“New” DDT inputs to North America: Atmospheric deposition

Measurement of untransformed (p,p'- and o,p'-) DDT in rain, snow, and peat indicates that input of “new” DDT continues over a large portion of eastern North America. Peat cores obtained from ombrotrophic bogs indicate that current atmospherically derived fluxes are about 10–20% of those which occurred during peak DDT usage (～1960). Since DDT has been banned in North America and considering the magnitude of present fluxes, these residues must result from atmospheric transboundary transport. It is suggested that “new” DDT is being transported from neighboring areas where current use is substantial, Mexico and Central America.     

Air pollution detection by satellites: The transport and deposition of air pollutants over oceans

Research is continuing towards the possible detection of air pollution by remote sensing techniques, and satellite imagery has been examined to find evidence of cross-Atlantic transport of air pollution. Pollution masses from industrial areas are often carried out over the Atlantic Ocean by tropospheric winds. However, the pollution mass is generally steered by convergent flows and fronts of extra-tropical cyclones, and wet deposition and scavenging of air pollutants within clouds occur primarily over the cold ocean, especially during the occlusion stage of a cyclone. As a result, the oceanic area from Cape Hatteras to 1500 km ENE of Newfoundland (the SW sector of the Icelandic low area) is often a ‘dumping ground’ (sink region) for air pollution from N America.However, a dust cloud generated by a volcanic eruption and a smoke plume from large-forest fires in western N America have been observed near the W coast of Europe. Saharan dust carried to N America by trade winds have been identified on satellite imagery. The massive smoke generation by large forest fires in Siberia is also identified in the present study. The results of research on forest fire smoke are currently being used by scientists studying the atmospheric effects of a large-scale nuclear war. It is suggested that the area between the S of Japan and the SW section of the Aleutian low is another principal sink of air pollutants and dust originating from NE Asia.     

Atmospheric deposition inputs and effects on lichen chemistry and indicator species in the Columbia River Gorge, USA

Topographic and meteorological conditions make the Columbia River Gorge (CRG) an 'exhaust pipe' for air pollutants generated by the Portland-Vancouver metropolis and Columbia Basin. We sampled fog, bulk precipitation, throughfall, airborne particulates, lichen thalli, and nitrophytic lichen distribution. Throughfall N and S deposition were high, 11.5-25.4 and 3.4-6.7 kg ha(-1) over 4.5 months at all 9 and 4/9 sites, respectively. Deposition and lichen thallus N were highest at eastern- and western-most sites, implicating both agricultural and urban sources. Fog and precipitation pH were frequently as low as 3.7-5.0. Peak NO(x), NH(3), and SO(2) concentrations in the eastern CRG were low, suggesting enhanced N and S inputs were largely from particulate deposition. Lichens indicating nitrogen-enriched environments were abundant and lichen N and S concentrations were 2x higher in the CRG than surrounding national forests. The atmospheric deposition levels detected likely threaten Gorge ecosystems and cultural resources.     

Levels of persistent organic pollutants in air in China and over the Yellow Sea

The occurrence of persistent toxic substances (PTS) in China and possibly their regional transport in the Yellow and East China Seas region was studied. Organochlorines in atmospheric gas-phase and particulate matter were collected by high-volume sampling (filters and polyurethane foams) during 2 weeks in June 2003 (dry season) simultaneously at a Yellow Sea coastal site in an urban area, Qingdao, China, and a rural island site, Gosan, Jeju Island, Korea. Using GC methods, the samples were analysed for 9 persistent organic pollutants (POPs) regulated under the global POP convention, namely aldrin, chlordane (cis- and trans-isomers CC and TC), DDT and metabolites (o,p′-DDT, p,p′-DDD, and p,p′-DDE), dieldrin, endrin, heptachlor, hexachlorobenzene (HCB), mirex and PCB (congeners number 28, 52, 101, 153 and 180), and for hexachlorocyclohexane (α-, β- and γ-isomers), a PTS and now considered for regulation under the convention, too. At the coastal site additionally o,p′-DDE and -DDD, β-endosulfan, isodrin, heptachlorepoxide and δ-HCH, and at the island site additionally p,p′-DDT and 12 additional PCB congeners were analysed. 9 samples were collected at the coastal and 15 (for PCBs 5) at the island site. Long-range advection pathways were determined based on analysed back-trajectory calculations.The mean concentrations of DDT and its metabolites, HCB, HCH, and PCB at the coast were in the 100–1000 pg m⁻³ range. Higher concentrations prevailed during nighttime. The levels were in general lower at the island site, but not for DDT. Local sources are likely. PCBs were even 2 orders of magnitude lower, suggesting that PCBs are not subject to regional transport but elevated concentrations in air are limited to the source areas. Organochlorine pesticide levels on the other hand were seemingly determined by regional transport over Mainland China rather than by emissions in the coastal area. The currently used pesticides mirex and chlordane were found at elevated levels, i.e. 79 (6.6–255) and 36 (<6–71) pg m⁻³, respectively, at the coast but not over the island. The POPs pesticides aldrin, dieldrin and endrin, never registered in China, were mostly found at <10 pg m⁻³ except for endrin at the coastal site (up to 400 pg m⁻³) and aldrin at the island site (up to 50 pg m⁻³).     

Sediment distribution on the continental shelf in relation to stream inputs and contamination: hydrodynamic,chemical, mineralogical,and sedimentological characteristics (Ligurian Sea,Italy)

River estuaries, continental shelf, and sediment contamination are closely linked from the point of view of sediment transport and diffusion that is governed by different factors such as sea waves and currents, river flows and floods, and sediment characteristics. Taking these factors into consideration, we have examined marine environmental and marine bottom sediments off the mouth of a stream to highlight the main ways of sediment and contaminant transport and diffusion on the continental shelf. For this purpose, we followed a multidisciplinary approach, studying circulation of water masses, hydrological characteristics of water column, distribution and main characteristics of sediment grain size, sediment mineralogical composition, and metal concentrations of bottom sediments. Our results allowed identifying the presence of preferential ways of sediment deposition and areas of sediment spread for the Entella Stream, as well as the origin of some metals.

     

Atmospheric nitrogen inputs to the Delaware Inland Bays: the role of ammonia

A previous assessment of nitrogen loading to the Delaware Inland Bays indicates that atmospheric deposition provides 15-25% of the total, annual N input to these estuaries. A large and increasing fraction of the atmospheric wet flux is NH(4)(+), which for most aquatic organisms represents the most readily assimilated form of this nutrient. Particularly noteworthy is a 60% increase in the precipitation NH(4)(+) concentration at Lewes, DE over the past 20 years, which parallels the increase in poultry production on the Delmarva Peninsula over this period (currently standing at nearly 585 million birds annually). To further examine the relationship between local NH(3) emissions and deposition, biweekly-integrated gaseous NH(3) concentrations were determined using Ogawa passive samplers deployed at 13 sampling sites throughout the Inland Bays watershed over a one-year period. Annual mean concentrations at the 13 sites ranged from <0.5 microg NH(3)m(-3) to >6 microg NH(3)m(-3), with a mean of 1.6+/-1.0 microg NH(3)m(-3). At most sites, highest NH(3) concentrations were evident during spring and summer, when fertilizer application and poultry house ventilation rates are greatest, and seasonally elevated temperatures induce increased rates of microbial activity and volatilization from soils and animal wastes. The observed north-to-south concentration gradient across the watershed is consistent with the spatial distribution of poultry houses, as revealed by a GIS analysis of aerial photographs. Based on the average measured NH(3) concentration and published NH(3) deposition rates to water surfaces (5-8 mm s(-1)), the direct atmospheric deposition of gaseous NH(3) to the Inland Bays is 3.0-4.8 kg ha(-1)yr(-1). This input, not accounted for in previous assessments of atmospheric loading to the Inland Bays, would effectively double the estimated direct dry deposition rate, and is on par with the NO(3)(-) and NH(4)(+) wet fluxes. A second component of this study examined spatial differences in NO(3)(-) and NH(4)(+) wet deposition within the Inland Bays watershed. In a pilot study, precipitation composition at the Lewes NADP-AIRMoN site (DE 02) was compared with that at a satellite site established at Riverdale on the Indian River Estuary, approximately 21 km southwest. While the volume-weighted mean precipitation NO(3)(-) concentrations did not differ significantly between sites, the NH(4)(+) concentration observed at Riverdale (26.3 micromoles L(-1)) was 73% greater than at Lewes (15.2 micromoles L(-1)). More recently, a NADP site was established at Trap Pond, DE (DE 99), which was intentionally located within the region of intense poultry production. A comparison of the initial two years (6/2001-5/2003) of precipitation chemistry data from Trap Pond with other nearby NADP-AIRMoN sites (Lewes and Smith Island) reveals fairly homogeneous NO(3)(-) wet deposition, but significant spatial differences ( approximately 60%) in the NH(4)(+) wet flux. Overall, these results suggest that local emissions and below-cloud scavenging provide a significant contribution to regional atmospheric N deposition.     

Atmospheric methane: Trends over the last 10,000 years

We have constructed a record of atmospheric methane (CH₄) over the last 10,000 γ which shows that CH₄ has increased to more than double the natural levels of a century ago. This record is based on systematic global measurements taken since 1975, the occasional measurements taken by various scientists between 1962 and 1981, and the record of CH₄ in bubbles of air trapped in polar ice. Our observations and calculations show that the concentrations of CH₄ remained virtually unchanged over thousands of years until about a few hundred years ago. Until the beginning of the 18th century there is no evidence of significant trends. Between 1700 and 1900 CH₄ increased slowly at an average rate of about 1.5 ppbvy⁻¹, between 1900 and 1925 CH₄ increased by about 2.2 ppbvy⁻¹, between 1927 and 1956 by 6.4 ppby y⁻¹, between 1962 and 1973 by about 11 ppbvy⁻¹ and during the last decade it has increased at a rate of about 17 ppbvy⁻¹. We explain these rates of increase by a global mass balance model. In the model, the increase of emissions from sources affected by human activities is taken to be proportional to the population and the atmospheric lifetime of CH₄ is taken to be increasing if human activities are slowly depleting OH radicals that remove CH₄ from the atmosphere.     

Mercury chemistry in the MBL: Mediterranean case and sensitivity studies using the AMCOTS (Atmospheric Mercury Chemistry over the Sea) model

The atmospheric oxidation of mercury in the Mediterranean marine boundary layer (MBL) has been studied using the Atmospheric Mercury Chemistry over the Sea (AMCOTS) model. The model results have been compared to measured data obtained during an oceanographic research campaign in 2000, with more success than previous modelling attempts. In light of the often high concentrations of ozone present in the Mediterranean boundary layer, seasonal case studies using typical meteorological conditions and average ozone concentrations have been performed to identify the main oxidants of elemental mercury. The sensitivity of the modelled reactive gaseous mercury (RGM) concentrations to the Hg+O₃ rate constant has been assessed using the two most recent rate determinations. The results using the higher of the two literature values gives results inconsistent with measured values of RGM when the reaction between Hg and O₃ is assumed to give a gas phase product. This does not necessarily indicate that the rate constant is incorrect but possibly that other rate constants in the model are overestimated or indeed that there may be reduction reactions occurring in the atmosphere which have yet to be identified. Alternatively, when the reaction product of Hg and O₃ is assumed to be a solid and therefore not contribute to RGM the modelled and measured results are comparable. The deposition rates calculated by the model when compared with calculated and measured sea surface emission fluxes available in the literature indicate that dry deposition flux of RGM is comparable to the sea surface emission flux. The calculated lifetime of Hg⁰ in the Mediterranean MBL is between one and two weeks.     

Atmospheric nitrogen deposition: revisiting the question of the importance of the organic component

The organic component of atmospheric reactive nitrogen plays a role in biogeochemical cycles, climate and ecosystems. Although its deposition has long been known to be quantitatively significant, it is not routinely assessed in deposition studies and monitoring programmes. Excluding this fraction, typically 25-35%, introduces significant uncertainty in the determination of nitrogen deposition, with implications for the critical loads approach. The last decade of rainwater studies substantially expands the worldwide dataset, giving enough global coverage for specific hypotheses to be considered about the distribution, composition, sources and effects of organic-nitrogen deposition. This data collation and meta-analysis highlights knowledge gaps, suggesting where data-gathering efforts and process studies should be focused. New analytical techniques allow long-standing conjectures about the nature and sources of organic N to be investigated, with tantalising indications of the interplay between natural and anthropogenic sources, and between the nitrogen and carbon cycles.     

Atmospheric nitrogen deposition on the east coast of Spain: relevance of dry deposition in semi-arid Mediterranean regions

Bulk deposition composition and pine branch washing were measured from April 1999 to March 2000 on the east coast of Spain. The main objective was to characterise N deposition patterns with special emphasis on dry deposition. Bulk deposition in the region is dominated by neutralisation processes by Ca2+ and HCO3-, ClNa of marine origin and a high correlation between NO3- and SO4(2-). SO4(2-) concentrations show a decrease with respect to previous studies in the region in agreement with generalized sulfur emission decreases while the remaining ions, including NO3-, are higher due to their general increase as well as to the inclusion of dry deposition in bulk collectors in the present study. An enrichment in NO3- has been observed in dry deposition composition branch washing) with respect to bulk deposition, while an impoverishment has been observed in the case of NH4+. Annual bulk deposition varies between 7.22-3.1 and 3.5-1.8 Kg ha(-1) year(-1) for S- SO4(2-) and N- NO3-, respectively. N total deposition goes from 9.78 to 6.8 Kg ha(-1) year(-1) at most stations, with the lowest deposition at the control station and Alcoi. The relative dry deposition with respect to the total was over 40% at most stations, going up to 75% at the southern station. N-deposition is expected to be higher considering that N-NH4+ deposition has been underestimated in this study.     

Organic contaminant loads into the Western Mediterranean Sea: estimate of Ebro River inputs

Annual input estimates for several organic contaminants from the Ebro River into the Northwestern Mediterranean Sea were carried out on the basis of monthly sampling from November 2002 to October 2003. Some organochlorine compounds (DDT and its degradation products, DDD and DDE, PCBs (9 congeners), HCB and gamma-HCH) were selected due to their reported occurrence in the river. Furthermore, some polar pesticides used in the Ebro Delta were also determined (atrazine, simazine, diazinon, fenitrothion and molinate). Concentrations ranged from 0.4 to 19.5 ng l(-1) for the organochlorine compounds (sum of particulate and dissolved phases) and from not detected (ND) to 170 ng l(-1) for the more polar pesticides, which were only found in the dissolved phase. The sum of PCB congeners (mean 8.9 ng l(-1)) showed the highest concentrations among the organochlorine compounds and atrazine (mean 82 ng l(-1)) among the polar pesticides. Based on the contaminant concentrations and on hydrological data, contaminant discharges into the sea were estimated amounting in total to 167 and 1,258 kg year(-1) of organochlorine compounds and polar pesticides, respectively. Furthermore, it was observed that PCBs, DDTs and HCB inputs were basically influenced by spate periods due to an increase in suspended particulate matter associated to runoff and sediment resuspension. Whereas for more water soluble contaminants, such as the agrochemicals, their seasonal use had a higher incidence in contaminant fluxes. Bulk chemical parameters such as SPM, DOC, POC, %OC, %ON and C/N ratio provided additional information on the organic matter sources. This provides a better understanding of the temporal variability of the contaminant concentrations.     

Atmospheric nitrogen deposition in south-east Scotland: Quantification of the organic nitrogen fraction in wet,dry and bulk deposition

Water soluble organic nitrogen (WSON) compounds are ubiquitous in precipitation and in the planetary boundary layer, and therefore are a potential source of bioavailable reactive nitrogen. This paper examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and “dry + wet” deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N55°51′44″, W3°12′19″). Bulk deposition collectors are denoted in this paper as “standard rain gauges”, and they are the design used in the UK national network for monitoring precipitation composition. “Dry + wet” deposition collectors are flushing rain gauges and they are equipped with a rain detector (conductivity array), a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, dissolved organic nitrogen (DON) represented 23% of the total dissolved nitrogen (TDN) in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk rain gauges and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers.     

Atmospheric dispersal and deposition of radioactive material from Chernobyl

This paper reports on the results of studies undertaken in the wake of the fire at the Chernobyl nuclear power station. Published upper air charts and the findings of scientists engaged in monitoring the fallout are used to reconstruct the clouds' trajectories. The results reveal the role of the various features of weather systems in determining the dispersal, transportation and ultimate fallout of radioactive matter. Most importantly, the situation over Europe at the time of the fire was such as to disperse the radioactive clouds northwards to Scandinavia and later westwards to Britain; directions counter to the dominant westerlies of these latitudes. However, eastwards global dispersal took place rapidly in the weeks following the fire. The paper also emphasizes the importance of rainfall in explaining the geographical variation in the deposition of radioactive material.     

Analysis of observations relevant to long-range transport and deposition of pollutants

Observations of annual wet deposition of sulfur made during 1980 at 62 stations in northeastern America are interpreted using a statistical long-range transport model. This work is meant to demonstrate the role of an empirical model in the analysis of observations. Our analysis points to the following conclusions:

• 1.(1) The parameters that represent the conversion of SO₂ to SO₄ and the wet and dry removal of sulfur are insensitive to concentration levels,
• 2.(2) the variation of the wet deposition field is closely related to the distribution of sulfur emissions and
• 3.(3) observations demand efficient wet scavenging of SO₂.

     

Atmospheric transport and deposition of trace elements onto the Greenland Ice Sheet

Airborne particles of diameter > 0.4 μm reaching Dye 3, Greenland during April–May 1983 were highly variable in size and concentration from day to day. Five-day backward air mass trajectories suggest the importance of long-range transport from more northerly latitudes on days with high concentrations; particle sizes were larger on these days. Lower concentrations and smaller particle sizes were associated with transport from the south. It is inferred that Dye 3 may receive material emitted from Eurasian sources and transported over the Pole, similar to inferences for more northern Arctic sites.Elemental analysis of individual particles showed an abundance of crustal material, with many particles also containing sulfur. Bulk chemical analyses of airborne particles and fresh snow, collected during three snowstorms where ice nucleation dominated, provided data which were used to estimate mass-basis scavenging ratios. Average scavenging ratios were in the range ~1000–2000 for the crustal elements Al, Fe, K, Mg, Mn, and Na. Similar values were observed for Cd, Cu and NO₃⁻. The corresponding ratios for Pb and SO₄²⁻ averaged less than 200. These ratios were used with precipitation rate data to estimate wet deposition velocities in the order of ~2 cm s⁻¹ for the first nine species, and ~0.2 cm s⁻¹ for Pb and SO₄²⁻. Comparing fresh and older surface snow concentrations gave an average dry deposition velocity of roughly 0.2 cm s⁻¹ for the crustal elements, with the small fraction of large particles (~5–10 μm) dominating deposition; much smaller values were associated with the remaining species. When used with other data in the literature, the results of this study suggest that total deposition velocities of Pb and SO₄²⁻ may be as small as 0.05 cm s⁻¹ in relatively dry regions of the Arctic.     

Atmospheric concentrations, occurrence and deposition of persistent organic pollutants (POPs) in a Mediterranean coastal site (Etang de Thau, France)

Atmospheric concentrations and deposition fluxes of PCDD/F and PCB have been evaluated over a 1-year period in a Mediterranean coastal lagoon (Etang de Thau, France). Indicative PBDE air concentrations in the hot season are also reported in this work. ∑2,3,7,8-PCDD/Fs and ∑18PCBs (gas + particulate) air concentrations ranged from 67 to 1700 fg m⁻³ and from 13 to 95 pg m⁻³, respectively whereas ∑8PBDEs (gas + particulate) summer time levels varied from 158 to 230 pg m⁻³. The PCDD/F and PCB atmospheric occurrence over Thau lagoon and subsequent inputs to the surface waters are determined by an assemble of factors, being the seasonality of atmospheric concentration, the air mass origin and meteorological conditions important drivers. Total (wet + dry) ∑2,3,7,8-PCDD/Fs and ∑18PCBs deposition fluxes to Thau Lagoon waters are 117 and 715 pg m⁻² d⁻¹, respectively.     

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.     

Atmospheric deposition of fluoride in the lower Tamar Valley,Tasmania

Soluble fluoride (F⁻), measured using an ion-selective electrode, was monitored during 1982–1983 in monthly bulk (wet and dry) atmospheric deposition samples collected at 17 locations in the lower Tamar Valley, Tasmania, where an aluminium (Al) smelter is located. Glass samplers (funnel-bottle type) were used, with duplications by plastic samplers at five locations later. The spatial and temporal variations in F⁻ deposition in relation to wind flow and rainfall are discussed, and its impact on the environment is highlighted. The mean deposition rates of F⁻, as measured from September 1982 to August 1983, ranged from about 90 μg m⁻² day⁻¹ at the intended ‘background’ location to 12,568 μg m⁻²day⁻¹ at a location about 1 km east-southeast from the smelter. The depositional fluxes of F⁻ and insoluble Al (another elemental tracer of the smelter) are significantly correlated (P < 0.001). They were much higher within 3 km of the smelter, where vegetation damage by fluoride contamination was most evident. However, air emissions from the smelter could travel at least 10 km up the valley. Wet deposition was the predominant removal process for F⁻ during autumn and winter, while dry deposition appeared to be more significant in summer. The plastic samplers collected about 8 and 17% more F⁻ and Al, respectively, but with higher standard deviations. Thus the variations observed could be largely due to sampling fluctuations.     

珠江口大气氮磷干湿沉降通量及其污染特征

为准确核定入海污染负荷和系统实施入海污染物总量控制,观测了珠江口地区大气氮磷的干湿沉降通量,并分析了其时空变异规律、化学组成特征以及主要的影响因素。结果显示,珠江口地区大气总氮和总磷的平均月沉降通量分别约为299.00、4.12kg/km2,其中湿沉降通量占总沉降通量的60%以上。干沉降和湿沉降通量均表现出明显的时空变异规律,前者的季节性变化主要受农业活动氮磷挥发的影响,而后者与年内降雨量分布以及季风作用下降雨云团来源的关系更为密切;沉降负荷的空间分布规律基本与不同区域受人类活动影响的特点相一致。由于不同污染来源和季风气候的影响,氮沉降化学组成的季节差异特征也较为明显,氨氮在秋冬季沉降中所占的比例明显高于春夏季,而有机氮则与之相反。