Growth rates of atmospheric molecular clusters based on appearance times and collision-evaporation fluxes: Growth by monomers
Growth rates of atmospheric molecular clusters based on appearance times and collision-evaporation fluxes: Growth by monomers
复制标题
DOI：
10.1016/j.jaerosci.2014.08.008
复制
发表时间：
2014-12-01
影响因子：
4.5
通讯作者：
Vehkamaki, Hanna
中科院分区：
文献类型：
--
作者：
Olenius, Tinja;Riipinen, Ilona;Vehkamaki, Hanna
二次气溶胶粒子的形成始于小分子团簇的形成和增长。新形成的簇达到更大尺寸的概率取决于它们相对于它们在预先存在的表面上丢失的速率的增长速率。目前，在凝聚粒子计数器和质谱仪技术的进步，使观察团簇生长通过时间演变的大小分辨团簇浓度，最近的研究已经利用测量的浓度来推断不同的团簇大小的出现时间的增长率。在这项工作中，我们使用一个动态模型来模拟人口的集群的质量直径高达2纳米的时间发展，并检查的增长率的关系确定的外观时间从集群之间的分子通量计算的增长率。本研究集中在一个简单的模型物质，其中集群的增长只通过单体添加和增长涉及一个单一的自由能垒。明确地处理由簇中分子的数量定义的每个簇大小，而不是将簇划分为大小类别。有限尺寸分辨率和集群集群碰撞的影响将在未来的工作中讨论。我们发现，与两种不同的方法确定的增长率可能会显着不同，无论是定量和定性，最小的集群与最高的蒸发率。随着团簇尺寸的增大和蒸发速率的减小，相对差异减小。除了簇的大小，差异取决于环境条件，包括外部损失和单体浓度的时间曲线。因此，定量比较不仅需要关于物质的信息，而且需要关于外部条件的信息。我们还表明，一个临界集群的大小，对应于集群形成的能量障碍的最大值，不能推断出在现实条件下的大小依赖的增长率。(C)2014爱思唯尔有限公司版权所有。
Formation of secondary atmospheric aerosol particles starts with the formation and growth of small molecular clusters. The probability that freshly formed clusters reach larger sizes depends on the rate at which they grow with respect to the rate at which they are lost on pre-existing surfaces. At present, advances in condensation particle counter and mass spectrometer techniques enable the observation of cluster growth via time evolution of size resolved cluster concentrations, and recent studies have utilized measured concentrations to deduce growth rates from the appearance times of different cluster sizes. In this work, we use a dynamic model to simulate the time development of a population of clusters of up to similar to 2 nm in mass diameter, and examine the relation of the growth rates determined from the appearance times to the growth rates calculated from the molecular fluxes between the clusters. This study concentrates on a simple model substance where the clusters grow only by monomer additions and the growth involves a single free energy barrier. Each cluster size defined by the number of molecules in the cluster is explicitly treated instead of dividing the clusters into size classes. Effects of finite size resolution and cluster cluster collisions will be discussed in future work. We find that the growth rates determined with the two different approaches may differ significantly, both quantitatively and qualitatively, for the smallest clusters with the highest evaporation rates. The relative difference decreases with increasing cluster size and decreasing evaporation rate. In addition to cluster size, the difference depends on ambient conditions including external losses and time profile of the monomer concentration. Thus a quantitative comparison requires information not only on the substance, but also on the external conditions. We also show that the size of a critical cluster, corresponding to the maximum of an energy barrier in cluster formation, cannot be inferred from the size-dependent growth rates in realistic conditions. (C) 2014 Elsevier Ltd. All rights reserved.