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Tree-ring oxygen isotope recorded precipitation variations over the past two centuries in the northeast Chinese Loess Plateau
No full textIt was shown in previous studies that tree-ring oxygen isotope (delta O-18(TR)) was a proxy of regional precipitation. Using two delta O-18(TR) chronologies of Pinus tabulaeformis Carr. in northeast Chinese Loess Plateau (CLP), we synthesized a master series which had a high correlation with regional precipitation from previous-year September to current-year August (P-SA) (r = -0.650, N = 52, p < .001). Thus we reconstructed the P-SA over the past two centuries (AD 1808-2009) for the northeast CLP. The results of calibration-verification tests indicated that the precipitation reconstruction was stable and reliable. Compared with reconstructions based on the tree-ring width and historical documents, the P-SA reconstruction reserved more decadal low-frequency climate signals such as the drying trend since the 1930s. Superposed epoch analysis (SEA) showed that the large tropical volcanic eruptions significantly reduced P-SA in the first year after the eruptions. The contrast of the regional precipitation reconstructions in the west, northeast, and southeast CLP demonstrated that spatial and temporal differences of precipitation variation. In terms of extreme climate events, major droughts in the mid-to-late 1920s were recorded in all three regional precipitation records, while the Ding-Wu Disaster (AD 1876-1878) was only found in the southeast CLP. Under the background of the weakening Asian monsoon and global warming, CLP was more prone to droughts in the last five decades
Source profiles of molecular structure and light absorption of PM2.5 brown carbon from residential coal combustion emission in Northwestern China
No full textResidential coal combustion is a prominent source of brown carbon (BrC) aerosols, but knowledge of their molecular structures and optical absorption were limited, which have notable used in ambient BrC source identification and radiative forcing calculation. In this study, the Fourier transform-ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis as well as Fourier transform infrared spectroscopy analysis were used to insight the molecular compounds and structures of BrC from anthracite and bituminous coal combustions between traditional and improved stoves. The absorption angstrom ngstro center dot m exponents (AAE) and mass absorption efficiency (MAE) values for the BrC emitted from the combinations of bituminous were both 1.2-2.5 times lower than those of anthracite, interpreting that the BrC from the anthracite emissions had greater light-absorbing capacity. In contrast, the emission factor of light absorption (EFAbs) at 365 nm for the bituminous coal combusted in the traditional stove was the highest among all the tested scenarios, which revealed that the incomplete combustion of bituminous coal could emit more BrC. It was noted that primary BrC emitted from the coal combustion with traditional stoves contains higher aromaticity groups of C-C and C=O and higher S containing organics, whereas more aliphatic groups were found in BrC using the improved stoves. N-containing (CHON and CHONS) compounds were dominated in the total molecular formula of BrC, whereas the sum of CHON and CHO groups had high double-bond equivalent (DBE) values contributed 53.5%-87.1% to the total BrC absorption. Moreover, for CHOS, the lowest of estimated molecular absorption, DBE, and DBE/C should attribute to the non-chromophoric or weak absorptive S-containing compounds. This study supplied an effective evaluation method to compare BrC emissions and their absorption for coal combustion on regional scale
Explorations of tire and road wear microplastics in road dust PM2.5 at eight megacities in China
No full textTire and road wear microplastics (TRWMPs) in road dust are a key source of atmospheric particulate matter and have an adverse impact on human health and the environment. In this study, samples of particulate matter with a diameter of 2.5 mu m or less (PM2.5) in road dust were collected from eight megacities in China to determine the TRWMP content, including that of natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). The total abundance of TRWMPs was the highest in Lanzhou (174.7 +/- 17.0 mu g g(-1)), followed by Xi'an (169.3 +/- 23.8 mu g g(-1)), Beijing (107.5 +/- 7.5 mu g g(-1)), Changchun (102.2 +/- 8.4 mu g g(-1)), Chengdu (101.6 +/- 12.9 mu g g(-1)), Guangzhou (98.8 +/- 6.5 mu g g(-1)), Wuhan (96.0 +/- 5.3 mu g g(-1)), and Shanghai (86.1 +/- 30.1 mu g g(-1)). A considerably higher TRWMP fraction in road dust PM2.5 was observed in the northern cities than in the southern cities and is attributable to the higher frictional resistance of roads subjected to less precipitation. The abundance of TRWMPs in the southern cities was dependent on road type, but this dependence was not observed in the northern cities. In the south, road dust PM2.5 on main roads contained more TRWMPs than that on branch roads. Correlation analysis indicated that TRWMPs were associated with tire, road, and break wear. In relation to intracellular oxidative stress factors, higher correlations were observed between TRWMPs and lactate dehydrogenase (r = 0.83) than between TRWMPs and reactive oxygen species (r = 0.59), possibly because TRWMPs destroy the integrity of the cell membrane, with NR exhibiting a higher cytotoxicity than SBR or BR. This study provides evidence that TRWMPs have an adverse impact on human health by inducing cellular oxidative stress. Therefore, further research on TRWMPs in respirable road dust is required
Indian summer monsoon variations during the Younger Dryas as revealed by a laminated stalagmite record from the Tibetan Plateau
No full textHigh-resolution and precisely dated hydroclimate records in the southeastern Tibetan Plateau (TP) remain sparse beyond the Holocene, which hampers our ability to understand the hydroclimate variability in this important Indian summer monsoon (ISM) fringe area and its global teleconnection. Here we present 3-y resolution delta O-18 and delta C-13 records from a laminated stalagmite (RG-3) from Rige Cave in the southeastern TP, spanning the Younger Dryas (YD). The records allow us to precisely characterize the timing, structure, and particularly centennial-scale events within the YD, and probe the control factors of precipitation delta O-18 ( delta O-18(p)) in the ISM fringe area. On centennial-millennial timescales, the Rige delta O-18 record shows coherent pattern with the East Asian summer monsoon (EASM) counterpart, combined with modeled delta O-18(p) results and spatial analysis, suggesting that delta O-18(p) in this part of the TP is largely controlled by the large-scale atmosphere circulation (or the ISM strength), and the altitude increase in the TP may not potentially result in an opposite delta O-18(p) pattern at least in the monsoonal TP regime. We also found significant delta C-13-delta O-18 covariation on the centennial timescale, suggesting a coincided ISM rainfall and biomass change during the YD. In the Rige records, one weak centennial-scale ISM event (namely the intra-Allerod cold period, [ACP) and three strong centennial-scale ISM events within the YD (namely A1'-A2'-A3') were prominent and occurred between similar to 12,470 and 12,310 +/- 14, similar to 12,210 -12,090 +/- 12 and similar to 12,010-11,920 +/- 12 y BP (before present, where present = 1950 CE), respectively. Spectral analyses of Rige records also revealed a significant similar to 200-y periodicity, which is nearly in-phase with observed centennial-scale variations of the North Atlantic temperature and mid-latitude westerlyjet during that time. These observations support the hypothesis that the solar de Vries cycle (207-y) triggered the centennial-scale climate variations in high northern latitude, leading to the ISM variations via fast atmospheric processes. (C) 2022 Elsevier Ltd. All rights reserved
Indian summer monsoon variations during the Younger Dryas as revealed by a laminated stalagmite record from the Tibetan Plateau
No full textHigh-resolution and precisely dated hydroclimate records in the southeastern Tibetan Plateau (TP) remain sparse beyond the Holocene, which hampers our ability to understand the hydroclimate variability in this important Indian summer monsoon (ISM) fringe area and its global teleconnection. Here we present 3-y resolution delta O-18 and delta C-13 records from a laminated stalagmite (RG-3) from Rige Cave in the southeastern TP, spanning the Younger Dryas (YD). The records allow us to precisely characterize the timing, structure, and particularly centennial-scale events within the YD, and probe the control factors of precipitation delta O-18 ( delta O-18(p)) in the ISM fringe area. On centennial-millennial timescales, the Rige delta O-18 record shows coherent pattern with the East Asian summer monsoon (EASM) counterpart, combined with modeled delta O-18(p) results and spatial analysis, suggesting that delta O-18(p) in this part of the TP is largely controlled by the large-scale atmosphere circulation (or the ISM strength), and the altitude increase in the TP may not potentially result in an opposite delta O-18(p) pattern at least in the monsoonal TP regime. We also found significant delta C-13-delta O-18 covariation on the centennial timescale, suggesting a coincided ISM rainfall and biomass change during the YD. In the Rige records, one weak centennial-scale ISM event (namely the intra-Allerod cold period, [ACP) and three strong centennial-scale ISM events within the YD (namely A1'-A2'-A3') were prominent and occurred between similar to 12,470 and 12,310 +/- 14, similar to 12,210 -12,090 +/- 12 and similar to 12,010-11,920 +/- 12 y BP (before present, where present = 1950 CE), respectively. Spectral analyses of Rige records also revealed a significant similar to 200-y periodicity, which is nearly in-phase with observed centennial-scale variations of the North Atlantic temperature and mid-latitude westerlyjet during that time. These observations support the hypothesis that the solar de Vries cycle (207-y) triggered the centennial-scale climate variations in high northern latitude, leading to the ISM variations via fast atmospheric processes. (C) 2022 Elsevier Ltd. All rights reserved
C-13 signatures of aerosol organic and elemental carbon from major combustion sources in China compared to worldwide estimates
No full textCarbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual 14C-13C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of 13C source signatures, which are seldom measured for EC. In this work, we present 13C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for 13C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the 13C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the 13C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in 13C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of 13C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite 13C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, 13C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, lowvolatile, and non-volatile OC fractions. Each source category shows a characteristic trend of 13C signatures with desorption temperature, which is likely related to different OC formation processes during combustion. (c) 2021 Elsevier B.V. All rights reserved
Seasonality of Aerosol Sources Calls for Distinct Air Quality Mitigation Strategies
No full textAn Aerosol Chemical Speciation Monitor (ACSM) was deployed to investigate the temporal variability of non-refractory particulate matter (NR-PM1) in the coastal city of Galway, Ireland, from February to July 2016. Source apportionment of the organic aerosol (OA) was performed using the newly developed rolling PMF strategy and was compared with the conventional seasonal PMF. Primary OA (POA) factors apportioned by rolling and seasonal PMF were similar. POA factors of hydrocarbon-like OA (HOA), peat, wood, and coal were associated with domestic heating, and with an increased contribution to the OA mass in winter. Even in summer, sporadic heating events occurred with similar diurnal patterns to that in winter. Two oxygenated OA (OOA) factors were resolved, including more-oxygenated OOA and less-oxygenated OOA (i.e., MO-OOA and LO-OOA, accordingly) which were found to be the dominant OA factors during summer. On average, MO-OOA accounted for 62% of OA and was associated with long-range transport in summer. In summer, compared to rolling PMF, the conventional seasonal PMF over-estimated LO-OOA by nearly 100% while it underestimated MO-OOA by 30%. The results from this study show residential heating and long-range transport alternately dominate the submicron aerosol concentrations in this coastal city, requiring different mitigation strategies in different seasons
Tree-Ring-Based Drought Reconstruction in Northern North China over the Past Century
No full textA tree-ring width chronology was developed from the Chinese pine (Pinus tabuliformis) in northern North China. To acquire a long-term perspective on the history of droughts in this region, the Standardized Precipitation Evapotranspiration Index (SPEI) from August of the previous year to February of the current year was reconstructed for the period of 1903-2012 AD. The reconstruction explained 46.6% of the instrumental records over the calibration period of 1952-2012. Five dry periods (1916-1927, 1962-1973, 1978-1991, 1994-1999 and 2002-2005) and three wet periods (1908-1915, 1928-1961 and 1974-1977) were found in the reconstructed period, and most of the dry years (periods) in the reconstruction were supported by historical records. Comparisons between the reconstruction and other nearby dryness/wetness indices and precipitation reconstructions demonstrated a good repeatability and high reliability in our reconstruction. Spatial correlation implied that the reconstruction could represent regional hydroclimatic characteristics on a larger regional scale. Significant periodicities and correlations were observed between the reconstructed data and the quasi-biennial oscillation (QBO), El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), which suggested that the hydroclimatic variation in northern North China may be closely connected to remote oceans. The significant and high correlation between the reconstructed series and sea surface temperatures (SSTs) in the eastern equatorial and Southeast Pacific Ocean indicated that ENSO may be the main factor influencing the regional climate
Effect of electron structure on the catalytic activity of LaCoO3 perovskite towards toluene oxidation
No full textLaCoO3 perovskites with different spin states of Co3+ were prepared by calcination at 600-1000 degrees C. LaCoO3 with electron filling in the e(g) orbital at 1 exhibited a moderate interaction between the surface oxygen, resulting in the best catalytic activity. This was verified by the O p-band center
Stable carbon isotopic characteristics of fossil fuels in China
No full textGood knowledge on the stable carbon isotopic composition (delta C-13) of fossil fuels is critical for the estimation of atmospheric CO2 sources. Here, we complied a comprehensive delta C-13 database including 336 coal, 580 oil, and 1160 natural gas data based on the extensive literature search, and conducted field measurements in two megacities, to characterize the delta C-13 signatures of Chinese fossil fuels. Results show that coal exhibits a narrow range and the most enriched in delta C-13 signature, oil displays intermediate variations both in the distribution and value of delta C-13. By contrast, natural gas is strongly depleted but became more enriched in delta C-13 signature due to the shift in production from isotopically light oil-type gas to isotopically heavy coal-type gas. We found an obvious overlap between the delta C-13 distributions of oil and natural gas, and the carbon isotopic difference between oil and natural gas is minimized in Ordos Basin. Therefore, we suggested that the geographic origin is a certain factor that must be considered when delta C-13 of fossil fuels is used to estimate CO2 source contributions, and the measurement of delta(CO2)-C-13 signatures of local end members is a better alternative in the absence of detailed information about the geographical origins of fossil fuels. This work is helpful in improving the ability to quantify CO2 sources of fossil fuel emissions in China, and also make a contribute to the global carbon isotope database. (C) 2021 Elsevier B.V. All rights reserved