Cross-Coupling of Benzylic and Aldehydic C-H Bonds via Photocatalytic Tandem Radical-Radical Coupling and Acceptorless Alcohol Dehydrogenation.

The construction of a C-C bond by cross-coupling of two different C-H bonds with the release of hydrogen gas represents an ideal yet challenging bond formation strategy. Herein, we report a photocatalytic metal-free cross-coupling of benzylic and aldehydic C-H bonds by synergistic catalysis of organophotocatalyst 4CzIPN and a thiol, which affords the corresponding α-aryl ketones in acceptable yields along with hydrogen evolution. The mechanistic investigation indicates a radical-radical coupling to give an intermediary alcohol, followed by an acceptorless alcohol dehydrogenation.

Volatile organic compounds in wintertime North China Plain: Insights from measurements of proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS).

The characteristics of wintertime volatile organic compounds (VOCs) in the North China Plain (NCP) region are complicated and remain obscure. VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a rural site in the NCP from November to December 2018. Uncalibrated ions measured by PTR-ToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector (GC-MS/FID). The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions, the secondary formation of oxygenated VOCs (OVOCs) is non-negligible in the wintertime, i.e., OVOCs accounts for 42% ± 7% in the total VOCs (151.3 ± 75.6 ppbV). We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes. The chemical changes of organic carbon in a pollution accumulation period were investigated, which suggests an essential role of fragmentation reactions for large, chemically reduced compounds during the heavy-polluted stage in wintertime pollution. The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of "coal to gas" strategies in curbing air pollutants. The high abundances of some key species (e.g. oxygenated aromatics) indicate the strong emissions of coal combustion in wintertime of NCP. The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.

An observation approach in evaluation of ozone production to precursor changes during the COVID-19 lockdown.

The increase of surface ozone during the Corona Virus Disease 2019 (COVID-19) lockdown in China has aroused great concern. In this study, we combine 1.5 years of measurements for ozone, volatile organic compounds (VOCs), and nitrogen oxide (NOX) at four sites to investigate the effect of COVID-19 lockdown on surface ozone in Dongguan, an industrial city in southern China. We show that the average concentrations of NOX and VOCs decreased by 70%-77% and 54%-68% during the lockdown compared to pre-lockdown, respectively. Based on the source apportionment of VOCs, the contribution of industrial solvent use reduced significantly (86%-94%) during the lockdown, and climbed back slowly along with the re-opening of the industry after lockdown. A slight increase in mean ozone concentration (3%-14%) was observed during the lockdown. The rise of ozone was the combined effect of substantial increase at night (58%-91%) and small reduction in the daytime (1%-17%). These conflicting observations in ozone response between day and night to emission change call for a more detailed approach to diagnostic ozone production response with precursor changes, rather than directly comparing absolute concentrations. We propose that the ratio of daily Ox (i.e. ozone + NO2) enhancement to solar radiation can provide a diagnostic parameter for ozone production response during the lockdown period. Smaller ratio of daily OX (ozone + NO2) enhancement to solar radiation during the lockdown were observed from the long-term measurements in Dongguan, suggesting significantly weakened photochemistry during the lockdown successfully reduces local ozone production. Our proposed approach can provide an evaluation of ozone production response to precursor changes from restrictions of social activities during COVID-19 epidemic and also other regional air quality abatement measures (e.g. public mega-events) around the globe.

High Concentrations of Atmospheric Isocyanic Acid (HNCO) Produced from Secondary Sources in China.

Isocyanic acid (HNCO) is a potentially toxic atmospheric pollutant, whose atmospheric concentrations are hypothesized to be linked to adverse health effects. An earlier model study estimated that concentrations of isocyanic acid in China are highest around the world. However, measurements of isocyanic acid in ambient air have not been available in China. Two field campaigns were conducted to measure isocyanic acid in ambient air using a high-resolution time-of-flight chemical ionization mass spectrometer (ToF-CIMS) in two different environments in China. The ranges of mixing ratios of isocyanic acid are from below the detection limit (18 pptv) to 2.8 ppbv (5 min average) with the average value of 0.46 ppbv at an urban site of Guangzhou in the Pearl River Delta (PRD) region in fall and from 0.02 to 2.2 ppbv with the average value of 0.37 ppbv at a rural site in the North China Plain (NCP) during wintertime, respectively. These concentrations are significantly higher than previous measurements in North America. The diurnal variations of isocyanic acid are very similar to secondary pollutants (e.g., ozone, formic acid, and nitric acid) in PRD, indicating that isocyanic acid is mainly produced by secondary formation. Both primary emissions and secondary formation account for isocyanic acid in the NCP. The lifetime of isocyanic acid in a lower atmosphere was estimated to be less than 1 day due to the high apparent loss rate caused by deposition at night in PRD. Based on the steady state analysis of isocyanic acid during the daytime, we show that amides are unlikely enough to explain the formation of isocyanic acid in Guangzhou, calling for additional precursors for isocyanic acid. Our measurements of isocyanic acid in two environments of China provide important constraints on the concentrations, sources, and sinks of this pollutant in the atmosphere.

Resonant-antiresonant coupled cavity VCSELs.

The wavelength tuning range of a tunable vertical-cavity surface-emitting laser (VCSEL) is strongly influenced by the design of the interface between the semiconductor cavity and the air cavity. A simplified model is used to investigate the origin of the dramatic differences in free spectral range (FSR) and tuning slope observed in semiconductor cavity dominant, extended cavity, and air cavity dominant VCSELs. The differences arise from the positioning of the resonant and antiresonant wavelengths of the semiconductor cavity with respect to the center wavelength. The air cavity dominant design is realized by designing an antiresonant semiconductor cavity, resulting in a larger tuning slope near the center of the tuning range and a wider FSR toward the edges of the tuning range. The findings from the simplified model are confirmed with the simulation of a full VCSEL structure. Using an air cavity dominant design, an electrically pumped laser with a tuning range of 68.38 nm centered at 1056.7 nm at a 550 kHz sweep rate is demonstrated with continuous wave emission at room temperature. This epitaxial design rule can be used to increase the tuning range of tunable VCSELs, making them more applicable in swept-source optical coherence tomography and frequency-modulated continuous-wave LIDAR systems.

Combining Traditional Chinese Herbs and csDMARDs for the Treatment of Rheumatoid Arthritis Involves Tapering and Discontinuing Glucocorticoids: Protocol for a Two-Stage Non-Randomized Controlled Trial.

Glucocorticoids (GC) are crucial in the treatment of rheumatoid arthritis (RA), but discontinuing GC effectively in RA patients poses a significant challenge for rheumatologists. In this two-stage, single-center, non-randomized controlled trial, we investigated the benefits of combining Chinese traditional herbal treatment with csDMARDs to aid GC discontinuation in terms of GC tapering, disease control, and safety. A total of 231 participants were enrolled, of which 150 eligible subjects were included in the first phase and allocated to three groups (control group, treatment group 1, and treatment group 2) based on their willingness to take traditional Chinese medicine and syndrome differentiation, in a 1:1:1 ratio. All groups received basic treatment consisting of methotrexate tablets (10 mg, qw), leflunomide (10 mg, qd), and stratified GC bridging therapy and tapering regimen (The intervention regimen was developed based on rigorous adherence to available evidence). Treatment group 1 received basic treatment combined with Juanbi Granule, while treatment group 2 received basic treatment combined with Yupingfeng Guizhi Decoction Granule. Efficacy was evaluated after a 12-week follow-up, with slightly adjustments to the treatment group based on efficacy and change of syndrome, followed by continued observation until 24 weeks to complete the study. The efficacy evaluation and data analysis were conducted in a blinded manner, including group label concealment, data cleaning, confounder and control regimen analysis, and outcome analysis. This project has received ethical approval from the Ethics Committee of Yunnan Provincial Hospital of Traditional Chinese Medicine (YLZ [2022] Ethical Review No. (006)-01) and has been registered with the China Clinical Trials Registry (Registration number: ChiCTR2300067676, Registered 17 January 2023, https://www.chictr.org.cn/showproj.html?proj=184908). This trial was the first to evaluate the clinical efficacy of combining Chinese herbal medicines with standard Western medicines to facilitate the discontinuation of glucocorticoid (GC) therapy in patients with rheumatoid arthritis (RA).

[Compositional Characteristics of Volatile Organic Compounds in Typical Industrial Areas of the Pearl River Delta: Importance of Oxygenated Volatile Organic Compounds].

Volatile organic compounds (VOCs) are key components of tropospheric chemistry, of which industrial emissions are an important source of atmospheric VOCs. In this study, online measurements of 74 VOCs were made in a typical industrial area of the Pearl River Delta in southern China during the early summer of 2021. The mean volume mixing ratio of total volatile organic compounds (TVOC) was (81.9±45.4)×10-9 during the campaign. Among them, oxygenated volatile organic compounds (OVOCs) accounted for the largest fraction of TVOC, with an average of 51.5%, followed by aromatics, accounting for 19.4% of TVOC. The proportion of OVOCs in TVOC gradually increased with the increase in TVOC concentration. Industry-related emissions were the main contributors to aromatics and OVOCs in this region. Aromatics and OVOCs were the two major contributors to the ozone formation potential (OFP), accounting for 56.4% and 26.7%, respectively. Furthermore, OVOCs also contributed 40.0% of the total ·OH reactivity from VOCs. Xylenes, toluene, acrolein, and ethyl acetate had a greater contribution to the formation of secondary pollution; thus, these species should be given priority for controlling secondary pollution. Our results underscore the severity of OVOCs pollution in industrial areas and the important roles of OVOCs in secondary pollution.

Photolysis frequency of nitrophenols derived from ambient measurements.

Nitrophenols, a class of important intermediate products from the oxidation of aromatics, can participate in photochemistry and influence the atmospheric oxidative capacity. However, the reported photolysis frequencies of nitrophenols show considerable discrepancies. Here, measurements of nitrophenol, and methyl nitrophenol using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at both urban and regional sites in southern China are used to constrain photolysis frequencies of nitrophenols. Considerable concentrations with a campaign average of 58 ± 32 ppt for nitrophenol and 97 ± 59 ppt for methyl nitrophenol were observed at the regional site. Based on the in-situ measurement dataset, a steady-state calculation was performed along with a zero-dimensional box model to analyze the budgets of nitrophenols. The result indicates that both primary emission and photolysis have significant impacts on nitrophenols. Primary emission contributes up to 88 % of the total nitrophenols production while photolysis accounts for up to 98 % of the total removal rate. The dominant sink of nitrophenols is photolysis with a rate of about 3.5 % ± 1.3 % of jNO2 for nitrophenol and 2.4 % ± 1.0 % of jNO2 for methyl nitrophenol. The results of this study suggest that using advanced mass spectrometry to accurately measure ambient nitrophenols, supplemented by an observation-based box model for budget analysis, provides an important indication for determining photolysis rate constants of nitrophenols.

Turnover at the Top: The Digital Transformation and Dismissal of Chairman and CEO.

Companies increasingly implement digital transformation strategies to promote efficiency. Nevertheless, there are few concerns about employees' acceptance of the changes, especially the executives' adaptability, which is an important part of digital transformation strategy implementation. By utilizing the "searching-matching" in keywords of the annual reports of public listed companies in China, we measured the degree of corporate digital transformation to analysis its influence on the turnover rate of the Chairman and CEO. We found that digital transformation decreases the possibility of Chairman and CEO's turnover. Derived from the dynamic managerial capital theory, we demonstrated that executives' social network and political connections both have a moderate effect on the relationship between digital transformation and the turnover rate of executives. These findings will contribute to the digital transformation research by integrating with executives' dynamic managerial capital which is attained through social networks and political connections.

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.

[Vertical Distribution of Surface Formaldehyde in the Pearl River Delta Urban Area Based on Observations at the Canton Tower].

To investigate the vertical distribution of atmospheric formaldehyde in the Pearl River Delta (PRD) urban area, simultaneous measurements were performed at three heights on Canton Tower for the first time. Carbonyls including formaldehyde were sampled with 2,4-dinitrophenylhydrazin (DNPH) at noon for 32 days in autumn of 2018, and then analyzed using high-performance liquid chromatography (HPLC). Average mass concentrations of formaldehyde at ground level, 118 m, and 488 m sites at Canton Tower were (5.10±1.93), (6.61±2.84), and (5.33±2.55) µg·m-3, respectively. The measured formaldehyde was positively correlated with atmospheric oxidant Ox at the three sites (R 0.65-0.75), indicating that photochemical formation is an important source for urban formaldehyde in PRD. Three different profiles were found for formaldehyde vertical distribution during the measurements. The most frequently observed one showed a higher value at 118 m while lower ones at ground level and 488 m, occurring when the boundary layer is in moderate convection state with high photochemical reactivity. The 118 m layer may be also influenced by transported high-chimney emissions from industries in suburban areas. Vertical columns of formaldehyde were also calculated according to its vertical profile. The average value was (11.23±4.80)×1015 molecules·cm-2, 19% lower than that from satellite retrieval, while in the same magnitude as values reported in reference papers.

Deriving emission fluxes of volatile organic compounds from tower observation in the Pearl River Delta, China.

Accurate estimation of speciated emissions of volatile organic compounds (VOCs) is challenging due to the complexity of both species and sources. Evaluation of the bottom-up emission inventory (EI) by atmospheric observation is needed to better understand the VOC emissions and then to control air pollutions caused by VOCs. This study conducts vertical measurements of VOCs between November 3 and 11, 2018 at the Canton Tower in the urban core of Pearl River Delta (PRD), China. A mixed layer gradient (MLG) technique is applied to the tower observation data to derive emission fluxes for individual VOC. The results show that the measured VOCs concentrations at ground level were always higher than those at the heights of 118 m and 488 m. Obvious vertical gradients of concentrations were found for VOC species, such as benzene, toluene and isoprene. The emission flux was estimated to be largest for propane (3.29 mg m-2 h-1), followed by toluene (2.55 mg m-2 h-1), isoprene (2.24 mg m-2 h-1), n-butane (2.10 mg m-2 h-1) and iso-pentane (1.73 mg m-2 h-1). The total VOC emission fluxes were around 3 times larger than those in the EI, suggesting 1.5-2 times underestimations of ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) by current EI. Substantial underestimations (3-20 times) were found for C2-C5 alkanes by current EI. Due to unmeasured input parameters, limited sample size and short sampling period, there are still large uncertainties (40%-117%) in the estimated emission fluxes for individual species. Whereas, this study shows that the tower observation and emission estimation using MLG method could provide useful information for better understanding vertical distributions and emission fluxes of VOCs, and pioneer in assessing the existing emission inventories at species-level and hour-level.