摘要：Research in aerosol properties and cloud characteristics have historically been considered two separate disciplines within the field of atmospheric science. As such, it has been uncommon for a single researcher, or even research group, to have considerable expertise in both subject areas. The recent attention paid to global climate change has shown that clouds can have a considerable effect on the Earth's climate and that one of the most uncertain aspects in their formation, persistence, and ultimate dissipation is the role played by aerosols. This highlights the need for researchers in both disciplines to interact more closely than they have in the past. This is the vision behind this focus issue of Environmental Research Letters. Certain interactions between aerosols and clouds are relatively well studied and understood. For example, it is known that an increase in the aerosol concentration will increase the number of droplets in warm clouds, decrease their average size, reduce the rate of precipitation, and extend the lifetime. Other effects are not as well known. For example, persistent ice super-saturated conditions are observed in the upper troposphere that appear to exceed our understanding of the conditions required for cirrus cloud formation. Further, the interplay of dynamics versus effects purely attributed to aerosols remains highly uncertain. The purpose of this focus issue is to consider the current state of knowledge of aerosol/cloud interactions, to define the contemporary uncertainties, and to outline research foci as we strive to better understand the Earth's climate system. This focus issue brings together laboratory experiments, field data, and model studies. The authors address issues associated with warm liquid water, cold ice, and intermediate temperature mixed-phase clouds. The topics include the uncertainty associated with the effect of black carbon and organics, aerosol types of anthropogenic interest, on droplet and ice formation. Phases of water which have not yet been fully defined, for example cubic ice, are considered. The impact of natural aerosols on clouds, for example mineral dust, is also discussed, as well as other natural but highly sensitive effects such as the Wegener–Bergeron–Findeisen process. It is our belief that this focus issue represents a leap forward not only in reducing the uncertainty associated with the interaction of aerosols and clouds but also a new link between groups that must work together to continue progress in this important area of climate science. Focus on Aerosol–Cloud Interactions Contents The global influence of dust mineralogical composition on heterogeneous ice nucleation in mixed-phase clouds C Hoose, U Lohmann, R Erdin and I Tegen Ice formation via deposition nucleation on mineral dust and organics: dependence of onset relative humidity on total particulate surface area Zamin A Kanji, Octavian Florea and Jonathan P D Abbatt The Explicit-Cloud Parameterized-Pollutant hybrid approach for aerosol–cloud interactions in multiscale modeling framework models: tracer transport results William I Gustafson Jr, Larry K Berg, Richard C Easter and Steven J Ghan Cloud effects from boreal forest fire smoke: evidence for ice nucleation from polarization lidar data and cloud model simulations Kenneth Sassen and Vitaly I Khvorostyanov The effect of organic coating on the heterogeneous ice nucleation efficiency of mineral dust aerosols O Möhler, S Benz, H Saathoff, M Schnaiter, R Wagner, J Schneider, S Walter, V Ebert and S Wagner Enhanced formation of cubic ice in aqueous organic acid droplets Benjamin J Murray Quantification of water uptake by soot particles O B Popovicheva, N M Persiantseva, V Tishkova, N K Shonija and N A Zubareva Meridional gradients of light absorbing carbon over northern Europe D Baumgardner, G Kok, M Krämer and F Weidle MAID: a model to simulate UT/LS aerosols and ice clouds H Bunz, S Benz, I Gensch and M Krämer Single-parameter estimates of aerosol water content S M Kreidenweis, M D Petters and P J DeMott Supersaturations, microphysics and nitric acid partitioning in a cold cirrus cloud observed during CR-AVE 2006: an observation–modelling intercomparison study I V Gensch, H Bunz, D G Baumgardner, L E Christensen, D W Fahey, R L Herman, P J Popp, J B Smith, R F Troy, C R Webster, E M Weinstock, J C Wilson, T Peter and M Krämer Connecting hygroscopic growth at high humidities to cloud activation for different particle types H Wex, F Stratmann, T Hennig, S Hartmann, D Niedermeier, E Nilsson, R Ocskay, D Rose, I Salma and M Ziese Modeling of the Wegener–Bergeron–Findeisen process—implications for aerosol indirect effects T Storelvmo, J E Kristjánsson, U Lohmann, T Iversen, A Kirkevåg and Ø Seland Droplet nuclei in non-precipitating clouds: composition and size matter Cynthia H Twohy and James R Anderson A laboratory investigation of the relative humidity dependence of light extinction by organic compounds from lignin combustion Melinda R Beaver, Rebecca M Garland, Christa A Hasenkopf, Tahllee Baynard, A R Ravishankara and Margaret A Tolbert Cirrus cloud formation and ice supersaturated regions in a global climate model Ulrike Lohmann, Peter Spichtinger, Stephanie Jess, Thomas Peter and Herman Smit Notes on state-of-the-art investigations of aerosol effects on precipitation: a critical review A P Khain
