Digital synthesis of free-form multimaterial structures for realization of arbitrary programmed mechanical responses.

SignificanceCreating structures to realize function-oriented mechanical responses is desired for many applications. Yet, the use of a single material phase and heuristics-based designs may fail to attain specific target behaviors. Here, through a deterministic algorithmic procedure, multiple materials with dissimilar properties are intelligently synthesized into composite structures to achieve arbitrary prescribed responses. Created structures possess unconventional geometry and seamless integration of multiple materials. Despite geometric complexity and varied material phases, these structures are fabricated by multimaterial manufacturing, and tested to demonstrate that wide-ranging nonlinear responses are physically and accurately realized. Upon heteroassembly, resulting structures provide architectures that exhibit highly complex yet navigable responses. The proposed strategy can benefit the design of function-oriented nonlinear mechanical devices, such as actuators and energy absorbers.

Exploring the Complexities of Dissolved Organic Matter Photochemistry from the Molecular Level by Using Machine Learning Approaches.

Dissolved organic matter (DOM) sustains a substantial part of the organic matter transported seaward, where photochemical reactions significantly affect its transformation and fate. The irradiation experiments can provide valuable information on the photochemical reactivity (photolabile, photoresistant, and photoproduct) of molecules. However, the inconsistency of the fate of irradiated molecules among different experiments curtailed our understanding of the roles the photochemical reactions have played, which cannot be properly addressed by traditional approaches. Here, we conducted irradiation experiments for samples from two large estuaries in China. Molecules that occurred in irradiation experiments were characterized by the Fourier transform ion cyclotron resonance mass spectrometry and assigned probabilistic labels to define their photochemical reactivity. These molecules with probabilistic labels were used to construct a learning database for establishing a suitable machine learning (ML) model. We further applied our well-trained ML model to "un-matched" (i.e., not detected in our irradiation experiments) molecules from five estuaries worldwide, to predict their photochemical reactivity. Results showed that numerous molecules with strong photolability can be captured solely by the ML model. Moreover, comparing DOM photochemical reactivity in five estuaries revealed that the riverine DOM chemistry largely determines their subsequent photochemical transformation. We offer an expandable and renewable approach based on ML to compatibly integrate existing irradiation experiments and shed insight into DOM transformation and degradation processes.

Atmospheric wet and dry depositions of polycyclic aromatic compounds in a megacity of Southwest China.

The dry and wet depositions of polycyclic aromatic hydrocarbons (PAHs) and related derivatives have rarely been characterized separately. Parent, oxygenated and nitrated PAHs (PAHs, OPAHs and NPAHs) have been measured in monthly-averaged wet and dry deposition samples collected from January to December 2019 in urban Chongqing. The annual average concentrations of Æ©17PAHs, Æ©9OPAHs and Æ©9NPAHs in wet deposition samples were 457 ± 375, 1311 ± 1416 and 8.25 ± 10.2 ng/L, respectively, with significant monthly variations introduced by rainfall and air-borne particle deposition. Most PAHs species were associated with the particulate phase in wet deposition, while OPAHs and NPAHs were mainly distributed in the dissolved phase, probably due to the lower octanol-water partitioning coefficient of N/OPAHs than that of PAHs. Annual deposition fluxes of PAHs, OPAHs and NPAHs in dry deposition were 25264, 25310 and 388 ng/m2/yr, respectively, higher than those in wet deposition (9869, 24083 and 207 ng/m2/yr). This indicates that PACs, especially PAHs, were removed from the atmosphere mainly via dry deposition. The contributions of wet deposition to total deposited PACs were larger for months with higher precipitation and for PACs with higher molecular weight. Composition pattern and temporal variation results indicated that wet deposition fluxes were mainly affected by precipitation-related particle deposition and chemical properties (e.g., water solubility), while dry deposition fluxes were affected more by factors such as gas/particle partitioning, particle size distribution and physicochemical properties of PACs. Principle component analysis combined with diagnostic ratios revealed that PACs in atmospheric deposition samples were from vehicle emission (48.6%), coal combustion (13.4%), petrogenic source (5.9%) and secondary formation (32.1%).

In-orbit geometric calibration of HaiYang-1C coastal zone imager with multiple fields.

The HaiYang-1C coastal zone imager (CZI) consists of two independent cameras with a total image swath of approximately 1000 km. In order to obtain precise imaging parameters of the CZI cameras, a feasible in-orbit geometric calibration approach with multiple fields is presented. First, the master CCD is calibrated with a calibration field. Then, the slave CCDs are respectively calibrated with different fields. Finally, the calibrated internal shift parameters of the slave CCDs are adjusted with tie points between adjacent sub-images. Seven HaiYang-1C CZI images were tested. The experimental results showed that the imaging parameters calibrated with the presented approach could perform as well as those calibrated with the conventional approach with a single field. However, the total swath of the calibration fields could be reduced from approximately 1000 km to 300 km. The application difficulties in collecting satisfactory calibration sub-images could be thereby significantly reduced in the geometric calibration.

Topological Insulators by Topology Optimization.

An acoustic topological insulator (TI) is synthesized using topology optimization, a free material inverse design method. The TI appears spontaneously from the optimization process without imposing explicit requirements on the existence of pseudospin-1/2 states at the TI interface edge, or the Chern number of the topological phases. The resulting TI is passive, consisting of acoustically hard members placed in an air background and has an operational bandwidth of ≈12.5% showing high transmission. Further analysis demonstrates confinement of more than 99% of the total field intensity in the TI within at most six lattice constants from the TI interface. The proposed design hereby outperforms a reference from recent literature regarding energy transmission, field confinement, and operational bandwidth.

Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities.

We present numerical studies of two photonic crystal membrane microcavities, a short line-defect cavity with a relatively low quality (Q) factor and a longer cavity with a high Q. We use five state-of-the-art numerical simulation techniques to compute the cavity Q factor and the resonance wavelength λ for the fundamental cavity mode in both structures. For each method, the relevant computational parameters are systematically varied to estimate the computational uncertainty. We show that some methods are more suitable than others for treating these challenging geometries.

[Systematic review of effectiveness and safety of pudilan Xiaoyan oral liquid in treating pediatric suppurative tonsilitis].

The review aims to assess the effectiveness and safety Pudilan Xiaoyan oral liquid in treating pediatric suppurative tonsillitis systematically through searching relevant electronic database and collecting relevant literature. Meta-analysis was performed with the RevMan 5.3 software. Eighteen RCTs of 1 883 patients of pediatric suppurative tonsillitis were included. Meta-analysis showed that： compared with the application of antibiotics alone, combined with Pudilan can effectively improve the treatment of pediatric suppurative tonsillitis in efficacy rate and shorten the time of recovering normal temperature, the time of tonsil purulent discharge and can also reduce the extinction time of sore throat, antiadoncus or congestion subsided and appetite recovery. There was no severe adverse reaction during the treatment. Compared with the application of antibiotics alone, combined with Pudilan may be more effective and safe in the treatment of pediatric suppurative tonsillitis, which can not be strongly proved at present for lack of studies with high quality.

Air-plant interaction and air-soil exchange of polycyclic aromatic hydrocarbons in a large human-influenced reservoir in southwest China.

The Three Gorges Reservoir (TGR) is totally manmade, strongly influenced by anthropogenic activity, and lies on the upper reaches of Yangtze River. The periodic storage and discharge of water from the Three Gorges Dam could have altered the original air-plant/soil interactions of contaminants in TGR. Herein, paired atmospheric gas-particle, air-plant, and air-soil samples were collected to investigate the air-plant interaction and air-soil exchange of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). The air-plant interaction based on McLachlan's framework to our datasets suggests that PAHs were absorbed via gaseous deposition that was restricted by the plant-gas dynamic equilibrium. The equilibrium indicates a dynamic balance between the gaseous phase and plant surface in PAH absorption. The main limiting factor influencing the PAH uptake was the plant species rather than the atmospheric PAH concentration. The air-soil exchange of PAHs exhibited a net volatilization flux of 16.71 ng/m2/d from the soil to the air based on annual average. There was more volatilization and less deposition in summer and more deposition and less volatilization in autumn and winter. The soil serves as a secondary source of atmospheric PAHs. As the first attempt on probing the multi-interface geochemical process of PAHs, this study highlights the influence of manual water level manipulation from the TGD and environmental factors (such as temperature, humidity, and soil properties) on the regional fate of PAHs in the TGR.

Probing the occurrence, sources and cancer risk assessment of polycyclic aromatic hydrocarbons in PM2.5 in a humid metropolitan city in China.

Fifty-two consecutive PM2.5 samples from December 2021 to February 2022 (the whole winter) were collected in the center of Chongqing, a humid metropolitan city in China. These samples were analysed for the 16 USEPA priority polycyclic aromatic hydrocarbons (16 PAHs) to explore their composition and sources, and to assess their cancer risks to humans. The total concentrations of the 16 PAHs (ng m-3) ranged from 16.45 to 174.15, with an average of 59.35 ± 21.45. Positive matrix factorization (PMF) indicated that traffic emissions were the major source (42.4%), followed by coal combustion/industrial emission (31.3%) and petroleum leakage/evaporation (26.3%). The contribution from traffic emission to the 16 PAHs increased from 40.0% in the non-episode days to as high as 46.2% in the air quality episode during the sampling period. The population attributable fraction (PAF) indicates that when the unit relative risk (URR) is 4.49, the number of lung cancer cases per million individuals under PAH exposure is 27 for adults and 38 for seniors, respectively. It was 5 for adults and 7 for seniors, when the URR is 1.3. The average incremental lifetime cancer risk (ILCR) for children, adolescents, adults and seniors was 0.25 × 10-6, 0.23 × 10-6, 0.71 × 10-6, and 1.26 × 10-6, respectively. The results of these two models complemented each other well, and both implied acceptable PAH exposure levels. Individual genetic susceptibility and exposure time were identified as the most sensitive parameters. The selection and use of parameters in risk assessment should be further deepened in subsequent studies to enhance the reliability of the assessment results.

A comprehensive exploration of characteristics and source attribution of carbonaceous aerosols in PM2.5 in an East China megacity.

A total of 84 PM2.5 (fine particulate matter) aerosol samples were collected between October 2020 and August 2021 within an urban site in Hangzhou, an East China megacity. Chemical species, such as organic carbon (OC), elemental carbon (EC), as well as char, soot, and n-alkanes, were analyzed to determine their pollution characteristics and source contributions. The mean yearly concentrations of OC, EC, char, soot, and total n-alkanes (∑n-alkane) were 8.76 ± 3.61 µg/m3, 1.44 ± 0.76 µg/m3, 1.21 ± 0.69 µg/m3, 0.3 ± 0.1 µg/m3, and 24.2 ± 10.6 ng/m3. The OC, EC, and ∑n-alkanes were found in the highest levels during winter and lowest during summer. There were strong correlations between OC and EC in both winter and spring, suggesting similar potential sources for these carbonaceous components in both seasons. There were poor correlations among the target pollutants due to summertime secondary organic carbon formation. Potential source contribution functions analysis showed that local pollution levels in winter and autumn were likely influenced by long-range transportation from the Plain of North China. Source index and positive matrix factorization models provided insights into the complex sources of n-alkanes in Hangzhou. Their major contributors were identified as terrestrial plant releases (32.7%), traffic emissions (28.8%), coal combustion (27.3%), and microbial activity (11.2%). Thus, controlling vehicular emissions and coal burning could be key measures to alleviate n-alkane concentrations in the atmosphere of Hangzhou, as well as other Chinese urban centers.

Self-bridging metamaterials surpassing the theoretical limit of Poisson's ratios.

A hallmark of mechanical metamaterials has been the realization of negative Poisson's ratios, associated with auxeticity. However, natural and engineered Poisson's ratios obey fundamental bounds determined by stability, linearity and thermodynamics. Overcoming these limits may substantially extend the range of Poisson's ratios realizable in mechanical systems, of great interest for medical stents and soft robots. Here, we demonstrate freeform self-bridging metamaterials that synthesize multi-mode microscale levers, realizing Poisson's ratios surpassing the values allowed by thermodynamics in linear materials. Bridging slits between microstructures via self-contacts yields multiple rotation behaviors of microscale levers, which break the symmetry and invariance of the constitutive tensors under different load scenarios, enabling inaccessible deformation patterns. Based on these features, we unveil a bulk mode that breaks static reciprocity, providing an explicit and programmable way to manipulate the non-reciprocal transmission of displacement fields in static mechanics. Besides non-reciprocal Poisson's ratios, we also realize ultra-large and step-like values, which make metamaterials exhibit orthogonally bidirectional displacement amplification, and expansion under both tension and compression, respectively.

Fundamental limitations to gain enhancement in periodic media and waveguides.

A common strategy to compensate for losses in optical nanostructures is to add gain material in the system. By exploiting slow-light effects it is expected that the gain may be enhanced beyond its bulk value. Here we show that this route cannot be followed uncritically: inclusion of gain inevitably modifies the underlying dispersion law, and thereby may degrade the slow-light properties underlying the device operation and the anticipated gain enhancement itself. This degradation is generic; we demonstrate it for three different systems of current interest (coupled-resonator optical waveguides, Bragg stacks, and photonic crystal waveguides). Nevertheless, a small amount of added gain may be beneficial.

Systematic design of loss-engineered slow-light waveguides.

This paper employs topology optimization to systematically design free-topology loss-engineered slow-light waveguides with enlarged group index bandwidth product (GBP). The propagation losses of guided modes are evaluated by the imaginary part of eigenvalues in complex band structure calculations, where the scattering losses due to manufacturing imperfections are represented by an edge-related effective dissipation. The loss engineering of slow-light waveguides is realized by minimizing the propagation losses of design modes. Numerical examples illustrate that the propagation losses of free-topology dispersion-engineered waveguides can be significantly suppressed by loss engineering. Comparisons between fixed- and free-topology loss-engineered waveguides demonstrate that the GBP can be enhanced significantly by the free-topology loss-engineered waveguides with a small increase of the propagation losses.

Temporal-spatial variations, source apportionment, and ecological risk of trace elements in sediments of water-level-fluctuation zone in the Three Gorges Reservoir, China.

The Three Gorges Reservoir (TGR) plays a crucial role in providing electricity for mega-cities across China. However, since the impoundment was completed in 2006, attention to environmental concerns has also been intensive. In order to determine the distribution, sources, and pollution status of trace elements in the water fluctuation zone of the TGR following ten years of repeated "submergence" and "exposure", we systematically collected 16 paired surface sediment samples (n = 32) covering the entire main body of the TGR in March 2018 (following 6 months of submergence) and September 2018 (after 6 months of exposure), and quantitatively analyzed 13 elements (e.g., Mn, Fe, V, Cr, Ni, Cu, Zn, As, Sr, Y, Zr, Ba, and Pb) using X-ray fluorescence spectrophotometry (XRF). The results showed that, except for Sr, concentrations of trace metals following submergence were generally higher than those after exposure due to the less settling of suspended solids at the faster flow velocity during the drawdown period. Assessment using enrichment factors (EFs) and a geo-accumulation index (Igeo) both characterized a relatively serious anthropogenic pollution status of metals in the upper reaches of the TGR with respect to the middle-lower reaches. Source apportionment by positive matrix factorization (PMF) analysis indicated that agricultural activities (24.8 and 24.3%, respectively) and industrial emissions (24.5 and 22.9%, respectively) were the two major sources in these two periods, followed by natural sources, domestic sewage, and ore mining. Ecological risk assessment showed that metalloid arsenic (As) could be the main potential issue of risk to aquatic organisms and human health. A new source-specific risk assessment method (pRI) combined with PMF revealed that agricultural activities could be the major source of potential ecological risk and should be prioritized as the focus of metal/metalloid risk management in the TGR.

The downward referral experiences of stroke caregivers in the regional medical alliance in China: A phenomenological study.

The downward referral platform in the regional medical alliance has provided more possibilities to follow-up rehabilitation and transitional care for increasing stroke survivors, which also has the most contributions in the rational use of resources and health promotion of stroke survivors. However the downward referral rate is low compared to upward referral. At present, no scholars have explored the downward referral experiences of medical demanders from the perspective of qualitative study, and these experiences may also most truly reflect the influencing factors of their unwillingness to downward referral. Therefore, this study explored the subjective experiences of stroke caregivers who had experienced the downward referral, because stroke attacks often lead to lack of autonomy of patients themselves, making it difficult to complete interviews with them. A descriptive phenomenological study was adopted. A purposive sampling strategy was used to recruit 13 stroke caregivers. Interviews were guided by a semi-structured interview-guide encouraging interviewees to reflect on their experiences with downward referral. Coliazzi's data analysis process was applied. The analysis of the data revealed 4 themes: coping challenges; disrupted information; gaps in medical and nursing transition, and potential enabling factors. The results of this study showed that the lack of knowledge of medical alliance, non-sharing of medical information and non-homogeneousness of medical quality were identified to be impeding positive attitude towards downward referral and be factors of bad experiences. Of course, the interviewees had positive experiences such as smooth referral and comfortable environment. These may be potential enabling factors to their attitude towards downward referral. The challenges and needs of medical demanders after downward referral are worthy of attention, and these should be solved by corresponding measures to improve the downward referral rate and referral experiences.

Per- and poly-fluoroalkyl substances in sediments from the water-level-fluctuation zone of the Three Gorges Reservoir, China: Contamination characteristics, source apportionment, and mass inventory and loadings.

Sixteen paired surface sediment samples (0-5 cm, n = 32) covering upstream to downstream of water-level-fluctuation zone of Three Gorges Reservoir, China were collected in March 2018 (following six months of submergence) and September 2018 (after six months of exposure). Seventeen per- and poly-fluoroalkyl substances (PFASs) were quantified to evaluate contamination characteristics, apportion source categories and estimate mass inventory and loadings. The concentration of ΣPFASs ranged from 0.26 to 0.82 ng·g-1 at high water-level (HWL) and 0.46-1.53 ng·g-1 at low water-level (LWL). Perfluorooctanoic acid (PFOA, mean: 0.32 ng·g-1) and perfluorooctane sulfonate (PFOS, mean: 0.12 ng·g-1) dominated, accounting 44.9% and 16.3% of the total PFASs, respectively. The distribution of PFASs was more influenced by anthropogenic activities than physicochemical parameters of the sediments. Positive matrix factorization (PMF) identified PFOA-based products was the major sources (40.1% and 38.6%, respectively). Besides, the direct sources of PFOA-, PFOS-, PFNA-and PFBA-based products played the predominant role, while the indirect degradation of precursors contributed relatively little. The sediment (0-5 cm) mass inventory of PFASs at LWL (57.5 kg) was higher than HWL (39.3 kg). The annual mass loadings of the total PFASs, PFOA, PFOS, perfluoroundecanoic acid (PFUdA) and perfluorononanoic acid (PFNA) from the upstream to the middle-lower reaches of Yangtze River were 27.4 kg, 11.1 kg, 4.63 kg, 2.89 kg and 2.57 kg, respectively. This study could provide the basic datasets of PFASs in surface sediments of the TGR, and also indicate an important transport of PFASs from upstream to the lower reaches, which should be further studied as well.

Nitrate-assisted biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the water-level-fluctuation zone of the three Gorges Reservoir, China: Insights from in situ microbial interaction analyses and a microcosmic experiment.

An increase in polycyclic aromatic hydrocarbon (PAH) pollution poses significant challenges to human and ecosystem health in the Three Gorges Reservoir (TGR) of the Yangtze River. Based on the combination of PAH analysis with qPCR and high-throughput sequencing of bacteria, 32 topsoil samples collected from 16 sites along the TGR were used to investigate the distribution and biodegradation pathways of PAHs in the water-level-fluctuation zone (WLFZ). The results indicated that the concentrations of PAHs were 43.8-228.2 and 30.8-206.3 ng/g soil (dry weight) under the high- and low-water-level (HWL and LWL) conditions, respectively. The PAH concentration in urban areas was higher than that in rural areas. Under both the HWL and LWL conditions, the abundance of the bamA gene, a biomarker of anaerobic PAH biodegradation, was significantly higher than that of the ring-hydroxylating-dioxygenase (RHD) gene, a biomarker of aerobic PAH biodegradation. The abundance of the bamA gene was significantly positively correlated with PAHs (R2 = 0.8), and the biodegradation percentage of PAHs incubated anaerobically was greater than that in the aerobically incubated microcosm experiments. These data implicated a key role of the anaerobic pathway in PAH biodegradation. Co-occurrence network analysis suggested that anaerobic Anaerolineaceae, Dechloromonas, Bacteroidetes_vadin HA17 and Geobacter were key participants in the biodegradation of PAHs. The diversity analysis of functional bacteria based on the bamA gene and microcosm experiments further demonstrated that nitrate was the primary electron acceptor for PAH biodegradation. These findings provide a new perspective on the mechanism of PAH biodegradation in the TGR and knowledge that can be used to develop strategies for environmental management.

Ultra-coherent nanomechanical resonators based on inverse design.

Engineered micro- and nanomechanical resonators with ultra-low dissipation constitute a promising platform for various quantum technologies and foundational research. Traditionally, the improvement of the resonator's performance through nanomechanical structural engineering has been driven by human intuition and insight. Such an approach is inefficient and leaves aside a plethora of unexplored mechanical designs that potentially achieve better performance. Here, we use a computer-aided inverse design approach known as topology optimization to structurally design mechanical resonators with optimized performance of the fundamental mechanical mode. Using the outcomes of this approach, we fabricate and characterize ultra-coherent nanomechanical resonators with, to the best of our knowledge, record-high Q ⋅ f products for their fundamental mode (where Q is the quality factor and f is the frequency). The proposed approach - which can also be used to improve phononic crystals and coupled-mode resonators - opens up a new paradigm for designing ultra-coherent micro- and nanomechanical resonators, enabling e.g. novel experiments in fundamental physics and extreme sensing.

Carbonaceous aerosols in urban Chongqing, China: Seasonal variation, source apportionment, and long-range transport.

Seventy-seven PM2.5 samples were collected at an urban site (Chongqing University Campus A) in October 2015 (autumn), December 2015 (winter), March 2016 (spring), and August 2016 (summer). These samples were analysed for organic carbon (OC), elemental carbon (EC), and their associated char, soot, 16 PAHs, and 28 n-alkanes to trace sources, and atmospheric transport pathways. The annual average of OC, EC, char, soot, ΣPAHs, and Σn-alkanes were 20.75 µg/m3, 6.18 µg/m3, 5.43 µg/m3, 0.75 µg/m3, 38.29 ng/m3, and 328.69 ng/m3, respectively. OC, ΣPAHs, and Σn-alkane concentrations were highest in winter and lowest in summer. EC, char, and soot concentrations were highest in autumn and lowest in winter. Source apportionment via positive matrix factorization (PMF) indicated that coal/biomass combustion-natural gas emissions (23.8%) and motor vehicle exhaust (20.2%) were the two major sources, followed by diesel and petroleum residue (21.1%), natural biogenic sources (17.7%), and evaporative/petrogenic sources (17.2%). The highest source contributor in autumn and winter was evaporative/petrogenic sources (30.6%) and natural biogenic sources (34.5%), respectively, whereas diesel engine emission contributed the most in spring and summer (32.1% and 38.0%, respectively). Potential source contribution function (PSCF) analysis identified southeastern Sichuan and northwestern Chongqing as the major potential sources of these pollutants. These datasets provide critical information for policymakers to establish abatement strategies for the reduction of carbonaceous pollutant emissions and improve air quality in Chongqing and other similar urban centres across China.

[Pollution Characteristics and Source Apportionment of Atmospheric VOCs During Ozone Pollution Period in the Main Urban Area of Chongqing].

In late August 2020, a period of O3 pollution occurred in the main urban area of Chongqing and lasted for approximately 2 weeks (till early September). Ambient air samples, collected using Summa Canisters and DNPH sampling columns at three observation sites in the main urban area, were used to study the composition, photochemical reaction activity, and source apportionment of volatile organic compounds (VOCs) during the period of O3 pollution. The results showed that the mean volume fraction of TVOCs in the main urban area of Chongqing during the observation period was 45.08×10-9, and the components were ranked by volume fraction in the following order:OVOCs, alkanes, halohydrocarbons, alkenes, aromatics, and alkynes. Formaldehyde, ethylene, and acetone made up the higher volume fraction of VOCs, together accounting for more than 30% of TVOCs. OVOCs and alkenes contributed more to · OH loss rate (Li·OH) and ozone formation potential (OFP) and were the key VOCs components for ozone generation. The main active species in the OVOCs component were formaldehyde, acetaldehyde, and acrolein; the main active species in the alkene component were isoprene, ethylene, and n-butene. The ratio of xylene to ethylbenzene in VOCs was low, and they showed a significant correlation, indicating that the VOCs air mass in the main urban area was highly aging and affected by long-distance transmission from other areas. The source apportionment results of the PMF model showed five main sources of VOCs, namely secondary generation (27.67%), vehicle exhaust (26.56%), industrial emission (17.86%), plant (14.51%), and fossil fuel combustion (13.4%).