Not all types of secondary organic aerosol mix: two phases observed when mixing different secondary organic aerosol types
Not all types of secondary organic aerosol mix: two phases observed when mixing different secondary organic aerosol types
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DOI：
10.5194/acp-22-13783-2022
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发表时间：
2022-11
影响因子：
6.3
通讯作者：
F. Mahrt;Long Peng;J. Zaks;Yuanzhou Huang;Paul E. Ohno;Natalie R. Smith;F. Gregson;Yiming Qin;C. Faiola;S. Martin;S. Nizkorodov;M. Ammann;A. Bertram
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作者：
F. Mahrt;Long Peng;J. Zaks;Yuanzhou Huang;Paul E. Ohno;Natalie R. Smith;F. Gregson;Yiming Qin;C. Faiola;S. Martin;S. Nizkorodov;M. Ammann;A. Bertram
抽象。二次有机气溶胶（SOA）是大气气溶胶的重要组成部分。为了评估其对气候和空气污染的影响，需要了解不同SOA类型内部混合物的相数。大气模型通常假设不同的SOA类型在混合时形成单一相。在这里，我们提出了视觉观察混合不同的人为和生物SOA类型后形成的阶段的数量。在氧碳比为0.34 - 1.05的环境室中混合SOA类型，我们发现两种SOA类型的15种混合物中有6种导致两相颗粒。我们证明了相的数量取决于两种SOA类型之间的平均O/C比（Δ（O/C））的差异。使用0.47的阈值Δ（O/C），我们可以预测超过90%的混合物的相行为，其中单相和两相颗粒分别预测为Δ（O/C）<0.47和Δ（O/C）≥ 0.47。这个阈值Δ O/C值提供了一个简单的参数来预测新鲜和老化SOA的混合物在大气中是否形成单相或两相颗粒。此外，我们表明，相分离的SOA颗粒形成时，挥发性有机化合物的混合物从真实的树木被氧化。
Abstract. Secondary organic aerosol (SOA) constitutes a large fraction of atmospheric aerosol. To assess its impacts on climate and air pollution, knowledge of the number of phases in internal mixtures of different SOA types is required. Atmospheric models often assume that different SOA types form a single phase when mixed. Here, we present visual observations of the number of phases formed after mixing different anthropogenic and biogenic SOA types. Mixing SOA types generated in environmental chambers with oxygen-to-carbon (O/C) ratios between 0.34 and 1.05, we found 6 out of 15 mixtures of two SOA types to result in two phase particles. We demonstrate that the number of phases depends on the difference in the average O/C ratio between the two SOA types (Δ(O/C)). Using a threshold Δ(O/C) of 0.47, we can predict the phase behavior of over 90 % of our mixtures, with one- and two-phase particles predicted for Δ(O/C)<0.47 and Δ(O/C)≥0.47, respectively. This threshold ΔO/C value provides a simple parameter to predict whether mixtures of fresh and aged SOA form one- or two-phase particles in the atmosphere. In addition, we show that phase-separated SOA particles form when mixtures of volatile organic compounds emitted from real trees are oxidized.