Data for: Low temperature ice nucleation of sea spray and secondary marine aerosols under cirrus cloud conditions

Sea spray aerosols (SSA) represent one of the most abundant aerosol types on a global scale and have been observed at all altitudes including the upper troposphere. SSA has been explored in recent years as a source of ice nucleating particles (INPs) in cirrus clouds due to the ubiquity of cirrus clouds and the uncertainties in their radiative forcing. This study expands upon previous works on low temperature ice nucleation of SSA by investigating the effects of atmospheric aging of SSA and the ice nucleating activity of newly formed secondary marine aerosols (SMA) using an oxidation flow reactor. Polydisperse aerosol distributions were generated from a Marine Aerosol Reference Tank (MART) filled with 120 L of real or artificial seawater and were dried to very low relative humidity to crystallize the salt constituents of SSA prior to their subsequent freezing, which was measured using a Continuous Flow Diffusion Chamber (CFDC). Results show that for both primary SSA (pSSA), and the aged SSA and SMA (aSSA+SMA) at temperatures > 220 K, homogeneous conditions (92–97 % relative humidity with respect to water (RHw)) were required to freeze 1 % of the particles. However, below 220 K, heterogeneous nucleation occurs for both pSSA and aSSA+SMA at much lower RHw, where up to 1 % of the aerosol population freezes between 75–80 % RHw. Similarities between freezing behaviors of the pSSA and aSSA+SMA at all temperatures suggest that the contributions of condensed organics onto the pSSA or alteration of functional groups in pSSA via atmospheric aging did not hinder the major heterogeneous ice nucleation process at these cirrus temperatures that has previously been shown to be dominated by the crystalline salts. Occurrence of 1% frozen fraction of SMA, generated in the absence of primary SSA, was observed at/near water saturation below 220 K, suggesting it is not an effective INP at cirrus temperatures, similar to findings in the literature of other organic aerosols. Thus, any SMA coatings on the pSSA would only decrease the ice nucleation behavior of pSSA if the organic components were able to significantly delay water uptake of the inorganic salts, and apparently, this was not the case. Results from this study demonstrate the ability of lofted primary sea spray particles to remain an effective ice nucleator at cirrus temperatures, even after atmospheric aging has occurred over a period of days in the marine boundary layer prior to lofting. We were not able to address aging processes under upper tropospheric conditions.

海洋飞沫气溶胶（Sea Spray Aerosols, SSA）是全球范围内丰度最高的气溶胶类型之一，且在包括对流层上层在内的所有海拔高度均已被观测到。近年来，由于卷云分布广泛且其辐射强迫存在不确定性，海洋飞沫气溶胶作为卷云中冰核粒子（Ice Nucleating Particles, INPs）的来源受到了广泛研究。本研究针对此前关于海洋飞沫气溶胶低温冰核化的工作进行拓展，采用氧化流动反应器（Oxidation Flow Reactor）探究了海洋飞沫气溶胶的大气老化效应，以及新生成的二次海洋气溶胶（Secondary Marine Aerosols, SMA）的冰核活性。本研究采用容积为120升的真实/人工海水海洋气溶胶参考罐（Marine Aerosol Reference Tank, MART）生成多分散气溶胶分布，并将其干燥至极低相对湿度，以使海洋飞沫气溶胶中的盐组分结晶，随后利用连续流扩散室（Continuous Flow Diffusion Chamber, CFDC）测量气溶胶的冻结行为。研究结果显示，在温度高于220 K时，无论是一次海洋飞沫气溶胶（Primary SSA, pSSA）还是老化海洋飞沫气溶胶与二次海洋气溶胶混合物（aSSA+SMA），均需要在均质冻结条件下（相对于水的相对湿度（RHw）为92%~97%）才能使1%的气溶胶粒子发生冻结。但在220 K以下时，一次海洋飞沫气溶胶与老化混合物均会在更低的相对湿度下发生异质核化，此时有多达1%的气溶胶粒子在RHw为75%~80%的区间内发生冻结。不同温度下一次海洋飞沫气溶胶与老化混合物的冻结行为高度相似，这表明附着于一次海洋飞沫气溶胶的冷凝有机物，或是通过大气老化改变的一次海洋飞沫气溶胶官能团，并未阻碍卷云温度下的主要异质冰核化过程——此前研究表明该过程主要由结晶盐组分主导。在无一次海洋飞沫气溶胶生成的条件下得到的二次海洋气溶胶，在220 K以下的水饱和或近饱和环境中仅观测到1%的冻结率，这表明其在卷云温度下并非有效的冰核粒子，这一结果与其他有机气溶胶的相关文献研究结论一致。因此，仅当有机组分能够显著延缓无机盐的吸水过程时，附着于一次海洋飞沫气溶胶的二次海洋气溶胶涂层才会降低其冰核活性，但显然实际情况并非如此。本研究结果证明，即使一次海洋飞沫气溶胶在海洋边界层中经历了数天的大气老化并随后被抬升，其在卷云温度下仍能保持有效的冰核活性。本研究未能探讨对流层上层环境下的老化过程。