Impacts of Photoinitiated Chemical Processing on Climate Relevant Aerosol Properties

阳光和大气气溶胶一直存在于我们的环境中。气溶胶(空气中的颗粒或水滴)会影响空气质量和气候。空气污染每年给英国造成150亿英镑的人类健康损失。世界卫生组织估计，全球近12%的死亡是由室内和室外空气污染造成的。气溶胶是我们理解气候的最大不确定性。气雾剂通过散射或吸收阳光与阳光相互作用，这会降低能见度(例如烟雾)或创造美丽的日落。然而，我们还没有研究阳光如何引发气溶胶中的化学作用并改变颗粒的性质。最近的实验表明，光引发的化学可能是一种常见的现象。然而，光引发的化学对一系列与气候和空气质量有关的气溶胶性质的影响尚不清楚。这些反应可能会改变组成气溶胶粒子的分子的身份，并可能改变其基本性质，包括其大小和散射或吸收光的能力。此外，这种化学可能会产生分配到气相中的分子，然后经过进一步的化学作用形成新的粒子。这项工作将研究光引发的化学对一系列与气候(它们散射或吸收阳光的程度)和空气质量(成分和大小)有关的气溶胶性质的作用。这项工作将使用单粒子测量和光化学气溶胶反应器的新组合来完成。在单粒子研究中，使用光学陷阱捕获气溶胶粒子，用选定波长的光照射，并监测粒子性质的变化。具体地说，将确定对颗粒的大小、折射率、吸湿性和物相的影响。折射率确定粒子散射和吸收光的能力。吸湿性决定了颗粒的大小如何随相对湿度变化，这最终也会影响折射率。阶段描述粒子是固体、液体还是介于两者之间，这可能会影响粒子对其环境的响应方式。此外，特定光诱导反应的产率将在不同的波长和颗粒大小下确定。进一步的实验将检验颗粒的表面成分如何影响化学。光化学气溶胶反应器实验将允许测试模拟，将单个粒子的测量结果缩放到整体测量，并允许精确地阐明实验中操作的分子路径。这些实验的结果将提供系统的理解，了解光如何与气溶胶相互作用产生化学作用，以及这种化学最终如何影响气候和空气质量相关的粒子特性。这种系统的理解将使预测光诱导化学对气候和空气质量的重要性成为可能。然后，我们计划通过将新分解的化学物质纳入气溶胶化学模型来评估其中的一些影响。

Sunlight and atmospheric aerosols are ever-present in our environment. Aerosols (airborne particles or droplets) can impact air quality and climate. Air pollution costs the UK £15 billion/year in damage to human health. The World Health Organization estimates nearly 12% of all deaths worldwide are due to indoor and outdoor air pollution. Aerosols are the largest uncertainty in our understanding of climate. Aerosols interact with sunlight by scattering or absorbing it, which can reduce visibility (e.g. smog) or create a beautiful sunset. However, we have not studied how sunlight can initiate chemistry in aerosols and change the properties of the particles. Recent experiments indicate that light-initiated chemistry may be a common occurrence. However, the impacts of light-initiated chemistry on a range of aerosol properties relevant to climate and air quality are not understood. These reactions may change the identities of the molecules that make up an aerosol particle and may alter fundamental properties including its size and ability to scatter or absorb light. Moreover, this chemistry may produce molecules that partition into the gas phase and can then undergo further chemistry to form new particles.This work will investigate the role of light-initiated chemistry on a range of aerosol properties that are relevant to climate (how much they scatter or absorb sunlight) and to air quality (composition and size). This work will be accomplished using a novel combination of single particle measurements and a photochemical aerosol reactor. In single particle studies, an aerosol particle is captured using an optical trap, irradiated with light of a chosen wavelength, and monitored for changes to the particle's properties. Specifically, the impacts on the size, refractive index, hygroscopic properties, and phase of the particle will be determined. Refractive index determines the ability of the particle to scatter and absorb light. Hygroscopicity determines how a particle's size changes with relative humidity, which also ultimately impacts on refractive index. Phase describes whether the particle is a solid, liquid, or between the two, which can affect how the particle responds to its environment. Additionally, the yield of specific light-induced reactions will be determined at different wavelengths and particle sizes. Further experiments will examine how the surface composition of the particle may impact the chemistry. The photochemical aerosol reactor experiments will allow testing of simulations that scale the single particle measurements to ensemble measurements as well as allow precise elucidation of the molecular pathways operative in the experiments.The results of these experiments will provide a systematic understanding of how light can interact with aerosols to induce chemistry and how that chemistry ultimately impacts climate and air quality relevant particle properties. This systematic understanding will enable predictions of the significance of light induced chemistry on climate and air quality. We then plan to assess some of these impacts by incorporating the newly resolved chemistry into an aerosol chemistry model.