4D dispersion of total gaseous mercury derived from a mining source: identification of criteria to assess risks related to high concentrations of atmospheric mercury
Authors: Esbrí José M. , Higueras Pablo L. , Martínez-Coronado Alba , Naharro Rocío 
Published: November 2020

Abstract. Mercury (Hg) is a global pollutant that can be transported
long distances after its emission from primary sources. The most common
problem of gaseous Hg in the vicinity of anthropogenic sources is its
presence in inorganic forms and in the gaseous state in the atmosphere. Risk
assessments related to the presence of gaseous Hg in the atmosphere at
contaminated sites are often based on episodic and incomplete data, which do
not properly characterize the Hg cycle in the area of interest or consider
spatial or temporal terms. The aim of this work was to identify
criteria to obtain the minimum amount of data with the maximum meaning and
representativeness in order to delimit risk areas, both in a spatial and
temporal respect. Data were acquired from May 2014 to August 2015 and
included vertical and horizontal Hg measurements. A statistical analysis was
carried out, and this included the construction of a model of vertical Hg
movements that could be used to predict the location and timing of Hg
inhalation risk. A monitoring strategy was designed in order to identify the
relevant criteria, and this involved the measurement of gaseous Hg in a
vertical section at low altitude (i.e. where humans are present) and in
horizontal transects to appropriately characterize the transport cycle of
gaseous Hg in the lower layers of the atmosphere. The measurements were
carried out over time in order to obtain information on daily and seasonal
variability. The study site selected was Almadenejos (Ciudad Real, Spain), a
village polluted with mercury related to decommissioned mining and
metallurgical facilities belonging to the Almadén mercury mining
district. The vertical profiles revealed that higher total gaseous mercury
concentrations are present at lower altitude during nocturnal hours and at
higher altitude at dawn and dusk. On a daily basis the most important
process involved in gaseous mercury movements is the mixing layer. Vertical
transferences are predominant when this process is active, i.e. in all
seasons except winter, while major sources act as constant suppliers of
gaseous Hg to the mixing cell, thus producing Hg deposition at dusk.
Conversely, horizontal transferences prevail during the hours of darkness
and the main factors are major and minor sources, solar radiation, wind
speed, and topography. The study has shown that it is important (i) to
identify the sources, (ii) to get data about Hg movements in vertical and
horizontal directions, (iii) to extend the measurements over time in a
sufficiently representative way both daily and seasonally, and (iv) to determine
the different populations of data to establish the background levels; this
work proposes the use of Lepeltier graphs to do so. In terms of risk assessment, the nights carry greater risk than the days in
all seasons except autumn. The main factors involved in the creation of
high-risk periods are those related to dilution (or its absence), namely
wind speed and solar radiation at null levels. The results of this study highlight the possible importance of relieving
the distribution of gaseous mercury in proximity to discrete sources.
Furthermore, systematic monitoring strategies can offer significant
information for the Minamata Convention emission reduction scenario. Further
studies, including a detailed topographic model of the area, are required in
order to make precise estimations of the influence of this parameter, which
appears in this study to be less important than the other factors but is
still appreciable.