Atmospheric O2 Concentrations Research Articles

Exploring fine-aerosol episodes in urban Seoul during the cold season of the 2021 SIJAQ campaign: Measurement evidences of heterogeneous reactions on black carbon particles

Significant PM2.5 pollution has been prevalent on a regional scale in East Asia including a megacity Seoul in South Korea. Here, we explore fine-aerosol episodes occurred in Seoul during the Satellite Integrated Joint monitoring of Air Quality (SIJAQ) campaign from October to November of the 2021, focusing on experimental evidences of heterogeneous reactions to form secondary aerosol under a highly oxidized atmospheric condition.At this urban site in Seoul, vehicle exhaust was the clear source of fresh emissions, leading to a high level of NO and small refractory black carbon (rBC) particles (mass median diameter of 162 nm ± 16 nm) in the morning time. The hourly mass concentration of PM2.5 ranged from 5.3 μg m−3 to 146.1 μg m−3, averaging at 24.5 ± 22.2 μg m−3. During the campaign, the most intense episode, EP3 (November 18–21), recorded an average PM2.5 concentration of 72.5 ± 38.2 μg m−3, peaking at 146.1 μg m−3, was characterized by relatively higher temperature (∼12 °C) and relative humidity (67 %) on average thoroughly governed by continental migratory high and westerly winds. While the average NO3− concentration was 27.7 μg m−3, four times the whole campaign's average, EP3 was highlighted by a high morning NO2/NOx ratio and significantly elevated daytime and nighttime Ox (O3+NO2) concentrations compared to non-episode days. Throughout the entire campaign, NOz surrogate (NO2(CL)-NO2(T)), Ox, and Fmoderate + thick (the combined number fractions of moderately and thickly coated-rBC particles) tended to increase with the PM2.5 concentration. During the daytime, as PM2.5 increased, Fmoderate + thick showed a monotonic increase, accompanied by RH rising from 54 ± 16% to 63 ± 11%. In contrast, at nighttime of humid condition with RH often exceeding 70% the enhancement of Fmoderate + thick was more sensitive to condensable gas levels than RH. Given that high levels of PM2.5 (>60 μg m−3) were observed only during EP3, enhanced levels of NOz surrogate, Ox, Fmoderate + thick, and RH were evident characteristics of EP3. Such chemical and meteorological conditions suggest that the chemically enhanced oxidation state was evident during EP3, which promoted the formation of secondary aerosols on primary particles including rBC, especially under conditions of elevated RH. Considering the recent trend of increasing number of vehicles and rising atmospheric O3 concentrations in East Asia, future studies should be well designed to investigate the detailed mechanisms involved in heterogeneous reactions that lead to the formation of secondary aerosols.

Atmospheric HONO Concentration Levels and Generation Mechanisms in Nanjing in Winter and Summer

HONO, or gaseous nitrous acid, has a significant impact on air quality and climate. An atmospheric gaseous nitrous acid （HONO） observation study was carried out in December 2021 （winter） and July 2022 （summer） in the Jiangbei New District of Nanjing City, respectively. Using the HONO concentration observation data, combined with the atmospheric NOx and O3 concentrations during the sampling period as well as the reaction rate of the HONO generation process and other parameters, we compared and analyzed the change rule of the atmospheric HONO concentration during winter and summer in the Nanjing area, quantitatively investigated the sources of diurnal atmospheric HONO and its generation mechanism, and explored the unknown sources of atmospheric HONO during the daytime. The results showed that the mean value of atmospheric ρ（HONO） in the Nanjing area during winter was （2.2±1.1） μg·m-3, which was 3.0 times the average concentration [（0.72±0.45） μg·m-3] during summer. The atmospheric HONO concentrations during winter and summer showed a significant daily pattern of low during the daytime and high at nighttime. Based on the reaction rates of different HONO generation pathways, it was calculated that the non-homogeneous reaction of NO2 was the main pathway of atmospheric HONO generation at night in Nanjing. The analysis of the atmospheric HONO balance during the daytime showed that there existed an important unknown source of HONO during the daytime （Punknown）, and its contribution to the daytime atmospheric HONO concentration was 69% during winter and 47% during summer, respectively. The results of correlation analysis showed that Punknown was related to the light-catalyzed reaction of NO2 during the daytime.

Accurate and efficient prediction of atmospheric PM1, PM2.5, PM10, and O3 concentrations using a customized software package based on a machine-learning algorithm.

Particulate matter (PM) and ozone (O3) pollution have been attracting increasing attention recently due to their severe harm to human health. PM and O3 are secondary pollutants, and there remain significant challenges in accurately and efficiently predicting their concentrations in the atmosphere. In this study, one-year monitoring data of PM1, PM2.5, PM10, and O3 concentrations as well as meteorological parameters and concentrations of various precursors (i.e., nitrogen oxides, SO2, CO, alkanes, aldehydes, and ketones) are obtained at a monitoring site in central China's Hunan province. The eXtreme Gradient Boosting model is trained and tested to achieve efficient and accurate predictions of the concentrations of the four pollutants. The effects of different datasets, input features, and model parameters on the prediction accuracy are investigated. Principal component analysis is employed to further reduce the dimensions of features, increasing the prediction efficiency. Finally, all model training and prediction processes are incorporated in an executable application using the PyQt5 framework to build a user interface. The customized software supports user-defined modeling. The software can simultaneously predict PM1, PM2.5, PM10, and O3 concentrations, making the prediction process convenient.

Predicting plateau atmospheric ozone concentrations by a machine learning approach: A case study of a typical city on the southwestern plateau of China

Atmospheric ozone (O3) has been placed on the priority control pollutant list in China's 14th Five-Year Plan. Due to their unique meteorological conditions, plateau regions contain high concentrations of atmospheric O3. However, traditional experimental methods for determining O3 concentrations using automatic monitoring stations cannot predict O3 trends. In this study, two machine learning models (a nonlinear auto-regressive model with external inputs (NARX) and a temporal convolution network (TCN)) were developed to predict O3 concentrations in a plateau area in the Kunming region by considering the effects of meteorological parameters, air quality parameters, and volatile organic compounds (VOCs). The plateau O3 prediction accuracy of the machine learning models was found to be much higher than those of numerical models that served as a comparison. The O3 values predicted by the machine learning models closely matched the actual monitoring data. The temporal distribution of plateau O3 displayed a high all-day peak from February to May. A correlation analysis between O3 concentrations and feature parameters demonstrated that humidity is the feature with the highest absolute correlation (−0.72), and was negatively correlated with O3 concentrations during all test periods. VOCs and temperatures were also found to have high positive correlation coefficients with O3 during periods of significant O3 pollution. After negating the effects of meteorological parameters, the predicted O3 concentrations decreased significantly, whereas they increased in the absence of NOx. Although individual VOCs were found to greatly affect the O3 concentration, the total VOC (TVOC) concentration had a relatively small effect. The proposed machine learning model was demonstrated to predict plateau O3 concentrations and distinguish how different features affect O3 variations.

Regulation of Rubisco activity by interaction with chloroplast metabolites.

Rubisco activity is highly regulated and frequently limits carbon assimilation in crop plants. In the chloroplast, various metabolites can inhibit or modulate Rubisco activity by binding to its catalytic or allosteric sites, but this regulation is complex and still poorly understood. Using rice Rubisco, we characterised the impact of various chloroplast metabolites which could interact with Rubisco and modulate its activity, including photorespiratory intermediates, carbohydrates, amino acids; as well as specific sugar-phosphates known to inhibit Rubisco activity - CABP (2-carboxy-d-arabinitol 1,5-bisphosphate) and CA1P (2-carboxy-d-arabinitol 1-phosphate) through in vitro enzymatic assays and molecular docking analysis. Most metabolites did not directly affect Rubisco in vitro activity under both saturating and limiting concentrations of Rubisco substrates, CO2 and RuBP (ribulose-1,5-bisphosphate). As expected, Rubisco activity was strongly inhibited in the presence of CABP and CA1P. High physiologically relevant concentrations of the carboxylation product 3-PGA (3-phosphoglyceric acid) decreased Rubisco activity by up to 30%. High concentrations of the photosynthetically derived hexose phosphates fructose 6-phosphate (F6P) and glucose 6-phosphate (G6P) slightly reduced Rubisco activity under limiting CO2 and RuBP concentrations. Biochemical measurements of the apparent Vmax and Km for CO2 and RuBP (at atmospheric O2 concentration) and docking interactions analysis suggest that CABP/CA1P and 3-PGA inhibit Rubisco activity by binding tightly and loosely, respectively, to its catalytic sites (i.e. competing with the substrate RuBP). These findings will aid the design and biochemical modelling of new strategies to improve the regulation of Rubisco activity and enhance the efficiency and sustainability of carbon assimilation in rice.

User-friendly carbon-cycle modelling and aspects of Phanerozoic climate change

Carbon-cycle modelling is essential for testing the main carbon sources and sinks as climate forcings, and we introduce and describe GEOCARB_NET, a graphical user interface for the geologic carbon and sulfur cycle model GEOCARBSULFvolc. The software system is menu-driven, user-friendly, and the user is never far removed from the basic input parameters from which atmospheric CO2 and O2 concentrations can be derived. GEOCARB_NET is supplied with several published models and the user can easily test and refine these models with different parametrizations. GEOCARB_NET also contains libraries of models and proxy data, which easily can be compared with each other. Our examples focus on how to use GEOCARB_NET in the context of Phanerozoic climate change and highlights how certain key input parameters can seriously affect reconstructed CO2 levels.

Reponses of morphological and biochemical traits of bamboo trees under elevated atmospheric O3 enrichment

Dwarf bamboo (Indocalamus decorus) is an O3-tolerant plant species. To identify the possible mechanism and response of leaf morphological, antioxidant, and anatomical characteristics to elevated atmospheric O3 (EO3) concentrations, we exposed three-year-old I. decorus seedlings to three O3 levels (low O3-LO: ambient air; medium O3-MO: Ambient air+70 ppb high O3–HO: Ambient air+140 ppb O3) over a growing season using open-top chambers. Leaf shape and stomatal characteristics, and leaf microscopic structure of I. decorus were examined. The results indicated that 1) the stomata O3 flux (Fst) of HO decreased more rapidly under EO3 as the exposure time increased. The foliar O3 injury of HO and MO occurred when AOT40 was 26.62 ppm h and 33.20 ppm h, respectively, 2) under EO3, leaf number, leaf mass per area, leaf area, and stomata length/width all decreased, while leaf thickness, stomatal density, width, and area increased compared to the control, 3) MDA and total soluble protein contents all showed significantly increase under HO (36.57% and 32.77%) and MO(31.91% and 19.52%) while proline contents only increased under HO(33.27%). 4) MO and HO increased bulliform cells numbers in the leaves by 6.28% and 23.01%, respectively. HO reduced the transverse area of bulliform cells by 13.73%, while MO treatments had no effect, and 5) the number of fusoid cells interspace, the transverse area of fusoid cells interspace, and mesophyll thickness of HO significantly increased by 11.16%, 28.58%, and 13.42%, respectively. In conclusion, I. decorus exhibits strong O3 tolerance characteristics, which stem from adaptions in the leaf's morphological, structural, antioxidant, and anatomical features. One critical attribute was the enlargement of the bulliform cell transverse area and the transverse area of fusoid cells interspace that drove this resistance to O3. Local bamboo species with high resistance to O3 pollution thus need to be promoted for sustained productivity and ecosystem services in areas with high O3 pollution.

Atmospheric oxygenation as a potential trigger for climate cooling

Secular changes in atmospheric CO2 and consequent global climate variations, are commonly attributed to global outgassing and the efficiency of silicate weathering, which may have been linked to mountain formation, land/arc distribution, and plant colonization through geological time. Although oxidative weathering has been shown to exert a significant role in the propagation of weathering fronts through the oxidation of Fe-bearing minerals, the influence of atmospheric O2 concentration (pO2) on silicate weathering, CO2 consumption, and global climate has not been thoroughly evaluated. This study presents a numerical model aimed at estimating the effects of pO2 on the climate, considering the influence of pO2 on the regolith thickness and thus weathering duration of granitic domains. Our model simulations reveal that an increase in weathering efficiency, through deeper penetration of the oxidative weathering front in the granitic regolith, would independently introduce a steady-state climate cooling of up to ∼8 °C, in step with one-order of magnitude rise in pO2. This temperature change may have repeatedly initiated the runaway ice-albedo feedback, leading to global glacial events (e.g., Neoproterozoic Snowball Earth). Increasing granitic weathering efficiency caused by a substantial pO2 increase may also have contributed to the development of icehouse climate during the Phanerozoic.

Breathing Planet Earth: Analysis of Keeling’s Data on CO2 and O2 with Respiratory Quotient (RQ), Part II: Energy-Based Global RQ and CO2 Budget

For breathing humans, the respiratory quotient (RQ = CO2 moles released/O2 mols consumed) ranges from 0.7 to 1.0. In Part I, the literature on the RQ was reviewed and Keeling’s data on atmospheric CO2 and O2 concentrations (1991–2018) were used in the estimation of the global RQ as 0.47. A new interpretation of RQGlob is provided in Part II by treating the planet as a “Hypothetical Biological system (HBS)”. The CO2 and O2 balance equations are adopted for estimating (i) energy-based RQGlob(En) and (ii) the CO2 distribution in GT/year and % of CO2 captured by the atmosphere, land, and ocean. The key findings are as follows: (i) The RQGlob(En) is estimated as 0.35 and is relatively constant from 1991 to 2020. The use of RQGlob(En) enables the estimation of CO2 added to the atmosphere from the knowledge of annual fossil fuel (FF) energy data; (ii) The RQ method for the CO2 budget is validated by comparing the annual CO2 distribution results with results from more detailed models; (iii) Explicit relations are presented for CO2 sink in the atmosphere, land, and ocean biomasses, and storage in ocean water from the knowledge of curve fit constants of Keeling’s curves and the RQ of FF and biomasses; (iv) The rate of global average temperature rise (0.27 °C/decade) is predicted using RQGlob,(En) and the annual energy release rate and compared with the literature data; and (v) Earth’s mass loss in GT and O2 in the atmosphere are predicted by extrapolating the curve fit to the year 3700. The effect of RQGlob and RQFF on the econometry and policy issues is briefly discussed.

Characterization and Source Analysis of Pollution Caused by Atmospheric Volatile Organic Compounds in the Spring, Kunming, China

The surface atmospheric O3 concentration in Kunming shows a significant upward trend, with high values mainly occurring in March–May. Volatile organic compounds (VOCs) are one of the most important precursors of O3. However, the sources of VOCs are complex and difficult to identify. In order to understand the pollution levels, the spatial distribution characteristics, and possible sources of VOCs, we conducted simultaneous offline sampling at representative sites in six different functional areas of Kunming using SUMMA canisters for one week. The VOC samples were analyzed via GC/MS. The VOC data were analyzed (using the feature ratio method, ozone formation potential (OFP), and Positive Matrix Factorization (PMF) model). Some important conclusions were drawn. Firstly, VOCs during the spring in Kunming were mainly derived from oxygenated VOCs, aromatic hydrocarbons, and halogenated hydrocarbons, with significant spatial differences. Secondly, we found that the potential for atmospheric ozone formation is higher in Kunming for aromatic hydrocarbons and oxygenated VOCs. Finally, the results of the Positive Matrix Factorization model (PMF) showed that Kunming’s ambient atmospheric VOCs mainly originate from anthropogenic source emissions. These conclusions can provide useful reference information for O3 pollution control in Kunming.

Elevated oxygen atmosphere maintains antioxidant capacity and inhibits cell wall metabolism in postharvest jujube

Fruit of jujube (Ziziphus jujube Mill. cv. Dongzao), known as a high-quality fresh edible variety, is popular among consumers on account of its bright color, crispy texture and abundant nutrients. However, the softening of jujube fruit after harvest seriously shortens its shelf life. To examine possible treatments to reduce softening rate, we evaluated the effect on fruit quality attributes of an elevated atmospheric O2 concentration during cold storage, ultimately unraveling its biological effect on jujube cell wall metabolism and antioxidant level. Our results demonstrated that an elevated O2 atmosphere during cold storage induced both the activity of antioxidant enzymes and relative expression levels of related genes, promoting the scavenging of hydrogen peroxide and superoxide anion. By the end of storage, the activities of superoxide dismutase, peroxidase, and catalase in elevated O2-treated jujubes were 1.9, 1.3, and 1.1 times, respectively, those in the control group. In addition, elevated O2 concentration inhibited the activities of polygalacturonase, pectin methyl esterase, cellulase and the relative abundance of related transcripts, thus delaying the degradation of cellulose and hemicelluloses and reducing the conversion of insoluble pectin to water-soluble pectin and ionic-soluble pectin. These changes presumably contribute to the maintenance of the cell wall components and cell microstructure. In conclusion, an elevated atmospheric O2 concentration of 60 % during cold storage promoted antioxidant capacity and inhibited cell wall metabolism in postharvest jujube fruit, reducing postharvest softening.

Distribution of polycyclic aromatic hydrocarbons in indoor/outdoor window films and the indoor film/air partition of northeastern Chinese college dormitories

Indoor window films can represent short-term air pollution conditions of indoor environment through rapidly capturing organic contaminants as effective passive air samplers. To investigate the temporal variation, influence factors of polycyclic aromatic hydrocarbons (PAHs) in indoor window films, and the exchange behavior with gas phase in college dormitories, 42 pairs window films of interior and exterior window surfaces and corresponding indoor gas phase and dust samples were collected monthly in six selected dormitories, Harbin, China, from August to December 2019 and September 2020. The average concentration of ∑16PAHs in indoor window films (398 ng/m2) was significantly (p < 0.01) lower than that in outdoors (652 ng/m2). In addition, the median indoor/outdoor ∑16PAHs concentration ratio was close to 0.5, showing that outdoor air acted as a major PAH source to indoor environment. The 5-ring PAHs were mostly dominant in window films whereas the 3-ring PAHs contributed mostly in gas phase. 3-ring PAHs and 4-ring PAHs were both important contributors for dormitory dust. Window films showed stable temporal variation, i.e. PAH concentrations in heating months were higher than those in non-heating months. The atmospheric O3 concentration was the main influence factor of PAHs in indoor window films. PAHs with low molecular weight in indoor window films rapidly reached film/air equilibrium phase within in dozens of hours. The large deviation in the slope of the log KF-A versus log KOA regression line from that in reported equilibrium formula might be the difference between the window film composition and octanol.

Diurnal variability of atmospheric O2, CO2, and their exchange ratio above a boreal forest in southern Finland

Abstract. The exchange ratio (ER) between atmospheric O2 and CO2 is a useful tracer for better understanding the carbon budget on global and local scales. The variability of ER (in mol O2 per mol CO2) between terrestrial ecosystems is not well known, and there is no consensus on how to derive the ER signal of an ecosystem, as there are different approaches available, either based on concentration (ERatmos) or flux measurements (ERforest). In this study we measured atmospheric O2 and CO2 concentrations at two heights (23 and 125 m) above the boreal forest in Hyytiälä, Finland. Such measurements of O2 are unique and enable us to potentially identify which forest carbon loss and production mechanisms dominate over various hours of the day. We found that the ERatmos signal at 23 m not only represents the diurnal cycle of the forest exchange but also includes other factors, including entrainment of air masses in the atmospheric boundary layer before midday, with different thermodynamic and atmospheric composition characteristics. To derive ERforest, we infer O2 fluxes using multiple theoretical and observation-based micro-meteorological formulations to determine the most suitable approach. Our resulting ERforest shows a distinct difference in behaviour between daytime (0.92 ± 0.17 mol mol−1) and nighttime (1.03 ± 0.05 mol mol−1). These insights demonstrate the diurnal variability of different ER signals above a boreal forest, and we also confirmed that the signals of ERatmos and ERforest cannot be used interchangeably. Therefore, we recommend measurements on multiple vertical levels to derive O2 and CO2 fluxes for the ERforest signal instead of a single level time series of the concentrations for the ERatmos signal. We show that ERforest can be further split into specific signals for respiration (1.03 ± 0.05 mol mol−1) and photosynthesis (0.96 ± 0.12 mol mol−1). This estimation allows us to separate the net ecosystem exchange (NEE) into gross primary production (GPP) and total ecosystem respiration (TER), giving comparable results to the more commonly used eddy covariance approach. Our study shows the potential of using atmospheric O2 as an alternative and complementary method to gain new insights into the different CO2 signals that contribute to the forest carbon budget.

Utilization of sludge templated carbide slag pellets for simultaneous desulfurization and denitrification: Low and moderate temperatures and synergetic mechanism

Higher SO2 and NO removal requirements have been proposed for a low carbon, flexible power generation. In this study, a low-carbon, high-efficiency, and low-cost mixed pellet was prepared through synergistic utilization of carbide slag and sludge. Further, this work systematically explored its combustive properties and SO2 and NO removal capabilities. The results indicated that more efficient mass transfer and catalyzed reactions were integrated into the unique pellet structure. The sludge-added mixed pellets exhibited good denitrification ability, at low and moderate temperatures, and improved the desulfurization performance of carbide slag. The pellets with carbide slag to sludge mass ratio of 10:3 has a 12.3% higher desulfurization efficiency than 10:0 pellets, as sludge extended the duration of the chemical reaction control phase and reduced the diffusion resistance of the product layer during desulfurization. The sludge-added pellets had satisfactory denitrification efficiencies of up to 70% at 550 °C, primarily due to the homogeneous and heterogeneous reductions between NO, pyrolysis gas, and char, which formed in the pre-combustion phase of sludge; these NO reduction processes were significantly catalyzed through carbide slag-CaO surface reduction and reoxidation. Notably, more C(O) and C(N) groups formed on the char surfaces under trace atmospheric O2 concentration (≤1%), enhancing NO reduction. This pellet combustion process conforms to the three-dimensional diffusion reaction model. This study will provide a theoretical direction for high value waste utilization of carbide slag and sludge and facilitates the industrial application of thermal power flexible variable load pollutant control.

Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

ABSTRACT The Great Oxidation Event was a period during which Earth’s atmospheric oxygen (O2) concentrations increased from ∼10−5 times its present atmospheric level (PAL) to near modern levels, marking the start of the Proterozoic geological eon 2.4 billion years ago. Using WACCM6, an Earth System Model, we simulate the atmosphere of Earth-analogue exoplanets with O2 mixing ratios between 0.1 and 150 per cent PAL. Using these simulations, we calculate the reflection spectra over multiple orbits using the Planetary Spectrum Generator. We highlight how observer angle, albedo, chemistry, and clouds affect the simulated observations. We show that inter-annual climate variations, as well short-term variations due to clouds, can be observed in our simulated atmospheres with a telescope concept such as LUVOIR or HabEx. Annual variability and seasonal variability can change the planet’s reflected flux (including the reflected flux of key spectral features such as O2 and H2O) by up to factors of 5 and 20, respectively, for the same orbital phase. This variability is best observed with a high-throughput coronagraph. For example, HabEx (4 m) with a starshade performs up to a factor of two times better than a LUVOIR B (6 m) style telescope. The variability and signal-to-noise ratio of some spectral features depends non-linearly on atmospheric O2 concentration. This is caused by temperature and chemical column depth variations, as well as generally increased liquid and ice cloud content for atmospheres with O2 concentrations of &amp;lt;1 per cent PAL.

A remote sensing based study of tropospheric ozone concentration amid COVID-19 lockdown over India using Sentinel-5P satellite data

Amid the COVID-19 crisis, governments all over the world, and not excluding India, took to lockdown measures to deaccelerate the spread of the COVID-19 virus. This led to reduction of atmospheric pollution by declining the harmful Nitrogen and Sulphur Oxide (NOX and SOX) concentrations. However, one hand while the stratospheric Ozone (O3) showed repair, the lower atmospheric O3 concentrations demonstrated a remarkable increase during lockdown phase over India. This study aims to estimate the O3 concentration during the Covid-19 lockdown over Pune city in India using freely available Sentinel-5P satellite datasets. The study makes use of the Ordinary Least Squares (OLS) and Random Forest (RF) regressions and compares the findings of the two algorithms based on estimation results. This study utilizes lower atmospheric O3 concentration data from Sentinel-5P satellite of the European Space Agency (ESA) over the Indian mainland for a month of lockdown scenario (March 22nd, 2020, to April 25th, 2020) and shows the remarkable increase in concentration of O3 gas as a pollutant. Despite the complete lockdown over India during this given time frame, there has been enough emission of O3 precursors from other sources such as stubble burning. The estimates of tropospheric O3 concentration for May 2020 for Pune city, using OLS and RF Regressions, have been validated with May 2020 data. The results have provided a RMSE of 1.05 and 1.23 with R2-statistics of 0.90 and 0.857 in training and testing phases for OLS and RMSE of 0.98 and MAE of 1.07 with R2-statistics of 0.968 and 0.895 in training and testing phases of the RF. The outcome of this study has proven that O3 gas concentrations in the atmosphere depends upon various other causative factors apart from the precursor gases. The study also shows that the remotely sensed Sentinel-5P datasets, supplemented with ground-based sensor data can help in time and cost saving estimation of O3 concentrations in the troposphere with considerable accuracy.

Sulfur cycling at natural hydrocarbon and sulfur seeps in Santa Paula Creek, CA.

Biogeochemical cycling of sulfur is relatively understudied in terrestrial environments compared to marine environments. However, the comparative ease of access, observation, and sampling of terrestrial settings can expand our understanding of organisms and processes important in the modern sulfur cycle. Furthermore, these sites may allow for the discovery of useful process analogs for ancient sulfur-metabolizing microbial communities at times in Earth's past when atmospheric O2 concentrations were lower and sulfide was more prevalent in Earth surface environments. We identified a new site at Santa Paula Creek (SPC) in Ventura County, CA-a remarkable freshwater, gravel-bedded mountain stream charged with a range of oxidized and reduced sulfur species and heavy hydrocarbons from the emergence of subsurface fluids within the underlying sulfur- and organic-rich Miocene-age Monterey Formation. SPC hosts a suite of morphologically distinct microbial biofacies that form in association with the naturally occurring hydrocarbon seeps and sulfur springs. We characterized the geology, stream geochemistry, and microbial facies and diversity of the Santa Paula Creek ecosystem. Using geochemical analyses and 16S rRNA gene sequencing, we found that SPC supports a dynamic sulfur cycle that is largely driven by sulfide-oxidizing microbial taxa, with contributions from smaller populations of sulfate-reducing and sulfur-disproportionating taxa. This preliminary characterization of SPC revealed an intriguing site in which to study geological and geochemical controls on microbial community composition and to expand our understanding of sulfur cycling in terrestrial environments.

Formation processes and source contributions of ground‐level ozone in urban and suburban Beijing using the WRF‐CMAQ modelling system

Beijing faces the challenge of high levels of ozone (O3) pollution. In this study, the Weather Research and Forecasting model and Community Multiscale Air Quality model (CMAQ) were used to simulate atmospheric O3 concentrations in Beijing. To investigate the formation mechanisms and source contributions of O3 pollution in different regions of Beijing, process analysis and the integrated source apportionment method within the CMAQ were applied to O3 concentrations in the summer of 2018. The process analysis results showed that vertical diffusion was the major contributor to O3 concentrations at all receptor sites in Beijing, at > 65.94 µg/(m3·hr). Gas-phase chemical reactions consumed a significant amount of O3 in urban and inner suburban areas (> −5.57 µg/(m3·hr)), while near-surface chemical reactions made positive contributions in outer suburban areas (> 4.72 µg/(m3·hr)). The O3 formation chemical reactions indicated that NO titration, which removes O3 at night-time, mainly occurred in urban areas. The weaker chemical reactions occurring near the surface in outer suburbs suggested that suburban-area O3 was produced in the upper atmospheric layers and was transported vertically to the lower layers. The O3 source apportionment results showed that boundary contributions were the dominant contributor to O3 pollution in Beijing (> 40%). The contribution of non-local emissions to O3 levels was significantly greater in the outer suburbs than in urban and inner suburban areas due to topography. This study increases the understanding of the complex processes of O3 formation in different areas of Beijing and informs the implementation of O3 control plans.

How Particle Size Influences Oxidation of Ancient Organic Matter during Weathering of Black Shale.

Weathering continuously converts rock to regolith at Earth's surface while regulating the atmospheric concentrations of CO2 and O2. Shale weathering is of particular interest because shale, the most abundant rock type exposed on continents, stores much of the ancient organic carbon (OCpetro) buried in rocks. Using geochemical and mineralogical analysis combined with neutron scattering and imaging, we investigated the weathering profile of OCpetro in saprock in a black shale (Marcellus Formation) in the Ridge and Valley Appalachians in Pennsylvania, U.S.A. Consistent with the low erosion rate of the landscape, we discovered that Marcellus is completely depleted in carbonate, plagioclase, and pyrite in saprock below the soil layer. On the contrary, only ∼60% of OCpetro was depleted in saprock. By comparing the pore structure of saprock to bedrock and samples combusted to remove organic matter (OM), we confirmed that the large particles of OM are preferentially depleted, leaving elongated pores of tens to hundreds of micrometers in length, while the smaller particulates of OM (ranging from ∼5 to ∼200 nm) are largely preserved during weathering. The retarded weathering of small OM particles is attributed to their close association with mineral surfaces in the shale matrix. The texture of OM in shale is underappreciated as an important factor that controls porosity generation and the weathering rate of OCpetro.

The response system of the growth, physiological and uptake characteristics of Pinus bungeana under ozone stress

Objective: To study the changes of growth, physiological and absorption characteristics of Pinus bungeana under ozone (O3) stress, to elucidate the correlations among the indicators, and to determine its degree of response to O3. Methods: The growth, physiological characteristics and O3 uptake capacity of Pinus bungeana seedlings were measured in an open-top O3 fumigation manual control experiment with three concentration gradients (NF: normal atmospheric O3 concentration, NF40: normal atmospheric O3 concentration plus 40 nmlol/mol; NF80: normal atmospheric O3 concentration plus 80 nmol/mol), and the relationships between the characteristics of Pinus bungeana under different O3 concentrations were investigated with correlation analysis, redundancy analysis and analysis of variance. Results: (1) Plant height growth (ΔH), diameter growth at 50 cm (ΔDBH), stomatal size (S), stomatal density (M), stomatal opening (K), stomatal conductance (Gs), net photosynthetic rate (Pn), transpiration rate (Et), water use efficiency (WUE), maximum photochemical efficiency (Fv/Fm), chlorophyll content (CHL), whole tree water consumption (W), and O3 uptake rate () all decreased with the increase of O3 concentration; while intercellular CO2 concentration () and relative conductivity (L) increased with the increase of O3 concentration; (2) growth indicators of Pinus bungeana under O3 stress (ΔH, ΔDBH) were the most correlated with O3 uptake status (, W), followed by photosynthetic indicators (, WUE, ,, ) and growth indicators (ΔH, ΔDBH) and stomatal characteristics (K, M, S) under O3 stress, some physiological indicators (L, ) were relatively weakly correlated with photosynthesis (, WUE,,, ) and stomatal (K, M, S); (3) all the indicators of Pinus bungeana were significantly different under O3 treatments of NF and NF80 (P &lt; 0.05), ΔH, ΔDBH, M, CHL, , , W and were most significantly different under NF and NF40 treatments, and K, S, WUE, , , , L were more significantly different under NF40 and NF80 treatments. Conclusion: The experiment proved that the growth of Pinus bungeana was slowed, photosynthetic capacity was reduced, and the absorption capacity of O3 was further reduced by long-term exposure to high concentration of O3. The growth of Pinus bungeana was most correlated with the changes of O3 absorption characteristics, and the stomatal characteristics were most correlated with photosynthetic physiological characteristics, and the reduction of photosynthetic capacity etc. further led to the curtailment of its growth.