Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
Environ Sci Technol. 2013 Jun 18;47(12):6173-80. doi: 10.1021/es400979k. Epub 2013 May 31.
The physical state and chemical composition of an organic aerosol affect its degree of mixing and its interactions with condensing species. We present here a laboratory chamber procedure for studying the effect of the mixing of organic aerosol components on particle evaporation. The procedure is applied to the formation of secondary organic aerosol (SOA) from α-pinene and toluene photooxidation. SOA evaporation is induced by heating the chamber aerosol from room temperature (25 °C) to 42 °C over 7 h and detected by a shift in the peak diameter of the SOA size distribution. With this protocol, α-pinene SOA is found to be more volatile than toluene SOA. When SOA is formed from the two precursors sequentially, the evaporation behavior of the SOA most closely resembles that of SOA from the second parent hydrocarbon, suggesting that the structure of the mixed SOA resembles a core of SOA from the initial precursor coated by a layer of SOA from the second precursor. Such a core-and-shell configuration of the organic aerosol phases implies limited mixing of the SOA from the two precursors on the time scale of the experiments, consistent with a high viscosity of at least one of the phases.
有机气溶胶的物理状态和化学组成会影响其混合程度以及与凝结物质的相互作用。我们在此介绍一种实验室腔室程序，用于研究有机气溶胶成分混合对颗粒蒸发的影响。该程序应用于从α-蒎烯和甲苯光氧化形成二次有机气溶胶（SOA）。通过将腔室气溶胶从室温（25°C）加热 7 小时至 42°C，SOA 蒸发被诱导，并通过 SOA 粒径分布的峰值直径的移动来检测。根据该方案，α-蒎烯 SOA 比甲苯 SOA 具有更高的挥发性。当 SOA 由两种前体顺序形成时，SOA 的蒸发行为最接近来自第二种母烃的 SOA，这表明混合 SOA 的结构类似于初始前体的 SOA 核，由第二种前体的 SOA 层覆盖。有机气溶胶相的这种核壳结构意味着在实验的时间尺度上，两种前体的 SOA 混合程度有限，这与至少一个相的高粘度一致。
