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The high cost of equipment is a significant entry barrier to research for smaller organisations in developing solutions to air pollution problems. Low-cost electrochemical sensors have shown sensitivity at parts-per-billion by volume (ppbV) mixing ratios but are subject to variations due to changing environmental conditions, particularly temperature. We have previously demonstrated that under isothermal/isohume conditions such as those found in kinetic studies, very stable electrochemical responses occur. In this paper, we demonstrate the utility of a low-cost IoT-based sensor system that employs four-electrode electrochemical sensors under isothermal/isohume conditions for studying the kinetics of the atmospheric oxidation of nitrogen oxides. The results suggest that reproducible results for NO and NO2 kinetics can be achieved. The method produced oxidation rates of 7.95 × 103 L2 mol−2 s−1 (±1.3%), for NO and 7.99 × 10−4 s−1 (±2.1%) for NO2. This study suggests that the oxidation kinetics of nitrogen oxides can be assessed with low-cost sensors, which can support a wide range of industrial applications, such as designing biocatalytic coatings for air pollution remediation. [ABSTRACT FROM AUTHOR]

The high cost of equipment is a significant entry barrier to research for smaller organisations in developing solutions to air pollution problems. Low-cost electrochemical sensors have shown sensitivity at parts-per-billion by volume (ppbV) mixing ratios but are subject to variations due to changing environmental conditions, particularly temperature. We have previously demonstrated that under isothermal/isohume conditions such as those found in kinetic studies, very stable electrochemical responses occur. In this paper, we demonstrate the utility of a low-cost IoT-based sensor system that employs four-electrode electrochemical sensors under isothermal/isohume conditions for studying the kinetics of the atmospheric oxidation of nitrogen oxides. The results suggest that reproducible results for NO and NO2 kinetics can be achieved. The method produced oxidation rates of 7.95 × 103 L2 mol−2 s−1 (±1.3%), for NO and 7.99 × 10−4 s−1 (±2.1%) for NO2. This study suggests that the oxidation kinetics of nitrogen oxides can be assessed with low-cost sensors, which can support a wide range of industrial applications, such as designing biocatalytic coatings for air pollution remediation.

Earth is expected to have acquired a reduced proto-atmosphere enriched in H2 and CH4 through the accretion of building blocks that contain metallic Fe and/or the gravitational trapping of surrounding nebula gas. Such an early, wet, reduced atmosphere that covers a proto-ocean would then ultimately evolve toward oxidized chemical compositions through photochemical processes that involve reactions with H2O-derived oxidant radicals and the selective escape of hydrogen to space. During this time, atmospheric CH4 could be photochemically reprocessed to generate not only C-bearing oxides but also organics. However, the branching ratio between organic matter formation and oxidation remains unknown despite its significance on the abiotic chemical evolution of early Earth. Here, we show via numerical analyses that UV absorptions by gaseous hydrocarbons such as C2H2 and C3H4 significantly suppress H2O photolysis and subsequent CH4 oxidation during the photochemical evolution of a wet proto-atmosphere enriched in H2 and CH4. As a result, nearly half of the initial CH4 converted to heavier organics along with the deposition of prebiotically essential molecules such as HCN and H2CO on the surface of a primordial ocean for a geological timescale order of 10–100 Myr. Our results suggest that the accumulation of organics and prebiotically important molecules in the proto-ocean could produce a soup enriched in various organics, which might have eventually led to the emergence of living organisms. [ABSTRACT FROM AUTHOR]

Sixty-four phenols grouped as nitrated, bromo, amino, methyl, chloro-phenols, and cresols, and thirty-eight organic acids grouped as mono-carboxylic and dicarboxylic are analyzed in forty-two fog samples collected in the Alsace region between 2015 and 2021 to check their atmospheric behavior. Fogwater samples are collected using the Caltech Active Strand Cloudwater Collector (CASCC2), extracted using liquid–liquid extraction (LLE) on a solid cartridge (XTR Chromabond), and then analyzed using gas chromatography coupled with mass spectrometry (GC-MS). The results show the high capability of phenols and acids to be scavenged by fogwater due to their high solubility. Nitro-phenols and mono-carboxylic acids have the highest contributions to the total phenolic and acidic concentrations, respectively. 2,5-dinitrophenol, 3-methyl-4-nitrophenol, 4-nitrophenol, and 3,4-dinitrophenol have the highest concentration, originating mainly from vehicular emissions and some photochemical reactions. The top three mono-carboxylic acids are hexadecenoic acid (C16), eicosanoic acid (C18), and dodecanoic acid (C12), whereas succinic acid, suberic acid, sebacic acid, and oxalic acid are the most concentrated dicarboxylic acids, originated either from atmospheric oxidation (mainly secondary organic aerosols (SOAs)) or vehicular transport. Pearson's correlations show positive correlations between organic acids and previously analyzed metals (p < 0.05), between mono- and dicarboxylic acids (p < 0.001), and between the analyzed acidic compounds (p < 0.001), whereas no correlations are observed with previously analyzed inorganic ions. Total phenolic and acidic fractions are found to be much higher than those observed for pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) measured at the same region due to their higher scavenging by fogwater. [ABSTRACT FROM AUTHOR]

The hydroxyl radical (OH) fuels atmospheric chemical cycling as the main sink for methane and a driver of the formation and loss of many air pollutants, but direct OH observations are sparse. We develop and evaluate an observation-based proxy for short-term, spatial variations in OH (ProxyOH) in the remote marine troposphere using comprehensive measurements from the NASA Atmospheric Tomography (ATom) airborne campaign. ProxyOH is a reduced form of the OH steady-state equation representing the dominant OH production and loss pathways in the remote marine troposphere, according to box model simulations of OH constrained with ATom observations. ProxyOH comprises only eight variables that are generally observed by routine ground- or satellite-based instruments. ProxyOH scales linearly with in situ [OH] spatial variations along the ATom flight tracks (median r2 = 0.90, interquartile range = 0.80 to 0.94 across 2-km altitude by 20° latitudinal regions). We deconstruct spatial variations in ProxyOH as a first-order approximation of the sensitivity of OH variations to individual terms. Two terms modulate within-region ProxyOH variations-water vapor (H2O) and, to a lesser extent, nitric oxide (NO). This implies that a limited set of observations could offer an avenue for observation-based mapping of OH spatial variations over much of the remote marine troposphere. Both H2O and NO are expected to change with climate, while NO also varies strongly with human activities. We also illustrate the utility of ProxyOH as a process-based approach for evaluating intermodel differences in remote marine tropospheric OH.

Tunable emission wavelength and excellent biocompatibility have positioned silicon quantum dots (Si QDs) as important optoelectronic materials in areas like displays, lighting, and biomedical imaging. However, the challenges of low luminescence efficiency impede the utilization of Si QDs, restraining the advancement of Si QDs‐based light‐emitting diode (LED) devices. This study primarily concentrates on optimizing the surface structure of Si QDs and refining the Si QDs‐based LED device structures. A strategy involving active oxidation followed by hydrofluoric etching and hydrosilylation is proposed to enhance the optical characteristics of Si QDs. A variety of characterization methods are employed to evaluate the impact of the active oxidation on the photoluminescence and surface structures of Si QDs. This approach ultimately achieves an impressive enhancement in the photoluminescence quantum yield (PL QY) of Si QDs from 6.7% to 60.3%. Furthermore, the atmospherically oxidized Si QDs with the highest PL QY are selected as the emitting‐layer material to fabricate LEDs with the structure of ITO/PEDOT:PSS/TFB/Si QDs/ZnMgO/Ag. The introduction of ZnMgO effectively balances charge injection in the Si‐QDs‐based LEDs. As a result, the devices achieve electroluminescence with an external quantum efficiency of 13.2%. [ABSTRACT FROM AUTHOR]

Aerosol-bound organic radicals, including environmentally persistent free radicals (EPFRs), are key components that affect climate, air quality, and human health. While putative structures have been proposed, the molecular characteristics of EPFRs remain unknown. Here, we report a surrogate method to characterize EPFRs in real ambient samples using mass spectrometry. The method identifies chemically relevant oxygenated polycyclic aromatic hydrocarbons (O x PAH) that interconvert with oxygen-centered EPFR (OC-EPFR). We found O x PAH compounds most relevant to OC-EPFRs are structurally rich and diverse quinones, whose diversity is strongly associated with OC-EPFR levels. Both atmospheric oxidation and combustion contributed to OC-EPFR formation. Redundancy analysis and photochemical aging model show pyrolytic sources generated more oxidized OC-EPFRs than photolytic sources. Our study reveals the detailed molecular characteristics of OC-EPFRs and shows that oxidation states can be used to identify the origins of OC-EPFRs, offering a way to track the development and evolution of aerosol particles in the environment. [ABSTRACT FROM AUTHOR]

Downward transport of stratospheric air into the troposphere (identified as stratospheric intrusions) could potentially modify the radiation budget and chemical of the Earth's surface atmosphere. As the highest and largest plateau on earth, the Tibetan Plateau including the Himalayas couples to global climate, and has attracted widespread attention due to rapid warming and cryospheric shrinking. Previous studies recognized strong stratospheric intrusions in the Himalayas but are poorly understood due to limited direct evidences and the complexity of the meteorological dynamics of the third pole. Cosmogenic 35S is a radioactive isotope predominately produced in the lower stratosphere and has been demonstrated as a sensitive chemical tracer to detect stratospherically sourced air mass in the planetary boundary layer. Here, we report 6-month (April-September 2018) observation of 35S in atmospheric sulfate aerosols (35SO4 2°) collected from a remote site in the Himalayas to reveal the stratospheric intrusion phenomenon as well as its potential impacts in this region. Throughout the sampling campaign, the 35SO4 2-concentrations show an average of 1,070 ± 980 atoms/m3. In springtime, the average is 1,620 ± 730 atoms/m3, significantly higher than the global existing data measured so far. The significant enrichments of 35SO4 2-measured in this study verified the hypothesis that the Himalayas is a global hot spot of stratospheric intrusions, especially during the springtime as a consequence of its unique geology and atmospheric couplings. In combined with the ancillary evidences, e.g., oxygen-17 anomaly in sulfate and modeling results, we found that the stratospheric intrusions have a profound impact on the surface ozone concentrations over the study region, and potentially have the ability to constrain how the mechanisms of sulfate oxidation are affected by a change in plateau atmospheric properties and conditions. This study provides new observational constraints on stratospheric intrusions in the Himalayas, which would further provide additional information for a deeper understanding on the environment and climatic changes over the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

In recent years, hydrogen is adopted as a clean source of energy to combat emissions and climate change resulting from fossil fuels. All along the value chain of hydrogen economy, leakage of hydrogen is possible which is expected to have profound impacts on air quality and climate. In the present study, quantum chemistry calculations are employed to understand the atmospheric oxidation mechanism of H 2 by OH and O 3. The results reveal that oxidation of H 2 by both the OH and O 3 are both possible and the reaction of H 2 with O 3 is thermodynamically favoured over its reaction with OH radical. The O 3 initiated reaction of H 2 is around 80 kcal/mol more exothermic than that of the OH initiated reaction. The O 3 initiated reactions of H 2 has longer lifetime in the atmosphere when compared to OH initiated reactions. This shows that in addition to undergoing OH radical initiated reaction, where ozone is formed as a product, the H 2 can also undergo oxidation by O 3 leading to the tropospheric ozone loss processes. Depending upon the background atmospheric concentration, either the OH radical generation is suppressed and methane is formed or the H 2 can undergo oxidation with O 3. The global warming potential (GWP) weighted emissions for hydrogen leakage incidents reported in the literature is obtained. The emissions are maximum from the hydrogen leakage in transportation and power sectors and minimum in the pipeline leakage. Taken together the atmospheric oxidation potential of H 2 by OH radical and O 3 oxidation and its GWP weighted emissions, it is clear from the study that the atmospheric and climate implications of H 2 leakage is relatively less. The present study is based on molecular level and a rigorous model accounting the atmospheric composition is required for better understanding of the atmospheric and climate implications. [Display omitted] • H 2 is oxidized possibly by OH and O 3 in the troposphere. • H 2 reaction with O 3 is thermodynamically favoured than that with OH radical. • Hydrogen leakage emissions maximum in transportation and power sectors. • Climate impacts are minimal. [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere. Plain Language Summary: This study presents measurements and a chemical budget analysis of NO2, O3, and OH in the clean marine boundary layer at the Tudor Hill Marine Atmospheric Observatory, Bermuda. The high solar noon abundance and atypical diel profile of NO2 challenged the classic U‐shape, indicating an unknown daytime NOx source. Assessments using a near‐explicit MCM chemical model (v3.3.1) yielded an unknown NOx source by 9.7–33.5 pptv hr−1 at solar noon and demonstrated that the photochemical nature of the unknown NOx source maximized perturbation of the O3 and OH budgets. In addition to halogen photochemistry, the unknown NOx source necessitates revision of the photochemistry in the clean marine boundary layer. Key Points: The atypical NO2 diel profile against its classic U‐shape indicates an unknown daytime source of NOx in the marine boundary layerThe unknown daytime NOx source, in addition to halogen photochemistry, greatly perturbs NOx, O3, and OH budgetsThe unknown NOx source appears to be due in part to a missing HONO source, that is, NOx is regenerated with HONO as an intermediate [ABSTRACT FROM AUTHOR]

PM2.5 pollution over Hangzhou Bay area, China has received continuous attention. In this study, PM2.5 samples were collected simultaneously in six typical cities in Zhejiang Province from 15 October 2019 to 15 January 2020 (autumn and winter) and from 1 June to 31 August 2020 (summer), and major water-soluble ions were analyzed. Average concentrations of NO3− and SO42− in the six cities were 3.93–15.64 μg/m3 and 4.61–7.58 μg/m3 in autumn and winter, with mass fractions of NO3− and SO42− in PM2.5 up to 19.6–34.2% and 13.6–26.3%, respectively, while in summer, they were 1.23–2.64 μg/m3 and 2.22–4.14 μg/m3, with mass fractions of 7.0–15.0% and 14.7~25.1%. Both NO3− and SO42− were mostly from gas-to-particle transformation of precursors. High relative humidity in the six cities was suggested to significantly promote the formation of NO3− and SO42−, particularly in autumn and winter, while enhanced atmospheric oxidation favored the formation of SO42− in summer. However, the formation of NO3− was inhibited under a high temperature of >15 °C. The concentrations of SO42− and NO3 were mostly correlated with each other among the six cities. Potential source contribution function analysis indicated that both SO42− and NO3− were mostly from local pollution of Hangzhou Bay area in Zhejiang Province and also transported from Shanghai and the southern region of Jiangsu Province. This study contributed to the understanding of regional characteristics of SO42− and NO3− in Hangzhou Bay area and suggested that joint prevention and control efforts should be strengthened to reduce regional PM2.5 pollution. [ABSTRACT FROM AUTHOR]

In recent years, the concentrations of PM2.5 in urban ambient air in China have been declining; however, the strong atmospheric oxidation capacity (AOC) represents challenges to the further reduction of PM2.5 concentration and the continuous improvement of ambient air quality in China in the future, since the overall AOC is still at a high level. For this paper, based on ground observation data recorded in Beijing from 2016 to 2019, the variation in AOC was characterized according to the concentration of odd oxygen (OX = O3 + NO2). The concentrations of the primary and secondary components of PM2.5 were analyzed using empirical formulas, the correlation between AOC and the concentrations of secondary PM2.5 and the secondary inorganic components (SO42−, NO3−, NH4+, and SNA) in Beijing were explored, the impact of atmospheric photochemical reaction activity on the generation of atmospheric secondary particles was evaluated, and the impact of atmospheric oxidation variations on PM2.5 concentrations and SNA in Beijing was investigated. The results revealed that OX concentrations reached their peak in 2016 and reached their lowest point in 2019. The OX concentrations followed a descending seasonal trend of summer, spring, autumn, and winter, along with a spatial descending trend from urban observation stations to suburban stations and background stations. The degree of photochemical activity and the magnitude of the AOC have a large influence on the production of atmospheric secondary particles. When the photochemical reaction was more active and the AOC was stronger, the mass concentrations of the secondary generated PM2.5 fraction were higher and accounted for a higher proportion of the total PM2.5 mass concentrations. In the PM2.5 fraction, SNA accounted for 50.7% to 94.4% of the total mass concentrations of water-soluble inorganic ions in the field observations. Higher concentrations of the atmospheric oxidant OX in ambient air corresponded to a higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR), suggesting that the increase in AOC could promote the increase of PM2.5 concentration. Based on a relationship analysis of SOR, NOR, and OX, it was inferred that the relationship between OX and SOR and the relationship between OX and NOR were both nonlinear. Therefore, when establishing PM2.5 control strategies in Beijing in the future, the impact of the AOC on PM2.5 generation should be fully considered, and favorable measures should be taken to properly regulate the AOC, which would be more effective when carrying out further control measures regarding PM2.5 pollution. [ABSTRACT FROM AUTHOR]

Comprehensive observations of hydroxyl (OH) and hydroperoxy (HO2) radicals were conducted in October 2019 at a coastal continental site in the Pearl River Delta (YMK site, 22.55°N, 114.60°E). The average daily maximum OH and HO2 concentrations were (4.7-9.5) × 106 cm-3 and (4.2-8.1) × 108 cm-3, respectively. The synchronized air mass transport from the northern cities and the South China Sea exerted a time-varying influence on atmospheric oxidation. Under a typical ocean30 atmosphere (OCM), reasonable measurement model agreement was achieved for both OH and HO2 using a 0-D chemical box model incorporating the regional atmospheric chemistry mechanism version 2-Leuven isoprene mechanism (RACM2-LIM1). Land mass (LAM) influence promoted more active photochemical processes, with daily averages of 7.1 × 106 cm-3 and 5.2 × 108 cm-3 for OH and HO2, respectively. Intensive photochemistry occurred after precursor accumulation, allowing local net ozone production comparable with surrounding suburban environments (5.52 ppb/h during the LAM period). The rapid oxidation process was accompanied by a higher diurnal nitrous acid (HONO) concentration (> 400 ppt). After a sensitivity test, HONO-related chemistry elevated the ozone production rate by 33% and 39% during the LAM and OCM periods, respectively, while the nitric acid and sulfuric acid formation rates were 52% and 35% higher, respectively. The simulated daytime HONO and ozone concentrations were reduced to a low level (~70 ppt and ~35 ppb) without the HONO constraint. This work challenges the conventional recognition of the MBL in a complex atmosphere. For coastal cities, the particularity of the HONO chemistry in the MBL tends to influence the ozone-sensitive system and eventually magnifies the background ozone. Therefore, the promotion of oxidation by elevated precursor concentrations is worth considering when formulating emission reduction policies. [ABSTRACT FROM AUTHOR]

Surface atomic arrangement and physical properties of aluminum ultrathin layers on c-Si(111)-7 × 7 and hydrogen-terminated c-Si(111)-1 × 1 surfaces deposited using molecular beam epitaxy were investigated. X-ray photoelectron spectroscopy spectra were collected in two configurations (take-off angle of 0° and 45°) to precisely determine the surface species. Moreover, 3D atomic force microscopy (AFM) images of the air-exposed samples were acquired to investigate the clustering formations in film structure. The deposition of the Al layers was monitored in situ using a reflection high-energy electron diffraction (RHEED) experiments to confirm the surface crystalline structure of the c-Si(111). The analysis of the RHEED patterns during the growth process suggests the settlement of aluminum atoms in Al(111)-1 × 1 clustered formations on both types of surfaces. The surface electrical conductivity in both configurations was tested against atmospheric oxidation. The results indicate differences in conductivity based on the formation of various alloys on the surface. [ABSTRACT FROM AUTHOR]

Reducing the levels of Fine particulate matter (PM _2.5 ) and ozone (O _3 ) is essential for further improving air quality in China. The intricate and non-linear interactions between PM _2.5 and O _3 on a national scale over long-term records are not well understood. Here, we proposed a novel multi-layer network approach to bridge the gap. Our findings reveal that the variability of O _3 precedes that of PM _2.5 by one day. The degree, weighted degree, and edge distance follow a power-law decay distribution, suggesting that their relationship is not a random process. O _3 concentration in the Yangtze River Delta (YRD) region and eastern Shandong Province significantly impacts the PM _2.5 levels in surrounding areas. Conversely, PM _2.5 concentrations in Shandong Province, Henan Province, YRD and Pearl River Delta (PRD) have a strong influence on O _3 levels. Moreover, we quantified the seasonality of the interactions and elucidated the underlying reasons. The results revealed the interactions between PM _2.5 and O _3 are intricately tied to atmospheric oxidation processes. More specifically, in summer, the atmospheric oxidation has a strong impact on the interactions in key regions, such as the Beijing–Tianjin–Hebei,YRD region and Fenwei Plain. However, the PRD region experiences a more pronounced effect from atmospheric oxidation on this relationship in winter. These findings demonstrate that it is crucial to effectively regulate atmospheric oxidation to mitigate PM _2.5 and O _3 . Our results also serve as a valuable methodological framework for understanding the characteristics of pollutants.

Chlorine radicals (Cl · ) are highly reactive and affect the fate of air pollutants. Several field studies in China have revealed elevated levels of daytime molecular chlorine (Cl 2 ), which, upon photolysis, release substantial amounts of Cl · but are poorly represented in current chemical transport models. Here, we implemented a parametrization for the formation of daytime Cl 2 through the photodissociation of particulate nitrate in acidic environments into a regional model and assessed its impact on coastal air quality during autumn in South China. The model could reproduce over 70% of the high Cl 2 level measured at a coastal site, revealing a discernible presence of Cl 2 and released Cl · in coastal and adjacent areas. Abundant Cl 2 alters the oxidative capacity of the atmosphere, consequently increasing O 3 (6-12%) and PM 2.5 (10-16%) concentrations in high-NO x areas and reducing O 3 (3%) concentration in low-NO x areas. Accounting for chlorine chemistry shifts the O 3 - precursor relationships from VOC limited to mixed or NO x -limited regimes, enhancing the benefits of NO x emission reduction in mitigating O 3 pollution. Our findings suggest that tightening emission control for two acidic pollutants, NO x and SO 2 , would alleviate reactive Cl · production and its adverse impact on air quality.

Biomass burning events, including wildfires, can emit large amounts of phenolic compounds such as guaiacol. These phenolic compounds can undergo oxidation by nitrate radicals (NO 3 ) to form secondary organic aerosol (SOA). Viscosity and hygroscopicity are key properties that affect SOA's role in atmospheric chemistry, air quality, climate and public health. However, these properties have not been quantified for SOA formed from the reaction of phenolic compounds with NO 3 . We used the poke-flow technique and a quartz crystal microbalance (QCM) to measure the viscosity and hygroscopicity of SOA particles generated from the reaction of NO 3 with guaiacol, termed guaiacol-NO 3 SOA. The viscosity of this SOA is extremely high (≳5 × 10 7 Pa s) at RH ≲ 70% and drastically higher than other SOA types previously investigated with the poke-flow technique at RH ≳ 40%. The high viscosity for guaiacol-NO 3 SOA can be attributed, at least in part, to the low hygroscopicity measured via the QCM. From the viscosity results, we calculated the mixing times of organic molecules within guaiacol-NO 3 SOA. The results suggest that mixing times within this type of SOA exceed 1 h for most tropospheric conditions, with possible implications for predicting the size, mass, and long-range transport of pollutants in phenolic SOA.

Organic acids are important aerosol compositions with significant implications on particle formation, growth, acidity, phase state, and environmental impacts. Oxalic acid was found to be the most abundant particulate organic diacid in Shanghai during the study period, accounting for ~58% of the total dicarboxylic acids (C2–C10). Biomass burning (BB) explained a small but non-negligible fraction (less than 10%) of oxalate. Significant correlations between oxalate and sulfate indicated a potentially synergistic formation mechanism of oxalate and sulfate. In addition, meteorological factors such as ambient temperature and relative humidity were found to influence the formation of oxalate. Higher oxalate relative to inorganic particulate content was found in summer. Potential source contribution function analysis suggested that most of the oxalate observed in Shanghai was produced locally. The formation of oxalate was largely impacted by atmospheric oxidation capacity as indicated by its significant correlations with both secondary organic carbon (SOC) and sulfur oxidation ratio (SOR). The evolution of oxalate, oxalate/sulfate, oxalate/organic carbon were consistent with the emission trend of volatile organic carbons (VOCs) in recent years, indicating that oxalate may be derived from secondary oxidation of VOCs, which is further confirmed by a positive relationship between Ox and oxalate/VOCs over the study period. With a detailed characterization of oxalate in Shanghai, our study highlights the importance of regulating primary emissions, such as VOCs, as well as mitigation of atmospheric oxidation capacity in controlling air pollution in a coastal megacity. [ABSTRACT FROM AUTHOR]

This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here. [ABSTRACT FROM AUTHOR]

Recent research has shown that microplastics are widespread in the atmosphere. However, we know little about their ability to nucleate ice and their impact on ice formation in clouds. Ice nucleation by microplastics could also limit their long-range transport and global distribution. The present study explores the heterogeneous ice-nucleating ability of seven microplastic samples in immersion freezing mode. Two polypropylene samples and one polyethylene terephthalate sample froze heterogeneously with median freezing temperatures of -20.9, -23.2, and -21.9 °C, respectively. The number of ice nucleation sites per surface area, n s ( T ), ranged from 10 -1 to 10 4 cm -2 in a temperature interval of -15 to -25 °C, which is comparable to that of volcanic ash and fungal spores. After exposure to ozone or a combination of UV light and ozone, simulating atmospheric aging, the ice nucleation activity decreased in some cases and remained unchanged in others. Our freezing data suggest that microplastics may promote ice formation in cloud droplets. In addition, based on a comparison of our freezing results and previous simulations using a global transport model, ice nucleation by microplastics will impact their long-range transport to faraway locations and global distribution.

We investigated the dissolution and oxidation behaviors of sulfuric waste from secondary batteries by reacting the waste with synthetic rainwater to examine the optimal management of this waste at a disposal site. Morphological observation and chemical analysis of bulk sulfur (S) wastes revealed heterogeneous distributions of sodium sulfide (NaS) and thiosulfate (Na2S2O3). Leaching experiments using crushed S-waste samples with oxygenated synthetic rainwater for 144 h showed that sulfide ion was the dominant eluent from the less-oxidized sample, whereas sulfate (SO4) and S2O3 ions were released from the well-oxidized sample (left for 6 months). An atmospheric oxidation experiment of S-waste was carried out to elucidate the relationship between sulfide oxidation on the S-waste surface and eluted species. X-ray photoelectron spectroscopy showed rapid oxidation of NaS to Na2S2O3 within the first 72 h, and time-of-flight secondary ion mass spectrometry revealed that the sulfide-oligomers species (S3 and S4) formed after reaction for 336 h. The kinetic analysis indicates that NaS was easily oxidized by atmospheric oxygen. The oxidation rate was 10–100 times higher than that of pyrite. The NaS oxidation and the formation of sulfide oligomer species inhibited the rapid dissolution of sulfuric components from a well-oxidized sample. Most S-waste could be exposed to atmospheric air before disposal; therefore, the main concern for this waste disposal could be SO4 and S2O3 ion dissolution and interaction (redissolution) with toxic compounds such as enhancement of leaching rate of heavy metals due to complex ion formulation. [ABSTRACT FROM AUTHOR]

Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 profiles. Leaf level emissions of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis.

We measured wavelength‐resolved ultraviolet (UV) irradiance in multiple indoor environments and quantified the effects of variables such as light source, solar angles, cloud cover, window type, and electric light color temperature on indoor photon fluxes. The majority of the 77 windows and window samples investigated completely attenuated sunlight at wavelengths shorter than 320 nm; despite variations among individual windows leading to differences in indoor HONO photolysis rate constants (JHONO) and local hydroxyl radical (OH) concentrations of up to a factor of 50, wavelength‐resolved transmittance was similar between windows in residential and non‐residential buildings. We report mathematical relationships that predict indoor solar UV irradiance as a function of solar zenith angle, incident angle of sunlight on windows, and distance from windows and surfaces for direct and diffuse sunlight. Using these relationships, we predict elevated indoor steady‐state OH concentrations (0.80–7.4 × 106 molec cm−3) under illumination by direct and diffuse sunlight and fluorescent tubes near windows or light sources. However, elevated OH concentrations at 1 m from the source are only predicted under direct sunlight. We predict that reflections from indoor surfaces will have minor contributions to room‐averaged indoor UV irradiance. These results may improve parameterization of indoor chemistry models. [ABSTRACT FROM AUTHOR]

Iron and oxalic acids are widely distributed in the atmosphere and easily form ferric oxalate complex (Fe(III)-Ox). The tropospheric aqueous-phase could provide a medium to enable the photo-Fenton reaction with Fe(III)-Ox under solar irradiation. Although the photolysis mechanisms of Fe(III)-Ox have been investigated extensively, information about the oxidation of volatile organic compounds (VOC), specifically the potential for Secondary Organic Aerosol (SOA) formation in the Fe(III)-Ox system, is lacking. In this study, a ubiquitous VOC methacrolein (MACR) is chosen as a model VOC, and the oxidation of MACR with Fe(III)-Ox is investigated under typical atmospheric water conditions. The effects of oxalate concentration, Fe(III) concentration, MACR concentration, and pH on the oxidation of MACR are studied in detail. Results show that the oxidation rate of MACR greatly accelerates in the presence of oxalate when compared with only Fe(III). The oxidation rate of MACR also accelerates with increasing concentration of oxalate. The effect of Fe(III) is found to be more complicated. The oxidation rate of MACR first increases and then decreases with increasing Fe(III) concentration. The oxidation rate of MACR increases monotonically with decreasing pH in the common atmospheric water pH range or with decreasing MACR concentration. The production of ferrous and hydrogen peroxide, pH, and aqueous absorbance are monitored throughout the reaction process. The quenching experiments verify that ·OH and O 2 . ¯ are both responsible for the oxidation of MACR. MACR is found to rapidly oxidize into small organic acids with higher boiling points and oligomers with higher molecular weight, which contributes to the yield of SOA. These results suggest that Fe(III)-Ox plays an important role in atmospheric oxidation. [ABSTRACT FROM AUTHOR]

Understanding ozone (O 3) formation regime is a prerequisite in formulating an effective O 3 pollution control strategy. Photochemical indicator is a simple and direct method in identifying O 3 formation regimes. Most used indicators are derived from observations, whereas the role of atmospheric oxidation is not in consideration, which is the core driver of O 3 formation. Thus, it may impact accuracy in signaling O 3 formation regimes. In this study, an advanced three-dimensional numerical modeling system was used to investigate the relationship between atmospheric oxidation and O 3 formation regimes during a long-lasting O 3 exceedance event in September 2017 over the Pearl River Delta (PRD) of China. We discovered a clear relationship between atmospheric oxidative capacity and O 3 formation regime. Over eastern PRD, O 3 formation was mainly in a NO x -limited regime when HO 2 /OH ratio was higher than 11, while in a VOC-limited regime when the ratio was lower than 9.5. Over central and western PRD, an HO 2 /OH ratio higher than 5 and lower than 2 was indicative of NO x -limited and VOC-limited regime, respectively. Physical contribution, including horizontal transport and vertical transport, may pose uncertainties on the indication of O 3 formation regime by HO 2 /OH ratio. In comparison with other commonly used photochemical indicators, HO 2 /OH ratio had the best performance in differentiating O 3 formation regimes. This study highlighted the necessities in using an atmospheric oxidative capacity-based indicator to infer O 3 formation regime, and underscored the importance of characterizing behaviors of radicals to gain insight in atmospheric processes leading to O 3 pollution over a photochemically active region. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We present a detailed analysis of OH observations from the BEACHON (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen)-ROCS (Rocky Mountain Organic Carbon Study) 2010 field campaign at the Manitou Forest Observatory (MFO), which is a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated forest environment. A comprehensive suite of measurements was used to constrain primary production of OH via ozone photolysis, OH recycling from HO2, and OH chemical loss rates, in order to estimate the steady-state concentration of OH. In addition, the University of Washington Chemical Model (UWCM) was used to evaluate the performance of a near-explicit chemical mechanism. The diurnal cycle in OH from the steady-state calculations is in good agreement with measurement. A comparison between the photolytic production rates and the recycling rates from the HO2 + NO reaction shows that recycling rates are ~20 times faster than the photolytic OH production rates from ozone. Thus, we find that direct measurement of the recycling rates and the OH loss rates can provide accurate predictions of OH concentrations. More importantly, we also conclude that a conventional OH recycling pathway (HO2 + NO) can explain the observed OH levels in this non-isoprene environment. This is in contrast to observations in isoprene-dominated regions, where investigators have observed significant underestimation of OH and have speculated that unknown sources of OH are responsible. The highly-constrained UWCM calculation under-predicts observed HO2 by as much as a factor of 8. As HO2 maintains oxidation capacity by recycling to OH, UWCM underestimates observed OH by as much as a factor of 4. When the UWCM calculation is constrained by measured HO2, model calculated OH is in better agreement with the observed OH levels. Conversely, constraining the model to observed OH only slightly reduces the model-measurement HO2 discrepancy, implying unknown HO2 sources. These findings demonstrate the importance of constraining the inputs to, and recycling within, the ROx radical pool (OH + HO2 + RO2).

Abstract Methyl ethyl ketone (MEK) is a relatively abundant but understudied oxygenated volatile organic compound that can serve as a source of both HOx and PAN when photooxidized. We use aircraft observations of MEK from the remote marine troposphere to show that the ocean serves as a source of MEK to the atmosphere during both meteorological winter and summer. There is pronounced seasonality in the MEK profiles in the extratropical troposphere, with higher MEK mixing ratios observed in summer than in winter. MEK in clean air over the remote oceans correlates with both acetone and acetaldehyde, whose primary sources in the ocean water are the photooxidation of organic material. We show that even a small (>1 nM) concentration of MEK in surface waters is sufficient to allow the ocean to be a net source of MEK to the atmosphere over ocean basins across multiple seasons.

Methyl ethyl ketone (MEK) is a relatively abundant but understudied oxygenated volatile organic compound that can serve as a source of both HOx and PAN when photooxidized. We use aircraft observations of MEK from the remote marine troposphere to show that the ocean serves as a source of MEK to the atmosphere during both meteorological winter and summer. There is pronounced seasonality in the MEK profiles in the extratropical troposphere, with higher MEK mixing ratios observed in summer than in winter. MEK in clean air over the remote oceans correlates with both acetone and acetaldehyde, whose primary sources in the ocean water are the photooxidation of organic material. We show that even a small (>1 nM) concentration of MEK in surface waters is sufficient to allow the ocean to be a net source of MEK to the atmosphere over ocean basins across multiple seasons. Plain language summary: Methyl ethyl ketone (MEK) is an abundant but understudied gas in Earth' atmosphere, which is emitted into the atmosphere from both human and natural sources. When MEK is broken apart by ultraviolet sunlight, the products released by those reactions play important roles in the formation and destruction of air pollution. In this paper, we show that the oceans are a source of MEK to the atmosphere. The oceanic emissions we document correlate strongly with some other gases that are known to be produced in the ocean but not those most closely associated with the growth of microscopic oceanic phytoplankton. Finding this new source helps us better understand the importance of MEK to the atmosphere and provides guidance for future oceanic and atmospheric research. Key Points: We use aircraft observations of MEK from the remote marine troposphere to suggest that the ocean is a source of MEK to the atmosphereEvidence exists for this source in both winter and summer in the tropical Pacific, south Atlantic and Pacific, and in the Southern OceanMEK in clean air over the remote oceans does not correlate with DMS, but it does correlate with acetone and acetaldehyde [ABSTRACT FROM AUTHOR]

A field campaign was conducted from November to December 2017 at the campus of Peking University (PKU) to investigate the formation mechanism of the winter air pollution in Beijing with the measurement of hydroxyl and hydroperoxyl radical (OH and HO 2) with the support from comprehensive observation of trace gases compounds. The extent of air pollution depends on meteorological conditions. The daily maximum OH radical concentrations are on average 2.0 × 106 cm−3 and 1.5 × 106 cm−3 during the clean and polluted episodes, respectively. The daily maximum HO 2 radical concentrations are on average 0.4 × 108 cm−3 and 0.3 × 108 cm−3 during the clean and polluted episodes, respectively (diurnal averaged for one hour bin). A box model based on RACM2-LIM1 mechanism can reproduce the OH concentrations but underestimate the HO 2 concentrations by 50% during the clean episode. The OH and HO 2 concentrations are underestimated by 50% and 12 folds during the polluted episode, respectively. Strong dependence on nitric oxide (NO) concentration is found for both observed and modeled HO 2 concentrations, with the modeled HO 2 decreasing more rapidly than observed HO 2 , leading to severe HO 2 underestimation at higher NO concentrations. The OH reactivity is calculated from measured and modeled species and inorganic compounds (carbon monoxide (CO), NO, and nitrogen dioxide (NO 2)) make up 69%–76% of the calculated OH reactivity. The photochemical oxidation rate denoted by the OH loss rate increases by 3 times from the clean to polluted episodes, indicating the strong oxidation capacity in polluted conditions. The comparison between measurements at PKU site and a suburban site from one previous study shows that chemical conditions are similar in both urban and suburban areas. Hence, the strong oxidation capacity and its potential contribution to the pollution bursts are relatively homogeneous over the whole Beijing city and its surrounding areas. Unlabelled Image • OH and HO 2 radical concentrations are measured in urban Beijing during winter. • Comparable radical concentrations are observed in clean and polluted episodes. • Chemical conditions and photochemical reactions show spatially homogeneity throughout Beijing. [ABSTRACT FROM AUTHOR]

The atmospheric oxidation of amines proceeds via initial radical attack at C–H or N–H bonds to form carbon‐ and nitrogen‐centered radicals, respectively. It is conventionally assumed that nitrogen‐centered aminyl radicals react slowly with oxygen in the troposphere and associate predominantly with the radicals •NO and NO2• to form toxic nitrosamines and nitramines. We have used theoretical kinetic modeling techniques to study the prototypical CH3N•H + O2 reaction and have shown that it proceeds to CH2NH + HO2• under tropospheric conditions with a rate coefficient of 3.6 × 10−17 cm3 molecule−1 s−1. Although this value is low compared to the competing NOx reactions (∼10−11 cm3 molecule−1 s−1), the much higher concentration of O2 versus NOx in air makes it the dominant process in the atmospheric oxidation of methylamine for NOx concentrations below 100 ppb. The mechanism identified here is available to amines with primary, secondary, and tertiary α carbons and suggests that they may be less likely to form nitramines and nitrosamines than is currently thought. [ABSTRACT FROM AUTHOR]

Ketone photolysis is a potentially important source of HOx radicals in the upper troposphere. To represent this photolysis, models need to include actinic flux, quantum yield, and absorption cross sections over a range of atmospherically relevant conditions. This work seeks to improve the representation of ketone ultraviolet (UV) absorption by quantifying it as a function of temperature. We present observations of 1‐nm resolution absorption cross sections from 200 to 335 nm of methyl ethyl ketone (MEK) and diethyl ketone (DEK) at temperatures between 242 and 320 K, as well as propyl ethyl ketone (PEK) cross sections at 296 K. Our measured room temperature absorption cross sections agree to within 2%, 2%, and 5% with previous studies for MEK, DEK, and PEK spectra, respectively. We parameterize the temperature dependence of the cross sections of MEK and DEK using a two‐state model, which reproduces our experimental results well. With additional assumptions, this model can be applied to the temperature dependence of PEK in the absence of experimental data. This model is appropriate for atmospherically relevant temperatures both inside and outside the temperatures used in this study and is suitable for incorporation into model atmospheric photolysis schemes. R programs to facilitate usage of these data are included in the supporting information. Inclusion of temperature‐dependent absorption cross sections in atmospheric photolysis calculations decreased the rate coefficients of MEK, DEK, and PEK photolysis in the upper troposphere when compared to those calculated using only the room temperature cross sections; the decrease can be as large as 20–25%. Key Points: We report UV absorption spectra of methyl ethyl (MEK) and diethyl ketone (DEK) at 242‐320 K and that of propyl ethyl ketone (PEK) at 296 KIncluding the temperature dependence of absorption reduces the photolysis rate of these species in the upper troposphere by ~25%We present a physical model representing of the temperature dependence of these spectra, suitable for inclusion in atmospheric models [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract In this work, a systematic investigation on the mechanism and kinetics of the reactions of t -amyl methyl ether (TAME) and t- amyl ethyl ether (TAEE) with OH radicals in the gas phase has been performed within the Density Functional Theory (DFT) framework. The potential energy surfaces were obtained at the M06-2X/6-311++G(d,p) level. Kinetic data for the initial step in the oxidative degradation of TAME and TAEE were obtained, as well as branching ratios between the possible reaction channels. The calculated total rate constants are 3.9 × 10−11 cm3 molecules−1 s−1 and 1.3 × 10−12 cm3 molecules−1 s−1, for TAME and TAEE, respectively. Contrary to what occurs in the case of the MTBE and ETBE oxidation initiated by OH radicals, for TAME and TAEE the H-abstraction from α methoxy or ethoxy groups is not favored. For both molecules, the contribution of the reaction channels involving H-abstraction from the t -amyl group amounts to about 70% of the total rate coefficients. Using our calculated rate constants and a chosen OH tropospheric concentration of 1 × 106 molecule cm−3, lifetimes of ∼43 and ∼128 min were obtained for TAME and TAEE, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The atmospheric oxidation mechanism of 2-furanaldehyde with NO 3 was investigated. • Nitrate esters and furanones are the main products of 2-furanaldehyde with NO 3. • The reactions of 2-furanaldehyde with NO 3 radicals can be a source of OH radicals. • We calculated the rate constants of 2-furanaldehyde with NO 3 at 298 K and 1 atm. • The lifetime of 2-furanaldehyde with NO 3 radicals is estimated to be 0.53 h. Abstract Furanaldehydes have raised environmental attention due to their large emission and high potential to generate secondary organic aerosol. In this study, the removal process of 2-furanaldehyde initiated by NO 3 in gas phase was investigated by quantum chemical calculations. The overall rate constant for trans -2-furanaldehyde initiated by NO 3 is 1.04 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. The atmospheric lifetime of 2-furanaldehyde with NO 3 is estimated to be 0.53 h. This study indicates that the night-time reactions of 2-furanaldehyde with NO 3 could contribute to the oxidative capacity of the atmosphere, secondary organic aerosol formation and new particle formation. [ABSTRACT FROM AUTHOR]

In recent years, the co-pollution of surface ozone (O 3) and fine particulate matter (PM 2.5) has emerged as a critical concern within specific regions of China's atmospheric environment. This study employed a comprehensive approach by integrating statistical analysis with the interpretable ensemble machine learning model. Delving deeply into the intricate mechanisms behind O 3 and PM 2.5 co-pollution in Lanzhou city from 2019 to 2022, the research synthesized and analyzed an array of data sources, including ground observations, a multi-parameter lidar system, and meteorological data. Our findings, derived from ground observations to vertical distribution, unequivocally confirm that the enhancement of atmospheric oxidation capacity serves as a critical driver in the genesis of secondary particles, playing a substantial role in the augmented levels of O 3 and PM 2.5 experienced during the warm season. Moreover, the impact of local weather patterns is indispensable as it precipitates a relatively stable mid-level atmosphere, culminating in elevated surface concentrations of both PM 2.5 and O 3. Overall, this study emphatically underscores the importance of adopting a comprehensive approach to address these environmental challenges. [Display omitted] • Ensemble model identifies key factors influencing co-pollution O 3 and PM 2.5. • O 3 -initiated co-pollution led to PM 2.5 spikes, driven by atmospheric oxidation. • PM 2.5 rise limits O 3 , but persistent high levels due to weakened titration effect. • Local weather pattern played a vital role in driving O 3 /PM 2.5 co-pollution. • Controlling O 3 precursors is a key for mitigating warm-season co-pollution. [ABSTRACT FROM AUTHOR]

In recent years, the co-pollution of surface ozone (O 3 ) and fine particulate matter (PM 2.5 ) has emerged as a critical concern within specific regions of China's atmospheric environment. This study employed a comprehensive approach by integrating statistical analysis with the interpretable ensemble machine learning model. Delving deeply into the intricate mechanisms behind O 3 and PM 2.5 co-pollution in Lanzhou city from 2019 to 2022, the research synthesized and analyzed an array of data sources, including ground observations, a multi-parameter lidar system, and meteorological data. Our findings, derived from ground observations to vertical distribution, unequivocally confirm that the enhancement of atmospheric oxidation capacity serves as a critical driver in the genesis of secondary particles, playing a substantial role in the augmented levels of O 3 and PM 2.5 experienced during the warm season. Moreover, the impact of local weather patterns is indispensable as it precipitates a relatively stable mid-level atmosphere, culminating in elevated surface concentrations of both PM 2.5 and O 3 . Overall, this study emphatically underscores the importance of adopting a comprehensive approach to address these environmental challenges., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Abstract: Atmospheric oxidation of methyl propanoate (MP) by the OH radical has been performed using density functional theory (BMK, BBIK) and ab initio (MP2, CBS-QB3) calculations. The thermodynamic and kinetic parameters are calculated. Three channels have been discussed. These reactions occur through low energy barriers of 3.2-4.3 kcal/mol. The energy barriers increase in the order α < µ < β at CBS-QB3. However, BMK shows slightly different order. Rate constants and branching ratios reveal that the H-abstraction from Cα is as the dominant reaction over the whole temperature range of 200-300 K, with a competition from Cβ channel at lower temperature. The BB1K data reproduce the available experimental rate constant. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • NO 3 prefers to react with the terminal carbon atom of VAC. • NO 3 (5.0 × 108 molecule cm−3) determined atmospheric life of VAC is 76.1 h. • Total rate coefficient of VAC + NO 3 exhibits negative dependence on temperature. • Over 90% of nitro-oxyl radical intermediates undergo collisional stabilization. • Formic anhydride is dominant product rather than oxirane derivatives. Abstract It is known the NO 3 radical contributes to the oxidation of volatile organic compounds in the atmosphere in the night, leading to the formation of carbonyl compounds and organic nitrates. The mechanistic and kinetic properties of NO 3 -initiated oxidative degradation of vinyl acetate (VAC), a typical unsaturated ester, have been studied using density functional method. According to the computational results, two types of primary reactions were identified: NO 3 -addition and H-abstraction. The NO 3 -addition reaction especially the C β -addition pathway dominates the entrance channel of NO 3 into VAC while the H-abstraction reaction is negligible. Further reactions of the two adducts were discussed in the presence of O 2 /NO x. The rate constants were estimated by using the MultiWell software. The overall rate constant of NO 3 -initiated oxidation of VAC was about 7.30 × 10−15 cm3 molecule−1 s−1 at 298.15 K and atmospheric pressure, in good agreement with the experimental value of (7.30 ± 1.8) × 10−15 cm3 molecule−1 s−1. The atmospheric lifetime of VAC reacting with NO 3 radicals (5.0 × 108 molecule cm−3) is about 76.1 h under atmospheric conditions. [ABSTRACT FROM AUTHOR]

OH-initiated atmospheric oxidation mechanism of 1-chloronaphthalene (1-CN) was investigated using density functional theory (DFT) calculations. The oxidation is predicted to be initiated by OH addition to the α -positions, and the additions to C4 and C5 are more favorable. 1-CN-OH adducts tend to react with ambient O 2 to produce peroxy intermediates, followed by intramolecular H-shifts producing C 10 H 7 OCl and diketone or unimolecular ring closure forming methyl glyoxal and Cl-substituted phthalaldialdehyde. Despite that the rate constants are influenced by the tunneling factors, intramolecular H-shift reactions are suggested to be more favorable. The OH-determined lifetime of 1-CN is 0.62 days. [ABSTRACT FROM AUTHOR]

Monoterpenes are prevalent organic compounds emitted to the atmosphere, via biogenic activities in various types of plants. Monoterpenes undergo atmospheric decomposition reactions derived by the potent atmospheric oxidizing agents, OH, O3, and NOx. This review critically surveys literature pertinent to the atmospheric removal of monoterpenes by ozone. In general, the ozonolysis reactions of monoterpenes occur through the so-called Criegee mechanism. These classes of reactions generate a wide array of chemical organic and inorganic low vapor pressure (LVP) species. Carbonyl oxides, commonly known as Criegee intermediates (CIs), are the main intermediates from the gas-phase ozonolysis reaction. Herein, we present mechanistic pathways, reactions rate constants, product profiles, thermodynamic, and kinetic results dictating the ozonolysis reactions of selected monoterpenes (namely carene, camphene, limonene, α-pinene, β-pinene, and sabinene). Furthermore, the unimolecular (vinyl hydroperoxide and ester channels) and bimolecular reactions (cycloaddition, insertion, and radical recombination) of the resulting CIs are fully discussed. The orientations and conformations of the resulting primary ozonides (POZs) and CIs of monoterpenes are classified to reveal their plausible effects on reported thermokinetic parameters. [ABSTRACT FROM AUTHOR]

Atmospheric polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic and mutagenic to human beings, and thus have attracted significant attention in recent decades. Compound-specific stable carbon isotopes (δ13C) of PAHs are indicative for source identification, but have not been extensively applied in tracing atmospheric oxidation processes. In this study, we examined the molecular compositions and δ13C values of PAHs in wintertime PM 2.5 in a highly polluted urban region in Norwest China. The average concentrations of total parent-PAHs (pPAHs) and oxygenated-PAHs (OPAHs) were measured as 70 ± 29 and 36 ± 17 ng m−3, respectively. The results obtained from the incremental lifetime cancer risk (ILCR) model suggested a high potential cancer risk of PAHs in the urban region. The temperoal variations of PAHs and carbonaceous fractions implied that the contribution of secondary organic compounds was limited during the severe pollution period (PM 2.5 > 115 μg m−3). Both molecular diagnostic ratios and δ13C values indicated that the major emission sources of the pPAHs were coal and/or biomass burning. The δ13C value of fluorene became heavier as the OPAHs concentration increased, while the concentrations of fluorene was negatively correlated with OPAHs, indicating the secondary formation of OPAHs from fluorene oxidation in the cold season. Our results also confirmed that δ13C values of pPAHs are indeed indicative of atmospheric oxidation processes. [Display omitted] • Molecular compositions and δ13C values of PAHs in urban Xi'an were quantified. • Contribution of SOA was limited during the severe pollution period in winter. • Diagnostic ratios and δ13C implied the major contribution from coal/biomass burning. • δ13C values proved the secondary OPAHs formation from fluorene oxidation. [ABSTRACT FROM AUTHOR]