College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China; School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.
College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China.
Sci Total Environ. 2022 Jul 10;829:154607. doi: 10.1016/j.scitotenv.2022.154607. Epub 2022 Mar 17.
New particle formation (NPF) induces a sharp increase in ultrafine particle number concentrations and potentially acts as an important source of cloud condensation nuclei (CCN). As the densely populated area of China, the Yangtze River Delta (YRD) region shows a high frequency of observed NPF events at the ground level, especially in spring. Although recent observational studies suggested a possible connection between NPF at the higher altitudes and ground level, the role played by vertical mixing, particularly in the planetary boundary layer (PBL) is not fully understood. Here we integrate measurements in Nanjing on 15-20 April 2018, and the NPF-explicit Weather Research and Forecast coupled with chemistry (WRF-Chem) model simulations to better understand the governing mechanisms of the NPF and CCN. Our results indicate that newly formed particles at the boundary layer top could be transported downward by vertical mixing as the PBL develops. A numerical sensitivity simulation created by eliminating aerosol vertical mixing suppresses both the downward transport of particles formed at a higher altitude and the dilution of particles at the ground level. The resulting higher Fuchs surface area at the ground level, together with the lack of downward transport, yields a sharp weakening of NPF strength and delayed start of NPF therein. The aerosol vertical mixing, therefore, leads to a more than double increase of surface CN and a one third decrease of boundary layer top CN. Additionally, the continuous growth of nucleated ultrafine particles at the boundary layer top is strongly steered by the upward transport of condensable gases, with close to half increase of particle number concentrations in Aitken mode and CCN at a supersaturation rate of 0.75%. The findings may bridge the gap in understanding the complex interaction between PBL dynamics and NPF events, reducing the uncertainty in assessing the climate impact of aerosols.
新粒子形成（NPF）会导致超细颗粒数浓度急剧增加，并可能成为云凝结核（CCN）的重要来源。作为中国人口密集的地区，长三角（YRD）地区在地面观测到的 NPF 事件频率很高，尤其是在春季。尽管最近的观测研究表明，高空 NPF 与地面之间可能存在联系，但垂直混合，特别是在行星边界层（PBL）中的作用尚未完全了解。在这里，我们整合了 2018 年 4 月 15 日至 20 日在南京进行的测量结果和 NPF 显式天气研究和预报与化学耦合（WRF-Chem）模型模拟，以更好地理解 NPF 和 CCN 的控制机制。我们的结果表明，随着边界层的发展，边界层顶部新形成的粒子可以通过垂直混合向下传输。通过消除气溶胶垂直混合创建的数值敏感性模拟抑制了更高海拔处形成的粒子的向下传输以及地面处粒子的稀释。结果，地面上的福克表面面积更高，而没有向下传输，导致 NPF 强度急剧减弱，NPF 开始延迟。因此，气溶胶垂直混合导致地面上的 CN 增加了一倍以上，边界层顶部的 CN 减少了三分之一。此外，边界层顶部的成核超细粒子的连续增长受到可凝结气体向上传输的强烈驱动，在过饱和度为 0.75%时，Aitken 模式的数浓度和 CCN 增加了近一半。这些发现可能缩小了理解 PBL 动力学和 NPF 事件之间复杂相互作用的差距，减少了评估气溶胶气候影响的不确定性。
