Identification and seasonal variation of specific particulate bound (halogenated) polycyclic aromatic hydrocarbons in air from different metal industrial parks in Northwest China.

During the process of industrial heating, a large amount of polycyclic aromatic hydrocarbons (PAHs) and their halogenated compounds (Cl/Br-PAHs) can be formed. However, there is still limited understanding of the chemicals from different metal smelting industrial parks. This study evaluated the seasonal variations, composition profiles, and source allocations of the atmospheric particulate-bound PAHs and Cl/Br-PAHs in different metal industrial parks in a typical industrial city in northwest China. The results showed that the main PAHs produced by metal smelting were low molecular weight isomers, and the concentrations of Cl-PAHs were lower compared to Br-PAHs. The main Br-PAHs were 1-Br-Pyr and 4-Br-Pyr, while 9-Cl-Fle, 1-Cl-Pyr, and 6-Cl-BaP were the dominated Cl-PAH isomers. No significant difference was found in the concentrations among the sites, whereas the levels of the target chemicals were higher during cold months compared to warm months. The main source of PAHs was coal combustion and gasoline vehicle emission during metal smelting, and that of Cl/Br-PAHs was also industrial coal burning. In addition to the primary source, the secondary chlorination of parent PAHs was also a significant source of Cl-PAHs in the production of high purity aluminum. This study suggests that Cl-PAHs and Br-PAHs may behave differently in the atmosphere.

Highly efficient removal of Se(IV) using reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO): selenium removal mechanism.

Se(IV) removal using nanoscale zero-valent iron (nZVI) has been extensively studied. Still, the synergistic removal of Se(IV) by reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) has not been reported. In this study, nZVI/rGO was successfully synthesized for Se(IV) removal from wastewater. The effects of different environmental conditions (load ratio, dosage, initial pH) on Se(IV) removal by nZVI/rGO were investigated. When the load ratio is 10%, the dosage is 0.3 g/L, the initial pH is 3, and the removal rate is 99%. The adsorption isotherm and kinetics accorded with the Langmuir isotherm and first-order kinetics models (R2 > 0.99). The fitted maximum adsorption capacity reached up to 173.53 mg/g. NZVI/rGo and Se(IV) is a spontaneous endothermic reaction (△G < 0, △H > 0) and is characterized by EDS, XRD, and XPS before and after the reaction, to further clarify the reaction mechanism. The XPS narrow spectrum analysis suggested that Se(IV) was reduced to elemental selenium (Se(0)), while the intermediate Fe(II) was oxidized to form hydroxide precipitation. Therefore, nZVI/rGO was favored for Se-contaminated wastewater remediation.

Effects of chemical boundary conditions on simulated O3 concentrations in China and their chemical mechanisms.

Chemical boundary conditions (BCs) are important inputs for regional chemical transport models. In this study, we use the brute-force method (BFM), process analysis (PA) and response surface model (RSM) to quantify the effects of BCs on simulated O3 concentrations in different regions of China by the weather research and forecasting with chemistry (WRF-Chem) model. We combine the model with an integrated gas-phase reaction rate (IRR) tool to further analyze the changes in the O3 chemical mechanisms. Our results show that the simulated O3 concentrations in western cities are significantly affected by the O3 in the BCs (BC-O3), which can increase the maximum simulated O3 concentration, such as in Lanzhou (36.6 µg/m3, 26.3 %), Wuhai (30.1 µg/m3, 25.5 %) and Urumqi (50.7 µg/m3, 41.2 %). In contrast, O3 generation in the eastern region is dominated by emissions. Subsequently, we compare the reaction rate changes in O3 generation and consumption under the effects of BC-O3 in the western city of Urumqi and the eastern city of Beijing. The results show that in Beijing, the O3 concentration and the related chemical reaction rates undergo little change, while in Urumqi, the concentration and reaction rates have significant differences. The BC-O3 significantly accelerates the O3 photochemical reaction process in Urumqi, resulting in increased O3 generation and consumption reaction rates; additionally, there may be a chemical reaction pathway for the formation of O3: BC-O3 + NO → NO2 + hv → O + O2 → O3. BC-O3 transmission is the main pathway of changes in the simulated O3 concentration in the study area, and the chemical reactions between BC-O3 and local pollutants are primarily characterized by O3 consumption. In conclusion, the study shows the importance of BCs for regional model simulation while providing supporting information for O3 formation in model studies.

[Sensitivity Analysis of Ozone Formation Using Response Surface Methodology].

Identifying the nonlinear relationship between O3 and its precursors accurately plays an important role for the policy-making of O3 pollution control. In this study, the response surface methodology based on the box model simulation was used to quickly and efficiently quantify the O3 response to their precursors with the optimal experimental design. The results showed that CO had a positive contribution to ozone generation, whereas NOx and VOCs had a significant nonlinear relationship with O3. When the ratio of φ(VOCs) to[φ(NOx)-13.75] was greater than 4.17, the ozone formation regime was NOx-limited and became VOCs-limited when the ratio was less than 4.17. Olefin was the key VOCs' component to affect the formation of O3; when the radio of φ(olefin) to[φ(NOx)-15] was less than 1.10 and the value of the φ(olefin) was less than 35×10-9, olefin went far towards generating O3. Response surface methodology demonstrated that it can be well used to explore the influence of multiple factors and their interactions on O3 formation and provides a new approach for efficient O3 sensitivity analysis.

Updating and evaluating the NH3 gas-phase chemical mechanism of MOZART-4 in the WRF-Chem model.

The accuracy of determining atmospheric chemical mechanisms is a key factor in air pollution prediction, pollution-cause analysis and the development of control schemes based on air quality model simulations. However, the reaction of NH3 and OH to generate NH2 and its subsequent reactions are often ignored in the MOZART-4 chemical mechanism. To solve this problem, the gas-phase chemical mechanism of NH3 was updated in this study. Response surface methodology (RSM), integrated gas-phase reaction rate (IRR) diagnosis and process analysis (PA) were used to quantify the influence of the updated NH3 chemical mechanism on the O3 simulated concentration, the nonlinear response relationship of O3 and its precursors, the chemical reaction rate of O3 generation and the meteorological transport process. The results show that the updated NH3 chemical mechanism can reduce the error between the simulated and observed O3 concentrations and better simulate the O3 concentration. Compared with the Base scenario (original chemical mechanism simulated), the first-order term of NH3 in the Updated scenario (updated NH3 chemical mechanism simulated) in RSM passed the significance test (p < 0.05), indicating that NH3 emissions have an influence on the O3 simulation, and the effects of the updated NH3 chemical mechanism on NOx-VOC-O3 in different cities are different. In addition, the analysis of chemical reaction rate changes showed that NH3 can affect the generation of O3 by affecting the NOx concentration and NOx circulation with radicals of OH and HO2 in the Updated scenario, and the change of pollutant concentration in the atmosphere leads to the change of meteorological transmission, eventually leading to the reduction of O3 concentration in Beijing. In conclusion, this study highlights the importance of atmospheric chemistry for air quality models to model atmospheric pollutants and should attract more research focus.

Insight into SO4(-II)- dependent anaerobic methane oxidation in landfill: Dual-substrates dynamics model, microbial community, function and metabolic pathway.

In anaerobic landfill, SO42- could serve as electron receptor for methane oxidation. In theory, concentrations of both methane and SO42- should be related to methane oxidation rate. However, the dynamics process has yet to be discovered, and the understanding of metabolic pathways of the sulfate-dependent anaerobic methane oxidation (S-DAMO) process in landfill remains limited. In this study, S-DAMO dynamics was investigated by observing the CH4 oxidation rates under different CH4/ SO42-counter-gradients. The CH4-SO42- dual-substrate model based on MichaeliseMenten equation was got (maximum substrate degradation rate Vmax [22.9 ± 1.31] µmol/[kg·d], half-saturation constants [Formula: see text] , and [Formula: see text] ). High-throughput sequencing analysis indicated Methanobacterials, Methanosarcinales, and Soil Crenarchaeotic were the main functional microorganisms for S-DAMO in landfill. The metabolic pathway of S-DAMO was speculated as the reverse methanogenesis pathway through Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUST) analysis, while methanogenesis was the methyl nutrition way based on methanol. The enzymes related to the carbon and sulfur cycles and their relative abundances in the microcosms were analyzed to graph the methane metabolic pathway and the sulfur metabolic pathway. The findings provide important parameters for CH4 mitigation in landfills, and give a new insight for understanding S-DAMO metabolic pathway in landfill.

Graphene oxide supported sulfidated nano zero-valent iron (S-nZVI@GO) for antimony removal: The role of active oxygen species and reaction mechanism.

Sulfidated nano zero-valent iron (S-nZVI) was used to remove various pollutants from wastewater. However, the instability, poor dispersibility, and low electron transfer efficiency of S-nZVI limit its application. Herein, graphene oxide supported sulfidated nano zero-valent iron (S-nZVI@GO) was successfully synthesized using graphene oxide (GO) as a carrier. The properties of S-nZVI@GO were characterized by scanning electron microscopy coupled to X-ray photoelectron spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) concerning the surface morphology, crystalline structure, and elemental components. S-nZVI@GO displayed an excellent capacity for antimony (Sb) removal under aerobic conditions (96.7%), with a high adsorption capacity (Qmax = 311.75 mg/g). It maintained a high removal rate (over 90%) during a wide pH range (3-9). More importantly, S-nZVI@GO activated the molecular oxygen in water via a single-electron pathway to produce •O2－ and H2O2, and then oxidized trivalent antimony (Sb(III)) to pentavalent antimony (Sb(V)) and further separated it by synergistic adsorption and co-precipitation. Therefore, S-nZVI@GO shows excellent potential for Sb contamination remediation.

Chemical reactivity of volatile organic compounds and their effects on ozone formation in a petrochemical industrial area of Lanzhou, Western China.

Measurements of ozone (O3) and its precursors were performed in the summer of 2019 in Lanzhou, a petrochemical industrial city, to better understand the reactivity of volatile organic compounds (VOCs) and their effects on O3 production. During the campaign, the daily maximum 8-hour average (MDA8) O3, NO2, and total VOC (TVOC) concentrations reached 72.2 ± 19.9 ppb, 24.9 ± 10.8 ppb, and 50.8 ± 46.1 ppb, respectively. Alkanes, alkenes, halocarbons, aromatics, and alkynes contributed 45.3%, 24.0%, 16.5%, 10.0%, and 4.2% to TVOCs, respectively. The OH reactivity and relative incremental reactivity (RIR) of VOCs at different times were calculated. The results indicated that alkenes played a predominant role, accounting for an average of 68.5% of the initial VOC reactivity. Compared to other regions, alkenes are relatively more important for O3 formation in the petrochemical industry area of Lanzhou, while aromatics are relatively less important. Generally, O3 formation occurred in a VOC-limited regime in the morning and in a transitional regime in the afternoon. The response surface methodology (RSM) combined with a chemical box model was applied to obtain relationships between O3 and its precursors and determine the most effective way to reduce the O3 concentration. Reduction in the non-alkene concentration slightly affected the O3 concentration. In contrast, the effect of nitrogen oxides (NOx) was closely related to the alkene concentration, and NOx concentration reduction could lead to an increase in the O3 concentration when alkenes were abated to less than 80% of the present concentration. To mitigate O3 pollution near the petrochemical industrial area of Lanzhou, reducing the alkene concentration, especially the C4 alkene concentration (1,3-butadiene, cis-2-butene, and trans-2-butene), was the fastest and most effective control strategy. The results of this study serve as a reference for O3 pollution control in petrochemical industrial areas.

Unraveling bacterial community structure and function and their links with natural salinity gradient in the Yellow River Delta.

Salinization can change the soil environment and affect microbial processes. In this study, soil samples were collected from Zone A (Phragmites australis wetlands), Zone B (P. australis and Suaeda salsa wetlands), and Zone C (Spartina alterniflora wetlands) in the Yellow River Delta. The microbial community and functional potential along the natural salinity gradient were investigated. Total nitrogen, ammonia nitrogen, and soil organic matter presented a downward trend, and salinity first increased and then decreased from Zone A to Zone C. Nitrospira and norank_f_Nitrosomonadaceae were widely distributed throughout the zones. Denitrifying bacteria Alcanivorax, Marinobacterter, and Marinobacterium were abundant in Zone B and preferred high salinity levels. However, denitrifying bacteria Azoarcus, Flavobacterium, and Pseudomonas were mainly distributed in low-salinity Zones A and C, suggesting their high sensitivity to salinity. Dissimilatory nitrate reduction to ammonia (DNRA) bacteria Aeromonas and Geobacter dominated Zone C, whereas Caldithrix performed DNRA in Zone B. Interestingly, DNRA with organic matter as the electron donor (C-DNRA) occurred in Zone A; DNRA coupled with sulfide oxidation (S-DNRA) was dominant in Zone B; and C-DNRA and DNRA with divalent iron as electron donor and S-DNRA occurred simultaneously in Zone C. Salinity was the key factor distinguishing low and high salinity zones, and total nitrogen and total phosphorus had important effects at the phylum and genus levels. The abundance of genes encoding cell growth and death was relatively stable, indicating that the microbial community had good environmental adaptability. The genes related to the biodegradation of xenobiotics and the metabolism of terpenoids and polyketides were abundant in Zone B, revealing high metabolic potential for exogenous refractory substances. The microorganisms under low-salinity Zones A and C were more sensitive to environmental changes than those under Zone B. These results suggest that salinity plays important roles in microbial processes and shapes specific functional zones in coastal wetlands.

Independent Component Analysis using clustering on motor imagery EEG.

Motor imagery is a popular paradigm in electrophysiology research and brain computer interface but the evoked EEG signals always contaminated significantly. In this paper we use the Independent Component Analysis to enhance the signal-to-noise ratio of multi trail EEG signals evoked by imaginary hand movement. Infomax algorithm was used to decompose multi channel EEG signals into independent components trail by trail, and then an automatic clustering method was used to group these components into several clusters. For the higher similarity between task relevant components, they can be assembled into one cluster that occupies the highest mean mutual information of pairwise components intra cluster. Furthermore, the reconstructed signals of task relevant cluster showed a high discrepancy features to left versus right hand task, which evaluated by Fisher criterion scores and served as the signal-to-noise ratio measurement.