Department of Mechanical Engineering, University of Minnesota, Twin Cities , Minneapolis, Minnesota, 55455 United States.
Environ Sci Technol. 2016 Feb 2;50(3):1251-9. doi: 10.1021/acs.est.5b04880. Epub 2016 Jan 19.
Secondary organic aerosol (SOA) particles are a major component of atmospheric particulate matter, yet their formation processes and ambient properties are not well understood. These complex particles often contain multiple interfaces due to internal aqueous- and organic-phase partitioning. Aerosol interfaces can profoundly affect the fate of condensable organic compounds emitted into the atmosphere by altering the way in which ambient organic vapors interact with suspended particles. To accurately predict the evolution of SOA in the atmosphere, we must improve our understanding of aerosol interfaces. In this work, biphasic microscale flows are used to measure interfacial tension of reacting methylglyoxal, formaldehyde, and ammonium sulfate aqueous mixtures with a surrounding oil phase. Our experiments show a suppression of interfacial tension as a function of organic content that remains constant with reaction time for methylglyoxal-ammonium sulfate systems. We also reveal an unexpected time dependence of interfacial tension over a period of 48 h for ternary solutions of both methylglyoxal and formaldehyde in aqueous ammonium sulfate, indicating a more complicated behavior of surface activity where there is competition among dissolved organics. From these interfacial tension measurements, the morphology of aged atmospheric aerosols with internal liquid-liquid phase separation is inferred.
二次有机气溶胶 (SOA) 粒子是大气颗粒物的主要组成部分，但它们的形成过程和环境特性尚未得到很好的理解。这些复杂的粒子由于内部水相和有机相的分配，通常含有多个界面。气溶胶界面可以通过改变环境有机蒸气与悬浮颗粒相互作用的方式，深刻影响进入大气的可冷凝有机化合物的命运。为了准确预测 SOA 在大气中的演化，我们必须加深对气溶胶界面的理解。在这项工作中，使用两相微尺度流来测量与周围油相反应的甲基乙二醛、甲醛和硫酸铵水溶液混合物的界面张力。我们的实验表明，随着甲基乙二醛-硫酸铵体系反应时间的增加，界面张力会抑制有机含量的增加，并且保持不变。我们还揭示了在 48 小时的时间内，三元溶液中甲基乙二醛和甲醛在硫酸铵水溶液中的界面张力表现出出乎意料的时间依赖性，这表明表面活性具有更复杂的行为，其中溶解有机物之间存在竞争。从这些界面张力测量中，可以推断出具有内部液-液相分离的老化大气气溶胶的形态。
