Atmospheric mercury cycles in northern Wisconsin

Total gaseous mercury (TGM) in the lower atmosphere of northern Wisconsin exhibits strong annual and diurnal cycles similar to those previously reported for other rural monitoring sites across mid-latitude North America. Annually, TGM was highest in late winter and then gradually declined until late summer. During 2002–04, the average TGM concentration was 1.4 ± 0.2 (SD) ng m^?3, and the amplitude of the annual cycle was 0.4 ng m^?3 (～30% of the long-term mean). The diurnal cycle was characterized by increasing TGM concentrations during the morning followed by decreases during the afternoon and night. The diurnal amplitude was variable but it was largest in spring and summer, when daily TGM oscillations of 20–40% were not uncommon. Notably, we also observed a diurnal cycle for TGM indoors in a room ventilated through an open window. Even though TGM concentrations were an order of magnitude higher indoors, (presumably due to historical practices within the building: e.g. latex paint, fluorescent lamps, thermometers), the diurnal cycle was remarkably similar to that observed outdoors. The indoor cycle was not directly attributable to human activity, the metabolic activity of vegetation or diurnal atmospheric dynamics; but it was related to changes in temperature and oxidants in outdoor air that infiltrated the room. Although there was an obvious difference in the proximal source of indoor and outdoor TGM, similarities in behavior suggest that common TGM cycles may be driven largely by adsorption/desorption reactions involving solid surfaces, such as leaves, snow, dust and walls. Such behavior would imply a short residence time for Hg in the lower atmosphere and intense recycling – consistent with the “ping-pong ball” or “multi-hop” conceptual models proposed by others.     

Atmospheric dry deposition to leaf surfaces at a rural site of India

Dry deposition flux of major ions (Na+, K+, Ca2+, Mg2+, NH4+, F-, Cl-, NO3- and SO4(2-) to natural surfaces [guava (Psidium guyava) and peepal (Ficus religiosa) leaves] are determined at Rampur, a rural site of semi-arid region of India. Dry deposition flux is the highest for Ca2+ on guava leaves and for NH4+ on peepal leaves. Overall dry deposition flux is higher on guava leaves than of peepal leaves. The variation in deposition flux may be due to surface characteristics (surface roughness) and arrangement of leaves. Peepal leaves are arranged along the axis of the stem, whereas guava leaves are at right angles to the stem. The deposition flux of cations contributes 66% and 76% of dry deposition of all major ions on guava and peepal leaves, respectively as soil is major contributor towards dry deposition flux in tropical regions. ANOVA revealed no significant seasonal difference in deposition, although there is a trend for higher in winter. Deposition velocities of NH4+, NO3- and SO4(2-) are greater on guava leaves than peepal leaves, which can be attributed to the rougher surface of the guava leaf.     

Atmospheric phosphorus deposition at a montane site: Size distribution,effects of wildfire,and ecological implications

The dry deposition of atmospheric particulate matter can be a significant source of phosphorus (P) to oligotrophic aquatic ecosystems, including high-elevation lakes. In this study, measurements of the mass concentration and size distribution of aerosol particles and associated particulate P are reported for the southern Sierra Nevada, California, for the period July–October, 2008. Coarse and fine particle samples were collected with Stacked Filter Units and analyzed for Total P (TP) and inorganic P (IP) using a digestion-extraction procedure, with organic P (OP) calculated by difference. Particle size-resolved mass and TP distributions were determined concurrently using a MOUDI cascade impactor. Aerosol mass concentrations were significantly elevated at the study site, primarily due to transport from offsite and emissions from local and regional wildfires. Atmospheric TP concentrations ranged from 11 to 75 ng m^?3 (mean = 37 ± 16 ng m^?3), and were typically dominated by IP. Phosphorus was concentrated in the coarse (>1 μm diameter) particle fraction and was particularly enriched in the 1.0–3.2 μm size range, which accounted for 30–60% of the atmospheric TP load. Wildfire emissions varied widely in P content, and may be related to fire intensity. The estimated dry depositional flux of TP for each daily sampling period ranged between 7 and 118 μg m^?2 d^?1, with a mean value of 40 ± 27 μg m^?2 d^?1. Relative rates of dry deposition of N and P in the Sierra Nevada are consistent with increasing incidence of N limitation of phytoplankton growth and previously observed long-term eutrophication of lakes.     

Atmospheric deposition of organochlorines (PCBs and pesticides) in northern France

Bulk deposition measurements were made in northern France for a number of organochlorines (PCBs, HCB, pp'DDE, alpha-HCH and gamma-HCH) over a 1-y period, at urban, semi-rural, rural and forest sites located in accordance with prevailing wind direction. The west-east rise of PCB bulk deposition (average annual values as sigma 7) ranged from 12.2 to 46.8 ng l(-1) and showed the anthropogenic influence arising from towns, industries, storage areas and landfills over continental areas. The values were maximal at the urban site 3, Paris (122 ng l(-1)) and were still high at the eastern site 6, Abreschviller near landfills (62 ng l(-1)). Also, the highest annual deposits were found at sites 3 and 6 (Paris and Abreschviller), 38.6 and 47.3 microgm-2, respectively, i.e. 3.6 and 4 times higher than the western site value: Pleumeur. A temporal trend was observed, at the urban site where a rise occurred (up to 441 ng l(-1)) in March and April. PCB distribution according to the chlorination degree displayed high proportions of 3 Cl and 4 Cl congeners, particularly in the forest area. Annual gamma-hexachlorocyclohexane (gamma-HCH) concentration values at sites 1 (Ouessant) and 2 (Pleumeur) were close to the background noise (1.7 ng l(-1)). At the agricultural (4) and the urban (3) sites, values were maximal (19.2 and 15.9 ng l(-1)) with peaks in spring and autumn. At Pleumeur, without any local input, negative correlations were found between PCB/temperature (r = -0.503, p < 0.05), HCB/temperature ( r = -0.549, p < 0.01) and gamma-HCH/temperature ( r = -0.675, p < 0.01). A clear influence of south-west winds upon the magnitude of PCB fluxes throughout the sites was noticed. Whereas there was no global decrease of PCB contamination since 1986, the general trend of gamma-HCH total deposits was a 10-time fall, as a result of the restricting legislation in use.     

Atmospheric deposition of organochlorine pesticides by precipitation in a coastal area

Wet deposition fluxes of organochlorine pesticides (OCPs) were determined for rain samples collected in a coastal area of Turkey. Seventeen precipitation samples were collected over a 1-year period from 2008 to 2009. Rainwater was accumulated at the beginning of rain events using real time monitoring. Atmospheric concentrations were also measured in parallel with deposition samples. Both atmospheric concentrations and deposition fluxes were determined as particle and gas phases. The particle phase and dissolved phase deposition fluxes were 794.26?±?756.70 ngm^?2 day^?1 and 800.77?±?672.63 ngm^?2 day^?1, respectively. The washout ratios for OCP compounds were calculated separately for the particle and dissolved phases using the atmospheric concentrations and rain concentrations. The minimum washout ratio for the particle phase was 2339.47 for Endrin aldehyde, whereas the maximum washout ratio was 497593.34 for Methoxychlor. The maximum washout ratio for the dissolved phase was 247523.89 for Endosulfan beta, whereas the minimum washout ratio was 10169.69 for p,p′-DDT. The dry deposition velocities ranged from 0.01 to 1.67 cms^?1. The partitioning of wet deposition between the particle and dissolved phases was 50 % in terms of total OCP deposition.     

Atmospheric deposition and canopy exchange processes in alpine forest ecosystems (northern Italy)

Throughfall and bulk precipitation chemistry were studied for five years (June 1994–May 1999) at two high elevation forest sites (Val Gerola and Val Masino) which were known to differ in terms of tree health, as assessed by live crown condition. The ion concentration of bulk precipitation samples did not differ significantly between sites, except for Mg²⁺, while the throughfall concentrations differed in the measured values of H⁺, N-NO₃⁻, Cl⁻, Na⁺, K⁺, DOC and weak organic acids. The results of the application of the canopy exchange model indicated a higher contribution from the dry deposition of N-NO₃⁻, N-NH₄⁺ and H⁺ at Val Gerola, where the damage symptoms were more evident. In addition, the canopy leaching of Ca²⁺, K⁺ and weak organic acids were 47%, 21% and 27% higher at Val Gerola than at Val Masino. Annual SO₄²⁻ deposition fluxes (21.3 kg ha⁻¹ yr⁻¹ at Val Masino and 23.6 kg ha⁻¹ yr⁻¹ at Val Gerola) were similar to those reported for moderately polluted European and U.S. sites. Annual N loads were 13.6 and 13.1 kg ha⁻¹ yr⁻¹ in the bulk input, and 15.0 and 18.0 kg ha⁻¹ yr⁻¹ in throughfall inputs, at Val Masino and Val Gerola, respectively. The contribution of the organic fraction to the total N atmospheric deposition load is significant, constituting 17% of the bulk flux and 40% of the throughfall flux. Measured nitrogen loads exceed the critical nutrient loads by several kg N ha⁻¹ at both stations. In particular the nitrogen throughfall load at Val Gerola was about 3 times higher than the critical values.     

太湖北部藻类生长旺盛期大气氮、磷沉降特征

按照<大气降水样品的采集与保存标准>(GB/T 153580.2-92)收集大气N、P沉降物和降水量,并测定了2007年5～11月太湖北部梅梁湾藻类生长旺盛期间大气TN、TP的干、湿沉降通量.结果表明,太湖北部梅粱湾大气TN月湿沉降通量和月总沉降通量的变化趋势均呈双峰型特征,与当地梅雨和台风侵袭时的降水量呈明显正相关,并且TN的月湿沉降通量高于月干沉降适量,但降水量最少的11月则相反;大气TP月干、月湿沉降通量呈相互交替的变化趋势.大气N沉降物中主要以溶解性氮(TDN)为主,平均约占91.4%;而P沉降物中溶解性磷(TDP)占的比例相对较低,平均约为65.1%.经测定,2007年太湖北部梅梁湾TN和TP的年沉降通量分别为2 976、84.0 kg/km2,相比2002年7月至2003年6月分别下降34.4%和78.7%;2007年太湖北部梅粱湾大气TN的年沉降量高达6 958 t,远超过太湖湖泊生态系统理论允许的TN年沉降量.     

Dry deposition fluxes and deposition velocities of PAHs at an urban site in Turkey

Even though dry deposition and air–water exchange of semivolatile organic compounds (SOCs) are important for surfaces in and around the urban areas, there is still no generally accepted direct measurement technique for dry deposition. In this study, a modified water surface sampler (WSS) configuration, including a filter holder and an XAD-2 resin column, was employed to investigate the polycyclic aromatic hydrocarbon (PAH) dry deposition in an urban area. The measured total (particle+dissolved) PAH fluxes to the WSS averaged to be 34 960±16 540 ng m⁻² d⁻¹. Average particulate PAH flux, determined by analyzing the filter in the WSS, was about 8% of the total PAH flux. Temporal flux variations indicated that colder months (October–April) had the highest PAH fluxes. This increase could be attributed to the residential heating as well as meteorological effects including lower mixing height. A high volume air sampler was concurrently employed to collect ambient air concentrations. The average total (gas+particle) atmospheric PAH concentration (456±524 ng m⁻³) was within the range of previously measured values at different urban locations. PAH concentrations in urban areas are more than two orders of magnitude higher than those measured in pristine areas and this result may indicate that urban areas have major source sectors and greater deposition rates are expected near to these areas. The average contribution of particle phase was about 10% in total concentration. Simultaneous particulate phase dry deposition and ambient air samples were collected in this study. Then, particulate phase apparent dry deposition velocities were calculated using the fluxes and concentrations for each PAH compound and they ranged from 0.1 to 1.2 cm s⁻¹. These values are in good agreement with previously reported values.     

Ozone dynamics and deposition processes at a deforested site in the Amazon basin

The goal of this study is to investigate the impact of deforestation on ozone dynamics and deposition in the Brazilian Amazon basin. This goal is accomplished through i) analyses of ozone levels and deposition rates at a deforested site during the rainy season; and ii) comparisons of these data with similar information derived at a forest. At the pasture site maximum ozone mixing ratios reach 20 parts per billion on a volume basis (ppbv) but about 6 ppbv prevail over the forest. Maximum ozone deposition velocities for pastures can reach 0.7 cm s-1, which is about threefold lower than values derived for forests. Combining ozone abundance and deposition velocities, pasture maximum ozone fluxes reach approximately 0.2 microgram (ozone) m-2 s-1. This flux represents approximately 70% of the deposition rates measured over the forest. Hence, this study suggests that conversion of rainforests to pastures could lead to a net reduction (30%) in the ozone sink in the Amazon.     

Height growth of northern red oak in relation to site and atmospheric deposition in Pennsylvania

A forest tree growth-response to atmospheric deposition is expected to arise indirectly through soil chemical changes and would probably be observable only in the long term. We examined this hypothesis by evaluating the relationship between periodic height growth of mature northern red oak (Quercus rubra L.) trees and soil, physiography and atmospheric sulfate deposition along a 170-km west-to-east gradient of decreasing sulfate deposition in north central Pennsylvania, USA. Height increments for three common 20-year periods beginning in 1929, 1949 and 1969 were estimated from exponential-monomolecular growth functions fitted to stem analysis data for each of 45 trees in 13 ecologically analogous stands along the deposition gradient. Canonical analysis was used to identify a statistically manageable subset of the original 48 independent soil, site and tree (age, crown width) variables strongly associated with height growth. Predictive models relating total (60-year) and the three 20-year height increments to the reduced variable set plus estimated average sulfate and nitrate deposition were derived by best subsets multiple regression. An inherent spatial gradient of decreasing height growth from western to eastern sites was apparent in even the earliest (1929-1948) increment. This inferred non-deposition-related spatial growth trend was accounted for in the 1949-1968 growth increment by introduction of the earliest (1929-1948) growth increment as a significant covariate in the regression model. The inherent growth largely disappeared by the 1969-1988 period as a probable consequence of converging growth rates reported to occur in oaks after age 60 years regardless of site quality. The 1969-1988 growth increment was not as strongly correlated with site factors as was growth in preceding periods, nor was early growth or sulfate deposition significantly related to this height increment. Growth effects from sulfate deposition, if any, would most likely occur within the recent (1969-1988) increment coincident with the period of naturally decreasing growth rate, when site differences and possibly environmental factors would have less influence on growth. Our results give no indication that wet sulfate inputs are affecting northern red oak height growth across the atmospheric deposition gradient.     

Atmospheric deposition of phthalate esters in a subtropical city

In Chinese cities, air pollution has become a serious and aggravating environmental problem undermining the sustainability of urban ecosystems and the quality of urban life. Bulk atmospheric deposition samples were collected two-weekly, from February 2007 to January 2008, at three representative areas, one suburban and two urbanized, in the subtropical city, Guangzhou, China, to assess the deposition fluxes and seasonal variations of phthalate esters (PAEs). Sixteen PAE congeners in bulk deposition samples were measured and the depositional fluxes of ∑₁₆PAEs ranged from 3.41 to 190 μg m^?2 day^?1, and were highly affected by local anthropogenic activities. The significant relationship between PAEs and particulate depositional fluxes (correlation coefficient R² = 0.72, P < 0.001) showed PAEs are associated primarily with particles. Temporal flux variations of PAEs were influenced by seasonal changes in meteorological parameters, and the deposition fluxes of PAEs were obviously higher in wet season than in dry season. Diisobutyl phthalate (DiBP), Di-n-butyl phthalate (DnBP), and Di(2-ethylhexyl) phthalate (DEHP) dominated the PAE pattern in bulk depositions, which is consistent with a high consumption of the plasticizer market in China. PAE profiles in bulk deposition showed similarities exhibited in both time and space, and a weak increase of high molecular weight PAE (HMW PAE) contribution in the wet season compared to those in the dry season. Average atmospheric deposition fluxes of PAEs in the present study were significantly higher than those from other studies, reflecting strong anthropogenic inputs as a consequence of rapid industrial and urban development in the region.     

Atmospheric pollution by PAHs, PCDD/Fs and PCBs simultaneously collected at a regional background site in central Italy and at an urban site in Rome

Concentrations of PAHs and PCDD/Fs were measured throughout one year, and PCBs during the second semester, at a rural site in a natural park representative of background pollution in central Italy; results were compared with simultaneous measurements performed at an urban site in Rome 60km away. Twenty-four daily samples were collected at each site by a high-volume PM(10) sampler from February 2000 to January 2001. After ultrasonic extraction and clean-up by TLC, samples were analysed by GC-MS. Mean concentrations of benzo[a]pyrene (BaP, as a marker of carcinogenic PAHs), summation operatorPCDD/Fs and summation operator64 PCBs in Rome were, respectively: 1.1ngm(-3), 65fgWHO-TEQm(-3), 553pgm(-3). The background concentrations were, respectively: 0.016ngm(-3), 3fgWHO-TEQm(-3), and 94pgm(-3). Hence, BaP, and the other PAHs, showed the highest urban-background gradient (two orders of magnitude) and PCBs the lowest. The background pollution levels of BaP and PCDD/Fs were in agreement with the few available background/remote measurements in Europe. In Rome PAHs and PCBs, but not PCDD/Fs, were clearly seasonal; the PCDD/F TEQ was moderately correlated with BaP (P<0.001). At the background site, the seasonality of PAHs was less marked, while it could not be assessed for PCDD/Fs and PCBs. The PCB TEQ accounted for 4% and 15% of total (PCDD/Fs+PCBs) TEQ at the urban and background site, respectively. Mean PM(10) concentration was 54microgm(-3) in Rome and 15microgm(-3) at the background site.     

Atmospheric phase distribution of oxidized and reduced nitrogen at a forest ecosystem research site

Atmospheric concentrations of gaseous NH3 and HNO3 and of particulate NH4+ and NO3- were measured during various seasons at a forest ecosystem research site in the "Fichtelgebirge" mountains in Central Europe. Air masses arriving at this site were highly variable with respect to trace compound concentration levels and their concentration ratios. However, the distributions of NH4+ and NO3- within the aerosol particle size spectra exhibited some very consistent patterns, with the former dominating the fine particle concentrations, and the latter dominating the coarse particles range, respectively. Overall, the particulate phase (NH4+ + NO3-) dominated the atmospheric nitrogen budget (particulate and gas phase, NH4+ + NO3- + NH3 + HNO3) by more than 90% of the median total mixing ratio in winter, and by more than 60% in summer. The phase partitioning varied significantly between the winter and summer seasons, with higher relative importance of the gaseous species during summer, when air temperatures were higher and relative humidities lower as compared to the winter season. Reduced nitrogen dominated over oxidized nitrogen, indicating the prevailing influence of emissions from agricultural activity as compared to traffic emissions at this mountainous site. A model has been successfully applied in order to test the hypothesis of thermodynamic equilibrium between the particulate and gas phases.     

Elevational patterns of sulfur deposition at a site in the Catskill Mountains,New York

In this paper we report measurements of SO^2-₄ fluxes in throughfall and bulk deposition across an elevational transect from 800 to 1275 m on Slide Mountain in the Catskill Mountains of southeastern New York State. The net throughfall flux of SO^2-₄ (throughfall-bulk deposition), which we attribute to cloud and dry deposition, increased by roughly a factor of 13 across this elevational range. Part of the observed increase results from the year-round exposure of evergreen foliage at the high-elevation sites, compared to the lack of foliage in the dormant season in the deciduous canopies at low elevations. Comparison of the net throughfall flux with estimates of cloud deposition suggests that both cloud deposition and dry deposition increased with elevation. Dry deposition estimates from a nearby monitoring site fall within the measured range of net throughfall flux for SO^2-₄. The between-site variation in net throughfall flux was very high at the high-elevation sites, and less so at the lower sites, suggesting that studies of atmospheric deposition at high-elevations will be complicated by extreme spatial variability in deposition rates. Studies of atmospheric deposition in mountainous areas of the eastern U.S. have often emphasized cloud water deposition, but these results suggest that elevational increases in dry deposition may also be important.     

Particulate- and vapor-phase n-alkanes in the northern Wisconsin atmosphere

n-Alkanes were present in the northern Wisconsin atmosphere in both the particulate and vapor state. Partitioning was operationally defined by a high-volume sampling methodology which used a glass fiber filter to separate particles and vapor. Concentrations, distributions and vapor/particle partitioning were seasonally dependent. Total n-alkane (C₁₁-C₃₂) concentrations in the vapor phase ranged from 25 to 75 ng m⁻³. Vapor concentrations of n-alkanes within the range C₁₁-C₁₇ were greatest during winter. Total n-alkane (C₁₁-C₃₂) concentrations in the particulate phase varied from 5.1 to 35 ng m⁻³ while those of the odd-numbered n-alkanes within the range C₂₅-C₃₁ ranged from 3.1 to 31 ng m⁻³. Highest concentrations of these n-alkanes were observed during spring and early summer. The CPI (20–32) of particulate n-alkanes was highest during spring (13.0) and early fall (8.0). The highest total n-alkane concentration and CPI (20–32) occurred in spring during a period of pine pollen disposal. A high-boiling unresolved complex mixture (UCM) was prominent in particles collected during winter, while a low-boiling UCM was typical of vapor collected during summer.     

Atmospheric gas and particle measurements at a rural northeastern U.S. site

Ammonia, nitric acid, sulfur dioxide and particles in two size ranges were collected at a rural site in northeastern U.S. in January–March 1984. Ammonia was collected with an oxalic acid coated denuder, all other components were collected on filters. The concentrations of ammonia ranged between 0.0 and 0.5 ppbv, nitric acid: 0.1 and 2.3 ppbv and sulfur dioxide: 1 and 52 ppbv. Ammonium and sulfate in the fine particles were highly correlated, the regression line indicated that the most abundant compound was ammonium sulphate. The content of free hydronium ions in the fine particles was well below the ammonium content. No correlation between NH₃ and NH⁺₄, HNO₃ and NO₃ SO₃ and SO⁻²₄ could be observed.     

Characteristics and impacts of trace elements in atmospheric deposition at a high-elevation site,southern China

To investigate the regional background trace element (TE) level in atmospheric deposition (dry and wet), TEs (Fe, Al, V, Cr, Mn, Ni, Cu, Zn, As, Se, Mo, Cd, Ba, and Pb) in 52 rainwater samples and 73 total suspended particles (TSP) samples collected in Mt. Lushan, Southern China, were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). The results showed that TEs in wet and dry deposition of the target area were significantly elevated compared within and outside China and the volume weight mean pH of rainwater was 4.43. The relative contributions of wet and dry depositions of TEs vary significantly among elements. The wet deposition fluxes of V, As, Cr, Se, Zn, and Cd exceeded considerably their dry deposition fluxes while dry deposition dominated the removal of pollution elements such as Mo, Cu, Ni, Mn, and Al. The summed dry deposition flux was four times higher than the summed wet deposition flux. Prediction results based on a simple accumulation model found that the content of seven toxic elements (Cr, Ni, Cu, Zn, As, Cd, and Pb) in soils could increase rapidly due to the impact of annual atmospheric deposition, and the increasing amounts of them reached 0.063, 0.012, 0.026, 0.459, 0.076, 0.004, and 0.145 mg kg^?1, respectively. In addition, the annual increasing rates ranged from 0.05% (Cr and Ni) to 2.08% (Cd). It was also predicted that atmospheric deposition induced the accumulation of Cr and Cd in surface soils. Cd was the critical element with the greatest potential ecological risk among all the elements in atmospheric deposition.     

Atmospheric deposition to the edge of a spruce forest in Denmark

Atmospheric deposition was measured during 1 year at the forest edge of a Norway spruce stand in Denmark. Inside the forest the deposition of H(+), Ca(2+), Mg(2+), Na(+), K(+), Cl(-), NO(3)(-), NH(4)(2) and SO(4)(2-) with canopy throughfall varies with the distance from the forest edge. The deposition at the edge is found to be 10-20 times as high as deposition to an open field and 2-8 times as high as deposition inside the stand. An exponential decrease in deposition as a function of the distance from the forest edge is found. Increased deposition of K(+) and non-sea salt Mg(2+), which mainly originates as a result of leaching from the needles may be explained by a larger leaf area index (LAI) at the forest edge. Deposition of particulate substances, especially Na(+), Cl(-), Mg(2+) and to some extent SO(4)(2-), NH(4)(+) and NO(3)(-) is increased much more than the LAI, which we believe to be caused by changes in wind movements at the forest edge.     

Metals in bulk deposition and surface waters at two upland locations in northern England

Concentrations of aluminium and minor metals (Mn, Ni, Cu, Zn, Sr, Cd, Ba, Pb) were measured in precipitation and surface water at two upland locations (Upper Duddon Valley, UDV; Great Dun Fell, GDF) in northern England for 1 year commencing April 1998. At both locations, the loads in bulk precipitation were at the lower ends of ranges reported for other rural and remote sites, for the period 1985-1995. The deposited metals were mostly in the dissolved form, and their concentrations tended to be greatest when rainfall volumes were low. The concentrations of Cu, Zn and Pb in deposition were correlated (r2 > or = 0.40) with concentrations of non-marine sulphate. Three streams, ranging in mean pH from 5.07 to 7.07, and with mean concentrations of dissolved organic carbon (DOC) < 1 mg l(-1). were monitored at UDV, and two pools (mean pH 4.89 and 6.83, mean DOC 22 and 15 mg l(-1)) at GDF. Aluminium and the minor metals were mainly in the dissolved form, and in the following ranges (means of 49-51 samples. microg l(-1)): Al 36-530. Mn 4.4-36, Ni 0.26-2.8, Cu 0.25-1.7, Zn 2.1-30, Cd 0.03-0.16, Ba 1.9-140, Pb 0.10-4.5. Concentrations were generally higher at GDF. Differences in metal concentrations between the two locations and between waters at each location, and temporal variations in individual waters, can be explained qualitatively in terms of sorption to solid-phase soil organic matter and mineral surfaces, complexation and transport by DOC, and chemical weathering. The UDV catchments are sinks for Pb and sources of Al, Mn, Sr, Cd and Ba. The GDF catchments are sources of Al, Mn, Ni, Zn, Sr, Cd and Ba. Other metals measured at the two locations are approximately in balance. Comparison of metal:silicon ratios in the surface waters with values for silicate rocks indicates enrichment of Ni and Cu, and substantial enrichment of Zn, Cd and Pb. These enrichments, together with high metal deposition in the past, make it likely that concentrations of the metals in the surface waters are governed by release from catchment pools of atmospherically-deposited metal. The catchments appear to be responding on a time scale of decades, possibly centuries, to changes in metal deposition. For the more acid waters at UDV, the calculated free-ion concentrations of Al are similar to published LC50 values for acute toxicity towards fish. The free-ion concentrations of Ni, Cu, Zn and Cd in all the surface waters are one-to-four orders of magnitude lower than reported LC50 values for fish.     

Atmospheric mercury pollution at an urban site in central Taiwan: mercury emission sources at ground level

Total gaseous mercury (Hg) (TGM), gaseous oxidized Hg (GOM), and particulate-bound Hg (PBM) concentrations and dry depositions were measured at an urban site in central Taiwan. The concentrations were 6.14 ± 3.91 ng m⁻³, 332 ± 153, and 71.1 ± 46.1 pg m⁻³, respectively. These results demonstrate high Hg pollution at the ground level in Taiwan. A back trajectory plot shows the sources of the high TGM concentration were in the low atmosphere (<500 m) and approximately 50% of the air masses coming from upper troposphere (>500 m) were associated with low TGM concentrations. This finding implies that Hg is trapped in the low atmosphere and comes from local Hg emission sources. The conditional probability function (CPF) reveals that the plumes of high TGM concentrations come from the south and northwest of the site. The plume from the south comes from two municipal solid waste incinerators (MSWIs). However, no significant Hg point source is located to the northwest of the site; therefore, the plumes from the northwest are hypothesized to be related to the combustion of agricultural waste. Dry deposition fluxes of Hg measured at this site considerably exceeded those measured in North America. Overall, this area is regarded as a highly Hg contaminated area because of local Hg emission sources.