Dry Deposition Estimates Research Articles

Atmospheric inputs of manganese and aluminium to the Sargasso Sea and their relation to surface water concentrations

Atmospheric wet and dry deposition estimates for aluminium and manganese are presented for Bermuda and extrapolated to the Sargasso Sea. These deposition estimates are compared to average surface water concentrations of these elements to infer surface water residence times and also to constrain the solubility estimates for these metals in seawater after atmospheric deposition. For aluminium, atmospheric input fluxes and solubility are consistent with the seasonality of surface seawater concentration data and yield an average residence time in the upper 100 m of 6.5 yr. For manganese, it is more difficult to reconcile these various data sets suggesting that the solubility of atmospherically delivered manganese may have been underestimated and that photochemistry may play an important role in the surface water cycling of manganese. Together these effects suggest an estimated manganese residence times at the lower end of a 5–21 yr range for the upper 100 m of the water column.

Acid deposition to nature areas in the Netherlands: Part I. Methods and results

In this paper estimates of dry and wet deposition of acidifying substances in the Netherlands are presented. The deposition was estimated from measured concentrations in the atmosphere and in precipitation or if these were not available, from modelled concentrations. The method was applied for the Netherlands on a 5×5 km scale. The most important components are sulphur oxides and ammonia and their reaction products. It was estimated that the annual average deposition of SO x in the Netherlands decreased from 1570 to 670 mol ha−1 a−1 between 1980 and 1989. In 1989, the annual average NO y deposition was estimated to be 1220 mol ha−1 a−1 in 1980 and 1160 mol ha−1 a−1 in 1989. The annual average NH x deposition in the Netherlands was estimated to be 2330 and 2190 mol ha−1 a−1 in 1980 and 1989 respectively. HCI deposition was about 100 mol ha−1 a−1 in all years. Dry deposition contributes most to the total deposition for each component. The spatial distribution of the total deposition shows a gradient over the Netherlands with highest values in the South and lowest in the North of the country. Meteorological conditions are also of influence on the deposition fluxes for all components. During 1988 and 1989 meteorological conditions favoured low deposition. The estimated uncertainty in the average fluxes of SO x , NO y , and NH x for the Netherlands is 15, 25, and 30% respectively. The wet deposition fluxes can be estimated more accurately than the dry deposition.

Dry deposition velocity estimates of SO2 from models and measurements over a deciduous forest in winter

Measurements were made of concentrations and vertical flux densities (using the eddy correlation technique) for SO2 over a deciduous forest during March and April 1990. These were compared with estimates of dry deposition velocities, obtained from resistance analogue models that employ measured meteorological data as input. The models include: (1) the dry deposition module that forms part of a larger Eulerian air quality model, known as ADOM (Acid Deposition and Oxidant Model), (2) a modified version of ADOM and (3) a new parameterization for Rc. The observations yielded Vdvalues of about 0.5 cm s−1 for the daytime and 0.1 cm s−1 at night. ADOM's estimates were much larger, averaging about 3.0 cm s−1 during the daytime and about 2.0 cm s−1 at night. When the ADOM canopy resistance was increased by modifying its formulation, the modified dry deposition estimates were slightly larger during the day than at night, averaging about 0.5 cm s−1. The new parameterization for Rcyielded smaller Vdestimates with no diurnal variation. An attempt is made to relate the observed diurnal cycle of the dry deposition velocity to meteorological parameters.

Atmospheric sulphur deposition to forest stands: Throughfall estimates compared to estimates from inference

Wet and dry deposition of sulphur was estimated for 30 forest stands in the Netherlands using a throughfall method and an inferential method. Dry deposition estimates of the throughfall method were significantly higher compared to estimates from inference. The major sources of uncertainty of the throughfall dry deposition estimates were associated with non-representative throughfall sampling, wet deposition estimates, canopy exchange processes, deposition of neutral salts, dry deposition directly onto the throughfall collectors, and with the omission of stemflow fluxes and dry deposition directly to the undergrowth vegetation and forest floor. These uncertainties were found to act both ways to approximately the same extent and were not able to explain the observed gap between the two dry deposition estimates. For the inferential method, major sources of uncertainty in the dry deposition estimates arose in calculation of the dry deposition velocity of SO 2 and the omission of occult deposition of SO 4 2−. In this study, uncertainties associated with the spatial averaging of air concentrations of SO 2 and SO 4 aerosol and the calculation of the deposition velocity of SO 4 aerosol were found to be relatively small. Modifying the R c parametrization of SO 2, based on recent dry deposition measurements made over heather in the Netherlands, resulted in fairly good agreement between both dry deposition estimates. Occult deposition of SO 4 2− was found to contribute significantly to the total sulphur deposition to the forest stands. Both the modified R c parametrization and the incorporation of occult deposition led to systematically higher sulphur deposition estimates by the inferential method compared to originally inferred deposition. This implies that in the Netherlands, sulphur deposition to forest ecosystems might have been underestimated heretofore.

A new method for estimation of dry deposition of particles based on throughfall measurements in a forest edge

Abstract Throughfall measurements are very often used to calculate the atmospheric input to ecosystems. Such attempts are normally complicated by canopy interaction processes which are difficult to assess. This study presents an approach to calculate dry deposition and canopy leaching of Ca 2+ , Mg 2+ and K + to forests. The calculations are based on throughfall measurements in a forest edge of a spruce stand and by use of Na + as a model substance for dry deposition of particles. This ‘forest edge approach’ is compared with an approach based on equal Na + to base cation ratios in wet and dry deposition (‘wet/dry ratio approach’), which has been widely used in the literature. Our calculations show that the wet/dry ratio approach may overestimate the dry deposition of Ca 2+ , Mg 2+ and K + by up to 100% and leaching will correspondingly be underestimated. The assumptions underlying the different approaches and the use of throughfall measurements to estimate dry deposition are discussed and it is suggested that throughfall measurements in forest edges may be a valuable improvement to studies of atmospheric deposition in forests.

Atmosphere‐surface exchange of mercury in a forest: Results of modeling and gradient approaches

We have modified recently published dry deposition models to estimate deposition velocities (Vd) for Hg in both fine aerosol and vapor form to forest canopy surfaces. Aerosol and total vapor phase Hg concentrations in air previously measured at Walker Branch Watershed in Tennessee have been used with model results to estimate dry deposition to a deciduous forest. The concentration data confirm that airborne Hg is dominated by vapor forms at this site and exhibits concentrations moderately above continental background levels. The modeled Vd values reflect published data which suggest that dry deposition of Hg vapor is strongly controlled by surface transport processes, notably stomatal and mesophyll resistances, the latter dominating. Weekly mean Vd values ranged from 0.006 (winter) to 0.12 (summer) cm s−1. We have also measured concentration gradients of Hg vapor in air above this forest to estimate air‐surface exchange during short‐term experiments. While the model results indicate that the canopy is a sink for Hg vapor, the concentration profiles suggest that the forest soils are a source during some periods, the combined effect of which is net Hg fluxes in the upward direction. Application of a detailed canopy turbulence model yielded soil emission rates of the order of 50 ng Hg m−2 h−1, ∼10% of which is deposited in the canopy. Our modeled dry deposition estimates plus limited measurements of wet deposition in this area suggest that dry and wet deposition may be comparable in magnitude.

Atmospheric concentrations and deposition of Hg to A deciduous forest atwalker branch watershed, Tennessee, USA

Aerosol and total vapor-phase Hg concentrations in air have been measured at Walker Branch Watershed, Tennessee for ≈ 2 yr. Airborne Hg at this site is dominated by vapor forms which exhibit a strong seasonal cycle, with summer maxima that correspond to elevated air temperature. Concentrations in this forest are near background levels; however, concentrations at a site within 3 km are significantly elevated due to emissions from Hg-contaminated soils. The concentration data have been combined with a recently modified dry deposition model to estimate dry deposition fluxes to the deciduous forest at Walker Branch. Weekly mean modeled Vd values for Hg° ranged from 0.1 (summer) cm s1. Weekly dry deposition fluxes ranged from 1.0 µgg m−2 in the summer. Our dry deposition estimates plus limited measurements of wet deposition in this area indicate that dry deposition may be the dominant input process in this forest, at least during the summer.

Deposition of atmospheric ions to pine branches and surrogate surfaces in the vicinity of emerald lake watershed, Sequoia National Park

Atmospheric dry deposition of ions to branches of native Pinus contorta and Pinus monticola (natural surfaces), and nylon filters and Whatman paper filters (surrogate surfaces) were measured in the summer of 1987 in the vicinity of Emerald Lake Watershed (ELW) of the Sequoia National Park located on the western slope of the Sierra Nevada in California. Deposition fluxes of airborne NO−3, NH+4 and SO2−4 to native pines at the ELW were much higher than in the eastern Sierra Nevada, but several times lower than deposition fluxes to natural and surrogate surfaces at the highly polluted site in the San Gabriel Mountains of southern California. Deposition fluxes of NO3− and NH4+ to the natural and surrogate surfaces at the ELW were much higher than deposition of SO42−, providing the importance of N compounds in atmospheric dry deposition in this part of the western U.S. A deficit of inorganic anions in materials deposited to various surfaces indicated a possibility of substantial participation of organic acids in atmospheric dry deposition processes. Nylon and paper filters proved to be poor surrogate surfaces for the estimation of ionic dry deposition to conifer branches.

Dry deposition of sulfur: a 23-year record for the Hubbard Brook Forest ecosystem

Dry deposition of S was estimated for watershed-ecosystems of the Hubbard Brook Experimental Forest from 1964–65 through 1986–87. Two approaches, a regression analysis of bulk precipitation inputs and stream outputs and a mass-balance method, gave similar average values for Watershed 6 (430 and 410 eq SO 4 = /ha-yr, respectively, for this 23-year period). Dry deposition contributed about 37% of total S deposition, varying from 12% in 1964–65 to 61% in 1983–84. Long-term data from “replicated” watershed-ecosystems showed that temporal variability in estimates of dry deposition was considerably greater than spatial (between watersheds) variability. DOI: 10.1034/j.1600-0889.1990.t01-3-00002.x

Dry deposition of sulfur: a 23-year record for the Hubbard Brook Forest ecosystem

Dry deposition of S was estimated for watershed-ecosystems of the Hubbard Brook Experimental Forest from 1964–65 through 1986–87. Two approaches, a regression analysis of bulk precipitation inputs and stream outputs and a mass-balance method, gave similar average values for Watershed 6 (430 and 410 eq SO 4 = /ha-yr, respectively, for this 23-year period). Dry deposition contributed about 37% of total S deposition, varying from 12% in 1964–65 to 61% in 1983–84. Long-term data from “replicated” watershed-ecosystems showed that temporal variability in estimates of dry deposition was considerably greater than spatial (between watersheds) variability. DOI: 10.1034/j.1600-0889.1990.t01-3-00002.x

Wet, occult and dry deposition of pollutants on forests

Mechanisms by which air pollutants are transferred to forests by wet and dry deposition and in wind-driven cloud water (occult deposition) are reviewed. New methods of making deposition estimates are described. In upland forests, orographic cloud can enhance the amount and ionic concentration of precipitation so that wet deposition may be 4–5 times larger than in nearby valleys. Recent work supports the use of a simple aerodynamic relation to estimate rates of occult deposition. Occult deposition rates to forests in identical weather conditions may vary by an order of magnitude depending on forest structure. Evaporation of deposited water may cause the solute concentration of water on foliage to be substantially larger than in cloud. Dry deposition of HNO 3 and HCl is controlled by aerodynamic properties of the canopy. Several kg N ha −1 year −1 are deposited to forests by this path. Transfer of SO 2, H 2O 2 and O 3 is restricted by surface and internal resistances of foliage. Controls of dry deposition of ammonia and nitrogen oxides and of particles are not well known. A canopy transfer model “Maestro” was modified to include gaseous pollutants, and agrees well with measured SO 2 fluxes to a forest. Estimates of wet, occult and dry deposition on Keilder Forest, England, and Whitetop Mountain, U.S.A., show substantial differences in occult deposition which are only partly explained by differences in cloud frequency. Regional cloud chemistry probably differs between the sites, and different models of occult deposition also disagree.

Sulfur dry deposition over the western North Atlantic: the role of coarse aerosol particles

A number of investigators have observed substantial amounts of coarse fraction ( D > 1 μm) non-sea-salt or excess sulfate (XSO 4 ) to prevail in marine boundary layer (MBL) aerosol. Its dry deposition velocity may be 1 cm s -1 or more with low uncertainty relative to the dry deposition velocity of fine-fraction XSO 4 . Estimates of total sulfur dry deposition using MBL ambient air data over the western North Atlantic Ocean are presented. It is shown, at distances of hundreds to 1000 km downwind from sulfur source regions, that sulfur dry removal from the western North Atlantic MBL is dominated by the dry deposition of XSO 4 rather than that of SO 2 . DOI: 10.1111/j.1600-0889.1989.tb00312.x

Variability of aerosol size distributions above the North Sea and its implication to dry deposition estimates

Variability of aerosol size distributions above the North Sea and its implication to dry deposition estimates

Atmospheric Sulfur Deposition to Agricultural Land in Northeastern Ohio

AbstractIn certain forms, S is an important acid‐forming substance deposited from the atmosphere to the earth's surface. Controversy surrounds estimates of total S deposition because of an inability to accurately measure S in dry deposition (particulate fallout and gaseous sorption). In a field experiment in northeastern Ohio, the amount of S in dry deposition was determined over a 3‐yr period using 20 lysimeters (4.8 m by 1.7 m) cropped with soybean [Glycine max (L.) Merr.]. Two treatments consisting of tillage (conventional or no‐tillage) and elemental S addition (0 or 50 kg ha−1) were applied to the lysimeters. Sulfur inputs to the lysimeters as precipitation and agricultural amendments and S outputs, as runoff and leachate waters, were determined using ion chromatography or alkaline oxidation techniques. The net S output (total outputs minus measured inputs) was considered to equal dry deposition. Precipitation and agricultural amendment inputs of S were 10.2 and 3.8 kg ha−1 yr−1, respectively. In comparison, S in dry deposition ranged from 14 to 26 kg ha−1 yr−1 for the conventional tilled treatment and from 25 to 39 kg ha−1 yr−1 for the no‐tilled treatment, with the upper values of these ranges considered most accurate. Dry deposition is clearly as important as precipitation in contributing to the total S load at this location. A sulfur dry deposition estimate of only 15 kg ha−1 yr−1 was made based on average deposition velocity and ambient SO2 levels. Total deposition models, which rely on dry deposition estimates obtained by the use of SO2 concentrations and an average deposition velocity, may yield inaccurate values of total S additions to the earth's surface.

Precipitation and throughfall chemistry in Pinuscontorta ssp. latifolia ecosystems, southeastern Wyoming

Precipitation and throughfall quantity and chemistry were measured in several Pinuscontorta ssp. latifolia ecosystems in southeastern Wyoming. Bulk deposition (open collector) was somewhat enriched chemically in comparison with wetfall (shielded collector), suggestive of dry deposition. With the exception of low S concentrations, atmospheric chemistry was comparable to other continental locations in North America. Concentrations of most solutes were much higher in canopy throughfall than rainfall. Canopy evaporation accounted for a 27% increase of dissolved solids in throughfall, the remaining differences being attributed to canopy leaching and washing of dryfall. Throughfall was most enriched in K+, Mg2+, and organic anions, indicating the importance of canopy leaching. Very high spatial variation was observed within the forests, precluding the detection of annual or site differences in throughfall chemistry. Our estimates of dry deposition to the lodgepole pine ecosystem were lower than for more polluted regions of eastern North America. Except for SO42−, wetfall supplied larger amounts of the major elements than dry deposition. Canopy leaching was a major flux pathway in these ecosystems, particularly for K+, Mg2+, and SO42−.

An estimate of the importance of dry deposition as a pathway of acidic substances from the atmosphere to the biosphere in eastern Canada

The relative importance of dry and wet deposition of sulphate and nitrate over southeastern Canada is examined using daily air and precipitation chemistry observations made at 6 rural stations of the Air and Precipitation Monitoring Network (APN) during the period 1979 to 1982. Dry deposition was calculated from these air concentrations using deposition velocity information on land-use types, on atmospheric wind speed and stability and on dry deposition rates from over 80 published studies. Despite the large uncertainty in dry deposition estimates which is associated with the complexity of the process, valuable conclusions emerge. It is estimated that total annual deposition varies between 10 to 86 mmole m −2 and 13 to 62 mmole m −2 for SO = 4 and NO - 3 , respectively. To eastern Canada 22% and 30% of the total SO=4 and NO−3 deposition is dry deposited, respectively. Depending on location, the contribution of SO2 to the dry deposition of sulphur ranges from 37% to 78%. It tends to decrease with increasing distance from major sources. In eastern Canada, the best estimate of the fraction of the total dry deposition of nitrogen contributed by NO2 and HNO3 is in the range 50% to 60% and 31 % to 45%, respectively, depending on location. The uncertainty in the NO2 estimate is large, approaching a factor of 3.5. Even if PAN dry deposition velocities are equal to that of NO 2 (they are expected to be lower), the contribution of PAN to total nitrate deposition is negligibly small. Both dry and wet deposition are episodic in nature. It is estimated that the top-20% deposition events yield 47% to 70% of the total deposition. DOI: 10.1111/j.1600-0889.1988.tb00213.x

Weathering and mass balance in small drainage basins : environmental applications in the Bohemian Massif (Central Europe). Altération et bilan de masse dans de petits bassins de drainage : applications au Massif bohémien (Europe centrale)

Data on inputs and outputs of chemical elements in small representative basins are used to demonstrate the application of mass balance equation to : (1) Evaluation of the rates of weathering and erosion, (2) Proton balance in acidified forested and agricultural basins, (3) Estimation of dry deposition of S0₂ and acumulation of sulphur in soil, (4) Derivation of rate constants of dissolution of feldspars. Specific mass balance equations are derived for all the cases. Calculations are performed step by step to serve as a guide for similar calculations by interested reader. The mathematical models are tested using field data from small catchments in the Bohemian Massif and the methods of gathering the data are described. The bedrock of the tested basins is biotitic gneiss. It is covered by regolith with well developed typical and acid brown earths. The basins represent forested and arable land which receives various doses of dry S0₂ emitted to atmosphere by industry. The mass balance calculations indicate that the rate of weathering of bedrock has been increased twice by modern agriculture and acid industrial depositions. Only 9 to 21 % of weathered rock are removed by chemical erosion in true solution while the rest is fixed in regolith as secondary and residual solids and minerals. The particles are removed by mechanical erosion. The environmental acidification is caused mainly by dry depositions of S02 and in lesser degree by acid rain and deposition of nitrogen oxides. The dissolution rate of oligoclase in bedrock derived from the measured fluxes of sodium is about two orders of magnitude lower then the rate determined by laboratory experiments with freshly ground feldspars. The processes and mass balance of weathering, erosion and environmental acidification strongly depend on the properties of the interface between minerals and natural aqueous solutions. A further research should be directed towards better understanding of the surface chemistry of the interface under field conditions.

Comparison of surrogate surface techniques for estimation of sulfate dry deposition

The dry deposition rates of sulfate particles to artificial surfaces within and above a mature hardwood forest were measured over an annual range of synoptic weather conditions. Artificial, or ‘surrogate’, surfaces representing both rough and smooth textural types included deposition buckets, petri dishes, filter paper, Teflon configurations and polycarbonate membranes. Ambient concentrations of sulfate and sulfur dioxide were also monitored. The artificial surfaces were evaluated on the basis of the magnitude of the sulfate dry deposition rates and measurement precision. Correlations between techniques and the magnitude of the deposition velocities identified technique similarities. Ambient concentrations of the sulfur oxides and the deposition rates were not well correlated. For diverse reasons, many of the techniques were found to have limited reliability. The petri dish, bucket inside and filter plate surfaces were found to represent the most precise devices for the estimation of dry deposition to smooth, complex and rough artificial surfaces, respectively. Seasonal averages for samplers exposed at all heights were 11.2, 27.7 and 71.2μg SO 4 2−m −2h −1, yielding mean deposition velocities to surfaces exposed within the forest canopy of 0.03,0.11 and 0.14 cm s −1 and an annual estimate of the potential dry deposition to a foliated hardwood forest of 4.0, 11.5 and 21.0 kg SO 4 2−ha −1 for the petri dish, bucket inside and filter plate surfaces, respectively. The indirect ratio between deposition rates and velocities results from varying concentrations of ambient sulfate between sampling periods. The accuracy of the filter plate data is suspect due to a significant correlation with sulfur dioxide concentrations. Sulfur concentration and deposition rate gradients indicate the forest is providing a net sink for sulfur pollutants during periods with foliage. The wide range of dry deposition rates estimated from the variety of deposition surfaces emphasizes the uncertainty of the artificial surface measurement techniques. In spite of these limitations, surrogate surfaces provide an estimate of sulfate flux rates not currently obtainable from natural surfaces.

Improved estimates of sulfate dry deposition in Eastern North America

AbstractSeasonable sulfate dry deposition, computed numerically with a Lagrangian regional‐scale model, appears to be smaller than previous estimates.

Transfer to terrestrial surfaces

The processes by which atmospheric pollutants are transferred to the ground may be placed into two categories. Wet deposition, which includes all pollution reaching the surface in precipitation, and dry deposition which includes the sorption of gases and capture of particulate pollutants by terrestrial surfaces. The properties of each of the removal mechanisms are described for the gases SO 2 , NO 2 , HNO 3 and the atmospheric aerosols containing sulphate and nitrate. Following a description of the processes, rates of deposition appropriate for a range of vegetation and atmospheric conditions are provided. The influence of changes in the properties of absorbing surfaces due to the presence of water or for vegetation to changes in stomatal conductance is discussed. The use of transfer resistances to describe the mechanism of deposition is then extended to provide estimates of dry deposition of SO 2 on to Great Britain which are contrasted with wet deposition. The resulting maps show that over most of England, including central, eastern and southern areas, dry deposition exceeds wet deposition. For north west England, Wales and northern Scotland, particularly the large rainfall districts of the west, wet deposition exceeds dry deposition.