Mercury exchange between the atmosphere and low mercury containing substrates

Mercury is emitted to the air from Hg-enriched and low Hg-containing (natural background) substrates. Emitted Hg can be geogenic, or can be derived from the re-emission of Hg that was previously deposited to the soil from the atmosphere. Atmospheric Hg can be derived from natural and/or anthropogenic sources and can be deposited by wet or dry processes. It is important to understand the relative magnitude of emission, deposition, and re-emission of Hg associated with terrestrial ecosystems with natural background soil Hg concentrations because these landscapes cover large terrestrial surface areas. This information is also important for developing biogeochemical mass balances, assessing the impacts of atmospheric Hg sources, and predicting the effectiveness of regulatory controls at local, regional, and global scales.The major focus of this paper is to discuss air–substrate Hg exchange for low Hg-containing soils (<0.1 μg Hg g⁻¹) from two areas in Nevada and one in Oklahoma, USA. Data collected with field and laboratory gas exchange systems are presented. Results indicate that in order to adequately characterize substrate–air Hg exchange, diel and seasonal data must be collected under a variety of environmental conditions. Field and laboratory data showed that dry deposition of gaseous Hg to substrates with low Hg concentrations is an important process. Environmental parameters important in influencing emissions include soil water content, incident light, temperature, atmospheric oxidants, and air Hg concentrations. There are synergistic and antagonistic effects between these parameters complicating prediction of flux.     

Source apportionment and distribution of atmospheric mercury in urban Beijing,China

The concentration of gaseous elemental mercury (GEM) in the atmosphere of urban Beijing was measured from October 2003 to September 2004 to investigate the origins and spatial-temporal variations of atmospheric Hg. The mean value of Hg concentration is 17.1 ng·m-3 (n=653). The atmospheric Hg data showed spatial-temporal variations throughout the duration of our observation. The maximum GEM concentration (53.7 ng·m-3) was observed at Gucheng in the western area of urban Beijing. The GEM concentrations increased from the north to the south of the studied area, and were higher in winter than in summer. The highest and lowest monthly averages of GEM concentrations were measured to be 23.3 and 4.1 ng·m-3 in January and July, respectively. In addition, GEM concentrations are higher in the daytime than at night in Autumn and from 14 March to 15 April, but daily GEM variation showed an inverse pattern from 22 April to 22 May. In winter, two peak values of GEM concentrations occurred at 13:30 and 21:30. Daily variation of GEM concentrations in summer was the lowest in the four seasons. Mercury from coal combustion was estimated to be the main source of anthropogenic emissions in Beijing from October 2003 to September 2004. Additionally, Hg emission from natural gas burning was estimated to be another dominant source of atmospheric Hg in Beijing.     

Mercury in soil near a long-term air emission source in southeastern Idaho

At the Idaho National Engineering and Environmental Laboratory in southeastern Idaho, a 500 °C fluidized bed calciner was intermittently operated for 37 years, with measured Hg emission rates of 9-11 g/h. Surface soil was sampled at 57 locations around the facility to determine the spatial distribution of Hg fallout and surface Hg variability, and to predict the total residual Hg mass in the soil from historical emissions. Measured soil concentrations were slightly higher (p<0.05) within 5 km of the source but were overall very low (15-20 ng/g) compared to background Hg levels published for similar soils in the USA (50-70 ng/g). Concentrations decreased 4%/cm with depth and were found to be twice as high under shrubs and in depressions. Mass balance calculations accounted for only 2.5-20% of the estimated total Hg emitted over the 37-year calciner operating history. These results suggest that much of the Hg deposited from calciner operations may have been reduced in the soil and re-emitted as Hg(0) to the global atmospheric pool.     

A non-steady-state compartmental model of global-scale mercury biogeochemistry with interhemispheric atmospheric gradients

A box model of mercury (Hg) cycling between the atmosphere and ocean is described and used to estimate Hg fluxes on a global scale (The Global/Regional Interhemispheric Mercury Model, GRIMM). Unlike previous simulations of this system, few assumptions are made concerning the rate of prominent marine biogeochemical processes affecting Hg (e.g., evasion, particle scavenging, and deep ocean burial). Instead, consistency with two observed atmospheric distributions was required: the interhemispheric gradient in total atmospheric Hg and the value for changes in the deposition of Hg from the atmosphere since industrialization observed in both hemispheres. Sensitivity analyses underscore the importance to modeling of the atmospheric lifetime of Hg, the magnitude of the interhemispheric gradient, the historical changes in Hg concentrations of various reservoirs, and vertical exchange between the surface ocean and the permanent thermocline. Results of the model indicate: lower evasional fluxes of Hg from the global ocean than previous estimates; a prominent role for particle scavenging as a removal mechanism from the surface ocean; a modest influence of dry processes (dust and gas) on Hg removal from the atmosphere; and an estimate of natural land-based sources of Hg to the atmosphere that is no more than about half that of anthropogenic sources.     

Atmospheric trace metals: global cycles and assessment of man's impact

Global data are presented for sources of atmospheric input for 20 trace metals, and the relative importance of natural and anthropogenic sources is assessed. Interference factors are calculated as (total anthropogenic emissions/total natural emissions) × 100. For lithophile metals such as Fe and Mn, interference factors are small. In contrast, the atmophile metals, such as As, Se and Hg, exhibit large interference factors. A significant degree of correlation exists between interference factors and enrichment factors, where enrichment factor is defined as the metal/Al ratio in atmospheric particulates divided by the metal/Al ratio in soils. For many of the trace metals, enrichment factors are of the same order of magnitude at high latitudes in both the Northern and Southern Hemispheres, and are larger at high latitude than at mid latitude.A simple mathematical model is used to calculate present-day enrichment factors in both hemispheres based on natural and anthropogenic influxes, effluxes, and transfer between hemispheres. The calculated enrichment factors are in good agreement with the observed enrichment factors for lithophile metals at both mid and high latitude, and for atmophile metals at mid latitude. However, calculated enrichment factors for atmophile metals are lower than observed enrichment factors at high latitude. To explain these results, we propose that for Hg, As and Se, and perhaps for other atmophile metals, there are significant fluxes from the sea surface to the atmosphere. If the estimated low-temperature fluxes of As, Se and Hg from the land and sea surfaces are included in the interference factor calculations for these metals, the factors are reduced to less than 100%.     

An update on the natural sources and sinks of atmospheric mercury

This paper summarizes recent advances in the understanding of the exchange of Hg between the atmosphere and natural terrestrial surfaces including substrates (soil, rocks, litter-covered surfaces and weathered lithological material) and foliage. Terrestrial landscapes may act as new sources of atmospheric Hg, and as repositories or temporary residences for anthropogenically and naturally derived atmospheric Hg. The role of terrestrial surfaces as sources and sinks of atmospheric Hg must be quantified in order to develop regional and global Hg mass balances, and to assess the efficacy of regulatory controls on anthropogenic point sources in reduction of human Hg exposure.     

Volcanic and anthropogenic contributions to global weathering budgets

We evaluate whether the global weathering budget is near steady state for the pre-anthropogenic modern environment by assessing the magnitude of acidity-generating volcanic exhalations. The weathering rate induced by volcanic acid fluxes, of which the CO₂ flux is the most important, can be expressed as an average release rate of dissolved silica, based on a model feldspar-weathering scheme, and the ratio of carbonate-to-silicate rock weathering. The theoretically predicted flux of silica from chemical weathering is slightly smaller than the estimated global riverine silica flux. After adjustment for carbonate weathering, the riverine dissolved bicarbonate flux is larger than the volcanic carbon degassing rate by a factor of about three. There are substantial uncertainties associated with the calculated and observed flux values, but the modern system may either not be in steady state, or additional, “unknown” carbon sources may exist. The closure errors in the predicted budgets and observed riverine fluxes suggest that continental weathering rates might have had an impact on atmospheric CO₂ levels at a time scale of 10³-10⁴ years, and that enhanced weathering rates during glacial periods might have been a factor in the reduced glacial atmospheric CO₂ levels. Recent anthropogenic emissions of carbon and sulfur have a much larger acid-generating capacity than the natural fluxes. Estimated potential weathering budgets to neutralize these fluxes are far in excess of observed values. A theoretical scenario for a return to steady state at the current anthropogenic acidity emissions (disregarding the temporary buffering action of the ocean reservoir) requires either significantly lower pH values in continental surface waters as a result of storage of strong acids, and/or higher temperatures as a result of enhanced atmospheric CO₂ levels in order to create weathering rates that can neutralize the total flux of anthropogenic and natural background acidity.     

北京市土壤Hg污染的区域生态地球化学评价

城市土壤Hg异常/污染是中国普遍存在的重大生态环境问题。文章对北京市近1000km2范围内的地表土壤、壤中气、大气干湿沉降、大气颗粒物、大气中的Hg含量水平和空间分布模式进行了系统研究,查明北京地表土壤Hg平均含量为0.41mg/kg,大气干湿沉降物中的Hg平均含量为0.194mg/kg,壤中气Hg的平均含量为559.65ng/m3,大气颗粒物PM10和PM2.5中的Hg含量分别为0.59和0.67ng/m3,大气中的Hg平均含量为3.13ng/m3。北京市自2000年起实现了由燃煤转变为燃气的减排措施,导致干湿沉降物中的Hg沉降通量显著减少,2006年大气干湿沉降物中Hg的沉降通量1.837mg·m-2·a-1,北京市城区(近1000km2)Hg全年沉降为1837kg,空气中总Hg浓度由1998年的8.3~24.7ng/m3下降到2006年的3.13ng/m3,大气颗粒物中Hg含量由2003年的1.18ng/m3下降到2006年的0.59ng/m3(PM10)和0.67ng/m3(PM2.5),表明北京市煤改气减排措施的实施显著改善了大气环境质量。通过对土壤中Hg的存在形式研究,发现土壤中有硫化物(辰砂)及各种Hg盐(HgCl2)的含Hg矿物,Hg也可以各种吸附方式或壤中气方式存在。研究证实北京壤中气Hg与大气Hg存在显著的相关性(n=131,R=0.267,p<0.01),表明壤中气Hg是大气Hg的重要来源之一。利用2005年地表土壤总Hg与Hg释放速率的线性方程估算,土壤Hg平均释放速率为102.42ng·m-2·h-1,2005年土壤释放进大气的Hg通量为936.70kg。在查明土壤中存在大量辰砂矿物的同时,还分布有大量具有高温熔融特征的金属微球粒和玻璃质微球粒,证明燃煤和冶金烟尘是地表土壤Hg的主要来源。土壤中Hg、S、pH和辰砂颗粒浓度在空间上的高度耦合性表明,碱性条件下,土壤中高含量的S和Hg是辰砂形成的重要原因。按国家土壤环境质量标准,北京市I级土壤Hg环境质量的面积为176km2,Ⅱ级为808km2,Ⅲ级为24km2,超Ⅲ为36km2。Ⅲ级、超Ⅲ级主要分布在二环路以内的中心城区。城南(长安街为界)大气Hg环境质量明显优于城北,在北四、北五环之间的部分地区,大气颗粒Hg的环境质量为Ⅲ级或超Ⅲ级。在地表土壤Hg含量较高的中心城区,居民每天因呼吸摄入的Hg高达364ng,对人体健康构成潜在风险。根据我国"十一五"规划中每年实现10%节能减排的目标,对北京市未来50年土壤Hg含量的时空演变趋势预测,预测2050年北京因干湿沉降带来的Hg输入量为16.03kg,地表土壤释放Hg的输出量为37.36kg,明显大于Hg的输入通量,土壤Hg的环境质量将得到根本改善。预测到2040年Ⅲ级土壤Hg环境质量的区域将完全消失,到2060年以Ⅰ级土壤为主。     

北极阿拉斯加春季积雪中汞的时空分布及其来源分析

开展北极雪冰中汞分布特征及其来源的探究,不仅可以丰富冰冻圈汞生物地球化学循环的认识,而且对评估北极环境中汞的潜在暴露风险具有现实意义.在2017年4月至5月对美国阿拉斯加的积雪进行大范围样品采集,探讨了该区域积雪中汞的空间分布特征及其成因、汞的沉降后过程以及潜在来源分析.研究表明:积雪中汞的空间分布受大气汞亏损事件(A...     

地质成因的甲烷释放对大气的影响

地质成因自然源的甲烷释放在整个大气甲烷估算中起着非常重要的作用,它既是不含放射性14C甲烷源(死碳源)缺失部分的重要代表,也是甲烷重碳源的重要部分.概述了国内外关于地质成因甲烷释放对大气甲烷源与汇影响的研究进展,详述了来自地质成因化石燃料泄漏的人为甲烷释放以及来自沉积盆地(含油气盆地)、泥火山、地热区、海洋和甲烷水合物的地质自然源甲烷释放对大气甲烷源与汇的贡献及其影响因素;说明由于地质成因甲烷分布的区域性、不均匀性和时空的高度变化性,以及目前地质成因甲烷的通量估算仅建立在区域性的少量甲烷通量测试基础上,造成了地质成因甲烷释放通量估算的高度不确定性;指出研究中国西北地区油气田集聚区的甲烷释放通量,对油气田地质成因甲烷释放通量的估算具有重要意义.     

人类巨量碳排放后果分析: 来自青藏高原综合调查的启示

人类巨量碳排放究竟导致什么后果,争议颇大,只有深入研究始新世以来大气CO₂浓度与环境变化,才有可能正确认识未来人类自身巨量碳排放之后果。大量研究揭示出: 从始新世到渐新世末期,大气CO₂浓度大幅下降,全球变冷,形成了大陆冰川; 中新世至今,大气CO₂浓度在低浓度背景之下长周期缓慢下降。当前尚不清楚何种机制主导了这一变化过程,也不清楚形成大陆冰川的水来自何方。为此,从青藏高原深部碳循环、表层水循环和环境变化的角度探讨这些问题,再分析未来人类巨量碳排放之后果。青藏高原在生长、隆升过程中,通过硅酸岩化学风化、植物光合作用、陆内俯冲(深埋)、水岩反应等方式,持续将巨量大气CO₂转化为富含碳元素的固、流体,封存在青藏高原新生的厚地壳之中,大幅降低了大气CO₂浓度,导致了全球变冷、大陆内陆(含青藏高原,下同)表层失水变干,形成了大陆冰川。渐新世—中新世之交,青藏高原生长到改变大气环流的规模,形成了亚洲季风,大陆内陆进一步荒漠化,捕获CO₂的量大幅下降,并与青藏高原内部所释放CO₂的量达到了准动态平衡,这是中新世以来大气CO₂浓度变化的主要机制。人类巨量碳排放彻底扭转了大气CO₂浓度长周期缓慢下降的趋势,大陆冰川因全球变暖所形成的液态水不会长期停留在海洋里,而以大气降水的方式重新回到干冷的大陆内陆,青藏高原将因此再次成为巨型水塔,缓解30多亿人的清洁饮用水问题。持续生长的高原和当前干冷荒漠化的大陆内陆通过前述多种方式固化人类排放的巨量CO₂,导致未来大气CO₂浓度在较高浓度背景下保持稳定,届时沙漠变绿洲,黄土高原变成有机质丰富的黑土高原,人居环境大幅改善; 但在盆地内部,PM2.5难以扩散,易形成雾霾。全球平均海平面因海水热膨胀而缓慢上升,上升速率约为1 mm/a。水主要在大陆冰川与内陆表层之间循环,与海平面升降之间没有因果关系。因此,人类巨量碳排放所导致的全球变暖对于人类自身的发展是利大于弊。     

Atmospheric emission inventory of cadmium from anthropogenic sources

To demonstrate the atmospheric emission characteristics of cadmium (Cd), which is considered an important contaminant to human health and environment, a comprehensive emission inventory of Cd has been established by applying the best available emission factors and activity data for the first time. This inventory covers major anthropogenic sources in China and a bottom-up approach is adopted to compile the inventory for the sources where possible. The total emissions of Cd are estimated at about 743.77 metric tons for the year 2009, of which the contributions of industrial processes and combustion sources are approximately 56.6 and 43.4 %, respectively. Nonferrous metals smelting including copper, lead, and zinc, ranks as the leading source accounting for about 40.6 % of the total. The high contribution results from the rapid growth of nonferrous metallurgical industry that reflects a new focus of Cd emission pollution in China. Cd emissions from coal combustion are estimated at approximately 273.69 metric tons, with a share of 36.8 %, in which industrial coal-burning sector is thought to be the primary source. Moreover, Cd emissions are spatially allocated onto grid cells with a resolution of 0.5° × 0.5°, indicating that the emissions are mainly distributed among the regions of eastern, central and southern China. In addition, the uncertainties in the inventory are quantified by using a Monte Carlo simulation, and the overall uncertainty falls within a range of ?15 to 48 %. It implies that more field tests for industrial coal combustion and metals smelting process are very necessary.     

Flow of metals into the global atmosphere

Concentrations of ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra, U, V, Pb, Cd and Hg have been measured in firn and ice deposited during the past three decades in accumulation zones of glaciers and also in pre-industrial glacier ice collected in Spitsbergen, Northern Norway, Alaska, Southern Norway, Alps, Himalayas, Ruwenzori, Peruvian Andes, and at King George Island in Antarctica. Except for Hg, the geographical distribution of mean concentrations of ²²⁶Ra, U and stable heavy metals in contemporary ice is not uniform, with the lowest concentrations found in Northern Norway, Alaska and Antarctica, and the highest in continental locations at equatorial and middle latitudes. We did not find evidence of changes in rate of metal deposition during the last three decades, as compared with pre-industrial period, however, our samples of pre-industrial ice might be contaminated in part by contemporary fallout migrating from the exposed surface of old parts of glaciers into the deeper ice layers. Using the data on annual injections of ¹³⁷Cs into the global atmosphere and mean global concentrations of radionuclides and heavy metals found in contemporary ice the global annual flows of ²²⁶Ra, ²¹⁰Pb, U,V, Pb, Cd and Hg were estimated as 6.6 kCi, 485 kCi, 12kt, 4870kt, 590 kt, 180 kt and 190 kt, respectively. These estimates are 1–2 orders of magnitude higher than estimates based on primary paniculate emissions. The anthropogenic contribution is a small fraction of the flows, which are dominated by natural processes leading to enrichment of metals in airborne dust.     

Impact of mercury emissions from incineration of automobile shredder residue in Japan

Mercury emissions from the incineration of automobile shredder residues (ASRs) were investigated. Continuous monitoring of elemental and reactive gaseous Hg in flue gas was performed in lab-scale and plant-scale ASR incineration. Results of continuous monitoring agreed with those obtained using the JIS K0222 method and Ontario-Hydro method. Before cleaning by air pollutant control devices (APCDs), reactive Hg was the dominant form of that element in both lab-scale and plant-scale results. Emission factors of reactive Hg before APCDs estimated from monitoring results showed large differences between plant-scale and lab-scale emissions. The emission factor in the plant scale was more than 10 times larger than that in the lab-scale, which is explainable by the different Hg contents of ASR. Based on plant-scale monitoring at the stack, emission factors after APCDs were estimated as 0.79 mg-Hg/Mg-ASR for elemental Hg and 6.8 mg-Hg/Mg-ASR for reactive Hg. Using these emission factors, total Hg emissions from ASR incineration were estimated as 2.2 kg/a. An ASR incineration plant investigated in this study used highly effective APCDs. Consequently, these emission factors might result in underestimation of national Hg emissions from ASR incineration. Emission factors estimated from lab-scale monitoring at a fabric filter outlet side might be more appropriate. However, even if emission factors calculated from plant-scale or the lab-scale monitoring are used, estimated emissions are still less than 1.0% of total Hg emissions in Japan. Therefore, Hg emissions from ASR incineration can be evaluated as insignificant. Unless Hg contents of ASR increase extremely, ASR incineration would be a minor source of Hg atmospheric emission in Japan, even if all ASRs were incinerated.     

A test of the overdue-glaciation hypothesis

According to a new hypothesis, greenhouse-gas concentrations in the atmosphere should have fallen throughout the last several thousand years and caused a significant cooling of Earth's climate, but early anthropogenic emissions of carbon dioxide and methane kept temperatures relatively warm. A further prediction is that ice should have begun accumulating in northeast Canada several thousand years ago. We carry out a preliminary test of this hypothesis by reducing atmospheric CO₂ and CH₄ concentrations to their estimated ‘natural’ levels in an experiment with the GENESIS climate model. In the absence of anthropogenic contributions, global climate is almost 2 °C cooler than today and roughly one third of the way toward full-glacial temperatures. The hypothesis of an overdue glaciation is confirmed, but at a small scale: parts of Baffin Island retain snow cover year-round, and snow cover persists on high terrain in Labrador for 11 months of the year.     

(Pre-) historic changes in natural and anthropogenic heavy metals deposition inferred from two contrasting Swiss Alpine lakes

Continuous high-resolution sedimentary record of heavy metals (chromium (Cr), copper (Cu), lead (Pb), zinc (Zn), manganese (Mn), and mercury (Hg)), from lakes Lucerne and Meidsee (Switzerland), provides pollutant deposition history from two contrasting Alpine environments over the last millennia. The distribution of conservative elements (thorium (Th), scandium (Sc) and titanium (Ti)) shows that in absence of human disturbances, the trace element input is primarily controlled by weathering processes (i.e., runoff and erosion). Nonetheless, the enrichment factor (EF) of Pb and Hg (that are measured by independent methods), and the Pb isotopic composition of sediments from the remote lake Meidsee (which are proportionally more enriched in anthropogenic heavy metals), likely detect early mining activities during the Bronze Age. Meanwhile, the deposition of trace elements remains close to the range of natural variations until the strong impact of Roman activities on atmospheric metal emissions. Both sites display simultaneous increases in anthropogenic trace metal deposition during the Greek and Roman Empires (ca 300 BC to AD 400), the Late Middle Ages (ca AD 1400), and the Early Modern Europe (after ca AD 1600). However, the greatest increases in anthropogenic metal pollution are evidenced after the industrial revolution of ca AD 1850, at low and high altitudes. During the twentieth century, industrial releases multiplied by ca 10 times heavy metal fluxes to hydrological systems located on both sides of the Alps. During the last decades, the recent growing contribution of low radiogenic Pb further highlights the contribution of industrial sources with respect to wood and coal burning emissions.     

Potentiel des méthodes de séparation et stockage du CO2 dans la lutte contre l'effet de serre

Increasing atmospheric level of greenhouse gases are causing global warming and putting at risk the global climate system. The main anthropogenic greenhouse gas is CO₂. Technical solutions exist to reduce CO₂ emission and stabilise atmospheric CO₂ concentration, including energy saving and energy efficiency, switch to lower carbon content fuels like natural gas and to energy sources that operate with zero CO₂ emissions such as renewable or nuclear energy, enhance the natural sinks for CO₂ (forests, soils, etc.), and last but not least, sequester CO₂ from fossil fuels combustion. The purpose of this paper is to provide an overview of the technology and cost for capture and storage of CO₂. Some of the factors that will influence application, including environmental impact, cost and efficiency, are also discussed. Capturing CO₂ and storing it in underground geological reservoirs appears as the best environmentally acceptable option. It can be done with existing technology; however, substantial R&D is needed to improve available technology and to lower the cost. Applicable to large CO₂ emitting industrial facilities such as power plants, cement factories, steel industry, etc., which amount to more than 30% of the global anthropogenic CO₂ emission, it represents a valuable tool in the battle against global warming. To cite this article: P. Jean-Baptiste, R. Ducroux, C. R. Geoscience 335 (2003).     

Trace metal profiles in the varved sediment of an Arctic lake

Varved (annually-laminated) sediments offer a rare and physically undisturbed archive of past trace metal deposition and limnological conditions. Here, a high-resolution 1,300 year record of metal accumulation is presented from a varved lake sediment on Devon Island in the Canadian High Arctic. Down-core concentration profiles of Cd, Cu and Zn were positively correlated (P < 0.01) with organic C (Cd, Zn) or with leachable Fe (Cu), while distinct sub-surface peaks of these metals coincided with those of Fe, S and other redox-sensitive elements such as Co, Cr and U. The fluxes of these metals since 1854 were correlated with elements such as Ca, Al and La (P < 0.001) which are predominantly of local geological origin. Furthermore, the Cd, Cu and Zn patterns did not match concurrent records in Greenland Summit ice over the last century, nor global industrial emission histories. These facts suggest that inputs from local geological sources, coupled with some degree of post-depositional mobility or association with organic matter inputs, explain the metals’ sedimentary profiles, which were apparently not affected by long-range atmospheric metal pollution. Mercury concentrations were strongly correlated with total diatom abundance over the last 400 yrs, especially during the 20th Century when a two-fold increase in Hg concentrations and a four order-of-magnitude increase in diatoms occurred in tandem. Since 1854, 81% of the variation in Hg flux was associated with diatom and Ca fluxes. A similar correspondence between Hg and diatoms was found in a second lake nearby, confirming that the relationship was not unique to the main study lake. Recent Hg increases in Arctic and sub-Arctic lakes have been attributed to global anthropogenic Hg emissions. We propose an alternative hypothesis for High Arctic lakes: the recent Hg increases may be partly or entirely the product of elevated rates of Hg scavenging from the water column caused by markedly greater algal productivity, which in turn was driven by accelerating climate warming during the 20th Century. Given the important environmental assessment and policy implications if the alternative hypothesis is true, the possible effects of climate warming on sedimentary Hg fluxes in this region deserve further study.     

Surface metal enrichment and partitioning of metals in a dated sediment core from a Norwegian fjord

A 24-cm long sediment core from an oxic fjord basin in Ranafjord, Northern Norway, was sliced in 2 cm sections and analysed for As, Co, Cu, Ni, Hg, Pb, Zn, Mn, Fe, ignition loss and Pb-210. Partitioning of metals between silicate, non-silicate and non-detrital phases was assessed by leaching experiments, in an attempt to understand the mechanisms of surface metal enrichment in sediments. Relative to metal concentrations in sediments deposited in the 19th century, metals in near surface sediments were enriched in the following order: Pb > Mn > Hg > Zn > Cu > As > Fe. Cobalt and Ni showed no enrichment. The non-detrital fraction of Cu, Pb, Mn and Zn was significantly higher in the upper 10 cm than at greater depth in the core. This corresponds to sediments deposited since 1900, when mining activities started in the area. The enrichment of Cu, Pb and Zn is assumed to be mainly a result of mining, while Mn is apparently enriched in the surface due to migration of dissolved Mn and precipitation in the oxic surface layer. Elevated concentrations of As and Fe in the upper 4 cm are presumably due to discharges from a coke plant and an iron works respectively. The excess Hg present in the near surface sediments is tightly bound, either in coal particles or ore dust introduced by local industry, or via long distance transport of atmospheric particles. Calculations of metal flux to the sediments indicate an anthropogenic flux of Zn equal to its natural flux, while the flux of Pb shows a threefold increase above natural input.     

大气中溴的环境地球化学研究进展

溴是大气平流层和对流层中的重要物种,能参与大气中的多种化学过程,对臭氧的损耗影响很大,同时也干扰大气的硫循环和汞循环,在大气化学中起着十分重要的作用.综述了近年来大气对流层和平流层溴的种类和含量、自然来源和人为来源,以及化学性质,并重点总结了活性溴物种BrO在大气中的存在情况及其在臭氧损耗中的作用.最后,提出了目前大气...