Transformations, volatilisation and speciation of organic and inorganic iodine in the marine environment

该项目旨在进一步了解海洋环境中有机和无机碘的光化学转化和化学形态，特别是在沿海和开阔海洋环境中碘和碘作为碘原子源的相对作用。在我们实验室以前工作的基础上，我们的目标是首先量化海带和其他欧洲大型植物在不同的臭氧和其他形式的氧化应激条件下产生的I2和新颗粒的通量。这将提供有关先前在Mace Head爱尔兰观测到的I2/粒子产生现象的性质和控制过程的信息，也将有助于我们了解这些过程的普遍程度。虽然现在很明显，碘对区域大气化学有重要影响，但其全球影响尚不清楚。目前的大气模型当然假设海洋中的碘是大气中碘的主要来源。然而，在沿海地区，最近的研究表明，分子碘(I2)可以提供比碘碳高1000倍的碘原子通量。沿海IO和OIO浓度并不显著高于在代表开阔海洋的空气中测得的浓度，这一事实表明，碘碳化物可能不像以前所假设的那样是偏远空气中的主要来源。几十年前，人们首次提出了通过大气中的臭氧与海水表面的I-反应，从海水表面直接挥发碘的可能性。然而，这种机制是否真的会导致从开阔海洋向空气中产生大量的I2仍是未知的。我们的目标是进行实验，以阐明臭氧吸收后从公海释放I2和有机碘的可能性。海水中无机碘和有机碘的化学通过I2/HOI与DOM反应生成溶解的有机碘(DOI)，以及DOI光解为I-而紧密相连。在快速时间尺度上发生的任何这种DOI到I的转换都可能增加表层海洋顶部几米处的I-浓度，超过大气模型中用来确定臭氧沉积速度的I-的表层海洋浓度。我们的工作将确定高丰度的非挥发性DOI和低丰度的VIOC的光解是否会导致表层碘的升高，从而促进臭氧在海洋表面的干沉积。海水中碘的总浓度约为0.45 mM，主要以碘酸盐、碘化物和DOI的形式存在。尽管DOI可以构成海水中溶解碘的主要形式，但目前还没有关于海水中存在的主要化学形式的DOI的公开记录。最近对海洋气溶胶研究的关注表明，主要来自生物来源的水溶性有机物在夏季可占气溶胶质量的20%(O-Dowd等人，2004年)。鉴于许多藻类在新陈代谢过程中含有并产生大量的卤化物，有理由认为海洋气溶胶中可能存在溶解的有机卤化物，包括DOI。在这里，我们将使用LC-MS(MS)来表征DOI的主要形式。

This project aims to further understanding of the photochemical transformations and chemical speciation of organic and inorganic iodine in the marine environment, and in particular, the relative roles of I2 and iodocarbons as iodine atom sources in coastal and open ocean environments. Expanding on previous work in our laboratories, we aim first to quantify the flux of I2 and new particles produced from Laminaria kelp and other European macrophytes under varying conditions of O3 and other forms of oxidative stress. This will provide information on the nature and controlling processes of the I2/particle production phenomenon previously observed at Mace Head Ireland, and also will help us to understand how widespread these processes are. Whilst it is now clear that iodine has an important impact on atmospheric chemistry on a regional basis, the global impact is as yet unknown. Current atmospheric models certainly assume oceanic iodocarbons to be the dominant source of iodine to the atmosphere. However, in coastal locations recent work has shown that molecular iodine (I2) can provide up to a 1000 x higher iodine atom flux than that from iodocarbons. The fact that coastal IO and OIO concentrations are not significantly greater than those measured in air representative of the open ocean suggests that iodocarbons may not be the dominant source in remote air, as has been previously assumed. The possibility of direct volatilisation of I2 from the seawater surface via reaction of the atmospheric O3 with surface I- was first proposed decades ago. Yet, whether this mechanism actually results in significant I2 production to air from the open ocean is still unknown. We aim to conduct experiments to elucidate the potential for both I2 and organoiodine release from the open ocean following ozone uptake. The chemistry of inorganic and organic iodine in seawater is closely linked via both the reaction of I2/HOI with DOM to form dissolved organic iodine (DOI), and the photolysis of DOI to I-. Any such DOI to I- conversions which occur on rapid timescales may enhance the concentration of I- in the top few m of the surface ocean, over and above the surface ocean concentrations of I- used in atmospheric models to determine the deposition velocity of O3. Our work will determine whether photolysis of highly abundant non-volatile DOI and less abundant VIOC leads to elevated surface-layer iodide and thus enhances dry deposition of O3 to the ocean surface. The total concentration of iodine in seawater is around 0.45mM, predominantly in the form of iodate, iodide and DOI. Despite the fact that DOI can comprise the major form of dissolved iodine in seawater, there is no published record of the main chemical forms of DOI present in seawater. Recent focus in marine aerosol research has shown that water-soluble organics, mainly of biogenic origin, can comprise up to 20% of aerosol mass during summer (O-Dowd et al., 2004). Given that many algal species contain and produce significant quantities of halides during their metabolism, it is reasonable to suggest that dissolved organic halides, including DOI, may be present in marine aerosol. Here we will characterise the main forms of DOI using LC-MS(MS).