Real-time measurements of PM2.5,PM10-2.5,and BC in an urban street canyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM_2.5.PM_10-2.5.and Black Carbon（BC）over a 12-month period in an urban street canyon of Hong Kong.Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded.The average weekly cycles of PM_2.5,PM_10-2.5.and BC suggested that all species are related to traffic,with high concentrations on workdays and low concentrations over the weekends.PM_2.5 exhibited two comparable concentrations at 10:00-11:00（63.4 μg/m³） and 17:00-18:00（65.0 μg/m³） local time（LT） during workdays,corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels:3179 and 2907 h^-1,respectively.BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration（31.2 μg/m³） during the midday period（10:00-11:00 LT） on workdays.A poor correlation was found between PM_2.5 concentration and wind speed（R = 0.51,P-value> 0.001）.In contrast,the concentration of PM_10-2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased（R = 0.98,P-value< 0.0001）.     

Variation of PM2.5 concentration in Hangzhou,China

This observational study investigates the variation of PM_2.5 concentration and its ratio against PM₁₀ concentration under different weather systems and pollution types.The study was conducted in Hangzhou on east China’s Yangtze River Delta using data collected at seven ambient air quality monitoring stations around the metropolitan area between 2006 and 2008 and using weather information in the same period, Nine predominant weather systems affecting the city were classified through careful analysis of the 11- year surface and upper air weather charts from 1996 to 2006,Each observational day was then assigned to one of the nine weather systems.It was found that the PM_2.5 concentration varied greatly for different weather systems,with the highest PM_2.5 concentration associated with the post-cold-frontal system at 0.091 mg/m³ and the lowest PM_2.5 concentration with the easterlies system at 0.038 mg/m³,although the PM_2.5/PM₁₀ ratio remained consistently above 0.5 for all systems.The post-cold-frontal system typically occurs in autumn and winter while the easterlies system is more a summer phenomenon.Among all types of pollution,the highest PM_2.5 concentration of 0.117 mg/m³ coincided with the large-scale continuous pollution events,suggesting that this type of pollution was more conducive to the formation of secondary particulate matters.The ratio of PM_2.5/PM₁₀ was above 0.5 in non-pollution days and all pollution types but one under the influence of dust storms when the ratio decreased to 0.3 or less.The outcomes of this study could be used to develop a rudimental predictive model of PM_2.5 concentration based on weather system and pollution type.     

Measurement of the concentration diffusion coefficient for Ne-Ar, Ne-Xe, Ne-H2, Xe-H2, H2-N2 and H2-O2 gas systems

The concentration diffusion coefficient, D ₁₂, is measured for the equimolar mixtures of Ne-Ar, Ne-Xe, Ne-H₂, Xe-H₂, H₂-N₂ and H₂-O₂ binary gas systems in a two-bulb metal apparatus in the temperature range 0 C to 100 C. These values are compared with the existing data on these systems and with the predictions of the kinetic theory in conjunction with the modified Buckingham exp-six potential. Unlike the thermal diffusion coefficient, with the simple theory it is possible to predict D ₁₂ within a few percent even for systems involving polyatomic gases. The smoothed experimental D ₁₂ values are also used to obtain data for the coefficients of viscosity and thermal conductivity at round temperatures and compositions for these systems.Nomenclature C ₂ ^t relative amount of a gas in the mixture in the bulb 2 at an instant t - C ₂ relative amount of the same gas in the mixture in the bulb 2 at equilibrium - D ₁₂ diffusion coefficient - X ₁ mole-fraction of the heavier component in the mixture - _mix viscosity coefficient - _mix thermal conductivity coefficient     

Kinetics of ultrafine coating of SiO2 nanoparticles, suspended in non-thermal CH4/C2H6 plasma

Capacitively coupled RF discharges in methane and ethane (1000–3000 Pa, 5–15 W/cm³) were used for the in-flight coating of SiO₂ nanopowders (NP) with an a-C:H layer [A. Kouprine, F. Gitzhofer, M. Boulos, A. Fridman, Polymer-like C:H thin film coating of nanopowders in capacitively coupled RF discharge, Plasma Chemistry and Plasma Processing 24 (2) (2004) 189–215]. In this present work a model of the chemical kinetics of this plasma processing has been developed, based on the GRI-Mech 3.0 mechanism [G.P. Smith, D.M. Golden, M. Frenklach, Gas Research Institute, Detailed chemical reaction mechanism. Available from: ], and calculations are performed, using the Chemkin-II code. The model includes the formation of two solid phases: an amorphous C:H coating, deposited on the suspended NP, and soot, incepted in the gas phase. Non-equilibrium plasma effects are taken into account by the rates of radical species’ production, using the reference data on the “G-value”. The CH₃ and H species appear to have key roles in surface activation and the nanofilm growth. The results demonstrate the competitive character of the formation of the two solid phases: the C:H coating is dominant under T_gas < 1400–1600 K, depending on the conditions, and soot commencing to dominate at higher temperatures. This division corresponds to the passage from non-thermal plasma conditions, with the dominance of single-valent radicals and solid phase growth on the substrate only, to the plasma thermalisation with the formation of two-valent radicals and v. inception of the solid phase. The results are validated experimentally by the observation of soot formation as a function of the gas temperature, by the mass spectrograph data on the gas composition after plasma reforming, and by the reference data on coating growth rates and induction times for soot formation.     

等离子喷涂Al2O3/TiO2纳米复合涂层的制备、结构及摩擦学性能

采用喷雾干燥法对溶胶-凝胶法合成的系列A l2O3/TiO2纳米复合粉体进行造粒,使用等离子喷涂技术制备系列A l2O3/TiO2纳米复合涂层.对涂层结构和形貌分析表明所制备的A l2O3/TiO2纳米复合涂层形成了具有熔融区和半熔融区的双区形态的纳米复合结构.使用UMT-2MT试验机研究了复合涂层的摩擦磨损性能,结果表明复合涂层的磨损率随TiO2含量的增加表现出先降低而后增大的趋势,TiO2质量百分数为10%的纳米复合涂层的磨损率最低;而涂层的摩擦系数随TiO2含量的增加变化不大.复合涂层的磨损机制为裂纹扩展导致的磨损剥落.     

Preparation of SiO2/TiO2 Janus particles by electrostatic assembly,hydrolysis and calcination

This paper describes a novel chemical method for preparing SiO₂/TiO₂ Janus particles.First,polystyrene（PSt）/SiO₂ particles with a raspberry-like structure are prepared by electrostatic assembly.The influences of the reaction time of sulfonation and the treatment times of polyelectrolyte solutions（PDADMAC,PSS）on PSt and SiO₂ are investigated with respect to the surface charge density of the particles.SiO₂/TiO₂ Janus particles are then obtained by hydrolysis of butyl titanate on the surface of PSt/SiO₂ particles followed by a calcination process.Particle size analyzer,Zeta potential instrument,FTIR,TEM and SEM are used to characterize the particle size,the amount of charge on the surface of PSt and SiO₂ particles and the compositions and morphologies of PSt/SiO₂,SiO₂/TiO₂ and PSt/SiO₂/TiO₂.The diameters of the PSt,SiO₂,PSt/SiO₂ and SiO₂/TiO₂ particles are 2.0 μm,303 nm,2.7 μm and 330nm,respectively.     

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu,China

Daily fine particulate(PM_2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms（DSs） and several types of pollution events, including haze（HDs）,biomass burning（BBs）,and fireworks displays（FDs）.The highest PM_2.5 mass concentrations were found during DSs（283.3μg/m³）,followed by FDs（212.7μg/m³）,HDs（187.3μg/m³）,and BBs（130.1μg/m³）.The concentrations of most elements were elevated during DSs and pollution events, except for BBs.Secondary inorganic ions(NO₃^-,SO₄^2-,and NH₄⁺) were enriched during HDs,while PM_2.5 from BBs showed high K⁺ but low SO₄^2-.FDs caused increases in K⁺ and enrichment in SO₄^2-.Ca²⁺ was abundant in DS samples.Ion-balance calculations indicated that PM_2.5 from HDs and FDs was more acidic than on normal days,but DS and BB particles were alkaline.The highest organic carbon（OC） concentration was 26.1μg/m³ during FDs,followed by BBs（23.6μg/m³）,HDs（19.6μg/m³）,and DSs（18.8μg/m³）. In contrast,elemental carbon（EC） concentration was more abundant during HDs（10.6μg/m³） and FDs （9.5μg/m³） than during BBs（6.2μg/m³） and DSs（6.0μg/m³）.The highest OC/EC ratios were obtained during BBs,with the lowest during HDs.SO₄^2-/K⁺ and TCA/SO₄^2- ratios proved to be effective indicators for differentiating pollution events.Mass balance showed that organic matter,SO₄^2-,and NO₃^- were the dominant chemical components during pollution events,while soil dust was dominant during DSs.     

PM2.5 in an industrial district of Zhengzhou,China:Chemical composition and source apportionment

Zhengzhou is a developing city in China,that is heavily polluted by high levels of particulate matter.In this study.fine particulate matter(PM_2.5) was collected and analyzed for their chemical composition（soluble ions,elements,elemental carbon（EC） and organic carbon（OC）） in an industrial district of Zhengzhou in 2010.The average concentrations of PM_2.5 were 181,122,186 and 211μg/m³ for spring,summer, autumn and winter,respectively,with an annual average of 175μg/m³,far exceeding the PM_2.5 regulation of USA National Air Quality Standards（15μg/m³）.The dominant components of PM_2.5 in Zhengzhou were secondary ions（sulphate and nitrate） and carbon fractions.Soluble ions,total carbon and elements contributed 41%,13%and 3%of PM_2.5 mass,respectively.Soil dust,secondary aerosol and coal combustion, each contributing about 26%,24%and 23%of total PM_2.5 mass,were the major sources of PM_2.5,according to the result of positive matrix factorization analysis.A mixed source of biomass burning,oil combustion and incineration contributed 13%of PM_2.5.Fine particulate matter arising from vehicles and industry contributed about 10%and 4%of PM_2.5,respectively.     

Characterization of summer PM2.5 aerosols from four forest areas in Sichuan,SW China

Aerosol samples were collected over 24 and 12 h to represent day/night aerosol characteristics in forest areas at Ya’an Baima Spring Scenic Area（BM）,Panzhihua Cycas National Nature Reserve（PZ）,Gongga Mountain National Nature Reserve（GG）,and Wolong National Nature Reserve（WL）,during the summers of 2010-2012.Mass and chemical component concentrations,including organic carbon,elemental carbon,and inorganic ions(F^-,Cl^-,NO₂^-,NO₃^-,SO₄^2-,C₂O₄^2-,PO₄^3-,K⁺,Na⁺,Ca²⁺,Mg²⁺,and NH₄⁺),of PM_2.5 aerosols were measured.The average PM2.5 concentrations for 24 h were 72.42,104.89,20.55,and29.19 μg/m³ at BM,PZ,GG,and WL,respectively.Organic matter accounted for 38.0-49.3%,while elemental carbon accounted for 2.0-5.7%of PM2.5 mass.The sum concentrations of SO₄^2-,NH₄⁺,and NO₃^-accounted for 23.0%,17.4%,22.1%,and 30.5%of PM2.5 mass at BM,PZ,GG,and WL,respectively.Soil dust was also an important source of PM2.5,accounting for 6.3%,17.0%,10.4%,and 19.1%of PM2.5 mass at BM,PZ,GG,and WL,respectively.These reconstructed masses accounted for 75.9-102.0%of PM2.5 mass from the four forest areas of SW China.     

纳米SiO2/CeO2复合磨粒的制备及其抛光特性研究

以尿素[CO(NH2)2]、(NH4)2Ce(NO3)6和SiO2为原料,采用均相沉淀法制备1种新型纳米SiO2/CeO2复合磨粒,通过X射线衍射仪、X射线光电子能谱仪、飞行时间二次离子质谱仪和扫描电子显微镜等分析手段对其结构进行表征,并将SiO2/CeO2复合磨粒配置成抛光液在数字光盘玻璃基片上进行化学机械抛光试验.结果表明所制备的SiO2/CeO2复合磨粒的平均晶粒度为19.64 nm,粒度分布均匀;经过1 h抛光后,玻璃基片的平均表面粗糙度(Ra)由1.644 nm降至0.971 nm;抛光后玻璃基片表面变得光滑、平坦,表面微观起伏较小.     

Structure cellulaire de la détonation des mélanges H2–NO2/N2O4Cellular structure of the detonation of gaseous mixtures H2–NO2/N2O4

Calculations of the detonation reaction zone of gaseous reactive mixtures of NO₂/N₂O₄ as oxidizer and H₂, CH₄ or C₂H₆ as fuel, in the range of equivalence ratio Φ between 0.5 and 2, show that, for Φ?1, the chemical energy is released in two distinct and successive exothermic steps with different chemical induction times. The first exothermic stage is mainly due to the reaction NO₂+H→NO+OH, NO being the main oxidizer of the second one.The experimental study conducted on the same range of equivalence ratio (0.5?Φ?2) shows that, for Φ?1, the detonation wave of these mixtures contains a double set of cellular structures. A similar result had already been obtained with the detonation of gaseous Nitromethane, the NO₂ group being here included in the molecule. Consequently, the oxidizer NO₂ being either initially separated from the fuel or included inside the molecule of a monopropellant (Nitromethane) is responsible, because of its specific chemical kinetics, of a chemical energy release in two main steps and of the existence of a double cellular structure in the detonation wave for the same range of equivalence ratio. These results reinforce the assumption that the cellular structure of the detonation finds its origin in the strong rates of chemical energy release inside the reaction zone. To cite this article: F. Joubert et al., C. R. Mecanique 331 (2003).     

Evaporation heat transfer coefficient in single circular small tubes for flow natural refrigerants of C3H8, NH3, and CO2

An experimental study of evaporation heat transfer coefficients for single circular small tubes was conducted for the flow of C₃H₈, NH₃, and CO₂ under various flow conditions. The test matrix encompasses the entire quality range from 0.0 to 1.0, mass fluxes from 50 to 600 kg m⁻² s⁻¹, heat fluxes from 5 to 70 kW m⁻², and saturation temperatures from 0 to 10 °C. The test section was made of circular stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 2000 mm in a horizontal orientation. The test section was uniformly heated by applying electric power directly to the tubes. The effects of mass flux, heat flux, saturation temperature, and inner tube diameter on the heat transfer coefficient are reported. Among the working refrigerants considered in this study, CO₂ has the highest heat transfer coefficient. Laminar flow was observed in the evaporative small tubes, and was considered in the modification of boiling heat transfer coefficients and pressure drop correlations.     

Molecular distribution and seasonal variation of hydrocarbons in PM2.5 from Beijing during 2006

Normal （n）-alkanes and polycyclic aromatic hydrocarbons （PAHs） in PM_2.5 were collected from Beijing in 2006 and analyzed using a thermal desorption-GC/MS technique. Annual average concentrations of n-alkanes and PAHs were 282±96 and 125± 150ng/m³, respectively: both were highest in winter and lowest in summer. C₁₉-C₂₅ compounds dominated the n-alkanes while benzo[b]fluoranthene, benzo[e]pyrene, and phenanthrene were the most abundant PAHs. The n-alkanes exhibited moderate correlations with organic carbon （OC） and elemental carbon （EC） throughout the year, but the relationships between the PAHs, OC and EC differed between the heating and non-heating seasons. The health risks associated with PAHs in winter were more than 40 times those in spring and summer even though the PM_2.5 loadings were comparable. Carbon preference index values （<1.5） indicated that the n-alkanes were mostly from fossil fuel combustion. The ratios of indeno[123-cd]pyrene to benzo[ghi]pyrelene in summer and spring were 0.58 ± 0.12 and 0.63 ± 0.09, respectively, suggesting that the PAHs mainly originated from motor vehicles, but higher ratios in winter reflected an increased influence from coal, which is extensively burned for domestic heating. A comprehensive comparison showed that PAH pollution in Beijing has decreased in the past 10 years.     

KH2PO4/SiO2复合粉体抑制铝粉爆燃效果及机理分析

为研究KH₂PO₄/SiO₂复合粉体抑爆剂对铝粉爆燃的抑制作用,采用球磨机将KH₂PO₄和SiO₂混合研磨制备出新型的KH₂PO₄/SiO₂复合粉体抑爆剂。在哈特曼管实验装置上,开展爆燃火焰传播抑制实验,结果表明:随着KH₂PO₄/SiO₂复合粉体抑爆剂含量的增加,爆燃火焰传播长度和速度逐渐减小,当添加质量比10∶6的KH₂PO₄/SiO₂复合粉体抑爆剂时,可实现铝粉爆燃火焰传播的抑制。在20 L球形爆炸装置上,开展复合粉体抑爆剂抑制铝粉爆炸压力测试实验,结果表明:随着KH₂PO₄/SiO₂复合粉体抑爆剂含量的增加,铝粉爆炸最大爆炸压力p_max和最大爆炸压力上升速率(dp/dt)_max逐渐减小,当添加质量比10∶9的KH₂PO₄/SiO₂复合粉体抑爆剂时,可实现铝粉爆燃的完全抑制。通过KH₂PO₄粉体、SiO₂粉体与复合粉体抑爆剂对比可知,复合粉体抑爆剂对铝粉火焰传播和爆炸压力的抑制效果都优于单体粉体抑爆剂。通过对铝粉在空气中燃烧的热分析研究,从化学和物理两个方面分析了KH₂PO₄/SiO₂复合粉体抑爆剂对铝粉爆燃的抑制机理。     

Elemental compositions of PM2.5 and TSP in Lijiang,southeastern edge of Tibetan Plateau during pre-monsoon period

PM_2.5 and total suspended particulate（TSP） samples were collected at Lijiang,southeastern Tibetan Plateau.China.Sixteen elements（Al,Si,S,K,Ca,Cr,Mn,Ti,Fe,Ni,Zn,As,Br,Sb,Pb and Cu） were analyzed to investigate their elemental compositions during the pre-monsoon period.The results showed that Ca was the most abundant element in both PM_2.5 and TSP samples.The enrichment factors（EFs） of Si,Ti,Ca, Fe,K and Mn were all below 10 for both PM_2.5 and TSP,and these elements also had lower PM_2.5/TSP ratios （0.32-0.34）,suggesting that they were mainly derived from crustal sources.Elements Cu,Zn,S,Br and Sb showed strong enrichment in PM_2.5 and TSP samples,with their PM_2.5/TSP ratios ranging from 0.66 to 0.97,indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al,Si,Ca,Ti,Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season,and that S,K,Ni,Br and Pb reached high concentrations during westerly transport from south Asia.Combined with the principle component analysis and correlation analysis,elements of PM_2.5 samples were mainly from crustal sources,biomass burning emissions and regional traffic-related sources.     

Measurement of propagation speeds in adiabatic cellular premixed flames of CH4 + O2 + CO2

Experimental measurements of the propagation speed of adiabatic flames of methane + oxygen + carbon dioxide are presented. The oxygen content O₂/(O₂ + CO₂) in the artificial air was 31.55% and 35%. Non-stretched flames were stabilized on a perforated plate burner at atmospheric pressure. A heat flux method was used to determine propagation speeds under conditions when the net heat loss of the flame is zero. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Measurements in cellular flames are presented and compared with those for laminar flat flames. Cellularity disappeared when the flames became only slightly sub-adiabatic. Visual and photographic observations of the flames were performed to quantify their cellular structure. Increasing the oxygen content in the artificial air and increasing the temperature of the burner plate led to increase of the number of cells observed.     

Etude de la détonation de mélanges pauvres H2NO2/N2O4

Calculations of the detonation reaction zone of gaseous H₂NO₂/N₂O₄ mixtures in the range of equivalence ratio Φ between 0.25 and 0.7 show that for 0.25Φ0.4 the chemical energy is released in two distinct and successive exothermic steps characterised by different chemical characteristic times. As for rich mixtures, the first exothermic step is mainly due to the reaction NO₂ + H → NO + OH, but the second one is different since it results from the exothermic decomposition of NO into N₂ and O₂. For Φ=0.3 the measured detonation velocity in a tube of 52 mm internal diameter is very much smaller than the calculated value and the mean size of the cellular structure is very much larger than the value extrapolated from data obtained with mixtures of higher but close equivalence ratio. All these results show that the detonation, though self-sustained and steady, is ‘non-ideal’, i.e. it is supported only by a part of the available chemical energy, that provided mainly by the first exothermic step. To cite this article: D. Desbordes et al., C. R. Mecanique 332 (2004).     

磁控溅射NbSe2和MoS2薄膜不同湿度下的摩擦学行为

针对MoS₂在潮湿环境易氧化和润滑失效的问题,从增强离子键强度的角度探索改善其抗氧化以及润滑湿度适应性. 选择了离子键更强的NbSe₂进行对比,采用磁控溅射法分别制备了NbSe₂和MoS₂薄膜,研究了两种薄膜在不同湿度下的摩擦学性能,对比其在摩擦稳定阶段的结构和化学组成,探讨了NbSe₂在大气高湿度环境下的优势与作用机理. 结果表明:NbSe₂薄膜在大气环境下的摩擦表现出更佳的湿度适应性,在20% RH、35% RH和55% RH下摩擦系数稳定在0.08左右,直到75% RH下摩擦系数才开始增大,而MoS₂薄膜在35% RH下面临润滑性能快速失效的问题,进一步结合XPS和XRD等表征结果发现:相较于MoS₂,NbSe₂在大气摩擦条件下更难氧化,其层层滑移状态能较好维持,能保持长时间的润滑性能,这为大气高湿度服役润滑材料的改进提供了新的思路.      

Ar稀释C2H2+2.5O2预混气高频爆轰的端面结构

为了研究预混气爆轰的内部结构,对不同浓度的Ar稀释的C₂H₂+2.5O₂预混气进行爆轰实验和数值计算。首先,在内径63.5 mm的管道内进行爆轰实验,使用烟熏玻璃记录了不同初始压力下C₂H₂+2.5O₂预混气的爆轰端面结构。使用数字化图像处理技术来分析烟熏玻璃记录的三波点轨迹,以减少人为误差。然后,观察实验结果并描绘规则图形,图像识别程序经过验证后,用于分析实验结果。从端面结构中对封闭图形进行圆的拟合,用胞格半径方差来表示胞格大小的均匀程度;用相邻胞格圆心距的方差来表示胞格分布的规则程度。通过对比不同Ar稀释下半径方差和圆心距方差随胞格数量的变化,给出不同浓度Ar稀释下C₂H₂+2.5O₂预混气的端面胞格尺寸及分布规律,随着Ar浓度的升高,预混气端面胞格分布更加规律。