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Characterizing the hygroscopicity of growing particles in the Canadian Arctic summer
Atmospheric Chemistry and Physics ( IF 6.3 ) Pub Date : 2022-06-22 , DOI: 10.5194/acp-22-8059-2022
Rachel Y.-W. Chang, Jonathan P. D. Abbatt, Matthew C. Boyer, Jai Prakash Chaubey, Douglas B. Collins

The impact of aerosols on clouds is a well-studied, although still poorly constrained, part of the atmospheric system. New particle formation (NPF) is thought to contribute 40 %–80 % of the global cloud droplet number concentration, although it is extremely difficult to observe an air mass from NPF to cloud formation. NPF and growth occurs frequently in the Canadian Arctic summer atmosphere, although only a few studies have characterized the source and properties of these aerosols. This study presents cloud condensation nuclei (CCN) concentrations measured on board the CCGS Amundsen in the eastern Canadian Arctic Archipelago from 23 July to 23 August 2016 as part of the Network on Climate and Aerosols: Addressing Uncertainties in Remote Canadian Environments (NETCARE). The study was dominated by frequent ultrafine particle and/or growth events, and particles smaller than 100 nm dominated the size distribution for 92 % of the study period. Using κ-Köhler theory and aerosol size distributions, the mean hygroscopicity parameter (κ) calculated for the entire study was 0.12 (0.06–0.12, 25th–75th percentile), suggesting that the condensable vapours that led to particle growth were primarily slightly hygroscopic, which we infer to be organic. Based on past measurement and modelling studies from NETCARE and the Canadian Arctic, it seems likely that the source of these slightly hygroscopic, organic, vapours is the ocean. Examining specific growth events suggests that the mode diameter (Dmax) had to exceed 40 nm before CCN concentrations at 0.99 % supersaturation (SS) started to increase, although a statistical analysis shows that CCN concentrations increased 13–274 cm−3 during all ultrafine particle and/or growth times (total particle concentrations >500 cm−3, Dmax<100 nm) compared with background times (total concentrations <500 cm−3) at SS of 0.26 %–0.99 %. This value increased to 25–425 cm−3 if the growth times were limited to times when Dmax was also larger than 40 nm. These results support past results from NETCARE by showing that the frequently observed ultrafine particle and growth events are dominated by a slightly hygroscopic fraction, which we interpret to be organic vapours originating from the ocean, and that these growing particles can increase the background CCN concentrations at SS as low as 0.26 %, thus pointing to their potential contribution to cloud properties and thus climate through the radiation balance.

中文翻译:

表征加拿大北极夏季生长颗粒的吸湿性

气溶胶对云的影响是大气系统的一个经过充分研究但仍缺乏约束的部分。新粒子形成 (NPF) 被认为贡献了全球云滴数浓度的 40%–80%,尽管观察从 NPF 到云形成的气团极其困难。NPF 和增长在加拿大北极夏季大气中经常发生,尽管只有少数研究描述了这些气溶胶的来源和特性。本研究介绍了在CCGS 阿蒙森号上测量的云凝结核 (CCN) 浓度2016 年 7 月 23 日至 8 月 23 日在加拿大东部北极群岛,作为气候和气溶胶网络的一部分:解决加拿大偏远环境中的不确定性 (NETCARE)。该研究以频繁的超细颗粒和/或生长事件为主,在 92% 的研究期间,小于 100 nm 的颗粒主导了尺寸分布。使用κ -Köhler 理论和气溶胶粒径分布,平均吸湿性参数 ( κ) 为整个研究计算得出的值为 0.12(0.06-0.12,第 25-75 个百分位数),这表明导致颗粒生长的可冷凝蒸汽主要是轻微吸湿性的,我们推断它是有机的。根据 NETCARE 和加拿大北极地区过去的测量和建模研究,这些略带吸湿性的有机蒸汽的来源似乎很可能是海洋。检查特定的生长事件表明,在 0.99% 过饱和 (SS) 下的 CCN 浓度开始增加之前,众数直径 ( D max ) 必须超过 40 nm,尽管统计分析表明 CCN 浓度在所有超细期间增加了 13–274 cm -3颗粒和/或生长时间(总颗粒浓度 >500  cm -3, D max <100  nm) 与 SS 为 0.26 %–0.99 % 的背景时间(总浓度<500  cm -3 )相比。如果生长时间限制D max也大于 40 nm。这些结果支持 NETCARE 过去的结果,表明经常观察到的超细颗粒和生长事件主要由轻微吸湿的部分组成,我们将其解释为来自海洋的有机蒸气,并且这些生长的颗粒可以增加背景 CCN 浓度SS 低至 0.26 %,因此表明它们对云特性的潜在贡献,从而通过辐射平衡影响气候。
更新日期:2022-06-22
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