The chemistry of the formation of nitrogen-containing compounds in secondary organic aerosols and their impact on aerosol optical properties

二次有机气溶胶（SOA）中吸光有机化合物（也称为棕色碳（BrC）发色团）的形成可以改变大气细颗粒物（亚微米颗粒物）的光学性质。含氮化合物的反应羰基物种和胺化合物之间的二次反应亚胺途径，是最近的研究活动的主题，并在文献中得到越来越多的关注。与不完全燃烧过程的局部排放相反，二次BrC发色团可以在整个对流层形成，潜在地影响全球辐射收支和非均匀气溶胶化学。在初始项目中，模拟含水大气气溶胶颗粒的反应系统中BrC发色团的批量和分子水平分析的分析方法，5-二羰基化合物和硫酸铵或氨基酸甘氨酸的反应，已经建立并应用于生物气溶胶中含氮化合物的进一步研究。方法包括分光光度法和最新技术水平的色谱法和质谱法。在所研究的反应体系中，已经确定了几类具有pH依赖性产率的氮杂环，包括咪唑、吡咯、吡咯二聚体（二吡咯亚甲基）和（二氢）吡啶，表明含氮杂环是BrC发色团的常见结构基序。对空气过滤器样本的分析证实了在巴西、欧洲和印度收集的大气气溶胶中存在咪唑类。此外，不同的二羰基化合物和胺亲核试剂的混合物的实验表明，交叉反应可以增强本体吸收，并可以产生新的BrC发色团吸收在可见光区附近的波长。因此，有必要通过进一步的实验室实验研究交叉反应机理、动力学和产物以及影响因素，例如，溶液中二羰基化合物的相对比例、胺类物质和pH值。应确定促进异质自由基化学反应的光敏剂和大气棕色碳标记化合物的潜在候选物。所获得的工艺知识应能够使用动力学多层模型在大气条件下对BrC形成进行数值建模。最后，动力学模拟的结果应该能够定量估计的BrC形成的二次反应在水性aerosol particle.The新的见解，在这个项目中获得的将有助于提高我们的理解如何在水性aerosol particle. The化学影响气溶胶的光学特性和非均相化学。

The formation of light-absorbing organic compounds, also termed brown carbon (BrC) chromophores, in secondary organic aerosols (SOA) can alter the optical properties of atmospheric fine particulate matter (sub-micrometer particles). Nitrogen-containing compounds produced by secondary reactions between reactive carbonyl species and amine compounds following an imine pathway, are subject of recent research activities and receive increasing attention in the literature. In contrast to local emissions by incomplete combustion processes, secondary BrC chromophores can be formed throughout the Troposphere, potentially affecting the global radiation budget and heterogeneous aerosol chemistry.In the initial project, analytical methods for bulk and molecular level analysis of BrC chromophores in reaction systems mimicking aqueous atmospheric aerosol particles, containing 1,2-, 1,3-, 1,4-, or 1,5-dicarbonyls and ammonium sulfate or the amino acid glycine, have been established and applied, also in further studies on nitrogen containing compounds in biogenic aerosols. The methods include spectrophotometry and state of the art chromatography and mass spectrometry. Several classes of nitrogen heterocycles with pH dependent yields have been identified in the studied reaction systems, including imidazoles, pyrroles, pyrrole dimers (dipyrromethenes), and (dihydro-)pyridines, demonstrating that nitrogen containing heterocycles are common structural motifs of BrC chromophores. Analysis of air filter samples confirmed the presence of imidazoles in atmospheric aerosols collected in Brazil, Europe, and India. Furthermore, experiments with mixtures of different dicarbonyls and amine nucleophiles revealed that cross-reactions can enhance bulk absorption and can yield new BrC chromophores absorbing at wavelengths near the visible region. This highlights the need to identify potentially important absorbers produced by such cross-reactions in atmospherically relevant dicarbonyl mixtures.Therefore, further laboratory experiments are necessary investigating the cross-reaction mechanisms, kinetics, and products as well as influencing factors, e.g., relative ratios of dicarbonyls in solution, amine species, and pH. Potential candidates for photosensitizers promoting heterogeneous radical chemistry and for marker compounds of atmospheric brown carbon shall be identified. The acquired process knowledge shall enable numerical modeling of BrC formation under atmospheric conditions using a kinetic multilayer model. Finally, kinetic modeling results should enable quantitative estimations of BrC formation from secondary reactions in aqueous aerosol particles.The new insights gained during this project will help to improve our understanding of how chemistry in aqueous aerosol particles affects aerosol optical properties and heterogeneous chemistry.