Heterogeneous sulfur conversion in sea-salt aerosol particles: the role of aerosol water content and size distribution

Meteorological and chemical conditions during the July 1988 Bermuda-area sampling appear to have been favorable for conversion of sulfur gases to particulate excess sulfate (XSO₄). Observed average XSO₄ and SO₄ concentrations of 11 and 2.1 nmol m⁻³, respectively, at 15 m a.s.l. in the marine boundary layer (MBL) upwind of Bermuda, indicate that conversion of SO₂ to XSO₄, over and above homogeneous conversion, may be necessary to explain the > 5.0 average molar ratio of XSO₄ to SO₂. Given an observed cloud cover of <15% over the region and the <3 nmol m⁻³ SO₃ concentrations observed by aircraft, heterogeneous conversion mechanisms, in addition to cloud conversion of SO₂, are necessary to explain the observed 11 nmol XSO₄ m⁻³.Aerosol water content, estimated as a function of particle size distribution plus consideration of SO₂ mass transfer for the observed particle size distribution, shows that SO₂ was rapidly transferred to the sea-salt aerosol particles. Assuming that aqueous-phase SO₂ reaction kinetics within the high pH sea-salt aerosol water are controlled by O₃ oxidation, and considering mass-transfer limitations, SO₂ conversion to XSO₄ in the sea-salt aerosol water occurred at rates of approximately 5% h⁻¹ under the low SO₂ concentration, Bermuda-area sampling conditions. All of the 2 nmol XSO₄ m⁻³ associated with sea-salt aerosol particles during low-wind-speed, Bermuda-area sampling can be explained by this conversion mechanism. Higher wind speed, greater aerosol water content and higher SO₂ concentration conditions over the North Atlantic are estimated to generate more than 4 nmol XSO₄ m⁻³ by heterogeneous conversion of SO₂ in sea-salt aerosol particles.     

Field studies of the SO2/aqueous S(IV) equilibrium in clouds

Concentrations of S(IV) were measured in cloudwater at Great Dun Fell and compared with theoretical HSO₃⁻ assuming equilibrium between aqueous and gaseous phases in cloud. Detectable concentrations of S(IV) in the range of 1 × 10⁻⁶ to 17.2 × 10⁻⁶ mol dm⁻³ were observed only in samples which contained low H₂O₂ concentrations, generally <1 × 10⁻⁶ mol dm⁻³. Concentrations of S(IV) were below the detection limit of 1 × 10⁻⁶ mol dm⁻³ in samples which contained hign H₂O₂ levels (1 × 10⁻⁶−80 × 10⁻⁶ mol dm⁻³) confirming that either SO₂ or H₂O₂ acts as the limiting reagent in the oxidation of SO₂ in cloudwater.Equilibrium HSO₃⁻ concentrations were estimated from the measured cloudwater pH, the gas phase SO₂ concentration and the ambient temperature and found to be on average about 5 times lower than the measured S(IV) concentrations. The possible role of formaldehyde in stabilizing S(IV) in cloudwater is discussed. The kinetic data available in the literature suggest that the complexation reaction between S(IV) and HCHO is too slow to account for the observed difference between measured and calculated S(IV) concentrations over the typical lifetime of clouds in our study.S(IV) accounted for up to 10% of the SO₄²⁻ measured in stored cloudwater samples.     

Metal ion catalyzed oxidation of SO2 in the presence of trace H2O2 in aqueous solution under environmental reaction conditions

Aqueous phase oxidation of SO₂ or S(IV) by H₂O₂-metal ions at a H₂O₂ concentration much lower than S(IV), was studied using a continuously flowing stirred reactor. Of the metal ions, Fe²⁺ showed the highest catalytic activity, i.e. the oxidation of S(IV) continued after most of the H₂O₂ was consumed. The dependence of the rate on the concentration of S(IV), H₂O₂, Fe²⁺ or H⁺ and temperature was determined. The following rate expression and low apparent activation energy of 40.7 kJ mole⁻¹ were evaluated,−d[S(IV)]/dt=620[S(IV)]²[Fe²⁺]^0.5(molel⁻¹S⁻¹). The significance of this reaction as the sulfate formation in atmospheric water droplets is discussed and a comparison of the rate with others using H₂O₂, O₃ and dissolved O₂ catalyzed by metal ions is made.     

Interactions of aerosols (ammonium sulfate,ammonium nitrate and ammonium chloride) and of gases (HCl,HNO3) with fogwater

The concentrations of aerosols (NH₄NO₃, (NH₄)₂SO₄ and NH₄Cl) and of gases (HCl_(g), HNO_3(g), NH_3(g) were determined by denuder methods under different conditions (in the absence of fog, before, during and after fog events). At this site situated in an urban region, high concentrations of the gaseous strong acids HCl_(g) and HNO_3(g) are observed. NH₄Cl and NH₄NO₃ aerosols represent a major fraction of the Cl⁻ and NO₃⁻ aerosols (<2.4 μm)collected by denuders. During a fog event, very high concentrations of SO₄²⁻ were found in small aerosols, which are attributed to the aqueous phase oxidation of SO₂ under the influence of high pH due to the presence of NH₃. Differences in SO₄²⁻ concentrations measured in aerosols (<2.4 μm) and in fog droplets were probably due to mass-transport limitations of the SO₂ oxidation. Ammonium sulfate aerosols represent in some cases a significant fraction of the total S present (SO_2(g) + SO₄²⁻. Soluble aerosols and gases contribute to the composition of fogwater and are released again after fog dissipation.     

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.     

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.     

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.     

Chemical composition of rain in Thessaloniki,Greece, in relation to meteorological conditions

Wet precipitation was collected in Thessaloniki, Greece, during the period March 1989–December 1990 by using an automatic wet-only precipitation sampler.Rainwater samples were analysed for major cations (H⁺, NH₄⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (Cl⁻, NO₃⁻, SO₄²⁻), in addition to acidity and conductivity measurements. The majority of rain had a neutral or alkaline character as a result of neutralization, primarily caused by calcareous soil dust and secondarily by atmospheric ammonia. In all rain, SO₄²⁻ concentration exceeded NO₃⁻ concentration. The contribution of maritime sources to the total SO₄²⁻ concentration was very low (<2%).The chemical composition of precipitation was analysed in conjunction with meteorological variables (season of the year, precipitation type, airflow patterns) to evaluate temporal variations and chemical source influence. Rain caused by weak, localized flows showed the highest acidity and the minimum influence of neutralization processes.     

Roles of SO2 oxidation in new particle formation events

The oxidation of SO₂ is commonly regarded as a major driver for new particle formation (NPF) in the atmosphere. In this study, we explored the connection between measured mixing ratio of SO₂ and observed long-term (duration > 3 hr) and short-term (duration <1.5 hr) NPF events at a semi-urban site in Toronto. Apparent NPF rates (J₃₀) showed a moderate correlation with the concentration of sulfuric acid ([H₂SO₄]) calculated from the measured mixing ratio of SO₂ in long-term NPF events and some short-term NPF events (Category I) (R² = 0.66). The exponent in the fitting line of J₃₀ ~ [H₂SO₄]ⁿ in these events was 1.6. It was also found that SO₂ mixing ratios varied a lot during long-term NPF events, leading to a significant variation of new particle counts. In the SO₂-unexplained short-term NPF events (Category II), analysis showed that new particles were formed aloft and then mixed down to the ground level. Further calculation results showed that sulfuric acid oxidized from SO₂ probably made a negligible contribution to the growth of >10 nm new particles.     

Roles of SO2 oxidation in new particle formation events

The oxidation of SO₂ is commonly regarded as a major driver for new particle formation (NPF) in the atmosphere. In this study, we explored the connection between measured mixing ratio of SO₂ and observed long-term (duration > 3 hr) and short-term (duration < 1.5 hr) NPF events at a semi-urban site in Toronto. Apparent NPF rates (J₃₀) showed a moderate correlation with the concentration of sulfuric acid ([H₂SO₄]) calculated from the measured mixing ratio of SO₂ in long-term NPF events and some short-term NPF events (Category I) (R² = 0.66). The exponent in the fitting line of J₃₀ ~ [H₂SO₄]ⁿ in these events was 1.6. It was also found that SO₂ mixing ratios varied a lot during long-term NPF events, leading to a significant variation of new particle counts. In the SO₂-unexplained short-term NPF events (Category II), analysis showed that new particles were formed aloft and then mixed down to the ground level. Further calculation results showed that sulfuric acid oxidized from SO₂ probably made a negligible contribution to the growth of > 10 nm new particles.     

Numerical modeling of long-range transport of acidic species in association with mesoβ-convective-clouds across the Japan sea resulting in acid snow over coastal Japan—II. Results and discussion

The acid snow/rain model [describedin Part I, Kitada et al., Atmospheric Environment27A, 1061–1076, 1993] was applied to investigate transport/transformation/deposition of acidic species in association with snow-precipitating cloud over the Japan Sea in winter. The model results showed: (1) The snow-precipitating clouds generated by relatively weak convective motions tend to trap aerosols of sulfate and nitrate and soluble gases such as SO₂ and HNO₃ below cloud levels, thus keeping their concentrations at higher levels than those for no-cloud situations. The mechanisms involved are: transfer of gas- and aerosol-phase species to cloud-phase through absorption and nucleation scavenging, then their transfer from cloud to snow through riming, and subsequent release from sublimating snow back to gas- and aerosol-phases below cloud base. (2) In-cloud oxidation enhanced the overall conversion of SO₂ to SO₄²⁻ by some 25% with respect to no-cloud situation after 12 h. Furthermore, contributions to the oxidation were 77.4%, 21.1% and 1.5% for S(IV)H₂O₂, S(IV)O₂ with catalysts of Fe³⁺ + Mn²⁺ and S(IV)O₃ reactions, respectively. (3) The sulfate wet deposited by precipitating snow for 12 h was due mostly to in-cloud scavenging and in-cloud oxidation, i.e. 66% by nucleation scavenging and the remaining by in-cloud oxidation of S(IV), while the contribution of below-cloud scavenging was negligible. (4) The adsorption process of HNO₃ onto the surface of falling snow was found to account for major below-cloud scavenging of snow, and thus in contrast to SO₄²⁻, the below-cloud scavenging contributed very significantly to the nitrate wet deposition. Throughout the stimulation, below-cloud scavenging was responsible for 75% of the snow-NO₃⁻ formation. Therefore, taking account of this process in acid snow models is important.     

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.     

Multiphase chemistry in a microphysical radiation fog model—A numerical study

A microphysical radiation fog model is coupled with a detailed chemistry module to simulate chemical reactions in the gas phase and in fog water during a radiation fog event. In the chemical part of the model the microphysical particle spectrum is subdivided into three size classes corresponding to non-activated aerosol particles, small and large fog droplets. Chemical reactions in the liquid phase are separately calculated in the small and in the large droplet size class. The impact of the chemical constitution of activated aerosols on fogwater chemistry is considered in the model simulations. The mass transfer of chemical species between the gas phase and the two liquid phases is treated in detail by solving the corresponding coupled differential equation system. The model also accounts for concentration changes of gas-phase and aqueous-phase chemical species which are induced by turbulence, gravitational settling and by evaporation/condensation processes.Numerical results demonstrate that fogwater chemistry is strongly controlled by dynamic processes, i.e. the vertical growth of the fog, turbulent mixing processes and the gravitational settling of the particles. The concentrations of aqueous-phase chemical species are different in the two droplet size classes. Reactands with lower water solubility are mainly found in the large droplet size class because the characteristic time for their mass transfer from the gas phase into the liquid phase is essentially longer than the characteristic time for the formation of large fog droplets. Species with high water solubility are rapidly transferred into the small fog droplets and are then washed out by wet deposition before these particles grow further to form large droplets. Thus, the concentrations of the major ions (NO₃⁻, NH₄⁺) are much higher in small than in large droplets, yielding distinctly lower pH values of the small particles. In the present study the reaction of sulfur with H₂O₂ and the Fe(III)-catalysed autoxidation of S(IV) are the major S(VI) producing mechanisms in fog water. Most of the time the sulfur oxidation rates are higher in the large than in the small droplets. Fogwater deposition by gravitational settling occurs mainly in the large droplet size class. However, since in the small droplets the concentrations of chemical species with very good water solubility are relatively high, in both droplet size classes the total wet deposition of these reactands is of the same order of magnitude.     

Sulfur(IV) oxidation by hydrogen peroxide in aqueous suspensions of SiO2, Al2O3, TiO2 and zeolite

Normal and stopped-flow spectrophotometry were used to study the rate of oxidation of sulfur(IV) (SO₃²⁻/HSO₃⁻) by H₂O₂ in aqueous suspensions of finely divided SiO₂, Al₂O₃, TiO₂ and Na-A-zeolite buffered at pH 8.2 and 4.0. Within the limits of error, the rate constants obtained agree with those measured in the absence of suspended material, i.e. under the given conditions there is no surface catalytic effect to be observed.     

无机阴离子对CuO-H2O2氧化苯酚废水的影响

以苯酚为模型底物,研究了中性低温常压条件下无机阴离子对CuO-H₂O₂氧化苯酚废水的影响及机制.结果表明,CuO-H₂O₂能高效彻底氧化苯酚,10 min氧化率达94.7%,氧化遵循羟基自由基机制.无机阴离子对氧化效果有不同影响,浓度越高影响越显著.HCO^-₃加速H₂O₂的无效分解,当浓度从0增加到20 mmol·L^-1 时,H₂O₂分解速率常数由0.373 8 min^-1提高到0.534 7 min^-1,TOC去除速率常数由0.267 min^-1下降到0.019 4 min^-1.HPO^2-₄通过抑制H₂O₂分解实现对苯酚的氧化抑制,H₂O₂分解速率常数及TOC去除速率常数分别由0.373 8 min^-1、0.267 min^-1降低到0.033 8 min^-1、 0.033 8 min^-1.Cl^-能够促进H₂O₂有效分解,对苯酚氧化有利,H₂O₂分解速率常数及TOC去除速率常数分别由0.373 8 min^-1、0.267 min^-1提高到0.604 0 min^-1、0.387 9 min^-1.NO^-₃、SO^2-₄对H₂O₂的分解及苯酚的氧化影响不大.     

冶炼厂SO2烟气化学催化吸收扩大试验研究

在单层塔板泡沫吸收塔中的ＳＯ２液相催化氧化进行了扩在试验研究,当ＳＯ２净化效率（单板效率）为５０％时,得到１６％（Ｗｔ）Ｈ２ＳＯ４,硫酸生成速率为１８％／ｈ,ＳＯ２吸收最佳敢化５Ｌ／Ｎｍ＾３,添加表面活性剂Ａｌ２（ＳＯ４）３及鼓氧操作对ＳＯ２液相催化氧化有明显促进作用,冶炼烟气ＳＯ２浓度波动吸收效率影响不大。     

模拟酸雨对混凝土影响的研究

采用周期浸泡和喷淋试验等２种加速腐蚀试验方法,分别研究ＰＨ为１．０、３．５、５．６和ＰＨ为１．０、ＳＯ＾２－４为０、０．０６、０．１ｍｏｌ／Ｌ等６种模拟酸雨对混凝土的影响。     

H2O2和NO互作调控SO2诱导的胡杨细胞死亡

二氧化硫(SO_2)是一种常见的大气污染物,目前关于SO_2对木本植物的毒害作用及相关机制并不清楚.本文以木本植物胡杨的愈伤细胞为材料,研究SO_2衍生物对胡杨细胞的致死效应,以及过氧化氢(H_2O_2)与一氧化氮(NO)在SO_2诱导胡杨细胞死亡中的信号调节作用.研究发现:SO_2衍生物处理(1~5 mmol·L-1)可诱发胡杨细胞死亡,且SO_2衍生物浓度越大、处理时间越长,细胞死亡率越高.2 mmol·L-1SO_2衍生物处理胡杨细胞后,胞内H_2O_2和NO水平显著升高,且H_2O_2水平的升高先于NO.一定浓度的外源H_2O_2或NO供体SNP能够提高SO_2胁迫下胡杨细胞的死亡率;而使用H_2O_2清除剂CAT和ASA、NO清除剂c PTIO、NO合成抑制剂钨酸钠后,SO_2诱导的细胞死亡率明显降低.进一步实验发现,外源H_2O_2可以提高SO_2胁迫下胡杨细胞的硝酸还原酶(NR)活性,促进胞内NO产生;而利用CAT和ASA清除H_2O_2后,细胞NR活性和NO产生均受到明显抑制.此外,SO_2胁迫下,外源SNP能够抑制抗氧化酶(CAT和APX)活性,增加胡杨细胞内的H_2O_2水平,而一定浓度的c PTIO和钨酸钠均可提高CAT和APX活性,降低胞内H_2O_2水平.结果表明:SO_2胁迫下,胡杨细胞快速产生的H_2O_2能够激活硝酸还原酶活性,促进NO生成,同时NO能够通过抑制抗氧化酶活性而提高H_2O_2水平.H_2O_2与NO互作调控SO_2诱导的胡杨细胞死亡.     

Wintertime measurements of aerosol acidity and trace elements in Wuhan,a city in central China

A 2-week intensive ambient aerosol study was conducted in December 1988 in Wuhan (Hubei Province), a city of nearly 2 million located on the Yangtze River in central China (P.R.C.). This is an industrial region where soft coal burning is widespread, and emission controls for vehicles and industrial facilities are minimal. The sampling site was located in one of the civic centers where residential and commercial density is highest. An Andersen dichotomous sampler was operated with Teflon membrane filters to collect fine (d_p < 2.5 μmad) and coarse (2.5 ⩽ d_p < 10 μmad) particles for total mass and element determinations. An annular denuder system (ADS) was used to collect fine fraction aerosols for analyses of ionic species including strong acidity (H⁺).The study was conducted between 18 and 30 December, which was rainless, consistently cool (3–10°C) and overcast, but without fog or acute stagnation. Fine particulate mass (PM, as μ m⁻³) averaged 139 (range 54–207); coarse PM averaged 86 (range 29–179). Trace element concentrations were also high. Crustal elements (Si, Al, Ca and Fe) were found primarily in the coarse fraction, while elements associated with combustion (S, K, Cl, Zn and Se) were enriched in the fine fraction. The concentrations of arsenic and selenium were evidence of a large source of coal burning, while vanadium levels (associated with fuel oil use) were not especially enriched.Despite the seemingly high PM loadings, ionic concentrations were not especially high. The average composition of soluble fine aerosol species (in neq m⁻³) were SO₄²⁻: 520 (range 180–980), NO₃⁻: 225 (range 50–470), Cl⁻: 215 (range 20–640), and NH₄⁺: 760 (range 280–1660). A deficit in accountable FP components (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³. (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³Aerosol acidity was negligible during most monitoring periods, H⁺: 14 (range 0–50 neq m⁻³, equivalent to 0–2.5 μm m⁻³ as H₂SO₄). Sulfur dioxide, measured by the West-Gaeke method for part of the study, concentrations were low. Although not directly measured, the aerosol measurments suggested that gaseous HCl (from refuse incineration) and NH₃ (animal wastes) concentrations might have been high. Higher aerosol acidity might be expected if HCl sources were more prominent and not neutralized by local ammonia or other base components.     

Effect of chromium oxide as active site over TiO2-PILC for selective catalytic oxidation of NO

This study introduced TiO2-pillared clays （TiO2-PILC） as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350℃, the NO conversion was 61% under conditions of GHSV = 23600 hr^-l. The BET data showed that the support particles had a mesoporous structure. Hz-TPR showed that Cr（10）TiP （10 wt.% Cr doping on TiO2-PILC） clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO ＋ O2 adsorption, the intensity of evolution of superoxide ions （O2^-） increased. The content of Cr^3＋ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr^3＋ increased to 50.28%. Additionally, Oα/Oβ increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO4^2-.