The direct alpha-vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that delta-oxocarboxylic acids can serve as masked vinyl ...compounds and be unveiled by palladium-catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of alpha-vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (-)-aspewentinsA, B, and C is demonstrated.
A new 9,11-secosteroid having an unprecedented tricyclic gamma-diketone structure, aplysiasecosterolA (1), was isolated from the sea hare Aplysia kurodai. The structure was determined by one- and ...two-dimensional NMR spectroscopic analysis, molecular modeling studies, a comparison of experimental and calculated ECD spectra, and a modified Mosher's method. AplysiasecosterolA (1) exhibited cytotoxicity against human myelocytic leukemia HL-60 cells. A biosynthetic pathway for 1 from a known cholesterol was proposed and includes twice alpha-ketol rearrangements and an intramolecular acetalization.
In contrast to summer smog, the contribution of photochemistry to the formation of winter haze in northern mid-to-high latitude is generally assumed to be minor due to reduced solar UV and water ...vapor concentrations. Our comprehensive observations of atmospheric radicals and relevant parameters during several haze events in winter 2016 Beijing, however, reveal surprisingly high hydroxyl radical oxidation rates up to 15 ppbv/h, which is comparable to the high values reported in summer photochemical smog and is two to three times larger than those determined in previous observations during winter in Birmingham (Heard et al. Geophys. Res. Lett. 2004, 31, (18)), Tokyo (Kanaya et al. J. Geophys. Res.: Atmos. 2007, 112, (D21)), and New York (Ren et al. Atmos. Environ. 2006, 40, 252–263). The active photochemistry facilitates the production of secondary pollutants. It is mainly initiated by the photolysis of nitrous acid and ozonolysis of olefins and maintained by an extremely efficiently radical cycling process driven by nitric oxide. This boosted radical recycling generates fast photochemical ozone production rates that are again comparable to those during summer photochemical smog. The formation of ozone, however, is currently masked by its efficient chemical removal by nitrogen oxides contributing to the high level of wintertime particles. The future emission regulations, such as the reduction of nitrogen oxide emissions, therefore are facing the challenge of reducing haze and avoiding an increase in ozone pollution at the same time. Efficient control strategies to mitigate winter haze in Beijing may require measures similar as implemented to avoid photochemical smog in summer.
Threats and response efficacyperceptions are core conceptsof the protection motivationtheory, and recent years have witnessed a considerable growth of research on the effect of thesefactors on ...adaptation to air pollution. However, few studies use appropriate designs to deal with endogeneity issues, a situation that raises serious questions on the validity of their findings. To overcome this problem, this study uses the instrumental variables method to test the effect of perceived threats and response efficacy on adaptation to smog episodes. The results of this study show that the conjunction of a moderate to high perception of threats with a high perception of response efficacy is positively associated with the adoption of the recommended behavior. The increase of perceived threats does not seem to have an effect on the behavior of individuals with low response efficacy perception. Moreover, change in perceived response efficacy does not lead to any change in the behavior of individuals with low threat perceptions. Concerning policy implications, this study suggests that smog warnings and health communication campaigns could be more effective if they provide accurate information simultaneously on air pollution level, its adverse effects, and advice on how to mitigate these effects.
It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of ...secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.
This study analyzed the differences in ozone (Osub.3) sensitivity in four different urban areas in China from February 2019 to January 2020 based on data on various near-surface pollutants from ...passive multi-axis differential optical absorption spectroscopy (MAX-DOAS) sites and nearby China National Environmental Monitoring Center (CNEMC) sites. Across the four cities, the nitrogen dioxide (NOsub.2) and formaldehyde (HCHO) concentrations varied seasonally. Xianghe consistently displayed the lowest NOsub.2 levels, suggesting reduced emissions compared to other cities. Guangzhou, a city with a robust economy and a high level of vehicle ownership, exhibited higher concentrations in spring. Summer brought elevated HCHO levels in Guangzhou, Xianghe, and Shenyang due to intensified photochemical processes. Autumn and winter showed higher HCHO concentrations in Guangzhou and Xianghe compared to Lanzhou and Shenyang. Overall, Guangzhou recorded the highest annual averages, due to its developed economy, while Xianghe’s lower NOsub.2 levels were offset by the elevated HCHO due to higher Osub.3 values. The analysis delved into primary and secondary HCHO sources across seasons and used carbon monoxide (CO) and Osub.3 data. Xianghe showcased the dominance of secondary sources in summer and autumn, while Lanzhou was characterized by primary dominance throughout the year. Shenyang mirrored Xianghe’s evolution due to industrial emissions. In Guangzhou, due to the high levels of vehicular traffic and sunlight conditions, secondary sources predominantly influenced HCHO concentrations. These findings highlight the interplay between primary and secondary emissions in diverse urban settings. This study explored Osub.3 sensitivity variations across seasons. Xianghe exhibited a balanced distribution among volatile organic compound (VOC)-limited conditions, nitrogen oxide (NOx)-limited conditions, and transitional influences. Lanzhou was mainly affected by VOC-limited conditions in winter and NOx-limited conditions in other seasons. Shenyang’s sensitivity varied with the seasons and was primarily influenced by transitions between VOCs and NOx in autumn and NOx-limited conditions otherwise. Guangzhou experienced varied influences. During periods of high Osub.3 pollution, all regions were affected by NOx-limited conditions, indicating the necessity of NOx monitoring in these areas, especially during summer in all regions and during autumn in Xianghe and Guangzhou.
Urbanization, industrialization, and increasing fossil fuel consumption are generally identified as the main contributors to poor air quality. Smog is a form of visible air pollution processes that ...can cause diverse health problems (e.g., pulmonary, respiratory, and skin diseases). In Lahore, the second-largest city of Pakistan, smog pollution has been a significant socioeconomic issue since 2013 of which situation has been worsening each year. In this systematic review, we discuss the major issues concerning smog in Pakistan: the causes, methods of detection, hazardous effects, and opportunities for preventive measures based on ground-level information. This study identifies smog as a potential source of human health risk as serious repercussions of economic development. It is thus suggested that adequate abatement measures should be established for the proper protection of public health.
The efficient, stable, and selective photocatalytic conversion of nitric oxide (NO) into harmless products such as nitrate (NOsub.3 sup.−) is greatly desired but remains an enormous challenge. In ...this work, a series of BiOI/SnOsub.2 heterojunctions (denoted as X%B-S, where X% is the mass portion of BiOI compared with the mass of SnOsub.2) were synthesized for the efficient transformation of NO into harmless NOsub.3 sup.−. The best performance was achieved by the 30%B-S catalyst, whose NO removal efficiency was 96.3% and 47.2% higher than that of 15%B-S and 75%B-S, respectively. Moreover, 30%B-S also exhibited good stability and recyclability. This enhanced performance was mainly caused by the heterojunction structure, which facilitated charge transport and electron-hole separation. Under visible light irradiation, the electrons gathered in SnOsub.2 transformed Osub.2 to ·Osub.2 sup.− and ·OH, while the holes generated in BiOI oxidized Hsub.2O to produce ·OH. The abundantly generated ·OH, ·Osub.2 sup.−, and sup.1Osub.2 species effectively converted NO to NOsup.− and NOsub.2 sup.−, thus promoting the oxidation of NO to NOsub.3 sup.−. Overall, the heterojunction formation between p-type BiOI and n-type SnOsub.2 significantly reduced the recombination of photo-induced electron-hole pairs and promoted the photocatalytic activity. This work reveals the critical role of heterojunctions during photocatalytic degradation and provides some insight into NO removal.
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![Identification of O[sub.3] ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2072-4292/small "Identification of O[sub.3] Sensitivity to Secondary HCHO and NO[sub.2] Measured by MAX-DOAS in Four Cities in China")
![BiOI-SnO[sub.2] Heterojunct...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1660-4601/small "BiOI-SnO[sub.2] Heterojunction Design to Boost Visible-Light-Driven Photocatalytic NO Purification")