The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the ...The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio . For disk like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod like particle, it is inverse. For sedimentation of a crowd of high frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.展开更多
An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for...An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for the velocity and a “twice coarser' triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two dimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particles than previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.展开更多
Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and termina...Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted “T” structure were observed, the pollutant particles for high ε and large ReT scattered wider than that for low ε and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on ε and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to ε. The orientation distributions of pollutant particles depended on ReT and ε, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on ε and ReT.展开更多
Three representative types of houses in Beijing were selected and, in each type, smoking and nonsmoking households were compared. IP, RP. and CO concentrations in the living room and kitchen were monitored during each...Three representative types of houses in Beijing were selected and, in each type, smoking and nonsmoking households were compared. IP, RP. and CO concentrations in the living room and kitchen were monitored during each season. and the level of COHb in the heads of the households were measured. The study showed that indoor air pollution was rather severe, especially during winter. when paniculate concentrations markedly exceeded the standard and CO concentration was as high as 47 ppm. Indoor air pollution was closely related to the type of house, particularly to the mode of heating. In houses. of the same type, pollution improved greatly after central heating facilities were installed. Analysis of 30 elements revealed that pollution was typically caused by coal burning. aggravated by dusty wind, but high indoor Pb levels were probably due to the use of LPG for cooking. In our study the effect of cigarette smoking was sometimes masked by the severe indoor pollution. (C)1990 Academic Press, Inc.展开更多
An observational study on trace gases and PM2.5 was conducted at three sites in and around Beijing, during the Olympic season from 2007 to 2009. Air quality improved significantly during the Olympic Games due to the s...An observational study on trace gases and PM2.5 was conducted at three sites in and around Beijing, during the Olympic season from 2007 to 2009. Air quality improved significantly during the Olympic Games due to the special emission control measures. However, concentrations of the primary pollutants and PM were found to have risen significantly after the Games. Although the major O3 precursors (NOx and VOCs) were well controlled during the Olympic season, O3 was still found to be the highest in 2008, based on the data of ground-based observation. All this information suggests that while control of regional emissions for the Beijing Olympic Games did improved the air quality in Beijing, more efforts will be needed for the continuous improvement of regional air quality, especially for significant reductions of O3 and fine particulate pollution, and not only in Beijing, but also in the B eijing-Tianjin-Hebei region.展开更多
To understand the pollution characteristics of atmospheric particles and heavy metals in winter in Chang-Zhu-Tan city clusters, China, total suspended particulate (TSP) and PMI0 samples were collected in cities of C...To understand the pollution characteristics of atmospheric particles and heavy metals in winter in Chang-Zhu-Tan city clusters, China, total suspended particulate (TSP) and PMI0 samples were collected in cities of Changsha, Zhuzhou and Xiangtan from December 2011 to January 2012, and heavy metals of Cd, Pb, Cr, and As were analyzed. It shows that the average TSP concentration in Changsha, Zhuzhou and Xiangtan were (183 ± 73), (201± 84) and (190 ±66) μg/m3 respectively, and the average PM10 were (171 ± 82), (178 ± 65) and (179 ± 55) μg/m3 respectively. The lowest TSP and PM10 concentrations occurred at the background Shaping site of Changsha. The average ratio of p(PM10)/p(TSP) was 91.9%, ranging from 81.3% to 98.9%. Concerning heavy metals, in TSP samples, the concentration of Cr, As, Cd and Pb were 28.8-56.5, 18.1-76.3, 3.9-26.1 and 148.0-460.9 ng/m3, respectively, while in PMI0 samples, were 16.4--42.1, 15.5-67.9, 3.3-22.2 and 127.9-389.3 ng/m3, respectively. The enrichment factor of Cd was the highest, followed by Pb and As, while that of Cr was the lowest.展开更多
To investigate the composition and possible sources of particles, especially during heavy haze pollution, a single particle aerosol mass spectrometer(SPAMS) was deployed to measure the changes of single particle spe...To investigate the composition and possible sources of particles, especially during heavy haze pollution, a single particle aerosol mass spectrometer(SPAMS) was deployed to measure the changes of single particle species and sizes during October of 2014, in Beijing. A total of 2,871,431 particles with both positive and negative spectra were collected and characterized in combination with the adaptive resonance theory neural network algorithm(ART-2a). Eight types of particles were classified: dust particles(dust, 8.1%), elemental carbon(EC, 29.0%), organic carbon(OC, 18.0%), EC and OC combined particles(ECOC, 9.5%),Na-K containing particles(Na K, 7.9%), K-containing particles(K, 21.8%), organic nitrogen and potassium containing particles(KCN, 2.3%), and metal-containing particles(metal,3.6%). Three haze pollution events(P1, P2, P3) and one clean period(clean) were analyzed,based on the mass and number concentration of PM_(2.5)and the back trajectory results from the hybrid single particle Lagrangian integrated trajectory model(Hysplit-4 model). Results showed that EC, OC and K were the major components of single particles during the three haze pollution periods, which showed clearly increased ratios compared with those in the clean period. Results from the mixing state of secondary species of different types of particles showed that sulfate and nitrate were more readily mixed with carbon-containing particles during haze pollution episodes than in clean periods.展开更多
Beijing suffered from serious air pollution in October, 2011 with the occurrence of three continuous episodes. Here we analyze the pollution status of particulate matter, the relationship between the gaseous pollutant...Beijing suffered from serious air pollution in October, 2011 with the occurrence of three continuous episodes. Here we analyze the pollution status of particulate matter, the relationship between the gaseous pollutants, physical and chemical properties of single particles, and the profile of water-soluble ions in PM2.5 during the three episodes. Regional and photochemically aged air masses, which were characterized as having high values of O3 and SO2, were hypothesized to have played a dominant role in the first episode. After mixing local air masses with freshly-emitted primary pollutants, the concentration of NOx continued to increase and the size of SO42-, NO3- and NH4+ in the particle population continued to become smaller. The amount of elemental carbon-rich and organic carbonrich particles in the scaled single particles (0.2-2 μm) and water-soluble K+ in PM2.s also increased in the episodes. All the available information suggests that the biomass or fuel burning sources in or around Beijing may have had a huge impact on the last two episodes.展开更多
Airborne inhalable particles are a potent environmental pollutant. Formed via industrial processes, separation of these particles is difficult using conventional clean up techniques. In this work, solid nuclei particl...Airborne inhalable particles are a potent environmental pollutant. Formed via industrial processes, separation of these particles is difficult using conventional clean up techniques. In this work, solid nuclei particles of different chemical compositions were introduced into an agglomeration chamber with simulated flue gases to investigate their ability to remove these particles. Organic nuclei were able to capture more inhalable particles from coal-derived fly ash than inorganic nuclei, though these proved more effective for the agglomeration of inhalable particles in refuse-derived fly ash. Increasing the diameter of the solid nuclei benefitted the agglomeration process for both types of ash. Varying the local humidity changed adhesion between the particles and encouraged them to aggregate. Increasing the relative humidity consistently increased particle agglomeration for the refuse-derived ash. For coal-derived fly ash, the removal efficiency increased initially with relative humidity but then further increases in humidity had no impact on the relatively high efficiencies. After agglomeration in an atmosphere of 62% relative humidity, the mean mass diameter of inhalable particles in the coal-derived fly ash increased from 3.3 to 9.2 μm. For refuse-derived fly ash, agglomeration caused the percentage of particles that were less than 2μm to decrease from 40% to 15%. After treatment at a relative humidity of 61%, the mean size of inhalable particles exceeded 10 μm.展开更多
Knowledge of particle number size distribution(PND) and new particle formation(NPF)events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air q...Knowledge of particle number size distribution(PND) and new particle formation(NPF)events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer(SMPS) at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations(PNCs) were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn^(-3) at the urban sites and were approximately 0.2 × 10~4 cm^(-3) at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode(25-100 nm) at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.展开更多
基金TheNationalNaturalSciencesFoundationforOutstandingYouthofChina (No .1 992 52 1 0 )
文摘The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio . For disk like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod like particle, it is inverse. For sedimentation of a crowd of high frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.
基金TheNationalNaturalSciencesFoundationforOutstandingYouthofChina (No .19925210)andZhejiangProvincialNaturalScienceFoundationofChina(No .10 10 4 7)
文摘An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for the velocity and a “twice coarser' triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two dimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particles than previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.
文摘Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted “T” structure were observed, the pollutant particles for high ε and large ReT scattered wider than that for low ε and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on ε and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to ε. The orientation distributions of pollutant particles depended on ReT and ε, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on ε and ReT.
文摘Three representative types of houses in Beijing were selected and, in each type, smoking and nonsmoking households were compared. IP, RP. and CO concentrations in the living room and kitchen were monitored during each season. and the level of COHb in the heads of the households were measured. The study showed that indoor air pollution was rather severe, especially during winter. when paniculate concentrations markedly exceeded the standard and CO concentration was as high as 47 ppm. Indoor air pollution was closely related to the type of house, particularly to the mode of heating. In houses. of the same type, pollution improved greatly after central heating facilities were installed. Analysis of 30 elements revealed that pollution was typically caused by coal burning. aggravated by dusty wind, but high indoor Pb levels were probably due to the use of LPG for cooking. In our study the effect of cigarette smoking was sometimes masked by the severe indoor pollution. (C)1990 Academic Press, Inc.
基金supported by the National Natural Scientific Foundation of China(No.41005065,41375132)the National Department Public Benefit Research Foundation(No.201409003,201009001,201309011)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB05030400)
文摘An observational study on trace gases and PM2.5 was conducted at three sites in and around Beijing, during the Olympic season from 2007 to 2009. Air quality improved significantly during the Olympic Games due to the special emission control measures. However, concentrations of the primary pollutants and PM were found to have risen significantly after the Games. Although the major O3 precursors (NOx and VOCs) were well controlled during the Olympic season, O3 was still found to be the highest in 2008, based on the data of ground-based observation. All this information suggests that while control of regional emissions for the Beijing Olympic Games did improved the air quality in Beijing, more efforts will be needed for the continuous improvement of regional air quality, especially for significant reductions of O3 and fine particulate pollution, and not only in Beijing, but also in the B eijing-Tianjin-Hebei region.
基金supported by the National Department Public Benefit Research Foundation(No.201109005)the National Natural Science Foundation of China(No.41205093)
文摘To understand the pollution characteristics of atmospheric particles and heavy metals in winter in Chang-Zhu-Tan city clusters, China, total suspended particulate (TSP) and PMI0 samples were collected in cities of Changsha, Zhuzhou and Xiangtan from December 2011 to January 2012, and heavy metals of Cd, Pb, Cr, and As were analyzed. It shows that the average TSP concentration in Changsha, Zhuzhou and Xiangtan were (183 ± 73), (201± 84) and (190 ±66) μg/m3 respectively, and the average PM10 were (171 ± 82), (178 ± 65) and (179 ± 55) μg/m3 respectively. The lowest TSP and PM10 concentrations occurred at the background Shaping site of Changsha. The average ratio of p(PM10)/p(TSP) was 91.9%, ranging from 81.3% to 98.9%. Concerning heavy metals, in TSP samples, the concentration of Cr, As, Cd and Pb were 28.8-56.5, 18.1-76.3, 3.9-26.1 and 148.0-460.9 ng/m3, respectively, while in PMI0 samples, were 16.4--42.1, 15.5-67.9, 3.3-22.2 and 127.9-389.3 ng/m3, respectively. The enrichment factor of Cd was the highest, followed by Pb and As, while that of Cr was the lowest.
基金supported by the National Natural Science Foundation of China (No.41205115)
文摘To investigate the composition and possible sources of particles, especially during heavy haze pollution, a single particle aerosol mass spectrometer(SPAMS) was deployed to measure the changes of single particle species and sizes during October of 2014, in Beijing. A total of 2,871,431 particles with both positive and negative spectra were collected and characterized in combination with the adaptive resonance theory neural network algorithm(ART-2a). Eight types of particles were classified: dust particles(dust, 8.1%), elemental carbon(EC, 29.0%), organic carbon(OC, 18.0%), EC and OC combined particles(ECOC, 9.5%),Na-K containing particles(Na K, 7.9%), K-containing particles(K, 21.8%), organic nitrogen and potassium containing particles(KCN, 2.3%), and metal-containing particles(metal,3.6%). Three haze pollution events(P1, P2, P3) and one clean period(clean) were analyzed,based on the mass and number concentration of PM_(2.5)and the back trajectory results from the hybrid single particle Lagrangian integrated trajectory model(Hysplit-4 model). Results showed that EC, OC and K were the major components of single particles during the three haze pollution periods, which showed clearly increased ratios compared with those in the clean period. Results from the mixing state of secondary species of different types of particles showed that sulfate and nitrate were more readily mixed with carbon-containing particles during haze pollution episodes than in clean periods.
基金supported by the National Natural Scientific Foundation of China(No.41005065,41375132)the National Department Public Benefit Research Foundation(No.201409003,201009001,201309011)Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB05030400)
文摘Beijing suffered from serious air pollution in October, 2011 with the occurrence of three continuous episodes. Here we analyze the pollution status of particulate matter, the relationship between the gaseous pollutants, physical and chemical properties of single particles, and the profile of water-soluble ions in PM2.5 during the three episodes. Regional and photochemically aged air masses, which were characterized as having high values of O3 and SO2, were hypothesized to have played a dominant role in the first episode. After mixing local air masses with freshly-emitted primary pollutants, the concentration of NOx continued to increase and the size of SO42-, NO3- and NH4+ in the particle population continued to become smaller. The amount of elemental carbon-rich and organic carbonrich particles in the scaled single particles (0.2-2 μm) and water-soluble K+ in PM2.s also increased in the episodes. All the available information suggests that the biomass or fuel burning sources in or around Beijing may have had a huge impact on the last two episodes.
基金The authors wish to acknowledge the financial supports from the National Natural Science Foundation of China (Contract No. 21206080) and from the Major Project of Shandong Province for Research and Development (Contract No. 2015GSF117026).
文摘Airborne inhalable particles are a potent environmental pollutant. Formed via industrial processes, separation of these particles is difficult using conventional clean up techniques. In this work, solid nuclei particles of different chemical compositions were introduced into an agglomeration chamber with simulated flue gases to investigate their ability to remove these particles. Organic nuclei were able to capture more inhalable particles from coal-derived fly ash than inorganic nuclei, though these proved more effective for the agglomeration of inhalable particles in refuse-derived fly ash. Increasing the diameter of the solid nuclei benefitted the agglomeration process for both types of ash. Varying the local humidity changed adhesion between the particles and encouraged them to aggregate. Increasing the relative humidity consistently increased particle agglomeration for the refuse-derived ash. For coal-derived fly ash, the removal efficiency increased initially with relative humidity but then further increases in humidity had no impact on the relatively high efficiencies. After agglomeration in an atmosphere of 62% relative humidity, the mean mass diameter of inhalable particles in the coal-derived fly ash increased from 3.3 to 9.2 μm. For refuse-derived fly ash, agglomeration caused the percentage of particles that were less than 2μm to decrease from 40% to 15%. After treatment at a relative humidity of 61%, the mean size of inhalable particles exceeded 10 μm.
基金supported by the National Natural Science Foundation of China(Nos.U1301234,21277003)the Shenzhen Science&Technology Plan,and the Ministry of Science and Technology of China(No.2013CB228503)
文摘Knowledge of particle number size distribution(PND) and new particle formation(NPF)events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer(SMPS) at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations(PNCs) were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn^(-3) at the urban sites and were approximately 0.2 × 10~4 cm^(-3) at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode(25-100 nm) at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.