Institute of Earth Environment
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Spatiotemporal variation, sources, and secondary transformation potential of volatile organic compounds in Xi'an, China
No full textAs critical precursors of ozone (O-3) and secondary organic aerosols, volatile organic compounds (VOCs) play a vital role in air quality, human health, and climate change. In this study, a campaign of comprehensive field observations and VOC grid sampling was conducted in Xi'an, China, from 20 June to 20 July 2019 to identify the spatiotemporal concentration levels, sources, and secondary transformation potential of VOCs. During the observation period, the average VOC concentrations at the Chanba (CB), Di Huan Suo (DHS), Qinling (QL), and gridded sampling sites were 27.8 +/- 8.9, 33.8 +/- 10.5, 15.5 +/- 5.8, and 29.1 +/- 8.4 ppb, respectively. Vehicle exhaust was the primary source of VOC emissions in Xi'an, and the contributions of vehicle exhaust to VOCs at the CB, DHS, and QL sites were 41.3 %, 30.6 %, and 23.6 %-41.4 %, respectively. While industrial emissions were the second-largest source of VOCs in urban areas, contributions from aging sources were high in rural areas. High potential source contribution function values primarily appeared in eastern and southern Xi'an near the sampling site, which indicates that Xi'an exhibits a strong local VOC source. Moreover, alkenes, aromatics, and oxygenated VOCs played a dominant role in secondary transformation, which is a major concern in reducing O-3 pollution in Xi'an
Speleothem record of mild and wet mid-Pleistocene climate in northeast Greenland
No full textThe five interglacials before the Mid-Brunhes Event (MBE) [c.430 thousand years (ka) ago] are generally considered to be globally cooler than those post-MBE. Inhomogeneities exist regionally, however, which suggest that the Arctic was warmer than present during Marine Isotope Stage (MIS) 15a. Using the first speleothem record for the High Arctic, we investigate the climatic response of northeast Greenland between c.588 and c.549 ka ago. Our results indicate an enhanced warmth of at least +3.5 degrees C relative to the present, leading to permafrost thaw and increased precipitation. We find that delta O-18 of precipitation was at least 3 parts per thousand higher than today and recognize two local cooling events (c.571 and c.594 ka ago) thought to be caused by freshwater forcing. Our results are important for improving understanding of the regional climatic response leading up to the MBE and specifically provide insights into the climatic response of a warmer Arctic
Study of Emissions from Domestic Solid-Fuel Stove Combustion in Ireland
No full textSolid-fuel stoves are at the heart of many homes not only in developing nations, but also in developed regions where there is significant deployment of such heating appliances. They are often operated inefficiently and in association with high emission fuels like wood. This leads to disproportionate air pollution contributions. Despite the proliferation of these appliances, an understanding of particulate matter (PM) emissions from these sources remains relatively low. Emissions from five solid fuels are quantified using a "conventional" and an Ecodesign stove. PM measurements are obtained using both "hot filter" sampling of the raw flue gas, and sampling of cooled, diluted flue gas using an Aerosol Chemical Speciation Monitor and AE33 aethalometer. PM emissions factors (EF) derived from diluted flue gas incorporate light condensable organic compounds; hence they are generally higher than those obtained with "hot filter" sampling, which do not. Overall, the PM EFs ranged from 0.2 to 108.2 g GJ(-1) for solid fuels. The PM EF determined for a solid fuel depends strongly on the measurement method employed and on user behavior, and less strongly on secondary air supply and stove type. Kerosene-based firelighters were found to make a disproportionately high contribution to PM emissions. Organic aerosol dominated PM composition for all fuels, constituting 50-65% of PM from bituminous and low-smoke ovoids, and 85-95% from torrefied olive stone (TOS) briquettes, sod peat, and wood logs. Torrefied biomass and low-smoke ovoids were found to yield the lowest PM emissions. Substituting these fuels for smoky coal, peat, and wood could reduce PM2.5 emissions by approximately 63%
One and a Half Million Yearlong Aridity During the Middle Eocene in North-West China Linked to a Global Cooling Episode
No full textThe Eocene record of substantial aridification near Tibet was reported to mimic the global climate cooling trend, overwriting the previously proposed dominant role of the Tibetan Plateau uplift in the aridification (Li et al., 2018, https://doi.org/10.1038/s41467-018-05415-x). Here we present new paleoclimate data from the red clay sequence deposited between 40 and 50 Ma in Altun Shan at the northeastern edge of the Tibetan Plateau. After building an age model using a compilation of magnetostratigraphy and cyclostratigraphy, we demonstrate that our record of magnetic susceptibility in the Altun Shan red clay exhibits variations linked to eccentricity cycles. Our age model allows us to estimate the age of eight short geomagnetic events, cryprochrons, in Altun Shan. Further we show that the aridification interval in Altun Shan coincides with (i) a cooling event recorded in the global oxygen isotope record, (ii) a sea surface temperature record on the east Tasmanian plateau, and (iii) an aridity record in the surrounding sedimentary basins of Central Asia. The middle Eocene aridity and cooling reached its maximum 45.5-44 Ma
Impacts of land-use conversions on the water cycle in a typical watershed in the southern Chinese Loess Plateau
No full textLand use change is one of the dominant driving factors of hydrological change at the watershed scale. Thus, understanding the hydrological responses to land use changes can facilitate development of sustainable water resource management. The land use of the Wei River (the largest tributary of the Yellow River) Basin (WRB) has changed greatly due to the large-scale ecological restoration program in the Chinese Loess Plateau (e.g., grain-for-green program), causing dramatic impacts on the water cycle. This study was to simulate the impacts of land use and land cover change (LUCC) on the key hydrological components, using the Soil and Water Assessment Tool (SWAT). We investigated the spatiotemporal changes of LUCC from 1980 to 2010 in terms of four subregions (i.e., three subbasins and one mid-downstream area) and three landforms (i.e., mountain, hill, and plain), respectively. Then, we quantified the spatial heterogeneity of hydrological responses to land use change scenarios. Our LUCC analysis showed that cropland declined by about 0.8%, from 58,776 km(2) in 1980 to 57,519 km(2) in 2010, whereas the forest and grassland areas correspondingly increased 552 km(2) and 16 km(2), respectively. The urban area changed more dramatically in the middle and lower reaches of the Wei River owing to the faster socioeconomic development in this region than the rest areas. In mountain area, the main types of land use were forest and grassland, and the main transformation was from cropland to forest land and grassland. The area of cropland in plain could be over 50%, and it was mainly converted to urban land. The hydrological simulation indicated that LUCC from 1980 to 2010 caused 5.3% of decrease in the water yield and 6.2% increase in soil water content, but there was nearly no change in evapotranspiration (ET). Scenarios about slopping land use conversion (SLC) program showed that the conversion of cropland to grassland or forest (i.e., grain-for-green) resulted in negative effects on soil water content and water yield, with a greater effect by the reforestation. In addition, we found that the change of ET was clear in areas where cropland with slope > 15. was converted to grassland or forest, suggesting slope is also an important factor for hydrological responses to LUCC. This study can provide valuable decision support for land use planning and water resources protection in the WRB
Quantifying proportions of different material sources to loess based on a grid search and Monte Carlo model: A case study of the Ili Valley, Central Asia
No full textThe Ili Valley is among the main distribution areas of loess deposits in Xinjiang Province, Central Asia, while the provenance of Ili loess remains under debate. In this study, samples from near-surface loess, two types of topsoil and modern riverbed sediment were analyzed for their concentrations of major and trace geochemical elements to determine the relative proportions of different provenances of loess deposits in different zones of the Ili Valley. The results obtained by the grid search technology and Monte Carlo model indicated that the proximal material is dominated in the Ili loess. Alluvial-diluvial sediments as the main local material source have significantly influenced loess in the western region of Ili Valley. Moreover, this influence gradually decreases in the eastern region and the Zhaosu Basin. The proportion of modern riverbed sediment in the eastern Ili Valley is significantly lower than that in the Zhaosu Basin and is lowest in the western Ili Valley. However, the proportion of dust and topsoil type-II with the mean value of 11.8% and 7.2%, respectively, is highest in the western Ili Valley and lowest in the Zhaosu Basin. The complex natural background of the Ili Valley can be used to interpret the quantitative results and the geochemical characteristics of Ili loess from different regions. The reliability of the proposed method can be assessed by environmental indicators such as grain size, and geomorphic-hydrological background and other published records
Quantifying proportions of different material sources to loess based on a grid search and Monte Carlo model: A case study of the Ili Valley, Central Asia
No full textThe Ili Valley is among the main distribution areas of loess deposits in Xinjiang Province, Central Asia, while the provenance of Ili loess remains under debate. In this study, samples from near-surface loess, two types of topsoil and modern riverbed sediment were analyzed for their concentrations of major and trace geochemical elements to determine the relative proportions of different provenances of loess deposits in different zones of the Ili Valley. The results obtained by the grid search technology and Monte Carlo model indicated that the proximal material is dominated in the Ili loess. Alluvial-diluvial sediments as the main local material source have significantly influenced loess in the western region of Ili Valley. Moreover, this influence gradually decreases in the eastern region and the Zhaosu Basin. The proportion of modern riverbed sediment in the eastern Ili Valley is significantly lower than that in the Zhaosu Basin and is lowest in the western Ili Valley. However, the proportion of dust and topsoil type-II with the mean value of 11.8% and 7.2%, respectively, is highest in the western Ili Valley and lowest in the Zhaosu Basin. The complex natural background of the Ili Valley can be used to interpret the quantitative results and the geochemical characteristics of Ili loess from different regions. The reliability of the proposed method can be assessed by environmental indicators such as grain size, and geomorphic-hydrological background and other published records
Early human impacts and ecosystem reorganization in southern-central Africa
No full textModern Homo sapiens engage in substantial ecosystem modification, but it is difficult to detect the origins or early consequences of these behaviors. Archaeological, geochronological, geomorphological, and paleoenvironmental data from northern Malawi document a changing relationship between forager presence, ecosystem organization, and alluvial fan formation in the Late Pleistocene. Dense concentrations of Middle Stone Age artifacts and alluvial fan systems formed after ca. 92 thousand years ago, within a paleoecological context with no analog in the preceding half-million-year record. Archaeological data and principal coordinates analysis indicate that early anthropogenic fire relaxed seasonal constraints on ignitions, influencing vegetation composition and erosion. This operated in tandem with climate-driven changes in precipitation to culminate in an ecological transition to an early, pre-agricultural anthropogenic landscape
Interactions of organosulfates with water vapor under sub- and supersaturated conditions
No full textOrganosulfates (OSs) are important constituents of secondary organic aerosols, but their hygroscopic properties and cloud condensation nucleation (CCN) activities have not been well understood. In this work we employed three complementary techniques to characterize interactions of several OSs with water vapor under sub- and supersaturated conditions. A vapor sorption analyzer was used to measure mass changes in OS samples with relative humidity (RH, 0 %-90 %); among the 11 organosulfates examined, only sodium methyl sulfate (methyl-OS), sodium ethyl sulfate (ethyl-OS), sodium octyl sulfate (octyl-OS) and potassium hydroxyacetone sulfate were found to deliquesce as RH increased, and their mass growth factors at 90 % RH were determined to be 3.65 +/- 0.06, 3.58 +/- 0.02, 1.59 +/- 0.01 and 2.20 +/- 0.03. Hygroscopic growth of methyl-, ethyl- and octyl-OS aerosols was also studied using a humidity tandem differential mobility analyzer (H-TDMA); continuous hygroscopic growth was observed, and their growth factors at 90 % RH were determined to be 1.83 +/- 0.03, 1.79 +/- 0.02 and 1.21 +/- 0.02. We further investigated CCN activities of methyl-, ethyl- and octyl-OS aerosols, and their single hygroscopicity parameters (kappa(cnn)) were determined to be 0.459 +/- 0.021, 0.397 +/- 0.010 and 0.206 +/- 0.008. For methyl- and ethyl-OS aerosols, kappa(cnn) values agree reasonably well with those derived from H-TDMA measurements (kappa(gf)) with relative differences being < 25 %, whereas kappa(cnn) was found to be similar to 2.4 times larger than kappa(gf) for octyl-OS, likely due to both the solubility limit and surface tension reduction
Assessment of Atmospheric Oxidizing Capacity Over the Beijing-Tianjin-Hebei (BTH) Area, China
No full textThe atmospheric oxidizing capacity (AOC) plays a key role in atmospheric chemistry, determining the removal of most reduced gases in the atmosphere. In this study, we assess the summertime AOC from 7 to 22 June 2014 associated with a field campaign conducted at Wangdu in the Beijing-Tianjin-Hebei region (BTH), China using the WRF-Chem model. The model reasonably well reproduces the incident solar radiation, ambient O-3 and fine particulate matter (PM2.5) concentrations, the photolysis rates of O-3 and NO2, and radical concentrations against measurements in the BTH. The model results show high daytime AOC levels in urban areas and relatively low AOC in remote areas of the BTH. The diurnal cycle of the AOC exhibits a unimodal pattern with peaks at noon. OH radical contributes about 68% of the daily average AOC in Beijing, followed by O-3 (27%) and NO3 (5%). At Wangdu, the production rate of OH radical reaches around 13 ppb h(-1) at noon, which is mainly resulted from the reaction of HO2 with NO. The OH radical loss is primarily contributed by reactions with volatile organic compounds, followed by CO and NO2. Statistically, the population hourly or afternoon average O-3 and O-x (=O-3 + NO2) concentrations are significantly correlated with the AOC in Beijing, constituting potential simplified tracers to indicate the AOC level