Estimates of ion sources in deciduous and coniferous throughfall

Estimates of external and internal sources of ions in net througfall deposition were derived for a deciduous and coniferous canopy by use of multiple regression. The external source component appears to be dominated by dry deposition of Ca²⁺, SO₂ and NO₃⁻ during dormant and growing seasons for the two canopy types. Increases in the leaching rates of K⁺ and Mg²⁺ during the growing season reflect the presence of leaves in the deciduous canopy and increased physiological activity in both canopies. Internal leaching rates for SO₄²⁻ doubled during the growing season presumably caused by increased physiological activity and uptake of SO₂ through stomates. Net deposition of SO₄²⁻ in throughfall during the growing season appears highly dependent on stomatal uptake of SO₂. Estimates of SO₂ deposition velocities were 0.06 cm s⁻¹ and 0.13 cm s⁻¹ for the deciduous and coniferous canopies, respectively, during the dormant seasons, and 0.30 cm s⁻¹ and 0.43 cm s⁻¹ for the deciduous and coniferous canopies, respectively, during the growing season. For the ions of major interest with respect to ecosystem effects, namely H⁺, NO₃⁻ and SO₄²⁻, precipitation inputs generally outweighed estimates of dry deposition input. However, net throughfall deposition of NO₃⁻ and SO₄²⁻ accounted for 20–47 and 34–50 per cent, respectively, of total deposition of those ions. Error estimates of ion sources were at least 50–100 per cent and the method is subject to several assumptions and limitations.     

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 (r_c) component of the SO₂ deposition velocity to various test materials. Initial studies of SO₂ deposition to limestone and marble indicate the r_c 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.     

Measurements of ammonia flux to a spruce stand in Denmark

This work demonstrates the existence of a linear relation between the deposition velocity of ammonia and the friction velocity measured above a spruce stand in the western part of Denmark. In order to estimate the ammonia deposition velocity and flux to a Norway spruce forest, concentration gradients of ammonia and several meteorological parameters were measured in a meteorology tower during two periods, 1 week in spring and 1 week in late summer 1991. The estimated deposition velocities lie in the range −0.125 to 0.201 m s⁻¹, with a mean of 0.026 m s⁻¹. The deposition velocity and the flux were generally largest in the afternoon. On the basis of 24-h measurements of ammonia and routine meteorological measurements the relation between deposition velocity and friction velocity is extrapolated to an estimate of the average flux for the growing season May to September 1991. The estimate gave an average flux of 87 μg NH₃N m⁻² h⁻¹ (=0.02 μg NH₃N m⁻² s⁻¹). The average deposition velocity for the period was 0.045 m s⁻¹.     

Monitoring the dry deposition of SO2 in the Netherlands: Results for grassland and heather vegetation

An automated system based on the micrometeorological gradient technique has been developed to measure the dry deposition of SO₂ on a routine basis. Measurements were made at two locations in the Netherlands. From these results dry deposition fluxes, dry deposition velocities and surface resistances for a heathland and for an agricultural grassland site were estimated using a selected set of data and a calculation procedure based on micrometeorological considerations. An extensive analysis was made to determine uncertainties in the resulting deposition parameters. From this analysis it has been concluded that the uncertainty in these parameters is almost completely determined by the random errors in measured concentrations. The meteorological surface exchange parameters can be estimated sufficiently accurately (<20% uncertainty). At the grassland site, average surface resistances to deposition of 6(±8) and 13(±12) s m⁻¹ were calculated for wet and dry conditions, respectively. At the heathland site, a similar distinct difference between R_c values for wet and dry conditions was found. These values are 20(±21) and 70(±90) s m⁻¹, respectively. The yearly average dry deposition flux for SO₂ at the grassland site amounts to 585(±330) mol ha⁻¹ yr⁻¹, while at the heathland site the yearly average flux was 300(±270) mol ha⁻¹ yr⁻¹. The yearly average dry deposition velocity at 4 m height was 1.2(±0.3) cm s⁻¹ at the grassland site and 0.8(±0.4) cm s⁻¹ at the heathland site.     

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 O₃, SO₂ and NO₂ 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 O₃V_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 SO₂ 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 SO₂ over a snow surface the V_d ranged from 0.0 to 0.15 cm s⁻¹. The NO₂V_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 NO₂V_d. The impact of the V_d model and its modified version on the concentrations of O₃ and SO₂ were tested with a comprehensive Eulerian air quality model.     

Stone degradation due to dry deposition of HCl and SO2 in a laboratory-based exposure chamber

The role of the gaseous pollutants, HCl and SO₂, has been investigated in a laboratory-based atmospheric flow rig. Using an HCl level of 25 ppm at a pollutant bulk presentation rate 10 times that found typically outdoors, a degradation acceleration factor of about 20 times was obtained, together with realistic degradation products. HCl was found to be a more reactive gas than SO₂, which was also studied at the 25 ppm level. This may be due either to factors involved in the adsorption of the gases on to the stone surfaces, or the extensive solubility of HCl, or the requirement of an extra step in the conversion of SO₂ to sulphate, which would limit the overall reaction rate. The soluble degradation product CaCl₂ is readily washed off the stone allowing continuous reaction, while the relatively insoluble CaSO₄.2H₂O can remain on, or in the stone surface regions and may inhibit or affect further reaction with SO₂.The reaction of limestone with HCl gas is mass-transport limited and greater material losses arise in locations of higher HCl concentration and deposition velocity, i.e. a close-to-source effect is highlighted due to its high solubility and reactivity, but the HCl concentration is, of course, generally about one-fiftieth of that of SO₂ outdoors. For SO₂, with lower solubility and a necessary oxidation stage to form SO₄²⁻, comparatively high deposition velocities are applicable more widely from the source. The consequences include a widespread formation of relatively insoluble CaSO₄.2H₂O and consequent crust development.     

Modeling of SO2, Pb and Cd atmospheric deposition over a one-year period

Atmospheric deposition of SO₂, and fine particles of Pb and Cd are calculated over a one-year period in a 66 km² airshed with a segment-puff model. Emission variations, hourly mixing heights and meteorological values are considered to compute monthly averages of concentrations and deposition. Dry deposition is calculated by means of deposition velocities which are season- and land use-dependent. Wet deposition is determined using a washout coefficient. To assess the simulation performance, calculated SO₂ results from the combination between the deposition velocity, the windspeed and direction and the location and type of sources. As annual averages, results for dry plus wet deposition are computed to be 0.84 mg m⁻²d⁻¹ for sulfur, 4.15 μgm⁻²d⁻¹ for lead and 0.0013 μgm⁻²d⁻¹ for cadmium. A variation factor is derived from a sensitivity analysis. This factor amounts to 2.3−2.8 for the concentrations and 2.6−3.1 for the deposition, depending on the pollutant.     

Aspects of wet,acidifying deposition in Arnhem: Source regions,correlations and trends (1984–1991)

A time series of wet deposition in Arnhem, the Netherlands, was analysed for the period 1984–1991. Precipitation was collected with four samplers on a daily basis. A comparative study by the Dutch National Precipitation Network showed significant biases for the observations of the National Network station due to longer exposure to dry deposition. Simultaneous operation of wet-only and bulk collectors demonstrated a concentration bias of about 10% for daily bulk sampling.Using a cluster analysis of backward trajectories, clear distinctions could be made between precipitation from continental and maritime origin. Event-to-event variations in deposition seemed to be determined largely by meteorological influences. As major anthropogenic source regions, the U.K., France, Belgium and the Netherlands itself were identified. The contribution of Dutch sources to wet acid deposition in Arnhem was estimated at 30–40%.Trends and seasonal variations were analysed with an advanced time-series model based on Kalman filtering. Similar seasonal variations were found for SO₄²⁻ and NH₄⁺. Also, seasonal variations in the concentrations of H⁺ and NO₃⁻ corresponded. Significant long-term changes in deposition and concentration were found for SO₄²⁻ (about −3% yr⁻¹) and H⁺ (about −9% yr⁻¹) only. The analysed trends were decreasing, but decreases were larger in the years 1984–1986 than in the following years. The relative decrease in the wet deposition of SO₄²⁻ was substantially smaller than decrease in dry-deposited SO₂ and SO₄²⁻.     

Atmospheric dry deposition on pines in the Eastern Brook Lake Watershed,Sierra Nevada,California

Atmospheric dry deposition to branches of Pinus contorta and P. albicaulis was measured during summer 1987 in a sub-alpine zone at Eastern Brook Lake Watershed (EBLW), eastern Sierra Nevada, California. Results are presented as deposition fluxes of NO₃⁻, SO₄²⁻, PO₄³⁻, Cl⁻, F⁻, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺, Zn²⁺, Fe³⁺, Mn²⁺, Pb²⁺ and H⁺, and compared with other locations in California and elsewhere. Deposition fluxes of anions and cations to the pine branches were low, several times lower than the values determined near the Emerald Lake Watershed (ELW), another sub-alpine location in the western Sierra Nevada. The sums of deposition fluxes of the measured cations and anions to pine surfaces were similar, in contrast to the ELW location where the sums of cation fluxes were much higher than the sums of anion fluxes. A strong positive correlation between depositions of NO₃⁻ and NH₄⁺, as well as SO₄²⁻ and Ca²⁺, suggested that large portions of these ions might have originated from particulate NH₄NO₃ and CaSO₄ deposited on pine surfaces. An estimated total N dry deposition (surface deposition of NO₃⁻ and NH₄⁺ and internal uptake of NO₂ and HNO₃) to the forested area of the EBLW was 29.54 eq ha⁻¹ yr⁻ (about 414 g H ha⁻¹ yr⁻¹).     

Spatial variability of urban precipitation chemistry and deposition: Statistical associations between constituents and potential removal processes of precursor species

The precipitation chemistry of Greater Manchester, a Metropolitan County in the northwest of England, has been examined for small scale spatial variability using a network of 18 bulk precipitation collectors. Significant spatial variability was found for concentrations of non-marine SO₄²⁻, NO₃⁻, NH₄⁺, Ca²⁺ and H⁺ ions. The statistical associations between the data were investigated using correlation, partial correlation and principal components analyses. It was found that zero-order correlation coefficients were inadequate for the interpretation of the data and that the computation of first, and higher order partial correlation coefficients was necessary in order to explain the interrelationships between the data and their spatial variability. The statistical associations between the data suggest relationships between Ca²⁺ and non-marine SO₄²⁻, and NO₃⁺ in precipitation which are discussed in terms of their possible precursor species. Potential source effects were examined in conjunction with atmospheric removal processes. The dry deposition of SO₄ particles, rather than the dry deposition of SO₂, may explain the spatial variability of non-marine SO₄²⁻. The erosion of CaSO₄ formed from the reaction of SO₂ with CaCO₃ on urban surfaces with subsequent resuspension is thought to be the basis of the relationship between Ca²⁺ and non-marine SO₄²⁻ concentrations in precipitation. The wet and dry deposition of CaCO₃ particles from local sources may be partially responsible for the spatial variability of H⁺, and dry deposition and scavenging of NH₃, in conjunction with the predominant wind direction may explain the spatial variability of NO₃⁻ and NH₄⁺ ions. Ammonia is thought to originate from sources both outside the study area and within it.     

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.     

Laboratory exposure systems to simulate atmospheric degradation of building stone under dry and wet deposition conditions

The design philosophy, construction and use of two exposure test systems are described, in which the objective is to simulate the degradation of stone samples under, respectively, the ‘dry’ and ‘wet’ deposition of atmospheric pollutants. Some element of realistic acceleration is possible in certain experiments. Particular emphasis is placed upon using known presentation rates of the pollutants, both in respect of typical depositions of pollutants and their oxidation products appropriate for an industrial atmosphere. In the dry deposition rig, SO₂, NO₂, NO, HCl and the oxidant O₃ are presented individually or together at realistic deposition rates. In the wet deposition apparatus, SO²⁻₄, NO⁻₃ and Cl⁻ at a pH of 3.5, simulating ‘acid rain’ but in a more concentrated form, are deposited. The dry deposition chamber can be operated at constant relative humidity (typically 84%) with pre-dried or precisely wetted stones to simulate episodic rain wetting, or using other methods of wet/dry cycling, which are also a feature of the wet deposition chamber. Heating and cooling of the samples is also possible, as is the use of shaped or coupled stones of different kinds such as are found in a building facade. The results are illustrated in terms of data on the weight change, the anion content of stone and run-off, the pH change of run-off and the total calcium reacted, using Portland stone, as a prelude to later papers in which behaviour of a whole matrix of stone types and environments is presented and discussed. Such an approach permits the eventual production of ‘pollutant-material response’ relationships and damage functions for comparison with and prediction of external exposure results.     

Physicochemical damage parameters for the action of SO2 and NO2 on single pieces of marble

The theoretical analysis for measurement of building-damage parameters by RF-GC technique is applied to the action of SO₂ and NO₂ on marble. The experiments with SO₂ were performed with five different geometric forms of single pieces of marble at 373.2 K and were repeated after washing these pieces 8 times with three-distilled water. All six physicochemical parameters determined show negligible variations for the same solid form at the same temperature, but they are different for the various geometrical forms. The mass transfer coefficients K_g and K_s and their ratio K seem to be the most invariant parameters with respect to the form. After washing with water, some of the parameters change considerably.The action of NO₂ was studied on a sphere only, but at five different temperatures. The physicochemical parameters for the action of this gas are three orders of magnitude smaller than those of SO₂ (except K), leading to 3700 times bigger resistance of marble to mass transfer of NO₂ than of SO₂. From the variation of the parameters with temperature, it is concluded that both mass transfer coefficients, K_g and K_s, pertain to activated processes with activation energies 39 and 27 kJ mol⁻¹, respectively. The reaction of the adsorbed gas with the solid is less activated, whereas the adsorption equilibrium constant K does not change with temperature.     

Effects of acidic deposition on the erosion of carbonate stone — experimental results from the U.S. National Acid Precipitation Assessment Program (NAPAP)

One of the goals of NAPAP-sponsored research on the effects of acidic deposition on carbonate stone has been to quantify the incremental effects of wet and dry deposition of hydrogen ion, sulfur dioxide and nitrogen oxides on stone erosion. Test briquettes and slabs of freshly quarried Indiana limestone and Vermont marble have been exposed to ambient environmental conditions in a long-term exposure program. Physical measurements of the recession of test stones exposed to ambient conditions at an angle of 30° to horizontal at the five NAPAP materials exposure sites range from ∼ 15 to ∼ 30 μm yr⁻¹ for marble, and from ∼ 25 to ∼ 45 μm yr⁻¹ for limestone, and are approximately double the recession estimates based on the observed calcium content of run-off solutions from test slabs. The difference between the physical and chemical recession measurements is attributed to the loss of mineral grains from the stone surfaces that are not measured in the run-off experiments. The erosion due to grain loss does not appear to be influenced by rainfall acidity, however, preliminary evidence suggests that grain loss may be influenced by dry deposition of sulfur dioxide between rainfall events. Chemical analyses of the run-off solutions and associated rainfall blanks suggest that ∼ 30% of erosion by dissolution can be attributed to the wet deposition of hydrogen ion and the dry deposition of sulfur dioxide and nitric acid between rain events. The remaining ∼ 70% of erosion by dissolution is accounted for by the solubility of carbonate stone in rain that is in equilibrium with atmospheric carbon dioxide (“clean rain”). These results are for marble and limestone slabs exposed at an angle of 30° from horizontal. The relative contribution of sulfur dioxide to chemical erosion is significantly enhanced for stone slabs having an inclination of 60° or 85°. The dry deposition of alkaline particulate material has a mitigating effect at the two urban field exposure sites at Washington, DC, and Steubenville, OH.     

Chemical characterization of acid precipitation in Albany,New York

Chemical composition of precipitation in Albany, NY from July 1986 to December 1988 has been studied. Mean volume-weighted concentrations (μeq^ℓ−1) were: acidity, 104.0; alkalinity, −63.7; SO₄²⁻, 52.8; NO₃⁻, 29.8; Cl⁻, 5.6; F⁻, 0.50; NH₄⁺, 19.3; Ca²⁺, 6.5; Mg²⁺, 2.8; Na⁺, 3.5; and K⁺, 1.4. Mean pH was 4.2 . Seasonal patterns were pronounced for most species. Concentrations of H⁺, SO₄²⁻, NO₃⁻, NH₄⁺ and Ca²⁺ peaked in the summer and spring. Deposition was related to rainfall amount by a power law relationship in which the exponent of the equation was ∮.6. Wet SO₄²⁻ deposition was 2.35 keq ha⁻¹ over a 30-month period. The SO₄²⁻ and NO₃⁻ deposition rates observed at Albany indicate that transport from midwestern sources have a major influence at this site. On the average, free H⁺ ion concentrations determined from pH measurements accounted for 51% of the measured total acidity. There were unknown species, most likely organic acids, that could contribute to the acidity. Correlation and regression analyses indicated that major anions, SO₄²⁻ and NO₃⁻, were closely associated with H⁺ and NH₄⁺ ions. Factor analysis revealed four common factors which are related to fossil-fuel combustion, sea spray, cement factory and biomass burning.     

The stem-II regional scale acid deposition and photochemical oxidant model—IV. The impact of emission reductions on mesoscale acid deposition in the lower ohio river valley

Assessment of the effect of reduction in emissions of primary sources on eventual levels of pollutants, pH of precipitation and total wet deposition is crucial in designing acid-rain control strategies. The STEM-II/ASM model is used to investigate the effect of reduction in emissions on the ultimate deposition patterns and amounts of major acidic pollutants in a mesoscale region. This work also investigates the effect of background levels of primary pollutant species on the eventual levels and deposition amounts of SO₄⁼ and NO₃⁻. A series of mesoscale simulations were conducted in which emissions of primary sources of NO_x and SO₂ were reduced and/or background concentrations of certain key species were changed. The results indicate that the dominant effect on the eventual deposition amounts of SO₄⁼ and NO₃⁻ is due to background concentrations of key precursor species such as SO_x and NO_x. With relatively high background concentrations, reducing SO₂ emissions by 50% and NO_x emissions by 40% resulted in reductions of 2–3% for SO₄⁼ wet deposition aand about 15% for NO₃⁻ wet deposition. However, reducing the background concentrations of SO₂ and SO₄⁼ by 50% and NO, NO₂ and HNO₃ by 40% resulted in substantial reductions in wet deposition; SO₄⁼ deposition was reduced by 40–50% and NO₃⁻ deposition was reduced by approximately 35%.     

Rainwater composition in Athens,Greece

Wet precipitation-only samplers were used to collect wet deposition at two sites in the Athens basin, Greece for the period March 1986–February 1987.Concentrations of major cations (H⁺, NH⁺₄, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and major anions (Cl⁻, NO⁻₃ and SO²⁻₄) were determined for the first time in rainwater samples in Greece. Bicarbonate concentrations were calculated. The relative importance of natural and anthropogenic sources were estimated by a chemical balance. The majority of rain collected has a neutral or alkaline character. Acidity was due to the presence of H₂SO₄ and HNO₃. The statistical analysis of the correlation between the concentration of chemical species confirm the influence of natural and anthropogenic sources. In all samples, SO²⁻₄ concentrations exceed NO⁻₃ concentrations despite the dominance of low S oil burning in the region. The wet flux of S was calculatd to be 0.34 gm⁻²a⁻¹.     

Studies on the formation of H2O2 in the ozonolysis of alkenes

The formation of H₂O₂ in the reactions of ozone with alkenes, isoprene and some terpenes has been studied with tunable diode laser absorption spectroscopy. The measured yields of H₂O₂ were found to be considerably enhanced in the presence of water vapour. H₂O₂ is thought to be formed in the ozonolysis of the alkene with O₃ by direct reaction of an intermediate with water vapour. The yield of H₂O₂ relative to the reacted alkene in the ozonolysis of trans-2-butene in the presence of water vapour was also studied with long path FTIR spectroscopy. Irrespective of the analytical methods and reaction conditions applied, the H₂O₂ yields in the reaction of O₃ with the different alkenes in the presence of water vapour were found to be in the range of a few per cent or less. Under the assumption that the reactive species forming H₂O₂ in the ozonolysis is the Criegee biradical, the overall rate constants for the reactions of some biradicals with water vapour were measured relative to the rate constant of the biradical with SO₂. For the H₂COO biradical a rate constant of (5.8 ± 2.5) × 10⁻¹⁷ cm³ s⁻¹ was determined and for the (CH₃)₂COO biradical (2.9 ± 1.5) × 10⁻¹⁷ cm³ s⁻¹; in the latter case with the assumption that (CH₃)₂COO reacts with SO₂ as fast as CH₂COO.     

Statistical analysis of errors in estimating wet deposition using five surface estimation algorithms

Wet deposition measurements of H⁺, SO₄²⁻ and NO₃⁻ from 29 monitoring sites located in (16) and around (13) Pennsylvania, U.S., were analyzed to quantify errors associated with extrapolating point estimates of deposition using five surface-fitting algorithms. The influence of site density on estimation errors associated with each surfacing algorithm was also investigated. The five surfacing differed little in their abilities to predict the concentration or deposition of individual ions found in precipitation in Pennsylvania. However, the size of estimation errors for all parameters, even those based on the densest network, were quite high relative to the variation observed among monitoring sites in Pennsylvania. All monitoring site observations were within 22.8, 17.6 and 23.1 per cent of the median concentration and 33.9, 35.3 and 36.7 per cent of the median deposition for H⁺, NO₃⁻ and SO₄²⁻, respectively. Maximum per cent errors indicate that estimation errors may severely obscure actual surface features in at least some portions of the estimated concentration and deposition grids in Pennsylvania. Deposition and concentration estimates based on higher density networks were generally more accurate; however, the improvements afforded by the additional sites were quite modest. Based on the magnitude of estimation errors, kriging produced the most accurate estimates, although no single algorithm consistently yielded the most accurate estimates for all parameters.     

Field study investigations of the impact of shape,size and orientation on dry deposition induced corrosion of galvanized steel

A controlled field study was conducted at Research Triangle Park, NC, to determine how shape, size and orientation of galvanized steel structures affect (1) dry deposition of SO_x and NO_x compounds and (2) dissolution of Zn corrosion products resulting from such deposition. Thirteen structures of various shapes, sizes and orientations were exposed to dry deposition only for 100 weeks, during which they were rinsed with deionized water every 2 weeks and the rinses were analysed for Zn, Ca, and their ionic contents. The rinse data are consistent with size, orientation and exposure history affecting dry deposition of SO²⁻₄ precursors such as SO₂. Dry deposition of precursors of surface NO⁻₃, including HNO₃, is affected by structure size. A model regression equation is presented that shows that Zn dissolution can be explained in terms of the SO⁻²₄ and NO⁻₃ rinse concentrations. The experimental results suggest that there is likely to be some error associated with extrapolating galvanized steel test panel results to actual structures.