An Airborne Time of Flight Aerosol Mass Spectrometer

众所周知，大气中含有大量的颗粒物。这些数字从每立方厘米污染空气中几万个颗粒物到更偏远地区的数百个颗粒物不等。除了已知会影响人类健康外，它们还对地球气候有很大的控制作用，因为它们可以散射和吸收太阳辐射。它们还被认为通过决定云的属性以及它们的微物理和光学属性来间接影响气候。然而，支配大气中气溶胶大部分生命周期的许多过程和性质在数量上仍然不确定，在某些情况下是未知的，必须解决这一问题，以改进对气溶胶效应的预测。这是通过实验室和实地测量方案以及模型开发来实现的，后者需要实地测量来检验其有效性。我们缺乏了解和缺乏可用的模型数据的部分原因是难以在各种环境中准确测量颗粒的大小和组成。有机部分尤其如此，它通常由不同化学物种的高度复杂的混合物组成。目前的模型往往在很大程度上低估了有机物的数量，特别是在高层大气中，那里的测量数据很少。传统上，测量颗粒组成的方法是离线的，因此需要大量的时间来收集样本。这不适用于需要在几分钟或更短的时间内进行测量的飞机工作。英国航空大气测量设施目前在其许多活动中使用Aerodyne气溶胶质谱仪(AMS)来实时测量颗粒组成和大小。虽然该仪器已被证明在研究污染环境中的气溶胶成分方面非常有用，但它缺乏能够研究背景颗粒的灵敏度，特别是在对流层内较高高度或在研究污染羽流和云系等快速变化的环境中的气溶胶成分时。我们建议进一步开发这一仪器，使用经过地面验证的技术，使我们能够探测气溶胶生命周期中的不确定领域，如自由对流层内的有机气溶胶；发射后大气中气溶胶的演变以及气溶胶-云相互作用的更详细程度。然后，我们将在一系列演示实验中展示它的能力和多功能性，这些实验集中在当前科学上不确定的两个领域：自由对流层内许多高度的气溶胶的组成，特别是它们的有机含量，以及污染羽流排放后不久大气中气溶胶的演变。该仪器还能够探测作为云滴形成地点的粒子的化学性质。我们将使用FAAM上已经安装的尺寸选择进气口来采样云滴，从而展示其有效性。这些实验将展示新仪器的威力，同样重要的是，将突出新仪器如何在未来探测大气中的气溶胶过程。

The atmosphere is known to contain large amounts of particulate matter. Numbers can range from several tens of thousands of particles per cubic centimetre of polluted air to mere hundreds in more remote locations. As well as being known to affect human health, they have a significant control on the earth's climate, as they can scatter and absorb solar radiation. They are also thought to indirectly affect climate by dictating the properties of clouds and hence their microphysical and optical properties. However, many of the processes and properties that govern large parts of the lifecycle of aerosols in the atmosphere remain quantitatively uncertain, or in some cases unknown, and this must be addressed to improve predictions of aerosol effects. This is being achieved through laboratory and field measurement programmes and model development, the latter requiring field measurements to test their validity. Part of our lack of understanding and the lack of available model data is due to difficulties in accurately measuring the size and composition of particles in a variety of environments. This is particularly true of the organic fraction, which normally consists of a highly complex mixture of different chemical species. Current models tend to under-predict the amounts of organics in by a large factor, especially in the upper atmosphere, where measurements are scarce. Traditionally methods for measuring particle compositions are offline and so need significant time for sample collection. This is unsuitable for aircraft work, where measurements taken over the course of minutes or less are desired. The UK Facility for Airborne Atmospheric Measurements currently uses an Aerodyne Aerosol Mass Spectrometer (AMS) on many of its activities to measure particle compositions and sizes in real time. While this instrument has proved highly useful in studying aerosol compositions in polluted environments, it lacks the sensitivity to be able to study background particles, especially at higher altitudes within the troposphere or when studying aerosol composition in rapidly changing environments such as pollution plumes and cloud systems. We are proposing to develop this instrument further, using technology proven on the ground, to allow us to probe areas of uncertainty in the aerosol lifecycle such as organic aerosols within the free troposphere; the evolution of aerosols within the atmosphere after emission and aerosol-cloud interaction in greater detail than was possible previously. We will then show its capability and versatility in a series of demonstration experiments that focus on two areas of current scientific uncertainty: the composition of aerosols at many altitudes within the free troposphere, especially their organic content, and the evolution of aerosols within the atmosphere shortly after emission in pollution plumes. The instrument is also capable of probing the chemical nature of the particles that act as sites for cloud droplet formation. We will show its effectiveness at doing this using a size selecting inlet already installed on the FAAM to sample cloud droplets. These experiments will demonstrate the power of the new instrument and, as importantly, will highlight how the new instrument can probe aerosol processes in the atmosphere in the future.