Aerosol

Atmospheric Aerosol
Properties and
Climate Impacts
U.S. Climate Change Science Program
Synthesis and Assessment Product 2.3
January 2009

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FEDERAL EXECUTIVE TEAM
Director, Climate Change Science Program: ................................ William J. Brennan
Director, Climate Change Science Program Of?ce: ..................... Peter A. Schultz
Lead Agency Principal Representative to CCSP,
Associate Director for Research, Earth Science Division,
National Aeronautics and Space Administration: ......................... Jack Kaye
Lead Agency Point of Contact, Earth Science Division,
National Aeronautics and Space Administration: ........................... Hal Maring
Product Lead, Laboratory for Atmospheres,
Earth Science Division, Goddard Space Flight Center,
National Aeronautics and Space Administration: .......................... Mian Chin
Chair, Synthesis and Assessment Product Advisory Group
Associate Director, National Center for Environmental
Assessment, U.S. Environmental Protection Agency: .................... Michael W. Slimak
Synthesis and Assessment Product Coordinator,
Climate Change Science Program Of?ce: ...................................... Fabien J.G. Laurier

EDITORIAL AND PRODUCTION TEAM
Editors: .......................................................................................... Mian Chin, NASA
.......................................................................................... Ralph A. Kahn, NASA
.......................................................................................... Stephen E. Schwartz, DOE
Graphic Design: ............................................................................ Sally Bensusen, NASA
............................................................................ Debbi McLean, NASA
This document, part of the Synthesis and Assessment Products described in the U.S. Climate Change Science
Program (CCSP) Strategic Plan, was prepared in accordance with Section 515 of the Treasury and General
Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554) and the information quality act
guidelines issued by the National Aeronautics and Space Administration pursuant to Section 515. The CCSP
Interagency Committee relies on National Aeronautics and Space Administration certi?cations regarding
compliance with Section 515 and Agency guidelines as the basis for determining that this product conforms with
Section 515. For purposes of compliance with Section 515, this CCSP Synthesis and Assessment Product is an
“interpreted product” as that term is used in National Aeronautics and Space Administration guidelines and is
classi?ed as “highly in?uential”. This document does not express any regulatory policies of the United States or
any of its agencies, or provides recommendations for regulatory action.

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Atmospheric Aerosol
Properties and
Climate Impacts
Synthesis and Assessment Product 2.3
Report by the U.S. Climate Change Science Program
and the Subcommittee on Global Change Research
COORDINATING LEAD AUTHOR:
Mian Chin, NASA Goddard Space Flight Center
LEAD AND CONTRIBUTING AUTHORS:
Ralph A. Kahn, Lorraine A. Remer, Hongbin Yu, NASA GSFC;
David Rind, NASA GISS;
Graham Feingold, NOAA ESRL; Patricia K. Quinn, NOAA PMEL;
Stephen E. Schwartz, DOE BNL; David G. Streets, DOE ANL;
Philip DeCola, Rangasayi Halthore, NASA HQ

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January 2009,
Members of Congress:
On behalf of the National Science and Technology Council, the U.S. Climate Change Science Pro-
gram (CCSP) is pleased to transmit to the President and the Congress this Synthesis and Assessment
Product (SAP) Atmospheric Aerosol Properties and Climate Impacts. This is part of a series of 21
SAPs produced by the CCSP aimed at providing current assessments of climate change science to
inform public debate, policy, and operational decisions. These reports are also intended to help the
CCSP develop future program research priorities.
The CCSP’s guiding vision is to provide the Nation and the global community with the science-based
knowledge needed to manage the risks and capture the opportunities associated with climate and
related environmental changes. The SAPs are important steps toward achieving that vision and help
to translate the CCSP’s extensive observational and research database into informational tools that
directly address key questions being asked of the research community.
This SAP reviews current knowledge about global distributions and properties of atmospheric aero-
sols, as they relate to aerosol impacts on climate. It was developed in accordance with the Guidelines
for Producing CCSP SAPs, the Information Quality Act (Section 515 of the Treasury and General
Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554)), and the guidelines is-
sued by the National Aeronautics and Space Administration pursuant to Section 515.
We commend the report’s authors for both the thorough nature of their work and their adherence to
an inclusive review process.
Sincerely,
Carlos M. Gutierrez
Samuel W. Bodman
John H. Marburger III
Secretary of Commerce
Secretary of Energy
Director, Office of Science and
Chair, Committee on Climate Change
Vice Chair, Committee on Climate
Technology Policy
Science and Technology Integration
Change Science and Technology
Executive Director, Committee
Integration
on Climate Change Science and
Technology Integration

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Executive Summary ...............................................................................................1
ES 1. Aerosols and Their Climate Effects .......................................................................................1
ES 1.1. Atmospheric Aerosols .......................................................................................................1
ES 1.2. Radiative Forcing of Aerosols ..........................................................................................1
ES 1.3. Reducing Uncertainties in Aerosol Radiative Forcing Estimates .............................2
ES 2. Measurement-Based Assessment of Aerosol Radiative Forcing ......................................2
ES 2.1. Assessments of Aerosol Direct Radiative Forcing ......................................................3
ES 2.2. Assessments of Aerosol Indirect Radiative Forcing ....................................................3
ES 3. Model Estimated Aerosol Radiative Forcing and Its Climate Impact .............................4
ES 3.1. The Importance of Aerosol Radiative Forcing in Climate Models ..........................4
ES 3.2. Modeling Atmospheric Aerosols .....................................................................................4
ES 3.3. Aerosol Effects on Clouds................................................................................................5
ES 3.4. Impacts of Aerosols on Climate Model Simulations ..................................................5
ES 4. The Way Forward ......................................................................................................................5
TABLE OF CONTENTS
CHAPTER
1 .............................................................................................................................9
Introduction
1.1 Description of Atmospheric Aerosols .....................................................................................9
1.2 The Climate Effects of Aerosols ............................................................................................. 12
1.3. Reducing Uncertainties in Aerosol-Climate Forcing Estimates ...................................... 16
1.4 Contents of This Report .......................................................................................................... 20
2 ...........................................................................................................................21
Remote Sensing and In Situ Measurements of Aerosol Properties, Burdens,
and Radiative Forcing
2.1. Introduction ............................................................................................................................... 21
2.2. Overview of Aerosol Measurement Capabilities ............................................................... 22
2.2.1. Satellite Remote Sensing .................................................................................................. 22
2.2.2. Focused Field Campaigns ................................................................................................. 27
2.2.3. Ground-based In situ Measurement Networks ......................................................... 27
2.2.4. In situ Aerosol Pro?ling Programs ................................................................................. 28
2.2.5. Ground-based Remote Sensing Measurement Networks ....................................... 29
2.2.6. Synergy of Measurements and Model Simulations..................................................... 32
2.3. Assessments of Aerosol Characterization and Climate Forcing .................................... 34
2.3.1. The Use of Measured Aerosol Properties to Improve Models ............................... 34
2.3.2. Intercomparisons of Satellite Measurements and Model Simulation of
Aerosol Optical Depth .................................................................................................... 37
2.3.3. Satellite Based Estimates of Aerosol Direct Radiative Forcing ............................... 38
2.3.4. Satellite Based Estimates of Anthropogenic Component of Aerosol Direct
Radiative Forcing ............................................................................................................... 44
2.3.5. Aerosol-Cloud Interactions and Indirect Forcing ...................................................... 44
2.4. Outstanding Issues ................................................................................................................... 49
2.5. Concluding Remarks ................................................................................................................ 52

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3 ...........................................................................................................................55
Modeling the Effects of Aerosols on Climate Forcing
3.1. Introduction ............................................................................................................................... 55
3.2. Modeling of Atmospheric Aerosols ...................................................................................... 56
3.2.1. Estimates of Emissions ..................................................................................................... 56
3.2.2. Aerosol Mass Loading and Optical Depth ................................................................... 58
3.3. Calculating Aerosol Direct Radiative Forcing ..................................................................... 61
3.4. Calculating Aerosol Indirect Forcing .................................................................................... 66
3.4.1. Aerosol Effects on Clouds ............................................................................................... 66
3.4.2. Model Experiments ........................................................................................................... 67
3.4.3. Additional Aerosol In?uences ......................................................................................... 69
3.4.4. High Resolution Modeling ............................................................................................... 70
3.5. Aerosol in the Climate Models .............................................................................................. 72
3.5.1. Aerosol in the IPCC AR4 Climate Model Simulations .............................................. 72
3.5.2. Additional considerations ................................................................................................ 77
3.6. Impacts of Aerosols on Climate Model Simulations ......................................................... 78
3.6.1. Surface Temperature Change .......................................................................................... 78
TABLE OF CONTENTS
3.6.2. Implications for Climate Model Simulations................................................................ 81
3.7. Outstanding Issues ................................................................................................................... 81
3.8 Conclusions ................................................................................................................................ 82
4 ...........................................................................................................................85
The Way Forward
4.1. Major Research Needs ............................................................................................................ 85
4.2. Priorities ..................................................................................................................................... 87
4.2.1. Measurements .................................................................................................................... 87
4.2.2. Modeling .............................................................................................................................. 89
4.2.3. Emissions ............................................................................................................................. 90
4.3. Concluding Remarks ................................................................................................................ 90
Glossary and Acronyms ......................................................................................91
References ............................................................................................................99

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Atmospheric Aerosol Properties and Climate Impacts
AUTHOR TEAM FOR THIS REPORT
Executive Summary
Lorraine A. Remer, NASA GSFC; Mian Chin, NASA GSFC; Philip DeCola, NASA
HQ; Graham Feingold, NOAA ERSL; Rangasayi Halthore, NASA HQ/NRL; Ralph
A. Kahn, NASA GSFC; Patricia K. Quinn, NOAA PMEL; David Rind, NASA GISS;
Stephen E. Schwartz, DOE BNL; David G. Streets, DOE ANL; Hongbin Yu, NASA
GSFC/UMBC
Chapter 1
Lead Authors: Ralph A. Kahn, NASA GSFC; Hongbin Yu, NASA GSFC/UMBC
Contributing Authors: Stephen E. Schwartz, DOE BNL; Mian Chin, NASA GSFC;
Graham Feingold, NOAA ESRL; Lorraine A. Remer, NASA GSFC; David Rind,
NASA GISS; Rangasayi Halthore, NASA HQ/NRL; Philip DeCola, NASA HQ
Chapter 2
Lead Authors: Hongbin Yu, NASA GSFC/UMBC; Patricia K. Quinn, NOAA PMEL;
Graham Feingold, NOAA ESRL; Lorraine A. Remer, NASA GSFC; Ralph A. Kahn,
NASA GSFC
Contributing Authors: Mian Chin, NASA GSFC; Stephen E. Schwartz, DOE BNL
Chapter 3
Lead Authors: David Rind, NASA GISS; Mian Chin, NASA GSFC; Graham Fein-
gold, NOAA ESRL; David G. Streets, DOE ANL
Contributing Authors: Ralph A. Kahn, NASA GSFC; Stephen E. Schwartz, DOE
BNL; Hongbin Yu, NASA GSFC/UMBC
Chapter 4
David Rind, NASA GISS; Ralph A. Kahn, NASA GSFC; Mian Chin, NASA GSFC;
Stephen E. Schwartz, DOE BNL; Lorraine A. Remer, NASA GSFC; Graham Feingold,
NOAA ESRL; Hongbin Yu, NASA GSFC/UMBC; Patricia K. Quinn, NOAA PMEL;
Rangasayi Halthore, NASA HQ/NRL
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ACKNOWLEDGMENTS
First, the authors wish to acknowledge the late Yoram J. Kaufman both for his inspiration
and contributions to aerosol-climate science throughout his career and for his early leader-
ship of the activity that produced this document. His untimely passing left it to the remain-
ing authors to complete this report. Yoram and his contributions to our community are
greatly missed.
This Climate Change Science Program Synthesis and Assessment Product (CCSP SAP) 2.3
has been reviewed by a group of experts, the public, and Federal Agencies. The purpose of
these independent reviews was to assure the quality of this product.
We wish to thank the following individuals for their expert review of this report: Sundar
Christopher (University of Alabama Huntsville), Daniel Jacob (Harvard University), Steven
Ghan (Paci?c Northwest National Laboratory), John Ogren (NOAA Earth System Research
Laboratory), and Susan Solomon (NOAA Earth System Research Laboratory).
We also wish to thank the following individuals/group for their public/federal agency re-
view of this report: Joel D. Scheraga (EPA), Samuel P. Williamson (NOAA/OFCM), Alan
Carlin, David L. Hagen, Douglas Hoyt, Forrest M. Mims III (Geronimo Creek observatory),
John Pittman, Nathan Taylor (Texas A&M University), Werner Weber (Technische Univer-
sity Dortmund, Germany), and the NOAA Research Council.
The work by Bates et al. (2006), Penner et al. (2006), Yu et al. (2006), Textor et al. (2006),
Kinne et al. (2006), Schulz et al. (2006), and the Fourth Assessment Report of the Intergov-
ernmental Panel on Climate Change (2007) provided important groundwork for the material
in Chapter 2 and Chapter 3.
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RECOMMENDED CITATIONS
For the Report as a Whole:
CCSP 2009: Atmospheric Aerosol Properties and Climate Impacts, A Report by the U.S. Climate Change Science
Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn, and Stephen E. Schwartz
(eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA, 128 pp.
For the Executive Summary:
Remer, L. A., M. Chin, P. DeCola, G. Feingold, R. Halthore, R. A. Kahn, P. K. Quinn, D. Rind, S. E. Schwartz, D.
Streets, and H. Yu, 2009: Executive Summary, in Atmospheric Aerosol Properties and Climate Impacts, A Report by the
U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn,
and Stephen E. Schwartz (eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA.
For Chapter 1:
Kahn, R. A., H. Yu, S. E. Schwartz, M. Chin, G. Feingold, L. A. Remer, D. Rind, R. Halthore, and P. DeCola, 2009:
Introduction, in Atmospheric Aerosol Properties and Climate Impacts, A Report by the U.S. Climate Change Science
Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn, and Stephen E. Schwartz
(eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA.
For Chapter 2:
Yu, H., P. K. Quinn, G. Feingold, L. A. Remer, R. A. Kahn, M. Chin, and S. E. Schwartz, 2009: Remote Sensing and
In Situ Measurements of Aerosol Properties, Burdens, and Radiative Forcing, in Atmospheric Aerosol Properties and
Climate Impacts, A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change
Research. [Mian Chin, Ralph A. Kahn, and Stephen E. Schwartz (eds.)]. National Aeronautics and Space Administration,
Washington, D.C., USA.
For Chapter 3:
Rind, D., M. Chin, G. Feingold, D. Streets, R. A. Kahn, S. E. Schwartz, and H. Yu, 2009: Modeling the Effects of
Aerosols on Climate, in Atmospheric Aerosol Properties and Climate Impacts, A Report by the U.S. Climate Change
Science Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn, and Stephen E.
Schwartz (eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA.
For Chapter 4:
Rind, D., R. A. Kahn, M. Chin, S. E. Schwartz, L. A. Remer, G. Feingold, H. Yu, P. K. Quinn, and R. Halthore, 2009:
The Way Forward, in Atmospheric Aerosol Properties and Climate Impacts, A Report by the U.S. Climate Change
Science Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn, and Stephen E.
Schwartz (eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA.
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The U.S. Climate Change Science Program
Earth observed from space. Much of the information contained in this image came from the MODIS instrument on the NASA Terra
satel ite. This 2002 “Blue Marble” features land surfaces, clouds, topography, and city lights. Credit: NASA (image processed by
Robert Simmon and Reto Stöckli).
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