Characteristics of atmospheric Total Gaseous Mercury (TGM) observed in urban Nanjing, China

Abstract. Long-term continuous measurements of total gaseous mercury (TGM = gaseous elemental mercury (GEM) + reactive gaseous mercury (RGM)) were conducted simultaneously along with meteorological variables and a suite of trace gases at an urban site in Nanjing, China from 18 January to 31 December 2011. Measurements were conducted using a high resolution mercury vapor analyzer (Tekran 2537B) with 5-min time resolution. The average concentration of TGM was 7.9 ± 7.0 ng m−3 with a range of 0.8–180 ng m−3 over the study period. TGM concentrations followed a typical lognormal pattern dominated by a range of 3–7 ng m−3, which was significantly higher than the continental background values (~1.5 ng m−3) in Northern Hemisphere. The mean seasonal TGM concentrations decreased in the following order: summer, spring, fall, and winter. This seasonal pattern was quite different from measurements at most other sites around the world. We attributed high monthly average concentrations to the re-volatilization of deposited mercury during the warm season due to high temperatures and greater solar radiation. Previous modeling studies suggested that Nanjing and the surrounding region have the largest Chinese natural emissions during the summer. Positive correlations between temperature, solar radiation, and TGM concentration combined with no correlation between CO and TGM in summer provide a strong indication that natural sources are important in Nanjing while most sharp peaks were caused by anthropogenic sources. TGM concentrations in Nanjing exhibited a noticeable diurnal pattern with a sharp increase after sunrise and peak of greater than 8 ng m−3 during 7–10 a.m. local time. Further, seasonally averaged diurnal cycles of TGM exhibited considerably different patterns with the largest variation in spring and insignificant fluctuations in winter. Using HYSPLIT backwards trajectories from six clusters, it was indicated that the highest TGM concentrations, 11.9 ng m−3, was derived from local air masses. The cleanest air masses, with an average TGM concentration of 4.7 and 5.9 ng m−3, were advected from the north via fast transport facilitated by sweeping synoptic flows.

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Characteristics of atmospheric total gaseous mercury (TGM) observed in urban Nanjing, China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-25037-2012 ◽

2012 ◽

Vol 12 (9) ◽

pp. 25037-25080 ◽

Cited By ~ 1

Author(s):

J. Zhu ◽

T. Wang ◽

R. Talbot ◽

H. Mao ◽

C. B. Hall ◽

...

Keyword(s):

Solar Radiation ◽

Seasonal Pattern ◽

Warm Season ◽

Elemental Mercury ◽

Average Concentration ◽

Anthropogenic Sources ◽

Urban Site ◽

Total Gaseous Mercury ◽

Air Masses ◽

Gaseous Mercury

Abstract. Long-term continuous measurements of total gaseous mercury (TGM = gaseous elemental mercury (GEM) + reactive gaseous mercury, RGM) were conducted simultaneously along with meteorological variables and a suite of trace gases at an urban site in Nanjing, China from 18 January to 31 December 2011. Measurements were conducted using a high resolution mercury vapor analyzer (Tekran 2537B) with 5-min time resolution. The average concentration of TGM was 7.9 ± 7.0 ng m−3 with a range of 0.8–180 ng m−3 over the study period. TGM concentrations followed a typical lognormal pattern dominated by a range of 3–7 ng m−3, which was significantly higher than the continental background values (~1.5 ng m−3) in Northern Hemisphere. The mean seasonal TGM concentrations decreased in the following order: summer, spring, fall, and winter. This seasonal pattern was quite different from measurements at most other sites around the world. We attributed high monthly average concentrations to the re-volatilization of deposited mercury during the warm season due to high temperatures and greater solar radiation. Previous Modeling studies suggested that Nanjing and the surrounding region have the largest Chinese natural emissions during the summer. Positive correlations between temperature, solar radiation, and TGM concentration combined with no correlation between CO and TGM in summer provide a strong indication that natural sources are important in Nanjing. While most sharp peaks were caused by anthropogenic sources. TGM concentrations in Nanjing exhibited a noticeable diurnal pattern with a sharp increase after sunrise and peak of greater than 8 m−3 during 7–10 a.m. LT. Further, seasonally averaged diurnal cycles of TGM exhibited considerably different patterns with the largest variation in spring and insignificant fluctuations in winter. Using HYSPLIT backwards trajectories from six clusters, it was indicated that the highest TGM concentrations, 11.9 m−3, was derived from lacal air masses. The cleanest air masses, with an average TGM concentration of 4.7 and 5.9 m−3, were advected from the north via fast transport facilitated by sweeping synoptic flows.

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

10.5194/acp-2019-1107 ◽

2020 ◽

Author(s):

José M. Esbrí ◽

Pablo L. Higueras ◽

Alba Martínez-Coronado ◽

Rocío Naharro

Keyword(s):

Wind Speed ◽

Solar Radiation ◽

Anthropogenic Sources ◽

Total Gaseous Mercury ◽

Lower Altitude ◽

Gaseous State ◽

Area Of Interest ◽

Gaseous Mercury ◽

The Hours ◽

Main Factors

Abstract. Mercury is a global pollutant that can be transported long distances after its emission by primary sources. Most of the problems associated with Hg as a toxic element dispersed worldwide arise due to its incorporation into the trophic chain and its conversion into organic forms. However, in the vicinity of anthropogenic sources, the most common problem is the presence of Hg in inorganic forms and in the gaseous state in the atmosphere. Risk assessments related to the presence of gaseous Hg in the atmosphere at these 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 the work described was to identify criteria to obtain the minimum amount of data with the maximum meaning and representativeness in order to delimitate risk areas, both in a spatial and temporal respect. Data were acquired from September 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 characterize appropriately 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. Horizontal profiles showed that the background values were close to 6 ng m−3 except in the spring months, when they rose to 13 ng m−3 and increased the area affected by mercury emissions to more than 4 km around the mining and metallurgical sites. On a daily basis the most important process involved in gaseous mercury movements is the mixing layer, which begins in the early morning and finishes at nightfall. 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. In terms of risk assessment, and based on the model constructed to infer atmospheric Hg concentrations based on micrometeorological parameters, the nights carry greater risk than the days in all seasons (54 % in spring and winter, 72 % in summer) except in autumn, when 99 % of the hours of risk occurred during the day. 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 extent of the area affected by an emission source is independent of its importance in terms of absolute emissions. The affected zone did not extend beyond 100 metres from the location of the source during the daytime period and 200 metres in the night-time. Under the worst micrometeorological conditions, it was predicted that the affected area would cover almost the entire town of Almadenejos, although these risk conditions only represent 11.34 % of the hours in an annual period. The results of this study highlight the possible importance of the relief in the distribution of gaseous mercury in the proximity of discrete sources. 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.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-12995-2020 ◽

2020 ◽

Vol 20 (21) ◽

pp. 12995-13010

Author(s):

José M. Esbrí ◽

Pablo L. Higueras ◽

Alba Martínez-Coronado ◽

Rocío Naharro

Keyword(s):

Wind Speed ◽

Solar Radiation ◽

Anthropogenic Sources ◽

Total Gaseous Mercury ◽

Significant Information ◽

Lower Altitude ◽

Gaseous State ◽

Gaseous Mercury ◽

Main Factors ◽

Over Time

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.

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Classification of clouds sampled at the puy de Dôme (France) based on 10 yr of monitoring of their physicochemical properties

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-1485-2014 ◽

2014 ◽

Vol 14 (3) ◽

pp. 1485-1506 ◽

Cited By ~ 58

Author(s):

L. Deguillaume ◽

T. Charbouillot ◽

M. Joly ◽

M. Vaïtilingom ◽

M. Parazols ◽

...

Keyword(s):

Statistical Analysis ◽

Chemical Composition ◽

Inorganic Compounds ◽

Average Concentration ◽

Anthropogenic Sources ◽

Back Trajectory ◽

Data Set ◽

Air Masses ◽

High Concentrations ◽

Inorganic Constituents

Abstract. Long-term monitoring of the chemical composition of clouds (73 cloud events representing 199 individual samples) sampled at the puy de Dôme (pdD) station (France) was performed between 2001 and 2011. Physicochemical parameters, as well as the concentrations of the major organic and inorganic constituents, were measured and analyzed by multicomponent statistical analysis. Along with the corresponding back-trajectory plots, this allowed for distinguishing four different categories of air masses reaching the summit of the pdD: polluted, continental, marine and highly marine. The statistical analysis led to the determination of criteria (concentrations of inorganic compounds, pH) that differentiate each category of air masses. Highly marine clouds exhibited high concentrations of Na+ and Cl−; the marine category presented lower concentration of ions but more elevated pH. Finally, the two remaining clusters were classified as "continental" and "polluted"; these clusters had the second-highest and highest levels of NH4+, NO3−, and SO24−, respectively. This unique data set of cloud chemical composition is then discussed as a function of this classification. Total organic carbon (TOC) is significantly higher in polluted air masses than in the other categories, which suggests additional anthropogenic sources. Concentrations of carboxylic acids and carbonyls represent around 10% of the organic matter in all categories of air masses and are studied for their relative importance. Iron concentrations are significantly higher for polluted air masses and iron is mainly present in its oxidation state (+II) in all categories of air masses. Finally, H2O2 concentrations are much more varied in marine and highly marine clouds than in polluted clouds, which are characterized by the lowest average concentration of H2O2. This data set provides concentration ranges of main inorganic and organic compounds for modeling purposes on multiphase cloud chemistry.

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Observation and analysis of speciated atmospheric mercury in Shangri-la, Tibetan Plateau, China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-11041-2014 ◽

2014 ◽

Vol 14 (8) ◽

pp. 11041-11074 ◽

Cited By ~ 2

Author(s):

H. Zhang ◽

X. W. Fu ◽

C.-J. Lin ◽

X. Wang ◽

X. B. Feng

Keyword(s):

Tibetan Plateau ◽

Atmospheric Transport ◽

Seasonal Pattern ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

North India ◽

Air Masses ◽

Gaseous Elemental Mercury ◽

Wet Scavenging ◽

In The Beginning

Abstract. This study reports the speciated concentration and the potential sources of atmospheric mercury measured at the Shangri-La Atmosphere Watch Regional Station (SAWRS), a pristine high-altitude site (3580 m a.s.l.) in Tibetan Plateau, China. The total gaseous mercury (TGM, defined as the sum of Gaseous Elemental Mercury, GEM, and gaseous oxidized mercury, GOM), GOM and particulate-bound mercury (PBM) were monitored from November 2009 to November 2010 to investigate the characteristics and atmospheric transport of mercury influenced by the Indian summer monsoon (ISM) and westerlies. The mean concentrations of TGM, PBM and GOM were 2.55 ± 0.73 ng m−3, 37.78 ± 31.35 pg m−3 and 7.90 ± 7.89 ng m−3. A notable seasonal pattern was observed with higher TGM concentrations in the beginning and end of the ISM. High TGM concentrations were associated with the transport of dry air that carried regional anthropogenic emissions from both domestic and foreign sources. The low PBM and GOM level was attributed to the deposition and wet scavenging during the ISM period. Backward trajectory analysis of air masses associated with TGM levels suggested that both the ISM and westerlies can carry Hg emitted in Burma, Bengal bay and north India to the SAWRS.

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Seasonal patterns of atmospheric mercury in tropical South America as inferred by a continuous total gaseous mercury record at Chacaltaya station (5240 m) in Bolivia

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3447-2021 ◽

2021 ◽

Vol 21 (5) ◽

pp. 3447-3472

Author(s):

Alkuin Maximilian Koenig ◽

Olivier Magand ◽

Paolo Laj ◽

Marcos Andrade ◽

Isabel Moreno ◽

...

Keyword(s):

South America ◽

Dry Season ◽

Atmospheric Mercury ◽

Small Scale ◽

Co2 Uptake ◽

Total Gaseous Mercury ◽

Wet Season ◽

Air Masses ◽

Gaseous Mercury ◽

Vegetation Activity

Abstract. High-quality atmospheric mercury (Hg) data are rare for South America, especially for its tropical region. As a consequence, mercury dynamics are still highly uncertain in this region. This is a significant deficiency, as South America appears to play a major role in the global budget of this toxic pollutant. To address this issue, we performed nearly 2 years (July 2014–February 2016) of continuous high-resolution total gaseous mercury (TGM) measurements at the Chacaltaya (CHC) mountain site in the Bolivian Andes, which is subject to a diverse mix of air masses coming predominantly from the Altiplano and the Amazon rainforest. For the first 11 months of measurements, we obtained a mean TGM concentration of 0.89±0.01 ng m−3, which is in good agreement with the sparse amount of data available from the continent. For the remaining 9 months, we obtained a significantly higher TGM concentration of 1.34±0.01 ng m−3, a difference which we tentatively attribute to the strong El Niño event of 2015–2016. Based on HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) back trajectories and clustering techniques, we show that lower mean TGM concentrations were linked to either westerly Altiplanic air masses or those originating from the lowlands to the southeast of CHC. Elevated TGM concentrations were related to northerly air masses of Amazonian or southerly air masses of Altiplanic origin, with the former possibly linked to artisanal and small-scale gold mining (ASGM), whereas the latter might be explained by volcanic activity. We observed a marked seasonal pattern, with low TGM concentrations in the dry season (austral winter), rising concentrations during the biomass burning (BB) season, and the highest concentrations at the beginning of the wet season (austral summer). With the help of simultaneously sampled equivalent black carbon (eBC) and carbon monoxide (CO) data, we use the clearly BB-influenced signal during the BB season (August to October) to derive a mean TGM / CO emission ratio of (2.3±0.6)×10-7 ppbvTGM ppbvCO-1, which could be used to constrain South American BB emissions. Through the link with CO2 measured in situ and remotely sensed solar-induced fluorescence (SIF) as proxies for vegetation activity, we detect signs of a vegetation sink effect in Amazonian air masses and derive a “best guess” TGM / CO2 uptake ratio of 0.058 ±0.017 (ng m−3)TGM ppmCO2-1. Finally, significantly higher Hg concentrations in western Altiplanic air masses during the wet season compared with the dry season point towards the modulation of atmospheric Hg by the eastern Pacific Ocean.

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Four years (2011–2015) of total gaseous mercury measurements from the Cape Verde Atmospheric Observatory

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5393-2017 ◽

2017 ◽

Vol 17 (8) ◽

pp. 5393-5406 ◽

Cited By ~ 6

Author(s):

Katie A. Read ◽

Luis M. Neves ◽

Lucy J. Carpenter ◽

Alastair C. Lewis ◽

Zoe L. Fleming ◽

...

Keyword(s):

Industrial Revolution ◽

Spatial Scales ◽

The United States ◽

Cape Verde ◽

Anthropogenic Sources ◽

Small Scale ◽

Anthropogenic Emissions ◽

The European Union ◽

Total Gaseous Mercury ◽

Gaseous Mercury

Abstract. Mercury is a chemical with widespread anthropogenic emissions that is known to be highly toxic to humans, ecosystems and wildlife. Global anthropogenic emissions are around 20 % higher than natural emissions and the amount of mercury released into the atmosphere has increased since the industrial revolution. In 2005 the European Union and the United States adopted measures to reduce mercury use, in part to offset the impacts of increasing emissions in industrialising countries. The changing regional emissions of mercury have impacts on a range of spatial scales. Here we report 4 years (December 2011–December 2015) of total gaseous mercury (TGM) measurements at the Cape Verde Observatory (CVO), a global WMO-GAW station located in the subtropical remote marine boundary layer. Observed total gaseous mercury concentrations were between 1.03 and 1.33 ng m−3 (10th, 90th percentiles), close to expectations based on previous interhemispheric gradient measurements. We observe a decreasing trend in TGM (−0.05 ± 0.04 ng m−3 yr−1, −4.2 % ± 3.3 % yr−1) over the 4 years consistent with the reported decrease of mercury concentrations in North Atlantic surface waters and reductions in anthropogenic emissions. The decrease was more visible in the summer (July–September) than in the winter (December–February), when measurements were impacted by air from the African continent and Sahara/Sahel regions. African air masses were also associated with the highest and most variable TGM concentrations. We suggest that the less pronounced downward trend inclination in African air may be attributed to poorly controlled anthropogenic sources such as artisanal and small-scale gold mining (ASGM) in West Africa.

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Four years (2011–2015) of Total Gaseous Mercury measurements from the Cape Verde Atmospheric Observatory

10.5194/acp-2016-1036 ◽

2016 ◽

Author(s):

Katie A. Read ◽

Luis M. Neves ◽

Lucy J. Carpenter ◽

Alastair C. Lewis ◽

Zoe Fleming ◽

...

Keyword(s):

Industrial Revolution ◽

Marine Boundary Layer ◽

Spatial Scales ◽

Cape Verde ◽

Anthropogenic Sources ◽

Small Scale ◽

Anthropogenic Emissions ◽

The European Union ◽

Total Gaseous Mercury ◽

Gaseous Mercury

Abstract. Mercury is a chemical with widespread anthropogenic emissions that is known to be highly toxic to humans, ecosystems and wildlife. Global anthropogenic emissions are around 20 % higher than natural emissions and the amount of mercury released into the atmosphere has increased since the industrial revolution. In 2005 the European Union and United States adopted measures to reduce mercury use, in part to offset the impacts of increasing emissions in industrialising countries. The changing regional emissions of mercury have impacts on a range of spatial scales. Here we report four years (Dec 2011–Dec 2015) of Total Gaseous Mercury (TGM) measurements at the Cape Verde Observatory (CVO), a global WMO-GAW station located in the sub-tropical remote marine boundary layer. Observed total gaseous mercury concentrations were between 1.03 and 1.33 ng m−3 (10th, 90th percentiles), close to expectations based on previous interhemispheric gradient measurements. We observe a decreasing trend in TGM (0.04 ± 0.03 ng m−3 yr−1, −3.4 % ± 2.4 % yr−1) over the four years consistent with the reported decrease of mercury concentrations in North Atlantic surface waters and reductions in anthropogenic emissions. The trend was more visible in the summer (Jul–Sep) than in the winter (Dec–Feb), when measurements were impacted by air from the African continent and Sahara/Sahel regions. African air masses were also associated with the highest and most variable TGM concentrations. We suggest that the less pronounced downward trend in African air may be attributed to poorly controlled anthropogenic sources such as artisanal and small-scale gold mining (ASGM).

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Distribution of toxic metals and relative toxicity of airborne PM2.5 in Puerto Rico

Environmental Science and Pollution Research ◽

10.1007/s11356-020-11673-4 ◽

2021 ◽

Author(s):

Héctor Jirau-Colón ◽

Jannette Toro-Heredia ◽

Josué Layuno ◽

Enrique Dionisio Calderon ◽

Adriana Gioda ◽

...

Keyword(s):

Puerto Rico ◽

Toxic Metals ◽

Airborne Particulate Matter ◽

Bronchial Epithelium ◽

Average Concentration ◽

Anthropogenic Sources ◽

Urban Site ◽

Relative Toxicity ◽

Potential Health ◽

Rural Sites

AbstractThe exposure to airborne particulate matter (PM) and its constituents is an important factor to be considered when evaluating their potential health risk. Transition metals found in PM are known to contribute significantly to the exacerbation of respiratory ailments. Exposure to these constituents results in the induction of oxidative stress in the bronchial epithelium, thus promoting the secretion of inflammatory mediators. Therefore, it is important to know the contributions of PM2.5 constituents to further investigate their relationship with toxic responses and associated health risks. PM2.5 samples from three rural (Humacao, Guayama, and Guayanilla) and two urban (more populated) sites (Bayamón and Ponce) from Puerto Rico were analyzed for various inorganic constituents. A total of 59 trace elements were analyzed, of which eight were considered with the greatest toxic potential. The highest annual average concentration of PM2.5 was reported at the urban site of Ponce (5.82 ± 1.40 μg m−3), while Bayamón’s average concentration was not as high (4.69 ± 1.30 μg m−3) compared to concentrations at the rural sites Humacao, Guayama, and Guayanilla (4.33 ± 1.20 μg m−3, 4.93 ± 1.50 μg m−3, and 4.88 ± 1.20 μg m−3 respectively. The concentration at the Ponce site exhibited the highest summer value (7.57 μg m−3) compared to that of all the rural sites (~ 6.40 μg m−3). The lowest summer PM2.5 values were obtained at the Humacao site with an average of 5.76 μg m−3. Average Cu and Zn concentrations were 3- and 2-fold higher at the urban sites (0.68 ng m−3 and 6.74 ng m−3 respectively) compared to the rural sites (0.17 ng m−3 and 4.11 ng m−3). Relative toxicity of inorganic PM extract indicates Bayamón (urban) and Guayama with similar low LC50 followed by Humacao, Guayanilla, and finally Ponce (urban) with the highest LC50. Of the eight potential toxic metals considered, only Fe was found to be higher at the rural sites. To our understanding, there are different sources of emission for these metals which potentially indicate main anthropogenic sources, together with the trade winds adding periodically volcanic and African Dust Storm particulates that affect Puerto Rico. These results are the first of their kind to be reported in Puerto Rico.

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