Estimation of S and NOx-N deposition budgets for the United States and Canada

Extensive wet deposition monitoring data, along with much sparser dry deposition monitoring data and isolated field characterizations of droplet deposition, are used to produce an annual deposition budget for S and NO_x-N for each contiguous U.S. state and Canadian province. The contribution to wet deposition from natural sources is estimated, and wet deposition is adjusted accordingly, to focus the analysis on deposition associated with anthropogenic emissions. The budgets, which are appropriate for 1985–1987, include adjustments for increased local wet and dry deposition near point sources and urban areas, which are generally avoided in selecting monitoring sites. When aggregated over the United States and Canada, estimated wet, dry, and droplet deposition account for about 30, 29, and 4% of anthropogenic S emissions, respectively, implying that 37% is exported. For NO_x-N, estimated wet, dry, and droplet deposition account for 30, 43, and 4% of anthropogenic emissions, with 23% exported. Results are in general agreement with a variety of other observational analyses and regional modeling simulations, particularly for eastern North America, and are consistent with estimates of net horizontal mass fluxes of S and NO_x-N across the Atlantic coast of North America.     

Sudbury smelter impact on atmospheric deposition of acidic substances in Ontario

During the period from June 1982 to March 1983, there was a prolonged shutdown of the INCO and Falconbridge smelters at Sudbury, Ontario. Taking advantage of this opportunity, the Air Resources Branch of the Ontario Ministry of the Environment undertook a detailed analysis of the impact that the resulting emission reductions had on the atmospheric deposition of acidity and SO_X in Ontario. This paper summarizes the various meteorological analyses and mathematical modeling estimates that were carried out in order to determine the contribution of the Sudbury smelters to atmospheric deposition in Ontario. For sulfates, the Sudbury contribution to the total wet deposition was typically less than 15% at the receptors studied. Furthermore, the smelters were found to contribute on the order of 10 to 20% of the total dry deposition of S compounds in central and northeastern Ontario, and less than 10% elsewhere.     

Study of wet and dry atmospheric deposition at two altitudes in central Switzerland

The analysis of various ions in atmospheric deposition at two altitudes (515 m and 950 m a.s.l.) in Switzerland during 1983/84 revealed that dry deposition depends more on altitude than wet deposition. During autumn and winter, when vertical air exchange is limited, dry deposition of substances from anthropogenic sources (e.g. SO₄-S) was higher at the lower site. In the course of the year, the pattern of wet deposition was independent of altitude and showed highest rates for S, N and Ca in summertime. A comparison between rates of wet, particulate and gaseous S and N deposition suggested that during the growing season wet deposition is the dominant flux. Total (wet + dry) deposition of S, N and Cl was lower than in other parts of Europe, but a substantial increase of NO₃-N deposition during the past 25 years must have occured.     

Wet and dry deposition of nutrients in Central Alberta

Dry and wet deposition rates of various forms of phosphate and N and of Fe, sulphate, Na, K, and silica ions are reported for a 1 yr period in central Alberta. The results are extrapolated from event samples of rain and snow, and from dry deposition samples in distilled water collectors and snowpack. Following corrections for contamination and evaporation the most reliable dry deposition rates are found for orthophosphate, organic and nitrate N, and Fe, sulphate, and K ions. Ion concentrations in snow are significantly lower than those in rain for ammonia, organic, and total N and for sulphate and silica ions. More than 50% of the concentrations of total phosphate and total N in wet deposition samples is dissolved or in fine particles (less than 0.45 μ) but only about one third of dry deposition sample concentrations is in such form. Dry-to-wet deposition ratios for the year exceed one for filtered total N, filtered total phosphate, Fe, and sulphate. The largest dry-to-wet deposition ratios are about 5 for sulphate and unfiltered total N.     

Atmospheric sulfur deposition for a red soil broadleaf forest in southern China

A two-year study in a typical red soil region of Southern China was conducted to determine 1) the dry deposition velocity (Vd) for SO2 and particulate SO4^2- above a broadleaf forest, and 2) atmospheric sulfur fluxes so as to estimate the contribution of various fractions in the total. Using a resistance model based on continuous hourly meteorological data, atmospheric dry sulfur deposition in a forest was estimated according to Va and concentrations of both atmospheric SO2 and particulate SO2^4-. Meanwhile, wet S deposition was estimated based on rainfall and sulfate concentrations in the rainwater. Results showed that about 99% of the dry sulfur deposition flux in the forest resulted from SO2 dry deposition.In addition, the observed dry S deposition was greater in 2002 than in 2000 because of a higher average concentration of SO2 in 2002 than in 2000 and not because of the average dry deposition velocity which was lower for SO2 in 2002. Also,dry SO2 deposition was the dominant fraction of deposited atmospheric sulfur in forests, contributing over 69% of the total annual sulfur deposition. Thus, dry SO2 deposition should be considered when estimating sulfur balance in forest ecological systems.     

Above-Ground Sulfur Cycling in Adjacent Coniferous and Deciduous Forests and Watershed Sulfur Retention in the Georgia Piedmont,U.S.A.

Atmospheric deposition and above-ground cycling of sulfur (S) were evaluated in adjacent deciduous and coniferous forests at the Panola Mountain Research Watershed (PMRW), Georgia, U.S.A. Total atmospheric S deposition (wet plus dry) was 12.9 and 12.7 kg ha-¹ yr-¹ for the deciduous and coniferous forests, respectively, from October 1987 through November 1989. Dry deposition contributes more than 40% to the total atmospheric S deposition, and SO₂ is the major source (～55%) of total dry S deposition. Dry deposition to these canopies is similar to regional estimates suggesting that 60-km proximity to emission sources does not noticeably impact dry deposition at PMRW. Below-canopy S fluxes (throughfall plus stemflow) in each forest are 37% higher annually in the deciduous forest than in the coniferous forest. An excess in below-canopy S flux in the deciduous forest is attributed to leaching and higher dry deposition than in the coniferous forest. Total S deposition to the forest floor by throughfall, stemflow and litterfall was 2.4 and 2.8 times higher in the deciduous and coniferous forests, respectively, than annual S growth requirement for foliage and wood. Although S deposition exceeds growth requirement, more than 95% of the total atmospheric S deposition was retained by the watershed in 1988 and 1989. The S retention at PMRW is primarily due to SO₄ ²- adsorption by iron oxides and hydroxides in watershed soils. The S content in white oak and loblolly pine boles have increased more than 200% in the last 20 yr, possibly reflecting increases in emissions.     

Some approximations for the wet and dry removal of particles and gases from the atmosphere

Semi-empirical formulae are presented which can be used to estimate precipitation scavenging and dry deposition of particles and gases. The precipitation scavenging formulae are appropriate both for in- and below-cloud scavenging and comparisons with data indicate the importance of accounting for aerosol particle growth by water vapor condensation and attachment of the pollutant to plume or cloud particles. It is suggested that both wet and dry removal of gases is usually dictated by other than atmospheric processes. Dry deposition of particles to a canopy is shown to depend on canopy height, biomass, vegetative type and mean wind. Two large-scale practical problems are addressed dealing with the relative importance of wet and dry deposition and with the sources which contribute to deposition in a specific location.     

Sulfate in lakes of eastern Canada: Calculated yields compared with measured wet and dry deposition

Sulfate yields in eastern Canada, calculated as lake concentration times runoff, are presented on an approximately west to east axis, and are compared with wet deposition data from CANSAP (Canadian Network for Sampling Precipitation) and APN (Air Pollution Network) data on dry deposition. The agreement is very good, and shows clearly that dry deposition is greatest near the center of the continental pollution plume and is less important in remote areas. The good agreement also indicates that most of the sulfate in these lakes is from atmospheric deposition and that there is little retention of sulfate in their watersheds.     

Atmospheric input and origin of selected elements in Walker Branch Watershed,Oak Ridge,Tennessee

The elemental composition and relative contribution to input of precipitation and aerosols have been determined for the Walker Branch Watershed in Oak Ridge, Tennessee, U.S.A. Comparison of elemental ratios in rain to those in local soils indicates that Cu, Hg, and Pb are enriched with respect to soil by a factor of 30 to 170 and must have a non-soil source. Due to inherent problems encountered in determining elemental deposition velocities, elemental input by dry deposition was calculated using literature value upper and lower limits. If the higher deposition velocities are chosen, dry deposition could constitute from 62 to 96% of the total input for selected elements to the watershed. Enrichment factor and chemical mass balance calculations have been applied to aerosol data in an attempt to distinguish between atmospheric particulates derived from soil, automobiles, and three nearby coal-fired steam plants. Elemental deposition by wet and dry fallout has also been calculated using published deposition velocities. Mass balance calculations indicate that no more than 5% of the total aerosol load can be attributed to the three coal-fired steam plants. The steam plants can, however, account for up to 20% of individual elements collected in air above the watershed.     

A field evaluation of the Hasl wet-dry deposition collector

Samples of precipitation, dry deposition and total deposition have been obtained from Tutuila Island, American Samoa, since April 1976. These collections are part of a study of global levels of pollutants. The volume of rain water collected by a HASL wet/dry collector has averaged within 4% of the volume expected based on data obtained using a standard rain gauge. The deposition of Cl^?, SO ₄ ^?2 , NA⁺. Mg^?2 and K⁺ in the total collector, which is exposed continuously to the atmosphere, is about 10% greater than the deposition in the wet plus dry sides of the HASL collector.     

Monthly mean spatial variations of dry deposition velocities of oxides of sulphur and nitrogen

Dry deposition processes play an important role in delivering acidic SO_x and NO_x to the surface. Modeled regional S and N budgets in North America indicate that about half of the total deposition is dry deposited. Thus, there is advantage to be gained in more accurately representing dry deposition in ‘acid deposition’ model calculations. A scheme, based on a resistance analogy, for estimating areal-average deposition velocities of gaseous and particulate oxides of S and N is used. From a literature review of observations, estimates of surface resistances for gases and near surface resistances for particles are obtained. Boundary layer theory and meteorological data are used to estimate aerodynamic resistances for gases and particulates as well as near surface resistance for gases. Coupled with information on land-use, monthly mean dry deposition velocity fields are obtained. This paper briefly reviews the parameterization schemes and the required data bases. It discusses spatial and temporal variation in dry deposition velocities of the oxides.     

An analysis of wet deposition of sulfate using a trajectory model for East Asia

A long-range transport model for East Asia was developed to estimate the wet deposition of sulfate. The model is a trajectory type which is appropriate for long-term analysis. Trajectories of air masses are calculated by tracing the wind field which changes spatially and temporally. The processes of reactions, rainout removal, intake of sulfate in cloud water into rain water, and dry and wet depositions are considered. It is possible to calculate the concentration of sulfate in precipitation at a receptor by performing material balance in a grid box containing the receptor.The results obtained by the long-range transport model were evaluated through comparison with observation data of acidic deposition. The observation was conducted at 21 stations throughout Japan for one year. The calculated amount of wet deposition of sulfate in Japan was 0.22Tg/y in S equivalent, while the observed amount was 0.29Tg/y. The long-range transport model can predict almost 80% of observed wet deposition. The contributions of domestic anthropogenic sources and volcanic eruption to wet deposition of sulfate in Japan were estimated using the longrange transport model. The ratio of the deposition of sulfate due to Japanese anthropogenic sources to that due to the Asian continental sources was about 1 to 2. Since air stream from the direction of the Asian continent dominates during winter, the contribution of Japan to wet deposition in the region which faces the Sea of Japan amounted to less than 15%. The contribution of the sulfur oxides from volcanoes was about 20%.     

Atmospheric Deposition of Trace Metals at Three Sites Near the Great Lakes

The concentrations of vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb) in precipitation and on airborne particles were measured at three Integrated Atmospheric Deposition Network (IADN) monitoring stations on Lakes Superior, Michigan and Erie during 1993 and 1994. These data were used to estimate annual wet and dry deposition fluxes at these sites. In most cases, both wet and dry deposition make an important contribution to the total atmospheric flux of trace metals. Total (wet + dry) annual loadings of Zn and Cr are higher at the Lake Erie site than at the Lake Michigan and Lake Superior sites. Atmospheric loadings of the other metals are similar at all three sites. Wet deposition of metals is more closely related to precipitation amount than to the concentration of metals in the precipitation. Dry deposition fluxes are controlled by the concentration of trace metals on large particles. Total particle mass concentrations are higher during the summer and fall at the Lake Erie site, however no seasonal trends in total particle mass at the other sites or trace metals at any of the sites were detected. The total atmospheric loadings calculated in this work are in agreement with other estimates of metals deposition to the Great Lakes.     

The role of alkaline materials in precipitation chemistry: A brief review of the issues

The purpose of this paper is to provide a brief overview of the relatively unexplored role of alkaline materials in precipitation chemistry. Clearly, they can play fully as important a role as acidic materials in determining pH. The first major issue concerns sources. Comparison of Ca/K and Ca/Mg ratios in precipitation and dry deposition with those in likely sources indicates that both unpaved roads and soils make important contributions. Elemental emissions fluxes have been derived from literature estimates of mass emissions fluxes and element abundances in the important sources, but are subject to large uncertainties owing to a lack of adequate data. It is quite clear, however, that conventional (smokestack) sources are minor compared to open sources such as those already identified. Another major issue concerns interactions between alkaline aerosols and water in the atmosphere. Reactions involving suspended solids that lead to removal of H-ions from solution include ion exchange and mineral weathering. A simplified model of acid buffering indicates that NH4, Ca, Mg, K, and Na buffer between 25 and 50% of the potential acids in U.S. precipitation everywhere east of the Mississippi River. The third major issue concerns wet and dry deposition fluxes of alkaline materials. Wet deposition fluxes are currently being measured adequately by a nationwide network of weekly samplers. There is no agreed-upon method for monitoring dry deposition, but available information suggests that dry deposition accounts for somewhat more than half of the Ca deposition. A list of research and data needs is also provided.     

Dry and wet atmospheric deposition of nitrogen, phosphorus and silicon in an agricultural region

We measured atmospheric nutrient deposition as wet deposition and dry deposition to dry and wet surfaces. Our analyses offer estimates of atmospheric transport of nitrogen (N), phosphorus (P) and silicon (Si) in an agricultural region. Annual dry and wet deposition (ha^?1 year^?1) was 0.3 kg of P, 7.7 kg of N, and 6.1 kg of Si; lower than or similar to values seen in other landscapes. N:P and Si:N imply that atmospheric deposition enhances P and Si limitation. Most P and soluble reactive P (SRP) deposition occurred as dryfall and most dry-deposited P was SRP so would be more readily assimilable by plant life than rainfall P. Dry deposition of N to wet surfaces was several times greater than to dry surfaces, suggesting that ammonia (NH _x ) gas absorbtion by water associated with wet surfaces is an important N transport mechanism. Deposition of all nutrients peaked when agricultural planting and fertilization were active; ratios of NH _x :nitrate (NO _x ) hbox{reflected} the predominant use of NH _x fertilizer. Wet deposition estimates were consistent over hundreds of km, but dry deposition estimates were influenced by animal confinements and construction. Precipitation wash-out of atmospheric nutrients was substantial but larger rain events yielded higher rates of wet deposition. Methodological results showed that local dust contaminated wet deposition more than dry; insects, bird droppings and leaves may have biased past deposition estimates; and estimating dry deposition to dry plastic buckets may underestimate annual deposition of N, especially NH _x .     

Lichen sulphur and lead levels in relation to deposition patterns in Eastern Canada

Marked differences exist between the S and Pb concentration in Cladina ranziferina collected from eastern Canada and the Northwest Territories, Canada. These differences reflected the differing emission/deposition rates in the two regions. The spatial distribution of S and Pb in the lichen from eastern Canada is described in detail. Mean S concentrations ranged from 329 to 959 μg g^?l; Pb concentrations varied in the range 3 to 21 μg g^?l. A regional gradient in lichen S concentrations was evident with the highest concentrations being found in central and north-central Ontario and the lowest in Newfoundland. A regional gradient for Pb was apparent but was not as well defined as that for S. The regional distribution of S illustrated by the lichen agreed with another indirect measurement of S deposition. Lichen S concentrations correlated with measured wet sulphate deposition.     

Meteorological variability of the wet and dry deposition of sulphur and nitrogen compounds over the baltic sea

The dry and wet deposition of N and S compounds to the Baltic Sea Basin were assessed using daily concentration measurements of air and precipitation concentrations, and actual meteorological data on precipitation, daily wind speed and wind direction, as well as the buoyant fluxes at the air- sea interface. The data cover the period 1980–86. Both concentrations and deposition levels show distinct south-north gradients and strong seasonal variability. Dry deposition is an important contribution in the case of S (25 to 80%) but is less significant for the N compounds (10 to 30%). The contribution of particles to dry deposition is negligible for S, equivalent to the gaseous contribution for oxidized N and about 10 to 20% for reduced nitrogen compounds. The obtained total annual deposition of about 1.4 to 1.8 g(S) m^?2 for the S compounds, and 1 g(N) m^?2 for the N compounds are comparable with, but on the upper side of, previous empirical and model estimates.     

Input of pesticides by atmospheric deposition

Sampling and analytical methods were developed to examine the input of various pesticides on noncultivated areas of the FAM (Research Network on Agroecosystems) Research Station Scheyern. Off-target drift from pesticide application on nearby cultivated land, as well as input due to long-range atmospheric transport, were measured. The wet deposition was determined by a cooled wet-only sampler. Bulk samplers and specially designed samplers with glass-fiber surface were used for total deposition measurements. Analysis of pesticides was carried out using liquid/liquid or solid-phase extraction and high performance liquid chromatography-UV (HPLC-UV) or gas chromatography-nitrogen/phosphorus-sensitive detector/MS (GC-NPD/MS) detection. Obtained results demonstrated that for several compounds, total deposition, i.e. the sum of wet and dry deposition, was marginally higher than wet deposition alone. In contrast, total deposition data of pesticides having been applied near the sampling site exceeded wet deposition values by orders of magnitude. In addition to direct drift, determined as droplets depositing near pesticide application areas, an indirect drift represented by particle-associated or gaseous transport was observed, both of which contributed considerably to total deposition. Therefore, to determine the input of pesticides to nontarget areas in the close vicinity of pesticide application, direct and indirect drift, and background deposition must be considered.     

Wet and Dry Deposition Fluxes of Polychlorinated Biphenyls (PCBs) in an Urban Area of Turkey

Atmospheric polychlorinated bihenyls (PCBs) deposit by dry and wet deposition mechanisms, and therefore they constitute a significant polluting source for lands and surface waters. Various samplers have been used to determine the PCB pollution level resulting from deposition. In the presented study, a modified wet deposition sampler (WDS) was used for sampling both wet and dry deposition samples with the same instrument by which wet deposition reservoir of the WDS is opened and dry deposition reservoir is closed when rain starts. Wet and dry deposition samples were collected between June 2008 and June 2009. In the samples taken from BUTAL which is known as an urban area with heavy traffic, ??PCB dry deposition fluxes were determined as 18?±?10 ng/m²??day, and wet deposition fluxes for dissolved and particle phase were measured as 480?±?1,185 and 475?±?1,000 ng/m²??day, respectively. The dissolved and particle-phase PCB concentrations in rain were 10?±?13 and 13?±?14 ng/l, respectively. The contribution of wet deposition to total PCB deposition was determined as 52%. PCB concentrations in the ambient air were measured to be 370?±?200 and 20?±?20 pg/m³ for gas and particle phases, respectively. Washout ratio was determined by proportioning rain concentration to concentration in air. The washout ratios of the samples were between 1,675?C311,800 and 12,775?C2,511,120 for dissolved and particulate phases, respectively.     

A Numerical Simulation of Acid Deposition in East Asia

The goal of the present study is to do a long term simulation and to derive a source receptor-relation using a comprehensive Eulerian acid deposition model coupled with a dynamic meteorological model. The selected modeling period is from March 1 to April 30, 1996. A dynamic meteorological model named MM5 was first used to calculate meteorological fields and then STEM preprocessors were invoked to generate dry deposition velocities and eddy diffusivities. Finally, a multi-scale STEM was applied to simulate both wet and dry acid deposition phenomena. The source-receptor relations were also estimated for sulfate and nitrate species using a counter species method. The model results for SO₂ and O₃ agree very well with measurements. However the model under-predicts the NO₂ concentration due to insufficient grid resolution as well as due to inaccurate field measurement. The transport contribution for total mass and wet deposition is much larger than that of dry deposition.