Institute of Earth Environment
Institutional Repository of Institute of Earth Environment, CASNot a member yet
7120 research outputs found
Sort by
Tree Rings Reveal the Impacts of the Northern Hemisphere Temperature on Precipitation Reduction in the Low Latitudes of East Asia Since 1259 CE
No full textFrom the late 1920s to the early 21st century, meteorological observations indicate a decreasing trend of precipitation in Taiwan, an island in the low latitudes of East Asia, with global warming. However, it is still unclear whether the decreasing trend of Taiwan precipitation can be physically linked to an increase in temperature. Here, we present an annually resolved precipitation reconstruction for Taiwan for 1259-2006 CE based on tree-ring width and oxygen isotope indices, which both reflect a high sensitivity to climatic changes. Over the past 748 years both, extremely dry and wet years accounted for 2.8% of all years and Taiwan precipitation can reflect the large-scale precipitation in the low latitudes of East Asia. Before the onset of global warming, the precipitation reconstruction exhibited four other significant decreasing trends during the 1380s-1440s, 1640s-1700s, 1720s-1790s, and 1790s-1860s, and each decreasing trend was accompanied by an increase in Northern Hemisphere temperature. This implies that the decreasing trends in precipitation were affected by increasing temperature. We also found that large volcanic eruptions in the low latitudes of the globe played an important role in precipitation changes by influencing the El Nino/Southern Oscillation and Asian summer monsoon. Precipitation usually decreased in the second year after large tropical volcanic eruptions. Our reconstruction is the longest annual-resolution precipitation reconstruction for the low latitudes of East Asia, and it is useful not only for understanding past hydroclimate changes but also for providing basic data to project future precipitation changes through climate modeling
Numerical simulation of the effects of canopy properties on airflow and pollutant dispersion in street canyons
No full textThe air flow and pollutant concentration fields in a street canyon affected by trees could affect the comfort and health of residents. At present, the description of the non-uniform/discontinuous distribution of leaves is difficult. In this study, the leaf distribution in the canopy was characterized by establishing non-continuous (uniform/random) algorithm based on a numerical simulation method, and the effects of canopy properties including, height, porosity and uniform/random leaf distribution, on the airflow and pollutant concentration fields in urban street canyons were investigated. The position of the tree canopy was found to directly affect the airflow field form and the air velocity distribution in the street canyon at low inflows. The average air velocity in the street canyon could be reduced significantly when the top of the tree canopy is near the top of the street canyon. The air velocity and pollutant concentration in the street canyon would vary only slightly due to the canopy porosity. Due to the increasing canopy porosity, the air velocity would increase, and the pollutant concentration would be reduced. The leaves are non-continuous and uniformly distributed at constant porosity, which does not significantly change the velocity distribution and pollutant concentration in the street canyon
Climate change drivers alter root controls over litter decomposition in a semi-arid grassland
No full textPlant roots are the primary source of soil organic carbon (C) and critically support the growth and activities of microbes in the rhizosphere. Climate change factors may, however, modify root-microbial interactions and impact C dynamics in the rhizosphere. Yet, the direction and magnitude of interactive climate change effects, as well as the underlying mechanisms, remain unclear. Here we show evidence from a field experiment demonstrating that warming and precipitation changes strengthen root controls over litter decomposition in a semi-arid grassland. While warming and precipitation reduction suppressed microbial decomposition of root litter regardless of the root presence, precipitation increase stimulated litter decomposition only in the absence of roots, suggesting that plant competition for water constraints the activities of saprophytic microbes. Root presence increased microbial biomass but reduced microbial activities such as respiration, C cycling enzymes and litter decomposition, indicating that roots exert differential effects on microbes through altering C or water availability. In addition, nitrogen (N) input significantly reduced microbial biomass and microbial activities (respiration). Together, these results showed that alterations in soil moisture induced by climate change drivers critically modulate root controls over microbial decomposition in soil. Our findings suggest that warming-enhanced plant water utilization, combined with N-induced suppression of microbes, may provide a unique mechanism through which moderate increases in precipitation, warming and N input interactively suppress microbial decomposition, thereby facilitating short-term soil C sequestration in the arid and semi-arid grasslands
Spatially Resolved Emission Factors to Reduce Uncertainties in Air Pollutant Emission Estimates from the Residential Sector
No full textThe residential sector is a major source of air pollutant emission inventory uncertainties. A nationwide field emission measurement campaign was conducted in rural China to evaluate the variabilities of realistic emission factors (EFs) from indoor solid fuel combustion. For a total of 1313 burning events, the overall average EFs (+/- standard deviation) of PM2.5 were 8.93 +/- 6.95 and 7.33 +/- 9.01 g/kg for biomass and coals, respectively, and 89.3 +/- 51.2 and 114 +/- 87 g/kg for CO. Higher EFs were found from burning of uncompressed straws, while lower EFs were found from processed biomass pellets, coal briquettes, and relatively clean anthracite coals. Modified combustion efficiency was found to be the most significant factor associated with variations in CO EFs, whereas for PM2.5, fuel and stove differences determined its variations. Weak correlations between PM2.5 and CO indicated high uncertainties in using CO as a surrogate for PM2.5. EFs accurately fit log-normal distributions, and obvious spatial heterogeneity was observed attributed to different fuel-stove combinations across the country. Emission estimation variabilities, which are determined by the interquartile ranges divided by the median values, were notably reduced when spatially resolved EFs were adopted in the inventory
In-situ generation of oxygen vacancies and metallic bismuth from (BiO)(2)CO3 via N-2-assisted thermal-treatment for efficient selective photocatalytic NO removal
No full textIn this study, a N-2-assisted thermal treatment method is proposed for in-situ formation of a series of oxygen vacancies (OVs)-rich Bi-0/Bi-based photocatalysts, including OVs-(BiO)(2)CO3, Bi-0/OVs-(BiO)(2)CO3, Bi-0/OVs(BiO)(2)CO3/beta-Bi2O3, Bi-0/OVs-beta-Bi2O3, Bi-0/OVs-beta-Bi2O3/alpha-Bi2O3 and Bi-0/alpha-Bi2O3. Mechanisms of in-situ formation of Bi-0 nanoparticles and generation of OVs in Bi-based photocatalysts are clarified. Apart from their contribution to the effective separation of photogenerated charge carriers and enhancement of light absorption, the effects of Bi-0 nanoparticles and OVs on selective photocatalytic oxidation of NO are also investigated. Among the synthesized Bi-based photocatalysts, Bi-0/OVs-(BiO)(2)CO3 shows the best photocatalytic activity and stability for photo-oxidative removal of NO. The systematic study of photocatalytic mechanism demonstrated that the Ohmic contact between OVs-(BiO)(2)CO3 and Bi-0 gradually promote the formation of center dot O-2(-) and center dot OH species. It is found that center dot O-2(-) plays an important role in the photocatalytic NO removal process, while center dot OH species can effectively inhibit the formation of NO2 during the NO removal process. The new approach demonstrated in this study can be applied for the in-situ formation of wide-solar-spectrum-responsive photocatalysts with efficient photo catalytic activity
Drivers for Asynchronous Patterns of Dust Accumulation in Central and Eastern Asia and in Greenland During the Last Glacial Maximum
No full textWe collected 143 loess optically stimulated luminescence (OSL) ages between 10 ka and 30 ka from Central Asia (CA), and analyzed their probability density functions (PDFs). The PDFs show dust accumulation was greater during the late Last Glacial Maximum (LGM) (23-19 ka) than that during the early LGM (26.5-23 ka). The temporal variability of dust accumulation of CA loess is generally similar to that of Chinese Loess Plateau (CLP) loess, following precession. In contrast, dust accumulation in Greenland was stronger during the early LGM than that during the late LGM, following obliquity. Supported by numerical modeling experiments and our newly dating OSL ages, we conclude dust accumulation in CA and CLP during the LGM was controlled by Siberian High forced by precession, while dust accumulation in Greenland was closely related to both intensity of summer westerlies forced by obliquity, and to intensity of dust emissions at source forced by precession
Organochlorine compounds pose health risks to the Qinling Giant Panda (Ailuropoda melanoleuca qinlingensis)
No full textTo assess organochlorine compound (OC) contamination, its possible sources, and adverse health impacts on giant pandas, we collected soil, bamboo, and panda fecal samples from the habitat and research center of the Qinling panda (Ailuropoda melanoleuca qinlingensis)-the rarest recognized panda subspecies. The polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) concentrations were comparatively low which suggests that moderate sources of OC pollution currently. OC levels were lower in samples from nature reserve than in those collected from pandas held in captivity, and OC levels within the reserve increased between functional areas in the order: core, buffer and experimental. The distribution patterns, and correlation analyses, combined with congener distributions suggested PCBs and OCPs originated from similar sources, were dispersed by similar processes, being transported through atmosphere and characterized by historical residues. Backward trajectory analyses results, and detected DRINs (aldrin, dieldrin, endrin and isodrin) both suggest long-range atmospheric transport of pollution source. PCBs pose potential cancer risk, and PCB 126 was the most notable toxicant as assessed be the high carcinogenic risk index. We provide data for health risk assessment that can guide the identification of priority congeners, and recommend a long-term monitoring plan. This study proposes an approach to ecotoxicological threats whereby giant pandas may be used as sentinel species for other threatened or endangered mammals. By highlighting the risks of long-distance transmission of pollutants, the study emphasizes the importance of transboundary cooperation to safeguard biodiversity. (C) 2021 Elsevier Ltd. All rights reserved
Preface (volume I): Quaternary paleoclimate and paleoenvironmental changes in Central Asia
No full textThe core area of Central Asia (CA), an arid Westerlies-dominated area, is crucial for analysis of interregional atmospheric circulation interactions along the Eurasian mid-latitude belt. However, it remains unclear how climate and environment in this region evolved during the Quaternary Period. Based on the articles in this special issue, this review recapitulates the spatio-temporal distribution of Quaternary sediments in CA, discusses paleoclimate and paleoenvironmental implications of various physicochemical and palaeontological proxies, and finally summarizes the paleoclimate and paleoenvironmental history since the middle Pleistocene. Field investigation and previous studies indicate that loess sediments are mainly distributed on the river terraces and windward piedmonts of Central Asian high mountains since the late Pliocene (mainly late Pleistocene). Multiple proxies analysis, e.g., grain size, geochemistry, sporopollen and magnetism, for the loess and fluvial deposits in this region reveal that the paleoclimate and paleoenvironment manifest a long-term stepwise drying or desertification trend of CA over the past 1 Myr, with at least one major drying event occurring at about similar to 0.5-0.6 Ma. One of the consequences is the development of the modern deserts in the Junggar Basin and the Tarim Basin. Despite the overall drying trend since the last interglacial period, the Holocene is characterized by a persistent wetting trend with millennial-scale oscillation. This special issue provides a useful glimpse into multi-scale climate and environmental changes in CA, facilitating climatic prediction in the future and climate modeling
Sulfate formation is dominated by manganese-catalyzed oxidation of SO2 on aerosol surfaces during haze events
No full textThe formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. As companions, SO2 and transition metals are mainly emitted from coal combustion. Here, we argue that the transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway and investigate this hypothesis by integrating chamber experiments, numerical simulations and in-field observations. Our analysis shows that the contribution of the manganese-catalyzed oxidation of SO2 on aerosol surfaces is approximately one to two orders of magnitude larger than previously known routes, and contributes 69.2%5.0% of the particulate sulfur production during haze events. This formation pathway could explain the missing source of sulfate and improve the understanding of atmospheric chemistry and climate change. Sulfate aerosols are an important component of wintertime haze events in China, but their production mechanisms are not well known. Here, the authors show that transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway in Northern China
Holocene variability of East Asian summer monsoon as viewed from the speleothem delta O-18 records in central China
No full textMonsoon precipitation in East China shows distinct spatial distribution and its variability is closely linked with the changes of the East Asian summer monsoon (EASM). Located in the transition zone between the southern subtropical humid climate and the northern warm temperate semi-humid climate, central China is a core region for recognizing and understanding the spatio-temporal variability of the EASM. Using U-series dating and stable isotope analysis on five stalagmites (MG-1, MG-2, MG-7, MG-40 and MG-64) from Magou Cave, Henan Province, Central China, we construct a high-resolution and precisely dated composite stalagmite delta O-18 time series covering most of the Holocene. This composite record reveals variations in precipitation delta O-18 between 11.7 and 1.1 ka BP with average resolution of similar to 4 yrs. The Magou composite record demonstrates that EASM intensity dominates long-term changes in precipitation delta O-18, which generally follows the northern hemisphere summer insolation (NHSI) trend. Both, Ensemble Empirical Mode Decomposition (EEMD) and wavelet filtering analyses real that the amplitudes of long-term (100-500 and 500-3000 yrs) components were slightly reduced between 8.5 and 4.9 ka BP, implying a weakened influence of climatic forcings on centennial and even millennial timescales during this warm period. Variance on 1-30-yr timescales is relatively low and ascribed to sampling resolution. Fourteen weak EASM intervals, including the 8.2 ka event, were identified within the period corresponding broadly with the Holocene Megathermal. Since no cold excursions other than the 8.2 ka event are found in the Greenland ice core records, we tentatively propose that oscillations in tropical sea surface temperature (SST) likely play an important role in steering other weak monsoon events. Aligning the Magou composite record and other moisture records with archaeological records from the study region, it seems that climate change influenced both the spatial distribution and agricultural practices of ancient cultures. However, overall moderate climatic changes in this region, most likely characterized by shifts between subtropical humid climate and warm temperate semi-humid climate, supported a generally consecutive development of ancient cultures without major hiatuses. (C) 2021 Elsevier B.V. All rights reserved