Chemical Heterogeneity Among Cloud Drop Populations and its Effects on Sulfur Oxidation

Collett云化学模型利用明确的云微物理处理预测云滴成分随云滴大小而变化。最近的实验观察证实，大的和小的云滴通常具有完全不同的化学成分。云滴种群之间的化学非均质性会影响单个溶质的去除速率，并且相对于根据平均云水性质预测的速率，也会提高硫氧化速率。云是全球大气硫酸盐生成的主要贡献者。因此，要准确描绘大气中硫酸盐的生成，就需要对真实的、化学性质不均匀的云中硫酸盐生成的速率有一个准确的了解。这个项目的主要目标是描述云滴在大小光谱上的化学变化，并确定云滴种群之间的化学异质性增加了云中硫酸盐产量的多少。数据将通过同时测量多个液滴大小类别的化学成分来收集。云水的收集将使用之前工作中使用的两台云收集器（分别为两段和三段），以及作为本项目一部分将建造的一台新的五段仪器。主要离子、pH值、游离和络合硫（IV）、氧化剂和催化剂将被测量并用于表征硫氧化速率作为液滴大小的函数。还将测量与大小有关的气溶胶组成和可溶性微量气体，以确定颗粒和气体清除对与大小有关的云水组成的水滴的影响。

9509596 Collett Cloud chemistry models utilizing explicit treatments of cloud microphysics predict that cloud drop composition varies with drop size. Recent experimental observations confirm that large and small cloud drops typically have quite different chemical compositions. Chemical heterogeneity among cloud drop populations can influence removal rates for individual solutes, and can also enhance rates of sulfur oxidation relative to rates predicted from average cloud water properties. Clouds are major contributors to global atmospheric sulfate production. Developing an accurate picture of the atmospheric production of sulfate therefore requires an accurate understanding of the rate of sulfate production in real, chemically heterogeneous clouds. The primary objective of this project is to characterize variations in cloud drop chemistry across the drop size spectrum and determine how much sulfate production in clouds is enhanced by chemical heterogeneity among cloud drop populations. Data will be collected through simultaneous measurements of the chemical composition of multiple drop size classes. Cloud water will be collected with two cloud collectors used in previous work (two-stage, and three-stage, respectively), as well as a new five-stage instrument to be constructed as part of this project. Major ions, pH, free and complexed sulfur (IV), oxidants, and catalysts will be measured and used to characterize sulfur oxidation rates as a function of drop size. Measurements of the size-dependent aerosol composition and of soluble trace gases also will be made to determine the influence of particle and gas scavenging on the drop size-dependence of the cloud water composition.