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Sea spray as an obscured source for marine cloud nuclei
No full textSea spray aerosols (SSAs) make up a substantial proportion of aerosols in the global atmosphere and, especially when considering marine haze and cloud layers, can have a large impact on cloud formation and atmospheric radiative balance. Although SSA has the highest cloud condensation nuclei (CCN) activation potential, the majority of its population, residing in sub-micrometre sizes, are often obscured by non-sea-spray CCN. Quantification of SSA-derived CCN is fundamental in understanding the radiative budget. Recent approaches to estimate the sub-micrometre SSA employed a free-monomodal lognormal analysis that depicts the global oceanic CCN population comprising less than 30% SSA. Here we derive SSA distributions from a unique five-year dataset of aerosol microphysics and hygroscopicity (water uptake ability) over Atlantic waters. This approach utilizes the distinctive ultra-high hygroscopicity signature of inorganic sea salt and is able to identify the sub-micrometre sea spray down to 35 nm diameter with high time and size resolution. In stark contrast to previous studies, the hygroscopicity coupled multimodal fitting analysis yields SSA-derived CCN as much as 500% in excess of estimates produced using the free-monomodal approach. Our results suggest the contribution of SSA to global CCN, particularly Aitken mode SSA, has probably been overlooked
Paleoclimatic changes during the penultimate interglacial period archived by multiple proxies of Xiashu Loess in the Chaohu Lake Basin, East China
No full textThe interglacial periods of the Pleistocene (MIS 5) and Holocene have been widely studied as analogs, whereas the records of the penultimate interglacial complex (MIS 7) are relatively sparse. In this study, based on a multitude of proxies, such as magnetic susceptibility, geochemical elements and their ratios, and grain size spanning MIS 7 of Xiashu Loess, the paleoclimatic changes that are synchronous with the five episodes during MIS 7 are reconstructed in the Chaohu Lake Basin, East China. It is proposed that the paleoclimate change in the Chaohu Lake Basin during MIS 7, on orbital time scale, might be controlled by low-latitude insolation; on millennium scales, might be directly driven by the global ice volume variations
Differences in soil water and nutrients under catchment afforestation and natural restoration shape herbaceous communities on the Chinese Loess Plateau
No full textThe Chinese Loess Plateau (CLP) is one of the areas with the most serious soil erosion worldwide. Vegetation restoration is the main way to control soil erosion and combat land degradation in this region. Using the methods of afforestation and natural restoration, there are large differences in the diversity pattern and community structure of the herbaceous plants, which affects the ecological security and restoration effectiveness. However, current studies are often less focused on this aspect, or only woody plants are considered. In this study, two adjacent catchments with similar geological backgrounds but different restoration methods on the CLP were selected; one catchment was subject to afforestation, and the other was subject to natural grassland revegetation. To clarify the environmental causes of the different performances of the herbaceous communities under these two restoration methods, the functional traits and species diversity patterns of the herbaceous plants, soil physicochemical properties and topographic factors in the two catchments were investigated. The results showed that there were significant differences in the functional traits of the herbaceous communities between these two different restoration methods. Natural restoration produced a significantly higher diversity of herbaceous plants than did afforestation. Differences in soil water, nitrate nitrogen and rapidly available phosphorus contents between the two catchments were the key reasons for the functional traits and diversity differences between the herbaceous communities. Moreover, we found that hillslopes and gullies showed different patterns in water related functional traits, especially in the naturally restored catchment, which was probably caused by the soil water differences in these two landforms. The results of this study can help us better understand the diversity patterns of herbaceous communities under the measures of natural and artificial vegetation restoration on the CLP
Mid-Holocene soil water and vegetation in the Xi'an area of the southern Chinese Loess Plateau
No full textThis paper investigates mid-Holocene palaeo-vegetation and soil water in the Xi'an area of the southern Chinese Loess Plateau (CLP). A well-dated (8.5-6.0 ka BP and 5.0-3.1 ka BP) loess-palaeosol (unit S-0) was logged, sampled and analyzed at four sites in the Xi'an area of the southern CLP, from which we report soil micromorphological (type and occurrence of root pores), particle size and geochemical data (CaCO3 and Sr concentration) to: (i) infer changes in soil water content, (ii) infer the limits of gravity water and the types of hydrologic cycle, and (iii) reconstruct the palaeovegetation. Numerous woody plant root holes were identified (2-4 mm diameter) within the illuvial horizon underlying palaeosol S-0, the morphology of which is consistent with those produced by woody plants. The clay-rich argillic horizon of palaeosol S-0 was found to contain high concentrations of kaolinite, which in concert with the geochemical indices, indicates that soil gravity water attained a depth of 2.2-2.8 m, whilst soil water content was similar to 20-25%. This implies that pedogenic processes at this site were more intense during the mid- compared to late Holocene loessic soils elsewhere on the CLP, and ultimately attests to relatively wet climatic conditions (e.g. up to 800 mm yr(-1) rainfall), the hydrologic cycle type of precipitation-soil water-groundwater, and the vegetation of deciduous broad-leaved forest. We propose that combined analyses of root-channel morphology and mobile element geochemistry can be used to infer changes in palaeo-hydrology and ultimately, the strength of the Asian Summer Monsoon
Distributions of environmental radionuclides in a marine core from the eastern continental shelf of Hainan Island, South China Sea and risk assessment
No full textSeveral long half-life natural and anthropogenic radionuclides, including Cs-137, Ra-226, Th-232, and K-40, in a 45 cm-long sediment core collected from the east continental shelf of Hainan Island, South China Sea, have been analyzed. The results showed that mean activity of Cs-137, Ra-226, Th-232, and K-40 were 2.03 +/- 1.2, 20.4 +/- 1.8, 45.7 +/- 3.0, and 520.0 +/- 20.0 Bq/kg, respectively. Radium equivalent activity and External hazard index imply a low radiation, and the study area could serve as a background reference value for environmental radionuclides in east continental shelf of Hainan Island, South China Sea
Streamflow variability in the past four centuries for the largest tributary of the Yellow River and its teleconnection with large-scale climate forcing
No full textUnderstanding long-term hydroclimate change and its evolution mechanism is beneficial to hydrological assessments and future planning in the Weihe River Basin, a region affected by the East Asian monsoon, as well as addressing increasing concerns about water resources due to social and economic development. The average June-July streamflow reconstruction was performed for the period from 1592 to 1988 for the Weihe River, based on the common growth responses relating tree-ring width, minimum density and hydrological variables, as inferred from the first principal component series of tree-ring width and density. The statistical results of calibration and verification confirmed that our model was credible and could explain 47.2% of the variance in the calibration period from 1937 to 1970. According to the criteria of one standard deviation less or greater than the mean value, 59 extremely low flow years and 62 high flow years were identified, accounting for 14.86% and 15.62%, respectively, of the past 397-year hydrological reconstruction. Severe dryness and wetness periods were in good agreement with other hydrological records in the basin, suggesting the coherence of hydroclimate changes at the basin scale, including extreme drought events from the 1920s to 1930s. The reconstructed streamflow had significant interannual and interdecadal periodic signals associated with spatial correlations with sea surface temperatures in the Pacific, Indian and Atlantic Oceans, indicating the relationships between hydrological variations in the Weihe River and the natural forcing related to the El Nino-Southern Oscillation, Pacific Decadal Oscillation, Indian Ocean Dipole pattern, North Atlantic Oscillation and Atlantic Multidecadal Oscillation (AMO). Our results provide new evidence for the potential of hydrological research using multiple tree-ring indicators, such as tree-ring width and minimum density, in the semiarid and semihumid areas of central China
Global warming-induced Asian hydrological climate transition across the Miocene-Pliocene boundary
No full textAcross the Miocene-Pliocene boundary (MPB; 5.3 million years ago, Ma), late Miocene cooling gave way to the early-to-middle Pliocene Warm Period. This transition, across which atmospheric CO2 concentrations increased to levels similar to present, holds potential for deciphering regional climate responses in Asia-currently home to more than half of the world's population- to global climate change. Here we find that CO2-induced MPB warming both increased summer monsoon moisture transport over East Asia, and enhanced aridification over large parts of Central Asia by increasing evaporation, based on integration of our similar to 1-2-thousand-year (kyr) resolution summer monsoon records from the Chinese Loess Plateau aeolian red clay with existing terrestrial records, land-sea correlations, and climate model simulations. Our results offer palaeoclimate-based support for 'wet-gets-wetter and dry-gets-drier' projections of future regional hydroclimate responses to sustained anthropogenic forcing. Moreover, our high-resolution monsoon records reveal a dynamic response to eccentricity modulation of solar insolation, with predominant 405-kyr and similar to 100-kyr periodicities between 8.1 and 3.4 Ma
A comprehensive study on ozone pollution in a megacity in North China Plain during summertime: Observations, source attributions and ozone sensitivity
No full textTropospheric ozone (O-3) pollution has been becoming prominent in North China Plain (NCP) in China since last decade. In order to clarify the source contribution and formation mechanism of O-3, the critical precursors of volatile organic compounds (VOCs) were measured with both on-line and off-line methods in Luoyang City in summer of 2019. The concentrations of nitrogen oxides (NOx, sum of NO and NO2) and O-3 were simultaneously monitored. Fifty-seven VOCs measured in U.S. Photochemical Assessment Monitoring Station (PAMS) showed daily concentrations in a range of 14.5 +/- 5.33 to 29.2 +/- 11.2 ppbv in Luoyang, which were comparable with those in other Chinese megacities. The mass compositions of VOCs were determined, with comparatively low proportions of alkanes (<50%) but high fractions of photoreactive alkenes and alkyne. Source apportionment of VOCs was conducted by Hybrid Environmental Receptor Model (HERM). The results indicated that industrial (38.5%) and traffic (32.0%) were the two dominated pollution sources of VOCs in the urban, while the biogenic and residential sources had contributions of 15.8% and 13.8%, respectively. To further measure the O-3 formation sensitivity and its source attribution, the WRF-CHEM model was adopted in this study. The variation of O3 between the observation and the stimulation using the local emission inventory showed an index of agreement (IOA) of 0.85. The simulation conducted by WRF-CHEM indicated an average of 43.5% of the O-3 was associated with the regional transportation, revealing the importance of inter-regional prevention and control policy. Traffic and biogenic emissions were the two major pollution sources to an O-3 episode occurred from July 21 to July 27, 2019 (when O-3 concentration over 150 mu gm(-3)) in Luoyang, with average contributions of 22.9% and 18.3%, respectively. The O-3 isopleths proved that its formation in the atmosphere of Luoyang was in transitional regime and collectively controlled by both VOCs and NOx. This was different from the observations in main cities of NCP before implantations of strict emission controls. The isopleths additionally designated that the O-3 formation regime would move forward or shift to NOx regime after a reduction of over 45% during the episode. Similar patterns were also reported in other Chinese megacities such as Beijing and Shanghai, due to the tightening of the NOx control policies. Our results do support that the simultaneous controls of NOx and VOCs were effective in reductions of tropospheric O-3 in Luoyang. Meanwhile, joint regional control policies on the emissions of NOx and VOCs can potentially overwhelm the current O-3 pollutions in China
Spatiotemporal variations, sources, water quality and health risk assessment of trace elements in the Fen River
No full textAs the largest river in Shanxi Province, the Fen River is the main water source for regional economic and ecological development. Water deficiency and industrialization have led to serious water pollution in the Fen River. The major and trace elements of seasonal river waters were measured to determine the spatiotemporal variations and assess the water quality as well as its controlling factors in the Fen River. Trace elements are divided into high abundance elements (B, Ba, Li, and Mn) and low abundance elements (As, Cu, Fe, Ni, Rb, Se, U, and V). The spatial variation of trace elements is obvious, with low values upstream, intermediate values downstream, and very high values midstream. The average values of the trace elements showed different seasonal variations, with high values of As, B, Ba, Mn, and Rb in the wet season, high Cu, V, and Li values in the dry season, and minor seasonal variations of Fe, Ni, Se, and U concentrations. Principal component analysis (PCA) and correlation analysis (CA) showed natural origins of Eta, Mn, Ni, and U, a nthropogenic input of As, B, Cu, Li, Rb, Se, and V. According to the results of absolute principal component sore-multivariate linear regression (APCS-MLR), the major pollution sources in the Fen River basin were related to human activities. The land use type significantly influenced the concentrations of trace elements, with high values in the cropland and low values in the forest. The water quality index (WQI) values were higher in the midstream and wet season. In comparison with other rivers in the world, the pollution of the Fen River is at a moderate level. Health risk assessment showed that As, Ba, Mn, Ni, V, and Se were the potential pollutants damaging in the Fen River, especially for children. This study highlights the importance of seasonal sample analysis and can provide vital data for water quality conservation in the Fen River basin. (C) 2020 Elsevier B.V. All rights reserved
Influence of sulfamethazine (SMT) on the adsorption of antimony by the black soil: Implication for the complexation between SMT and antimony
No full textThis paper reported when sulfamethazine (SMT) and antimony (Sb(V)) coexisted in aqueous solution at pH of 3.0, 5.0 and 7.0, the complexation between SMT and Sb(V) occurred. Such a complexation impeded the adsorption of Sb(V) on the black soil. The higher the solution pH value was, the more the amount of Sb(V) was prevented from adsorbing on the black soil. The maximum adsorption capacity (qm) of Sb(V) at the presence of SMT under pH of 3.0, 5.0 and 7.0was 5.28, 3.45 and 1.95 mg/g, respectively. -NH2, N-H, S = O and C-\N of pyrimidine ring carried by SMT acted as the complexation sites with Sb(V). The complexation constant K were- 3.15,-3.26 and- 3.48 at pH of 7.0, 5.0 and 3.0, respectively, indicating that the complexation strength between SMT and Sb(V) followed the order of pH 7.0 > pH 5.0 > pH 3.0. The binding energy between Sb(V) and the C-N group of pyrimidine ring was the highest (1.42 eV), and then followed by the groups of -NH (1.37 eV), S = O (0.66 eV) and -NH2 (0.39 eV). Besides S = O and C-N, Sb(V) tends to complex with N-H via coordination bond at pH of 7.0 while -NH2 via cation-p interaction at pH 3.0 and 5.0. Compared to pH of 5.0, the strength of cation-p interaction at pH of 3.0 weakened according to the molecular electrostatic potentialmap. These results demonstrated that different from the situation where Sb(V) exists in aqueous solution alone, the coexistence of SMT with Sb(V) affected the adsorption behavior of Sb(V) in soil and solution pH was also an influence factor. These findings in this paperwould be helpful for further understanding themobility, bioavailability and other environmental behavior of Sb(V) in soil when Sb(V) coexists with antibiotics even other organic compounds. (C) 2020 Elsevier B.V. All rights reserved