Effects of operational mode on particle size and number emissions from a biomass gasifier cookstove

Interest in the size distribution of particles emitted from biomass cookstoves stems from the hypothesis that exposure to ultrafine particles is more detrimental to human health than exposure to accumulation mode or other size regimes. Previous studies have reported that gasifier cookstoves emit smaller particles than other cookstove designs under steady operating conditions. In the present study, the number size distribution of particles emitted from a forced-air gasifier cookstove was measured at 1 Hz as the stove transitioned between several steady and transient operating modes. During normal operation, when the stove functioned as a top-lit updraft gasifier, the distribution was bimodal, with peaks at 10 nm and 40 nm, when a pot of water was on the stove. The distribution became unimodal with a peak at 10 nm when the pot was removed. Once the fuel bed had completely gasified and the secondary flame extinguished, the concentration of particles increased and the peak in number concentration shifted to approximately 80 nm. After refueling, when the stove operated as a conventional updraft gasifier, the peak in number concentration decreased to 10 nm. When the secondary flame extinguished a second time, the peak in number concentration increased to approximately 100 nm before decreasing to 20 nm during the char burn-out phase. These results demonstrate that changes in operational mode influence the combustion process and produce distinct changes in the size distribution and rate of particle emissions.

Copyright © 2018 American Association for Aerosol Research     

Impact of necking and overlapping on radiative properties of coated soot aggregates

The impact of necking and overlapping on the radiative properties of coated soot aggregates was investigated numerically by using the Discrete Dipole Approximation (DDA). The present study concerns the situations of slight overlapping between primary particles and small to moderate necking. The effects of overlapping, necking, and coating on the aggregate volume equivalent radius were presented. To show the overlapping effect, the radiative properties of aggregates consisting of N = 200 particles were evaluated with and without coating at refractive indices of m = 1.60 + 0.60i for the soot core and m = 1.46 for the coating material at four different wavelengths in the visible and near-infrared. The radiative properties of coated soot aggregates with three overlapping values of 0.05, 0.1, and 0.2 were calculated. In addition, the relationship between absorption cross-section and wavelength was illustrated at overlapping values of 0.05, 0.1, and 0.2 for uncoated and 25%, 50%, 75%, and 100% coated aggregates. As overlapping and necking increased, the calculated extinction, absorption, and scattering properties also increased in the visible and near-infrared regions. It was found that the volume equivalent radii of coated aggregates increased linearly with coating thickness when the necking values were 0.40–0.50.

Copyright © 2017 American Association for Aerosol Research     

Optical properties of non-absorbing mineral dust components and mixtures

Mineral dust is the second largest emission by mass into the atmosphere. Aerosol particles affect the radiative forcing budget by directly scattering and absorbing light, acting as cloud condensation and ice nuclei, and by providing surfaces for heterogeneous chemistry. Factors that affect how the particles scatter and absorb light include their composition, shape, size, and concentration. In this study, we characterize the most common components of mineral dust, quartz, and aluminosilicate clay minerals. In addition, we apply our results from calcite, feldspars, quartz, and aluminosilicate clay minerals to model the optical properties of Arizona test dust (ATD). We use cavity ring-down spectroscopy to measure the extinction cross sections of size-selected particles, electron microscopy to characterize the size selection, and Mie theory as well as the discrete dipole approximation as models. For quartz, the extinction cross sections can be well modeled assuming the particles are spheroids or spheres. For clay minerals, even spheroids fail to model the extinction cross sections, potentially due to orientation effects and lift forces in our flow system. In addition, aluminosilicate clay minerals experience weak size selectivity in the differential mobility analyzer. For ATD, the extinction cross sections are best modeled by treating each component of the mixture separately in terms of shape and size distribution. Through the application to ATD, our study outlines the procedure that can be used to model the optical properties of complex airborne dust mixtures.

Copyright © 2016 American Association for Aerosol Research     

Improved technique for measuring the size distribution of black carbon particles in liquid water

We developed an improved technique for measuring the size distribution of black carbon (BC) particles suspended in liquid water to facilitate quantitative studies of the wet deposition of BC. The measurement system, which consists of a nebulizer and a single-particle soot photometer, incorporates two improvements into the system that we developed earlier. First, we extended the upper limit of the detectable BC size from 0.9 μm to about 4.0 μm by modifying the photo-detector for measuring the laser-induced incandescence signal. Second, we introduced a pneumatic nebulizer (Marin-5) with a high extraction efficiency (～50.0%) that was independent of particle diameter up to 2.0 μm. For BC mass concentrations less than 70 μg L^?1, we experimentally showed that the diameters of BC particles did not appreciably change during the Marin-5 extraction process, consistent with theoretical calculations. Finally, we demonstrated by laboratory experiments that the size distributions of ambient BC particles changed little during their growth into cloud droplets under supersaturation of water vapor. Using our improved system, we measured the size distributions of BC particles simultaneously in air and rainwater in Tokyo during summer 2014. We observed that the size distributions of BC particles in rainwater shifted to larger sizes compared with those observed in ambient air, indicating that larger BC particles in air were removed more efficiently by precipitation.

Copyright © 2016 American Association for Aerosol Research     

On the use of the field Sunset semi-continuous analyzer to measure equivalent black carbon concentrations

This study describes a method to calculate equivalent black carbon (EBC) concentrations comparable to those obtained from optical filter-based EBC instrumentation from data obtained with a semi-continuous thermo-optical analyzer (Sunset Laboratory Inc., USA) without any need of instrument alterations or extra costs. A correction for the reflection of the Sunset analyzer laser beam by the walls of the sampling tube is introduced. EBC_Sunset concentrations obtained during two intensive campaigns in Prague (one in winter and one in summer) were compared also to EBC measured by an AE31 Aethalometer (EBC_aeth), an AE51 MicroAethalometer (EBC_micro), and a Multi Angle Absorption Photometer (EBC_MAAP). Good agreement was observed in both campaigns. The EBC_Sunset data were also corrected for loading effects in two ways—a simple loading correction and a total correction using data also from the MAAP and a nephelometer. The loading corrections gave similar results for EBC_Sunset and the aethalometer data except for the simple correction for summer EBC_Sunset data. The multiple scattering correction factors computed for EBC_Sunset agreed well with those calculated for EBC_aeth. The wall reflection correction for the Sunset analyzer data further improves the agreement between EBC_Sunset and EBC_MAAP.

Copyright © 2016 American Association for Aerosol Research     

Physical and chemical characterization of aerosol in fresh and aged emissions from open combustion of biomass fuels

Biomass burning (BB) emissions and their atmospheric oxidation products can contribute significantly to direct aerosol radiative forcing of climate. Limited knowledge of BB organic aerosol chemical and optical properties leads to large uncertainties in climate models. In this article, we describe the experimental setup and the main findings of a laboratory BB study aimed at comprehensive optical, physical, and chemical characterization of fresh and aged BB emissions. An oxidation flow reactor (OFR) was used to mimic atmospheric oxidation processes. The OFR was characterized in terms of OH? production rate, particle transmission efficiency, and characteristic lifetimes of condensible compounds. Emission factors (EFs) of main air pollutants (particulate matter, organic carbon [OC], elemental carbon [EC], carbon monoxide [CO], and nitrogen oxides [NO_x]) were determined for five globally and regionally important biomass fuels: Siberian (Russia), Florida (USA), and Malaysian peats; mixed conifer and aspen fuel from Fishlake National Forest, Utah, USA; and mixed grass and brush fuel representative of the Great Basin, Nevada, USA. Measured fuel-based EFs for OC ranged from 0.85?±?0.24 to 6.56?±?1.40?mg g^?1. Measured EFs for EC ranged from 0.02?±?0.01 to 0.16?±?0.01?mg g^?1. The ratio of organic mass to total carbon mass for fresh emissions from these fuels ranged from 1.04?±?0.04 to 1.34?±?0.24. The effect of OFR aging on aerosol optical properties, size distribution, and concentration is also discussed.

Copyright © 2018 American Association for Aerosol Research     

Evolution of maturity levels of the particle surface and bulk during soot growth and oxidation in a flame

We performed a study of the evolution of soot composition and fine structure, i.e., maturity level, in an atmospheric ethylene-air diffusion flame. We used laser-induced incandescence (LII) to provide information about maturity level of the bulk primary particle and X-ray photoelectron spectroscopy (XPS) to provide complementary information about particle-surface-maturity level. The results demonstrate that the bulk material and the particle surface evolve separately in the flame. Increased soot-maturity level is associated with increased long-range order of the particle fine structure. This increased order leads to an increase in the absorption cross-section in the visible and near-infrared and a shift of the absorption to longer wavelengths with increasing maturity level of the bulk particle. These trends result in a decrease in the dispersion exponent (?) and increase in the absorption cross-section scaling factor (?), as inferred from LII measurements. LII measurements demonstrate that bulk-maturity level increases with height-above-the-burner (HAB) until it reaches a plateau in the center of the flame at the maximum in the soot volume fraction. Bulk-maturity level only slightly decreases as soot is oxidized at larger HABs. Increased maturity level also leads to an increase in long-range sp² hybridization. XPS measurements of the sp²/defect ratio demonstrate an increase in soot surface-maturity level with increasing HAB, but the surface-maturity level increases more gradually with HAB than the bulk-maturity level. Whereas the bulk-fine-structure order decreases slightly in the oxidation region, the surface order decreases dramatically, indicating that oxidation occurs preferentially at the surface under these conditions.

Copyright © The Authors. Published with license by American Association for Aerosol Research     

Interfacial and conductive properties of liquid marbles coated with carbon black

Liquid marbles coated with carbon black are reported first. Carbon black is a strongly hydrophilic material; an energetic reasoning for coating water drops with the hydrophilic powder is supplied. The shape of marbles is well-described by the oblate spheroid model. The effective surface tension of the marbles is reported. The factors exerting an influence on the effective surface tension of marbles are discussed. Scaling laws governing the marbles' shape are presented. Electrical properties of liquid marbles coated with carbon black are reported first.     

涂覆导电碳黑的尼龙平纹布的电热性能研究

研究了涂覆导电碳黑尼龙平纹布(以下简称为导电布)的表面形貌、电热性能及其在采暖过程中的换热过程。结果表明,导电布的表面均匀附着着导电碳黑颗粒;导电布的升温速率快,且其表面温度和功率密度存在线性关系;以导电布为热源的封闭测试小室内温度均匀,辐射换热量占总换热量中的60%左右。     

Combining sensor-based measurement and modeling of PM2.5 and black carbon in assessing exposure to indoor aerosols

Accurate, cost-effective methods are needed for rapid assessment of traffic-related air pollution (TRAP). Typically, real-time data of particulate matter (PM) from portable sensors have been adjusted using data from reference methods such as gravimetric measurement to improve accuracy. The objective of this study was to create a correction factor or linear regression model for the real-time measurements of the RTI’s Micro Personal Exposure Monitor (MicroPEM?) and AethLab’s microAeth^® black carbon (AE51) sensor to generate accurate real-time data for PM_2.5 (PM_2.5RT) and black carbon (BC_RT) in Cincinnati metropolitan homes. The two sensors and an SKC PM_2.5 Personal Modular impactor were collocated in 44 indoor sampling events for 2?days in residences near major roadways. The reference filter-based analyses conducted by a laboratory included particle mass (SKC PM_2.5 and MicroPEM? PM_2.5) and black carbon (SKC BC); these methods are more accurate than real-time sensors but are also more cumbersome and costly. For PM_2.5, the average correction factor, a ratio of gravimetric to real time, for the MicroPEM? PM_2.5 and SKC PM_2.5 utilizing the PM_2.5RT and was 0.94 and 0.83, respectively, with a coefficient of variation (CV) of 84% and 52%, respectively; the corresponding linear regression model had a CV of 54% and 25%. For BC, the average correction factor utilizing the BC_RT and SKC BC was 0.74 with a CV of 36% with the associated linear regression model producing a CV of 56%. The results from this study will help ensure that the real-time exposure monitors are capable of detecting an estimated PM_2.5 after an appropriate statistical model is applied.

Copyright © 2019 American Association for Aerosol Research     

Development of novel hybrid materials from polylactic acid and nano-silver coated carbon black with distinct antimicrobial and electrical properties

This work aims to prepare nanosilver coated carbon black via benzoxazine oxidation as a filler for polylactic acid (PLA) to produce novel hybrid materials with improved electrical and antimicrobial properties. Nanosilver coated carbon black exhibited antimicrobial activity against S.aureus, B.subtilis, M.luteus, E.coli, P.aeruginosa and C.albicans. It was found that the nanosilver coated carbon black (10CB-Ag) was the most effective filler since it showed largest inhibition zones. Thermogravimetric analysis (TGA) showed that the silver content in 10CB-Ag was 5.68% by weight. The hybrid materials of PLA with uncoated carbon black and nanosilver coated carbon black fillers were prepared by injection molding. The optimal composition of the prepared hybrid materials was found to be 15 phr of nanosilver coated carbon black in PLA (15AgCB-PLA). This material showed quite good properties, e.g. tensile strength of 50 MPa, % elongation at break of 1.68 and electrical conductivity of 2.78 × 10^?9 S?m^?1. Moreover, it exhibited the S. aureus inhibition of about 99%. This work revealed the possibility of using this material for anti-electrostatic and antimicrobial applications.     

碳包覆氧化锌材料在锌镍二次电池中的应用研究

为了提高锌镍二次电池的电化学性能,将高能球磨法制备的碳包覆氧化锌(ZnO/C)材料作为负极活性物质,与纯氧化锌比,碳包覆氧化锌作为负极活性物质的电池,具有更低的充电平台电压以及更高的放电平台电压,并能有效减小电极的欧姆电阻与反应电阻,显著提高了锌镍电池的循环性能。因此,碳包覆后的氧化锌负极材料能够有效的提高锌镍二次电池的电化学性能。     

炭黑技术讲座 第2讲炭黑的结构和性质

炭黑的结构和性质决定其使用性能，全面了解炭黑的结构和性质对合理应用炭黑十分重要。     

碳纳米管炭黑天然橡胶复合材料的制备与性能研究

碳纳米管以其特殊的结构与优异的性能成为橡胶补强的理想填料。本文中我们采用两种不同牌号的碳纳米管(分别为Flotube 7000、9011)与炭黑N660作为实验原料,制备了碳纳米管/炭黑/天然橡胶复合材料,并对其性能进行了探讨。结果发现：碳纳米管的加入能明显提高复合材料的定伸应力,具有一维取向排列且长径比较大的Flotube 7000(以下简称7000)对力学性能的提高程度最大。且我们将碳纳米管7000、9011分别与炭黑N660并用,对于提高复合材料的导热性能并没有如我们预期的一样存在所谓的“叠加关系”甚至是“协同效应”,而是对于提高复合材料导热有着一定的“负协同效应”。     

Formation and evolution of the carbon black network in polyethylene/carbon black composites: Rheology and conductivity properties

We report a detailed investigation on the effect of carbon black (CB) morphology on network formation and evolution in high‐density polyethylene/CB composites. There were three types of networks in our study, the electrical network in the solid state and the electrical and rheological networks in the melt state. The evolution of the network in the polymer melt was traced by simultaneous electrical resistivity (R) and dynamic rheology testing. An oscillation strain sweep was used to investigate the network stability with a large strain. We found that with high‐structure CB with a branched morphology, it was easier to form a filler–polymer or filler–filler network than with low‐structure CB with a spherical morphology in the composite melt. The high‐structure CB network was more stable with a large strain compared to the low‐structure one. Meanwhile, the low‐structure CB aggregates had stronger capability of movement and re‐aggregation in the polymer melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39953.     

二次盐水中总有机碳的测定

介绍采用Multi n/c-2100检测仪,利用高温催化燃烧氧化-非色散红外探测原理测定盐水中的总有机碳的方法以及测定中的注意事项。     

Structure and electrical properties of carbon black

The incorporation of conductive particles into a polymer matrix modifies fundamentally the electrical conductivity of the composite. The importance of carbon black structure on other mechanical and rheological properties is also well documented. Besides common techniques, like DBP-absorption and CDBP-absorption, void-volume, determined by the measurement of the volume of a given quantity of carbon black under a given pressure, has been considered as a more absolute technique. The present work considers the void-volume technique under a broader angle. The evolution of the volume of a given carbon black weight under increasing pressure as well as the evolution of the electrical resistivity is recorded and analysed.     

西安城市主干道黑碳排放特征及源解析

本文以西安不同功能区黑碳浓度为研究对象,探讨西安市城市道路交通碳排放的问题。通过AE-51型微型黑碳仪对长乐东路黑碳质量浓度进行质量检测,揭示西安市典型道路黑碳排放特征及源解析。结果表明,黑碳每日浓度在早高峰为3.70～7.57μg·m^-3及晚高峰为2.89～7.00μg·m^-3,明显大于非高峰期(2.03～5.86μg·m^-3),且工作日浓度(4.38～10.82μg·m^-3)高于休息日浓度(3.28～8.58μg·m^-3);西安市不同年份下,大气中黑碳浓度有较大变化,大致呈现出逐年下降的变化规律,最高浓度出现在2003年(16μg·m^-3);最低浓度发生在2019年(3.66μg·m^-3);与其他城市相较,西安黑碳浓度属于中等水平,黑碳排放浓度受车流量、森林覆盖率、人均生产总值等社会指标影响。可见,合理规划和适当限制机动车使用频率是缓解城市空气污染的有效途径。     

Investigations of the electrochemical properties of activated carbon and carbon black

Potentiometric studies have been carried out on activated carbon and carbon black immersed in aqueous solutions of electrolytes. The samples studied were subjected to various modifying treatments: demineralization, oxidation in liquid and gaseous phases, saturation with hydrogen, and degassing. It was found that the potential of carbon increases during contact with the electrolyte solution; the amount of anions in the solution decreases with a simultaneous rise of the solution pH. Measurements of the potentials of the carbon samples of large specific surface area immersed in buffer solutions or solutions of established pH have shown that in the range 2.0 < pH < 7.00 the potential of the carbon material decreases with increasing pH. It was also found that the potential of the carbon powder electrode depends on the kind and concentration of the electrolyte solution as well as on the modification of the carbon surface.