Competition between water uptake and ice nucleation by glassy organic aerosol particles
Competition between water uptake and ice nucleation by glassy organic aerosol particles
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DOI：
10.5194/acp-14-12513-2014
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发表时间：
2014-01-01
影响因子：
6.3
通讯作者：
Koop, T.
中科院分区：
文献类型：
--
作者：
Berkemeier, T.;Shiraiwa, M.;Koop, T.
有机气溶胶粒子作为云和降水的核心，在气候中发挥着关键作用。它们的来源和成分变化很大，在大气条件下，它们的相态从液态到固态，影响着云滴和冰晶的活化途径。由于水在颗粒相中的扩散缓慢，有机颗粒可能在相态和形态上偏离其热力学平衡状态，从而妨碍预测其对云形成的影响。我们通过将估计水扩散率的新型半经验方法与显式处理水扩散的动力学通量模型相结合来克服这个问题。我们估计颗粒潮解的时间尺度，以及各种各样的有机物质，包括二次有机气溶胶（SOA）的氧化异戊二烯，α-蒎烯，萘，和十二烷的各种冰成核途径。模拟结果表明，在典型的大气上升气流中，玻璃态和固/液核-壳形态可以持续足够长的时间，使得沉积和浸没模式中的非均质冰成核可以主导均质冰成核。这种竞争强烈地依赖于环境温度和相对湿度以及增湿速率和颗粒尺寸。由于不同SOA的玻璃化转变温度、吸湿性和原子O/C比的差异，萘SOA颗粒具有最高的作为异质冰核的潜力。我们的研究结果表明，在大气条件下，水扩散到有机气溶胶颗粒的动力学限制可能会遇到，并会强烈影响冰成核途径。对于有机气溶胶粒子到大气模型中的冰成核，我们的研究结果表明，模型形式主义的需求，占分子扩散的影响，不仅描述冰成核发病作为温度和相对湿度的函数，但也包括上升气流速度，颗粒大小和组成。
Organic aerosol particles play a key role in climate by serving as nuclei for clouds and precipitation. Their sources and composition are highly variable, and their phase state ranges from liquid to solid under atmospheric conditions, affecting the pathway of activation to cloud droplets and ice crystals. Due to slow diffusion of water in the particle phase, organic particles may deviate in phase and morphology from their thermodynamic equilibrium state, hampering the prediction of their influence on cloud formation. We overcome this problem by combining a novel semi-empirical method for estimation of water diffusivity with a kinetic flux model that explicitly treats water diffusion. We estimate timescales for particle deliquescence as well as various ice nucleation pathways for a wide variety of organic substances, including secondary organic aerosol (SOA) from the oxidation of isoprene, alpha-pinene, naphthalene, and dodecane. The simulations show that, in typical atmospheric updrafts, glassy states and solid/liquid core-shell morphologies can persist for long enough that heterogeneous ice nucleation in the deposition and immersion mode can dominate over homogeneous ice nucleation. Such competition depends strongly on ambient temperature and relative humidity as well as humidification rate and particle size. Due to differences in glass transition temperature, hygroscopicity and atomic O/C ratio of the different SOA, naphthalene SOA particles have the highest potential to act as heterogeneous ice nuclei. Our findings demonstrate that kinetic limitations of water diffusion into organic aerosol particles are likely to be encountered under atmospheric conditions and can strongly affect ice nucleation pathways. For the incorporation of ice nucleation by organic aerosol particles into atmospheric models, our results demonstrate a demand for model formalisms that account for the effects of molecular diffusion and not only describe ice nucleation onsets as a function of temperature and relative humidity but also include updraft velocity, particle size and composition.