Maple在气溶胶云下清除数值模拟中的应用  

Application of Maple to numerical simulation of below-cloud scavenging of aerosols

作　　者：方志华[1] 刘兆荣[1] 白郁华[1] 李金龙[1] 

机构地区：[1]北京大学环境科学与工程学院,北京100871

出　　处：《计算机与应用化学》2009年第6期783-788,共6页Computers and Applied Chemistry

基　　金：国家高技术研究发展计划(863)项目(2006AA06A309);国家重点基础研究发展计划(973)项目(2005CB422204)

摘　　要：云下清除是大气气溶胶粒子一个重要的清除机制,清除效果与粒径大小及雨强等气象条件密切相关,一般采用质量平均清除系数和雨强的参数化关系来定量描述。本文采用数值计算方法模拟气溶胶粒子的云下清除过程,综合考虑布朗扩散、拦截作用和惯性碰撞等机制的贡献,结合不同模态气溶胶粒子的化学成分,在Maple平台上,通过对M-P雨滴谱、雨滴终速经验公式、气溶胶粒子对数正态分布谱、雨滴对气溶胶粒子捕获系数等,基于雨滴或气溶胶粒径的多个函数进行统一符号处理和数值计算,得到CaCO_3、(NH_4)_2SO_4两种典型的大气气溶胶粒子质量平均清除系数和雨强的参数化关系:CaCO_3粒子为(?)(h^(-1))=0.83·p_0^(0.74),(NH_4)_2SO_4粒子为(?)(h^(-1))=1.8×10^(-3)·p_0^(0.64)。分析了降雨过程中大气气溶胶质量浓度和雨水中Ca^(2+),NH_4^+,SO_4^(2-)离子浓度的变化趋势。Below-cloud scavenging is an important deposition mechanism for airborne aerosol particles. The scavenging coefficient depends on the aerosol size and meteorological conditions, Especially the precipitation rate significantly. The traditional bulk parameterization represents the mean wet scavenging coefficient for the whole aerosol size range. This parameterization overestimates the scavenging of aerosol mass and ion concentration of rainwater during a heavy or medium precipitation. In this study, the scavenging of aerosol particles in the below-cloud scavenging process was simulated, considering the contribution of collection mechanisms due to Brownian diffusion, directional interception and inertial impaction and the chemical composition of different mode aerosols. With the application of Maple software, multi functions based on either rain drop diameter or aerosol diameter were mathematically simulated and symbol processed. Those included the Marshall-Palmer raindrop size distribution, the raindrop terminal velocity, the log-normal size distribution of aerosols of selected chemical composition and the collision efficiency between a single rain droplet and particles. The relationship between the weighted mean scavenging coefficients of typical coarse and fine aerosol particles and the rainfall intensity were parameterized. The new parameterization for CaCO3 and （ NH4 ） 2 SO4 were determined as ↑（-）A （ h^-1） = 0. 83·p0^0.74 and ↑（-）A （ h^-1） = 1.8 ×10^-3·p0^0.64 respectively. The predicted aerosols mass concentration in the air and the concentration variation trend of Ca^2＋ , NH4^＋ and SO4^2- in the rainwater were analyzed based on the above simulation.

关 键 词：MAPLE 气溶胶 云下清除 捕获系数 

分 类 号：X13[环境科学与工程—环境科学] X517