Collaborative Research: The impact of bromine chemistry on the isotopic composition of nitrate at Summit, Greenland

合作研究：格陵兰峰会上溴化学对硝酸盐同位素组成的影响

• 批准号: 0909374
• 负责人: Meredith Hastings
• 金额: $ 33.16万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0909374&HistoricalAwards=false
• 关键词: Collaborative; Research; impact; bromine; chemistry

Nitrate is one of the major ions found in alpine and polar snow, yet it continues to be one of the least understood chemical components in ice core records. Recent work ahs shown nitrate isotope ratios to be a powerful tool for the study of nitrate in snow and ice cores. The isotopic composition of nitrate has been shown to contain information about the source of the nitrate (nitrogen oxides) and the oxidation processes that convert nitrogen oxides to nitrate in the atmosphere prior to deposition. Because hydroxyl and peroxy radicals have very different isotopic compositions than ozone, one can now distinguish the impact of the different oxidation processes that produce nitrate in the atmosphere. Seasonal observations of the oxygen isotopic composition of nitrate in snow at Summit, Greenland, cannot be understood in terms of standard, local photochemistry. The most likely causes of the model and observation discrepancy are that the box model lacks transport of nitrate from regions outside of Summit and the influence of halogen chemistry (i.e., BrO) on nitrate. Recent measurements suggest a higher than expected presence of BrO in the boundary layer above Summit. The aim of this project is to quantify the influence of bromine chemistry on nitrate production in the spring and summer. The approach includes field and laboratory measurements as well as modeling. During spring and summer field seasons, BrO and multiple gas-phase measurements will be conducted on-site, while isotopic analyses of snow and atmospheric samples will be completed in the laboratory. The oxygen isotopic composition of nitrate in snow and glacial ice holds potential for quantitatively reconstructing paleoatmospheric oxidant concentrations, but it is important to constrain how much this tracer reflects local versus regional or hemispheric scale chemistry. Furthermore, since BrO at Summit most likely originates from a natural source, and this source is affected by changes in climate, the influence of halogen chemistry on nitrogen oxides has important implications for the interpretation of recent and deep ice core records of nitrate.

硝酸盐是高山和极性降雪中发现的主要离子之一，但它仍然是冰核记录中最知名的化学成分之一。最近的工作AHS表明硝酸盐同位素比是降雪和冰芯研究硝酸盐的强大工具。硝酸盐的同位素组成已被证明包含有关硝酸盐来源（氮氧化物）的信息，以及在沉积之前将氮氧化物转化为硝酸盐的氧化过程。由于羟基和过氧自由基的同位素组成与臭氧具有非常不同的同位素组成，因此现在可以区分在大气中产生硝酸盐的不同氧化过程的影响。在格陵兰岛萨米特（Summit）雪地中硝酸盐的氧同位素组成的季节性观察不能用标准的局部光化学来理解。该模型和观察差异的最可能原因是，该框模型缺乏硝酸盐从山顶以外的地区运输，以及卤素化学（即BRO）对硝酸盐的影响。最近的测量表明，在山顶上方的边界层中，BRO的存在高于预期。该项目的目的是量化春季和夏季溴化学对硝酸盐生产的影响。该方法包括现场和实验室测量以及建模。在春季和夏季的季节中，将在现场进行BRO和多个气相测量，而实验室将完成对雪和大气样品的同位素分析。硝酸盐和冰川冰中硝酸盐的氧同位素组成具有定量重建paaotospheric氧化剂浓度的潜力，但重要的是要限制该示踪剂反映局部与区域或半球尺度化学的程度。此外，由于在山顶上的BRO最有可能起源于自然来源，并且该来源受到气候变化的影响，因此卤素化学对氮氧化物的影响对解释硝酸盐的最新和深层冰核心记录具有重要意义。