NSFGEO-NERC:BLEACH

对流层中活性卤素的丰度可能对大气的氧化能力产生深远影响，既直接作为碳氢化合物和其他还原痕量气体的氧化剂，也间接通过它们对羟基自由基和臭氧丰度的影响。然而，我们对对流层活性卤素的丰度以及空间和时间变化的理解仍然非常不确定。直到最近，全球化学传输模型才开始包括全面的反应性卤素化学。最近的建模研究表明，活性卤素显著降低了大气的氧化能力[施密特等人，2016]，并且由于人为排放，自工业化前以来活性卤素增加[Sherwen等人，2017年]。建模研究还表明不同反应性卤素物质（Cl、Br、I）之间的正相互作用，其中一种反应性卤素物质的增加使其它反应性卤素物质增加[Wang等人，2019年]。然而，这些模式的结果的评估是阻碍了缺乏观测约束。此外，观察到反应性卤素物质（例如，使用不同的测量技术可以产生非常不同的结果，进一步复杂化模型评估。我们建议在BIOS都铎山海洋大气观测站测量一组前所未有的活性气体和颗粒卤素丰度在两个季节（冬季和夏季）与三种不同的仪器。观测将包括我们预计最丰富的气态溴、氯和碘物质（HCl、BrO、ClNO 2、IO等）及其气溶胶相对应物（Br-、Cl-、I-），气相物质来自这些物质。对于气相测量，我们将使用三种不同的观测技术（CIMS，LP-DOAS，TILDAS）来比较一些关键活性卤素的测量结果，同时还扩展了测量卤素物种的套件。由于海盐气溶胶（SSA）和海洋表面的非均相反应是对流层活性卤素的最大来源，热带岛屿是一个理想的位置。此外，由于夏季存在百慕大高压系统，百慕大的风向具有季节性，导致冬季从北美输送污染物，夏季则是清洁的海洋条件，这使我们能够测试我们以前的模型结果，表明人类活动增加了对流层活性卤素丰度，对大气的氧化能力产生影响。将把使用全球对地观测系统-化学全球化学迁移模型进行的模型模拟纳入研究计划，并将作为该项目的一部分进一步开发该模型的化学机制。拟议的实地活动将为模型提供目前缺失的观测约束，从而允许模型评估和改进模型的反应性卤素化学的化学机制。该模型还将用于帮助解释观测结果，这将通过模型敏感性模拟以及观测结果与模型的比较来实现。这里提出的测量将提供一个定量的观测约束的依赖活性卤素丰度污染水平，以及允许我们评估模型的代表性的丰度和物种的活性卤素在热带，海洋的位置和它们之间的相互作用。

The abundance of reactive halogens in the troposphere may have a profound influence on the oxidation capacity of the atmosphere both directly as oxidants of hydrocarbons and other reduced trace gases and indirectly through their influence on hydroxyl radical and ozone abundances. However, our understanding of the abundance and the spatial and temporal variability of tropospheric reactive halogens remains highly uncertain. Only recently have global chemical transport models begun to include comprehensive reactive halogen chemistry. Recent modeling studies suggest that reactive halogens significantly reduce the oxidation capacity of the atmosphere [Schmidt et al., 2016], and that reactive halogens have increased since the preindustrial due to anthropogenic emissions [Sherwen et al., 2017]. Modeling studies also suggest positive interactions between different reactive halogen species (Cl, Br, I), with increases in one reactive halogen species increasing the others [Wang et al., 2019]. However, assessment of these model results is hindered by a dearth of observational constraints. Additionally, observations of reactive halogen species (e.g., BrO) using different measurement techniques can yield very different results, further complicating model assessment. We propose to measure an unprecedented set of reactive gaseous and particulate halogen abundances at the BIOS Tudor Hill Marine Atmospheric Observatory during two seasons (winter and summer) with three different instruments. Observations will include what we expect to be among the most abundant gaseous bromine, chlorine and iodine species (HCl, BrO, ClNO2, IO, among several others) and their aerosol-phase counterparts (Br-, Cl-, I-) from which the gas-phase species are derived. For gas-phase measurements, we will three different observational techniques (CIMS, LP-DOAS, TILDAS) allowing for comparison of the measurements of some key reactive halogens while also expanding the suite of measured halogen species. Since heterogeneous reactions on sea salt aerosol (SSA) and the ocean surface are the largest source of tropospheric reactive halogens, a tropical island is an ideal location. Additionally, Bermuda experiences a seasonality in wind direction due to the summertime presence of the Bermuda high-pressure system, resulting in transport of pollution from North America in winter and clean, marine conditions during summer, allowing us to test our previous model results suggesting that anthropogenic activity increases tropospheric reactive halogen abundances, with implications for the oxidizing capacity of the atmosphere. Model simulations using the GEOS-Chem global chemical transport model will be integrated into the research plan, and the model's chemical mechanism will be further developed as part of this project. The proposed field campaign will provide currently missing observational constraints for the model, allowing for model assessment and improvement of the model's chemical mechanism for reactive halogen chemistry. The model will also be used to help interpret the observations, which will be accomplished through model sensitivity simulations coupled with comparison of the observations with the model. Measurements proposed here will provide a quantitative observational constraint for the dependence of reactive halogen abundances on pollution levels, as well as allow us to assess the model's representation of the abundance and speciation of reactive halogens at a tropical, marine location and their interactions with one another.