Annual Wet Deposition Research Articles

From icy roads to salty streams

For most of human history, salt was a precious commodity. People prized it for flavoring and preserving food and for use in religious ceremonies and burials. The Roman occupation of Britain peppered the English language with a legacy of salt. We retain those Latin links in words such as “salary” and “salami” and in place names like Greenwich and Sandwich, their suffix denoting a salt-works. Today salt is no longer precious. The U.S. mines ≈36 million metric tons [1 metric ton = 1 megagram (Mg)] of rock salt a year (1). Eighteen million Mg is spread on paved surfaces for deicing, making winter roads safer for people and vehicles (2). However, once the salt dissolves, it washes into streams or soil and is forgotten. A new article by Kaushal et al . (3) in a recent issue of PNAS suggested that it should not be. The use of rock salt (NaCl) on U.S. roads has skyrocketed in the last 65 years (Fig. 1), and chloride (Cl) concentrations in waters of the northeast have risen as a consequence (4-6). The mobility of salt in water leads to its potential problems in the environment. These problems include toxicity to plants and fish, groundwater contamination, and human health interactions, particularly salt intake and hypertension (7-9). In consequence, researchers have been monitoring increased salt concentrations in streams and groundwater for decades (4-6, 10). Fig. 1. Sales of rock salt for highway use in the U.S. from 1940 to 2004 in millions of metric tons (Mg) (1, 2). The dashed line denotes our estimate of the calculated annual wet deposition of Na and Cl in the U.S., derived primarily from sea salt. The amount of Na and Cl in road salt topped Na and Cl deposition for the …

Atmospheric nitrogen deposition from a remote source enriches macroalgae in coral reef ecosystems near Green Turtle Cay, Abacos, Bahamas

Over the past several decades, the fixation of “new” nitrogen to the biosphere has doubled. For the early 21st century, the most significant rate increases in atmospheric nitrogen deposition are predicted for developing nations. Wet nitrogen deposition was assessed on the remote island of Green Turtle Cay, Bahamas in a dry and wet season from January to July 2000. Episodic deposition of nitrate (∼1–137 μM) and ammonia (∼2–122 μM) represented a mean deposition rate of ∼0.2 mg DIN m −2 yr −1. Wet deposition of nitrogen to the climatologically-linked east coast of Florida is ∼4 times greater than the estimated annual wet nitrogen deposition value at Green Turtle Cay, suggesting the continental US as a principal airshed for this loading source. Short-term bioassays of macroalgal productivity with a 5% rainfall solution caused depressed net productivity and increased dark respiration, well known “transient metabolic” responses by nutrient-limited tropical macroalgae. Wet deposition of inorganic nitrogen from episodic rainfall events may provide up to 20% of the “new” nitrogen necessary to meet growth demands of macroalgae on coral reefs near Green Turtle Cay.

Wet and dry deposition fluxes of mercury in Japan

Wet and dry deposition fluxes of mercury were measured concurrently from December 2002 to November 2003 at 10 sites in Japan (nine sites for dry deposition measurements). Precipitation and dry deposition (gases and particles) were collected every half-month using an automatic wet and dry deposition sampler. This sampler is composed of a precipitation sampler and a water surface sampler for dry deposition. The results showed that wet deposition fluxes of mercury increase generally during summer when the precipitation amount increases. In contrast, the seasonal variations of the dry deposition fluxes were very small compared to those of the wet deposition fluxes. It was found that wet deposition plays a dominant role in mercury deposition in Japan, contributing fluxes ranging from 0.99 to 2.2 times (1.6 times on average at nine sites) those of the dry deposition fluxes. There was a high correlation between the annual wet deposition flux of mercury and annual precipitation amount (r2=0.73, P<0.01). Thus, about 70% of the variance of mercury wet deposition in Japan is explained by precipitation amount. This is probably because mercury wet deposition is dominated by the scavenging of reactive gaseous mercury (RGM) by precipitation via oxidation of gaseous elemental mercury (Hg0) in the gas and aqueous phases. In addition, a similar relationship between the annual wet deposition flux and precipitation amount (r2=0.55, P<0.001) was observed at the Mercury Deposition Network (MDN) sites in North America, suggesting that about 55% of the variance of mercury wet deposition is due to precipitation amount.

Organic nitrogen in precipitation across the United Kingdom

The concentration of water-soluble organic nitrogen (WSON) in precipitation has been measured at seven sites across the United Kingdom, over a period of 1–2 years, using protocols developed in a pilot study. Samples were collected over 1–2 weeks in continuously open funnels made of stainless steel, draining to a glass bottle, and were preserved during and after collection by the addition of thymol. After chemical analysis, samples were excluded from the long-term average if they showed signs of contamination (significant concentrations of K+ or PO43−). Two methods of measuring total dissolved N were used, persulphate oxidation and high-temperature chemiluminescence. The latter generally gave the larger values, and has been used to asses the organic component of dissolved N. The long-term data set confirms the original results from the pilot study - organic N contributes between 24 and 40% to the total annual wet deposition of dissolved N across the United Kingdom. The fraction of WSON was greatest at western sites, and was strongly correlated with ammonium concentrations. However, the seasonal pattern across all sites showed a late spring maximum for ammonium and nitrate, but a late summer maximum for WSON. The magnitude of the contribution of WSON to wet-deposited N has implications for the setting and assessment of critical loads for N deposition.

The impact of volcanic gases from Miyake island on the chemical constituents in precipitation in the Tokyo metropolitan area

The volcano on Miyake Island first erupted in July 2000 and continuous emission of volcanic gas from the collapsed caldera has been observed from the middle of August 2000. The large volcanic emission of SO 2 had a strong influence on Tokyo metropolitan area, which is located approximately 150 km north of Miyake Island. We measured major ions in precipitation and dry deposition samples which had been collected at five sampling sites (Yokohama, Kashiwa, Fujisawa, Yokosuka, and Hachioji) in the Tokyo metropolitan area for 12 years since 1990. We have evaluated quantitatively the impact of the volcanic SO 2 gas emitted from Miyake Island on the Tokyo metropolitan area by comparing depositional ionic constituents in the volcanic degassing period (from September 2000 to August 2001) with those in the normal period of the past 10 years (September 1990 to August 2000). nss-SO 4 2− concentrations in precipitation at the sampling sites in the Tokyo metropolitan area were 59.5–77.0 μeq/L during the degassing period, and 33.3–44.1 μeq/L during the normal period, respectively. The difference of nss-SO 4 2− concentrations between the two periods was statistically significant. In contrast, no significant differences were observed in the concentrations of the other major ions (NH 4 +, nss-Ca 2+, Cl −, and NO 3 −) between the two periods. The impact of volcanic degassing from Miyake Island on the ionic concentrations in the precipitation of the Tokyo metropolitan area was seen only in the H + and nss-SO 4 2− concentrations. The annual wet deposition amount of volcanic nss-SO 4 2− into the Tokyo metropolitan area has been quantitatively estimated. The annual wet deposition amounts were calculated as 701±277 Meq/year (22.4±8.9 kt SO 2/year) on the total area of the Tokyo metropolitan area (14,000 km 2). The wet deposition amount of nss-SO 4 2− corresponds to only 0.15% of the total annual amount of volcanic SO 2 (15 Mt/year) emitted from Miyake Island from September 2000 to August 2001. This estimation is consistent with a previous study which reported that 0.3% of the atmospheric discharge of SO 2 from the volcano in Mt. Etna in Sicily was deposited by precipitation to the surrounding area (1200 km 2). The annual wet deposition amount of volcanic SO 2 to the Tokyo metropolitan area was at the same order of the magnitude (37±15%) as the annual anthropogenic SO 2 amount (60 kt/year) emitted from the Tokyo metropolitan area.

Long-term changes in precipitation and stream water chemistry in small forest and moorland catchments at Beddgelert Forest, north Wales

Abstract. Changes in the chemistry of bulk precipitation and stream water between 1982 and 2000 are described for small moorland and forest catchments located within Beddgelert Forest in north Wales. Two forest catchments were partially clearfelled in 1984 (D2; 68% and D4; 28%) whilst a third (D3) remained as an unfelled control until autumn / winter 1998/99 when partial felling took place in the headwaters. Over the monitoring period, the annual mean pH of bulk precipitation increased from 4.6 to 5.1 whilst the annual mean non-seasalt sulphate concentration decreased from 0.53 mg S l-1 in 1985 to 0.24 mg S l-1 in 2000. Since 1985, the annual wet deposition flux of non-seasalt sulphur decreased by 50% to 8.4 kg S ha-1 yr–1 in 2000. Annual mean inorganic nitrogen concentrations and annual wet deposition fluxes have remained relatively unchanged since 1982. The decrease in atmospheric sulphur deposition is reflected by decreased annual mean concentrations of non-seasalt sulphur, acidity, aluminium and calcium in all four streams irrespective of clearfelling activities. Annual variations in nitrate-N and potassium concentrations in the forest streams, largely determined by pulses of leaching following forest clearance, had no effect on stream acidity. In common with UK upland catchments, annual mean concentrations of dissolved organic carbon have increased from about 1 mg C l-1 in 1985 to between 1.5 and 2 mg C l-1 in 2000, although there is considerable year to year variability. Two boreholes drilled adjacent to catchments D3 and D4 have confirmed the presence of alkaline, base rich groundwater at Beddgelert. Although the boreholes are only 150 m apart, there are large differences in chemistry suggesting that different groundwater reservoirs have been intercepted providing further evidence of the complexity and heterogeneity of groundwater systems in upland catchments. Keywords: acid deposition, acidification, recovery, forestry, clearfelling, trends, Beddgelert, streams, rainfall

Atmospheric wet deposition of trace elements to a suburban environment, Reston, Virginia, USA

Abstract Wet deposition from a suburban area in Reston, Virginia was collected during 1998 and analyzed to assess the anion and trace-element concentrations and depositions. Suburban Reston, approximately 26 km west of Washington, DC, is densely populated and heavily developed. Wet deposition was collected bi-weekly in an automated collector using trace-element clean sampling and analytical techniques. The annual volume-weighted concentrations of As, Cd, and Pb were similar to those previously reported for a remote site on Catoctin Mt., Maryland (70 km northwest), which indicated a regional signal for these elements. The concentrations and depositions of Cu and Zn at the suburban site were nearly double those at remote sites because of the influence of local vehicular traffic. The 1998 average annual wet deposition (μg m −2 yr −1 ) was calculated for Al (52,000), As (94), Cd (54), Cr (160), Cu (700), Fe (23,000), Mn (2000), Ni (240), Pb (440), V (430), and Zn (4100). The average annual wet deposition (meq m −2 yr −1 ) was calculated for H + (74), Cl − (8.5), NO 3 − (33), and SO 4 2− (70). Analysis of digested total trace-element concentrations in a subset of samples showed that the refractory elements in suburban precipitation comprised a larger portion of the total deposition of trace elements than in remote areas.

Regression equations for estimating throughfall nutrient fluxes using wet deposition data and their applicability for simulating the soil acid–base status using the dynamic forest soil–atmosphere model SAFE

Throughfall may contribute large amounts of nutrients to forest soils via the leaching of accumulated dry particulates on the canopy, and by altering incoming precipitation, it may have some control on the acid–base status of the soil. Unfortunately, information about throughfall in forests is sparse and thus, scientists must deal with this gap in knowledge before conducting regional applications of dynamic soil acidification models. The first objective of this paper was to test the possibility of developing regression equations that could allow modellers to estimate throughfall nutrient fluxes using wet deposition nutrient fluxes as input data. The second objective was to test the relative importance of this simplification on regional applications of the dynamic soil–atmosphere model Soil Acidification in Forested Ecosystems (SAFE) using one published application of this model as the base case. Annual throughfall nutrient fluxes were estimated successfully from annual wet deposition fluxes for individual ions. The success of these relationships were however inversely proportional to the intensity at which an ion was involved in exchange reactions: models generally performed better with more conservative ions. The simulation of the soil acid–base status with SAFE suggested that it was appropriate to use the throughfall estimates yielded using the regression equations. Also, testing of the SAFE output using different regression equations in throughfall showed that, in the case of base cations, the key for modelling the soil acid–base status was to produce accurate throughfall estimates of Ca and Mg, and that K had marginal effects. However, a small bias in solution pH was introduced as the balance between alkalinity and acidity in the different categories of deposition appeared to be diverging from the base case (measured) values. The use of our approach at other sites may indicate if there is a systematic bias or not in the regressions. Yet, results suggest that the regression equations are appropriate for the purpose of modelling the soil acid–base status at the scale of the landscape because it assures that the same set of assumptions in throughfall are used for each application.

Divalent inorganic reactive gaseous mercury emissions from a mercury cell chlor-alkali plant and its impact on near-field atmospheric dry deposition

Abstract The emission of inorganic divalent reactive gaseous mercury (RGM) from a mercury cell chlor-alkali plant (MCCAP) cell building and the impact on near field (100 km) dry deposition was investigated as part of a larger collaborative study between EPA, University of Michigan, Oak Ridge National Laboratory, Chlorine Institute, and Olin Corporation in February 2000. Measurements in the cell building roof vent showed that RGM constituted 2.1±0.7% (median±variance) of the concurrently measured elemental gaseous mercury (Hg 0 ). This relationship was used to calculate an estimated RGM emission rate from the cell building roof vent of 10.4 g day −1 . The percentage of RGM/Hg 0 at ambient monitoring sites 350 m (1.5%) and 800 m (1.3%) away while being impacted by cell building emissions suggests the rapid deposition of RGM species. The observed 2% relative emission of RGM/Hg 0 was substantially lower than the 30% estimate utilized by EPA to model the impact of MCCAPs for the 1997 Mercury Report to Congress. However, the MCCAP was still found to present a significant impact on near field mercury atmospheric dry deposition. A Lagrangian transport and deposition modeling framework using only emissions from the MCCAP found the mean annualized dry deposition of mercury within a 10 km radius of the facility contributed the annual equivalent of 4.6 μg m −2 . For comparison, the total annual wet mercury deposition measured at the Savannah River National Mercury Deposition Network sampling site ∼30 km away was 9.8 μg m −2 .

An annual wet sulfate deposition index

Averages of annual wet deposition data are often used as an indicator of acid amounts in the atmosphere. From the view point of statistics, the average is a meaningful estimator only for identically distributed data with specific types of probability distribution. Wet deposition data usually carry seasonal trends. To learn about year-to-year concentration changes, a more accurate summary information accommodating the trend is thus necessary. This paper suggests a quantity (index) describing the annual wet deposition of SO4 and formulas for its calculation. The formulas are in some sense optimal in case the data can be considered independent, lognormally distributed and have a time dependent trend. Generalization of these assumptions is also discussed. The index is derived from specific features of the average applied to data with lognormal distribution. The theory is utilized to analyze a set of SO4 precipitation concentrations observed in the Ontario region.

Atmospheric Budget of Non-Seasalt Chlorine in the Kanto District, Japan

To evaluate the influence of anthropogenic emission of HCl on the air quality in the Kanto district of Japan, the atmospheric budgetof non-seasalt Cl (nssCl) was analyzed. The Kanto district, which consists of the Tokyo metropolis and the six surrounding prefectures, is the most densely populated region in Japan. The emission intensity of HCl is extremely high compared with those in other regions and most western countries. In this study, the annual wet and dry depositions of nssClwere estimated on a 0.25 × 0.25° grid over the Kanto district based on the concentration monitoring resultsand meteorological data. The budget analysis was conducted by comparing the estimated deposition with the emission of HCl. As a result, the annual total (wet + dry) deposition of nssCl was estimated to be 32 kt yr-1, which closely agreed with HCl emission (36 kt yr-1) from waste incineration in this area. The result suggested that the anthropogenic emission of HCl had a significant influence on the air quality and the deposition of acidity in this area.

Atmospheric wet deposition of soluble macro-nutrients in the Cilician Basin, north-eastern Mediterranean sea

In order to estimate wet deposition atmospheric fluxes of macro-nutrients into the eastern Mediterranean coastal waters, soluble inorganic phosphate (PO4(3-)), nitrate (NO3-) and nitrite (NO2-) concentrations in precipitation (from February 1996 to June 1997) have been measured at a coastal sampling site, Erdemli, Turkey. Water-soluble inorganic PO4(3)-P, a reactive, bioavailable, limiting macro-nutrient in the oligotrophic waters of the eastern Mediterranean was studied with respect to its contribution to biological productivity. Reactive PO4(3-)-P and NO2(-) + NO3(-)-N concentrations were found to be highly variable in rainwater samples. One of the aims of the study was to determine the contribution of dust transport to the soluble macro-nutrient budget of the eastern Mediterranean. No differences were found between the mean reactive P and NO(2-) + NO3(-)-N concentrations of "red rain" and normal rain events. Most likely as a result of low solubility of crustal phosphorus, dust episodes were not found to be important sources of reactive P, in terms of wet deposition. The annual wet deposition fluxes of reactive PO4(3-)-P and NO2(-) + NO3(-)-N into the Cilician Basin were respectively estimated to be 0.010 g P m(-2) per year and 0.23 g N m(-2) per year, which are comparable to the fluxes from land-based sources in the north-eastern Mediterranean. The incorporation of water soluble bioavailable PO4(3-)-P and NO2(-) + NO3(-)-N delivered via atmospheric wet deposition could be responsible for approximately 3.3% (0.40 g C m(-2) per year) and 11.0% (1.31 g C m(-2) per year) respectively, of the mean annual new production in the north-eastern Mediterranean.

Wet Deposition of Trace Metals in Singapore

The concentrations of 12 trace metals (Al, Cd, Cr, Cu, Co, Fe,Mn, Ni, Pb, Zn, V, and Ti) in wet depositions are reported. Eighty four rainwater samples were collected using an automated wet-only sampler in Singapore for one year (2000) and subjected to chemical analysis using ICP-MS. Based on the volume-weighted meanconcentrations measured, the trace metals were classified into three groups: Al and Fe with an average concentration of largerthan 15 μg L-1, Cr, Cu, Mn, Ni, Pb, Zn, V, and Ti withconcentrations between 1 and 10 μg L-1, and finally Co and Cd with concentrations lower than 1 μg L-1. Elementenrichment factors were calculated to distinguish between naturaland anthropogenic sources. The calculation of crustal enrichmentfactors with Al as the reference element indicated that while Ti,Fe and Mn originated from crustal sources, the remaining trace metals (Cd, Cr, Co, Cu, Ni, Pb, Zn and V) were mainly derived from anthropogenic sources. The removal of the trace metals from the atmosphere by precipitation was influenced by the rainfall amount as well as pH. The magnitude of the measured average annual wet deposition fluxes of Al, Fe, and combustion-generatedelements such as V, Ni, and Cu is higher than that reportedfor other sites outside Singapore, owing to abundant rainfallthroughout the year in this region.

A regional atmospheric fate and transport model for atrazine. 2. Evaluation.

The Community Multiscale Air Quality (CMAQ) modeling system has been adapted to simulate the regional fate and transport of atrazine. Model modifications and simulations spanning April to mid-July 1995 are described in a previous paper. CMAQ results for atrazine concentrations in air and rainfall are evaluated against field observations taken along the Mississippi River and the shores of Lake Michigan in 1995. CMAQ results agree within 10% of published annual wet deposition load estimates for Lake Michigan and predicted annual dry deposition lies within published error bounds. Comparisons of weekly observed and predicted air and rainfall concentrations along the Mississippi River yield order-of-magnitude differences. Precipitation weighting of concentrations in rainfall good agreement for seasonal time frames. Weekly ambient gas form concentrations tend to be overpredicted by the CMAQ and semivolatile particulate fractons are underpredicted. Uncertainty in CMAQ predictions of air and rainfall concentrations for atrazine appear to derive primarily from uncertainty in emissions estimates, simulated precipitation, and spatial scale.

Potential effects of changes in precipitation and temperature on wet deposition in central Pennsylvania

Changes in regional climate can alter conditions that control the transport, chemical transformation, and eventual deposition of atmospheric pollutants. In Pennsylvania, climate change is projected to increase mean annual temperatures by 4°C and annual precipitation amounts by about 5% through 2100. The objective of this study was to determine how increases in temperature and precipitation would affect concentrations and wet deposition of SO 4 2−, NO 3 −, NH 4 +, and H + ions at a National Atmospheric Deposition Program site (NADP, PA15) in central Pennsylvania. Event-based wet deposition data were obtained from the Multi-State Atmospheric Power Production Pollution Study (MAP3S) monitoring program for the period 1976–1989. Forward stepwise regression was used to predict log-normal concentrations per event using mean temperature, precipitation, Julian Date, and interactions of temperature and precipitation with Julian Date as predictor variables. Julian Date was included to adjust for time trends in precipitation chemistry and climate data. Results were categorized by annual periods, growing season/dormant season, and synoptic climate types. Significant positive effects of temperature on concentration and deposition were found for SO 4 2−, NH 4 +, and H + but not for NO 3 −. Precipitation increases reduced the concentration of each ion due to dilution, but the lower concentration only minimally offset the increase in wet deposition due to the increased precipitation. The effects of climate change during the growing season (April–September) were projected to cause greater increases in the magnitude of SO 4 2−, NO 3 −, and H + concentrations and wet deposition than in the dormant season (October–March). Ammonium (NH 4 +) increases were greatest during the dormant season. Climate change effects on wet deposition were generally similar among synoptic climate types with the greatest effects occurring for cold fronts and warm fronts. The impacts of climate change for this central PA site could increase overall annual wet deposition of SO 4 2− by up to 29%, NO 3 − by up to 6%, NH 4 + by up to 23%, and H + by up to 17% through the year 2100, assuming that the statistical relationships hold true and that no changes in the emission of these ions occur.

Assessing decadal changes in rainwater alkalinity at a rural Mediterranean site in the Montseny Mountains (NE Spain)

Annual volume-weighted mean (VWM) concentrations in rainwater collected at La Castanya (LC, Montseny Mountains, NE Spain) were analysed from 1983 to 2000 to study the temporal trends in precipitation chemistry, and the causes behind the changes. A significant positive correlation was found between annual rainwater SO 4 2− concentrations at LC and Spanish SO 2 emissions ( r=0.73, P=0.0008) both decreasing remarkably during this period. Rainwater alkalinity increased during the period, shifting from negative values at the beginning (VWM in the 5 initial years=−2.7 μeq l −1) to alkaline values in recent years (VWM in the 5 final years=18.0 μeq l −1). Stepwise regression analysis indicated that 88% of the variation of alkalinity could be accounted for by the variability of non-marine Ca 2+ and non-marine SO 4 2−, with a more prominent dependence on Ca 2+. Rains of African provenance were highly enriched in alkalinity and Ca 2+, but no significant increases in their occurrence were found for the study period. Because of the reported higher dust updraft in northern Africa during years of high North Atlantic Oscillation (NAO) index, we also explored the relationship between rainwater variables associated with an African provenance and NAO. Annual precipitation was inversely related to NAO ( r=−0.61, P=0.007). The annual wet deposition of African dust-related elements showed no correlation with NAO, probably because wet deposition of these elements depends on two factors (precipitation and dust updraft) which have opposite behaviour with respect to NAO. We hypothesise that dry deposition of African dust during dry spells (not sampled in this study) might be higher during high NAO-index years.

Trends in sulphate and nitrate wet deposition over the United Kingdom: 1986–1999

Since 1986 annual wet deposition of non-sea-salt sulphur has decreased over all regions of the United Kingdom, with the largest decrease in eastern areas. Nationally wet deposited sulphur has decreased by about one-third compared with an approximately two-thirds decrease in sulphur dioxide emissions. Over the same period daily measurements of sulphur dioxide and particulate sulphate concentrations at a small number of sites showed a statistically significant decrease at all but the most remote locations. The comparative magnitude of the changes in UK emissions and wet deposition suggests some change in the partitioning between wet and dry sulphur deposition. Trajectory analyses of precipitation events show that background sulphate deposition has not changed significantly in northwestern coastal regions, where it accounts for approximately half of the total. Wet nitrate deposition has decreased at a slower rate and increased slightly in some remote western areas. Sector analyses suggest that this increase is linked with increased deposition during easterly airflow while particulate sulphate concentrations in these airmasses have decreased. Nitrate now accounts for at least one-third of the acidifying effect of the combined wet deposition of non-sea-salt sulphate and nitrate over all parts of the United Kingdom.

Status and trends in atmospheric deposition and emissions near Atlanta, Georgia, 1986–99

Wet and dry atmospheric deposition were investigated from weekly data, 1986–99 (1986–97 for dry deposition) at the Panola Mountain Research Watershed (PMRW), a forested research site 25 km, southeast of Atlanta, Georgia. Furthermore, the wet deposition was compared to that at three adjacent National Atmospheric Deposition Program's National Trends Network (NTN) sites (GA41, 50 km south of PMRW; AL99, 175 km northwest; NC25, 175 km north-northeast) and dry deposition was compared to that at adjacent Clean Air Status and Trends Network (CASTNET) sites, co-located at the NTN sites. The pH of precipitation is acidic and the dominant acid anion is SO 4; the pH (derived from the volume-weighted mean H concentration) averages 4.44 for 1986–99, and varies seasonally with average lowest values in summer (4.19) and highest in winter (4.63). From 1986–99, the annual wet deposition of sulfur (S) and nitrogen (N) averaged 400 and 300 eq ha −1 (6.4 and 4.2 kg ha −1), respectively. Inferential model estimates of annual dry S and N deposition from 1986–97 averaged 130 and 150 eq ha −1 (2.1 and 2.1 kg ha −1), respectively. From 1993–99, net S deposition (dry deposition plus canopy interactions) for coniferous and deciduous throughfall (throughfall minus wet-only deposition) averaged 400 and 150 eq ha −1 (6.4 and 2.1 kg ha −1), respectively. The annual wet deposition of S and N species at PMRW was comparable to that at NTN sites, with the exception of higher N species deposition at AL99 and relatively lower H, SO 4 and NO 3 deposition at GA41. Dry S deposition at PMRW differed markedly from the CASTNET sites despite similarity in S concentrations for all but NC25; the differences are attributed to differences in model parameters associated with the landscape and vegetation characteristics at the sites. At PMRW, atmospheric deposition trends were not detected for the entire sampling period, but were detected for shorter periods (4–5 yr). Annual S and N deposition increased from 1986 to 1991, decreased to 1995 and then increased to 1999. SO 2 emissions from seven major point sources within 120 km of PMRW decreased markedly from the late 1980s to 1995 and have remained relatively constant or increased slightly from 1995 to 1998 Annual wet and dry S deposition at PMRW significantly correlates ( p<0.01) with SO 2 emissions, and the correlation is dominated by the large SO 2 emissions decreases in the early 1990s, consistent with the implementation of Phase I of Title IV of the 1990 Clean Air Act Amendments.

Occurrence, emissions and deposition of mercury during coal combustion in the province Guizhou, China

Forty-eight coal samples from the major coal mines in Guizhou were collected by means of subterranean channel sampling. The average mercury content in coal from this Chinese province is 0.53 mg kg-1, which is substantially higher than coal produced in any other province of China. A strong link is proposed to exist between atmospheric mercury emissions and the combustion of coal. During the last two decades, the amount of mercury emitted from coal combustion in Guizhou has increased invariably to 8.3 tons in 1998. Being concentrated to the pyrite fraction in the coal, the implementation of physical coal cleaning is likely to be an effective way to reduce the mercury content. Total and fractionated mercury in air and precipitation was measured in the provincial capital. During a measurement campaign in October 1999, the reactive gaseous mercury (RGM) concentration averaged at 450 pg m-3, which is much higher than that in pristine area (less than 20 pg m-3). The average total mercury in rainwater of 1996 was estimated to be 33 ng L-1, and the total annual wet deposition of mercury in the area was 39 g km-2 in 1996.

Mapping of Base Cation Deposition in South Korea

Deposition of non-seasalt base cations (Ca2+ + Mg2++ K+) in South Korea was mapped for 1994 to 1997 on a 11 × 14 km grid using the so-called inferential modeling technique. It is found that the annual mean wet deposition of non-seasalt base cations is about 290 eq ha-1 yr-1 with a maximum of 470 eq ha-1 yr-1 and a minimum of 120 eq ha-1 yr-1 while the annual mean dry deposition is about 130 eq ha-1 yr-1 with a maximum of 240 eq ha-1 yr-1 and a minimum 70 eq ha-1 yr-1. Theannual mean total deposition of non-seasalt Ca2+ + Mg2+ + K+ is found to be about 420 eq ha-1 yr-1 with the predominant range of 400 eq ha-1 yr-1 to 550 eq ha-1 yr-1 thatoccupies more than 45% of total deposition of non-seasalt base cations and dry deposition constitutes on average30% of the total base cation deposition. About 30% of the annualtotal deposition of sulfur is found counteracted by depositionof non-seasalt base cations over South Korea.