372 research outputs found
Determinants of stagnating carbon intensity in China
No full textChina committed itself to reduce the carbon intensity of its economy (the amount of CO2 emitted per unit of GDP) by 40-45% during 2005-2020. Yet, between 2002 and 2009, China experienced a 3% increase in carbon intensity, though trends differed greatly among its 30 provinces. Decomposition analysis shows that sectoral efficiency gains in nearly all provinces were offset by movement towards a more carbon-intensive economic structure. Such a sectoral shift seemed to be heavily affected by the growing role of investments and capital accumulation in China's growth process which has favoured sectors with high carbon intensity. Panel data regressions show that changes in carbon intensity were smallest in sectors dominating the regional economy (so as not to endanger these large sectors, which are the mainstay of the provincial economy), whereas scale and convergence effects played a much smaller role
The Promise of Beijing: Evaluating the Impact of the 2008 Olympic Games on Air Quality
No full textTo prepare for the 2008 Olympic Games, China adopted a number of radical measures to improve air quality. Using officially reported air pollution index (API) from 2000 to 2009, we show that these measures improved the API of Beijing during and after the Games, but 60% of the effect faded away by the end of October 2009. Since the credibility of API data has been questioned, an objective and indirect measure of air quality at a high spatial resolution – aerosol optimal depth (AOD), derived using the data from the NASA satellites – was analyzed and compared with the API trend. The analysis confirms that the improvement was real but temporary and most improvement was attributable to plant closure and traffic control. Our results suggest that it is possible to achieve real environmental improvement in an authoritarian regime but the magnitude of the effect and how long it lasts depend on the political motivation behind the policy interventions.
An inventory of primary air pollutants and CO2 emissions from cement production in China, 1990–2020
No full textDirect emissions of air pollutants from the cement industry in China were estimated by developing a technology-based methodology using information on the proportion of cement produced from different types of kilns and the emission standards for the Chinese cement industry. Historical emissions of sulfur dioxide (SO2), nitrogen oxides (NOX), carbon monoxide (CO), particulate matter (PM) and carbon dioxide (CO2) were estimated for the years 1990e2008, and future emissions were projected up to 2020 based on current energy-related and emission control policies. Compared with the historical high (4.36 Tg of PM2.5, 7.16 Tg of PM10 and 10.44 Tg of TSP in 1997), PM emissions are predicted to drop substantially by 2020, despite the expected tripling of cement production. Certain other air pollutant emissions, such as CO and SO2, are also predicted to decrease with the progressive closure of shaft kilns. NOX emissions, however, could increase because of the promotion of precalciner kilns and the rapid increase of cement production. CO2 emissions from the cement industry account for approximately one eighth of China’s national CO2 emissions. Our analysis indicates that it is possible to reduce CO2 emissions from this industry by approximately 12.8% if advanced energy-related technologies are implemented. These technologies will bring co-benefits in reducing other air pollutants as well.Engineering and Applied SciencesVersion of Recor
Characteristics and source identification of fine particulate n-alkanes in Beijing, China
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Three-dimensional and nonlinear metamaterials at terahertz frequencies
No full textThesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at [email protected]. Thank you.During the past decade metamaterials have emerged as a unifying theme across a large swath of the electromagnetic spectrum. Scale invariance of the underlying equations enables translation of phenomena realized in one region of the spectrum to others. To date, the majority of metamaterials studies focus in the microwave, and infrared to visible regimes, while leaving a span in between. This region, called terahertz regime from 0.3 to 10 terahertz, is of particular interest because of its increasing technological importance, which includes as examples, security screening and embedded imaging. This lag in development of metamaterials is due to enormous challenges with two most important being fabrication strategies and available terahertz sources and detectors. This, in turn, restricts multifunctional responses of metamaterials that are particularly important for implementing dynamic devices at terahertz frequencies. The object of this thesis is to describe our progress on developing a fabrication strategy to construct three-dimensional metamaterials and taking advantage of recent advances in high field terahertz generation to realize nonlinear metamaterials.
The first part of this thesis details the developed multilayer electroplating technique for fabrication of stand-up metamaterials on rigid and conformally flexible substrate. The strong resonance resulting from the coupling to the incident magnetic field indicates a significant magnetic response and negative permeability of metamaterials at terahertz frequencies. Extending our fabrication technique, we also experimentally demonstrated broadband three-dimensional metamaterials with dynamic tuning range over 30%. Through photoexcitation of active medium of silicon that is incorporated in the metamaterial active region, the resonant frequency can be effectively tuned. Next, with the judicious incorporation of field enhancement of metamaterials with state-of-the-art technique of high field terahertz generation, field-dependent nonlinear metamaterials fabricated on semiconductors are presented. Modeling and numerical simulations indicate that the origin of nonlinearity arises from nonequilibrium carrier transport within the capacitive regions of resonators. With increasing field, the retrieved off-resonance permittivity exhibits tinting between negative and positive values. Our innovative work opens up numerous possibilities for nonlinear metamaterials at terahertz frequencies. This thesis provides a route forward to create novel metamaterial-based devices for sensing and manipulating electromagnetic waves.2999-01-0
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