Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China; University of Science and Technology of China, Hefei 230031, China.
Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China.
Sci Total Environ. 2022 Mar 25;814:152693. doi: 10.1016/j.scitotenv.2021.152693. Epub 2021 Dec 30.
The vertical distribution of aerosols has important implications on haze formation as development, which is manifested to some extent by the planetary boundary layer (PBL)-aerosol interactions. Information on the number concentration and size of particles is essential to understand these processes, but studies on vertical profiles of particle number-size distribution are limited. Herein, an unmanned aerial vehicle (UAV) equipped with a custom-built optical particle counter (0.4-10 μm) was used to investigate the vertical profiles of particle number-size distribution in Hefei (China) during January 20-30, 2021. Combining ground-based scanning mobility particle sizer and meteorological data, the pollution accumulation and diffusion mechanisms were analyzed in depth. Results showed that as the pollution episode developed, the vertical distribution of the particle number concentration changed from a flat profile to a sharp vertical gradient. Under polluted conditions, a three-layer structure was clearly evident: uniform distribution in a mixed layer near the ground, a sharply reduced transition layer, and a low number concentration layer in the free atmosphere. Analysis revealed that fundamental to this conversion is that aerosols are highly affected by the PBL dynamics. Concurrent on-UAV and ground-based observations revealed that the ratio of particle numbers in the accumulation mode to that in the Aitken mode was 0.92 ± 0.05 in polluted days, which was almost three times that of clean days. This difference in the ratio of large to small particles suggests that hygroscopic growth of aerosol particles under high humidity conditions played an important role in haze development. Moreover, the sharp vertical gradient of the particle number concentration in the transition layer was identified as an important parameter for characterizing PBL height. The findings in this study highlight the importance of PBL dynamics on the under-studied vertical profiles of particle number-size distribution, especially during heavy pollution episodes.
气溶胶的垂直分布对霾的形成有重要影响，这在一定程度上表现为行星边界层（PBL）-气溶胶相互作用。了解这些过程的关键是有关粒子数浓度和粒径的信息，但对粒子数-粒径垂直分布的研究有限。本文利用配备定制光学粒子计数器（0.4-10μm）的无人机（UAV），于 2021 年 1 月 20-30 日在中国合肥调查了粒子数-粒径垂直分布。结合地面扫描迁移率颗粒粒径仪和气象数据，深入分析了污染积累和扩散机制。结果表明，随着污染事件的发展，粒子数浓度的垂直分布从平坦分布变为急剧的垂直梯度。在污染条件下，明显存在三层结构：地面附近混合层中的均匀分布、急剧减少的过渡层和自由大气中的低数浓度层。分析表明，这种转变的根本原因是气溶胶受到 PBL 动力学的强烈影响。同时进行的无人机和地面观测表明，污染天积聚模态和艾肯模态的粒子数之比为 0.92±0.05，几乎是清洁天的三倍。大粒子与小粒子的比例差异表明，在高湿度条件下气溶胶粒子的吸湿增长在霾发展中起重要作用。此外，过渡层中粒子数浓度的急剧垂直梯度被确定为表征 PBL 高度的重要参数。本研究结果强调了 PBL 动力学对粒子数-粒径垂直分布研究不足的重要性，尤其是在重污染事件期间。
