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Spatial distribution and sources of winter black carbon and brown carbon in six Chinese megacities
No full textThe light-absorbing carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC), influenced heavily on aerosol environmental quality and the Earth's radiation. Here, a winter campaign to characterize BC and BrC in PM2.5 was conducted simultaneously in six Chinese megacities (i.e., Harbin, Beijing, Xi'an, Shanghai, Wuhan, and Guangzhou) using continual aethalometers. The combinations of advanced aethalometer and generalized additive model (GAM) were used to precisely quantify the BC and BrC sources in these megacities. The averaged light-absorbing coefficients of BC (b(abs)-BC) and BrC (b(abs)-BrC) were 28.6 and 21.8 Mm(-1) in northern cities, they were 1.4 and 2.7 times higher than those in southern cities. The BrC dominated the total b(abs) (>40%) in northern cities but low to 20% in southern cities. On the other hand, the BC fractions were high in the southern cities, with the contributions of 62.4-79.7%, where as much lower values of 53.7-59.4% in the northern cities. Source apportionment showed that the combustion of liquid fuels (e.g., gasoline or diesel) was highly dominant to b(abs)-BC (>80%) in Guangzhou and Wuhan. This was further supported by the high NO2 loadings in the GAM model. Solid fuels (i.e., biomass or coal) contributed a substantial portion to total b(abs)-BC in the other four cities where the high abundances of primary b(abs)-BrC were observed. The diurnal trend showed the peaks of secondary-BrC (b(abs)-BrCS) and b(abs)-BrCS/Delta CO in the northern cities occurred at high relative humidity in nighttime, implying the secondary BrC formation was possibly related to aqueous reactions in winter. In contrast, in the southern cities of Shanghai and Guangzhou, the accumulation of vehicle emissions during the morning traffic rush hours lead the formation of secondary BrC through photochemical reactions. The results of this work can be applied for the development of more effective practices to control BC and BrC on regional scale. (C) 2020 Elsevier B.V. All rights reserved
A July-August relative humidity record in North China since 1765 AD reconstructed from tree-ring cellulose delta O-18
No full textSince the late 1970s, East Asian summer monsoon (EASM) has shown a significant weakening trend, and sustained drought has occurred across North China. Placing recent climate changes in the paleoclimatic context can better understand the EASM variations. Four delta O-18 sequences based on tree-ring cellulose of Chinese pine were developed from Mt. Beiwudang, North China, covering a period from 1700 to 2013. Based on a climatic response analysis, a transfer function was designed to reconstruct the relative humidity from July to August (RHJA hereafter). The RHJA spans from 1765 to 2013 and explains 49% (R-adj(2)= 48%) of the instrumental variance during the calibration period (1961-2013, r = - 0.70, p < 0.0001). The RHJA is mainly influenced by precipitation in the summer rainy season and reflect EASM variations. Spatial representation analysis indicates that RHJA represents the dry/wet variations across North China. At the interannual scale, RHJA records many extreme dry/wet events, among which the events in 1876-1878, 1900, and the 1920s are extensive droughts. Those events correspond well to ENSO events, plus further correlation and periodicity analysis indicate that RHJA contains ENSO signals. At the interdecadal scale, RHJA shows a decreasing trend and unprecedented low values from 1981 to 2013, suggesting that the weakening of EASM since the late 1970s is unprecedented in the past 249 years. Similarly, the significantly correlating region in the spatial correlation analysis, covering the Meiyu/Baiu/Changma rainfall belt and India, have also undergone a climatic shift since the late 1970s according to previous papers
Development of the Leeuwin Current on the northwest shelf of Australia through the Pliocene-Pleistocene period
No full textAlthough the Leeuwin Current (LC) is thought to play a pivotal role in climatic and oceanic systems of the western Australian region, how the LC developed through the Pliocene-Pleistocene period remains elusive. Here we used biomarker records to reconstruct variations of temperatures and primary productivity on the northwest shelf of Australia over the last 6 million years. Since similar to 1.2 million years ago (Ma), our sea surface temperature record indicates progressive warming, with temperature values comparable to those in the Indo-Pacific Warm Pool, in contrast with the long-term global cooling trend. The regional surface warming was accompanied by suppressed primary productivity, together indicating prevailing warm, low-salinity, nutrient-deficient surface water, and thus a stronger LC since the Mid-Pleistocene Transition. During 4-1.2 Ma, greater surface temperature gradient between the Indo-Pacific Warm Pool and the northwest shelf of Australia and higher primary productivity seem to suggest a generally weaker LC. Warmer temperatures and lower productivity suggest a plausible existence of the LC during 6-4 Ma, but more work is required to confirm this. Impact of sea level and the Indonesian Throughflow on the LC strength may exist, but did not dominate through the Pliocene-Pleistocene period, considering different variation patterns among them. We propose the stronger LC after similar to 1.2 Ma was more likely triggered by enhanced atmospheric circulation. Although the increased LC after similar to 1.2 Ma may have potentially brought additional moisture to the Australian continent during the interglacial periods, it has not overturned the long-term drying trend through the Pliocene-Pleistocene period. (C) 2021 Elsevier B.V. All rights reserved
Exploring the Influences of Temperature on "H-Shaped" Glycerol Dialkyl Glycerol Tetraethers in a Stratigraphic Context: Evidence From Two Peat Cores Across the Late Quaternary
No full textUnusual "H-Shaped" branched and isoprenoidal glycerol monoalkyl glycerol tetraethers (GMGTs, or H-GDGTs) have been found in peat, lake, and ocean sediments. A survey of recent samples from a modern global peat database suggested that there is a relationship between the abundance of H-GDGTs relative to regular GDGTs and temperature. However, this relationship has not been widely explored, including in a historical, stratigraphic or geological context. Here, we report the abundance and distribution of H-iso- and H-brGDGTs in two (Hani and Gushantun) peat cores from northeastern China through the late Quaternary (last 15 kyr) to examine whether the relationship between temperature and the relative abundance of H-GDGTs is preserved downcore. The results indicate that high relative abundances of H-brGDGTs are associated with high (or increasing) reconstructed mean annual air temperature (MAAT(peat)), albeit with considerable divergence in some intervals. On the other hand, high relative abundances of H-isoGDGTs are generally associated with low (or decreasing) MAAT(peat). These findings are partly inconsistent with the observations from the modern database of globally distributed peats, which showed that the abundance of both (br- and iso-) H-GDGTs is positively correlated with temperature. The deviation in the relationship between H-isoGDGTs and temperature suggests that additional factors, for example pH and shifts in archaeal community related to hydrology, exert an influence on the abundance of H-isoGDGTs on the long-term
Megadrought and cultural exchange along the proto-silk road
No full textArid Central Asia (ACA), with its diverse landscapes of high mountains, oases, and deserts, hosted the central routes of the Silk Roads that linked trade centers from East Asia to the eastern Mediterranean. Ecological pockets and ecoclines in ACA are largely determined by local precipitation. However, little research has gone into the effects of hydroclimatic changes on trans-Eurasian cultural exchange. Here, we reconstruct precipitation changes in ACA, covering the mid-late Holocene with a U-Th dated, similar to 3 a resolution, multi-proxy time series of replicated stalagmites from the southeastern Fergana Valley, Kyrgyzstan. Our data reveal a 640-a megadrought between 5820 and 5180 a BP, which likely impacted cultural development in ACA and impeded the expansion of cultural traits along oasis routes. Instead, it may have diverted the earliest transcontinental exchange along the Eurasian steppe during the 5th millennium BP. With gradually increasing precipitation after the megadrought, settlement of peoples in the oases and river valleys may have facilitated the opening of the oasis routes, ''prehistoric Silk Roads", of trans-Eurasian exchange. By the 4th millennium BP, this process may have reshaped cultures across the two continents, laying the foundation for the organized Silk Roads. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press
Is Current Research on How Climate Change Impacts Global Food Security Really Objective?
No full textGlobal food insecurity is becoming more severe under the threat of rising global carbon dioxide concentrations, increasing population, and shrinking farmlands and their degeneration. We acquired the ISI Web of Science platform for over 31 years (1988-2018) to review the research on how climate change impacts global food security, and then performed cluster analysis and research hotspot analysis with VosViewer software. We found there were two drawbacks that exist in the current research. Firstly, current field research data were defective because they were collected from various facilities and were hard to integrate. The other drawback is the representativeness of field research site selection as most studies were carried out in developed countries and very few in developing countries. Therefore, more attention should be paid to developing countries, especially some African and Asian countries. At the same time, new modified mathematical models should be utilized to process and integrate the data from various facilities and regions. Finally, we suggested that governments and organizations across the world should be united to wrestle with the impact of climate change on food security.</p
Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics
No full textA prominent source of hydroxyl radicals ((OH)-O-center dot), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol, n-butanol, or formate as (OH)-O-center dot scavengers, the average intrinsic quantum yield of nitrite [Phi-(NO2-)] was 0.75 +/- 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Phi(NO2-) was strongly pHdependent, reaching 8.0 +/- 2.1% at a pH of 8 and 1.5 +/- 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2 for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments
A GPU-Accelerated Hydrodynamic Model for Urban Rainstorm Inundation Simulation: A Case Study in China
No full textFrequent urban rainstorm inundations can cause serious damages to human life and social economy. Reliable simulation of urban rainstorm inundation is an effective approach for performing flood risk analysis to reduce losses. In this work, a full 2D high-performance hydrodynamic model for urban rainstorm inundation simulation based on Graphic Processing Unit (GPU) was developed. The idealized V-shape catchment and sponge city district of Fengxi New City were selected as the study areas to assess performance of the model. The model was validated against analytical benchmark results of the idealized V-catchment test which show good agreement between the modelled flow and analytical solutions. The model was then applied to simulate actual urban rainstorm inundation process under measured rainfall. The results indicated that the model can be applied to high-resolution urban region simulations. Specifically, the validation results indicated that the proposed model had a good performance, with an accepted error of less than 15%. When applied to compute the Fengxi New city under design rainstorms with different annual return periods of 1, 5, 10, 20, 50, and 100 years, it was found that the model effectively evaluated the temporal and spatial variation process of urban inundation, and quantitatively investigated flood risks according to the water depth change. The model has been substantially accelerated on GPU to quickly predict urban inundation. The accuracy and rapid simulation speed of the model were verified based on the actual study area. Therefore, the proposed model can help to predict the dynamic processes of urban flood inundation and thus reduce flood inundation disasters. This is essential for future optimal sponge urban construction planning in China
A GPU-Accelerated Hydrodynamic Model for Urban Rainstorm Inundation Simulation: A Case Study in China
No full textFrequent urban rainstorm inundations can cause serious damages to human life and social economy. Reliable simulation of urban rainstorm inundation is an effective approach for performing flood risk analysis to reduce losses. In this work, a full 2D high-performance hydrodynamic model for urban rainstorm inundation simulation based on Graphic Processing Unit (GPU) was developed. The idealized V-shape catchment and sponge city district of Fengxi New City were selected as the study areas to assess performance of the model. The model was validated against analytical benchmark results of the idealized V-catchment test which show good agreement between the modelled flow and analytical solutions. The model was then applied to simulate actual urban rainstorm inundation process under measured rainfall. The results indicated that the model can be applied to high-resolution urban region simulations. Specifically, the validation results indicated that the proposed model had a good performance, with an accepted error of less than 15%. When applied to compute the Fengxi New city under design rainstorms with different annual return periods of 1, 5, 10, 20, 50, and 100 years, it was found that the model effectively evaluated the temporal and spatial variation process of urban inundation, and quantitatively investigated flood risks according to the water depth change. The model has been substantially accelerated on GPU to quickly predict urban inundation. The accuracy and rapid simulation speed of the model were verified based on the actual study area. Therefore, the proposed model can help to predict the dynamic processes of urban flood inundation and thus reduce flood inundation disasters. This is essential for future optimal sponge urban construction planning in China
Oxygen vacancy defects-boosted deep oxidation of NO by beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst in situ synthesized from Bi/Ce(CO3) (OH) precursor
No full textFlower-like n-type CeO2-delta is hybridized with p-type beta-Bi2O3 nanoparticles to design a novel beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst via a thermal treatment process of Bi/Ce(CO3)(OH) precursor. The synthesized beta-Bi2O3/CeO2-delta exhibits a remarkable enhancement in NO removal and significant suppression of toxic intermediates nitrogen dioxide (NO2) under visible light irradiation. The superior photocatalytic activity of beta-Bi2O3/CeO2-delta for NO removal is mainly derived from the synergistic effects of the oxygen vacancies (OVs) and p-n heterojunction. The OVs not only enhance the visible light utilization and boost the separation of electronhole pairs but also improve the adsorption and activation of NO and O-2. Particularly, the p-n heterojunction is beneficial for the interfacial migration of photogenerated charge carriers. Electron spin resonance (ESR) and trapping experiment reveal that the synergistic effects of OVs and p-n heterojunction can induce the generation of more active species. The electrochemical measurements and density-functional theory (DFT) calculations indepth confirm that both p-n heterojunction and OVs can accelerate the interfacial charge transfer, resulting in the deep oxidation of reactants. Therefore, the flower-like beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst exhibits an advanced photocatalytic activity for deep NO removal and a suppressed NO2 generation. In addition, monitoring the reaction products by in situ Fourier transform infrared spectrum (FTIR) further validates that the main products of nitrates are formed during the photocatalytic process. This work demonstrates a straightforward approach for construction of p-n heterojunction photocatalysts, which can enhance the effective photocatalytic activity and stability for NO removal