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Cao J.,CAS Institute of Earth Environment | Xu H.,CAS Institute of Earth Environment | Xu Q.,Peking Union Medical College | Chen B.,Fudan University | Kan H.,Fudan University
Environmental Health Perspectives | Year: 2012

Background: Although ambient fine particulate matter (PM 2.5; particulate matter ≤ 2.5 μm in aerodynamic diameter) has been linked to adverse human health effects, the chemical constituents that cause harm are unknown. To our knowledge, the health effects of PM 2.5 constituents have not been reported for a developing country. Objectives: We examined the short-term association between PM 2.5 constituents and daily mortality in Xi'an, a heavily polluted Chinese city. Methods: We obtained daily mortality data and daily concentrations of PM 2.5, organic carbon (OC), elemental carbon (EC), and 10 water-soluble ions for 1 January 2004 through 31 December 2008. We also measured concentrations of fifteen elements 1 January 2006 through 31 December 2008. We analyzed the data using overdispersed generalized linear Poisson models. Results: During the study period, the mean daily average concentration of PM 2.5 in Xi'an was 182.2 μg/m 3. Major contributors to PM 2.5 mass included OC, EC, sulfate, nitrate, and ammonium. After adjustment for PM 2.5 mass, we found significant positive associations of total, cardiovascular, or respiratory mortality with OC, EC, ammonium, nitrate, chlorine ion, chlorine, and nickel for at least one lag period. Nitrate demonstrated stronger associations with total and cardiovascular mortality than PM 2.5 mass. For a 1-day lag, interquartile range increases in PM 2.5 mass and nitrate (114.9 and 15.4 μg/m 3, respectively) were associated with 1.8% [95% confidence interval (CI): 0.8%, 2.8%] and 3.8% (95% CI: 1.7%, 5.9%) increases in total mortality. Conclusions: Our findings suggest that PM 2.5 constituents from the combustion of fossil fuel may have an appreciable influence on the health effects attributable to PM 2.5 in Xi'an.

Sun Y.,CAS Institute of Earth Environment | Wang X.,CAS Institute of Earth Environment | Liu Q.,CAS Institute of Geology and Geophysics | Clemens S.C.,Brown University
Earth and Planetary Science Letters | Year: 2010

Rapid East Asian Monsoon oscillations recorded by Chinese loess are thought to be dynamically linked to north Atlantic climate. However, few efforts have been made to assess the effects of post-depositional processes (e.g., surface mixing and pedogenesis) on loess paleoclimatic records. Here a detailed optically stimulated luminescence dating of a thick loess sequence from the western Loess Plateau is presented, offering a reliable chronology for last glacial deposits. Magnetic susceptibility and mean grain size records from three loess-paleosol sequences along a northwest-southeast transect are investigated to evaluate impacts of post-depositional processes on these loess-based proxy records. Our results indicate that: (1) loess sequences developed within the flat tableland of the central and western Loess Plateau are nearly continuous during the last glaciation; and (2) post-depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions. In the central Loess Plateau, rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity. In the northwestern Loess Plateau, however, due to high sedimentation rate and relatively weak pedogenesis, high-resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the Greenland ice core and Hulu cave stalagmite. © 2009 Elsevier B.V. All rights reserved.

Sun J.,CAS Institute of Earth Environment | Liu Y.,CAS Institute of Earth Environment | Liu Y.,Xi'an University of Science and Technology
Journal of Geophysical Research: Atmospheres | Year: 2012

A tree ring (Sabina przewalskii Kom.) based millennial precipitation reconstruction on the south slope of the middle Qilian Mountains in the northeastern margin of Tibetan Plateau, China, was completed, which explains 48.5% of the variance in the instrumental precipitation from 1958 to 2004. The long-term precipitation variation patterns were confirmed on the basis of the duration, magnitude, and intensify of the multidecadal dry (wet) events. There are several stronger multidecadal dry periods, 1092-1172, 1441-1517, and 1564-1730, whereas there is only one outstanding severe wet event of 1352-1440. The variations of the precipitation reconstruction are accordant with the glacier accumulation and dust contents of Dunde ice core and also with the variations of the precipitation, runoff, Palmer Drought Severity Index, and tree ring width series in the northeastern Tibetan Plateau. The spatial extent of the great drought in the latter half of the 15th century also concentrated on the northeastern Tibetan Plateau. The moisture variations in the northeastern Tibetan Plateau are synchronous over a large spatial and temporal range in multidecadal scale for the last millennium, especially during dry periods. Wavelet analyses and comparisons with the minimal solar activity show that the precipitation variations for the last millennium may have some association with the solar activity on multidecadal to centennial scales. © 2012 by the American Geophysical Union.

Zhou X.,CAS Institute of Earth Environment | Li X.,CAS Institute of Vertebrate Paleontology and Paleoanthropology
Holocene | Year: 2012

Based on published pollen data from 44 sites in the Loess Plateau and surrounding areas, we recalculate values of Picea abundance digitized from the original diagrams and construct six isopoll maps to reconstruct the distribution of spruce forest at 2000 yr intervals during the Holocene. Spruce forest gradually expanded from about 10 ka BP ago and reached its peak distribution around 8 ka BP. It retained its maximum extent between 8 ka BP and 6 ka BP, broadly covering the subalpine area and stretching to the valleys of the western Loess Plateau with high densities and even reaching the edges of the adjacent desert regions. After 6 ka BP, spruce forest began to retreat to higher elevations. This trend was accelerated after 4 ka BP. After 2 ka BP, it disappeared completely from the Loess Plateau and most of its surrounding areas. Precipitation strongly dominated by the Asian summer monsoon was the primary controlling factor in the distribution of spruce before 2 ka BP. After about 2 ka BP, the increasing intensity of human activity became the primary factor in the disappearance of spruce in the Loess Plateau, resulting in an enormous impact on the present landscape. © The Author(s) 2011.

Sun Y.,CAS Institute of Earth Environment | Clemens S.C.,Brown University | Morrill C.,University of Colorado at Boulder | Lin X.,Ocean University of China | And 2 more authors.
Nature Geoscience | Year: 2012

The last glacial period was characterized by abrupt, millennial-scale climate change. These climate fluctuations are particularly pronounced in records of the East Asian monsoon system, and seem to be linked to changes in North Atlantic circulation. Here we present records of grain size variations from the northwestern Chinese Loess Plateau, dated using optically stmulated luminescence. We reconstruct changes in the strength of the East Asian winter monsoon over the past 60,000 years and find reconstructed millennial-scale variations that are broadly correlated with temperature variations over Greenland, suggesting a common forcing. We investigate the effect of a slow-down of Atlantic meridional overturning circulation on the monsoon system using a coupled climate model simulation with added freshwater flux into the northern North Atlantic, and find a strengthening winter monsoon circulation over the regions that supply dust to the Loess Plateau and a reduction in summer monsoon precipitation over East Asia. We conclude that Atlantic meridional overturning circulation is a driver of abrupt change in the East Asian winter and summer monsoon systems, and that the northern westerlies play a role in transmitting this signal from the North Atlantic to the Asian monsoon regions.

Clemens S.C.,Brown University | Prell W.L.,Brown University | Sun Y.,CAS Institute of Earth Environment
Paleoceanography | Year: 2010

Southeast China cave δ18O, often interpreted as a pure East Asian summer monsoon proxy, lags maximum northern hemisphere summer insolation by 2.9±0.3 kyrs at the precession cycle. The Arabian Sea summer monsoon stack lags by 8±1 kyr, consistent with 13 other Indian and East Asian summer monsoon proxies from marine, lake, and terrestrial archives. This 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology; it requires reconciliation in the context of proxy interpretation. Both of these lags are incompatible with a direct response to northern hemisphere summer insolation, implicating additional forcing mechanisms. Analysis of heterodynes in the cave δ18O spectrum demonstrates that variance contained in the Arabian Sea summer monsoon proxies also resides in the cave δ18O record. This variance is subtracted from the cave δ18O record yielding a residual that is highly coherent and in phase with precession minima, reflecting the impact of winter temperature change on cave δ18O (meteorological precipitation under cold conditions). Thus, we argue that the timing of light cave δ18O peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone. The 2.9 kyr precession band phase lag of cave δ18O reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima. This interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast China. © 2010 by the American Geophysical Union.

Xu H.,CAS Institute of Earth Environment | Hong Y.,Chinese Academy of science | Hong B.,Chinese Academy of science
Climate Dynamics | Year: 2012

The trend of the Indian summer monsoon (ISM) intensity and its nature during the past 100 and 200 years still remain unclear. In this study we reconstructed the ISM intensity during the past 270 years from tree ring δ18O at Hongyuan, eastern edge of the Tibet Plateau. The monsoon failures inferred from δ18Otree ring correlate well with those recorded in ice cores, speleothem, and historical literature sources. 22.6, 59.0, and 110.9-years frequency components in the Hongyuan δ18Otree ring series, which may be the responses to solar activities, synchronize well with those recorded in other ISM indices. A notable feature of the reconstructed ISM intensity is the gradually decreasing trend from about 1860 to the present, which is inversely related to the increasing temperature trend contemporaneously. Such "decreasing ISM intensity-increasing temperature" tendency can also be supported by ice core records and meteorological records over a wide geographic extension. The decrease in sea surface temperature gradient between tropical and north Indian Ocean, and the decrease in land-sea thermal contrast between tropical Indian Ocean and "Indian sub-continent-western Himalaya" are possibly responsible for the observed decreasing ISM trend. © 2012 Springer-Verlag.

Yin J.,China Earthquake Administration | Yin J.,CAS Institute of Earth Environment | Yang X.,China Earthquake Administration | Zheng Y.,China Earthquake Administration
Scientific Reports | Year: 2014

Several attempts have been made to directly date phytoliths, but most 14 C results are not consistent with other independent chronologies. Due to the limited dataset, there is not a clear explanation for these discrepancies. Herein, we report the 14 C ages of phytolith-occluded carbon (PhytOC) from contemporary rice and millet crops that were combusted at different temperatures to investigate the relationship between the combustion temperature and resulting 14 C age. Our results show that the 14 C age of PhytOC increases directly with combustion temperature (up to 1100°C) and results in age overestimations of hundreds of years. Considerably older ages are observed at higher temperatures, suggesting that it may be possible to distinguish between two fractions of organic carbon in phytoliths: labile and recalcitrant carbon. These findings challenge the assumption that PhytOC is homogeneous, an assumption made by those who have previously attempted to directly date phytoliths using 14 C.

Shi Z.,CAS Institute of Earth Environment | Liu X.,CAS Institute of Earth Environment | Cheng X.,Shaanxi Climate Center
Quaternary Science Reviews | Year: 2012

The timing of orbital-scale Asian monsoon changes, as a direct response of northern summer insolation or remarkably lagged by southern insolation, is still unclear. In particular, various monsoon records obtained in the East Asian monsoon region show distinct phase relationships, indicating additional forcing/feedback mechanisms. Here, monsoon proxies covering the past several precession cycles, either from cave stalagmites or from land/ocean deposits, are first reviewed to present the nearly inverse precipitation responses to the precession forcing between southern and northern East Asia. Modern meteorological observations show that, different modes of tropical Pacific sea surface temperature (SST) could lead to an out-of-phase interannual change in the East Asian summer precipitation. This ENSO influence is also found in the precession scale monsoon variability from the long-term transient modeling, which can explain the phase differences among monsoon proxies. At precession maxima, the East Asian summer monsoon strengthens, causing more precipitation in the north and less precipitation in the south. The SST-precipitation teleconnection is closely associated with a high pressure anomaly due to surface cooling over northwestern Pacific. Therefore, the timing of Asian paleo-monsoon might be significantly influenced by the "internal" ocean feedbacks and one can not expect all the monsoon proxies are consistently responded to the "external" insolation forcing. © 2012 Elsevier Ltd.

Xiao J.,CAS Institute of Earth Environment
Environmental Earth Sciences | Year: 2016

Major ions, pH and electric conductivity (EC) in rainwater samples collected from June 2011 to July 2012 were analyzed to evaluate chemical characteristics and source apportionment of rainwater in Xi’an, a city located on the loess deposits. The rainwater was slightly alkaline with a daily volume-weighted mean (VWM) pH of 7.7, which ranged from 7.4 to 8.4. The VWM concentrations of major ions followed the order of Ca2+ > SO4 2− > NH4 + > NO3 − > Cl− > Na+ > K+ > Mg2+ > F−. Ca2+ and SO4 2− dominated in cations and anions, respectively. Investigations of neutralization factors indicated that the acidity of rainwater in Xi’an was neutralized by NH4 + and Ca2+, which presented relatively higher neutralization capability than cities in southern China. The back trajectory analysis showed that the chemistry of rainwater in Xi’an is influenced by local pollutions sources and soil dust in local and remote area. Large inputs of soil dust and coal combustion during the winter and spring led to higher values of major ions and pH values during dry seasons than wet seasons. The principal factor analysis, correlation analysis, and source apportionment indicated that SO4 2− and NO3 − were from anthropogenic sources, while Ca2+, K+, and Mg2+ were from crust fractions. The estimated annual wet depositions for sulfur, nitrogen, and calcium were 3.9, 1.5, and 4.2 t/km2, respectively. Although rainwater acidity in Xi’an was mainly caused by H2SO4, the contribution of HNO3 will be enhanced due to increasing NOx and relatively stable SO2 emissions in the future. The high concentrations of EC, SO4 2−, and NO3 − in rainwater indicated Xi’an is severely polluted. To improve air quality in Xi’an, simultaneous reduction of particle emissions and fossil fuel and vehicles emissions are worthy of advocating. The results have implications for identification of potential sources in rainwater and for evaluation of air quality improvement in Xi’an and other similar cities in China. © 2015, Springer-Verlag Berlin Heidelberg.

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