The COVID-19 lockdown was a typical example of extreme emission reduction,providing an opportunity to study the impact of lockdown measures on air pollution.Particle number concentrations(PNC)originate from direct emi...The COVID-19 lockdown was a typical example of extreme emission reduction,providing an opportunity to study the impact of lockdown measures on air pollution.Particle number concentrations(PNC)originate from direct emissions or through new particle formation events.However,their variations during the lockdown period are under investigation.This study focuses on Luohe,a city on the southern edge of the North China Plain,analyzing the changes in PNC and its sources before,during,and after the COVID-19 lockdown.From March 25^(th)to May 31^(st),2022,real-time PNC measurements were conducted using a Scanning Mobility Particle Sizer for particle size.Results showed an 11.2%decrease in PNC during the lockdown compared to pre-lockdown and a 3.6%decrease compared to post-lockdown,indicating reduced local emissions and weakened regional transportation during the lockdown.Positive Matrix Factorization analysis identified six sources contributing to the total PNC,including photochemical nucleation,aged photochemical nucleation,gasoline vehicle emissions,diesel vehicle emissions,coal and biomass combustion,and secondary aerosols.The significant changes in source emissions indicate a substantially reduced traffic volume after the implementation of lockdown measures(2644.8#/cm^(3),2202.2#/cm^(3),2792.7#/cm^(3)).Concurrently,photochemical nucleation(310.1#/cm^(3),306.3#/cm^(3),393.1#/cm^(3))and photochemical nucleation aging(592.8#/cm^(3),744.1#/cm^(3),810.7#/cm^(3))exhibited increasing trends,while coal/biomass combustion(1656.6#/cm^(3),1586.2#/cm^(3),980.0#/cm^(3))and secondary sources(999.4#/cm^(3),791.1#/cm^(3),804.1#/cm^(3))showed decreasing trends.In summary,the contributions of traffic emissions to PNC highlight the potential for targeted traffic management strategies to improve urban air quality.展开更多
New particle formation is a key process in shaping the size distribution of aerosols in the atmosphere.We present here the measurement results of number and size distribution of aerosol particles （10–10000 nm in dia...New particle formation is a key process in shaping the size distribution of aerosols in the atmosphere.We present here the measurement results of number and size distribution of aerosol particles （10–10000 nm in diameter） obtained in the summer of 2008,at a suburban site in Beijing,China.We firstly reported the pollution level,particle number size distribution,diurnal variation of the particle number size distribution and then introduced the characteristics of the particle formation processes.The results showed that the number concentration of ultrafine particles was much lower than the values measured in other urban or suburban areas in previous studies.Sharp increases of ultrafine particle count were frequently observed at noon.An examination of the diurnal pattern suggested that the burst of ultrafine particles was mainly due to new particle formation promoted by photochemical processes.In addition,high relative humidity was a key factor driving the growth of the particles in the afternoon.During the 2-month observations,new particle formation from homogeneous nucleation was observed for 42.7% of the study period.The average growth rate of newly formed particles was 3.2 nm/hr,and varied from 1.2 to 8.0 nm/hr.The required concentration of condensable vapor was 4.4×10 7 cm-3,and its source rate was 1.2×10 6 cm-3 sec-1.Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rates was 28.7%.展开更多
In this study,the particle size-resolved distribution from a China-3 certificated light-duty diesel vehicle was measured by using a portable emission measurement system（PEMS）.In order to examine the influences of ve...In this study,the particle size-resolved distribution from a China-3 certificated light-duty diesel vehicle was measured by using a portable emission measurement system（PEMS）.In order to examine the influences of vehicle specific power（VSP） and high-altitude operation,measurements were conducted at 8 constant speeds,which ranged from 10 to 80 km/hr at10 km/hr intervals,and two different high altitudes,namely 2200 and 3200 m.The results demonstrated that the numbers of particles in all size ranges decreased significantly as VSP increased when the test vehicle was running at lower speeds（〈 20 km/hr）,while at a moderate speed（between 30 and 60 km/hr）,the particle number was statistically insensitive to increase VSP.Under high-speed cruising conditions,the numbers of ultrafine particles and PM2.5were insensitive to changes in VSP,but the numbers of nanoparticles and PM10 surged considerably.An increase in the operational altitude of the test vehicle resulted in increased particle number emissions at low and high driving speeds;however,particle numbers obtained at moderate speeds decreased as altitude rose.When the test vehicle was running at moderate speeds,particle numbers measured at the two altitudes were very close,except for comparatively higher number concentrations of nanoparticles measured at 2200 m.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
Ultrafine particles are associated with adverse health effects. Total Particle Number Concentration（TNC） of fine particles were measured during 2002 at the St. Louis — Midwest supersite. The time series showed over...Ultrafine particles are associated with adverse health effects. Total Particle Number Concentration（TNC） of fine particles were measured during 2002 at the St. Louis — Midwest supersite. The time series showed overall low level with frequent large peaks. The time series was analyzed alongside criteria pollutant measurements and meteorological observations. Multiple regression analysis was used to identify further contributing factors and to determine the association of different pollutants with TNC levels. This showed the strong contribution of sulfur dioxide（SO2） and nitrogen oxides（NO x） to high TNC levels. The analysis also suggested that increased dispersion resulting from faster winds and higher mixing heights led to higher TNC levels. Overall, the results show that there were intense particle nucleation events in a SO2 rich plume reaching the site which contributed around 29% of TNC. A further 40% was associated with primary emissions from mobile sources. By separating the remaining TNC by time of day and clear sky conditions,we suggest that most likely 8% of TNC are due to regional nucleation events and 23% are associated with the general urban background.展开更多
Particle number size distribution(PNSD) between 10 nm and 20 μm were measured in the Pearl River Delta(PRD) region in winter 2011.The average particle number concentration of the nucleation mode(10-20 nm),Aitken mode...Particle number size distribution(PNSD) between 10 nm and 20 μm were measured in the Pearl River Delta(PRD) region in winter 2011.The average particle number concentration of the nucleation mode(10-20 nm),Aitken mode(20-100 nm),accumulation mode(100 nm-1μm) and coarse mode(1-20 μm) particles were 1 552,7 470,4 012,and 19 cm-3,respectively.The volume concentration of accumulation mode particles with peak at 300 nm accounted for over 70% of the total volume concentration.Diurnal variations and dependencies on meteorological parameters of PNSD were investigated.The diurnal variation of nucleation mode particles was mainly influenced by new particle formation events,while the diurnal variation of Aitken mode particles correlated to the traffic emission and the growth process of nucleation mode particles.When the PRD region was controlled by a cold high pressure,conditions of low relative humidity,high wind speed and strong radiation are favorable for the occurrence of new particle formation(NPF) events.The frequency of occurrence of NPF events was 21.3% during the whole measurement period.Parameters describing NPF events,including growth rate(GR) and source rate of condensable vapor(Q),were slightly larger than those in previous literature.This suggests that intense photochemical and biological activities may be the source of condensable vapor for particle growth,even during winter in the PRD.展开更多
Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground l...Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6：00, 12：00, and 21：00 （Beijing Time） for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT-4） model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length.展开更多
Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The ...Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.展开更多
This study discusses the evolution of particle number size distribution during episodes of heavy pollution and new particle formation in the urban atmosphere of Beijing to quantify the effects of dynamic processes (co...This study discusses the evolution of particle number size distribution during episodes of heavy pollution and new particle formation in the urban atmosphere of Beijing to quantify the effects of dynamic processes (coagulation and condensation) on the particle number size distribution.During a heavy-pollution event,an extremely low number concentration of 3-10 nm particles (on average 46 cm-3) was observed.This is because nucleation-mode particles were easily removed by strong coagulational scavenging of larger particles under this condition.In addition,a large condensation sink (on average 0.13 s-1) restrained nucleation,which is one of the major sources of nucleation-mode particles.Conversely,during a new-particle formation event,the small condensation sink (0.01 s-1) of precursor facilitated nucleation.At the same time,preexisting particles had little ability to scavenge newly formed particles (around 1 nm) and allowed them to grow to a detectable size (larger than 3 nm currently).We suggest that the effects of dynamic processes (coagulation and condensation) on particle size distribution should be stressed under some extreme conditions of the relatively polluted urban atmosphere in addition to traffic and meteorological factors.展开更多
Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle ma...Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.展开更多
Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on empric...Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on emprical estimation of cloud particle number concentration(N_(c))in China,and scientific verification and quantitative identification criteria are urgently needed.In this study,the observations are from the Fast Cloud Droplets Probe,Rosemount ice detector(RICE),and Cloud Particle Imager(CP_(i))onboard a King Air aircraft during seven flights in 2018 and 2019 over central and eastern China.Based on this,the correlation among N_(c),the proportion of spherical particles(P_(s)),and the probability of icing(P_(i))in supercooled stratiform and cumulus-stratus clouds is statistically analyzed.Subsequently,this study proposes a method to identify SLW areas using N_(c) in combination with ambient temperature.The reliability of this method is evaluated through the true skill statistics(TSS)and threat score(TS)methods.Numerous airborne observations during the seven flights reveal a strong correlation among Nc,P_(s),and P_(i)at the temperature from 0 to−18°C.When Nc is greater than a certain threshold of 5 cm^(−3),there is always the SLW,i.e.,P_(i)and P_(s)are high.Evaluation results demonstrate that the TSS and TS values for Nc=5 cm^(−3)are higher than those for Nc<5 cm^(−3),and a larger Nc threshold(>5 cm^(−3))corresponds to a higher SLW identification hit rate and a higher SLW content.Therefore,Nc=5 cm^(−3)can be used as the minimum criterion for identifying the SLW in clouds at temperature lower than 0°C.The SLW identification method proposed in this study is especially helpful in common situations where aircraft are equipped with only Nc probes and without the CP_(i)and RICE.展开更多
The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdo...The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdoor concentrations were examined and discussed, and linear regression analysis was employed to correlate the indoor and outdoor concentrations. The diurnal cycles of indoor and outdoor particle concentrations of different particle size ranges all showed positive correlations between indoor and outdoor number concentrations, The I/O ratios of number concentrations varied with the increase of particle size in the range of 0.89 （±0.19） to 0.99 （±0.15）.展开更多
A fixed particle number BCS （FBCS） approach is formulated in the relativistic mean field （RMF） model. It is shown that the RMF＋FBCS model obtained can describe the weak pairing limit. We calculate the ground-stat...A fixed particle number BCS （FBCS） approach is formulated in the relativistic mean field （RMF） model. It is shown that the RMF＋FBCS model obtained can describe the weak pairing limit. We calculate the ground-state properties of the calcium isotopes ＆32-74Ca and compare the results with those obtained from the usual RMF＋BCS model. Although the results are quite similar to each other, we observe the interesting phenomenon that for ^54Ca, the FBCS approach can enhance the occupation probability of the 2p1/2 single particle level and slightly increases its radius, compared with the RMF＋BCS model. This leads to the unusual scenario that although ^54Ca is more bound with a spherical configuration, the corresponding size is not the most compact. We anticipate that such a phenomenon might happen for other neutron-rich nuclei and should be checked by further more systematic studies.展开更多
Revised September 2013 by J.-F. Arguin LBNL）, L. Garren （Fermilab）, F. Krauss （Durham U.）, C.-J. Lin （LBNL）, S. Navas （U. Granada）, P. Richardson （Durham U.）, and T. Sjostrand （Lund U.）.
Particle number size distribution from 10 to 10,000 nm was measured by a wide-range particle spectrometer （WPS-1000XP） at a downwind site north of downtown Lanzhou, western China, from 25 june to 19 July 2006. We fi...Particle number size distribution from 10 to 10,000 nm was measured by a wide-range particle spectrometer （WPS-1000XP） at a downwind site north of downtown Lanzhou, western China, from 25 june to 19 July 2006. We first report the pollution level, diurnal variation of particle concentration in different size ranges and then introduce the characteristics of the particle formation processes, to show that the number concentration of ultrafine particles was lower than the values measured in other urban or suburban areas in previous studies, However, the fraction of ultrafine particles in total aerosol number concentration was found to be much higher. Furthermore, sharp increase of ultrafine particle concentration was frequently observed at noon. An examination of the diurnal pattern suggests that the burst of the ultrafine particles was mainly due to nucleation process. During the 25-day observation, new particle formation （NPF） from homogeneous nucleation was observed during 33% of the study period. The average growth rate of the newly formed particles was 4.4 nm/h, varying from 1.3 to 16,9 nm/h. The needed concentration of condensable vapor was 6.1 × 10^7 cm-3, and its source rate was 1.1× 10^6 cm-3 s 1. Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rate was 68.3%.展开更多
We study the behaviors of thermalization in Fermi–Pasta–Ulam–Tsingou(FPUT) system with small number of particles using periodic boundary conditions. The total energy has initially equidistributed among some of the ...We study the behaviors of thermalization in Fermi–Pasta–Ulam–Tsingou(FPUT) system with small number of particles using periodic boundary conditions. The total energy has initially equidistributed among some of the lowest frequency modes. The thermalization time t_(eq) depending on system's energy density ε scales as t_(eq) ∝ε^(-4) only within a certain range of nonlinearity. In this range of nonlinearity, energies can interchange between the initial excited modes and other modes continuously with time until reaching the thermalized state. With a further decreasing nonlinearity, a steeper growth than ε^(-4) will appear. In the very weakly nonlinear regime, energies on low frequency modes are found to be frozen on large time scales. Redistribution of mode energies happens through the resonances of high frequency modes.展开更多
The total number of atmospheric particle (AP) is an important datum for planetary science and geoscience. Estimating entire AP number is also a familiar question in general physics. With standard atmosphere model, con...The total number of atmospheric particle (AP) is an important datum for planetary science and geoscience. Estimating entire AP number is also a familiar question in general physics. With standard atmosphere model, considering the number difference of AP caused by rough and uneven in the earth surface below, the sum of dry clean atmosphere particle is . So the whole number of AP including water vapor is . The rough estimation for the total number of AP on other planets (or satellites) in condensed state is also discussed on the base of it.展开更多
The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time dis...The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time distribution(RTD)in vertical single-screw reactors.The results will help in the selection of the right screw design that would help achieve the desired residence time,which is necessary for a reaction to happen.Experiments were conducted in three vertical screw reactors(having fixed shaft diameter)with varying dimensions using granular free-flowing powders of sodium chloride and silica with a mean particle size of∼25μm.RTD behavior was modeled using the radial particle velocities in the screw reactor's centrifugal field.Further,a method is proposed for estimating the axial dispersion coefficient of dry powders in such sheared flows using true and bulk densities of the powder and the screw shear rate.This dispersion coefficient is used in the axially dispersed plug flow model to describe the RTD behavior of screw reactors with acceptable accuracy.The theoretically predicted and experimentally obtained dispersion coefficients are found to be similar thereby confirming the suitability of the model.展开更多
Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to e...Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to evaluate their effects on NO2, smoke and particle number emissions. The results showed that the application of the after-treatments increased the emission ratios of NO2/NOx significantly. The results of smoke emissions and particle number （PN） emissions indicated that both CRDPFs had sufficient capacity to remove more than 90% of total particulate matter （PM） and more than 97% of solid particles. However, the POC was able to remove the organic components of total PM, and only partially to remove the carbonaceous particles with size less than 30 nm. The negligible effects of POC on larger particles were observed due to its honeycomb structure leads to an inadequate residence time to oxidize the solid particles or trap them. The particles removal efficiencies of CRDPFs had high degree of correlations with the emission ratio of NO2/NOx. The PN emission results from two CRDPFs indicated that more NO2 generating in diesel oxidation catalyst section could obtain the higher removal efficiency of solid particles. However this also increased the risk of NO2 exposure in atmosphere.展开更多
Novel applications of nanotechnology may lead to the release of engineered nanoparticles（ENPs）, which result in concerns over their potential environmental hazardous impact. It is essential for the research workers ...Novel applications of nanotechnology may lead to the release of engineered nanoparticles（ENPs）, which result in concerns over their potential environmental hazardous impact. It is essential for the research workers to be able to quantitatively characterise ENPs in the environment and subsequently to assist the risk assessment of the ENPs. This study hence explored the application of nanoparticle tracking system（NTA） to quantitatively describe the behaviour of the ENPs in natural sediment-water systems. The NTA allows the measurement of both particle number concentration（PNC） and particle size distribution（PSD） of the ENPs. The developed NTA method was applied to a range of gold and magnetite ENPs with a selection of surface properties. The results showed that the positively-charged ENPs interacted more strongly with the sediment than neutral and negatively-charged ENPs. It was also found that the citrate coated Au ENPs had a higher distribution percentage（53%） than 11-mercaptoundecanoic acid coated Au ENPs（20%） and citrate coated magnetite ENPs（21%）. The principles of the electrostatic interactions between hard（and soft） acids and bases（HSAB） are used to explain such behaviours; the hard base coating（i.e. citrate ions） will interact more strongly with hard acid（i.e. magnetite） than soft acid（i.e. gold）.The results indicate that NTA is a complementary method to existing approaches to characterise the fate and behaviour of ENPs in natural sediment.展开更多
基金supported by the National Research Program for Key Issues in Air Pollution Control in China(No.DQGG202137)the National Natural Science Foundation of China(No.42277429)。
文摘The COVID-19 lockdown was a typical example of extreme emission reduction,providing an opportunity to study the impact of lockdown measures on air pollution.Particle number concentrations(PNC)originate from direct emissions or through new particle formation events.However,their variations during the lockdown period are under investigation.This study focuses on Luohe,a city on the southern edge of the North China Plain,analyzing the changes in PNC and its sources before,during,and after the COVID-19 lockdown.From March 25^(th)to May 31^(st),2022,real-time PNC measurements were conducted using a Scanning Mobility Particle Sizer for particle size.Results showed an 11.2%decrease in PNC during the lockdown compared to pre-lockdown and a 3.6%decrease compared to post-lockdown,indicating reduced local emissions and weakened regional transportation during the lockdown.Positive Matrix Factorization analysis identified six sources contributing to the total PNC,including photochemical nucleation,aged photochemical nucleation,gasoline vehicle emissions,diesel vehicle emissions,coal and biomass combustion,and secondary aerosols.The significant changes in source emissions indicate a substantially reduced traffic volume after the implementation of lockdown measures(2644.8#/cm^(3),2202.2#/cm^(3),2792.7#/cm^(3)).Concurrently,photochemical nucleation(310.1#/cm^(3),306.3#/cm^(3),393.1#/cm^(3))and photochemical nucleation aging(592.8#/cm^(3),744.1#/cm^(3),810.7#/cm^(3))exhibited increasing trends,while coal/biomass combustion(1656.6#/cm^(3),1586.2#/cm^(3),980.0#/cm^(3))and secondary sources(999.4#/cm^(3),791.1#/cm^(3),804.1#/cm^(3))showed decreasing trends.In summary,the contributions of traffic emissions to PNC highlight the potential for targeted traffic management strategies to improve urban air quality.
基金supported by the National Department Public Benefit Research Foundation of China (No.201009001)the National Natural Science Foundation of China (No.41005065)the Basic Foundation for Public Benefit-Research Academies from the Central Government (No.2008KYYW01)
文摘New particle formation is a key process in shaping the size distribution of aerosols in the atmosphere.We present here the measurement results of number and size distribution of aerosol particles （10–10000 nm in diameter） obtained in the summer of 2008,at a suburban site in Beijing,China.We firstly reported the pollution level,particle number size distribution,diurnal variation of the particle number size distribution and then introduced the characteristics of the particle formation processes.The results showed that the number concentration of ultrafine particles was much lower than the values measured in other urban or suburban areas in previous studies.Sharp increases of ultrafine particle count were frequently observed at noon.An examination of the diurnal pattern suggested that the burst of ultrafine particles was mainly due to new particle formation promoted by photochemical processes.In addition,high relative humidity was a key factor driving the growth of the particles in the afternoon.During the 2-month observations,new particle formation from homogeneous nucleation was observed for 42.7% of the study period.The average growth rate of newly formed particles was 3.2 nm/hr,and varied from 1.2 to 8.0 nm/hr.The required concentration of condensable vapor was 4.4×10 7 cm-3,and its source rate was 1.2×10 6 cm-3 sec-1.Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rates was 28.7%.
基金financially supported by the National Natural Science Foundation of China(Nos.51576016 and 51476012)
文摘In this study,the particle size-resolved distribution from a China-3 certificated light-duty diesel vehicle was measured by using a portable emission measurement system（PEMS）.In order to examine the influences of vehicle specific power（VSP） and high-altitude operation,measurements were conducted at 8 constant speeds,which ranged from 10 to 80 km/hr at10 km/hr intervals,and two different high altitudes,namely 2200 and 3200 m.The results demonstrated that the numbers of particles in all size ranges decreased significantly as VSP increased when the test vehicle was running at lower speeds（〈 20 km/hr）,while at a moderate speed（between 30 and 60 km/hr）,the particle number was statistically insensitive to increase VSP.Under high-speed cruising conditions,the numbers of ultrafine particles and PM2.5were insensitive to changes in VSP,but the numbers of nanoparticles and PM10 surged considerably.An increase in the operational altitude of the test vehicle resulted in increased particle number emissions at low and high driving speeds;however,particle numbers obtained at moderate speeds decreased as altitude rose.When the test vehicle was running at moderate speeds,particle numbers measured at the two altitudes were very close,except for comparatively higher number concentrations of nanoparticles measured at 2200 m.
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.
基金funded the present analysis through grant number RD-83455701the original measurements through cooperative agreement R-82805901-0
文摘Ultrafine particles are associated with adverse health effects. Total Particle Number Concentration（TNC） of fine particles were measured during 2002 at the St. Louis — Midwest supersite. The time series showed overall low level with frequent large peaks. The time series was analyzed alongside criteria pollutant measurements and meteorological observations. Multiple regression analysis was used to identify further contributing factors and to determine the association of different pollutants with TNC levels. This showed the strong contribution of sulfur dioxide（SO2） and nitrogen oxides（NO x） to high TNC levels. The analysis also suggested that increased dispersion resulting from faster winds and higher mixing heights led to higher TNC levels. Overall, the results show that there were intense particle nucleation events in a SO2 rich plume reaching the site which contributed around 29% of TNC. A further 40% was associated with primary emissions from mobile sources. By separating the remaining TNC by time of day and clear sky conditions,we suggest that most likely 8% of TNC are due to regional nucleation events and 23% are associated with the general urban background.
基金Natural Science Foundation of China(41375156)Natural Science Foundation of Guangdong Province,China(S2013010013265)+2 种基金Special R&D fund for research institutes(2014EG137243)National Key Project of Basic Research(2011CB403403)Science and Technology Planning Project for Guangdong Province(2012A061400012)
文摘Particle number size distribution(PNSD) between 10 nm and 20 μm were measured in the Pearl River Delta(PRD) region in winter 2011.The average particle number concentration of the nucleation mode(10-20 nm),Aitken mode(20-100 nm),accumulation mode(100 nm-1μm) and coarse mode(1-20 μm) particles were 1 552,7 470,4 012,and 19 cm-3,respectively.The volume concentration of accumulation mode particles with peak at 300 nm accounted for over 70% of the total volume concentration.Diurnal variations and dependencies on meteorological parameters of PNSD were investigated.The diurnal variation of nucleation mode particles was mainly influenced by new particle formation events,while the diurnal variation of Aitken mode particles correlated to the traffic emission and the growth process of nucleation mode particles.When the PRD region was controlled by a cold high pressure,conditions of low relative humidity,high wind speed and strong radiation are favorable for the occurrence of new particle formation(NPF) events.The frequency of occurrence of NPF events was 21.3% during the whole measurement period.Parameters describing NPF events,including growth rate(GR) and source rate of condensable vapor(Q),were slightly larger than those in previous literature.This suggests that intense photochemical and biological activities may be the source of condensable vapor for particle growth,even during winter in the PRD.
基金sponsored by National Key Development Program for Fundamental Research (973 Program) Project(Nos.2006CB403703 and 2006CB403701)
文摘Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6：00, 12：00, and 21：00 （Beijing Time） for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT-4） model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11675261 and 21403297the Scientific Research Foundation of Ludong University under Grant No LY2014010
文摘Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.
基金supported by National Natural Science Foundation of China (Grant No. 20977001,21025728)
文摘This study discusses the evolution of particle number size distribution during episodes of heavy pollution and new particle formation in the urban atmosphere of Beijing to quantify the effects of dynamic processes (coagulation and condensation) on the particle number size distribution.During a heavy-pollution event,an extremely low number concentration of 3-10 nm particles (on average 46 cm-3) was observed.This is because nucleation-mode particles were easily removed by strong coagulational scavenging of larger particles under this condition.In addition,a large condensation sink (on average 0.13 s-1) restrained nucleation,which is one of the major sources of nucleation-mode particles.Conversely,during a new-particle formation event,the small condensation sink (0.01 s-1) of precursor facilitated nucleation.At the same time,preexisting particles had little ability to scavenge newly formed particles (around 1 nm) and allowed them to grow to a detectable size (larger than 3 nm currently).We suggest that the effects of dynamic processes (coagulation and condensation) on particle size distribution should be stressed under some extreme conditions of the relatively polluted urban atmosphere in addition to traffic and meteorological factors.
文摘Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.
基金Supported by the National Key Research and Development Program of China(2016YFA0601701)Fengyun Application Pioneering Project(FY-APP-2021.0102)National High Technology Research and Development Program of China(2012AA120902).
文摘Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on emprical estimation of cloud particle number concentration(N_(c))in China,and scientific verification and quantitative identification criteria are urgently needed.In this study,the observations are from the Fast Cloud Droplets Probe,Rosemount ice detector(RICE),and Cloud Particle Imager(CP_(i))onboard a King Air aircraft during seven flights in 2018 and 2019 over central and eastern China.Based on this,the correlation among N_(c),the proportion of spherical particles(P_(s)),and the probability of icing(P_(i))in supercooled stratiform and cumulus-stratus clouds is statistically analyzed.Subsequently,this study proposes a method to identify SLW areas using N_(c) in combination with ambient temperature.The reliability of this method is evaluated through the true skill statistics(TSS)and threat score(TS)methods.Numerous airborne observations during the seven flights reveal a strong correlation among Nc,P_(s),and P_(i)at the temperature from 0 to−18°C.When Nc is greater than a certain threshold of 5 cm^(−3),there is always the SLW,i.e.,P_(i)and P_(s)are high.Evaluation results demonstrate that the TSS and TS values for Nc=5 cm^(−3)are higher than those for Nc<5 cm^(−3),and a larger Nc threshold(>5 cm^(−3))corresponds to a higher SLW identification hit rate and a higher SLW content.Therefore,Nc=5 cm^(−3)can be used as the minimum criterion for identifying the SLW in clouds at temperature lower than 0°C.The SLW identification method proposed in this study is especially helpful in common situations where aircraft are equipped with only Nc probes and without the CP_(i)and RICE.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 50578034, Grant No. 40475047）Shanghai Educational Development Foundation Titled ＂Shuguang Project＂, P.R. China （Grant No. 03SG30）.
文摘The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdoor concentrations were examined and discussed, and linear regression analysis was employed to correlate the indoor and outdoor concentrations. The diurnal cycles of indoor and outdoor particle concentrations of different particle size ranges all showed positive correlations between indoor and outdoor number concentrations, The I/O ratios of number concentrations varied with the increase of particle size in the range of 0.89 （±0.19） to 0.99 （±0.15）.
基金Supported by the National Natural Science Foundation of China(11522539,11735003,11775014,11375022)
文摘A fixed particle number BCS （FBCS） approach is formulated in the relativistic mean field （RMF） model. It is shown that the RMF＋FBCS model obtained can describe the weak pairing limit. We calculate the ground-state properties of the calcium isotopes ＆32-74Ca and compare the results with those obtained from the usual RMF＋BCS model. Although the results are quite similar to each other, we observe the interesting phenomenon that for ^54Ca, the FBCS approach can enhance the occupation probability of the 2p1/2 single particle level and slightly increases its radius, compared with the RMF＋BCS model. This leads to the unusual scenario that although ^54Ca is more bound with a spherical configuration, the corresponding size is not the most compact. We anticipate that such a phenomenon might happen for other neutron-rich nuclei and should be checked by further more systematic studies.
文摘Revised September 2013 by J.-F. Arguin LBNL）, L. Garren （Fermilab）, F. Krauss （Durham U.）, C.-J. Lin （LBNL）, S. Navas （U. Granada）, P. Richardson （Durham U.）, and T. Sjostrand （Lund U.）.
基金funded by the National Basic Research Program of China (2005CB422203, 2005CB422208)National Department Public Benefit Research Foundation (No.201009001)National Natural Science Foundation of China(Grant No. 41005065)
文摘Particle number size distribution from 10 to 10,000 nm was measured by a wide-range particle spectrometer （WPS-1000XP） at a downwind site north of downtown Lanzhou, western China, from 25 june to 19 July 2006. We first report the pollution level, diurnal variation of particle concentration in different size ranges and then introduce the characteristics of the particle formation processes, to show that the number concentration of ultrafine particles was lower than the values measured in other urban or suburban areas in previous studies, However, the fraction of ultrafine particles in total aerosol number concentration was found to be much higher. Furthermore, sharp increase of ultrafine particle concentration was frequently observed at noon. An examination of the diurnal pattern suggests that the burst of the ultrafine particles was mainly due to nucleation process. During the 25-day observation, new particle formation （NPF） from homogeneous nucleation was observed during 33% of the study period. The average growth rate of the newly formed particles was 4.4 nm/h, varying from 1.3 to 16,9 nm/h. The needed concentration of condensable vapor was 6.1 × 10^7 cm-3, and its source rate was 1.1× 10^6 cm-3 s 1. Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rate was 68.3%.
基金supported by the Fundamental Research Funds for the Central Universities,China (Grant Nos. 2017B17114 and B210202152)。
文摘We study the behaviors of thermalization in Fermi–Pasta–Ulam–Tsingou(FPUT) system with small number of particles using periodic boundary conditions. The total energy has initially equidistributed among some of the lowest frequency modes. The thermalization time t_(eq) depending on system's energy density ε scales as t_(eq) ∝ε^(-4) only within a certain range of nonlinearity. In this range of nonlinearity, energies can interchange between the initial excited modes and other modes continuously with time until reaching the thermalized state. With a further decreasing nonlinearity, a steeper growth than ε^(-4) will appear. In the very weakly nonlinear regime, energies on low frequency modes are found to be frozen on large time scales. Redistribution of mode energies happens through the resonances of high frequency modes.
文摘The total number of atmospheric particle (AP) is an important datum for planetary science and geoscience. Estimating entire AP number is also a familiar question in general physics. With standard atmosphere model, considering the number difference of AP caused by rough and uneven in the earth surface below, the sum of dry clean atmosphere particle is . So the whole number of AP including water vapor is . The rough estimation for the total number of AP on other planets (or satellites) in condensed state is also discussed on the base of it.
基金funding from CSIR(MLP100926)and SERB(DST,Govt.of India)(CRG//2023/001897-G)for this work.
文摘The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time distribution(RTD)in vertical single-screw reactors.The results will help in the selection of the right screw design that would help achieve the desired residence time,which is necessary for a reaction to happen.Experiments were conducted in three vertical screw reactors(having fixed shaft diameter)with varying dimensions using granular free-flowing powders of sodium chloride and silica with a mean particle size of∼25μm.RTD behavior was modeled using the radial particle velocities in the screw reactor's centrifugal field.Further,a method is proposed for estimating the axial dispersion coefficient of dry powders in such sheared flows using true and bulk densities of the powder and the screw shear rate.This dispersion coefficient is used in the axially dispersed plug flow model to describe the RTD behavior of screw reactors with acceptable accuracy.The theoretically predicted and experimentally obtained dispersion coefficients are found to be similar thereby confirming the suitability of the model.
基金supported by the National Natural Science Foundation of China (No. 50876013)
文摘Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to evaluate their effects on NO2, smoke and particle number emissions. The results showed that the application of the after-treatments increased the emission ratios of NO2/NOx significantly. The results of smoke emissions and particle number （PN） emissions indicated that both CRDPFs had sufficient capacity to remove more than 90% of total particulate matter （PM） and more than 97% of solid particles. However, the POC was able to remove the organic components of total PM, and only partially to remove the carbonaceous particles with size less than 30 nm. The negligible effects of POC on larger particles were observed due to its honeycomb structure leads to an inadequate residence time to oxidize the solid particles or trap them. The particles removal efficiencies of CRDPFs had high degree of correlations with the emission ratio of NO2/NOx. The PN emission results from two CRDPFs indicated that more NO2 generating in diesel oxidation catalyst section could obtain the higher removal efficiency of solid particles. However this also increased the risk of NO2 exposure in atmosphere.
基金CEFIC LRI,Natural Science Foundation of Jiangsu Province(No.BK20130186)the Fundamental Research Funds for the Central Universities(No.2013QNA18)for funding this project
文摘Novel applications of nanotechnology may lead to the release of engineered nanoparticles（ENPs）, which result in concerns over their potential environmental hazardous impact. It is essential for the research workers to be able to quantitatively characterise ENPs in the environment and subsequently to assist the risk assessment of the ENPs. This study hence explored the application of nanoparticle tracking system（NTA） to quantitatively describe the behaviour of the ENPs in natural sediment-water systems. The NTA allows the measurement of both particle number concentration（PNC） and particle size distribution（PSD） of the ENPs. The developed NTA method was applied to a range of gold and magnetite ENPs with a selection of surface properties. The results showed that the positively-charged ENPs interacted more strongly with the sediment than neutral and negatively-charged ENPs. It was also found that the citrate coated Au ENPs had a higher distribution percentage（53%） than 11-mercaptoundecanoic acid coated Au ENPs（20%） and citrate coated magnetite ENPs（21%）. The principles of the electrostatic interactions between hard（and soft） acids and bases（HSAB） are used to explain such behaviours; the hard base coating（i.e. citrate ions） will interact more strongly with hard acid（i.e. magnetite） than soft acid（i.e. gold）.The results indicate that NTA is a complementary method to existing approaches to characterise the fate and behaviour of ENPs in natural sediment.
