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

最近的现场测量表明，有大量的、持续的、不明来源的二次有机气溶胶(SOA)。乙二醛和甲基乙二醛作为潜在的SOA来源正受到越来越多的关注，因为它们是人为和生物前体，它们被大气水滴和液体气溶胶粒子有效地吸收，以及它们形成低聚物的潜力。最近的工作表明，水相α-二羰基反应的关键是脱水，然后是亲核攻击。在大气中云和雾的水滴中发现了亲核试剂甲胺和几种氨基酸，其微摩尔浓度与α-二酮化合物相似。在初步实验中，这些亲核试剂已被确定为与乙二醛和甲基乙二醛的有效反应伙伴，干燥后形成的产物即使在重新溶解时也不可逆地改变反应物的气粒分配。本研究的目标是表征这些反应并确定它们的反应产物，测量实际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和低聚物方面的大气意义。这些反应将用几种方法来研究。首先，干燥单分散云滴的扫描流动性粒度研究将确定在一系列大气条件下的反应程度，以及反应对粒子挥发性、放气和后续云处理周期的影响。其次，对干燥和重新溶解以模拟云处理的水溶液进行大量ESI-MS和核磁共振研究，将用于对反应产物进行化学表征和确定反应路径。第三，对模拟云处理和直接气溶胶相反应产生的颗粒进行气溶胶质谱仪(AMS)分析，将确定大气相反应产物和途径是否适用于大气条件。最后用核磁共振仪测定了反应动力学随温度的变化。通过这些实验获得的信息将确定阿尔法-二羰基+胺反应的大气意义。空气中的颗粒物影响气候，降低能见度，并影响人类健康。这一结果将有助于改进用于理解有机气溶胶来源的大气模型。这些模式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.