Isotopic signature of nitrate in the remote troposphere

遥远对流层中硝酸盐的同位素特征

• 批准号: NE/F000987/1
• 负责人: Jan Kaiser
• 金额: $ 15.47万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF000987%2F1
• 关键词: Isotopic; signature; nitrate; remote; troposphere

Atmospheric nitric acid (HNO3) is mostly known for its contribution to acid rain and the associated negative effects on plants, soils and buildings. HNO3 is the end-product of atmospheric nitrogen oxidation, but relatively stable itself. Therefore, it is only lost by wet or dry deposition (precipitation or direct transfer to the Earth's surface). HNO3 gas can be converted to or adsorbed onto particles (aerosol) before deposition, which often involves splitting HNO3 into H+ and nitrate ions. Here, we only consider the sum of nitrate species, i.e., gaseous and particulate HNO3 plus particulate nitrate. The precursors to atmospheric nitrate are nitrogen oxides (NOx = NO + NO2). NOx levels are rising on a global scale, due to fossil fuel combustion, biomass burning and aircraft emissions. Higher NOx levels lead to increased nitrate deposition. Even though nitrate is an important plant nutrient, too much of it can cause algal blooms in rivers, lakes and coastal areas. Atmospheric nitrate deposition also contributes to ground water pollution by nitrate fertilisers, which can lead to toxic levels of nitrate in drinking water (causing, e.g., 'blue baby syndrome'). To understand the impacts of human perturbations of the nitrogen cycle, it is important to establish the rate of natural NOx production from soils and lightning. Unfortunately, there is nothing to distinguish natural and anthropogenic NOx sources chemically. However, the stable isotope composition of trace gases and aerosols can provide unique information on their origin and fate in chemical and biological processes. Isotopes are different species of the same element, which react in the same way chemically, but at slightly different speeds. In addition, changes in the 'isotopic signature' of a compound help tracing its way in nature. One of the goals of the present study is to establish the isotopic signature of nitrate dominated by natural NOx sources. We therefore chose to analyse a set of aerosol samples from ships across the North and South Atlantic. The contribution of anthropogenic NOx is large in the Northern hemisphere, but the isotopic composition of aerosol in the remote South Atlantic should reveal the signature of natural NOx. Also, NOx production in the tropical Atlantic is dominated by lightning. There are different pathways of HNO3 formation in the atmosphere, and whereas the source of NOx is encoded in the nitrogen isotopes of nitrate, the relative importance of these pathways (albeit not the absolute magnitudes) can be studied using the oxygen isotopes. NOx inherits an isotopic anomaly from ozone. Depending on the pathways of HNO3 formation, this anomaly is expressed to various degrees in ozone. Different pathways dominate during day and night and we hope to find evidence of their relative contributions in diurnal studies at a polluted coastal site in North Norfolk. We also hypothesise that the isotopic signature of nitrate will help us distinguish between different explanations for the diurnal cycle of nitrate concentrations. Prior to the measurements outlined above, we have to build a suitable method for isotopic analysis of atmospheric nitrate. For these analyses, a specific kind of mass spectrometer is used that can only take gaseous samples. We therefore have to convert nitrate into a gas. The direct conversion to the elements is difficult. Instead we plan to use a bacterial strain that can convert nitrate to laughing gas (N2O). It does this much more efficiently than any chemical method. JK has learnt to use this method in the lab at Princeton University (USA) that is renowned for first adapting it to environmental samples. JK has further developed it to analyse the oxygen isotope anomaly of nitrate. He plans to use this method at a later stage for direct studies of nitrate formation reactions and, possibly, nitrate in old snow samples and polar ice cores, as a constraint on pre-industrial and glacial atmospheric chemistry.

大气中的硝酸（HNO3）以对酸雨的贡献以及对植物，土壤和建筑物的相关负面影响而闻名。 HNO3是大气氮氧化的最终产物，但本身相对稳定。因此，仅由于湿或干沉积（降水或直接转移到地球表面）而丢失。沉积前可以将HNO3气体转换为或吸附到颗粒（气溶胶）上，这通常涉及将HNO3拆分为H+和硝酸盐离子。在这里，我们仅考虑硝酸盐物种的总和，即气体和颗粒HNO3和颗粒硝酸盐。大气硝酸盐的前体是氮氧化物（NOX = NO + NO2）。由于化石燃料燃烧，生物质燃烧和飞机排放，NOX水平在全球范围内上升。较高的NOX水平导致硝酸盐沉积增加。尽管硝酸盐是一种重要的植物营养素，但过多的硝酸盐可能会在河流，湖泊和沿海地区引起藻类开花。大气硝酸盐沉积也有助于硝酸盐肥料的地下水污染，这可能导致饮用水中硝酸盐的毒性水平（例如，例如“蓝色婴儿综合征”）。要了解氮循环人类扰动的影响，重要的是要确定土壤和闪电的天然NOx产生速率。不幸的是，没有什么可以从化学上区分天然和人为的NOX来源。但是，痕量气体和气溶胶的稳定同位素组成可以提供有关其起源和化学和生物过程中命运的独特信息。同位素是同一元素的不同种类，它以化学的方式反应，但速度略有不同。此外，化合物的“同位素签名”的变化有助于追踪其自然界。本研究的目标之一是建立以天然NOX来源为主的硝酸盐的同位素特征。因此，我们选择分析来自北大西洋和南大西洋船只的一组气溶胶样品。北半球人为NOx的贡献很大，但是偏远南大西洋气溶胶的同位素组成应揭示天然NOX的特征。同样，热带大西洋中的NOX产生由闪电主导。在大气中，HNO3形成的途径不同，而NOX的来源是在硝酸盐的氮同位素中编码的，而这些途径的相对重要性（尽管不是绝对大小）可以使用氧同位素研究。 NOX从臭氧继承了同位素异常。根据HNO3形成的途径，该异常在臭氧中以各种程度表示。在白天和黑夜中，不同的途径占主导地位，我们希望在北诺福克的一个受污染的沿海地点找到其在昼夜研究中的相对贡献的证据。我们还假设，硝酸盐的同位素特征将有助于我们区分硝酸盐浓度的昼夜周期的不同解释。在上面概述的测量之前，我们必须构建一种合适的大气硝酸盐同位素分析方法。对于这些分析，使用一种特定的质谱仪，只能采用气态样品。因此，我们必须将硝酸盐转化为气体。直接转换为元素很困难。取而代之的是，我们计划使用可以将硝酸盐转化为笑气（N2O）的细菌菌株。它比任何化学方法更有效地做到这一点。 JK学会了在普林斯顿大学（美国）的实验室中使用这种方法，该方法首先将其改编为环境样本。 JK进一步开发了它来分析硝酸盐的氧同位素异常。他计划在以后的阶段使用这种方法，以直接研究硝酸盐形成反应，并可能在旧的雪样和极地冰核中使用硝酸盐，以限制对工业前和冰川大气化学的限制。

项目成果

Nitrate postdeposition processes in Svalbard surface snow

• DOI: 10.1002/2013jd021234
• 发表时间: 2014-11
• 期刊: Journal of Geophysical Research: Atmospheres
• 作者: M. Björkman;C. Vega;R. Kühnel;F. Spataro;A. Ianniello;G. Esposito;J. Kaiser;A. Marca;A. Hodson;E. Isaksson;T. Roberts

Diurnal variations in the nitrogen and oxygen isotope composition of aerosol nitrate at a rural site

农村地区硝酸盐气溶胶氮氧同位素组成的日变化

• 发表时间: 2009
• 作者: Kaiser J

A 60 yr record of atmospheric carbon monoxide reconstructed from Greenland firn air

• DOI: 10.5194/acp-13-7567-2013
• 发表时间: 2013-01-01
• 期刊: ATMOSPHERIC CHEMISTRY AND PHYSICS
• 影响因子: 6.3
• 作者: Petrenko, V. V.;Martinerie, P.;White, J. W. C.
• 通讯作者: White, J. W. C.