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.     

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.     

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.     

pH值对石灰(石灰石)湿法脱硫反应机理的影响

为了探讨ｐＨ值对石灰石湿法脱硫反应机理的影响,进行了用亚硫酸钙沉淀与水的混合液吸收ＳＯ２的实验,研究表明,溶液中离子化合物的型态与体系的ｐＨ值密切相关。体系ｐＨ值小于７时,硫阴离子主要以ＨＳＯ＾－３型态存在,脱硫反应以生成Ｃａ（ＨＳＯ３）２为主;体系ｐＨ值大于７时,硫阴离子主要以ＳＯ＾－２３型态存在,脱硫反应以生成ＣａＳＯ３．１／２Ｈ２Ｏ或ＣａＳＯ４．２Ｈ２Ｏ为主。     

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.     

Origin of soluble chemical species in bulk precipitation collected in Tokyo,Japan: Statistical evaluation of source materials

An iterative least-squares method with a receptor model was applied to the analytical data of the precipitation samples collected at 23 points in the suburban area of Tokyo, and the number and composition of the source materials were determined. Thirty-nine monthly bulk precipitation samples were collected in the spring and summer of 1987 from the hilly and mountainous area of Tokyo and analyzed for Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, F⁻, Cl⁻, Br⁻, NO₃⁻ and SO₄²⁻ by atomic absorption spectrometry and ion chromatography. The pH of the samples was also measured. A multivariate ion balance approach (Tsurumi, 1982, Anal. Chim. Acta138, 177–182) showed that the solutes in the precipitation were derived from just three major sources; sea salt, acid substance (a mixture of 53% HNO₃, 39% H₂SO₄ and 8% HCl in equivalent) and CaSO₄. The contributions of each source to the precipitation were calculated for every sampling site. Variations of the contributions with the distance from the coast were also discussed.     

Regeneration of commercial selective catalyst reduction catalysts deactivated by Pb and other inorganic elements

The regeneration of commercial SCR(Selective Catalyst Reduction) catalysts deactivated by Pb and other elements was studied.The deactivated catalyst samples were prepared by chemical impregnation with mixed solution containing K_2SO_4,Na_2SO_4,CaSO_4,Pb(NO_3)_2and NH_4H_2PO_4.A novel method combining Ethylenediaminetetraacetic acid disodium salt(EDTA-2Na) and H_2SO_4solution(viz.catalysts treated by dilute EDTA-2Na and H_2SO_4 solution in sequence) was used to recover the activity of deactivated samples,and the effect was compared with single H_2SO_4,oxalic acid,acetic acid,EDTA or HNO_3 solutions.The surface structure,acidity and reducibility of samples were characterized by N_2adsorption–desorption,inductively coupled plasma optical emission spectrometer(ICP-OES),scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray fluorescence(XRF),H-2-temperature programmed section(H_2-TPR),NH3-temperature programmed desorption(NH3-TPD) and in situ DRIFTS.Impurities caused a decrease of specific surface area and surface reducibility,as well as Br?nsted acid sites,and therefore led to severe deactivation of the SCR catalyst.The use of an acid solution alone possibly eliminated the impurities on the deactivated catalyst to some extent,and also increased the specific surface area and Br?nsted acid sites and promoted the surface reducibility,thus recovered the activity partially.The combination of EDTA-2Na and H_2SO_4 could remove most of the impurities and improve the activity significantly.The removal of Pb should be an important factor for regeneration.Due to a high removal rate for Pb and other impurities,the combination of EDTA-2Na and H_2SO_4 solutions provided the best efficiency.     

A numerical experiment on the relative importance of H2O2 O3 in aqueous conversion of SO2 to SO42-

The importance of the three major aqueous reactions thought to be responsible for the in-cloud conversion of SO₂ to SO₄^2- was studied using the acidic deposition and oxidants model by supressing each reaction individually and all reactions simultaneously. The reactions are the oxidation of SO₂ by H₂O₂, or O₃ and catalytic oxidation by O₂ in the presence of Fe and Mn. The model simulations were 19–24 April 1981. It was found that SO₄^2- precipitation concentrations were generally more sensitive to H₂O₂ oxidation than to O₃ oxidation. The contribution of catalytic oxidation of SO₂ in the presence of Fe and Mn is insignificant everywhere and at all times. The contributions of H₂O₂ oxidation to SO₄^2- in precipitation is strongest in light precipitation areas while O₃ oxidation can be greater than H₂O₂ oxidation in heavy precipitation areas. The effect of supressing one reaction is mitigated by compensation through another mechanism. This is seem from the significant difference observed in the effects when individual suppressions were added together and when all reactions were suppressed simultaneously. From this, it is estimated that the contribution of aqueous oxidation of SO₂ to SO₄^2- in precipitation is approximately 50–80 per cent. Further simulations show that the relationship between SO₂ emissions and SO₄^2- production in the aqueous-phase through the oxidation reaction with O₃ is always non-linear in view of the pH dependence of the reaction rates.     

The chemical and mineralogical composition of the water-soluble fraction of power-plant ash and its effect on the process of crystallization of water

The content of the water-soluble fraction of power-plant fly ash from nine power plants burning brown and black coal varied in the range 0.43–1.34%. It was found, on the basis of chemical analysis and X-ray diffraction measurements, that the soluble fraction consists mostly of anhydrous CaSO₄, 3MgSO₄.CaSO₄, Na₂Ca(SO₄)₂ and other double sulphates. The sample from one power plant burning black coal also contained CaCO₃, CaO and K₂CO₃. The nucleation activity of the original ash sample, the ash without the water-soluble fraction and the separated fraction was found by the methods of nucleation deposition and the freezing of water drops. These measurements demonstrated that the soluble components, which, by themselves, exhibit low nucleation activity, considerably increase the nucleation activity of the ash when associated with the ash particles.     

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.     

不同阴离子对水溶性磷酸盐稳定污染土壤中重金属的影响

在重金属污染土壤中加入磷酸盐是稳定重金属的有效方法.本研究的目的是探讨不同阴离子对水溶性磷酸盐稳定污染土壤铅、镉和锌的影响.在重金属复合污染土壤(全铅、镉和锌的含量分别为2337、21.4和391 mg·kg^-1)中按P:Pb=2:1 (mol:mol)加入磷酸二氢钙,之后按P:阴离子=3:1或3:2 (mol:mol)加入盐酸、氯化钠、硫酸、硫酸钠或氟化钠,并设置只加磷酸盐、不加其它试剂的对照,培养55 d,之后测定土壤性质.结果表明,与对照相比,HCl处理、2HCl处理、NaCl处理和2NaCl处理土壤DTPA-Pb含量下降比例依次为5.72%、9.29%、6.38%和8.80%(p<0.05),加入硫酸、硫酸钠的处理土壤DTPA-Pb含量与对照无显著差异(p>0.05),而加入氟化钠的处理升高4.70%(p<0.05).加入盐酸或氯化钠的处理土壤镉有效性显著高于对照(升高5.24%~12.8%)(p<0.05),其它处理对DTPA-Cd含量无显著影响(p>0.05).各处理对土壤DTPA-Zn含量和pH影响较小,但均引起土壤电导率明显升高.以上结果表明,氯离子可促进水溶性磷酸盐对土壤铅的稳定,但可促进镉有效性.氯磷酸铅的生成是加氯情况下磷酸盐稳定铅的重要机制.     

Oxidation of SO2 in thin water films containing NH3

The reaction between NH₃ and SO₂ in thin water films was studied with a focus on the formation of sulfate. The reactions were conducted at 5 and 60% relative humidities or partial pressure of water vapor and at 0.04, 0.16 or 0.20 atm O₂ for temperatures between 20 and 50°C using a flow reactor and static flask reactors. In the presence of water vapor, the oxidation of SO₂ to sulfate was observed only when NH₃ was present. The product was primarily (NH₄)₂SO₄. Conversion of as much as 81% of the SO₂ to sulfate was observed after 10 min of reaction when the initial concentrations of SO₂ and NH₃ were 1 ppm and the relative humidity was 60%. Conversion was only 1–3% when NH₃ and/or water vapor were absent from the system. The surface of the reactor was found to influence the reaction by providing a place for a film of liquid water to form, and for the first several hours of reaction in the film, th e rate of sulfate formation was observed to be faster than oxidation in liquid water. In general, these results suggest that thin water films on environmental surfaces play a greater role in the deposition of atmospheric gases and the accumulation of their reaction products on surfaces than previously considered.     

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.     

基于碳捕集的富氧燃煤烟气联合脱硫脱硝试验研究

富氧燃煤烟气压缩液化CO2的高压低温工况为NO氧化为易溶于水的NO2提供了十分有利的条件.基于小型高压吸收试验装置,采用配制的富氧燃煤模拟烟气,在高压常温下进行了NO、SO2、O2与H2O的吸收反应试验.根据反应前后的气液产物分析,测定了不同组分比例与不同压力下混合气体中NO与SO2的转化率.NO氧化与吸收试验表明,NO转化为HNO3的比率随压力升高而增加,在0.5 ～2 MPa之间增加很快,在2 ～3 MPa之间增速趋丁平缓,压力达3 MPa以上时,90％以上的NO均转化为稀硝酸,且初始NO浓度越高,NO的转化率越大.混合气体中同时存在5O2与NO的联合吸收试验发现,只有少量的NO转化成了NO3-,SO2向H2SO4的转化率随压力升高而增加,初始SO2浓度越大,转化率越高.分析表明,SO2与NO同时存在时SO2先行转化为SO3,NO充当了催化剂,但SO2转化为SO3的一次转化率小于35％,反应酸液产物的多次循环能使SO2的转化率达到90％以上.建议的工艺流程中需采用两座吸收反应塔顺序脱除SO2与NO并回收稀酸溶液,有望在富氧燃煤发电捕集CO2系统中降低脱硫脱硝成本,部分地弥补富氧燃烧机组发电成本的增加.     

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.     

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.     

聚硅酸对不同形态铝沉积行为的影响

针对给水管网中残余铝沉积和再溶解现象可能引起的水质问题,研究了聚硅酸对不同水解聚合形态铝沉积、再溶解的影响,并以石英微晶天平为表征手段,初步探讨了聚硅酸对不同形态铝沉积、再溶解过程影响的机理.结果表明,聚硅酸能显著改变不同水解聚合形态铝的沉积、再溶解行为.聚硅酸可与3种水解聚合形态的铝迅速结合而生成可沉积产物,但产物性质不同.以单体形态为主的Al_0与聚硅酸的反应产物性质较稳定,部分以溶解态存在,部分以非溶解态(可沉积态)存在;尽管铝的两种聚合形态Al_(13)和Al_(30)与聚硅酸反应也生成了部分可沉积产物,但随着时间的推移,这些产物又逐渐向溶解态转化.铝硅比对Al_0体系中铝的沉积溶解行为影响较小,而对Al_(13)和Al_(30)影响较大,且在0.2∶20(以Al和SiO_2计的质量比)时,沉积态铝的溶解速率最快.     

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).     

Air pollutant concentrations in Varanasi,India

This study reports the diurnal patterns in the concentrations of ozone (O₃), nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and total suspended particulate matter (TSP) in the urban atmosphere of Varanasi city in India during 1989. The city was divided into five zones and three monitoring stations were selected in each zone.Ambient concentrations of NO₂ and SO₂ were maximum during winter but ozone and TSP concentrations were highest during summer. The measured maximum concentrations (2-h average) were 150 and 231 μg m⁻³ (0.078 and 0.086 ppm) for NO₂ and SO₂, respectively, for the winter season. Ozone and TSP concentrations reached a maximum of 160 (0.08 ppm) and 733 μg m⁻³, respectively, in the summer. NO₂ and SO₂ concentrations peaked in the morning and evening. Peak concentrations of O₃ occurred in the afternoon, generally between noon and 4 p.m. Maximum concentrations of O₃, NO₂, SO₂ and TSP were measured in zones I and II, and minimum in zone V.