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来源:Atmospheric Chemistry and Physics

作者:J. Curtius, S. Ehrhart

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来源:Atmospheric Chemistry and Physics

作者:C. Chen;L. Qiao;H. Wang;等

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来源:Atmospheric Chemistry and Physics

作者:U. Lohmann, O. Stetzer, L. A. Ladino Moreno

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This manuscript compiles both theoretical and experimental information oncontact freezing with the aim to better understand this potentially importantbut still not well quantified heterogeneous freezing mode. There is nocomplete theory that describes contact freezing and how the energy barrierhas to be overcome to nucleate an ice crystal by contact freezing.Experiments on contact freezing conducted using the cold plate techniqueindicate that it can initiate ice formation at warmer temperatures thanimmersion freezing. Additionally, a qualitative difference in the freezingtemperatures between contact and immersion freezing has been found usingdifferent instrumentation and different ice nuclei. There is a lack of dataon collision rates in most of the reported data, which inhibits aquantitative calculation of the freezing efficiencies. Thus, new or modifiedinstrumentation to study contact nucleation in the laboratory and in thefield are needed to identify the conditions at which contact nucleation couldoccur in the atmosphere. Important questions concerning contact freezing andits potential role for ice cloud formation and climate are also summarized.

    来源:Atmospheric Chemistry and Physics

    作者:B.-L. Li;A. D. Nobre;D. Sheil;等

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    Phase transitions of atmospheric water play a ubiquitous role in theEarth's climate system, but their direct impact on atmosphericdynamics has escaped wide attention. Here we examine and advancea theory as to how condensation influences atmospheric pressurethrough the mass removal of water from the gas phase witha simultaneous account of the latent heat release.Building from fundamental physical principles we show that condensation is associated with a decline in air pressure in the lower atmosphere.This decline occurs up to a certain height, which ranges from 3 to4 km for surface temperatures from 10 to 30 °C. We thenestimate the horizontal pressure differences associated with watervapor condensation and find that these are comparable in magnitudewith the pressure differences driving observed circulation patterns.The water vapor delivered to the atmosphere via evaporation representsa store of potential energy available to accelerate air and thus drivewinds.Our estimates suggest that the global mean power at which thispotential energy is released by condensation is around one per cent ofthe global solar power – this is similar to the known stationarydissipative power of general atmospheric circulation.We concludethat condensation and evaporation merit attention as major, ifpreviously overlooked, factors in driving atmospheric dynamics.

      来源:Atmospheric Chemistry and Physics

      作者:Z. Shen;Y. Zhao;Z. Chen;等

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      In this study, 121 daily PM2.5 (aerosol particle with aerodynamicdiameter less than 2.5 μm) samples were collected from an urban site inBeijing in four months between April 2009 and January 2010 representing thefour seasons. The samples were determined for various compositions,including elements, ions, and organic/elemental carbon. Various approaches,such as chemical mass balance, positive matrix factorization (PMF),trajectory clustering, and potential source contribution function (PSCF),were employed for characterizing aerosol speciation, identifying likelysources, and apportioning contributions from each likely source. Our resultshave shown distinctive seasonality for various aerosol speciationsassociated with PM2.5 in Beijing. Soil dust waxes in the spring andwanes in the summer. Regarding the secondary aerosol components, inorganicand organic species may behave in different manners. The formerpreferentially forms in the hot and humid summer via photochemicalreactions, although their precursor gases, such as SO2 and NOx,are emitted much more in winter. The latter seems to favorably form in thecold and dry winter. Synoptic meteorological and climate conditions canoverwhelm the emission pattern in the formation of secondary aerosols. ThePMF model identified six main sources: soil dust, coal combustion, biomassburning, traffic and waste incineration emission, industrial pollution, andsecondary inorganic aerosol. Each of these sources has an annual meancontribution of 16, 14, 13, 3, 28, and 26%,respectively, to PM2.5. However, the relative contributions of theseidentified sources significantly vary with changing seasons. The results oftrajectory clustering and the PSCF method demonstrated that regional sourcescould be crucial contributors to PM pollution in Beijing. In conclusion, wehave unraveled some complex aspects of the pollution sources and formationprocesses of PM2.5 in Beijing. To our knowledge, this is thefirst systematic study that comprehensively explores the chemicalcharacterizations and source apportionments of PM2.5 aerosol speciationin Beijing by applying multiple approaches based on a completely seasonalperspective.

        来源:Atmospheric Chemistry and Physics

        作者:J. C. Wenger;G. J. Evans;J. R. Sodeau;等

        使用许可:署名(BY)

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