (USA),
Electrict´e de France, ExxonMobil Corporation (USA), Ford Motor Company (USA), General
Motors (USA), Mirant (USA), Murphy Oil Corporation (USA), Oglethorpe Power Corporation
(USA), RWE/Rheinbraun (Germany), Shell International Petroleum (Netherlands/UK), Statoil
(Norway), Tennessee Valley Authority (USA), Tokyo Electric Power Company (Japan), TotalFi-
nalElf (France), Vetlesen Foundation (USA), We Energies (USA)). It was also supported by NASA
Grant NAG-5-12099.
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Contents
1 Introduction 23
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.2 The Role of Aerosols in the Climate System . . . . . . . . . . . . . . . . . . . . . . . 25
1.2.1 The Effects of Aerosols on the Global Climate . . . . . . . . . . . . . . . . . 25
1.2.2 The Scale Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.2.3 Microphysical Scale Modeling of Aerosol / Cloud Interaction . . . . . . . . . 34
1.3 Goals and Outline of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2 Overview of the Mixed Eulerian-Lagrangian Aerosol Model 41
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.2 Aerosol Size Representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3 Chemical Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.4 Gas-Phase and Aqueous-Phase Chemistry . . . . . . . . . . . . . . . . . . . . . . . . 48
2.5 Aerosol Chemical Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.6 Gas-Aerosol Transfer: Condensation and Dissolution . . . . . . . . . . . . . . . . . . 51
2.7 Aerosol Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.8 Boundary Conditions for Microphysical Studies of Aerosol Activation: UpdraftModels 58
2.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3 Representation of Aerosols and Droplets 61
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.2 Functional Representations of Observed Aerosol Size Distributions . . . . . . . . . . 62
3.3 Representing Size Distributions in Models . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.1 Bulk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.2 Method of Moments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.3 Modal Representations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
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3.3.4 Sectional Representations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.3.5 Continuous and Lagrangian Representations . . . . . . . . . . . . . . . . . . . 71
3.3.6 Mixed Sectional and Lagrangian Representations . . . . . . . . . . . . . . . . 74
3.4 Representation of Aerosol Composition and Mixing State . . . . . . . . . . . . . . . 76
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4 Aerosol Chemical Thermodynamics 81
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.2 Chemical Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.3 Equilibrium Dissociation of Electrolytes and Acids . . . . . . . . . . . . . . . . . . . 84
4.3.1 Equilibrium Coefficients for Dissociating Species . . . . . . . . . . . . . . . . 85
4.3.2 Solving for Equilibrium Concentrations . . . . . . . . . . . . . . . . . . . . . 86
4.4 Thermodynamic Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.4.1 Calculating Binary Activity Coefficients when Binary Data is Available . . . 91
4.4.2 Calculating Binary Activity Coefficients when Binary Data is Not Available . 98
4.4.3 Calculating Activity Coefficients and Equilibrium for Partially Dissociating
Species: Sulfuric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.4.4 Calculating Activity Coefficients in Mixtures . . . . . . . . . . . . . . . . . . 106
4.5 Mixing Rules for Other Thermodynamic Properties . . . . . . . . . . . . . . . . . . . 109
4.6 Surface Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.6.1 Surface Tension of Flat Surfaces of Pure Water . . . . . . . . . . . . . . . . . 111
4.6.2 Surface Tension of Flat Surfaces of Electrolytic Solutions . . . . . . . . . . . 111
4.6.3 SurfaceTensionsCalculatedUsingtheGibbsDividingSurfaceforElectrolytic
Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.6.4 Influence of Soluble and Slightly Soluble Organic Species . . . . . . . . . . . 114
4.7 Solution Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5 Mass Transfer to and from Particles: Condensation and Dissolution 119
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.2 Continuity Between Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.3 Coupling between Condensation and Aqueous Chemistry and Thermodynamics . . . 121
5.4 Equilibrium and Non-Equilibrium Across the Gas and Aerosol Phases . . . . . . . . 122
5.4.1 The Equilibration of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
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