Accurate and Direct Measurements of Brown Carbon Aerosol Optical Properties During Formation and Atmospherically-Relevant Ageing Processes

准确、直接测量地层和大气相关老化过程中棕碳气溶胶的光学特性

• 批准号: NE/S014314/2
• 负责人: Michael Cotterell
• 金额: $ 17.63万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS014314%2F2
• 关键词: Accurate; Direct; Measurements; Brown; Carbon

Aerosols are liquid or solid particles suspended in a gas and are pervasive in our atmosphere, with sources including anthropogenic emissions from burning of fossil fuels, and natural sources including from sea spray, desert dust and wildfire biomass burning. These aerosols have significant impacts on our atmosphere, affecting human health through, for example, smog events and global climate through interacting with Sun light and cloud droplets. Indeed, aerosols represent one of the largest uncertainties in predicting future climate change. The net aerosol cooling effect, provided by aerosol scattering sunlight back to space, partially offsets the warming impact of greenhouse gases. However, large uncertainties in this aerosol-light interaction degrade the confidence we have in models of future climate. Improvements to our understanding of aerosol-light interactions could lead to more effective risk mitigation strategies in managing climate change impacts.The important parameters to measure for constraining estimates of aerosol-light interactions are the magnitudes of light scattering and absorption by aerosol. In particular, light absorption is studied poorly for carbonaceous aerosol, with the optical properties of a class of aerosol called brown carbon aerosol (BrC) understood very poorly. BrC particles are formed readily in biomass burning regions where gaseous organic molecules emitted during burning rapidly condense onto liquid or solid particles, with these organic molecules reacting on particle surfaces or inside liquid particles to form light absorbing chromophores. The subsequent BrC particles possess strong wavelength-dependent absorption spectra, with stronger absorption at shorter (blue) optical wavelengths compared to longer (red) wavelengths giving a brown appearance. Also, atmospheric BrC consists of a variety of molecular species with differing light absorption spectra, while the compositions of these chromophores evolve significantly with atmospheric ageing. The uncertainties in BrC optical properties, and how they evolve with time and atmospheric processing, are understood so poorly that many climate models - including UK Met Office climate models - are devoid of any BrC representation. Thus, it is of paramount importance that our understanding of BrC optical properties is improved for better BrC representations in climate models.Traditional measurement approaches have shortcomings in measuring BrC optical properties accurately due to the relatively weak absorption by BrC. Moreover, common laboratory techniques for probing aerosol properties do not access the long ageing timescales of >50 hours that often pertain to atmospheric BrC. This work uses new state-of-the-art instruments available only in the UK to provide measurements of both light scattering and absorption by weakly absorbing aerosol with unrivalled accuracy, precision and sensitivity. Such tools include Single Particle Cavity Ring-Down Spectroscopy (SP-CRDS) and photoacoustic spectroscopy, with single particle trapping techniques such as SP-CRDS allowing measurements of aerosol optical properties on unlimited ageing timescales while particles are subjected to controlled ambient conditions. BrC optical properties will be measured during the BrC formation process and for subsequent ageing and atmospheric processing, such as changes in humidity, exposure to ultraviolet light and reaction with ozone. Furthermore, the proposal addresses both of the common BrC formation pathways, from reaction of gas precursors in aqueous droplets or from the heterogeneous reactions of gas precursors directly on particle surfaces. These results will be used to assess the sensitivity of aerosol-radiation models used at the UK Met Office to measured variations in BrC optical properties and to develop parameterisations of the ageing of BrC optical properties for comparison to recent field studies and future implementation in the next generation of climate models.

气溶胶是悬浮在气体中的液体或固体颗粒，在我们的大气中普遍存在，包括燃烧化石燃料的人为排放，以及包括海上喷雾，沙漠灰尘和野火生物量燃烧的天然来源。这些气雾剂对我们的大气产生了重大影响，通过与阳光和云滴相互作用，通过例如烟雾事件和全球气候影响人类健康。实际上，气溶胶是预测未来气候变化的最大不确定性之一。净气溶胶冷却效果由气溶胶散射回到太空提供，部分抵消了温室气体的变暖影响。但是，在这种气溶胶相互作用中，大的不确定性降低了我们对未来气候模型的信心。改善我们对气雾光相互作用的理解可能会导致更有效的降低风险策略来管理气候变化影响。衡量衡量气溶胶相互作用估计值的重要参数是光散射和气溶胶吸收的幅度。特别是，对于碳质气溶胶的光吸收率很差，一类称为棕色碳气溶胶（BRC）的气溶胶的光学性质非常差。 BRC颗粒在生物质燃烧区域中很容易形成，在燃烧过程中发出的气态有机分子将迅速凝结到液体或固体颗粒上，这些有机分子在颗粒表面或内部液体颗粒上反应以形成光吸收的光团。随后的BRC颗粒具有较强的波长依赖性吸收光谱，与更长的（红色）波长相比，在较短（蓝色）光波长下的吸收更强。此外，大气BRC由各种具有不同光吸收光谱的分子物种组成，而这些发色团的组成随着大气衰老而显着发展。 BRC光学特性的不确定性以及它们如何随时间和大气加工而演变的方式得多，以至于许多气候模型（包括英国大都会办公室气候模型）都没有任何BRC代表。因此，至关重要的是，在气候模型中，我们对BRC光学特性的理解得到改善。传统测量方法由于BRC的相对较弱的吸收而准确地测量BRC光学性能存在缺陷。此外，用于探测气溶胶特性的常见实验室技术无法访问较长的衰老时间尺度> 50小时，通常与大气中的BRC有关。这项工作使用仅在英国可用的新最先进的仪器来通过以无与伦比的精度，精度和敏感性来弱吸收气溶胶来提供光散射和吸收。这样的工具包括单个颗粒腔圆环光谱（SP-CRD）和光声光谱，其单个粒子捕获技术（例如SP-CRD）允许在无限的老化时间表上测量气溶胶光学性能，而粒子则受到控制的环境条件的约束。将在BRC形成过程中测量BRC光学特性，以及随后的衰老和大气加工，例如湿度的变化，暴露于紫外线的光和与臭氧反应。此外，该提案从水滴中的气体前体的反应或直接在颗粒表面上的气体前体的异质反应中解决了这两种常见的BRC形成途径。这些结果将用于评估英国Met Office使用的气溶胶放射模型的敏感性，以测量BRC光学性质的变化，并开发BRC光学性质衰老的参数化，以与最近的现场研究和下一代气候模型中的未来实施进行比较。