Black carbon (BC) is an atmospheric pollutant that adversely affects air quality, global climate, and human health. As an important BC source region, China has achieved substantial emission reductions over the past decade through stringent clean air policies, offering a unique opportunity to study changes of BC sources and properties under rapid emission changes. Concurrently, BC research in China has progressed rapidly, shifting from studying emission sources toward atmospheric processes and health impacts. This review focuses on five key topics in BC research, including ambient concentrations, emission sources, atmospheric aging, mixing state, and health effects. Ground observation networks and gridded datasets have shown a significant decrease in BC concentrations due to clean air policies, particularly in Northern and Eastern China. Emission inventories and source apportionment studies consistently identified fossil fuel combustion as the dominant BC source in China. Laboratory, field, and modeling studies have advanced understanding of BC aging and mixing state. The health evidence from China has linked BC exposure to respiratory, cardiovascular, and neurological diseases. The rapid expansion and heterogeneity of datasets underscore the urgent need for measurement standardization and cross-regional dataset comparison. In addition, this review calls for stronger integration of measurement and modeling to better study BC sources, aging, and mixing states, and highlights the need for assessing source-specific health impacts and understanding how atmospheric aging modifies BC toxicity.

Haze episodes pose substantial health risks to human-beings, yet the connections between the sources and chemical composition of fine particulate matter (PM2.5) and health effects remain inadequately understood. This study employed the high time-resolution (1-h) offline sampling and investigated the chemical characteristics and oxidative potential (OP) of the methanol-soluble organic matter (MSOM) in PM2.5 during three haze events in the North China Plain in 2020. The average volume-normalized and mass-normalized OP (OPv and OPm) during the three episodes (EP1-EP3) were 4.1 ± 1.6, 3.4 ± 1.2, 5.5 ± 1.9 pmol/min/m3, and 20.3 ± 4.9, 27.9 ± 6.7, 22.4 ± 5.3 pmol/min/μg, respectively. Positive matrix factorization model analysis revealed that the contributions of primary combustion (vehicle emission, biomass burning and coal combustion) accounted for ∼60% of total OPm, and the first- and secondary-generation aqueous-phase secondary organic aerosol formation processes (aqSOA I and aqSOA Ⅱ) contributed ∼36% of total OPm. The average OPm in nighttime showed higher values than that in daytime, with the nighttime OPm being predominantly influenced by primary emissions, whereas daytime SOA processes making a major contribution to OPm. Non-targeted screening based on Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis suggested that nitrogen-containing organic compounds were the dominant contributors to OPm (61%), especially those nitro-/oxygenated-condensed aromatics (Nitro-/O-ConA) and high-oxygen highly unsaturated compounds (HO-HUPC). By integrating the source information with molecular fingerprinting, we find that nitro- ConA were key toxic components in primary emissions, whereas secondary sources were enriched with HO-HUPC. Overall, our results improved the molecular-level understanding of the sources and evolution of key toxic components during haze events.

Ship-emitted soot exerts substantial climate forcing, yet its effects remain uncertain because models often oversimplify particle mixing state and structure. Key microphysical properties of ship-emitted soot under real-world operating conditions remain poorly constrained. Here we deployed an unmanned aerial vehicle to intercept ship exhaust plumes and applied electron microscopy to characterize the mixing state, size, and fractal dimension (Df) of 5714 individual soot particles. Fresh ship-emitted soot was dominated by partly-coated soot (62.4%), followed by bare-like (29.3%) and embedded soot (8.3%). Vanadium and nickel were detected mainly in the coatings of internally mixed soot. Partly-coated soot showed the largest modal diameter (443 nm) and a lower compactness (Df = 1.85), whereas embedded soot was the smallest (278 nm) and most compact (Df = 2.34). This overall size-morphology pattern remained broadly similar across operational modes. Higher engine loads were associated with larger and less compact soot aggregates, and lower-sulfur fuels appeared to suppress particle growth. These results provide the first in situ constraints for improving representation of ship-emitted soot in climate models and support targeted emission controls to mitigate climate effects.

Dissolved black carbon (DBC) is recognized as the most abundant molecularly identified refractory dissolved organic carbon pool in the ocean. However, its dynamics within major river-estuary systems remain poorly constrained, hindering a more robust assessment of negative carbon cycle-climate feedback. Through multiseason sampling in the Changjiang River Estuary (CRE), we elucidated the spatiotemporal patterns and drivers of DBC and estimated its annual export under contrasting hydrological regimes. We found that, across all sampling seasons and layers, water mixing was strongly associated with the spatiotemporal variations of DBC, as indicated by the significant positive correlations between DBC concentrations and salinity. Annual DBC export from Changjiang showed an approximately twofold variation, ranging from 28.02 +/- 3.62 Gg-C in a dry year (2023) to 65.51 +/- 12.94 Gg-C in a wet year (2020). Summer with abundant freshwater discharges consistently contributed the largest share (>43%) despite considerable interannual variability. These findings highlighted hydrological controls upon DBC dynamics in major river-estuary systems. Nevertheless, large uncertainties persist, calling for higher resolution sampling and molecular characterization of multiple DBC pools in landocean interfaces under a changing climate.

Residential solid fuel combustion (RSFC) emits particulate polycyclic aromatic compounds (PACs), but their distribution across the full particle size spectrum and their age-specific deposition are still not well quantified. Here, we combusted six Chinese coals and six biomass fuels at 500 °C (LIT) and 800 °C (HIT). We measured PM and particle-phase PACs (16 parent PAHs and 9 oxygenated PAHs) in 14 size bins ranging from 0.016 to 10 μm. Higher ignition temperature shifted PAC composition toward more toxic species, with biomass showing a stronger shift than coal. Submicron particles (0.10-0.60 μm) carried most of the PAC burden and toxicity, accounting for >60% of total PACs and dominating the equivalent toxicity. Ultrafine particles (UFPs, <0.10 μm) contributed only ∼3% of PM mass but carried up to ∼20% of total PACs. Their mass-specific toxicity (equivalent toxicity per unit PM mass) was 2-10 times higher than that of submicron particles. Respiratory deposition modeling showed clear age dependence: under the same exposure scenario, children had ∼40% higher total respiratory deposition of particulate PACs than adults. About 70% of UFP-bound PACs deposited in the pulmonary region, with their contribution to pulmonary deposition being higher in children than in adults.

Abstract Black carbon (BC) is a refractory, light‐absorbing carbonaceous aerosol, yet how structural heterogeneity among combustion sources drives variability in light absorption remains poorly constrained. Here, we investigate the relationship between aromatic structure and light absorption of freshly emitted BC from major combustion sources by combining benzene polycarboxylic acid analysis with filter‐based optical attenuation measurements. We observe substantial source‐dependent differences in aromatic condensation, with estimated aromatic cluster sizes increasing from residential coal combustion to biomass burning, on‐road diesel vehicles, and non‐road engines. These differences are associated with combustion‐related conditions, including modified combustion efficiency and engine operating state. Aromatic condensation was positively associated with , and the association persisted after adjustment for source category, suggesting that differences in aromatic structure may partially explain source‐dependent variability in freshly emitted BC light absorption.These results support a chemical continuum description of BC and highlight the need to account for source‐related structural heterogeneity when interpreting BC optical properties and radiative effects.

Biomass burning (BB) is a major global source of atmospheric pollutants. Understanding the size distributions and compositional transformations of toxic organic components in BB smoke during atmospheric aging is critical for assessing the associated health risks. Here, emissions from six biomass fuels combusted at 500 and 800°C were aged in an oxidation flow reactor coupled to a tube furnace and characterized by high-resolution size-segregated sampling. We quantified organic carbon (OC) and 25 PACs, including 16 parent polycyclic aromatic hydrocarbons (pPAHs) and 9 oxygenated PAHs (oPAHs). Aging substantially degraded pPAHs, decreasing totals from 170 to 120 mg kg⁻¹ fuel (-30 %) and ultrafine-range pPAHs (Dp < 0.1 μm) from 16.6 to 12.1 mg kg⁻¹ fuel (-27 %), driven mainly by preferential losses of 2-4 ring species while 5-6 ring pPAHs remained comparatively stable. oPAHs showed concurrent loss and formation, reshaping their size distribution: 79 % of fresh oPAHs resided in the submicron particles (0.1-0.5 μm), but the submicron particles contribution declined by ∼30 % after aging, whereas ultrafine-range oPAHs increased from 3.3 ± 1.08-16.1 ± 4.1 mg kg⁻¹ fuel (∼5-fold), with anthraquinone and benzanthrone increasing most (5.65-fold). QSAR-based evaluation indicates that total PAC-associated carcinogenic potency decreased by 21 %, but increased by 38 % in the ultrafine range due to enhanced oPAH contributions (∼5-fold). Overall, these findings suggest that assessments based on fresh-emission metrics may underestimate the toxicity-relevant chemical burden in the UFPs after aging, highlighting the need for further characterization of oxygenated PACs and related oxygenated organic constituents in UFPs. SYNOPSIS: The toxic effects of atmospheric aging on biomass burning organic aerosols (BBOA) are not fully understood, and this study reveals that atmospheric aging could enhance the toxicity of ultrafine particles in BBOA.

Residential coal combustion is an important heating source in rural China and a major source of particulate matter (PM) and elemental carbon (EC) during winter haze episodes. However, how combustion temperature governs the physicochemical properties of individual particles from coal combustion remains poorly understood. This study investigated emissions from a typical bituminous coal combusted at 400, 600, and 800 degrees C. Results showed that temperature dramatically altered pollutant formation: the emission factor of organic carbon (OC) decreased from 20.99 g/kg to 2.38 g/kg with rising temperature, whereas that of EC increased from 0.76 g/kg to 3.85 g/kg. Single-particle analysis further revealed that both the abundance of EC particles (which increased from 15% to 89%) and the size of EC aggregates (which increased nearly threefold) increased significantly with rising temperature, confirming that higher temperatures directly promote the growth and aggregation of EC particles. Notably, metal particles exhibited distinct volatilization and transformation behaviors. For instance, Zn exists in the form of mineral particles at low temperatures, droplet-like Zn-rich particles at medium temperatures, and nanosized crystal at high temperatures. This research underscores combustion temperature as a fundamental driver controlling the physicochemical properties of coal combustion particles. It suggests that stove upgrades focusing solely on increasing combustion temperature, without complementary fuel or emission control measures, may lead to unintended adverse consequences for climate and public health.

The physicochemical properties and atmospheric aging behavior of black carbon (BC) are critical for assessing its climatic impact, yet how these vary across emission sources remains poorly understood. Here, the relationship between the microphysical properties and aging processes of BC subgroups (Char and Soot) from major emission sources, including biomass burning (BB), diesel vehicle exhaust (DV), and industrial coal combustion (ICC) were investigated at single particle level. Our results revealed that BB emissions contained 84 ± 5% Char, significantly higher than DV/ICC sources (17-30%). The monomer diameter (dm) and graphitic interplanar spacing of BB-derived BC were twice of those DV- and ICC-derived BC, and the aggregate diameter (da) and O/C ratio were approximately 10-fold higher, along with a weaker degree of necking. Based on the high-time-resolution sampling analysis of BB processes, we found that lower combustion efficiency favored Char formation, resulting in the increasing of dm, da, and O/C ratio of BC particle. Moreover, under equivalent aging, Soot-dominated DV-BC aggregates grew 50% in da versus only 2% for Char-dominated BB-BC. This work demonstrates that the proportion of Char and Soot determine BC's physicochemical properties and aging behavior in different sources, emphasizing the need for subgroup-specific parametrizations in climate models.

Black carbon is a short-lived climate forcer that occurs as a continuum of particulate matter with varying physical, chemical and optical properties. However, current global climate assessments treat black carbon as a single compound, overlooking the distinct properties of its subtypes and introducing substantial uncertainty in determining its climate impact. Here we evaluate the climate relevance of this overlooked heterogeneity using approximately 2,500 thermal–optical measurements of carbon fractions across emission sources to develop a global inventory distinguishing between less light-absorbing char and more light-absorbing soot from 1750 to 2019. We observed an increase in the soot fraction of total anthropogenic black carbon emissions, from 16% in 1750 to 35% in 2019, primarily driven by increased fossil fuel consumption. This shift, aligning with sediment records, suggests that contemporary black carbon emissions possess greater global warming potential per unit mass than those at the onset of the industrial era. Our findings underscore the need to resolve black carbon subtypes in climate models and prioritize soot-rich sources for mitigation. The soot fraction of global black carbon emissions increased from 16% in 1750 to 35% in 2019, mainly driven by fossil fuel consumption, suggesting a higher warming potential per unit mass, according to an analysis of atmospheric measurements.

Biomass burning is a substantial source of pyrogenic dissolved organic matter (PyDOM), yet the molecular-level differences between PyDOM derived from charcoal and soot remain poorly constrained. This study systematically compared the molecular characteristics of PyDOM from charcoal and soot coproduced by the combustion of rice straw under different temperatures and oxygen levels via ultrahigh-resolution mass spectrometry. The molecular composition of charcoal PyDOM showed significant temperature-dependent variations, whereas soot PyDOM exhibited negligible alterations with different temperatures. Moreover, common molecules shared by both PyDOM types were consistently dominated by lignin-like features, indicating a fuel-inherited emission profile that dominated overall composition. By contrast, unique molecules for each PyDOM type retained signatures related to their formation pathways and combustion conditions. PyDOM derived from charcoal showed a strong response to combustion temperature, with the enrichment of more condensed formulas under harsher conditions. PyDOM derived from soot remained relatively stable, featuring highly oxygenated CHO and CHON compounds and a strong presence of lignin- and carbohydrate-like groups. Furthermore, CHOS compounds were consistently more abundant in charcoal than in soot, suggesting charcoal preferentially retains sulfur. This study provides the first molecular-level features for distinguishing PyDOM in coproduced charcoal and soot, offering insights for assessing its environmental effect and behavior.

Against China's backdrop of substantial on-road vehicle emission reductions, nonroad sources-particularly agricultural machinery (AM)-have become significant contributors to elemental carbon (EC). The impact of rapidly updated fuels and emission standards on AM's particle size-resolved EC and health effects remains unclear. This study measured EC size distributions from five AM units, further evaluating fuel types (petrodiesel B0 vs biodiesel B5/B20) and emission standards (Stage II vs Stage III) on emission characteristics and size distributions. The results show that (1) AM's mean EC emission factor (EF) was 367.3 +/- 476.5 mg/kg-exceeding typical on-road mobile sources-with char-EC and soot-EC comprising 7.3% and 92.7% of EFEC respectively. (2) Fuel type and emission standards exerted significant influence on EC emissions, particularly within the ultrafine particle fraction. Newer standards increased ultrafine EC emissions by 3.6-fold and using B20 elevated total EC by 24.3% versus using B0. (3) By incorporating deposition and clearance efficiency across different particle sizes, modeled respiratory deposition of EC yielded 237.9 mg/kg (children) and 163.9 mg/kg (adults). The pulmonary region constituted the primary deposition target site, then head airways, with the tracheobronchial receiving the least. This work provides essential data for evaluating AM emissions under new frameworks.

Residential solid fuels are widely used for cooking and heating, but the atmospheric evolution of their particulate emissions remains insufficiently characterized. To address this gap, we constructed an integrated quartz-tube furnace-dilution-oxidation flow reactor (OFR) system for direct comparison of fresh and OFR-aged emissions across fuel types and combustion temperatures. Six biomass fuels and six coals were burned at 500 degrees C and 800 degrees C. Organic carbon (OC) subfractions and polycyclic aromatic compounds (PACs), including 16 parent polycyclic aromatic hydrocarbons (pPAHs) and 9 oxygenated polycyclic aromatic hydrocarbons (oPAHs), were quantified. In fresh emissions, increasing temperature reduced OC emission factors for both fuel types, whereas PAC emission factors increased for biomass but decreased for coal. OFR aging generally increased particulate OC and shifted OC toward less volatile or more thermally stable fractions. For coal burned at 500 degrees C, pPAHs decreased by 64%, whereas oPAHs increased by 127%. Although the overall quantitative structure-activity relationship (QSAR)-derived carcinogenicity indicator of PACs decreased by 46%, the oPAH contribution increased from 7% to 18%. These findings show that metrics based only on fresh emissions cannot fully capture the chemical evolution and toxicity-related implications of residential solid fuel emissions.

The use of biodiesel as an alternative to diesel remains controversial because of its potential impact on organic matter emissions. Herein, intermediate-volatility organic compounds (IVOCs) from five agricultural machines (AMs) using three types of fuels (pure diesel (B0), diesel mixed with 5 and 20% biodiesel (B5 and B20), respectively) were collected and analyzed. The following results were obtained: (1) Reasonable biodiesel ratios reduced IVOC emissions. The average emission factors of IVOCs (EFIVOCs) of B5-fueled AMs were 485.8 ± 272.9 mg/kg fuel, 24.2% reduction from that of B0-fueled AMs. (2) The chemical compositions and secondary organic aerosol formation potentials (SOAFPs) of IVOCs changed during AMs fueled by different biodiesel blend ratios. The highest EFIVOCs values for B5- and B20-fueled AMs were within the Bin12 interval. Consequently, the SOAFPs of n-alkanes for B5-fueled AMs were lower than those for B0. (3) The oxygen contents of B5 and B20 increased their combustion efficiency, and long-chain carbons in biodiesel were pyrolyzed and fragmented. However, high-viscosity biodiesel inhibited engine performance because more volatile organic matter was condensed and adsorbed on unburned fuel. In the future, some technologies should be developed to reduce the viscosity of biodiesel.

Elemental carbon (EC), an important pollutant component in the atmosphere, is composed of two subcategories: Char-EC and Soot-EC. Their differences in chemical structure and light absorption capacity need further investigation. This study focused on an hourly time-resolved haze event in Wangdu, Hebei Province, eliminating potential interference from organic carbon, to compare the differences in aromatic condensation degree and mass absorption cross-section (MAC) between Soot-EC and Char-EC. The results indicate that, in terms of chemical structure, Soot-EC is a EC component with a higher aromatic condensation degree than Char-EC. During the haze event, the average number of carboxyl groups (NCOOH) and the ratio of B6CA/B6CA (B6/B5) in Soot-EC were higher than those in Char-EC (NCOOHSoot-EC 5.88 ± 0.17 > NCOOHChar-EC 5.42 ± 0.20; (B6/B5)Soot-EC 10.57 ± 4.27>(B6/B5)Char-EC 4.71 ± 2.59). In terms of light absorption capacity, the average MAC of Char-EC (9.52 ± 3.17 m2/g) was 1.64 times higher than that of Soot-EC (5.82 ± 2.88 m2/g) during this haze event. However, aromatic condensation degree could only explain a small portion of the difference in MAC between Soot-EC and Char-EC. Source apportionment results indicated that EC emissions during this haze event were mainly attributed to significant contributions from biomass burning (BB). The higher light absorption capacity of Char-EC may be due to the higher oxygen-containing group content in Char-EC emitted from BB.

Haze events pose substantial health risks, yet the link between the chemical composition of particulate matter (PM) and the exacerbated health impacts during such episodes remains unclear. This study conducted hourly off-line measurements of the chemical composition and oxidative potential (OP) of water-soluble fractions (WSF) of PM2.5 during three haze episodes in the North China Plain (NCP). Results revealed that water-soluble inorganic ions were the primary contributors to the increase in WSF mass (60.8 %), while water-soluble organic carbon (WSOC) was the key driver of OP enhancement, accounting for 78.7 % of OP per unit WSF mass (OPm). Molecular characterization via excitation-emission matrix spectroscopy (EEM) and high-resolution mass spectrometry (Orbitrap) identified highly oxygenated humic-like substances (HO-HULIS) as the major contributors to OPm (43 %). Notably, secondary organic aerosol (SOA)-related HO-HULIS, including highly oxygenated and unsaturated compounds, oxygenated/nitro polycyclic aromatic hydrocarbons (o/n-ConA), and oxygenated/nitro polyphenols (o/n-Poly), were identified as key toxic components. Source apportionment (PMF) analysis indicated that secondary organic aerosols (SOA), particularly those formed through aqueous-phase reaction, contributed 64.8 % of OPm, underscoring the critical role of aqueous-phase SOA in health risk enhancement during haze events.

Emissions of shipping have great influences on atmospheric environment and global climate with the growth of maritime trade. Previous studies identified that shipping black carbon (BC) constitutes the main aerosol component that responsible for light absorption, while shipping organic carbon (OC) was generally considered non-absorbing. Recent studies have indicated that organic components derived from shipping emissions exhibit light absorption at short wavelengths (brown carbon, BrC). However, there is a lack of quantification regarding the absorption effects of shipping BrC. This study investigates the radiative absorption effect (RAE) of shipping BrC, updating models with measured shipping BrC light absorption ability. Surface concentrations of shipping BrC contribute ~ 40% to fossil fuel OC. The global annual average RAE of shipping BrC is +0.15 to +0.36 mW m⁻ 2 , peaking in boreal summer. The warming effect of shipping BrC is 8%–19% relative to shipping BC. With the low-sulfur standard, the RAE of shipping BrC increases to +0.52 mW m⁻ 2 , which is close to that of shipping BC (+0.52 mW m⁻ 2 ) and could offset ~ 40% of direct cooling effect of shipping sulfate. For the radiative absorption of shipping aerosols, BrC is an important part, whose contribution is greater with the upgrade of ship fuels. Graphical Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental endocrine disruptors (EDCs) that enter the human body through respiratory, digestive, and dermal exposure. Prolonged exposure has been associated with adverse health outcomes, including carcinogenicity, mutagenicity, and reproductive toxicity. However, whether genetic variation in apoptosis-related pathways modifies the reproductive effects of PAH exposure remains unclear. To investigate gene-environment interactions between urinary PAH metabolites and polymorphisms in apoptosis-related genes in relation to sperm apoptosis, we conducted a cross-sectional study involving 176 male participants from an infertility clinic in Wuhan, China, who completed structured questionnaires and provided biological samples. Ten OH-PAH metabolites in repeated urine samples were measured, along with genotyping of single-nucleotide polymorphisms (SNPs) at apoptosis-related genes (Fas, FasL, and caspase-3) in whole blood DNA, and sperm apoptosis. Multivariable linear regression evaluated the interaction between urinary OH-PAH levels and apoptotic gene SNPs on apoptotic sperm, with genotype-stratified analyses. PAH exposure appeared to interact with SNPs in FasL rs763110, Fas rs2234767, and caspase-3 rs12108497 to jointly influence sperm cell apoptosis. Specifically, for the FasL rs763110, higher 9-OHFlu was associated with fewer viable sperm and more apoptotic sperm, and this association was more pronounced among CC genotype homozygotes. For the caspase-3 rs12108497, higher 2-OHFlu was associated with more dead sperm, and this association was significant among TC and TC/CC genotypes. These findings suggest that genetic variation in apoptosis-related genes may modify susceptibility to PAH-induced sperm apoptosis, highlighting the importance of gene-environment interactions in male reproductive toxicity.

delta 15N-NO3- is widely used to trace the NOx/NO3- emission sources without unique source tracers. However, there is still controversy regarding the 15N fractionation effects during NO3- formation, leading to uncertain source apportionment. To address this, this study introduces dual oxygen isotopes (triangle 17O and delta 18O) to constrain the 15N fractionation (triangle 15N-triangle 17O/triangle 15N-delta 18O) of NO3- formation and compare the impact of delta 15N-NOx (triangle 17O) and delta 15N-NOx (delta 18O) on NOx/NO3- source apportionment. Results found significant differences in triangle 15N-triangle 17O (-3.7 similar to +16.1 parts per thousand) and triangle 15N-delta 18O (+8.5 similar to +16.2 parts per thousand) in haze, reflecting the triangle 15N from three pathways (NO2 + OH, NO3 + HC, N2O5 hydrolysis) and two pathways (NO2 + OH and N2O5 hydrolysis), respectively. The 15N fractionation value differences obtained by dual oxygen isotopes increases with the increase of NO3 + HC contribution (0.02-0.65). Additionally, different results of NOx/NO3- sources apportionment were obtained by delta 15N-NOx(triangle $\mathit{{\increment}}$17O) and delta 15N-NOx(delta 18O) in NO3 + HC-induced haze. For example, delta 15N-NOx(triangle $\mathit{{\increment}}$17O) identified coal combustion (46 +/- 8%) and biomass burning (32 +/- 3%) as major NOx/NO3- sources in Zibo haze. Conversely, delta 15N-NOx(delta 18O) revealed mobile sources (55 +/- 8%) and biomass burning (22 +/- 5%) as main contributors. Evidence from diurnal variation of sources and characteristics of source tracers show that delta 15N-NOx(triangle $\mathit{{\increment}}$17O) analysis is more sensitive and accurate than delta 15N-NOx(delta 18O). These results highlight the non-negligible role of NO3 + HC in 15N fractionation during NO3- formation and provide insight into improving 15N tracing techniques for NOx/NO3- source identification through the constraint of dual oxygen isotopes.

Polycyclic aromatics are ubiquitous in the interstellar medium and meteorites, yet the search for lunar polycyclic aromatics remains a significant challenge. Here, we analyze Chang’E-5 lunar soil samples, revealing polycyclic aromatic concentrations of 5.0–9.2 µg/g (average: 7.4 ± 1.4 µg/g). Their aromatic structures are highly condensed, comparable to ~4 nm graphene sheets, and distinct from terrestrial analogs, such as wood char, soot and kerogen. While meteorite impacts are the most likely sources, the stable carbon isotope composition of polycyclic aromatics in Chang’E-5 lunar soil (δ 13 C: −5.0 ± 0.6‰ to +3.6 ± 1.3‰) is more enriched in 13 C compared to that in meteorites. This enrichment suggests a de novo formation mechanism during meteorite impacts, involving the conversion of non-aromatic organic matter—which is more enriched in δ 13 C—into polycyclic aromatics. This process may play a significant role in carbon accretion in lunar regolith, as the resulting polycyclic aromatics are more stable and resistant to degradation compared to smaller organic molecules (e.g., amino acids), which are largely destroyed during impact events.