Search

Both the size and mixing state of black carbon (BC)-containing aerosols are crucial in estimating the environmental, health and climate impacts of BC. Traffic emissions are a major global source of BC; however, parameterization of BC mass size distributions and mixing states associated with traffic remains lacking due to its dependence on vehicle types and driving conditions. To investigate BC mass size distributions and mixing states associated with traffic emissions, a field campaign was conducted in the Guangzhou urban area during winter, which used a system coupling a differential mobility analyzer (DMA) and a single-particle soot photometer (SP2) to measure BC mass size distributions in the range of 100 to 700 nm. The resolved primary organic aerosols were hydrocarbon-like organic aerosols (HOA) and cooking-like organic aerosols (COA), as well as refractory BC (rBC), which was detected by the DMA–SP2 and correlated highly with HOA (R2=0.88), confirming that traffic emissions are the dominant source of atmospheric BC during the observations. The BC mass size distribution was found to be best fitted by a lognormal distribution, with a geometric mean (Dg,BC) of 258±16 nm, varying between 200 and 300 nm. During daytime, active formation of secondary nitrate and organic aerosols was observed, but it had little effect on the variations of BC mass size distributions. Further analyses revealed that Dg,BC was moderately correlated with rBC / HOA (R2=0.41) in a linear form of Dg,BC=34×rBC/HOA+177, demonstrating that the BC content of traffic emissions significantly impacts the BC mass size distributions. In addition, the size-dependent fractions of BC-containing aerosols in all types of aerosols (fBCc) and the fraction of identified externally mixed (bare/thinly coated) BC particles in all BC-containing aerosols (fext) were also characterized. It was found that the daytime secondary aerosol formation reduced both fBCc and fext, with the decrease in fext being more pronounced for larger particles, possibly due to the higher relative coating thickness. Variations in fext during nighttime were mainly controlled by the emission conditions. For example, fext for 600 nm particles decreased from 0.82 to 0.46 as rBC / HOA increased from 1 to 3.5, while the mass ratios of secondary aerosols to rBC varied little, demonstrating that the BC content also significantly affects the mixing states of freshly emitted BC from traffic emissions. This study suggests that BC content can be used as the key factor to parameterize both the BC mass size distribution and mixing states from traffic emissions, which warrants future comprehensive investigation. In addition, other sources such as biomass burning and coal combustion also contribute substantially to BC emissions, and it was important to investigate whether BC content of other major BC sources than traffic is also important in determining BC mass size distributions and mixing states. Overall, results of this study have significant implications for accurate representation of BC from different sources when modeling the impacts of BC.

Emission controls have substantially brought down aerosol pollution in China; however, aerosol mass reductions have slowed down in recent years in the Pearl River Delta (PRD) region, where secondary organic aerosol (SOA) formation poses a major challenge for air quality improvement. In this study, we characterized the roles of SOA in haze formation in urban Guangzhou in the PRD using year-long aerosol mass spectrometer measurements for the first time and discussed possible pathways of SOA formations. On average, organic aerosols (OA) contribute dominantly (50 %) to nonrefractory submicron aerosol mass (NR-PM1). The average mass concentration of SOA (including by less- and more-oxidized OA, LOOA and MOOA) contributed most to NR-PM1, reaching about 1.7 times that of primary organic aerosols (POA, including hydrocarbon-like and cooking-related OA) and accounting for 32 % of NR-PM1, even more than sulfate (22 %) and nitrate (16 %). Seasonal variations of NR-PM1 revealed that haze-formation mechanisms differed much among distinct seasons. Sulfate mattered more than nitrate in fall, while nitrate was more important than sulfate in spring and winter, with SOA contributing significantly to haze formations in all the seasons. Daytime SOA formation was weak in winter under low oxidant levels and air relative humidity, whereas prominent daytime SOA formation was observed in fall, spring and summer almost on a daily basis, suggesting important roles of photochemistry in SOA formations. Further analysis showed that the coordination of gas-phase photochemistry and subsequent aqueous-phase reactions likely played significant roles in quick daytime SOA formations. Obvious nighttime SOA formations were also frequently observed in spring, fall and winter, and it was found that daytime and nighttime SOA formations together had resulted in the highest SOA concentrations in these seasons and contributed substantially to severe haze formations. Simultaneous increases in nitrate with SOA after sunset suggested the important roles of NO3 radical chemistry in nighttime SOA formations, and this was further confirmed by a continuous increase in the NO+ / NO2+ fragment ratio that related to measured particulate nitrate after sunset. The findings of this study have promoted our understanding of haze pollution characteristics of the PRD and laid down future directions for investigations of SOA-formation mechanisms in urban areas of southern China that share similar emission sources and meteorological conditions.

Secondary organic aerosols (SOAs) account for a large fraction of atmospheric aerosol mass and play significant roles in visibility impairment by scattering solar radiation. However, comprehensive evaluations of SOA scattering abilities under ambient relative humidity (RH) conditions on the basis of field measurements are still lacking due to the difficulty of simultaneously direct quantifications of SOA scattering efficiency in dry state and SOA water uptake abilities. In this study, field measurements of aerosol chemical and physical properties were conducted in winter in Guangzhou (lasting about 3 months) using a humidified nephelometer system and aerosol chemical speciation monitor. A modified multilinear regression model was proposed to retrieve dry-state mass scattering efficiencies (MSEs, defined as scattering coefficient per unit aerosol mass) of aerosol components. The more oxidized oxygenated organic aerosol (MOOA) with an O/C ratio of 1.17 was identified as the most efficient light scattering aerosol component. On average, 34 % mass contribution of MOOA to total submicron organic aerosol mass contributed 51 % of dry-state organic aerosol scattering. The overall organic aerosol hygroscopicity parameter κOA was quantified directly through hygroscopicity closure, and hygroscopicity parameters of SOA components were further retrieved using a multilinear regression model by assuming hydrophobic properties of primary organic aerosols. The highest water uptake ability of MOOA among organic aerosol factors was revealed with κMOOA reaching 0.23, thus further enhancing the fractional contribution of MOOA in ambient organic aerosol scattering. In particular, the scattering abilities of MOOA were found to be even higher than those of ammonium nitrate under RH of %, which was identified as the most efficient inorganic scattering aerosol component, demonstrating that MOOA had the strongest scattering abilities in ambient air (average RH of 57 %) during winter in Guangzhou. During the observation period, secondary aerosols contributed dominantly to visibility degradation (∼70 %), with substantial contributions from MOOA (16 % on average), demonstrating significant impacts of MOOA on visibility degradation. The findings of this study demonstrate that more attention needs to be paid to SOA property changes in future visibility improvement investigations. Also, more comprehensive studies on MOOA physical properties and chemical formation are needed to better parameterize its radiative effects in models and implement targeted control strategies on MOOA precursors for visibility improvement.

The aerosol mixing state is a crucial physical-chemical property that affects their optical properties and cloud condensation nuclei (CCN) activity. Multiple techniques are commonly employed to determine aerosol mixing states for various applications, and comparisons between these techniques provide insights of the variations in aerosol chemical and physical properties. These techniques include size-resolved CCN activity measurements using a system with CCN counter (CCNC) coupled with a differential mobility analyzer (DMA), a Humidified/Volatility Tandem differential mobility analyzer (H/V-TDMA) which measures aerosol hygroscopicity/volatility distributions, and a single particle soot photometer (SP2) which directly quantifies black carbon (BC) mixing states. This study provides a first time intercomparisons of aerosol mixing state parameters obtained through simultaneous measurements of a DMA-CCNC, a H/VTDMA and a DMA-SP2. The impact of primary aerosols emissions and secondary aerosol formations on the aerosol mixing states and intercomparison results were analyzed. The results showed that differences in mixing state parameters measured by different techniques varied greatly under different conditions. The V-TDMA and DMA-SP2 measurements showed that the non-volatile population identified by the V-TDMA was mainly contributed by BC-containing aerosols. The HTDMA and DMA-SP2 measurements indicated that a substantial proportion of nearly hydrophobic aerosols were not contributed from BC-containing aerosols, but likely originated from fossil fuel combustion and biomass burning emissions. Synthesized comparison results between DMA-CCNC, HTDMA and DMA-SP2 measurements revealed that some of the nearly hydrophobic BC-free particles were CCN-inactive under supersaturated conditions, likely from fossil combustion emissions, while others were CCN-active under supersaturated conditions linked to biomass burning emissions. Fossil fuel combustion-emitted BC-containing aerosols tended to be more externally mixed with other aerosol compositions compared to those emitted from biomass burning activities. These results highlight significant disparities in the mixing states as well as physiochemical properties between aerosol originated from fossil fuel combustion and biomass burning. The formation of secondary nitrate and organic aerosols exerted significant impacts on variations in aerosol mixing states, generally enhancing aerosol hygroscopicity and volatility, while reducing differences in mixing state parameters derived from different techniques, resulting in a reduction in aerosol heterogeneity. The variations in BC-free particle number fractions showed that secondary aerosols tended to form more quickly on BC-free particles than on BC-containing particles. Further comparison of mixing state parameters revealed that the two resolved SOA factors in this study exhibited remarkably different physical properties, indicating that they were likely formed through different pathways. These findings suggest that intercomparisons among aerosol mixing states derived from different techniques can provide deeper insight into aerosol physical properties and how they are impacted by secondary aerosol formation, aiding the investigation of secondary aerosol formation pathways.

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu2 Se hexagonal nanosheets@Co3 Se4 nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu2 Se and the remarkable cycling stability of Co3 Se4 , Cu2 Se@Co3 Se4 can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu2 Se@Co3 Se4 electrode displays high specific capacitance of 1005 F g-1 at 1 A g-1 with enhanced rate capability (56 % capacitance retention at 10 A g-1 ), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g-1 ). An asymmetric supercapacitor is assembled applying the Cu2 Se@Co3 Se4 as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg-1 at 0.74 kW kg-1 ), high power density (21.0 Wh kg-1 at 7.50 kW kg-1 ), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g-1 ).

Supercapacitors are regarded as a promising energy storage system. Transition metal compounds have been widely used as electrode materials for pseudocapacitors, which possess variable oxidation valence states. Among them, Ni-based materials have drawn a substantial amount of attention. In this work, Ni nanoparticles (NiNPs/NiF) were successfully synthesized on Ni foam by a facile ion implantation method and first studied for the supercapacitor application. At the same time, NiO nanofibers were grown on a Ni foam (NiOF/NiF) for comparison. The NiNPs/NiF electrode delivered a better performance than the NiOF/NiF. The NiNPs/NiF electrode showed a high specific capacitance of 3862 F g-1 at 5 A g-1 and good long-term endurance at a current density of 50 A g-1 after a charge-discharge test of 1000 cycles. The good performance can be attributed to the uniform deposition of the Ni nanoparticles, which provided abundant active sites for the Faradaic reaction. Moreover, the three-dimensional (3D) structure of Ni foam facilitated the electron transfer between the electrode and electrolyte. The excellent performance and facile fabrication make the NiNPs/NiF electrode a promising candidate for high-performance supercapacitors.

This work reports the preparation and characterization of the CuO nanorods grown vertically on graphene nanosheets, denoted as CuO/rGO@NF. Graphene is deposited by electrostatic attraction showing the morphology of folded nanosheets, which improves the electrical conductivity of the electrode, while CuO is modified by filtered cathodic vacuum arc technology and subsequent electrochemical oxidation presenting the morphology of nanorods, which increases the contact area of active sites and shortens the ion and electronic diffusion path. The results show that the CuO/rGO@NF electrode deliver an ultrahigh specific capacity (2.51 C cm−2 at 2 mA cm−2), remarkable rate performance (64.6%) and improved conductivity. A symmetrical supercapacitor is assembled by two identical electrodes, presenting the maximum energy density of 38.35 W h kg−1 at a power density of 187.5 W kg−1. Therefore, the CuO/rGO@NF electrode can be used as a prospective electrode for energy storage devices. In addition, the whole electrode preparation process is short in time, safe and environmentally friendly, which provides a new idea for the preparation of other electrode materials.

Bimetallic Ni and Ti nanoparticle-modified indium tin oxide electrode (Ni–Ti NPs/ITO) were prepared by a two-step ion implantation method, and their electrocatalytic activity toward the oxidation of ethanol and glycol was evaluated. The ion-implantation method is simple, low-cost and environmental friendly without the use of any binder. The Ni–Ti NPs/ITO electrode were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). SEM and AFM showed that the nanoparticles on the Ni–Ti NPs/ITO electrode had a small range of dispersion (10–20 nm) and high dispersion. Electrochemical performances were measured by cyclic voltammetry (CV) and chronoamperometrics. The Ni–Ti NPs/ITO electrode exhibited much higher electrocatalytic activity and stability for ethanol and ethylene glycol oxidation than NiNPs/ITO. Keywords: Bimetallic, Ni–Ti nanoparticles, Electrocatalytic oxidation, Ethanol, Ethylene glycol

Transition metal and transition metal sulfides have been widely used as electrode materials in the field of energy storage and conversion. In this work, we fabricate uniform and compact NiCu film on the surface of nickel foam (NF) by a facile filtered cathodic vacuum arc technique (NiCu/NF). Then the electrode is sulfurized via electrochemical process (NiCu2S2/NF), which possesses abundant electroactive sites. Both the electrodes display good electrochemical performance in methanol electrooxidation and supercapacitors, simultaneously. NiCu2S2/NF electrode exhibits higher electrocatalytic activity of 825 mA mg−1 for methanol oxidation in KOH solution. In supercapacitors, NiCu2S2/NF electrode delivers a superior specific capacity of 1975.2 C g−1 at 0.5 mA cm−2 and better rate capability. NiCu2S2/NF electrode exhibits an improved electrochemical activity. Particularly, NiCu/NF electrode displays a higher cycle stability (76.8% retention) after 3000 cycles at 10 mA cm−2, owing to the stable adhesion of NiCu film. Hopefully, filtered cathodic vacuum arc technique can be applied to prepare binary transition metal, which can be simultaneously applied in fuel cells and supercapacitors.

Although transition metal sulfides have gotten extensive attention due to their high electrical conductivity, fast charge transfer kinetics, outstanding mechanical stability, the performances of them applied separately to supercapacitors are not satisfactory, and one solution is to hybridize with other metal sulfide materials. Therefore, in the study, the flower-like structure Cu-Mn bimetallic sulfide on Ni-foam (CuS/MnS@NF) was firstly synthesized by a hierarchical two-step solvothermal reaction to our knowledge, which was directly utilized as electrodes without binders or conductive agents. The CuS/MnS@NF electrode possesses flower-like morphology, superior electrical conductivity, and there are the synergistic effect and intense interaction between CuS and MnS. They can display higher specific capacitance of 1517.07 F g−1 at 1 A g−1 and excellent cyclic stability with specific capacity retention of 115.6% at 10 A g−1 after 3000 cycles, which is more admirable than their individual metal sulfide electrodes (CuS@NF and MnS@NF) and other recently reported metal-based electrodes. In short, the CuS/MnS@NF electrodes are promising candidate when used in battery-type supercapacitors.

In this work, a facile and unique electrode is fabricated by ion implantation and hydrothermal sulfurization methods for the first time. A spicules-like Ni3S2 shell is directly grown on the molybdenum nanoparticles doped nickel foam (MoNPs/NF@Ni3S2), which exhibits a special hierarchical structure. It is employed as the electrode of supercapacitor, exhibiting good electrochemical performance with high areal capacity of 1.06 C cm−2 (361 C g−1) at 1 mA cm−2, good rate capability, and long cycling life (168% of the initial capacity) for 7000 cycles at 20 mA cm−2. Compared with Ni3S2/NF, the electrode possesses better performance, which is attributed to the doped MoNPs, special morphology of Ni3S2, the hierarchical structure, as well as the synergistic effect between Ni3S2 and MoNPs. A symmetric supercapacitor based on MoNPs/NF@Ni3S2 electrodes maintains 108% of the original capacity after cycling for 7000 cycles at 0.5 mA cm−2. The results mean that MoNPs/NF@Ni3S2 could be used as a battery-type electrode for supercapacitors.

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu

Direct methanol fuel cells (DMFCs) have been seen as one of the desirable power sources, and the performance always depends on the ability of electrode materials to oxidize methanol. In this work, ...

In this paper, we focus on some properties and the maximum distribution estimates for one-dimensional Brownian motion with Markov switching. The explicit expressions for density functions, the mean exit time and Laplace transform of the exit time are obtained by solving the corresponding Poisson problem. The results of this paper disclose the impact on mean exit time and the Laplace transform of the exit time as σ 1 tends to σ 2 . Furthermore, an appropriate upper bound and an appropriate lower bound on the probabilities are given for Brownian motion with Markov switching.

The chitinase-producing bacteria Paenibacillus sp. was isolated from soil samples. The chitinase was purified successively by ammonia sulfate fractional precipitation followed by chromatography on DEAE 52-cellulose column and then on Sephadex G-75 column. The chitinase has a molecular weight of ca. 30 kDa as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis. Its optimum pH is 4.5, and its optimum temperature is 50 °C with colloidal chitin as a substrate. The enzyme is stable below 45 °C and in pH ranges between 4.5 and 5.5. It is activated by glucosamine, glucose, N-acetylglucosamine, and metal ions including Ca2+ , Fe2+ , Fe3+ , and Ni2+ . It is inhibited by SDS, H2 O2 , ascorbic acid, Cu2+ , Mg2+ , Ba2+ , Sn2+ , Cr3+ , and K+ . With colloidal chitin as substrate, the Km and the Vmax of the chitinase are 4.28 mg/mL and 14.29 μg/(Min·mL), respectively, whereas the end products of the enzymatic hydrolysis are 14.33% monomer and 85.67% dimer of N-acetylglucosamine. The viscosity of carboxymethyl chitin decreased rapidly at the initial stages when subjected to chitinase hydrolysis, which indicates that the chitinase acts in an endosplitting pattern.

Formaldehyde (FA) has been linked to the detrimental cardiovascular effects. Here, we explored the effects and mechanisms of FA on rat aortas both in vivo and in vitro. The results presented that FA evidently lowered the blood pressures of rats. The expression levels of BKCa subunits α and β1 and iNOS of the aortas were up-regulated by FA in vivo. However, FA markedly reduced the levels of Cav1.2 and Cav1.3, which are the subunits of L-Ca2+ channel. Furthermore, the contents of NO, cGMP and iNOS in the aortas were augmented by FA. To further confirm these findings, the mechanisms accredited to these effects were examined in vitro. The data showed that FA contracted the isolated aortic rings at low concentrations ( 500 μM). The FA-induced vasoconstriction at low concentrations was blocked partly by an inhibitor of ACE. The relaxation caused by FA at high concentrations was attenuated by the inhibitors of NO-cGMP pathway, L-Ca2+ channel and BKCa channel, respectively. Similarly, the expression of iNOS was strongly enhanced by FA in vitro. The effects of FA on the aortic rings with endothelium were significantly greater than those on the rings without endothelium. Our results indicate that the vasoconstriction of FA at low concentrations might be partially pertinent to endothelin, and the FA-caused vasorelaxation at high concentrations is possibly associated with the NO-cGMP pathway, L-Ca2+ channel and BKCa channel. This study will improve our understanding of the pathogenic mechanisms for FA-related cardiovascular diseases.

To observe rice cadmium level in a contaminated area where has being continuously polluted for 19 years since last investigation.Samples of late rice (polished) grown in 2006 were collected from farmer household in contaminated and control area and its cadmium concentration were detected with IPC-MS.Samples of polished rice from the polluted and control areas were detected. The average cadmium concentration from last investigation area 19 years before was 0.59 mg/kg (0.05 mg/kg for rice from control area), it upraises about 30% corresponding to average of rice from the same areas detected before 19 years. The average cadmium level of rice from whole contaminated areas (including last investigation and expanding areas) was 0.26 mg/kg and it is greater than that in control areas (0.06 mg/kg) and the limited value of national hygiene standard (0.20 mg/kg). There was about 64%, 23.17% and 11% of samples have higher level than 0.20 mg/kg (the limited value of national hygiene standard), 0.4 mg/kg (the limited value of Codex General Standard) and 1.0 mg/kg (cadmium-rice) respectively. There was a higher percentage (36.8%) of Cadmium-rice (greater than 1.0 mg/kg) in some heavy contamination villages.Environmental cadmium pollution has being existing for 19 years since last investigation. Average cadmium concentration of rice from whole country polluted areas was higher than that of national hygiene standard. Percentage of "cadmium-rice" might be higher in some villages.