Vertical profile of particle hygroscopicity and CCN effectiveness during winter in Beijing: insight into the hygroscopicity transition threshold of black carbon.
Vertical profile of particle hygroscopicity and CCN effectiveness during winter in Beijing: insight into the hygroscopicity transition threshold of black carbon.
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DOI：
10.1039/d0fd00077a
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发表时间：
2020-11
影响因子：
3.4
通讯作者：
Dawei Hu;Yu Wang;Chenjie Yu;Q. Xie;Siyao Yue;D. Shang;Xin Fang;Rutambhara Joshi;Dantong Liu-Danton
中科院分区：
文献类型：
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作者：
Dawei Hu;Yu Wang;Chenjie Yu;Q. Xie;Siyao Yue;D. Shang;Xin Fang;Rutambhara Joshi;Dantong Liu-Danton
气溶胶粒子的吸湿性和作为云凝结核（CCN）的能力在决定其寿命和在气溶胶-云相互作用中的作用方面很重要，从而影响云的形成和气候。以往的研究使用在地面测量的气溶胶吸湿性来评估对大气中云形成的影响，这可能会引入与气溶胶吸湿性随高度变化相关的不确定性。在这项研究中，CCN行为和吸湿特性的日常过滤收集的PM2. 5从三个不同的高度（8，120，260米）在北京的塔在实验室中使用水，水/甲醇和甲醇作为雾化溶剂。虽然有大量的时间变化的颗粒浓度和成分，有一点明显的差异，在不同高度的气溶胶CCN和吸湿行为，虽然行星边界层的高度（PBLH）降低到塔的高度以下，在夜间，这表明使用表面吸湿测量是足够的估计气溶胶粒子激活云。此外，临界涂层厚度（涂层/耐火BC的质量比，MRc）定义之间的疏水性到亲水性的BC过渡，通过结合吸湿串联微分迁移率分析仪（H-TDMA），离心颗粒质量分析仪（CPMA）和单颗粒烟尘光度计（SP2）的测量确定。在纳米颗粒生长事件开始时，250 nm含BC颗粒的MRc从0.8和1.6之间的背景值增加到约4.6，随着事件的进展单调地降低回到背景水平。这表明大颗粒在纳米颗粒生长事件期间不充当吸湿蒸汽的有效的预先存在的冷凝槽，导致250 nm BC颗粒需要更多的涂层材料来在疏水性和亲水性之间转变。这些发现表明，大颗粒在抑制大气中新颗粒的形成和随后的生长方面可能不太重要。
The hygroscopicity and ability of aerosol particles to act as cloud condensation nuclei (CCN) is important in determining their lifetime and role in aerosol-cloud interactions, thereby influencing cloud formation and climate. Previous studies have used the aerosol hygroscopic properties measured at the ground to evaluate the influence on cloud formation in the atmosphere, which may introduce uncertainty associated with aerosol hygroscopicity variability with altitude. In this study, the CCN behaviour and hygroscopic properties of daily filter collections of PM2.5 from three different heights (8, 120, 260 m) on a tower in Beijing were determined in the laboratory using water, water/methanol and methanol as the atomization solvents. Whilst there was substantial temporal variability in particle concentration and composition, there was little obvious difference in aerosol CCN and hygroscopic behaviour at different heights, although the planetary boundary layer height (PBLH) reduced to below the tower height during the nighttime, suggesting that use of surface hygroscopicity measurements is sufficient for the estimation of aerosol particle activation in clouds. Additionally, the critical coating thickness (in terms of mass ratio of coating/refractory BC, MRc) defining the BC transition between being hydrophobic to hydrophilic, was determined by combining hygroscopic tandem differential mobility analyser (H-TDMA), centrifugal particle mass analyzer (CPMA) and single particle soot photometer (SP2) measurements. The MRc of 250 nm BC-containing particles increased from a background value of between 0.8 and 1.6 to around 4.6 at the onset of the growth event of nanoparticles, decreasing monotonically back to the background level as the event progressed. This indicates that large particles do not act as an effective pre-existing condensation sink of the hygroscopic vapours during the nanoparticle growth events, leading to the 250 nm BC particles requiring more coating materials to transition between being hydrophobic and hydrophilic. These findings show that large particles may be less important in suppressing the new particle formation and subsequent growth in the atmosphere.