Abstract. Understanding seasonal variation in cloud condensation nuclei (CCN) activity and the impact of anthropogenic emissions in marine environments is crucial for assessing climate change. In this study, two shipborne observations in the South China Sea (SCS) during the summer and winter of 2021 were conducted. During summer, higher particle number concentrations but lower mass concentrations of non-refractory submicron particles (NR-PM₁) were observed. These differences were attributed to the dominance of particles in the Aitken mode during summer and in the accumulation mode during winter. Moreover, particles during summer were more hygroscopic with higher activation ratios (ARs) at all supersaturation (SS). Based on backward trajectory analysis, the whole campaign was classified into terrestrial and mixed air mass influence periods. Particles measured during the terrestrial period consistently exhibited lower hygroscopicity values. Additionally, minor variations were shown for all NR-PM₁ components under different air mass influences during summer, while the mass fraction of nitrate increased significantly under terrestrial influence during winter. Particle number size distribution (PNSD) exhibited unimodal distribution during terrestrial period and bimodal distribution during mixed air mass influence period, with winter displaying a more pronounced bimodal pattern than summer. The impact of PNSD on AR was greater than on aerosol hygroscopicity in summer, and vice versa in winter. During terrestrial period, significant variations in PNSD were observed with the offshore distance, and the largest variation was seen in Aitken mode during both summer and winter. Meanwhile, aerosol hygroscopicity shows an increasing trend with the offshore distance, which is primarily attributed to the increase of sulfate fraction during summer and the decrease of the black carbon fraction during winter. Using a single parameterized PNSD in the N_CCN prediction can lead to errors exceeding 100 % during both summer and winter, with dominant terrestrial air masses in the SCS atmosphere, while using a constant hygroscopicity parameter would lower the errors in the N_CCN prediction (~15 % during winter and ~10 % during summer). Our study shows significant differences in aerosol properties between winter and summer seasons and highlights the influence of anthropogenic emissions on the CCN activity in the SCS.

中文翻译：

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测量报告：南海云凝结核（CCN）活动的季节变化和人为影响：2021年夏季和冬季船载观测的见解

摘要。了解云凝结核（CCN）活动的季节性变化以及人为排放对海洋环境的影响对于评估气候变化至关重要。在这项研究中，于2021年夏季和冬季在南海（SCS）进行了两次船载观测。在夏季，观察到非难熔亚微米颗粒（NR-PM ₁ ）的颗粒数量浓度较高，但质量浓度较低。这些差异归因于夏季艾特肯模式和冬季积累模式中粒子的主导地位。此外，夏季颗粒物吸湿性更强，在所有过饱和度（SS）下活化率（AR）更高。根据后向轨迹分析，将整个活动分为陆地气团影响期和混合气团影响期。在陆地时期测量的颗粒始终表现出较低的吸湿性值。此外，夏季不同气团影响下，所有NR-PM ₁组分均表现出微小变化，而冬季陆地影响下硝酸盐质量分数显着增加。颗粒物数量分布（PNSD）在陆地时期表现出单峰分布，在混合气团影响时期表现出双峰分布，冬季比夏季表现出更明显的双峰分布。夏季PNSD对AR的影响大于对气溶胶吸湿性的影响，冬季反之亦然。在陆地期间，PNSD随离岸距离的变化显着，夏季和冬季的艾特肯模态变化最大。同时，气溶胶吸湿性随着离岸距离的增加呈增加趋势，这主要归因于夏季硫酸盐含量的增加和冬季黑碳含量的减少。在 N _CCN预测中使用单一参数化的 PNSD会导致夏季和冬季误差超过 100%，南海大气中的陆地气团占主导地位，而使用恒定的吸湿性参数会降低 N _CCN预测的误差（~冬季约 15%，夏季约 10%）。我们的研究表明冬季和夏季气溶胶特性存在显着差异，并强调了人为排放对南海 CCN 活动的影响。