Beijing, the capital of China, has experienced rapid industrialization, urbanization and motorization in recent decades. Consequently, air pollution in Beijing, especially fine particulate matter ...(PM2.5) pollution, has gradually become a severe environmental issue, due to the continuing growth in energy consumption and the resulting multiple pollutant emissions. In response to the increasingly serious PM2.5 pollution, Beijing's government implemented a series of policies, measures and regulations on air pollution prevention and control and took some concrete actions to improve air quality. In this paper, firstly, we summarize China's ambient air quality standards, China's policies and regulations on air pollution prevention and control. Secondly, we illustrate historical evolution and current status of air pollution in Beijing. Finally, we introduce control measures and actions in Beijing and its surrounding areas. The paper aims to help environmental scientists and policy makers around the world understand the past and current air pollution in Beijing and control strategies and actions taken by Beijing's government. Display omitted
Stable graphene suspensions are prepared using a new, green, and intriguing synthetic route. Graphene can be directly prepared by the fast deoxygenation of exfoliated graphite oxide in strong ...alkaline solutions at low temperatures (50–90 °C), in the absence of reducing agents. This study opens an opportunity towards the production of processable graphene on an industrial scale.
Open biomass burning plays an important role in atmospheric pollution and in climate change. However, the current emission inventory of open biomass burning is generally of highly uncertainty because ...of missing small fire data and limited resolution because of the lack of localized vegetation data. In this study, the MODIS (MODerate Resolution Imaging Spectroradiometer) burned area product MCD64Al combined with the active fire product MCD14 ML, as well as a high-resolution land cover data set, were applied to develop a high-resolution emission inventory of open biomass burning in China in 2013. Total CO, CH4, NO x , NMVOC (nonmethane volatile organic compounds), SO2, NH3, PM2.5, PM10, OC (organic carbon), BC (black carbon), and CO2 emissions were estimated to be 1.03 × 104, 666, 536, 1.91 × 103, 87, 138, 1.45 × 103, 2.09 × 103, 741, 137, and 2.45 × 105 Gg, respectively. The provinces that contributed the most emissions included Heilongjiang, Henan, Shandong, and Jilin. The major source for all pollutants was cropland burning, whereas Xizang, Xinjiang, and Heilongjiang had greater emissions from natural vegetation. The temporal distribution of average provincial emissions showed that the peaks were in June and October. This study updated the emission information that may support future research and policy-making on air pollution control and GHG emission abatement.
Ciphertext-policy attribute-based encryption (CP-ABE) has been a preferred encryption technology to solve the challenging problem of secure data sharing in cloud computing. The shared data files ...generally have the characteristic of multilevel hierarchy, particularly in the area of healthcare and the military. However, the hierarchy structure of shared files has not been explored in CP-ABE. In this paper, an efficient file hierarchy attribute-based encryption scheme is proposed in cloud computing. The layered access structures are integrated into a single access structure, and then, the hierarchical files are encrypted with the integrated access structure. The ciphertext components related to attributes could be shared by the files. Therefore, both ciphertext storage and time cost of encryption are saved. Moreover, the proposed scheme is proved to be secure under the standard assumption. Experimental simulation shows that the proposed scheme is highly efficient in terms of encryption and decryption. With the number of the files increasing, the advantages of our scheme become more and more conspicuous.
O3 and PM2.5 were introduced into the newly revised air quality standard system in February 2012, representing a milestone in the history of air pollution control, and China＇s urban air quality will ...be evaluated using six factors （SO2, NO2, O3, CO, PM2.5 and PM10） from the beginning of 2013. To achieve the new air quality standard, it is extremely important to have a primary understanding of the current pollution status in various cities. The spatial and temporal variations of the air pollutants were investigated in 26 pilot cities in China from August 2011 to February 2012, just before the new standard was executed. Hourly averaged SO2, NO2 and PMlo were observed in 26 cities, and the pollutants O3, CO and PM2.5 were measured in 15 of the 26 cities. The concentrations of SO2 and CO were much higher in the cities in north China than those in the south. As for O3 and NO2, however, there was no significant difference between northern and southern cities. Fine particles were found to account for a large proportion of airborne particles, with the ratio of PM2.5 to PMI0 ranging from 55% to 77%. The concentrations of PM2.5 （57.5 μg/m3） and PMlo （91.2 μg/m3） were much higher than the values （PM2.5：11.2μg/m3; PMI0：35.6 μg/m3） recommended by the World Health Organization. The attainment of the new urban air quality standard in the investigated cities is decreased by 20% in comparison with the older standard without considering O3, CO and PM2.5, suggesting a great challenge in urban air quality improvement, and more efforts will to be taken to control air pollution in China.
Photocatalytic overall water splitting (OWS) without using any sacrificial reagent to realize H2 and O2 production in the stoichiometric ratio of 2:1 is viewed as the “holy grail” in the field of ...solar fuel production. Developing stable, low cost, and nontoxic photocatalysts that have satisfactory solar‐to‐hydrogen conversion efficiency is of significance but challenging for realizing the large‐scale use of this sustainable technology. Among various photocatalysts, graphitic carbon nitride (GCN) has shown great potential as an ideal candidate to fulfill the breakthrough in this dynamic research field due to its attractive physicochemical properties. Herein, for the first time, the state‐of‐the‐art research progress of GCN for photocatalytic OWS is reviewed. We first summarize the basic principle of photocatalytic OWS along with the advantages/challenges of GCN introduced. The strategies that have been used to modulate the OWS activity of GCN are then reviewed, including cocatalyst investigation, morphology modulation, atomic structure modification, crystallinity engineering, and heterostructure construction. Toward the end of the review, the concluding remarks and perspectives for the future development are presented, with our expectation to provide some new ideas for the design of advanced OWS photocatalysts.
Developing proper photocatalysts for overall water splitting is of great significance for the sustainable and clean energy production. The research progress of photocatalytic overall water splitting by graphitic carbon nitride with the focus on its developed modulation strategies is systematically reviewed in this work, which aims to provide some strategies and in‐depth understanding for the design of high performance photocatalysts for overall water splitting.
Agricultural crop residue burning, including open field burning and burned as household fuel, is a significant emission source of primary fine particulate matter (PM2.5) and gaseous precursors of ...secondary PM2.5. However, limited information exists on emission characterization, environmental impact, and control measure of PM2.5 emitted from agricultural crop residue burning in China. In this study, laboratory simulation experiments were conducted to characterize emission factors of PM2.5 and PM2.5-bound chemical compositions from the burning of three typical agricultural crop residues (rice, wheat and corn straw). PM2.5-bound chemical compositions in our measurements include elemental carbon (EC) and organic carbon (OC), water-soluble ions (WSI), polycyclic aromatic hydrocarbons (PAHs) and alkyl-polycyclic aromatic hydrocarbons (APAHs). Emission factors of PM2.5 and PM2.5-bound EC, OC, WSI, PAHs and APAHs were 13.1, 1.38, 7.68, 1.40, 0.99 × 10−3 and 0.20 × 10−3 g kg−1 for rice straw, 6.2, 0.55, 2.93, 1.53, 0.85 × 10−3 and 0.22 × 10−3 g kg−1 for wheat straw, and 10.5, 0.94, 5.93, 1.53, 0.93 × 10−3 and 0.22 × 10−3 g kg−1 for corn straw, respectively. PM2.5 emissions from agricultural crop residue burning were estimated to be 1248, 1485, and 1826 Gg in 2003, 2008, and 2013, respectively. Environmental impacts resulted from open field burning of agricultural crop residue, including visibility impairment, air quality degradation (sometimes heavy haze pollution) and adverse health effects, were explored in this study. Furthermore, in order to ensure the attainment of good ambient air quality during the harvest season, some control measures, such as straw returning to soil, power generation, biogas production and animal feed supply etc., were proposed to prohibit open field burning of agricultural crop residue in China.
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•Emission factors of PM2.5, its precursors and chemical compositions from agricultural crop residue burning were characterized.•Emission inventories of primary PM2.5 from agricultural crop residue burning were evaluated.•Potential environmental impacts due to agricultural crop residue burning were explored.•Effective control measures about agricultural crop residue burning were proposed.
Atmospheric particles were studied before, during, and after the period of the Olympic Summer Games in Beijing, China, in August 2008 in order to investigate the efficiency of the mitigation measures ...implemented by the Chinese Government. Total suspended particles (TSP) and fine particles (PM2.5 and PM1) were collected continuously from October 2007 to February 2009 and were analyzed in detail with regard to mass and element concentrations, water-soluble ions, and black carbon (BC). Mass as well as element concentrations during the Olympic air quality control period were lower than the respective concentrations during the time directly before and after the Olympic Games. The results showed that the applied aerosol source control measures, such as shutting down industries and reducing traffic, had a huge impact on the reduction of aerosol pollution in Beijing. However, the meteorological conditions, especially rainfall, certainly also contributed to the successful reduction of particulate air pollution.
Coarse particles were reduced more efficiently than finer particles, which indicates that long-range transport of atmospheric particles is difficult to control and that presumably the established mitigation area was not large enough. The study further showed that elements from predominantly anthropogenic sources, such as S, Cu, As, Cd, and Pb, as well as BC, were reduced more efficiently during the Olympic Games than elements for which geogenic sources are more significant, such as Al, Fe, Rb or Sr. Furthermore, the mentioned anthropogenic element concentrations were reduced more in the finer PM2.5 samples whereas geogenic ones were reduced stronger in TSP samples including the coarser fraction. Consequently, it can be assumed that the mitigation measures, as intended, were successful in reducing more toxic and health-relevant particles from anthropogenic sources. Firework displays, especially at the Opening Ceremony, could be identified as a special short-time source for atmospheric particles during the Olympic Games.
► Effects of mitigation measures during the Olympic Games 2008 in Beijing were studied. ► Atmospheric particles were analyzed for element, water-soluble ion, and BC concentrations. ► Concentrations decreased due to the implemented measures and meteorological conditions. ► Finer particles were reduced less compared to coarser fractions due to long-range transport. ► In the fine fraction anthropogenic elements were reduced more than those from geogenic sources.
To evaluate PM2.5 contributions to light scattering under different air pollution levels, PM2.5 and its major chemical components, PM10, size-segregated water-soluble ions, and aerosol scattering ...coefficient (bsp) under dry conditions were measured at an urban site in Beijing in January 2013 when heavy pollution events frequently occurred. Measurements were categorized into three pollution levels including heavy-polluted (Air Quality Index (AQI) ≥ 200), light-polluted (200 > AQI ≥ 100) and clean periods (AQI < 100). The average PM2.5 mass concentration was 248 μg m−3 during the heavy-polluted period, which was 2.4 and 5.6 times of those during the light-polluted (104 μg m−3) and clean (44 μg m−3) periods, respectively. The concentrations of SO42−, NO3− and NH4+ increased much more than those of OC and EC during the heavy-polluted period compared with those during the light-polluted and clean periods. Good correlations between PM2.5 and bsp were found (R2 > 0.95) during the different pollution levels. The mass scattering efficiency (MSE) of PM2.5 was 4.9 m2 g−1 during the heavy-polluted period, which was higher than those during the light-polluted (4.3 m2 g−1) and clean periods (3.6 m2 g−1). To further evaluate the impact of individual chemical components of PM2.5 on light scattering, a multiple linear regression equation of measured bsp against the mass concentration of (NH4)2SO4, NH4NO3, Organic Matter (OM), EC, Fine Soil (FS), Coarse Matter (CM) and Other chemical compounds were performed. (NH4)2SO4, NH4NO3 and OM were the dominant species contributing to bsp under both dry and ambient conditions. OM contributed more to bsp than the sum of (NH4)2SO4 and NH4NO3 did under the dry condition during all the pollution periods and this was also the case under the ambient condition during the light-polluted and clean periods. However, the total contributions of (NH4)2SO4 and NH4NO3 to bsp under the ambient condition was 55%, much more than the 29% contribution from OM during the heavy-polluted period. High (NH4)2SO4 and NH4NO3 concentrations and their hygroscopicity were the main reasons causing visibility degradation during the heavy-polluted period, and the effect can be enhanced under high RH conditions.
•Aerosol chemical and optical properties were compared in different pollution levels.•Contributions of dominant chemical components to light scattering were quantified.•Causes of heavy pollution events and related visibility degradation were explored.
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