Influence of organic films on the evaporation and condensation of water in aerosol
Influence of organic films on the evaporation and condensation of water in aerosol
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DOI：
10.1073/pnas.1305277110
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发表时间：
2013-05-28
影响因子：
11.1
通讯作者：
Reid, Jonathan P.
中科院分区：
文献类型：
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作者：
Davies, James F.;Miles, Rachael E. H.;Reid, Jonathan P.
大气气溶胶中水分蒸发和凝结动力学的不确定性是预测云滴数量和气溶胶对气候的间接影响的不确定性的重要原因。气溶胶颗粒表面成分的影响，特别是表面活性有机膜的影响，对冷凝和蒸发系数仍然是模糊的。在这里，我们报告的有机薄膜的蒸发和凝结的水从气溶胶颗粒的影响的测量。当长链醇[CnH（2n+1）OH]单层形成冷凝膜时，蒸发系数显着降低，随着n从12增加到17，蒸发系数值从2.4 x 10（-3）降低到1.7 x 10（-5）。依赖于温度的测量证实，必须形成长程有序的冷凝膜，以抑制蒸发系数低于0.05。在冷凝膜中涂覆的液滴上的水的冷凝被示出为是快速的，随着水滴的生长，长链醇分子的强相干性导致孤岛化，从而打开水可以快速冷凝的未涂覆表面的宽区域。我们的结论是，大气气溶胶颗粒表面上的有机膜的多组分组合物可能会排除冷凝膜的形成，并且在气溶胶活化形成云滴的过程中，水冷凝的动力学可能会保持快速。
Uncertainties in quantifying the kinetics of evaporation and condensation of water fromatmospheric aerosol are a significant contributor to the uncertainty in predicting cloud droplet number and the indirect effect of aerosols on climate. The influence of aerosol particle surface composition, particularly the impact of surface active organic films, on the condensation and evaporation coefficients remains ambiguous. Here, we report measurements of the influence of organic films on the evaporation and condensation of water from aerosol particles. Significant reductions in the evaporation coefficient are shown to result when condensed films are formed by monolayers of long-chain alcohols [CnH(2n+1)OH], with the value decreasing from 2.4 x 10(-3) to 1.7 x 10(-5) as n increases from 12 to 17. Temperature-dependent measurements confirm that a condensed film of long-range order must be formed to suppress the evaporation coefficient below 0.05. The condensation of water on a droplet coated in a condensed film is shown to be fast, with strong coherence of the long-chain alcohol molecules leading to islanding as the water droplet grows, opening up broad areas of uncoated surface on which water can condense rapidly. We conclude that multicomponent composition of organic films on the surface of atmospheric aerosol particles is likely to preclude the formation of condensed films and that the kinetics of water condensation during the activation of aerosol to form cloud droplets is likely to remain rapid.