The Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation are important target strata for shale gas exploration in the Sichuan Basin, China. In this paper, the sedimentary facies and palaeogeography of the two formations in Chongqing area have been analyzed, and total organic carbon (TOC) contents are correlated with the sedimentary facies to prospect the favorable areas for shale gas exploration. According to the lithological characteristics and sedimentary structures, five sedimentary facies are identified, i.e., siliceous deep-water shelf, muddy deep-water shelf, calcareous shallow-water shelf, muddy shallow-water shelf, and silty-muddy shallow-water shelf facies, respectively. The palaeogeography reconstruction is based on the lithological distribution in the study area. The lower part of Wufeng Formation was developed with the muddy deep-water shelf, siliceous deep-water shelf, and calcareous shallow-water shelf facies. The Guanyinqiao Member, representing the upper part of Wufeng Formation, was developed with the transition from siliceous deep-water shelf and muddy deep-water shelf facies to a domination of muddy shallow-water shelf and calcareous shallow-water shelf facies, which was deposited during the glacial-induced global regression. The Lower Member of Longmaxi Formation was characterized by the expansion of siliceous deep-water shelf facies and contraction of muddy shallow-water shelf and calcareous shallow-water shelf facies, signifying a rapid sea level rise associated with global warming. The Upper Member of Longmaxi Formation was developed with muddy shallow-water shelf facies, with the expansion of calcareous shallow-water shelf and silty-muddy shallow-water shelf facies. The shales with higher TOC content tend to be developed in the siliceous deep-water shelf and muddy deep-water shelf facies that were distributed in the Nanchuan, Shizhu, Yongchuan, and Wuxi areas. The results of lithofacies palaeogeography reconstruction have a certain significance to predict shale-gas target areas in Wufeng and Longmaxi formations of Chongqing.

Deep coalbed methane (CBM) reservoirs represent a frontier in unconventional gas exploration, yet the pore structure characteristics controlling their adsorption capacity remain insufficiently quantified. This study investigates the fractal pore structure of low- to middle- rank coals at depths exceeding 3300 m in the Taibei Sag, Tuha Basin, using core samples from the Kexin 1H well, by means of low-temperature nitrogen adsorption and methane isothermal adsorption experiments. Two fractal dimensions, D1 (pore surface roughness) and D2 (pore structure complexity), were calculated based on the Frenkel-Halsey-Hill model. Results show that the coal adsorption-desorption isotherms in the study area can be categorized into three types, with Type I (dominated by open slit-shaped and ink-bottle pores) exhibiting the highest specific surface area and methane adsorption capacity. D1 is significantly positively correlated with Langmuir volume (a key adsorption parameter), while D2 has no correlation with Langmuir volume and limited predictive value. Fractal analysis also indicates that vitrinite reflectance and content significantly influence pore heterogeneity: D1 shows no correlation with vitrinite, whereas D2 decreases with increasing vitrinite content. This result quantifies the intrinsic pore structure related to adsorption in deep coal reservoirs, establishes D1 as a practical evaluation index for the adsorption potential and quality of deep CBM reservoirs in the Taibei Sag, provides a precise quantitative basis for exploration target selection, development decision optimization and reservoir reconstruction in this structurally complex basin, and facilitates the efficient exploration and development of regional deep CBM.

The adverse health effects of air pollution are being increasingly recognized as major causes of disease. Atmospheric particles, as a major component of air pollution, have been extensively studied in terms of their sources, physicochemical characteristics, transport in the atmosphere, and changes in particulate composition during their time in the atmosphere. The relationships between particles and diseases are complex, so research on the health effects and damage mechanisms of particulate matter (PM) is of significant importance. This study reviews the health effects of PM and provides an overview of the hazards of atmospheric PM to various human organs. In addition, this review explores the mechanisms of damage, summarizes the research methods used to determine the health effects, and discusses the influential health factors caused by PM. In combination with current Chinese and global research, the modern technologies and research trends on the health effects of particles are elucidated.

The architecture and preserved sedimentary structures of alluvium have been shown to correlate to variations in river discharge patterns and reflect the paleoclimatic conditions of the time of deposition. The co-efficient of variance of annual peak discharge (CVQp = standard deviation of the annual peak flood discharge over the mean annual peak flood discharge) has been used as a basis for a new set of fluvial facies models independent of river planform. Deposits of rivers with low CVQp are internally dominated by dune-scale cross-bedding and preserve macroform architecture in full with limited lateral and vertical lithological variability, whereas increasing values of CVQp are associated with increasing abundance of flow transcritical structures, poor preservation of macroform architecture, increasing lithological variability, and increasing evidence of high magnitude/low frequency flow events that are often high-concentration flows. This paper investigates the lithofacies and sedimentary structures of the Liujiagou Formation in the Shuiyuguan Section of Shanxi Province. Additionally, it examines the fluvial styles represented by the fluvial architectural elements. Paleocurrent measurements indicate that Liujiagou Formation channels consistently flowed from NNW to SSE. Vertically, the lower part of this formation was dominated by cross-bedding, indicating deposits of moderate CVQp rivers. The middle part was characterized by cross-bedding and flat/low-angle-stratification, reflecting an alternation of moderate-to-high CVQp river deposits. The upper part is almost entirely composed of high-flow structures, signifying deposits of high CVQp rivers. High CVQp rivers dominated the Early Triassic Liujiagou Formation. This pattern indicates that the climate in the Early Triassic became increasingly arid, with intensified seasonal flash floods. The evolution of the CVQp of fluvial deposits from moderate to high was coupled with the transition from semi-arid climate to seasonally arid climate from the Permian-Triassic transition to the Early Triassic. This evolutionary model reveals the important control of paleoclimates on fluvial sequences, and it uses a recently-published model to provide insights into some fluvial deposits and their formative paleoclimatic controls.

To investigate the health risks of particulate matter during spring dust storms in Beijing, this study selected atmospheric particulate samples collected during a typical dust storm event in March 2021. The DNA damage rates induced by PM(2.5 )and PM10 were measured using the Plasmid Scission Assay (PSA) and were used as an indicator of their oxidative potential. Water-soluble heavy metal elements (WSHM) in the samples were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Results indicate that due to the influence of the dust storm, the monthly average PM(2.5 )mass concentration in March 2021 reached as high as 83 mu g/m(3), which could potentially raise the difficulty of air pollution control. It was found that during the dust storm event, PM(2.5 )induced a higher DNA damage rate (mean 42.35% at an experimental dose of 200 mu g/mL in the PSA) than PM10 (mean 40.46% under the same experimental dosage). The DNA damage rates of dust storm particles showed a positive correlation trend (r = 0.60) with total WSHM concentrations. Exposure toxicity, calculated by multiplying the DNA damage rates under certain experimental PM doses by the PM mass concentrations, showed that the exposure risk of PM(2.5 )during dust storms even exceeded that of PM(2.5 )during haze events. This study reveals the potential toxicity and health risks associated with PM during dust storms, which calls for increased attention.

The Skagerrak-Centered large igneous province (SCLIP) was active 299 million years ago when Earth's climate transitioned into an interval of intensified glaciation. A link between the SCLIP and global climate change has been hypothesized but there is little direct evidence of concurrent volcanism and climate change in coeval sedimentary layers from the late Carboniferous to the early Permian. We combined carbon isotopes, mercury contents and isotopes, and elemental geochemistry of the Taiyuan Formation in the Hedong Coalfield, North China to identify two episodes of volcanism during the early and late Gzhelian (latest Carboniferous). Both episodes are marked by Hg enrichments, positive Delta 199Hg excursions and negative delta 13Corg excursions; only late Gzhelian volcanism was associated with reduced rates of continental weathering and was followed by global cooling. We hypothesize that the late Gzhelian volcanic episode had a greater environmental impact than that in the early Gzhelian because late Gzhelian volcanism was likely more intense and of longer duration. The SCLIP may have contributed to global cooling via the release of sulfate aerosols that results in atmospheric cooling and/ or from ocean fertilization and increased removal of organic carbon via the biological pump.

Heterogeneous reactions on aerosol particles are important pathways for atmospheric sulfur transformation and secondary aerosol formation. Using high-resolution scanning electron microscopy coupled with energy-dispersive X-ray spectrometer, we investigated sulfur enrichment on individual particles during a persistent haze-to-dust transition in urban Beijing. Dust aerosols were dominated by mineral particles, whereas haze aerosols contained abundant sulfate and anthropogenic particles. During dust periods, all particle types exhibited weak sulfur enrichment, with sulfur contents generally below 5%. In contrast, carbonate/sulfate and clay-Na/Mg/Ca particles during haze periods showed intense sulfation, with average sulfur weight ratios reaching 56.4% and 23.2%, respectively. Nevertheless, equivalent pure sulfate particle concentrations remained comparable between haze and dust periods because of the much higher abundance of mineral dust particles during dust events. These findings reveal fundamentally different sulfur uptake pathways under haze and dust conditions and provide new insights into aerosol aging, dust-pollution interactions, and sulfur cycling under improving air quality in northern China.

The Late Triassic Carnian Pluvial Episode (CPE; similar to 234-232 Ma) witnessed profound changes in terrestrial ecosystems, vegetation, and climate, which could be related to eruptions of Wrangellia Large Igneous Province (LIP). Nonetheless, the scarcity of detailed terrestrial plant records limits understanding of whether these floral and climate changes were synchronized with Wrangellia's eruption pulses. Here, we investigated high-resolution palynological data through the CPE from the Jiyuan terrestrial Basin in North China. Our data reveal four distinct phases of terrestrial vegetation transition from xerophytes to hygrophytes, with each shift accompanied by pronounced climate transformations from relatively cool-dry to relatively warm-humid conditions. Each vegetation shift is linked temporally with volcanic activity indicators including negative organic carbon isotope excursions, Hg and Hg/TOC peaks, and near-zero Delta Hg-199 isotope values. After the first, third and fourth eruptions, vegetation recovery showed resilience with floral reassembly broadly similar to pre-eruption floras. In contrast, the impact of the second eruption was apparently larger and triggered more dramatic changes including a surge in terrestrial plant diversity and hygrophytic species, with vegetation recovery having a distinct and more modern floral composition (e.g., Dipteridaceae, Matoniaceae, Pinaceae, and Podocarpaceae) that persisted after the CPE. Our findings offer new insights into the links between LIP volcanism and terrestrial vegetation and climate changes during the CPE, and demonstrates differential floral and climatic responses to different scales of major CO2-driven global warming events in deep time in otherwise similar environmental contexts.

Wildfires are important disturbances in many of the Earth’s ecosystems and are of great significance for understanding the interactions among environmental, atmospheric and vegetational changes in deep time. The Jurassic palaeoclimates were constantly changing, experiencing diverse climate states. Studying Jurassic palaeoclimates and palaeoenvironments provides crucial knowledge for understanding the complexity of our rapidly changing planet in the present day. The well-developed coal seams of Middle Jurassic in northern China are a source of deep-time information, including inertinites as the fossil evidence of palaeowildfires, providing insights into the evolution and behavior of fire-prone ecosystems. In this study, we collected underground coal samples and inertinite content from the Yan’an Formation in the Ordos Basin, and investigated palaeowildfire regime by analyzing coal macerals, inertinite reflectance, and polycyclic aromatic hydrocarbons (PAHs). The presence of high levels of inertinite and abundant combustion-derived PAHs demonstrates that widespread wildfires occurred during the Aalenian in the northeastern Ordos Basin. Inertinite reflectance values, including the data from abundant semifusinite, ranging from 1.42

Major carbon cycle fluctuations and climate changes triggered by the main eruptive phase of the Emeishan Large Igneous Province (ELIP) have attracted widespread attention. However, few studies have focused on the climatic effects of the massive volcanic ash eruptions that characterized the waning stage of the ELIP. This study integrates natural gamma ray-logging (GR) and geochemical, petrological, and mineralogical analysis of core samples from Borehole ZK10 (Nayong County, Bijie City, Guizhou Province) from the western part of the South China Block (WSCB). We establish an astronomical timescale based on Milankovitch cycles and integrate this with geochemical, petrological, and mineralogical analyses to reconstruct variations in water column redox conditions, paleoproductivity, organic carbon burial, δ13Corg, and volcanic activity during the Wuchiapingian (late Permian). The ELIP waning stage volcanic activity and carbon cycle fluctuations in the Wuchiapingian can be divided into early (259.95–257.52 Ma), middle (257.52–255.98 Ma), and late (255.98–254.59 Ma) phases. The intensity of volcanic activity is strongly correlated with climate fluctuations. In the early phase, intense volcanic activity coincided with increased productivity, the development of marine anoxia, enhanced organic carbon burial, and a positive shift in δ13Corg, during an interval of cooling. In the middle phase, volcanic activity weakened, waters reoxygenated, productivity declined, organic carbon burial decreased, and δ13Corg shifted negatively during an interval warming. In the late phase, volcanic activity intensified once more, resulting in the reestablishment of anoxic conditions through elevated productivity, and increasing organic carbon burial, with no significant shift in δ13Corg. In addition to extensive silicate weathering, the increased burial of organic carbon caused by multiple volcanic eruptions during the ELIP waning stage are seen as key drivers of global climate cooling during the Wuchiapingian.

Hyperthermal warming and biotic crisis occurred immediately before and during the Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE) at similar to 183 Ma. Wildfire episodes have been evidenced for hyperthermal events in the geological past which is associated with mass extinction. However, the impact of the T-OAE on wildfire occurrence and the processes that led to biotic crisis, especially floral turnover, are not yet well understood. Here we present high-resolution analyses of fossil charcoal, maceral inertinite, reflectance (R-o), and polycyclic aromatic hydrocarbons (PAHs) from the Pliensbachian-Toarcian interval, together with bulk organic carbon isotopes for the Dameigou section of the Qaidam Basin, China. These rocks record prominent changes before, during and after the T-OAE. Wildfire activity evolved from moderate low-temperature wildfires of the Pliensbachian, to intense high-temperature wildfires in the Early Toarcian, and to high-frequency but suppressed low-temperature wildfires in the Late Toarcian. These findings indicate that intense wildfires in the East Tethyan hinterland occurred during the Early Toarcian due to hyperthermal warming and aridity, probably linked to the intensive Karoo-Ferrar volcanism. The coincidence of the terrestrial floral turnover with intense wildfires in the Qaidam Basin suggest that wildfire during the Early Toarcian was one of the important factors governing the terrestrial biotic crisis. Further, widespread variegated rocks after the T-OAE in the East Tethyan inland basins indicate the scarcity of organic matter influx and, at least locally, there was a delayed recovery of land vegetation ecosystems. Our results imply that wildfire played an important role in both the deforestation and the later suppressed recovery of land plant ecosystems during the late Early Jurassic in the Qaidam Basin.

The Middle Jurassic Aalenian Epoch represents a key greenhouse interval, yet the interplay between high-frequency climate variability, wildfire activity, and carbon-cycle feedbacks remains poorly constrained. Here we present a high-resolution, multi-proxy study of the Aalenian lower Dameigou Formation in the northern Qaidam Basin, integrating sedimentology, kerogen petrography, polycyclic aromatic hydrocarbons (PAHs), stable carbon isotopes, and elemental geochemistry. Our results document three distinct episodes of intensified wildfire activity, expressed as peaks in inertinite abundance, elevated high-molecular-weight PAH concentrations, and combustion-diagnostic ratios such as BaA/(BaA + Chr). These wildfire episodes are closely synchronous with transient arid intervals, indicated by depressed Chemical Index of Alteration (CIA) values and complementary shifts in Rb/Sr and Sr/Cu ratios, superimposed on an overall warm and humid climate. We infer that the recurrent wildfires were driven by a combination of short-term aridity oscillations, elevated atmospheric oxygen levels, and the dominance of flammable conifer-fern vegetation. Crucially, we show that wildfires exerted a dual role in the regional carbon cycle: during peak aridity, they acted as a net carbon source through direct CO2 release and suppression of the biological pump, whereas under conditions of enhanced weathering they promoted a net carbon sink via sequestration of refractory pyrogenic carbon (inertinite) and nutrient-stimulated increases in productivity and organic carbon burial. This study highlights the sensitivity of deep-time wildfire regimes to climate variability and underscores the context-dependent role of wildfires in carbon cycling during greenhouse states.

Atmospheric microplastics in respirable PM2.5 (MP2.5) have attracted widespread attention, yet their characteristics, major sources, and factors influencing their emission remain poorly understood. We present the first long-term (2010-2024) observation of atmospheric MP2.5 in Beijing, quantified with pyrolysis-gas chromatography / mass spectrometry. Our investigation of type-specific trends and driving factors revealed an overall increasing trend in MP2.5 concentration, with an average level of 264 ng/m3 and a peak of 417.6 ng/m3 in 2021. The distinct trends of MP2.5 and PM2.5 concentrations suggest that their major sources differ, necessitating different regulation measures for each. PVC (polyvinyl chloride), PS (polystyrene), PP (polypropylene), PE (polyethylene), and PA66 (polyamide 66) are the predominant types of MP2.5, differing markedly from the pattern in dustfall or total suspended particulate matter. PS, PP, and PP correlated positively with express delivery volume and total retail sales of consumer goods, implicating packaging material as a potential major source. PA66 and PVC, which are widely used in disposable medical supplies such as protective suits, responded sensitively to the COVID-19 pandemic. Our findings reveal that socioeconomic activities strongly influence the long-term evolution of MP2.5 patterns, and provide a scientific basis for related risk assessments.

Microplastics have emerged as a relatively new type of pollutant and have attracted significant global attention. This study focuses on toxicology of microplastics in ambient PM2.5 and road dustfall in Beijing. It utilizes the Plasmid Scission Assay to toxicologically evaluate the oxidative damage capacity of microplastics as a component of PM2.5. The Pollution Load Index (PLI) method, based on the mass concentration of microplastics in ambient air, was employed to assess the ecological risk of atmospheric dustfall microplastics in Beijing. The results showed that both standard microplastic samples and mixed samples of microplastics with ambient PM2.5 exhibited a dose-response relationship in DNA damage rates. At the same dose, microplastic samples with smaller particle sizes have a higher DNA damage rate. Based on the PLI results, most road dustfall microplastics in Beijing exhibit significant spatial variation. Analysis of road dustfall along the east-west main road across Beijing's urban area revealed that microplastic pollution levels are higher in the eastern zone than in the western zone. Comparisons of pollution levels across functional areas in Beijing showed that university areas > residential areas > industrial areas > commercial areas > agricultural areas. In vertically collected samples, higher elevations (PLI13.6m = 3.54) exhibit greater pollution levels than lower (PLI1.5m = 1), which warrants special attention. These findings highlight the complex relationship between atmospheric microplastic accumulation and their oxidative capacity, providing essential insights for the design of targeted emission reduction strategies.

Basal upper Permian strata of SW China host extensive Nb-Zr-rare earth elements and yttrium (REY)-Ga ore beds in non-coal sequences characterized by significant natural gamma-ray logging (GR) positive anomalies and are named the Xuanwei Nb-Zr-REE-Ga deposit. Since past work has largely focused on single section or borehole records, the spatial distribution of ore beds within the Western Yangtze Cratonic Basin (WYCB) remains incompletely understood. This study integrates lithological and GR data from 56 boreholes and one outcrop section across the WYCB coal measures, supplemented by geochemical analyses of samples from the Xia'aimao village section and Borehole ZX1302. We integrated this dataset to investigate the spatial distribution, geochemical characteristics, petrology, and mineralogy of critical metals ore beds across the basin. The depositional center is located in the Yanjin-Yiliang-Zhenxiong areas of northeastern Yunnan, from where the singlelayer thickness, cumulative bed count and thickness, and grain size of the ore beds gradually decrease from west to east and from south to north. Geochemical data reveal that the primary magmatic source of volcanic ash was predominantly derived from Nb-Ta mineralized syenites in the Panxi region. Widespread air-fall volcanic ash sequences bearing typical pyroclastic minerals, coupled with the occurrence of ore beds on paleo-uplifts, suggest an air-fall transport mechanism rather than a fluvial one. The distribution and preservation of ore beds were significantly influenced by sedimentary environments and tectonics. The ore beds underwent intense lowtemperature hydrothermal alteration. Plants may also play an important role in volcanic ash preservation and critical metals enrichment. The deposit covers an area of over 11 & times; 104 km2 , with estimated total resources amounting to 3.55 & times; 108 t of Nb, 2.32 & times; 109 t of Zr, 1.18 & times; 109 t of REY, and 5.90 & times; 107 t of Ga, constituting a globally important super-large-scale critical metal deposit.

At the end of the Paleozoic Era, the Earth experienced an extreme ecosystem disturbance event, which was the Permian–Triassic Mass Extinction (PTME); causing an irreversible global catastrophe for animals and plants. Fossil evidence from marine strata correlated by zircon U–Pb dating of volcanic ash supports the view of a rapid and short-lived extinction. In contrast, the associated disturbance processes of terrestrial ecosystems were relatively prolonged and complex, leading different scholars to propose various extinction mechanisms and models for these ecosystem disturbances. Evidence of wildfires in late Permian–Early Triassic transitional strata have been reported globally, and many scholars believe that wildfires during the PTME were a significant contributing factor to terrestrial ecosystem disturbance. Globally, palaeowildfires may have served as an important driver for terrestrial ecosystem disturbance during the Permian–Triassic transition, promoting and accelerating the processes of environmental degradation. Palaeowildfires during the Permian–Triassic transition played a crucial role in the changing of terrestrial ecosystems with potential implications for the evolution of larger ecosystems. This study systematically reviews progress in recent research on the terrestrial PTME and wildfires. It summarizes and considers the mechanisms of terrestrial ecosystem disturbance during the P–T transition and responses to palaeowildfires, considering the palaeoenvironmental background and plant evolution processes.

Sulfate aerosols formed within industrial plumes, particularly from steel plants, are major sources of atmospheric particles, yet their formation pathways and physicochemical properties remain poorly resolved due to a lack of direct observation. In this study, we employed computer-controlled scanning electron microscopy (CCSEM) to investigate the morphological features, elemental composition, and size distribution of individual particles collected at five sampling sites within a typical steel plant and the surrounding environment. A total of 91,185 individual particles were automatically analyzed and classified, and Na-rich (46.6 %), Ca-rich (21.5 %), and Si-rich (8.2 %) particles were the three major types in number proportions with a wide size range of 0.2–43.6 μm in equivalent diameter. Most notably, elongated submicron Na2SO4 particles accounted for 72.8 % of total particle number nearest the exhaust outlet of the steel plant. These sulfate particles underwent rapid atmospheric aging processes, evidenced by a 96.2 % depositional removal within the plant and a significant increase in average size from 1.1 to 3.4 μm. When transported to the ambient sites outside the plant (6–20 km away), their abundance significantly decreased to only 5.3 % (range: 2.2 %–11.7 %), indicating limited long-term transport. This study provides the first microscopic evidence that inorganic sulfate aerosols exhibit considerable near-source emission but undergo rapid sedimentation. Our findings highlight the significance of sulfate aerosols as a major component of PM2.5 near industrial areas, underscoring the urgent need to control this emission pathway.

To quantitatively characterize the intrinsic relationships between pore structure evolution and coal metamorphism, typical middle-high rank coals were sampled from Anhe, Jiaozuo, Huaibei, and Huainan coalfields in northern China. The variations of physical composition and pore structure with coal rank were analyzed by a suite of experimental tests and methods. The results show that with the enhancement of coalification degree, the moisture content decreases first and then increases, and the lowest point corresponding to the maximum vitrinite reflectance (Ro, max) is about 1.3 %. With increasing coal rank, the specific surface area of coal pores reduces, and the pore surface roughness decreases, leading to a decrease in DNA1. The total pore volume and average pore size decrease, while the pore structure complexity is enhanced, resulting in an increase in DNA2. The Ro, max boundary approximately corresponds to the onset of the second coalification jump. The poly-carbon, dehydrogenation, and deoxygenation processes lead to apparent changes in various pore volumes of coals. Consequently, the fractal dimensions characterizing the pore surface and structure exhibit marked changes with increasing coal rank. When Ro, max is greater than 1.08 %, the second coalification jump progressively completes with the increase of coal rank. Coalification and strata pressure compress larger primary pores, accompanied by the generation of thermogenic gas. Therefore, the volume and surface area of micropores gradually increase, and the abundance micropores provide more adsorption space for methane gas. The pore structure becomes progressively more complex and the molecular structure is gradually ordered. Furthermore, during the occurrence of the second coalification jump, the pore size distribution of samples changes obviously. The proportions of mesopore and transition pore reach the peak, while the proportions of micropore and macropore decrease to the lowest. Compared with before the second coalification jump, the transition pore and mesopore contents after the second coalification jump decrease slightly, the macropore content increases, and the pore structure is also complicated. Quantitatively characterizing the coal reservoir physical properties and thoroughly investigating the pore structure evolution around the second coalification jump is of great significance to guide the exploration and development of middle-high rank coalbed methane.

Iron (Fe) redox cycling in dust aerosols impacts the supply of bioavailable Fe to marine ecosystems and the formation of reactive oxygen species. It has been suggested that photochemical processes taking place on mineral particles could reduce large fractions of Fe(III) to Fe(II), which is a more bioavailable form of Fe. Moreover, soluble Fe(III) is also bioavailable. Here, we carried out atmospheric observations and laboratory simulations to show that dust aging processes influenced Fe(II)/Fe(III) redox cycling and enhanced the Fe solubility during long-range transport. Our results show one contrast phenomenon: increasing Fe solubility accompanied by more soluble Fe(III) enrichment in aged dust aerosols. The increasing NOX-to-SO2 ratios and thus the increasing availability of HNO3 enhance soluble Fe(III)-to-Fe(II) ratios. The dissolution experiment of Fe-containing dust demonstrated that high nitrate concentrations suppressed soluble Fe(II) formation at low pH. This enrichment is likely due to a surface-mediated redox mechanism involving nitric acid and Fe(II) when dust plumes are mixed with urban air pollutants. This mechanism is potentially the major mechanism for enhancing Fe solubility in aged dust aerosols and should be included by modeling to better understand the effect of Fe(II)/Fe(III) redox cycling on ocean biological productivity and atmospheric oxidation capacity.