Synergistic Effect of Surface p-Doping and Passivation Improves the Efficiency, Stability, and Reduces Lead Leakage in All-Inorganic CsPbIBr2 -Based Perovskite Solar Cells.

Wide-bandgap inorganic cesium lead halide CsPbIBr2 is a popular optoelectronic material that researchers are interested in because of the character that balances the power conversion efficiency and stability of solar cells. It also has great potential in semitransparent solar cells, indoor photovoltaics, and as a subcell for tandem solar cells. Although CsPbIBr2 -based devices have achieved good performance, the open-circuit voltage (Voc ) of CsPbIBr2 -based perovskite solar cells (PSCs) is still lower, and it is critical to further reduce large energy losses (Eloss ). Herein, a strategy is proposed for achieving surface p-type doping for CsPbIBr2 -based perovskite for the first time, using 1,5-Diaminopentane dihydroiodide at the perovskite surface to improve hole extraction efficiency. Meanwhile, the adjusted energy levels reduce Eloss and improve Voc of the CsPbIBr2 PSCs. Furthermore, the Cs- and Br-vacancies at the interface are filled, reducing structural disorder and defect states and thus improving the quality of the perovskite film. As a result, the target device achieves a high efficiency of 11.02% with a Voc of 1.33 V, which is among the best values. In addition to the improved performance, the stability of the target device under various conditions is enhanced, and the lead leakage is effectively suppressed.

Comparison of short- and long-term outcomes between laparoscopic and open gastrectomy for locally advanced gastric cancer following neoadjuvant chemotherapy: a propensity score matching analysis.

BACKGROUND: This study was performed to evaluate the safety and efficacy of laparoscopic gastrectomy (LG) in patients with locally advanced gastric cancer (LAGC) who received neoadjuvant chemotherapy (NACT). METHODS: We retrospectively analyzed patients who underwent gastrectomy for LAGC (cT2-4aN+M0) after NACT from January 2015 to December 2019. The patients were divided into a LG group and an open gastrectomy (OG) group. The short- and long-term outcomes in both groups were examined following propensity score matching. RESULTS: We retrospectively reviewed 288 patients with LAGC who underwent gastrectomy following NACT. Of these 288 patients, 218 were enrolled; after 1:1 propensity score matching, each group comprised 81 patients. The LG group had significantly lower estimated blood loss than the OG group [80 (50-110) vs. 280 (210-320) mL, P < 0.001) but a longer operation time [205 (186.5-222.5) vs. 182 (170-190) min, P < 0.001], a lower postoperative complication rate (24.7% vs. 42.0%, P = 0.002), and a shorter postoperative hospitalization period [8 (7-10) vs. 10 (8-11.5) days, P = 0.001]. Subgroup analysis revealed that patients who underwent laparoscopic distal gastrectomy had a lower rate of postoperative complications than patients in the OG group (18.8% vs. 38.6%, P = 0.034); however, such a pattern was not seen in patients who underwent total gastrectomy (32.3% vs. 45.9%, P = 0.251). The 3-year matched cohort analysis showed no significant difference in overall survival or recurrence-free survival (log-rank P = 0.816 and P = 0.726, respectively) (71.3% and 65.0% in OG vs. 69.1% and 61.7% in LG, respectively). CONCLUSION: In the short term, LG following NACT is safer and more effective than OG. However, the long-term results are comparable.

The nitrogen and carbon footprints of ammonia synthesis in China based on life cycle assessment.

The global nitrogen (N) cycle has emerged as an earth system process with more serious artificial disruption than climate change. Artificially synthesized reactive nitrogen (Nr) already accounts for nearly 50% of the total Nr in the earth system. The massive anthropogenic conversion of inert nitrogen (N2) to Nr is a major driver of imbalance and disruption of the earth's N cycle, where the artificial ammonia (NH3) synthesis process is the main trigger. Existing studies on life cycle environmental impacts of ammonia synthesis mainly focused on the greenhouse effect but lacked or underestimated the interference with the nitrogen cycle due to currently incomplete nitrogen footprint frameworks. In addition, the comprehensive evaluation of the nexus between nitrogen and carbon footprint of NH3 synthesis systems is also insufficient. Attempting to solve the above-mentioned problems, life cycle assessment models of seven ammonia synthesis systems were established considering different raw material pathways and production technologies under China's context, assisted by the Brightway2 platform. The general framework of nitrogen footprint accounting (GFNFA) that was established by the authors previously was employed to assess the ammonia synthesis on nitrogen footprint covered all ecosphere. The performance and hotspots of the system nitrogen footprint, carbon footprint (CF) and nitrogen-carbon nexus were then systematically quantified and analyzed. Results indicated that electrolysis-based ammonia powered by renewable and nuclear energy had the lowest Nr emission (0.499-1.148 kg Nr/t NH3) and carbon emission (592.822-1045.494 kg CO2-eq/t NH3). Among the seven ammonia synthesis systems investigated, biomass-based ammonia had the largest Nr emission and system nitrogen accumulation, and it converts the most N2 to Nr per ton ammonia produced, due to the extensive resources consumption and emissions during straw growth and direct Nr emission in gasification process. Thus, it caused the most significant disturbance to the earth's nitrogen cycle. The nexus between nitrogen and carbon footprints was revealed that the system's energy consumption was found to be a common driver through hotspots and contribution analysis. NH3 synthesis efficiency was the most determining factor in the system's Nr and carbon emissions. With a 15% increase in synthesis efficiency, nitrogen and carbon footprints can be reduced by more than 12.5%. This study can help researchers better understand the life cycle impacts of ammonia synthesis systems on earth's nitrogen and carbon cycle from multidisciplinary ecological origins.

Perovskite Films Regulation via Hydrogen-Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long-term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high-quality perovskite film. Owing to the low defect density and gradient energy-level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen-bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb2+ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high-performance flexible PSCs.

Significance of using dynamic land-use data and its threshold in hydrology and water quality simulation models.

Land-use changes have a significant impact on the hydrological cycle and non-point source (NPS) pollution discharge and transport. Thus, using dynamic land-use inputs in the simulation models is important. However, there is currently no clear standard for which situation the land-use data should be updated in the models. In this study, we quantified the impacts of land-use change on hydrological and NPS pollution simulation outputs, and analyzed the thresholds for land-use change level and time nodes. The results indicated that the error caused by land-use change had a linear relationship with the land-use change level. The total nitrogen (TN) output error was the most sensitive to land-use change, with a gradient of 0.73. The impact of land-use change on the model outputs was different at different temporal scales. Flow and TN had the highest output errors at a daily scale, while sediment had the highest output error at an annual scale. The threshold analysis results revealed that the land-use change thresholds for the flow, sediment, and TN simulations were 40%, 30%, and 10%, respectively. When the land-use change level exceeded the threshold, the model simulation error increased dramatically. The land-use change time node would also affect the simulation performance, especially for TN. This study initially explored the quantified standard for land-use data updates in the SWAT model. The results could be useful for improving the simulation accuracy of the SWAT model and may provide ideas for follow-up studies.

A Declining Trend in China's Future Cropland-N2O Emissions Due to Reduced Cropland Area.

Croplands are the largest anthropogenic source of nitrous oxide (N2O), a powerful greenhouse gas that contributes to the growing atmospheric N2O burden. However, few studies provide a comprehensive depiction of future cropland-N2O emissions on a national scale due to a lack of accurate cropland prediction data. Herein, we present a newly developed distributed land-use change prediction model for the high-precision prediction of national-scale land-use change. The high-precision land-use data provide an opportunity to elucidate how the changes in cropland area will affect the magnitude and spatial distribution of N2O emissions from China's croplands during 2020-2070. The results showed a declining trend in China's total cropland-N2O emissions from 0.44 ± 0.03 Tg N/year in 2020 to 0.39 ± 0.07 Tg N/year in 2070, consistent with a cropland area reduction from (1.78 ± 0.02) × 108 ha to (1.40 ± 0.15) × 108 ha. However, approximately 31% of all calculated cities in China would emit more than the present level. Furthermore, different land use and climate change scenarios would have important impacts on cropland-N2O emissions. The Grain for Green Plan implemented in China would effectively control emissions by approximately 12%.

Stroke and osteoporosis: a Taiwan cohort study.

BACKGROUND: Osteoporosis and stroke are major health problems that have potentially overlapping pathophysiological mechanisms. The aim of this study was to estimate osteoporosis risk in Taiwan patientswho had a stroke. METHOD: This study retrieved data contained in the Taiwan National Health Insurance Research Database for a population-based sample of consecutive patients either hospitalised for stroke or treated for stroke on an outpatient basis. A total of 7550 newly diagnosed patientswho had a stroke were enrolled during 1996-2010. Osteoporosis risk in these patients was then compared with a matched group of patients who had not had a stroke randomly selected from the database at a ratio of 1:4 (n=30 200). The relationship between stroke history and osteoporosis risk was estimated with Cox proportional hazard regression models. RESULTS: During the follow-up period, osteoporosis developed in 1537 patients who had a stroke and in 5830 patients who had not had a stroke. The incidence of osteoporosis for cohorts with and without stroke was 32.97 and 14.28 per 1000 person-years, respectively. After controlling for covariates, the overall risk of osteoporosis was 1.82-fold higher in the stroke group than in the non-stroke group. The relative osteoporosis risk contributed by stroke had apparently greater impact among male gender and younger age groups. CONCLUSION: History of stroke is a risk factor for osteoporosis in Taiwan. Much attention to stroke-targeted treatment modalities might minimise adverse outcomes of osteoporosis.

Anomalous Symmetry Protected Topological States in Interacting Fermion Systems.

The classification and construction of symmetry protected topological (SPT) phases have been intensively studied in interacting systems recently. To our surprise, in interacting fermion systems, there exists a new class of the so-called anomalous SPT (ASPT) states which are only well defined on the boundary of a trivial fermionic bulk system. We first demonstrate the essential idea by considering an anomalous topological superconductor with time-reversal symmetry T^{2}=1 in 2D. The physical reason for this is that the fermion parity might be changed locally by certain symmetry action, but it is conserved if we introduce a bulk. Then we discuss the layer structure and systematical construction of ASPT states in interacting fermion systems in 2D with a total symmetry G_{f}=G_{b}×Z_{2}^{f}. Finally, potential experimental realizations of ASPT states are also addressed.

Design, Synthesis, and Safener Activity of Novel Methyl (R)-N-Benzoyl/Dichloroacetyl-Thiazolidine-4-Carboxylates.

A series of novel methyl (R)-N-benzoyl/dichloroacetyl-thiazolidine-4-carboxylates were designed by active substructure combination. The title compounds were synthesized using a one-pot route from l-cysteine methyl ester hydrochloride, acyl chloride, and ketones. All compounds were characterized by IR, ¹H NMR, 13C NMR, and HRMS. The structure of 4q was determined by X-ray crystallography. The biological tests showed that the title compounds protected maize from chlorimuron-ethyl injury to some extent. The ALS activity assay showed that the title compounds increased the ALS activity of maize inhibited by chlorimuron-ethyl. Molecular docking modeling demonstrated that Compound 4e competed against chlorimuron-ethyl to combine with the herbicide target enzyme active site, causing the herbicide to be ineffective.

Future carbon storages of ecosystem based on land use change and carbon sequestration practices in a large economic belt.

Assessments of ecosystem carbon storage are needed to form the scientific basis for carbon policies. Due to lack of data, there are few accurate, large-scale, and long-term predictions of ecosystem carbon storage. This study used the Distributed Land-Use Change Prediction (DLUCP) model with ten socioeconomic and two climate change scenarios for a total of 20 combinations that take into account population increase, technology innovation, climate change, and Grain for Green Project to make high-resolution predictions of land use change in the Yangtze River Economic Belt. Low and high carbon sequestration practices were considered to predict future carbon densities. Land use change data, carbon densities data, and the InVEST model were used to predict changes in ecosystem carbon storage from now to 2070. The results show a slight increase (1.88-4.17%) in carbon storage in the study area only based on land use change. Grain for Green Project has the largest impact on carbon storage among population increase, technology innovation, climate scenarios, and Grain for Green Project, which increases carbon storage by 4.17%. After the implementation of carbon sequestration practices, there is an increase in carbon storages from 28.51 to 56.77% in the study area from now to 2070, and increasing carbon storages of forest in each stream and carbon storage of cropland in downstream are efficient ways to achieve carbon neutralization.

Programmable spatial deformation by controllable off-center freestanding 4D printing of continuous fiber reinforced liquid crystal elastomer composites.

Owing to their high deformation ability, 4D printed structures have various applications in origami structures, soft robotics and deployable mechanisms. As a material with programmable molecular chain orientation, liquid crystal elastomer is expected to produce the freestanding, bearable and deformable three-dimensional structure. However, majority of the existing 4D printing methods for liquid crystal elastomers can only fabricate planar structures, which limits their deformation designability and bearing capacity. Here we propose a direct ink writing based 4D printing method for freestanding continuous fiber reinforced composites. Continuous fibers can support freestanding structures during the printing process and improve the mechanical property and deformation ability of 4D printed structures. In this paper, the integration of 4D printed structures with fully impregnated composite interfaces, programmable deformation ability and high bearing capacity are realized by adjusting the off-center distribution of the fibers, and the printed liquid crystal composite can carry a load of up to 2805 times its own weight and achieve a bending deformation curvature of 0.33 mm-1 at 150 °C. This research is expected to open new avenues for creating soft robotics, mechanical metamaterials and artificial muscles.

Spatial 3D Printing of Continuous Fiber-Reinforced Composite Multilayer Truss Structures with Controllable Structural Performance.

Continuous fiber-reinforced composite truss structures have broad application prospects in aerospace engineering owing to their high structural bearing efficiency and multifunctional applications. This paper presents the design and fabrication of multilayer truss structures with controlled mechanical properties based on continuous fiber-reinforced thermoplastic composite 3D printing. Continuous fiber composite pyramid trusses fabricated by 3D printing have high specific stiffness and strength, with maximum equivalent compression modulus and strength of 401.91 MPa and 30.26 MPa, respectively. Moreover, the relative density of a truss structure can be as low as 1.45%. Additionally, structural units can be extended in any direction to form a multilayer truss structure. Structural performance can be controlled by designing the parameters of each layer. This study offers a novel approach for designing a multifunctional multilayer truss structure, a structure with low-density needs and unique load-bearing effects.

Intraoperative performance and outcomes of robotic and laparoscopic total gastrectomy for gastric cancer: A high-volume center retrospective propensity score matching study.

BACKGROUND: Studies on robotic total gastrectomy (RTG) are currently limited. This study aimed to compare the intraoperative performance as well as short- and long-term outcomes of RTG and laparoscopic total gastrectomy (LTG). METHODS: A total of 969 patients underwent robotic (n = 161) or laparoscopic (n = 636) total gastrectomy between October 2014 and October 2021. The two groups of patients were matched 1:3 using the propensity score matching (PSM) method. The intraoperative performance as well as short- and long-term outcomes of the robotic (n = 147) and the laparoscopic (n = 371) groups were compared. RESULTS: After matching, the estimated intraoperative blood loss was lower (80.51 ± 68.77 vs. 89.89 ± 66.12, p = 0.008), and the total number of lymph node dissections was higher (34.74 ± 12.44 vs. 29.83 ± 12.22, p < 0.001) in the RTG group compared with the LTG group. More lymph node dissections at the upper edge of the pancreas were performed in the RTG group than in the LTG (12.59 ± 4.18 vs. 10.33 ± 4.58, p = 0.001). Additionally, postoperative recovery indicators and laboratory data were greater in the RTG group than those in the LTG group, while postoperative complications were comparable between the two groups (19.0% vs. 18.9%, p = 0.962). For overweight or obese patients with body mass indexes (BMIs) ≥25, certain clinical outcomes of the RTG remained advantageous, and no significant differences in three-year overall survival (OS) or relapse-free survival (RFS) were observed. CONCLUSIONS: Robotic total gastrectomy demonstrated better intraoperative performance, could improve the short-term clinical outcomes of patients, and was more conducive to patient recovery. However, the long-term efficacies of the two approaches were similar. Robotic surgical systems may reduce surgical stress responses in patients, allowing them to receive postoperative chemotherapy sooner.

Unexpectedly minor nitrous oxide emissions from fluvial networks draining permafrost catchments of the East Qinghai-Tibet Plateau.

Streams and rivers emit substantial amounts of nitrous oxide (N2O) and are therefore an essential component of global nitrogen (N) cycle. Permafrost soils store a large reservoir of dormant N that, upon thawing, can enter fluvial networks and partly degrade to N2O, yet the role of waterborne release of N2O in permafrost regions is unclear. Here we report N2O concentrations and fluxes during different seasons between 2016 and 2018 in four watersheds on the East Qinghai-Tibet Plateau. Thawing permafrost soils are known to emit N2O at a high rate, but permafrost rivers draining the East Qinghai-Tibet Plateau behave as unexpectedly minor sources of atmospheric N2O. Such low N2O fluxes are associated with low riverine dissolved inorganic N (DIN) after terrestrial plant uptake, unfavorable conditions for N2O generation via denitrification, and low N2O yield due to a small ratio of nitrite reductase: nitrous oxide reductase in these rivers. We estimate fluvial N2O emissions of 0.432 - 0.463 Gg N2O-N yr-1 from permafrost landscapes on the entire Qinghai-Tibet Plateau, which is marginal (~0.15%) given their areal contribution to global streams and rivers (0.7%). However, we suggest that these permafrost-affected rivers can shift from minor sources to strong emitters in the warmer future, likely giving rise to the permafrost non-carbon feedback that intensifies warming.

Climate factors affect N2O emissions by influencing the migration and transformation of nonpoint source nitrogen in an agricultural watershed.

Precipitation can affect the residence time of nitrogen compounds, and temperature can influence nitrogen transformation in soil. Therefore, we hypothesized that climate factors can affect the emissions of N2O, an important greenhouse gas produced via nitrogen transformation, by influencing the migration and transformation of nonpoint source nitrogen in soil. To test this hypothesis and quantify the effect of climate factors on N2O emissions, the SWAT model and the modified SWAT-N2O coupler were used to study the effect of climate factors on the migration and transformation of nonpoint source nitrogen and N2O emissions in an agricultural watershed from 2009 to 2018. Temperature affected N2O emissions more significant than precipitation, and N2O emissions increased with temperature and reached a plateau when the average monthly temperature was 23.0 °C. The N2O emissions first increased rapidly with precipitation due to the increase in moisture. However, when the average monthly precipitation reached 78.8 mm, the N2O emissions began to decrease because the residence time of nitrogen compounds in soil were reduced due to fast removal via runoff, which inhibits N2O emissions. Under the context of climate change with three scenarios (RCP2.6, RCP4.5, RCP8.5), temperature would increase gradually while precipitation would not change significantly from 2021 to 2080, as a result, the changes would increase N2O emissions by 6.7%, 32.3%, and 70.7%, respectively. This study quantifies the feedback of N2O emissions to climate change in croplands, providing a scientific basis for climate change mitigation and agricultural management.

Non-Abelian three-loop braiding statistics for 3D fermionic topological phases.

Fractional statistics is one of the most intriguing features of topological phases in 2D. In particular, the so-called non-Abelian statistics plays a crucial role towards realizing topological quantum computation. Recently, the study of topological phases has been extended to 3D and it has been proposed that loop-like extensive objects can also carry fractional statistics. In this work, we systematically study the so-called three-loop braiding statistics for 3D interacting fermion systems. Most surprisingly, we discover new types of non-Abelian three-loop braiding statistics that can only be realized in fermionic systems (or equivalently bosonic systems with emergent fermionic particles). On the other hand, due to the correspondence between gauge theories with fermionic particles and classifying fermionic symmetry-protected topological (FSPT) phases with unitary symmetries, our study also gives rise to an alternative way to classify FSPT phases. We further compare the classification results for FSPT phases with arbitrary Abelian unitary total symmetry Gf and find systematical agreement with previous studies.

Survival analysis and prognostic factors of palliative radiotherapy in patients with metastatic colorectal cancer: a propensity score analysis.

BACKGROUND: Radiation therapy (RT) is known to have beneficial effects on the palliative treatment of patients with advanced cancer. However, valid data on this treatment method are limited, especially for patients with metastatic colorectal cancer (mCRC). This study aimed to identify prognostic factors and investigate the outcomes of mCRC patients who received palliative RT. METHODS: A total of 488 mCRC patients who underwent systemic therapy with or without palliative RT between 2014 and 2019 were included in the study. Of the 488 patients, 155 received systemic treatment combined with palliative RT (RT group), while 333 were only administered systemic treatment (non-RT group). Propensity score matching (PSM) was conducted to eliminate possible bias, and overall survival (OS) was calculated using the Kaplan-Meier (KM) method. A log-rank test was used to compare the survival outcomes of each group, and a multivariate analysis was conducted using a Cox proportional hazards model. RESULTS: The RT group had a higher OS than that of the non-RT group (P=0.001). After PSM, the median OS of the RT group was 50.8 months, and for the non-RT group it was 32.2 months (P=0.003). Subgroup analysis revealed that RT had a better effect on the OS of patients who had synchronous metastasis, or who didn't receive targeted therapy or local treatment (including surgery, ablation, and intervention). Multivariate analysis of the whole cohort showed that palliative RT was associated with improved OS. Moreover, multivariate analysis of the RT group showed that systemic therapy before RT, and the site of RT was in the liver and lung, were independent prognostic factors affecting survival time. CONCLUSIONS: We demonstrated that systemic treatment followed by palliative RT led to a better OS for mCRC patients. This combination method can therefore be seen as a suitable treatment approach for patients with mCRC.

Identification and uncertainty analysis of high-risk areas of heavy metals in sediments of the Yangtze River estuary, China.

In this study, ordinary kriging (OK) and indicator kriging (IK) were used to analyze the uncertainty associated with high-risk areas of seven heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) in sediments of the Yangtze River estuary during four seasons. The OK results showed that the high-risk areas of Cd, Cr, Cu, Hg, and Pb had a high proportion, with the highest corresponding to Cr pollution (up to 60%). Predictions based on IK revealed that the proportion of high-risk areas of Cr, Cd, and Hg pollution were high, especially that of Cr was higher than 90%. However, there were uncertainties between the OK and IK results. The uncertainty results revealed that the uncertainty areas of Cr pollution were relatively large, accounting for about 30%, while those of Cd, Cu, and Hg pollution were lower than 10%.

Study of uncertainty of satellite and reanalysis precipitation products and their impact on hydrological simulation.

Satellite and reanalysis precipitation products are potential alternatives in hydrological studies, and it is very important to evaluate their accuracy and potential use for reliable simulations. In this study, three precipitation products (Tropical Rainfall Measuring Mission 3B43 Version 7 (TRMM 3B43), spatial interpolation grid data based on 2472 national meteorological observation stations in China (GRID_0.5), and National Centers for Environmental Prediction-Climate Forecast System Reanalysis (NCEP-CFSR)) were evaluated against gauge observations in the Xiangxi River watershed of Hubei Province. The performance results indicated that the results of the three precipitation products were correlated with those of the rain gauges; however, there were differences among the three products. TRMM 3B43 tended to overestimate precipitation with the highest correlation coefficient, while NCEP-CFSR tended to underestimate precipitation with the least satisfactory performance, and the performance of GRID_0.5 ranked between them. However, the annual and monthly mean errors differed, as the errors of most of the results driven by NCEP-CFSR were lowest. The errors varied at different time scales. During years with high precipitation, the results were often underestimated, while the results are often overestimated during years with low precipitation. According to the average monthly results, the GRID_0.5 results were closest to the gauge observations for most months. During the wet season, TRMM 3B43 performed better, while NCEP-CFSR precipitation performed better during the dry season. The errors from precipitation to streamflow, NPS pollution, and water environmental capacity (WEC) driven by the three precipitation products increased gradually, ranging from 10% for precipitation to over 20% for NPS pollution and almost 100% for WEC. The error increase for NCEP-CFSR was lower than that of the other two products. Although the simulation error from precipitation to the WEC results driven by the three precipitation products gradually increased, the degree of overestimation and underestimation became smaller.

Temporal variations of levels and sources of health risk associated with heavy metals in road dust in Beijing from May 2016 to April 2018.

To analyze the temporal variations of heavy metals, health risk, and source-specific health risk, 24 road dust samples were collected from Beijing in each month in two years. The temporal variations of Hg, Pb, and Ni were higher than other heavy metals. Most heavy metals reached their highest concentrations either in winter or in spring, then the concentrations decreased and reached the lowest values in autumn. Human health risk assessment (HHRA) model showed that As, Cr, and Ni might pose cautionary carcinogenic risk (CR) to children (CR > 10-6). CR for adults were only 0.15 to 0.19 times of that for children. Four sources were identified based on positive matrix factorization model and HHRA model, they were traffic exhaust, fuel combustion, construction, and use of pesticides and fertilizers. Influenced by the difference of carcinogenicity of heavy metals, traffic exhaust contributed the largest to heavy metals (36.02%, over 42.24% higher than other sources), while contributions of fuel combustion to CR (36.95%) was similar to traffic exhaust (37.17%). Monte-Carlo simulation showed that the 95th percentile of probability density functions of CR posed by Cr and Ni from each source were 9.90 × 10-5 to 2.64 × 10-4, posing cautionary carcinogenic risk to children. The seasonal change of CR varied among different sources. CR from use of pesticides and fertilizers in spring was 35.06 times of that in winter, and that from fuel combustion in winter was 1.15-2.40 times of that in other seasons. CR from each source was sensitive to ingestion rate and skin adherence factor.