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Libin Yan
,
Xiaodong Liu
,
Ping Yang
,
Zhi-Yong Yin
, and
Gerald R. North

1. Introduction Aerosols—that is, the liquid and solid particulates suspended in the atmosphere—constitute an important atmospheric component not only by directly absorbing and scattering solar radiation and terrestrial thermal infrared emission, but also by affecting the water cycle through their indirect effect [i.e., acting as efficient cloud condensation nuclei (CCN) or ice nuclei (IN) ( Ramanathan et al. 2001 )]. Substantial uncertainties in our current knowledge of the aerosol impact on

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Janek Uin
,
Allison C. Aiken
,
Manvendra K. Dubey
,
Chongai Kuang
,
Mikhail Pekour
,
Cynthia Salwen
,
Arthur J. Sedlacek
,
Gunnar Senum
,
Scott Smith
,
Jian Wang
,
Thomas B. Watson
, and
Stephen R. Springston

1. Introduction a. Inception of ARM Aerosols are ubiquitous in Earth’s atmosphere and are directly emitted from natural and anthropogenic sources as well as formed in the atmosphere. They alter Earth’s radiative budget directly by absorbing and scattering light and indirectly by altering cloud properties and processes such as formation, lifetime, and albedo. To achieve radiative closure at Earth’s surface, knowledge of local aerosol loading and optical properties are required. Because of their

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Yu Liu
,
Xuepeng Zhao
,
Weiliang Li
, and
Xiuji Zhou

1. Introduction The stratospheric aerosol layer consists of submicrometer-sized particles composed primarily of liquid solutions of sulfuric acid and water, with traces of other materials, such as ammonium sulfates. The layer was first identified by Junge et al. (1961) ; hence, it is often referred to as the “Junge” layer. Many studies have been performed to explain the formation, growth, and removal of stratospheric particles (e.g., Castleman et al. 1974 ; Hofmann et al. 1976 ; Turco et al

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J. Shen
,
M. Yu
,
A. J. Koivisto
,
H. Jiang
,
Y. Liu
,
L. Wang
, and
T. Hussein

1. Introduction In the study of atmospheric aerosols, a major discovery was that with time, tropospheric aerosols might lose their “birthmarks” and acquire a size distribution independent of the physical properties of the medium (e.g., temperature, viscosity, and density) and time ( Pruppacher and Klett 1997 ; Clark and Whitby 1967 ). This phenomenon puzzled scientists in the first half of the last century before Friedlander established the self-preserving size distribution (SPSD) theory

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Jiacheng Wang
,
Qiang Zhao
,
Shengcheng Cui
, and
Chengjie Zhu

1. Introduction With some assumptions, the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol algorithm can derive three primary products: the spectral aerosol optical depth, the effective radius of the aerosol, and the fraction of the total optical depth contributed by the fine mode aerosol ( Tanré et al. 1997 ). Some evaluation works on the MODIS aerosol retrieval over ocean have been done. For example, Remer et al. (2005 , 2006 ) reported that two-thirds of the retrieved aerosol

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Jian Wang
,
Rob Wood
,
Michael P. Jensen
,
J. Christine Chiu
,
Yangang Liu
,
Katia Lamer
,
Neel Desai
,
Scott E. Giangrande
,
Daniel A. Knopf
,
Pavlos Kollias
,
Alexander Laskin
,
Xiaohong Liu
,
Chunsong Lu
,
David Mechem
,
Fan Mei
,
Mariusz Starzec
,
Jason Tomlinson
,
Yang Wang
,
Seong Soo Yum
,
Guangjie Zheng
,
Allison C. Aiken
,
Eduardo B. Azevedo
,
Yann Blanchard
,
Swarup China
,
Xiquan Dong
,
Francesca Gallo
,
Sinan Gao
,
Virendra P. Ghate
,
Susanne Glienke
,
Lexie Goldberger
,
Joseph C. Hardin
,
Chongai Kuang
,
Edward P. Luke
,
Alyssa A. Matthews
,
Mark A. Miller
,
Ryan Moffet
,
Mikhail Pekour
,
Beat Schmid
,
Arthur J. Sedlacek
,
Raymond A. Shaw
,
John E. Shilling
,
Amy Sullivan
,
Kaitlyn Suski
,
Daniel P. Veghte
,
Rodney Weber
,
Matt Wyant
,
Jaemin Yeom
,
Maria Zawadowicz
, and
Zhibo Zhang

There are large uncertainties in the magnitude of the global aerosol radiative forcing ( Lohmann and Feichter 2005 ; IPCC 2013 ; Bellouin et al. 2020 ). Major contributions to this uncertainty derive from poor understanding of cloud and precipitation processes ( Gettelman et al. 2013 ), the cloud and precipitation responses to aerosol changes ( Rosenfeld et al. 2014a , b ), and the natural aerosol state that is being perturbed by anthropogenic emissions ( Carslaw et al. 2013 ). Remote

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F. Waquet
,
J. Riedi
,
L. C. Labonnote
,
P. Goloub
,
B. Cairns
,
J-L. Deuzé
, and
D. Tanré

1. Introduction Aerosol particles affect the climate of the earth directly by scattering and absorbing solar radiation and indirectly by affecting cloud microphysical properties ( Bréon et al. 2002 ) and cloud lifetime. Although their net radiative effect may compensate for increases in the effects of greenhouse gases, the current magnitude and even the regional sign of their net effect remains uncertain ( Forster et al. 2007 ). The constellation of National Aeronautics and Space Administration

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Xin Huang
,
Yu Song
,
Chun Zhao
,
Xuhui Cai
,
Hongsheng Zhang
, and
Tong Zhu

1. Introduction Atmospheric aerosol, mainly comprising sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), dust, and sea salt, is generated from primary anthropogenic and natural emissions as well as by secondary transformation. Aerosol has impacts on radiative transfer directly through scattering and absorbing solar radiation and indirectly by modifying microphysical properties of clouds, thereby exerting a cooling or heating effect on the planet ( Rosenfeld et al. 2008

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Lucas Craig
,
Arash Moharreri
,
David C. Rogers
,
Bruce Anderson
, and
Suresh Dhaniyala

1. Introduction Accurate sampling of aerosol particles from aircraft requires appropriately designed inlets that can representatively sample particles from the freestream and transport them to the measurement devices in the cabin. In clear air, this is often achieved using isokinetic sampling with diffuser-style inlets, where the sample velocity is matched with the freestream velocity. In clouds, accurate sampling of nonactivated or interstitial aerosol is complicated by the breakup or shatter

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Virendra P. Ghate
,
Annmarie G. Carlton
,
Thomas Surleta
, and
Alyssa Marie Burns

.g., Carlton et al. 2018 ) and debated with studies proposing it to be a result of any or all of the following: “dimming” due to aerosols ( Leibensperger et al. 2012 ; Mickley et al. 2012 ; Saxena and Yu 1998 ; Tosca et al. 2017 ; Silvern et al. 2017 ; Zheng et al. 2020 ); an increase in cloudiness, precipitation, and soil moisture variability ( Napton et al. 2010 ; Liang et al. 2006 ; Yu et al. 2014 ; Cusworth et al. 2017 ); variability of sea surface temperatures (SSTs) in both the Atlantic and

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