Guangzhou Institute of Geochemistry
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Insights Into Formation and Aging of Secondary Organic Aerosol From Oxidation Flow Reactors: A Review
No full textPurpose of ReviewThis review aims to provide a comprehensive examination of oxidation flow reactor (OFR) studies and their applications in both laboratory and field investigations. OFRs play a crucial role in understanding secondary organic aerosol (SOA) formation and aging processes in the atmosphere. By evaluating the advancements and limitations of OFR technology, this review seeks to identify key research directions and challenges for future studies in atmospheric chemistry and air quality research.Recent FindingsIn recent years, OFR has emerged as an encouraging alternative to smog chambers for SOA study. The high oxidative capacity and short residence time of OFR enable its wide application in both laboratory and field studies. Research utilizing OFR has uncovered the critical role of semi-volatile and intermediate-volatility organic compounds (S/IVOCs) in the formation of SOA from various sources, including vehicle emissions, biomass burning, cooking activities, and non-traditional emissions such as volatile chemical products. Notably, field studies have observed considerable variability in the SOA formation potential across different environments globally, generally showing higher formation potential in urban areas compared to rural and forest regions.SummaryOFR studies have significantly advanced our understanding of SOA formation and aging processes, identifying key precursors, evaluating influencing factors, and quantifying SOA formation potential. However, challenges remain in unraveling detailed mechanisms due to the complexity of SOA sources and properties. Future OFR research should focus on innovations in OFR design, study non-traditional emissions, conduct long-term field observations, develop standardized calibration procedures, and establish SOA yield parameterization schemes for S/IVOCs
Early Cretaceous fayalite-, ferrosilite-, and biotite-bearing rhyolitic porphyries in the Baishuizhai area, South China: Formation by fractional crystallization in the shallow crust
No full textFayalite- and ferrosilite-bearing felsic igneous rocks are a distinctive category of A-type granitic magmas, and the origins of these rocks have proved controversial. In addition, the shallow-crust high-silica rhyolitic magmas responsible for such rocks are considered to have higher viscosities than their plutonic equivalents, which casts doubt on whether fractional crystallization could have occurred during the evolution of these high-silica melts. Here, we report a study of earliest Early Cretaceous (145-142 Ma) fayalite- and ferrosilite-bearing rhyolitic porphyries (FFBRPs) and closely associated biotite-bearing rhyolitic porphyries (BBRPs) from the Baishuizhai area, Guangzhou, Guangdong Province, South China. The Baishuizhai suite provides an excellent opportunity to establish the magmatic origins and evolutionary processes responsible for the FFBRPs. Rocks from the Baishuizhai suite have SiO2 contents of 73.2-77.7 wt%, Na2O + K2O contents of 7.83-9.42 wt%, and Fe2O3T contents of 1.52-2.97 wt%. They have A-type granite features including mineral assemblages (euhedral fayalite and ferrosilite in addition to anhedral amphibole and biotite) and geochemical characteristics [e.g., high 10,000 x Ga/Al values (3.7-4.7), high FeOT/MgO ratios (13.0-34.8), and high Zr (245-514 ppm) and Nb (56.4-96.5 ppm) contents]. The rocks have slightly enriched in situ plagioclase Sr [(Sr-87/Sr-86)(i) = 0.7070-0.7076] and whole-rock Nd [epsilon(Nd)(t) = -2.3 to -2.0] compositions and depleted zircon Hf isotopic compositions [epsilon(Hf)(t) = -0.9 to +7.0] relative to chondrite, as well as higher zircon delta O-18 values (6.3 parts per thousand-7.8 parts per thousand) and intermediate in situ plagioclase Pb isotopic compositions [(Pb-206/Pb-204)(i) = 18.368-18.727, (Pb-207/Pb-204)(i) = 15.488-15.673, and (Pb-208/Pb-204)(i) = 38.049-38.801] compared with depleted mantle. We infer that the primary magmas of this rock suite were formed by mixing of mantle-derived magmas with subordinate (20%-50%) metasedimentary-rock-derived magmas. Fayalite and ferrosilite in the FFBRPs were most likely crystallized from dry, hot, and reduced magma in a lower (<16.5 km depth) chamber. The lower magma gradually evolved during ascent to a water-enriched magma in an intermediate chamber at a shallow depth (3-4 km), forming the FFBRPs (elevation: 129-168 m). Finally, the residual melts migrated upward and resided in an upper (<3 km depth) chamber, forming the BBRPs (elevation: 196-824 m). According to the established temporal-spatial distribution of Early Cretaceous A-type granites and adakitic rocks in South China, we suggest that the Paleo-Pacific plate underwent diachronous rollback, starting during the earliest Early Cretaceous. This rollback enhanced the degree of crust-mantle interaction in the Guangzhou area
The petrogenesis of Cenozoic basalts from Daihai, western North China Craton: Constraints from <SUP>40</SUP>Ar-<SUP>39</SUP>Ar chronology, major and trace elements, and Sr-Nd-Pb-Hf isotopes
No full textThe Daihai Cenozoic intraplate basalts are distributed in the western North China Craton (NCC), which is a part of the Cenozoic volcanic province in eastern China, and they are all alkaline basalts. The fine-scale determination of their mantle source region properties, partial melting mechanisms, and petrogenesis can provide crucial information for exploring lithospheric destruction and thinning in the western NCC. Ar-40- Ar-39 dating of potassium feldspar grains from the Daihai alkaline basalts yielded plateau ages of 18.22 +/- 1.84 Ma and 26.86 +/- 0.72 Ma, indicating that the Daihai basalts underwent multiple eruptive cycles during the Late Oligocene- Middle Miocene. These basalts exhibit ocean island basalt (OIB)-like geochemical features and were subjected to negligible crustal contamination. Moreover, basaltic magmas underwent intense fractional crystallization of olivine and clinopyroxene. The geochemical differences in the Daihai basalts were controlled by partial melting. The Daihai basaltic magmas were composed of at least two types (type I-enriched mantle and prevalent mantle) of mantle end-members that partially melted and then mixed, and the lithology of the mantle source region was predominantly peridotite. Under enriched mantle conditions, the mixing of garnet lherzolite partial melts ( <1%) and spinel lherzolite partial melts (2- 5%) can reasonably explain the elemental variations characteristic of the Daihai basalts. Most importantly, the melting depth and lithospheric thickness of the Daihai basalts were < 70 km or even close to 50 km, implying that the western NCC underwent lithospheric destruction and thinning during the Cenozoic. However, these effects were spatially heterogeneous. The most plausible genetic mechanism for the generation of the Daihai basalts was the coupled effects of subduction of the Pacific slab and subduction -collision of the Indo -Eurasian Plate since the Oligocene. The mantle flows generated by these two events convected, blocked and triggered upwelling mantle flows at the eastern margin of the Ordos Block. The upwelling mantle flows resulted in frequent magmatism in the region
Mineralization process of the Changjiang uranium orefield in South China: Constraints from pitchblende geochemistry
No full textThe Changjiang uranium (U) orefield in northern Guangdong (South China) contains several important graniterelated uranium deposits, including the Mianhuakeng deposit. The hydrothermal evolution and mineralization mechanism of the deposit remain unclear, and hence in this study we analyzed the mineral compositional variations of pitchblende from different elevation (-300 to -50 m) in the orebody at Mianhuakeng deposit. The results indicate that with decreasing depth, the hydrothermal mineral assemblage changes from a reducing one (pitchblende, pyrite, and chlorite) to a moderately oxidizing one (pitchblende, coffinite, hematite, and goethite). The contents of U, Sr, & sum;REE, U/Th, and LREE/HREE ratios in the pitchblende decrease (whereas the Cu-Pb-ZnNi-Co-Sc-Rb contents increase) progressively with decreasing depth. Also, Ce anomaly (Ce/Ce*) changes from positive to negative, and Eu anomaly (Eu/Eu*) becomes more negative with decreasing depth. We interpreted such vertical variations to be caused by the ascent of deep, mid-to-high temperature, highly-oxidizing oreforming fluid, which was reduced by early-stage reducing minerals in the wallrock, a process that also formed the mineralization at Changjiang. In addition, the pitchblende REE distribution patterns and Eu/Eu* at depth (-300 m) resemble those of the Zhuguang pluton, indicating that the ore-forming materials were originated from the Ubearing granite wallrocks. Therefore, the Ce/Ce* and Eu/Eu* variations of pitchblende can be used to guide deep uranium ore exploration
Constraining Trifluoromethane (HFC-23) Emission in Eastern China Based on Two-Year Online Measurements
No full textTrifluoromethane (CHF3, HFC-23) is one of the most potent greenhouse gases (GHGs), and eastern China has been recognized as a major source region, yet highly inconsistent emission estimates warrant more extensive studies. In this study, we conducted 2-year online measurements of halocarbons during 2021-2023 at an urban site in the Pearl River Delta region. The observed average HFC-23 mixing ratios of 43.6 +/- 7.8 ppt were similar to 20% enhanced compared to observations at the Mace Head global baseline station. Unlike other halocarbons with significant local emissions, HFC-23 mixing ratios showed distinct seasonal variations with peak values in winter and bottom values in summer. Similar seasonal patterns and highly significant correlation were observed between HFC-23 and perfluorocyclobutane (c-C4F8, PFC-318), a co-product from manufacturing PTFE using chlorodifluoromethane (CHClF2, HCFC-22) as feedstock. The weighted potential source contribution function analysis also demonstrated eastern China was the major source area for both HFC-23 and PFC-318. Tracer-based estimation revealed HFC-23 emissions of 6.7 +/- 3.1 Gg yr-1 (equivalent to 98 Tg-CO2 yr-1 or 0.7% China's annual GHG emissions in 2021) in eastern China. Our results highlight the importance of HFC-23 emission control in eastern China for China's GHG and F-gases emission reductions, and suggest that greater attention should be given to HFC-23 emissions from PTFE production, which is emerging as a more substantial source than previously anticipated.
Trifluoromethane, also known as HFC-23, is a very strong greenhouse gas produced unintentionally during the manufacturing of chlorodifluoromethane (HCFC-22). It is among target fluorine-containing greenhouse gases whose emissions should be controlled under the Kigali Amendment. While a lot of HFC-23 is believed to come from eastern China, it is hard to say exactly how much. From 2021 to 2023, we measured HFC-23 and other fluorinated gases in air at an urban site in the Pearl River Delta region. We found HFC-23 levels were about 20% higher than that at global background sites. We noticed that HFC-23 and another gas called perfluorocyclobutane (PFC-318), which is a co-product when manufacturing PTFE with HCFC-22, were strongly linked and both had seasonal patterns quite different from other fluorinated gases. Our analysis shows that PFC-318 and HFC-23 mostly come from eastern China. By using PFC-318 as a tracer, we estimated the amount of HFC-23 emissions in eastern China at 6.7 +/- 3.1 Gg yr-1, making up a small but important part of China's overall greenhouse emissions. This highlights the need to lower HFC-23 emissions, particularly those from the process of making PTFE with HCFC-22.
HFC-23 mixing ratios measured online during 2021-2023 were 43.6 +/- 7.8 ppt, similar to 20% higher than that at the Mace Head baseline station HFC-23 emissions mainly occurred in eastern China with estimated emissions of 6.7 +/- 3.1 Gg yr-1 during 2021-2023 Feedstock use of HCFC-22 for producing PTFE is emerging as an increasingly significant emission source of HFC-2
A hybrid pore-network-continuum modeling framework for flow and transport in 3D digital images of porous media
No full textUnderstanding flow and transport in multiscale porous media is challenging due to the presence of a wide range of pore sizes. Recent imaging advances offer high-resolution characterization of the multiscale pore structures. However, simulating flow and transport in 3D digital images requires models to represent both the resolved and sub-resolution pore structures. We develop a hybrid pore-network-continuum modeling framework. The hybrid framework treats the smaller pores below the image resolution as a continuum using the Darcy-scale formalism and explicitly represents the larger pores resolved in the images employing a pore network model. We validate the hybrid model against direct numerical simulations for single-phase flow and solute transport and further demonstrate its applicability for simulating two-component gas transport in a shale rock sample. The results indicate that the new hybrid model represents the flow and transport process in multiscale porous media while being much more computationally efficient than direct numerical simulation methods for the range of simulated conditions
Effect of Al Substitution on Visible Short-Wave Infrared Reflectance Spectroscopy (VSWIR) of Goethite and Ferrihydrite
No full textGoethite and ferrihydrite are the two major iron hydroxides, essential mineral constituents in the terrestrial surface system. Aluminum (Al) is the most common substituent in iron hydroxides, and it may significantly change the bulk and surficial physicochemical properties of iron hydroxides. Consequently, a practical and convenient approach is needed to efficiently identify the Al substitution degrees of iron hydroxides in natural occurrences. This study presents a comprehensive investigation of the VSWIR characteristics of laboratory-synthesized Al-substituted goethite and ferrihydrite, to establish diagnostic VSWIR parameters for the identification and quantification of Al substitution levels in iron hydroxides. The findings revealed that Al substitution can affect the band positions (P) of goethite and ferrihydrite at similar to 650 nm, similar to 900 nm, and similar to 1400 nm. The relationships between the Al substitution of ferrihydrite and VSWIR parameters can be expressed as P900 = -0.43 x Al(%) + 931 and P1400 = -0.07 x Al(%) + 1428, while that of goethite can be expressed as P650 = 0.42 x Al(%) + 657 and P900 = 2.29 x Al(%) + 936. The peak fitting results showed that the absorption intensity at 480-550 nm linearly decreases with increased Al substitution. The obtained VSWIR spectra of Al-substituted goethite and ferrihydrite provide a critical supplement to the spectral library for (Al) iron hydroxides, and these VSWIR parameters can be utilized for the semi-quantitative determination of Al substitution in natural iron hydroxide
Marine sulfate sulfur isotopic evidence for enhanced terrestrial weathering and expansion of oceanic anoxia during the Devonian-Carboniferous transition
No full textThe Hangenberg mass extinction during the Devonian-Carboniferous (D-C) transition represents one of the largest biodiversity losses of the Phanerozoic, while the underlying cause remains controversial. An improved understanding of the contemporaneous sulfur cycle can provide insights into the latest Devonian environmental changes that potentially affected marine biotas. Here, we report on a high-resolution chemostratigraphic study of the sulfur isotopic composition of carbonate-associated sulfate (CAS) through the D-C transition in the Long'an and Qilinzhai sections of South China. The delta S-34(CAS) profiles exhibit a long-term (i.e., >10(5) yr) negative excursion from +19.0 parts per thousand in the upper Lower Si. praesulcata Zone to +13.0 parts per thousand in the middle Upper Si. praesulcata Zone, and terminated with a recovery to 20.3 parts per thousand in the lower Si. sulcata - Si. duplicata zones, representing a depositional interval of similar to 0.9 Myr. In addition, this long-term negative excursion is punctuated by episodic sharp negative shifts. The negative delta S-34(CAS) excursion coincided with the end-Devonian biotic crisis, a positive shift in carbonate delta C-13, and negative shifts in bulk-sediment delta N-15 values and I/Ca ratios. Increasing organic carbon burial indicated by the positive shift in delta C-13 precludes decreased pyrite burial as an explanation for the negative shift of delta S-34(CAS), supported by intensified marine anoxia revealed by the negative shifts in delta N-15 and I/Ca. We attribute the long-term negative shift in delta S-34(CAS) to enhanced inputs of S-34-depleted riverine sulfate in conjunction with low seawater sulfate concentrations within the semi-restricted Yangtze Sea, whereas the transient negative spikes in delta S-34(CAS) were possibly caused by episodic upwelling and oxidation of H2S in expanded oceanic oxygen-minimum zones. In conjunction with the positive shift in delta C-13, the negative shift in delta S-34(CAS) supports a significant role for enhanced subaerial weathering in intensifying marine anoxia and triggering the biotic crises that occurred during the latest Devonian, the most likely driver of which was the spread of vascular (especially seed-bearing) land plants