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

小行星9712603 据信，全球二氧化硫氧化的大部分发生在云中。主要机制是在微量金属（如铁和锰）存在下，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着影响水相硫氧化的速率，导致更快的硫酸盐生产在大滴。在一个化学不均匀的云滴人口的平均氧化率可能会显着超过预期的平均下降组合物的速度。 该项目将由科罗拉多州立大学和纽约纽约州立大学的奥尔巴尼/州立大学卫生部的小组联合进行，将测试以下假设：当过氧化氢是主要氧化剂时，硫酸盐的产生不随液滴大小而变化，但当臭氧或痕量金属催化氧化占主导地位时，硫酸盐的产生会随液滴大小而显著变化。这项研究将采用最近由L.侯赛因测量硫酸盐生产的云滴。硫酸盐与保守的气溶胶示踪剂（Se，As或Sb）的比率将在云前气溶胶和云水中测量，表明云中产生的硫酸盐的比例。大小云滴将使用分级云滴收集器收集。还将测量二氧化硫、臭氧和过氧化氢的液滴成分和气相浓度，以预测硫氧化速率作为液滴尺寸的函数，与示踪剂技术确定的速率进行比较。选择了两个环境（Whiteface Mountain，纽约和加州的贝克斯菲尔德）进行研究，以确保在过氧化氢是和不是主要氧化剂的情况下将遇到的条件。

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.