Abundance Of O2 Research Articles

Molecular Oxygen Abundance in Galactic Massive Star Formation Regions Based on SWAS Observations

Molecular oxygen abundance is a key parameter in understanding the chemical network of the interstellar medium. We estimate the molecular oxygen column density and abundance for a sample of Galactic massive star formation regions based on observations from the Submillimiter Wave Astronomy Satellite (SWAS) survey. We obtained an averaged O2 spectrum based on this sample using the (SWAS) survey data (O2, 487.249 GHz, N = 3–1, J = 3–2). No emission or absorption feature is seen around the supposed central velocity with a total integration time of t total = 8.67 × 103 hr and an rms noise per channel of 1.45 mK. Assuming a kinetic temperature T kin = 30 K, we derive the 3σ upper limit of the O2 column density to be 3.3 × 1015 cm−2, close to the lowest values reported in Galactic massive star formation regions in previous studies. The corresponding O2 abundance upper limit is 6.7 × 10−8, lower than all previous results based on SWAS observations and is close to the lowest reported value in massive star formation regions. On a galactic scale, our statistical results confirm a generally low O2 abundance for Galactic massive star formation regions. This abundance is also lower than results reported in extragalactic sources.

An investigation into Venusian atmospheric chemistry based on an open-access photochemistry-transport model at 0–112 km

Atmospheric chemistry plays a crucial role in the evolution of climate habitability on Venus. It has been widely explored by chemistry-transport models, but some characteristics are still poorly interpreted. This study is devoted to developing an open-access chemistry-transport model spanning both the middle and lower atmospheres of Venus. It provides a scheme for the structure of the chemistry, especially for the sulfur and oxygen, and investigates the influence of the cloud diffusivity and the SO2 dissolution that are adopted in the clouds. The developed model is based on the VULCAN framework and was updated with the state-of-the-art Venusian atmospheric chemistry. It includes vertical eddy diffusion retrieved recently with the Venus Express observations, and it resolves radiative transfer containing gas absorption and scattering, Mie scattering of the cloud droplets, and absorption of the unknown UV absorber. The obtained abundance profiles of SO, SO2, CO, COS, O, O2, O3, HCl, and NO are in overall agreement with the observations. The results show that the increase in cloud diffusivity has slight effects on the chemical structure. The SO2 mainly dissolves in 50–90 km and evaporates below the clouds. The rapid dissolution-release cycle is responsible for the large upward flux of SO2 at 58 km. At around 70 km, SO has a significant peak that is larger than that of previous studies by an order of magnitude, and S and SO2 also show slight increases. They are attributed to the buffering effects of liquid SO2 in the clouds. O2 is significantly eliminated by SO in this layer. We emphasize the superior regulation of the sulfur cycle on O2 at 70 km and its potential contributions to the long-standing problem of the overestimated O2 abundance.

High O3 pollution initiated by cold front passage over Pearl River Estuary

The influence of cold fronts on the formation of ozone (O3) pollution, particularly the contributions of physical and chemical processes to O3 abundance during the passage of cold fronts in winter over the Pearl River Estuary (PRE) region was still unclear. This study provided an in-depth analysis on the occurrence of high O3 pollution based on data from field measurements and simulation of a chemical transport model (i.e., WRF-Chem) over the PRE region during winter 2021 when cold fronts were frequently observed. Totally 7 high O3 episode days were observed during pre- and post-frontal stages at DWS (i.e., Da Wan Shan island), a downwind island site of the inland Pearl River Delta (PRD) region, which were accompanied with the prevailing northerly wind patterns with insignificant variations of wind speeds in a stable boundary layer over the whole PRE region. The quantitative analysis based on simulation results indicated that horizontal transport and chemical processes accounted for the buildup of O3 abundance at DWS, with the highest mean rates of 7.3 and 5.6 ppbv/h at pre- and post-frontal stages, respectively. The high contributions from horizontal transport to O3 levels at DWS were associated with the persistent northerly winds with small variations, while the contributions of chemical processes were varied with the abundance of precursors and meteorological conditions. However, vertical transport made negative contributions to O3 abundance, with the most significant mean diffusion rate of −2.6 ppbv/h at the frontal stage because of the control of high-pressure system, while the less influence of vertical transport at pre- and post-frontal stages was associated with the weak pressure gradient forces and wind patterns. The sensitivity analysis further demonstrated that the emissions of precursors from the inland PRD region contributed 50–76% to O3 abundance over PRE at different stages. Overall, the above results quantitatively confirmed the dominant role of transport from inland PRD to the O3 pollution over the downwind PRE region and were helpful for better understanding of O3 pollution in winter over PRE.

In situ measurements of dissolved gases in xylem sap as tracers in plant physiology

Abstract Trees transport gases from the ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in the tree sap in situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2 and CO2) from the soil, through the trees, into the atmosphere. We constructed and inserted custom-made semi-permeable membrane probes in the xylem of a fir tree and measured gas abundances at different heights using a portable gas equilibrium membrane-inlet mass spectrometer (‘miniRUEDI’). With this method, we were able to continuously measure the abundances of He, Ar, Kr, N2, O2 and CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of the concept that trees do uptake dissolved gases in soil water, we irrigated the tree with He-enriched water in a tracer experiment and were able to determine upward sap flow velocity. Measurements of inert gases together with reactive species, such as CO2 and O2, allowed separation of the physical transport and exchange of gases derived from the soil or atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in situ measurements of gases in the tree sap.

MnO2-coated nanodiamond-driven photodynamic therapy for enhanced antitumor effect by addressing hypoxia and glutathione depletion

The generation of reactive oxygen species (ROS) at the tumor site to induce destruction is emerging as a novel strategy for cancer treatment, which involves photodynamic therapy (PDT). Nevertheless, tumors typically create a hypoxic environment and are equipped with an endogenous antioxidant defense system that could potentially impede the efficiency of the therapeutic approach. To overcome these drawbacks, herein, a tumor microenvironment-responsive the ND-PAA-CD-Ce6@MnO2 (NPCC@M) delivery system was fabricated by disulfide bond coupling chlorin e6 (Ce6) to nanodiamond (ND) and further wrapped by MnO2 nanosheets to facilitate PDT. The use of disulfide bond not only stabilizes Ce6 in the blood circulation to prevent premature leakage, but also destroys the antioxidant barrier of overexpressed glutathione (GSH) in tumor cells. Moreover, the outer MnO2 was rapidly degraded by the endogenous hydrogen peroxide (H2O2) in the acidic pH and GSH within the tumor cells, which leads to an abundance of O2 and while increases the level of 1O2 under laser irradiation. The results eventually broke the redox homeostasis and attenuate hypoxia, thereby inducing apoptosis and necrosis of tumor cells. Detailed in vitro and in vivo biological effect has revealed a good biosafety profile and a high tumor suppression effect. Such a novel ND-based system with tumor microenvironment-modulating capability to elevate oxygen content and promote GSH consumption in tumor cells opens new opportunities for enhanced ROS treatment paradigms.

Comprehensive characterization of organics in oil sands process water in constructed mesocosms utilizing multiple analytical methods

This study aims to provide a thorough characterization of dissolved organics in oil sands process water (OSPW) in field-based aquatic mesocosms at both molecular and bulk measurement levels using multiple analytical methods. In a 3-year outdoor mesocosm experiment, the analysis of naphthenic acid (NA) species was conducted using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS). The results revealed the removal of both total NAs (38% and 35%) and classical NAs (O2–NAs, 58% and 49%) in undiluted and half-diluted OSPW, respectively. The increased ratios of oxidized NAs (O3–O6 NAs) to classical NAs suggested a transformation trend. The results also indicated that O2–NAs with higher carbon number and lower double bond equivalent (DBE) were more easily degraded in the mesocosm systems. Biomimetic extraction using solid-phase microextraction (BE-SPME) measurement displayed 26% (undiluted OSPW) and 30% (half-diluted OSPW) decrease in total bioavailable organics over 3 years. Naphthenic acids fraction compounds (NAFCs) obtained by liquid-liquid extraction (LLE) were also determined using Fourier transform infrared spectroscopy (FTIR). Reduction in acute toxicity for undiluted (43%) and half-diluted (26%) OSPW was observed over 3 years, which are well correlated with the decreases of NAs and BE-SPME concentrations. Moreover, BE-SPME values were found to be linearly correlated with total NAs concentrations (r = 0.96) and NAFCs (r = 0.96). Additionally, the linear relationships of individual O2–O6 NA species and BE-SPME concentrations unveiled the changes in the relative abundances of O2–O6 NA species in total bioavailable organics over time in the mesocosms. The present study has provided comprehensive insights by integrating various analytical methods, contributing valuable information for assessing the effectiveness of aquatic mesocosm systems in studying the temporal changes of organics in OSPW.

Roles of photochemical consumption of VOCs on regional background O3 concentration and atmospheric reactivity over the pearl river estuary, Southern China

Understanding of the photochemical ozone (O3) pollution over the Pearl River Estuary (PRE) of southern China remains limited. We performed an in-depth analysis of volatile organic compounds (VOCs) data collected on an island (i.e., the Da Wan Shan Island, DWS) located at the downwind of Pearl River Delta (PRD) from 26 November to 15 December 2021. Abundances of O3 and its precursors were measured when the air masses originated from the inland PRD. We observed that the VOCs levels at the DWS site were lower, while the mixing ratio of O3 was higher, compared to those reported at inland PRD, indicating the occurrence of photochemical consumption of VOCs during the air masses transport, which was further confirmed by the composition and diurnal variations of VOCs, as well as ratios of specific VOCs. The simulation results from a photochemical box model showed that the O3 level in the outflow air masses of inland PRD (O3(out-flow)) was the dominant factor leading to the intensification of O3 pollution and the enhancement of atmospheric radical concentrations (ARC) over PRE, which was mainly contributed by the O3 production via photochemical consumption of VOCs during air masses transport. Overall, our findings provided direct quantitative evidence for the roles of outflow O3 and its precursors from inland PRD on O3 abundance and ARC over the PRE area, highlighting that alleviation of O3 pollution over PRE should focus on the impact of photochemical loss of VOCs in the outflow air masses from inland PRD.

Oxygen production from dissociation of Europa’s water-ice surface

Jupiter’s moon Europa has a predominantly water-ice surface that is modified by exposure to its space environment. Charged particles break molecular bonds in surface ice, thus dissociating the water to ultimately produce H2 and O2, which provides a potential oxygenation mechanism for Europa’s subsurface ocean. These species are understood to form Europa’s primary atmospheric constituents. Although remote observations provide important global constraints on Europa’s atmosphere, the molecular O2 abundance has been inferred from atomic O emissions. Europa’s atmospheric composition had never been directly sampled and model-derived oxygen production estimates ranged over several orders of magnitude. Here, we report direct observations of H2+ and O2+ pickup ions from the dissociation of Europa’s water-ice surface and confirm these species are primary atmospheric constituents. In contrast to expectations, we find the H2 neutral atmosphere is dominated by a non-thermal, escaping population. We find 12 ± 6 kg s−1 (2.2 ± 1.2 × 1026 s−1) O2 are produced within Europa’s surface, less than previously thought, with a narrower range to support habitability in Europa’s ocean. This process is found to be Europa’s dominant exogenic surface erosion mechanism over meteoroid bombardment.

Retrievals Applied to a Decision Tree Framework Can Characterize Earthlike Exoplanet Analogs

Exoplanet characterization missions planned for the future will soon enable searches for life beyond our solar system. Critical to the search will be the development of life detection strategies that can search for biosignatures while maintaining observational efficiency. In this work, we adopted a newly developed biosignature decision tree strategy for remote characterization of Earthlike exoplanets. The decision tree offers a step-by-step roadmap for detecting exoplanet biosignatures and excluding false positives, based on Earth’s biosphere and its evolution over time. We followed the pathways for characterizing a modern-Earth-like planet and an Archean-Earth-like planet and evaluated the observational trades associated with coronagraph bandpass combinations of designs consistent with the Habitable Worlds Observatory precursor studies. With retrieval analyses of each bandpass (or combination), we demonstrate the utility of the decision tree and evaluate the uncertainty on a suite of biosignature chemical species and habitability indicators (i.e., the gas abundances of H2O, O2, O3, CH4, and CO2). Notably for modern Earth, less than an order of magnitude spread in the 1σ uncertainties was achieved for the abundances of H2O and O2, planetary surface pressure, and atmospheric temperature, with three strategically placed bandpasses (two in the visible and one in the near-infrared). For the Archean, CH4 and H2O were detectable in the visible with a single bandpass.

Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE). II. Using Grid-based Nested Sampling in Coronagraphy Observation Simulations for O2 and O3

We present the results for the detectability of the O2 and O3 molecular species in the atmosphere of an Earth-like planet using reflected light at visible wavelengths. By quantifying the detectability as a function of the signal-to-noise ratio (S/N), we can constrain the best methods to detect these biosignatures with next-generation telescopes designed for high-contrast coronagraphy. Using 25 bandpasses between 0.515 and 1 μm and a preconstructed grid of geometric albedo spectra, we examined the spectral sensitivity needed to detect these species for a range of molecular abundances. We first replicate a modern-Earth twin atmosphere to study the detectability of current O2 and O3 levels, and then expand to a wider range of literature-driven abundances for each molecule. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective S/N of the data, and define the requirements for the possibility of simultaneous molecular detection. We present our findings of O2 and O3 detectability as functions of the S/N, wavelength, and abundance, and discuss how to use these results for optimizing future instrument designs. We find that O2 is detectable between 0.64 and 0.83 μm with moderate-S/N data for abundances near that of modern Earth and greater, but undetectable for lower abundances consistent with a Proterozoic Earth. O3 is detectable only at very high S/N data in the case of modern-Earth abundances; however, it is detectable at low-S/N data for higher O3 abundances that can occur from efficient abiotic O3 production mechanisms.

Observational Evidence of Unknown NOx Source and Its Perturbation of Oxidative Capacity in Bermuda's Marine Boundary Layer

AbstractNitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere.

Heterogeneous Processes in the Atmosphere of Mars and Impact on H2O2 and O3 Abundances

AbstractCurrent models underestimate the highest observed ozone (O3) column densities on Mars. These estimates could be improved by including the uptake of odd hydrogen species (HOx) on water ice clouds, but the reported uptake coefficient of HO2 is likely overestimated for atmospheric conditions. This leaves a fundamental problem in Mars' atmospheric chemistry unsolved. Here, using the GEM‐Mars general circulation model, we explore a range of processes involving multiple phases (gas, adsorbed and solid) that may contribute to an alternative solution. First, we focus on hydrogen peroxide (H2O2) and discuss its physical states on Mars and its chemical impact. We also conjecture its photolytic destruction in ices with model simulations and Compact Reconnaissance Imaging Spectrometer for Mars observations. Then, we include in the model all relevant (for Mars) heterogeneous reactions, both on dust and water ice, recommended by the International Union of Pure and Applied Chemistry for terrestrial atmospheric studies. We find that only the uptake of HO2 and H2O2 on dust are efficient on Mars. Finally, we find that attenuation of sunlight by water ice clouds in the calculation of photolysis rates leads to increased O3 and H2O2 abundances below the ice clouds. The combination of the proposed processes leads to O3 increases without the need for strong uptake of HO2 on ice, but it remains difficult to find a good agreement with O3 and H2O2 observations on the global scale. We provide specific recommendations for future work in observations, laboratory experiments and modeling to advance our understanding of fundamental chemistry on Mars.

Seasonal discrepancies and inter-relationship of peroxyacetyl nitrate (PAN), ozone, and other environmental factors in Hangzhou, East China

Peroxyacetyl nitrate (PAN, CH3C(O)OONO2) and ozone (O3) are both important photochemical products, both of which are detrimental to air quality, human health and ecosystem. In this study, we measured atmospheric PAN, O3 and other pollutants in Hangzhou during the whole 2021 year. Observed results revealed that the average concentrations of PAN and O3 during the whole observation period were 1.59 and 27.09 ppbv, respectively. PAN concentrations declined from the weekday to weekend, while O3 presented the reverse pattern. The abundance of PAN and O3 showed different variations in all seasons. Serious photochemical pollution in spring and autumn were featured by higher PAN levels (mean of 1.74 and 1.66 ppbv); whereas those in summer and spring were characterized by higher O3 levels (mean of 32.34 and 30.98 ppbv). With the extremely higher PAN/O3 ratio of 0.10, the results suggested the high-level photochemical pollution in Hangzhou. In all seasons, the diurnal peak of PAN appeared earliest in summer could be associated with rapid decomposition rate of PAN at noon with higher temperatures. The correlation between PAN and other factors varies across all seasons due to the environmental conditions are unique in each season. Through analysis of conditional probability function (CPF) and toluene/benzene ratio, traffic sources were identified as the main factor contributing to high PAN and O3 accumulation at a regional scale. Furthermore, backward trajectory analysis revealed that marine air masses affected the air of the monitoring site in both summer and autumn; whereas continental air masses impacted it in both spring and winter. This study provides novel insights into photochemical pollution process in a coastal city, eastern China.

Deep Search for Molecular Oxygen in TW Hya

The dominant form of oxygen in cold molecular clouds is gas-phase carbon monoxide (CO) and ice-phase water (H2O). Yet, in planet-forming disks around young stars, gas-phase CO and H2O are less abundant relative to their interstellar medium values, and no other major oxygen-carrying molecules have been detected. Some astrochemical models predict that gas-phase molecular oxygen (O2) should be a major carrier of volatile oxygen in disks. We report a deep search for emission from the isotopologue 16O18O (N J = 21 − 01 line at 233.946 GHz) in the nearby protoplanetary disk around TW Hya. We used imaging techniques and matched filtering to search for weak emission but do not detect 16O18O. Based on our results, we calculate upper limits on the gas-phase O2 abundance in TW Hya of (6.4–70) × 10−7 relative to H, which is 2–3 orders of magnitude below solar oxygen abundance. We conclude that gas-phase O2 is not a major oxygen carrier in TW Hya. Two other potential oxygen-carrying molecules, SO and SO2, were covered in our observations, which we also do not detect. Additionally, we report a serendipitous detection of the C15N N J = 25/2 − 13/2 hyperfine transitions, F = 3 − 2 and F = 2 − 1, at 219.9 GHz, which we found via matched filtering and confirm through imaging.

Evaluating the attenuation of naphthenic acids in constructed wetland mesocosms planted with Carex aquatilis

Surface oil sands mining and extraction in northern Alberta’s Athabasca oil sands region produce large volumes of oil sands process–affected water (OSPW). OSPW is a complex mixture containing major contaminant classes including trace metals, polycyclic aromatic hydrocarbons, and naphthenic acid fraction compounds (NAFCs). Naphthenic acids (NAs) are the primary organic toxicants in OSPW, and reducing their concentrations is a priority for oil sands companies. Previous evidence has shown that constructed wetland treatment systems (CWTSs) are capable of reducing the concentration of NAs and the toxicity of OSPW through bioremediation. In this study, we constructed greenhouse mesocosms with OSPW or lab process water (LPW) (i.e., water designed to mimic OSPW minus the NAFC content) with three treatments: (1) OSPW planted with Carex aquatilis; (2) OSPW, no plants; and (3) LPW, no plants. The OSPW–C. aquatilis treatment saw a significant reduction in NAFC concentrations in comparison to OSPW, no plant treatments, but both changed the distribution of the NAFCs in similar ways. Upon completion of the study, treatments with OSPW saw fewer high-molecular-weight NAs and an increase in the abundance of O3- and O4-containing formulae. Results from this study provide invaluable information on how constructed wetlands can be used in future remediation of OSPW in a way that previous studies were unable to achieve due to uncontrollable environmental factors in field experiments and the active, high-energy processes used in CWTSs pilot studies.

Callisto's Atmosphere: The Oxygen Enigma

AbstractObservations of Callisto's atmosphere have indicated an O2 component should exist, but the evolution from its initial source to its inferred steady‐state abundance is not well understood. Herein we constrain the production of O2 via radiolysis within Callisto's exposed ice patches and determine the corresponding O2 column density. To do so, for the first time we simulate the thermal and energetic components of the Jovian magnetospheric plasma irradiating Callisto's atmosphere and estimate energy deposited therein by the impinging charged particles along their trajectories to the surface. We then calculate O2 source fluxes corresponding to the energy of the impacting plasma fluxes, which is coupled with estimated atmospheric lifetimes to determine the steady‐state abundance of O2. Our results suggest that production of O2 via radiolysis within the exposed ice on Callisto's surface does not produce a sufficiently dense atmosphere relative to the column densities inferred from observations by about 2–3 orders of magnitude. To resolve this discrepancy between estimated and observed abundances, we provide the first estimates for other potential sources of atmospheric O2. We also make similar estimates for the production of H2 in Callisto's atmosphere relative to constraints provided in the literature, and the conclusion is the same: a sufficiently dense atmosphere is not produced. Thus, we have shown that a better understanding of the production and fate of radiolytic products in Callisto's regolith is required in order to place firmer constraints on the generation mechanisms of its atmosphere in preparation for future observations.

Abundance of microbial community genes encoding terminal proteins of the aerobic and denitrification respiratory chains as indicators of ecohydrologic gradients in a coastal temperate rainforest

The persistence of soil organic carbon (SOC) is closely linked to the capacity of the soil microbial community to catalyze oxidative degradation of organic matter. This study uses a landscape-scale metagenomics approach to examine the relative abundances of genes encoding different terminal electron acceptors used for aerobic respiration and denitrification between soil microbial communities across an ecohydrologic gradient. The perhumid zone of the North Pacific coastal temperate rainforest serves as a template to test the associations between these differing respiratory pathways, soil conditions, and tree species biomass. We used the occurrence of reads in soil metagenomes as a proxy for the relative abundance of genes across the ecohydrologic gradient and identified distinct microbial fingerprints differentiating the driest (upland forest) and wettest (palustrine scrub-shrub and palustrine emergent wetland) ecosystem types. There was little gene-based differentiation between the ecosystem types at the wettest end of the ecohydrologic gradient - scrub-shrub wetland and emergent wetlands – while forested wetlands, which occur as gradient sites between upland forests and emergent wetlands on the landscape, were characterized by substantial metagenomic variability and, consequently, overlapped in their soil metagenome with the other ecosystem classes. Hydrology, as measured by groundwater depth was a predictor of O2 and N-oxide reductase abundances. High affinity O2 reductase genes were associated with wetter topographic positions, which has not been shown at the ecosystem scale, or in soils in-situ previously. N-oxide reductase genes were more associated with plant communities found at wetland sites but were not related to soil inorganic nitrogen, suggesting that nitrate supply may be limiting to denitrifiers ubiquitously across this gradient. Two plant species, Tsuga heterophylla (TSHE) and Pinus contorta spp. contorta (PICO), were more strongly correlated with O2-reductase and N-oxide reductase genes than site hydrology, respectively. This research represents a step toward fingerprinting the ecosystem microbiome using genes coding for specific terminal electron acceptors that control the fate of SOC and their ecohydrologic controls.

Rational regulating the Zn/Cd-S-Sn bond and oxygen vacancy environment of CdZnS/Eu2Sn2O7 heterointerface luminophore for highly efficient ratiometric electrochemiluminescence intelligent monitoring of sunset yellow

Inspired by the metal coordination bond structure of interface engineering strategy, CdZnS/Eu2Sn2O7 with heterointerfaces and enrich oxygen vacancies (OVs) were elaborately designed as cathode luminophores. The ratiometric electrochemiluminescence (RECL) system was reasonably constructed though incorporating biomass-derived nitrogen-doped carbon dots (BD-NCDs) as the anode luminophore, and H2O2 installed as co-reagent. We showed here that the formation of Zn/Cd-S-Sn bonds at the interface was induced, which promoted electron transfer and electrochemical reaction kinetics. Both experiments and density functional theory (DFT) calculations systemically revealed that CdZnS/Eu2Sn2O7 possessed the ability to achieve self-reinforced RECL though employing Zn/Cd-S-Sn bond and OVs as the main catalytic active sites, respectively. The numerous •OH was formed to significantly amplify the ECL intensity of the cathode by 4.7 and 14.4 times respectively, compared to CdZnS and Eu2Sn2O7. Interestingly, it was also confirmed that the OVs directly participate in the electrochemical reaction as the active site for catalyzing H2O2 to generate an abundance of O2•- to accomplish sharp amplification of the anode signal by 5.7-fold. Additionally, benefiting from the outstanding performance of the CdZnS/Eu2Sn2O7/GCE+BD-NCDs+H2O2 RECL system, the sensing system was designed for the detection of sunset yellow from 0.1 to 4000 nM. More importantly, the successful construction of machine learning-assisted portable devices integrated with smartphones also provides a novel strategy for SY on-site detection. This work not only guides further elucidation of the self-enhanced RECL catalytic mechanism but also facilitates the future development of rational luminophore designs for the point-of-care test.

Seasonal variations of O3 formation mechanism and atmospheric photochemical reactivity during severe high O3 pollution episodes in the Pearl River Delta region

In this study, the seasonal differences of O3 formation and photochemical reactivity were investigated during the high O3 episodes observed in autumn of 2014 and winter of 2017 at a downwind rural site of Pearl River Delta region (Heshan site). The mixing ratios of O3 and NO2 were highest in the Period I of autumn, followed by the Period II of autumn and the winter period. Though the total concentrations of VOCs were comparable in these periods, alkenes made greater fraction of VOCs during Period I of autumn, while those of OVOCs and aromatics were higher in winter period, resulting in the largest contributions of alkenes (ROH(alkenes)) and OVOCs (ROVOCs) to the photochemical reactivity in autumn and winter, respectively. The ozonolysis of alkenes (especially for 1-pentene and isoprene) dominated HOx production during Period I of autumn, while in winter period, photolysis of OVOCs increased before noon, and made the greatest contribution to HOx production in late afternoon. As for the HOx destruction, reaction of OH + NO2 dominated in both seasons, with higher rates in Period I of autumn because of higher levels of radical and NO2. Furthermore, the variations in O3 precursors and radical budget resulted in different O3 formation and destruction rates, with the highest contribution from RO2 and NO to O3 formation, as well as photolysis and ozonolysis of alkenes for O3 destruction in Period I of autumn. The net O3 production from photochemistry and contributions of physical processes indicated that local photochemistry dominated the O3 accumulation at noon and in the early afternoon, while dilution in O3 levels caused by physical process increased before noon and in the late afternoon. O3 formation sensitivity could be changed during the photochemical consumption of precursors, which was more NOx-limited in the late afternoon. Overall, our findings highlighted that control measures of photochemical pollution should consider the seasonal variations in the abundance of O3 and its precursors, and O3 formation sensitivity regime.

Seasonal Changes in the Vertical Structure of Ozone in the Martian Lower Atmosphere and Its Relationship to Water Vapor

AbstractThe mid‐infrared channel of the Atmospheric Chemistry Suite (ACS MIR) onboard the ExoMars Trace Gas Orbiter is capable of observing the infrared absorption of ozone (O3) in the atmosphere of Mars. During solar occulations, the 003←000 band (3,000‐3,060 cm−1) is observed with spectral sampling of ∼0.045 cm−1. Around the equinoxes in both hemispheres and over the southern winters, we regularly observe around 200–500 ppbv of O3 below 30 km. The warm southern summers, near perihelion, produce enough atmospheric moisture that O3 is not detectable at all, and observations are rare even at high northern latitudes. During the northern summers, water vapor is restricted to below 10 km, and an O3 layer (100–300 ppbv) is visible between 20 and 30 km. At this same time, the aphelion cloud belt forms, condensing water vapor and allowing O3 to build up between 30 and 40 km. A comparison to vertical profiles of water vapor and temperature in each season reveals that water vapor abundance is controlled by atmospheric temperature, and H2O and O3 are anti‐correlated as expected. When the atmosphere cools, over time or over altitude, water vapor condenses (observed as a reduction in its mixing ratio) and the production of odd hydrogen species is reduced, which allows O3 to build up. Conversely, warmer temperatures lead to water vapor enhancements and ozone loss. The LMD Mars Global Climate Model is able to reproduce vertical structure and seasonal changes of temperature, H2O, and O3 that we observe. However, the observed O3 abundance is larger by factors between 2 and 6, indicating important differences in the rate of odd‐hydrogen photochemistry.