Dark Oxidation Research Articles

Effects of acid mine drainage on microbial community development and physicochemical properties of mine contaminated sites in Southwest China

Investigations of the microbial community structures, potential functions and physicochemical property are useful for risk assessments, microbial monitoring, and the biogeochemical behaviour of contained environment by Acid Mine Drainage (AMD). In this study, nine sediment sampling sites were selected at Panjiaozhuang Town, in Guizhou, China to analyze the pollution conditions and their influences on microorganisms. The physicochemical property results showed significant differences in sediment and water physico chemical properties at different group. Compared to the DS group, further studies revealed that US group (severely affected areas) showed strong acidity and high concentrations of heavy metals and salts. The community structure analysis indicated that AMD might enhance the functional bacteria, such as Thiomonas and Ferrovum (increases of 1.2 and 8.1 percent, respectively), and significantly increased the concentrations of Fe and sulfate through the oxidation of pyrite. The KEGG enrichment analysis demonstrated showed that the AMD promoted the migration of sulfur and Fe into water by enhancing bacterial metabolic pathways, such as dark oxidation of sulfur compounds and dark iron oxidation. This article is of great significance for understanding the transformation of pollutants by AMD and provides reference for subsequent bioremediation.

•OH Dominates the Dark Oxidation of Elemental Mercury at the Liquid–Ice Interface during Environmentally Relevant Freeze–Thaw Cycles

•OH Dominates the Dark Oxidation of Elemental Mercury at the Liquid–Ice Interface during Environmentally Relevant Freeze–Thaw Cycles

Pathways of Oxygen-Dependent Oxidation of the Plastoquinone Pool in the Dark After Illumination.

The redox state of the plastoquinone (PQ) pool in thylakoids plays an important role in the regulation of chloroplast metabolism. In the light, the PQ pool is mostly reduced, followed by oxidation after light cessation. It has been believed for a long time that dark oxidation depends on oxygen, although the precise mechanisms of the process are still unknown and debated. In this work, we analyzed PQ pool oxidation kinetics in isolated pea (Pisum sativum) thylakoids by tracking the changes in the area above the OJIP fluorescence curve (Afl) over time intervals from 0.1 s to 10 min in the dark following illumination. Afl served as an indirect measure of the redox state of the PQ pool that enabled quantification of the rate of PQ pool oxidation. The results showed a two-phase increase in Afl. The "fast" phase appeared to be linked to electron flow from the PQ pool to downstream acceptors of the photosynthetic electron transport chain. The "slow" phase involved oxidation of PQH2 through oxygen-dependent mechanisms. Adding octyl gallate, an inhibitor of plastid terminal oxidase (PTOX), to isolated thylakoid suspensions decreased the rate of the "slow" phase of PQ pool oxidation in the dark after illumination. The addition of either H2O2 or catalase, an enzyme that decomposes H2O2, revealed that H2O2 accelerates oxidation of the PQ pool. This indicates that under conditions that favor H2O2 accumulation, H2O2 can contribute substantially to PQ pool oxidation in the dark after illumination. The contribution of PTOX and H2O2 to the modulation of the PQ pool redox state in plants in the dark after illumination is discussed.

Comparative analysis of winter composite-PM2.5 in Central Indo Gangetic Plain cities: Combined organic and inorganic source apportionment and characterization, with a focus on the photochemical age effect on secondary organic aerosol formation

Comparative analysis of winter composite-PM2.5 in Central Indo Gangetic Plain cities: Combined organic and inorganic source apportionment and characterization, with a focus on the photochemical age effect on secondary organic aerosol formation

Improving HONO Simulations and Evaluating Its Impacts on Secondary Pollution in the Yangtze River Delta Region, China

Abstract Secondary air pollution, especially ozone (O3) and secondary aerosols, are emerging air quality challenges confronting China. Nitrous acid (HONO), as the predominant source of hydroxyl radicals (OH), are acknowledged to be essential for secondary pollution. However, HONO concentrations are usually underestimated by current air quality models due to the inadequate representations of its sources. In the present study, we revised the Weather Research and Forecasting & Chemistry (WRF‐Chem) model by incorporating additional HONO sources, including primary emissions, photo‐/dark oxidation of NOx, heterogeneous uptake of NO2 on surfaces, and nitrate photolysis. By combining in‐situ measurements in the Yangtze River Delta (YRD) region, we found the improved model show much better performance on HONO simulation and is capable of reproducing observed high concentrations. The source‐oriented method is employed to quantitatively understand the relative importance of various processes, which showed that heterogeneous NO2 uptake on the ground surface was the major contributor to HONO formation in urban areas. Comparatively, photo‐oxidation of NOx is a main contributor in rural areas. The introduction of multiple sources of HONO led to an apparent increase in OH and hydroperoxyl (HO2) radicals. The promoted HO2 levels further increased diurnal O3 concentration by 4.5–12.9 ppb, while secondary inorganic and organic concentrations were also increased by 14%–32% during a typical secondary pollution event. The improved description of HONO emission and formation in the model substantially narrowed the gaps between simulations and observations, highlighting the great importance in understanding and numerical representations of HONO in secondary pollution study.

Intertwining of the C-N-S cycle in passive and aerated constructed wetlands.

The microbial processes occurring in constructed wetlands (CWs) are difficult to understand owing to the complex interactions occurring between a variety of substrates, microorganisms, and plants under the given physicochemical conditions. This frequently leads to very large unexplained nitrogen losses in these systems. In continuation of our findings on Anammox contributions, our research on full-scale field CWs has suggested the significant involvement of the sulfur cycle in the conventional C-N cycle occurring in wetlands, which might closely explain the nitrogen losses in these systems. This paper explored the possibility of the sulfur-driven autotrophic denitrification (SDAD) pathway in different types of CWs, shallow and deep and passive and aerated systems, by analyzing the metagenomic bacterial communities present within these CWs. The results indicate a higher abundance of SDAD bacteria (Paracoccus and Arcobacter) in deep passive systems compared to shallow systems and presence of a large number of SDAD genera (Paracoccus, Thiobacillus, Beggiatoa, Sulfurimonas, Arcobacter, and Sulfuricurvum) in aerated CWs. The bacteria belonging to the functional category of dark oxidation of sulfur compounds were found to be enriched in deep and aerated CWs hinting at the possible role of the SDAD pathway in total nitrogen removal in these systems. As a case study, the percentage nitrogen removal through SDAD pathway was calculated to be 15-20% in aerated wetlands. The presence of autotrophic pathways for nitrogen removal can prove highly beneficial in terms of reducing sludge generation and hence reducing clogging, making aerated CWs a sustainable wastewater treatment solution.

Effects of copper on chemical kinetics and brown carbon formation in the aqueous ˙OH oxidation of phenolic compounds.

Many phenolic compounds (PhCs) in biomass burning and fossil fuel combustion emissions can partition into atmospheric aqueous phases (e.g., cloud/fog water and aqueous aerosols) and undergo reactions to form secondary organic aerosols (SOAs) and brown carbon (BrC). Redox-active transition metals, particularly Fe and Cu, are ubiquitous species in atmospheric aqueous phases known to participate in Fenton/Fenton-like chemistry as a source of aqueous ˙OH. However, even though the concentrations of water-soluble Cu are close to those of water-soluble Fe in atmospheric aqueous phases in some areas, unlike Fe, the effects that Cu have on SOA and BrC formation in atmospheric aqueous phases have scarcely been studied and remain poorly understood. We investigated the effects of Cu(II) on PhC reaction rates and BrC formation during the aqueous oxidation of four PhCs (guaiacol, catechol, syringol, and vanillin) by ˙OH generated from Fenton-like chemistry under different pH conditions. While the PhCs reacted when both H2O2 and Cu(II) were present in the absence (i.e., dark oxidation) and presence (i.e., photooxidation) of light, the reaction rates were at least one order of magnitude higher during photooxidation. Higher PhC reaction rates were measured at higher pH during both dark oxidation and photooxidation as a result of higher ˙OH concentrations produced by Fenton-like chemistry. Only water-soluble BrC was formed during dark oxidation and photooxidation when Cu(II) was present. Mass absorption coefficients (103 to 104 cm2 g-1) comparable to those of biomass burning BrC were measured during dark oxidation and photooxidation when Cu(II) was present. Light absorption was enhanced at higher pH during dark oxidation and photooxidation, which indicated that higher quantities and/or more absorbing BrC chromophores were formed at higher pH. The effects that Cu(II) had on the PhC reaction rates and the composition of SOAs and BrC formed depended on the PhC base structure (i.e., benzenediol vs. methoxyphenol). Overall, these results show how aqueous reactions involving Cu(II), H2O2, and PhCs can be an efficient source of daytime and nighttime water-soluble BrC and SOAs, which can have significant implications for how the atmospheric fates of PhCs are modeled for areas with substantial concentrations of water-soluble Cu in highly to moderately acidic cloud/fog water and aqueous aerosols.

Real-time chemical characterization of primary and aged biomass burning aerosols derived from sub-Saharan African biomass fuels in smoldering fires†

The influence of biomass burning (BB)-derived organic aerosol (OA) emissions on solar radiation via absorption and scattering is related to their physicochemical properties and can change upon atmospheric aging. We systematically examined the compositionally-resolved mass concentration and production of primary and secondary organic aerosol (POA and SOA, respectively) in the NC A&T University smog chamber facility. Mass spectral profiles of OA measured by the Aerosol Chemical Speciation Monitor (ACSM) revealed the influence of dark- and photo-aging, fuel type, and relative humidity. Unit mass resolution (UMR) mapping, the ratio of the fraction of the OA mass spectrum signal at m/z 55 and 57 (f55/f57) vs. the same fraction at m/z 60 (f60) was used to identify source-specific emission profiles. Furthermore, Positive Matrix Factorization (PMF) analysis was conducted using OA mass spectra, identifying four distinct factors: low-volatility oxygenated OA (LV-OOA), primary biomass-burning OA (BBOA), BB secondary OA (BBSOA), and semi-volatile oxygenated OA (SV-OOA). Data supports a robust four-factor solution, providing insights into the chemical transformations under different experimental conditions, including dark- and photo-aged, humidified, and dark oxidation with NO3 radicals. This work presents the first such laboratory study of African-derived BBOA particles, addressing a gap in global atmospheric chemistry research.

Bacterial community responses of the hydrothermal vent crab Xenograpsus testudinatus fed on microplastics

Microplastics (MPs) provide persistent contaminants in freshwaters and the oceans from anthropogenic sources worldwide. MP contamination in ecosystems has emerged as a global environmental issue. While increasing research focused on the ecological consequences of plastic pollution, health-related implications of plastic pollution have been somewhat overlooked. In this study, we evaluated the effects of polyethylene MP contamination on microbial, physical, and biochemical characteristics of the hydrothermal vent crab Xenograpsus testudinatus over a 7-day food exposure. Different concentrations (0%, 0.3%, 0.6%, and 1.0%) of polyethylene MPs were used for feed intake experiments. Oxford Nanopore Technologies’ full-length sequencing of the 16S rDNA gene was used to explore the changes of the microbial composition in vent crab tissues. At the phylum level, the content of Firmicutes significantly decreased in the digestive gland tissue. Furthermore, the predicted functions of genes in the microbial community were significantly influenced by MPs. In contrast, there were eight functions in gill and 11 functions in digestive gland tissues identified at low and high intake levels. The dominant functions of methylotrophy, dark thiosulfate oxidation, dark oxidation of sulfur compounds, aromatic hydrocarbon degradation, and aromatic compound degradation were significantly increased at high intake levels in the digestive gland. These findings indicate that MP ingestion causes not only a short-term decrease in energy intake for crustaceans but also a change in microbial communities and their functions. This study provided a first account on the toxicity of MPs in a hydrothermal vent crab to aid in the assessment of health risks provided by polyethylene MP to marine invertebrates.

Dark oxidation of mercury droplet: Mercurous [Hg(I)] species controls transformation kinetics

Dark oxidation of mercury droplet: Mercurous [Hg(I)] species controls transformation kinetics

Impact of laser marking on microstructure and fatigue life of medical grade titanium

Medical devices are required to feature a unique device identification marking to enable traceability. These identification tags are extensively applied directly onto metallic devices. Universally, the technology utilized to apply such markings is laser marking, where the device is heated locally in atmospheric air to form a dark oxide layer and generate contrast. Despite the wide application, the consequences of laser marking on materials performance are largely unknown. In this study, the effect of laser marking on the most common titanium alloys in the medical industry, i.e., commercially pure titanium and Ti6Al4V, is investigated. The morphology and composition of the generated oxide layer were investigated, along with a characterization of the heat affected zone. Additionally, the effect on fatigue strength is investigated in relation to the application of laser-marked titanium in a dental implant. Morphologically the laser-marked titanium surfaces exhibited signs of melting on the very surface and the generation of an abundance of cracks which formed upon cooling. Scanning electron microscopy shows that these cracks are perpendicular to the surface and reach deep into the HAZ. Evidence of substantial oxygen ingress was demonstrated: various titanium-based oxides were identified via X-ray diffraction, as well as oxygen stabilized α-phase. The fatigue analysis showed a severe reduction in endurance limit for all investigated parameters and materials of up to 80%. This was attributed the notch effect resulting from crack formation during laser marking. The fractured surfaces were investigated and showed a clear crack propagation from the entire laser-marked surface.

Microbiome of High-Rank Coal Reservoirs in the High-Production Areas of the Southern Qinshui Basin.

To study the distribution features of microorganisms in distinct hydrological areas of the southern Qinshui Basin, C-N-S microorganisms were studied using 16S RNA sequencing, metagenome sequencing and geochemical technologies, showing the high sensitivity of microorganisms to the hydrodynamic dynamics of coal. The hydrodynamic intensity of the #3 coal gradually decreased from the runoff areas to the stagnant areas. The stagnant zones have higher reservoir pressure, methane content, δ13CDIC and TDS and lower SO42-, Fe3+ and NO3- concentrations than the runoff areas. C-N-S-cycling microorganisms, including those engaged in methanogenesis, nitrate respiration, fermentation, nitrate reduction, dark oxidation of sulfur compounds, sulfate respiration, iron respiration, chlorate reduction, aromatic compound degradation, denitrification, ammonification and nitrogen fixation, were more abundant in the stagnant areas. The relative abundance of C-N-S functional genes, including genes related to C metabolism (e.g., mcr, mer, mtr, fwd and mtd), N metabolism (e.g., nifDKH, nirK, narGHI, nosZ, amoB, norC and napAB) and sulfur metabolism (e.g., dsrAB and PAPSS), increased in the stagnant zones, indicating that there was active microbiological C-N-S cycling in the stagnant areas. The degradation and fermentation of terrestrial plant organic carbon and coal seam organic matter could provide substrates for methanogens, while nitrogen fixation and nitrification can provide nitrogen for methanogens, which are all favorable factors for stronger methanogenesis in stagnant areas. The coal in the study area is currently in the secondary biogenic gas generation stage because of the rising of the strata, which recharges atmospheric precipitation. The random forest model shows that the abundance of C-N-S microorganisms and genes could be used to distinguish different hydrological zones in coal reservoirs. Since stagnant zones are usually high-gas-bearing zones and high-production areas of CBM exploration, these microbiological indicators can be used as effective parameters to identify high-production-potential zones. In addition, nitrate respiration and sulfate respiration microorganisms consumed NO3- and SO42-, causing a decrease in the content of these two ions in the stagnant areas.

Secondary aerosol formation during the dark oxidation of residential biomass burning emissions

Secondary aerosol formation during the dark oxidation of residential biomass burning emissions

Characterization and dark oxidation of the emissions of a pellet stove.

Pellet combustion in residential heating stoves has increased globally during the last decade. Despite their high combustion efficiency, the widespread use of pellet stoves is expected to adversely impact air quality. The atmospheric aging of pellet emissions has received even less attention, focusing mainly on daytime conditions, while the degree to which pellet emissions undergo night-time aging as well as the role of relative humidity remain poorly understood. In this study, environmental simulation chamber experiments were performed to characterize the fresh and aged organic aerosol (OA) emitted by a pellet stove. The fresh pellet stove PM1 (particulate matter with an aerodynamic diameter less than 1 μm) emissions consisted mainly of OA (93 ± 4%, mean ± standard deviation) and black carbon (5 ± 3%). The primary OA (POA) oxygen-to-carbon ratio (O : C) was 0.58 ± 0.04, higher than that of fresh logwood emissions. The fresh OA at a concentration of 70 μg m-3 (after dilution and equilibration in the chamber) consisted of semi-volatile (68%), low and extremely low volatility (16%) and intermediate-volatility (16%) compounds. The oxidation of pellet emissions under dark conditions was investigated by injecting nitrogen dioxide (NO2) and ozone (O3) into the chamber, at different (10-80%) relative humidity (RH) levels. In all dark aging experiments secondary organic aerosol (SOA) formation was observed, increasing the OA levels after a few hours of exposure to NO3 radicals. The change in the aerosol composition and the extent of oxidation depended on RH. For low RH, the SOA mass formed was up to 30% of the initial OA, accompanied by a moderate change in both O : C levels (7-8% increase) and the OA spectrum. Aging under higher RH conditions (60-80%) led to a more oxygenated aerosol (increase in O : C of 11-18%), but only a minor (1-10%) increase in OA mass. The increase in O : C at high RH indicates the importance of heterogeneous aqueous reactions in this system, that oxidize the original OA with a relatively small net change in the OA mass. These results show that the OA in pellet emissions can chemically evolve under low photochemical activity (e.g. the wintertime period) with important enhancement in SOA mass under certain conditions.

Insight into the shaping of microbial communities in element sulfur-based denitrification at different temperatures

Insight into the shaping of microbial communities in element sulfur-based denitrification at different temperatures

Ti doped α-Fe2O3 electrodes for water oxidation

Ti doped α-Fe2O3 electrodes for water oxidation

Different spatiotemporal dynamics, ecological drivers and assembly processes of bacterial, archaeal and fungal communities in brackish-saline groundwater

Different spatiotemporal dynamics, ecological drivers and assembly processes of bacterial, archaeal and fungal communities in brackish-saline groundwater

Optimization of peroxone oxidation for removal of TNT from aqueous solutions using a process-intensified hydrogen peroxide dosing strategy

Optimization of peroxone oxidation for removal of TNT from aqueous solutions using a process-intensified hydrogen peroxide dosing strategy

Secondary aerosol formation during the dark oxidation of residential biomass burning emissions†

Particulate matter from biomass burning emissions affects air quality, ecosystems and climate; however, quantifying these effects requires that the connection between primary emissions and secondary aerosol production is firmly established. We performed atmospheric simulation chamber experiments on the chemical oxidation of residential biomass burning emissions under dark conditions. Biomass burning organic aerosol was found to age under dark conditions, with its oxygen-to-carbon ratio increasing by 7–34% and producing 1–38 μg m−3 of secondary organic aerosol (5–80% increase over the fresh organic aerosol) after 30 min of exposure to NO3 radicals in the chamber (corresponding to 1–3 h of exposure to typical nighttime NO3 radical concentrations in an urban environment). The average mass concentration of SOA formed under dark-oxidation conditions was comparable to the mass concentration formed after 3 h (equivalent to 7–10 h of ambient exposure) under ultraviolet lights (6 μg m−3 or a 47% increase over the emitted organic aerosol concentration). The dark-aging experiments showed a substantial increase in secondary nitrate aerosol (0.12–3.8 μg m−3), 46–100% of which is in the form of organic nitrates. The biomass burning aerosol pH remained practically constant at 2.8 throughout the experiment. This value promotes inorganic nitrate partitioning to the particulate phase, potentially contributing to the buildup of nitrate aerosol in the boundary layer and enhancing long-range transport. These results suggest that oxidation through reactions with the NO3 radical is an additional secondary aerosol formation pathway in biomass burning emission plumes that should be accounted for in atmospheric chemical-transport models.

Effect of Biomass Burning on PM2.5 Composition and Secondary Aerosol Formation During Post‐Monsoon and Winter Haze Episodes in Delhi

Abstract Delhi metropolitan area suffers from extreme haze during the post‐monsoon and winter season, impacting climate, public health, and economy. We used a high‐resolution time‐of‐flight aerosol mass spectrometer (HR‐ToF‐AMS) and aethalometer at two urban locations in Delhi to capture non‐refractory PM2.5 (NR‐PM2.5) and black carbon (BC) during the post‐monsoon and winter season of 2019–2020. Four haze periods with high composition based‐PM2.5 (C‐PM2.5 = NR‐PM2.5 + BC) concentration and distinct chemical composition were identified, during all of which organics dominated but with varying contribution (∼[50%–70%] of C‐PM2.5). Biomass burning organic aerosol (BBOA) was dominant in all periods (∼[31%–45%] of OA), but the majority of it was highly aged ∼(45%–50%) with high O/C (0.71 and 0.46 at the two sites), formed most likely through rapid dark oxidation of freshly emitted and partially oxidized BBOA. High polycyclic aromatic hydrocarbons (PAH) signals in the fresh BBOA mass spectra suggest incomplete combustion activities such as open biomass burning emissions as major source. During an agricultural burning event in north‐western India, we estimated that ∼(44%–53%) of total C‐PM2.5 (combined contribution of aged BBOA and oxygenated OA) measured in Delhi was influenced by long‐range transported biomass burning emissions. During winter, secondary inorganics constituted a significant fraction apart from organics ∼(48%–55%), mainly in the form of ammonium nitrate (NH4NO3; up to ∼[19%–25%] of C‐PM2.5) and ammonium sulfate (NH4SO4; up to ∼[27%–38%]). Enhanced formation of NH4NO3 and related‐secondary organic aerosol (SOA) were linked to nighttime oxidation of BBOA, while NH4SO4 and related‐SOA were linked to heterogeneous aqueous phase oxidation under high RH conditions (>90%).