An airborne dual ionisation Chemical Ionisation Mass Spectrometer

机载双电离化学电离质谱仪

• 批准号: NE/E018505/1
• 负责人: Carl Percival
• 金额: $ 11.37万
• 依托单位: NERC CEH (Up to 30.11.2019)
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE018505%2F1
• 关键词: airborne; dual; ionisation; Chemical; Ionisation

Ammonia (NH3) and nitric acid (HNO3) are important components of the atmospheric nitrogen burden on regional scales and are major contributors to the nitrogen budget across the UK and western continental Europe. The gases are semi-volatile and can readily partition to aerosol particles as ammonium nitrate (NH4NO3), changing their pathways through the atmosphere. Deposited atmospheric nitrogen can change the nutrient balance of an ecosystem and has been shown to make an important contribution to excess nitrogen in aquatic and marine environments around the UK. NH3 is primarily emitted from agricultural sources and, since the introduction of catalytic converters, increasingly from urban environments. However, NH3 is efficiently lost to the semi-natural vegetation, typical of many natural upland ecosystems important in the UK. HNO3 is produced primarily by photooxidation of nitrogen oxides, which are emitted from combustion sources, mainly motor vehicles. Its production depends on photochemistry and is highest in the plumes of large urban areas. As sulphur declines across western Europe, regions of excess ammonia are becoming more widespread and ammonium nitrate aerosol is becoming a significant component for atmospheric nitrogen. Unlike, NH3 and HNO3, NH4NO3 has a low deposition velocity and is predominately removed by precipitation, hence the nitrogen footprint of a source region changes substantially depending on its phase. As these pathways become more important, so NH4NO3 becomes a significant contributor to regional climate as well as air quality. However, as NH4NO3 is relatively volatile, its concentration is dependent on the associated gaseous NH3 and HNO3 concentrations and evaporation can readily take place in the boundary layer. Furthermore, the particulate and gaseous species have very different surface loss rates. These complexities have made it difficult to obtain an accurate picture of the nitrogen burden. A major part of the problem is the lack of measurement capability. Whilst new instruments for NH3 and HNO3 exist within the UK and have been applied to the problem at the land surface, they cannot be used on mobile platforms, especially aircraft. This is necessary to study the important problem of larger scale transformations and spatial variability and link to models. This proposal hopes to deliver such capability to the UK community by using Chemical Ionisation Mass Spectrometric methods (CIMS). The CIMS technique generates ions of known gases, which are reacted with the atmospheric gas of interest in the inlet to a mass spectrometer where the known reactant ions are sampled. The choice of reactant ions is crucial as this determines the selectivity and sensitivity of the instrument to the sample gas. NH3 and HNO3 have both been measured by CIMS in the past with high sensitivity and selectivity using technological advances made in the USA over the last few years but the ion reaction schemes necessary for their detection are different for the two gases so the instrument has only been capable of measuring one or the other gas at any one time. We intend to purchase such an instrument and develop it by incorporating both ion reaction schemes together and rapidly switch between them providing data on both HNO3 and NH3 at the same time. We will test it in the laboratory, demonstrate its capabilities in a comparison exercise with several other instruments, and perform a surface based study using a mobile laboratory to probe surface heterogeneities in NH3, HNO3, and NH4NO3 fields. The instrument will be installed in the UK FAAM aircraft and then used together with particle measurements to probe the system on a regional scale around the UK in order to tackle the very important, but poorly understood problem of nitrogen transformation, transport and deposition.

氨（NH3）和硝酸（HNO3）是区域尺度上大气氮负担的重要组成部分，并且是英国和欧洲西部欧洲西部氮预算的主要贡献者。这些气体是半挥发性的，可以轻松地将其作为硝酸铵（NH4NO3）划分为气溶胶颗粒，从而改变了通过大气的途径。沉积的大气氮可以改变生态系统的养分平衡，并已被证明对英国水生和海洋环境中的过量氮做出了重要贡献。 NH3主要是从农业来源发出的，自从引入催化转化器以来，越来越多地从城市环境中。但是，NH3有效地损失了半自然的植被，这是英国许多天然高地生态系统的典型代表。 HNO3主要是由氮氧化物的光氧化产生的，氮氧化物是由燃烧源（主要是机动车辆）发出的。它的生产取决于光化学，在大型城市地区的羽毛中最高。随着西欧硫的下降，过量氨的区域变得越来越普遍，硝酸铵气溶胶正在成为大气氮的重要组成部分。与NH3和HNO3不同，NH4NO3的沉积速度较低，主要通过降水量去除，因此，源区域的氮足迹大大变化，这取决于其相。随着这些途径变得越来越重要，因此NH4NO3成为区域气候和空气质量的重要贡献。但是，由于NH4NO3相对挥发性，因此其浓度取决于相关的气态NH3和HNO3浓度，并且蒸发很容易在边界层发生。此外，颗粒物和气态物种具有非常不同的表面损失率。这些复杂性使得很难获得氮负担的准确图片。问题的主要部分是缺乏测量能力。虽然英国境内存在NH3和HNO3的新仪器，并已应用于陆地表面的问题，但它们不能在移动平台上，尤其是飞机上使用。这对于研究大规模转换和空间变异性以及与模型的链接的重要问题是必不可少的。该建议希望通过使用化学电离质谱法（CIMS）为英国社区提供这种能力。 CIMS技术会产生已知气体的离子，这些气体与对入口的大气气体反应到对已知反应物离子进行采样的质谱仪的反应。反应物离子的选择至关重要，因为这决定了仪器对样品气体的选择性和敏感性。在过去的几年中，使用美国在美国取得的技术进步，CIMs在过去曾通过CIMS测量NH3和HNO3，但其检测到的离子反应方案是两种气体的不同之处，因此只有两种仪器仅是该仪器能够一次测量一种或另一种气体。我们打算购买这样的仪器并通过将两个离子反应方案合并在一起，并在它们之间迅速切换，并同时提供HNO3和NH3的数据。我们将在实验室中对其进行测试，证明其在与其他几种仪器的比较练习中的能力，并使用移动实验室进行基于表面的研究，以探测NH3，HNO3和NH4NO3领域的表面异质性。该仪器将安装在英国FAAM飞机中，然后与粒子测量一起使用，以在英国各地的区域尺度上探测该系统，以解决氮转化，运输和沉积的非常重要但知之甚少的问题。