For the 2008 Beijing Olympic Games full‐scale control (FSC) of atmospheric pollution was implemented to improve the air quality from 20 July to 20 September 2008, resulting in a significant decrease in the emission of pollutants in urban Beijing, especially vehicular emissions. The combination of reduced emissions and weather condition changes provided us with a unique opportunity to investigate urban atmospheric chemistry. Hydrogen peroxide (H 2 O 2 ) and organic peroxides play significant roles in atmospheric processes, such as the cycling of HO x radicals and the formation of secondary sulfate aerosols and secondary organic aerosols. We measured atmospheric H 2 O 2 and organic peroxides in urban Beijing, at the Peking University campus, from 12 July to 30 September, before and during the FSC. The major peroxides observed were H 2 O 2 , methyl hydroperoxide (MHP), and peroxyacetic acid (PAA), having maximal mixing ratios of 2.34, 0.95, and 0.17 ppbv (parts per billion by volume), respectively. Other organic peroxides were detected occasionally, such as bis‐hydroxymethyl hydroperoxide, hydroxymethyl hydroperoxide, ethyl hydroperoxide, and 1‐hydroxyethyl hydroperoxide. On sunny days the concentrations of H 2 O 2 , MHP, and PAA exhibited pronounced diurnal variations, with a peak in the afternoon (1500–1900) and, occasionally, a second peak in the evening (2000–0200). The night peaks can be attributed to local night production from the ozonolysis of alkenes, coupled with the reaction between NO 3 radicals and organic compounds. Sunny‐day weather dominated during 16–26 July, and we found that the concentrations of H 2 O 2 , MHP, and PAA increased strikingly on 22–26 July, compared with the concentrations during 16–19 July. This effect was mainly attributed to the NO x (NO and NO 2 ) decline because of the FSC, due to (i) the suppressing effect of NO and NO 2 on the production of peroxides and (ii) the indirect effect of reduced NO x on the concentration of peroxides via O 3 production in the volatile organic compound‐sensitive area. Although the time period from 29 July to 15 August fell within the FSC, the concentrations of H 2 O 2 , MHP, and PAA decreased significantly. This can be explained by a combination of chemical and physical factors during this period, when rainy‐ and cloudy‐day weather dominated. Weaker irradiation and lower temperatures resulted in a lower photochemical production of peroxides; the higher humidity resulted in their greater loss through their aqueous‐phase oxidation of S(IV) and through heterogeneous removal, and lower temperatures and higher nighttime humidity resulted in a quicker surface deposition of peroxides. Furthermore, our observations seem to imply that the heterogeneous removal of H 2 O 2 is faster than that of MHP, as indicated by the strong negative correlation between the H 2 O 2 ‐to‐MHP ratio and the aerosol surface area.
Gas-phase vanadium oxide cluster cations and anions are prepared by laser ablation. The small cluster ions (<1000 amu) are mass-selected using a quadrupole mass filter and reacted with benzene in a linear ion trap reactor; large clusters (>1000 amu) with no mass selection are reacted with C6H6 in a fast flow reactor. Rich product variety is encountered in these reactions, and the reaction channels for small cationic and anionic systems are different. For large clusters, the reactivity patterns of (V2O5) n+ (n = 6-25) and (V2O5) n O- (n = 6-24) cluster series are very similar to each other, indicating that the charge state has little influence on the oxidation of benzene. In sharp contrast to the dramatic changes of reactivity of small clusters, a weakly size dependent reaction behavior of large (V2O5)6-25+ and (V2O5)6-24O- clusters is observed. Therefore, the charge state and the size are not the major factors influencing the reactivity of nanosized vanadium oxide cluster ions toward C6H6, which is not common in cluster science. In the reactions with benzene, the small and large reactive vanadium oxide cations show similar reactivity of hydroxyl radicals (OH•) toward C6H6 at higher and lower temperatures, respectively; different numbers of vibrational degrees of freedom and the released energy during the formation of adduct complexes can explain this intriguing correlation. The reactions investigated herein might be used as the models of how to realize the partial oxidation of benzene to phenol in a single step, and the observed mechanisms are helpful to understand the corresponding heterogeneous reactions, such as those over vanadium oxide aerosols and vanadium oxide catalysts.
Drought is one of the main natural disasters that man has suffered since the ancient era. In China nation-wide droughts occur year after year, imposing severe threats to the food security and constraining the sustainable development of social economy.The Water Resources Information Centre of the Ministry of Water Resources of China (WRIC/MWR) developed an operational drought monitoring system in 1996, based on a river basin hydrological model. This system produces daily nation-wide maps of soil waterdeficit. However, it is felt that two aspects need to be improved: the spatial resolution is low (only 590 sites for whole China) and the hydrological model used in this system is a single-point model (interpolation between the points cannot reveal the actual situation). Alterra has developed the Surface Energy Balance System (SEBS) to estimate drought characteristic parameters using satellite remote sensing images. In order to import this advanced technique and apply it for the nation-wide drought monitoring, the Ministry of Water Resources of China funded a technique import project. This report shows the design, transplantation and modification of this technique to the Chinese situation, and the analysis of the first results of the new approach.
중국의 관완화 형사정책의 실체는 ‘관대함과 엄격함이 서로 보완되는(寬嚴相濟) 형사사법정책’을 중국의 기본적인 형사 정책으로 하되, 사회의 급격한 변화로 인해 증가하는 비교적 가벼운 범죄에 관하여 비교적 관대한 형사처분을 내려 교정부담을 줄이고자 하는 취지에 있다. 이는 현재 중국 범죄 구조의 변화에 부합한다. 또한, 범죄의 예방과 통제에 더불어 피해규모에 대한 형평과 범죄자의 인권 보호의 관계를 중요시하는 형벌에 대한 현대적 요구를 반영한 결과이다.BR 이러한 생각의 연장선에서 형벌을 보다 가볍게 하려는 의도인 공동체 교정 제도는 보다 인도적이고 이성적인, 민주적인 시대가치를 내포하고 있다고 볼 수 있을 것이다. 궁극적으로는 지역사회의 교정을 추진하는 것은 관대함과 엄격함이 서로 보완되는 형사정책을 보다 현실화하여 전통적인 형벌의 사회적 오류나 폐단을 완화하는 데 목적이 있다.BR 비교적 가벼운 범죄에 관하여 형사처분을 경미화 하여야 한다는 시각을 전반적인 개혁 방향으로 삼고, 지역교정을 중심으로 비금고형 적용률을 높이고, 지역교정 적용대상 범위 확대 및 지역교정 제도 자체를 최적화하는데 초점을 맞추는 데 이 정책의 의미가 있다.
Four experimental methods of determining the x parameter of M18R1 martensite are described, using X-ray and electron diffraction, including both relative intensity comparison and geometrical measurement. The good agreement of the experimental values of the x parameter determined with these four methods proves their correctness. The x parameters of M18R1 martensites in Cu–Zn–Al alloys, formed by step quenching and direct quenching, are rather large. They approach the value of 1/3 found in N18R1 as the aging (after direct quenching) temperature is raised, but they remain unchanged during the aging process after step quenching.
Single-atom catalysts (SACs) have attracted broad interest recently due to their superior catalytic properties. However, a facile fabrication method for the large-scale synthesis of SACs is still in demand. This study reports a mechanochemical approach for the mass production of noble metal SACs. The successful formation of atomically dispersed palladium species on zinc oxide (Pd1/ZnO) was verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy. Furthermore, our method exhibited little scaling-up effect on the mass production of Pd1/ZnO at ranges of 10–1,000 g, in which the catalyst structure and catalytic performance were retained. Meanwhile, the versatility of this approach was demonstrated by the large-scale fabrication of Rh and Ru SACs, and Pd1/Cu single-atom alloys. Thus, this promising strategy provides the potential for cost-effective mass production of SACs and subsequently may open a window for their industrial application.
Heterogeneous oxidation of oxygenated volatile organic compounds (OVOCs) serves as an important sink of OVOCs as well as a source of secondary organic material. However, the roles of gas phase oxidants in these reactions are poorly understood. In this work, we present the first laboratory study of the heterogeneous reactions of methacrolein (MACR) on various mineral dust particles in the presence of gaseous H2O2. It is found that the presence of gaseous H2O2 significantly promotes both the uptake and oxidation of MACR on kaolinite, α-Al2O3, α-Fe2O3, and TiO2, but not on CaCO3. The oxidation of MACR produces organic acids as its major low-molecular-weight product, whose yields are enhanced by a factor of 2-6 in the presence of H2O2. In addition, organic peroxides such as methyl hydroperoxide, peroxyformic acid, and peroxyacetic acid are only formed in the presence of H2O2, and the formation of methyl hydroperoxide indicates that MACR oxidation on the surface involves reaction with OH radicals. A probe reaction using salicylic acid verifies the production of OH radicals from H2O2 decomposition on kaolinite, α-Al2O3, α-Fe2O3, and TiO2, which rationalizes the enhanced MACR oxidation observed on these particles. The uptake coefficients of MACR on kaolinite, α-Fe2O3, and TiO2 in the presence of H2O2 are on the order of 10(-5)-10(-4). Our results provide new insights into the formation and chemical evolution of organic species in the atmosphere.
Abstract Organosulfates (OSs) are important components of secondary organic aerosols (SOA) in the atmosphere. Despite the frequent observation of OSs in field and laboratory studies, the sources and detailed formation pathways of these species, particularly in polluted regions, are still not well understood. In this study, a total of 156 ambient PM 2.5 filter samples were collected in a Chinese megacity (Shanghai) over four seasons in both 2015–2016 and 2018–2019. More than 270 OS formulas were detected in ambient aerosols using high‐resolution liquid chromatography‐mass spectrometry. Interestingly, a series of alkyl OSs, C n H 2n+1 O 4 S − (C 5 –C 11 ), were observed, which are most likely to be produced from the heterogeneous reactions of organic peroxides with sulfur dioxide or sulfate. The observation of these compounds provides the first field evidence for atmospheric OS formation involving organic peroxides. By employing a positive matrix factorization model, the possible precursors of OSs were classified into six groups, that is, isoprene‐derived, monoterpene‐derived, aromatic, short‐chain aliphatic, long‐chain aliphatic, and anthropogenic C 2 /C 3 OSs. Biogenic (isoprene and monoterpenes) and anthropogenic sources (the remaining factors) contributed to 57.2% and 42.8% of OS formation in 2015–2016, respectively, and their contributions just slightly changed in 2018–2019. In addition, the OS sources exhibited strong seasonality. Isoprene‐derived OSs contributed to the largest fraction of total OSs in summer, while anthropogenic sources dominated OS formation in other seasons. Our findings provide valuable insight into OS sources and formation mechanisms in the atmosphere and highlight the importance of both biogenic and anthropogenic emissions for the formation of OSs in a typical Chinese megacity.
The heterogeneous reactions of methacrolein (MAC) and methyl vinyl ketone (MVK) on α-Al2O3 surfaces have been studied in a flow reactor using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy to monitor the reaction progress. Unlike SiO2 particles where MAC and MVK are weakly physisorbed, the results in this work demonstrate that on α-Al2O3 particles MAC and MVK are irreversibly adsorbed and can rapidly react on the surface to form various products such as aldehydes, organic acids, hydrogen peroxide, and even higher molecular weight compounds. The initial uptake rates and initial uptake coefficients for MAC and MVK on α-Al2O3 under dry conditions were determined to explore the reactivity of the particles. Furthermore, the effect of water vapor on the heterogeneous reactions was also investigated as a function of relative humidity. Both the heterogeneous uptake and transformation of MAC and MVK on α-Al2O3 were largely suppressed under humid conditions due to the depletion of surface active sites by water molecules. On the basis of experimental results, atmospheric implications of heterogeneous reactions of MAC and MVK were discussed. Our work suggests that heterogeneous reactions on α-Al2O3 can be important sinks for MAC and MVK as well as possible contributors to atmospheric organic aerosol.
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