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Measurement report: Source apportionment of carbonaceous aerosol using dual-carbon isotopes (C-13 and C-14) and levoglucosan in three northern Chinese cities during 2018-2019
No full textTo investigate the characteristics and changes in the sources of carbonaceous aerosols in northern Chinese cities after the implementation of the Action Plan for Air Pollution Prevention and Control in 2013, we collected PM2.5 samples from three representative inland cities, i.e., Beijing (BJ), Xi'an (XA), and Linfen (LF), from January 2018 to April 2019. Elemental carbon (EC), organic carbon (OC), levoglucosan, stable carbon isotope, and radiocarbon were measured in PM2.5 to quantify the sources of carbonaceous aerosol, combined with Latin hypercube sampling. The best estimate of source apportionment showed that the emissions from liquid fossil fuels contributed 29.3 +/- 12.7 %, 24.9 +/- 18.0 %, and 20.9 +/- 12.3% of the total carbon (TC) in BJ, XA, and LF, respectively, whereas coal combustion contributed 15.5 +/- 8.8 %, 20.9 +/- 18.0 %, and 42.9 +/- 19.4 %, respectively. Non-fossil sources accounted for 55 +/- 11 %, 54 +/- 10 %, and 36 +/- 14% of the TC in BJ, XA, and LF, respectively. In XA, 44.8 +/- 26.8% of non-fossil sources were attributed to biomass burning. The highest contributors to OC in LF and XA were fossil sources (74.2 +/- 9.6% and 43.2 +/- 10.8 %, respectively), whereas those in BJ were non-fossil sources (66.8 +/- 13.9 %). The main contributors to EC were fossil sources, accounting for 91.4 +/- 7.5 %, 66.8 +/- 23.8 %, and 88.4 +/- 10.8% in BJ, XA, and LF, respectively. The decline (6 %-16 %) in fossil source contributions in BJ since the implementation of the Action Plan indicates the effectiveness of air quality management. We suggest that specific measures targeted at coal combustion, biomass burning, and vehicle emissions in different cities should be strengthened in the future
Quantifying the provenance of dune sediments in the Taklimakan Desert using machine learning, multidimensional scaling and sediment source fingerprinting
No full textStudy of windborne sediments in the Taklimakan Desert is of great significance in the context of global change. Much effort has gone into characterizing the Taklimakan dune sediments, but quantitative understanding of the source contributions from the surrounding mountains is lacking. Accordingly, using elemental data, we applied random forest (RF), multidimensional scaling (MDS) and sediment source fingerprinting (SSF) to examine homogenization of the dune sediments in the desert, and to quantify the contributions of key sources. The results underscored the heterogeneity of geochemistry in dune sediments in the Taklimakan Desert. On the basis of dominant wind directions and the drainage network in the Tarim Basin, as well as lithologic features in the surrounding mountains, potential sources of sand dune sediments comprised three groups: "Tianshan", "PamirsKunlun", and "Kunlun-Altun". Using the FingerPro and MixSIAR fingerprinting models, our results suggested that the contributions of the three sources to the target dune sediments were: "Kunlun-Altun" > "Pamirs-Kunlun" > "Tianshan". However, substantial variations in the respective contributions were observed for different target dune samples. Although both the frequentist and Bayesian models performed well in the calculations of the relative source proportions based on goodness of fit (GOF) (0.97 on average for the two models respectively), virtual mixtures (VM) tests indicated that the frequentist model returned more accurate predictions. Consequently, using the frequentist results, we propose that the "Kunlun-Altun"-derived sediment (an average of 56%) is mainly delivered to the Taklimakan Desert via fluvial transport; sediment supply from the "Pamirs-Kunlun" source (33%) depends on fluvial and wind transport and that aeolian processes are mainly responsible for distribution of the "Tianshan"-derived sediment (11%) in the desert by transporting the fine fraction. Our findings thereby highlight the interaction between fluvial and aeolian transport within the Tarim Basin
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
High-resolution late Pliocene-quaternary magnetostratigraphy of the Yinchuan Basin, NE Tibetan Plateau
No full textThe Yinchuan Basin, one of the most important basins in the area adjacent to the northeastern Tibetan Plateau, contains a continuous sequence of fluvio-lacustrine deposits, which makes it an ideal area to study the in-teractions between the Tibetan Plateau uplift, climate change, and geomorphological evolution. Here, a 1200-m -deep drill core (YNZK01) is described with an average recovery rate of 96% in the depo-center of the Yinchuan Basin to establish a high-resolution palaeoenvironmental and tectonic reconstruction. Stepwise alternating-field demagnetization results showed a stable and high-qualified remanent magnetization of the samples. The polarity sequences consisted of 8 normal and 8 reverse zones that correlate well with the geomagnetic polarity timescale. Magnetostratigraphic results date the entire YNZK01 core from 3.927 Ma to the present. The B/M boundary (0.781 Ma) is at a depth of 246.4 m while the M/G boundary (2.581 Ma) is at a depth of 863.4 m. The G/Gi boundary (3.596 Ma) is identified at 1117.8 m and the bottom of the core was extrapolated to 3.927 Ma (1201 m) with an average sedimentation rate of 863.4-1117.8 m. This high-resolution magnetostratigraphy record pro -vides a baseline chronological framework for further research and publications on the tectonic, paleoclimatic, and paleoenvironmental proxy data of the YNZK01 core in the Yinchuan Basin, NE Tibetan Plateau
Oxygen isotope temperature calibrations for modern Tridacna shells in western Pacific
No full textThe oxygen isotope ratio of carbonate in Tridacna shell (delta O-18(shell)) is assumed to be precipitated in isotopic equilibrium with surrounding seawater and thus reflects a combination of the Sea surface temperature (SST) and the delta O-18 of seawater (delta O-18(SW)). Accordingly, Tridacna delta O-18(shell) has been widely used for high-resolution paleoclimate reconstructions. However, the influences of interspecific differences, spatial heterogeneity, as well as the "growth effect" on the delta O-18(shell)-SST relationship, have not been fully tested. Here, we present a monthly resolved delta O-18(shell) record of a Tridacna squamosa specimen from Yagong Island, South China sea (SCS). Our results suggested that the monthly resolved delta O-18(shell) from northern SCS was dominated by the seasonal SST variations, which was highly correlated with measured SST after excluding the influence of delta O-18(SW). Then, the SST = f(delta O-18(shell)-delta O-18(SW)) equations of all published monthly delta O-18(shell) records of modern Tridacna from the Indo-Pacific were collected. The resulting investigation revealed that similar SST = f(delta O-18(shell)-delta O-18(SW)) equations for each shell, indicating the minor influences of spatial heterogeneity and interspecific differences. The average equation for Tridacna (Tridacna gigas, Tridacna derasa, Tridacna squamosa, Tridacna maxima and Hippopus hippopus) was SST = - 3.56 +/- 1.26 (delta O-18(shell)-delta O-18(sw)) + 22.44 +/- 2.77 (- 0.28 +/- 0.08 parts per thousand degrees C-1, VPDB) (2 sigma), which was close to the equations set up for other mollusks (without Tridacna) and inorganic aragonite. Finally, although the growth rates varied greatly among Tridacna specimens and within different growth stages of each specimen, we did not find a significant influence of the growth rates on SST = f(delta O-18-(shell) - delta O-18(SW)) equations, indicating that the "growth effect" might have at best a slight impact on the delta O-18(shell) of Tridacna
Oxygen isotope temperature calibrations for modern Tridacna shells in western Pacific
No full textThe oxygen isotope ratio of carbonate in Tridacna shell (delta O-18(shell)) is assumed to be precipitated in isotopic equilibrium with surrounding seawater and thus reflects a combination of the Sea surface temperature (SST) and the delta O-18 of seawater (delta O-18(SW)). Accordingly, Tridacna delta O-18(shell) has been widely used for high-resolution paleoclimate reconstructions. However, the influences of interspecific differences, spatial heterogeneity, as well as the "growth effect" on the delta O-18(shell)-SST relationship, have not been fully tested. Here, we present a monthly resolved delta O-18(shell) record of a Tridacna squamosa specimen from Yagong Island, South China sea (SCS). Our results suggested that the monthly resolved delta O-18(shell) from northern SCS was dominated by the seasonal SST variations, which was highly correlated with measured SST after excluding the influence of delta O-18(SW). Then, the SST = f(delta O-18(shell)-delta O-18(SW)) equations of all published monthly delta O-18(shell) records of modern Tridacna from the Indo-Pacific were collected. The resulting investigation revealed that similar SST = f(delta O-18(shell)-delta O-18(SW)) equations for each shell, indicating the minor influences of spatial heterogeneity and interspecific differences. The average equation for Tridacna (Tridacna gigas, Tridacna derasa, Tridacna squamosa, Tridacna maxima and Hippopus hippopus) was SST = - 3.56 +/- 1.26 (delta O-18(shell)-delta O-18(sw)) + 22.44 +/- 2.77 (- 0.28 +/- 0.08 parts per thousand degrees C-1, VPDB) (2 sigma), which was close to the equations set up for other mollusks (without Tridacna) and inorganic aragonite. Finally, although the growth rates varied greatly among Tridacna specimens and within different growth stages of each specimen, we did not find a significant influence of the growth rates on SST = f(delta O-18-(shell) - delta O-18(SW)) equations, indicating that the "growth effect" might have at best a slight impact on the delta O-18(shell) of Tridacna
Early Oligocene-Late Miocene Wildfire History in the Northern Tibetan Plateau and Links to Temperature-Driven Precipitation Changes
No full textLate Cenozoic wildfire evolution in Inner Asia has been attributed to both ice-volume modulating precipitation changes and surface uplift of the Tibetan Plateau. Whether this is the case or not requires additional research and wildfire records from older periods. In this study, 251 microcharcoal samples from the Huatugou section in the western Qaidam Basin are used to reconstruct the early Oligocene-middle Miocene wildfire history of the northern Tibetan Plateau. The results show that wildfires remained relatively frequent before similar to 26 Ma, then reduced gradually until similar to 14 Ma, and finally increased slightly but still at low level between 14 and 12 Ma. The wildfire variations can be correlated to the steppe-based dryness changes, and both of which are coincident with global temperature changes. We infer that mean annual temperature might have played a dominant role in controlling wildfire frequencies in the northern Tibetan Plateau through modulating atmospheric moisture content. This conclusion is in line with previous studies including microcharcoal-based wildfire records of 18-5 Ma successions from the Qaidam Basin as well as soot-based wildfire records from Quaternary glacial-interglacial cycles of the Chinese Loess Plateau
Heterogeneous HONO formation deteriorates the wintertime particulate pollution in the Guanzhong Basin, China
No full textDespite implementation of strict emission mitigation measures since 2013, heavy haze with high levels of secondary aerosols still frequently engulfs the Guanzhong Basin (GZB), China, during wintertime, remarkably impairing visibility and potentially causing severe health issues. Although the observed low ozone (O3) concentrations do not facilitate the photochemical formation of secondary aerosols, the measured high nitrous acid (HONO) level provides an alternate pathway in the GZB. The impact of heterogeneous HONO sources on the wintertime particulate pollution and atmospheric oxidizing capability (AOC) is evaluated in the GZB. Simulations by the Weather Research and Forecast model coupled with Chemistry (WRF-Chem) reveal that the observed high levels of nitrate and secondary organic aerosols (SOA) are reproduced when both homogeneous and heterogeneous HONO sources are considered. The heterogeneous sources (HET-sources) contribute about 98% of the near-surface HONO concentration in the GZB, increasing the hydroxyl radical (OH) and O3 concentration by 39.4% and 22.0%, respectively. The average contribution of the HET-sources to SOA, nitrate, ammonium, and sulfate in the GZB is 35.6%, 20.6%, 12.1%, and 6.0% during the particulate pollution episode, respectively, enhancing the mass concentration of fine particulate matters (PM2.5) by around 12.2%. Our results suggest that decreasing HONO level or the AOC becomes an effective pathway to alleviate the wintertime particulate pollution in the GZB
Tree-ring-based drought variability in northern China over the past three centuries
No full textDroughts are the most frequent natural disaster in regions at the margins of the East Asian summer monsoon (EASM), which pose threats to agriculture, the economy, and human lives. However, the limitations of only approximately 60 years of meteorological observations hamper our understanding of the characteristics and mechanisms of local hydroclimate. Trees growing in the marginal region of the EASM are usually sensitive to moisture variations and have played important roles in past hydroclimatic reconstructions. Here, a 303-year tree-ring-width chronology of Pinus tabulaeformis from Mt. Lama, which is located in the junction of the Liaoning Province and Inner Mongolia, China, was used to reconstruct the May-August Palmer drought severity index (PDSI) in the marginal region of the EASM. The transfer function explains 48.0% (or 47.2% after adjusting for the loss of the degrees of freedom) of the variance over the calibration period from 1946 to 2012. A spatial correlation analysis demonstrates that our PDSI reconstruction can represent the drought variability on the northernmost margin of the EASM. The winter Asian polar vortex area index showed a delayed impact on the summer EASM precipitation in the following year
Multiple-Year Changes (2014-2018) in Particulate Vanadium Linked to Shipping Regulations in the World's Largest Port Region
No full textChina introduced an emission control area (ECA) along the coastline of the Yangtze River Delta (YRD) region in 2016 in a bid to reduce its shipping emissions. Performed at a costal site in the YRD region from 2014 to 2018, we found a significant reduction (16-22%, p < 0.01) in vanadium concentrations, the exclusive marker for heavy fuel oil combustion, after the full-scale implementation of lower sulfur fuel change for marine ships. Another site closer to the coastline showed a larger reduction (24- 30%, p < 0.01) during the corresponding period. The reduction of vanadium was consistent with an overall decrease rate of 17% in the annual SO2 concentrations of 10 sites across the region from 2016 to 2017. We thus provide a robust assessment of the positive effects of regulating shipping emissions on air quality in coastal China. The future trajectories of shipping-related emissions are also discussed