A comparison between wet and bulk deposition at an urban site in the U.K.

As a part of an ongoing investigation into urban acidic deposition in Greater Manchester, a wet-only collector was collocated with a bulk collector in the city centre of Manchester, one of 18 sites of an urban precipitation monitoring network. A comparison of data from these collocated bulk and wet-only collectors allowed estimates of the contribution of dry deposition to the bulk collector to be made. Dry deposition was found to contribute between 15 and 17% to elevated deposition and concentrations of non marine sulphate, nitrate and ammonium in the bulk collector. By a statistical analysis between ion concentrations with gas concentrations and an evaluation of the available literature, the form of the dry deposited material was inferred. The contribution of dry deposited Ca²⁺ to concentration and deposition in the bulk collector was found to be 46%. Calcium species are suggested as being those which reduce acidity most. Statistical analyses revealed significant differences between concentrations of ions found in the bulk and wet-only collectors. An evaluation of the data from the collocated collectors has identified possible sampling artifacts introduced by the use of bulk collectors in urban areas.     

Atmospheric Ionic Deposition in Tropical Sites of Central Sulawesi Determined by Ion Exchange Resin Collectors and Bulk Water Collector

In the light of global change, the necessity to monitor atmospheric depositions that have relevant effects on ecosystems is ever increasing particularly for tropical sites. For this study, atmospheric ionic depositions were measured on tropical Central Sulawesi at remote sites with both a conventional bulk water collector system (BWS collector) and with a passive ion exchange resin collector system (IER collector). The principle of IER collector to fix all ionic depositions, i.e. anions and cations, has certain advantages referring to (1) post-deposition transformation processes, (2) low ionic concentrations and (3) low rainfall and associated particulate inputs, e.g. dust or sand. The ionic concentrations to be measured for BWS collectors may easily fall below detection limits under low deposition conditions which are common for tropical sites of low land use intensity. Additionally, BWS collections are not as independent from the amount of rain fallen as are IER collections. For this study, the significant differences between both collectors found for nearly all measured elements were partly correlated to the rainfall pattern, i.e. for calcium, magnesium, potassium and sodium. However, the significant differences were, in most cases, not highly relevant. More relevant differences between the systems were found for aluminium and nitrate (434-484?%). Almost five times higher values for nitrate clarified the advantage of the IER system particularly for low deposition rate which is one particularity of atmospheric ionic deposition in tropical sites of extensive land use. The monthly resolution of the IER data offers new insights into the temporal distribution of annual ionic depositions. Here, it did not follow the tropical rain pattern of a drier season within generally wet conditions.     

Comparison of Long-Term Precipitation Chemistry Measurements at the Hubbard Brook Experimental Forest,New Hampshire

From 1978 through 1989, a wet-onlyprecipitation collector operated for the NationalAtmospheric Deposition Program, an independantwet-only collector, and a bulk precipitation collectorwere co-located at the Hubbard Brook ExperimentalForest (HBEF) in central New Hampshire. A secondbulk precipitation collector was maintained at anotherlocation within the HBEF. There were statisticallysignificant differences between the chemistry fromco-located wet-only collections for Ca²⁺,K⁺, NH₄ ⁺, pH, and NO₃ ^-. Thedifferences for K⁺ and pH though statisticallysignificant were very small but consistant. Thedifferences for Ca²⁺ were related to earlycontamination problems, and differences inNH₄ ⁺ and NO₃ ^- were related toepisotic events. Bulk precipitation was significantlyricher in K⁺ than wet-only precipitation. Therewere no differences for any ions between the bulkcollections at the two locations. While there wereminor differences, after 1981 when the contaminationproblems had been resolved, data from all collectorsat all locations adequately characterized theprecipitation chemistry of the site.     

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.     

Precipitation chemistry within Kvarner Bay area,Northern Adriatic (Croatia), 1984–1991

The results of rainwater analyses collected at five sampling sites within Kvarner Bay area are presented for the period 1984–1991. The samples were collected on a daily basis in open buckets thus representing bulk samples. Although measurements are referred to as wet deposition samples, they are actually an upper limit for the wet deposition. The rainwater was initially analysed for pH, sulphate and nitrate content, while during the period March 1990 — May 1991 the analyses were extended to major ion concentrations: hydrogen, sulphate, nitrate, chloride, ammonium, sodium, potassium, calcium and magnesium. The pH frequency distribution, pH medians and precipitation weighted average (PWA) concentrations of hydrogen, sulphate and nitrate are presented, as well as wet deposition rates of sulphur (as sulphate) and nitrogen (as nitrate). The dependence of hydrogen, sulphate and nitrate mean concentrations on wind directions and seasons for Site 1 is also given. The highest precipitation acidity is obtained at urban and industrial Site 1 (city of Rijeka) because of the local washout of the atmosphere and influence of dry deposition, and at remote Site 4 (Lake Vrana) due to long-range transport. The neutralizing potential of sea salt and soil dust is responsible for partial neutralization of rainwater at other sites. The influence of sea salt on chemical composition of rainwater is observed at all sites. The estimated wet deposition rates of sulphate and nitrate are close to the values reported for Southeast Europe. The wet deposition rate for ammonium ion at Site 1 is almost double comparative regional values.     

The effect of a local source on the composition of precipitation in south-central Maine

Bulk precipitation samples were collected from ten sites in south-central Maine during the period 18 June to 30 September, 1974. Data from the chemical analyses of the precipitation were used to determine regional deposition patterns of the ionic constituents. Acidic pH values ranging from 3.8 to 5.0 are characteristic of the region, but relatively alkaline pH values of 5.5 to 7.0 were observed in the precipitation from one collection site. Systematic increases in sulphate and Na deposition in the samples from this site suggest a local source. The observations of the bulk precipitation analysis lead to a study of the chemical composition of precipitation near a kraft paper mill. Samples were collected during single precipitation events. The results indicate that this source can affect background levels of composition up to a distance of at least 20 km and that considerable care must be taken in the selection of sites for sampling background precipitation.     

Orographic enhancement of wet deposition in the United Kingdom: Continuous monitoring

Continuous monitoring of cloud and rain samples at three mountain sites in the UK has allowed consideration of the long term impact of the enhancement of the wet deposition of pollutants by orographie effects, specifically the scavenging of cap cloud droplets by rain falling from above (the seeder-feeder effects). The concentration of the major pollutant ions in the cloud water is related to the relative proximity of each site to marine and anthropogenic sources of aerosol. In general, the concentrations of major ions in precipitation at summit sites exceed those in precipitation to low ground nearby by 20% to 50%. Concentrations in orographie cloud exceed those in upwind rain by between a factor of five and ten. The results are consistent with seeder-feeder scavenging of hill cloud by falling precipitation in which the average concentration of ions in scavenged hill cloud exceed those in precipitation upwind by a factor of 1.7 to 2.3 for sulphate and nitrate respectively at Dunslair Heights and 1.5 to 1.8 for sulphate and nitrate at Holme Moss. The results suggest that the parameterisation of this relationship with scavenged feeder cloud water concentrations assumed to exceed those in seeder rain by a factor of two for the production of predictive maps of wet deposition in mountainous regions of the U.K. is satisfactory.     

Bulk and wet atmospheric deposition chemistry at pallanza (N. Italy)

The chemistry of wet only and bulk depositions collected weekly at Pallanza from May, 1984 to December, 1986 is compared and discussed in relation to the composition of dust fall. The comparison shows a very good agreement between pH values (volume weighted mean values of 4.35 and 4.36, respectively, for wet only and bulk samples) and differences between 6 and 12% for ammonium, sulphate, nitrate, and Na. For Ca, Mg, and K the difference range is 30 to 50%. The amount of precipitation over Pallanza (mean value 1951–1985,1709 mm), together with the solute concentrations in atmospheric deposition, mean that there is high bulk deposition of acidifing substances. The values found during the study period were 76, 93, 143, and 81 meq m² yr^?1 for H⁺, ammonium, sulphate, and nitrate, respectively.     

Acidity of atmospheric precipitation in Polish Tatra Mountains

A three-year (1991–93) study on atmospheric precipitation (bulk and throughfall) and stream chemistry was carried out in two — granitic (Waksmundzka Val.) and calcareous (Mietusia) valleys (Polish Tatra Mountains). It was found that both valleys were under acid rain influence — chemical analysis showed strong seasonal fluctuations of the studied elements. Chemistry of precipitation was dominated by sulphate ions, buffered more efficiently in Mietusia Val. than Waksmundzka Val. mainly by calcium and ammonium ions. In both valleys an increase of throughfall acidity compared to bulk precipitation was observed. There were also found differences between bulk and throughfall chemistry — amounts of hydrogen, calcium, potassium and ammonium ions in throughfall were higher whereas amounts of phosphate, copper and zinc ions were lower in throughfall than in bulk precipitation. In both valleys significant seasonal variation of most of the studied elements in bulk and throughfall was detected.     

Dissolved nitrogen supersaturation of a heated effluent

A three month experimental study to evaluate the relative performance of three different designs of ‘event’ precipitation chemistry samplers was carried out at Woodbridge, Ontario beginning in August 1979. The samplers evaluated were an automatic Aerochem Metrics, ‘wet-only’ type (A), a funnel-and-bottle type (F), and a large-mouth plastic bucket with a specially-fabricated polyethylene bag insert (S). Each sampler was run in duplicate, with a sampling period of 24 hr. The results show that at sites where dry deposition is important, bulk samplers (‘F’ and ‘S’ types) yield significantly different results from the wet-only collector including rainfall amount, H⁺ , SO₄ ^?, NO₃ ^?, Na⁺, K⁺, Ca⁺⁺, and Mg⁺⁺. However, the bulk samplers, especially the ‘S’ type, are found to be satisfactory under certain conditions. For conditions which correspond to daily rainfall less than 2.8 mm and windier and drier sampling, there is even evidence of dry contamination of the wet-only type sampler.     

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) in the bulk collectors. All other ion concentrations were significantly higher (p <0.05) in the bulk collectors except for ammonium (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.     

ACID DEPOSITION DURING TWO CONTRASTING FRONTAL RAINFALL EVENTS

Analysis of the chemical composition of rain at high temporal resolution provides additional information on wet deposition processes. High resolution data was obtained using a microprocessor-based acid rain monitor at two sites in SW Scotland and SE England. Meteorological details of the transport and wet deposition processes during two frontal rain events were examined and related to rainfall composition. Rapid depletions of ion concentrations during heavy rainfall in the first event were interpreted using a rainfall scavenging model. The sub-event data for the second event showed the influence of frontal discontinuities. Increasing ionic concentrations during this second event were attributed both to the change in air mass, and to diminished upwind precipitation scavenging.     

Rapid Time Variations in Chemical Composition of Precipitation in South Korea

Data from a monitoring program on precipitation at four sites in South Korea during the period from 1993 to 1998 were analyzed for determining a time trend relationship in chemical composition of precipitation. The concentrations of nss-sulphate, ammonium and calcium were found to have decreased over time at a statistically significant level in Seoul (p<0.05). The concentration of nss-sulphate had declined by a rate of 12% per year for the period from 1993 to 1998. The concentrations of ammonium and calcium decreased by 11% and 12% per year respectively for the same period. The concurrent reduction of cation offsets the change in strong acid anion, thus the annual mean pH of precipitation has been approximately constant. In contrast to the rapid change of sulphate, the second most abundant anion, nitrate, showed no statistically significant decrease. As a result, the nitrate to nss-sulphate ratio (N/S ratio) has increased rapidly; the N/S ratio in precipitation has increased from less than 0.1 in 1985 to nearly 0.5 in 1998 at Seoul. In spite of the short monitoring period, a significant upward trend in the N/S ratio was also observed at all of the other sites suggesting that the nitrogen species contribute more to precipitation acidity throughout Korea.     

Monitoring of Acid Rain over Korean Peninsula

In order to investigate the temporal and spacial deposition characteristics of acid rain, five monitoring sites were set up in the central part of Korean Peninsula. Rainwater samples were collected by wet-only sampler from 1992 to 1997. The pH and conductivity values were measured and the major water soluble ionic components were also analyzed. Ion balance between anion and cation sum was calculated to check out the data quality of samples. The acidity of rainwater was influenced by the local sources and meteorological factors such as surface wind, moving path of storm, precipitation process, and so on. Backward trajectories were depicted to investigate the effect due to moving path of weather system. The rainwater shows strong acidity in winter and weak in summer. The pH and ion concentrations were highly dependent on synoptic weather system. In addition, we sampled fog/cloud at Mt. Sobaek (BAPMoN Station) from June to August 1995 and characterized the fog/cloud chemistry according to surface wind system of sampling site. The volume-weighted mean pH of fog/cloud samples is 4.39 at Mt. Sobaek during the sampling period.     

Effects of sulphuric acid and acidifying ammonium deposition on water quality and vegetation of simulated soft water ecosystems

In a greenhouse, seven identical mini-ecosystems, simulating soft water ponds, were exposed to different types of artificial rain water. The effects of rain water containing H₂SO₄ and nitrate, and rain water containing ammonium sulphate on water quality and vegetation were studied and compared. Causal relations were established between rain water quality, water chemistry and changes in floristic composition. Ammonium sulphate deposition, particularly, strongly affected water quality and vegetation development. Although ammonium sulphate deposition was only slightly acid, due to nitrification it acted as an important acid source, causing acidification to pH=3.8. Under acidified conditions, ammonium sulphate deposition lead to a luxuriant growth ofJuncus bulbosus andAgrostis canina. In the mini-ecosystems, H₂SO₄ deposition with a pH of 3.5 only decreased the pH of the water to 5.1 within 1 yr. The acidification of water appeared to be coupled with changes in alkalinity, sulphate, Al, Cd, Ca, Mg, K and inorganic-N. It is concluded that in NH₃-affected regions in The Netherlands, the high atmospheric deposition of ammonium sulphate probably contributes to a large extent in the acidification, eutrophication and floristic changes of oligotrophic soft waters.     

Spatial and temporal variability in precipitation chemistry in the urban area of Greater Manchester

To investigate the spatial and temporal variability of acid deposition in the urban environment a small-scale intensive network of bulk collectors has been deployed around Greater Manchester, UK. This network has been in operation since 1986. The concentrations and deposition rates of non-marine (nm) sulphate, nitrate, ammonium, calcium and hydrogen are reported for 1994. Acidity was generally lower in the city centre of Manchester where calcium concentrations were highest. Calcium compounds in the urban atmosphere effectively buffer the precipitation acidity.     

The status of wet deposition of nitrogen compounds in an intensive dairy farming area in central Japan

(pp. 47–52)

The wet deposition of nitrogen compounds in the intensive dairy farming area and its environs in the northern part of the Kanto region in central Japan was investigated from April 2003 to April 2005. Open-bulk samplers were used to collect open-bulk precipitation, which approximates the sum of wet and dry deposition. Furthermore, wet-only samplers were applied to collect the precipitation for every 1 mm in a rainfall, termed the wet sample. The concentrations of total nitrogen and ammonium ions in the open-bulk precipitation were high in the central part of the dairy farming area and low in the remote mountainous area more than 15 km away the concentrations were generally high during winter and spring, and low during summer and autumn. There was a large difference in the annual deposition of nitrogen between the farming area and the surrounding area. The annual deposition of nitrogen in the farming area was significantly high compared to the values of existing data in Japan and Europe. The concentrations of respective nitrogen compounds in the wet sample, which accounted for 40 of the total rainfalls events, were notably high at the beginning of precipitation and rapidly decreased by 8 mm of continuous precipitation. The nitrogen concentrations at the beginning of precipitation were high in the farming area, and relatively low in the surrounding area. It was thought that the cause of the large wet deposition in the farming area was due to ammonia emissions, mainly from cattle manure produced at dairy farms. The factors of the seasonal changes were considered to be the frequency and the amount of precipitation, and the change in ammonia emissions from manure management performed by dairy farmers.     

Ionic composition of acid lakes in relation to airborne inputs and watershed characteristics

Present acid forming emissions to the atmosphere have the potential to alter significantly the chemistry of rain, snow, and surface water of weakly buffered lakes in the Upper Midwest. Average precipitation pH from field measurements during 1979–1983 declined from west to east from 4.8, 4.6, and 4.3 along a cross-section of sites in Minnesota, Wisconsin, and Michigan respectively where 990 lake and stream sampling sites were studied. Measurements of weakly buffered lakes show a parallel decline in lake water pH with the lowest values measured, 5.1, 4.6 and 4.4, respectively in the same regions. Correspondingly, the percentage of lakes sampled with little or no acid neutralizing capacity (ANC) was found to increase from 0 to 4 and 13%, respectively. The geographic patterns in ionic composition of airborne acids and bases, and the resultant surface water concentrations are compared. The acid forming capacity (AFC) from airborne inputs is calculated using mass balance and in-lake processes. Stoichiometric acid-base reactions are used to balance the observed chemical differences between airborne inputs and surface water composition considering nitrification, denitrification, other oxidation-reduction reactions, and the evaporation concentration process. Microbial activity in surface water can result in a net decrease in ionic strength from the conversion of most of the ammonium and nitrate to neutral compounds and biomass, but only a partial reduction of about 20% of the sulfate inputs to weakly buffered lakes. The resulting AFC of airborne inputs are calculated to range from 30 to 60, 50 to 90, and 80 to 130 μeq H+L-l, respectively, in northeastern Minnesota-Ontario, northcentral Wisconsin and northern Michigan-Ontario. The differences in AFC of airborne inputs from west to east, and differences in in-lake processes explain the observed acidity of weakly buffered lakes across the region.     

Nine years of measurements of atmospheric nitrogen and sulphur deposition to Danish forest

Since 1985 measurements of gasses, aerosols, precipitation and throughfall have been carried out at three forest sites in Denmark with equal aged Norway Spruce plantations. The times series show a downward trend in the concentration of sulphur dioxide. Particulate sulphate, ammonia and particulate ammonium and the total nitrate seem to have a more constant concentration level. The wet deposition measurements show a decreasing trend in the content of acid (protons), sulphate, ammonium and nitrate, though for the nitrogen compounds it is only a slight fall. A decrease in concentrations of protons and sulphate is also seen in the throughfall measurements, in throughfall the nitrogen compounds hardly seem to decrease.     

Episodicity of Sulphate Deposition in Finland

A characteristic of daily acid deposition data, in particular at remote sites, is the occurrence of some extreme peaks above the base level of moderate values. A large proportion of the annual acid deposition is accumulated in a few days: 5 worst days at the Finnish background stations can bring 20–30 % of the annual bulk sulphate load. The aim of this study was to determine whether there is a difference between stations in the number of extreme daily bulk acid depositions. The bulk deposition of sulphate in the 1990's at five Finnish monitoring stations was used as a reference. Days on which the deposition value exceeded the annual median value of the station by a factor of 10 were counted as episode days. The number of episode days in central and northern Finland differed significantly (p<0.05) from the number in the south, when tested with the non-parametric Kruskal-Wallis test. The episodes cannot be completely explained by high precipitation amounts: the mean sulphate concentration in episodic rain was higher than the annual mean concentration. The episodes were mostly imported: the air mass arriving at the station had passed over areas with high emissions outside Finland. A more exact knowledge of the episodicity benefits an examination of the ecological stress caused by acid deposition as well as a study of the critical load and the crossing of this threshold.