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Fe nanoflakes were prepared by the ball-milling technique, and then were coated with 20 nm-thick SiO(2) to prepare Fe/SiO(2) core-shell nanoflakes. Compared with the uncoated Fe nanoflakes, the permittivity of Fe/SiO(2) nanoflakes decreases dramatically, while the permeability decreases slightly. Consequently, reflection losses exceeding - 20 dB of Fe/SiO(2) nanoflakes are obtained in the frequency range of 3.8-7.3 GHz for absorber thicknesses of 2.2-3.6 mm, while the reflection loss of uncoated Fe nanoflakes almost cannot reach - 10 dB in the same thickness range. The enhanced microwave absorption of Fe/SiO(2) nanoflakes can be attributed to the combination of the proper electromagnetic impedance match due to the decrease of permittivity and large magnetic loss due to strong and broadband natural resonance. The key to the combination is the coexistence of the nanoshell microstructure and the nanoflake morphology.

Abstract. A snow survey was carried out to collect 13 surface snow samples (10 for fresh snow, and 3 for aged snow) and 79 subsurface snow samples in seasonal snow at 13 sites across northeastern China in January 2014. A spectrophotometer combined with chemical analysis was used to quantify snow particulate absorption by insoluble light-absorbing particles (ILAPs, e.g., black carbon, BC; mineral dust, MD; and organic carbon, OC) in snow. Snow albedo was measured using a field spectroradiometer. A new radiative transfer model (Spectral Albedo Model for Dirty Snow, or SAMDS) was then developed to simulate the spectral albedo of snow based on the asymptotic radiative transfer theory. A comparison between SAMDS and an existing model -the Snow, Ice, and Aerosol Radiation (SNICAR) -indicates good agreements in the model-simulated spectral albedos of pure snow. However, the SNICAR model values tended to be slightly lower than those of SAMDS when BC and MD were considered. Given the measured BC, MD, and OC mixing ratios of 100-5000, 2000-6000, and 1000-30 000 ng g −1 , respectively, in surface snow across northeastern China, the SAMDS model produced a snow albedo in the range of 0.95-0.75 for fresh snow at 550 nm, with a snow grain optical effective radius (R eff ) of 100 µm. The snow albedo reduction due to spherical snow grains assumed to be aged snow is larger than fresh snow such as fractal snow grains and hexagonal plate or column snow grains associated with the increased BC in snow. For typical BC mixing ratios of 100 ng g −1 in remote areas and 3000 ng g −1 in heavy industrial areas across northern China, the snow albedo for internal mixing of BC and snow is lower by 0.005 and 0.036 than that of external mixing for hexagonal plate or column snow grains with R eff of 100 µm. These results also show that the simulated snow albedos by both SAMDS and SNICAR agree well with the observed values at low ILAP mixing ratios but tend to be higher than surface observations at high ILAP mixing ratios.

The characteristics of aerosol particles have been poorly evaluated even though haze episodes frequently occur in winter in Northeast China. OC/EC analysis, ion chromatography, and transmission electron microscopy (TEM) were used to investigate the organic carbon (OC) and elemental carbon (EC), and soluble ions in PM and the mixing state of individual particles during a severe wintertime haze episode in Northeast China. The organic matter (OM), NH, SO, and NO concentrations in PM were 89.5 μg/m, 24.2 μg/m, 28.1 μg/m, and 32.8 μg/m on the haze days, respectively. TEM observations further showed that over 80% of the haze particles contained primary organic aerosols (POAs). Based on a comparison of the data obtained during the haze formation, we generate the following synthetic model of the process: (1) Stable synoptic meteorological conditions drove the haze formation. (2) The early stage of haze formation (light or moderate haze) was mainly caused by the enrichment of POAs from coal burning for household heating and cooking. (3) High levels of secondary organic aerosols (SOAs), sulfates, and nitrates formation via heterogeneous reactions together with POAs accumulation promoted to the evolution from light or moderate to severe haze. Compared to the severe haze episodes over the North China Plain, the PM in Northeast China analyzed in the present study contained similar sulfate, higher SOA, and lower nitrate contents. Our results suggest that most of the POAs and secondary particles were likely related to emissions from coal-burning residential stoves in rural outskirts and small boilers in urban areas. The inefficient burning of coal for household heating and cooking should be monitored during wintertime in Northeast China.

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h i g h l i g h t sWe collected 92 snow samples from 13 sites across northeastern China. The snow in the remote northeast on the border near Siberia was extremely clean. Al, and Fe were primarily derived from natural sources. Cu, Zn, As, V, and Cd in snow samples were likely derived from anthropogenic sources. a b s t r a c tWe collected 92 snow samples from 13 sites across northeastern China from January 7 to February 15, 2014. The surface snow samples were analyzed for the major water-soluble ions (SO 2À 4 , NO À 3 , F e , Cl e , Na þ , K þ , Ca 2þ , Mg 2þ , and NH þ 4 ) and trace element (Al, As, Mn, V, Cd, Cu, Pb, Zn, Fe, Cr, and Ni). The results indicated that the higher concentrations of NO À 3 and SO 2À 4 and the trace elements Zn, Pb, Cd, Ni, and Cu were likely attributable to enhanced local industrial emissions in East Asia especially in China. In addition, snow samples characterized by higher enrichment factors of trace elements (Cu, Cd, As, Zn, Pb) were indicative of an anthropogenic source. Emissions from fossil fuel combustion and biomass burning were likely important contributors to the chemical elements in seasonal snow with long-range transport. On the other hand, the large attribution of K þ appeared in the higher latitude demonstrated that biomass burning was a dominated factor of the chemical species in seasonal snow in the higher latitude of China than that in the lower latitude. Finally, an interannual comparison with the 2010 China snow survey also confirmed the source attributions of chemical speciation in seasonal snow in these regions.

Electromagnetic interference (EMI) shielding materials made of Ni-Co coated on web-like biocarbon nanofibers were successfully prepared by electroless plating. Biocarbon nanofibers (CF) with a novel web-like structure comprised of entangled and interconnected carbon nanoribbons were obtained using bacterial cellulose pyrolyzed at 1200°C. Paraffin wax matrix composites filled with different loadings (10, 20, and 30 wt%, resp.) of CF and Ni-Co coated CF (NCCF) were prepared. The electrical conductivities and electromagnetic parameters of the composites were investigated by the four-probe method and vector network analysis. From these results, the EMI shielding efficiencies (SE) of NCCF composites were shown to be significantly higher than that of CF at the same mass fraction. The paraffin wax composites containing 30 wt% NCCF showed the highest EMI SE of 41.2 dB (99.99% attenuation), which are attributed to the higher electrical conductivity and permittivity of the NCCF composites than the CF composites. Additionally, EMI SE increased with an increase in CF and NCCF loading and the absorption was determined to be the primary factor governing EMI shielding. This study conclusively reveals that NCCF composites have potential applications as EMI shielding materials.

We analyzed the suspended particle size distribution in the range of 0.5 to 10 µm and the optical properties of the particles from March 2007 to December 2010 at a site on the Loess Plateau (SACOL; 35.57°N, 104.08°E; 1965.8 m a.s.l.) about 48 km southeast of the center of Lanzhou. The results indicated that the variation in PM 10 was much larger in spring than in winter because of frequent dust events or local blowing soil dust during spring. The highest number concentrations of coarse-mode particles were likely attributable to dust events that transported mineral dust or soil dust in the spring season, caused by cold fronts or strong local winds. In contrast, the fine-mode particles that dominated in the cold season at SACOL were probably indicative of anthropogenic sources related to fossil-fuel combustion and biomass burning. The comparison of dust events and anthropogenic air pollution shows a clear distinction of lower PM 10 with higher B ap for pollution episodes and higher PM 10 with lower B ap for dust events. These findings suggest that the results in the cold season were likely attributable to light absorption of black carbon, and the coarse mode particles were dominant during dust events in spring.