Bulk Precipitation Collectors Research Articles

Deposition of Sulfur, Nitrogen and Mercury in Two Typical Forest Ecosystems in Southern China

Bulk precipitation collectors and canopy throughfall collectors were applied to measure the deposition of sulfur, nitrogen, and mercury at two forest ecology stations, Qianyanzhou (QYZ) in Jiangxi Province and Huitong (HT) in Hunan Province, from December 2013 to November 2014. During the observation period, the volume weighted average concentrations of SO42--S, NO3--N, NH4+-N, and Hg at QYZ station were 1.89 mg·L-1, 0.957 mg·L-1, 0.401 mg·L-1, and 12.5 ng·L-1 in the bulk precipitation, respectively, and 2.39 mg·L-1, 1.18 mg·L-1, 0.897 mg·L-1, and 22.2 ng·L-1 in the throughfall, respectively. The concentrations of these components increased by different proportions for the bulk precipitation compared to the throughfall. At HT station, the average concentrations of SO42--S, NO3--N, NH4+-N, and Hg in the throughfall were 2.93 mg·L-1, 1.60 mg·L-1, 0.502 mg·L-1, and 22.0 ng·L-1, respectively. In addition, atmospheric deposition fluxes based on the throughfall were 3.56 g·(m2·a)-1 for sulfur, 3.02 g·(m2·a)-1 for nitrogen, and 30.6 μg·(m2·a)-1 for mercury at QYZ station, while the corresponding fluxes were 6.18 g·(m2·a)-1, 4.48 g·(m2·a)-1, and 37.3 μg·(m2·a)-1 at HT station. The deposition rates of all three elements were the highest in summer. The contribution of dry deposition to the total deposition of mercury was similar to that of wet deposition, while wet deposition contributed more to the total deposition of sulfur and nitrogen than did dry deposition. Unlike sulfur and nitrogen depositions, which were mainly derived from anthropogenic sources, mercury deposition might have a greater contribution from natural sources, especially at HT station.

POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) IN REMOTE BULK AND THROUGHFALL DEPOSITION: SEASONAL AND SPATIAL TRENDS

Polycyclic aromatic hydrocarbons (PAHs) were measured in atmospheric deposition in a Nature Reserve located in the North of Spain over a period of one year (June 2010 – May 2011). Total PAH deposition was evaluated monthly by combining samples collected over two-week periods, using 6 throughfall and 2 bulk precipitation collectors distributed over the study area. The latter consisted of glass funnels (with vertical sides) attached to Pyrex glass bottles. PAH determination was performed by liquid liquid extractions and analysis by high-performance liquid chromatography associated with fluorescence detection. Throughfall deposition revealed a loss under the canopy of 12% of the total atmospheric PAH deposition due to precipitation interception. Spatial variability between the 6 throughfall collectors reached a maximum of 25% during the wet season. Temporal trends showed significant variations of 27 to 54% throughout the year. PAH deposition increased during winter, due to higher emissions from domestic heating, less photoreactivity of the compounds and intense leaching of the atmosphere by wet deposition. Average daily fluxes were estimated for 6 quantified PAHs (PHE, ANT, PYR, B(b)F, B(k)F and B(a)P) at 182 ± 27 ng m-2 d-1, which agreed with studies previously carried out in other local rural areas. The major compounds were phenanthrene and pyrene, both markers of traffic emissions.

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.

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.

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.

Wet deposition at the sub-20 km scale in a rural upland area of England

A network of 10 bulk precipitation collectors was established in an upland region of northern England to examine the small-scale variability of precipitation composition in a rural area. Significant spatial variability was shown for non sea-salt sulphate, calcium and hydrogen ion concentrations. Although nitrate concentrations did not show significant variability, a coherent gradient across the study area was observed. The large variability of calcium ion concentration across the area was related to limestone quarrying, which is prevalent in the south of the study area. Calcareous wind-blown soil may have also made a minor contribution to the abundance of calcium in the rain-water samples. It is likely, however, that a large fraction of the calcium was dry deposited to the funnels of the collectors in the form of particles. The network was not designed to study orographic enhancement of deposition, but it is suggested that this mechanism, along with wind-drift of scavenged cap-cloud droplets, cannot explain the spatial variation in ion concentrations. It is speculated that the variability in non-sea-salt sulphate concentrations may also be partially explained by reaction of CaCO 3 particles deposited to the funnels of the collectors with SO 2. Critical load exceedances in terms of deposited acidity from non-sea-salt sulphate were calculated using different spatially resolved deposition data. A better estimate of deposition in the study area was achieved by combining rainfall concentration data from the national network with the 5 km rainfall field, than the current methodology used for mapping of U.K. deposition which utilises a 20 km rainfall field. However, 20 km is considered to be the minimum resolution at which a procedure for parameterising orographic enhancement can be incorporated. Deposition and critical load exceedances in 2005 were calculated using a long-range transport model and significant improvements in the protection of soils were predicted from the projected emissions reductions.

Spatial variability of urban precipitation chemistry and deposition: Statistical associations between constituents and potential removal processes of precursor species

The precipitation chemistry of Greater Manchester, a Metropolitan County in the northwest of England, has been examined for small scale spatial variability using a network of 18 bulk precipitation collectors. Significant spatial variability was found for concentrations of non-marine SO 4 2−, NO 3 −, NH 4 +, Ca 2+ and H + ions. The statistical associations between the data were investigated using correlation, partial correlation and principal components analyses. It was found that zero-order correlation coefficients were inadequate for the interpretation of the data and that the computation of first, and higher order partial correlation coefficients was necessary in order to explain the interrelationships between the data and their spatial variability. The statistical associations between the data suggest relationships between Ca 2+ and non-marine SO 4 2−, and NO 3 + in precipitation which are discussed in terms of their possible precursor species. Potential source effects were examined in conjunction with atmospheric removal processes. The dry deposition of SO 4 particles, rather than the dry deposition of SO 2, may explain the spatial variability of non-marine SO 4 2−. The erosion of CaSO 4 formed from the reaction of SO 2 with CaCO 3 on urban surfaces with subsequent resuspension is thought to be the basis of the relationship between Ca 2+ and non-marine SO 4 2− concentrations in precipitation. The wet and dry deposition of CaCO 3 particles from local sources may be partially responsible for the spatial variability of H +, and dry deposition and scavenging of NH 3, in conjunction with the predominant wind direction may explain the spatial variability of NO 3 − and NH 4 + ions. Ammonia is thought to originate from sources both outside the study area and within it.

Sulphur and seasalt deposition as reflected by throughfall and runoff chemistry in forested catchments

At forested catchments at Lake Gårdsjön on the Swedish west coast the deposition and runoff chemistry has been followed during the period 1979–1990 by throughfall and runoff measurements as well as by measurements of atmospheric concentrations. The 10-year means in throughfall and runoff are very similar for sulphur and the main seasalt ions sodium and chloride; for sulphur 26·1 and 27·6 kg ha −1 yr −1, for sodium 49 and 52 kg ha −1 yr −1 and for chloride 96 kg ha −1 yr −1 and 93 kg ha −1 yr −1, respectively. The actual flows are 100–200% higher than the wet deposition as collected in open bulk precipitation collectors indicating a very large input by dry deposition. One important question is to what extent the throughfall and runoff values can be used as measures of total deposition. We present results from studies at different experimental catchments illustrating the possibilities of using throughfall and runoff data as measures of atmospheric deposition of sulphur and seasalt.

A comparison of bulk and wet-only precipitation collectors at rural sites in the United Kingdom

Co-Located wet-only and bulk precipitation collectors have been used to measure precipitation amount and ionic composition at nine rural sites in the United Kingdom. The wet-only collector collects less rain, particularly at more exposed, windier sites. This is believed to arise primarily from aerodynamic blockage rather than from late opening of the collector at the onset of rain. In general, agreement between the two types of collector for ionic composition is good. However, at two sites which experience low rainfall and elevated concentrations of primary and secondary pollutants in easterly airflow, the bulk collector yields larger concentrations of non-marine sulphate. Measurements of particulate sulphate suggest that dry deposition of particles is sufficient to explain the observed differences. In contrast, larger ammonium concentrations are measured with the wet-only collector. The observations are consistent with loss of ammonium from the bulk collector, particularly at sites of low annual mean acidity. These differences are greater in summer than in winter suggesting a biological loss mechanism.

Inter-storm comparisons from the OSCAR high density network experiment

The high density network component of the Oxidation and Scavenging Characteristics of April Rains (OSCAR) experiment combined aircraft, surface and sequential precipitation chemistry measurements to characterize the physicochemical and dynamic features of four storms sampled during an April 1981 field investigation. A surface network of 47 precipitation sampling stations, covering a region roughly 110 km by 110 km, was established in the area surrounding Fort Wayne, Indiana. The network provided temporal and spatial resolution of rainfall chemistry via the use of specially designed automatic sequential bulk precipitation collectors, while aircraft and surface sampling provided measurements of the major aerosols and trace gases in the boundary-layer inflow region. Composite concentration and ion ratio profiles for the events were analyzed to investigate potential pollutant scavenging pathways. This analysis led to the following observations: 1. (i) dryfall deposition during pre-rainfall exposure periods influenced initial sampler stage chemistry; 2. (ii) relative precipitation acidity increased throughout the events; SO 4 2− and NO 3 − were the major contributors to this acidity; 3. (iii) evidence exists for the in-cloud oxidation of SO 2 during Events 3 and 4, while scavenging of HNO 3 and aerosol NO 3 − probably produced precipitation NO 3 −; 4. (iv) the non-frontal meteorology of Event 3 influenced the precipitation chemistry associated with this storm and led to distinct concentration profiles; 5. (v) an anomalous pattern of NH 4 + concentrations observed during Event 1 cannot be explained by known NH 4 + scavenging behavior or by non-scavenging related influences, such as local source contamination or NH 3 volatilization; 6. (vi) Event 4 is more suitable for analysis by one- and two-dimensional diagnostic wet removal models. Analysis of the other events is complicated by more complex meteorological behavior and, in some cases, a less complete chemistry data set. This paper enlarges on these observations with comparisons of the major meteorological and chemical characteristics of the four events.

Atmospheric input of nitrogen to a coastal fynbos ecosystem of the south-western Cape Province, South Africa

Results are presented of nitrogen input via bulk precipitation over a two-year period, to coastal fynbos vegetation occurring on soils of low nutrient status. The annual precipitation recorded during the study periods of 1980 – 81 and 1981 – 82 was 381 mm and 466 mm respectively which was below the 40-year mean of 577 mm recorded for the area. Total nitrogen input during 1980 – 81 was 1,99 kg N ha − 1 y − 1 . Of this 1,12 kg N ha − 1 y − 1 was inorganic nitrogen in the form of NO 3 -N and NH 4 -N. Inorganic N input occurred predominantly in the winter rainfall months of June to August. Inorganic N input during 1981 – 82 was 1,79 kg N ha − 1 y − 1 with an NH 4 -N to NO 3 -N quotient of 1. Logarithmic relationships exist between NO 3 -N and NH 4 -N concentrations in bulk precipitation and the volume of precipitation collected at weekly intervals. Bulk precipitation collectors at 1,5 m and 4 m were not suitable to determine the infuence of local recycling of dust aerosols. It is probable that although atmospheric N deposition may contribute a portion of the extra-system N, it alone is not sufficient to replenish N lost by coastal fynbos ecosystems as a result of recurrent short interval fires. Rather the low input of nitrogen to the Pella site reported gives an indication of the levels of N deposition to be expected in the fynbos region where N is derived mainly from oceanic sources and few anthropogenic activities influence precipitation composition.

Acid deposition near a sour gas plant in southwestern Alberta

Atmospheric fallout in the vicinity of a sour gas plant in southwestern Alberta was collected on an event basis with bulk precipitation collectors during June, July and August of 1972, 1973 and 1982. Samples were collected at 9 sites within 20 km of the plant. Total atmospheric sulfation measurements defined a higher exposure area located downwind of the plant, but the precipitation measurements did not. Bulk deposition of H+ ion in the study area was an average 10.77 mmol H+ m−2 3 mol−1 in 1972 and 0.014 and 0.049 in 1973 and 1982, respectively. 1972 samples were also significantly more acidic (average pH of 4.3 vs 5.7 in 1973 and 5.3 in 1982). Deposition of SO4= averaged 2.1 kg S ha−1 3 mol−1 in 1972 and 0.96 and 0.72 in 1973 and 1982. The higher deposition of both S and H+ in 1972 is mainly a result of more precipitation. There was no significant correlation between H+ and SO4= species in the samples. There was no significant relationship between plant S emissions and deposition rates, or plant S emissions and average total atmospheric sulfation measurements.

The deuterium content of raindrops : Woodcock A. H. and I. Friedman, 1963. J. Geophys. Res., 68 (15): 4477–4483

A network of 10 bulk precipitation collectors was established in an upland region of northern England to examine the small-scale variability of precipitation composition in a rural area. Significant spatial variability was shown for non sea-salt sulphate, calcium and hydrogen ion concentrations. Although nitrate concentrations did not show significant variability, a coherent gradient across the study area was observed. The large variability of calcium ion concentration across the area was related to limestone quarrying, which is prevalent in the south of the study area. Calcareous wind-blown soil may have also made a minor contribution to the abundance of calcium in the rain-water samples. It is likely, however, that a large fraction of the calcium was dry deposited to the funnels of the collectors in the form of particles. The network was not designed to study orographic enhancement of deposition, but it is suggested that this mechanism, along with wind-drift of scavenged cap-cloud droplets, cannot explain the spatial variation in ion concentrations. It is speculated that the variability in non-sea-salt sulphate concentrations may also be partially explained by reaction of CaCO3 particles deposited to the funnels of the collectors with SO2. Critical load exceedances in terms of deposited acidity from non-sea-salt sulphate were calculated using different spatially resolved deposition data. A better estimate of deposition in the study area was achieved by combining rainfall concentration data from the national network with the 5 km rainfall field, than the current methodology used for mapping of U.K. deposition which utilises a 20 km rainfall field. However, 20 km is considered to be the minimum resolution at which a procedure for parameterising orographic enhancement can be incorporated. Deposition and critical load exceedances in 2005 were calculated using a long-range transport model and significant improvements in the protection of soils were predicted from the projected emissions reductions.