Application of a Tracer Technique to Study Sulfur Dioxide Oxidation in Cloud Drops as a Function of Drop Size

9712603 Collett 全球大部分二氧化硫氧化被认为发生在云中。主要机制是在微量金属（例如铁和锰）存在下被臭氧、过氧化氢和分子氧氧化。最近的测量和云化学模型表明，云滴成分随滴大小而变化。云滴群体之间的这种化学异质性有可能显着影响水相硫氧化的速率，从而导致大滴中更快地产生硫酸盐。化学异质云滴群体中的平均氧化速率可能显着超过平均滴组成所预期的速率。 该项目由科罗拉多州立大学和纽约州立大学奥尔巴尼分校/纽约州卫生部的研究小组联合进行，将测试这样的假设：当过氧化氢是主要氧化剂时，硫酸盐的产生不会随液滴尺寸的变化而变化，但当臭氧氧化或微量金属催化氧化占主导地位时，硫酸盐的产生会随着液滴尺寸的变化而显着变化。该研究将应用 L. Husain 最近开发的示踪技术来测量云滴中硫酸盐的产生。将在云前气溶胶和云水中测量硫酸盐与保守气溶胶示踪剂（Se、As 或 Sb）的比率，表明云中产生的硫酸盐的比例。将使用尺寸分级云收集器来收集大大小小的云滴。还将测量液滴成分和二氧化硫、臭氧和过氧化氢的气相浓度，以预测硫氧化速率作为液滴尺寸的函数，以便与示踪技术确定的速率进行比较。选择了两个环境（纽约州怀特菲斯山和加利福尼亚州贝克斯菲尔德）进行研究，以确保过氧化氢既是又不是主要氧化剂的条件。

9712603 Collett The majority of the global sulfur dioxide oxidation is believed to occur in clouds. The primary mechanisms are oxidation by ozone, hydrogen peroxide, and molecular oxygen in the presence of trace metals, such as iron and manganese. Recent measurements and cloud chemistry models indicate that cloud drop composition varies with drop size. This chemical heterogeneity among cloud drop populations has the potential to significantly influence the rate of aqueous phase sulfur oxidation, resulting in faster sulfate production in large drops. The average oxidation rate in a chemically heterogeneous cloud drop population could significantly exceed the rate expected from the average drop composition. This project, to be conducted jointly by groups at Colorado State University and at the State University of New York at Albany/ New York State Department of Health, will test the hypothesis that sulfate production does not vary with drop size when hydrogen peroxide is the dominant oxidant, but can vary significantly with drop size when oxidation by ozone or trace metal catalyzed oxidation are dominant. The study will apply a tracer technique which was recently developed by L. Husain to measure sulfate production in cloud drops. The ratios of sulfate to a conservative aerosol tracer (Se, As, or Sb) will be measured both in pre-cloud aerosol and cloud water, indicating the proportion of the sulfate that was produced in the cloud. Large and small cloud drops will be collected using a size-fractionating cloud collector. Measurements of droplet composition and gas phase concentrations of sulfur dioxide, ozone, and hydrogen peroxide will also be made to permit prediction of sulfur oxidation rates as a function of drop size for comparison with rates determined by the tracer technique. Two environments (Whiteface Mountain, New York, and Bakersfield, California) have been selected for study to ensure that conditions will be encountered where hydrogen peroxide both is and is not the dominant oxida nt.