RUI: Secondary Organic Aerosol Formation by Cloud Processing of Alpha-Dicarbonyl and Amine Compounds

最近的野外测量表明，有大量的、持续的、未确定的二次有机气溶胶（SOA）来源。由于α -二羰基化合物乙二醛和甲基乙二醛具有人为和生物前体，可被大气水滴和液体气溶胶颗粒有效吸收，且具有形成低聚物的潜力，因此它们作为潜在的SOA来源正受到越来越多的关注。最近的研究表明，水相α -二羰基反应活性的关键是脱水，然后是亲核攻击。亲核试剂甲胺和几种氨基酸已在大气中的云和雾水滴中被鉴定出微摩尔浓度，与α -二羰基化合物相似。这些亲核试剂在初步实验中被确定为乙二醛和甲基乙二醛的有效反应伙伴，在干燥后形成的产物不可逆地改变了反应物的气粒分配，即使在重新溶解时也是如此。本研究的目的是表征这些反应并确定其反应产物，测量现实条件下的反应动力学，从而确定这些反应在通过云和气溶胶处理形成SOA和低聚物中的大气意义。将用几种方法研究这些反应。首先，干燥单分散云滴的扫描迁移率粒度研究将确定一系列大气条件下反应的程度，以及反应对颗粒挥发性、脱气和随后的云处理周期的影响。其次，对干燥和再溶解的水溶液进行大量ESI-MS和NMR研究，以模拟云处理，将用于化学表征反应产物并确定反应途径。第三，气溶胶质谱（AMS）对模拟云处理和直接气溶胶相反应产生的颗粒进行分析，将确定体相反应产物和途径是否适用于大气条件。最后，通过核磁共振测量温度依赖性反应动力学。这些实验获得的信息将决定α -二羰基+胺反应在大气中的意义。空气中的微粒影响气候、降低能见度并影响人类健康。这些结果将有助于改进用于了解有机气溶胶起源的大气模型。这些模型被广泛用于评估气溶胶对全球气候、区域能见度和空气质量的潜在影响，这些都是重要的社会问题。该项目还将支持一些本科生的教育。

Recent field measurements have shown that there are large, sustained, unidentified sources of secondary organic aerosol (SOA). The alpha-dicarbonyl compounds glyoxal and methylglyoxal are receiving increasing scrutiny as potential SOA sources because of their anthropogenic and biogenic precursors, their efficient uptake by atmospheric water droplets and liquid aerosol particles, and their oligomer-forming potential. Recent work shows that the key to aqueous phase alpha-dicarbonyl reactivity is dehydration followed by nucleophilic attack. The nucleophiles methylamine and several amino acids have been identified in cloud- and fog-water droplets in the atmosphere in micromolar concentrations similar to the alpha-dicarbonyl compounds. These nucleophiles have been identified in preliminary experiments as efficient reaction partners with glyoxal and methylglyoxal, forming products upon drying that irreversibly alter gas-particle partitioning of the reactants, even when re-dissolved. The goal of this research is to characterize these reactions and determine their reaction products, measure the reaction kinetics under realistic conditions, and thereby determine the atmospheric significance of these reactions in forming SOA and oligomeric material via cloud and aerosol processing. The reactions will be studied by several methods. First, scanning mobility particle sizing studies of drying monodispersed cloud droplets will determine the extent of reaction under a range of atmospheric conditions and the effect of reactions on particle volatility, off-gassing, and subsequent cloud processing cycles. Second, bulk ESI-MS and NMR studies on aqueous solutions that have been dried and re-dissolved to simulate cloud processing will be used to chemically characterize reaction products and determine reaction pathways. Third, aerosol mass spectrometric (AMS) analysis of particles produced by simulated cloud processing and by direct aerosol phase reactions will determine if bulk phase reaction products and pathways are applicable under atmospheric conditions. Finally, temperature dependent reaction kinetics will be measured by NMR. Information gained by these experiments will determine the atmospheric significance of alpha-dicarbonyl + amine reactions.Airborne particles influence climate, degrade visibility, and impact human health. The results will help improve atmospheric models used to understand the origin of organic aerosols. These models are widely used to assess the potential effects of aerosols on global climate, regional visibility, and air quality, which are all important societal problems. The project will also support the education of a number of undergraduate students.