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

全球二氧化硫氧化的大部分被认为发生在云中。主要机理是在铁和锰等微量金属存在的情况下，臭氧、过氧化氢和分子氧的氧化作用。最近的测量和云化学模型表明，云滴的组成随云滴的大小而变化。云滴种群之间的这种化学异质性有可能显著影响水相硫氧化的速率，导致大雨滴中硫酸盐的生成更快。化学上不均匀的云滴群的平均氧化速率可能显著超过平均云滴组成的预期速率。该项目将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开展，将检验这样一种假设，即当过氧化氢是主要氧化剂时，硫酸盐的产量不随液滴大小而变化，但当臭氧或微量金属催化氧化是主要氧化剂时，硫酸盐的产量会随液滴大小而显著变化。该研究将应用L. Husain最近开发的示踪技术来测量云滴中的硫酸盐产量。硫酸盐与保守气溶胶示踪剂（Se， As或Sb）的比例将在云前气溶胶和云水中测量，表明在云中产生的硫酸盐的比例。大小云滴将使用大小分馏云收集器收集。还将测量液滴组成和二氧化硫、臭氧和过氧化氢的气相浓度，以预测硫氧化速率作为液滴大小的函数，以便与示踪技术确定的速率进行比较。我们选择了两种环境（纽约的白面山和加利福尼亚的贝克斯菲尔德）进行研究，以确保过氧化氢是和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.