Effects of Shape and Surface Physical and Chemical Heterogeneities on Condensation/Evaporation of Aerosol Particles

摘要-9904139S。洛亚阿尔卡。提议进行一项为期三年的综合理论研究，以调查不同表面条件在水蒸气和气体在可能被润湿或可能不被润湿的任意形状的异质气溶胶颗粒上的凝结/蒸发和反应中的作用。我们将考虑一个或多个任意形状和大小的粒子，它们位于无限广阔的气体-蒸汽混合物中，其中扩散的蒸汽分子只有少量存在。颗粒表面条件将被允许在成分和/或化学上是不同的，以对应于各种自然和人为颗粒。也要考虑被润湿的颗粒，例如最终由表面张力效应决定形状的吸湿颗粒。对于连续区域和跳跃区域，我们将使用格林函数技术将拉普拉斯方程及其边界条件转换为边界积分方程。这允许将三维拉普拉斯方程简化为二维积分方程，从而更容易处理表面形态和吸附性质。然后对积分方程式进行离散化，并开发一个通用的计算机程序来获得局部和全局凝结(或蒸发)速率。对于某些粒子尺寸与蒸汽分子平均自由程相当的过渡区，我们将得到线性Boltzmann方程的解。我们将结合我们以前在球形粒子方面的工作，探索边界拟合坐标技术以及多重网格方法的应用。复杂的润湿团聚体的形状可以通过求解Young-Laplace方程和与之相关的自由边界条件得到，这些条件涉及接触点的润湿角。我们将使用微分几何来刻画任意曲面，并结合有限差分和牛顿方法来求解液体曲面的形状。这项研究将产生确定局部和全球冷凝率的通用和通用的数学和数值框架。具体地说，对湿润颗粒、链状凝聚体和生物气溶胶生长的速率表达式与表面非均质性的关系将有新的理解。这些速率表达式将用于各种自然和工程过程的建模的计算机代码中(例如，用于评估或预测空气质量、全球变暖趋势、最佳催化剂表面等的程序)。细颗粒物是空气质量风险评估领域以及全球变暖问题中的一个高度优先问题。本研究将允许对这些风险进行更现实的估计，并将有助于改进颗粒合成和制造技术。

ABSTRACTCTS-9904139S. LoyalkaU. of Missouri @ ColumbiaA comprehensive three-year theoretical study is proposed to investigate the role of variable surface conditions in the condensation/evaporation and reaction of vapors and gases on arbitrarily shaped, heterogeneous aerosol particles that may or may not be wetted. We will consider one or more particles of arbitrary shape and size situated in an infinite expanse of a gas-vapor mixture in which diffusing vapor molecules are present in small amounts. The particle surface conditions will be allowed to be compositionally and/or chemically heterogeneous to correspond to various natural and anthropogenic particles. Also to be considered and particles that are wetted, e.g. Hygroscopic particles that ultimately acquire shapes dictated by surface tension effects. For the continuum and jump regimes, we will use a Green's function technique to convert the Laplace equation together with its boundary conditions into a boundary integral equation. This allows the reduction of the 3-D Laplace equation to a 2-D integral equation and thus easier handling of the surface morphology and adsorption properties. The integral equation will then be discretized, and a generalized computer program will be developed to obtain local and global condensation (or evaporation) rates. For the transition regime, in which some particle dimension is comparable to the vapor molecular mean free path, we will obtain solutions of the linear Boltzmann equation. We will explore applications of boundary fitted coordinate techniques as well as multigrid methods in conjunction with our previous work on spherical particles. The shapes of complex wetted agglomerates will be obtained by solving the Young-Laplace equation with the associated free boundary conditions that involve the wetting angles at the contact points. We will use differential geometry to characterize arbitrary surfaces, and a combination of finite differencing and Newton's method to solve for the shapes of liquid surfaces. This research will result in the development of general and versatile mathematical and numerical frameworks for the determination of local and global condensation rates. Specifically, new understanding of the dependence of rate expressions for the growth of wetted particles, chain-like agglomerates, and bio-aerosols on surface heterogeneities will become available. These rate expressions will find use in computer codes for the modeling of various natural and engineered processes (e.g., programs for assessing or predicting air quality, global warming trends, optimal catalyst surfaces, etc.). Fine particles are a high priority issue in the area of air quality risk assessment as well as with respect to global warming issues. The present research will permit more realistic estimations of these risks and will aid in improving particle synthesis and manufacturing techniques.