Heterogeneous Reactions of NO2 in Dispersed Aqueous Systems

气液滴相互作用通常不被视为 表面化学反应，但被认为是一系列的质量 水相均相迁移过程 反应. 用于描述的机制和速率方程 水反应是从本体溶液获得的那些反应 假设直接测量 适用于云和雾等分散系统。 这 该项目解决了散装与分散状态的问题 实验室二氧化氮水溶液反应化学 云 其目的是实验评估两个工作 假设制定来解释我们以前的结果，这是 与传统的二氧化氮图片不一致 化学. 我们的主要发现是：（1）硝酸盐的形成迅速， 二氧化氮与实验室的云反应。(2)硝酸盐 亚饱和氯化钠浓度 气溶胶，尤其是云滴， 清除硝酸杂质的预期最大水平 存在于二氧化氮供应中，即有一个净 产生气溶胶或云水硝酸盐。 (3)的 暴露在二氧化氮中的云滴的组成是 与暴露于二氧化氮的大量水完全不同 来自同一个来源。 我们的两个假设中的第一个是观察到的与。 体积差异是由于内在的，可能是表面的 高比表面积含水系统的化学性质。 第二个是二氧化氮的吸收及其 在分散的含水体系中转化为硝酸根离子， 强烈增强的微量硝酸吸附在 不饱和气溶胶、云滴或气溶胶颗粒， 是云的凝结核

Gas-liquid drop interactions are usually not viewed as surface chemical reactions but considered as a sequence of mass transport processes followed by aqueous-phase homogeneous reactions. The mechanisms and rate equations used to describe the aqueous reactions are those obtained from bulk solution measurements that are assumed to assumed to be directly applicable to dispersed systems such as clouds and fogs. This project addresses the question of bulk vs. dispersed state chemistry in aqueous reactions of nitrogen dioxide in laboratory clouds. Its objective is to evaluate experimentally two working hypotheses formulated to explain our previous results, which are inconsistent with the conventional picture of nitrogen dioxide chemistry. Our main findings are: (1) Nitrate forms rapidly when nitrogen dioxide reacts with a laboratory cloud. (2) The nitrate concentrations associated with subsaturated sodium chloride aerosol and especially with cloud drops substantially exceeds the maximum level expected from scavenging the nitric acid impurity present in the nitrogen dioxide supply, i.e. there is a net production of aerosol or cloud water nitrate. (3) The composition of cloud drops exposed to nitrogen dioxide is radically different from bulk water exposed to nitrogen dioxide from the same source. The first of our two hypotheses is that the observed vs. bulk differences are due to an intrinsic, possibly surface chemical, property of high surface-to-volume aqueous systems. The second is that the uptake of nitrogen dioxide and its conversion to nitrate ion in a dispersed aqueous system is strongly enhanced by trace amounts of nitric acid adsorbed on subsaturated aerosols, cloud drops, or aerosol particles that serve as cloud condensation nuclei.