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Asian Winter Monsoon Imprint on the Water Column Structure at the Northern South China Sea Coast
No full textCoastal regions of the northern South China Sea (SCS) strongly interact with the Asian monsoon circulation (AMC). Thus, variations of sea surface temperature (SST) here are newly suggested to document AMC changes in an effective manner, but additional physical parameters of oceanic conditions, probably also in relation to the AMC system, remain poorly understood. In this study, we analyzed glycerol dialkyl glycerol tetraethers (GDGTs) from a well-dated sediment core YJ, retrieved at the northern SCS coast, to further scrutinize the intrinsic response of water column to winter AMC strength. It shows that within the time frame of past similar to 1,000 years, the tetraether index of lipids with 86 carbon atoms (TEX86 ) and published alkenone ( U-37(K)') temperature records together confirm a reduced thermal gradient during the Little Ice Age (LIA), in comparison to that during the Medieval Climate Anomaly (MCA). Considering concurrent variations of the branched and isoprenoid tetraether (BIT) and the ratio of archaeol to caldarchaeol (ACE), for example, with decreased values (<similar to 0.3) for the former and relatively high values for the latter at the LIA, indicative of stratification and salinity changes, respectively, these multiple lines of evidence thereby call for well mixing of onsite water at site YJ correspondingly. Our results suggest that winter AMC strength is a critical factor for mixing subsurface waters and modifying thermal/saline conditions at the northern SCS coasts through the last millennium and also, perhaps, on longer timescales.</p
Characteristics and sources of amine-containing particles in the urban atmosphere of Liaocheng, a seriously polluted city in North China during the COVID-19 outbreak
No full textThe Chinese government issued an unprecedentedly strict lockdown policy to control the spread of the novel coronavirus disease 2019 (COVID-19), significantly mitigating air pollution because of the dramatic reduction of industrial and traffic emissions. To explore the impact of COVID-19 lockdown (LCD) on organic aerosols, the mixing states and evolution processes of amine-containing particles were studied using a single particle aerosol mass spectrometer from January to March 2020 in Liaocheng, which is a seriously polluted city in North China. The counts and percentages of amine-containing particles in total obtained particles during the pre-LCD (547832, 29.8 %) were higher than those during the LCD (283983, 20.7 %) and post-LCD (102026, 18.4 %), mainly due to the reduced emission strength of amines and suppressed gas-to-particle partitioning of amines during the LCD and post-LCD. (74)(C2H5)(2)NH2+ was the most abundant amine marker, which accounted for 98.2 %, 98.4 %, and 96.7 % of all amine-containing particles during the pre-LCD, LCD, and post-LCD, respectively. Correlation analysis and temporal variations indicated that the gas-to-particle partitioning of amines was facilitated by the stronger acidic environment and lower temperature, while the effect of RH and aerosol liquid water content was minor. The A-OC particles were the most abundant type (accounting for similar to 40 %) throughout the observation period. The temporal profiles and correlation analysis suggested that the impact of the increased O-3 on the amines and their oxidation products (e.g., trimethylamine oxide) was minor. The identified particle types, correlation analysis, and the potential source contribution function results implied that the amine-containing particles were mainly derived from local and surrounding sources during the LCD, while those were mainly affected by long-range transport during the pre-LCD and post-LCD. Our results could deepen the comprehension of the sources and atmospheric processing of amines in the urban area of North China during the COVID-19 outbreak
Probing the historic thermal and humid environment in a 2000-year-old ancient underground tomb and enlightenment for cultural heritage protection and preventive conservation
No full textThe development and utilization of urban underground space have contributed to more excavation of ancient tombs in recent years. The microclimate in the burial environment is crucial for the sustainability of historical artifacts. In this paper, the variation in thermal and humid conditions during the burial time from the closure of a tomb to excavation was investigated by field testing and computational fluid dynamics (CFD) modeling. The selected object is the famous M1 tomb chamber of the mausoleum Zhang An-shi, which has a 2000-year history. It was found that the average air temperature (T) and relative humidity (RH) of the M1 tomb chamber before excavation were 12.7 degrees C and 93.0%, respectively. The results of the CFD simulation suggest that the burial time of an ancient tomb consists of a very short variable phase and a long stable phase. The very beginning phase may be as short as 0.3 h. The dramatic changes in temperature and RH were more than 10 degrees C and 20%, respectively. Consequently, dramatic changes in the thermal and humid environment will trigger the deterioration of historical artifacts. Current findings further suggest that the local annual average temperature is optimal for the conservation of underground artifacts excavated from the soil thermostatic layer. This study paves the way for characterizing the environment of an ancient tomb chamber, as well as museum design, energy savings that support cultural heritage protection and preventive conservation. (c) 2021 Elsevier B.V. All rights reserved
Species specific Sr/Ca-delta O-18 relationships for three Tridacnidae species from the northern South China Sea
No full textSkeletal remains of marine bivalves, Tridacna spp., can provide multi-proxy records of environmental variables. Sr/Ca ratio, which has been widely used in corals as a paleo-temperature proxy, has also been explored in Tridacna spp. shells in recent decades, but some controversies remain, especially regarding the different Sr/CaSST relationships across Tridacnidae species. In this study, ten specimens of three different species (Tridacna gigas, Tridacna squamosa and Tridacna derasa) were collected from the northern South China Sea and the monthly resolution Sr/Ca and delta O-18 ratios were investigated. Almost all high-resolution Sr/Ca profiles, determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer), show pronounced annual cycles and are significantly correlated with paired delta O-18 value. However, Sr/Ca ratios of T. gigas are positively correlated with paired delta O-18 values, suggesting a negative correlation between T. gigas Sr/Ca and in-situ SST, while Sr/Ca ratios of T. derasa and T. squamosa are negatively correlated with paired delta O-18, suggesting a positive correlation between SST and Sr/Ca in T. derasa and T. squamosa. These interspecies differences highlight the necessity of species identification before using Tridacnidae Sr/Ca ratios in paleoclimate reconstructions. Although the Sr/Ca-delta O-18 relationship has obvious interspecies differences, the clear annual cycles in all these specimens indicate that the Sr/Ca ratios of Tridacna spp. may have the potential to be used in reconstructing the past climate seasonality, ENSO variability and so on
Pollution characterization and source identification of nitrogen-containing species in fine particulates: A case study in Hefei city, East China
No full textTo identify the nitrogen sources in atmospheric particulate matter, the stable isotope technique has been proven as an effective method. In this study, PM2.5 samples at different pollution levels were collected from March 2018 to February 2019 in Hefei to analyze and compare the chemical composition. The results showed that the concentrations of PM2.5, total nitrogen (TN) and nitrogenous species, as well as the total nitrogen isotopic composition (delta 15N) increased with the aggravation of pollution. Ammonium nitrogen (NH4+-N, 54%) was the dominant nitrogen-containing specie during the whole campaign, followed by nitrate nitrogen (NO3 -N, 34%) and organic nitrogen (ON, 12%). The delta 15N was positively correlated with NH4+-N/TN but negatively correlated with NO3xe213; -N/TN. NH4NO3 and NH4HSO4 were the dominant forms of the secondary inorganic aerosols. In addition, a significant positive correlation was observed between the temperature and delta 15N. Nitrogen source identification of PM2.5 was conducted using Positive Matrix Factorization (PMF) model, delta 15N values and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results indicated that the contributions of the four main nitrogen sources were obtained and shown in descending order: combustion and industrial emission (42.06%) > secondary aerosols (24.04%) > vehicle exhaust (23.57%) > re-suspended dust (10.33%). The nitrogen aerosols might be mainly influenced by local emissions on normal and slight pollution days, while by both local emissions and transport from other areas on moderate and serious pollution days. Furthermore, nitrogen-containing species in PM2.5 primarily originated from long/medium-distance transportation in two serious pollution events during the entire campaign
On the use of reference mass spectra for reducing uncertainty in source apportionment of solid-fuel burning in ambient organic aerosol
No full textReference mass spectra are routinely used to facilitate source apportionment of ambient organic aerosol (OA) measured by aerosol mass spectrometers. However, source apportionment of solid-fuel-burning emissions can be complicated by the use of different fuels, stoves, and burning conditions. In this study, the organic aerosol mass spectra produced from burning a range of solid fuels in several heating stoves have been compared using an aerosol chemical speciation monitor (ACSM). The same samples of biomass briquettes and smokeless coal were burnt in a conventional stove and Ecodesign stove (Ecodesign refers to a stove conforming to EU Directive 2009/125/EC), while different batches of wood, peat, and smoky coal were also burnt in the conventional stove, and the OA mass spectra were compared to those previously obtained using a boiler stove. The results show that although certain ions (e.g., m/z 60) remain important markers for solid-fuel burning, the peak intensities obtained at specific m/z values in the normalized mass spectra were not constant with variations ranging from 100 %. Using the OA mass spectra of peat, wood, and coal as anchoring profiles and the variation of individual m/z values for the upper/lower limits (the limits ap- proach) in the positive matrix factorization (PMF) analysis with the Multilinear Engine algorithm (ME-2), the respective contributions of these fuels to ambient submicron aerosols during a winter period in Dublin, Ireland, were evaluated and compared with the conventional a-value approach. The ME2 solution was stable for the limits approach with uncertainties in the range of 2 %-7 %, while relatively large uncertainties (8 %-29 %) were found for the a-value approach. Nevertheless, both approaches showed good agreement overall, with the burning of peat (39 % vs. 41 %) and wood (14 % vs. 11 %) accounting for the majority of ambient organic aerosol during polluted evenings, despite their small uses compared to electricity and gas. This study, thus, accounts for the source variability in ME-2 modelling and provides better constraints on the primary factor contributions to the ambient organic aerosol estimations. The finding from this study has significant implications for public health and policymakers considering that it is often the case that different batches of solid fuels are often burnt in different stoves in real-world applications
Millennial-scale erosion patterns of the northern Qinling Mountains, Central China: Implications for topographical evolution
No full textThe northern Qinling Mountains stretch from east to west in Central China. They have undergone distinct surface uplift during the Late Cenozoic and have become the geographical boundary between northern and southern China. To investigate the topographic evolution of the northern Qinling Mountains over millennial timescales and to explore the major controlling factors of relief development we have calculated Be-10-derived catchment averaged erosion rates. Results show that the catchment-averaged erosion rates ranged between similar to 67.4 and 327 m Ma(-1). These erosion rates are nonlinearly correlated with topographic parameters, indicating that topographic steepness controls the spatial variability of the erosion rates. Comparison of local erosion rates reveals that lithology and precipitation have limited influence. Instead, the spatial distribution of erosion in the northern Qinling Mountains is primarily controlled by active tectonics, which can be attributed to uplift along the Qinling Piedmont Fault and the Taibai Fault. Due to the intensive tectonic activity of the Qinling Piedmont Fault since the Late Miocene, the Heihe River Basin has developed as a transient landscape. Finally, comparison between the vertical fault slip rates of the Qinling Piedmont Fault and erosion rates indicates that the topography of the northern Qinling Mountains has undergone continuous uplift and growth since at least the Late Pleistocene. Our results suggest that the northeastward growth of the Tibetan Plateau has regulated the modern erosion of the northern Qinling Mountains and shaped their modern topography. (C) 2021 Elsevier B.V. All rights reserved
Climatology and physical mechanisms of the tropospheric warm cores over the Tibetan Plateau and its vicinity
No full textThe frequently observed tropospheric warm cores over the Tibetan Plateau (TP) are unique climate phenomena and are crucial to the Asian summer monsoon development. However, their climatological structure and formation mechanisms remain elusive and inconsistent among previous studies. In this work, two vertically separated warm cores, the upper-level warm cores (ULWCs) and lower-level warm cores (LLWCs), are identified based on the zonal temperature deviation. The LLWCs are basically confined below 450 hPa, and the ULWCs are mostly observed at 200-400 hPa. The active region of the LLWCs is generally within the TP domain and characterized by regional patches with high frequency occurrences. In contrast, the active region of the ULWCs is featured by a zonally elongated band along the southern TP. The physical mechanisms for the formations of these two distinct types of warm cores are revealed: the LLWCs are mainly generated and maintained by the surface diabatic heating, while the ULWCs are dominated by the large-scale circulation associated with the convection over the Indo-Pacific warm pool. During March-June, the ULWCs within the TP domain occur most frequently and the intensities attain their maxima. In March-April, the ULWCs are mainly determined by the TP adiabatic subsidence induced by the convection over the Indo-Pacific warm pool. In May-June, the warm advection induced by westerlies generates the downstream ULWCs and enhances the ULWCs formed in previous months. Hence it might be inappropriate in traditional view to attribute the tropospheric warm cores around the TP solely to the direct thermal effect of the elevated topography
Effects of Aerosol Water Content on the formation of secondary inorganic aerosol during a Winter Heavy PM2.5 Pollution Episode in Xi'an, China
No full textSulfate, nitrate and ammonium are the most abundant secondary inorganic aerosols (SIA) in atmospheric fine particle matter (PM2.5). Meteorological conditions, gas-particle transportation process, and aerosol acidity (pH) can influence SIA formation. In this study, we conducted semi-continuous measurements of water-soluble inorganic ions during a winter extreme pollution event (from January 9th to January 17th, 2015, average PM2.5 concentrations of similar to 250 mu g m(-3) and peak concentrations of similar to 700 mu g m(-3)) in Xi'an to elucidate on the SIA formation mechanism. The hourly mean level of the total water-soluble ion was 137.4 mu g m(-3), accounting for 55.3% of PM2.5 on average. The dominant ions concentrations of SO42-, NO3- and NH4+ accounted for 15.8%, 19.0% and 13.2% of PM2.5 mass, respectively. PM2.5 was moderately acidic, with an average pH of 4.8 +/- 0.4. Compared to the clean periods, sulfate content decreased by 6.9% during the polluted periods, while those of nitrate and ammonium increased by 2.2% and 5.0%, respectively. The increase in nitrogen oxidation ratios (NOR) and ammonia conversion ratio (NHR) from normal days to haze days were greater when comparison to sulfur oxidation ratios (SOR). In the polluted periods, sulfate and nitrate formations were facilitated by water content increase. Strong linear correlation coefficients between SOR (R-2 = 0.81) and NOR (R-2 = 0.55) with aerosol water content indicated that the gas-liquid reaction of SO2 and NO2 is the major pathway of sulfate and nitrate formation during severe haze episodes. In contrast, the NHR and aerosol water content exhibited a logarithmic relationship, which reveals that when water content was greater than 100 mu g m(-3), the gas-particle partitioning ratio of ammonium was basically unchanged following an increase in water content
Effects of Aerosol Water Content on the formation of secondary inorganic aerosol during a Winter Heavy PM2.5 Pollution Episode in Xi'an, China
No full textSulfate, nitrate and ammonium are the most abundant secondary inorganic aerosols (SIA) in atmospheric fine particle matter (PM2.5). Meteorological conditions, gas-particle transportation process, and aerosol acidity (pH) can influence SIA formation. In this study, we conducted semi-continuous measurements of water-soluble inorganic ions during a winter extreme pollution event (from January 9th to January 17th, 2015, average PM2.5 concentrations of similar to 250 mu g m(-3) and peak concentrations of similar to 700 mu g m(-3)) in Xi'an to elucidate on the SIA formation mechanism. The hourly mean level of the total water-soluble ion was 137.4 mu g m(-3), accounting for 55.3% of PM2.5 on average. The dominant ions concentrations of SO42-, NO3- and NH4+ accounted for 15.8%, 19.0% and 13.2% of PM2.5 mass, respectively. PM2.5 was moderately acidic, with an average pH of 4.8 +/- 0.4. Compared to the clean periods, sulfate content decreased by 6.9% during the polluted periods, while those of nitrate and ammonium increased by 2.2% and 5.0%, respectively. The increase in nitrogen oxidation ratios (NOR) and ammonia conversion ratio (NHR) from normal days to haze days were greater when comparison to sulfur oxidation ratios (SOR). In the polluted periods, sulfate and nitrate formations were facilitated by water content increase. Strong linear correlation coefficients between SOR (R-2 = 0.81) and NOR (R-2 = 0.55) with aerosol water content indicated that the gas-liquid reaction of SO2 and NO2 is the major pathway of sulfate and nitrate formation during severe haze episodes. In contrast, the NHR and aerosol water content exhibited a logarithmic relationship, which reveals that when water content was greater than 100 mu g m(-3), the gas-particle partitioning ratio of ammonium was basically unchanged following an increase in water content