Evidence for a kinetically controlled burying mechanism for growth of high viscosity secondary organic aerosol
Evidence for a kinetically controlled burying mechanism for growth of high viscosity secondary organic aerosol
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DOI：
10.1039/c9em00379g
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发表时间：
2020-01-01
影响因子：
5.5
通讯作者：
Finlayson-Pitts, Barbara J.
中科院分区：
文献类型：
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作者：
Vander Wall, Allison C.;Perraud, Veronique;Finlayson-Pitts, Barbara J.
二次有机气溶胶(SOA)颗粒在空气中普遍存在，了解它们生长的机制对于预测它们对能见度和气候的影响至关重要。研究了在添加或不添加羟基清除剂的情况下，α-蒎烯臭氧化生成的半固体SOA颗粒对三种有机硝酸盐的吸附情况。这里介绍了四种类型的实验。在A系列中，选择的有机硝酸盐(2-乙基己基硝酸酯(2EHN)；β-羟丙基硝酸酯(HPN)；β-羟基己基硝酸盐(HHN))通过衰减全反射(ATR)-傅立叶变换红外光谱(FTIR)检测被冲击的SOA颗粒中的吸收情况。在这种情况下，达到了平衡，测得分配系数(K-SOA=[-ONO2](SOA)/[-ONO2](AIR))为：K-2EHN=(3.2-11)x 10(4)，K-HPn=(4.4-5.4)x 10(5)，K-HHN=(4.9-9.0)x 10(6)。在B系列中，将SOA颗粒在飞行中暴露到气相有机硝酸盐中，以与A系列进行比较，并通过HR-ToF-AMS分析对有机硝酸盐的吸收进行定量，得到了类似的结果。在C系列(AMS)和D系列(ATR-FTIR)中，随着颗粒的形成和生长，每个有机硝酸盐都被引入到SOA中。在C系列和D系列(生长期间)中，RONO2的掺入量要大得多，超过了A系列和B系列(生长后)确定的平衡值。这表明，在SOA形成和增长过程中对有机硝酸盐的增强吸收是由于动力学控制的“埋藏”机制，而不是平衡分配。这对于理解在粒子为半固态的条件下的SOA的形成和增长具有重要的意义，这是准确预测此类SOA的属性的核心。
Secondary organic aerosol (SOA) particles are ubiquitous in air and understanding the mechanism by which they grow is critical for predicting their effects on visibility and climate. The uptake of three organic nitrates into semi-solid SOA particles formed by alpha-pinene ozonolysis either with or without an OH scavenger was investigated. Four types of experiments are presented here. In Series A, uptake of the selected organic nitrates (2-ethylhexyl nitrate (2EHN); beta-hydroxypropyl nitrate (HPN); beta-hydroxyhexyl nitrate (HHN)) into impacted SOA particles was interrogated by attenuated total reflectance (ATR)-FTIR. In this case, equilibrium was reached and partition coefficients (K-SOA = [-ONO2](SOA)/[-ONO2](air)) were measured to be K-2EHN = (3.2-11) x 10(4), K-HPN = (4.4-5.4) x 10(5), and K-HHN = (4.9-9.0) x 10(6). In Series B, SOA particles were exposed on-the-fly to gas phase organic nitrates for comparison to Series A, and uptake of organic nitrates was quantified by HR-ToF-AMS analysis, which yielded similar results. In Series C (AMS) and D (ATR-FTIR), each organic nitrate was incorporated into the SOA as the particles formed and grew. The incorporation of the RONO2 was much larger in Series C and D (during growth), exceeding equilibrium values determined in Series A and B (after growth). This suggests that enhanced uptake of organic nitrates during SOA formation and growth is due to a kinetically controlled "burying" mechanism, rather than equilibrium partitioning. This has important implications for understanding SOA formation and growth under conditions where the particles are semi-solid, which is central to accurately predicting properties for such SOA.