Luis Fhernando Mendonça da
Silva
a,
Caio Silva Assis
Felix
bc,
Madson Moreira
Nascimento
bcd,
Jailson Bittencourt de
Andrade
bcd,
Maria Cristina
Canela
e,
Cibele Maria Stivanin de
Almeida
e,
Carla Semiramis
Silveira
f,
Renato da Silva
Carreira
a and
Adriana
Gioda
*a
aDepartamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, Brazil. E-mail: agioda@puc-rio.br
bCentro Interdisciplinar em Energia e Ambiente – CIEnAm, Universidade Federal da Bahia, Salvador, BA, Brazil
cInstituto Nacional de Ciência e Tecnologia em Energia e Ambiente – INCT, Universidade Federal da Bahia, Salvador, BA, Brazil
dCentro Universitário SENAI-CIMATEC, Salvador, BA, Brazil
eUniversidade Estadual do Norte Fluminense Darcy Ribeiro, Laboratório de Ciências Químicas, Brazil
fUniversidade Federal Fluminense – UFF, Niterói, RJ, Brazil
First published on 25th June 2024
Despite its low atmospheric concentration, mercury in particulate matter (PHg) significantly impacts its biogeochemical cycle. This research focused on the airborne Hg concentrations in fine particulate matter (PM2.5) collected from three distinct sites: an urban area, an urban area affected by sugarcane burning, and protection reserve area within the state of Rio de Janeiro, Brazil, across various seasons during 2022–2023. The findings revealed average concentration of PM2.5 in Gávea was 19 ± 8 μg m−3 (with values ranging from 8 to 37 μg m−3), in PARNASO, it was 24 ± 11 μg m−3 (with values ranging from 0.2 to 46 μg m−3), and in Campos, it was 10 ± 6 μg m−3 (with values ranging from 1 to 19 μg m−3). Given these values, no day surpassed the threshold outlined by Brazilian regulations. However, 63% of the samples showed daily concentrations exceeding the standards established by the World Health Organization. The average mercury concentrations in PM2.5 were 81 ± 116 (3–366) pg m−3, 169 ± 139 (2–392) pg m−3, and 110 ± 71 (8–272) pg m−3 for the urban region of the capital, interior with sugarcane burning and forest locations, respectively, throughout the study period. The study also found that PHg concentrations were about twice as high during the dry period compared to the summer season, suggesting contributions from both local sources and transboundary pollution. Furthermore, significant seasonal variation in PHg concentrations was observed, with notably higher levels detected in the interior urban area impacted by burns than in the capital and preserved sites.
Environmental significanceThis research paper makes a significant contribution to atmospheric science and the understanding of air quality in South America. It addresses the emerging issue of mercury found in PM2.5 concentrations in three regions of Rio de Janeiro, Brazil: urban areas, areas affected by sugarcane burn, and forested areas. The study reveals that 63% of the samples showed daily concentrations exceeding the standards established by the World Health Organization (WHO) for PM2.5 concentrations. Additionally, it was found that regions affected by sugarcane burning and environmental preservation areas exhibited the highest concentrations of particulate mercury. The study also highlights seasonal variability and the contribution of both local and transboundary pollution. |
The global distribution of mercury emissions exhibits marked heterogeneity, shaped by regional disparities in industrial practices, energy generation methods, and natural emissions. The origins of mercury are attributed to natural phenomena such as forest fires and volcanic activity.5 While anthropogenic activities such as coal combustion, non-ferrous metal production, and cement manufacturing stand as primary contributors to atmospheric mercury releases, the interplay of natural sources and re-emissions from previously deposited Hg further complicates the global Hg cycle.4,6,7 The intricate transport dynamics of Hg, encompassing atmospheric processes, precipitation regimes, and interactions with terrestrial and aquatic surfaces, further underscore its complex behavior on a global scale.7–9 Researchers have been widely concerned about Hg in recent decades, and the WHO has listed it as one of the ten most important chemicals for public health.10,11
In Brazil, Hg contamination has garnered significant attention, mainly stemming from the nation's extensive historical and ongoing gold mining endeavors, particularly prevalent in the Amazon region, where Hg amalgamation is utilized in gold extraction from sediments, resulting in widespread environmental degradation and health ramifications. In addition to mining activities, Brazil's industrial operations, energy production, and urban pollutants collectively contribute to its Hg emission landscape.6,12,13 Notably, the state of Rio de Janeiro serves as a pertinent case study, representing a pivotal nexus of industrialization and urbanization, emblematic of the challenges associated with managing Hg emissions in rapidly developing urban locales. Detecting particulate mercury (PM) within urban environments underscores broader concerns regarding air quality and public health.
A comprehensive understanding of the dynamics surrounding particle-bound mercury, encompassing its sources, transport mechanisms, and deposition patterns, is imperative for formulating effective mitigation strategies to curb its deleterious effects.9 This study endeavors to augment our comprehension of particulate mercury dynamics, specifically focusing on quantifying concentrations, delineating seasonal variations, and discerning potential emission sources within the global and Brazilian contexts.
Campos dos Goytacazes, situated in the interior of the state of Rio de Janeiro within the Southeastern region of Brazil, is a prominent city in the Northern Fluminense region. With a population exceeding 500 thousand inhabitants, it ranks as the seventh most populous city in the state's interior.17 Spanning a vast territorial extension of 4,032 km2, Campos dos Goytacazes boasts significant industrial and economic activity, notably as the host of Brazil's largest oil platform, the P-51, located in the Campos basin. Alongside Macaé, it is dubbed the National Petroleum Capital.17,18 Additionally, serving as the primary urban center in the Northern Fluminense region, Campos functions as a residential hub for workers employed in Porto do Açu, the largest port-industry complex in Latin America. In Campos dos Goytacazes, sugarcane dominates agriculture, comprising 55.7% of the planted area and 53.5% of the state's production in 2018. Despite legislation targeting the gradual cessation of sugarcane burning, manual harvesting preceded by burning remains prevalent in the region.18–20
PM2.5 samples were collected from three monitoring sites situated at Gávea (GÁVEA, 22°58′50′′ S and 43°13′58′′ W), Campos dos Goytacazes (CAMPOS, 21°45′39.1′′S 41°17′31.1′′ W), and the Serra dos Órgãos National Park (PARNASO, 22°29′47.5′′ S and 43°00′05.2′′ W) (Fig. 1). A concise overview of these monitoring stations is presented in Table 1.
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Fig. 1 PM2.5 sampling sites: GAVEA: Gávea, PARNASO: Serra dos Órgãos National Park, and CAMPOS: Campos dos Goytacazes. QGIS 3.26.3. |
Location | Surrounding characteristics |
---|---|
Gávea | It is located in the Pontifical Catholic University of Rio de Janeiro (PUC-Rio), a few meters from the subway line 4 and 8.5 km from the André Rebouças Tunnel, and near the sea |
Serra dos Órgãos National Park (PARNASO) | Environmental protection area located in the cities of Teresópolis, Petrópolis, Magé and Guapimirim |
Campos dos Goytacazes (CAMPOS) | Region where sugarcane is cultivated and subjected to combustion for processing and production of hydrated ethanol and sugar. In addition to the burning, there is also the large Port of Açu, which already has 12 companies installed in its area and another 15 using its infrastructure |
The climate seasonality in state of Rio de Janeiro is characterized by two seasons with different characteristics. The rainy season (October–March) also corresponds to the winter and summer, with higher temperatures and insulation, what leads from one side to a more intense atmospheric washing-out process and from the other to more favorable conditions for secondary aerosol formation. The autumn and winter seasons correspond to a dryer period (April–September) with more soil dust and frequent vegetation fires. The winter is also characterized by frequent thermal inversions.21,22Fig. 2 illustrates the precipitation volume during the study period for each station.
PM2.5 concentrations were observed to be relatively elevated during the dry season (April to September) in contrast to the wet season (October to March). This pattern has been documented in numerous prior studies.27–30 Many researchers attribute this phenomenon to the cleansing impact of rainfall, which captures and deposits suspended particles in the atmosphere.
Location | Classif. | Time | PHg concentration (pg m−3) | ||
---|---|---|---|---|---|
Range | Mean | S.D. | |||
Gávea | Urban | Feb/2022–Jun/2023 | 3–366 | 81 | 116 |
Campos dos Goytacazes | Urban with sugarcane burning | 2–392 | 169 | 139 | |
PARNASO | Preserved | 7–272 | 110 | 71 | |
Navy base of Aratu (Brazil)25 | Urban | 2010 | 118 | 45 | |
Maré Island (Brazil)25 | 82 | 27 | |||
Itaparicá (Brazil)25 | 20 | 5 | |||
Southeast coastal cities of China4 | Urban | Nov/2010, Jan, Apr, and Aug/2011 | 8–956 | 141 | 128 |
Rural | 6–89 | 37 | 19 | ||
Remote | 3–60 | 24 | 15 | ||
Detroit (USA)31 | Urban | 2003 | 2–611 | 21 | 30 |
The results showed that PHg concentrations at urban sites in coastal cities are considerably lower than those in other cities, such as Gávea, a city on the coast of China, and regions in Bahia (Brazil). The surface winds in coastal areas influence the concentrations of PM in these regions.32 PHg concentrations in urban areas were 5.9–11.3 times higher than the nearby values found in Asian countries, and North America (Detroit, USA), indicating that a large amount of anthropogenic Hg has been released into the atmosphere in Brazil.
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Fig. 3 Distribution of the average concentrations and percentages of mercury in at three sites (Gavea, PARNASO, and Campos). |
The seasonal concentrations of PHg at individual sampling sites are shown in Fig. 4. There was a statistically significant difference in PHg concentration between the seasons (ANOVA test; p < 0.05). The highest levels of PHg were found in Campos and PARNASO, while the lowest concentrations of PHg were present in Gavea (Fig. 4). The high concentration of PHg at the sites may be associated with anthropogenic emissions. In Campos, the most significant contributions may come from vehicular traffic, the port area and, above all, the burning of sugar cane. PARNASO, despite being an environmental conservation area, usually receives many visitors to the park, with vehicles being the primary commuter. In addition, it is less than 200 m away from BR-116, one of the main avenues linking the metropolitan region of Rio de Janeiro to the Serra and other states in the country, with heavy vehicle traffic.40
PHg concentrations were lowest in rainy at all sampling sites. Precipitation is a pivotal element in atmospheric dynamics, influencing the dispersion of airborne pollutants. It is well-established that rainwater has the capacity to capture atmospheric particles, thereby aiding in their removal from the air.41 However, despite the recognized role of precipitation in mitigating pollutant concentrations, our study did not reveal any significant correlation between precipitation and the levels of mercury and particulate matter.
The atmospheric concentration of PHg in the rainy season may be influenced by air masses coming from the ocean. Most of the mercury was emitted in Hg0 species from the ocean and contributed less to PHg (Fig. 4). On the other hand, clean air masses could dilute the PHg concentration to a large extent. In addition, wet precipitation was more frequent and intense in the summer, eliminating a large amount of PHg in the ambient air.36,42 In Campos, in the summer, the sugar cane crop is growing and there is no burning during this period, which also explains the low concentration of Hg in the area.
It is widely recognized that air masses originating from different regions carry various chemical components within aerosols, thus providing information on their possible sources.43,44
It was found that PHg concentrations in the dry season were evidently higher compared to the rainy season at all the sampling sites. There are several reasons for this. Firstly, the autumn and winter sampling period in this study took place during the beginning (mid-September) and end (mid-March) of the heating season; therefore, the northwest monsoon can transport a large amount of particles with condensed Hg to southeastern coastal cities in spring and autumn, as well as in winter, which can be confirmed by reverse trajectory analysis.
The results of the analysis of the reverse trajectory of the air are shown in Fig. 5. Very different origins were observed for the air masses that arrived at Gávea and PARNASO at different levels and in different seasons. In spring, the air masses at heights of 500 and 1000 m originated from the continental areas of the Andes with volcanoes, Central Brazil, while the trajectory at a height of less than 100 m came from the south of the country. At a height of 1000 m, they passed through other areas of South America, such as Bolivia, Paraguay and the interior of Brazil. The rainy season usually began at the end of November and lasted until mid-March, so the air masses brought a large amount of mercury emitted and ultimately increased the concentrations of PHg in the areas investigated during the dry season. Completely different trajectories were found during the summer. In this season, the trajectories originated from the Atlantic Ocean until they reached the study sites, Gavea and Campos. In contrast to the continental air masses, the oceanic air masses led, to a certain extent, to a decrease in PHg concentrations. Campos during the rainy season and in the dry season does not receive any influence from other countries, being mostly from the ocean in both seasons.
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Fig. 5 A-week air parcel backward trajectories for different seasons. The end point is at 100, 500, and 1000 m AGL at (A) Gávea, (B) Campos, and (C) PARNASO stations. |
Mercury levels were found to be highest at urban fire sites, surpassing those in both urban and preserved areas. The summer season recorded the lowest PHg concentrations in comparison to other seasons, with a consistent pattern of significantly elevated PHg levels during the dry season across all examined periods.
Analysis of backward air trajectories revealed that air masses reaching the study area predominantly originated from oceanic sources, leading to a dilution of PHg concentrations in the atmosphere during the summer at Gávea and Campos dos Goytacazes. In contrast, during other seasons, PHg levels were primarily affected by air masses coming from other South American countries and the continental areas of the Andes with volcanoes at PARNASO and Gávea. This explains why PHg concentrations were similar during the dry season but significantly higher than those recorded in the rainy season. Furthermore, Campos during the rainy season and in the dry season does not receive any influence from other countries, being mostly from the ocean in both seasons.
The main limitation of this study is that the sampling in the preservation area (PARNASO) is close to the highway. Ideally, it would have been conducted in a more central part of the park to get natural samples, but this was not possible due to the lack of electricity. In addition, for future studies we intend to do more research on Hg in the regions in particulate and gaseous form, in order to understand the cycle of this pollutant in the Rio de Janeiro region.
This journal is © The Royal Society of Chemistry 2024 |