Bulk Collectors Research Articles

Chemical composition of precipitation at background level

Abstract Chemical composition of precipitation collected from a rural forest station near Bhubaneswar in the east coast of India during 2005–2007 was studied. The rainwater and dust-fall washings were collected through a wet-only collector and a bulk collector placed together and the second bulk collector located 500 m apart in the same locality. NH4+ and NO3− were observed to be the dominating cation and anion respectively. The volume weighted mean pH over three years was >5.5 indicating neutrality of collected samples. pH of

Comparison of methods for measuring atmospheric deposition of arsenic, cadmium, nickel and lead

A comprehensive field intercomparison at four different types of European sites (two rural, one urban and one industrial) comparing three different collectors (wet only, bulk and Bergerhoff samplers) was conducted in the framework of the European Committee for Standardization (CEN) to create an European standard for the deposition of the four elements As, Cd, Ni and Pb. The purpose was to determine whether the proposed methods lead to results within the uncertainty required by the EU's daughter directive (70%). The main conclusion is that a different sampling strategy is needed for rural and industrial sites. Thus, the conclusions on uncertainties and sample approach are presented separately for the different approaches. The wet only and bulk collector ("bulk bottle method") are comparable at wet rural sites where the total deposition arises mainly from precipitation, the expanded uncertainty when comparing these two types of sampler are below 45% for As, Cd and Pb, 67% for Ni. At industrial sites and possibly very dry rural and urban sites it is necessary to use Bergerhoff samplers or a "bulk bottle+funnel method". It is not possible to address the total deposition estimation with these methods, but they will give the lowest estimate of the total deposition. The expanded uncertainties when comparing the Bergerhoff and the bulk bottle+funnel methods are below 50% for As and Cd, and 63% for Pb. The uncertainty for Ni was not addressed since the bulk bottle+funnel method did not include a full digestion procedure which is necessary for sites with high loads of undissolved metals. The lowest estimate can however be calculated by comparing parallel Bergerhoff samplers where the expanded uncertainty for Ni was 24%. The reproducibility is comparable to the between sampler/method uncertainties. Sampling and sample preparation were proved to be the main factors in the uncertainty budget of deposition measurements.

Chemistry of Monsoon and Post-Monsoon Rains at a High Altitude Location, Sinhagad, India

Rainwater samples collected at Sinhagad on 65 rain occasions during monsoon season (June-September 2005) and on 23 rain occasions during post-monsoon season (October-November 2005) with standard rain collection instruments, i.e. wet-only (WO) and bulk collectors (BC), were considered for the present study. Sinhagad is a hill station on a mountaintop in the Western Ghats, located about 40 km southwest of Pune. The following ionic components were determined: H(superscript +), NH4(superscript +), Ca(superscript 2+) Mg(superscript 2+) K(superscript +) Na(superscript +) SO4(superscript 2-) NO3(superscript 2-) Cl(superscript -) and F(superscript -). The pH analyses showed that rainwater in both the seasons were alkaline. The major neutralizing component was associated with Ca(superscript 2+). In monsoon rains, the major anion was Cl(superscript -) and the major cation was Na(superscript +); whereas in post-monsoon the major anion was SO4(superscript 2-) and the major cation was Ca(superscript 2+). The concentrations of nss SO4(superscript 2-), NO3(superscript 2-) and NH4(superscript +) were found to be higher during post-monsoon than monsoon. Surprisingly high concentrations of Ca(superscript 2+) and SO4(superscript 2-) were found during the monsoon season. Since no large upwind sources of these compounds are expected, one is led to conclude that long-range transport may be involved, possibly even including African sources. Since the local sources didn't seem to influence the samples significantly, this rural site is useful for obtaining regionally representative precipitation data.

Measurement of dry deposition to bulk precipitation collectors using a novel flushing sampler

Bulk precipitation samplers, which are continuously open, also sample gases and particles deposited on the funnel surface. Wet-only samplers, which open only during precipitation, avoid this problem, but can be bulky (leading to disruption of air flow and droplet collection) and need electrical power. We describe here a simple battery-powered modification to a standard bulk sampler that allows the separate measurement of deposition to the funnel surface and wet deposition by washing the funnel surface when precipitation is detected. Comparison of this design with a standard bulk sampler over 3 months at a site in eastern Scotland showed that dry deposition to the funnel surface contributed around 20% of sulfate, 20-30% of nitrate and 20-40% of ammonium ions. There was also a significant loss of ammonium and nitrate in the modified sampler, presumably in the tubing, even though a biocide had been added to the sample bottles. This observation has implications for bulk samplers of similar design, with a sample bottle at ground level. Deposition of sea salts and calcium was greater to the flushing collectors than to the bulk collectors, implying that regular cleaning of funnel surfaces with 10% methanol solution subtly alters the capture efficiency for larger particles.

Comparison of wet-only and bulk deposition at Chiang Mai (Thailand) based on rainwater chemical composition

The chemical composition of 122 rainwater samples collected daily from bulk and wet-only collectors in a sub-urban area of Chiang Mai (Thailand) during August 2005–July 2006 has been analyzed and compared to assess usability of a cheaper and less complex bulk collector over a sophisticated wet-only collector. Statistical analysis was performed on log-transformed daily rain amount and depositions of major ions for each collector type. The analysis of variance (ANOVA) test revealed that the amount of rainfall collected from a rain gauge, bulk collector and wet-only collector showed no significant difference ( ∝=0.05). The volume weight mean electro-conductivity (EC) values of bulk and wet-only samples were 0.69 and 0.65 mS/m, respectively. The average pH of the samples from both types of collectors was 5.5. Scatter plots between log-transformed depositions of specific ions obtained from bulk and wet-only samples showed high correlation ( r>0.91). Means of log-transformed bulk deposition were 14% (Na + and K +), 13% (Mg 2+), 7% (Ca 2+), 4% (NO 3 −), 3% (SO 4 2− and Cl −) and 2% (NH 4 +) higher than that of wet-only deposition. However, multivariate analysis of variance (MANOVA) revealed that ion depositions obtained from bulk and wet-only collectors were not significantly different ( ∝=0.05). Therefore, it was concluded that a bulk collector can be used instead of a wet-only collector in a sub-urban area.

Integrated and sequential bulk and wet-only samplings of atmospheric precipitation in Londrina, South Brazil (1998–2002)

The present study investigated the chemical composition of bulk and wet atmospheric precipitation samples in Londrina city, in south Brazil. The samples were collected from April 1998 to November 2002. A total of 350 rainwater samples were collected on an event basis, integrated for 24 h, and analyzed for pH, conductivity, Na +, K +, NH 4 + , Cl - , NO 3 - , and SO 4 2 - . The concentration variability of rainwater was evaluated through sequential analysis of fractionated rainwater samples during three rainfall events. The comparison of bulk and wet-only sample results revealed that there are differences between collectors as to ionic composition and conductivity. Acid rain was characterized in 34% (bulk collector) and 35% (wet-only collector) of the samples. The correlation (>0.5) of NH 4 + with Cl - , NO 3 - and SO 4 2 - suggests that NH 4 + is the neutralizing constituent. Below cloud scavenging processes were observed due to the decline in the concentrations of all chemical species analyzed in the fractions along event. The total wet deposition rate of NH +, NO 3 - and SO 4 2 - were, respectively, 18.3, 17.1 and 13.4 meq m −2 yr −1. The composition of the rainwater collected appeared to be controlled by the following potential sources: crustal, agricultural activity (animal/fertilizer), and biomass and fossil fuel combustion. The precipitation chemistry in Londrina seems to be controlled by man-made emissions of S and N gases.

Studies of Atmospheric Nitrogen Deposition in a Mire of the German National Park Hochharz Mountains Using Two Different Methods

The purpose of this study was to determine the nitrogen (N) deposition in a mire of the German National Park Hochharz Mountains in regard to different input pathways of open area and forest stand deposition. High N deposition rates strongly affect the development and growth of mires in general. For determination of the open area N deposition two methods were applied: the bulk deposition method and the Integral Total Nitrogen Input (ITNI) method. This method is based on the 15N isotope dilution technique and was adapted at this study to evaluate its applicability for natural ecosystems as well as to compare with the traditional bulk method. The forest stand deposition included canopy throughfall, stemflow and fog was measured by means of bulk collectors. On the test site, bulk deposition measurements showed an input of 27 kg N ha− 1 yr− 1 in the open area and 47 kg N ha− 1 yr− 1 in the forest stand. The higher N input in the forest stand is caused by interception of fog by the canopy. N concentrations in fog were up to more than six times higher than in rain. The ITNI system yielded a total N deposition of 30 kg N ha− 1 yr− 1 on average in the open area. The small differences between the two simultaneously applied measuring techniques were caused by a minimum biomass development of the autochthonous plant Calamagrostis villosa in the ITNI system. With increasing biomass production the influence of plants on the atmospheric N input also increased. It can be concluded that the ITNI system is beneficial for the application in a natural ecosystem when using more robust and biomass producing plants. The measured atmospheric N deposition exceeds the critical load for nutrient poor mires and represents therefore a potential risk for the continuity of this ecosystem.

Chemical composition of rainwater and dustfall at Bhubaneswar in the east coast of India

Chemical composition of rainwater and dustfall was studied in two different stations of Bhubaneswar, located in the east coast of India. A wet-only and a bulk collector were placed at Regional Research Laboratory (RRL), a suburban area, during 1995–1997 and in the State Botanical Garden (SBG), a rural forest area, during 1997–1998. Of the rain events, 93% recorded alkaline pH (>5.6) at RRL while at SBG, 57% of the rain events were alkaline and the rest were acidic. Non-sea salt (nss) Ca 2+ and NH 3 were the primary neutralizing agents of rainwater acidity at both the locations. Low concentrations of alkaline constituents in the dustfall are an important finding in this study under Indian conditions. The Cl − /Na + ratio in rainwater at RRL was same as the seawater ratio (1.167) which indicates that sea salt contribution is local to RRL. It may be of indirect marine origin and resuspended locally. Rainwater samples were enriched with nss SO 4 2− , nss Ca 2+ and nss Mg 2+ at both the sites. Most of the nss SO 4 2− and NO 3 − were of anthropogenic origin, while a part of those might be soil derived.

Effect of storage on the isotopic composition of nitrate in bulk precipitation.

Stable isotopic analysis of atmospheric nitrate is increasingly employed to study nitrate sources and transformations in forested catchments. Large volumes have typically been required for delta18O and delta15N analysis of nitrate in precipitation due to relatively low nitrate concentrations. Having bulk collectors accumulate precipitation over an extended time period allows for collection of the required volume as well as reducing the total number of analyses needed to determine the isotopic composition of mean annual nitrate deposition. However, unfiltered precipitation left in collectors might be subject to microbial reactions that can alter the isotopic signature of nitrate in the sample. Precipitation obtained from the Turkey Lakes Watershed was incubated under conditions designed to mimic unfiltered storage in bulk precipitation collectors and monitored for changes in nitrate concentration, delta15N, and delta18O. Results of this experiment indicated that no detectable nitrate production or assimilation occurred in the samples during a two-week incubation period and that atmospheric nitrate isotopic ratios were preserved. The ability to collect unfiltered precipitation samples for an extended duration without alteration of nitrate isotope ratios is particularly useful at remote study sites where daily retrieval of samples may not be feasible.

The contribution of dry deposited ammonia and sulphur dioxide to the composition of precipitation from continuously open gauges

A series of experiments using bulk precipitation collectors of the type used in the UK precipitation chemistry network measured the amounts of NH 4 +, SO 4 2− and other ions that could be washed from funnels (diameter 15 cm) exposed to a wide range of NH 3 and SO 2 concentrations over periods from hours to days. In dry conditions, the average deposition flux of NH 3 was between 50 and 120 nmol NH 4 + funnel −1 d −1 (0.1–0.3 kg N ha −1 yr −1), and was independent of the concentration of NH 3. Dry deposition of NH 3 to wet funnels at small NH 3 concentrations was almost 5 times that to dry funnels under the same conditions (average 240 nmol funnel −1 d −1; 0.7 kg ha −1 yr −1), and increased with increasing NH 3 concentrations. The amount of NH 4 + ions remaining on the funnel surface was inversely proportional to the vapour pressure deficit during the experiment. This result was interpreted as a dependence on the duration of surface wetness, with greater deposition of NH 4 + when evaporation rates of surface water were small. The amount of SO 2 deposited on funnel surfaces was closely related to the amount of NH 3 deposited, in both wet and dry conditions, but was not strongly correlated with the SO 2 concentration. At low NH 3 and SO 2 concentrations the average deposition to dry funnels was 70 nmol SO 4 2− funnel −1 d −1 (0.5 kg ha −1 yr −1), and to wet funnels was approximately 2.5 times larger. The results are interpreted in terms of the balance between the rate of evaporation of surface water, and the rate of oxidation of SO 2, which leads to the ‘fixing’ of NH 4 + ions on the surface as involatile salts. It is predicted that dry deposition of NH 3 to funnel surfaces across the UK Secondary Network could account for as much as one-half of the measured bulk wet deposition at sites where wet deposition of NH 4–N is small. The amount of dry deposition depends on how long and how often funnel surfaces are wetted by rain or dew, and on the air concentrations of NH 3. These predictions are based on funnels being wetted only once per day. More frequent wetting would increase the contribution from dry deposition, and the consequent overestimate of wet deposition of NH 4–N across the UK by using data obtained from bulk collectors. To some extent this overestimate may be offset by microbial degradation and loss of NH 4–N in weekly bulk precipitation samples during collection and storage.

Airborne Nitrogen Input at Four Locations in the German State of Saxony-Anhalt - Measurements using the 15N-Based ITNI-System

The amount of atmospheric N deposition in Germany is actual rather uncertain. Estimates using standard methods indicate an N deposition of 30–35 kg N/ha × year. However, the results of long-term field experiments and newly by the ITNI (Integrated Total Nitrogen Input) system could prove a much higher N input of about 50–60 kg N/ha × year. The reason for this difference is that standard methods use wet-only or bulk collectors, which neglect gaseous and organic N deposition as well as direct N uptake by aerial plant parts. By contrast, the ITNI-system is able to measure the total atmospheric N input using the 15N isotope dilution method. The input of airborne N into a soil/plant system leads to a dilution of the abundance of a previously applied 15N tracer over a defined time period. The atmospheric N deposition can be calculated from this dilution. To estimate the actual N input in Central Germany, ITNI measurements were carried out from autumn 1998 to autumn 2000 at four locations in the German state of Saxony-Anhalt. Atmospheric N depositions between 45 and 75 kg N/ha × year were determined depending on the location. These results closely match to N balances of longterm field experiments. Furthermore, a relationship was found between N deposition and the plant species used as well as plant development.

Biological fluxes conversion and SXRF experiment with a new active biomonitoring tool for atmospheric metals and trace element deposition

A new active biomonitoring tool, keeping alive mosses for 2 months, had demonstrated the buffering action of the water presence on the biological activity of three moss species (chlorophyll fluorescence induction method on Pleurozium schreberi, Scleropodium purum, Eurhynchium praelongum). The two more resistant mosses were exposed on four different sites with parallel exposure of monthly bulk collectors during three successive periods of 2 months. The coarse and sedimentable particles of bulk collectors were separated into different size classes (>1 mm; 1000–200 μm; 200–40 μm; 40–20 μm). Dry depositions and mosses were analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for a stock (μg g −1)– fluxes (μg m −2 t −1) conversion. The “moss plate” allowed relative site (Ba, Cs, Sb, Sr, U) and species (Pb, Sb, Ti, V) comparisons. Two months were enough for a significant enrichment (Ba, Cd, Pb, Sb, Ti, U, V). Good explicative models were elaborated for Ba, Pb, Sb and Ti (r 2>70%) including categorical (sites, moss species) and quantitative variables (fluxes of particles size classes). Entire and intact shoots of Scleropodium purum were analysed by detected synchrotron radiation induced X-ray fluorescence (SXRF). The in vivo distribution of the multielemental short term enrichment along the moss stem was mainly localized in the plant older parts (Pb, Ti, Cl, Se).

Atmospheric deposition of phosphorus to the everglades: concepts, constraints, and published deposition rates for ecosystem management.

This paper summarizes concepts underlying the atmospheric input of phosphorus (P) to ecosystems, published rates of P deposition, measurement methods, and approaches to future monitoring and research. P conveyed through the atmosphere can be a significant nutrient source for some freshwater and marine ecosystems. Particle sources and sinks at the land-air interface produce variation in P deposition from the atmosphere across temporal and spatial scales. Natural plant canopies can affect deposition rates by changing the physical environment and surface area for particle deposition. Land-use patterns can alter P deposition rates by changing particle concentrations in the atmosphere. The vast majority of P in dry atmospheric deposition is conveyed by coarse (2.5 to 10 μm) and giant (10 to 100 μm) particles, and yet these size fractions represent a challenge for long-term atmospheric monitoring in the absence of accepted methods for routine sampling. Most information on P deposition is from bulk precipitation collectors and wet/dry bucket sampling, both with questionable precision and accuracy. Most published annual rates of P deposition are gross estimates derived from bulk precipitation sampling in locations around the globe and range from about 5 to well over 100 mg P m year, although most inland ecosystems receive between 20 and 80 mg P m year. Rates below 30 mg P m year are found in remote areas and near coastlines. Intermediate rates of 30 to 50 mg P m year are associated with forests or mixed land use, and rates of 50 to 100 mg P m year or more are often recorded from urban or agricultural settings. Comparison with other methods suggests that these bulk precipitation estimates provide crude boundaries around actual P deposition rates for various land uses. However, data screening cannot remove all positive bias caused by contamination of bucket or bulk collectors. As a consequence, continued sampling with these standard collectors in a region will not reduce the large uncertainty in rates derived from existing data. Calibrated surface accumulation methods hold promise as a primary means to estimate P flux in future monitoring. New methods for long-term P deposition monitoring will require an intercomparison of P flux estimates from surrogate surfaces, impactor sampling of particle concentrations combined with deposition models, and “throughfall” estimates for natural canopies. With better sampling methods and more long-term monitoring data, the importance of atmospheric P deposition in ecosystem dynamics and management can be better understood and predicted.

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 Ca 2+ and HCO 3 −, ClNa of marine origin and a high correlation between NO 3 − and SO 4 2−. SO 4 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 NO 3 −, 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 NO 3 − has been observed in dry deposition composition (branch washing) with respect to bulk deposition, while an impoverishment has been observed in the case of NH 4 +. Annual bulk deposition varies between 7.22–3.1 and 3.5–1.8 Kg ha −1 year −1 for S- SO 4 2− and N- NO 3 −, 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-NH 4 + deposition has been underestimated in this study.

Studies of Wet Deposition and Dustfall at Pune, India

Rain water and dustfall deposition samples were collected at Pune, an urban site (1992–98) and at Sinhagad, a rural site (1992–94). The samples were collected with wet-only and bulk collectors at Pune and with bulk collector at Sinhagad. The samples were analyzed for major ions, pH and conductivity. The study showed that the rain water at both places is alkaline (pH > 5.6). The average pH at Pune was 6.1. Neutralising components, indicated by Ca and non sea salt (nss) Mg have higher concentrations than the acidifying components SO4 and NO3. The wet deposition fluxes of all the ionic components were higher than the dustfall fluxes. Relative contribution from dustfall was largest for K, Ca, Mg and NO3. Dustfall was greater at Pune, compared to Sinhagad for all components and up to double for Ca.

A new approach to determine the total airborne N input into the soil/plant system using 15N isotope dilution (ITNI): results for agricultural areas in Central Germany.

The atmospheric deposition of nitrogen (N) in the environment is of great concern due to its impact on natural ecosystems including affecting vegetation, reducing biodiversity, increasing tree growth in forests, and the eutrophication of aquatic systems. Taking into account the average annual N emission into the atmosphere in Germany of about 2 million t N (ammonia/ammonium, NOx), and assuming homogeneous distribution throughout Germany, an average N deposition of 45 kg/ha x year can be calculated. Such high atmospheric N deposition could be confirmed by N balances from long-term field experiments in Central Germany (e.g., the Static Fertilization Experiment in Bad Lauchstädt). By contrast, estimates by standard methods indicate a deposition of only about 30 kg N/ha x year. This is because the standard methods are using wet-only or bulk collectors, which fail to take into account gaseous deposition and the direct uptake of atmospheric N by aerial plant parts. Therefore, a new system was developed using N isotope dilution methodology to measure the actual total atmospheric N input into a soil/plant system (Integrated Total Nitrogen Input, ITNI). A soil/plant system is labeled with [N]ammonium-[N]nitrate and the total input of airborne N is calculated from the dilution of this tracer by N from the atmosphere. An average annual deposition of 64 ± 11 kg/ha x year from 1994–2000 was measured with the ITNI system at the Bad Lauchst?dt research farm in the dry belt of Central Germany. Measurements in 1999/2000 at three other sites in Central Germany produced deposition rates of about 60 kg/ha x year. These data clearly show that the total atmospheric N deposition into the soil/plant system determined by the newly developed ITNI system significantly exceeds that obtained from standard wet-only and bulk collectors. The higher atmospheric N depositions found closely match those postulated from the N balances of long-term agricultural field experiments.

Atmospheric Deposition in a Rural Area in India - Net and Potential Acidity

Atmospheric deposition in India is generally described as alkaline and well buffered against an increase of acidifying components. Such conclusion has been based on measurements usually performed in urban or suburban areas. Our data on deposition in NE India (in the countryside N of Bhubaneswar) obtained with wet-only and bulk collectors show that: 1) the weighted mean concentrations (and wet deposition) of H+ and HCO3 − are almost equal, with dustfall contributing a negligible amount of HCO3 −, 2) the deposition of potential acidity, defined as the acidity that would give the same acidity contribution to the receiving surface as the actual deposition provided that all ammonium was converted to nitrate in the soil, could be as high as 40 mmol H+ m−2 a−1 corresponding to a pH of 4.3 in precipitation. The low buffer capacity against acidification and high potential acidity were discovered from long- term measurements in a vegetation covered rural area. Similar measurements in a nearby suburban area gave a much higher input of HCO3 − both in wet deposition and dustfall. Further increase of the emission of acidifying components in the region will increase the acid deposition.

Air emission and the acidity of rain water of Hanoi City

The aim of this paper is to summarize the results of a study about the chemical composition of rain water of Hanoi City-Vietnam and its surrounding provinces that are representative for the coastal, and interior of North Vietnam. Precipitation chemistry was carried out in the mentioned regions by using semi-automatic and bulk collectors. Parallel, the calculation of air emission are presented to prove the correlation between the most pollutant parameters of rainwater such as pH, SO 4 −2, NO 3 −1, NH 4, SO 2, NOx emitted into the air. Data collected from 1990–1997 show a rather uniform variation in rainwater composition. In the averaged monthly data, a winter maximum can be identified for all concerned ions. No significant pollution is measured at Hanoi City.

Transfers of Airborne PCDD/Fs to Bulk Deposition Collectors and Herbage

PCDD/F air concentrations, deposition fluxes, and grass concentrations/offtakes (pg m-2 day-1) were measured concurrently in Bolsover, Derbyshire, England over 1 year during 1992−1993. The data are used here to discuss spatial and temporal differences in atmospheric PCDD/F concentrations and how the airborne PCDD/Fs transferred to the bulk deposition collectors and grass. Three sample sites are discussed, namely, a regional background site (RBS), an urban site (US), and a site close to an industrial complex (IS) that has been a suspected source of selected PCDD/F homologs. Generally, the mixture of PCDD/F 2,3,7,8-substituted congeners and homologs was the same in the air, in the bulk deposition, and in the grass over a given sampling period and site. This suggests that PCDD/Fs of different levels of chlorination were transferring with similar efficiencies from the air to the collectors and grass, despite different gas−particle partitioning in the air. Deposition or transfer velocities for individual congeners/homologs to the bulk collectors throughout the whole study ranged between 0.034 and 0.82 cm s-1 at the sites, averaging 0.27 cm s-1 for PCDD/Fs at the RBS. An experiment conducted to assess potential volatilization of soil-borne PCDD/Fs from contaminated areas near the IS showed that all the compounds had a strong affinity for the soil and that volatilization is not likely to significantly contaminate herbage growing in the contaminated soil or the overlying atmosphere near this site. Herbage PCDD/Fs were therefore derived almost exclusively from the atmosphere in this study. The similarities in the PCDD/F mixture in air and grass suggest that the different PCDD/Fs are scavenged by the grass sward from the atmosphere with similar efficiencies; the implications of this are discussed.

The use of bulk collectors in monitoring wet deposition at high-altitude sites in winter

Concentrations of dissolved ions from samples collected by wet/dry collectors were compared to those collected by bulk collectors at Halfmoon Creek and Ned Wilson Lake in western Colorado to determine if bulk collectors can be used to monitor wet deposition chemistry in remote, high-altitude regions in winter. Hydrogen-ion concentration was significantly lower (p 0.05) at Halfmoon Creek. Wet deposition concentrations were predicated from bulk deposition concentrations through linear regression analysis. Results indicate that anions (chloride, nitrate and sulfate) can be predicted with a high degree of confidence. Lack of significant differences between seasonal (winter and summer) ratios of bulk to wet deposition concentrations indicates that at sites where operation of a wet/dry collector during the winter is not practical, wet deposition concentrations can be predicted from bulk collector samples through regression analysis of wet and bulk deposition data collected during the summer.