Dynamic Surface Properties of Atmospheric Aerosol and Resulting Climate Impacts

摘要：大气气溶胶通过直接散射或吸收太阳辐射，以及作为云凝结核（CCN）和形成云滴的方式间接影响气候。大气气溶胶提供了最大的负辐射强迫，同时仍然是最大不确定性的贡献。大气气溶胶的表面特性至关重要，因为它们的表面体积比很高，同时还决定了可能形成云滴的大气气溶胶的比例。大多数气候模型仍然假设活化的CCN具有相当于纯水的表面张力，但目前对这一假设的实验验证不足。正如在现场测量中发现的那样，大气中发现的表面活性剂可能会使液滴的表面张力降低到低于水的表面张力，而液滴的尺寸依赖性是影响其动态表面张力的另一个因素。该研究将使用两种实验方法来研究皮升液滴内表面活性剂的动态表面张力和表面体积分配，这两种实验方法都用于评估液滴中观察到的阻尼振荡。首先，利用全息光学镊子研究液滴在平衡表面组成和表面张力下的表面张力，并考虑其表面活性剂的表面体积分配的尺寸依赖性。第二种方法将评估具有新鲜表面年龄（亚毫秒）的液滴中表面活性剂的表面-体分配时间尺度，同时评估分配过程对其动态表面张力的重要性。这些实验数据将与合作者共享，以修改单层划分模式，从而改进气候模式估算，减少气溶胶相关辐射强迫预估中的不确定性。

Abstract:Atmospheric aerosols affect climate by direct scattering or absorption of solar radiation and indirectly, by serving as Cloud Condensation Nuclei (CCN) and forming cloud droplets. Atmospheric aerosols provide the largest negative radiative forcing, whilst remaining as the contribution with the largest uncertainty. The surface properties of atmospheric aerosol are crucial due to their high surface-to-volume ratios, whilst determining the fraction of atmospheric aerosol that may form cloud droplets. Most climate models still assume that activating CCN have a surface tension equivalent to pure water, but current experimental validation of this assumption is insufficient. Surfactants found in the atmosphere may depress the surface tension of droplets below that of water, as found in field measurements, whilst size-dependency of droplets is another contributing factor to their dynamic surface tension. The proposed research will investigate the dynamic surface tension and surface-bulk partitioning of surfactants within picolitre droplets using two experimental approaches, both used to evaluate damped oscillations observed in droplets. First, droplet coalescence using holographic optical tweezers will investigate surface tension of droplets at equilibrium surface composition and surface tension, considering size-dependency of their surface-bulk partitioning of surfactants. The second method will evaluate surface-bulk partitioning timescales for surfactants in droplets with fresh surface ages (sub-millisecond), whilst assessing the significance of the partitioning process on their dynamic surface tension. These experimental data will be shared with collaborators to modify monolayer partitioning models and thus, to improve climate modelling estimates, reducing uncertainty found in aerosol-related radiative forcing projections.