A large fraction of atmospheric aerosols can be characterized as primary organic aerosol (POA) and secondary organic aerosol (SOA). Knowledge of the phase behavior, that is, the number and type of phases within internal POA + SOA mixtures, is crucial to predict their effect on climate and air quality. For example, if POA and SOA form a single phase, POA will enhance the formation of SOA by providing organic mass to absorb SOA precursors. Using microscopy, we studied the phase behavior of mixtures of SOA proxies and hydrocarbon-like POA proxies at relative humidity (RH) values of 90%, 45%, and below 5%. Internal mixtures of POA and SOA almost always formed two phases if the elemental oxygen-to-carbon ratio (O/C) of the POA was less than 0.11, which encompasses a large fraction of atmospheric hydrocarbon-like POA from fossil fuel combustion. SOA proxies mixed with POA proxies having 0.11 ≤ O/C ≤ 0.29 mostly resulted in particles with one liquid phase. However, two liquid phases were also observed, depending on the type of SOA and POA surrogates, and an increase in phase-separated particles was observed when increasing the RH in this O/C range. The results have implications for predicting atmospheric SOA formation and policy strategies to reduce SOA in urban environments.

中文翻译：

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基于元素氧碳比的类烃初级有机气溶胶和次级有机气溶胶代理的相行为

大部分大气气溶胶可分为一次有机气溶胶 (POA) 和二次有机气溶胶 (SOA)。了解相行为，即内部 POA + SOA 混合物中相的数量和类型，对于预测它们对气候和空气质量的影响至关重要。例如，如果 POA 和 SOA 形成单相，POA 将通过提供有机物质来吸收 SOA 前体来促进 SOA 的形成。我们使用显微镜研究了 SOA 代理和类烃 POA 代理的混合物在 90%、45% 和低于 5% 的相对湿度 (RH) 值下的相行为。如果 POA 的元素氧碳比 (O/C) 小于 0.11，则 POA 和 SOA 的内部混合物几乎总是形成两相，其中包括来自化石燃料燃烧的大部分大气类烃类 POA。SOA 代理与具有 0.11 ≤ O/C ≤ 0.29 的 POA 代理混合，主要导致粒子具有一个液相。然而，也观察到两个液相，这取决于 SOA 和 POA 替代物的类型，并且当在此 O/C 范围内增加 RH 时，观察到相分离颗粒的增加。结果对预测大气 SOA 形成和减少城市环境中 SOA 的政策策略具有影响。