An integrated urban air quality modeling system was applied to assess the effects of a short-term odd-even day traffic restriction scheme (TRS) on traffic-related air pollution in the urban area of Beijing (UAB) before, during and after the 2008 Olympic Games. Using traffic flow data retrieved from an on-line traffic monitoring system, concentration levels of CO, PM10, NO2 and O3 on the 2nd, 3rd, 4th Ring Roads (RR) and Linkage Roads (LRs), the main roads distributed around the UAB, were predicted for the pre- (10th-19th, July), during- (20th July-20th September) and post-TRS (21st-30th, September) periods. A widely used statistical framework for model evaluation was adopted, the dependences of model performance on time-of-the-day and on wind direction were investigated, and the model predictions turned out reasonably satisfactory. Results showed that daily average concentrations on the 2nd, 3rd, 4th RR and LRs decreased significantly during the TRS period, by about 35.8, 38.5, 34.9 and 35.6% for CO, about 38.7, 31.8, 44.0 and 34.7% for PM10, about 30.3, 31.9, 32.3 and 33.9% for NO2, and about 36.7, 33.0, 33.4 and 34.7% for O3, respectively, compared with the pre-TRS period. Hourly average concentrations were also reduced significantly, particularly for the morning and evening peaks for CO and PM10, for the evening peak for NO2, and for the afternoon peak for O3. Consequently, both the daily and hourly concentration level of CO, PM10, NO2 and O3 conformed to the China National Ambient AirQuality Standards Grade II during the Games. In addition, notable reduction of concentration levels was achieved in different regions of Beijing, with the traffic-related air pollution in the downwind northern and western areas relieved most significantly. The TRS policy was therefore effective in alleviating traffic-related air pollution and improving short-term air quality in Beijing during the Games.
Daily to weekly integrated PM2.5 samples were collected consecutively from August 2005 through November 2007 at Egbert, a rural site in southern Ontario with two collocated samplers to characterize temporal variations of organic and elemental carbon (OC and EC) concentrations and to review the effects of different sampling intervals on their respective concentrations. OC and EC concentrations from both samplers had reasonable agreements for the samples with identical sampling intervals, whereas for the samples with different sampling intervals, they did not coincide. Considering sampling artifacts, analytical challenges and highly varied daily concentrations, it is suggested and would be advantageous to adopt the weekly integrated sampling strategy other than 29-h sampling on selected days for long-term trend studies on ambient carbonaceous PM. Both OC and EC concentrations varied seasonally by factors of 2.4 and their concentrations in warm seasons (May-October) were higher than those in cold seasons (November-April). Greater fluctuations were also found in warm seasons during the study period. Weekly concentrations of carbonaceous species at Egbert and urban Toronto show similar temporal variations and small urban excess during the one-year parallel sampling period, indicating a relatively large regional contribution from transport instead of local emissions to the paired urban-rural sites. The continental background level of total carbon mass (TCM) in PM2,5 in southern Ontario, constrained by surface air mass directions and back trajectories, was estimated to be 0.5 mu g m(-3). It is likely that the elevated OC level during the warm season in 2007 compared with those in 2006 was due to more smog days in 2007. (C) 2011 Elsevier Ltd. All rights reserved.
An asymmetric single-nanoslit with lateral dimension of only 370 nm is demonstrated to work as an efficient SPP unidirectional generator at wavelength of 830 nm.
By coating a metal with a finite-thickness dielectric film, evident differences in the wave-vector magnitude between surface plasmon polaritons (SPPs) and quasicylindrical waves (quasi-CWs) emerge. This brings modulation patterns to the total field on the metal surface near the electromagnetic source. Based on such an effect, an ultracompact SPP splitter with a lateral dimension of only 800 nm is experimentally demonstrated at wavelengths of 740 nm and 832 nm in a dielectric-film-coated asymmetric single nanoslit. These results imply that the additional modulation of quasi-CWs to the total field provide new possibilities for the design of ultracompact plasmonic devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3564935]
By exciting a plasmonic lens with femtosecond laser and utilizing the optical nonlinearity of the gold, an ultrasmall and ultrafast all-optical modulation spot was achieved inside a thin gold film. Near-field pump-probe measurements indicated a modulation spot size of about 600 nm, and a response time of about 1.5 ps. Even smaller spot size of about 300 nm was inferred from numerical simulations, beyond the diffraction limit given an incident wavelength of 1000 nm. Moreover, the optical nonlinearity and the modulation depth were increased by one order of magnitude at the focus compared to that at positions without structures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581895]
