A Case Study on Estimation of Dry Deposition of Sulfur and Nitrogen Compounds by Inferential Method

In order to estimate dry deposition, deposition velocity calculation and concentration measurement were carried out in Niigata, Japan. Deposition velocities of SO₂ and HNO₃ for some surfaces such as coniferous forest, deciduous forest, agricultural land, and water were calculated taking into account diurnal variations of meteorological elements using routine meteorological data. Deposition velocities of fine and coarse aerosols were also estimated respectively. Concentrations of SO₂, HNO₃, sulfate and nitrate in fine and coarse aerosols respectively were measured from July to December in 1998 using filter pack and denuder methods. The results indicate that HNO₃ dry deposition for the high aerodynamic roughness surfaces such as forests is quite large. It is suggested that sulfate and nitrate aerosols depositions as well as the gases depositions should be taken into account to estimate dry deposition of sulfur and nitrogen compounds. It is also indicated that dry depositions of sulfur and nitrogen compounds are unable to ignore compared with their wet depositions.     

Atmospheric Deposition of Acidifying Components to a Japanese Cedar Forest

One-year field measurements were conducted in a Japanese cedar (Cryptomeria japonica) forest, located in Gunma Prefecture, Japan. On the basis of the meteorological and atmospheric concentration data, the dry deposition of SO₂, HNO₃, NO₂ and HCl was estimated using the inferential method. The annual dry deposition of H⁺ was estimated at 721 eq ha^?1yr^?1, which was 40% larger than the measured annual wet deposition of H⁺ (514 eq ha^?1yr^?1). Therefore, dry deposition is an important pathway for the atmospheric input of H⁺ to the forest in the study site. The contribution of each gas to the dry deposition of H⁺ was as follows: SO₂, 25%; HNO₃, 32%; NO₂, 10%; and HCl, 33%. The extremely high contribution of HCl appeared to be caused by the high emission intensity of HCl due to waste incineration in the site region. The differences between estimated deposition and throughfall and stemflow measurements indicated that about 80% of the total deposition of H⁺ was taken up by the canopy.     

Simulation of Dry Deposition Rates of Acidic Pollutants—An Assessment of Deposition Pathways in Hiroshima, Japan

A eulerian grid photochemical transport and dispersion model was used to simulate the dry deposition rates of nitrogen (as HNO₃) and sulfur (as SO₂) in Hiroshima, west Japan. Seasonal patterns of predicted dry deposition fluxes reveal that HNO₃ is most prevalent at more remote locations while SO₂ is deposited near to and slightly downwind from the major emission sources. The predicted dry deposition rates of HNO₃ and SO₂ were compared to the values measured at Mt. Gokurakuji (located in Hatsukaichi) and in Hiroshima City. The simulation results show that the model under-predicted (about 44% and 80%, respectively) both nitrogen and sulfur deposition rates at Mt. Gokurakuji and in Hiroshima City, indicating that the acid deposition in Hiroshima prefecture is possibly affected by long-range transboundary transport of acidic pollutants. Comparison of wet to dry deposition ratios (4.5 and 8.7 for nitrogen and 4.6 and 7.0 for sulfur) from the two observation sites above indicates that wet deposition maybe the most important acid deposition pathway in Hiroshima, Japan.     

On the variability of simulated source-receptor relationships for sulfur deposition

The use of Lagrangian models to estimate source-receptor relationships for ambient SO₄ ⁼ concentrations and S deposition has become fairly widespread over the past several years. This paper addresses the sensitivity of long-term simulations of a Lagrangian S transport and deposition model to actual variations in SO₂ emissions and meteorological conditions. The variations of predicted source-receptor relationships due to (1) the inclusion of day to day variations in emissions strength as opposed to the use of the annual average daily emission rate and (2) year-to-year variations in meteorological conditions were studied to identify causes of uncertainty in a Lagrangian model. The results suggested that adding information on day to day emission variations for a specific point source resulted in variations in estimated S wet deposition of the order of only 20% within 500 km of the source.Year-to-year variations in meteorological conditions, on the other hand, resulted in variations in predicted S wet deposition of the order of 50% for some receptors. The variation in estimated source-receptor relationships for a given source/receptor combination was found to range as high as 70% over a 5-yr modeling period.     

Relationship of ambient atmospheric hydrocarbon (C12–C32) concentrations to deposition

Anthropogenic and biogenic high molecular weight (C₁₂–C₃₂) hydrocarbons (HC) were deposited from the atmosphere in association with both wet and dry deposition. Wet deposition generally removes HC at a faster rate (22 to 670 μg m^?2 day^?1) than dry deposition (4 to 189 μg m^?2 day^?1). However, due to longer periods during which dry deposition occurred, the removal of atmospheric HC by wet and dry deposition is almost equal during this sampling period. Atmospheric HC concentrations ranged from 0.8 to 4.1 μg m^?3 and show no simple relationship to wet or dry deposition rates. Large variabilities in deposition rates for individual events were found, but long-term average deposition was relatively constant.     

Modeling atmospheric effects — An assessment of the problems

Our ability to simulate atmospheric processes that affect the life cycle of pollution is reviewed. The transport process is considered on three scales: (a) the near-source or single-plume dispersion problem, (b) the multiple-source dispersion problem, and (c) the long-range transport. Modeling the first of these is shown to be well within the capability of generally available techniques, although determining the input parameters is often difficult. The second scale has been well studied within the context of urban diffusion and is a very productive area of current research. Finally, long range transport is treated mainly as a meteorological problem. The state of the art in modeling the various meteorological processes is reviewed. Removal of pollutants is discussed in the form of both dry deposition and precipitation scavenging. It is suggested that dry removal is especially effective in forested areas, and that the forests may enhance accumulation of pollutants. An approximate transport model is developed which is used to calculate the ambient concentration of SO₂ throughout the United States. Associated calculations include dry deposition and the ratio of dry to wet removal for each State of the contiguous United States.     

Comparison of dry deposition velocities for SO2, HNO3 and SO4 2− estimated with two inferential models

Dry deposition velocity estimates of SO, HNO₃ and SO₄ ^2? were computed for six locations in eastern North America using two different inferential models; a Big-Leaf model utilized by the U. S. National Dry Deposition Network (NDDN) and, a land-use based model (LUM) that has been used in the past to estimate the relative importance of dry versus wet deposition over selected Canadian regions. There were consistent differences between models that were related to the surface type, chemical species and time of year. Mean monthly dry deposition velocities based upon the 1990–91 time period were compared at two locations. The seasonal cycles in deposition velocity were similar between models, but there were considerable differences in the amplitude of the cycles. The LUM predicted about a 400% increase in S042- deposition velocity from the winter to the summer months, while there was a 50 to 100% increase in the NDDN model estimates, depending upon location. According to the LUM, HN03 deposition to crop land increased by about a factor of 6 from winter to summer, while the big leaf model predicted a 50% increase. Overall, there was better agreement for SO₂. Averaged over 12 months, the differences in deposition velocity between models were smaller and generally within the range of uncertainty associated with inferential models. For all six sites, the mean percent difference between models in deposition velocity for SO₂, HNO₃ and SO₄ ^2? were 13, 35 and 79, respectively. These differences highlight the effect of using different methods for estimating dry deposition and the importance of applying the same model when examining regional patterns in dry/total deposition rates.     

Chemical deposition to a high elevation red spruce forest

A preliminary analysis of O₃, SO₂, SO _inf4 ^sup2? , and total NO _inf3 ^sup? deposition to the red spruce forest on the summit of Whitetop Mountain, Virginia, illustrates uncertainties in analysis methodologies, establishes the relative importance of three deposition pathways, and suggests areas for further research. Results are presented here for an analysis of the dry, wet (precipitation), and cloud water deposition pathways for the four chemical species during a 26-day period in April and May 1986. Dry and cloud water depositions are estimated using available models along with air and cloud water chemistry measurements made at the summit. For water soluble species, depositions by precipitation and cloud interception are found to be comparable in magnitude, while dry deposition appears to be about an order of magnitude less. High levels of atmospheric O₃ lead to a large estimate of 03 deposition (on a mass flux basis) when compared to the estimated deposition of gaseous SO₂. This is in spite of the fact that computed SO₂ dry deposition velocities exceed those for O₃. Model uncertainties are large for both dry deposition velocity and cloud water flux computations, and some bias in computations probably exists because of the application of the models to a complex terrain situation. Field evaluation of the cloud water deposition model is of greatest priority because of the apparent relative importance of that deposition pathway.     

Trends in wet and dry deposition of sulphur in the United Kingdom

UK data on sulphur deposition trends between the 1960's and 1990's are presented. Long term data sets of sulphur dioxide (SO₂) concentrations at two sites have been analysed and dry deposition determined using a resistance model. Wet deposition has been calculated from non-marine sulphate concentration and rainfall fields for 1978–80 and 1989–93. These maps have been interpolated and corrected for seeder feeder enhancement. The wet deposition of sulphur declined by about 43 % between 1979 and 1993 whereas emissions of sulphur declined by about 32 %. An indication of the trends in sulphur dry deposition is provided by data from Eskdalemuir, a site in southern Scotland where wet deposition and SO₂ concentration have been measured since 1979. Dry deposition at Eskdalemuir has decreased by 70 % and wet deposition by 48 %. Hence, while wet deposition has responded approximately linearly with the decline in UK emissions of sulphur dioxide, dry deposition has declined at twice the rate of decline in UK emissions.     

Simultaneous Determination of Gas and Particle Dry Deposition onto Conditioned Surrogate Surfaces

Aerodynamically designed surrogate surfaces were used to determine the relative importance of gaseous (SO₂, HNO₃, NH₃) and particulate species (SO₄ ^2?, NO₃ ^?, NH₄ ⁺, Ca²⁺) in the dry deposition flux. For 11 sampling periods, we measured the deposition fluxes, ambient gaseous concentrations, size distributions of atmospheric aerosols and some meteorological parameters in Uji. The dry deposition of the gas to a nearly perfect sink was calculated by subtracting the greased surface flux from the total deposition flux to both the greased and reagent impregnated (or water) surface. It was found that the gas phase deposition contributed significantly more (60–93%) than the particulate phase to overall deposition of sulfur and nitrogen compounds. The dry deposition velocities of the species were also calculated using the deposition fluxes and the measured ambient concentrations. Comparisons were made between the measured and modeled particulate deposition flux.     

Urban wet deposition nitrate: A comparison to non-urban deposition

The concentration of nitrate in both wet and dry deposition has both increased historically and currently, and recently parallels emissions in NO_x. Since NO_x is produced in amounts comparable to SO₂, it is an important contributor to acid deposition, and is produced in higher amounts in urban areas due to concentrated sources. Prior to this study, national acid deposition monitoring networks in the United States have been and remain established in non-urban areas. This research study consisted of a comparison of precipitation sampling and analysis of wet deposition nitrate and pH for each deposition event in each of two urban sites over a 15 mo period. Also, a comparison of urban data and data generated at a nearby non-urban NADP site was made by examination of both monthly and seasonal data. This research suggests that national monitoring programs should consider inclusion of urban and non-urban monitoring sites in order to achieve a more representative regional assessment.     

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.     

Dry and Wet Deposition of Nitrogen Emitted in Buenos Aires City to Waters of de la Plata River

Dry and wet deposition of atmospheric nitrogen species (NO₂ and HNO₃) coming from nitrogen oxides emissions in Buenos Aires city to surface waters of de la Plata River were estimated. Atmospheric dispersion models DAUMOD-RD (v.2) and CALPUFF were applied to area and point sources, respectively. These models were run considering 1 year of hourly meteorological data. Emission information included a typical diurnal variation of area source emissions. Annual atmospheric nitrogen (N–NO₂?+?N–HNO₃) deposition to 1,763 km² of the river was 35,600 kg-N year^?1. Dry deposition processes accounted for 89% of this value. The small contribution of wet deposition was a consequence of the very few cases (5%) of rain events during offshore wind conditions. Monthly dry deposition to 1,763 km² of the river varied from 1,628 kg-N month^?1 in February to 3,799 kg-N month^?1 in December, following the monthly occurrence of offshore winds. Monthly wet deposition varied from 1 kg-N month^?1 in June to 1,162 kg-N month^?1 in February. These results came from the combination of favorable conditions for formation of HNO₃ and the occurrence of precipitation during offshore wind situations. Spatial distribution of annual atmospheric N deposition showed a strong coastal gradient. Deposition values reached a maximum of 137.1 kg-N km^?2 year^?1 near the shoreline, which was reduced to the half at 4 km from the coast.     

Dry deposition to snow in an urban area

Ambient particle and gas concentrations, wet deposition and dry deposition were measured in Warren, MI between December 18, 1983 and April 6, 1984. Dry deposition was measured to various surfaces in a cutoff bucket, including a snow surface, a snow/water surface during melting and a deionized water surface. Dry deposition velocities were calculated for various species from the ratio of the dry flux to the ambient concentrations. The dry deposition velocities measured to a snow surface were 0.082 cm s^?1 SO₂ 2.0 for HNO₃, 0.083 for NH₄ ⁺, 2.0 for Ca⁺⁺ and 4.3 for Cl^?. The values were not significantly different for a snow/water surface during melting compared to a snow surface. However, higher values of 0.69 cm s^?1 for SO₂, 6.2 for HNO₃, 0.33 for NH₄ ⁺, and 4.2 for Ca⁺⁺ were found to a deionized water surface in the spring. These higher values could be due to the higher air temperature, the pH of the liquid or to increased atmospheric mixing during this period.     

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.     

Fine and Coarse Ionic Aerosol Components in Relation to Wet and Dry Deposition

The distribution of acidic andalkaline constituents (SO₄ ^2-,NO₃ ^-, Cl^-, NH₄ ⁺, Na⁺,K⁺, Ca²⁺) between the fine and coarseparticle range has been examined in an urban locationin Thessaloniki, N. Greece over an 8-month period. The chemistry of wet and dry deposition collected overthe same period was also examined. Statisticalassociations between species within each environmentalphase were investigated using correlation analysis.Use of principal component analysis was made toinvestigate compositional similarities betweenaerosol, deposited dust and rain. It was found thatSO₄ followed by NO₃, NH₄ and Caprevailed in fine aerosol. Sulphates and Ca were alsothe prevailing ions in the coarse particle fraction.Wet deposition was found to be the dominant depositionmechanism for all species. The high dry depositionrates observed for Ca and SO₄ suggest that mostof the dry deposited sulphate is in the form ofCaSO₄. Scavenging ratios of ionic speciesassociated with coarse aerosol were higher than thecorresponding ratios for fine particles. Principalcomponent analysis suggested that variations in ioniccomposition of fine aerosol could be interpretedprimarily by gas-to-particle neutralization reactionsinvolving atmospheric ammonia. In contrast, theinteraction between SO₂ and HNO₃ with Cacompounds seems to be the most likely factor that canexplain variations in wet and dry deposition ioniccontents.     

Measurements of wet and dry deposition in a Northern Hardwood forest

Inputs of wet and dry deposition were monitored at the Huntington Forest in the Adirondack Mountains of New York for two years in the open and beneath the canopy of a northern hardwood forest. In the open, ion flux estimates were similar using wet-only weekly (NADP protocol) and event collections, but bulk collections were higher for all ions except H⁺, which was much lower. These differences were due to the contribution of dry deposition and possible biotic alterations in bulk collectors. Dry deposition was estimated using air concentrations and ion-specific depositional velocities modeled with meteorological data, and contributed substantially to the input of all ions [H⁺ (45%), Na⁺ (24%), K⁺ (22%), NH₄ ⁺ (12%), Ca²⁺ (58%), Mg²⁺(43%), NO₃ ^? (55%), Cl^? (27%) and SO₄ ^?2 (26%)]. Dry input of base cations was dominated by coarse particles, whereas gaseous inputs were more important for S and NO₃ ^?. Atmospheric concentrations of SO₂ and inputs of SO₄ ^2? and H⁺ were lower at this site than sites closer to point sources of S gas emission. The importance of estimating atmospheric inputs was examined using examples of elemental budgets. For example, different estimates of the contribution of dry deposition of SO₄ ^2? (9–21 meq m^?2 y^?1) resulted in conclusions ranging from no net retention to a net loss of this element. Such differences have important implications in assessing the current and future role of atmospheric inputs in affecting elemental cycling.     

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 R _c . The observations yielded V _d values 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 R _c yielded smaller V _d estimates with no diurnal variation. An attempt is made to relate the observed diurnal cycle of the dry deposition velocity to meteorological parameters.     

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.     

Comparison of the Effects of Wet N Deposition (NH4Cl) and Dry N Deposition (NH3) on UK Moorland Species

Increases in N deposition (wet and dry) have been associated with a decline in semi-natural plant communities, adapted for growth on nutrient poor soils in the UK and Europe. The impacts of N deposition applied as either wet NH₄ ⁺ or gaseous NH₃ on vegetation (7 species) from acid moorland in SE Scotland were compared in a dose-response study. Wet N deposition at 0, 8, 16, 32, 64, 128 kg N ha^?1 y^?1 was applied as NH₄Cl, and dry deposition as gaseous NH₃ (2, 6, 20, 50, 90 µg NH₃ m^?3) under controlled conditions in open-top chambers. A strong linear dose-response relationship (p<0.05) was found between foliar N content in all seven plant species and applied NH₄?N. However, in the NH₃ treatment, only C. vulgaris and P. commune showed a significant response to increasing N additions. NH₃ was found to increase the rate of water loss in Calluna in both autumn and winter by comparison with wet deposition. For Eriophorum vaginatum, the NH₃ and NH₄ ⁺ treatments showed significant N dose response relationships for biomass. A significant increase in above ground biomass, proportional to the added N, was found for Narthecium ossifragum when N was applied as NH₃ compared to NH₄ ⁺.