Loss Of Group Research Articles

Formation of Temporary Negative Ions and Their Subsequent Fragmentation upon Electron Attachment to CoQ0 and CoQ0 H2.

Ubiquinone molecules have a high biological relevance due to their action as electron carriers in the mitochondrial electron transport chain. Here, we studied the dissociative interaction of free electrons with CoQ0, the smallest ubiquinone derivative with no isoprenyl units, and its fully reduced form, 2,3‐dimethoxy‐5‐methylhydroquinone (CoQ0H2), an ubiquinol derivative. The anionic products produced upon dissociative electron attachment (DEA) were detected by quadrupole mass spectrometry and studied theoretically through quantum chemical and electron scattering calculations. Despite the structural similarity of the two studied molecules, remarkably only a few DEA reactions are present for both compounds, such as abstraction of a neutral hydrogen atom or the release of a negatively charged methyl group. While the loss of a neutral methyl group represents the most abundant reaction observed in DEA to CoQ0, this pathway is not observed for CoQ0H2. Instead, the loss of a neutral OH radical from the CoQ0H2 temporary negative ion is observed as the most abundant reaction channel. Overall, this study gives insights into electron attachment properties of simple derivatives of more complex molecules found in biochemical pathways.

Sources of ambient non-methane hydrocarbon compounds and their impacts on O3 formation during autumn, Beijing

The field observation of 54 non-methane hydrocarbon compounds (NMHCs) was conducted from September 1 to October 20 in 2020 during autumn in Haidian District, Beijing. The mean concentration of total NMHCs was 29.81 ± 11.39 ppbv during this period, and alkanes were the major components. There were typical festival effects of NMHCs with lower concentration during the National Day. Alkenes and aromatics were the dominant groups in ozone formation potential (OFP) and OH radical loss rate (LOH). The positive matrix factorization (PMF) running results revealed that vehicular exhaust became the biggest source in urban areas, followed by liquefied petroleum gas (LPG) usage, solvent usage, and fuel evaporation. The box model coupled with master chemical mechanism (MCM) was applied to study the impacts of different NMHCs sources on ozone (O3) formation in an O3 episode. The simulation results indicated that reducing NMHCs concentration could effectively suppress O3 formation. Moreover, reducing traffic-related emissions of NMHCs was an effective way to control O3 pollution at an urban site in Beijing.

Comparison of Outcomes of the Radial Forearm Free Flap Vs Pectoralis Major Pedicled Flap for the Reconstruction of Oral Soft Tissue Defects

Introduction: Head and neck cancers are one of common cancers with peri oral cancers are more prevailing in areas with use of tobacco, ghutka and alcohol. Peri oral soft tissue defects can occur after tumor ablation or trauma. Objectives/Aim: To assess the flap survival and oral competence in radial forearm free flap versus pedicled pectoralis major myocutaneous flap. Method: A randomized control trial was conducted at Department of Plastic Surgery BVH, Bahawalpurfrom July 2019 to December 2020. A total of 60 patients were randomly divided in two equal groups. In Group A, radial forearm free flap and in Group B pedicledpectoralis major myocutaneous flap were used for reconstruction offull thickness defects. Data was entered and analyzed by using SPSS version 27.0. Mean and Standard Deviation were calculated for quantitative variables. Frequency and percentages were calculated for qualitative variables.Chi-square test was used to compare the flap survival and oral competence between the groups and p 0.05 which is not statistically significant. Results: The mean age of patients in group A was 47.47 ± 12.28 years and in group B was 48.40 ± 12.02 years. Out of 60 patients, 80%& 60% of patients in group A & B were males respectively. Partial Flap lossin group A was 6.67% and in Group B 10%. Overall flap survival was 93.33% in Group A & 86.67% in Group B with the p > 0.05 which is not statistically significant. Conclusion: Radial forearm free flap is comparable option for head and neck reconstruction to the pectoralis major myocutaneous flap with fewer complication rate and overall successful outcome.

Determination of Uptake Coefficient of Peroxy Radical Loss by Aerosols Using HOx Reactivity Measurement Technique

Determination of Uptake Coefficient of Peroxy Radical Loss by Aerosols Using HO_x Reactivity Measurement Technique

Source Apportionment of VOCs and O3 Production Sensitivity at Coastal and Inland Sites of Southeast China

Urbanization and industrialization levels have a significant impact on the pollution of O3 and its precursors. However, current studies of VOC sources and O3 formation sensitivity in the regions with different urbanization and industrialization levels remained limited. Therefore, offline and online VOC observations were conducted at coastal sites (CS) and inland sites (IS) of southeast China to analyze spatial-temporal characteristics, source apportionment of VOCs based on the positive matrix factorization (PMF) model, and their effects on O3 formation using the observation-based model (OBM). The results showed that the average concentrations of TVOCs at CS and IS were 49.1 ± 14.4 and 28.4 ± 9.6 ppb, respectively, with higher levels in autumn compared to those in spring and summer. Alkene species contributed the largest to the OH radical loss rate (LOH) and ozone formation potential (OFP). The contributions of vehicle exhaust and combustion sources, industrial sources, solvent usage, biogenic sources, and fuel evaporation at CS and IS were 42.2% and 34.5%, 22.4% and 18.2%, 12.7% and 4.5%, 11.7% and 19.4%, and 11.0% and 23.4%, respectively. Meanwhile, vehicle exhaust and combustion sources (31.8%), fuel evaporation (21.3%) were the major contributors to O3 formation in Ningde. The results of sensitivity analysis indicated that O3 formation at CS was mainly VOC control in spring and autumn, and controlled by both VOCs and NOx in summer, but the VOCs is the key factor for the O3 formation at IS, and the emission control of alkenes and aromatics was conductive to decrease O3 levels. The scenario analysis suggested that the 20% reduction of VOC concentrations and 3% reduction of NOx concentrations could realize the 5% reduction of O3 concentrations. This study might enhance the understanding of O3 and its precursors in southeast China with different urbanization levels, as well as the emission reduction strategies.

Spatial-temporal Characteristics and Source Apportionment of Ambient VOCs in Southeast Mountain Area of China

Seasonal variations and sources of ambient volatile organic compounds (VOCs) were conducted at the county and rural sites in a mountain area of southeastern China. The results showed that the pattern of VOC concentrations was dominated by oxygenated VOCs (37.6%) and alkanes (25.8%), followed by halocarbons (16.8%), alkenes (11.9%), aromatics (6.87%), and alkynes (1.04%). Based on the OH radical loss rate (LOH) and ozone formation potential (OFP) analysis, alkenes had the highest chemical activity, especially the contribution of isoprene in rural areas. Aromatics contributed the most to secondary organic aerosols (SOA) formation in both county and rural areas. Source apportionment of VOCs were quantified by the positive matrix factorization (PMF) model, including industrial emissions and combustion burning (30.1% and 43.3% in the county and rural areas, respectively) and vehicle exhausts (30.3% and 10.8%), followed by solvent usage (17.1% and 5.2%), liquid petroleum gas (LPG) usage and fuel evaporation (14.2% and 10.0%), and biogenic source (8.3% and 30.6%). The backward air trajectories showed that air mass in spring was mainly originated from the intercity transmission, while the air clusters in autumn came from the northern areas through long-range transport. The study was helpful to understand the pollution characteristics in the mountainous area and provides a scientific basis for local O3 and PM2.5 pollution control.

Photoionization of Two Potential Biofuel Additives: γ-Valerolactone and Methyl Butyrate.

The photoionization of two potential biofuel additives, γ-valerolactone (GVL, C5H8O2) and methyl butyrate (MB, C5H10O2) has been studied by imaging photoelectron photoion coincidence spectroscopy (iPEPICO) at the VUV beamline of the Swiss Light Source (SLS). The vibrational fine structure in the photoelectron spectrum is compared with a Franck-Condon simulation for the electronic ground-state band of the GVL cation. In the lowest energy dissociative photoionization channel of GVL, CO2 is lost, resulting in a 1-butene fragment ion with a 0 K appearance energy of E0 = 10.35 ± 0.01 eV. A newly calculated 1-butene ionization energy of 9.595 ± 0.015 eV establishes the reverse barrier height to CO2 loss as 66.6 ± 4.3 kJ mol-1. Methyl butyrate cations undergo McLafferty rearrangement, which explains the missing ion signal at the computed adiabatic ionization energy of 9.25 eV. After H transfer, ethylene is lost in the lowest energy dissociation channel to yield the methyl acetate enol ion at E0 = 10.24 ± 0.04 eV. This value connects the energetics of methyl butyrate with that of methyl acetate enol ion, which is established at ΔfHo0K[CH2C(OH)OCH3+] = 502 ± 6 kJ mol-1. Parallel to ethylene loss, methyl loss is also observed from the enol tautomer of the parent ion. Both samples exhibit low-energy nonstatistical dissociative ionization channels. In GVL, the methyl-loss abundance rises quickly but levels off suddenly in the energy range of the first electronically excited states, indicating nonstatistical competition between CH3 and CO2 loss. In MB, the major parallel dissociation channel is the loss of a methoxy radical. Calculations indicate that McLafferty rearrangement is inhibited on the excited-state surface. Indeed, breakdown curve modeling of this and a sequential CO-loss channel confirms a second statistical regime in dissociative photoionization, decoupled from ethylene loss.

Tower-based measurements of NMHCs and OVOCs in the Pearl River Delta: Vertical distribution, source analysis and chemical reactivity

Measurements of vertical distribution of volatile organic compounds (VOCs) have attracted wide attentions, which could help to understand atmospheric oxidation mechanism and provide implications for VOC control. This study measured the non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) simultaneously for the first time at three different heights, namely ground, 118 m and 488 m, in the Canton Tower located in the urban core of the Pearl River Delta (PRD). The results show that NMHCs decreased while some OVOC species such as formaldehyde and acetaldehyde increased with increasing height. It was mainly attributed to the dilution and chemical loss of NMHCs but secondary production of OVOCs during vertical transport. Ratio analysis and receptor modeling indicate that vehicle exhausts (47%) and fuel evaporation (39%) were major sources of the total NMHCs. Interestingly, industry contributed much more at 118 m, probably affected by organic gas discharge from the high chimney of industrial factories. The chemical reactivities in terms of OH radical loss rate (LOH), ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were lowest at 118 m, smaller than those influenced by high fresh NMHC emissions at ground and strong formation of secondary species (e.g. OVOCs) at 488 m. OH exposure estimated by isoprene and m,p-xylene/ethylbenzene was different depending on their time scale of vertical turbulent mixing and chemical loss. OVOC species measured at different heights were positively correlated with Ox (R = 0.48–0.87), indicating that OVOCs were largely contributed by secondary formation in photochemical process. The tower measurements of NMHCs and OVOCs provided a unique opportunity to investigate the VOC distribution and chemical behaviors, which could give important information for understanding O3 and PM2.5 pollution mechanism in the PRD region with fast developing urban setting and substantially changing air quality.

Atmospheric photo-oxidation of myrcene: OH reaction rate constant, gas-phase oxidation products and radical budgets

Abstract. The photo-oxidation of myrcene, a monoterpene species emitted by plants, was investigated at atmospheric conditions in the outdoor simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a Large Reaction Chamber). The chemical structure of myrcene consists of one moiety that is a conjugated π system (similar to isoprene) and another moiety that is a triple-substituted olefinic unit (similar to 2-methyl-2-butene). Hydrogen shift reactions of organic peroxy radicals (RO2) formed in the reaction of isoprene with atmospheric OH radicals are known to be of importance for the regeneration of OH. Structure–activity relationships (SARs) suggest that similar hydrogen shift reactions like in isoprene may apply to the isoprenyl part of RO2 radicals formed during the OH oxidation of myrcene. In addition, SAR predicts further isomerization reactions that would be competitive with bimolecular RO2 reactions for chemical conditions that are typical for forested environments with low concentrations of nitric oxide. Assuming that OH peroxy radicals can rapidly interconvert by addition and elimination of O2 like in isoprene, bulk isomerization rate constants of 0.21 and 0.097 s−1 (T=298 K) for the three isomers resulting from the 3′-OH and 1-OH addition, respectively, can be derived from SAR. Measurements of radicals and trace gases in the experiments allowed us to calculate radical production and destruction rates, which are expected to be balanced. The largest discrepancies between production and destruction rates were found for RO2. Additional loss of organic peroxy radicals due to isomerization reactions could explain the observed discrepancies. The uncertainty of the total radical (ROx=OH+HO2+RO2) production rates was high due to the uncertainty in the yield of radicals from myrcene ozonolysis. However, results indicate that radical production can only be balanced if the reaction rate constant of the reaction between hydroperoxy (HO2) and RO2 radicals derived from myrcene is lower (0.9 to 1.6×10-11 cm3 s−1) than predicted by SAR. Another explanation of the discrepancies would be that a significant fraction of products (yield: 0.3 to 0.6) from these reactions include OH and HO2 radicals instead of radical-terminating organic peroxides. Experiments also allowed us to determine the yields of organic oxidation products acetone (yield: 0.45±0.08) and formaldehyde (yield: 0.35±0.08). Acetone and formaldehyde are produced from different oxidation pathways, so that yields of these compounds reflect the branching ratios of the initial OH addition to myrcene. Yields determined in the experiments are consistent with branching ratios expected from SAR. The yield of organic nitrate was determined from the gas-phase budget analysis of reactive oxidized nitrogen in the chamber, giving a value of 0.13±0.03. In addition, the reaction rate constant for myrcene + OH was determined from the measured myrcene concentration, yielding a value of (2.3±0.3)×10-10 cm3 s−1.

Distribution of the Deposition Rates in an Industrial-Size PECVD Reactor Using HMDSO Precursor

The deposition rates of protective coatings resembling polydimethylsiloxane (PDMS) were measured with numerous sensors placed at different positions on the walls of a plasma-enhanced chemical vapor deposition (PECVD) reactor with a volume of approximately 5 m3. The plasma was maintained by an asymmetric capacitively coupled radiofrequency (RF) discharge using a generator with a frequency 40 kHz and an adjustable power of up to 8 kW. Hexamethyldisiloxane (HMDSO) was leaked into the reactor at 130 sccm with continuous pumping using roots pumps with a nominal pumping speed of 8800 m3 h−1 backed by rotary pumps with a nominal pumping speed of 1260 m3 h−1. Deposition rates were measured versus the discharge power in an empty reactor and a reactor loaded with samples. The highest deposition rate of approximately 15 nm min–1 was observed in an empty reactor close to the powered electrodes and the lowest of approximately 1 nm min–1 was observed close to the precursor inlet. The deposition rate was about an order of magnitude lower if the reactor was fully loaded with the samples, and the ratio between deposition rates in an empty reactor and loaded reactor was the largest far from the powered electrodes. The results were explained by the loss of plasma radicals on the surfaces of the materials facing the plasma and by the peculiarities of the gas-phase reactions typical for asymmetric RF discharges.

Flame edge dynamics in counterflow nonpremixed flames of CH4/He versus air at low strain rates: An experimental and numerical study

The characteristics of the flame structure, stabilization, and extinction of counterflow nonpremixed flames of CH4/He versus air at low strain rates are investigated by performing a series of experiments and two-dimensional (2-D) numerical simulations. By adopting an experimental methodology using He curtain flow, we can locate the flames near the center of the counterflow burner and measure the critical He mole fraction in the fuel stream, XHe,cr, for flame extinction at very-low strain rates. XHe,cr obtained from 2-D numerical simulations in normal and zero gravity show a good agreement with those from the experiments, which substantiates that the experimental methodology can effectively reduce the buoyancy effect at low strain rates. It is found from various steady and unsteady 2-D numerical simulations that the dynamics of flame edge plays a critical role in determining the flame stabilization and extinction, and the edge flame is stabilized at a location where negative edge flame propagation speed, Se, balances positive local flow velocity, Ue. The transport budget analysis reveals that despite the negative Se by the diffusive loss of heat and radicals, the edge flame can survive by the help of the convective gain of heat and radicals from the trailing diffusion flame. It is also found that the counterflow flame can survive the increase of He mole fraction in the fuel stream, XHe, by shrinking its flame length since the local chemical reaction at the flame edge is enhanced with decreasing the flame length. However, as XHe exceeds XHe,cr, a slight inward movement of the edge flame induces a large magnitude of negative Se compared to positive Ue such that the counterflow flame is totally extinguished by the shrinkage of the outer edge flame toward the flame center.

Kinetics and impacting factors of HO<sub>2</sub> uptake onto submicron atmospheric aerosols during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan

Abstract. HO2 uptake kinetics onto ambient aerosols play pivotal roles in tropospheric chemistry but are not fully understood. Field measurements of aerosol chemical and physical properties should be linked to molecular-level kinetics; however, given that the HO2 reactivity of ambient aerosols is low, traditional analytical techniques are unable to achieve this goal. We developed an online approach to precisely investigate the lower-limit values of (i) the HO2 reactivities of ambient gases and aerosols and (ii) HO2 uptake coefficients onto ambient aerosols (γ) during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan. We identified the effects of individual chemical components of ambient aerosols on γ. The results were verified in laboratory studies on individual chemical components: transition metals play a key role in HO2 uptake processes, and chemical components indirectly influence such processes (i.e., by altering aerosol surface properties or providing active sites), with smaller particles tending to yield higher γ values than larger particles owing to the limitation of gas-phase diffusion being smaller with micrometer particles and the distribution of depleting species such as transition metal ions being mostly distributed in accumulation mode of aerosol. The modeling of γ utilized transition metal chemistry derived by previous studies, further confirming our conclusion. However, owing to the high NO concentrations in Yokohama, peroxy radical loss onto submicron aerosols has a negligible impact on O3 production rate and sensitivity regime.

VOCs characteristics and their ozone and SOA formation potentials in autumn and winter at Weinan, China.

Frequent ozone and fine particulate matter (PM2.5) pollution have been occurring in the Guanzhong Plain in China. To effectively control the tropospheric ozone and PM2.5 pollution, this study performed measurements of 102 VOCs species from Sep.19-25 (autumn) and Nov.27-Dec. 8, 2017 (winter) at Weinan in the central Guanzhong Plain. The total volatile organic compounds (TVOCs) concentrations were 95.8 ± 30.6 ppbv in autumn and 74.4 ± 37.1 ppbv in winter. Alkanes were the most abundant group in both of autumn and winter, accounting for 33.5% and 39.6% of TVOCs concentrations, respectively. The levels of aromatics and oxygenated VOCs were higher in autumn than in winter, mainly due to changes in industrial activities and combustion strength. Photochemical reactivities and ozone formation potentials (OFPs) of VOCs were calculated by applying the OH radical loss rate (LOH) and maximum incremental reactivity (MIR) method, respectively. Results showed that Alkenes and aromatics were the key VOCs in term ozone formation in Weinan, which together contributed 59.6% ̶ 65.3% to the total LOH and OFP. Secondary organic aerosol formation potentials (SOAFP) of the measured VOCs were investigated by employing the fractional aerosol coefficient (FAC) method. Aromatics contributed 94.9% and 96.2% to the total SOAFP in autumn and winter, respectively. The regional transport effects on VOCs and ozone formation were investigated by using trajectory analysis and potential source contribution function (PSCF). Results showed that regional anthropogenic sources from industrial cities (Tongchuan, Xi'an city) and biogenic sources from Qinling Mountain influenced VOCs levels and OFP at Weinan. Future studies need to emphasize on meteorological factors and sources that impact on VOCs concentrations in Weinan.

Chemical characteristics and source apportionments of volatile organic compounds (VOCs) before and during the heating season at a regional background site in the North China Plain

We investigated the characteristics and sources of volatile organic compounds (VOCs) at a regional background station on the North China Plain from 12 October to 31 December 2017. This study is unique in that emission sources of VOCs and their influence on ozone formation were identified for the first time at a regional background site in North China. The average total mixing ratio of VOCs was 16.0 ± 10.0 ppbv before the heating period (NHP, 12 October to 14 November), and this value was 43% higher than that during the heating period (HP, November 15 to 31 December). Alkanes were the dominant contributors to total VOCs and ranged from 59.9% to 67.1% during the HP and NHP. Relative humidity (RH) and temperature (T) dependence were observed before the HP, and high VOC mixing ratios were observed at relatively low T (−4 °C to 5 °C) and high RH (>60%) conditions and medium T (5 °C < T < 14 °C) and low RH (< 60%) conditions. High mixing ratios of VOCs were observed under RH > 55% and T < −1 °C conditions during the HP. Through bivariate polar plots, medium or low mixing ratios of total VOCs (TVOCs) were found at low wind speeds (<2 m s−1) before the HP, whereas a high mixing ratio was found during the HP, highlighting the important role of local source emissions during the HP. In addition, southwest winds at high wind speeds (>4 m s−1) were essential for the regional transport of pollutants. The contributions of alkenes to LOH (OH radical loss rate) and OFP (ozone formation potential) before and during the HP were as high as 48.8%–62.9% and 49.7% -64.4%, respectively. The OFP and LOH of ethene presented higher levels before and during the HP, elucidating the significant role of alkenes in the formation of O3 at SDZ site. Four emission sources of VOCs, including coal burning, liquefied petroleum gas (LPG) and natural gas (NG) usage, vehicular emissions and gasoline evaporation, were resolved using a positive matrix factorization (PMF) model, with contributions of 45.4%, 15.8%, 23.4% and 15.4%, respectively. The concentration weighted trajectory (CWT) analysis indicated that the main potential source regions were located to the south and southwest of Shangdianzi (SDZ) before the HP, and they were characterized by a narrow pollution band along Hengshui-Baoding-Langfang-Beijing. High CWT values were primarily distributed in a small region in southern SDZ during the HP, emphasizing the role of local emissions and transport from surrounding regions, especially urban areas of Beijing.

A Crossed Molecular Beams and Computational Study of the Formation of the Astronomically Elusive Thiosilaformyl Radical (HSiS, X2A').

The formation pathways to silicon- and sulfur-containing molecules are crucial to the understanding of silicon-sulfur chemistry in interstellar and circumstellar environments. While multiple silicon- and sulfur-containing species have been observed in deep space, their fundamental formation mechanisms are largely unknown. The crossed molecular beams technique combined with electronic structure and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations was utilized to study the bimolecular reaction of atomic silicon (Si(3Pj)) with thiomethanol (CH3SH, X1A') leading to the thiosilaformyl radical (HSiS, X2A') via an exclusive methyl radical (CH3, X2A2″) loss via indirect scattering dynamics which involves barrierless addition and hydrogen migration in an overall exoergic reaction, indicating the possibility that HSiS can form in cold molecular clouds. The astronomically elusive thiosilaformyl radical may act as a tracer of an exotic silicon-sulfur chemistry to be deciphered toward, for example, the star-forming region SgrB2, thus leading to a better understanding of the formation of silicon-sulfur bonds in deep space.

Ex situ conservation in botanical gardens – challenges and scientific potential preserving plant biodiversity

In the Anthropocene, the world’s plant diversity is threatened with extinction and the erosion of the genetic diversity of natural populations. According to the State of the World’s Plants and Fungi 2020 of the Royal Botanic Gardens, Kew, two out of five of the ~350,000 known vascular plant species are at risk of extinction. Despite the considerable toolkit of biodiversity conservation practices, usually it is hard to choose the best option to stop biodiversity loss. Ex situ conservation has seen massive development due to radical losses of natural ecosystems, and its incrementing necessity has been underscored by Target 8 of the 2011-2020 Global Strategy for Plant Conservation. As we crossed the finish line of this strategy in 2020, a review of the accumulated knowledge on the ex situ living collections has become particularly important. Despite the increasing attention received by ex situ conservation, studies on the sustainability, quality, and usability of the plant material prior to establishing the garden collections are few, leaving major gaps unfilled in terms of best ex situ conservation practices. Here we present an overview of the results and experiences in ex situ conservation focusing on living plant collections, with the aim of guiding conservation practitioners towards the most efficient working methods. We evaluate the future needs and perspectives of this conservation technique, based on case studies on both woody and herb species. Possible conservation applications and priorities suggested for future works are summarized.

Ozone and its precursors in a high-elevation and highly forested region in central China: Origins, in-situ photochemistry and implications of regional transport

Atmospheric chemistry observation and modelling in alpine areas have strong indication of regional air quality. In this study, one-month continuous ozone (O3) measurement at a high-elevation and highly forested site in central China, in combination with observations at similar stations, indicated elevated O3 levels in the free troposphere (FT) over China. Uninterrupted O3 injuries to the old-growth forest in the study region were expected. FT O3 overwhelmed daytime photochemical formation at the site, and the transport of O3 from the north (e.g., Guanzhong Plain) was most significant. Air masses from the adjacent southwest and south regions (e.g., Chongqing) contained higher levels of nitric oxide, sulfur dioxide, fine particles and volatile organic compounds (VOCs) in association with vehicular and industrial emissions. In contrast, air masses from the northeast (e.g., North China Plain) were laden with combustion tracers. The in-situ photochemistry modelling confirmed weak O3 formation at the site. For the reasons, the insufficient nitrogen oxides suppressed transformation of peroxyl radicals to alkoxy and hydroxyl radicals, resulting in considerable losses of peroxyl radicals via self-reactions. VOCs showed little impact on in-situ O3 production, and accounted for net consumption of OH, with isoprene as the most predominant OH depleting species. This study fills the gaps in observation of O3 and its precursors and modelling of in-situ photochemistry in high-elevation regions of central China, and provides hints for the impacts of transport on air pollution in this region.

Fate of Protonated Formates in the Gas Phase.

Formates are a class of organic molecules emitted into the atmosphere from fuel additives and industrial solvents. Formate-derived esters can undergo a vast range of chemical reactions in the atmosphere, most of which are initiated by oxidation by hydroxyl radicals. One potential reaction upon their interaction with atmospheric water is proton transfer to form protonated formates. The goal of the present work is to explore the dissociation of these protonated species and thus their possible atmospheric fate. Tandem mass spectrometry was employed to study the unimolecular dissociation of the protonated forms of methyl- (1), ethyl- (2), isopropyl- (3), tert-butyl- (4), and phenylformate (5). 1 and 2 lose CO as a common fragmentation product, forming a protonated alcohol, and 2 also generates neutral ethanol (forming protonated CO). 3 and 4 readily lose the stable isopropyl and tert-butyl radicals as well as neutral alkenes propene and isobutene. Methanol loss is also observed from both ions. 5 exhibits both phenyl radical loss (similar to 3 and 4) and CO loss (like 1 and 2). Density functional theory was used to explore the observed minimum energy reaction pathways for each ion, and CBS-QB3 single-point energy calculations provided reliable energetics.

Rice Transcription Factor OsWRKY55 Is Involved in the Drought Response and Regulation of Plant Growth.

WRKY transcription factors (TFs) have been reported to respond to biotic and abiotic stresses and regulate plant growth and development. However, the molecular mechanisms of WRKY TFs involved in drought stress and regulating plant height in rice remain largely unknown. In this study, we found that transgenic rice lines overexpressing OsWRKY55 (OsWRKY55-OE) exhibited reduced drought resistance. The OsWRKY55-OE lines showed faster water loss and greater accumulation of hydrogen peroxide (H2O2) and superoxide radical (O2−·) compared to wild-type (WT) plants under drought conditions. OsWRKY55 was expressed in various tissues and was induced by drought and abscisic acid (ABA) treatments. Through yeast two-hybrid assays, we found that OsWRKY55 interacted with four mitogen-activated protein kinases (MAPKs) that could be induced by drought, including OsMPK7, OsMPK9, OsMPK20-1, and OsMPK20-4. The activation effects of the four OsMPKs on OsWRKY55 transcriptional activity were demonstrated by a GAL4-dependent chimeric transactivation assay in rice protoplasts. Furthermore, OsWRKY55 was able to reduce plant height under normal conditions by decreasing the cell size. In addition, based on a dual luciferase reporter assay, OsWRKY55 was shown to bind to the promoter of OsAP2-39 through a yeast one-hybrid assay and positively regulate OsAP2-39 expression. These results suggest that OsWRKY55 plays a critical role in responses to drought stress and the regulation of plant height in rice, further providing valuable information for crop improvement.

Oxygen Recombination Probability Data for Plasma-Assisted Atomic Layer Deposition of SiO2 and TiO2.

Atomic layer deposition (ALD) can provide nanometer-thin films with excellent conformality on demanding three-dimensional (3D) substrates. This also holds for plasma-assisted ALD, provided that the loss of reactive radicals through surface recombination is sufficiently low. In this work, we determine the surface recombination probability r of oxygen radicals during plasma ALD of SiO2 and TiO2 for substrate temperatures from 100 to ∼240 °C and plasma pressures from 12 to 130 mTorr (for SiO2). For both processes, the determined values of r are very low, i.e., ∼10–4 or lower, and decrease with temperature and pressure down to ∼10–5 within the studied ranges. Accordingly, deposition on trench structures with aspect ratios (ARs) of <200 is typically not significantly limited by recombination and obtaining excellent film conformality is relatively facile. For higher AR values, e.g., approaching 1000, the plasma time needed to reach saturation increases exponentially and becomes increasingly dependent on the process conditions and the corresponding value of r. Similar dependence on process conditions can be present for plasma ALD of other materials as well, where, in certain cases, film growth is already recombination-limited for AR values of ∼10. Radical recombination data and trends as provided by this work are valuable for optimizing plasma ALD throughput and feasibility for high-AR applications and can also serve as input for modeling of radical recombination mechanisms.