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Traditional animal dung fuel use is a prominent source of brown carbon (BrC) in the Tibetan Plateau (TPL) region. Changes in burning conditions, fuel types, and uses of dung fuels in Plateau areas can lead to considerable uncertainties about molecular absorption properties and their radiative forcing influence on BrC. Here, the constituents of BrC’s chromophoric molecules emitted from residential heating and cooking scenarios using dung fuels were proposed using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry in the TPL region, China. Our results show that dung fuels in this study can release abundant BrC emissions with substantial high BrC absorption when compared with those observed in bitumite. Particularly, the linkage between BrC molecules and their absorption properties was quantified by partial least squares regression. Among detected BrC’s molecular groups, above 70 % of N-containing compounds (CHON and CHONS) with low-oxygen-containing and unsaturated aromatic bonds and 20.9–27.5 % of CHO compounds measured from the dung combustion samples were lies in the potential BrC chromophores regions. Further, a significantly enhanced contribution of molecular absorption coefficient (Mbabs) to total Mbabs (up to 99.7 %) was observed in the presence of both CHO and CHON (N2+N4) with distinctive characteristics of long carbon chains and high levels of unsaturation. Interestingly, the identified CHONS markers were highly oxygenated with abundant unsaturated double-bonds and high Mbabs, but were rarely produced under insufficient oxygen conditions at the high-altitude plateau. Meanwhile, the incomplete combustion of dung produced high values of integrated simple forcing efficiency and thus destroyed the radiation balance over the TPL region.

We here described a ceftriaxone-resistant Neisseria gonorrhoeae FC428 clone (YL201) with moderate-level resistance to azithromycin in Shenzhen, South China in 2020. The NG-STAR type of YL201 is ST2238, containing a mosaic penA-60.001 allele, which is a typical characteristic of FC428 clone. YL201 harbours four copies of the 23S rRNA C2611T mutation, conferring moderate-level resistance to azithromycin. The MLST type is ST1600, identical with two N. gonorrhoeae FC428 clones identified in Hangzhou. Genome-wide phylogeny analysis demonstrates that YL201 is clustered with other FC428 clones from Hangzhou (South-east China) and Chengdu (South-west China). Isolates within this cluster have relatively higher MIC for ceftriaxone and display closely related MLST STs (ST1600 and ST7363) but are different from the ST of typical FC428 clone (ST1903). As ST1600 and ST7363 are common STs in Shenzhen, the further spread of FC428 clones may increase the severity of gonococcal resistance. In summary, identifying a multidrug-resistant (MDR) N. gonorrhoeae isolate in Shenzhen showed FC428 clones have undergone further transmission in China and presented more extensive and concerning antimicrobial resistance (AMR) characteristics during the spread.

Ageing is an unavoidable process in humans and a major factor for the increasing risk of various diseases. In the United States, more than 50% of rheumatoid arthritis patients are middle-aged or elderly, but the risk factors and mechanisms by which ageing increases the incidence of rheumatoid arthritis are not known. It has been suggested that the accumulation of DNA fragments increases the risk of autoimmune diseases, such as systemic lupus erythematosus. DNA fragments are a common nucleic acid metabolite in ageing organisms as well as in the serum of humans and animals with rheumatoid arthritis; therefore, we hypothesize that DNA fragments are one of the factors contributing to the development of rheumatoid arthritis due to ageing. First, we analysed two in vitro DNA damage response models by using a gene silencing approach and determined that the DNA fragment clearance gene TREX1 can regulate inflammatory factor release in normal cells. Second, after TREX1 expression was knocked down locally or systemically in rats via the Cre-LoxP system and compared with that in AIA(adjuvant-induced arthritis) model rats treated with AAV-TREX1, it was determined that DNA fragments can result in manifestations of arthritis and abnormal activation of the immune system in rats. These results, including the low expression of the TREX1 gene in clinical patient and AIA model samples and the results of immunohistochemical, Western blot, and transcriptome analyses, revealed that the TREX1 gene can regulate cellular senescence-associated secretory phenotype (SASP)-related manifestations and showed that dysregulation of c-Jun and c-Fos, components of the TREX1 transcription factor AP-1, is associated with SASP induction. Finally, it was confirmed in vitro that different causes of decreased c-Fos expression can inhibit TREX1 expression. These DNA fragments are potent producers of inflammation-releasing mediators, and TREX1 is an effective degrader of DNA fragments; it is also a key gene that regulates cellular immunity and ageing. Therefore, effectively clearing excess DNA fragments from the body and ensuring the health of senescent cells may be a potential prevention strategy for RA.

Since timely determination of nvCT is critical for restricting further infection spread in the population, we have developed a screening assay based on high‐resolution melting (HRM) that can detect C. trachomatis and identify nvCT. Our results showed that the HRM scanning assay is not only able to directly identify C. trachomatis in clinical specimens, but also to correctly differentiate nvCT with mutation C1514T, C1515T and G1523A from the wild‐type., Summary Chlamydia trachomatis is the most common sexually transmitted pathogen globally, causing serious health problems and representing a burden on public health. A new variant of C. trachomatis (nvCT) that carries mutations (C1514T, C1515T and G1523A) in the 23S rRNA gene has eluded detection in Aptima Combo 2 assays. This has led to false negatives in diagnostics tests and poses a challenge for C. trachomatis diagnostics on a global level. In this study, we developed a simple and cost‐effective assay to identify C. trachomatis, with a potential application to screen for nvCT. We developed a screening assay based on high‐resolution melting (HRM), targeting the 23S rRNA gene and cryptic plasmid. To evaluate the performance of the assay, 404 archived C. trachomatis DNA specimens and 570 extracted clinical specimens were analysed. Our HRM assay not only identified C. trachomatis in clinical specimens, but also correctly differentiated nvCT carrying C1514T, C1515T and G1523A mutations from the wild‐type. We observed no cross‐reactions with other clinically related agents, and the limit of detection was 11.26 (95% CI; 7.61–31.82) copies per reaction. Implementation of this screening assay could reduce detection times and costs for C. trachomatis diagnoses, and facilitate increased research on the presence and monitoring of nvCT.

Background Antimicrobial resistance (AMR) of Neisseria gonorrhoeae has spread worldwide. Rapid and comprehensive methods are needed to describe N. gonorrhoeae AMR profiles accurately. A method based on multiplex amplicon sequencing was developed to simultaneously sequence 13 genes related to AMR in N. gonorrhoeae directly from clinical samples. Methods Nine N. gonorrhoeae strains were used for the establishment and validation of the method. Eleven urethral swabs and their corresponding cultured isolates were matched as pairs to determine the accuracy of the method. Mock samples with different dilutions were prepared to determine the sensitivity of the method. Five nongonococcal Neisseria strains and 24 N. gonorrhoeae negative clinical samples were used to evaluate the cross-reactivity. Finally, the method was applied to 64 clinical samples to assess its performance. Results Using Sanger sequencing as a reference method, sequences recovered from amplicon sequencing had a base accuracy of over 99.5% and the AMR sites were correctly identified. The limit of detection (LOD) was lower than 31 copies/reaction. No significant cross-reactivity was observed. Furthermore, target genes were successfully recovered from 64 clinical samples including 9 urines, demonstrating this method could be used in different types of samples. For clinical samples, the results can be obtained within a time frame of 7 h 40 min to 10 h 40 min, while for isolates, the turnaround time was approximately 2 h shorter. Conclusions This method can serve as a versatile and convenient culture-free diagnostic method with the advantages of high sensitivity and accuracy.

The emerging cephalosporin-resistant Neisseria gonorrhoeae poses an urgent threat to the continued efficacy of the last-line monotherapy for gonorrhea. Consequently, high-throughput, accurate, and reasonable molecular assays are urgently needed for strengthening antimicrobial-resistance surveillance in N. gonorrhoeae .

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disorder which is associated with the dysregulation of autoimmune response. In recent years, early diagnosis, aggressive treatment and alternative therapeutic options of disease-modifying anti-rheumatic drugs (DMARDs) markedly improve both the management and long-term prognosis of RA. Since the discovery of non-coding RNA (ncRNA) including microRNA (miRNA), long non-coding RNA (lncRNA) and others, their altered expressions have been unraveled to be deregulated in various diseases including RA. Several lines of evidence are emerging that ncRNA may contribute to the pathogenesis, disease progression and treatment of RA. For example, SNP rs2850711 within lnc00305 was indicated to associate with RA development susceptibility, whereas a higher level of miR-10a represented a good response to methotrexate (MTX) treatment in RA patients. In the aspect of refractory RA, ncRNA also plays an important role by affecting or regulating drug sensitivity in RA patients. Of note, lower expression of miR-20a in rheumatoid arthritis synovial fibroblast (RASFs) was demonstrated to activate the Janus Kinase (JAK)- signal transducer and activator of transcription 3(STAT3)-mediated inflammation, thereby promoting cell proliferation and apoptosis-resistant. In this review, we have illustrated the changes of ncRNAs and their underlying mechanisms in the whole developing period of RA pathogenesis and disease progression, as well as highlighted the novel therapeutic targets/strategies and bio-markers for RA therapy.

Residential coal combustion is a prominent source of brown carbon (BrC) aerosols, but knowledge of their molecular structures and optical absorption were limited, which have notable used in ambient BrC source identification and radiative forcing calculation. In this study, the Fourier transform-ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis as well as Fourier transform infrared spectroscopy analysis were used to insight the molecular compounds and structures of BrC from anthracite and bituminous coal combustions between traditional and improved stoves. The absorption Ångström exponents (AAE) and mass absorption efficiency (MAE) values for the BrC emitted from the combinations of bituminous were both 1.2-2.5 times lower than those of anthracite, interpreting that the BrC from the anthracite emissions had greater light-absorbing capacity. In contrast, the emission factor of light absorption (EF

Gonorrhea is one of the most common sexually transmitted diseases worldwide. To cure infection and prevent transmission, timely and appropriate antimicrobial therapy is necessary. Unfortunately, Neisseria gonorrhoeae, the etiological agent of gonorrhea, has acquired nearly all known mechanisms of antimicrobial resistance (AMR), thereby compromising the efficacy of antimicrobial therapy. Treatment failure resulting from AMR has become a global public health concern. Whole-genome sequencing is an effective method to determine the AMR characteristics of N. gonorrhoeae. Compared with next-generation sequencing, the MinION sequencer (Oxford Nanopore Technologies (ONT)) has the advantages of long read length and portability. Based on a pilot study using MinION to sequence the genome of N. gonorrhoeae, we optimized the workflow of sequencing and data analysis in the current study. Here we sequenced nine isolates within one flow cell using a multiplexed sequencing strategy. After hybrid assembly with Illumina reads, nine integral circular chromosomes were obtained. By using the online tool Pathogenwatch and a BLAST-based workflow, we acquired complete AMR profiles related to seven classes of antibiotics. We also evaluated the performance of ONT-only assemblies. Most AMR determinants identified by ONT-only assemblies were the same as those identified by hybrid assemblies. Moreover, one of the nine assemblies indicated a potentially novel antimicrobial-related mutation located in mtrR which results in a frame-shift, premature stop codon, and truncated peptide. In addition, this is the first study using the MinION sequencer to obtain complete genome sequences of N. gonorrhoeae strains which are epidemic in China. This study shows that complete genome sequences and antimicrobial characteristics of N. gonorrhoeae can be obtained using the MinION sequencer in a simple and cost-effective manner, with hardly any knowledge of bioinformatics required. More importantly, this strategy provides us with a potential approach to discover new AMR determinants.

Background Population movement could extend multidrug-resistant tuberculosis (MDR-TB) transmission and complicate its global prevalence. We sought to identify the high-risk populations and geographic sites of MDR-TB transmission in Shenzhen, the most common destination for internal migrants in China. Methods We performed a population-based, retrospective study in patients diagnosed with MDR-TB in Shenzhen during 2013–2017. By defining genomic clusters with a threshold of 12–single-nucleotide polymorphism distance based on whole-genome sequencing of their clinical strains, the clustering rate was calculated to evaluate the level of recent transmission. Risk factors were identified by multivariable logistic regression. To further delineate the epidemiological links, we invited the genomic-clustered patients to an in-depth social network investigation. Results In total, 105 (25.2%) of the 417 enrolled patients with MDR-TB were grouped into 40 genome clusters, suggesting recent transmission of MDR strains. The adjusted risk for student to have a clustered strain was 4.05 (95% confidence interval, 1.06–17.0) times greater than other patients. The majority (70%, 28/40) of the genomic clusters involved patients who lived in different districts, with residences separated by an average of 8.76 kilometers. Other than household members, confirmed epidemiological links were also identified among classmates and workplace colleagues. Conclusions These findings demonstrate that local transmission of MDR-TB is a serious problem in Shenzhen. While most transmission occurred between people who lived distant from each other, there was clear evidence that transmission occurred in schools and workplaces, which should be included as targeted sites for active case finding. The average residential distance between genomic-clustered cases was more than 8 kilometers, while schools and workplaces, identified as sites of transmission in this study, deserve increased vigilance for targeted case finding of multidrug-resistant tuberculosis.

Saccharides are important constituents in atmospheric aerosols but studies in northwestern China are still very limited. Here, we have measured anhydrosugars (levoglucosan, mannosan and galactosan), primary sugars (glucose, fructose, sucrose and trehalose), and sugar alcohols (arabitol, mannitol, sorbitol and inositol) in ambient PM2.5 samples during summer and winter in Xi'an city, northwestern China. The abundance of total saccharides showed no clear seasonal variation, but apparent distinctions on the levels of the three categories and individual saccharide compounds were found. Primary sugars and particularly sucrose were dominant in summer. In contrast, levoglucosan was the predominant species in winter, contributing 60% of total saccharides. Source apportionment by positive matrix factorization revealed that airborne pollen was a major source of PM2.5 associated-saccharides in summer, accounting for 35% of total saccharides; while biomass burning activities contributed to 60% of the winter saccharides. Furthermore, an increasing trend of biomass/biofuel burning contribution to winter PM2.5 was observed in comparison with previous studies in Xi'an, suggesting a change in emission sources may be underway in northwestern China.

The growing antimicrobial resistance (AMR) in Neisseria gonorrhoeae is a serious global threat to gonococcal therapy. Molecular typing is an ideal tool to reveal the association between specific genotype and resistance phenotype that provides effective data for tracking the transmission of resistant clones of N. gonorrhoeae In our study, we aimed to describe the molecular epidemiology of AMR and the distribution of resistance-associated genotypes in Shenzhen during 2014-2018. In total, 909 isolates were collected from Shenzhen from 2014-2018. Two typing schemes, multilocus sequence typing (MLST) and N. gonorrhoeae Sequence Typing for Antimicrobial Resistance (NG-STAR), were performed for all isolates. The distribution of resistance-associated genotypes was described using goeBURST analysis combined with data of logistic regression. Among 909 isolates, ST8123, ST7363, ST1901, ST7365, and ST7360 were most the common MLST sequence types (STs), and ST348, ST2473, ST497, and ST199 were the most prevalent NG-STAR STs. The logistic regression analysis showed that NG-STARST497, MLSTST7365, and MLSTST7360 were typically associated with decreased susceptibility to ceftriaxone. Furthermore, the internationally spreading ESC-resistant clone MLSTST1901 has been prevalent at least in 2014 in Shenzhen and showed a significant increase during 2014-2018. Additionally, MLSTST7363 owns the potential to become the next internationally spreading ceftriaxone-resistant ST. In conclusions, we performed a comprehensive epidemiological study to explore the correlation between AMR and specific STs, which provided important data for future studies of the molecular epidemiology of AMR in N. gonorrhoeae Besides, these findings provide insight for adjusting surveillance strategies and therapy management in Shenzhen.

Solid fuel is a the most dominant energy source for household usages in developing countries. In this study, emission characteristics on organic carbon (OC), elemental carbon (EC) and fifty-two polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate phases from seven fuel-stove combinations were studied in a typical rural village in northwest China. For the PAHs, the highest gaseous and particulate phase emission factors (EFs) were both observed for bituminous coal with one-stage stoves, ranging from 459 ± 154 to 1.09 ± 0.36 × 10

The growing antimicrobial resistance (AMR) in Neisseria gonorrhoeae is a serious global threat to gonococcal therapy. Molecular typing is an ideal tool to reveal the association between specific genotypes and resistance phenotypes that provide effective data for tracking the transmission of resistant clones of N. gonorrhoeae. In our study, we aimed to describe the molecular epidemiology of AMR and the distribution of resistance-associated genotypes in Shenzhen, China, during 2014 to 2018. In total, 909 isolates were collected from Shenzhen from 2014 to 2018. Two typing schemes, multilocus sequence typing (MLST) and N. gonorrhoeae sequence typing for antimicrobial resistance (NG-STAR), were performed for all isolates. The distribution of resistance-associated genotypes was described using goeBURST analysis combined with logistic regression data. Among 909 isolates, sequence type 8123 (ST(8123)), ST(7363), ST(1901), ST(7365), and ST(7360) were the most common MLST sequence types, and ST(348), ST(2473), ST(497), and ST(199) were the most prevalent NG-STAR STs. Logistic regression analysis showed that NG-STAR(ST497), MLST(ST7365), and MLST(ST7360) were typically associated with decreased susceptibility to ceftriaxone. Furthermore, the internationally spreading extended-spectrum cephalosporin (ESC)-resistant clone MLST(ST1901) has been prevalent since at least 2014 in Shenzhen and showed a significant increase during 2014 to 2018. Additionally, MLST(ST7363) owns the potential to become the next internationally spreading ceftriaxone-resistant ST. In conclusion, we performed a comprehensive epidemiological study to explore the correlation between AMR and specific STs, which provided important data for future studies of the molecular epidemiology of AMR in N. gonorrhoeae. Besides, these findings provide insight for adjusting surveillance strategies and therapy management in Shenzhen.

Antimicrobial resistance in Neisseria gonorrhoeae persists as a major public health concern globally. We developed and evaluated a multiplex assay that relied on high-resolution melting (HRM) technology as a rapid, simple, and cost-effective method for simultaneously detecting and identifying different molecular markers associated with extended-spectrum cephalosporins (ESCs) and azithromycin (AZM) resistance in N. gonorrhoeae. Forty-eight well-characterized N. gonorrhoeae clinical isolates were selected for initial assay establishment. The multiplex HRM assays were able to accurately identify different nucleotide variations of the antimicrobial resistance determinants related to ESCs and AZM resistance. Specificity and cross-reactivity were assessed by testing 15 nongonococcal strains. Then, the assay was validated on 218 archived DNA specimens that had been sequenced using whole-genome sequencing technology. Compared with whole-genome sequencing, these assays had a sensitivity of 98.6%, with a specificity of 99.2%. For further validation of the assay's performance, a total of 338 samples (156 clinical isolates and 182 clinical specimens) were screened using the multiplex HRM assay. The results showed good concordance with the results of PCR sequencing. Given its rapidity (within 90 minutes), ease of performing, and low cost ($1.00 per sample), this method may be applied to large-scale epidemiologic programs for increasing surveillance of ESCs and AZM resistance in N. gonorrhoeae.

Ozone (O3) pollution has become an increasing concern in China since elevated surface O3 concentrations were observed in recent years. In this study, five provincial cities (Beijing, Shanghai, Guangzhou, Xi&rsquo, an, and Hefei) located in different regions of China were selected to study the spatiotemporal variations and affecting factors of O3 concentrations during 2014&ndash, 2015. Beijing, Shanghai, and Guangzhou had suffered more severe O3 pollution, yet Beijing had the highest number of days that exceeded the Chinese MDA8 (maximum daily 8 h average) standard of 160 &micro, g m&minus, 3. MDA8 O3 exhibited different seasonal patterns among the five cities. In Beijing and Xi&rsquo, an, MDA8 O3 showed the highest in summer and lowest in winter. Guangzhou also had the highest O3 concentration in summer, but had similar levels in other three seasons. The O3 levels were similarly high in Shanghai during spring, summer, and autumn, while in Hefei, O3 concentration peaked in autumn. No significant difference between weekend and weekday O3 levels was observed in all the five cities. The diurnal cycle reached a maximum in the afternoon and a minimum in the early morning, which was consistent in the five cities. Correlation analyses showed that the associations between O3 and the other five criteria air pollutants, as well as meteorological parameters, were substantially different among the five cities. Air mass cluster analyses during episodic days revealed that the short-distance transport of O3 and its precursors had a greater impact for high O3 pollution in the five cities. Overall, our results demonstrate that O3 pollution exhibited great divergence among different regions and thus region-oriented control measures are suggested to reduce O3 pollution in China.

Isoprene is a crucial precursor of secondary organic aerosols (SOAs) that reacts with radicals or oxidants such as OH, O3, and NO3. The reaction mechanisms under various conditions have been elucidated through years of research. In this study, the UV–vis light absorptive ability of oxydates for isoprene was calculated at the PBE1PBE/6-311g (d) level using Gaussian 09. The results indicated that reactions of isoprene with OH and O3 would produce less absorptive organics; the intensity of the absorption peaks and the maximum absorption wavelength decreased relative to those of the precursor. The oxydates formed from isoprene through an NO3-initiated reaction had different light absorption properties. The optical properties of the oxydates exhibited a bathochromic shift and hyperchromic effect relative to those of the precursor. NO3 mainly originated from vehicular traffic, indicating that anthropogenic activity heavily affected the formation of oxydates and light absorption. The light absorption properties and irradiation effect of SOAs caused by isoprene heavily depended on the reaction route. Transformation of functional groups was the dominated factor in photobleaching and photoenhancement of oxidative products. This study provides a detailed mechanism that explains the changes in optical absorption properties during isoprene oxidation.

The emission factors (EFs) of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were measured from commonly used stoves and fuels in the rural Guanzhong Plain, China. The toxicity of the PM2.5 also was measured using in vitro cellular tests. EFs of PAHs varied from 0.18 mg kg−1 (maize straw charcoal burning in a clean stove) to 83.3 mg kg−1 (maize straw burning in Heated Kang). The two largest influencing factors on PAH EFs were air supply and volatile matter proportion in fuel. Improvements in these two factors could decrease not only EFs of PAHs but also the proportion of 3-ring to 5-ring PAHs. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability but an increase in reactive oxygen species (ROS), tumor necrosis factor a (TNF-α) and interleukin 6 (IL-6). PM2.5 emitted from maize burning in Heated Kang showed the highest cytotoxicity, and EFs of ROS and inflammatory factors were the highest as well. In comparison, maize straw charcoal burning in a clean stove showed the lowest cytotoxicity, which indicated a clean stove and fuel treatment were both efficient methods for reducing cytotoxicity of primary PM2.5. The production of these bioreactive factors were highly correlated with 3-ring and 4-ring PAHs. Specifically, pyrene, anthracene and benzo(a)anthracene had the highest correlations with ROS production (R = 0.85, 0.81 and 0.80, respectively). This study shows that all tested stoves emitted PM2.5 that was cytotoxic to human cells; thus, there may be no safe levels of exposure to PM2.5 emissions from cooking and heating stoves using solid fuels. The study may also provide a new approach for evaluating the cytotoxicity of primary emitted PM2.5 from solid fuel burning as well as other PM2.5 sources.

Real-time particulate matter (PM) size distributions, 4-hour time resolution, PM2.5, carbonaceous materials, and their optical properties were measured during a severe pollution event in Xi’an, China. High PM2.5/PM10 ratios were observed on both pollution (0.83) and non-pollution (0.73) days, emphasizing the abundance of fine particles during sampling days. The particle number (PN) first peaked with a wide size range (30–100 nm) before morning rush hours (approximately 01:00–05:00) on pollution and non-pollution days, demonstrating that PN was governed by the accumulation of freshly emitted diesel particles and characterized by distinct aerosol condensation growth. By contrast, the second peak time and size range differed between pollution and non-pollution days because of different formation mechanisms. The light-absorbing coefficients of both black carbon (BC, babs-880nm, BC) and brown carbon (BrC, babs-370nm, BrC) were high on pollution days and decreased to approximately half of those values on non-pollution days, indicating that the degree of light absorption is reduced by rain. The diurnal variation in babs-880nm, BC pollution peaked with traffic on January 1 and 2. By contrast, it remained in relatively stable and high ranges (120–160 Mm–1) in the second period (January 3–5) without traffic peaks, illustrating that the dominant sources changed even during the same pollution period. High values of both babs-370nm, BrC and babs-880nm, BC coincided in the afternoon and evening due to emissions from primary sources, and abundant aqueous secondary organic carbon, respectively. A highly variable mass absorption coefficient of BrC also indicated the variety of fuel combustion sources of primary BrC in Xi’an.

Solid fuel is a the most dominant energy source for household usages in developing countries. In this study, emission characteristics on organic carbon (OC), elemental carbon (EC) and fifty-two polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate phases from seven fuel-stove combinations were studied in a typical rural village in northwest China. For the PAHs, the highest gaseous and particulate phase emission factors (EFs) were both observed for bituminous coal with one-stage stoves, ranging from 459 ± 154 to 1.09 ± 0.36 × 103 mg kg−1. In contrast, the PAHs EFs for the clean briquette coal with two-stage stoves were two orders of magnitude lower than those of the bituminous coals. For parent PAHs (pPAHs) and total quantified PAHs (∑PAHs), they mainly contributed in gaseous phases with compositions of 69–79% and 64–70%, respectively. The gas-to-particle partitioning was mostly governed by the absorption. Moreover, the correlation coefficient (r) between EC and ∑PAHs, OC and parent PAHs (pPAHs), OC and nitro PAHs (nPAHs) were 0.81, 0.67 and 0.85, respectively, supporting that the PAHs species were potential precursors to the EC formation during the solid fuel combustion. The correlation analyses in this study further deduced that the formations of pPAHs and nPAHs were more closely related to that of OC than alkylated PAHs (aPAHs) and oxygenated PAHs (oPAHs). Diagnostic ratios of selective PAHs were calculated and evaluated as well. Among those, the ratio of retene (RET)/[RET + chyrene (CHR)] was found to be an efficient tool to distinguish coal combustion and biomass burning. In general, it was found that the amounts of pollutant emissions from clean briquette coal combustion were definitely lower than those from bituminous coal and biomass combustions. It is thus necessary to introduce and recommend the use of cleaner briquette coal as energy source.

There is growing evidence suggesting the enhancement of brown carbon (BrC) in severe haze episodes. In this study, hourly measurements of BrC in PM

Humic-like substances (HULIS) in fine particulate matter (PM2.5) were investigated during May 2015 to January 2016 in an urban environment in Xi'an, China. UV-VIS spectrometer and Fourier transform infrared spectroscopy (FTIR) were used to investigate optical properties and chemical structures of HULIS. Annual mean concentrations of HULIS-C (the carbon content of HULIS) was 2.9 ± 2.1 μg m−3. On average, the contributions of HULIS-C to PM2.5, TC, and OC were 6.1%, 27.2%, and 34.5%, respectively. Seasonal average of HULIS-C concentration followed a decreasing order of winter, spring, summer, and autumn. The UV absorption intensity of PM2.5 HULIS showed the highest in winter and the lowest in summer. The chemical functional groups for PM2.5 HULIS were highlighted with the presence of aliphatic C H, hydroxy, carbonyl, carboxyl and aromatic rings structures. SUVA254 and SUVA280 values in autumn and winter exhibited more dispersive distribution than those in spring and summer, which indicated sources of HULIS in autumn and winter samples were relative complicated. The E2/E3 ratio showed a summer maximum and a winter minimum, indicating greater conjugation and aromaticity of HULIS in winter. In addition, strong correlations between HULIS-C with K+ and OC1 + OP2 in spring, autumn and especially winter implied the important source of biomass burning to PM2.5 HULIS. The C O stretching of COH, carbonyl groups (C O) and O H stretching of carboxylic acid were abundance both in winter and summer, implied that secondary organic aerosol (SOA) formation was found to be the dominant mechanism producing HULIS in Xi'an.

There is growing evidence suggesting the enhancement of brown carbon (BrC) in severe haze episodes. In this study, hourly measurements of BrC in PM2.5 were conducted in Xi'an, a typical city in northwestern China during winter and summer. The absorption coefficient for methanol exacts at 365 nm (babs365, methanol, which is typically used as a proxy of methanol-soluble BrC) in the winter sampling period was over 7 times than that in summer. The mass absorption cross-section for methanol extracts (MAC365, methanol, normalized by babs365, methanol to organic carbon, OC) in winter sampling period was nearly 1.5 times of that in the summer. During the winter haze days, the average babs365,methanol peaked at midnight and the lowest values in the morning, in contrast to high levels in afternoon and low levels at night in non haze days. Unlike the diurnal patterns in winter, summer babs365, methanol diurnal variation presented high midday and low afternoon levels in haze days. However, in non haze days, the pattern showed high morning levels and night low levels. Haze and non haze variations of chemical species levels, babs365, methanol, and MAC365, methanol during winter and summer sampling time showed that the effects of atmospheric aging were complex and could either enhance or reduce light absorption of BrC. Source apportionment based on positive matrix factorization receptor model and multiple linear regressions showed that primary emission was an important contributor to BrC emissions during the winter sampling period, whereas secondary formation played an important role in summer.

Day-night PM10-bound PAHs were studied at an urban site of Xi’an from 20 December 2006 to 28 October 2007. The annual mean concentration of nighttime PAHs (285.0 ng m−3) was higher than that in daytime (239.4 ng m−3). A significant difference of PAH concentrations between daytime and nighttime was found in autumn with a coefficient of divergence (CD) of 0.23 (significant level 0.2). However, no distinct difference was observed in other seasons (with CD values < 0.2), although the difference of PAHs partition capacity in PM10 between daytime and nighttime was significant in the four seasons. Remarkable seasonal variations were observed in the total PAH levels, with a highest mean concentration of 344.6 ng m−3 in winter and a lowest mean concentration of 177 ng m−3 in summer. Positive matrix factorization results revealed that residential emission for heating is the major contributor of the elevated PAH levels in winter, accounting for 49% of the total PAH levels. The coal combustion including industrial and residential usage, contributed over 40% of the PAH emissions in PM10 of Xi’an during the one-year sampling period. These results can provide guidance for taking measures in reducing PAHs levels in the air.

The emission factors (EFs) of polycyclic aromatic hydrocarbons (PAHs) in PM