The oxidation of SO2 on carbon particles in the presence of O3, NO2 and N2O

The oxidation of SO₂ on carbon particles at 65 % relative humidity (RH) by O₃, NO₂ and N₂O was investigated gravimetrically and compared with oxidation by air. Approximately 1 mg samples of carbon black were exposed to continuously flowing mixtures of SO₂, SO₂ + O₃, SO₂ + NO₂, and SO₂ + N₂O in air (or in N₂). Both O₃ and NO₂ in the 0.07–10ppmv range with 20–40ppmv SO₂ were found to produce sorption and desorption coverages significantly higher than those for corresponding SO₂ in air exposures. N₂O was determined to be much less effective as an oxidant than O₃ or NO₂. Identical concentrations of O₃ or NO₂ were found to produce equivalent conversions of SO₂ to sulfate on carbon for equal exposure times. Wet chemical analysis of the residue following desorption indicated that sulfate generally accounted for well over half of the retained weight.Exposure at low concentrations (0.10 ppmv SO₂ + 0.02 ppmv O₃ or NO₂), however, appeared to produce little, if any, enhancement in SO₂ transformation when compared with equivalent SO₂ in air. Weight retentions for these runs were very small, however, and measurement errors of up to 25% would be anticipated.     

Influence of NO2 on S(IV) oxidation in aqueous suspensions of aerosol particles from two different origins

The influence of soluble compounds leached from real atmospheric aerosol particles (size range D_ae: 0.17–1.6 μm) and dissolved NO₂ on S(IV) oxidation in aqueous solution is presented. Experiments were conducted with aerosol particles of two different origins (i.e., urban and industrial) and at concentrations of trace gases in the gas mixtures (SO₂/air and SO₂/NO₂/air) typical for a polluted atmosphere. During the introduction of SO₂/air into the aqueous aerosol suspensions under dark conditions at pH 4, the formation of SO₄²⁻ was very slow with a long induction period. However, in the presence of NO₂ the oxidation rate of dissolved SO₂ in suspensions of aerosols from both origins increased substantially (about 10 times). The results suggest that soluble compounds eluted from atmospheric aerosols have not only a catalytic (e.g. Fe, Mn), but also a pronounced inhibiting effect (e.g., oxalate, formate, acetate, glycolate) on S(IV) autoxidation. When NO₂ was also introduced into the aerosol suspensions, the inhibition was not so highly expressed. An explanation for this is that the radical chain mechanism is mainly initiated by the interaction of dissolved NO₂ and HSO₃⁻. Therefore, at conditions typical for a polluted atmosphere dissolved NO₂ can have a significant influence on the secondary formation of SO₄²⁻.     

The inportance of organic and elemental carbon in the fine atmospheric aerosol particles

During a field campaign the chemical character of fine (d<2.5 μm) aerosol particles was studied at K-puszta, Hungary within the framework of a project of the European Union. The organic and elemental carbon fraction, as well as the concentration of major inorganic constituents with respect to the total fine aerosol mass are presented in this paper. It was found that organic compounds constituted a significant fraction of the total fine aerosol mass, their contribution is comparable to or larger than that of the major water soluble ions. The diurnal variation of aerosol composition was also studied. It can be concluded that the relative abundance of the major constituents is practically the same during the day and at night. The samples were also classified and studied according to the air mass history. It is stated that the aerosol can be separated into two populations with different regression lines between organic and elemental carbon.     

CO2高温活化活性炭材料对苯酚的吸附行为研究

以CO2为活化气体,在高温条件下对国产椰壳活性炭进行活化。研究了活化前后的活性炭在不同温度和pH等条件下对水溶液中苯酚的吸附行为。结果表明,活性炭经活化后,微孔体积和中孔体积增加,吸附容量明显提高;苯酚在活性炭上的吸附符合Freundlich吸附等温方程和准二级反应动力学方程;在一定范围内降低温度有利于吸附的进行;在pH为2～8时,吸附效果较好;在pH9时,吸附效率明显降低。     

颗粒物吸附乐果的动力学特征

研究了乐果在颗粒物表面上吸附的动力学特征,观察了颗粒物的性质对吸附行为的影响.结果表明,乐果在3种颗粒物上的吸附过程均符合一级动力学规律,其相关系数在0.986 2～0.990 5,达到极显著水平.颗粒物的性质与吸附量相关分析发现,不同颗粒物对乐果的吸附程度是由颗粒物的有机质、粘粒、阳离子交换容量(CEC)和pH等理化特征综合作用的结果.pH对吸附行为影响的实验结果指出,随着体系的pH逐渐增大,颗粒物对乐果的吸附能力增强.     

The enhanced oxidation of SO2 by NO2 on carbon particulates

The oxidation of SO₂ on carbon particles in dry air and in air at 65% relative humidity (RH) was found to be greatly enhanced by the presence of gaseous NO₂. Exposures of 20–80 ppm SO₂ + 10 ppm NO₂ on 1 mg samples of commercial carbon black were found to produce both sorption and desorption coverages (weight retained after desorption into N₂) of over one order of magnitude greater than for corresponding SO₂ exposures. Significant agglomeration and wetting were observed to occur progressively during exposures at 65% RH and samples, even after 150 h exposure, rarely reached steady-state weight gain. The wetting may have regenerated fresh reactive carbon surface. Sorptions conducted in nitrogen atmospheres, rather than in air, appeared to produce slightly higher sorptions and weight retentions for equivalent exposure concentrations and times, indicating that NO₂ served as the oxidizer and that molecular oxygen, or some trace constituents in air, may have weakly inhibited the oxidation by NO₂. Wet chemical analysis of the desorbed phase indicated that sulfate, presumably H₂SO₄, accounted for over half of the retained weight. Measurements of pH from water-quenched samples indicated a highly acidic surface phase and suggested the oxidation process could process in an acidic environment.     

油茶果壳炭对低浓度油烟的吸附行为

利用油茶果壳直接炭化法制备油茶果壳炭,其BET比表面积和孔容积测定结果分别为1 244 m2·g-1和1.02 cm3·g-1,SEM的分析表明,油茶果壳炭含有不同孔径的孔隙和裂缝,有利于油烟这种含有复杂组分污染物分子的吸附作用;等温吸附实验结果表明,低温低油烟浓度有利于油茶果壳炭对油烟的吸附作用,吸附量可达378.79 mg·g-1,其吸附等温线符合Langmuir吸附模型,热力学参数ΔG0、ΔH0、ΔS0均为负值,表明油茶果壳炭对油烟的吸附是一个自发的放热的物理过程。     

Impact and growth phenomena observed with sub-micrometer atmospheric aerosol particles collected on polished silicon at low coverage

The processes occurring during the initial stages of size-selected sampling of atmospheric aerosol matter were explored by means of high-resolution scanning electron microscopy and energy dispersive X-ray spectrometry. The final four stages of a Berner impactor served to collect particles with aerodynamic diameters between 60 nm and 1 μm on polished silicon substrates at sampling times between 10 s and 16 min. In the single-particle impact regime (fractional coverage below 5%), most of the particles produced circular black tracks, of which 15 to 30% contained cores of carbonaceous nanoparticles. At a fractional coverage above about 10%, initially generated deposits became increasingly active as centres of preferred aerosol collection. As a result, the number of black spots remained almost constant, but the area per spot increased rapidly. At this stage of fractional coverage, structured aerosol matter became visible within large black areas of random shape. The deposits showed clear evidence for the onset of phase separation between carbon nanoparticles and material rich in sulphur, probably a mixture of alkaline and alkaline earth sulphates. After some time of sample storage in air the low-coverage sulphate matter tended to attain a fractal pattern. At a fractional coverage of several hundred per cent, large amorphous or crystalline objects had grown, but 30% or more of the nominal impact area still did not contain any aerosol matter. Moreover, carbon nanoparticles were found to be phase separated from the newly grown, very uniform aerosol material. The observations imply that sub-micrometer aerosol matter collected in impactors has lost memory of the original particle morphology.     

Quantitative determination of sulphate in individual aerosol particles

The vapour-deposited thin-film method of analysing individual aerosol particles is shown to provide a method for quantitative determination of sulphate. The method utilizes a calibration curve which relates the mass of sulphate in a particle to the diameter of the reaction ring it produces with a thin layer of barium chloride. A single calibration curve was shown to apply to ammonium sulphate, sulphuric acid and mixed ammonium sulphate/sodium chloride particles. Masses of as little as 10⁻¹⁷ g sulphate, corresponding to particle diameters of ~0.03 μm, were determined to +41%, −29% accuracy with this technique.     

二氧化钛气溶胶颗粒在石英玻璃纤维上的沉积

利用雾化挥发发生原理制备二氧化钛气溶胶,将二氧化钛气溶胶颗粒负载在石英玻璃纤维上,制备二氧化钛-石英玻璃纤维功能性空气过滤材料。实验研究了二氧化钛气溶胶发生相关参数、石英玻璃纤维直径分布、透过率曲线、最易透过粒径,并对二氧化钛气溶胶颗粒在石英玻璃纤维上的负载过程和负载形态进行了探讨。研究结果表明,发生的二氧化钛气溶胶具有可控的粒径分布和较好的分散性;中值粒径128 nm的二氧化钛气溶胶颗粒能够稳定负载在3 μm的石英玻璃纤维上;二氧化钛在石英玻璃纤维上的沉积量受沉积时间的影响,沉积过程中阻力开始变化不大,随后在沉积饱和点后阻力迅速增大,滤料填充度越高沉积饱和点出现时间越早;二氧化钛粒子在纤维表面的负载形态除颗粒、团簇外,还有三维的树枝状空间结构。     

三氯生在碳纳米管上的吸附

药品和个人护理用品(PPCPs)已成为一个引起广泛关注的新的环境问题。采用碳纳米管（CNTs）对水溶液中的三氯生进行吸附处理,考察了碳纳米管粒径及用量、温度、pH、振荡时间等因素对三氯生去除率的影响。研究结果表明,碳纳米管能快速吸附水中的三氯生,粒径较小的碳纳米管可获得较高的三氯生去除率;低温有利于吸附反应的进行;pH在6.5～7.0时,三氯生的去除率可达97%。三氯生在碳纳米管上的吸附可以很好地用Langmuir和Freundlich吸附等温方程进行描述。     

Adsorption and oxidation of sulfur dioxide on particles

The role of atmospheric participated matter in affecting atmospheric SO₂ and its reactions has been investigated. A variety of dusts of various sources (urban particulated matters and stack emissions of industrial plants) have been characterized in terms of their physical and chemical properties and submitted to a SO₂ adsorption process at room temperature and desorption at 175°C.The interaction between particles and SO₂ can occur through two processes: adsorption and conversion to sulphate. The extent of these processes depends upon the particles, chemical composition and their nature, which can be defined in terms of pH, titratable acidity, surface area, humidity and degree of surface coverage by adsorbed components.SO₂ adsorption by particles is the primary process which occurs in two steps, only the first one being apparently of environmental significance. Humidity has an important role in the adsorption, the higher its value the higher results the amount of adsorbed SO₂. The behaviour of atmospheric dusts collected in different areas and seasons is very similar, the reaction constant of the first order process being 4–5 × 10⁻²min⁻¹.Both ‘fresh’ particles coming from stacks, which do not carry SO₂, as well as ‘aged’ atmospheric particles adsorb SO₂ the relative extent of the process being mainly determined by the dust reaction. The former in most cases do not release SO₂ by heating, this behaviour being taken as an example of chemisorption, whereas the latter lose SO₂ by heating, SO₂ being retained by only a physical bond.Conversion to sulphate occurs with a very high rate on particles coming from industrial emissions, the alkaline reaction being the determining factor, whereas it does not take place on urban atmospheric dusts to an appreciable extent.This mechanism is supported by measurements by differential thermal analysis and by X-ray photoelectron spectroscopy.Though, in the atmosphere, it is impossible to discriminate various effects due to homogeneous and heterogeneous reactions, the main interaction between SO₂ and particulated matter is adsorption, most catalytic reactions occurring at high temperature and most probably at the chimney outlet.     

Mixing properties of individual submicrometer aerosol particles in Vienna

Individual aerosol particles were collected on 5 days with different meteorological conditions in March, April and June 1991 in the urban atmosphere of Vienna in Austria. The samples collected with an impactor were examined by electron microscopy. The mixing properties of submicrometer aerosol particles with radii between 0.1 and 1 μm were studied by using the dialysis (extraction) of water-soluble material. The averaged results showed that more than 85% of particles with radii between 0.1 and 0.7 μm were hygroscopic. However, more than 50% of particles with radii larger than 0.2 μm were mixed particles (hygroscopic particles with water-insoluble inclusions), and they were dominant (80%) in the size range 0.5–0.7 μm radius. The results also showed that the number proportion of mixed particles increased with increasing radius and the abundance increased with increasing particle loading in the atmosphere. The volume fraction of water-soluble material (ε) in mixed particles tended to decrease with increasing radius, implying the formation of mixed particles by heterogeneous processes such as condensation and/or surface reaction. Some results of elemental composition in individual particles analyzed with an energy-dispersive X-ray (EDX) analyzer equipped with an electron microscope are also presented in this paper.     

Equilibrium temperatures of aerosol particles in outdoor exposure chambers

It has been suggested that radiational heating of atmospheric soot particles could affect the stability of organic compounds on the aerosols as these systems age in the atmosphere. To investigate this possibility, we introduce a simple equation for calculating the equilibrium temperature of atmospheric particles. The results show that under typical conditions, the temperature difference between the particles and the surrounding air is less than 0.01 K.     

活性炭负载I-TiO2对气体中甲苯的吸附

利用溶胶凝胶-浸渍烧结法制备了碘掺杂二氧化钛修饰的活性炭复合吸附剂。利用XRD、SEM、BET、Boehm滴定、亚甲蓝吸附值等手段研究了活性炭负载前后表面结构与性质。利用动态吸附实验研究了活性炭负载I-TiO2复合材料（IT/AC）和再生IT/AC对气体中甲苯的吸附。考察了活性炭粒径、气体的流速、吸附床层高度和气体中甲苯的浓度对活性炭吸附性能的影响及甲苯在活性炭固定床上的吸附动力学。结果表明：由于介孔I-TiO2和活性炭的协同作用,负载适量I-TiO2对活性炭结构和吸附性能影响较小。活性炭的粒径越小、复合材料的吸附穿透点和饱和吸附量越大;气体的流速和甲苯的初始浓度越大,复合材料的吸附穿透点越小但饱和吸附量越大。YOON-NELSON模型可以预测复合材料吸附甲苯的动力学过程。     

On the relative contributions of NO2 and particles to the color of smoke plumes

This paper studies the relative influences of NO₂ absorption and particle scattering on plume appearance. Theoretical results are summarized in compact nomograms which permit the direct comparison of absorption and scattering effects. These show the strong variation of scattering effects with viewing angle and particle size. Available data from several coal and oil-fired power plants in the southwestern U.S. are collated and evaluated in the light of the theory. From the limited data base, it is concluded that particle scattering: (a) controls plume-horizon contrast under most conditions at the older coal-fired plants; (b) is an important near-stack plume colorant at oil-fired plants; (c) may be a significant plume colorant at coal-fired plants equipped with wet scrubbers and (d) does not contribute to brown plume color at coal-fired plants equipped with electrostatic precipitators. Throughout the paper, all results and data are expressed in forms which are invariant under plume dilution, so that fundamental optical relationships are not obscured by the large variations encountered in atmospheric transport and dispersion.     

三价铁改性活性炭对水中微量砷的吸附特性

研究了三价铁改性对不同活性炭(颗粒和粉末)对水中砷的吸附特性的影响。结果表明,三价铁改性有效提高了活性炭对不同形态砷的吸附性能。其中,对于2种活性炭,As(Ⅲ)和As(Ⅴ)的最佳铁离子改性浓度分别为0.1和0.05 mol/L。此时,通过Langmuir等温线方程拟合得到:粉末和颗粒活性炭对As(Ⅲ)的最大吸附量qm分别为2.38 mg/g和9.39 mg/g;而对As(Ⅴ)的qm分别为5.12 mg/g和2.32 mg/g。此外,当溶液的pH从3升高到9的过程中,吸附量先增加后有所下降,当pH 为7时,改性前后的活性炭对砷的吸附量达到最高。     

Estimation of actinic flux and photolysis rate constant of NO2 from aerosol size data

Aerosol mass measurements made using Andersen cascade impactor at different locations in an urban area were used to study the variation in power-law exponent in the Junge-type number distribution. The discrete mass size data were inverted by modified Twomey algorithm to obtain continuous mass size distribution from which number distributions were derived. These were used for evaluating actinic fluxes and hence NO₂ photolysis rate constants employing a radiative transfer model with delta-Eddington approximation.Results of the spatial variation of Junge power-law exponent over the urban region are presented. The relative magnitude of photolysis rate constants over regions with differing aerosol emission characteristics are illustrated. Parametric studies indicated the importance of considering fractional elemental carbon content of the aerosols in the atmosphere. Results of a limited validation study of the model are also presented using quartz crystal microbalance impactor data at one of the sites.