Inter-annual variations of wet deposition in Beijing from 2014-2017: implications of below-cloud scavenging of inorganic aerosols
Inter-annual variations of wet deposition in Beijing from 2014-2017: implications of below-cloud scavenging of inorganic aerosols
复制标题
2014-2017年北京湿沉降的年际变化：云下无机气溶胶清除的影响
DOI：
10.5194/acp-21-9441-2021
复制
发表时间：
2021-06-22
影响因子：
6.3
通讯作者：
Wang, Zifa
中科院分区：
文献类型：
--
作者：
Ge, Baozhu;Xu, Danhui;Wang, Zifa
湿式净化是去除大气中颗粒物的有效途径。高水平的PM一直是北京空气污染的主要原因，但在2013年启动的《大气污染防治行动计划》下，PM水平大幅下降。在这项研究中，4年的观测湿沉降已进行了连续采样技术，通过每次降雨事件调查化学成分的详细变化。我们发现，2013-2017年期间，主要离子SO 42-、Ca 2+、NO3-和NH 4+均显著下降（分别下降39%、35%、12%和25%），揭示了行动计划的影响。提出了一种改进的基于序贯采样的云下清除比例估算方法，并用于估算云下和云内湿沉降对4 a的贡献。总体而言，在行动计划初期，云下清除对四种主要离子的湿沉降起主导作用。云下清除Ca 2+、SO 42-和NH 4+的贡献从2014年的50%以上下降到2017年的40%以下。这表明行动计划减轻了表层的PM污染，从而减少了冲刷过程造成的清除。相比之下，我们发现NO3的年体积加权平均浓度几乎没有变化-其中云下清除的贡献在2015-2017年期间保持在44%左右。在强调不同湿清除过程的重要性的同时，本文对《行动计划》的影响提出了一个独特的新视角，并明确将氧化态氮物种确定为未来空气污染控制的主要目标。
Wet scavenging is an efficient pathway for the removal of particulate matter (PM) from the atmosphere. High levels of PM have been a major cause of air pollution in Beijing but have decreased sharply under the Air Pollution Prevention and Control Action Plan launched in 2013. In this study, 4 years of observations of wet deposition have been conducted using a sequential sampling technique to investigate the detailed variation in chemical components through each rainfall event. We find that the major ions, SO42-, Ca2+, NO3-, and NH4+, show significant decreases over the 2013-2017 period (decreasing by 39 %, 35 %, 12 %, and 25 %, respectively), revealing the impacts of the Action Plan. An improved method of estimating the below-cloud scavenging proportion based on sequential sampling is developed and implemented to estimate the contribution of below-cloud and in-cloud wet deposition over the four-year period. Overall, below-cloud scavenging plays a dominant role to the wet deposition of four major ions at the beginning of the Action Plan. The contribution of below-cloud scavenging for Ca2+, SO42-, and NH4+ decreases from above 50 % in 2014 to below 40 % in 2017. This suggests that the Action Plan has mitigated PM pollution in the surface layer and hence decreased scavenging due to the washout process. In contrast, we find little change in the annual volume weighted average concentration for NO3- where the contribution from below-cloud scavenging remains at similar to 44 % over the 2015-2017 period. While highlighting the importance of different wet scavenging processes, this paper presents a unique new perspective on the effects of the Action Plan and clearly identifies oxidized nitrogen species as a major target for future air pollution controls.