G4B Atmospheric Mercury: Measurement and Monitoring

Tuesday, 26 July, 2011

TG4B-O1 — 8:30-8:45
Authors: KRISHNAMURTHY, Nishanth1, LANDING, William M.1, CAFFREY, Jane M.2, HOLMES, Christopher D.3
(1) Florida State University, nkrishnamurthy@fsu.edu; (2) University of West Florida; (3) University of California, Irvine.

Event-based (24-hour integrated) rainfall deposition of mercury, trace metals, and major ions has been monitored over the last 6 years at 3 inland locations and at a “Beach” site close to the coast over the past 2 years in the Pensacola Bay watershed to evaluate the temporal and spatial patterns in atmospheric wet deposition. Samples were analyzed for total mercury and a suite of 50 other trace elements. One goal of this project was to attempt to quantify the contribution of local emission sources to atmospheric deposition of mercury and other heavy metals. There were no significant differences in the rainfall Hg flux between the three inland sites or between nearby Mercury Deposition Network monitoring sites along the Gulf Coast. However, the inland sites saw Hg fluxes in the range of 20-46% greater than that of the Beach site for the year 2010 and two of the nearby MDN sites saw a range of 35-71% greater over the first half of 2010 compared to the Beach site. We seek to explain these differences for sites that are relatively close together geographically. Mercury deposition during the summer months is higher than other months due to higher concentrations in the rainfall and higher summer-time rainfall rates throughout the region. Multivariate statistical analysis was used to sort these trace elements into factors that represent potential sources that contribute to the rainfall chemistry. Four significant factors were identified: (1) crustal dust factor (Al, Ba, Co, Cs, Fe, Li, Si), (2) sea-salt factor (Cl, Na, Mg, Sr), (3) Cd/Zn factor (Cd, Cr, Zn, P), and (4) a “pollution” factor (acidity, nitrate, excess-sulfate, ammonia, As, Bi, Hg, Pb, Sb, Se, Sn). Using ratios of Hg to volatile trace elements and excess sulfate, we can estimate that 22-33% of the rainfall mercury fluxes could be the result of emissions from coal combustion in the region while factor analysis suggests slightly over 40%. However, we cannot definitively distinguish the impacts from local vs. regional or distant sources on wet deposition of Hg. We also conduct a positive matrix factorization to account for source variations and percent contributions between seasons.

TG4B-O2 — 8:45-9:00
Authors: GRATZ, Lynne E1, KEELER, Gerald J2
(1) CNR-IIA, l.gratz@iia.cnr.it; (2) University of Michigan.

Underhill, VT, USA is a remote location in the northeastern United States where atmospheric Hg deposition is a critical issue due to elevated levels of mercury (Hg) in the region’s fish and wildlife. Daily-event precipitation samples were collected in Underhill, VT from 1995 to 2006 and analyzed for Hg and trace elements in order to quantify and understand the wet deposition of Hg to the ecosystem. This long-term dataset provides a unique opportunity to study source contributions to Hg wet deposition over time using source apportionment and hybrid-receptor modeling techniques. Over the 12-year period, annual Hg deposition levels at Underhill did not decline significantly despite regulatory efforts to reduce Hg emissions in the U.S. Mercury and trace element wet deposition data were examined using the multivariate receptor model EPA PMF 3.0 to identify the sources contributing to Hg deposition at the Underhill site. Results indicate that coal combustion, a mixture of incineration and non-ferrous metal smelting, and a phosphorus source contributed to the observed Hg wet deposition. The model indicated that coal combustion, which was characterized by the highest loadings of sulfur (S) and selenium (Se), contributed ~60% of the total Hg measured in wet deposition during the 12-year period. The annual contribution to Hg deposition from coal combustion was 50-70% and did not change significantly over time. Mercury and trace element deposition were further analyzed using quantitative transport bias analysis (QTBA). QTBA is a trajectory-based hybrid-receptor model that weights air mass back-trajectories with the measured amounts of analytes at the receptor site to determine the most probable source regions of those species. Results from QTBA indicate that the majority of Hg deposition at Underhill was due to transport from the Midwestern U.S., where the density of coal-fired utility boilers (CFUBs) in the U.S. is largest. Sulfur and Se deposition were also dominantly associated with transport from the same region. The substantial contribution from Midwestern CFUBs to the observed Hg deposition at Underhill is consistent with past findings that the highest levels of Hg deposition at Underhill occur with southwesterly transport. The combined PMF and QTBA analysis provides strong corroborative evidence to suggest that total annual Hg wet deposition at Underhill from 1995 to 2006 did not decline due to consistent transport of CFUB Hg emissions from the Midwestern U.S.

TG4B-O3 — 9:00-9:15
Authors: CARLING, Gregory T.1, JOHNSON, William P.1
(1) University of Utah, greg.carling@utah.edu

Snow columns were collected at peak snowpack at 12 sites across the central Wasatch Mountains, Utah, during March and April 2010 to determine concentrations of mercury, trace elements, major anions and cations, and pH. The timing of sample collection coincided with the onset of dust events driven by southerly pre-frontal winds. Snow samples were melted in the laboratory and subsampled for analyses of filtered (0.45 µm) and unfiltered fractions. Most trace elements displayed large increases in concentration (for example, factor of 3 increase for mercury, and factors of 2-13 increases for arsenic, cadmium, copper, lead, and uranium) between the 6 sites sampled in March (prior to dust deposition), and the 6 sites sampled in April (after dust deposition). April snowpack was elevated relative to March snowpack in concentrations of the following trace elements: Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Ni, Pb, Sb, Sr, Ti, U, V, and Zn; and major ions: K+, Na+, Cl-, and SO42-. Acid neutralizing capacity and pH were also elevated in April relative to March snowpack. Comparison of elemental mass fraction associated with particles >0.45 µm (calculated as the difference between unfiltered and filtered concentrations) and <0.45 µm (filtered concentration) shows that the increase in concentrations between March and April snowpack is primarily a result of elemental association with dust particles >0.45 µm. The results suggest that the majority of trace and major element loading to the Wasatch snowpack occurs via dust deposition. The dust-derived elements remained within the snowpack over the course of the study, in contrast to non-particulate mercury (for example) which is typically volatilized to the atmosphere following deposition. To our knowledge, no other studies have demonstrated that dust deposition is the major vector of trace element loading to snowpack. Comparison with the published literature also shows that concentrations of some trace elements and major ions from the “clean” (March) snowpack in the central Wasatch are elevated compared to those in other locations due, most likely, to the influence of urban pollution sources.

TG4B-O4 — 9:15-9:30
Author: STEINNES, Eiliv1
(1) Norwegian University of Science and Technology, eiliv.steinnes@chem.ntnu.no

Deposition of trace metals such as Pb, Zn, Cd, As, and Sb in Norway shows a substantial decrease with northern latitude as evident from bulk deposition measurements and supported by moss analysis. Bulk deposition of Hg follows a corresponding trend. Hg in terrestrial moss however shows a more uniform distribution, with a minimum in the middle part of the country and then increasing towards the north. A similar latitudinal distribution is evident in surface peat from ombrotrophic bogs. Reasons for this observation remain speculative, but two possible mechanisms might be suggested: (1) The residence time of deposited Hg0 from the hemispheric pool on terrestrial surfaces increases with northern latitude and provides more time for photochemical oxidation to occur before re-emission; (2) Reactive Hg produced during Polar sunrise episodes in the High Arctic may undergo relatively fast atmospheric transport to land areas farther south and eventually be deposited.

TG4B-O5 — 9:30-9:45
Authors: HOLSEN, Thomas1, HUANG, Jiaoyan1, CHOI, Hyun-Deok1
(1)Clarkson University, holsen@clarkson.edu

Tekran Hg speciation systems were used at a rural site (Huntington Forest, NY) and an urban site (Rochester, NY) to measure gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and fine particle-bound mercury (PBM2.5) for a year. Averaged PBM2.5, GOM, and GEM were 198, 395, and 16% higher at the urban site than at the rural site. PBM2.5 concentrations were higher in winter at both sites, which was indicative of bio-fuel combustion for space heating in winter. During the warmer seasons, GOM concentrations and O3 were positively correlated suggesting atmospheric oxidant reactions were occurring. The observed GOM reaction time (time from the lowest to the highest GOM concentration) in Rochester was approximately 6.0 h while the theoretical time (calculated from chemical reaction time among GEM, GOM, and O3) was from 5.5 to 11.8 h. In winter, GEM concentrations increased when the temperature rose above freezing suggesting GEM was released from melting snow at both sites. A GEM diurnal pattern was occasionally seen during warmer seasons however different patterns were seen at different sites. At the urban site, there were 12 events selected with enhanced GEM/CO ratios to identify Hg sources. Two of them did not have enhanced GOM/SO2 ratios or precipitation during transport or at the site and these two events were considered as Hg transport from regional sources. The others were associated with local Hg emissions. Hg concentrations at the rural site were also impacted by Hg emissions near the urban site. In cases where transport from Rochester to Huntington was seen about 80% of the GOM was removed by deposition, reactions, and dispersion during transport.

TG4B-O6 — 9:45-10:00
Authors: SUZUKI, Noriyuki1, SHIBATA, Yasuyuki1, OGASAWARA, Koyo2, NAGASAKA, Hiromitsu2, HATTORI, Tatsuya2, HOSHI , Shuji2
(1)National Institute for Environmental Studies, nsuzuki@nies.go.jp; (2) IDEA Consultants, Inc.;

The monitoring project for measurement of atmospheric mercury and other heavy metals at Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) has been conducted by the Ministry of the Environment, Japan (MOEJ). CHAAMS operated by National Institute for Environmental Studies (NIES) is at the north-west edge of Okinawa Island and facing to the East China Sea and the Pacific Ocean. Gaseous elemental mercury (GEM), divalent reactive gaseous mercury (RGM), and particulate-bound mercury (PBM) are continuously measured with Tekran mercury speciation system coupled to a cold vapor atomic fluorescence spectroscopy (CVAFS) detector.

We developed Standard Operation Procedure (SOP) of atmospheric mercury analysis for hot and humid climate in Okinawa based on the procedure recommended by USEPA. In order to assure data quality of GEM, measurements of four seasons were compared with values of the MOEJ manual method based on gold amalgamation with cold vapor atomic absorption spectrometry (CVAAS). GEM data of Tekran 2537 shows a good correlation with those of the established MEOJ method. Data quality assurance of RGM and PBM are also studied using a manually operated off-line system. RGM is sampled with an annular denuder and analyzed by CVAFS. PBM is captured on a quartz filter using a high volume sampler and analyzed by CVAAS.

The measurements from FY2006 to current are analyzed to assess the background levels of heavy metals and obtain information on their long-rage transport in Asia- Pacific region. The monthly mean of observed GEM concentration was 1.3 to 2.5 ngm-3 and hourly mean was 0.8 - 6.0 ngm-3. The GEM monthly means are relatively higher from winter to spring and lower in summer. Frequency of GEM peak episodes increases from winter to spring related to a certain meteorological condition. When the air mass is blowing from the high pressure system in the Asian continent after the front line passes over Okinawa Island, the high GEM episodes are observed. Diurnal variation in GEM with lower in the day and higher at night was observed especially in summer.

In addition to the Cape Hedo monitoring project, we are conducting the monitoring campaign of atmospheric mercury at Yaizu City from January to March in 2011. Measurement results of GEM, RGM and PBM are compared with those of Cape Hedo which shows slightly higher averaged level than Cape Hedo maybe reflecting more impact from local sources in urban/industrial activities.

TG4B-O7 — 10:00-10:15
Author: FU, Xuewu1
(1) Institute of Geochemistry, Chinese Academy of Sciences, fuxuew@gmail.com

Anthropogenic emission of mercury (Hg) has been increasing for many years due to the fast increased energy consumption. In order to assess the regional budget of atmospheric over China, from May 2005, we carried out measurements of atmospheric Hg in Mt. Waliguan (In Qinghai province, Northwest China, from Sep 2007 to present), Mt. Leigong (In Guizhou province, South China, from May 2008 to May 2009), Mt. Changbai (In Jilin province, Northeast China, from Oct 2008 to present), and Zhuzhang baseline station (In Yunan province, Southwest China, from Nov 2009 to present). Averaged Total gaseous mercury (TGM) concentrations at Mt. Waliguan, Mt. Leigong, Mt. Changbai, and Zhuzhang station were 2.11 ± 1.05, 2.80 ± 1.51, 1.57 ± 0.54, and 2.56 ± 0.64 ng m-3, respectively. Averaged fine particulate mercury (PHg, Hg bounded to particulate matter with an aerodynamic diameter < 2.5 µm) and RGM concentrations were 8.8 ± 9.9 and 4.7 ± 3.1 pg m-3 at Mt. Waliguan and 37.9 ± 23.4 and 7.4 ± 5.9 at Zhuzhang station, respectively. Generally, atmospheric Hg species in remote areas of China were higher than those observed from North America, and this corresponds very well with the large anthropogenic emissions in China. Atmospheric Hg showed a clear regional pattern in China with the descending order of South China, Southwest China, Northwest China and Northeast China. Seasonal variations in the four remote sites differed obviously. The highest seasonal concentrations for atmospheric TGM were observed in winter for South and Northeast China, autumn for Northwest China, Spring for Southwest China. The temporal variations of atmospheric TGM were controlled by regional emissions and long-range transport, and atmospheric PHg and RGM were mainly affected by regional sources.

TG4B-O8 — 10:15-10:30
Authors: HALL, Naima1, DVONCH, J. Tim1, MARSIK, Frank1, LANDIS, Matthew2, KEELER, Gerald1
(1) University of Michigan, hallnai@umich.edu; (2) US EPA;

A study was conducted in southeastern Michigan to quantify the impact of near-field emissions and to determine the relative importance of local and regional sources of atmospheric wet and dry mercury (Hg) deposition. During a three-week intensive in summer 2007, three sites were chosen in urban and/or industrial areas of Detroit thought to be impacted by near-field emissions and one rural site was chosen to provide regional background deposition amounts. Wet deposition was measured through the collection of daily, event precipitation samples, while dry deposition was measured using water surrogate surface sampling methods for 12 and 24-hour collection periods. In addition, ambient speciated mercury was measured at all four sites. Over the sampling period there was a significant difference between the total deposition at urban/industrial Detroit sites and the rural site. While the total wet deposition (1254-1390 ng/m2) for the sampling period averaged 1.4 times greater at the urban sites relative to the background site (943 ng/m2), the difference in total dry deposition was further enhanced, nearly 4 times greater at the urban sites (463-778 ng/m2) relative to the background site (158 ng/m2). Examining the ratio of dry to wet deposition in proximity to different emission source types can help inform and improve our understanding of dry deposition processes within an urban/industrial airshed and contribute to the improvement of models of Hg dry deposition.

Tuesday, 26 July, 2011