PM_(2.5) and PM_(10-2.5) chemical composition and source apportionment near a Hong Kong roadway

Twenty-four-hour PM2.5 and PM10 samples were collected simultaneously at a highly trafficked road-side site in Hong Kong every sixth day from October 2004 to September 2005. The mass concentrations of PM2.5, PMlo-2.5 （defined as PM10 - PM2.5）, organic carbon （OC）, elemental carbon （EC）, water-soluble ions, and up to 25 elements were determined. Investigation of the chemical compositions and potential sources revealed distinct differences between PM2.5 and PM10-2.5. The annual average mass concentrations were 55.5 ＋ 25.5 and 25.9±15.7μg/m^3 for PM2.5 and PM10-2.5, respectively. EC, OM （OM = OC × 1.4）, and ammonium sulfate comprised over -82% of PM2.5, accounting for -29%, -27%, and -25%, respectively, of the PM2.5 mass. Low OC/EC ratios （less than 1） for PM2.5 suggested that fresh diesel-engine exhaust was a major contributor. Seven sources were resolved for PM2.5 by positive matrix factorization （PMF） model, including vehicle emissions （-29%）, secondary inorganic aerosols （-27%）, waste incinera- tor/biomass burning （-23%）, residual oil combustion （-10%）, marine aerosols （-6%）, industrial exhaust （-4%）, and resuspended road dust （-1%）. EC and OM comprised only -19% of PM10-2.5. The average OC/EC ratio of PM10-2.5 was 7.8± 14.2, suggesting that sources other than vehicular exhaust were important contributors. The sources for PM10-2.5 determined by the PMF model included -20% traffic-generated resuspension （e.g., tire dust/brake linear/petrol evaporation）, -17% locally resuspended road dust, -17% marine aerosols, -12% secondary aerosols/field burning, and -11% vehicle emissions.

Technical measures to achieve a cleaner production mode for recycled paper mills

China’s paper production reached 79.8×10^(6) t in 2008 and ranked number one in the world.Because of its high consumption of water,energy and materials and its serious pollution,the present processes are not likely to be sustainable.An alternative,the closed Water Loop-Papermaking Integration(WLPI)method,is put forward in this paper.The WLPI method can be realized in a recycled paper mill by adding technologies and using recycled water.Many industrial case studies have shown that a large quantity of water,energy and materials can be saved,and the quantity of waste sludge and wastewater discharge was minimized by using the WLPI method.The design of the water reuse system,control of calcium hardness,water recycling and minimal waste sludge are discussed.Anaerobic technology plays an important role in the WLPI method to lower cost,energy use and waste.In the brown paper and coated white board production,zeroeffluent discharge can be realized.Fresh water consumption is only 1-2m^(3)·t^(-1).For the paper mills with deinking and bleaching processes,about 10 m^(3)·t^(-1) of fresh water and a similar amount of effluent discharge are needed.Power saving using anaerobic technology is 70%when recycled water is used in comparison with the conventional activated sludge process.Waste sludge can be decreased to about 5%of the initial process due to reuse of the waste sludge and the lower bio-sludge production of the anaerobic process.

An efficient algorithm for detecting particle contact in non-uniform size particulate system

Algorithms for detecting particle collision play an important role in the discrete element method （DEM） for the simulation of granular flow systems since the time taken to detect the contact pairs usually occupies a considerable proportion of the total CPU time for the simulation. In this study, we developed a new octree algorithm called multi-octree algorithm, for detecting candidate contact pairs. The so-called multi- octree algorithm adopts the topology of octree for detecting possible contacts, in which the particles are managed by hierarchical classification according to particle size and then mapped to different level nodes of an octree, instead of mapping all particles into the leaf nodes of an octree in Vemuri-octree algorithm. The present algorithm speeds up the detecting process by reducing the number of candidate particles for possible contacts. A non-uniform size particulate system with three particle sizes was simulated by the multi-octree and the Vemuri-octree algorithms simultaneously. The simulation results showed that the multi-octree algorithm is relatively insensitive to the volumetric fraction of particles and particle shapes, and takes much shorter time to find candidate particles for possible contacts than the Vemuri-octree algorithm for non-uniform size particulate systems. 2009 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Numerical simulation of nanoparticle pattern fabricated by electrostatic spray deposition

Electrospray deposition （ESD） as a patterning method of nanoparticles deposited on a substrate has attracted much attention due to several advantages over other methods. However, obtaining an optimum ESD processing condition for nanoparticle pattern relies much on trial experiments because of the lack of reliable numerical simulation. In this study, the deposition characteristics of nanoparticle generated by electrospray were investigated by using a three-dimensional Lagrangian model. Three important process parameters, including solution dielectric constant, applied voltage and surface charge density on mask were considered by fixing the geometrical parameters of the ESD device. Simulation result showed that under the condition of without a mask, the spray diameter increases with increasing solvent dielectric constant, and higher applied voltage makes the spray area wider. Controllability of focusing by changing surface charge density on the mask was confirmed： higher surface charge density on the mask results in more focused deposition. Validity of the numerical simulation developed in this study was verified by comnarison with exoerimental data.

Charging states on atmospheric aerosol particles affected by meteorological conditions

Previous studies on haze formation focused mainly on the various chemical components in aerosol particles and their physicochemical effects on particle behaviour(e.g.,generation,growth,and agglomeration).This paper describes the measurement of the charging state on atmospheric aerosol particles,which could be affected by meteorological conditions.A series of experiments on particle charging state and meteorological factors was undertaken on the roof of the west 4th building on the Qujiang Campus at Xi'an Jiaotong University(China).Measurements were conducted approximately 20 m above ground level,Our results showed that most atmospheric particles carried net negative or positive charge and that the electric charge on the particles varied diurnally and seasonally.The average amount of charge on particles was higher in winter than in summer.The number concentration of charged particles was higher during the day than overnight.Obvious difference in the average charge of aerosol particles was found between sand-dust days and haze days.A strong relationship was found between the PM2.s concentration,charge amount on particles,and humidity.Our findings show that particle formation and growth could partly be attributed to variation in particle charging state,which is related to meteorological conditions including atmospheric humidity.

A Gaussian process regression accelerated multiscale model for conduction-radiation heat transfer in periodic composite materials with temperature-dependent thermal properties

Prediction of the coupled conduction-radiation heat transfer in composite materials with periodic structure is important in high-temperature applications of the materials. The temperature dependence of thermal properties complicates the problem. In this work, a multiscale model is proposed for the conduction-radiation heat transfer in periodic composite materials with temperature-dependent thermal properties. Homogenization analysis of the coupled conduction and radiative transfer equations is conducted, in which the temperature dependence of thermal properties is considered. Both the macroscopic homogenized equations and the local unit cell problems are derived. It is proved that the macroscopic average temperature can be used in the unit cell problems for the first-order corrections of the temperature and radiative intensity, and the calculations of effective thermal properties. The temperature dependence of thermal properties only influences the higher-order corrections. A multiscale numerical method is proposed based on the analysis. The Gaussian process (GP) regression is coupled into the multiscale algorithm to build a correlation between thermal properties and temperature for the macroscale iterations and prevent the repetitive solving of unit cell problems. The GP model is updated by additional solutions of unit cell problems during the iteration according to a variance threshold. Numerical simulations of conduction-radiation heat transfer in composite with isotropic and anisotropic periodic structures are used to validate the proposed multiscale model. It is found that the accuracy and efficiency of the multiscale method can be guaranteed by using a proper variance threshold for the GP model. The multiscale model can provide both the average temperature and radiative intensity fields and their detailed fluctuations due to the local structures.