Increasing O2 Concentration Research Articles

Impact of aerosol-photolysis interaction on the ozone concentration in the upper boundary layer on Mountain Everest.

Previous research has revealed that, during the late afternoon, the ozone (O3) concentration tends to elevate at the northern perimeter of Mount Everest (5200m above sea level). This increase is attributed to the natural gradient of rising O3 concentration with height, exacerbated by the corresponding downstream mountain winds. Our recent field observations corroborate this finding, showing a consistent increase in O3 concentrations by approximately 13.5±2.5 ppbv/km at a similar observational site. Despite these observations, the precise cause of this height-dependent increase in O3 remains elusive. In this study, we show that the influence of aerosol-photolysis interaction can partially explain the increment of O3 with height based on the field measurement results of the aerosol microphysical properties. Results show that the mean aerosol single scattering albedo, asymmetry factor, scattering angstrom index, and absorption angstrom index on the edge of the Mountain Everest were 0.98, 0.70, 1.3, and 0.66 respectively. The photolysis ratio increases with the height based on the tropospheric ultraviolet and visible model simulations with the measured aerosol optical properties. Sensitivity experiments further demonstrate that the unique microphysical properties of aerosols at Mount Everest result in a higher increment rate of the nitrate oxide photolysis rate with height (1.93×10-3/kms) compared to those observed in Beijing (1.53×10-3/kms). This difference leads to an additional increase in ozone concentration by 1.8 ppbv (from 69.1 ppbv to 70.9 ppbv) at the top of the boundary layer. Our study underscores the significant impact of aerosol-photolysis interactions on ozone concentrations and offers insights that could potentially advance our understanding of the sources of ozone in the upper troposphere over the Tibetan Plateau.

Research on the impact of land use and land cover changes on local meteorological conditions and surface ozone in the north China plain from 2001 to 2020

Land use and land cover changes (LULCC) alter local surface attributes, thereby modifying energy balance and material exchanges, ultimately impacting meteorological parameters and air quality. The North China Plain (NCP) has undergone rapid urbanization in recent decades, leading to dramatic changes in land use and land cover. This study utilizes the 2020 land use and land cover data obtained from the MODIS satellite to replace the default 2001 data in the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model. It simulates and analyzes the direct impact of LULCC on meteorological parameters and the indirect impact on surface ozone (O3) concentration through physical and chemical processes in the North China Plain during July in the summer. Six rapidly urbanizing cities were selected to represent the North China Plain. The results show that LULCC significantly increased sensible heat flux and 2-m temperature in rapidly urbanizing areas throughout the diurnal cycle, with more pronounced effects during the daytime, ranging from 6.49 to 23.46 W/m2 and 0.20–0.59 °C, respectively. The 10-m wind speed decreased at night and increased during the day, with changes ranging from − 0.43 to 0.27 m/s at night and − 0.16 to 0.15 m/s during the day. The planetary boundary layer height generally increased, with a larger rise during the daytime, ranging from 23.63 to 84.74 m. Simultaneously, surface O3 concentrations increased during both daytime and nighttime. The daytime increase ranged from 2.89 to 9.82 μg/m3, while the nighttime increase ranged from 1.76 to 7.77 μg/m3. LULCC enhanced meteorological and chemical processes as well as vertical transport, leading to an increase in O3. At the same time, it reduced the increase in O3 through horizontal transport and dry deposition processes. These changes are related to the meteorological variations. The impact on O3 concentrations was not limited to the surface but extended to the top of the planetary boundary layer (approximately 1500 m). Below 500 m, vertical transport increased O3 concentrations, while horizontal transport decreased O3 concentrations. Additionally, the meteorological and chemical processes induced by LULCC showed enhanced effects above the surface, whereas the dry deposition process had a smaller impact on O3 concentrations above the surface. This study reveals the significant impact of urban expansion on regional meteorological parameters and air quality. It optimizes the model’s simulation of regional air quality and provides new insights into understanding the effects of urbanization on meteorological conditions and air quality.

A synaptic transistor with a stacked layer of SiNx and SiO2 deposited from hexamethyldisiloxane/O2

Herein, we employed inductively coupled plasma enhanced chemical vapor deposition using a hexamethyldisiloxane/O2 precursor to deposit SiO2 with electrical double layer capacitance on SiNx forming SiO2/SiNx stacked films as a dielectric layer, achieving high-performance synaptic transistors. The effect of O2 concentration during SiO2 deposition on the transistor performance was investigated. The results of Fourier transform infrared spectroscopy and x-ray photoemission spectroscopy confirm that increasing O2 concentration during deposition boosts the amounts of protons moving between the bridging oxygen in the Si–O–Si network, improving the electrical double layer capacitance of SiO2. Furthermore, SiNx in the stacked structure exhibits a higher relative permittivity than SiO2, resulting in a more concentrated electric field within the SiO2 layer, facilitating proton ionization. SiO2/SiNx stacked film with SiO2 deposited at the oxygen flow rate of 150 sccm exhibited the maximum capacitance of 2.87 μF/cm2 at 4 Hz. The transistor with SiO2 deposited at the oxygen flow rate of 150 sccm achieved the maximum paired pulse facilitation index of 132.9% and the maximum A50/A1 index of 155.4%. This work demonstrates that SiO2 deposited via inductively coupled plasma enhanced chemical vapor deposition using a hexamethyldisiloxane/O2 precursor for application potential in artificial neuromorphic computing.

Surface Hydrophilic Modification of Polypropylene by Nanosecond Pulsed Ar/O2 Dielectric Barrier Discharge.

Polypropylene (PP) membranes have found diverse applications, such as in wastewater treatment, lithium-ion batteries, and pharmaceuticals, due to their low cost, excellent mechanical properties, thermal stability, and chemical resistance. However, the intrinsic hydrophobicity of PP materials leads to membrane fouling and filtration flux reduction, which greatly hinders the applications of PP membranes. Dielectric barrier discharge (DBD) is an effective technique for surface modification of materials because it generates a large area of low-temperature plasma at atmospheric pressure. In this study, O2 was added to nanosecond pulsed Ar DBD to increase its reactivity. Electrical and optical diagnostic techniques were used to study the discharge characteristics of the DBD at varying O2 contents. The uniformity of the discharge was quantitatively analyzed using the observed discharge images. Water contact angle measurements were used to assess the surface hydrophilicity of polypropylene. The surface morphology and chemical composition of the PP materials before and after treatment were analyzed using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that the moderate addition of O2 enhances surface hydrophilicity and the uniformity of the modification. By increasing the O2 addition from 0% to 0.1%, the average power increased from 4.19 W to 5.79 W, and the energy efficiency increased from 17.78% to 21.51%. The water contact angle of the DBD-treated PP showed a tendency to decrease and then increase with increasing O2 content, with the optimum O2 addition determined to be 0.1%. Under this condition, the water contact angle of the PP surface decreased by 31.88°, which is 52.31% lower than the untreated surface. O2 increases the number of oxygen-containing polar groups (-OH, C=O, and O-C=O) on the surface of the material, and deepens and densifies the grooves on the surface of the PP material, resulting in an increase in the hydrophilicity of the PP surface.

Ambient air pollution exposure and adult asthma incidence: a systematic review and meta-analysis.

Ambient (outdoor) air pollutant exposures have emerged as a plausible risk factor for incident childhood asthma. However, the effect of ambient air pollutant exposures on risk of incident adult asthma is unclear. We aimed to investigate associations between specific ambient air pollutants and the risk of incident adult asthma. In this systematic review and meta-analysis, we searched MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and Web of Science from inception to Nov 27, 2023. We included observational studies with the outcome of new-onset asthma during adulthood (onset at ≥18 years), and metric of exposure of ambient air pollutants (particulate matter [PM]2·5, nitrogen dioxide [NO2], ozone [O3], and sulphur dioxide [SO2]). Study data were extracted independently by two reviewers and study quality was assessed using the Newcastle-Ottawa scale. When four or more eligible studies were available for a given pollutant, we applied meta-analysis using inverse variance weighting in a random effects model to estimate pooled relative risk (RR), and used meta-regression to explore sources of heterogeneity. The protocol was registered with PROSPERO, CRD42023420139. Our search identified 1891 references. After excluding 651 (34%) duplicates and ineligible studies, we included 25 studies in the systematic review. After excluding studies with overlapping populations or reporting effect estimates that could not be pooled, we performed meta-analysis for PM2·5 (nine studies), NO2 (nine studies), and O3 (four studies). Pooled random effects RRs for incident adult asthma per 5 μg/m3 increase in PM2·5 were 1·07 (95% CI 1·01 to 1·13) and per 10 μg/m3 in NO2 were 1·11 (1·03 to 1·20). We found no significant association between increasing O3 concentration and incident adult asthma (per 60-μg/m3 increase in O3, pooled RR 1·04 [0·79 to 1·36]). We found substantial heterogeneity across studies (I2=88% for all analyses). In exploratory meta-regression, average exposure level was a significant source of heterogeneity for the pooled NO2 estimate (95% CI -0·0077 to -0·0025 per μg/m3). Exposure to increased ambient PM2·5 or NO2 might present an additional risk factor for incident adult asthma, although high heterogeneity among included studies warrants caution in interpretation. Evidence was inconsistent for O3 and insufficient for SO2. To increase confidence and population representation in pooled estimates, further primary investigations are necessary, ideally with aligned methodology and reporting. None.

Incentivizing emission controls toward clean air and carbon neutrality in China: Perspectives from a risk-based approach for air quality management.

Air Quality Standards (AQSs) worldwide have continued to employ concentration-based approaches since their first implementation under the 1970 Clean Air Act in the United States. The primary objective of establishing these AQSs is widely recognized as protecting public health. With the significantly improved understanding of the health risks associated with air pollutants today, it is an opportune time to reassess air pollution management from a fundamental risk perspective. This study applied a risk-based AQS system to assess the overall mortality risks associated with both long- and short-term exposure to air pollution in China between 2015 and 2022. The analyses revealed that the health benefits resulting from reductions in concentrations of non-ozone (O3) pollutants exceeded the health risks associated with increasing O3 concentrations. As a result, the overall mortality risk across China showed a significant descending trend. During the initial phase of decarbonization, emission reductions may unintentionally lead to increased O3 concentrations in China due to the non-linear response of O3 to its precursors. Nevertheless, the overall health benefits derived from emission controls incentivize governments to implement stringent measures toward achieving carbon neutrality. These findings highlight the substantial benefits of applying the risk-based AQS system for synergistic health and carbon management.

Numerical simulation of homogeneous elemental mercury oxidation within an electrostatic precipitator

The corona discharge in electrostatic precipitator (ESP) can contribute to homogenous Hg0 oxidation, thus favoring the simultaneous removal of mercury by the existing air pollution control devices in coal-fired power plant. A multi-field model consisting of reaction kinetics and dynamics was established to simulate the Hg0 oxidation performance in ESPs. The HCl dissociation products (i.e., Cl and Cl2) were responsible for the oxidation of Hg0 to HgCl2 and HgCl, in which the Hg0 oxidation efficiency (EHg) was increased from 13.3 % to 52.6 % with the increase of HCl concentration from 1 to 4 ppm. The increase of O2 concentration from 2 % to 8 % resulted in 2.1 % reduction of EHg, which was primary attributed to the inhibition of HCl dissociation process to form Cl-containing species. As the H2O content increased from 3 % to 12 %, EHg rose from 25.9 % to 29.1 %, due to H2O dissociation products (i.e., H and OH) enhancing the formation of Cl-containing species from HCl dissociation. The voltage fluctuations demonstrated dual effects on EHg: increasing from 35 kV to 40 kV reduced efficiency from 27.3 % to 26.4 %, attributed to diminished Cl-containing species, whereas further increasing to 50 kV enhanced efficiency to 32.1 % due to increased production of O-containing substances. A higher flow rate facilitated the escape of reactive chemical species from ESPs. The EHg decreased from 36.3 % to 17.5 % when the flow velocity increased from 0.1 to 0.25 m/s. These results clarified the key factors for affecting Hg0 oxidation within an ESP, which provides the fundamental to simultaneously control Hg0 emission from coal-fired power plants.

Nocturnal Ozone Enhancement Induced by Sea-Land Breezes During Summertime in Northern Coastal City Qingdao, China

This study investigated the influence of sea–land breezes on nocturnal spatial and temporal distribution of ozone (O3) and its potential effects on particulate nitrate formation in Qingdao, a coastal city in northern China. Observation campaigns were conducted to measure surface air pollutants and meteorological factors during a typical sea–land breezes event from 22 to 23 July 2022. A coherent Doppler lidar (CDL) system was employed to continuously detect three-dimensional wind fields. The results revealed that nocturnal ozone levels were enhanced by a conversion of sea–land breezes. Initially, the prevailing northerly land breeze transported high concentrations of O3 and other air pollutants from downtown to the Yellow Sea. As the sea breeze developed in the afternoon, the sea breeze front advanced northward, resulting in a flow of high O3 concentrations back into inland areas. This penetration of the sea breeze front led to a notable spike in O3 concentrations between 16:00 on 22 July and 02:00 on 23 July across downtown areas, with an average increase of over 70 μg/m3 within 10 min. Notably, a time lag in peak O3 concentration was observed with southern downtown areas peaking before northern rural areas. During this period, combined pollution of O3 and PM2.5 was also observed. These findings indicated that the nighttime increase in O3 concentrations, coupled with enhanced atmospheric oxidation, would likely promote the secondary conversion of gaseous precursors into PM2.5.

Characteristics, Transport Routes, and Potential Sources of PM2.5 and O3 Pollution in Suzhou

Based on the air quality and meteorological data in Suzhou from 2015 to 2022, the long-term variations in PM2.5 and O3, meteorological characteristics, and their correlations were analyzed in this study. The HYSPLIT model was used to explore the main transport pathways and potential source areas of PM2.5 and O3. The results showed that： ① The annual averaged concentrations of PM2.5 in Suzhou decreased steadily during the study period, and the annual average concentration from 2020 to 2022 reached the national second-level standard limit. However, the annual average concentrations of O3 all exceeded the national second-level standard limit. After 2017, the annual number of days that O3 exceeded the standard was always higher than that for PM2.5. The number of days of compound pollution continuously decreased from nine days in 2015 to zero days in 2020, and there was no compound pollution since then. ② The most severe pollution seasons for PM2.5 and O3 were winter and summer, respectively. PM2.5 pollution was more likely to occur in low-temperature and high-humidity weather, while O3 pollution was more frequent in high-temperature and low-humidity weather. Wind direction played an important role, with northwest winds amplifying PM2.5 pollution and southeast winds boosting O3. These two pollutants showed a strong correlation in summer with a coefficient reaching 0.73. ③ Cluster analysis revealed that trajectory two from Hebei Province in spring and trajectory four from Shaanxi Province in winter were prone to an increase in PM2.5 concentration. The short to medium distance trajectory 1 from Shandong Province in summer and trajectory two from Hebei Province in spring were prone to an increase in O3 concentration. ④ The analysis of potential source areas showed that transportation outside the province had a significant impact on PM2.5 and O3 pollution in Suzhou. The potential source areas of PM2.5 in spring and winter were mainly distributed in Anhui Province, Henan Province, and Hubei Province； the potential source areas in autumn were mainly distributed in Hubei Province and Jiangxi Province； and the potential source areas of O3 in spring and summer were mainly located in the Beijing-Tianjin-Hebei Region, Shandong Province, Henan Province, and Shanxi Province. Valuable management insights for the coordinated control of PM2.5 and O3 pollution in Suzhou were put forward based on this study.

Influence of Electrolyte Saturation on the Performance of Li-O2 Batteries.

Electrolyte saturation can strongly affect the Li-O2 battery performance. However, it is unclear to what extent saturation reduction will impact the battery capacity. In this study, we investigated the influence of electrolyte saturation and distribution within a porous positive electrode on the deep discharge-charge capacities and cycling stability. The study used both models and experiments to investigate the change of electrolyte distribution, double-layer capacitance, ohmic resistance, and O2 concentration in the positive electrode at different electrolyte saturations. Results revealed that electrodes with 60% electrolyte saturation achieved almost the same maximum discharge (6.38 vs 6.76 mAh/cm2) and charge (5.52 vs 5.65 mAh/cm2) capacities with fully saturated electrodes. The partially wet positive electrode (40% saturation) obtained more cycles than the electrode with 100% saturation before the discharge capacity dropped below the cutoff point. However, the electrode with 40% saturation had a low average charging efficiency of 88.76%, whereas the fully saturated electrode obtained 98.96% charging efficiency. Moreover, the fully wet positive electrode had the lowest overpotential during cycling (1.26-1.39 V). The measured electrochemically active surface areas showed that even 40% saturation could sufficiently wet the positive electrode surface and obtain a double-layer capacitance (18.12 mF) similar to that with 100% saturation (20.4 mF). Furthermore, a considerable increase in O2 concentration at wetted surface areas was observed for the electrolyte saturation of less than 60% due to the significantly higher O2 diffusivity in the gas phase.

Effects of valley topography on ozone pollution in the Lanzhou valley: A numerical case study

Valley topography is recognized for its role in constraining pollutant dispersion, which frequently results in elevated pollutant concentrations within valley regions. However, the specific mechanisms by which valley topography influences daytime ozone (O3) production, nighttime O3 depletion, and diurnal variations in O3 concentrations remain inadequately understood. This study employs the online WRF-Chem air quality model to conduct sensitivity analyses, examining the effects of valley topography on summer O3 concentrations in Lanzhou, a valley city in western China. The results indicate that valley topography generally reduces surface temperature and wind speed while also lowering the planetary boundary layer height (PBLH), which ultimately leads to increased concentrations of primary pollutants. Nevertheless, the impact of valley terrain on O3 is time-dependent, with concentrations decreasing during the day and increasing at night. In Lanzhou, valley topography contributes to a 4.4% reduction in daytime O3 concentrations. This reduction is largely due to the blocking of solar radiation by surrounding mountains, which results in a 7% decrease in shortwave radiation (SR) and a 17% decline in PBLH, subsequently limiting O3 chemical production. Although valley topography restricts pollutant dispersion, the overall effect during the day is a net decrease in O3 levels. In contrast, nighttime valley topography leads to a notable 19.8% increase in O3 concentrations. This increase is driven by mountain breezes transporting O3-rich air from the slopes into urban areas, along with a 67.4% reduction in nitrogen oxide (NO) levels. Despite intensified NO titration within the valley, the combined effect of these local wind patterns contributes to elevated O3 concentrations at night. These findings offer valuable insights into the unique factors contributing to urban O3 pollution in areas with complex valley topography.

Research on Ozone Pollution Characteristics and Source Apportionment During the COVID-19 Lockdown in Jilin City in 2022

The increasing Ozone (O3) concentration in various regions of China has garnered significant attention, highlighting the need to understand the mechanisms of O3 formation. This study focuses on the source apportionment of O3 in Jilin City during and after the COVID-19 lockdown countermeasure, and also the influence of anthropogenic emissions on O3 concentration. The contributions of different O3 emission sources were quantified using the Weather Research and Forecasting Community Multi-Scale Air Quality (WRF-CMAQ) model in conjunction with the Integrated Source Apportionment Method (ISAM). The results indicate a significant increase in O3 concentrations during the lockdown in Jilin City, which were particularly characterized by long-distance transportation. Transportation is identified as the primary direct source of O3 in Jilin City, with Yongji County contributing the most among the six designated regions. This study highlights variations in the causes and sources of O3 pollution among the different regions of Jilin City. Simply controlling anthropogenic emissions is inadequate for effectively managing O3 pollution and may even worsen the situation. It is more effective to focus on controlling O3’s precursors. These findings improve the understanding of O3 pollution in Jilin City and provide valuable insights for developing O3 control policies. Similarly, this research is applicable to other countries and regions.

Analysis of characteristics and mechanisms of iron-based oxygen carrier-aided oxy-fuel combustion of coal char in a bubbling fluidized bed

Oxygen carrier aided combustion (OCAC) technology, utilizing activated oxygen carriers within the fluidized bed material, aims to regulate oxygen distribution within the furnace and enhance the combustion environment through redox reactions with the macroscopic flow in the chamber. Oxy-fuel combustion is recognized as one of the mature technologies to capture CO2 from coal-fired power plants. Here, the effect of iron-based oxygen carriers (AR-Fe2O3, hematite, and steel slag) on the combustion characteristics of three coal chars (lignite, bituminous, and anthracite) are investigated in a bubbling fluidized bed operating at 850 °C and varying O2 concentrations ranging from 5 % to 21 % in CO2. The results indicate that the combustion rate of coal char and CO emission level are increased and the burnout time is shortened after replacing the quartz sand bed material with AR-Fe2O3. However, the combustion of lignite chars aided by hematite and steel slag exhibits opposite characteristics compared to those observed when substituting quartz sand bed material with AR-Fe2O3. With an increase in O2 concentration, the combustion behavior improved due to the increased mass transfer of O2 in CO2. The promoting effect of oxygen carrier on coal char combustion is in the following order: steel slag < hematite < AR-Fe2O3. The higher the fuel rank, the more obvious promoting effect of oxygen carrier. Analysis of OCAC mechanism combined with thermodynamic calculations shows that oxygen carrier serves a dual role: it provides oxygen to the fuel and simultaneously competes with the fuel for available oxygen. When coal char exhibits high reactivity, the competition for oxygen between the oxygen carrier and the fuel becomes more significant than the oxygen provision by the carrier. This heightened competition leads to an inhibition effect, as observed in the oxygen carriers aided combustion of lignite char.

Consecutive Northward Super Typhoons Induced Extreme Ozone Pollution Events in Eastern China

Typhoons are one of the most important weather systems that can cause severe ozone (O3) pollution in eastern China. While the effects of individual typhoons on O3 concentrations have been extensively studied, the effects of consecutive northward typhoons and the underlying mechanisms remain unclear, partly due to the complex processes involved. Here, Typhoons Maysak and Haishen, two consecutive northward typhoons in 2020, are selected to investigate their impact on the O3 pollution in eastern China. The results show that consecutive northward typhoons not only produced and maintained meteorological conditions conducive to O3 generation (e.g., elevated temperatures and intensified solar radiation), but also facilitated local accumulation and cross-regional transport of O3. These factors jointly led to a 30% increase in O3 concentration in eastern China with a prolonged period of O3 pollution. Our work underscores the significance of complex meteorological conditions in O3 pollution occurrences during extreme weather events, advancing our understanding of how consecutive northward typhoons affect air quality.

Responses of surface ozone under the tropical cyclone circulations: Case studies from Fujian Province, China

The circulation of tropical cyclones (TCs) exerts a multifaceted influence on the spatial and temporal distribution of surface pollutants. This study investigates the response of surface ozone (O3) concentration to the TCs in Fujian Province from June to December 2022 by analyzing the contributions of atmospheric pollutants, meteorological conditions, and dynamical transports. Empirical orthogonal function (EOF) decomposition methods are used to analyze the spatio-temporal distribution patterns of affected O3, and a Gradient Boosting Regression Trees (GBRT) machine learning model is employed to estimate surface O3 concentration, quantifying the influence of each factor. The results indicate an anomaly increase in O3 concentration during this period, with photochemistry-related meteorological conditions being the primary influencer, accounting for 66.9% of O3 variations, elucidating the interpretability of the GBRT model for attributing changes in O3 concentration. Low relative humidity and high temperature conditions have been identified as pivotal factors influencing the rise in O3 concentrations. The presence of TC undermines this predominant influence, amplifying the role of transport factors and other atmospheric pollutants. In the case studies of TC (Muifa and Nanmadol, 2022), the slow or stagnant TCs triggered persistent downdrafts in its periphery and brought favorable meteorological conditions such as clear sky and warm temperature for photochemistry. TCs also enhances the impact of horizontal and vertical dynamic transport on O3 concentrations. This work provides vital insights into the complex interplay between TCs and surface O3 concentrations, highlighting the need for targeted environmental and air quality management strategies in regions frequently impacted by TCs.

Effects of regulating the cathode gas properties on the ammonia-fueled solid oxide fuel cell. Part I. Parasitic power consumption and electrical efficiency after increasing O2 and H2O

This study designed and simulated a kW-scale SOFC system equipped with liquified O2 and NH3 tanks for unmanned underwater vehicles (UUVs). Optimizing the parasitic power consumption and electrical efficiency was performed via using oxygen-enriched cathode gas, in-cell cracking of ammonia and adding steam into cathode gas coupled with phase change of recycle steam. The results show increasing O2 concentration helps improve the net system electrical efficiency from 47.9% at simulate air to 51.7% at pure O2. The use of in-cell cracking increases the net system electrical efficiency by 1.3% on this basis. Interestingly, substitution of O2 to H2O would slightly reduce the net electrical efficiency of the system with O2-enriched cathode gas (e.g., decreased by 0.2% when using 40% H2O); however, substitution of N2 to H2O would help improve the net electrical efficiency of the system with simulated air as cathode gas (e.g., increased by 1.2% when using 40% H2O).

Impact of Lockdowns on Air Pollution: Case Studies of Two Periods in 2022 in Guangzhou, China

The photochemical mechanisms of ozone (O3) formation are complex, and simply reducing nitrogen oxide (NOx) emissions is insufficient to reduce O3 concentrations. The lockdown due to the Coronavirus Disease 2019 (COVID-19) pandemic provided a rare opportunity to explore the mechanisms of O3 formation and evaluate the performance of NOx emission control strategies through practical observations. This study integrates data from ground stations with observations from the TROPOMI sensor on the Sentinel-5P satellite to analyze air quality changes during the two one-month lockdown periods in Guangzhou, China, in March and November 2022. Our analysis particularly focuses on the impact of these lockdowns on O3 and NO2 concentrations, along with shifts in the sensitivity of ozone formation. Furthermore, we have assessed concentration changes of four major pollutants: PM2.5, PM10, SO2, and CO. The results show that the average O3 concentration in Guangzhou decreased during the March lockdown, while the average O3 concentration at three stations in the western part of Guangzhou increased during the November lockdown. The western part of Guangzhou is a VOCs (volatile organic compounds)-limited zone, and the NO2 emission reduction from the lockdown reduced the titration effect on O3, which led to the increase in O3 concentration. Overall, the impact of COVID-19 lockdowns on O3 concentrations depended on the local O3 producing sensitive system, and emissions of other major pollutants were reduced substantially, as reported in many other cities around the world.

Spatiotemporal Variation Characteristics of Ozone and Identification of Key Influencing Factors Based on Random Forest Model： A Case Study of Chuzhou City

The cause of ozone pollution is a complex scientific problem. Studying the spatiotemporal variation characteristics of O3 at different time scales and analyzing the key influencing factors of O3 concentration is of great significance for the precise formulation of urban air pollution control measures and the improvement of urban air quality. Based on the analysis of the spatiotemporal variation characteristics of O3 concentration in Chuzhou City, we studied the 12 ozone-influencing factors of meteorology and pollutants at multiple time scales using Spearman correlation analysis and a random forest model. The results showed that： ① The O3 pollution level of Chuzhou City showed an aggravating trend, and the O3 concentration distribution showed a spatial pattern of "high in the southeast and low in the northwest." ② From February to May, SO2 concentration had a strong impact on the increase in O3 concentration. From June to September, PM2.5 and PM10 were significantly positively correlated with ozone and had a greater impact. ③ Relative humidity, temperature, and wind speed had a significant impact on O3, whereas barometric pressure and hourly rainfall had a weak impact. ④ The O3 pollution mechanism in Chuzhou City changed from "pollutant-controlled" to "meteorology-controlled." ⑤ Among meteorological and pollutant factors, the three influencing factors that had the greatest influence on O3 concentration were temperature, wind speed, and relative humidity, with PM10 concentration, PM2.5 concentration, and SO2 concentration also contributing. All of the above six influencing factors had a significant nonlinear relationship with the O3 concentration.

Effects of Increasing Ozone Levels on Leaf Biochemistry and Flower Development in Petunia Varieties with Different Floral Pigmentation

In this work, we assessed the effects of increasing ozone (O3) on four petunia varieties with different floral pigmentation (pink, red, rose-red, and white). Plants were exposed, in open-top chambers located in China, to three O3 concentrations, i.e., (i) ambient air (AA), (ii) AA + 60 ppb O3 (AA + 60), and (iii) AA + 120 ppb O3 (AA + 120), for 85 days (9 h day−1). Flower diameter and duration were assessed, together with leaf chlorophyll and flavonoid contents. White petunia showed a reduced flower diameter and longevity under AA + 60 (−7 and −6%, respectively, in comparison to AA), whereas pink and red petunias only showed this under AA + 120 (−8 and −7%, on average, respectively). Chlorophyll loss occurred in all varieties under AA + 60 (−30%, on average), and at AA + 120 in white and red petunias (−54%, on average). The total flavonoid content in the pink and white varieties increased only under AA + 120 (around +85%), while it grew at both AA + 60 and AA + 120 (+92% and two-fold higher, respectively) in the red variety. Increasing O3 concentrations did not affect particularly the red-rose variety. The white variety showed the strongest correlations among flower and leaf properties, confirming a variety-related O3 response, as well as demonstrating that it had the highest O3 sensitivity.

Nitric and nitrous acid formation in plasma-treated water: Decisive role of nitrogen oxides (NOx=1–3)

Nitrogen fixation using low-temperature plasma, particularly in relation to plasma-treated water (PTW) and its chemical and physical properties, has received a renewed research focus. Dissolving highly concentrated nitrogen oxides (NOx = 1–3) generated by air discharge into water results in the formation of two aqueous oxiacids (nitrous and nitric acids; HNOy = 2,3) and their conjugates (nitrate and nitrite ions; NOy-). Nonlinear formation of these species in PTW with respect to plasma conditions has been observed; however, the significance of the time-varying NOx on this nonlinearity has not yet been thoroughly investigated. Here, we demonstrate real-time observations of HNOy/NOy- as well as NOx production in a surface dielectric barrier discharge reactor containing distilled water. Synchronized two optical absorption spectroscopy systems were employed to simultaneously measure gas-phase NOx and liquid-phase HNOy/NOy- in the plasma reactor operated under different oxygen contents of 5, 20, and 50%. Our results showed that reducing the oxygen content in the reactor accelerated the chemical transition from O3 and NO3 to NO1,2, leading to a predominance of nitrite in PTW. Specifically, the NO3-rich period was extended with increasing O2 content, resulting in the production of nitrate-dominant PTW at low pH levels. Our findings highlight the potential for the selective generation of HNOy/NOy- in PTW through the active and passive control of NOx in a plasma reactor. The direct, real-time observation of NOx–HNOy/NOy- conversion presented here has potential for improving the control and optimization of PTW, thereby enhancing its applicability.