Oxygen isotope signatures of quartz from major Asian dust sources: Implications for changes in the provenance of Chinese loess

We present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions (&lt;16 and 16-63 mu m) from major dust source regions in East Asia, including the Mongolian Gobi, the northern Chinese deserts, the Taklimakan desert, and the Qaidam Basin. The results demonstrate that the quartz oxygen isotope ratios of the Taklimakan desert and the Mongolian Gobi are more heterogeneous compared with the other areas. The quartz delta O-18 values of both the fine and coarse fractions from the various sources are overlapped to varying degrees, thus making it difficult to differentiate them. Nevertheless, the quartz delta O-18 values of both fractions exhibit an increasing trend from the Mongolian Gobi, to the northern Chinese deserts, and then to the Taklimakan desert. This implies that the geological settings of the source areas are different, which in turn results in differing contributions of high-temperature igneous rocks. The combination of quartz delta O-18 results with other quartz-based provenance tracers can clearly differentiate the three major source areas, i.e., the Taklimakan desert, the Mongolian Gobi, and the northern Chinese deserts. In addition, comparison of our results with previous delta O-18 measurements of fine-grained quartz from the Luochuan loess sequence suggests the likely glacial interglacial fluctuations in dust provenance. Finally, we suggest that the combination of quartz delta O-18 signatures and other dust provenance tracers can potentially improve the recognition of long-term fluctuations in the provenance of Chinese loess-red clay deposits.</p

Magnetic properties and microstructure of Nd-Fe-B sintered magnets with DyHx addition

The effects of DyHx addition on magnetic properties and microstructure of Nd-Fe-B sintered magnets were investigated. In order to obtain the best magnetic properties, the effects of sintering temperature and annealing time on magnetic properties were also investigated. The results shown that the addition of DyHx can affect the microstructure, increase the intrinsic coercivity (Hcj), and improve the thermal stability of sintered Nd-Fe-B magnets. The remanence (Br) and Hcj showed different variation trends as sintering temperature changes. Within a reasonable range, sintering at higher temperature can get higher Br but lower Hcj. The Hcj was further increased by heat treatment and annealing time was extended. VC 2012 American Institute of Physics

Provenance fluctuations of aeolian deposits on the Chinese Loess Plateausince the Miocene

The evolution of the provenance of aeolian deposits on the Chinese Loess Plateau (CLP) is closely linked to changes in source aridity and dust transport dynamics. Although previous studies have revealed that the provenance of Chinese aeolian deposits may have fluctuated on tectonic timescales, the exact timing and cause of the provenance shifts remain poorly constrained due to limitations of the isotopic and mineralogical tracers used. Here we report the results of electron spin resonance (ESR) signal intensity and crystallinity index (CI) of fine-grained (<16 lm) quartz isolated from two aeolian sequences on the CLP, in order to address tectonic-scale shifts in dust provenance over the last 23.5 Ma. The ESR–CI results spanning the interval 7–5 Ma for two aeolian sequences are comparable, implying a broadly similar provenance of dust deposits over the entire CLP. The ESR–CI values are lower after 7 Ma than before 9.5 Ma, indicating that a significant provenance shift occurred during 9.5–7 Ma. Comparison of the ESR–CI results for fine-grained quartz in desert surface samples and for the loess and Red Clay sequences indicates that the provenance shift may have been caused by increased dust input from the Mongolian Gobi and western China (i.e., the Taklimakan desert) since the late Miocene. The combination of our results with regional tectonic evidence and global climate record suggests that tectonically-driven climate changes in the dust sources may have played a dominant role in driving the late Miocene provenance shift

Polluted dust derived from long-range transport as a major end memberof urban aerosols and its implication of non-point pollution innorthern China

The contribution of polluted dust transported from local and distal sources remains poorly constrained due to their similar geophysical and geochemical properties. We sampled aerosols in three cities in northern China (Xi'an, Beijing, Xifeng) during the spring of 2009 to determine dust flux, magnetic susceptibility and elemental concentrations. Combining dust fluxes with wind speed and regional visibility records enabled to differentiate between dust transported from long range and derived from local sources, while the combination of magnetic susceptibility and enrichment factors (EF) of heavy metals (Pb, Zn) allowed to distinguish natural aerosols from polluted ones. Our results indicate that polluted dust from long-range transport became a major end member of urban dust aerosols. Human settlements as its potential sources were confirmed by a pollutant enriched regional dust event originating from populated areas to the south as inferred by back trajectory modeling, implying their non-point source nature of dust pollution

Timing and Spatial Distribution of Loess inXinjiang, NW China

Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess– paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin

ESR signal intensity and crystallinity of quartzfrom Gobi and sandy deserts in East Asia andimplication for tracing Asian dust provenance

Electron spin resonance (ESR) signal intensity and crystallinity index (CI) of fine- (&lt;16 mm) and coarse-grained (&gt;16 mm) quartz were measured in surface samples from the Taklimakan desert in western China, the Badain Juran, Tengger and Mu Us deserts in northern China, and the Gobi desert in southern Mongolia to evaluate whether these geophysical parameters can serve as reliable provenance tracers of Asian dust. The results indicate that spatial variability of both ESR signal intensity and CI is evident within the Taklimakan deserts and the Mongolian Gobi, but less significant in the three deserts of northern China. Coarse-grained quartz from the Mongolian Gobi and northern China deserts can be differentiated from the Taklimakan desert using the ESR signal intensity. Fine-grained quartz originating from three major Asian dust sources, i.e., the Gobi-sandy deserts in western China, northern China and southern Mongolia, can be distinguished effectively using the combination of ESR and CI signals. Our results suggest that ESR signal intensity and CI can discriminate the sources of fine-grained quartz better than coarse-grained quartz, providing an effective approach to trace the provenance of fine-grained dust deposition on the land and in the ocean.</p

The "inverse altitude effect'' of leaf wax- derived n- alkane dD on the northeastern Tibetan Plateau

The response of soil wax derived n-alkane hydrogen isotope values (dDwax, the abundance weighted average dD values of the C29 and C31 n-alkanes) and isotopic lapse rates (the average change in dDwax with elevation) to factors other than elevation change should be assessed and taken into account for quantitative elevation reconstructions. To shed more light on how plant wax derived n-alkanes may be used for this purpose, soil and Gramineae samples analyzed for dDwax values. Those were derived from the foreland basin, the mountain vegetation zone and glacier catchment areas along the Beida River (a tributary in the Heihe River Basin; up to the headwaters of the Qiyi glacier), and the Xiying River catchment (up to the headwaters and glaciated areas of the Lenglong Range), located on the northeastern Tibetan Plateau. For comparison, this study analyzed surface soils from the Maxian Mountains for dDwax. As a whole, the trend in dDwax in the study regions seems to primarily reflect dDrw (dD values of river water) and/or dDp (dD values of precipitation). These data show good inverse linear relationships between Gramineae and soil dDwax values and elevation (altitude effect) in the mountain vegetation zone of the Xiying River catchment (2200&ndash;3500 m) and Maxian Mountains (2800&ndash;3700 m), where the elevation effect becomes the main control factor even in the dry Qilian Mountains. However, at the low elevation sites, soil and Gramineae dDwax values from the Xiying River (1750&ndash;2200 m) and Maxian Mountains (2060&ndash;2800 m) show the &lsquo;&lsquo;inverse altitude effect&rsquo;&rsquo;. The recycled fraction and trajectory of water vapor may result in these positive dDwax elevation gradients in dry continental settings. The &lsquo;&lsquo;inverse altitude effect&rsquo;&rsquo; has also been observed in periglacial regions below the Qiyi glacier and from the Lenglong Range. We interpret this effect as evidence of stronger fractionation processes occurring in the freeze&ndash;thaw mass exchange between the solid and liquid phases at high elevations. Thus, the &lsquo;&lsquo;inverse altitude effect&rsquo;&rsquo; can be attributed to the decrease of precipitation amount in the upper valley and to marked fractionation in soil water and the residual or melting snow in periglacial regions, which may complicate the isotope thermometry. When interpreting changes of long term dD and d18O records for determining elevation change, one must consider all possible influences on the lapse rate of dDwax values with elevation, including the patterns of atmospheric circulation in the past, topography, recycling of moisture in dry continental settings, and strong fractionation processes effecting soil and glacier melt water in the periglacial regions.</p

Astronomical and glacial forcing of East Asian summer monsoonvariability

The dynamics of glacialeinterglacial monsoon variability can be attributed to orbitally induced changes in summer insolation and internal boundary conditions. However, the relative impacts of astronomical and internal factors on East Asian summer monsoon variability remain controversial. Here we combine proxy data and model results to evaluate the response of East Asian summer monsoon change to these forcings. d13C of loess carbonate, a sensitive summer monsoon proxy from the western Chinese Loess Plateau, demonstrates coexistence of distinct 100-, 41- and 23-ka periods, in contrast to precession-dominated speleothem d18O records in South China. Model results indicate that insolation, ice and CO2 have distinct impacts on summer precipitation changes in East Asia, whereas their relative impacts are spatially different, with a relatively stronger insolation effect in south China and a more dominant ice/CO2 influence in north China. Combined proxy data and model results indicate that East Asian summer monsoon variability was induced by integrated effects of summer insolation and changing boundary conditions (e.g., ice sheets and CO2 concentration). Our proxy-model comparison further suggests that gradual weakening of the summer monsoon related to slowly decreasing summer insolation at astronomical timescales will be likely overwhelmed by the projected ongoing anthropogenic CO2 emissions.</p

Plasmonic Bi/ZnWO4 Microspheres with Improved PhotocatalyticActivity on NO Removal under Visible Light

In this work, bismuth (Bi) nanoparticle anchored ZnWO4 microspheres (Bi/ZnWO4) were prepared and used as robust and efficient photocatalysts for NO removal at parts-per-billion level under visible light irradiation. The as-synthesized composite with a proper mass ratio of Bi (50%) displayed a higher reaction rate (0.067 min&ndash;1) than its single counterparts ZnWO4 (0.004 min&ndash;1) and Bi (0.027 min&ndash;1), respectively. Due to the surface plasmon resonance (SPR) effect of Bi nanoparticles, the Bi/ZnWO4 composites showed broad light absorption in the visible spectrum. Moreover, the formation of the Bi/ZnWO4 heterointerface promoted the separation of photoexcited electron&ndash;hole pairs, which is demonstrated by the increased photocurrent density in comparison to the pristine materials. The above characteristics endowed the Bi/ZnWO4 composites with superior photocatalytic activity for NO removal. The radical scavanger tests revealed that the superoxide radical was the main active species to initiate NO oxidation, while the hydroxyl radical was not involved in the process. This study shows practical value in air pollutant abatement, because it provides an economical and feasible route to fabricate SPR-enhanced composite photocatalysts using earth abundant Bi material instead of noble metals.</p

Real-time measurements of PM2.5, PM10–2.5, and BC in an urban streetcanyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM2.5, PM10&ndash;2.5, and Black Carbon (BC) over a 12-month period in an urban street canyon of Hong Kong. Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded. The average weekly cycles of PM2.5, PM10&ndash;2.5, and BC suggested that all species are related to traffic, with high concentrations on workdays and low concentrations over the weekends. PM2.5 exhibited two comparable concentrations at 10:00&ndash;11:00 (63.4&nbsp;&mu;g/m3) and 17:00&ndash;18:00 (65.0&nbsp;&mu;g/m3) local time (LT) during workdays, corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels: 3179 and 2907&nbsp;h&minus;1, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2&nbsp;&mu;g/m3) during the midday period (10:00&ndash;11:00 LT) on workdays. A poor correlation was found between PM2.5 concentration and wind speed (R&nbsp;=&nbsp;0.51, P-value&nbsp;&gt;&nbsp;0.001). In contrast, the concentration of PM10&ndash;2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R&nbsp;=&nbsp;0.98, P-value&nbsp;&lt;&nbsp;0.0001).</p