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The surface defect detection (SDD) problem is one of the crucial techniques during production process, so it has become a key research area to control the quality of industrial products, which has been increasingly of greater interest to the researchers especially with the rapid development of artificial neural networks technology in recent years. Therefore, this paper proposes a novel deep convolutional neural network algorithm aiming at SDD. Firstly, a dense cross-stage partial Darknet backbone network is designed for feature extraction by optimizing cross-stage partial Darknet through the idea of dense connections, which can, not only enhance feature reuse but also greatly alleviate the overfitting issue. Secondly, a new cross-stage hierarchy module is presented combining the cross-stage feature fusion strategy and depthwise separable convolution technique for each node of the path aggregated feature pyramid network (PAN). Finally, an efficient channel attention (ECA) mechanism is introduced in PAN to construct a novel ECA PAN. The experimental results on three surface defect datasets show that the mean average precision of this network is 2.63, 5.48, and 1.16$\%$ which is higher than that of the baseline network, respectively. The proposed network outperforms not only the classical models but state-of-the-art models, which indicates the proposed algorithm can achieve higher accuracy and speed with fewer calculation parameters. And what is more, the proposed algorithm also has outstanding generalization ability.

ObjectivesAssisted reproductive technology (ART) is an important part of reproductive medicine, whose possible effects on offspring’s health have drawn widespread attention in recent years. However, relevant studies are limited to postnatal short-term follow-up and lack of diverse sample sources analysis other than blood.MethodsIn this study, a mouse model was used to explore the effects of ART on fetal development and gene expression in the organs of offspring in the adulthood using next-generation sequencing. The sequencing results were then analyzed.ResultsThe results showed that it caused abnormal expression in 1060 genes and 179 genes in the heart and spleen, respectively. Differentially expressed genes (DEGs) in the heart are mainly enriched in RNA synthesis and processing, and the cardiovascular system development also shows enrichment. STRING analysis identified Ccl2, Ptgs2, Rock1, Mapk14, Agt, and Wnt5a as the core interacting factors. DEGs in the spleen are significantly enriched in anti-infection and immune responses, which include the core factors Fos, Jun and Il1r2. Further exploration revealed the abnormal expression of 42 and 5 epigenetic modifiers in the heart and spleen, respectively. The expression of the imprinted genes Dhcr7, Igf2, Mest and Smoc1 decreased in the hearts of ART offspring, and the DNA methylation levels of Igf2- and Mest-imprinting control regions (ICRs) increased abnormally.ConclusionIn the mouse model, ART can interfere with the gene expression pattern in the heart and spleen of the adult offspring and that these changes are related to the aberrant expression of epigenetic regulators.

Furfural residue (FR), a solid waste, was applied as the precursor to prepare activated carbon by steam activation. The Box-Behnken design (BBD) approach-based response surface methodology (RSM) was utilized to optimize the preparation conditions to evaluate their effects on the performance of activated carbon from furfural residue (FRAC). The optimum preparation conditions of FRAC were found as follows: activation temperature of 922 °C, activation time of 62 min, and the mass ratio of char to H2O of 1:4.5, resulting in 1,501.84 mg/g of iodine adsorption capacity and 1,662.41 m2/g of specific surface area. The FRAC was characterized and then the adsorption performance of bisphenol S (BPS) on FRAC was investigated. Langmuir and Koble-Corrigan isotherm models were well fitted to the experimental data, and the adsorption kinetics process was perfectly described by the pseudo-second-order model. Thermodynamic parameters showed that the adsorption of BPS was a spontaneous exothermic process. Besides, the regeneration efficiency of FRAC was over 97% after five consecutive cycles. The maximum monolayer adsorption capacity of FRAC for BPS was 3.2848 mmol/g at 298 K, indicating that the FRAC was an excellent adsorbent for the removal of BPS from aqueous solutions.

In this letter, the performance of reconfigurable intelligent surface (RIS)-assisted non-orthogonal multiple access (NOMA) system is studied in the cooperative scenarios, where the quality of the received signals for the far user is enhanced by the assistance of the near user. We respectively derive the exact closed-form expressions for the outage probabilities of near user and far user under Nakagami-m fading. Further, to give more insights into the system performance, the asymptotic outage probability is obtained at the high signal-to-noise ratio (SNR) regime. The results show that the near user can achieve a diversity order of m, while the far user can achieve a diversity order relating to a and m, where m denotes the shape parameter of Nakagami-m distribution, and a is a function of m and the number of reflecting elements N. Simulation result are provided to verity the theoretical analysis.

Cryopreservation has important application in assisted reproductive technology (ART). The vitrification technique has been widely used in the cryopreservation of oocytes and embryos, as a large number of clinical results and experimental studies have shown that vitrification can achieve a higher cell survival rate and preimplantation development rate and better pregnancy outcomes. Ovarian tissue vitrification is an alternative method to slow freezing that causes comparatively less damage to the original follicular DNA. At present, sperm preservation mainly adopts slow freezing or rapid freezing (LN2 vapor method), although the vitrification method can achieve higher sperm motility after warming. However, due to the use of high-concentration cryoprotectants and ultra-rapid cooling, vitrification may cause strong stress to gametes, embryos and tissue cells, resulting in potentially adverse effects. Imprinted genes are regulated by epigenetic modifications, including DNA methylation, and show single allele expression. Their accurate regulation and correct expression are very important for the placenta, fetal development and offspring health. Considering that genome imprinting is very sensitive to changes in the external environment, we comprehensively summarized the effect of cryopreservation—especially the vitrification method in ART—on imprinted genes. Animal studies have found that the vitrification of oocytes and embryos can have a significant impact on some imprinted genes and DNA methylation, but the few studies in humans have reported almost no influence, which need to be further explored. This review provides useful information for the safety assessment and further optimization of the current cryopreservation techniques in ART.

Using AgNO3 as the Ag source, the Ag@BiOCl photocatalyst was prepared by depositing noble metal Ag on the surface of BiOCl by solvothermal method. Ag exists as spherical particles with a diameter of 40 nm. Based on the surface plasmon resonance effect (SPR) of Ag, the photoresponse range of BiOCl was successfully extended to the visible light region, which reduced the photo-generated electron-hole recombination efficiency and improved the charge transfer efficiency. The photocatalytic performance of Ag@BiOCl was studied under visible light. The results show that when the Ag content is 10wt%, it exhibits excellent effects on the degradation of acid red B (ARB), and its degradation rate constant is 11 times larger than that of BiOCl. The active substance-capturing test results show that the main role in photocatalytic degradation of ARB is voids.

NBT-xBT@BT-BZN composite ceramic materials were prepared by wet solid-phase reaction method. The effects of NBT-xBT (x = 6, 7, 8, 9 mol%) on the phase structure, morphology and dielectric propertie...

The powder samples of (Na0.5Bi0.5)0.705Ba0.045Sr0.25TiO3-xNb2O5 (NBBSNT) were synthesized by a wet solid-phase method. The effects of Nb-doping on morphology, ferroelectric and dielectric propertie...

Biomass burning activities are ubiquitous in China, especially in northern China, where there is a large rural population and winter heating custom. Biomass burning tracers (i.e., levoglucosan, mannosan and potassium (K + )), as well as other chemical components, were quantified at a rural site (Gucheng, GC) in northern China from 15 October to 30 November, during a transition heating season, when the field burning of agricultural residue was becoming intense. The measured daily average concentrations of levoglucosan, mannosan and K + in PM 2.5 (particulate matter with aerodynamic diameters less than 2.5 µ m) during this study were 0.79 ± 0.75, 0.03 ± 0.03 and 1.52 ± 0.62 µ g m −3 , respectively. Carbonaceous components and biomass burning tracers showed higher levels during nighttime than daytime, while secondary inorganic ions were enhanced during daytime. An episode with high levels of biomass burning tracers was encountered at the end of October 2016, with high levoglucosan at 4.37 µ g m −3 . Based on the comparison of chemical components during different biomass burning pollution periods, it appeared that biomass combustion can obviously elevate carbonaceous component levels, whereas there was essentially no effect on secondary inorganic aerosols in the ambient air. Moreover, the levoglucosan / mannosan ratios during different biomass burning pollution periods remained at high values (in the range of 18.3–24.9); however, the levoglucosan / K + ratio was significantly elevated during the intensive biomass burning pollution period (1.67) when air temperatures were decreasing, which was substantially higher than in other biomass burning periods (averaged at 0.47).

As a clean and efficient method of lignocellulosic biomass separation, organic acid pretreatment has attracted extensive research. Hemicellulose or lignin is selectively isolated and the cellulose structure is preserved. Effective fractionation of lignocellulosic biomass is achieved. The separation characteristics of hemicellulose or lignin by different organic acids were summarized. The organic acids of hemicellulose were separated into hydrogen ionized, autocatalytic and α-hydroxy acids according to the separation mechanism. The separation of lignin depends on the dissolution mechanism and spatial effect of organic acids. In addition, the challenges and prospects of organic acid pretreatment were analyzed. The separation of hemicellulose and enzymatic hydrolysis of cellulose were significantly affected by the polycondensation of lignin, which is effectively inhibited by the addition of green additives such as ketones or alcohols. Lignin separation was improved by developing a deep eutectic solvent treatment based on organic acid pretreatment. This work provides support for efficient cleaning of carbohydrate polymers and lignin to promote global carbon neutrality.

To analyze the treatment of elderly femoral intertrochanteric fracture (EFIF) using InterTan intramedullary nail (InterTanIN) and proximal femoral nail antirotation (PFNA). A total of 75 patients suffering from EFIF receiving intramedullary fixation were retrospectively collected. According to intramedullary fixation methods, the patients were separated into InterTanIN group and PFNA group. Parameters including the surgery time, blood loss, number of X-ray fluoroscopy, hospital stays, bone-healing time, postoperative Harris hip score (HIS) (1 month, 3 months, 6 months, and 12 months), and complications were collected and analyzed. The results showed surgery time, blood loss, and number of X-ray fluoroscopy in InterTanIN group were higher than those in PFNA group ( P < 0.05 ). The mean hospital stay in the InterTanIN group was comparable to that in the PFNA group ( P > 0.05 ). There was no significant difference in bone-healing time between the InterTanIN group and PFNA group ( P > 0.05 ). The postoperative HIS of InterTanIN group was statistically better than PFNA group at the 3rd month and the 6th month ( P < 0.05 ). With the extension of recovery time, the gap between the two groups gradually narrowed. The postoperative implant displacement happened more often in the PFNA group than in the InterTanIN group. EFIF treated with InterTanIN or PFNA could achieve good long-term efficacy. Although InterTanIN has the disadvantages of increased operative time, blood loss, and radiation exposure compared to PFNA, the postoperative hip function recovery of InterTanIN seems to be more reliable and stable than PFNA.

Oocyte vitrification is an important assisted reproductive technology (ART) that preserves the fertility of unmarried patients with malignant tumors, and promotes the development of the oocyte donation program. In recent years, the effects of ART, including the vitrification of oocytes and embryos on the health of offspring, have attracted much attention; however, it is difficult to conduct long-term follow-up and biochemical evaluation in humans. In this study, we detected the effect of oocyte vitrification on gene expression in the organs of adult mice offspring by RNA sequencing for the first time. Our results showed that only a small amount of gene expression was significantly affected. Seven genes (Tpm3, Hspe1-rs1, Ntrk2, Cyp4a31, Asic5, Cyp4a14, Retsat) were abnormally expressed in the liver, and ten genes (Lbp, Hspe1-rs1, Prxl2b, Pfn3, Gm9008, Bglap3, Col8a1, Hmgcr, Ero1lb, Ifi44l) were abnormal in the kidney. Several genes were related to metabolism and disease occurrence in the liver or kidney. Besides, we paid special attention to the expression of known imprinted genes and DNA methylation-related genes in adult organs, which are susceptible to oocyte cryopreservation in the preimplantation stage. As a result, some of these transcripts were detected in adult organs, but they were not affected by oocyte vitrification. In conclusion, we first report that oocyte vitrification did not significantly change the global gene expression in offspring organs; nonetheless, it can still influence the transcription of a few functional genes. The potential adverse effects caused by oocyte vitrification need attention and further study.

The NO–NO2 cycle determines the formation of O3 and hence plays a critical role in the oxidizing capacity of troposphere. Traditional view concluded that the heterogeneous oxidation of NO to NO2 wa...

To assess the influence of rs2910164 G/C single nucleotide polymorphism (SNP) of the miR-146a gene on its expression and susceptibility to gastric cancer.Fifty three gastric cancer patients and six gastric cancer cell lines were selected for determining the miR-146a expression by Taqman quantitative PCR. A model was constructed to assess the influence of miR-146a overexpression on the growth of AGS gastric cancer cells. A case-control study involving 417 gastric cancer patients and 420 cancer-free individuals was then conducted, and the allelic and genotypic frequencies of the rs2910164 G/C SNP were compared. The genotypes of all subjects were determined by using a Taqman allelic discrimination assay. A Taqman assay was also used to quantify mature and pri-miR-146a transcripts among 65 gastric cancer patients with known genotypes.The expression of miR-146a was down-regulated among the 53 gastric cancer patients and six gastric cancer cell lines. Over-expression of miR-146a has suppressed the growth of gastric cancer by inhibiting the G1/S-phase transition of AGS cells. The case-control study showed that subjects with GC/CC genotypes had significantly lower risk for gastric cancer compared with those with GG genotype. In addition, miR-146a G/C SNP has significantly increased the level of mature miR-146a in those with GC/CC genotype compared with GG genotype.Down-regulation of miR-146a may play an important role in the pathogenesis of gastric cancer. The rs2910164 polymorphism of the miR-146a gene may reduce the risk of gastric cancer by influencing the processing of mature miR-146a.

Objective: To explore the feasibility and accuracy of liver iron deposition based on dual-energy CT in thalassemia patients. Materials and methods: 105 thalassemia patients were examined with dual-energy CT and MR liver scanning. Dual-energy CT was performed to measure CT values on 80kVp, 140kVp and virtual iron content (VIC) imaging, ΔH was figured out by the difference CT values between 80kVp and 140kVp. Using the liver iron concent (LIC) obtained by FerriScan as standard setting, the correlation between CT measurements and LIC was compared. Receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic performance for dual-energy CT in liver iron quantification and stratification. Results: The correlation analysis between CT measurements and LIC showed that 80kVp, 140kVp, VIC and ΔH all had a high-positive correlation with LIC (P0.05). ROC analysis revealed that the corresponding optimal cutoff value of VIC were -2.8, 6.3,11.9 HU (corresponds to 3.2,7.0,15.0 mg/g dry weight) respectively, while the ΔH were 5.1, 8.4, 17.8HU, respectively. The area under the receiver operating characteristic curves (AUCs) for both VIC and ΔH increased with the increase of LIC thresholds. Conclusion: Dual-energy CT can accurately evaluate liver iron deposition quantification and stratification, which contribute to predict the status of liver iron deposition of thalassemia patients.

Coastal downwelling is generally considered to have a limited biological effect compared with coastal upwelling. In this study, downslope transport of nearshore, nutrient-enriched waters during downwelling is found to induce distinct biological productivity in the water column over the northeastern South China Sea (NSCS). By conducting a process-driven study over a widened shelf with intensified downwelling in the NSCS, we investigated the biophysical processes associated with strong nutrient enrichment in the water column of downwelled waters. These processes and underlying mechanisms are largely unreported and remain unclear. Field measurements and a three-dimensional coupled physical-biological model incorporating nitrate (N), phytoplankton (P), zooplankton (Z), and detritus (D) were utilized to investigate distinct cross-shore nutrient transport over the uniquely widened NSCS shelf. We revealed that intensified downwelling circulation, dynamically induced by the widened shelf topography, enhanced chlorophyll a and biological productivity in a strip of well-mixed water over the inner shelf as well as in the downwelled water over the mid-shelf. Strong time lags and spatial differences existed among N, P, and Z because of the physical transport and the ensuing biogeochemical response. The intensified downslope transport of nutrient-rich coastal water formed distinct cross-shore wedge-shaped P, Z, and D structures, while N was rapidly consumed in the water column. This study illustrates the underlying coupled physical-biogeochemical processes associated with the observed biogeochemical response to wind-driven downwelling circulation over the variable shelf, which are commonly found in coastal oceans worldwide.

The genesis of submarine channels is often controlled by gravity flows, but channels can also be \udformed by oceanographic processes. Using multibeam bathymetry and two-dimensional seismic data from the \udwestern South China Sea, this study reveals how pockmarks can ultimately form channels under the effect of \udbottom currents and gravity-driven sedimentary processes. We demonstrate that alongslope and across-slope \udchannels were initiated by pockmark trains on the seafloor. Discrete pockmarks were elongated due to the \uderosion of gravity-driven sedimentary processes and bottom currents, and later coalesced to form immature \udchannels with irregular thalwegs. These gradually evolved into mature channels with continuous overbanks and \udsmooth thalwegs. Submarine channel evolution was significantly influenced by seafloor topography since the \udLate Miocene. The evolutionary model documented here is a key to understanding how channels are formed in \uddeep-water environments.

In situ N-doped porous carbon (NPC) derived from wheat bran via a convenient salt sealing and air-assisted strategy was prepared for the removal of doxycycline (DOX) from aqueous solution. The NPC was precisely characterized by SEM, FTIR, XPS and BET analysis. Additionally, the experimental variables including contact time, adsorbent dosage of NPC and pH were optimized by using Box-Behnken design (BBD) under response surface methodology (RSM). The predicted adsorption capacity of DOX was found to be 291.14 mg g

Severe haze hovered over Harbin during the heating season of 2019–2020, making it one of the ten most polluted Chinese cities in January of 2020. Here we focused on the optical properties and sources of brown carbon (BrC) during the extreme atmospheric pollution periods. Enhanced formation of secondary BrC (BrCsec) was evident as relative humidity (RH) became higher, accompanied with a decrease of ozone but concurrent increases of aerosol water content and secondary inorganic aerosols. These features were generally similar to the characteristics of haze chemistry observed during winter haze events in the North China Plain, and indicated that heterogeneous reactions involving aerosol water might be at play in the formation of BrCsec, despite the low temperatures in Harbin. Although BrCsec accounted for a substantial fraction of brown carbon mass, its contribution to BrC absorption was much smaller (6 vs. 28%), pointing to a lower mass absorption efficiency (MAE) of BrCsec compared to primary BrC. In addition, emissions of biomass burning BrC (BrCBB) were inferred to increase with increasing RH, coinciding with a large drop of temperature. Since both the less absorbing BrCsec and the more absorbing BrCBB increased as RH became higher, the MAE of total BrC were largely unchanged throughout the measurement period. This study unfolded the contrast in the source apportionment results of BrC mass and absorption, and could have implications for the simulation of radiative forcing by brown carbon.

Regional transport is a key source of carbonaceous aerosol in many Chinese megacities including Beijing. The sources of carbonaceous aerosol in urban areas have been studied extensively but are poorly known in upwind rural areas. This work aims to quantify the contributions of fossil and non-fossil fuel emissions to carbonaceous aerosols at a rural site in North China Plain in winter 2016. We integrated online high resolution-time of flight-aerosol mass spectrometer (HR-TOF-AMS) observations and radiocarbon (

In this paper, BiOCl1-xIx (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) solid solution was synthesized by one-step ultrasound-assisted solvothermal method. A series of samples with different band gap values was obtained by varying the amount of components. The synthesized photocatalysts were characterized by XRD, SEM, UV–Vis DRS, ESR, and BET specific surface area. The PL and EIS methods were used to evaluate the separation efficiency of the photogenerated electrons and holes. Photocatalytic experiments under visible light show that the degradation efficiency of BiOCl0.6I0.4 for acid red B (ARB) is 96.4% under 2 h irradiation time. After five times of recycling, the degradation rate of ARB was 91%. The results of free radical quenching experiments showed that the dominant role of BiOCl0.6I0.4 in the photocatalytic degradation of ARB is the oxidation of h+. A preliminary discussion on the photocatalytic mechanism was made.

This study examines the osteogenic differentiation promotion effect of micro/nanostructures of raffia on human adipose-derived stem cells to confirm the potential application of plant-derived micro/nanotopographies in tissue regeneration. The results confirm that the nanorod array on the front surface and the honeycomb-like microstructure on the back surface of raffia can not only regulate the adhesion, spreading, and migration of stem cells but also promote the osteogenic differentiation of the stem cells at a subsequent stage of cell culture. The osteocalcin expressions by the 21-day cultured cells on the front and back surfaces of raffia were 55-fold and 36-fold higher compared to the expression on a tissue culture plate. This indicates that plant-derived micro/nanotopographies can significantly promote stem cell differentiation. Furthermore, a general strategy for the application of plant-derived materials to stem-cell differentiation and bone-tissue engineering is suggested.

With an ever-increasing dependence on temperature-stability for operating at extreme condition, Nb5+ ions were used as effective dopants to prepare dielectric materials satisfying EIA X9R specifica...

To investigate the impacts of relative humidity (RH) on secondary organic aerosol (SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon (OC) and element carbon (EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon (SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH, photochemistry was weakened, gaseous oxidant concentrations was lowered (e.g., significantly decreased O3 levels), and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings, which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates, airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.

Water-soluble pollutants, especially oil-production related pollutants, are nowadays a major form of public-health-threatening environmental hazard. In this work, we report a new design of Ni based photoelectrocatalyst for the degradation of polyacrylamide (PAM), this particularly malignant by product of oil recovery can be decomposed into harmless product using the proposed method. Specifically, a full spectrum Sn3O4 nanosheet/Ni foam heterostructure photoelectrocatalyst has been developed. The Ni foam not only supports, as a substrate, the Sn3O4 nan-catalyst, but can also interact with the catalyst extending the absorption spectrum into the NIR range. Our heterostructure has exhibited an excellent photoelectrocatalytic activity, resulted from an enhanced efficiency of light harvesting, as well as the more stabilized photogenerated charge pairs, and a higher rate of charge transfer at the interface of hetero-material.

The study of atmospheric nitrous acid (HONO), which is the primary source of OH radicals, is crucial with respect to understanding atmospheric photochemistry and heterogeneous chemical processes. Heterogeneous NO2 chemistry under haze conditions has been identified as one of the missing sources of HONO on the North China Plain, and also produces sulfate and nitrate. However, controversy exists regarding the various proposed HONO production mechanisms, mainly regarding whether SO2 directly takes part in the HONO production process and what roles NH3 and the pH value play. In this paper, never before seen explosive HONO production was reported and evidence was found – for the first time in field measurements during fog (usually with 4

In order to improve the signal-to-noise ratio (SNR) gain and lower the bit error rate (BER) when a weak signal is buried in the noise, the parameter-tuned stochastic resonator (PSR) is studied in more detail. In this study, the authors explore the impact of the number of branches on performance. Hence, they build the parameter-tuned bistable parallel array system, which consists of a group of PSRs and propose a novel method to derive the probability density function (PDF) of the output signal, which combines the conventional PDF based on the approximation theory with Gaussian distribution. Based on this method, an analytical expression for BER of the system is derived. It is of interest to note that for an input binary pulse amplitude modulation signal buried in noise, the weak signal can be detected by using the parameter-tuned bistable parallel array system. It is found that via the array PSR effect, the system output SNR gain can be improved. Moreover, the BER can also be reduced with the increase of the array size as the array size increases.

Black carbon (BC) is important due to its complex influences on the environment and on climate in particular. However, reported BC data are largely dependent on measurement techniques due to the multitude of measurement principles. Here we focused on thermal-optical method which has been widely used to determine BC mass (as elemental carbon, EC). Several factors influencing EC measurement were investigated. Results from source samples representing vehicle engine emissions pointed to a continuum of EC components in thermal stability and provided direct observational evidence for the premature evolution of EC in inert atmosphere. It was also found that EC masses may be substantially underestimated for the vehicle exhaust samples if the adopted protocol requires an oxidizing atmosphere to define the split point between organic carbon (OC) and EC. Results from a field campaign conducted during winter in Beijing showed that the optical attenuation (ATN; i.e., the filter transmittance signal, I) was largely saturated for the samples with relatively high loadings, indicating their EC results were unreliable. Improved measurement of EC was achieved by extracting these heavily loaded filters using methanol, given that ATN was considerably reduced by the extraction and, moreover, saturation of ATN (or I) became not evident for the extracted samples. The methanol extraction also significantly reduced the transformation of OC to char-OC, by removing the majority (i.e., ~85%) of the deposited organic aerosols. Higher EC were measured for the extracted samples compared with the untreated ones, indicating that EC tends to be underestimated due to the charring-induced uncertainties. In addition, the methanol extraction largely reduced the inter-protocol discrepancy in the EC measurement results. Similar effects of methanol extraction have been observed during summer in Beijing, despite the seasonal variations of aerosol sources and compositions. This study indicates the potential benefits of methanol extraction for EC measurement.

Despite the growing interest in understanding haze formation in Chinese megacities, air pollution has been largely overlooked for the Harbin–Changchun (HC) metropolitan area, located in the severe cold climate region in northeast China. In this study, we unfolded significant variations of fine particulate matter (PM2.5) in HC's central city (Harbin) during two sequential heating seasons of 2018–2019 and 2019–2020, and we explored major drivers for the observed variations. The two campaigns showed comparable organic carbon (OC) levels but quite different OC sources. The biomass burning (BB) to OC contribution decreased substantially for 2019–2020, which was attributed primarily to the transition of local policies on agricultural fires, i.e., from the “legitimate burning” policy released in 2018 to the “strict prohibition” policy in 2019. Meanwhile, the contribution of secondary OC (OCsec) increased significantly, associated with the much more frequent occurrences of high relative humidity (RH) conditions during the 2019–2020 measurement period. Similar to OCsec, the major secondary inorganic ions, i.e., sulfate, nitrate and ammonium (SNA), also exhibited RH-dependent increases. Given the considerable aerosol water contents predicted for the high-RH conditions, heterogeneous reactions were likely at play in secondary aerosol formation even in the frigid atmosphere in Harbin (e.g., with daily average temperatures down to below −20 ∘C). In brief, compared to 2018–2019, the 2019–2020 measurement period was characterized by a policy-driven decrease of biomass burning OC, a RH-related increase of OCsec and a RH-related increase of SNA, with the first two factors generally offsetting each other. In addition, we found that open burning activities were actually not eliminated by the strict prohibition policy released in 2019, based on a synthesis of air quality data and fire count results. Although not occurring during the 2019–2020 measurement period, agricultural fires broke out within a short period before crop planting in spring of 2020, and this resulted in off-the-charts air pollution for Harbin, with 1 h and 24 h PM2.5 concentrations peaking at ∼ 2350 and 900 µg/m3, respectively. This study indicates that sustainable use of crop residues remains a difficult challenge for the massive agricultural sector in northeast China.