Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) for aircraft and ground-based applications

挥发性有机化合物(VOCs)是一种痕量气体，在许多大气和生物地球化学过程中发挥着重要作用。它们是空气污染的主要组成部分，由运输、工业加工、生物质燃烧、溶剂使用等自然和人为来源直接排放到大气中，也是大气中化学反应形成的副产品。挥发性有机化合物有助于低层大气中臭氧和颗粒物的形成。臭氧是一种呼吸刺激物，是一种温室气体，会降低作物产量，导致重大经济损失。细颗粒物，如PM2.5(直径小于2.5微米的颗粒)，与许多人类健康疾病(如哮喘、心脏病)有关，并影响地球表面的辐射平衡(与气候有关)。挥发性有机化合物在决定大气氧化能力(地球清除大气污染物的能力)方面也起着关键作用，而且越来越明显的是，挥发性有机化合物对室内空气污染的贡献越来越大。在极地地区，挥发性有机化合物的生物和光化学产生发生在冰雪界面和表层海洋中。然而，北极大气中VOC形成的生物地球化学循环仍然描述得很少，对北极海冰下降的反馈反应尚不清楚。随着我们对大气过程的了解加深和计算机模型变得更加复杂，在分析灵敏度(测量较小的量)、化学形态(识别和测量更大范围的化合物)和速度(更快的响应时间，使我们能够研究，例如，在移动的飞机上或测量快速通量)方面，需要更好的测量。这将有助于我们理解控制这些往往复杂的大气相互作用的基本原理。对于挥发性有机化合物的测量，飞行质谱仪的质子转移反应时间(PTR-ToF-MS)将在这方面发挥巨大的作用，并将部署在广泛的测量平台(飞机、实验室/室内研究、天文台)和专题研究领域(全球大气组成、室内/室外空气质量、力学研究、通量)。目前用于FAAM飞机的PTR-QMS是17年前购买的。它基于一个四极检测系统，这限制了强大的PTR技术的能力。这些缺陷包括低质量分辨率(无法分解相同质量的化合物)，需要预先选择有限数量的化合物(通常为~10)，低灵敏度，特别是在较高质量时(&gt；100 Da)。因此，我们建议用最先进的PTR-TOF仪器取代目前的PTRMS，这将有助于FAAM飞机保持在全球大气研究的前沿。PTR-TOF的优点包括：(1)测量的化合物数量大幅增加(ToF记录了大质量范围内的所有质量，而四极杆只记录了少量预先选择的化合物)；(2)改进了质量范围(1-1000Da)而不损失质量&gt；100Da；(3)提高了灵敏度(检测下限)；(4)更高的质量分辨率(例如，四极杆无法区分重要的生物来源化合物异戊二烯(质量68.117)和生物质燃烧的产物呋喃(质量68.075)；(5)更快的扫描；(6)选择性试剂电离(使用不同的离子源试剂可以提高仪器的专属性，例如醛和酮的分离)。在独特的RVG-Air-Sea-Ice小室中部署PTR-TOF-MS将使我们能够在受控环境中研究VOC的产生过程，增强我们对海冰地区VOC循环的关键参数的了解。除了RVG-ASIC，PTR-TOF-MS将为极地海洋的实地活动开辟新的途径，例如，航运活动增加对北极空气质量的影响。

Volatile organic compounds (VOCs) are trace gases that play an important role in many atmospheric and biogeochemical processes. They are a major component of air pollution, being emitted directly to the atmosphere by natural and anthropogenic sources, e.g. transport, industrial processes, biomass burning, solvent use, etc., and also formed as secondary products by chemical reactions in the atmosphere. VOCs contribute to the formation of ozone and particulate matter in the lower atmosphere. Ozone is a respiratory irritant, a greenhouse gas and can decrease crop yields, leading to substantial economic losses. Fine particulate matter, such as PM2.5 (particles less than 2.5 um in diameter), is linked to numerous human health conditions (e.g. asthma, heart disease) and affects the radiation balance at the Earth's surface (links to climate). VOCs also play a key role in determining the oxidising capacity of the atmosphere (the Earth's ability to cleanse pollutants from the atmosphere), and it is becoming increasingly apparent that VOCs contribute significantly to indoor air pollution. In polar regions, biological and photochemical production of VOCs occurs at the snow-ice interface and in the surface ocean. However, the biogeochemical cycles of VOC formation in Arctic atmosphere remain poorly described, with unknown feedback responses to Arctic sea ice decline. As our understanding of atmospheric processes increases and computer models become more sophisticated, there is a requirement for ever-better measurements, in terms of analytical sensitivity (measuring smaller amounts), chemical speciation (identifying and measuring a larger range of compounds) and speed (faster response times to enable us to study, e.g., from a moving aircraft or to measure fast fluxes). This will help us to understand the fundamentals which are controlling these often-complex atmospheric interactions. For VOC measurements the Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS) will be of great benefit in this respect and will be deployable across a broad range of measurement platforms (aircraft, lab/chamber studies, observatories) and topical research areas (global atmospheric composition, indoor/outdoor air quality, mechanistic studies, fluxes).The PTR-QMS currently used on the FAAM aircraft was bought 17 years ago. It is based on a quadrupole detection system which limits the capability of the powerful PTR technique. These deficiencies include low mass resolution (inability to resolve compounds of equal mass), the necessity to pre-select a limited number of compounds (typically ~10), low sensitivity, particularly at higher masses (>100 Da). We therefore propose to replace the current PTRMS with a state-of-the-art PTR-ToF instrument which will help keep the FAAM aircraft at the cutting edge of global atmospheric research. Advantages of the PTR-ToF include: (1) Large increase in the number of compounds measured (ToF records all masses over a wide mass range, whereas the quadrupole only records a small number of pre-selected compounds); (2) Improved mass range (1-1000 Da) without loss of sensitivity at masses >100 Da; (3) Improved sensitivity (lower limit of detection); (4) Higher mass resolution (e.g. quadrupole cannot distinguish between isoprene (mass 68.117), an important biogenic compound, and furan (mass 68.075), a product of biomass burning; (5) Faster scanning; (6) Selective reagent ionisation (the use of different ion source reagents allows for improved specificity of the instrument, e.g. separation of aldehydes and ketones).The deployment of the PTR-ToF-MS in the unique RVG-Air-Sea-Ice chamber will allow the study of VOC production processes in a controlled environment, enhancing our understanding of the key parameters of VOC cycles in sea ice areas. Beyond the RvG-ASIC, the PTR-ToF-MS will open new avenues for field campaigns in polar seas, e.g. the impact of increasing shipping activity on air quality in the Arctic.