Pacific Northwest National Lab, 902 Battelle Boulevard, Richland, WA 99352, USA.
Proc Natl Acad Sci U S A. 2010 Apr 13;107(15):6658-63. doi: 10.1073/pnas.0911206107. Epub 2010 Mar 1.
Primary organic aerosol (POA) and associated vapors can play an important role in determining the formation and properties of secondary organic aerosol (SOA). If SOA and POA are miscible, POA will significantly enhance SOA formation and some POA vapor will incorporate into SOA particles. When the two are not miscible, condensation of SOA on POA particles forms particles with complex morphology. In addition, POA vapor can adsorb to the surface of SOA particles increasing their mass and affecting their evaporation rates. To gain insight into SOA/POA interactions we present a detailed experimental investigation of the morphologies of SOA particles formed during ozonolysis of alpha-pinene in the presence of dioctyl phthalate (DOP) particles, serving as a simplified model of hydrophobic POA, using a single-particle mass spectrometer. Ultraviolet laser depth-profiling experiments were used to characterize two different types of mixed SOA/DOP particles: those formed by condensation of the oxidized alpha-pinene products on size-selected DOP particles and by condensation of DOP on size-selected alpha-pinene SOA particles. The results show that the hydrophilic SOA and hydrophobic DOP do not mix but instead form layered phases. In addition, an examination of homogeneously nucleated SOA particles formed in the presence of DOP vapor shows them to have an adsorbed DOP coating layer that is approximately 4 nm thick and carries 12% of the particles mass. These results may have implications for SOA formation and behavior in the atmosphere, where numerous organic compounds with various volatilities and different polarities are present.
一次有机气溶胶（POA）和相关蒸气在决定二次有机气溶胶（SOA）的形成和性质方面可发挥重要作用。如果 SOA 和 POA 可混溶，POA 将显著促进 SOA 的形成，并且一些 POA 蒸气将并入 SOA 颗粒中。当两者不可混溶时，SOA 在 POA 颗粒上的冷凝会形成具有复杂形态的颗粒。此外，POA 蒸气可以吸附在 SOA 颗粒的表面，增加它们的质量并影响它们的蒸发速率。为了深入了解 SOA/POA 的相互作用，我们使用单颗粒质谱仪对在邻苯二甲酸二辛酯（DOP）颗粒存在下，臭氧氧化α-蒎烯形成 SOA 时的颗粒形态进行了详细的实验研究，将 DOP 颗粒作为疏水性 POA 的简化模型。使用紫外激光深度剖析实验来表征两种不同类型的混合 SOA/DOP 颗粒：通过氧化α-蒎烯产物在大小选择的 DOP 颗粒上冷凝形成的混合 SOA/DOP 颗粒和通过 DOP 在大小选择的α-蒎烯 SOA 颗粒上冷凝形成的混合 SOA/DOP 颗粒。结果表明，亲水性 SOA 和疏水性 DOP 不混合，而是形成分层相。此外，对在 DOP 蒸气存在下形成的均相成核 SOA 颗粒的检查表明，它们具有约 4nm 厚的吸附 DOP 涂层，并且携带颗粒质量的 12%。这些结果可能对大气中 SOA 的形成和行为具有重要意义，因为存在许多挥发性和极性不同的有机化合物。
