A diagnostic evaluation of modeled mercury wet depositions in Europe using atmospheric speciated high-resolution observations

Abstract

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 modelled wet deposition of mercury was difficult because of a lack of long term measurements of oxidized and elemental mercury. The oxidized mercury species GOM (Gaseous Oxidized Mercury) and PBM (Particle Bound Mercury) which are found in the atmosphere in typical concentrations of a few to a few tens pg/m³ 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 modelled with the chemistry transport model (CTM) CMAQ and to analyse 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 modelled depositions could be explained by the bias of precipitation fields and atmospheric concentrations of GOM and PBM. A correction of the modelled 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 analyse model deficiencies in wet deposition processes due to the non-linear 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.

Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

“…An investigation of the experimental model runs indicated that the overestimation at the surface is due to anthropogenic emissions and was reduced significantly in the ANTSPEC run, while concentrations above the surface are mainly driven by atmospheric chemistry. This is in line with the findings of Bieser et al (2014a) and .…”

“…Consequently, mercury oxidation processes have been the focus of the international mercury community in recent years Cohen et al, 2016;Amos et al, 2015;Dastoor et al, 2015;Song et al, 2015;Bieser et al, 2014a;De Simone et al, 2014;Qureshi et al, 2011;Travnikov et al, 2010).…”

Sensitivity model study of regional mercury dispersion in the atmosphere

“…The principal differences between the models used concern the parametrisations of some of the processes, for instance GEM dry deposition, convective precipitation and GEM evasion from the sea surface (see Gencarelli et al, 2015, andBieser et al, 2014, for details). Other differences result from the use of different BC sets and meteorological input.…”

“…The chemical IC/BC were taken from the GLEMOS model (Travnikov et al, 2009). For further details on the models see Gencarelli et al (2014aGencarelli et al ( , 2015 for WRF/Chem-Hg and Bieser et al (2014) and Zhu et al (2015) for CMAQ-Hg.…”

“…Within GMOS global chemical transport models (CTMs) have been used to evaluate the intercontinental transport of anthropogenic Hg and analyse different future Hg emission scenarios (Pacyna et al, 2016), source-receptor relationships (Travnikov et al, 2010) and Hg cycles in the polar regions . Regionalscale models have been used for a closer study of the processes that occur in specific areas at much higher spatial resolution than the global CTMs Bieser et al, 2014). In a recent review Ariya et al (2015) give a exhaustive summary of modelling progress and of the uncertainties still present concerning the atmospheric Hg cycle.…”