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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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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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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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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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Lucas Craig, Allen Schanot, Arash Moharreri, David C. Rogers, and Suresh Dhaniyala

1. Introduction The contribution of aerosol particles to the earth’s radiative balance is a major uncertainty in modeling long-term global climate ( Denman et al. 2007 ). A particular challenge in climate modeling is in accurately representing the indirect effect, that is, the aerosol interaction with water vapor to form clouds ( Andreae and Rosenfeld 2008 ; Seinfeld and Pandis 2006 ). In global climate models, for simplicity of numerical calculations, aerosol–cloud processes are often just

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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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Yi Ming and V. Ramaswamy

1. Introduction Anthropogenic aerosols from burning fossil fuels and biomass affect the earth’s radiation balance in multiple ways. They scatter and absorb shortwave (SW) and longwave (LW) radiation in the clear sky (the direct effect; e.g., Haywood and Ramaswamy 1998 ). Atmospheric warming exerted by absorbing aerosols (e.g., black carbon) facilitates dissipation of clouds through evaporating droplets (the semidirect effect; e.g., Hansen et al. 1997 ). Water-soluble aerosol particles (e

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Shuyun Zhao, Hua Zhang, Zhili Wang, and Xianwen Jing

the increase in CO 2 would generally cause a drier climate. Using a regional climate model, the International Centre for Theoretical Physics Regional Climate Model (ICTP RegCM), Gao and Giorgi (2008) found that the increase in greenhouse gases under the Intergovernmental Panel on Climate Change (IPCC) A2 and B2 scenarios could cause a northward expansion of dry lands in the Mediterranean region by the end of the twenty-first century. In addition to greenhouse gases, aerosols are also important

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Dorothy Koch, Surabi Menon, Anthony Del Genio, Reto Ruedy, Igor Alienov, and Gavin A. Schmidt

1. Introduction Atmospheric aerosols have multiple and complex impacts on climate. Distinguishing and quantifying these effects remains a major challenge of climate studies. The net effect of aerosol changes in the twentieth century on climate is thought to be cooling of surface air temperatures (SAT), partially offsetting warming from increasing greenhouse gas (GHG) concentrations. However, some aerosol effects can contribute to warming. Furthermore, aerosols and GHG affect not only SAT, but

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