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. Mercury (Hg) is a global pollutant that can be transportedlong distances after its emission from primary sources. The most commonproblem of gaseous Hg in the vicinity of anthropogenic sources is itspresence in inorganic forms and in the gaseous state in the atmosphere. Riskassessments related to the presence of gaseous Hg in the atmosphere atcontaminated sites are often based on episodic and incomplete data, which donot properly characterize the Hg cycle in the area of interest or considerspatial or temporal terms. The aim of this work was to identifycriteria to obtain the minimum amount of data with the maximum meaning andrepresentativeness in order to delimit risk areas, both in a spatial andtemporal respect. Data were acquired from May 2014 to August 2015 andincluded vertical and horizontal Hg measurements. A statistical analysis wascarried out, and this included the construction of a model of vertical Hgmovements that could be used to predict the location and timing of Hginhalation risk. A monitoring strategy was designed in order to identify therelevant criteria, and this involved the measurement of gaseous Hg in avertical section at low altitude (i.e. where humans are present) and inhorizontal transects to appropriately characterize the transport cycle ofgaseous Hg in the lower layers of the atmosphere. The measurements werecarried out over time in order to obtain information on daily and seasonalvariability. The study site selected was Almadenejos (Ciudad Real, Spain), avillage polluted with mercury related to decommissioned mining andmetallurgical facilities belonging to the Almadén mercury miningdistrict. The vertical profiles revealed that higher total gaseous mercuryconcentrations are present at lower altitude during nocturnal hours and athigher altitude at dawn and dusk. On a daily basis the most importantprocess involved in gaseous mercury movements is the mixing layer. Verticaltransferences are predominant when this process is active, i.e. in allseasons except winter, while major sources act as constant suppliers ofgaseous Hg to the mixing cell, thus producing Hg deposition at dusk.Conversely, horizontal transferences prevail during the hours of darknessand the main factors are major and minor sources, solar radiation, windspeed, and topography. The study has shown that it is important (i) toidentify the sources, (ii) to get data about Hg movements in vertical andhorizontal directions, (iii) to extend the measurements over time in asufficiently representative way both daily and seasonally, and (iv) to determinethe different populations of data to establish the background levels; thiswork proposes the use of Lepeltier graphs to do so. In terms of risk assessment, the nights carry greater risk than the days inall seasons except autumn. The main factors involved in the creation ofhigh-risk periods are those related to dilution (or its absence), namelywind speed and solar radiation at null levels. The results of this study highlight the possible importance of relievingthe distribution of gaseous mercury in proximity to discrete sources.Furthermore, systematic monitoring strategies can offer significantinformation for the Minamata Convention emission reduction scenario. Furtherstudies, including a detailed topographic model of the area, are required inorder to make precise estimations of the influence of this parameter, whichappears in this study to be less important than the other factors but isstill appreciable.

atmospheric chemistry and physics

4D dispersion of total gaseous mercury derived from a mining source: identification of criteria to assess risks related to high concentrations of atmospheric mercury