Mixing state of individual carbonaceous particles during a severe haze episode in January 2013, Nanjing,China

Chemical composition, hourly counts, and sizes of atmospheric carbonaceous particles were measured to investigate their mixing state on clear and hazy days. 623,122 carbonaceous particles with sizes 0.2–2.0 μm was analyzed using a single-particle aerosol mass spectrometer from 1st to 17th January 2013. Particle types included biomass/biofuel burning particles (biomass), element carbon (EC-dominant) particles that were also mixed with biomass/biofuel burning species (EC-biomass) or secondary species (EC-secondary), organic carbon (OC), internally mixed OC and EC (OCEC), ammonium-containing (ammonium) and sodium-containing (sodium) particles. On clear days the top ranked carbonaceous particle types were biomass (48.2%), EC-biomass (15.7%), OCEC (11.1%), and sodium (9.6%), while on hazy days they were biomass (37.3%), EC-biomass (17.6%), EC-secondary (16.6%), and sodium (12.7%). The fractions of EC-secondary, ammonium (10%), and sodium particle types were elevated on hazy days. Numbers of EC-secondary particles were more than four times those on clear days (4.1%). Thus, carbonaceous particles mixed with ammonium, nitrate and sulfate during aging and transport, enhancing their light extinction effects and hygroscopic growth under high relative humidity on hazy days, further reducing visibility. Our real-time single-particle data showed that changes to mixing state had a significant impact on light extinction during haze events in Nanjing.     

Particle size distribution and characteristics of polycyclic aromatic hydrocarbons during a heavy haze episode in Nanjing,China

A heavy haze episode caused by agricultural burning occurred in Nanjing from November 7 to November 8, 2009. PM₁₀ samples were collected on normal and hazy days from November 1 to November 14, 2009 at both city and suburban sites of Nanjing. Sixteen PAHs were measured during the day and at night. The results show that the concentrations of the particles were as high as 579.55 and 573.43 μg/m³ during the haze episode at the city and suburban sites, respectively, 3–4 times higher than those on a normal day. The proportions of fine particles during the haze episode were also higher than those on a normal day. The changes in the concentrations of PAHs were in accordance with the concentrations of the particles. High-molecular-weight PAHs composed approximately 80% of the total PAHs on normal days and during the haze episode. The concentration of PAHs in fine fractions significantly increased during the haze episode, and this increase was most obvious at night at the city site. The proportion of total carcinogenic PAHs in fine particles was relatively high during the haze episode at both sampling sites, particularly at night at the city site.     

Particle size distribution and characteristics of polycyclic aromatic hydrocarbons during a heavy haze episode in Nanjing,China

A heavy haze episode caused by agricultural burning occurred in Nanjing from November 7 to November8,2009.PM₁₀ samples were collected on normal and hazy days from November 1 to November 14,2009 at both city and suburban sites of Nanjing.Sixteen PAHs were measured during the day and at night.The results show that the concentrations of the particles were as high as 579.55 and 573.43 μg/m³ during the haze episode at the city and suburban sites,respectively,3-4 times higher than those on a normal day.The proportions of fine particles during the haze episode were also higher than those on a normal day.The changes in the concentrations of PAHs were in accordance with the concentrations of the particles.Highmolecular-weight PAHs composed approximately 80% of the total PAHs on normal days and during the haze episode.The concentration of PAHs in fine fractions significantly increased during the haze episode,and this increase was most obvious at night at the city site.The proportion of total carcinogenic PAHs in fine particles was relatively high during the haze episode at both sampling sites,particularly at night at the city site.     

Chemical characteristics and source apportionment of PM_(10) during a brown haze episode in Harbin, China

This study investigates the correlation between PM 10 and meteorological factors such as wind speed, atmospheric visibility, dew point, relative humidity, and ambient temperature during a brown haze episode. In order to identify the potential sources of PM 10 during brown haze episode, respirable particulate matter (PM 10 ) was collected during both non-haze days and haze days and further analyzed for metallic elements, ionic species, and carbonaceous contents. Among them, ionic species contributed 45-64% t...     

Effect of COVID-19 lockdown on the characterization and mixing state of carbonaceous particles in the urban atmosphere of Liaocheng,the North China Plain

To investigate the effect of COVID-19 control measures on aerosol chemistry, the chemical compositions, mixing states, and formation mechanisms of carbonaceous particles in the urban atmosphere of Liaocheng in the North China Plain (NCP) were compared before and during the pandemic using a single particle aerosol mass spectrometry (SPAMS). The results showed that the concentrations of five air pollutants including PM_2.5, PM₁₀, SO₂, NO₂, and CO decreased by 41.2%–71.5% during the pandemic compared to those before the pandemic, whereas O₃ increased by 1.3 times during the pandemic because of the depressed titration of O₃ and more favorable meteorological conditions. The count and percentage contribution of carbonaceous particles in the total detected particles were lower during the pandemic than those before the pandemic. The carbonaceous particles were dominated by elemental and organic carbon (ECOC, 35.9%), followed by elemental carbon-aged (EC-aged, 19.6%) and organic carbon-fresh (OC-fresh, 13.5%) before the pandemic, while EC-aged (25.3%), ECOC (17.9%), and secondary ions-rich (SEC, 17.8%) became the predominant species during the pandemic. The carbonaceous particle sizes during the pandemic showed a broader distribution than that before the pandemic, due to the condensation and coagulation of carbonaceous particles in the aging processes. The relative aerosol acidity (R_ra) was smaller before the pandemic than that during the pandemic, indicating the more acidic particle aerosol during the pandemic closely related to the secondary species and relative humidity (RH). More than 95.0% and 86.0% of carbonaceous particles in the whole period were internally mixed with nitrate and sulfate, implying that most of the carbonaceous particles were associated with secondary oxidation during their formation processes. The diurnal variations of oxalate particles and correlation analyses suggested that oxalate particles before the pandemic were derived from aqueous oxidation driven by RH and liquid water content (LWC), while oxalate particles during the pandemic were originated from O₃-dominated photochemical oxidation.     

Mixing of cohesive particles in a shear cell

This paper discusses two series of experiments performed in a shear cell device with six different amounts of silicone oils and using 2-mm soda lime beads as the granular materials. The first series of experiments were mixing experiments, and the developments of mixing layer thicknesses were measured. The second series of experiments had the same experimental conditions as the first series but used different combinations of colored particles. In the second series of experiments, the motions of granular materials were recorded by a high-speed camera. Using the image processing technology and particle tracking method, the positions and velocities of particles were measured. The self-diffusion coefficient could be found from the history of the particle displacements.     

Chemical characteristics of PM2.5 during haze episodes in the urban of Fuzhou,China

Atmospheric fine particles (PM_2.5) were collected in this study with middle volume samplers in Fuzhou, China, during both normal days and haze days in summer (September 2007) and winter (January 2008). The concentrations, distributions, and sources of polycyclic aromatic hydrocarbons (PAHs), organic carbon (OC), elemental carbon (EC), and water soluble inorganic ions (WSIIs) were determinated. The results showed that the concentrations of PM_2.5, PAHs, OC, EC, and WSIIs were in the orders of haze > normal and winter > summer. The dominant PAHs of PM_2.5 in Fuzhou were Fluo, Pyr, Chr, BbF, BkF, BaP, BghiP, and IcdP, which represented about 80.0% of the total PAHs during different sampling periods. The BaPeq concentrations of ∑PAHs were 0.78, 0.99, 1.22, and 2.43 ng/m³ in summer normal, summer haze, winter normal, and winter haze, respectively. Secondary pollutants (SO₄^2?, NO₃^?, NH₄⁺, and OC) were the major chemical compositions of PM_2.5, accounting for 69.0%, 55.1%, 63.4%, and 64.9% of PM_2.5 mass in summer normal, summer haze, winter normal, and winter haze, respectively. Correspondingly, secondary organic carbon (SOC) in Fuzhou accounted for 20.1%, 48.6%, 24.5%, and 50.5% of OC. The average values of nitrogen oxidation ratio (NOR) and sulfur oxidation ratio (SOR) were higher in haze days (0.08 and 0.27) than in normal days (0.05 and 0.22). Higher OC/EC ratios were also found in haze days (5.0) than in normal days (3.3). Correlation analysis demonstrated that visibility had positive correlations with wind speed, and negative correlations with relative humidity and major air pollutants. Overall, the enrichments of PM_2.5, OC, EC, SO₄^2?, and NO₃^? promoted haze formation. Furthermore, the diagnostic ratios of IcdP/(IcdP + BghiP), IcdP/BghiP, OC/EC, and NO₃^?/SO₄^2? indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Fuzhou.     

Mixing and segregation assessment of bi-disperse solid particles in a double paddle mixer

A double paddle blender's flow patterns and mixing mechanisms were analyzed using discrete element method (DEM) and experiments. The mixing performance of this type of the blender containing bi-disperse particles has been rarely studied in the literature. Plackett-Burman design of experiments (DoE) methodology was used to calibrate the DEM input parameters. Subsequently, the impact of the particle number ratio, vessel fill level, and paddle rotational speed on mixing performance was investigated using the calibrated DEM model. The mixing performance was assessed using relative standard deviation and segregation intensity. Mixing performance was significantly affected by the paddle rotational speed and particle number ratio. Moreover, the Peclet number and diffusivity coefficient were used to evaluate the mixing mechanism in the blender. Results revealed that the diffusion was the predominant mixing mechanism, and the best mixing performance was observed when the diffusivity coefficients of 3 mm and 5 mm particles were almost equal.     

Composition of carbohydrates,surfactants, major elements and anions in PM2.5 during the 2013 Southeast Asia high pollution episode in Malaysia

Haze episodes have become a major concern in Malaysia over the past few decades and have an increasingly important impact on the country each and every year. During haze episodes from biomass burning in Southeast Asia, particularly from Sumatra, Indonesia, particulate matter PM_2.5 is found to be one of the dangerous sources of airborne pollution and is known to seriously affect human health. This study determines the composition of carbohydrates (as levoglucosan), surfactants, major elements, and anions in PM_2.5 during a 2013 haze episode. PM_2.5 samples were collected from Universiti Kebangsaan Malaysia, Bangi, using a high volume sampler during a seven-day monitoring campaign during the peak of that year’s haze episode. PM_2.5 concentrations ranged between 14.52 and 160.93 μg/m³, exceeding the 2005 WHO air quality guidelines for PM_2.5 (25 μg/m³ for 24-h mean). The patterns for levoglucosan, surfactants, major elements, and anionic compositions were proportional to the PM_2.5 concentrations. Changes in PM_2.5 observed on days 3 and 4 were influenced by a combination of meteorological factors, which substantiate the theory that such factors play a pivotal role in haze episodes.     

Characteristics of black carbon aerosol in Jiaxing,China during autumn 2013

We conducted measurements of black carbon (BC) aerosol in Jiaxing, China during autumn from September 26 to November 30, 2013. We investigated temporal and diurnal variations of BC, and its correlations with meteorological parameters and other major pollutants. Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m³, with an average of 5.1 μg/m³. The diurnal variation of BC exhibited a bimodal distribution, with peaks at 07:00 and 18:00. The morning peak was larger than the evening peak. The mass percentages of BC in PM_2.5 and PM₁₀ were 7.1% and 4.8%, respectively. The absorption coefficient of BC was calculated to be 44.4 Mm⁻¹, which accounted for 11.1% of the total aerosol extinction. BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m³ during the measurement period. Correlation analysis indicated that the main sources of BC were motor vehicle exhaust, and domestic and industrial combustion.     

Characteristics of black carbon aerosol in Jiaxing,China during autumn 2013

We conducted measurements of black carbon（BC） aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m³,with an average of 5.1 μg/m³.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM_2.5 and PM₁₀ were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm^-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m³ during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.     

Comparison of aerosol characteristics during haze periods over two urban agglomerations in China using CALIPSO observations

Using CALIPSO (cloud-aerosol lidar and infrared pathfinder satellite observation) vertical observation data during haze periods from January 2007 to December 2008, we analyzed differences in aerosol characteristics near the surface, as well as in the middle troposphere between the Beijing–Tianjin–Hebei metropolitan region (Area A) and the Yangtze River Delta region (Area B) in China. One significant difference was that haze pollution in Area A was related to local and non-local aerosols, while in Area B it was related to local anthropogenic sources. In all seasons apart from autumn, aerosol pollution in Area A was more severe than in Area B, both near the surface and at higher altitudes. In Area A, non-spherical aerosols were dominant from 0 to 4 km in spring, summer, and winter; while in autumn, there were considerably high numbers of non-spherical aerosols below 0.5 km, and near-spherical aerosols from 0.5 to 4 km. In Area B, both near-spherical and non-spherical aerosols were common in all seasons. Moreover, aerosols with attenuated color ratios of 0–0.2 were more common in all seasons in Area A than in Area B, indicating that fine particle pollution in Area A was more serious than in Area B. Finally, relatively large aerosols linked to gravity settling appeared more frequently near the surface in Area A than in Area B.     

Dynamics of two elliptical particles sedimentation in a vertical channel: chaotic state

The LB-DF/FD method derived from the Lattice Boltzmann Method and direct forcing/fictitious domain method is used to numerically investigate the dynamics and interaction of two elliptical particles settling in an infinitely long channel. One particle (EP0) is initially kept horizontal (major axis perpendicular to sedimentation) for all simulations while the other's (EP1) orientation is varied. It is found that if EP1strays away from horizontality, the particles undergo transitions from a steady state to reach a chaotic state. Furthermore, there are two distinct chaotic states for the particle motion when EP1 orientation is varied, in which a turning point is observed to distinguish the two states.     

Mixing and segregation of solid particles in a conical spouted bed: Effect of particle size and density

In this work, the mixing and segregation of binary mixtures of particles with different sizes and densities in a pseudo-2D spouted bed were studied experimentally. A binary mixture of solid particles including sand, gypsum, and polyurethane was used. To determine the particles mass fraction, and their mixing and segregation in the bed, an image-processing technique was developed and used. Important hydrodynamic parameters, such as the axial and radial segregation profiles of the solid particles, were measured. The effects of air velocity, particle size, and particle mass fraction were also evaluated. The flow regime in the spouted bed and the time required for reaching the equilibrium state of the solid particles were discussed. The results showed that the segregation of solid particles and the time to equilibrium both decreased when the air velocity increased to much larger than the minimum spouting velocity. The axial segregation increased with the diameter ratio of the particles. Upon completion of the test, coarse particles were concentrated mainly in the spout region, while fine particles were aggregated in the annulus region. Examination of the flow pattern in the spouted bed showed that the particles near the wall had longer flow paths, while those near the spout region had shorter flow paths.     

Flow characteristics of mixed particles with a simulated cold state in moving bed reactor

The funnel flow of high-temperature circulating ash and coal in moving bed with height restrictions directly influences the efficiency of coal pyrolysis and scale-up design of reactor. It is one of the technical bottlenecks in the use of moving bed. In order to provide data support for the particle flow and pyrolysis model close to the actual working conditions in the future, this study describes the flow characteristics of solid–solid mixed particles in a cold two-dimensional moving bed. The results indicate that flow characteristics of mixed particles in the quartz sand–coal system are better than those in the cold circulating ash–coal system. The optimized conditions were obtained, the insert half angle is 20° and a heat carrier to coal ratio of 6:1. As the mixture progressed downstream, secondary separation of the heat carrier and coal become apparent. Furthermore, mixture residence time has been investigated to explore the relationship between regional residence time and to predict accurately the actual pyrolysis progress in pyrolyzer.     

Modeling study of a severe aerosol pollution event in December 2013over Shanghai China:An application of chemical data assimilation

This study focuses on the importance of initial conditions to air-quality predictions.We ran assimilation experiments using the WRF-Chem model and grid-point statistical interpolation(GSI),for a 9-day severe particulate matter pollution event that occurred in Shanghai in December 2013.In this application,GSI used a three-dimensional variational approach to assimilate ground-based PM2.5 observations into the chemical model,to obtain initial fields for the aerosol species.In our results,data assimilation significantly reduced the errors when compared to a simulation without assimilation,and improved forecasts of PM_(2.5)concentrations.Despite a drop in skill directly after the assimilation,a positive effect was present in forecasts for at least 12-24 h,and there was a slight improvement in the 48-h forecasts.In addition to performing well in Shanghai,the verification statistics for this assimilation experiment are encouraging for most of the surface stations in China.     

Deformation, stress state and thermodynamic force for a growing void in an elastic–plastic material

The growth of a spherical void in an elastic–plastic body, subjected to external pressure or tension and a gas pressure as well as a surface stress at the void surface, is investigated. The deformation, strain and stress state in the full body is presented. In addition, the local and global energy terms are calculated. Finally the total thermodynamic force on the void surface as well as the total dissipation are evaluated and compared allowing the calculation of the mechanical contribution to void growth due to diffusion of vacancies generated by plastification or irradiation.     

Characteristics of organic and elemental carbon in atmospheric fine particles in Tianjin, China

PM2.5 samples were collected at urban, industrial and coastal sites in Tianjin during winter, spring and summer in 2007. Concentrations of elemental carbon （EC） and organic carbon （OC） were analyzed using the IMPROVE thermal-optical reflectance （TOR） method. Both OC and EC exhibited a clear seasonal pattern with higher concentrations observed in the winter than in the spring and summer, due to cooperative effect of changes in emission rates and seasonal meteorology. The concentrations of carbonaceous species were also influenced by the local factors at different sampling sites, ranking in the order of industrial〉 urban 〉 coastal during winter and spring. In the summer, the port emissions, enriched with EC, had a significant impact on carbonaceous aerosols at the coastal site. Total carbonaceous aerosol accounted for 40.0% in winter, 33.8% in spring and 31.4% in summer of PM2.5 mass. Good correlation （R = 0.84-0.93） between OC and EC indicated that they had common dominant sources of combustion such as coal burning and traffic emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, the elevated OC/EC ratios being found in the winter. The estimated secondary organic carbon （SOC） accounted for 46.9%, 35.3% and 40.2% of the total OC in the winter, spring and summer, respectively, indicating that SOC may be an important contributor to fine organic aerosol in Tianjin.