Deposition Velocity Of SO2 Research Articles

Ozone and sulfur dioxide dry deposition to forests: Observations and model evaluation

Fluxes and deposition velocities of O3 and SO2 were measured over both a deciduous and a mixed coniferous‐deciduous forest for full growing seasons. Fluxes and deposition velocities of O3 were measured over a coniferous forest for a month. Mean deposition velocities of 0.35 to 0.48 cm/s for O3 and 0.6 to 0.72 cm/s for SO2 were observed during the growing seasons of 1997 and 1998. Weekly averages of O3 deposition velocity ranged from 0.25 cm/s at the beginning and end of the season to 1.25 cm/s in late June. SO2 had a smaller seasonal variation, from 0.75 to 1.5 cm/s between the beginning and peak of the season. Because O3 concentrations are higher, the flux of O3 to forests is considerably greater than the flux of SO2. Daytime deposition velocities are very similar at each site, from 0.75 to 0.79 cm/s for O3, and from 1.01 to 1.04 cm/s for SO2. Diurnal cycles for both gases are discussed, as are the impact of some weather events. The peak time for O3 deposition velocity is in midmorning, while it is near midday for SO2. Surface wetness is usually associated with a small increase in deposition velocity, but for some rain events a major increase was noted. Minimum deposition velocities usually occur at night and increase slowly in the predawn hours before light. Comparisons are made between observations of deposition velocity and predictions made with the Meyers multilayer deposition velocity model. While the model is, on average, unbiased for O3, it tends to underpredict the higher deposition velocity values. The model is slightly biased low (underpredicts) for SO2 deposition velocity. The strengths of the model are noted, as are opportunities for improvement.

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The Lausanne Atmospheric Simulation Chamber (LASC) has been constructed with the aim of studying the SO2 effects on different materials. It allows the carrying out of numerous measurements on large stone samples simultaneously and on line. The behaviour of two carbonatic stone types (limestone and sandstone), either naked or covered with fly ash or soot particles, exposed at the following conditions, SO2 = 125 ppb (340 μg m−3), NO2 = 50 ppb (98 μg m−3), relative humidity = 79%, temperature = 13°C, has been studied. This experiment has been carried out over a 1 yr period. It has been observed that SO2 deposition velocity decreases with time and in different ways for each of the two stone types, naked or covered with fly ash or soot particles. During the first four months, the deposition velocity is higher on naked stones; later on, it is higher on the stone samples covered with fly ash. Throughout the experiment the SO2 deposition velocity on stone samples covered with soot particles is lower than on naked samples and those covered by fly ash. Finally, the values of SO2 deposition velocity are confirmed by the chemical analysis of sulphur in the samples. Sulphur is present from the stone surface down to about 0.8 mm depth.

Modeling the Dry Deposition Velocity of Sulfur Dioxide and Sulfate in Asia

Abstract The dry deposition model was created to estimate SO2 and sulfate dry deposition velocities over nine land use types in Asia. The study domain is 20°S–50°N, 39°–154°E. Monthly averaged 1° × 1° dry deposition velocities are estimated for four seasons. Model results show that the dry deposition velocity of SO2 demonstrates strong seasonal and diurnal variability in summer, fall, and spring. In summer, the daytime velocity (in centimeters per second) for SO2 forests is 0.4, over cultivation is 0.2, grassland is 0.5, and ocean is 0.8. Nighttime values of SO2 are two or three times less than daytime values. In winter, the deposition velocity of SO2 does not show much diurnal variability—the value is 0.1–0.2 except over ocean, when it is 0.5. Contrary to SO2, the dry deposition velocity of sulfate only slightly varies with seasons and time of the day. Generally, its value is less than 0.1.

A multilayer model for inferring dry deposition using standard meteorological measurements

In this paper, we describe the latest version of the dry deposition inferential model, which is used to estimate the deposition velocities (Vd) for SO2, O3, HNO3, and particles with diameters less than 2 μm. The dry deposition networks operated by the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA) use this model to estimate dry deposition on a weekly basis. This model uses a multilayer approach, discretizing the vegetated canopy into 20 layers. The use of canopy radiative transfer and simple wind profile models allows for estimates of stomatal (rs) and leaf boundary layer (rb) resistances to be determined at each layer in the plant canopy for both sunlit and shaded leaves. The effect of temperature, water stress, and vapor pressure deficits on the stomatal resistance (rs) have been included. Comparisons of modeled deposition velocities are made with extensive direct measurements performed at three different locations with different crops. The field experiment is discussed in some detail. Overall, modeled O3 deposition velocities are in good agreement with measured values with the average mean bias for all surfaces of the order of 0.01 cm/s or less. For SO2, mean biases range from −0.05 for corn to 0.15 cm/s for soybeans, while for HNO3, they range from 0.09 for corn to 0.47 cm/s for pasture.

Effects of Dry Deposition on Near-Surface Concentrations of SO2during Medium-Range Transport

The method for estimating dry deposition velocity using local routine surface measurements with some empirical constants used in the Regional Acid Deposition Model is developed and implemented to the Lagrangian particle dispersion model to more accurately estimate near-surface concentrations of the SO2 pollutant. A test is performed for the synoptic case of a weak westerly geostrophic wind at 850 hPa with the cloud amount of less than 5/10. Hourly surface data from 64 sites located in South Korea are hourly averaged for five spring seasons from 1989 to 1993 for the chosen synoptic situation and used to construct 3D meteorological fields and turbulent fields in the boundary layer. The dry deposition velocity of SO2 estimated by the present model ranges from 0.01 to 1.4 cm s−1 with relatively large values in the daytime. The estimated near-surface concentrations at the height of 1.5 m above the ground through the Lagrangian particle dispersion model including the effect of dry deposition indicate that the impact of the dry deposition on the near-surface concentration is significant during the day when the convective turbulent intensity is strong and the deposition velocity is large. The maximum reduction of the near-surface concentration due to the dry deposition process is more than 10% of the estimated concentration with the perfect reflection of the Lagrangian particle at the surface within 70 km in the downwind direction from the source during the daytime, while less than 5% reduction occurs within 50 km from the source during the night.

A dry deposition parameterization for sulfur oxides in a chemistry and general circulation model

A dry deposition scheme, originally developed to calculate the deposition velocities for the trace gases O3, NO2, NO, and HNO3 in the chemistry and general circulation European Centre Hamburg Model (ECHAM), is extended to sulfur dioxide (SO2) and sulfate (SO42−). In order to reduce some of the shortcomings of the previous model version a local surface roughness and a more realistic leaf area index (LAI), derived from a high‐resolution ecosystem database are introduced. The current model calculates the deposition velocities from the aerodynamic resistance, a quasi‐laminary boundary layer resistance and a surface resistance of the surface cover, e.g., snow/ice, bare soil, vegetation, wetted surfaces, and ocean. The SO2 deposition velocity over vegetated surfaces is calculated as a function of the vegetation activity, the canopy wetness, turbulent transport through the canopy to the soil, and uptake by the soil. The soil resistance is explicitly calculated from the relative humidity and the soil pH, derived from a high‐resolution global soil pH database. The snow/ice resistance of SO2 is a function of temperature. The SO2 deposition velocity over the oceans is controlled by turbulence. The sulfate deposition velocity is calculated considering diffusion, impaction, and sedimentation. Over sea surfaces the effect of bubble bursting, causing the breakdown of the quasi‐laminary boundary layer, scavenging of the sulfate aerosol by sea spray, and aerosol growth due to high local relative humidities are considered. An integrated sulfate deposition velocity is calculated, applying a unimodal mass size distribution over land and a bimodal mass size distribution over sea. The calculated sulfate deposition velocity is about an order of magnitude larger than that based on a monodisperse aerosol, which is often applied in chemistry‐transport models. Incorporation of the new dry deposition scheme in the ECHAM model yields significant relative differences (up to ∼50%) in mass flux densities and surface layer concentrations compared to those calculated with a simple, constant dry deposition scheme.

Vertical Gradients of Pollutant Concentrations and Deposition Fluxes on a Tall Limestone Building

The role of air pollutants in the soiling of a limestone building was investigated by measuring pollutant airborne concentrations and deposition at different heights at the Cathedral of Learning in Pittsburgh, Pennsylvania. Airborne concentrations of sulfate particles (SO42−), carbon particles, sulfur dioxide gas (SO2), and total NO3− (particles + HNO3) were measured simultaneously on the 5th floor, 16th floor, and roof (42d floor), while laser particle counts of >0.5 μm and >5 μm particles were obtained on the 5th and 16th floors. SO2 deposition fluxes to wall-mounted surrogate surfaces were measured at a total of nine locations on the 5th and 16th floors. Measurements were conducted during four 4- week time periods over one year. Results showed that airborne concentrations of the chemical species were invariant with height. Airborne number concentrations of >0.5 μm particles corroborated this result. Although not reflected in the chemical data, measured number concentrations of >5 μm particles on the 16th floor were on average 30% greater than those on the 5th floor. The spatially averaged highest and lowest deposition velocities of SO2 (1.0 cm/s and 0.6 cm/s) never differed by more than a factor of two for the different time periods. The relative differences in deposition velocities from one location to another were consistent throughout all of the sampling experiments. The 16th floor deposition velocities were greater than those on the 5th floor due, at least in part, to the fact that sampling locations on the 16th floor were more exposed to wind. The absence of gradients suggests that soiling patterns on the cathedral are determined by the competing processes of pollutant deposition ahd rain washing. This hypothesis is supported by comparing soiling patterns on the cathedral from the 1930s with recent patterns: Archival photographs show much greater amounts of soiling, consistent with the greater air pollution levels that existed then. Results of this study can assist in designing cleaning and treatment protocols for other buildings with similar geometry in similar environments.

The Importance of Humidity Effect in Determining Flux-Profile Parameters of a Marine Surface Layer

Abstract The role of humidity in estimating marine surface layer stratification in terms of the ratio, R, of the humidity contribution to the total static stability is evaluated. A recent study of Geernaert and Larsen employs a system of simultaneous equations for calculating R. The present study requires only simple algebraic relations to arrive at the approximate solution of R. In the approximate solution, the value of R is explicitly represented in a single equation as a function of potential temperatures and the corresponding virtual potential temperatures. The exact solution of R is obtained directly using the Monin-Obukhov stability parameters with and without humidity effect. Static stability and transfer coefficients, as well as deposition velocity of SO2 over an air-sea interface, are calculated using the direct bulk aerodynamic method similar to that of Lo. Detailed study on characteristics of humidity effect on atmospheric stratification, especially for cases of large sea-air temperature differ...

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

Dry deposition velocity estimates of SO, HNO3 and SO42− 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 SO42− 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.

Sulfur dioxide plume dispersion and subsequent absorption by coniferous forests: Field measurements and model calculations

A Forest SO2 Absorption Model (ForSAM) was developed to simulate (1) SO2 plume dispersion from an emission source, (2) subsequent SO2 absorption by coniferous forests growing downwind from the source. There are three modules: (1) a buoyancy module, (2) a dispersion module, and (3) a foliar absorption module. These modules were used to calculate hourly abovecanopy SO2 concentrations and in-canopy deposition velocities, as well as daily amounts of SO2 absorbed by the forest canopy for downwind distances to 42 km. Model performance testing was done with meteorological data (including ambient SO2 concentrations) collected at various locations downwind from a coal-burning power generator at Grand Lake in central New Brunswick, Canada. Annual SO2 emissions from this facility amounted to about 30,000 tonnes. Calculated SO2 concentrations were similar to those obtained in the field. Calculated SO2 deposition velocities generally agreed with published values.

Seasonal contrasts in modelled and observed dry deposition velocities of O3, SO2 and NO2 over three surfaces

Results of modelled and observed deposition velocities ( V d ) for O 3 , SO 2 and NO 2 for time-averaged diurnal cycles and sometimes for a collection of hourly values taken from different days are discussed for different seasons. From the observations, it was found that the O 3 V d values over a deciduous forest had a daytime representative value of 1.0 cm s −1 in the summer and 0.3 cm s −1 in the winter. For SO 2 over the same forest and over a carrot field the daytime values ranged from 0.0 to 0.65 cm s −1 in the autumn, and for SO 2 over a snow surface the V d ranged from 0.0 to 0.15 cm s −1 . The NO 2 V d was mostly negative over the forest and the carrot field in the autumn and had a range of 0.0-0.15 cm s −1 over snow. From the model, it was found that for the three seasons the V d values over all the land-use types were much larger than the observations. The model could not simulate the observed negative values of the NO 2 V d . The impact of the V d model and its modified version on the concentrations of O 3 and SO 2 were tested with a comprehensive Eulerian air quality model.

Environmental chamber for study of the deposition flux of gaseous pollutants to material surfaces

A specially designed recirculating environmental chamber was constructed to study the environmental factors affecting the deposition of pollutant gases to the surface of stone and other building materials. The chamber and sample holder are designed to place samples in an aerodynamically well-defined air flow. The system is designed to permit use of radioactive 35SO2 as a tracer if necessary. A wide range of typical environmental conditions can be continuously maintained in the chamber. Wind speeds in the test section can range up to about 5 ms−1, exposing replicate samples to air flow that is uniform to within approximately 3%. Relative humidity in the chamber can be maintained to within 3%, and SO2, NO2 and O3 concentrations in the chamber air can be maintained to within 4%. Test results indicate SO2 deposition and wind speed in the chamber are closely correlated, allowing for a direct determination of the surface resistance (rc) component of the SO2 deposition velocity to various test materials. Initial studies of SO2 deposition to limestone and marble indicate the rc values are approximately 1.3 s cm−1 for fresh limestone and 34 s cm−1 for fresh marble at 75% relative humidity, 26°C and 50 ppb SO2.

An investigation of the ADOM dry deposition module using summertime O3 measurements above a deciduous forest

The dry deposition module in the Acid Deposition and Oxidant Model (ADOM) has been isolated from the complete model to accept local meteorological measurements in order to provide local estimates of dry deposition velocities. These are compared with observed O3 data obtained during the summer of 1988 over a deciduous forest. The comparison shows that the model systematically overpredicts by about 70% the dry deposition velocity for two selected days and for the average diurnal variations, obtained from the entire observed time series for July and August of 1988. The canopy resistance, to transfer of O3, is the major contributor to the model's total resistance for O3. In addition to the possible errors due to the “Big Leaf” approximation, sensitivity studies show that key parameters for reducing the systematic bias in the model are the Leaf Area Index, as well as mesophyll, stomatal, ground and cuticle resistances. For dry deposition velocities of SO2, the model also shows sensitivity to these parameters as well as the canopy wetness. A brief discussion on some mathematical approximations in the model is provided.

Atmospheric deposition and sulphur cycling in chalk grasslandA mechanistic model simulating field observations

Sulphate fluxes in bulk deposition, throughfall and soil solution were monitored during two years, and integrated within a model describing the cycling of S in a chalk grassland ecosystem. Throughfall fluxes were strongly determined by interceptive properties of the grassland canopy. Seasonal variation in Leaf Area Index resulted in dry deposition velocities for SO2 varying between 0.1 cm.s−1 (snow cover, almost no aerodynamic resistance) to 0.9–1.8 cm.s−1 in periods with a fully developed canopy. On an annual basis net canopy exchange (assimilation of SO2 minus foliar leaching) was estimated to be −15% of net throughfall. Simulated soil solution concentrations, being the result of throughfall input, leaching, adsorption, biomass uptake and mineralization, closely fitted actual values (r > 0.92; p > 0.001). Actual and simulated leaching were 1.74 ± 0.03 and 2.00 keq.-ha−1.yr−1, respectively. Sulphur budgets for the soil showed net accumulation from April to October and net losses from October to April. Annual budgets for the ecosystem showed atmospheric input (2.02keq.ha−1.yr−1) and actual output (2.05keq.ha−1.yr−1) to be almost balanced. Apart from increased soil solution concentrations, additional input of sulphate (3.55 keq.ha−1.yr−1) to experimental plots resulted in additional accumulation in the ecosystem of 0.62 keq.ha−1.yr−1

Comparison of RADM dry deposition algorithms with a site-specific method for inferring dry deposition

Data collected during 1986 at seven widely separated sites in the eastern United States were used to estimate weekly averages of deposition velocities for SO2, O3, HNO3, and SO inf4 sup2− with both a modified version of the RADM dry deposition module and a site-specific inferential technique developed by the Atmospheric Turbulence and Diffusion Division of the National Oceanic and Atmospheric Administration's Air Resources Laboratory. The results show some systematic differences between the two techniques, even when the module uses distributions of landuse types that match as closely as possible the observed vegetation coverages used in the inferential technique. When one ignores the systematic differences that easily could be removed by minor changes in the algorithms for computing resistances to deposition, weekly averages of the deposition velocities calculated with the two methods are within approximately ±30% of each other for SO2 and O3. Overall, the relative differences in the deposition velocities for HNO3 and SO inf4 sup2− are about ±30 and ±50%, respectively. Use of the module with landuse types extrapolated to areas as large as RADM grid cells (approximately 80 km square) around the measurement stations produces weekly averages within ±20% of the site-specific estimates for SO2, O3, and SO inf4 sup2− and approximately ±30% for HNO3 if one avoids landuse types such as urban and water areas that are both nonrepresentative and have very different characteristics from the measurement sites. These estimates are not complete measures of the true uncertainty associated with the two techniques because they do not account for such effects as differences in the siting of instrumentation for collecting input data and the inability of the computational algorithms to include the many surface nonuniformities that typically exist in the areas surrounding measurement sites.

Acid dew and the role of chemistry in the dry deposition of reactive gases to wetted surfaces

Using the resistance model for mass transfer, a formulation is derived for the dry deposition rate of a reactive, soluble gas depositing on a wetted, vegetative surface. The deposition velocity is expressed in terms of a dynamical resistance, which is a function of the physical state of the atmosphere, and a surface resistance, which is a function of the chemical and physical properties of the surface. This formulation is then used in a model to simulate the generation of acidic dew from the dry deposition of HNO3 and SO2, as well as the SIV oxidants, H2O2 and O3. Dewdrop pHs of about 4 are calculated by the end of the night, however these pHs can rapidly fall to potentially toxic levels soon after sunrise as the dewdrops evaporate. The deposition velocities to the dew for highly soluble species such as HNO3 and H2O2 are found to be entirely determined by the dynamical resistance; for the conditions adopted here a value of 0.4 cm s−1 is calculated for these species. However, much smaller deposition velocities are predicted for SO2 and O3 because of their lower solubilities and hence larger surface resistances. In the case of SO2, a nocturnally averaged deposition velocity of only about 0.03 cm s−1 is calculated for the standard model. Because the chemical lifetime of SO2 in the dew is influenced by the atmospheric levels of H2O2, O3, and SO2, the SO2 deposition velocity is found to be a strong function of these species' atmospheric abundances. These results imply that the deposition velocities of species such as SO2 to wetted surfaces may be influenced by the chemical as well as the physical state of the atmosphere; the assumption typically adopted that dry deposition velocities are independent of the species' atmospheric abundance may not always be appropriate.

A comparison of estimated and measured SO2 deposition velocities

A nested-network program for obtaining data on the dry deposition of SO2 and SO4− has been initiated at a small array of locations (6 in 1985, presently 13) across North America. The procedures involved rely on the availability of models for deriving dry deposition rates from observations of air concentrations and of meteorological and surface properties known to influence the deposition velocity. At a subset of locations (i.e., 3), the results obtained by this indirect method are tested by comparison against more direct methods. One of the first comparison experiments of this series was conducted at Oak Ridge in July 1985 when the fluxes determined by inferential methods were compared to those measured by eddy correlation. The results obtained suggest that initial computer routines, developed to estimate deposition velocity for SOz on a routine basis, overestimate the deposition velocity by about 20% to a mixed-species deciduous forest. The difference is possibly due to the omission of water stress as a contributing factor in the initial computer routines, but might also be associated with chemical processes at the substomatal level.

Sulfur dioxide deposition velocity by a concentration gradient measurement system

Instrumentation for the measurement of the dry deposition velocity of SO2 by the concentration gradient method has been developed. The instrumentation consists of a sensitivity enhanced Meloy SA260 sulfur analyzer together with appropriate sampling hardware. The system was field tested at the U.S. EPA sponsored dry deposition intercomparison study held in June 1982 at Champaign, Illinois.

Comparison of forest water and energy exchange models. Proceedings of an IUFRO workshop, uppsala (Sweden), September 24–30, 1978

Turbulence controls the vertical transfer of momentum, heat and trace constituents in the atmospheric boundary layer. In the lowest 10% of this layer lies the surface boundary layer (SBL) where the vertical fluxes of transferred quantities have been successfully parameterized using the Monin-Obukhov similarity theory in weather forecast, climate and atmospheric chemistry models. However, there is a large degree of empiricism in the stability-correction parameterizations used to formulate eddy diffusivity and aerodynamic resistance particularly under strongly stable ambient conditions. Although the influence of uncertainties in stability-correction parameterizations on eddy diffusivity is actively studied in boundary-layer meteorological modeling, its impact on dry deposition in atmospheric chemistry modeling is not well characterized. In this study, we address this gap by providing the mathematical basis for the relationship between the formulations of vertical surface flux used in meteorological and atmospheric chemistry modeling communities, and by examining the sensitivity of the modeled dry deposition velocities in statically stable SBL to the choice of stability-correction parameterizations used in three operational and/or research environmental models (GEM/GEM-MACH, ECMWF IFS and CMAQ-MM5). Aerodynamic resistances (ra) calculated by the three sets of parameterizations are notably different from each other and are also different from those calculated by a “z-less” scaling formulation under strongly stable conditions (the bulk Richardson number > 0.2). Furthermore, we show that many atmospheric chemistry models calculate ra using formulations which are inconsistent with the derivation of micro-meteorological parameters. Finally, practical implications of the differences in stability-correction algorithms are discussed for the computations of dry deposition velocities of SO2, O3 and reactive bromine compounds for specific cases of stable SBL.

A field estimate of SO2 deposition velocities to rapidly growing soybeans

Field-grown soybeans were exposed to elevated SO2 levels in an open-air fumigation system which produced minimal alteration of the crop environment. The increase in S content of the fumigated plants as compared to unfumigated controls was used to estimate the deposition velocity of SO2 to the crop. Estimates ranged from 0.5 to 0.9 cm s−1, which is in the lower part of the range found by micrometeorological techniques, confirming that estimates based on short-term gradient measurements are realistic.