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Secondary organic aerosol (SOA) has been identified as a major contributor to fine particulate matter (PM2.5) in the North China Plain (NCP). However, the chemical mechanisms involved are still unclear due to incomplete understanding of its multiple formation processes. Here we report field observations in summer in Handan of the NCP, based on high-resolution online measurements. Our results reveal the formation of SOA via photochemistry and two types of aqueous-phase chemistry, the latter of which include nocturnal and daytime processing. The photochemical pathway is the most important under high-Ox (i.e., O3 + NO2) conditions (65.1 ± 20.4 ppb). The efficient SOA formation from photochemistry (Ox-initiated SOA) dominated the daytime (65 % to OA), with an average growth rate of 0.8 µgm-3h-1. During the high-relative-humidity (RH; 83.7 ± 12.5 %) period, strong nocturnal aqueous-phase SOA formation (aqSOA) played a significant role in SOA production (45 % to OA), with a nighttime growth rate of 0.6 µgm-3h-1. Meanwhile, an equally fast growth rate of 0.6 µgm-3h-1 of Ox-initiated SOA from daytime aqueous-phase photochemistry was also observed, which contributed 39 % to OA, showing that photochemistry in the aqueous phase is also a non-negligible pathway in summer. The primary-related SOA (SOA attributed to primary particulate organics) and aqSOA are related to residential coal combustion activities, supported by distinct fragments from polycyclic aromatic hydrocarbons (PAHs). Moreover, the conversion and rapid oxidation of primary-related SOA to aqSOA were possible in the aqueous phase under high-RH conditions. This work sheds light on the multiple formation pathways of SOA in ambient air of complex pollution and improves our understanding of ambient SOA formation and aging in summer with high oxidation capacity.

We prepared a quercitrin nano micellar delivery system in this study to evaluate its oral bioavailability. The optimal formulation of quercetin nano micelles was determined through an orthogonal test. Characteristics (size of particles-SOP, morphology, efficiency of encapsulation-EE and stability) and the therapeutic property of quercitrin nano micelles on unexplained recurrent abortion (URSA) were evaluated. The SOP of quercitrin nano micelles was 111.88±3.70 nm with an EE of 95.66±0.57. A substantially increased release rate of quercetin from the micellar system was observed in different dissolution media comparable to that of quercitrin. Also, through quercitrin micelles, the oral bioavailability of quercetin was increased by 15.45-fold compared to quercitrin solution. Significantly, quercetin could reduce the levels of LDH and SOD as well as increase the level of MDA in serum restricted HTR-8/SVneo cells. Western blotting (WB) experiments showed that quercitrin had a protective effect on H2O2 induced oxidative stress injury of a human placental trophoblast HTR8-SVneo cell line. The developed nano micelles are a potential carrier that could enhance the aqueous solubility, oral in vivo availability and potential therapeutic abortion effect of quercitrin.

Glyoxal (Gly) and methylglyoxal (Mgly) are key precursors globally for secondary organic aerosol (SOA) formation. These two species were often thought to be formed in the atmosphere via photochemical oxidation of organics from biogenic and anthropogenic origins, although few studies have shown their direct emissions. In this study, we report direct emissions of particulate Gly and Mgly from different residential fuels typically used in north China. The emission ratios (ERs) and emission factors (EFs) of particulate Gly and Mgly for biomass burning were approximate 5-fold and 7-fold higher than those for coal combustion, respectively. The large variances in emissions of Gly and Mgly could be attributed to the different combustion processes, which influenced by the fuel types and combustion conditions. The averaged ERs and EFs of particulate Gly and Mgly were about one order of magnitude lower than their gaseous counterparts due to the low Henry's law constant, which was also consistent with the low particle-to-gas ratio of Gly (0.04) and Mgly (0.02). Our results suggest that the direct emissions of Gly and Mgly from emission sources should be considered when estimating the formation of SOA from Gly and Mgly.

Nitrated aromatic compounds (NACs) are a group of key chromophores for brown carbon (light-absorbing organic carbon, i.e., BrC) aerosol, which affects radiative forcing. The chemical composition and sources of NACs and their contributions to BrC absorption, however, are still not well understood. In this study, PM 2.5 -bound NACs in Xi'an, Northwest China, were investigated for 112 daily PM 2.5 filter samples from 2015 to 2016. Both the total concentrations and contributions from individual species of NACs show distinct seasonal variations. The seasonally averaged concentrations of NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56 ng m −3 (winter). Thereinto, 4-nitrophenol is the major NAC component in spring (58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol dominate in summer (70 %), and the concentrations of 4-nitrocatechol and 4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species show different seasonal patterns in concentrations, indicating differences in emissions and formation pathways. Source apportionment results using positive matrix factorization (PMF) further show large seasonal differences in the sources of NACs. Specifically, in summer, NACs were highly influenced by secondary formation and vehicle emissions ( ∼ 80 %), while in winter, biomass burning and coal combustion contributed the most ( ∼ 75 %). Furthermore, the light absorption contributions of NACs to BrC are wavelength-dependent and vary greatly by season, with maximum contributions at ∼ 330 nm in winter and fall and ∼ 320 nm in summer and spring. The differences in the contribution to light absorption are associated with the higher mass fractions of 4-nitrocatechol ( λ max⁡ = 345 nm) and 4-nitrophenol ( λ max⁡ = 310 nm) in fall and winter, 4-nitrophenol in spring, and 5-nitrosalicylic acid ( λ max⁡ = 315 nm) and 4-nitrophenol in summer. The mean contributions of NACs to BrC light absorption at a wavelength of 365 nm in different seasons are 0.14 % (spring), 0.09 % (summer), 0.36 % (fall), and 0.91 % (winter), which are about 6–9 times higher than their mass fractional contributions of carbon in total organic carbon. Our results indicate that the composition and sources of NACs have profound impacts on the BrC light absorption.

Secondary organic aerosol (SOA) has been identified as a major contributor to fine particulate matter (PM2.5) in North China Plain (NCP). However, the chemical mechanisms involved are still unclear due to incomplete understanding of its multiple formation processes. Here we report field observations in summer in Handan of NCP, based on high-resolution online measurements. Our results reveal the formation of SOA via photochemistry and two types of aqueous-phase chemistry, the latter of which include nocturnal and daytime processing. The photochemical pathway is the most important under high Ox (=O3 + NO2) conditions (65.1 ± 20.4 ppb). The efficient SOA formation from photochemistry (phochem-SOA) dominated the daytime (65 % to OA) with an average growth rate of 0.8 μg m−3 h−1. During the high relative humidity (RH: 83.7 ± 12.5 %) period, strong nocturnal aqueous-phase SOA formation (aq-SOA) played a significant role in SOA production (45 % to OA) with a nighttime growth rate of 0.6 μg m-3 h-1. Meanwhile, an equally fast growth rate of 0.6 μg m-3 h-1 of phochem-SOA from daytime aqueous-phase photochemistry was also observed, which contributed 39 % to OA, showing that photochemistry in the aqueous phase is also a non-negligible pathway in summer. The primary-related-SOA (SOA attributed to primary particulate organics) and aq-SOA are related to residential coal combustion activities, supported by distinct fragments from polycyclic aromatic hydrocarbons (PAHs). Moreover, the conversion and rapidly oxidation of primary-related-SOA to aq-SOA could be possible in the aqueous phase under high-RH conditions. This work sheds light on the multiple formation pathways of SOA in ambient air of complex pollution, and improves our understanding of ambient SOA formation and aging in summer with high oxidation capacity.

To get a comprehensive source apportionment of the nonrefractory submicron aerosol (NR-PM1), a merged dataset of the organic fragments and the inorganic species, measured by an aerosol chemical spe...

To investigate the physio-chemical properties of aerosol transported from major pollution regions in China, observations were conducted ∼ 200 m above the ground at the junction location of the North China Plain and Fenwei Basin, which are two regions of top priority for China's Blue Sky Campaign. We identified three pollution transport sectors including those from Beijing–Tianjin–Hebei (BTH), urban Guanzhong Basin (GZB) and northern China and one clean transport sector from the rural Guanzhong Basin region. Secondary inorganic aerosol (SIA) constituted a major fraction (39 %–46 %) in all pollution transport sectors, with a high sulfur oxidation ratio (0.44–0.58) and a high nitrogen oxidation ratio (0.24–0.29), suggesting efficient formation of secondary inorganic aerosol during regional transport. More oxidized oxygenated organic aerosol (MO-OOA) played a dominant role in the source of organic aerosol in all sectors including the clean one, accounting for 42 %–58 % of total organic aerosol. Elemental analysis (O and C) shows that aerosol particles at this receptor site were much more oxidized than in urban regions, pointing that long-range transport contributed markedly to the organic aerosol oxidation and aging. Case studies of pollution events with high sulfate, nitrate and more-oxidized oxygenated organic aerosol production rate indicate the strong formation efficiency of secondary aerosol during regional transport in the Beijing–Tianjin–Hebei transport sector.

Carbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual 14C-13C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of 13C source signatures, which are seldom measured for EC. In this work, we present 13C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for 13C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the 13C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the 13C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in 13C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of 13C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite 13C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, 13C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, low-volatile, and non-volatile OC fractions. Each source category shows a characteristic trend of 13C signatures with desorption temperature, which is likely related to different OC formation processes during combustion.

The you-only-look-once (YOLO) model identifies objects in complex images by framing detection as a regression problem with spatially separated boundaries and class probabilities. Object detection from complex images is somewhat similar to underwater source detection from acoustic data, e.g., time-frequency distributions. Herein, YOLO is modified for joint source detection and azimuth estimation in a multi-interfering underwater acoustic environment. The modified you-only-look-once (M-YOLO) input is a frequency-beam domain (FBD) sample containing the target and multi-interfering spectra at different azimuths, generated from the received data of a towed horizontal line array. M-YOLO processes the whole FBD sample using a single-regression neural network and directly outputs the target-existence probability and spectrum azimuth. Model performance is assessed on both simulated and at-sea data. Simulation results reveal the strong robustness of M-YOLO toward different signal-to-noise ratios and mismatched ocean environments. As tested on the data collected in an actual multi-interfering environment, M-YOLO achieved near-100% target detection and a root mean square error of 0.54° in azimuth estimation.

This study investigates the sources and atmospheric processes of size-resolved carbonaceous aerosols in winter 2018 in urban Beijing, based on analysis of dual-carbon isotopes (i.e., radiocarbon and the stable isotope 13C). We found a size dependence of fossil source contributions to elemental carbon (EC), but no clear size dependence for organic carbon (OC). Comparable fossil source contributions to water-insoluble OC (WIOC; 55 ± 3%) and to water-soluble OC (WSOC; 54 ± 4%) highlight the importance of secondary aerosol formation, considering that fossil sources emit only small amounts of primary WSOC. OC concentrations increased during high PM2.5 pollution events, with increased fossil and non-fossil WSOC concentrating at larger particles (0.44–2.5 µm) than WIOC (0.25–2.5 µm), highlighting the aqueous-phase chemistry as an important pathway for OC production. The ratio of 13C/12C (expressed as δ13C) of total carbon (−27.0‰ to −23.3‰) fell in the range of anthropogenic aerosol, reflecting small biogenic influence. δ13C of OC increased with desorption temperature steps (200 °C, 350 °C and 650 °C). The strongly enriched δ13COC,650 (−26.9‰ to −20.3‰) and large mass fraction of OC650°C in total desorbed OC, both increasing with the increase of particle sizes, were caused by photochemical aging, especially during low and moderate PM2.5 pollution events, when regional, aged aerosol played an important role. During low pollution events, higher δ13COC,650 and WSOC/OC ratios reflect a larger contribution and more extensive chemical processing of aged aerosol. In contrast, relatively low δ13COC,200 (−27.2‰ to −25.7‰) suggests the influence of secondary OC formation on the more volatile OC desorbed at 200 °C. δ13COC,200 was similar for all particle sizes and for different pollution events, pointing to an internal mixture of local and aged regional OC. Our results show that the organic aerosol in Beijing arises from a mixture of various sources and complex formation processes, spanning local to regional scales. Particle sizes < 250 nm show strong contribution from local secondary OC formation, whereas refractory OC in particles around 1 µm shows strong evidence for regional aging processes. In summary, primary emission, secondary and aqueous-phase formation, and (photo-)chemical aging all need to be considered to understand organic aerosol in this region and their importance varies with particle size.

A bacterium, designated HX2-24 T, was isolated from activated sludge treating pesticide-manufacturing wastewater. Colonies of the strain on nutrient agar were circular, transparent, and colorless. Strain HX2-24 T shared 98.1% 16S rRNA gene sequence similarity with Extensimonas vulgaris S4T, and less than 97% similarities with other type strains. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the strain formed a clade with E. vulgaris S4T. The major cellular fatty acids were C16:0, summed feature 3 (C16:1ω7c and/or C16:1ω6c) and C17:0 cyclo, the major polar lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), aminophospholipid (APL), glycophospholipid (GPL), and aminoglycolipid (AGL). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between HX2-24 T and E. vulgaris S4T were 92% and 41%, respectively. The G + C content of strain HX2-24 T was 64.4 mol%. Thus, based on the phenotypic, chemotaxonomic, and genotypic characteristics, strain HX2-24 T represents a novel species in the genus Extensimonas, for which the name Extensimonas perlucida HX2-24 T sp. nov. is proposed. The type strain is HX2-24 T (= KCTC 72472 T = CCTCC AB 2019178 T).

Topramezone is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor. Due to its broad-spectrum, high efficiency, and low toxicity, topramezone is a candidate herbicide for the construction of genetically modified (GM) herbicide-resistant crops. In the present study, we screened a topramezone-resistant isolate Sphingobium sp. TPM-19 and cloned a topramezone-resistant HPPD gene (SphppD) from this isolate. SpHPPD shared the highest similarity (53%) with an HPPD from Vibrio vulnificus CMCP6. SpHPPD was synthesized in Escherichia coli BL21(DE3) and purified to homogeneity using Co2+-affinity chromatography. SpHPPD was found to be a monomer. The Km and kcat of SpHPPD for 4-hydroxyphenylpyruvate (4-HPP) were 82.8 μM and 15.0 s-1, respectively. SpHPPD showed high resistance to topramezone with half maximal inhibitory concentration (IC50) and Ki values of 5.2 and 2.5 μM, respectively. Additionally, SpHPPD also showed high resistance to isoxaflutole (DKN) (IC50: 8.7 μM; Ki: 6.0 μM) and mesotrione (IC50: 4.2 μM; Ki: 1.3 μM) and moderate resistance to tembotrione (IC50: 2.5 μM; Ki: 1.0 μM). The introduction of the SphppD gene into Arabidopsis thaliana enhanced obvious resistance against topramezone. In conclusion, this study provides a novel topramezone-resistant HPPD gene for the genetic engineering of GM herbicide-resistant crops.

Microbial degradation plays a major role in the dissipation of pendimethalin, and nitroreduction is an initial and detoxicating step. Previously, a pendimethalin nitroreductase, PNR, was identified...

We present the design and evaluation of an automated system for the conversion of elemental and organic carbon aerosol to CO2 for subsequent radiocarbon analysis. The system allows heating the sample in pure oxygen or helium at user defined temperature steps, followed by catalytic conversion of incomplete carbonaceous combustion products to CO2. The resulting CO2 is quantified using an NDIR detector and can be separated from other combustion by-products in a reduction oven. The purified CO2 is cryogenically collected in glass ampoules that can be sealed for storage until 14C analysis. We show that (1) the CO2 amount measured by the calibrated NDIR sensor compares well to an independent manometric method, (2) that we successfully remove combustion by-products such as SO2, H2O, and NOx, resulting in pure CO2 samples, and (3) that the system has low contamination and negligible cross contamination making it ideal for the analysis of very small samples in the order of 10–50 µgC.

The extracellular matrix (ECM), with its multilayer fiber structure, regulates diverse functions including cell proliferation, migration, differentiation and tissue regeneration effects. To mimic and replace the native ECM, the structures and properties of three single-layer fabric substrates including warp/weft-knitted and woven fabrics were analyzed, then two-layer warp/weft-knitted composite fabrics prepared by polyurethane (PU) bonding, and woven composite fabrics prepared by polycaprolactone (PCL)/collagen solution bonding or PU bonding, were studied. After PCL/collagen solution bonding or PU bonding, properties such as pore diameter, air permeability, stress and the contact angle of composite fabrics decreased by some degree, while fiber diameter, thickness and the thermal conductivity of composite fabrics increased. In combination with fiber diameter, pore diameter and physical properties, we know that warp- or weft-knitted composite fabrics are ideal scaffolda for potential applications in nerve, myocardium and tendon tissue engineering.

Two-component systems (TCSs) are highly conserved in prokaryotes, endowing cells with multiple physiological functions to respond to changes in the ambient environment. The signaling pathway of a typical TCS consists of a sensory histidine kinase and a response regulator. The TCSs of Kocuria rhizophila, which is usually used as a target strain for various antibiotics and other adverse factors, have captured our interest due to their potential roles in bacterial adaptation for survival. Herein, the distribution and putative biological functions of the TCSs of K. rhizophila DC2201 were analyzed by using bioinformatics, and a preliminary TCS regulatory network was constructed. A representative and important TCS (i.e., HK8700-RR8701 system), which is homologous to the LiaS-LiaR system previously discovered in Bacillus subtilis, was identified and characterized through yeast two-hybrid screening and phosphorylation assays. Detailed information of TCSs is expected to offer novel insights into the adaptation mechanism of K. rhizophila and thus boost its application.

In order to reduce the operating voltage of FinFET and increase the flexibility of integrated circuit design, we have proposed a Negative Capacitance Independent Multi-Gate FinFET (NC-IMG-F...

Microbially driven iron and sulfur geochemical cycles co-exist ubiquitously in subsurface environments and are of environmental relevance. Shewanella species (dissimilatory metal-reducing bacteria) are capable of reducing Fe(III)-(oxyhydr)oxide minerals and diverse sulfur sources using corresponding metabolic pathways and producing FeS secondary minerals. In spite of the ability in promoting bacterial extracellular electron transfer (EET), the specific role of FeS in mediating EET between microbe/mineral interface is still unclear. In this work, the electron-mediating function of biogenic FeS on promoting the reduction of ferrihydrite by S. oneidensis MR-1 using thiosulfate as sulfur source was investigated in terms of Fe(III) reduction percentage, X-ray diffraction and scanning electron microscopy. The results showed that the microbial ferrihydrite reduction was pH-dependent and positively correlated with the addition of thiosulfate. In the presence of thiosulfate, biogenic FeS in nano-scale were formed and deposited on the surfaces of S. oneidensis MR-1 and ferrihydrite to build an interfacial electron transfer bridge between them. The addition of either thiosulfate and in-vitro FeS could rescue the entirely inactivated ability of the mutant (△omcA/mtrC) in ferrihydrite reduction to some extent, but which was obviously inferior to the wild-type strain. Meanwhile, the effect of the biogenic FeS in-situ coating on the surfaces of S. oneidensis MR-1 cells on promoting microbial ferrihydrite reduction was significantly superior to the in-vitro ones. Thus, the in-situ formed biogenic FeS secondary minerals were demonstrated to mediate and accelerate interfacial electron transfer from S. oneidensis MR-1 cells to ferrihydrite through interfacing with the bacterial EET routes, especially Mtr pathway. This work provides an insight into the secondary minerals-mediating interfacial electron transfer between microbes and minerals in the presence of biological S (-II), which has important biogeochemical and environmental implications.

We describe and thoroughly evaluate a method for

The health effects of trace metal elements in atmospheric fine particulate matter (PM

A low-cost, portable bioluminescence detector based on a silicon photomultiplier (SiPM) was developed for on-site colony detection, the main components of which are a low-noise photoelectric signal detection and processing circuit, power management module, and high-performance embedded microcontroller subsystem with peripheral circuits. Balanced chopper modulation and lock-in amplification techniques were adopted to improve the signal-to-noise ratio, and a zero-adjustment technique was used to eliminate the dark current of the SiPM to expand the dynamic range. Using this bioluminescence detector, adenosine triphosphate could be determined in the range of 3.6 × 10−6 to 3.6 × 10−11 mol/L, and bacterial colonies could be determined in the range of 1.0 × 103 to 1.0 × 109 CFU/mL, with a limit of quantitation of 1.0 × 103 CFU/mL. Satisfactory recoveries and precision were obtained. Actual samples were accurately tested and the data were verified by comparison with those from the national standard method. The manufacturing cost of the bioluminescence detector was only $30, which is only approximately 1% of the price of current commercial instruments. This study provides a tool for rapid on-site detection of bacterial colonies, as well as a new concept for the development of low-cost portable detection equipment.

This study investigates the sources and atmospheric processes of size-resolved carbonaceous aerosols in winter 2018 in urban Beijing, based on analysis of dual-carbon isotopes (i.e., radiocarbon and the stable isotope

Smog chamber experiments were conducted to characterize the light absorption of brown carbon (BrC) from primary and photochemically aged coal combustion emissions. Light absorption was measured by the UV-visible spectrophotometric analysis of water and methanol extracts of filter samples. The single-scattering albedo at 450 nm was 0.73 ± 0.10 for primary emissions and 0.75 ± 0.13 for aged emissions. The light absorption coefficient at 365 nm of methanol extracts was higher than that of water extracts by a factor of 10 for primary emissions and a factor of 7 for aged emissions. This suggests that the majority of BrC is water-insoluble even after aging. The mass absorption efficiency of this BrC (MAE365) for primary OA (POA) was dependent on combustion conditions, with an average of 0.84 ± 0.54 m2 g-1, which was significantly higher than that for aged OA (0.24 ± 0.18 m2 g-1). Secondary OA (SOA) dominated aged OA and the decreased MAE365 after aging indicates that SOA is less light absorbing than POA and/or that BrC is bleached (oxidized) with aging. The estimated MAE365 of SOA (0.14 ± 0.08 m2 g-1) was much lower than that of POA. A comparison of MAE365 of residential coal combustion with other anthropogenic sources suggests that residential coal combustion emissions are among the strongest absorbing BrC organics.

Isotopic source apportionment is commonly used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (coal/biomass burning and traffic emissions) using a dual 14C-13C isotope approach. However, dual-isotope source apportionment crucially relies on accurate knowledge of the 13C source signatures, which are seldom measured directly for EC. In this work, we present extensive measurements of organic carbon (OC) and EC 13C signatures for relevant sources in China. The EC 13C source signatures are provided first time using the optical split point in a thermal-optical analyzer to isolate EC, which can greatly reduce the influence of pyrolyzed organic carbon (pOC). A series of sensitivity studies (pOC/EC separation) were conducted to investigate the reliability of our method and its relation to other EC isolation methods. Meanwhile, we summarized and compared the literature 13C signatures in detail of raw source materials, total carbon (TC) and EC using a variety of thermal methods. Finally, we recommend composite EC 13C source signatures with uncertainties and detailed application conditions. There are two points worth noting. First, the traffic 13C signatures of raw materials and EC are separated into three groups according to geographical distribution. Second, the EC 13C signature of C4 plant combustion can be influenced greatly if pOC and EC are not well separated, so the thermal-optical method is necessary. Using these EC 13C source signatures in an exemplary dual-isotope source apportionment study shows improvement in precision. In addition, some interesting distinct and repeatable patterns were discovered in 13C source signatures of semi-volatile, low-volatile, and non-volatile primary OC fractions.

To mitigate haze pollution in China, a better understanding of the sources of carbonaceous aerosols is required due to the complexity in multiple emissions and atmospheric processes. Here we combined the analysis of radiocarbon and the stable isotope 13C to investigate the sources and formation of carbonaceous aerosols collected in two Chinese megacities (Beijing and Xi’an) during severe haze events of “red alarm” level from December 2016 to January 2017. The haze periods with daily PM2.5 concentrations as high as ~400 µg m-3 were compared to subsequent clean periods (i.e., PM2.5 < median concentrations during the winter 2016/2017), with PM2.5 concentrationsbelow 100 µg m-3 in Xi’an and below 20 µg m-3 in Beijing. In Xi’an, liquid fossil fuel combustion was the dominant source of elemental carbon (EC; 44%–57%), followed by biomass burning (25%–29%) and coal combustion (17%–29%). In Beijing, coal combustion contributed 45%–61% of EC and biomass burning (17%–24%) and liquid fossil fuel combustion (22%–33%) contributed less. Non-fossil sources contributed 51%–56% of organic carbon (OC) in Xi’an and fossil sources contributed 63%–69% of OC in Beijing. Secondary OC (SOC) was largely contributed by non-fossil sources in Xi’an (56 ± 6%) and by fossil sources in Beijing (75 ± 10%), especially during haze periods. The fossil vs. non-fossil contributions to OC and EC did not change drastically during haze events in both Xi’an and Beijing. However, compared to clean periods, the contribution of coal combustion to EC during haze periods increased in Xi’an and decreased in Beijing. During clean periods, primary OC from biomass burning and fossil sources constituted ~70% of OC in Xi’an and ~53% of OC in Beijing. From clean to haze periods, the contribution of SOC to total OC increased in Xi’an, but decreased in Beijing, suggesting that contribution of secondary organic aerosol formation to increased OC during haze periods was more efficient in Xi’an than in Beijing. In Beijing, the high SOC fraction in total OC during clean periods was mainly due to elevated contribution from non-fossil SOC. In Xi’an, a slight day-night difference was observed during the clean period, with enhanced fossil contributions to OC and EC during the day. This day-night difference was negligible during severe haze periods, likely due to enhanced accumulation of pollutants under stagnant weather conditions.

To mitigate haze pollution in China, a better understanding of the sources of carbonaceous aerosols is required due to the complexity in multiple emissions and atmospheric processes. Here we combined the analysis of radiocarbon and the stable isotope 13C to investigate the sources and formation of carbonaceous aerosols collected in two Chinese megacities (Beijing and Xi'an) during severe haze events of a “red alarm” level from December 2016 to January 2017. The haze periods with daily PM2.5 concentrations as high as ∼ 400 µg m−3 were compared to subsequent clean periods (i.e., PM2.5 less than median concentrations during the winter 2016/2017) with PM2.5 concentrations below 100 µg m−3 in Xi'an and below 20 µg m−3 in Beijing. In Xi'an, liquid fossil fuel combustion was the dominant source of elemental carbon (EC; 44 %–57 %), followed by biomass burning (25 %–29 %) and coal combustion (17 %–29 %). In Beijing, coal combustion contributed 45 %–61 % of EC, and biomass burning (17 %–24 %) and liquid fossil fuel combustion (22 %–33 %) contributed less. Non-fossil sources contributed 51 %–56 % of organic carbon (OC) in Xi'an, and fossil sources contributed 63 %–69 % of OC in Beijing. Secondary OC (SOC) was largely contributed by non-fossil sources in Xi'an (56±6 %) and by fossil sources in Beijing (75±10 %), especially during haze periods. The fossil vs. non-fossil contributions to OC and EC did not change drastically during haze events in both Xi'an and Beijing. However, compared to clean periods, the contribution of coal combustion to EC during haze periods increased in Xi'an and decreased in Beijing. During clean periods, primary OC from biomass burning and fossil sources constituted ∼ 70 % of OC in Xi'an and ∼ 53 % of OC in Beijing. From clean to haze periods, the contribution of SOC to total OC increased in Xi'an but decreased in Beijing, suggesting that the contribution of secondary organic aerosol formation to increased OC during haze periods was more efficient in Xi'an than in Beijing. In Beijing, the high SOC fraction in total OC during clean periods was mainly due to an elevated contribution from non-fossil SOC. In Xi'an, a slight day–night difference was observed during the clean period with enhanced fossil contributions to OC and EC during the day. This day–night difference was negligible during severe haze periods, likely due to the enhanced accumulation of pollutants under stagnant weather conditions.