Direct Comparison of the Submicron Aerosol Hygroscopicity of Water-Soluble Sugars
Direct Comparison of the Submicron Aerosol Hygroscopicity of Water-Soluble Sugars
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DOI：
10.1021/acsearthspacechem.0c00159
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发表时间：
2020-12-17
影响因子：
3.4
通讯作者：
Freedman, Miriam Arak
中科院分区：
文献类型：
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作者：
Dawson, Joseph Nelson;Malek, Kotiba A.;Freedman, Miriam Arak
水溶性有机化合物(WSOCs)很容易吸收水分并形成大气水滴。了解这些WSOC的吸水能力可以提高我们对其辐射效应的理解，从而可以改进当前的气候模型。在这项研究中，我们测量了四种WSOC：左旋葡聚糖、蔗糖、棉子糖和海藻糖的过饱和和过饱和液滴生长。具体地说，我们使用了三种不同的纳米级液滴生长方法：腔衰荡光谱(CRDS)、吸湿串联微分迁移率分析(H-TDMA)和云凝聚核(CCN)计数，并报告了每个气溶胶系统的光学生长因子(FRH)、生长因子(G(F))、折射率和临界激活直径(d(P50))。Kohler理论(假设液滴表面张力等于纯水)应用于所有液滴生长测量，并报告了在不同平台上测量的四个WSOC的单参数吸湿性kappa。三种实验方法都表明，随着WSOC分子量的增加，吸湿性降低。当假设液滴为稀释液滴时，测量得到的卡伯值与已知值一致。这三种实验方法具有相当的精密度，每种方法的平均卡伯值都有系统偏差。很少有研究使用FRH数据来获得卡伯值。目前从FRH数据估算kappa的两种方法产生了类似的结果，它们依赖于干燥气溶胶的大小，并与假设稀溶液行为的kappa值相一致。因此，所提供的测量数据集和分析有助于比较来自光学和几何方法的有机气溶胶的过饱和和过饱和数据。
Water-soluble organic compounds (WSOCs) readily uptake water and form atmospheric droplets. Understanding the water-uptake ability of these WSOCs can improve our understanding of their radiative effects and thus can improve current climate models. In this study, we measure the subsaturated and supersaturated droplet growth of four WSOCs: levoglucosan, sucrose, raffinose, and trehalose. Specifically, we use three distinct nanoscale droplet growth methods: cavity ring-down spectroscopy (CRDS), hygroscopic tandem differential mobility analysis (H-TDMA), and cloud condensation nuclei (CCN) counting and report optical growth factor (fRH), growth factor (G(f)), refractive indices, and critical activation diameters (d(p50)) for each aerosol system. Kohler theory (assuming a droplet surface tension equal to that of pure water) is applied to all droplet growth measurements, and the single-parameter hygroscopicity, kappa, is reported for the four WSOCs measured on the different platforms. The three experimental methods measure decreased hygroscopicity with an increase in WSOC molecular weight. When assuming the droplets are dilute, kappa values from measurements are consistent with known values. The three experimental methods have comparable precision with systematic deviations in the average kappa for each method. Few studies have employed fRH data to obtain kappa values. The current two methods to estimate kappa from fRH data produce similar results, are dry aerosol size-dependent, and agree with kappa values that assume dilute solution behavior. Thus, the presented measured data set and analysis contribute to the comparison of subsaturated and supersaturated data from optical and geometric methods for organic aerosol.