MacDonald Alexander B, Dadashazar Hossein, Chuang Patrick Y, Crosbie Ewan, Wang Hailong, Wang Zhen, Jonsson Haflidi H, Flagan Richard C, Seinfeld John H, Sorooshian Armin
Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA.
Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA.
J Geophys Res Atmos. 2018 Apr 16;123(7):3704-3723. doi: 10.1002/2017JD027900. Epub 2018 Feb 21.
This study uses airborne cloud water composition measurements to characterize the vertical structure of air-equivalent mass concentrations of water-soluble species in marine stratocumulus clouds off the California coast. A total of 385 cloud water samples were collected in the months of July and August between 2011 and 2016 and analyzed for water-soluble ionic and elemental composition. Three characteristic profiles emerge: (i) a reduction of concentration with in-cloud altitude for particulate species directly emitted from sources below cloud without in-cloud sources (e.g., Cl and Na), (ii) an increase of concentration with in-cloud altitude (e.g., NO and formate), and (iii) species exhibiting a peak in concentration in the middle of cloud (e.g., non-sea-salt SO , NO , and organic acids). Vertical profiles of rainout parameters such as loss frequency, lifetime, and change in concentration with respect to time show that the scavenging efficiency throughout the cloud depth depends strongly on the thickness of the cloud. Thin clouds exhibit a greater scavenging loss frequency at cloud top, while thick clouds have a greater scavenging loss frequency at cloud base. The implications of these results for treatment of wet scavenging in models are discussed.
本研究利用机载云水成分测量来表征加利福尼亚海岸外海洋层积云中水溶性物种的空气等效质量浓度的垂直结构。在2011年至2016年的7月和8月期间，共采集了385个云水样本，并对其水溶性离子和元素组成进行了分析。出现了三种特征剖面：(i) 对于没有云内源的云下源直接排放的颗粒物种（如Cl和Na），其浓度随云内高度降低；(ii) 浓度随云内高度增加（如NO和甲酸盐）；(iii) 物种在云中部浓度出现峰值（如非海盐SO、NO和有机酸）。降雨参数（如损失频率、寿命以及浓度随时间的变化）的垂直剖面表明，整个云深度的清除效率强烈依赖于云的厚度。薄云在云顶表现出更大的清除损失频率，而厚云在云底有更大的清除损失频率。讨论了这些结果对模型中湿清除处理的影响。
