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The impact of brown carbon aerosol (BrC) on the Earth's radiative forcing balance has been widely recognized but remains uncertain, mainly because the relationships among BrC sources, chromophores and optical properties of aerosol are poorly understood. In this work, the light absorption properties and chromophore composition of BrC were investigated for samples collected in Xi'an, northwestern China, from 2015 to 2016. Both absorption Ångström exponent (AAE) and mass absorption efficiency (MAE) show distinct seasonal differences, which could be attributed to the differences in sources and chromophore composition of BrC. Three groups of light-absorbing organics were found to be important BrC chromophores, including compounds that have multiple absorption peaks at wavelengths > 350 nm (12 polycyclic aromatic hydrocarbons and their derivatives) and compounds that have a single absorption peak at wavelengths < 350 nm (10 nitrophenols and nitrosalicylic acids and 3 methoxyphenols). These measured BrC chromophores show distinct seasonal differences and contribute on average about 1.1 % and 3.3 % of light absorption of methanol-soluble BrC at 365 nm in summer and winter, respectively, about 7 and 5 times higher than the corresponding carbon mass fractions in total organic carbon. The sources of BrC were resolved by positive matrix factorization (PMF) using these chromophores instead of commonly used non-light-absorbing organic markers as model inputs. Our results show that vehicular emissions and secondary formation are major sources of BrC (∼ 70 %) in spring, coal combustion and vehicular emissions are major sources (∼ 70 %) in fall, biomass burning and coal combustion become major sources (∼ 80 %) in winter, and secondary BrC dominates (∼ 60 %) in summer.

Sources of organic carbon (OC) and elemental carbon (EC) in Xi'an, China, are investigated based on 1-year radiocarbon and stable carbon isotope measurements. The radiocarbon results demonstrate that EC is dominated by fossil sources throughout the year, with a mean contribution of 83±5 % (7±2 µgm-3). The remaining 17±5 % (1.5±1 µgm-3) is attributed to biomass burning, with a higher contribution in the winter (∼24 %) compared to the summer (∼14 %). Stable carbon isotopes of EC (δ13CEC) are enriched in winter (-23.2±0.4 ‰) and depleted in summer (-25.9±0.5 ‰), indicating the influence of coal combustion in winter and liquid fossil fuel combustion in summer. By combining radiocarbon and stable carbon signatures, relative contributions from coal combustion and liquid fossil fuel combustion are estimated to be 45 % (median; 29 %–58 %, interquartile range) and 31 % (18 %–46 %) in winter, respectively, whereas in other seasons more than one half of EC is from liquid fossil combustion. In contrast with EC, the contribution of non-fossil sources to OC is much larger, with an annual average of 54±8 % (12±10 µgm-3). Clear seasonal variations are seen in OC concentrations both from fossil and non-fossil sources, with maxima in winter and minima in summer because of unfavorable meteorological conditions coupled with enhanced fossil and non-fossil activities in winter, mainly biomass burning and domestic coal burning. δ13COC exhibited similar values to δ13CEC, and showed strong correlations (r2=0.90) in summer and autumn, indicating similar source mixtures with EC. In spring, δ13COC is depleted (1.1 ‰–2.4 ‰) compared to δ13CEC, indicating the importance of secondary formation of OC (e.g., from volatile organic compound precursors) in addition to primary sources. Modeled mass concentrations and source contributions of primary OC are compared to the measured mass and source contributions. There is strong evidence that both secondary formation and photochemical loss processes influence the final OC concentrations.

Carbonaceous aerosol plays an important role in climate, but its sources and atmospheric processes are least understood in the Tibetan Plateau (TP), a remote yet climatically sensitive region. This study presents the first seasonal cycle of radiocarbon and stable isotope 13C of organic and elemental carbon (OC and EC) in the atmosphere of the northeastern TP. Large seasonal variations of EC and OC concentrations were explained by non‐fossil sources. Regardless of the season, fossil contribution to OC was strongly correlated with inverse OC concentrations. This allowed the separating a constant background source and a source responsible for OC variability that was mostly of non‐fossil origin. The 13C signature of OC shows that OC was highly atmospherically processed and thus less volatile than OC found near sources or in urban areas. The 13C‐depleted secondary sources contributed strongly to more volatile OC, whereas the 13C‐enriched less volatile OC suggests the influence of atmospheric aging. Plain Language Summary The climate effects of carbonaceous aerosols (CAs) are highly uncertain and debated. The high‐altitude Tibetan Plateau (TP) is sensitive to climate change, however, sources and atmospheric processes of CAs in the TP are poorly known. This is particularly challenging for organic aerosols, due to the large number of species involved in their formation and transformation processes in the atmosphere. In recent years, dual‐carbon isotope characterization (i.e., radiocarbon 14C and the stable carbon isotope 13C) has become a promising tool to elucidate the sources and formation processes of organic aerosols. With this approach, we found that organic aerosols in the northeastern TP (Qinghai Lake) are highly atmospheric processed, and their seasonal variability is driven by a variable largely non‐fossil source. Findings from this study lead to a better understanding of the sources and formation mechanisms of organic aerosols in different seasons, and thus organic aerosols' effects on climate change. Key Points High seasonality of elemental carbon (EC) and organic carbon (OC) concentrations in the northeastern Tibetan Plateau (TP) was driven by non‐fossil sources In the monsoon season, low EC and OC concentrations reflected local sources, with most evident contributions from fossil sources OC in the northeastern TP was highly atmospherically processed and thus less volatile compared to OC near sources or in urban areas

A thermal desorption aerosol gas chromatograph coupled to a high resolution – time of flight – aerosol mass spectrometer (TAG-AMS) was connected to an atmospheric chamber for the molecular characterization of the evolution of organic aerosol (OA) emitted by woodstove appliances for residential heating. Two log woodstoves (old and modern) and one pellet stove were operated under typical conditions. Emissions were aged during a time equivalent to 5 h of atmospheric aging. The five to seven samples were collected and analyzed with the TAG-AMS during each experiment. We detected and quantified over 70 compounds, including levoglucosan and nitrocatechols. We calculate the emission factor (EF) of these tracers in the primary emissions and highlight the influence of the combustion efficiency on these emissions. Smoldering combustion contributes to a higher EF and a more complex composition. We also demonstrate the effect of atmospheric aging on the chemical fingerprint. The tracers are sorted into three categories according to the evolution of their concentration: primary compounds, non-conventional primary compounds, and secondary compounds. For each, we provide a quantitative overview of their contribution to the OA mass at different times of the photo-oxidative process.

Carbon dioxide (CO2) and methane (CH4) are important greenhouse gases emitted by vehicles, yet their spatial pattern within urban road networks remains poorly characterized. This study conducts mobile measurements of CO2 and CH4 along the 1st Ring Road (mean speed of the monitoring vehicle: 22 km h−1), 2nd Ring Road (22 km h−1), and Ring Expressway (90 km h−1) in Xi’an, China, to investigate their spatial distribution and influencing factors. Average CO2 and CH4 concentrations on the three ring roads exhibited a clear decline with increasing distance from the city center. Both CO2 and CH4 showed higher concentrations at lower vehicle speeds and at higher traffic volumes, but CH4 hotspots differed spatially from CO2 and exhibited weaker dependence on vehicle speed, indicating additional off-road CH4 sources (e.g., natural gas leaks, nearby livestock farms). In a tunnel case study, CO2, CH4, and CO concentrations increased concurrently from entrance to exit, resulting in strong correlations between CH4 and CO2 (R2 = 0.86) and between CO and CO2 (R2 = 0.66). This produced emission ratios (ΔCH4/ΔCO2 = 0.160 ppb ppm−1; ΔCO/ΔCO2 = 3.151 ppb ppm−1), representative of incomplete combustion under congestion. Our results provide direct observational evidence linking urban traffic dynamics to greenhouse gas emissions and emphasize the need for congestion mitigation to reduce on-road climate-relevant emissions.

To investigate the sources and formation mechanisms of carbonaceous aerosols, a major contributor to severe particulate air pollution, radiocarbon (14C) measurements were conducted on aerosols sampled from November 2015 to November 2016 in Xi'an, China. Based on the 14C content in elemental carbon (EC), organic carbon (OC) and water-insoluble OC (WIOC), contributions of major sources to carbonaceous aerosols are estimated over a whole seasonal cycle: primary and secondary fossil sources, primary biomass burning, and other non-fossil carbon formed mainly from secondary processes. Primary fossil sources of EC were further sub-divided into coal and liquid fossil fuel combustion by complementing 14C data with stable carbon isotopic signatures. The dominant EC source was liquid fossil fuel combustion (i.e., vehicle emissions), accounting for 64 % (median; 45 %–74 %, interquartile range) of EC in autumn, 60 % (41 %–72 %) in summer, 53 % (33 %–69 %) in spring and 46 % (29 %–59 %) in winter. An increased contribution from biomass burning to EC was observed in winter (∼28 %) compared to other seasons (warm period; ∼15 %). In winter, coal combustion (∼25 %) and biomass burning equally contributed to EC, whereas in the warm period, coal combustion accounted for a larger fraction of EC than biomass burning. The relative contribution of fossil sources to OC was consistently lower than that to EC, with an annual average of 47±4 %. Non-fossil OC of secondary origin was an important contributor to total OC (35±4 %) and accounted for more than half of non-fossil OC (67±6 %) throughout the year. Secondary fossil OC (SOCfossil) concentrations were higher than primary fossil OC (POCfossil) concentrations in winter but lower than POCfossil in the warm period. Fossil WIOC and water-soluble OC (WSOC) have been widely used as proxies for POCfossil and SOCfossil, respectively. This assumption was evaluated by (1) comparing their mass concentrations with POCfossil and SOCfossil and (2) comparing ratios of fossil WIOC to fossil EC to typical primary OC-to-EC ratios from fossil sources including both coal combustion and vehicle emissions. The results suggest that fossil WIOC and fossil WSOC are probably a better approximation for primary and secondary fossil OC, respectively, than POCfossil and SOCfossil estimated using the EC tracer method.

A Gram-stain-negative, orange-colored bacterium, designated HX-22-17T, was isolated from activated sludge of an agricultural chemical plant in Maanshan, Anhui province, China (118° 52′ E 31° 68′ N). The strain was strictly aerobic, non-endospore forming, non-motile, and ellipse. Growth of the strain was observed at 16–42 °C (optimum between 25 and 30 °C) at pH 6.0–9.0 (optimum at pH 7.0) and with 0–6.0% (w/v) NaCl (optimum at 1.0%). 16S rRNA gene sequence analysis showed that the strain was most closely related to Rudanella lutea KACC 12603T (99.5% similarity). The predominant cellular fatty acids were summed feature 3 (C16:1ω7c and/or C16:1ω6c), iso-C15:0, and anteiso-C15:0. The major polar lipids included posphatidylethanolamine (PE), aminolipid (AL), and phospholipids (PL). The genomic DNA G+C content of the strain was 54.1 mol%. The ANI and dDDH values obtained between the genomes of HX-22-17T and R. lutea KACC 12603T were 89.3% and 39.3%, respectively. The phenotypic, chemotaxonomic, and genotypic data clearly showed that strain HX-22-17T represents a novel species of the genus Rudanella, for which the name R. paleaurantiibacter sp. nov. is proposed. The type strain is HX-22-17T (=KCTC 72656T = CCTCC AB 2019347T).

Many countries around the world feature raw fish in their cuisine, which is valued for its unique flavor. However, raw fish may be easily contaminated with foodborne pathogens including Listeria monocytogenes, Salmonella, Vibrio parahaemolyticus, and Staphylococcus aureus. Herein, a method was established that integrated a multiplex polymerase chain reaction (PCR) and high-resolution melting (HRM) curve assay for the simultaneous detection of these four foodborne pathogens. The target genes of the bacteria were amplified by PCR and subsequently analyzed using HRM. Differentiation was achieved based on the melting temperature (Tm) values of their respective amplicons. The detection limit of the PCR-HRM assay was 0.02–0.1 ng/µL. In addition, the Tm remained nearly constant across various concentrations of genomic DNA derived from the target bacteria. The assay demonstrated perfect specificity (8/8) and a sensitivity of 5/5 for L. monocytogenes, 2/2 for Salmonella, 3/3 for V. parahaemolyticus, and 3/3 for S. aureus. No significant interference occurred when genomic DNA from the four target bacteria was co-extracted with DNA from eight non-target strains. Furthermore, the assay offers advantages including operational simplicity, high efficiency, accurate results, reduced detection time, and lower costs, rendering it well-suited for food safety applications in the aquatic products processing industry.

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).

The relationship between the refractory black carbon (rBC) aerosol mixing state and the atmospheric oxidation capacity was investigated to assess the possible influence of oxidants on the particles' light absorption effects at two large cities in China. The number fraction of thickly-coated rBC particles (FrBC) was positively correlated with a measure of the oxidant concentrations (OX = O3 + NO2), indicating an enhancement of coated rBC particles under more oxidizing conditions. The slope of a linear regression of FrBC versus OX was 0.58% ppb−1 for Beijing and 0.84% ppb−1 for Xi'an, and these relationships provide some insights into the evolution of rBC mixing state in relation to atmospheric oxidation processes. The mass absorption cross-section of rBC (MACrBC) increased with OX during the daytime at Xi'an, at a rate of 0.26 m2 g−1 ppb−1, suggesting that more oxidizing conditions lead to internal mixing that enhances the light-absorbing capacity of rBC particles. Understanding the dependence of the increasing rates of FrBC and MACrBC as a function of OX may lead to improvements of climate models that deal with the warming effects, but more studies in different cities and seasons are needed to gauge the broader implications of these findings.