Laboratory simulation of SO_2 heterogeneous reactions on hematite surface under different SO_2 concentrations

The variations of sulfate formation and optical coefficients during SO2 heterogeneous reactions on hematite surface under different SO2 concentrations were examined using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatograph (IC). Laboratory experiments revealed that within ambient SO2 of 0.51–18.6 ppmv, sulfate product, producing velocity, absorption and backward scattering coefficients showed an increasing trend with SO2 concentration. Under given SO2 concentra...     

Heterogeneous reaction of SO2 on CaCO3 particles: Different impacts of NO2 and acetic acid on the sulfite and sulfate formation

Despite the heterogeneous reaction of sulfur dioxide (SO₂) on mineral dust particles significantly affects the atmospheric environment, the effect of acidic gases on the formation of sulfite and sulfate from this reaction is not particularly clear. In this work, using the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique, we employed a mineral dust particle model (CaCO₃) combined with NO₂ and acetic acid to investigate their effects on the heterogeneous reaction of SO₂ on CaCO₃ particles. It was found that water vapor can promote the formation of sulfite and simulated radiation can facilitate the oxidation of sulfite to sulfate. The addition of NO₂ or acetic acid to the reaction system altered the production of sulfate and sulfite accordingly. There was a synergistic effect between NO₂ and SO₂ that promoted the oxidation of sulfite to sulfate, and a competitive effect between acetic acid and SO₂ that inhibited the formation of sulfite. Moreover, light and water vapor can also affect the heterogeneous reaction of SO₂ with the coexistence of multiple gases. These findings improve our understanding of the effects of organic and inorganic gases and environmental factors on the formation of sulfite and sulfate in heterogeneous reactions.     

Heterogeneous reactions of SO2 and NO2 on carbonaceous surfaces

Four different types of carbonaceous material (active carbon, graphitized carbon black, source samples from a power plant and from an urban heating boiler) were exposed to synthetic gas mixtures of SO₂ and SO₂ + NO₂ in sub-ppm ranges at two different relative humidities (60 and 90% r.h.). The interaction of SO₂ and NO₂ with the carbonaceous materials led to sulfate and to three other products: NO, HONO and NO₂⁻. Formation of NO and NO₂⁻ was observed only on active carbon while the other three materials yielded HONO. It was also found that NO₂ enhances the deposition of SO₂ only on the source sample from the power plant at 60% r.h., whereas the material from the urban heating boiler had no effect both at low and high r.h. The results obtained show that no general statements on the effect of NO₂ on the heterogeneous reaction of SO₂ on these carbonaceous materials can be made and also that NO₂ reactions in the presence of SO₂ on carbon-containing surfaces should be considered as a source for the production of HONO in the urban environment.     

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.     

Knudsen cell and smog chamber study of the heterogeneous uptake of sulfur dioxide on Chinese mineral dust

The heterogeneous uptake processes of sulfur dioxide on two types of Chinese mineral dust（Inner Mongolia desert dust and Xinjiang sierozem） were investigated using both Knudsen cell and smog chamber system. The temperature dependence of the uptake coefficients was studied over a range from 253 to 313 K using the Knudsen cell reactor, the initial uptake coefficients decreased with the increasing of temperature for these two mineral dust samples, whereas the steady state uptake coefficients of the Xinjiang sierozem increased with the temperature increasing, and these temperature dependence functions were obtained for the first time. In the smog chamber experiments at room temperature, the steady state uptake coefficients of SO2 decreased evidently with the increasing of sulfur dioxide initial concentration from 1.72 × 1012 to 6.15 × 1012mol/cm3. Humid air had effect on the steady state uptake coefficients of SO2 onto Inner Mongolia desert dust.Consequences about the understanding of the uptake processes onto mineral dust samples and the environmental implication were also discussed.     

A case study of Asian dust storm particles: Chemical composition, reactivity to SO2 and hygroscopic properties

Mineral dust comprises a great fraction of the global aerosol loading, but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties. In this work, a case study characterizing Asian dust storm particles was conducted by multiple analysis methods, including SEM-EDS, XPS, FT-IR, BET, TPD/mass and Knudsen cell/mass. The morphology, elemental fraction, source distribution, true uptake coefficient for SO₂, and hygroscopic behavior were studied. The major components of Asian dust storm particles are aluminosilicate, SiO₂ and CaCO₃, with organic compounds and inorganic nitrate coated on the surface. It has a low reactivity towards SO₂ with a true uptake coefficient, 5.767×10^-6, which limits the conversion of SO₂ to sulfate during dust storm periods. The low reactivity also means that the heterogeneous reactions of SO₂ in both dry and humid air conditions have little effect on the hygroscopic behavior of the dust particles.     

A laboratory study on the scavenging of SO2 by snow crystals

A laboratory experiment is described where the uptake of SO₂ by dendritic snow crystals was studied. In a first experimental series the uptake of SO₂ was investigated during the growth of the snow crystals from water vapor with and without the presence of H₂O₂ in the air. In a second series of experiments we studied the uptake of SO₂ by snow crystals which had completed their growth. The results of our experiments showed that under both conditions SO₂ became scavenged by snow crystals. The uptake of SO₂ was particularly pronounced during the growth of the snow crystals, and at temperatures close to 0°C where a quasi-liquid layer exists at the surface of ice. As expected, the SO₂ uptake becomes enhanced in the presence of H₂O₂. The present results are in qualitative agreement with previous studies involving bulk ice.     

Heterogeneous oxidation of SO2 by O3-aged black carbon and its dithiothreitol oxidative potential

Ozone (O₃) is an important atmospheric oxidant. Black carbon (BC) particles released into the atmosphere undergo an aging process via O₃ oxidation. O₃-aged BC particles may change their uptake ability toward trace reducing gases such as SO₂ in the atmosphere, leading to different environmental and health effects. In this paper, the heterogeneous reaction process between O₃-aged BC and SO₂ was explored via in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Combined with ion chromatography (IC), DRIFTS was used to qualitatively and quantitatively analyze the sulfate product. The results showed that O₃-aged BC had stronger SO₂ oxidation ability than fresh BC, and the reactive species/sites generated on the surface had an important role in the oxidation of SO₂. Relative humidity or 254 nm UV (ultraviolet) light illumination enhanced the oxidation uptake of SO₂ on O₃-aged BC. The oxidation potentials of the BC particles were detected via dithiothreitol (DTT) assay. The DTT activity over BC was decreased in the process of SO₂ reduction, with the consumption of oxidative active sites.     

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.     

Heterogeneous uptake of gaseous hydrogen peroxide on mineral dust

The heterogeneous uptake processes of hydrogen peroxide on Arizona test dust and two types of authentic Chinese mineral dusts, i.e., Inner Mongolia desert dust and Xinjiang calciferous dust, were investigated using a Knudsen cell reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of H_2O_2 from 2.6 × 10~(11) to 1.2 × 10~(12)molecules/cm~3, and the temperature dependence of the uptake coefficients was investigated over a range from 253 to 313 K. The concentration of H_2O_2 showed little effect on the uptake coefficients of these heterogeneous processes. As a function of temperature, the initial uptake coefficients decrease with increasing temperature, whereas the steady state uptake coefficients of Arizona test dust and Inner Mongolia desert dust increase with increasing temperature. Implications for the understanding of the uptake processes onto mineral dust samples were also discussed.     

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 effect of wind velocity,air temperature and humidity on NH3 and SO2 transfer into bean leaves (phaseolus vulgaris L.)

The influence of wind velocity, air temperature and vapour pressure deficit of the air (VPD) on NH₃ and SO₂ transfer into bean leaves (Phaseolus vulgaris L.) was examined using a leaf chamber. The measurements suggested a transition in the properties of the leaf boundary layer at a wind velocity of 0.3–0.4 ms⁻¹ which corresponds to aRe_crit value of about 2000. At higher wind velocities the leaf boundary layer resistance (r_b) was 1.5–2 times lower than can be calculated from the theory. Nevertheless, the assessed relationships betweenr_b and wind velocity appeared to be similar to the theoretical derived relationship forr_b. The NH₃ flux and in particular the SO₂ flux into the leaf strongly increased at a VPD decline. The increase of the NH₃ flux could be attributed to an increase of the stomatal conductance (g_s). However, the increase of the SO₂ flux could only partly be explained by an increase ofg_s. An apparent additional uptake was also observed for the NH₃ uptake at a low temperature and VPD. The SO₂ flux was also influenced by air temperature which could be explained by a temperature effect ong_s. The results suggest that calculation of the NH₃ and SO₂ flux using data ofg_s gives a serious understimation of the real flux of these gases into leaves at a low temperature and VPD.     

NOx和/或NH3气氛下SO2在高岭土表面非均相转化的实验研究

利用自制气溶胶反应器研究了NO_x和/或NH_3气氛下SO_2在高岭土表面的非均相转化过程,应用扫描电镜(SEM)对高岭土颗粒物形貌进行了表征.结果表明:高岭土颗粒表面的SO_2非均相转化致使其成分和形貌产生了较大变化.相同实验条件下,SO_2转化的协同作用程度由高到低依次为NH_3、NO_x/NH_3和NO_x气氛,相对湿度40%、有光照条件下,SO_2转化量增幅最高可分别达125%、75%和50%.所有气氛下,协同作用在无光照时在高相对湿度(40%~70%)区间更为突出,有光照时其显著性则体现在低相对湿度(20%~40%)区间.SO_2、NO_x、NH_3三者共存时,在高岭土颗粒表面发生的非均相反应过程既有协同作用又存在竞争反应.     

Inhibition of photosynthesis and leaf conductance interactions induced by SO2, NO2 and SO2 + NO2

Effects of 2-h exposures to 0–1 μmol mol⁻¹ SO₂, NO₂ and (1:1) SO₂ + NO₂ on CO₂ uptake by standardized snap bean leaves were studied. Interactions resulting from pollutant-induced changes in leaf conductance were evaluated. Minimum exposure concentrations required to depress CO₂ exchange rates (CER) under the test conditions were:0.17 μmol mol⁻¹ SO₂, 0.38 μmol mol⁻¹ NO₂, and 0.08 μmol mol⁻¹ of each pollutant in the 1:1 mixture. Treatments with 1 μmol mol⁻¹ NO₂ reduced CER 10% without affecting leaf conductance. One μmol mol⁻¹ SO₂ depressed CER by 50%. Leaf conductances increased in SO₂-treated leaves showing 30% inhibition of CER. Greater inhibition led to subsequent stomatal closure. Inhibition caused by the individual pollutants (applied singly) was linear over the range of concentrations investigated. The dual-pollutant mixture produced a synergistic response that was most pronounced at the lower pollutant concentrations. The potentiated effect was correlated with marked stomatal closure.Experimental plants for this study were grown under low moisture stress conditions to enhance stomatal opening in the plant stock material and reduce (damp) the potential for further SO₂-induced stimulation of stomatal opening. The experiments were designed to obtain limiting data for the test conditions.     

海藻酸锆/聚N-异丙基丙烯酰胺半互穿网络凝胶球的除磷性能

利用离子交联和自由基聚合反应制备了一种海藻酸锆/聚(N-异丙基丙烯酰胺)半互穿网络凝胶球(ZA/PNIPAM),用于吸附水中的磷酸盐.考察了溶液初始pH、吸附剂投加量、初始磷酸盐浓度和共存阴离子等因素对凝胶球吸附性能的影响.结果表明:ZA/PNIPAM在pH=2时可获得较大的吸附能力;随着投加量的减少、初始磷酸盐浓度的升高,凝胶球的吸附性能逐渐增大;SO_4~(2-)对吸附性能影响较Cl~-和NO_3~-明显.准二级动力学模型和颗粒内部扩散模型可以较好地拟合动力学吸附数据,表明表面吸附和颗粒内部扩散是吸附速率的主要控制步骤.吸附等温线数据可以较好地被Freundlich模型描述,表明吸附过程为非均匀多分子层吸附.FTIR、XPS、零电荷点(pH_(pzc))的结果以及相关吸附数据揭示凝胶球吸附磷酸盐的机制为静电吸附(物理吸附)以及配位交换(化学吸附)的共同作用.经过4次循环再生后,ZA/PNIPAM吸附性能保持稳定,具有良好的重复使用性.     

The impact of Swedish SO2 policy instruments on SO2 emissions 1990–2012

Sulphur dioxide (SO₂) emissions cause acidification and human health problems which are, despite present policy instruments, projected to remain even after 2030 in Europe. Additional instruments are needed to solve the problems, and impact analysis of already used policy instruments would contribute to the development of new effective instruments. We present a study on how much of the decoupling of SO₂ emissions from economic growth 1990–2012 that was due to SO₂ policy instruments in general and to what extent it is possible to estimate the impact of individual instruments. Focus is on Sweden, a country with problems reaching its SO₂-related environmental policy targets and with detailed data available.We applied decomposition analysis combined with an analysis of the chronological development of emission factors and mandated emission limits. Our use of official emission inventory data and publicly available data on the development of SO₂ policy instruments increase the usefulness of our results to policy makers.The results indicate that at least 26–27% (corresponding to ∼35–36 ktonne annually) of the decoupling 1990–2012 was due to SO₂ policy instruments. 4–5% (∼6–7 ktonne) of the decoupling was caused by one environmental permit decision and stricter sulphur emission limit for marine oils. Most of the total impact of SO₂ policy instruments could not be causally connected to an individual instrument, because many events and developments overlap in time.The implications of the results are that: a) SO₂ policy instruments should still be important to reduce SO₂ emissions in many countries; b) a lower boundary total emission impact of SO₂ policy instruments can be estimated, but with current knowledge and data the impacts of individual instruments are rarely possible to estimate. Research on how to increase the precision in total impact estimates of SO₂ policy instruments is needed to improve future impact analyses. More detailed emission inventory data would improve impact analysis of individual instruments.     

A lagrangian one-layer model of long-range transport of SO2

The daily mean concentrations of SO₂ have been estimated using a simple trajectory model of long-range transport. Seasonal variations in the transformation rate of SO₂ to sulphate are assumed. The mixing height varied from day to day depending on the stability conditions. The dry deposition velocity above the ground varies according to the season, cloud cover and time of day, while a constant value is applied above the sea. Under present model assumptions the variation of pollutant concentration with time at the receptor point arises only due to variable meteorological conditions. During the test period measured concentrations were often higher than estimated. However, the order of magnitude of pollutant concentration was well predicted. In future work, input meteorological data should have a finer resolution. Further, better parameterizations of sulphur dioxide concentrations at the start points of trajectories and wet deposition should be employed.     

Formation of sulfur oxide groups by SO2 and their roles in mercury adsorption on carbon-based materials

The presence of SO₂ display significant effect on the mercury (Hg) adsorption ability of carbon-based sorbent. Yet the adsorption and oxidation of SO₂ on carbon with oxygen group, as well as the roles of different sulfur oxide groups in Hg adsorption have heretofore been unclear. The formation of sulfur oxide groups by SO₂ and their effects on Hg adsorption on carbon was detailed examined by the density functional theory. The results show that SO₂ can be oxidized into SO₃ by oxygen group on carbon surface. Both C-SO₂ and C-SO₃ can improve Hg adsorption on carbon site, while the promotive effect of C-SO₂ is stronger than C-SO₃. Electron density difference analyses reveal that sulfur oxide groups enhance the charge transfer ability of surface unsaturated carbon atom, thereby improving Hg adsorption. The experimental results confirm that surface active groups formed by SO₂ adsorption is more active for Hg adsorption than the groups generated by SO₃.     

APEC前后北京SO2垂直分布特征及其对二次硫酸盐生成的影响

SO_2是北京大气中重要的污染气体.为探讨亚太经合组织(APEC)峰会前后北京大气SO_2的垂直分布及其对二次硫酸盐(SO_4~(2-))生成的影响,我们于2014年10月21日至11月30日在地面和北京325 m气象塔260 m高度处同步开展了气体SO_2和亚微米颗粒物中硫酸盐(SO_4~(2-))实时连续在线观测.结果显示,采暖前,北京地面SO_2浓度较低,但高层由于显著受到区域输送的影响浓度较高,两层污染物变化趋势也存在明显差异.采暖后,即APEC后,受本地供暖排放影响,SO_2和SO_4~(2-)浓度显著增加,两层的总体差异也相应减小,变化趋势也更为一致.湿度对SO_2的液相转化起关键作用.我们发现近地面SO_2的转化率(SOR)显著高于260 m,这主要与地面较高的湿度相关.事实上,SOR随着湿度增加而迅速增大,进一步凸显了湿度对SO_2液相氧化的影响.另外,我们也发现SO_2特别是260 m在低湿范围(RH40%)内随湿度增加而逐渐升高,但在高湿范围(RH50%)内则呈下降趋势,说明不同湿度范围内的来源或者生成机制可能有所不同.SO_4~(2-)和PM_(2.5)浓度均随着湿度的增加而增加,但不同湿度范围,增加速率不同.通过相关性和和后向轨迹分析表明,区域输送(特别是途经北京西部和南部的气团)和本地燃煤排放分别是采暖前后污染物的主要来源.     

关中盆地NO2和SO2对颗粒物污染的协同效应

基于WRF-Chem模式模拟了关中盆地2019年1月2—14日一次颗粒物污染事件,评估了NO_x和SO₂减排及其在颗粒物污染中的协同作用对PM_2.5污染的影响。敏感性实验结果表明：NO_x减排可使PM_2.5中硝酸盐含量下降,但大气中O₃浓度上升,大气氧化能力增强,其他二次组分上升,导致PM_2.5下降不明显;SO₂人为源减排可使硫酸盐质量浓度下降,但由于硫酸盐在PM_2.5中占比较低,当SO₂减排75%时,PM_2.5仅下降1.74%;当减排比例较高时,NO_x和SO₂同时减排更有利于颗粒物污染防治。PM_2.5质量浓度在NO_x和SO₂同时减排75%时比分开减排75%时多下降0.75%,主要是硫酸盐下降所致;对气溶胶含水量进行分析,发现NO_x对气溶胶含水量影响较大,当NO_x减排75%时,气溶胶含水量可下降15.51%;此外,NO_x和SO₂同时减排比分开减排时气溶胶含水量更低,更不利于二次颗粒物生成。