scholarly journals Speciated mercury at marine, coastal, and inland sites in New England – Part 1: Temporal variability

2012 ◽  
Vol 12 (11) ◽  
pp. 5099-5112 ◽  
Author(s):  
H. Mao ◽  
R. Talbot
Keyword(s):  
New England ◽  
Marine Boundary Layer ◽  
Limit Of Detection ◽  
Inversion Layer ◽  
Warm Season ◽  
Elemental Mercury ◽  
Positive Trend ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Nocturnal Inversion

Abstract. 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.

scholarly journals Speciated mercury at marine, coastal, and inland sites in New England – Part 1: Temporal variability

2011 ◽  
Vol 11 (12) ◽  
pp. 32301-32336 ◽  
Author(s):  
H. Mao ◽  
R. Talbot
Keyword(s):  
New England ◽  
Marine Boundary Layer ◽  
Limit Of Detection ◽  
Inversion Layer ◽  
Warm Season ◽  
Elemental Mercury ◽  
Rural Site ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Nocturnal Inversion

Abstract. A comprehensive analysis was conducted using long-term continuous measurements of gaseous elemental mercury (Hgo), reactive 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. Decreasing trends in background Hgo 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−1 and 6.3 ppqv yr−1, respectively. Common characteristics at these sites were the reproducible annual cycle of Hgo 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 Hgo 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 Hgo 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 Hgo during the day in the marine boundary layer, which is consistent with the hypothesis of Hgo 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 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 with higher levels during the day and smaller but above the LOD at night.

scholarly journals Investigation of processes controlling GEM oxidation at mid-latitudinal marine, coastal, and inland sites

2016 ◽  
Author(s):  
Z. Ye ◽  
H. Mao ◽  
C.-J. Lin ◽  
S. Y. Kim
Keyword(s):  
Marine Boundary Layer ◽  
State Of The Art ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Chemical Mechanism ◽  
Atmospheric Conditions ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Marine Site ◽  
Study Sites

Abstract. A box model incorporating a state-of-the-art chemical mechanism for atmospheric mercury (Hg) cycling was developed to investigate oxidation of gaseous elemental mercury (GEM) at three locations in the northeastern United States: Appledore Island (marine), Thompson Farm (coastal, rural), and Pack Monadnock (inland, rural, elevated). The chemical mechanism improved model's ability to simulate the formation of gaseous oxidized mercury (GOM) at the study sites. At the coastal and inland sites, GEM oxidation was predominated by O3 and OH, contributing 80–99 % of total GOM production during daytime. H2O2 initiated GEM oxidation was significant (~ 33 % of the total GOM) at the inland site during nighttime. In the marine boundary layer (MBL), Br and BrO were dominant GEM oxidants contributing ~ 70 % of the total GOM production during mid-day, while O3 dominated GEM oxidation (50–90 % of GOM production) over the remaining day. Following the production of HgBr from GEM + Br, HgBr was oxidized by BrO, HO2, OH, ClO, and IO to form Hg(II) brominated GOM species. However, under atmospheric conditions, the prevalent GEM oxidants in the MBL could be Br / BrO or O3 / OH depending on Br and BrO mixing ratios. Relative humidity and products of the CH3O2 + BrO reaction possibly affected significantly the mixing ratios of Br or BrO radicals and subsequently GOM formation. Gas-particle partitioning could be potentially important in the production of GOM as well as Br and BrO at the marine site.

scholarly journals Investigation of processes controlling summertime gaseous elemental mercury oxidation at midlatitudinal marine, coastal, and inland sites

2016 ◽  
Vol 16 (13) ◽  
pp. 8461-8478 ◽  
Author(s):  
Zhuyun Ye ◽  
Huiting Mao ◽  
Che-Jen Lin ◽  
Su Youn Kim
Keyword(s):  
Marine Boundary Layer ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Box Model ◽  
Chemical Mechanism ◽  
Gaseous Elemental Mercury ◽  
Diurnal Cycles ◽  
Mixing Ratios ◽  
Halogen Chemistry ◽  
Marine Site

Abstract. A box model incorporating a state-of-the-art chemical mechanism for atmospheric mercury (Hg) cycling was developed to investigate the oxidation of gaseous elemental mercury (GEM) at three locations in the northeastern United States: Appledore Island (AI; marine), Thompson Farm (TF; coastal, rural), and Pack Monadnock (PM; inland, rural, elevated). The chemical mechanism in this box model included the most up-to-date Hg and halogen chemistry. As a result, the box model was able to simulate reasonably the observed diurnal cycles of gaseous oxidized mercury (GOM) and chemical speciation bearing distinct differences between the three sites. In agreement with observations, simulated GOM diurnal cycles at AI and TF showed significant daytime peaks in the afternoon and nighttime minimums compared to flat GOM diurnal cycles at PM. Moreover, significant differences in the magnitude of GOM diurnal amplitude (AI > TF > PM) were captured in modeled results. At the coastal and inland sites, GEM oxidation was predominated by O3 and OH, contributing 80–99 % of total GOM production during daytime. H2O2-initiated GEM oxidation was significant (∼ 33 % of the total GOM) at the inland site during nighttime. In the marine boundary layer (MBL) atmosphere, Br and BrO became dominant GEM oxidants, with mixing ratios reaching 0.1 and 1 pptv, respectively, and contributing ∼ 70 % of the total GOM production during midday, while O3 dominated GEM oxidation (50–90 % of GOM production) over the remaining day when Br and BrO mixing ratios were diminished. The majority of HgBr produced from GEM+Br was oxidized by NO2 and HO2 to form brominated GOM species. Relative humidity and products of the CH3O2+BrO reaction possibly significantly affected the mixing ratios of Br or BrO radicals and subsequently GOM formation. Gas–particle partitioning could potentially be important in the production of GOM as well as Br and BrO at the marine site.

scholarly journals Overview of the 2007 and 2008 campaigns conducted as part of the Greenland Summit Halogen-HO<sub>x</sub> Experiment (GSHOX)

2012 ◽  
Vol 12 (7) ◽  
pp. 17135-17150
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
J. Stutz ◽  
R. von Glasow ◽  
S. Brooks ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Vertical Mixing ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
The North ◽  
Polar Snow ◽  
Active Bromine

Abstract. From 10 May through 17 June, 2007 and 6 June through 9 July, 2008 intensive sampling campaigns at Summit, Greenland confirmed that active bromine chemistry is occurring in and above the snow pack at the highest part of the Greenland ice sheet (72°36' N, 38° 25' W and 3.2 km a.s.l.). Direct measurements found BrO and soluble gas phase Br− mixing ratios in the low pptv range on many days (maxima <10 pptv). Conversion of up to 200 pg m−3 of gaseous elemental mercury (GEM) to reactive gaseous mercury (RGM) and enhanced OH relative to HO2 plus RO2 confirm that active bromine chemistry is impacting chemical cycles even at such low abundances of reactive bromine species. However, it does not appear that Bry chemistry can fully account for observed perturbations to HOx partitioning, suggesting unknown additional chemical processes may be important in this unique environment, or that our understanding of coupled NOx-HOx−Bry chemistry above sunlit polar snow is incomplete. Rapid transport from the North Atlantic marine boundary layer occasionally caused enhanced BrO at Summit (just two such events observed during the 12 weeks of sampling over the two seasons). In general observed reactive bromine was linked to activation of bromide (Br−) in, and release of reactive bromine from, the snowpack. A coupled snow-atmosphere one-dimensional model that assumed snow photochemistry as the only source successfully simulated observed NO and BrO at Summit during a three day interval when winds were weak (transport not a factor). The source of Br− in surface and near surface snow at Summit is not entirely clear, but concentrations were observed to increase when stronger vertical mixing brought free tropospheric air to the surface. Reactive Bry mixing ratios above the snow often increased in the day or two following increases in snow concentration, but this response was not consistent. On seasonal time scales concentrations of Br− in snow and reactive bromine in the air were directly related.

scholarly journals Overview of the 2007 and 2008 campaigns conducted as part of the Greenland Summit Halogen-HO<sub>x</sub> Experiment (GSHOX)

2012 ◽  
Vol 12 (22) ◽  
pp. 10833-10839 ◽  
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
J. Stutz ◽  
R. von Glasow ◽  
S. Brooks ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Vertical Mixing ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
The North ◽  
Polar Snow ◽  
Active Bromine

Abstract. From 10 May through 17 June 2007 and 6 June through 9 July 2008 intensive sampling campaigns at Summit, Greenland confirmed that active bromine chemistry is occurring in and above the snow pack at the highest part of the Greenland ice sheet (72°36´ N, 38°25´ W and 3.2 km above sea level). Direct measurements found BrO and soluble gas phase Br− mixing ratios in the low pptv range on many days (maxima < 10 pptv). Conversion of up to 200 pg m−3 of gaseous elemental mercury (GEM) to reactive gaseous mercury (RGM) and enhanced OH relative to HO2 plus RO2 confirm that active bromine chemistry is impacting chemical cycles even at such low abundances of reactive bromine species. However, it does not appear that Bry chemistry can fully account for observed perturbations to HOx partitioning, suggesting unknown additional chemical processes may be important in this unique environment, or that our understanding of coupled NOx-HOx-Bry chemistry above sunlit polar snow is incomplete. Rapid transport from the north Atlantic marine boundary layer occasionally caused enhanced BrO at Summit (just two such events observed during the 12 weeks of sampling over the two seasons). In general observed reactive bromine was linked to activation of bromide (Br−) in, and release of reactive bromine from, the snowpack. A coupled snow-atmosphere model simulated observed NO and BrO at Summit during a three day interval when winds were weak. The source of Br− in surface and near surface snow at Summit is not entirely clear, but concentrations were observed to increase when stronger vertical mixing brought free tropospheric air to the surface. Reactive Bry mixing ratios above the snow often increased in the day or two following increases in snow concentration, but this response was not consistent. On seasonal time scales concentrations of Br− in snow and reactive bromine in the air were directly related.

Gaseous mercury in coastal urban areas

2010 ◽  
Vol 7 (6) ◽  
pp. 537 ◽  
Author(s):  
Anne L. Soerensen ◽  
Henrik Skov ◽  
Matthew S. Johnson ◽  
Marianne Glasius
Keyword(s):  
Urban Areas ◽  
Marine Boundary Layer ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Mercury Deposition ◽  
Mercury Emissions ◽  
Gaseous Elemental Mercury ◽  
Gaseous Mercury ◽  
Range Transport ◽  
Aquatic Food

Environmental context Mercury is a neurotoxin that bioaccumulates in the aquatic food web. Atmospheric emissions from urban areas close to the coast could cause increased local mercury deposition to the ocean. Our study adds important new data to the current limited knowledge on atmospheric mercury emissions and dynamics in coastal urban areas. Abstract Approximately 50% of primary atmospheric mercury emissions are anthropogenic, resulting from e.g. emission hotspots in urban areas. Emissions from urban areas close to the coast are of interest because they could increase deposition loads to nearby coastal waters as well as contribute to long range transport of mercury. We present results from measurements of gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) in 15 coastal cities and their surrounding marine boundary layer (MBL). An increase of 15–90% in GEM concentration in coastal urban areas was observed compared with the remote MBL. Strong RGM enhancements were only found in two cities. In urban areas with statistically significant GEM/CO enhancement ratios, slopes between 0.0020 and 0.0087 ng m–3 ppb–1 were observed, which is consistent with other observations of anthropogenic enhancement. The emission ratios were used to estimate GEM emissions from the areas. A closer examination of data from Sydney (Australia), the coast of Chile, and Valparaiso region (Chile) in the southern hemisphere, is presented.

scholarly journals Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX

2010 ◽  
Vol 10 (5) ◽  
pp. 13609-13642 ◽  
Author(s):  
J. E. Dibb ◽  
L. D. Ziemba ◽  
J. Luxford ◽  
P. Beckman
Keyword(s):  
Boundary Layer ◽  
Arctic Basin ◽  
Elemental Mercury ◽  
The Arctic ◽  
Free Troposphere ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Summer Time ◽  
Trace Concentrations ◽  
Photochemical Activation

Abstract. Measurements of gas phase soluble bromide in the boundary layer and in firn air, and Br− in aerosol and snow, were made at Summit, Greenland (72.5° N, 38.4° W, 3200 m a.s.l.) as part of a larger investigation into the influence of Br chemistry on HOx cycling. The soluble bromide measurements confirm that photochemical activation of Br− in the snow causes release of active Br to the overlying air despite trace concentrations of Br− in the snow (means 15 and 8 nmol Br− kg−1 of snow in 2007 and 2008, respectively). Mixing ratios of soluble bromide above the snow were also found to be very small (mean <1 ppt both years, with maxima of 3 and 4 ppt in 2007 and 2008, respectively), but these levels clearly oxidize and deposit long-lived gaseous elemental mercury and may perturb HOx partitioning. Concentrations of Br− in surface snow tended to increase/decrease in parallel with the specific activities of the aerosol-associated radionuclides 7Be and 210Pb. Earlier work has shown that ventilation of the boundary layer causes simultaneous increases in 7Be and 210Pb at Summit, suggesting there is a pool of Br in the free troposphere above Summit in summer time. Speciation and the source of this free tropospheric Br are not well constrained, but we suggest it may be linked to extensive regions of active Br chemistry in the Arctic basin which are known to cause ozone and mercury depletion events shortly after polar sunrise. If this hypothesis is correct, it implies persistence of the free troposphere Br− for several months after peak Br activation in March/April. Alternatively, there may be a~ubiquitous pool of Br− in the free troposphere, sustained by currently unknown sources and processes.

Global Concentrations of Gaseous Elemental Mercury and Reactive Gaseous Mercury in the Marine Boundary Layer

2010 ◽  
Vol 44 (19) ◽  
pp. 7425-7430 ◽  
Author(s):  
Anne L. Soerensen ◽  
Henrik Skov ◽  
Daniel J. Jacob ◽  
Britt T. Soerensen ◽  
Matthew S. Johnson
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Elemental Mercury ◽  
Gaseous Elemental Mercury ◽  
Reactive Gaseous Mercury ◽  
Gaseous Mercury

scholarly journals Taklimakan Desert nocturnal low-level jet: climatology and dust activity

2016 ◽  
Vol 16 (12) ◽  
pp. 7773-7783 ◽  
Author(s):  
Jin Ming Ge ◽  
Huayue Liu ◽  
Jianping Huang ◽  
Qiang Fu
Keyword(s):  
Inversion Layer ◽  
Warm Season ◽  
Cold Season ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
Taklimakan Desert ◽  
Convective Boundary ◽  
Low Level ◽  
Low Level Jets ◽  
Nocturnal Inversion

Abstract. While nocturnal low-level jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs' features well by comparison with radiosonde data from two surface sites. The NLLJs occur in more than 60 % of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 m s−1. Most NLLJs are located above the nocturnal inversion during the warm season, while they are embedded in the inversion layer during the cold season. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the magnitude of momentum in the lower atmosphere from the top of the surface layer to the top of mixed layer is larger for NLLJ cases than for non-NLLJ cases, and in the warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, and these summer and autumn winds are coincident with an enhancement of aerosol optical depth. This indicates that the NLLJ is an important mechanism for dust activity and transport during the warm season over the Taklimakan.

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