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Is the efficacy of satellite-based inversion of SO2 emission model dependent?
No full textAbstractSatellite-based inverse modeling has the potential to drive aerosol precursor emissions, but its efficacy for improving chemistry transport models (CTMs) remains elusive because of its likely inherent dependence on the error characteristics of a specific CTM used for the inversion. This issue is quantitively assessed here by using three CTMs. We show that SO2 emissions from global GEOS-Chem adjoint model and OMI SO2 data, when combined with spatial variation of bottom-up emissions, can largely improve WRF-Chem and WRF-CMAQ forecast of SO2 and aerosol optical depth (in reference to moderate resolution imaging spectroradiometer data) in China. This suggests that the efficacy of satellite-based inversion of SO2 emission appears to be high for CTMs that use similar or identical emission inventories. With the advent of geostationary air quality monitoring satellites in next 3 years, this study argues that an era of using top-down approach to rapidly update emission is emerging for regional air quality forecast, especially over Asia having highly varying emissions
Accommodation of India-Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold-thrust belt, northern margin of the Tibetan Plateau
No full textExisting models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold-thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west-east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a(-1), which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west-east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE-SW India-Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent. Supplementary material: Luminescence dating procedures and protocols is available at Thematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at
Soil erosion fluxes on the central Chinese Loess Plateau during CE 1811 to 1996 and the roles of monsoon storms and human activities
No full textEvaluating the effects of soil and water conservation on the Chinese Loess Plateau (CLP) during the past 60 years depends mainly on understanding the historical processes of soil erosion fluxes and their mechanism. However, little was known about the historical variation in soil erosion and its driving factors due to the lack of few ideal geological carriers on the CLP. A representative Heshui (HS) landslide-dammed reservoir that formed 200 years ago was drilled with a 31.39 m length sediment sequence. The HS sequence was composed of 165 deposition couplets with 56 annual freeze-thaw layers based on the elemental distributions by X-ray fluorescence core scanners. Mean couplet and annual specific sediment yields (CSSY and ASSY) were 1.44 x 10(4) t/km(2) and 1.28 x 10(4) t/km(2)/yr, respectively. The HS sequence was deposited over CE 1811-1996, which was dated by multi-methods crossing among Cs-137 activities, annual freeze-thaw layers, CSSY, recent rainfall records, and historical flood index grades. Besides, the threshold value of hydrological events that generated sediments in the HS reservoir was greater than 40 mm. As a result, there were eight periods of high ASSY between CE 1811 and 1996, although the total tendency of the ASSY was decreased, especially under the management of soil and water since the 1960s on the CLP. Interannual change of monsoon storms under El Nino-Southern Oscillation events was the primary factor affecting the variations in ASSY and storms in the HS region. Besides, human activities, such as policies and wars, also had significant influences on the historical soil erosion processes in this region. These results not only shed light on the historical changes in soil erosion fluxes and corresponding hydrological events during the past 200 years in the plateau-gully area of the CLP, but the active mechanisms under the different driving factors were also better understood
Genomic insights into the formation of human populations in East Asia
No full textThe deep population history of East Asia remains poorly understood owing to a lack of ancient DNA data and sparse sampling of present-day people(1,2). Here we report genome-wide data from 166 East Asian individuals dating to between 6000 BC and AD 1000 and 46 present-day groups. Hunter-gatherers from Japan, the Amur River Basin, and people of Neolithic and Iron Age Taiwan and the Tibetan Plateau are linked by a deeply splitting lineage that probably reflects a coastal migration during the Late Pleistocene epoch. We also follow expansions during the subsequent Holocene epoch from four regions. First, hunter-gatherers from Mongolia and the Amur River Basin have ancestry shared by individuals who speak Mongolic and Tungusic languages, but do not carry ancestry characteristic of farmers from the West Liao River region (around 3000 BC), which contradicts theories that the expansion of these farmers spread the Mongolic and Tungusic proto-languages. Second, farmers from the Yellow River Basin (around 3000 BC) probably spread Sino-Tibetan languages, as their ancestry dispersed both to Tibet-where it forms approximately 84% of the gene pool in some groups-and to the Central Plain, where it has contributed around 59-84% to modern Han Chinese groups. Third, people from Taiwan from around 1300 BC to AD 800 derived approximately 75% of their ancestry from a lineage that is widespread in modern individuals who speak Austronesian, Tai-Kadai and Austroasiatic languages, and that we hypothesize derives from farmers of the Yangtze River Valley. Ancient people from Taiwan also derived about 25% of their ancestry from a northern lineage that is related to, but different from, farmers of the Yellow River Basin, which suggests an additional north-to-south expansion. Fourth, ancestry from Yamnaya Steppe pastoralists arrived in western Mongolia after around 3000 BC but was displaced by previously established lineages even while it persisted in western China, as would be expected if this ancestry was associated with the spread of proto-Tocharian Indo-European languages. Two later gene flows affected western Mongolia: migrants after around 2000 BC with Yamnaya and European farmer ancestry, and episodic influences of later groups with ancestry from Turan
Defect Engineering in Two-Dimensional Graphitic Carbon Nitride and Application to Photocatalytic Air Purification
No full textSince the pioneering work on polychlorinated biphenyl photodegradation by Carey in 1976, photocatalytic technology has emerged as a promising and sustainable strategy to overcome the significant challenges posed by energy crisis and environmental pollution. In photocatalysis, sunlight, which is an inexhaustible source of energy, is utilized to generate strongly active species on the surface of the photocatalyst for triggering photo-redox reactions toward the successful removal of environmental pollutants, or for water splitting. The photocatalytic performance is related to the photoabsorption, photoinduced carrier separation, and redox ability of the semiconductor employed as the photocatalyst. Apart from traditional and noble metal oxide semiconductors such as P25, bismuth-based compounds, and Pt-based compounds, 2D g-C3N4 is now identified to have enormous potential in photocatalysis owing to the special pi-pi conjugated bond in its structure. However, some inherent drawbacks of the conventional g-C3N4, including the insufficient visible-light absorption ability, fast recombination of photogenerated electron-hole pairs, and low quantum efficiency, decrease its photocatalytic activity and limit its application. To date, various strategies such as heterojunction fabrication, special morphology design, and element doping have been adopted to tune the physicochemical properties of g-C3N4. Recent studies have highlighted the potential of defect engineering for boosting the light harvesting, charge separation, and adsorption efficiency of g-C3N4 by tailoring the local surface microstructure, electronic structure, and carrier concentration. In this review, we summarize cutting-edge achievements related to g-C3N4 modified with classified non-external-caused defects (carbon vacancies, nitrogen vacancies, etc.) and external-caused defects (doping and functionalization) for optimizing the photocatalytic performance in water splitting, removal of contaminants in the gas phase and wastewater, nitrogen fixation, etc. The distinctive roles of various defects in the g-C3N4 skeleton in the photocatalytic process are also summarized. Moreover, the practical application of 2D g-C3N4 in air pollution control is highlighted. Finally, the ongoing challenges and perspectives of defective g-C(3)N(4 )are presented. The overarching aim of this article is to provide a useful scaffold for future research and application studies on defect-modulated g-C3N4
Water depth control on n-alkane distribution and organic carbon isotope in mid-latitude Asian lakes
No full textThe relative proportion of mid-chain to long chain n-alkane homologues and isotopic compositions of total organic carbon (P-aq and delta C-13(org)) have been proposed as potential lake-level proxies since such features mainly come from submerged aquatic plants living within an optimum range of lake water depth. With limited dataset available, the applicability of both indices and their sensitivity to lake water depth changes across a broad geographic extent need further investigation. Here we report P-aq and delta C-13(org) values in surface sediments collected from 55 lakes in mid-latitude Asia. We have found an arched relationship between P-aq index and water depth, with high Paq values occurring at the depth of similar to 1-10 m, while sediments from shallower and deeper water lakes have relatively low P-aq values. delta C-13(org) variation resembles an arched pattern with depth in freshwater and brackish lakes, with relatively high delta C-13(org) values also corresponding to the depth of similar to 1-10 m, but substantially high delta C-13(org) values in hypersaline environments (salinity > similar to 100,000 mg/L) obscure the arched delta C-13(org)-depth relationship. We suggest that both indices respond to the structure of aquatic plant community, especially the biomass of submerged plants. Our results confirm that P-aq and delta C-13(org) can be used to infer lake-level changes in mid-latitude Asia, but other influencing factors have to be considered before applying the two proxies to downcore reconstructions, and combined utilization of the P-aq and delta C-13(org) indicators could improve the reliability of paleohydrological reconstructions
Decreasing concentrations of carbonaceous aerosols in China from 2003 to 2013
No full textCarbonaceous aerosols were characterized in 19 Chinese cities during winter and summer of 2013. Measurements of organic carbon (OC) and elemental carbon (EC) levels were compared with those from 14 corresponding cities sampled in 2003 to evaluate effects of emission changes over a decade. Average winter and summer OC and EC decreased by 32% and 17%, respectively, from 2003 to 2013, corresponding to nationwide emission control policies implemented since 2006. The extent of carbon reduction varied by season and by location. Larger reductions were found for secondary organic carbon (SOC, 49%) than primary organic carbon (POC, 25%). PM2.5 mass and total carbon concentrations were three to four times higher during winter than summer especially in the northern cities that use coal combustion for heating
Climate Change along the Silk Road and Its Influence on Scythian Cultural Expansion and Rise of the Mongol Empire
No full textClimate change and cultural exchange both influenced cultural development along the continental Silk Road during the late Holocene, but climate change and its influence on nomadic civilizations during that time has yet to be systematically assessed. In this study, we analyzed records of climate change along the Silk Road covering key periods in the late Holocene, based on multiproxies from various archives including lake sediments, shorelines/beach ridges, peatlands, ice cores, tree rings, aeolian sediments, moraines, and historical documents. Combined with archaeological data, we assessed the influence of climate on development and expansion of representative pastoral nomadism. Our results show that the most notable climate changes in Central Asia were characterized by decreasing temperature, expanding glaciers, increasing precipitation, and increasing humidity during transitions from the Sub-Boreal to Sub-Atlantic Period (ca. 9-8th century BC) and from the Medieval Warm Period to the Little Ice Age (ca. 13-14th century AD). The two periods coincided with Scythian Cultural expansion across the steppe landscape of Central Asia and rise of the Mongol Empire, respectively. These temporal coincidences are interpreted as causally related, where temperature fall and glacial advance may have forced the pastoral nomadism to southward migration. Coeval wetness and southward migration of steppe landscape in Central Asia were beneficial for these cultural expansions, which spanned the Eurasian arid and semi-arid zone westward. Therefore, during the historical period when productivity was underdeveloped, although expansions of pastoral nomadism were closely related to internal social structures, climate change was possibly the most critical controlling factor for sustainability development and collapse
Late Miocene-Pliocene Asian summer monsoon variability linked to both tropical Pacific temperature and Walker Circulation
No full textThe Pliocene climate, characterized by sustained global warmth and weakened Walker Circulation, might be a potential analogue of our future climate. How Asian Summer Monsoon (ASM) evolved over this period and its controlling mechanisms remain controversial, which limits our understanding of future monsoon behavior. Here, we present alkenone- and GDGT-based records reconstructed from the northern coast of the South China Sea, interpreted to document the strength of ASM-induced upwelling/mixing effect, to infer Late Miocene-Pliocene ASM variability. Cooler local sea surface temperatures occurred between similar to 5.6 million years ago (Ma) and 4.3 Ma, corresponding to Pliocene warmer conditions, effectively capturing the cooling signal induced by summer upwelling. Our multiple biomarker records consistently indicate three phases of Late Miocene-Pliocene ASM evolution: weak ASM strength at similar to 6.5-5.6 Ma, substantially enhanced strength at 5.6-4.3 Ma, and reduced strength but with a slightly strengthening trend after similar to 4.3 Ma. The three features have been reported collectively from previous terrestrial and marine records. The close correspondence of the ASM strength to tropical temperature before similar to 4.3 Ma suggests a dominant tropical temperature control, whereas the increasing ASM strength after that, opposite to temperature changes, implies that the developed Walker Circulation started to influence ASM strength over the Late Pliocene. Hence, tropical temperature and Walker Circulation appear to have exerted competing roles in the Late Miocene-Pliocene ASM evolution. (C) 2021 Elsevier B.V. All rights reserved
The roles of aqueous-phase chemistry and photochemical oxidation in oxygenated organic aerosols formation
No full textThe formation mechanism and evolution process of secondary organic aerosol (SOA) remain poorly understood due to measurement uncertainties and chemical complexities. Here, we present the characterization of non-refractory fine particles (NR-PM2.5) analyzed by means of a time-of-flight ACSM (ToF-ACSM) at a rural site in the North China Plain during winter. Our results show that air quality in rural areas was heavily polluted by primary organic aerosols (POA), which accounted for 83% of total organic aerosol (OA). The oxygenated organic aerosols (OOA) were mainly generated from local emissions. As pieces of evidence, firstly, less-oxidized OOA (LO-OOA) had good correlations with primary species like biomass burning OA (BBOA) (R2 = 0.54), EC (R2 = 0.46), and chloride (R2 = 0.46), implying LO-OOA was formed with the POA emission processes; secondly, there was a significant increase in OOA concentration after sunrise, indicating a lot of local generation during the daytime; thirdly, the potential source region of OOA was restricted in that of POA, implying that OOAs were converted from where primary emission exists. The formation processes of LO-OOA and more-oxidized OOA (MO-OOA) are different. Aqueous-phase chemistry had a dominant effect on the formation of LO-OOA due to the better correlation between aerosol liquid water content (ALWC) with LO-OOA (R2 = 0.54) than MO-OOA (R2 = 0.15). In comparison, both aqueous -phase and photochemical processes acted on the MO-OOA formation, when odd oxygen (Ox = O3+NO2) was low (Ox 35 ppb), photochemical oxidation played an essential role in MO-OOA formation