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.     

Effect of dry deposition of NOx and SO2 gaseous pollutants on the degradation of calcareous building stones

A laboratory-based atmospheric flow chamber, using realistic presentation rates of SO₂, NO and NO₂ pollutants directed to various dry and wetted surfaces, has been employed to quantify the effects of the individual pollutants and the role of ozone as an oxidant. For the individual pollutant gases reacting with stone surfaces coming to equilibrium with 84% relative humidity (r.h.), chemical reaction in the presence of a moisture film proceeds and the extent of this reaction is related to pollutant gas solubility in the moisture film, i.e. SO₂ > NO₂ > NO. After dissolution in the moisture film, the pollutant gases are oxidized in the presence of catalysts associated with the stones. The additional presence of ozone promotes oxidation of the pollutant gases and thus their reaction with the stones. For SO₂ pollutant, oxidation in the gas phase is not significant compared with that in the moisture film, with enhanced oxidation in the presence of catalysts. Ozone increases oxidation of NO and NO₂ pollutant gases in the gas phase and moisture film; however, the oxidation of SO₂ in the moisture film is more significant than that of NO or NO₂. Wetting of the stone surfaces, in the absence of ozone, reveals the consistently greatest chemical reaction with SO₂ compared with NO and NO₂, which is related to SO₂ solubility, oxidation in the presence of catalysts and production of sulphuric acid. Generally similar behaviour is evident of NO and NO₂, but NO shows a reduced extent of chemical reaction, implying that its oxidation in surface water, in the presence of catalytic species, is slow and hence the reactants are lost in the form of run-off. In the additional presence of ozone, the SO₂ pollutant gas gives rise to enhanced chemical reaction, whereas both NO and NO₂ show lower extents of chemical reaction than for the dry stones. This arises from the relatively slow conversion of N₂O₅ in the liquid phase to nitric acid, allowing loss of reactants in run-off.     

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%.     

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.     

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.     

Laboratory measurements of sulfur dioxide deposition velocity on marble and dolomite stone surfaces

The deposition velocity of SO₂ on marble and dolomite stone surfaces in a humid atmosphere was measured as a function of time in the laboratory using continuous monitoring techniques. The deposition velocity of SO₂ on marble varied between 0.02 and 0.23 cm s⁻¹, and was generally observed to decrease with time. The deposition velocity of SO₂ on dolomite varied between 0.02 and 0.10 cm s⁻¹, and gradually increased over the first 2000 ppm-h of exposure. For both types of stones, the deposition velocity increased significantly when condensed moisture was observed on the stone surface. Chemical analysis of the stone samples indicated that the SO₂ deposited reacted with the stone materials to form gypsum (CaSO₄·2H₂O) on the marble surfaces and gypsum and epsomite (MgSO₄·7H₂O) on the dolomite surfaces.     

Atmospheric pollutant deposition to high-elevation ecosystems

Current knowledge regarding deposition of atmospheric pollutants to mountain ecosystem is reviewed focusing on the mountains of eastern North America. Despite a general paucity of published data on the subject, some generalization emerge. Wet deposition (i.e. precipitation input) of SO₄²⁻, NO₃⁻, H⁺ and Pb tends to increase with elevation, primarily because of the orographic increase in precipitation amount. Cloud water deposition of these substances can be very significant for mountain forests, but is highly variable spatially because of its strong dependence on wind speed, cloud characteristics, and vegetation canopy structure, which are all heterogeneously distributed. Dry deposition has not been quantified sufficiently to draw empirical generalizations, but the processes involved are discussed with regard to expected elevational trends. Based on the few studies in which total annual deposition (wet, dry, plus cloud water inputs for an entire year) has been measured, it appears that some high-elevation sites in the Appalachian Mountains receive substantially more SO₄²⁻, NO₃⁺ deposition than do typical low-elevation sites. The amount of elevational increase depends largely on the amount of cloud water deposition at the mountain site. Data from two clusters of sites in the northern Appalachians indicate that total deposition of SO₄²⁻, NO₃⁻, and H⁺ to mountaintop sites is typically 3–7 times greater than deposition to nearby lowland sites. Similarly, some studies of Pb accumulation in organic soil horizons suggest a two- to four-fold increase from lowlands to mountaintops. Deposition in mountain areas can be highly variable over short distances because of the patchiness of meteorological conditions and vegetation canopy characteristics, and also because exposed trees and forest edges can receive deposition loads much higher than the landscape average. Night-time and early-morning O₃ concentrations are greater at high-elevation than at low-elevation sites. Daytime O₃ levels are equal or slightly higher at high-elevation sites. Additional studies are suggested which would allow better characterization of pollutant exposure along elevational gradients.     

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.     

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.     

太原市五年降尘及降水中主要离子特征

随着我国工业化和城镇化的深入推进,人们对城市大气环境质量关注日益增加。连续五年对山西省太原市5个点位进行监测,考察降水中主要离子时间变异及大气干湿沉降规律。结果表明:太原市五个监测点年均干沉降量排序为太钢工业区坞城(东)桃园(市中)晋祠(景区)上兰(市郊),其中太钢年均沉降量是上兰的三倍。降尘量除了在不同点位差异较大外,相同点上不同季节也有较大波动,表现为各监测点春季和冬季降尘量为全年最高。而夏季由于降雨较多,干沉降最少。总体上,近五年各点干沉降量呈现逐年下降的趋势。湿沉降方面以桃园为市区代表分析,SO_4~(2-)、NO_3~-、Ca~(2+)和NH_4~+是太原市桃园降水中主要的无机离子,其加权平均浓度范围为3.1～19 mg/L,各离子浓度在干燥的冬春季较高,且近五年其浓度及沉降量快速增加。桃园降雨中SO_4~(2-)和NO_3~-仍然是最主要的致酸离子,SO_4~(2-)年均沉降量分别是NO_3~-、Ca~(2+)和NH_4~+的1.7、3.9、5.9倍。Ca~(2+)、NH_4~+和Mg~(2+)的中和因子分别是0.42、0.30、0.14,说明Ca~(2+)、NH_4~+对酸雨缓冲作用大于Mg~(2+)。2013～2017年太原市桃园降雨SO_4~(2-)/NO_3~-和NH_4~+/NO_3~-比值分别为1.7和0.3,表明酸雨类型由硫酸型向混合型发展,主要是近年来NO_3~-浓度增幅大于SO_4~(2-)和NH_4~+。总的来看,近些年太原市政府大力提倡节能减排带来明显效果,但工业厂矿区周边降尘污染依然严重,属于今后城市环境治理的重点。     

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).     

Scavenging ratios and deposition of sulphur,nitrogen and chlorine species in eastern England

Measurements of wet deposited NH₄⁺, SO₄²⁻, NO₃⁻ and Cl⁻, as well as airborne concentrations of these species and gaseous HNO₃, HCl and NH₃, have been made at a site in eastern England. Scavenging ratios based solely upon aerosol-associated species and upon aerosol plus gaseous airborne species are presented and compared with literature values. It appears that HCl and HNO₃ have only a rather minor influence upon wet deposition at our site. Gaseous NH₃ influences ground-level air chemistry appreciably, but scavenging ratios for NH₄⁺ are low, even when based upon aerosol NH₄⁺ concentrations alone, presumably due to altitudinal gradients in this species. The problems inherent in interpretation of scavenging ratios are discussed. Deposition of nitrogen in various chemical forms is estimated from rainwater and air composition. If a transport-limited deposition velocity is assumed for ammonia gas, dry deposition of this species accounts for around 40% of total nitrogen deposition to the ground.     

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.     

Characterization of pollen deposition in a forest environment

Measurements of the dry deposition of pollen were made during the months of May and June 1987 in northern Wisconsin, using a smooth surrogate surface. Samples were taken on a raft located on Little Rock Lake and at a nearby field monitoring station. Rain samples were also collected at the field station. The wet SO₄²⁻ flux was 102.7 mg m⁻², compared with a dry SO₄²⁻ flux of 118 mg m⁻² at the field monitoring site and 45 mg m⁻² at the lake site.The SO₄²⁻ content of pollen ranged from 0.2 to 0.8% of the weight of the pollen, and NO₃⁻ concentrations were an order of magnitude lower. Between 9 and 22% of the pollen weight was available as total organic carbon (TOC) upon addition to water.The addition of pollen to distilled water produced an acid reaction, due to organic acids and not inorganic acidity.     

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⁻.     

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.     

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.     

Source-receptor relationships for wet SO42− and NO3− production

Precipitation chemistry data for the years 1982–1985 from 110 stations distributed across the continental U.S. and southern Ontario Province are used to describe the geographic distributions of SO₄²⁻ and NO₃⁻ in precipitation. Volume-weighted, wet SO₄²⁻ and NO₃⁻ concentrations, averaged over the 4 years of observation by season and annullly, show coherent patterns with maxima in the northeastern U.S. and southeastern Canada about ten times greater than the minima observed in the Intermountain and Pacific Northwest regions.Tests for empirical source-receptor relationships indicate that, in land areas with relatively low emissions of SO₂ and NO_x, the associations between wet SO₄²⁻ concentrations and SO₂ emissions and between wet NO₃⁻ concentrations and NO_x emissions within 560 km of each precipitation chemistry station are weak or nonexistent (r²⩽0.42). The remaining land areas show moderate to strong associations between SO₂ and SO₄²⁻ and NO_x and NO₃⁻ during the spring and summer, but only weak to nonexistent associations during the winter. The associations between emissions and concentrations, e.g. SO₂ and SO₄²⁻, are equally well represented by either a linear or a power law function. However, at the level of aggregation employed, the data do not substantiate a linear-proportional relationship between concentrations and anthropogenic emissions. Furthermore, emissions of SO₂ and NO_x are highly correlated, as are the emissions of RHC and NO_x.     

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.     

广州干湿季典型灰霾过程水溶性离子成分对比分析

利用广州气象台2011年地面逐时能见度和相对湿度数据,以及广州番禺南村大气成分站2011年逐时Marga数据、PM数据,对比分析了一次湿季(4—9月)灰霾过程和干季(10月—次年3月)灰霾过程的污染特征.研究表明,相对干季灰霾过程,湿季灰霾过程颗粒物浓度较低,且细粒子所占比例较高;由于湿季较干季光化学反应较为活跃及可能受气象因素的不同影响,导致干湿季灰霾过程颗粒物浓度的总体变化趋势相反;湿季灰霾过程二次无机离子(SO_4~(2-)、NH_4~+和NO_3~-)占PM_(2.5)质量百分比的76%,是PM_(2.5)的主要成分;干季灰霾过程二次无机离子(SO_4~(2-)、NH_4~+和NO_3~-)仅占PM_(2.5)质量百分比的34%;湿季硫氧化率(Sulfur Oxidation Ratio,SOR)、氮氧化率(Nitrogen Oxidation Ratio,NOR)值大于干季,说明二次离子对湿季灰霾的贡献比干季要大;湿季灰霾过程中气溶胶酸性比干季弱.根据相关性分析结果可知,湿季灰霾过程中,NH_4~+主要与SO_4~(2-)结合,Na+主要与Cl-及NO_3~-结合,K+主要与Cl-和NO_3~-结合,极少部分与SO_4~(2-)结合;而在干季灰霾过程中,NH_4~+除了与SO_4~(2-)结合之外,还以NH_4NO_3和NH_4Cl的形式存在,K~+主要与Cl~-和SO_4~(2-)结合,Na+主要与Cl~-及SO_4~(2-)结合.