科研成果 by Year: 2012

Radiocarbon (C-14) has become a powerful tracer in source apportionments of atmospheric carbonaceous particles. Fine particles (PM2.5) were collected at a rural site of Beijing in the summer and winter of 2007. The fractions of contemporary carbon (f(C)) in total carbon (TC) and elemental carbon (EC) are presented using C-14 measurements. This value directly represents the contemporary biogenic contribution, since recently living biomass and biogenic organic compound emissions have f(C) = 1, whereas anthropogenic emissions from fossil carbon have f(C) = 0 because the C-14 in the latter has completely decayed. The measured f(C) (TC) values range from 0.30 to 0.38 (n = 12) in winter and 0.31 to 0.44 (n = 12) in summer, respectively. The levels of f(C) values are lower than those from other rural sites in the world, indicating that the Yufa site was heavily influenced by anthropogenic emissions. The high TC concentrations in winter with the lower average f(C) (TC) suggest that coal burning for residential heating was significant contributors to the TC concentrations. The sources of contemporary carbon are primary emissions due to biomass burning, and biogenic secondary organic aerosol. Biomass burning was a dominant contributor in the winter. Fossil fuels represented 80-87% of EC in both seasons. (C) 2012 Elsevier Ltd. All rights reserved.

Radiocarbon (C-14) has become a powerful tracer in source apportionments of atmospheric carbonaceous particles. Fine particles (PM2.5) were collected at a rural site of Beijing in the summer and winter of 2007. The fractions of contemporary carbon (f(C)) in total carbon (TC) and elemental carbon (EC) are presented using C-14 measurements. This value directly represents the contemporary biogenic contribution, since recently living biomass and biogenic organic compound emissions have f(C) = 1, whereas anthropogenic emissions from fossil carbon have f(C) = 0 because the C-14 in the latter has completely decayed. The measured f(C) (TC) values range from 0.30 to 0.38 (n = 12) in winter and 0.31 to 0.44 (n = 12) in summer, respectively. The levels of f(C) values are lower than those from other rural sites in the world, indicating that the Yufa site was heavily influenced by anthropogenic emissions. The high TC concentrations in winter with the lower average f(C) (TC) suggest that coal burning for residential heating was significant contributors to the TC concentrations. The sources of contemporary carbon are primary emissions due to biomass burning, and biogenic secondary organic aerosol. Biomass burning was a dominant contributor in the winter. Fossil fuels represented 80-87% of EC in both seasons. (C) 2012 Elsevier Ltd. All rights reserved.

Polycyclic aromatic hydrocarbons (PAHs) associated with inhalable particles are harmful to human health, especially to people in urban indoor environments. To evaluate human respiratory exposure to indoor PAHs properly, respiratory deposition fluxes of size-fractioned PAHs were estimated based on size-segregated distribution of PAHs in indoor air of an urban community of Guangzhou, China. The concentrations of Sigma(16)PAH (sum of the 16 priority PAHs designated by the United States Environmental Protection Agency) were 28.9 +/- 10.0 ng/m(3), with the mean benzo(a)pyrene equivalent (BaPE) concentration at 4.1 +/- 1.6 ng/m(3). Particle size distributions of both Sigma(16)PAH and BaPE concentrations peaked in the 1.0-1.8 mu m fraction. The mean respiratory deposition flux of Sigma(16)PAH was 5.9 ng/h, and accumulation mode particles contributed 20.5-83.8% of the respiratory deposition fluxes for individual PAHs. In addition, 8.6-10.2% of inhaled Sigma(16)PAH were calculated to be deposited in the alveoli region, with accumulation particles as the largest contributor. In particular, ultrafine particles contributed 0.4-21.7% of individual PAHs deposited in the alveoli region, more than twice the fraction of the PAHs in the ultrafine particles (0.2-8.5%). Finally, lifetime cancer risk via inhalation of indoor particulate PAHs may be greater than the cancer risk guideline value (10(-6)). depending on specific assumptions used in this risk assessment. (C) 2012 Elsevier B.V. All rights reserved.

We investigate the control of electron injection in the cascaded laser wakefield accelerators, optimization of seeding phase and the self-guided propagation of laser pulses between the two accelerators. The maximum acceleration gradient with energy spread narrowing was obtained when the seeding phase and the laser pulse propagation were optimized.

Fan, Shenggen, Li, Lixing, and Zhang, Xiaobo-Challenges of creating cities in China: Lessons from a short-lived county-to-city upgrading policy #n#It has been widely observed that China is under-urbanized. The central government has tried to use various policies to promote urbanization. In this paper, we evaluate one of these policies - count-to-city upgrading. Under China's hierarchical governance structure, a city status can only be determined and awarded by the central government. In the 1980s and 1990s, China adopted a formula-based county-to-city upgrading policy. Based on a large panel dataset covering all counties in China, we find that the formula was not strictly enforced in the practice. Moreover, jurisdictions that were upgraded to cities prior to 1998 do not perform better than their counterparts that remained county status in terms of both economic growth and providing public services. Largely because of these problems, this policy was called off in 1997. Given the strong need for urbanization, more indigenous institutional innovations are needed to find a viable way of creating cities, which would also provide compatible incentives to local governments. Journal of Comparative Economics 40 (3) (2012) 476-491. International Food Policy Research Institute (IFPRI), Washington, DC, United States; China Center for Economic Research, National School of Development, Peking University, Beijing 100871, China. (C) 2012 Association for Comparative Economic Studies Published by Elsevier Inc.