Bieser J, De Simone F, Gencarelli C, Geyer B, Hedgecock I, Matthias V, Travnikov O, Weigelt A
Institute of Coastal Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, 21502, Geesthacht, Germany,
Environ Sci Pollut Res Int. 2014;21(16):9995-10012. doi: 10.1007/s11356-014-2863-2. Epub 2014 Apr 25.
This study is part of the Global Mercury Observation System (GMOS), a European FP7 project dedicated to the improvement and validation of mercury models to assist in establishing a global monitoring network and to support political decisions. One key question about the global mercury cycle is the efficiency of its removal out of the atmosphere into other environmental compartments. So far, the evaluation of modeled wet deposition of mercury was difficult because of a lack of long-term measurements of oxidized and elemental mercury. The oxidized mercury species gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) which are found in the atmosphere in typical concentrations of a few to a few tens pg/m(3) are the relevant components for the wet deposition of mercury. In this study, the first European long-term dataset of speciated mercury taken at Waldhof/Germany was used to evaluate deposition fields modeled with the chemistry transport model (CTM) Community Multiscale Air Quality (CMAQ) and to analyze the influence of the governing parameters. The influence of the parameters precipitation and atmospheric concentration was evaluated using different input datasets for a variety of CMAQ simulations for the year 2009. It was found that on the basis of daily and weekly measurement data, the bias of modeled depositions could be explained by the bias of precipitation fields and atmospheric concentrations of GOM and PBM. A correction of the modeled wet deposition using observed daily precipitation increased the correlation, on average, from 0.17 to 0.78. An additional correction based on the daily average GOM and PBM concentration lead to a 50% decrease of the model error for all CMAQ scenarios. Monthly deposition measurements were found to have a too low temporal resolution to adequately analyze model deficiencies in wet deposition processes due to the nonlinear nature of the scavenging process. Moreover, the general overestimation of atmospheric GOM by the CTM in combination with an underestimation of low precipitation events in the meteorological models lead to a good agreement of total annual wet deposition besides the large error in weekly deposition estimates. Moreover, it was found that the current speciation profiles for GOM emissions are the main factor for the overestimation of atmospheric GOM concentrations and might need to be revised in the future. The assumption of zero emissions of GOM lead to an improvement of the mean normalized bias for three-hourly observations of atmospheric GOM from 9.7 to 0.5, Furthermore, the diurnal correlation between model and observation increased from 0.01 to 0.64. This is a strong indicator that GOM is not directly emitted from primary sources but is mainly created by oxidation of GEM.
本研究是全球汞观测系统（GMOS）的一部分，GMOS是一个欧洲第七框架计划项目，致力于改进和验证汞模型，以协助建立全球监测网络并支持政治决策。关于全球汞循环的一个关键问题是其从大气中去除到其他环境介质中的效率。到目前为止，由于缺乏对氧化态汞和元素汞的长期测量，对汞模拟湿沉降的评估一直很困难。大气中典型浓度为几到几十皮克/立方米的氧化汞物种气态氧化汞（GOM）和颗粒态汞（PBM）是汞湿沉降的相关成分。在本研究中，利用在德国瓦尔德霍夫获取的首个欧洲长期汞形态数据集，来评估用化学传输模型（CTM）社区多尺度空气质量（CMAQ）模拟的沉降场，并分析控制参数的影响。针对2009年的各种CMAQ模拟，使用不同的输入数据集评估了降水和大气浓度参数的影响。结果发现，基于每日和每周的测量数据，模拟沉降的偏差可以用降水场以及GOM和PBM的大气浓度偏差来解释。使用观测到的每日降水量对模拟湿沉降进行校正后，相关性平均从0.17提高到了0.78。基于每日平均GOM和PBM浓度的额外校正使所有CMAQ情景下的模型误差降低了50%。由于清除过程的非线性性质，发现月度沉降测量的时间分辨率过低，无法充分分析湿沉降过程中的模型缺陷。此外，CTM对大气GOM的普遍高估，再加上气象模型对低降水事件的低估，导致除了每周沉降估计存在较大误差外，年度总湿沉降结果吻合较好。此外，还发现当前GOM排放的形态分布是大气GOM浓度高估的主要因素，未来可能需要进行修正。假设GOM零排放使得大气GOM三小时观测的平均归一化偏差从9.7改善到了0.5，此外，模型与观测之间的日相关性从0.01提高到了0.64。这有力地表明GOM并非直接从主要源排放，而是主要由气态单质汞（GEM）氧化产生。
