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Preface (volume I): Quaternary paleoclimate and paleoenvironmental changes in Central Asia
No full textThe core area of Central Asia (CA), an arid Westerlies-dominated area, is crucial for analysis of interregional atmospheric circulation interactions along the Eurasian mid-latitude belt. However, it remains unclear how climate and environment in this region evolved during the Quaternary Period. Based on the articles in this special issue, this review recapitulates the spatio-temporal distribution of Quaternary sediments in CA, discusses paleoclimate and paleoenvironmental implications of various physicochemical and palaeontological proxies, and finally summarizes the paleoclimate and paleoenvironmental history since the middle Pleistocene. Field investigation and previous studies indicate that loess sediments are mainly distributed on the river terraces and windward piedmonts of Central Asian high mountains since the late Pliocene (mainly late Pleistocene). Multiple proxies analysis, e.g., grain size, geochemistry, sporopollen and magnetism, for the loess and fluvial deposits in this region reveal that the paleoclimate and paleoenvironment manifest a long-term stepwise drying or desertification trend of CA over the past 1 Myr, with at least one major drying event occurring at about similar to 0.5-0.6 Ma. One of the consequences is the development of the modern deserts in the Junggar Basin and the Tarim Basin. Despite the overall drying trend since the last interglacial period, the Holocene is characterized by a persistent wetting trend with millennial-scale oscillation. This special issue provides a useful glimpse into multi-scale climate and environmental changes in CA, facilitating climatic prediction in the future and climate modeling
Characteristics of indoor dust in an industrial city: Comparison with outdoor dust and atmospheric particulates
No full textThere is a considerable connection between indoor and outdoor environments. However, few studies have explored their intrinsic relationship until now. This study conducted morphologic observation, heavy metal monitoring and isotopes analysis in indoor and outdoor dust, as well as the atmospheric particulates in Hefei. Morphologic analysis demonstrated atmospheric particulates were affected by fly ash and construction, road dust mainly came from automobile exhaust and indoor dust particles were interfered by multiple sources, including the secondary reaction of fly ash. Chemical speciation analysis of heavy metals showed the exchange of heavy metals between atmospheric particulates and indoor dust was dominated by non-residual metals, while the exchange between road dust and indoor dust tended to rely on residual metals. The assessment results of heavy metals in particulates showed that indoor carcinogenic risks were greater than outdoor for children, however, for adults, outdoor carcinogenic risks were greater than indoor. Stable isotopes analysis indicated carbon in the dust outside buildings was derived from flying dust, and atmospheric particulates might derive from vehicle exhaust, or partly from natural gas. While sulfur in atmospheric particulates was derived mainly from coal combustion. The release from indoor activities, especially natural gas exhaust emitted from cooking had a certain impact on atmospheric particulates. (C) 2021 Elsevier Ltd. All rights reserved
Time series of atmospheric Delta(CO2)-C-14 recorded in tree rings from Northwest China (1957-2015)
No full textRadiocarbon (C-14) is a unique and important tool for understanding carbon cycle in the nature, and its use can be significantly enhanced where reliable historical atmospheric Delta(CO2)-C-14 records can be established. In China, continuous atmospheric Delta(CO2)-C-14 records since the 1950s are scarce, a period when dramatic variations of Delta(CO2)-C-14 occurred caused by intensive human activities. In this research, Delta C-14 of Qinghai spruce tree rings collected from Huangzhong (HZ) (36.27 degrees N, 101.67 degrees E, 2982 m amsl) were measured by Accelerator Mass Spectrometry, and a Delta(CO2)-C-14 time series from 1957 to 2015 was reconstructed. The results show that HZ Delta C-14 was generally higher than the contemporaneous average level in the mid-high latitudes of the Northern Hemisphere. The peak value of HZ Delta C-14 occurred in 1964 (as bomb peak) was higher than that of other tree ring records in East Asia at a similar latitude, likely due to the impact of the atmosphere nuclear tests at Semipalatinsk (Kazakhstan). The record shows no obvious disturbance of Lop Nor nuclear weapons tests (in Northwest China) during 1964-1980, except for 1971. A local Suess effect began to appear since 2001, and the estimated atmospheric fossil fuel-derived CO2 (CO2ff) concentration increased from 3.5 ppm to 8.8 ppm from 2006 to 2015. This is associated with the implementation of the "Western Development" strategy in China. HZ Delta C-14 records document background Delta C-14 data, useful for regional carbon cycle research and atmospheric CO2ff quantification in the region. These data also provide baseline values for assessment environmental safety connected with nuclear power plants in China. (C) 2021 Elsevier Ltd. All rights reserved
Measurement report: PM2:5-bound nitrated aromatic compounds in Xi'an, Northwest China - seasonal variations and contributions to optical properties of brown carbon
No full textNitrated aromatic compounds (NACs) are a group of key chromophores for brown carbon (light-absorbing organic carbon, i.e., BrC) aerosol, which affects radiative forcing. The chemical composition and sources of NACs and their contributions to BrC absorption, however, are still not well understood. In this study, PM2:5-bound NACs in Xi'an, Northwest China, were investigated for 112 daily PM2:5 filter samples from 2015 to 2016. Both the total concentrations and contributions from individual species of NACs show distinct seasonal variations. The seasonally averaged concentrations of NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56 ng m(-3) (winter). Thereinto, 4-nitrophenol is the major NAC component in spring (58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol dominate in summer (70 %), and the concentrations of 4-nitrocatechol and 4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species show different seasonal patterns in concentrations, indicating differences in emissions and formation pathways. Source apportionment results using positive matrix factorization (PMF) further show large seasonal differences in the sources of NACs. Specifically, in summer, NACs were highly influenced by secondary formation and vehicle emissions (similar to 80 %), while in winter, biomass burning and coal combustion contributed the most (similar to 75 %). Furthermore, the light absorption contributions of NACs to BrC are wavelength-dependent and vary greatly by season, with maximum contributions at similar to 330 nm in winter and fall and similar to 320 nm in summer and spring. The differences in the contribution to light absorption are associated with the higher mass fractions of 4-nitrocatechol ((lambda)max = 345 nm) and 4-nitrophenol ((lambda)max = 310 nm) in fall and winter, 4-nitrophenol in spring, and 5-nitrosalicylic acid ((lambda)max = 315 nm) and 4-nitrophenol in summer. The mean contributions of NACs to BrC light absorption at a wavelength of 365 nm in different seasons are 0.14% (spring), 0.09% (summer), 0.36% (fall), and 0.91% (winter), which are about 6-9 times higher than their mass fractional contributions of carbon in total organic carbon. Our results indicate that the composition and sources of NACs have profound impacts on the BrC light absorption
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
In-situ generation of oxygen vacancies and metallic bismuth from (BiO)(2)CO3 via N-2-assisted thermal-treatment for efficient selective photocatalytic NO removal
No full textIn this study, a N-2-assisted thermal treatment method is proposed for in-situ formation of a series of oxygen vacancies (OVs)-rich Bi-0/Bi-based photocatalysts, including OVs-(BiO)(2)CO3, Bi-0/OVs-(BiO)(2)CO3, Bi-0/OVs(BiO)(2)CO3/beta-Bi2O3, Bi-0/OVs-beta-Bi2O3, Bi-0/OVs-beta-Bi2O3/alpha-Bi2O3 and Bi-0/alpha-Bi2O3. Mechanisms of in-situ formation of Bi-0 nanoparticles and generation of OVs in Bi-based photocatalysts are clarified. Apart from their contribution to the effective separation of photogenerated charge carriers and enhancement of light absorption, the effects of Bi-0 nanoparticles and OVs on selective photocatalytic oxidation of NO are also investigated. Among the synthesized Bi-based photocatalysts, Bi-0/OVs-(BiO)(2)CO3 shows the best photocatalytic activity and stability for photo-oxidative removal of NO. The systematic study of photocatalytic mechanism demonstrated that the Ohmic contact between OVs-(BiO)(2)CO3 and Bi-0 gradually promote the formation of center dot O-2(-) and center dot OH species. It is found that center dot O-2(-) plays an important role in the photocatalytic NO removal process, while center dot OH species can effectively inhibit the formation of NO2 during the NO removal process. The new approach demonstrated in this study can be applied for the in-situ formation of wide-solar-spectrum-responsive photocatalysts with efficient photo catalytic activity
Evolution of the Miocene megalake in the western Qaidam Basin, northwestern China
No full textThick Miocene lacustrine deposits have been identified across the Qaidam Basin on the northeast Tibetan Plateau, indicative of a relatively unified megalake then. How this megalake evolved at its final stage and associated controlling factors, e.g., global climate or tectonic uplift, remain largely elusive. Here we use the KC-1 well, drilled at the depo-center of the western Qaidam Basin, to investigate the megalake evolution over the mid- and late Miocene. A set of lipid biomarker indices, namely beta-carotane/n-C-36, gammacerane index, terrigenous/aquatic ratio and long-chain saturated ketone content, altogether indicate substantial lake level fluctuations, with lower lake level at the intervals of similar to 18-17 Ma, 13.5-11.5 Ma, 10.5-8 Ma and 7-6 Ma, and higher level at the intervals of similar to 7-13.5 Ma, 11.5-10.5 Ma, 8-7 Ma and 6-5 Ma, superimposed on the long-term shrinking trend. Direct comparison with existing regional and global temperature records suggests that such lake dynamics was largely associated with global climatic conditions, i.e., shrinking under relatively cool conditions and vice versa, for both its long-term evolution and secondary fluctuations. It thus appears that global climatic conditions had controlled the megalake status during the mid- and late Miocene, whereas tectonic activities then might have also contributed to its long-term gradual demise
Variability of PDO identified by a last 300-year stalagmite delta O-18 record in Southwest China
No full textStalagmite oxygen isotope (delta O-18) record has been widely used in characterizing Asian Monsoon variations. In southwest (SW) China, although the stalagmite delta O-18 was usually suggested as a precipitation proxy, it remains a subject of debate. Here we present two replicated, high-precise-dated stalagmite delta O-18 records for the interval 1710-2003 AD from Yunnan province, SW China. The stalagmite delta O-18 shows no correlation with the local monsoon precipitation, but a significantly positive correlation with the Pacific Decadal Oscillation (PDO) index. It demonstrates that the stalagmite delta O-18 in SW China is most likely influenced by the atmospheric circulation associated with the PDO through the upstream depletion mechanism. During the warm (cold) PDO period, the deficit rainfall over India would make the delta O-18 of water vapor transporting to SW China less (more) negative due to the weaker Rayleigh distillation process, which would lead to the less (more) negative stalagmite delta O-18. Consequently, the stalagmite delta O-18 in SW China is suitable to reconstruct the PDO variations. It is important to note that the other factors, such as El Nino-Southern Oscillation (ENSO) or sea surface temperature (SST) also possibly affect the stalagmite delta O-18 in SW China, and the relationship between them requires further studies. (C) 2021 Elsevier Ltd. All rights reserved
Spatially Resolved Emission Factors to Reduce Uncertainties in Air Pollutant Emission Estimates from the Residential Sector
No full textThe residential sector is a major source of air pollutant emission inventory uncertainties. A nationwide field emission measurement campaign was conducted in rural China to evaluate the variabilities of realistic emission factors (EFs) from indoor solid fuel combustion. For a total of 1313 burning events, the overall average EFs (+/- standard deviation) of PM2.5 were 8.93 +/- 6.95 and 7.33 +/- 9.01 g/kg for biomass and coals, respectively, and 89.3 +/- 51.2 and 114 +/- 87 g/kg for CO. Higher EFs were found from burning of uncompressed straws, while lower EFs were found from processed biomass pellets, coal briquettes, and relatively clean anthracite coals. Modified combustion efficiency was found to be the most significant factor associated with variations in CO EFs, whereas for PM2.5, fuel and stove differences determined its variations. Weak correlations between PM2.5 and CO indicated high uncertainties in using CO as a surrogate for PM2.5. EFs accurately fit log-normal distributions, and obvious spatial heterogeneity was observed attributed to different fuel-stove combinations across the country. Emission estimation variabilities, which are determined by the interquartile ranges divided by the median values, were notably reduced when spatially resolved EFs were adopted in the inventory
Interactive assessment of lignite and bamboo-biochar for geochemical speciation, modulation and uptake of Cu and other heavy metals in the copper mine tailing
No full textThis study was designed to examine the combined effect of bamboo-biochar (BC) and water-washed lignite (LGT) at copper mine tailings (CuMT) sites on the concentration of Cu and other metals in pore water (PW), their bioavailability, and change in geochemical speciation. Rapeseed (first cropping-season) and wheat (second cropping-season) were grown for 40-days each and the influence of applied-amendments on both cropping seasons was observed and compared. A significant increase in pH, water holding capacity (WHC), and soil organic carbon (SOC) was observed after the applied amendments in second cropping-seasons. The BC-LGT significantly reduced the concentration of Cu in PW after second cropping seasons; however, the concentration of Pb and Zn were increased with the individual application of biochar and LGT, respectively. BC-LGT and BC-2% significantly reduced the bioavailability of Cu and other HMs in both cropping seasons. The treated-CuMT was subjected to spectroscopic investigation through X-ray photoelectron spectroscopy (XPS), Fourier transform Infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The results showed that Cu sorption mainly involved the coordination with hydroxyl and carboxyl functional groups, as well as the co-precipitation or complexation on mineral surfaces, which vary with the applied amendment and bulk amount of Mg, Mn, and Fe released during sorption-process. The co-application of BC-LGT exerted significant effectiveness in immobilizing Cu and other HMs in CuMT. The outcomes of the study indicated that co-application of BC-LGT is an efficacious combination of organic and inorganic materials for Cu adsorption which may provide some new information for the sustainable remediation of copper mine tailing.
(c) 2021 Elsevier B.V. All rights reserved