During the Marine Aerosol Cloud and Wildfire Study (MACAWS) in June and July of 2018, aerosol composition and cloud condensation nuclei (CCN) properties were measured over the N.E. Pacific to characterize the influence of aerosol hygroscopicity on predictions of ambient CCN and stratocumulus cloud droplet number concentrations (CDNC). Three vertical regions were characterized, corresponding to the marine boundary layer (MBL), an above‐cloud organic aerosol layer (AC‐OAL), and the free troposphere (FT) above the AC‐OAL. The aerosol hygroscopicity parameter (κ) was calculated from CCN measurements (κ_CCN) and bulk aerosol mass spectrometer (AMS) measurements (κ_AMS). Within the MBL, measured hygroscopicities varied between values typical of both continental environments (~0.2) and remote marine locations (~0.7). For most flights, CCN closure was achieved within 20% in the MBL. For five of the seven flights, assuming a constant aerosol size distribution produced similar or better CCN closure than assuming a constant “marine” hygroscopicity (κ = 0.72). An aerosol‐cloud parcel model was used to characterize the sensitivity of predicted stratocumulus CDNC to aerosol hygroscopicity, size distribution properties, and updraft velocity. Average CDNC sensitivity to accumulation mode aerosol hygroscopicity is 39% as large as the sensitivity to the geometric median diameter in this environment. Simulations suggest CDNC sensitivity to hygroscopicity is largest in marine stratocumulus with low updraft velocities (<0.2 m s⁻¹), where accumulation mode particles are most relevant to CDNC, and in marine stratocumulus or cumulus with large updraft velocities (>0.6 m s⁻¹), where hygroscopic properties of the Aitken mode dominate hygroscopicity sensitivity.

中文翻译：

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东北太平洋气溶胶吸湿性特征：对 CCN 和层积云液滴数浓度预测的影响

在 2018 年 6 月和 7 月的海洋气溶胶云和野火研究 (MACAWS) 期间，测量了东北太平洋上空的气溶胶成分和云凝结核 (CCN) 特性，以表征气溶胶吸湿性对环境 CCN 和层积云液滴预测的影响数量浓度（CDNC）。表征了三个垂直区域，分别对应于海洋边界层（MBL）、云上有机气溶胶层（AC-OAL）和AC-OAL上方的自由对流层（FT）。气溶胶吸湿性参数 ( κ ) 通过 CCN 测量值 ( κ _CCN ) 和散装气溶胶质谱仪 (AMS) 测量值 ( κ _AMS )计算得出。在 MBL 内，测得的吸湿性在大陆环境 (~0.2) 和偏远海洋位置 (~0.7) 的典型值之间变化。对于大多数航班，CCN 关闭在 MBL 中实现在 20% 以内。对于 7 次飞行中的 5 次，假设气溶胶粒径分布恒定，与假设“海洋”吸湿性恒定 ( κ  = 0.72) 相比，产生类似或更好的 CCN 闭合效果。气溶胶云包裹模型用于表征预测的层积云 CDNC 对气溶胶吸湿性、尺寸分布特性和上升气流速度的敏感性。CDNC 对累积模式气溶胶吸湿性的平均敏感度是该环境中对几何中位直径的敏感度的 39%。^{模拟表明，CDNC 对吸湿性的敏感性在低上升气流速度 (<0.2 m s -1} ) 的海洋层积云中最大，其中堆积模式粒子与 CDNC 最相关，以及在具有大上升气流速度 (>0.6 m s ^{-1 )}的海洋层积云或积云中，其中艾特肯模式的吸湿特性主导吸湿敏感性。