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Mercury speciation in the marine boundary layer along a 6000km cruise path around the Mediterranean Sea
Abstract
In the framework of the Med-Oceanor project simultaneous measurements of two atmospheric mercury species elemental mercury (Hg0) and reactive gaseous mercury (RGM) over the Mediterranean Sea were performed in order to investigate the dynamic patterns of mercury in the Marine Boundary Layer. Measurements of atmospheric mercury were performed on board the Italian Research Vessel (URANIA) along a 6000 km cruise path in the western and eastern sector of the Mediterranean Sea from 14 July to 9 August 2000. Hg0 ranged between 0.4 and 11.2 ng m−3 with an average of 1.9±1.02 ng m−3 over the entire period. Higher concentrations were observed in the Gulf of Naples due primarily to air masses transported from the mainland reflecting the contribution from anthropogenic sources. RGM levels were measured using KCl-coated annular denuders coupled to an automated gas phase mercury analyser (Tekran 2537A). RGM concentrations varied from 0.2 to 30.1 pg m−3 with an average of 7.9 pg m−3. A diurnal cycle of the RGM concentration was observed during the entire sampling period with the maximum around midday and the minimum during the night; the oxidation by daytime oxidants, i.e., OH, may have determined the observed diurnal cycle of RGM concentration in the MBL.
... Numerous previous studies have shown that Hg 0 in the marine boundary layer (MBL) can be rapidly oxidized to form RGM in situ (Laurier et al., 2003;Sprovieri et al., 2003Sprovieri et al., , 2010Laurier and Mason, 2007;Soerensen et al., 2010a;Wang et al., 2015;Mao et al., 2016;Ye et al., 2016). Ozone and OH could potentially be important oxidants on aerosols Ye et al., 2016), while the reactive halogen species (e.g., Br, Cl, and BrO, generated from sea-salt aerosols) may be the dominant sources for the oxidation of Hg 0 in the MBL (Holmes et al., 2006(Holmes et al., , 2010Auzmendi-Murua et al., 2014;Gratz et al., 2015;Steffen et al., 2015;Shah et al., 2016;Horowitz et al., 2017). ...
... Numerous previous studies have shown that Hg 0 in the marine boundary layer (MBL) can be rapidly oxidized to form RGM in situ (Laurier et al., 2003;Sprovieri et al., 2003Sprovieri et al., , 2010Laurier and Mason, 2007;Soerensen et al., 2010a;Wang et al., 2015;Mao et al., 2016;Ye et al., 2016). Ozone and OH could potentially be important oxidants on aerosols Ye et al., 2016), while the reactive halogen species (e.g., Br, Cl, and BrO, generated from sea-salt aerosols) may be the dominant sources for the oxidation of Hg 0 in the MBL (Holmes et al., 2006(Holmes et al., , 2010Auzmendi-Murua et al., 2014;Gratz et al., 2015;Steffen et al., 2015;Shah et al., 2016;Horowitz et al., 2017). ...
... Another obvious feature was that the amplitude of the RGM concentration was much greater than the GEM, and this further indicated that the RGM was easily removed from the atmosphere through both the wet and dry deposition. In addition, we found that the RGM concentrations in the nearshore area were not always higher than those in the open sea, except for the measurements in the PRE, suggesting that the RGM in the remote marine atmosphere presumably did not originate from land but from the in situ photo-oxidation of Hg 0 , which had been reported in previous studies (e.g., Hedgecock and Pirrone, 2001;Lindberg et al., 2002;Laurier et al., 2003;Sprovieri et al., 2003Sprovieri et al., , 2010Sheu and Mason, 2004;Laurier and Mason, 2007;Soerensen et al., 2010a;Wang et al., 2015). ...
The characteristics of the reactive gaseous mercury (RGM) and particulate mercury (HgP) in the marine boundary layer (MBL) are poorly understood, due in part to sparse data from the sea and ocean. Gaseous elemental Hg (GEM), RGM, and size-fractionated HgP in the marine atmosphere, and dissolved gaseous Hg (DGM) in surface seawater, were determined in the South China Sea (SCS) during an oceanographic expedition (3–28 September 2015). The mean concentrations of GEM, RGM, and Hg2.5P were 1.52±0.32 ng m−3, 6.1±5.8 pg m−3, and 3.2±1.8 pg m−3, respectively. A low GEM level indicated that the SCS suffered less influence from fresh emissions, which could be due to the majority of air masses coming from the open oceans, as modeled by back trajectories. Atmospheric reactive Hg (RGM + Hg2.5P) represented less than 1 % of total atmospheric Hg, indicating that atmospheric Hg existed mainly as GEM in the MBL. The GEM and RGM concentrations in the northern SCS (1.73±0.40 ng m−3 and 7.1±1.4 pg m−3, respectively) were significantly higher than those in the western SCS (1.41±0.26 ng m−3 and 3.8±0.7 pg m−3), and the Hg2.5P and Hg10P levels (8.3 and 24.4 pg m−3) in the Pearl River estuary (PRE) were 0.5–6.0 times higher than those in the open waters of the SCS, suggesting that the PRE was polluted to some extent. The size distribution of HgP in PM10 was observed to be three-modal, with peaks around
... Frequency distributions of 24 h average GOM and PBM concentrations from a site situated in the Mediterranean MBL exhibited log-normal distributions with the maximum frequency at around 59 and 48 pg m −3 , respectively . One of the major findings from Sprovieri et al. (2003) was constant presence of GOM averaged at 7.9 ± 0.8 pg m −3 in the MBL over a 6000 km long cruise path around the Mediterranean Sea. In a 1 year dataset from 2008, Beldowska et al. (2012) showed 24 h PBM concentrations varied over 2-142 pg m −3 averaged at 20 ± 18 pg m −3 with 93 % on average in the coarse fraction (> 2 µm) over the southern Baltic Sea. ...
... While some studies found a lack of diurnal variation in GOM Aspmo et al., 2006;Temme et al., 2003b), many reported distinct diurnal variation with noonafternoon peaks and nighttime minimums in various oceanic regions Mason and Sheu, 2002;Lindberg et al., 2002;Laurier et al., 2003;Sprovieri et al., 2003Sprovieri et al., , 2010Laurier and Mason, 2007;Mao et al., 2008;Chand et al., 2008;Sigler et al., 2009b;Soerensen et al., 2010;Wang et al., 2014). Over the Atlantic amplitude values varied from 0.27 pg m −3 in winter 2010 near the coast of southern New Hampshire, USA , to > 80 pg m −3 on the cruise from Barbados via Bermuda to Baltimore, Maryland, USA (Mason and Sheu, 2002;Laurier and Mason, 2007). ...
... Larger concentrations of GOM in spring and/or summer were generally associated with stronger photo oxidation, biological activity, biomass burning, oceanic, and anthropogenic emissions, whereas low concentrations with wet deposition (Lindberg et al., 2002;Mason and Sheu, 2002;Temme et al., 2003b;Pirrone et al., 2003;Sprovieri et al., 2003;Hedgecock et al., 2004;Laurier and Mason, 2007;Sprovieri and Pirrone, 2008;Sprovieri et al., 2010;Soerensen et al., 2010;Obrist et al., 2011;Angot et al., 2014;Wang et al., 2014). The positive correlation between GOM concentration and solar radiation was used to explain warm season maximums of GOM based on the same line of reasoning that was used to explain daytime peaks of GOM (Mason and Sheu, 2002;Pirrone et al., 2003;. ...
Atmospheric mercury (Hg) is a global pollutant and thought to be the main source
of mercury in oceanic and remote terrestrial systems, where it becomes
methylated and bioavailable; hence, atmospheric mercury pollution has
global consequences for both human and ecosystem health. Understanding of
spatial and temporal variations of atmospheric speciated mercury can advance
our knowledge of mercury cycling in various environments. This review
summarized spatiotemporal variations of total gaseous mercury or gaseous
elemental mercury (TGM/GEM), gaseous oxidized mercury (GOM), and
particulate-bound mercury (PBM) in various environments including oceans,
continents, high elevation, the free troposphere, and low to high latitudes.
In the marine boundary layer (MBL), the oxidation of GEM was generally
thought to drive the diurnal and seasonal variations of TGM/GEM and GOM in
most oceanic regions, leading to lower GEM and higher GOM from noon to
afternoon and higher GEM during winter and higher GOM during spring–summer.
At continental sites, the driving mechanisms of TGM/GEM diurnal patterns
included surface and local emissions, boundary layer dynamics, GEM
oxidation, and for high-elevation sites mountain–valley winds, while
oxidation of GEM and entrainment of free tropospheric air appeared to
control the diurnal patterns of GOM. No pronounced diurnal variation was
found for Tekran measured PBM at MBL and continental sites. Seasonal
variations in TGM/GEM at continental sites were attributed to increased
winter combustion and summertime surface emissions, and monsoons in Asia,
while those in GOM were controlled by GEM oxidation, free tropospheric transport,
anthropogenic emissions, and wet deposition. Increased PBM at continental
sites during winter was primarily due to local/regional coal and wood
combustion emissions. Long-term TGM measurements from the MBL and
continental sites indicated an overall declining trend. Limited measurements
suggested TGM/GEM increasing from the Southern Hemisphere (SH) to the Northern Hemisphere (NH) due
largely to the vast majority of mercury emissions in the NH, and the latitudinal
gradient was insignificant in summer probably as a result of stronger
meridional mixing. Aircraft measurements showed no significant vertical
variation in GEM over the field campaign regions; however, depletion of GEM
was observed in stratospherically influenced air masses. In examining the
remaining questions and issues, recommendations for future research needs
were provided, and among them is the most imminent need for GOM speciation
measurements and fundamental understanding of multiphase redox kinetics.
... Some studies also suggested that oceanic evasion was an important 393 source contributing to higher concentrations ( Seiler et al., 1980;Sigler et al., 2009b), while 394 others thought otherwise ( Slemr et al., 1981Slemr et al., , 1985Slemr and Langer, 1992). Strong 395 photoreduction could have caused higher TGM/GEM concentrations under favorable 396 meteorological conditions ( Sprovieri et al., 2003;Sprovieri and Pirrone, 397 2008). These influences often occurred in multitude simultaneously leading to elevated ambient 398 ...
... Mediterranean Sea Basin ( Sprovieri et al., 2003;Sprovieri and Pirrone, 414 2008). 415 ...
... While some studies found a lack of diurnal variation in GOM ( Sheu and Mason, 2001;662 Aspmo et al., 2006;Temme et al., 2003b), many studies reported pronounced diurnal variation in 663 various oceanic regions ( Mason et al., 2001;Mason and Sheu, 2002;Lindberg et al., 2002;664 Laurie et al., 2003;Sprovieri et al., 2003Sprovieri et al., , 2010Laurier and Mason, 2007;Mao et al., 2008;665 Chand et al., 2008;Sigler et al., 2009b;Soerensen et al., 2010;Mao and Talbot, 2012;Wang et 666 al., 2014). In only one out of seven 24-hr GOM sampling sessions did Sheu and Mason (2001) to >80 pg m -3 from Barbados via Bermuda to Baltimore, Maryland, USA ( Mason and Sheu, 2002;672 Laurier and Mason, 2007). ...
Understanding of spatial and temporal variations of atmospheric speciated mercury can advance our knowledge of mercury cycling in various environments. This review summarized spatiotemporal variations of total gaseous mercury or gaseous elemental mercury (TGM/GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM) in various environments including oceans, continents, high elevation, the free troposphere, and low to high latitudes. In the marine boundary layer (MBL), the oxidation of GEM was generally thought to drive the diurnal and seasonal variations of TGM/GEM and GOM in most oceanic regions, leading to lower GEM and higher GOM from noon to afternoon and higher GEM during winter and higher GOM during spring-summer. At continental sites, the driving mechanisms of TGM/GEM diurnal patterns included surface and local emissions, boundary layer dynamics, GEM oxidation, and mountain-valley winds at high elevation sites. Oxidation of GEM and entrainment of GOM from the free troposphere influenced the diurnal patterns of GOM at continental sites. No pronounced diurnal variation was found for Tekran measured PBM at MBL and continental sites. Seasonal variations in TGM/GEM at continental sites were attributed to increased winter combustion, increased surface emissions during summer, and monsoons in Asia. GEM oxidation, free tropospheric transport, anthropogenic emissions, and wet deposition appeared to affect the seasonal pattern of GOM at continental sites. Since measurements were predominantly in the northern hemisphere (NH), increased PBM at continental sites during winter was primarily due to local/regional coal combustion and wood burning emissions. Long-term TGM measurements from the MBL and continental sites indicated an overall declining trend consistent with those of anthropogenic and natural emissions and potentially redox chemistry. The latitudinal gradient in TGM/GEM showed an increase from the southern to northern hemisphere due largely to the vast majority of Hg emissions in the NH. This gradient was insignificant during summer probably as a result of weaker meridional mixing. Aircraft measurements indicated no significant GEM gradient with altitude over the field campaign regions; however depletion of GEM was observed in air masses under stratospheric influence. Remaining questions and issues related to factors potentially contributing to the observed spatiotemporal variations were identified, and recommendations for future research needs were provided.
... Especially since the industrial age about 200 years ago (UNEP, 2013), human activities have contributed most to the high mercury concentrations in the air. Previous studies have shown higher GEM concentrations in cities (Kim and Kim, 2001;Sakata and Marumoto, 2002;Song et al., 2009;Friedli et al., 2011;Zhang et al., 2014), as well as in rural areas (Han et al., 2004) and remote areas (Fu et al., 2008;Wan et al., 2009) than compared to the ocean (Fitzgerald, 1995;Sprovieri et al., 2003;Temme et al., 2003). Gaseous elemental mercury (GEM) can stay in the atmosphere for 0.7-1 years (Linqvist and Rodhe, 1985;Hedgecock et al., 2005). ...
... Changbai (3.58 ng/m 3 ,Wan et al., 2009) in China. The mean GEM concentration was compared to that in Okinawa (2.04 ng/m 3 ,Jaffe et al., 2005), Mediterranean Sea (1.95 ng/m 3 ,Sprovieri et al., 2003), and Atlantic Ocean (2.02 ng/m 3 ,Temme et al., 2003) (Table 1). It was higher than the open Alantic Ocean (1.07 ng/m 3 ,Temme et al., 2003), India ocean (0.9 ng/m 3 ,Xia et al., 2010) and the coast of California (1.40 ng m 3 ,Weiss-Penzias et al., 2013), which reflects the influence of continental land. ...
East Asia is one of the primary sources of atmospheric gaseous elemental mercury (GEM) among the world. In this study, GEM concentrations were measured during two cruises in late autumn and winter of 2012 and 2013 which passed through the marginal seas of China. The results show that the mean GEM concentration was 1.65 ng/m³ from the South China Sea to the Yellow Sea during the 2012 cruise. While the mean GEM concentration was 2.38 ng/m³ in the South Yellow Sea, and 1.75 ng/m³ in the North Yellow and Bohai Seas during the 2013 cruise. High GEM contents were detected when the steering wind was offshore. There is a significant positive relationship between GEM and air temperature for these two cruises. Low GEM content was presented when the cold northerly monsoon prevailed while air masses mainly came from the clean northern oceanic region. Dissolved gaseous mercury (DGM) concentration in the surface water of the south Yellow and Bohai seas were 74.4 ± 28 pg/L. DGM concentrations were correlated with water temperature (r = 0.244, p < 0.05). Sea-air flux of mercury in the Yellow Sea and Bohai Sea were 11.3 ng/(m²·h), ranging between − 9.4 and 59.3 ng/(m²·h) which was different from other seasons. The deposition of mercury appeared in the Bohai Sea affected by land polluted air and low wind speed. High flux values were caused by the northerly monsoon which carried remote clean air to the sea, with large wind speeds. The northerly monsoon is an important factor affecting the GEM transport offshore to marginal sea and the cycle of mercury in the sea in late autumn and winter.
... In earlier studies, the wet deposition was considered the only primary pathway (Mason et al., 1994). Recently, due to the significant instrumental improvement for atmospheric Hg speciation measurements (Landis et al., 2002 ), increasing field studies have shown that gaseous elemental mercury (GEM, or Hg(0)) in the marine boundary layer (MBL) can be rapidly oxidized to form reactive gaseous mercury (RGM) in situ (e.g., Hedgecock et al., 2003; Laurier et al., 2003; Laurier and Mason, 2007; Chand et al., 2008; Sprovieri et al., 2003 Sprovieri et al., , 2010a Soerensen et al., 2010a ). Because of the high water solubility and surface reactivity, the dry deposition of RGM (direct or uptake by sea-salt aerosol) represents an important fraction of Hg deposition flux to the ocean (Mason and Sheu, 2002; Holmes et al., 2009). ...
... ng m −3 , Witt et al., 2010; Soerensen et al., 2010a). Compared with these oceans in the North Hemisphere, the GEM concentrations in the Yellow Sea also were higher than those of many other oceans, such as the Mediterranean Sea (1.5–2.0 ng m −3 , Sprovieri et al., 2003 Sprovieri et al., , 2010a) and the Adriatic Sea (1.6 ± 0.4 ng m −3 , Sprovieri and Pirrone, 2008), but were comparable to the Atlantic Ocean (∼1.5–2.5 ng m −3 , Temme et al., 2003; Laurier and Mason, 2007; Soerensen et al., 2010a) and the North Pacific Ocean (2.5 ± 0.5 ng m −3 , Laurier et al., 2003 ). Elevated Hg(0) evasion from the sea surface and long-range transport of anthropogenic emissions from industrial regions might explain those elevated atmospheric Hg levels (Soerensen et al., 2010a). ...
The Yellow Sea, surrounded by East China and the Korea Peninsula, is a potentially important receptor for anthropogenic mercury (Hg) emissions from East Asia. However, there is little documentation about the distribution and cycle of Hg in this marine system. During the cruise covering the Yellow Sea in July 2010, gaseous elemental mercury (GEM or Hg(0)) in the atmosphere, total Hg (THg), reactive Hg (RHg) and dissolved gaseous mercury (DGM, largely Hg(0)) in the waters were measured aboard the R/V Kexue III . The mean (±SD) concentration of GEM over the entire cruise was 2.61±0.50 ng m<sup>−3</sup> (range: 1.68 to 4.34 ng m<sup>−3</sup>), which were generally higher than other open oceans. The spatial distribution of GEM generally reflected a clear gradient with high levels near the coast of East China and low levels in open waters, suggesting the significant atmospheric Hg outflow from East China. The mean concentration of THg in the surface waters was 1.69±0.35 ng l<sup>−1</sup> and the RHg accounted for a considerable fraction of THg (RHg: 1.08±0.28 ng l<sup>−1</sup>, %RHg/THg=63.9%). The mean concentration of DGM in the surface waters was 63.9±13.7 pg l<sup>−1</sup> and always suggested the supersaturation of Hg(0) in the surface waters with respect to Hg(0) in the atmosphere (the degree of saturation: 7.83±2.29 with a range of 3.58–14.00). The mean Hg(0) flux at the air-sea interface was estimated to be 22.58±14.56 ng m<sup>−2</sup> h<sup>−1</sup> based on a two-layer exchange model. The high wind speed and DGM levels induced the extremely high Hg(0) emission rates. Measurements at three selected stations showed no clear vertical patterns of all three species of Hg in the water column. Overall, the elevated Hg levels in the Yellow Sea compared with other open oceans suggested that the human activity has significantly influenced the oceanic Hg cycle downwind of East Asia.
... Our analysis of the AMNet dataset, including both rural and urban sites, showed that median GOM values ranged from 0.05 to 1.4 ppqv (Fig. 3), generally lower than previous measurements. It was also lower when compared with the measurements in the Mediterranean as well as Northern Europe (MOE and MAMCS campaigns) (Pirrone et al., , 2003Sprovieri et al., 2003;Wangberg et al., 2001), but consistent with a few rural sites measurements in the US, such as Chesapeake Bay, Maryland (6-13 pg m −3 ) (0.7-1.5 ppqv) (Laurier and Mason, 2007) and Pompano Beach, Florida (1.6-4.9 pg m −3 ) (0.2-0.5 ppqv) (Malcom et al., 2003). An apparent characteristic of GOM was its great diversity across the US (Fig. 3, Table 3). ...
... Our analysis of the AMNet dataset, including both rural and urban sites, showed that median GOM values ranged from 0.05 to 1.4 ppqv (Fig. 3), generally lower than previous measurements. It was also lower when compared with the measurements in the Mediterranean as well as Northern Europe (MOE and MAMCS campaigns) (Pirrone et al., , 2003Sprovieri et al., 2003;Wangberg et al., 2001), but consistent with a few rural sites measurements in the US, such as Chesapeake Bay, Maryland (6-13 pg m −3 ) (0.7-1.5 ppqv) (Laurier and Mason, 2007) and Pompano Beach, Florida (1.6-4.9 pg m −3 ) (0.2-0.5 ppqv) (Malcom et al., 2003). An apparent characteristic of GOM was its great diversity across the US (Fig. 3, Table 3). ...
Speciated atmospheric mercury observations collected over the period
from 2008 to 2010 at the Environmental Protection Agency and National
Atmospheric Deposition Program Atmospheric Mercury Network sites (AMNet)
were analyzed for its spatial, seasonal, and diurnal characteristics
across the US. Median values of gaseous elemental mercury (GEM), gaseous
oxidized mercury (GOM) and particulate bound mercury (PBM) at 11
different AMNet sites ranged from 148-226 ppqv (1.32-2.02 ng
m-3), 0.05-1.4 ppqv (0.47-12.4 pg m-3) and
0.18-1.5 ppqv (1.61-13.7 pg m-3), respectively. Common
characteristics of these sites were the similar median levels of GEM as
well as its seasonality, with the highest mixing ratios occurring in
winter and spring and the lowest in fall. However, discernible
differences in monthly average GEM were as large as 30 ppqv, which may
be caused by sporadic influence from local emission sources. The largest
diurnal variation amplitude of GEM occurred in the summer. Seven rural
sites displayed similar GEM summer diurnal patterns, in that the lowest
levels appeared in the early morning, and then the GEM mixing ratio
increased after sunrise and reached its maxima at noon or in the early
afternoon. Unlike GEM, GOM exhibited higher mixing ratios in spring and
summer. The largest diurnal variation amplitude of GOM occurred in
spring for most AMNet sites. The GOM diurnal minima appeared before
sunrise and maxima appeared in the afternoon. The increased GOM mixing
ratio in the afternoon indicated a photochemically driven oxidation of
GEM resulting in GOM formation. PBM exhibited diurnal fluctuations in
summertime. The summertime PBM diurnal pattern displayed daily maxima in
the early afternoon and lower mixing ratios at night, implying
photochemical production of PBM in summer.
... In the marine environment, Hg o is reportedly around 1.6 ng m −3 over the North Atlantic (Laurier 20 and Mason, 2007), 1.6–4.7 ng m −3 over the North Pacific (Laurier et al., 2003), and 0.4–11.2 ng m −3 over the Mediterranean Sea (Sprovieri et al., 2003). In comparison, there is much less coverage of RGM and Hg P measurements in space and time. ...
... Hg P m −3 was measured at Mace Head, Ireland (Ebinghaus et al., 2002), compared to much higher values of 31 (±44) pg m −3 in coastal Maryland (Mason and Sheu, 2002). The four two-week measurement campaigns during the MAMCS project in the Mediterranean region over the 1998–2000 period showed that RGM concentrations in the Mediterranean, far from sources and particularly with onshore winds, were comparable 10 to those in industrial northern Europe (Pirrone et al., 2003). In the northeastern US, we showed an annual mean RGM mixing ratio of 0.41 (±0.93) ppqv with a range of 0–22 ppqv at a rural site on the southern New Hampshire coastline in 2007 compared to the annual mean of 0.13 (±0.25) ppqv and a median below the limit of detection (LOD) (0.1 ppqv) at an elevated (700 m altitude) 185 km in- 15 land site) (Sigler et al., 2009). ...
A comprehensive analysis was conducted using long-term continuous
measurements of gaseous elemental mercury (Hg0), reactive
gaseous mercury (RGM), and particulate phase mercury (HgP) at
coastal (Thompson Farm, denoted as TF), marine (Appledore Island,
denoted as AI), and elevated inland (Pac Monadnock, denoted as PM) sites
from the AIRMAP Observatories in southern New Hampshire, USA. Decreasing
trends in background Hg0 were identified in the 7.5- and
5.5-yr records at TF and PM with decline rates of 3.3 parts per
quadrillion by volume (ppqv) yr-1 and 6.3 ppqv
yr-1, respectively. Common characteristics at these sites
were the reproducible annual cycle of Hg0 with its maximum in
winter-spring and minimum in fall, comprised of a positive trend in the
warm season (spring - early fall) and a negative one in the cool season
(late fall - winter). Year-to-year variability was observed in the warm
season decline in Hg0 at TF varying from a minimum total
(complete) seasonal loss of 43 ppqv in 2009 to a maximum of 92 ppqv in
2005, whereas variability remained small at AI and PM. The coastal site
TF differed from the other two sites with its exceptionally low levels
(as low as below 50 ppqv) in the nocturnal inversion layer possibly due
to dissolution in dew water. Measurements of Hg0 at PM
exhibited the smallest diurnal to annual variability among the three
environments, where peak levels rarely exceeded 250 ppqv and the minimum
was typically 100 ppqv. It should be noted that summertime diurnal
patterns at TF and AI were opposite in phase indicating strong sink(s)
for Hg0 during the day in the marine boundary layer, which
was consistent with the hypothesis of Hg0 oxidation by
halogen radicals there. Mixing ratios of RGM in the coastal and marine
boundary layers reached annual maxima in spring and minima in fall,
whereas at PM levels were generally below the limit of detection (LOD)
except in spring. RGM levels at AI were higher than at TF and PM
indicating a stronger source strength in the marine environment. Mixing
ratios of HgP at AI and TF were close in magnitude to RGM
levels and were mostly below 1 ppqv. Diurnal variation in HgP
was barely discernible at TF and AI in spring and summer. Higher levels
of HgP were observed during the day, while values that were
smaller, but above the LOD, occurred at night.
... In terms of daily averaged GEM levels, we obtained 784 valid daily averaged GEM data, varying from 1.32 to 2.39 with a median value of 1.72 ng m −3 and a mean value of 1.73 ng m −3 . The mean value found at MSA over the entire measurement period calculated from the daily GEM averages is perfectly in line with concentrations typically found in the Mediterranean area (Hedgecock et al. 2003;Pirrone et al. 2003;Sprovieri et al. 2003Sprovieri et al. , 2010Sprovieri and Pirrone 2008;Kotnik et al. 2014). Even if obtained with different methods, no difference exists between TGM and GEM from the point of view of the obtained measurement data (Brown et al. 2010;Sprovieri et al. 2016 (Sprovieri et al., 2010). ...
In the framework of the Italian Special Network for Mercury (ISNM) “Reti Speciali”, a sampling campaign to monitor atmospheric mercury (Hg) was carried out at Monte Sant’Angelo (MSA). This is a coastal monitoring station in the Apulia region, representative of the Southern Adriatic area, within the Mediterranean basin. This work presents continuous Gaseous Elemental Mercury (GEM) measurements over about three years at MSA, using the Lumex RA-915AM mercury analyzer. The aim was to obtain a dataset suitable for the analysis of Hg concentrations in terms of source and transport variation. Diurnal cycles of GEM were evaluated to observe the influence of local atmospheric temperature and wind speed on potential re-emissions from surrounding sea and soil surfaces. Data were also analyzed in terms of long-range transport, using backward trajectory cluster analysis. The spatial distribution of potential sources, contributing to higher measured GEM values, was obtained employing Potential Source Contribution Function (PSCF) statistics. The influence of major Hg anthropogenic point sources, such as mining activities and coal-fuel power plants, both regionally and continentally, from mainland Europe, was observed. The role of the vegetation GEM uptake in modulating the seasonal GEM variability was also investigated. The potential of wildfire influence over the highest detected GEM levels was further examined using active fire data and the evaluation of the vegetation dryness index during the selected episodes.
Graphical abstract
... Since the year 2000, numerous oceanographic and more local near-coast 179 measurement campaigns have been carried out to determine Hg species concentrations 180 in the marine boundary layer and the water column 52,53,54,55,56 . Evasion fluxes of Hg are 181 calculated using measured dissolved gaseous mercury (DGM) and Hg 0 (g) concentrations, 182 wind speed, and sea surface temperature, and several approaches can and have been 183 used to estimate MED efflux/volatilization/atmospheric rates 57,58,59,60 . ...
... The GOM concentrations observed in the oceanic region during this cruise were the lowest compared to coastal Antarctica and sea-ice regions ( Figure 2c and Table 1); the average was similar to the global average (3.1 ± 11 pg·m 3 ) (Soerensen et al., 2010), and observations in seas in the northern hemispheric (the Mediterranean, Bohai, Yellow, and South China seas and off Okinawa) (Chand et al., 2008;Sprovieri et al., 2003;C. Wang et al., 2016 (Table S2). ...
Antarctica and the surrounding Southern Ocean act as an important sink in the global mercury cycle; however, corresponding studies of atmospheric mercury species in these regions are still scarce. Here, we report large‐scale observations of atmospheric gaseous elemental mercury (GEM) and gaseous oxidized mercury (GOM) in the Antarctic marine boundary layer (MBL) taken during a summer cruise. There is large variability in the spatial distribution of GOM, which is likely attributable to the diverse land surface types, including coastal Antarctica, sea‐ice region, and oceanic region, along the cruise route. In coastal Antarctica, the highest GOM level (56.23 ± 47.74 pg·m⁻³) might be attributed to the significant in‐situ oxidation there. Significant in‐situ oxidation of GEM could also occur in the sea‐ice region, causing the significant increase of GOM (up to 87.01 pg·m⁻³), while the uptake of the high content of sea‐salt aerosols in sea‐ice regions might efficiently eliminate GOM in the air, resulting in generally lower content of GOM (13.10 ± 14.48 pg·m⁻³) in the sea‐ice region. In the oceanic region, the lowest level of GOM (3.95 ± 4.69 pg·m⁻³) is due to both the uptake of sea‐salt aerosols and the seasonal melting of first‐year sea‐ice. This study provides insight to understand the mechanisms of the atmospheric mercury cycle in various land surface types in the Antarctic MBL.
... Of them ultraviolet spectrophotometry is the most popular for surface ozone monitoring and is applied in many commercial instruments. The common ones, such as Thermo 49C (Liu et al., 2006), API 400E (Sprovieri et al., 2003), ESA O342M (Lei and Min, 2014) and Ecotech 9810B (Moura et al., 2011), have been used in many regions for their larger measuring range and high precision, but they are expensive and need plenty of power supply and regular maintenance. Recently, more and more studies have chosen portable ozone monitors (POMs), such as Model 205 Aeroqual Series 500 POM, due to their advantages of small volume, low price, low energy consumption and good applicability for field observation (e.g., Johnson et al., 2014;Lin et al., 2015;Sagona et al., 2018). ...
Dome A, the summit of the East Antarctic Ice Sheet, is an area
challenging to access and is one of the harshest environments on Earth. Up
until recently, long-term automated observations from Dome A (DA) were only
possible with very low power instruments such as a basic meteorological
station. To evaluate the characteristics of near-surface O3, continuous
observations were carried out in 2016. Together with observations at the
Amundsen–Scott Station (South Pole – SP) and Zhongshan Station (ZS, on the
southeast coast of Prydz Bay), the seasonal and diurnal O3
variabilities were investigated. The results showed different patterns
between coastal and inland Antarctic areas that were characterized by high
concentrations in cold seasons and at night. The annual mean values at the
three stations (DA, SP and ZS) were 29.2±7.5, 29.9±5.0 and 24.1±5.8 ppb, respectively. We investigated the effect of
specific atmospheric processes on near-surface summer O3 variability,
when O3 enhancement events (OEEs) are systematically observed at DA
(average monthly frequency peaking at up to 64.5 % in December). As deduced
by a statistical selection methodology, these O3 enhancement events
(OEEs) are affected by significant interannual variability, both in their
average O3 values and in their frequency. To explain part of this
variability, we analyzed the OEEs as a function of specific atmospheric
processes: (i) the role of synoptic-scale air mass transport over the
Antarctic Plateau was explored using the Lagrangian back-trajectory analysis Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) method,
and (ii) the occurrence of “deep” stratospheric intrusion events was
investigated using the Lagrangian tool STEFLUX. The specific atmospheric
processes, including synoptic-scale air mass transport, were analyzed by the
HYSPLIT back-trajectory analysis and the potential source contribution
function (PSCF) model. Short-range transport accounted for the O3
enhancement events (OEEs) during summer at DA, rather than efficient local
production, which is consistent with previous studies of inland Antarctica.
Moreover, the identification of recent (i.e., 4 d old) stratospheric-intrusion events by STEFLUX suggested that deep events only had a minor
influence (up to 1.1 % of the period, in August) on deep events
during the variability in near-surface summer O3 at DA. The deep
events during the polar night were significantly higher than those during
the polar day. This work provides unique data on ozone variation at DA and
expands our knowledge of such events in Antarctica. Data are available at
https://doi.org/10.5281/zenodo.3923517 (Ding and Tian, 2020).
... During most of the measured time, registered GEM concentration values were within the range of background data reported for the northern hemisphere, estimated at * 2 ng m -3 (Lindberg et al. 2007;Slemr et al. 1981;Sprovieri et al. 2010;Travnickov 2005). In recent works, several authors have calculated total gaseous Hg (TGM) background in the northern hemisphere at around 1.6-2 ng m -3 (Sprovieri et al. 2010), slightly higher than previously reported values of 1.75 and 1.96 ng m -3 (Sprovieri et al. 2003;Sprovieri and Pirrone 2008), whereas Travnickov (2005) reported TGM average background concentration of about 1.5 ng m -3 in remote areas (i.e., the Pacific Ocean). The background GEM level during this survey was calculated at 1.39 ± 0.55 ng m -3 , which represents the average of data recorded during the measurement time when no volcanic activities were evident. ...
The contribution of Hg from volcanic emanations is decisive for assessing global mercury emissions given the impact of this highly toxic contaminant on human health and ecosystems. Atmospheric Hg emissions from Popocatépetl volcano and their dispersion were evaluated carrying out two gaseous elemental mercury (GEM) surveys during a period of intense volcanic activity. Continuous GEM measurements were taken for 24 h using a portable mercury vapor analyzer (Lumex RA-915M) at the Altzomoni Atmospheric Observatory (AAO), 11 km from the crater. In addition, a long-distance survey to measure GEM was conducted during an automobile transect around the volcano, covering a distance of 129 km. The evaluation of the GEM data registered in the fixed location showed that heightened volcanic activity clearly intensifies the concentration of atmospheric Hg, extreme values around 5 ng m−3. Highest concentrations of GEM recorded during the mobile survey were about 10 ng m−3. In both surveys, the recorded concentrations during most of the measurement time were below 2 ng m−3, but measurements were taken at a considerable distance from the crater, and GEM is subject to dilution processes. During both surveys, recorded GEM did not exceed the 200 ng m−3 concentration recommended by the WHO (Air quality guidelines for Europe, 2000) as the regulatory limits for Hg in the atmospheric environment for long-term inhalation. Because this study was carried out in inhabited areas around the volcano during a period of intense volcanic activity, it can be concluded that the Popocatépetl does not represent a risk to human health in terms of Hg.
... In the northern hemisphere, the GEM mean background has been estimated at~2 ng m −3 (Lindberg et al., 2007;Slemr et al., 1981;Sprovieri et al., 2010;Travnickov, 2005;Ebinghaus et al., 2002). Previously, several authors have reported GEM background values of 1.75 and 1.96 ng m −3 (Sprovieri et al., 2003;Pirrone, 2008) in remote areas (e.g. the Pacific Ocean or the Mediterranean Sea). ...
... The Mediterranean Sea basin contains extensive geotectonic activity, which jointly with the large deposits of cinnabar in Spain, Italy, and Slovenia and active volcanoes located through the entire region may constitute natural sources of Hg to the basin in addition to anthropogenic sources (mines, chlor-alkali facilities, coal combustion) concentrated along the northern shore Sprovieri et al. 2010b;Wängberg et al. 2008). Previous oceanographic campaigns performed in the Mediterranean Sea highlight the combination of factors described above, but many have focused on the physical, (photo) chemical, and biological processes governing Hg inputs and cycling particularly regarding abiotic concentrations in the water column (Horvat et al. 2003;Kotnik et al. 2017;Kotnik et al. 2007) or air:sea exchange and atmospheric concentrations (Andersson et al. 2007;Fantozzi et al. 2013;Sprovieri et al. 2010a;Sprovieri et al. 2003). Increasing measurements of bioaccumulation particularly in lower trophic levels continues to be a goal (Cinnirella et al. 2013). ...
Studies of mercury (Hg) in the Mediterranean Sea have focused on pollution sources, air-sea mercury exchange, abiotic mercury cycling, and seafood. Much less is known about methylmercury (MeHg) concentrations in the lower food web. Zooplankton and small fish were sampled from the neuston layer at both coastal and open sea stations in the Mediterranean Sea during three cruise campaigns undertaken in the fall of 2011 and the summers of 2012 and 2013. Zooplankton and small fish were sorted by morphospecies, and the most abundant taxa (e.g. euphausiids, isopods, hyperiid amphipods) analyzed for methylmercury (MeHg) concentration. Unfiltered water samples were taken during the 2011 and 2012 cruises and analyzed for MeHg concentration. Multiple taxa suggested elevated MeHg concentrations in the Tyrrhenian and Balearic Seas in comparison with more eastern and western stations in the Mediterranean Sea. Spatial variation in zooplankton MeHg concentration is positively correlated with single time point whole water MeHg concentration for euphausiids and mysids and negatively correlated with maximum chlorophyll a concentration for euphausiids, mysids, and "smelt" fish. Taxonomic variation in MeHg concentration appears driven by taxonomic grouping and feeding mode. Euphausiids, due to their abundance, relative larger size, importance as a food source for other fauna, and observed relationship with surface water MeHg are a good candidate biotic group to evaluate for use in monitoring the bioavailability of MeHg for trophic transfer in the Mediterranean and potentially globally.
... Due to supersaturation, mercury emitted from open ocean to the atmosphere is mostly Hg 0 , whereas the majority of deposited Hg is oxidised mercury (SPROVIERI et al., 2010). It is easily deposited to surface waters by wet deposition because of high solubility (HEDGE-COCK et al., 2003;HOLMES et al., 2009;SPROVIERI et al., 2003). ...
Study of planktonic foraminifera, sampled from two levels of a 26 cm thick core, recovered at 1,200 m water depth, sheds some lights on the composition of foraminiferal assemblages that occur in the Southern Adriatic. Altogether 15 planktonic species (including one referred as undeterminable and two species recorded for the first time in the eastern Adriatic Sea) identified from 0-2 cm and 24-26 cm sediment intervals, were grouped into two assemblages: >63 μm fraction Turborotalita quinqueloba and >125 μm fraction as Globigerina bulloides-Globigerinoides ruber. The differences in core-top and core-bottom assemblages lie in: a) change in the relative proportion of some species; and b) slight differences in diversity indices. The relative proportions of species are strongly controlled by sieve mesh size, whereas the slight increase in diversity follows the increase in sieve mesh size. The benthic foraminifera, although constituting a negligible quantitative factor, show a slight increase in abundance and diversity of species with age.
... Atmospheric Hg varied significantly with the maximum GEM (5-min mean), PBM (hourly mean), and GOM (hourly mean) concentrations of 13.9 ng/m 3 , 422 pg/m 3 , and 97 pg/m 3 , respectively ( Figure S2). The mean GEM, PBM, and GOM levels at HNI were consistent with observations in remote areas of China (Fu et al., 2015) but relatively higher than those observed in MBL in the North Pacific Ocean, Mediterranean Sea, East Pacific Ocean, Subtropical Atlantic Ocean, and South Indian Ocean (GEM = 0.85 to 2.04 ng/m 3 , PBM = 1 to 3 pg/m 3 , and GOM = 2 to 8 pg/m 3 ; Chand et al., 2008;Laurier & Mason, 2007;Mao et al., 2016;Slemr et al., 2015;Sprovieri et al., 2003;Wang et al., 2014). ...
Characterizing the speciation and isotope signatures of atmospheric mercury (Hg) downwind of mainland China is critical to understanding the outflow of Hg emission and the contributing sources. In this study, we measured the concentrations of gaseous elemental mercury (GEM), particulate bound mercury, gaseous oxidized mercury, and the GEM isotopic composition in the marine boundary layer of East China Sea from October 2013 to January 2014. Mean (±1σ) GEM, particulate bound mercury, and gaseous oxidized mercury concentrations were 2.25 ± 1.03 ng/m³, 26 ± 38 pg/m³, and 8 ± 10 pg/m³, respectively. Most events of elevated GEM are associated with the outflow of Hg emissions in mainland China. The 24- and 48-hr integrated GEM samples showed large variations in both δ²⁰²Hg (-1.63‰ to 0.34‰) and Δ¹⁹⁹Hg (-0.26‰ to -0.02‰). GEM δ²⁰²Hg and Δ¹⁹⁹Hg were negatively and positively correlated to its atmospheric concentrations, respectively, suggesting a binary physical mixing of regional background GEM and Hg emissions in mainland China. Using a binary mixing model, highly negative δ²⁰²Hg (-1.79 ± 0.24‰, 1σ) and near-zero Δ¹⁹⁹Hg (0.02 ± 0.04‰, 1σ) signatures for China GEM emissions are predicted. Such isotopic signatures are significantly different from those found in North America and Europe and the background global/regional atmospheric GEM pool. It is likely that emissions from industrial and residential coal combustion (lacking conventional air pollutant control devices), cement and mercury production, biomass burning, and soil emissions contributed significantly to the estimated isotope signatures of GEM emissions in China.
... In fact, the occurrence of Globorotalia inflata indicate an age not older than~15 ka for the base of the Tea C1-A core succession (Fig. 8c). This is in agreement with the re-entry time of this species in the Sicily Channel and in the South Adriatic Sea, which, on the contrary, is rare during the last part of the last glacial period (Sprovieri et al., 2003;Rouis-Zargouni et al., 2010;Siani et al., 2001Siani et al., , 2010) According with analogous results obtained in nearby areas from core Tea C6 (unpublished data) and in the core MD90-917 recovered in the South Adriatic (Siani et al., 2010), the strong increase in the ratio between Globigerinoides ruber alba and Neogloboquadrina that occurs slightly above the erosional surface (TED in Fig. 8a) can be dated at 11.5 cal ka. This suggests, in turn, an age of~11.7-11.8 ...
The occurrence of articulated seafloor morphology over continental shelf-upper slope environments, may result in a significant change in the patterns and intensity of basin-scale thermohaline circulation during eustatic sea-level fluctuations. These changes may cause, in turn, erosion, deposition and/or transport of sediments at the seafloor, to form shallow-water contourite drifts. Here we investigate this process in the NW sector of the Gulf of Taranto (Ionian Sea) during and following the Last Glacial Maximum (LGM), by integrating multibeam bathymetric data, ultra-high resolution seismic-reflection data and gravity core data. Sea level fall caused subaerial exposure of the summit of the Amendolara Bank, forming a short-lived island off the eastern coast of Calabria, and also creating a narrow passageway between the island and the northern Calabria mainland. Integrated seismic-stratigraphic data show that Upper Quaternary shallow-water contourite drifts and associated erosional features locally formed both around the flanks of the Amendolara Bank (AMBK), and the continental shelf and upper slope off the Amendolara village. Contourite drifts are bounded at the bottom and at the top by two major unconformities, indicating that the formation of the sediments drifts occurred between the onset of the LGM and the GS-1/Younger Dryas event. The stratal architecture suggests the occurrence of various types of contourite deposits, mostly represented by: a) Axial and lateral channel-patch drifts, and channel-related drifts along the incision to the NE of the AMBK; b) Sheeted drifts along the northeastern slope of the AMBK; c) Elongated drifts along the continental shelf and upper slope off the coast of Amendolara village. Erosional features also developed on the south-eastern flank of the AMBK, where the Levantine Intermediate Water flows from the central Ionian Sea towards the Gulf of Taranto, until the present-day. Both processes and timing responsible for erosion of the seafloor and the formation of sediment drifts in the Gulf of Taranto may be similar to that occurred in the Tyrrhenian margins during the Late Quaternary.
... A similar decline of Hg 0 concentrations during the daytime was observed in winter on three Atlantic coastal sites (Kellerhals et al., 2003), in summer on an island site in the Gulf of Maine (Atlantic Ocean) (Mao and Talbot, 2012), in winter and summer on two Dead Sea coastal sites (Moore et al., 2013), and in spring and fall in the Yellow sea (Wang et al., 2016). As a result of studies conducted in the Mediterranean and Adriatic seas (Hedgecock et al., 2003;Sprovieri et al., 2003; and on Dead sea coastal sites (Moore et al., 2013), it was established that a process similar to Arctic and Antarctic springtime atmospheric mercury depletion occurred in daytime in the MBL, when halogens (mainly Br) contained in the maritime air turned into active forms as a result of photolysis, and were able to oxidize Hg 0 . It should be noted that, in all marine studies mentioned above, air sampling was performed on the top decks of research vessels. ...
Gaseous elemental mercury (Hg0) is a prolific and persistent contaminant in the atmosphere. Atmospheric concentrations of Hg0 were determined from 17 September to 7 October 2015 in the northwest Sea of Japan aboard the Russian research vessel Professor Gagarinsky. Simultaneous measurements of Hg0 concentrations were performed 2 m and 20 m above the sea surface using automatic Hg0 analysers RA-915M and RA-915+, respectively. Concentrations ranged from 0.3 to 25.9 ng/m3 (n = 5207) and from 0.3 to 27.8 ng/m3 (n = 4415), with medians of 1.7 and 1.6 ng/m3, respectively. Elevated Hg0 was observed during three episodes from 19 to 22 September, likely caused by one or more of the following factors: 1) atmospheric transport of Hg0 from the west and south-west (from N. Korea, China, and the Yellow Sea region); 2) Hg0 emission from the sea due to pollution by water from the Tumannaya River; or 3) underwater geological activities. Increased Hg0 concentration was observed during periods when air masses flowed from the south, and low concentrations were observed when air masses came from the north. A daytime increase of Hg0 concentrations at a height of 2 m occurred simultaneously with decreasing Hg0 at a height of 20 m. These diurnal variations suggest that two contrasting processes occur during the daytime in the marine boundary layer (MBL): Hg0 emission from the sea surface and Hg0 oxidation in the MBL by active halogens formed by photolysis.
... Due to supersaturation, mercury emitted from open ocean to the atmosphere is mostly Hg 0 , whereas the majority of deposited Hg is oxidised mercury (SPROVIERI et al., 2010). It is easily deposited to surface waters by wet deposition because of high solubility (HEDGE-COCK et al., 2003;HOLMES et al., 2009;SPROVIERI et al., 2003). ...
This review focuses on mercury speciation in the Adriatic Sea, a marginal sea of the Mediterranean,
which represents its distinct biogeochemical subunit due to anthropogenic mercury loadings. The
current knowledge about mercury cycling in the Adriatic is presented through an overview of the
state of the art of research in this area: temporal and spatial distributions and occurrence of mercury
species in seawater and sediment, and chemical transformations. We summarised research results
of mercury speciation in order to describe its presence and fate in the Adriatic Sea. The Adriatic
Sea represents a net source of mercury to the Mediterranean Sea due to the highest total mercury
concentrations observed in the North Adriatic Sea and the highest methylmercury concentrations
in the South Adriatic Pit. However, the biogeochemical cycle of mercury is not completely known
and our understanding of mercury transport between compartments and its (bio)transformations
is limited. Future research needs to focus on microbial and chemical processes of mercury
transformations to improve our understanding of the impacts of mercury contamination on the
environment and human health in the Adriatic Sea. (CC BY 4.0)
... Both AMS and CGR, for most of the time, receive clean marine air masses (Slemr et al., 2014; Angot et al., 2014 ). Previous studies (Mason and Sheu, 2002; Holmes et al., 2009; Sprovieri et al., 2003 Sprovieri et al., , 2010a, b) analyzed atmospheric observations of GOM from Mediterranean, Pacific, and Atlantic cruises in terms of Hg chemistry and deposition in the marine atmosphere , and suggested that elevated levels of halogen atoms, and in particular of bromine (Br) in the marine boundary layer (MBL) are an important source of GOM from oxidation of GEM that are more readily deposited throughout seasalt aerosols followed by aerosol deposition. GEM evasion from marine waters therefore could represent a significant source of atmospheric Hg which contributes to depositional fluxes in marine regions (Mason and Sheu, 2002), such as AMS and CGR. ...
The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet scavenging by precipitation events. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, wet deposition samples were collected for approximately 5 years at 17 selected GMOS monitoring sites located in the Northern and Southern hemispheres in the framework of the Global Mercury Observation System (GMOS) project. Total mercury (THg) exhibited annual and seasonal patterns in Hg wet deposition samples. Interannual differences in total wet deposition are mostly linked with precipitation volume, with the greatest deposition flux occurring in the wettest years. This data set provides a new insight into baseline concentrations of THg concentrations in precipitation worldwide, particularly in regions such as the Southern Hemisphere and tropical areas where wet deposition as well as atmospheric Hg species were not investigated before, opening the way for future and additional simultaneous measurements across the GMOS network as well as new findings in future modeling studies.
... We are therefore reasonably confident that the model is reproducing the OH concentration with a fair degree of accuracy. The chemical mechanism employed for the summer 2005 results was used to re-run the simulations for the summer 2000 oceanographic campaign described in Sprovieri et al. (2003) and modelled in Hedgecock et al. (2003Hedgecock et al. ( , 2005. The comparison between the simulated and observed RGM concentrations proved to be similar to those previously published with the Index of Agreement metric (see Hedgecock et al., 2005) differing by just 0.06, having a value in this case of 0.63 rather than 0.69. ...
Atmospheric mercury species concentrations were measured during two oceanographic cruise campaigns covering the Adriatic Sea, the first during the autumn in 2004 and the second in the summer of 2005. The inclement weather during the autumn campaign meant that no clear in-situ production of oxidised gas phase mercury was seen. Events where high values of Hg<sup>II</sup><sub>(g)</sub> and/or Hg associated with particulates (Hg<sup>P</sup>) were observed, could be linked to probable anthropogenic emission source areas. During the summer campaign however, the by now rather familiar diurnal variation of Hg<sup>II</sup><sub>(g)</sub> concentration, with maxima around midday, was observed. Again there were events when high Hg<sup>II</sup><sub>(g)</sub> and particulates (Hg<sup>P</sup>) concentrations were seen which did not fit with the pattern of daily in-situ Hg<sup>II</sup><sub>(g)</sub> production. These events were traceable, with the help of back trajectory calculations, to areas of anthropogenic emissions. The back trajectories for all the events during which high Hg species concentrations were encountered showed that the airmass being sampled had passed near port areas in the previous 24 h. Not all these ports are associated with major industrial installations, it is possible therefore (bearing in mind the uncertainty associated with the back trajectory calculations) that either shipping or port activities are a Hg source. Box modelling studies of the summer 2005 campaign show that although the in-situ production of Hg<sup>II</sup><sub>(g)</sub> occurs in the MBL, the exact chemical mechanism responsible is difficult to determine. However given the high O<sub>3</sub> concentrations encountered during this campaign it seems clear that if Hg<sup>0</sup> does react with O<sub>3</sub>, it does not produce gas phase Hg<sup>II</sup>. Equally, the reaction between Hg<sup>0</sup> and OH if it occurs, does not contribute appreciably to Hg<sup>II</sup><sub>(g)</sub> production.
... Both AMS and Cape Grim for most of the time receive clean marine air masses(Slemr et al., 2014;Angot et al., 2014). Previous studies(Mason and Sheu, 2002;Sprovieri et al., 2003;Holmes et al., 2009;Sprovieri et al., 2010b, a) analyzed atmospheric observations of GOM from Mediterranean, Pacific and Atlantic cruises in terms of Hg chemistry and deposition in the marine15 atmosphere, and suggested that elevated levels of halogen atoms, and in particular of Br in the marine boundary layer(MBL) are an important source of GOM from oxidation of GEM, that more readily deposited throughout sea-salt aerosols followed by aerosol deposition. GEM evasion from marine waters therefore, could represent a significant source of atmospheric Hg which contributes to depositional fluxes in marine regions(Mason and Sheu, 2002), such as Amsterdam Island, and Cape Grim. ...
The atmospheric deposition of mercury (Hg) occurs via several mechanisms including dry and wet scavenging by precipitation events. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, wet deposition samples were collected for approximately five years at 17 selected GMOS monitoring sites located in the Northern and Southern Hemispheres in the framework of the Global Mercury Observation System (GMOS) project. Total mercury (THg) exhibited annual and seasonal patterns in Hg wet deposition samples. Inter-annual differences in total wet deposition are mostly linked with precipitation volume, with the greatest deposition flux occurring in the wettest years. This data set provides a new insight into baseline concentrations of THg concentrations in precipitation worldwide, particularly in regions, such as the Southern Hemisphere and tropical areas where wet deposition as well as atmospheric Hg species were not investigated before, opening the way for future and additional simultaneous measurements across the GMOS network as well as new findings in future modeling studies.
... Our results were consistent with the previous multiple-sites (e.g., coastal, oceanic, and urban sites) studies (Cheng et al., 2014;Engle et al., 2008;Laurier and Mason, 2007;Liu et al., 2007), which showed that the RGM typically followed a diurnal pattern with lower concentrations in the nighttime and higher concentrations in the daytime. Numerous field studies have shown that GEM in the MBL can be rapidly oxidized to form RGM in-situ (Chand et al., 2008;Hedgecock and Pirrone, 2001;Hedgecock et al., 2003;Laurier et al., 2003;Laurier and Mason, 2007;Soerensen et al., 2010;Sprovieri et al., 2003Sprovieri et al., , 2010. In addition, the oxidation of GEM must be photochemical, as evidenced by the observed seasonal cycle of GEM and the diurnal cycle of RGM (Laurier and Mason, 2007). ...
The objectives of this study are to identify the spatial and temporal distributions of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and fine particulate mercury (HgP2.5) in the marine boundary layer (MBL) of the Bohai Sea (BS) and Yellow Sea (YS), and to investigate the relationships between mercury species and meteorological parameters. The mean concentrations of GEM, RGM, and HgP2.5 were 2.03 ng m−3, 2.5 pg m−3, and 8.2 pg m−3 in spring, and 2.09 ng m−3, 4.3 pg m−3, and 8.3 pg m−3 in fall. Reactive mercury (RGM + HgP2.5) represented < 1% of total atmospheric mercury (GEM + RGM + HgP2.5), which indicated that most mercury export in the MBL was GEM and the direct outflow of reactive mercury was very small. Moreover, GEM concentrations over the BS were generally higher than those over the YS both in spring and fall. Although RGM showed a homogeneous distribution over the BS and YS both in spring and fall, the mean RGM concentration in fall was significantly higher than that in spring. In contrast, the spatial distribution of HgP2.5 generally reflected a gradient with high levels near the coast of China and low levels in the open sea, suggesting the significant atmospheric mercury outflow from China. Interestingly, the mean RGM concentrations during daytime were significantly higher than those during nighttime both in spring and fall, while the opposite results were observed for HgP2.5. Additionally, RGM positively correlates with air temperature while negatively correlates with relative humidity. In conclusion, the elevated atmospheric mercury levels in the BS and YS compared to other open seas suggested that the human activities had a significant influence on the oceanic mercury cycle downwind of China.
... The use of observations and models together determined that the MBL has bromine photochemistry and was not affected by the hydroxyl (OH) radical. This drives the midday photochemical peak in GOM concentrations in the MBL and that scavenging by sea salt was driving rapid deposition at night (Holmes et al., 2009; Selin et al., 2007; Obrist et al., 2010; Pirrone, 2001, 2004; Hedgecock et al., 2003; Jaffe et al., 2005; Laurier and Masson, 2007; Laurier et al., 2003; Sprovieri et al., 2003). Model–observation comparisons consistently suggest models overestimate GOM surface concentrations, sometimes by as much as an order of magnitude (Amos et al., 2012; Kos et al., 2013; Holloway et al., 2012; Bieser et al., 2014 ). ...
Mercury (Hg) is a global health concern due to its toxicity and ubiquitous presence in the environment. Here we review current methods for measuring the forms of Hg in the atmosphere and models used to interpret these data. There are three operationally defined forms of atmospheric Hg: gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM). There is relative confidence in GEM measurements (collection on a gold surface), but GOM (collection on potassium chloride (KCl)-coated denuder) and PBM (collected using various methods) are less well understood. Field and laboratory investigations suggest the methods to measure GOM and PBM are impacted by analytical interferences that vary with environmental setting (e.g., ozone, relative humidity), and GOM concentrations measured by the KCl-coated denuder can be too low by a factor of 1.6 to 12 depending on the chemical composition of GOM. The composition of GOM (e.g., HgBr2, HgCl2, HgBrOH) varies across space and time. This has important implications for refining existing measurement methods and developing new ones, model/measurement comparisons, model development, and assessing trends. Unclear features of previously published data may now be re-examined and possibly explained, which is demonstrated through a case study. Priorities for future research include identification of GOM compounds in ambient air and development of information on their chemical and physical properties and GOM and PBM calibration systems. With this information, identification of redox mechanisms and associated rate coefficients may be developed.
... In addition, the fact that the Mediterranean is a semi-closed sea bordered by numerous industrialized nations, with a large population living close to the coast, has led to concerns that pollutants and contaminants could build up within the Basin and affect wildlife. The lack of knowledge of the magnitude of the air-sea exchange mechanisms is one of the main factors affecting the overall uncertainty associated with the assessment of net fluxes of Hg between the atmospheric and marine environments in the Mediterranean region Hedgecock and Pirrone, 2004;Horvat et al., 2001Horvat et al., , 2003Gardfeldt et al., 2003;Kotnik et al., 2007;Sprovieri and Pirrone, 2008;. The aim of this work is to provide a review of measurements and modeling results obtained during the last ten years of studies carried out in the western and eastern sector of the Mediterranean Sea Mediterranean sea basin on board the Italian Research Vessel URANIA (CNR). ...
Only a few years ago the presence of Reactive Gaseous Mercury (RGM) was believed to be almost exclusively the result of anthropogenic emissions and that sustained high RGM concentrations in the MBL were not considered likely. During the past ten years, an in-depth investigation was carried out in the Marine Boundary Layer (MBL) of the Mediterranean Sea to quantify and possibly explain spatial and temporal patterns of Hg-species concentrations. This paper provides an overview of modeling results and atmospheric measurements performed during several cruise campaigns performed aboard the Research Vessel (RV) URANIA of the CNR over the Mediterranean sea basin. RGM concentrations have been modelled using a photochemical box model of the MBL and compared to measured data obtained during the research cruises. The comparison results supports the hypothesis that there are daytime mercury oxidation reactions occurring which have not yet been identified. Major findings of key studies carried out during ten years of ship-borne activities have been highlighted.
... Measurements from six oceanographic campaigns and from EMEP network monitoring stations have been used for comparison with the modeled O 3 concentrations. From 2000, an almost yearly series of oceanographic campaigns, primarily to study Hg cycling in the Mediterranean marine BL (MBL), surface and column water, sediments and the exchange of Hg species between the atmosphere and the sea surface have been performed aboard the R. V. Urania by the CNR-IIA (Italain Research Council Institute of Atmospheric Pollution Research) [30][31][32][33][34]. In addition to Hg species, a number of gas and aerosol phase atmospheric species were measured. ...
Ozone concentrations in the Mediterranean area regularly exceed the maximum levels set by the EU Air Quality Directive, 2008/50/CE, a maximum 8-h mean of 120 µg·m −3 , in the summer, with consequences for both human health and agriculture. There are a number of reasons for this: the particular geographical and meteorological conditions in the Mediterranean play a part, as do anthropogenic ozone precursor emissions from around the Mediterranean and continental Europe. Ozone concentrations measured on-board the Italian Research Council's R. V. Urania during summer oceanographic campaigns between 2000 and 2010 regularly exceeded 60 ppb, even at night. The WRF/Chem (Weather Research and Forecasting (WRF) model coupled with Chemistry) model has been used to simulate tropospheric chemistry during the periods of the measurement campaigns, and then, the same simulations were repeated, excluding the contribution of maritime traffic in the Mediterranean to the anthropogenic emissions inventory. The differences in the model output suggest that, in large parts of the coastal zone of the Mediterranean, ship emissions Atmosphere 2014, 5 938 contribute to 3 and 12 ppb to ground level daily average ozone concentrations. Near busy shipping lanes, up to 40 ppb differences in the hourly average ozone concentrations were found. It seems that ship emissions could be a significant factor in the exceedance of the EU directive on air quality in large areas of the Mediterranean Basin.
... This indicates that the anthropogenic Hg emission has substantially enhanced the GEM concentration over the downwind region of East Asia. The GEM concentrations are comparable or lower compared to marine regions that impacted by direct human activities or historical Hg releases, such as the SCS (2.8-5.7 ng m À3 , Fu et al., 2010;Tseng et al., 2012Tseng et al., , 2013, the Mediterranean Sea (1.5-2.1 ng m À3 , Sprovieri et al., 2003;Bagnato et al., 2013) and the Atlantic Ocean (2.26 ng m À3 , Soerensen et al., 2010a), but are significantly higher than remote oceans, such as the south-west Indian Ocean (1.2 ng m À3 , Witt et al., 2010) and the oceans in the South Hemisphere (1.0-1.5 ng m À3 , Soerensen et al., 2010a), and also higher than the coast of Central and Southern California in North America (1.40 ng m À3 , Weiss-Penzias et al., 2013). Fig. 2 shows the spatial variation of GEM during the two cruises. ...
The Yellow Sea in East Asia receives great Hg input from regional emissions. However, Hg cycling in this marine system is poorly investigated. In late spring and late fall 2012, we determined gaseous elemental Hg (GEM or Hg(0)) in air and dissolved gaseous Hg (DGM, mainly Hg(0)) in surface waters to explore the spatial-temporal variations of Hg(0) and further to estimate the air/sea Hg(0) flux in the Yellow Sea. The results showed that the GEM concentrations in the two cruises were similar (spring: 1.86±0.40ngm(-3); fall: 1.84±0.50ngm(-3)) and presented similar spatial variation pattern with elevated concentrations along the coast of China and lower concentrations in the open ocean. The DGM concentrations of the two cruises were also similar with 27.0±6.8pgL(-1) in the spring cruise and 28.2±9.0pgL(-1) in the fall cruise and showed substantial spatial variation. The air/sea Hg(0) fluxes in the spring cruise and fall cruise were estimated to be 1.06±0.86ngm(-2)h(-1) and 2.53±2.12ngm(-2)h(-1), respectively. The combination of this study and our previous summer cruise showed that the summer cruise presented enhanced values of GEM, DGM and air/sea Hg(0) flux. The possible reason for this trend was that high solar radiation in summer promoted Hg(0) formation in seawater, and the high wind speed during the summer cruise significantly increased Hg(0) emission from sea surface to atmosphere and subsequently enhanced the GEM levels.
... Also in the Pacific Ocean measurements date back in the early 1980s (Kim and Fitzgerald 1988). Within the framework of the MED-OCEANOR programme an in-depth investigation has continued since 2000 in the Mediterranean, measuring mercury concentrations in the air, surface and deep water, sediments, and gaseous exchange rates at the air-water interface, to assess the spatial and temporal patterns of mercury species concentrations in the Mediterranean Sea Sprovieri et al. 2003Sprovieri et al. , 2009Andersson et al. 2007;Kotnik et al. 2007;Sprovieri and Pirrone 2008). The spatial and seasonal variability of the gaseous elemental mercury fluxes at the air-sea interface was shown for the Baltic Sea in 2006 (Kuss and Schneider 2007). ...
The need for coordinated, systematized and catalogued databases on mercury in the environment is of paramount importance as improved information can help the assessment of the effectiveness of measures established to phase out and ban mercury. Long-term monitoring sites have been established in a number of regions and countries for the measurement of mercury in ambient air and wet deposition. Long term measurements of mercury concentration in biota also produced a huge amount of information, but such initiatives are far from being within a global, systematic and interoperable approach. To address these weaknesses the on-going Global Mercury Observation System (GMOS) project ( www.gmos.eu ) established a coordinated global observation system for mercury as well it retrieved historical data ( www.gmos.eu/sdi ). To manage such large amount of information a technological infrastructure was planned. This high-performance back-end resource associated with sophisticated client applications enables data storage, computing services, telecommunications networks and all services necessary to support the activity. This paper reports the architecture definition of the GMOS Cyber(e)-Infrastructure and the services developed to support science and policy, including the United Nation Environmental Program. It finally describes new possibilities in data analysis and data management through client applications.
... ng m À3 in the winter and summer, respectively (Table 1 ). The time-weighted average GEM concentrations show to some extent seasonal variations, as previously reported in literature for other geographic areas (Sprovieri et al., 2003; Sprovieri and Pirrone, 2008; Wangberg et al., 2008 ). Variability in our collected Hg data may be ascribed to the different intensity of the natural sunlight between winter and summer which represents a key parameter in controlling rates of % Hg 0 produced and then escaped from seawater surface (Costa and Liss, 1999); anyway the intensity of solar radiation has not been determined in this study. ...
Mercury (Hg) is emitted in the atmosphere by anthropogenic and natural
sources, these last accounting for one third of the total emissions.
Since the pre-industrial age, the atmospheric deposition of mercury have
increased notably, while ocean emissions have doubled owing to the
re-emission of anthropogenic mercury. Exchange between the atmosphere
and ocean plays an important role in cycling and transport of mercury.
We present the preliminary results from a study on the distribution and
evasion flux of mercury at the atmosphere/sea interface in the Augusta
basin (SE Sicily, southern Italy), a semi-enclosed marine area affected
by a high degree of contamination (heavy metals and PHA) due to the oil
refineries placed inside its commercial harbor. It seems that the
intense industrial activity of the past have lead to an high Hg
pollution in the bottom sediments of the basin, whose concentrations are
far from the background mercury value found in most of the Sicily Strait
sediments. The release of mercury into the harbor seawater and its
dispersion by diffusion from sediments to the surface, make the Augusta
basin a potential supplier of mercury both to the Mediterranean Sea and
the atmosphere. Based on these considerations, mercury concentration and
flux at the air-sea interface of the Bay have been estimated using a
real-time atomic adsorption spectrometer (LUMEX - RA915+) and an
home-made accumulation chamber, respectively. Estimated Total
Atmospheric Mercury (TGM) concentrations during the cruise on the bay
were in the range of 1-3 ng · m-3, with a mean value of about 1.4
ng · m-3. These data well fit with the background Hgatm
concentration values detected on the land (1-2 ng · m-3, this
work), and, more in general, with the background atmospheric TGM levels
found in the North Hemisphere (1.5-1.7 ng · m-3)a. Besides, our
measurements are in the range of those reported for other important
polluted marine areas. The mercury evasion flux at the air-sea interface
measured during the first cruise ranges from about 110 to 1500 ng
· m-2day-1. This range is 1-2 order of magnitude higher than most
of marine environments (Pacific Ocean, Mediterranean Sea, Artic Ocean)
and some important polluted marine areas, such as the Tokyo Bay (19-259
ng · m-2day-1)b and the Yellow Sea (156-722 ng ·
m-2day-1)c. Further estimates on Hg atmospheric deposition flux (wet and
dry) and biomonitoring are required for finally assessing a mass balance
of Hg in Augusta basin. aLindberg et al., 2007. A Journal of the
Human Environment, 3, 19-33. bNarukawa et al., 2006. Journal of
Oceanography, 62, 249-257. cCi et al., 2011. Atmosphere Chemistry and
Physics, 11, 2881-2892.
... During this campaign, measurements were performed aboard the CNR's R. V. Urania, mostly in the Tyrrhenian Sea. The measurements made during oceanographic campaigns have been described elsewhere (Sprovieri et al. 2003Sprovieri et al. , 2010). Briefly, collection and analysis of Hg 0 , Hg II and Hg P were performed using an automated Tekran (Toronto, Canada) Model 2537A cold vapour atomic fluorescence spectrophotometry (CVAFS), coupled to a Tekran Model 1130 speciation unit and a Tekran Model 1135 system . ...
The emission, transport, deposition and eventual fate of mercury (Hg) in the Mediterranean area has been studied using a modified version of the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem). This model version has been developed specifically with the aim to simulate the atmospheric processes determining atmospheric Hg emissions, concentrations and deposition online at high spatial resolution. For this purpose, the gas phase chemistry of Hg and a parametrised representation of atmospheric Hg aqueous chemistry have been added to the regional acid deposition model version 2 chemical mechanism in WRF/Chem. Anthropogenic mercury emissions from the Arctic Monitoring and Assessment Programme included in the emissions preprocessor, mercury evasion from the sea surface and Hg released from biomass burning have also been included. Dry and wet deposition processes for Hg have been implemented. The model has been tested for the whole of 2009 using measurements of total gaseous mercury from the European Monitoring and Evaluation Programme monitoring network. Speciated measurement data of atmospheric elemental Hg, gaseous oxidised Hg and Hg associated with particulate matter, from a Mediterranean oceanographic campaign (June 2009), has permitted the model's ability to simulate the atmospheric redox chemistry of Hg to be assessed. The model results highlight the importance of both the boundary conditions employed and the accuracy of the mercury speciation in the emission database. The model has permitted the reevaluation of the deposition to, and the emission from, the Mediterranean Sea. In light of the well-known high concentrations of methylmercury in a number of Mediterranean fish species, this information is important in establishing the mass balance of Hg for the Mediterranean Sea. The model results support the idea that the Mediterranean Sea is a net source of Hg to the atmosphere and suggest that the net flux is ≈30 Mg year(-1) of elemental Hg.
... These data limitations make it difficult to interpret longterm trends in atmospheric concentrations and the role of oceanic processes. Recently, simultaneous measurements of atmospheric at the airewater interface and dissolved Hg 0 in the top-water microlayer and in the water column have been performed at several ocean and sea locations in the world (Ferrara et al., 2000;Sprovieri et al., 2003;Gårdfeldt et al., 2003;Hedgecock et al., 2003;Andersson et al., 2007). Such measurements would be extremely useful in refining global estimates of airesea exchange and factors controlling spatial and temporal variability in concentrations but need to be extended to cover a greater range of physical and chemical conditions. ...
... As the results of recent investigations demonstrate, in the marine atmosphere saturated with the salts of Cl and Br, the daily photochemical reactions occur of Hg 0 oxidation with the formation of less volatile, more soluble, and more chemically active compounds of Hg 2+ having the short period of existence in the at-AKSENTOV, KALINCHUK mosphere (several days) due to their sorption by aerosol particles with the subsequent joint falling to the sea surface [19]. From the ecological point of view, this is important for the marine ecosystems, because if the Hg 0 concentration in the atmosphere increases, the content of chemically responsive forms of mercury falling to the sea increases as well. ...
Presented are the results of mercury content measurements in the surface air layer in the Sea of Japan in the period from October 27 to November 11, 2010. It is revealed that the mercury content varied from 0.6 to 3.8 ng/m3. It is demonstrated that the mercury concentration distribution has geographical zoning and depends on the movement of air masses and on the closeness of anthropogenic sources. The maximum mercury concentration is detected in the central part of the sea at the southwestern and southern directions of the wind, that is associated with the industrial emissions of East Asia countries. The minimum mercury concentration corresponding to the concentration in the surface air layer of the Arctic, Atlantic Ocean (Northern Hemisphere), and the Sea of Okhotsk and Bering Sea was observed along the coast of Primorye at the northwestern wind direction.
The Mediterranean is a crossroad region for different air masses and, therefore, of many contrasted aerosol types. It has been a natural laboratory to study their long-range transport, the formation of secondary particles from gaseous precursors, the effects of aerosols on the local and regional radiation budgets, and their consequences on air quality, atmospheric dynamics, clouds, precipitation, and climate. This chapter reviews the evolution of observational studies on tropospheric aerosols over the Mediterranean basin and surrounding areas after almost six decades of research. The dispersion of radionuclides following worldwide atmospheric nuclear bomb tests and then intense desert dust episodes were the motivations of the first studies in the 1960s. Our historical perspective describes the evolution of observation strategies in the Mediterranean region. It reflects to what extent the development of new instruments and observation strategies, or the expansion of high quality-high resolution remote sensing data, has contributed to our knowledge of aerosol phenomenology in this region. We review actions including intensive land and cruise field campaigns, surface monitoring stations, air quality studies, ground-based aerosol networks with a special focus on AERONET, satellite surveys, and finally, address aerosol speciation and health impacts.KeywordsMediterranean aerosolObservational studiesList of past aerosol studiesSurface stationsIn situ measurementsAirborne measurementsField campaignsOceanographic cruisesAircraftUltra-light aircraft (ULA)Unmanned aircraft (UA)BalloonsRadionuclidesUltra-fine particlesAir qualityPMDustAzores anticycloneMonitoringGround-based networksAERONETEARLINETSKYNETRemote sensingLidarSatellite surveyMeteosatMSGTOMSAVHRRSeaWIFSMODISPOLDERLiteCALIOPCALIPSOAIRSIASIGOME-2Aerosol speciation studiesHealth impactsMEDPOLBAPMoNEOLOMEIDEXPANACEAEMEPMEDCAPHOT-TRACESECAPPAURADIOSMINOSFAMETHALESEROS-2000ARACHNEMEDUSESTAAARTEMERCYMSSUB-AEROEL CIDMINATROCCYCLOPSCIRCEAIRUSEAPICEPEGASOSPYREXPIPAPOESCOMPTEVELETAGAMARFMORESAPUSSKRIPISChArMExChArMEx-SOP0/TRAQAChArMEx-SOP1A/ADRIMEDChArMEx-SOP1B/SAFMEDChArMEx-SOP2A/SAFMED+ChArMEx-SOP2B/GLAMBACCHUS-ChArMEX/CyArCAREPEACETIMEA-LIFEQUESTVESSAEROPERAEUSAARACTRISAPHEA
Measurements of speciated atmospheric mercury (Hg) were conducted at the Changdao Island from October 2013 to July 2015 to characterize their seasonal and diurnal patterns, to identify the relationships between atmospheric Hg and meteorological parameters as well as trace gases, and furthermore to verify the potential sources of atmospheric Hg. There was a seasonal variation of gaseous elemental Hg (GEM) with the order of winter (2.87 ± 1.16 ng m⁻³), spring (2.58 ± 0.84 ng m⁻³), summer (2.25 ± 0.51 ng m⁻³), and fall (2.15 ± 0.39 ng m⁻³). The mean GEM value (2.52 ± 0.82 ng m⁻³) in the Changdao Island was about 1.7 times higher than that in the Northern Hemisphere, indicating that the Changdao and peripheral regions were polluted to some extent. Gaseous oxidized Hg (GOM) shows a clear seasonal variation with the highest value in summer (12.2 ± 9.4 pg m⁻³) and the lowest value in winter (4.6 ± 4.2 pg m⁻³). Moreover, the mean GOM concentration was significantly higher in daytime (11.9 ± 9.4 pg m⁻³) than in nighttime (6.3 ± 4.8 pg m⁻³) mainly due to the influence of solar radiation. In contrast, fine particulate Hg (HgP2.5) exhibited a distinct seasonal trend opposite to that of GOM. There was no significant difference between daytime HgP2.5 concentration (25.6 ± 23.9 pg m⁻³) and nighttime concentration (30.4 ± 31.2 pg m⁻³). The size distribution of HgP in PM10 was observed to be one-modal with the peak around the range of 1.1–2.1 μm in the winter, while it was bi-modal with a higher peak in the range of 1.1–2.1 μm and a lower peak in the range of 4.8–5.9 μm in other seasons. Generally, more than half of HgP was concentrated on fine particles (PM2.1). The temporal variation pattern of PM2.5/PM10 ratio was similar to those of HgP2.1/HgP10 or HgP3.3/HgP10. This further supports that HgP is mainly concentrated in fine particles. Correlation analysis shows that the GEM was positively correlated with SO2 and NO2. The average dry deposition flux of HgP10 was calculated to be 4.76 ng m⁻² d⁻¹ with a range of 0.86–13.46 ng m⁻² d⁻¹ based on all the size-fractionated HgP over the Changdao Island. This indicates that the dry deposition of HgP is an important part of atmospheric Hg deposition in coastal region because it happens all the time.
The characteristics of the reactive gaseous mercury (RGM) and particulate mercury (HgP) in the marine boundary layer (MBL) is poorly understood due in part to sparse data from sea and ocean. Gaseous elemental Hg (GEM), RGM and size-fractioned HgP in marine atmosphere, and dissolved gaseous Hg (DGM) in surface seawater were determined in the South China Sea (SCS) during an oceanographic expedition (3–28 September 2015). The mean concentrations of GEM, RGM and HgP2.5 were 1.52 ± 0.32 ng m−3, 6.1 ± 5.8 pg m−3 and 3.2 ± 1.8 pg m−3, respectively. Low GEM level indicated that the SCS suffered less influence from human activities, which could be due to the majority of air masses coming from the open oceans as modeled by backward trajectories. Atmospheric reactive Hg (RGM + HgP2.5) represented less than 1 % of total atmospheric Hg, indicating that atmospheric Hg existed mainly as GEM in the MBL. The GEM and RGM concentrations in the northern SCS were significantly higher than those in the western SCS, and the HgP2.5 and HgP10 levels in the Pearl River Estuary were significantly higher than those in the open waters of the SCS, indicating that the Pearl River Estuary was polluted to some extent. The size distribution of HgP in PM10 was observed to be bi-modal with a higher peak (5.8–9.0 μm) and a lower peak (0.7–1.1 μm), but the coarse modal was the dominant size, especially in the open SCS. There was no significant diurnal variation of GEM and HgP2.5, but we found the RGM concentrations were significantly higher in daytime than in nighttime mainly due to the influence of solar radiation. In the northern SCS, the DGM concentrations in nearshore areas were higher than those in the open sea, but this pattern was not significant in the western SCS. The sea–air exchange fluxes of Hg⁰ in the SCS varied from 0.40 to 12.71 ng m−2 h−1 with a mean value of 4.99 ± 3.32 ng m−2 h−1. The annual emission flux of Hg⁰ from the SCS to the atmosphere was estimated to be 159.6 tons yr−1, accounting for about 5.54 % of the global Hg⁰ oceanic evasion though the SCS only represents 1.0 % of the global ocean area. Additionally, the annual dry deposition flux of atmospheric reactive Hg represented more than 18 % of the annual evasion flux of Hg⁰, and therefore the dry deposition of atmospheric reactive Hg was an important pathway for the input of atmospheric Hg to the SCS.
In the framework of the ongoing MEDOCEANOR measurements program, an oceanographic cruise campaign was carried out during summer 2015 in the Western sector of Mediterranean Sea basin, on-board the research
vessel ”Minerva Uno” of the Italian National Research Council (CNR). The overall goal was to investigate the
dynamic patterns of mercury in the Marine Boundary Layer (MBL) and the main factors affecting mercury
behaviour at both coastal and offshore locations. The mean concentrations of the recorded Hg species were 1.6 ±0.5 ngm−3, 11.8 ± 15.0 pgm−3, and 2.4 ± 1.1 pgm−3, respectively for GEM, GOM, and PBM. Moreover, during the measurement period typical fair-weather conditions of the Mediterranean summer were encountered with high levels of solar radiation and temperature that favoured photochemical reactions. Atmospheric pollutants such as ozone, sulphur oxides and nitrogen oxides and other meteorological parameters were in addition recorded and jointly discussed with selected mercury events in terms of their spatio-temporal variations. Changes in air pollutant concentrations were also argued in the light of their likely influencing sources, among which, anthropogenic activities, such as the mercury cell chlor-alkali complex in Tuscany, Italy, and natural influence, like volcanic ashes, detected around the Aeolian area and the in-situ production of reactive gaseous mercury within the Marine Boundary Layer.
Long-term continuous measurements of gaseous elemental mercury (Hg<sup>0</sup>), reactive gaseous mercury (RGM), and particulate phase mercury (Hg<sup>P</sup>) were conducted at coastal (Thompson Farm, denoted as TF), marine (Appledore Island, denoted as AI), and elevated inland rural (Pac Monadnock, denoted as PM) monitoring sites of the AIRMAP Observing Network. Diurnal, seasonal, annual, and interannual variability in Hg<sup>0</sup>, RGM, and Hg<sup>P</sup> from the three distinctly different environments were characterized and compared in Part 1. Here in Part 2 relationships between speciated mercury (i.e., Hg<sup>0</sup>, RGM, and Hg<sup>P</sup>) and climate variables (e.g., temperature, wind speed, humidity, solar radiation, and precipitation) were examined. The best point-to-point correlations were found between Hg<sup>0</sup> and temperature in summer at TF and spring at PM, but there was no similar correlation at AI. Subsets of data demonstrated regional impacts of episodic dynamic processes such as strong cyclonic systems on ambient levels of Hg<sup>0</sup> at all three sites, possibly through enhanced oceanic evasion of Hg<sup>0</sup>. A tendency of higher levels of RGM and Hg<sup>P</sup> was identified in spring and summer under sunny conditions in all environments. Specifically, the 10th, 25th, median, 75th, and 90th percentile mixing ratios of RGM and Hg<sup>P</sup> increased with stronger solar radiation at both the coastal and marine sites. These metrics decreased with increasing wind speed at AI indicating enhanced loss of RGM and Hg<sup>P</sup> through deposition. RGM and Hg<sup>P</sup> levels correlated with temperature positively in spring, summer and fall at the coastal and marine locations. At the coastal site relationships between RGM and relative humidity suggested a clear decreasing tendency in all metrics from <40% to 100% relative humidity in all seasons especially in spring, compared to less variability in the marine environment. The effect of precipitation on RGM at coastal and marine locations was similar. At the coastal site, RGM levels were a factor of 3–4 to two orders of magnitude higher under dry conditions than rainy conditions in all seasons. In winter RGM mixing ratios appeared to be mostly above the limit of detection (LOD) during snowfalls suggesting less scavenging efficiency of snow. Mixing ratios of Hg<sup>P</sup> at the coastal and marine sites remained above the LOD under rainy conditions. Precipitation had negligible impact on the magnitude and pattern of diurnal variation of Hg<sup>P</sup> in all seasons in the marine environment.
A comprehensive analysis was conducted using long-term continuous measurements of gaseous elemental mercury (Hg<sup>o</sup>), reactive mercury (RGM), and particulate phase mercury (Hg<sup>P</sup>) at coastal (Thompson Farm, denoted as TF), marine (Appledore Island, denoted as AI), and elevated inland (Pac Monadnock, denoted as PM) sites from the AIRMAP Observatories. Decreasing trends in background Hg<sup>o</sup> were identified in the 7- and 5-yr records at TF and PM with decline rates of 3.3 parts per quadrillion by volume (ppqv) yr<sup>−1</sup> and 6.3 ppqv yr<sup>−1</sup>, respectively. Common characteristics at these sites were the reproducible annual cycle of Hg<sup>o</sup> with its maximum in winter-spring and minimum in fall as well as a decline/increase trend in the warm/cool season. The coastal site TF differed from the other two sites with its exceptionally low levels (as low as below 50 ppqv) in the nocturnal inversion layer probably due to dissolution in dew water. Year-to-year variability was observed in the warm season decline in Hg<sup>o</sup> at TF varying from a minimum total seasonal loss of 20 ppqv in 2010 to a maximum of 92 ppqv in 2005, whereas variability remained small at AI and PM. Measurements of Hg<sup>o</sup> at PM, an elevated inland rural site, exhibited the smallest diurnal to annual variability among the three environments, where peak levels rarely exceeded 250 ppqv and the minimum was typically 100 ppqv. It should be noted that summertime diurnal patterns at TF and AI are opposite in phase indicating strong sink(s) for Hg<sup>o</sup> during the day in the marine boundary layer, which is consistent with the hypothesis of Hg<sup>o</sup> oxidation by halogen radicals there. Mixing ratios of RGM in the coastal and marine boundary layers reached annual maximum in spring and minimum in fall, whereas at PM levels were generally below the limit of detection (LOD) except in spring. RGM levels at AI were higher than at TF and PM indicating a stronger source strength(s) in the marine environment. Mixing ratios of Hg<sup>P</sup> at AI and TF were close in magnitude to RGM levels and were mostly below 1 ppqv. Diurnal variation in Hg<sup>P</sup> was barely discernible at TF and AI in spring and summer with higher levels during the day and smaller but above the LOD at night.
A year-long observation of PM2.5-bounded mercury (PBM) and its species was conducted at a urban site (Shanghai, Xuhui; XH) and an island site (Shengsi, SS) in eastern China from September 2014 to August 2015. The seasonal variation of mercury species including hydrochloric soluble particle-phase mercury (HPM), element soluble particle-phase mercury (EPM) and residual soluble particle-phase mercury (RPM), as well as particulate halogen (Br, I) were determined. Annual average concentration of PBM at urban was 0.32 ± 0.13 ng·m− 3, and was 0.22 ± 0.18 ng·m− 3 at island, which might be attributed to anthropogenic sources. Include more results here, such as EPM, RPM, and with comparison like “The speciated mercury in PM2.5 was found to be HPM > RPM > EPM at the urban site, while RPM > HPM > EPM at island site, respectively.” The speciated mercury in PM2.5 showed distinct different concentrations between the two sites. HPM concentration is the highest at urban, but RPM showed the largest fraction at island. Higher mass contents of all PM2.5-bounded mercury species were found at island site than those at urban site, which indicated atmospheric mercury is more easily scavenged by particles at ocean atmosphere. Additionally, the correlation between bromine and mercury was stronger at urban site than that at island site, while iodine had the stronger correlation with mercury at island site than that urban site. These results showed marine aerosols played an important role to the transport of mercury.
Mercury is a global pollutant. Evidence from ice cores and lake sediments indicates that mercury deposition has increased significantly due to human activities. Most mercury is released into the environment in inorganic forms, but through methylation it is converted to organic mercury compounds. These compounds can be bioaccumulated into fish and other organisms. Mercury released into water will have regional impacts. Mercury released into the atmosphere can have regional implication, but can also be transported and deposited thousands of kilometers away. The chemistry of mercury is complex and has a strong influence on the global cycling.
Elevated concentrations of ground level ozone are both hazardous to human health and detrimental to agricultural production. The Mediterranean Basin, due to its position under the descending branch of the Hadley Cell circulation during the summer months, enjoys periods of stable, sunny and warm weather which provide ideal conditions for the production of ozone. The presence of major population centres and numerous industrialised areas in the coastal zone result in both a continual supply of ozone precursor compounds and also a significant number of people to suffer the consequences of high ozone concentrations. Using the WRF/Chem model validated with data obtained from seven oceanographic measurement campaigns, performed between 2000 and 2010, aboard the Italian Research Council's R. V. Urania, and also from a number of EMEP monitoring stations located around the Mediterranean Basin, the importance of emissions from maritime traffic in the region has been investigated. The model results indicate that over large areas of the Mediterranean emissions from shipping contribute between 5 and 10 ppb to the ground level O<sub>3</sub> daily average concentration during the summer. The contribution to the hourly average O<sub>3</sub> is up to 40 ppb in some particularly busy shipping lanes. Importantly the results suggest that in a number of coastal areas the contribution from ship emissions to the local O<sub>3</sub> concentration can make the difference between complying with the EU Air Quality standard of a maximum 8 h mean of 120 μg m<sup>−3</sup> and exceeding it.
Приведены результаты измерения концентрации атомарной ртути (Hg0) с 28 по 30 августа 2012 г в приводном слое атмосферы над акваторией Уссурийского залива Японского моря во время прохождения тайфуна Болавен. Установлено, что концентрация Hg0 в это время изменялась от 1,7 до 3,3 нг/м3. Максимальные значения наблюдались с приходом обогащенных ртутью воздушных масс из района Желтого моря, при одновременном понижении атмосферного давления и увеличении скорости ветра.
There is a general agreement in the scientific community that the marine ecosystem can be a sink and/or source of the mercury that is cycling in the global environment, and current estimates of the global mercury budget for the Mediterranean region are affected by high uncertainty, primarily due to the little progress made so far in evaluating the role of chemical, physical and biological processes in the water system and in the lower atmosphere above the sea water (air-water interface). The lack of knowledge of the magnitude of the air-sea exchange mechanisms is, therefore, one of the main factors affecting the overall uncertainty associated with the assessment of net fluxes of Hg between the atmospheric and marine environments in the Mediterranean region. Results obtained during the last 15 years in the Mediterranean basin indicate the quantitative importance of such emission in the biogeochemical cycle of this element, highlighting the need for thorough investigations on the mechanisms of production and volatilization of dissolved gaseous mercury in waters.
In Italy there are 25 Large Industrial Point Sources whose mercury emissions in air exceed the established threshold of 10 kg year(-1). Many of these mercury point sources, mostly distributed along the Italian coastal area, are located at sites qualified as National Interest Rehabilitation Sites because of documented contamination in qualitative and/or quantitative terms and of potential health impact. Atmospheric mercury emissions related to Italian Large Industrial Point Sources, with a value of 1.04 Mg.yr(-1) for 2007, have a not negligible contribution, accounting, on their own, for more than 10% of the total mercury emissions resulting from all activity sectors at a national level. Among others, thermal power stations, pig iron and steel as well as basic inorganic chemical production, result to be the main contributing industrial activities. In order to assess how mercury species concentrations and distribution in the Marine Boundary Layer (MBL) change with vicinity to large industrial sites, measurements of atmospheric mercury were performed during three oceanographic campaigns aboard the Research Vessel (R.V.) Urania of the Italian CNR. Collection of GEM, GOM and PBM was conducted across the Adriatic sea, during autumn 2004 (27th of October to 12th of November) and summer 2005 (17th to 29th of June), and across the Tyrrhenian sea during autumn 2007 (12th of September to 1st October). Analysis were carried out with reference to the period in which the R. V. Urania has stopped close to the main Italian industrial contaminated sites. Explorative statistical parameters of atmospheric mercury species were computed over each single stop-period and then compared with the overall cruise campaign measurements. Results are herein presented and discussed.
The present paper provides an overview of mercury studies performed in the Mediterranean Sea region in the framework of several research projects funded by the European Commission and on-going national programmes carried out during the last 15 years. These studies investigated the temporal and spatial distribution of mercury species in air, in the water column and sediments, and the transport mechanisms connecting them. It was found that atmospheric concentrations of Hg compounds, particularly oxidised Hg species observed at five coastal sites in the Mediterranean Sea Basin, are significantly higher compared with those recorded at five coastal sites distributed across N Europe, most probably due to natural emissions. Hg levels in water are comparable to other oceans. Anthropogenic and natural point sources show locally limited enrichments, while natural diffusive sources influence Hg speciation over larger areas. Results and statistic comparison of mercury species concentrations within Mediterranean compartments will be presented and discussed.
Speciated atmospheric mercury observations collected over the period
from 2008 to 2010 at the Environmental Protection Agency and National
Atmospheric Deposition Program Atmospheric Mercury Network sites (AMNet)
were analyzed for its spatial, seasonal, and diurnal characteristics
across the US Median values of gaseous elemental mercury (GEM), gaseous
oxidized mercury (GOM) and particulate bound mercury (PBM) at 11
different AMNet sites ranged from 148-226 ppqv (1.32-2.02 ng
m-3), 0.05-1.4 ppqv (0.47-12.4 pg m-3) and
0.18-1.5 ppqv (1.61-13.7 pg m-3), respectively. Common
characteristics of these sites were the similar median levels of GEM as
well as its seasonality, with the highest mixing ratios occurring in
winter and spring and the lowest in fall. However, discernible
differences in monthly average GEM were as large as 30 ppqv, which may
be caused by sporadic influence from local emission sources. The largest
diurnal variation amplitude of GEM occurred in the summer. Seven rural
sites displayed similar GEM summer diurnal patterns, in that the lowest
levels appeared in the early morning, and then the GEM mixing ratio
increased after sunrise and reached its maxima at noon or in the early
afternoon. However, sites in Utah (UT96, UT97) and New York (NY95)
showed a distinctly different pattern, with the lowest mixing ratios
appearing in the afternoon and the highest mixing ratios at night.
Unlike GEM, GOM exhibited higher mixing ratios in spring and summer. The
largest diurnal variation amplitude of GOM occurred in spring for most
AMNet sites. GOM diurnal minima appeared before sunrise and maxima
appeared in the afternoon, and the variation in magnitude for all
seasons at most monitoring sites fell in the range of 0 to 2 ppqv,
except the Utah sites (up to 5 ppqv). The increased GOM mixing ratio in
the afternoon indicated a photochemically driven oxidation of GEM
resulting in GOM formation. PBM exhibited diurnal fluctuations in
summertime instead of wintertime, although the PBM mixing ratio in
summer was not as high as in winter. The summertime PBM diurnal pattern
displayed a daily maximum in the early afternoon and lower mixing ratios
at night, implying photochemical production of PBM in summer. The marine
sea salt aerosol uptake of GEM and GOM was not apparent in the PBM data
collected at coastal sites, with PBM being higher at inland sites.
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.
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.
1] It is well known that due to its long atmospheric residence time, mercury is distributed on a global scale and aeolian transport is believed to be the major contributor to mercury in polar environments. No measurements of reactive gaseous mercury (RGM) at all have ever been performed in the Antarctic before. Hg 0 (g) concentrations were in the range 0.29 to 2.3 ng m À3 , with an average value of 0.9 ± 0.3 ng m À3 . RGM was measured using KCl-coated annular denuders and a speciation unit coupled to a TGM analyzer; concentrations ranged from 10.5 to 334 pg m À3 , with an average of 116.2 ± 77.8 pg m À3 . The Hg 0 (g) measurements are in good agreement with the few data available for such southerly latitudes. The RGM concentrations are as high as those found in some industrial environments; the high concentrations in the absence of local sources (anthropogenic or natural) show that in situ gas phase oxidation of Hg 0 is the most important factor influencing RGM production and therefore also Hg deposition. The toxicity of Hg means that the consequences of high concentrations of oxidized and soluble Hg species depositing in the fragile Antarctic environment could be serious indeed.
Mercury -in the chemical/physical forms present in the biosphere -is a persistent, toxic, bioaccumulative pol-lutant that is dispersed throughout the environment on a global scale, mainly via the atmosphere. It is among the "heavy metals" for which the natural biogeochemical cy-cle has been perturbed by a wide range of human activi-ties, including fossil-fuel combustion and waste incineration. Results of our recent measurements of gaseous elemental mercury (GEM), as well as total particulate-phase mercury (TPM) concentrations in Arctic air, 'total Hg' concentra-tions in Arctic snow, and tropospheric BrO concentrations from an earth-orbiting-satellite platform are presented and discussed. Findings of our research, and the conclusions de-rived therefrom, are important for environmental protection as well as the health and well-being of aboriginal people in Arctic circumpolar nations.
We have measured total gaseous mercury concentrations(Hg) at Point Barrow, Alaska since September 1998 in aneffort to determine the geographic extent and reaction mechanismof the so-called mercury depletion events (MDE) previouslyreported in the high Arctic at Alert, Canada. Hg has beensampled now for nearly 2 years at Barrow. In September, 1999, webegan making the first automated measurements of reactive gaseousmercury (RGM) attempted in the Arctic, along with measurements ofHg accumulation in snowpack to determine the fate of the depleted Hg. During the fall and early winter, Hgand RGM exhibit only minor variation, Hg remaining within10% of global background, near 1.6–1.8 ng m-3. The MDEperiods are quite different, however; within days of Arcticsunrise in January, Hg exhibits major variations from themean, rapidly dropping as low as 0.05 ng m-3 and then cyclingback to typical levels, sometimes exceeding global background. These events continue throughout Arctic spring, then end abruptlyfollowing snowmelt, in early June. Prior to Arctic sunrise, RGMremains near detection (-3), but after sunriseincreases dramatically (to levels as high as 900 pg/m3) insynchrony with the depletion of Hg. Both phenomenaexhibit a strong diel cycle, in parallel with UV-B. We concludethat MDE''s involve rapid in-air oxidation of Hg to aspecies of RGM by photochemically-driven reactions, probablyinvolving the same reactive bromine and chlorine compoundsinvolved in ozone destruction. Sharp increases in Hg in thesurface snowpack after sunrise coincident with periods of peakRGM suggest surface accumulation of the RGM by dry deposition.
To understand further the cycling of mercury at the earth's surface we discuss the results of recent measurements of Hg concentration and speciation in the upper ocean and marine boundary layer of the Atlantic Ocean. In water, dissolved gaseous Hg (DGHg) and total Hg measurements are reported; for the atmosphere, total gaseous Hg, reactive gaseous Hg (RGHg) and particulate Hg measurements were made. These measurements allow estimation of gas evasion to the atmosphere and deposition to the ocean. In conjunction with the field collections, incubation experiments both on board ship and in the laboratory have examined further the processes controlling the oxidation and reduction of Hg species in water. Our results suggest that dry deposition of RGHg. could be significant.
An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.
On the spring 1995 cruise of the National Oceanic and Atmospheric Administration research vessel Malcolm Baldrige, we measured very large diurnal variations in ozone concentrations in the marine boundary layer. Average diurnal variations of about 32% of the mean were observed over the tropical Indian Ocean. We simulated these observations with the Model of Chemistry in Clouds and Aerosols, a photochemical box model with detailed aerosol chemistry. The model was constrained with photolysis rates, humidity, aerosol concentrations, NO, CO, and O3 specified by shipboard observations and ozonesondes. Conventional homogeneous chemistry, where ozone photolysis to O(1D) and HOx chemistry dominate ozone destruction, can account for a diurnal variation of only about 12%. On wet sea-salt aerosols (at humidities above the deliquescence point), absorption of HOBr leads to release of BrCl and Br2, which photolyze to produce Br atoms that may provide an additional photochemical ozone sink. After 8 days of simulation, these Br atoms reach a peak concentration of 1.2×107cm-3 at noon and destroy ozone through a catalytic cycle involving BrO and HOBr. Reactive Br lost to HBr can be absorbed into the aerosol phase and reactivated. The model predicts a diurnal variation in O3 of 22% with aerosol-derived Br reaction explaining much, but not all, of the observed photochemical loss. The lifetime of ozone under these conditions is short, about 2 days. These results indicate that halogens play an important role in oxidation processes and the ozone budget in parts of the remote marine boundary layer.
A parameterized description of the ambient aerosol is the basis of a
model that treats both gas-particle partitioning and aqueous phase
chemical transformations of semivolatile contaminants. Dividing the
aerosol population into source, size, hygroscopic, and compositional
classes, it is possible to assess the importance of contaminant-aerosol
interactions under varying meteorological conditions. Using mercury as a
test case, the model provides not only the quantity and speciation of
mercury associated with particulate matter for use in dry deposition
models and in conjunction with dispersion/meteorological models, but
shows conclusively that deliquesced aerosol particles are not simply
transporters of adsorbed mercury, but play an active and significant
role in the transformation of elemental to oxidized mercury. The
sensitivity analysis carried out using a version of the Direct Decoupled
Method has shown the transfer of Hg(II) to the gas phase from the
aqueous phase to be highly dependent on the chloride ion concentration
in the initial parameterization array which describes the ambient
aerosol. The chloride ion concentration has a notable effect on the
oxidized Hg that is associated with the particle when the chemistry
model reaches steady state. The reason for this is clarified by the
dependencies of the neutral Hg containing species concentrations on the
rates of mass transfer and the initial concentrations. The presence of
soot in the aerosol particles is shown to be particularly important in
the partitioning of Hg(II) between the gas, aqueous and particulate
phases. The implications, given the higher solubility of most oxidized
mercury species compared to elemental mercury, are fundamental for the
understanding of the cycling and fate of mercury in the environment.
An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41°S. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h-1 in mid-summer and in mid-winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the O3-HOx destruction cycle that peaks at mid-day, and occurs at similar rates in mid-summer and in mid-winter. The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary-layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.
A new mechanism of ozone loss is found in the sub-tropical marine boundary layer over the north Pacific. This ozone destruction occurs just after sunrise (hereafter Sunrise Ozone Destruction, SOD) and is commonly found throughout the year. SOD is a predominant ozone loss mechanism in winter, which takes place after sunrise in a few hours with 1~2ppbv of ozone depletion for 40~50ppbv of background ozone, while, in summer, SOD is weaker than in winter with small ozone depletion for 10~20ppbv of background ozone. In summer, daytime ozone destruction (hereafter, DOD) associated with UV photolysis and subsequent HOx reaction is more active. Since DOD is not active in early morning, SOD should be a new ozone loss mechanism. After demonstrating the observational findings, halogen chemistry associated with sea-salt aerosols is described as a possible mechanism.
Eleven laboratories from North America and Europe met at Mace Head, Ireland for the period 11–15 September 1995 for the first international field intercomparison of measurement techniques for atmospheric mercury species in ambient air and precipitation at a marine background location. Different manual methods for the sampling and analysis of total gaseous mercury (TGM) on gold and silver traps were compared with each other and with new automated analyzers. Additionally, particulate-phase mercury (Hgpart) in ambient air, total mercury, reactive mercury and methylmercury in precipitation were analyzed by some of the participating laboratories. Whereas measured concentrations of TGM and of total mercury in precipitation show good agreement between the participating laboratories, results for airborne particulate-phase mercury show much higher differences. Two laboratories measured inorganic oxidized gaseous mercury species (IOGM), and obtained levels in the low picogramm-3 range.
Annual emissions of anthropogenic Hg to the atmosphere in different regions of the world during the last decade show an interesting dichotomy: the emissions in the developed countries increased at the rate of about 4.5–5.5% yr−1 up to 1989 and have since remained nearly constant, while in developing countries the emissions continue to rise steadily at the rate of 2.7–4.5% yr−1. On a global basis, however, the total anthropogenic emissions of Hg increased by about 4% yr−1 during the 1980s, peaked in 1989 at about 2290 t and are currently decreasing at the rate of about 1.3% yr−1. Solid waste disposal through incineration processes is the dominant source of atmospheric mercury in North America (∼ 40%), Central and South America (∼34%), western Europe (∼28%) and Africa (∼30%), whereas coal combustion remains the dominant source in Asia (∼42%) and eastern Europe and the former USSR (∼40%). Mining and smelting of Zn and Pb represent the major industrial source of Hg in Oceania (∼35%).
The authors make two statements in the Introduction to their paper which we feel are misleading based on newly available data. We offer these comments to clarify any confusion among the readership. We are not commenting on the data or modeling presented in this interesting paper. The first statement is that ''Mercury in the atmo-sphere exists predominantly in the gaseous state, which in remote areas such as the Arctic, consists almost exclusively of the elemental form, Hg 0 ''. Although unknown to the authors at the time of writing, we now know that airborne gaseous Hg is not almost exclusively Hg 0 in the Arctic, but that significant levels of reactive gaseous mercury (RGM, or oxidized gaseous mercury, e.g. Lindberg and Stratton, 1998) and some particle bound Hg are also found. With the discovery of mercury depletion events (MDE) at Polar sunrise (Schroeder et al., 1998), there has been a significant increase in research on the atmospheric behavior of Hg in the Arctic, as evidenced in the paper by Berg et al. (2001), and Hg speciation measurements at both Poles are now being performed by a number of research teams. Of the various theories surrounding MDE, most would agree that during Hg depletion, unlike ozone depletion, Hg is neither created nor destroyed. We would also agree that elemental Hg vapor (Hg 0) exhibits a long atmospheric lifetime and low deposition velocity, which does not support direct deposition as an explanation for MDEs. Rather, it is likely that the speciation of Hg 0 is somehow altered following Polar sunrise to a species with a shorter lifetime. We have made atmospheric mercury speciation measurements in Barrow, Alaska since September 1999 in an effort to determine the geographic extent and reaction mechanism of MDEs. During the year 2000 we made the first automated measurements of RGM attempted in the Arctic, along with concurrent measure-ments of Hg 0 (Lindberg et al., 2001). RGM was measured with annular denuders (Landis, 2000), and Hg 0 with a portable automated cold vapor atomic fluorescence unit (Lindberg et al., 2000). Prior to Arctic sunrise, RGM remains near our detection limit (o2 pg/ m 3), but after sunrise RGM increases dramatically (to levels as high as 900 pg/m 3) in synchrony with the ''depletion'' of Hg 0 (which drops as low as 100 pg/m 3). During April and May 2000 we measured several events in which RGM comprised over 60% of the total gaseous mercury (TGM) in the air over Barrow. Recent (March–April 2001) automated measurements of elemental Hg, RGM and particle-phase Hg (Hg-p) in Barrow by Landis and Stevens (2001) reveal that both RGM and some particulate Hg species are formed during polar sunrise, a new finding that further complicates deducing the mechanism for these transformations. The second statement regards the MDE mechanism, stating that ''preliminary observations have indicated that this atmospheric Hg 0 depletion mechanism involves conversion of mercury from the gas phase to the particulate phaseyytransformation process is unique to the Arcticy''. (Lu et al., 1998). Again, our recent data refute the idea that only particulate Hg is being formed. Since the measurements of Lu et al. (1998) did not utilize denuders, but rather a ''total particulate mercury'' filtration system, we believe that their observations were the result of RGM causing a positive artifact in the sampling apparatus. In addition to Hg-p, RGM also adheres to the ''total particle filter'' to some extent during sampling and, when heated during analysis, this sorbed RGM is converted to Hg 0 along with the conversion of the particulate Hg to Hg 0 . In this analysis, the resulting Hg 0 signal is interpreted (inaccu-rately in our opinion) as total particulate Hg. We have already discussed this artifact with the authors, and they are currently preparing to test a denuder system in the Arctic to quantify this potential artifact (Schroeder, personal communication). From the data at Barrow, it is now clear that the Hg depletion mechanism involves oxidation of Hg 0 primar-ily to some form of RGM followed by both uptake on aerosol surfaces and direct gaseous dry deposition to the local snowpack (Lindberg et al., 2001). RGM is well known to deposit much more rapidly than Hg-p, and deposition velocities for RGM as high as 5 cm/s have been measured elsewhere (Lindberg and Stratton, 1998). If only Hg-p were being formed, with its characteristi-cally lower deposition velocities (typically, 0.1–0.3 cm/s under Arctic conditions), it could not explain the rapid increase in, or the ultimate levels of, Hg reported in Arctic snow after Polar sunrise (e.g. SHEBA site, Welch et al., 1999; Barrow site, Lindberg et al., 2001). Finally, while most of these recent measurements have been directed towards understanding the formation of RGM in the Arctic troposphere, we simply do not know at this time if the reactions are limited to the Arctic, and suspect they may also occur in the marine boundary layer to some extent. Our understanding of the biogeochemical cycling of Hg in the Arctic is changing rapidly, and it is becoming appa-rent that the Arctic may represent a previously unquan-tified but important global sink for Hg. The research in this field is as dynamic as the chemistry of Hg itself.
A PROPER inventory of atmospheric emissions from natural sources is basic to our understanding of the atmospheric cycle of the trace metals (and metalloids), and is also needed for assessing the extent of regional and global pollution by toxic metals1. It is generally presumed that the principal natural sources of trace metals in the atmosphere are wind-borne soil particles, volcanoes, seasalt spray and wild forest fires2–6. Recent studies have shown, however, that particulate organic matter is the dominant component of atmospheric aerosols in non-urban areas7–10 and that over 60% of the airborne trace metals in forested regions can be attributed to aerosols of biogenic origin11,12. Here I estimate that biogenic sources can account for 30–50% of the global baseline emissions of trace metals. For most of the toxic metals, the natural fluxes are small compared with emissions from industrial activities, implying that mankind has become the key agent in the global atmospheric cycle of trace metals and metalloids.
The Arctic ecosystem is showing increasing evidence of contamination by persistent, toxic substances, including metals such as mercury1, that accumulate in organisms. In January 1995, we began continuous surface-level measurements of total gaseous mercury in the air at Alert, Northwest Territories, Canada (82.5° N, 62.5° W). Here we show that, during the spring (April to early June) of 1995, there were frequent episodic depletions in mercury vapour concentrations, strongly resembling depletions of ozone in Arctic surface air, during the three-month period following polar sunrise (which occurs in March)2,3.
The formation of dissolved gaseous mercury (DGM, mainly composed of elemental mercury, Hg-0) in the surface ocean and it subsequent removal through volatilization is an important component of the global mercury (Hg) cycle. We studied DGM production and loss in the coastal waters of the Gulf of Mexico using 4-26 h in situ incubation experiments. DGM production was only induced in the presence of sunlight. Once produced, DGM was rapidly lost from solution [with a first order rate constant of k = 0.1 h(-1)], apparently as a result of oxidation. Furthermore, laboratory experiments showed that dissolved gaseous Hg-0 could be rapidly oxidized in the presence of chloride. In the field, most DGM production (about 60%) was associated with the dissolved nad colloidal Hg[11] phases. Spiking of samples with inorganic Hg[11] prior to in situ incubation greatly increased DGM production rates, suggesting that photoreducible Hg[11] complexes were limiting DGM production. Diurnally, DGM seems to be formed through photoproduction in the morning; DGM production halts when substrate is exhausted, and DGM levels decrease afterwards, presumably by oxidation of Hg-0.
The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3210–20 cm3 molec.–1 s–1 at 20 C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 03 concentration of 30 ppb.
Following a modelling investigation of the role of the ambient aerosol in the cycling—that is the transport, transformation and deposition—of mercury in the atmosphere, the precise part played by the sea salt component of the marine aerosol in the remote marine boundary layer has been studied using a combination of models to describe the photolytic, gas phase and aqueous phase and heterogeneous chemistry of the marine boundary layer, in conjunction with inter phase mass transport and mercury chemistry. The role of the ocean in the emission of elemental mercury is, as yet, not entirely understood, but certainly the speciation of mercury deposited to the ocean surface is important as regards its re-emission. Models of mercury chemistry to date have tended to focus on cloud chemistry, and with good reason, as precipitation accounts for a large part of the global mercury deposition pattern; however, the composition of the marine aerosol is entirely different from that of cloud or fog droplets and the modelling studies here show that it plays a more local role being partially responsible for the gas phase speciation of mercury. The role of photochemical processes is investigated and particular attention is paid to halogen chemistry, as the chloride ion has been shown previously to have a notable effect on the concentration of oxidised mercury associated with particles, or better, solution droplets. The role of the sea salt component of the marine aerosol in the production of gas phase oxidised mercury species is described qualitatively and quantitatively.
This paper presents a broad overview and synthesis of current knowledge and understanding pertaining to all major aspects of mercury in the atmosphere. The significant physical, chemical, and toxicological properties of this element and its environmentally relebant species encountered in the atmosphere are examined. Atmospheric pathways and processes considered herein include anthropogenic as well as natural sources of Hg emissions to the atmosphere, aerial transport and dispersion (including spatial and temporal variability), atmospheric transformations (both physical and chemical types), wet and dry removal/deposition processes to Earth's surface. In addition, inter-compartmental (air-water/soil/vegetation) transfer and biogeochemical cycling of mercury are considered and discussed. The section on numerical modelling deals with atmospheric transport models as well as process-oriented models. Important gaps in our current knowledge of mercury in the atmospheric environment are identified, and suggestions for future areas of research are offered.
Dissolved gaseous mercury (DGM) was measured in coastal Atlantic seawater and in the Mediterranean Sea. The Atlantic measurements were performed during September 1999 at the Mace Head Atmospheric Research Station, situated on the Irish west coast. The measurements in the Mediterranean Sea were made along a 6000 km cruise path from 14 July to 9 August 2000 in the framework of the Med-Oceanor project. Total gaseous mercury (TGM) concentrations in air were continuously measured with a 5 min time resolution using an automated mercury analyser (Tekran 2537A) during both expeditions. Paired TGM and DGM samples from all campaigns showed that the surface water was supersaturated with elemental mercury. The mercury evasion was estimated using a gas exchange model (J. Geophys. Res. 97 (1992) 7373), which uses salinity, wind speed and water temperature as independent parameters. The predicted average mercury evasion from the coastal Atlantic water was 2.7 ng m−2 h−1 implying that the concentration of TGM in the Atlantic air is enhanced by mercury evasion from the sea.Measurements in different regions of the Mediterranean Sea showed spatial variations in DGM concentrations. The highest DGM concentration (∼90 pg l−1) was observed at a location in the Strait of Sicily (37°16N 11°52E). The mercury evasion in the eastern sector of the Mediterranean Sea (area: 32–36°N, 17–28°E) was generally higher (7.9 ng m−2 h−1) than that observed in the Tyrrhenian Sea (4.2 ng m−2 h−1) or in the western sector (2.5 ng m−2 h−1) (areas: 38–42°N, 8–13°E and 38–41°N, 7–8°E, respectively). Estimations of mercury evasion were also made at Mediterranean coastal sites using a dynamic chamber technique.In addition, a newly developed method making continuous in situ DGM measurements possible was tested.
Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.
Gold and silver production in North America (included United States, Canada and Mexico) released a large amount of mercury to the atmosphere until well into this century when mercury (Hg) amalgamation was replaced by cyanide concentration. Since then, emissions from industries have been the dominant anthropogenic sources of atmospheric Hg in North America as a whole. Past Hg emissions from gold and silver extractions in North America during the 1800s do not show a clear evidence of atmospheric deposition occurred at the coring sites considered in this study. Estimated atmospheric emissions of Hg in North America peaked in 1879 (at about 1708 t yr−1) and 1920 (at about 940 t yr−1), primarily due to Hg emissions from gold and silver mining. After the Great Economic Depression (1929) Hg emissions peaked again in the 1947 (274 t yr−1), in 1970 (325 t yr−1) and in 1989 (330 t yr−1) as result of increased Hg emissions from industrial sources, though improvements in the emissions control technology in United States and Canada have been substantial. Estimates of total atmospheric deposition fluxes of Hg to water and terrestrial receptors were in the range of 14.3–19.8 μg m−2 yr−1 in North America as a whole, and averaged 135 μg m−2 yr−1 (global background + local emissions) in the Great Lakes. These values were in good agreement with recent estimates reported in literature. The comparison of atmospheric Hg deposition fluxes with Hg accumulation rates in sediment cores suggests that atmospheric deposition was the major source of Hg entering the lakes system at coring sites, however, important contributions to Lake Ontario sediment cores sites from 1940 to 1970 were likely originated from local point sources (i.e. direct discharges).
Reactive gaseous mercury (RGM) concentrations have been modelled using a photochemical box model of the marine boundary layer (MBL) and compared to measured data obtained during a research cruise. The model has been constrained by using measured concentrations of elemental Hg and ozone, as well as measured temperature and relative humidity. The results show good qualitative agreement both during the rough weather encountered on the first part of the voyage and the second, calmer period of the campaign. Quantitative agreement is obtained using a box height of 100 m during the first leg of the campaign. The modelled and measured results from the second leg agree as far as the nocturnal RGM concentration minima are concerned but underestimate the daytime maxima by a factor of two. The comparison of the modelled with measured results supports the hypothesis that there are daytime mercury oxidation reactions occurring which have not yet been identified.
A summary of data recently obtained for mercury analysis and speciation (reactive Hg, total Hg and monomethylmercury (MMHg)) in filtered and non-filtered seawater samples, dissolved gaseous mercury (DGM) and dimethylmercury (DMHg) in open and coastal waters of the Mediterranean Sea is presented. The majority of the results were obtained during an oceanographic cruise aboard the research vessel Urania from 14 July to 9 August, 2000, as part of the MED-OCEANOR Project funded by the National Research Council of Italy. The results are compared with those obtained in contaminated coastal environments of the Adriatic (The Gulf of Trieste and Kaštela Bay) and non-contaminated coastal waters of the eastern Adriatic coast obtained in 1998. Total mercury concentrations in surface ocean waters are relatively low with an average of 0.81 pM (0.49–1.91 pM). Reactive Hg represents a substantial part with an average of 57% of total Hg (15–97%). Most mercury in open ocean waters was present in the dissolved form (32–95%, av. 70%), which is mainly due to the low abundance of particulate matter, a phenomenon well known for the Mediterranean open ocean waters. On average the percentage of Hg as MMHg was about 20%, of which about 66% was present in the dissolved form. The percentage of DGM in the surface ocean waters represents about 9% of total Hg (2.5–24.5%) and may originate from photochemical, biologically mediated mechanisms or diffusion from deeper layer either due to biological and/or to tectonic activity which is typical of the Mediterranean region. The presence of DMHg was confirmed only in waters below 20 m (up to 12 fM), while in surface waters DMHg was below the limit of detection (<0.1 fM). Surface concentrations of Hg in the eastern and western parts are comparable, except for DGM which shows significantly higher concentrations in the eastern part (mean value: 0.22 pM) as compared to the western Mediterranean (mean value: 0.09 pM). The distribution of Hg species with depth was only measured at two stations, and indicated variability comparing the eastern and the western leg of the Urania cruise. The depth profile pattern confirms the importance of dynamic processes at the surface layers, while deep water continuously supplies DGM to the surface layer. The importance of analytical quality control is also discussed in this paper.
Profiles of dissolved gaseous mercury (DGM) concentration were systematically measured on a wide geographical scale for the first time in the Mediterranean basin during the international oceanographic cruise MED-OCEANOR on board the R/V Urania of the National Research Council of Italy from 14 July to 10 August 2000. Generally, DGM levels increase from the surface to the first hundred meters and remain constant down to the bottom, suggesting that DGM is produced not only in surface water via photo-induced reactions, but also in deep water as a consequence of bacterial activity, even if it is not possible to exclude a contribution of the geothermal activity at the bottom. The Western Mediterranean basin resulted to be characterised by an average DGM concentration value (0.088 pM) in surface water, lower than that observed in the Eastern basin (0.211 pM).
The atom is the dominating species of mercury in the atmosphere. Its oxidation processes are of great interest since it is mainly oxidised mercury that undergoes deposition and thereby spreads into the ecosystems and becomes bioaccumulated. The kinetics of the gas-phase reaction between atomic mercury and hydroxyl radical has been determined at room temperature and atmospheric pressure of air by relative rate technique. OH radicals were produced by photolysis employing methyl nitrite. By using cyclohexane as the reference compound, the rate coefficient obtained was leading to natural lifetimes of mercury at global mean conditions of 4–7 month due to this reaction.
The Mediterranean Atmospheric Mercury Cycle System (MAMCS) project was performed between 1998 and 2000 and involved the collaboration of universities and research institutes from Europe, Israel and Turkey. The main goal of MAMCS was to investigate dynamic processes affecting the cycle of mercury in the Mediterranean atmosphere by combining ad hoc field measurements and modelling tasks. To study the fate of Hg in the Mediterranean Basin an updated emission inventory was compiled for Europe and the countries bordering the Mediterranean Sea. Models were developed to describe the individual atmospheric processes which influence the chemical and physical characteristics of atmospheric Hg, and these were coupled to meteorological models to examine the dispersion and deposition of Hg species in the Mediterranean Basin. One intercomparison and four two-week measurement campaigns were carried out over a three-year period. The work presented here describes the results in general terms but focuses on the areas where definite conclusions were unforthcoming and thus highlights those aspects where, in spite of advances made in the understanding of Hg cycling, further work is necessary in order to be able to predict confidently Hg and Hg compound concentration fields and deposition patterns.
Estimates of atmospheric emissions of mercury from anthropogenic sources in Europe in 1995 are presented with the information on emissions of both total mercury and its major chemical and physical forms. The 1995 anthropogenic emissions of total emissions were estimated to be about , a decrease of 45% compared to these emissions in 1990. Combustion of fuels, particularly coal has been the major source of anthropogenic emissions contributing to more than half to the total emissions. The emissions from coal combustion have not changed significantly over the past decade. Major decrease has been estimated for emissions from industrial processes, particularly the chlor-alkali production using the Hg cell process. In 1995 the European emissions of anthropogenic mercury contributed about 13% to the global emissions of this element from anthropogenic sources. The anthropogenic Hg emissions in Europe were still higher than the natural emissions in the region, estimated to be about 250– per year. The accuracy of estimates of anthropogenic emissions of Hg in Europe in 1995 is considered to be between 25 and 50%. The most accurate seem to be the estimates for combustion sources, while the most incomplete data were collected and/or estimated for waste disposal. The emissions of gaseous elemental mercury contributed about 61% to the emissions of the total mercury, while the contribution of gaseous bivalent mercury and particulate mercury was 32 and 7%, respectively.
The mercury species over Europe (MOE) project was aimed at identifying sources, occurrence and atmospheric behaviour of atmospheric Hg species. Within MOE, emission measurements, ambient air measurements, process and regional-scale modelling and laboratory measurements were conducted. In this work, a summary of some of the main results is given. From the emission measurements, information on stack gas concentrations and emission factors for five coal fired power plants and three waste incinerators are presented. Results from field measurements of mercury species in ambient air at five locations in Northern Europe are presented. Examples from regional-scale atmospheric modelling are also given. The results emphasise the importance of information on Hg species for instance in emission inventories and measurement data from background sites. Furthermore, the importance of considering the role of the global cycling of mercury in future control strategies is emphasised.
This report discusses past, current and projected mercury emissions to the atmosphere from major industrial sources, and presents a first assessment of the contribution to the regional mercury budget from selected natural sources. Emissions (1995 estimates) from fossil fuels combustion , cement production and incineration of solid wastes , all together account for about 82% of the regional anthropogenic total . Other industrial sources in the region are smelters , iron–steel plants and other minor sources (chlor-alkali plants, crematoria, chemicals production) that have been considered together in the miscellaneous category . Regional emissions from anthropogenic sources increased at a rate of from 1983 to 1995 and are projected to increase at a rate of in the next 25 years, if no improvement in emission control policy occurs. On a country-by-country basis, France is the leading emitter country with followed by Turkey , Italy , Spain , the former Yugoslavia , Morocco , Bulgaria , Egypt , Syria , Libya , Tunisia and Greece , whereas the remaining countries account for less than 7% of the regional total. The annual emission from natural sources is , although this figure only includes the volatilisation of elemental mercury from surface waters and emissions from volcanoes, whereas the contribution due to the degassing of mercury from top soil and vegetation has not been included in this first assessment. Therefore, natural and anthropogenic sources in the Mediterranean region release annually about of mercury, which represents a significant contribution to the total mercury budget released in Europe and to the global atmosphere.
To determine the extent of comparability of sampling and analytical procedures for atmospheric mercury (Hg) being used by different scientific groups around the world and hence the compatibility of measurement results, the Atmospheric Environment Service (AES) co-ordinated a field intercomparison study in Windsor, Ontario, over a period of 5 days- during Sept./Oct.,1993. This study brought together 2 groups (University of Michigan Air Quality Laboratory; Chemistry Institute of GKSS) which performed conventional (manual) sample collection procedures for total gaseous mercury (TGM) and for particulate-phase mercury (PPM), followed by cold-vapor atomic fluorescence spectrophotometric (CVAFS) analysis in the respective laboratories. Two other groups (Ontario Hydro, and the Ontario Ministry of Environment & Energy) each operated a novel mercury vapor analyzer produced by Tekran Inc. of Toronto. As is the case for the manual methods, this analyzer also uses gold amalgamation and CVAFS. During the intercomparison, meteorological parameters (air temperature, barometric pressure, wind speed/direction and relative humidity) were obtained at the study site. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/43915/1/11270_2005_Article_BF01189713.pdf
Results from a numerical model of the global emissions, transport, chemistry, and deposition of mercury (Hg) in the atmosphere are presented. Hg (in the form of Hg(O) and Hg(II)) is emitted into the atmosphere from natural and anthropogenic sources (estimated to be 4000 and 2100 Mg/ yr, respectively). It is distributed between gaseous, aqueous and particulate phases. Removal of Hg from the atmosphere occurs via dry deposition and wet deposition, which are calculated by the model to be 3300 and 2800 Mg/ yr, respectively. Deposition on land surfaces accounts for 47% of total global deposition. The simulated Hg ambient surface concentrations and deposition fluxes to the Earth's surface are consistent with available observations. Observed spatial and seasonal trends are reproduced by the model, although larger spatial variations are observed in Hg(O) surface concentrations than are predicted by the model. The calculated atmospheric residence time of Hg is -1.7 years. Chemical transformations between Hg(O) and HG(II) have a strong influence on Hg deposition patterns because HG(II) is removed faster than Hg(O). Oxidation of Hg(O) to HG(II) occurs primarily in the gas phase, whereas HG(II) reduction to Hg(O) occurs solely in the aqueous phase. Our model results indicated that in the absence of the aqueous reactions the atmospheric residence time of Hg is reduced to 1.2 from 1.7 years and the Hg surface concentration is -25% lower because of the absence of the HG(II) reduction pathway. This result suggests that aqueous chemistry is an essential component of the atmospheric cycling of Hg.
The photoreduction of mercury (Hg2+ to Hg0) in natural seawater was investigated by means of a radiotracer (203Hg2+) solution exposed to natural and simulated sunlight. Different light regimes (dark, natural daylight, and a solar simulator), and dissolved organic carbon (DOC) levels from commercially available humic acids concentrations, were tested in the laboratory to evaluate the possibility of occurrence of the reaction in the environment. The natural seawater prepared accordingly to each experimental condition was continuously purged of the Hg0 formed, which was then re-oxidised in an acid trap and determined. The use of a solar simulator permitted the test of light intensity and wavelength dependence of the process under investigation. The reaction is dependent on the concentration of DOC in the experimental solution, increasing light intensity and decreasing wavelength. Reduction rates were in the range of 0.04-2.2% h(-1) for the DOC concentrations and light regimes tested. The process might have geochemical implications for the cycling of mercury around the air-sea interface.
Unlike other heavy metals that are inherently associated with atmospheric aerosols, mercury in ambient air exists predominantly in the gaseous elemental form. Because of its prolonged atmospheric residence time, elemental mercury vapor is distributed on a global scale. Recently, Canadian researchers have discovered that total gaseous mercury levels in the lower tropospheric boundary layer in the Canadian Arctic are often significantly depleted during the months after polar sunrise. A possible explanation may involve oxidation of elemental mercury, followed by adsorption and deposition of the oxidized form, leading to an increased input of atmospheric mercury into the Arctic ecosystem. Here we present the first continuous high-time-resolution measurements of total gaseous mercury in the Antarctic covering a 12-month period between January 2000 and January 2001 at the German Antarctic research station Neumayer (70 degrees 39' S, 8 degrees 15' W). We report that mercury depletion events also occur in the Antarctic after polar sunrise and compare our measurements with a data setfrom Alert, Nunavut, Canada. We also present indications that BrO radicals and ozone play a key role in the boundary-layer chemistry during springtime mercury depletion events in the Antarctic troposphere.
Atmospheric mercury is predominantly present in the gaseous elemental form (Hg0). However, anthropogenic emissions (e.g., incineration, fossil fuel combustion) emit and natural processes create particulate-phase mercury(Hg(p)) and divalent reactive gas-phase mercury (RGM). RGM species (e.g., HgCl2, HgBr2) are water-soluble and have much shorter residence times in the atmosphere than Hg0 due to their higher removal rates through wet and dry deposition mechanisms. Manual and automated annular denuder methodologies, to provide high-resolution (1-2 h) ambient RGM measurements, were developed and evaluated. Following collection of RGM onto KCl-coated quartz annular denuders, RGM was thermally decomposed and quantified as Hg0. Laboratory and field evaluations of the denuders found the RGM collection efficiency to be >94% and mean collocated precision to be <15%. Method detection limits for sampling durations ranging from 1 to 12 h were 6.2-0.5 pg m(-3), respectively. As part of this research, the authors observed that methods to measure Hg(p) had a significant positive artifact when RGM coexists with Hg(p). This artifact was eliminated if a KCl-coated annular denuder preceded the filter. This new atmospheric mercury speciation methodology has dramatically enhanced our ability to investigate the mechanisms of transformation and deposition of mercury in the atmosphere.
Formation of reactive gaseous mercury in the Arctic: evidence of oxidation of Hg 0 to gas-phase Hg (II)
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The role of the ambient aerosol in the atmospheric processing of semi-volatile contaminants
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Dynamic processes of mercury over the Mediterranean region
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