Ultrahigh spatiotemporal resolved pump-probe signal on a metal nanostructure is detected by femtosecond-SNOM. By using two-color pump-probe configuration, ultrafast hot electron transportation is clearly observed on a time scale of a few hundred femtoseconds. (C) 2010 Optical Society of America
Ultrahigh spatiotemporal resolved pump-probe signal near a gold nano-slit is detected by femtosecond-SNOM. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polariton is avoided and spatiotemporal evolvement of excited electrons is successfully observed. From the contrast decaying of the periodical distribution of the pump-probe signal, ultrafast diffusion of excited electrons with a time scale of a few hundred femtoseconds is clearly identified. For comparison, such phenomenon cannot be observed by the one-color pump-probe configuration. (C) 2010 Optical Society of America
Dichlorodiphenyltrichloroethane (DDT) has been banned in China for decades, and yet high DDT concentrations are still being detected in the Chinese environment. This might be at least partly due to the current use of dicofol formulation, which contains DDT as an impurity. In this study, a method based on the ratios of two DDT isomers, o,p '-DDT and p,p '-DDT, was established and used to estimate the relative contributions of dicofol formulation and those of technical DDT to overall environmental DDT. Based on this method and field data from the literature, we calculated that dicofol formulation contributed >72% of atmospheric DDT in 2004 in the Taihu Lake region, China, and this value was >84% in summer when dicofol was applied for agricultural purposes. Sediment and soil, however, contained mostly residual DDT from the historical use of technical DDT. In most other regions of China, we found that dicofol contributed to a significant fraction of DDT in air samples. (C) 2010 Elsevier Ltd. All rights reserved.
In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 mu m at BG was (1.7 +/- 0.8) x 10(4) cm(-3), about 40% lower than that at GZ, (2.9 +/- 1.1) x 10(4) cm(-3). The total particle volume concentration at BG was 94 +/- 34 mu m(3) cm(-3), similar to that at GZ, 96 +/- 43 mu m(3) cm(-3). More 20-100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100-660 nm particle number concentrations were similar at both sites as they are more regional. PM(2.5) values were similar at GZ (69 +/- 43 mu g m(-3)) and BG (69 +/- 58 mu g m(-3)) with R(2) of 0.71 for the daily average PM(2.5) at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 60% in 100-660 nm particle mass and PM(2.5) increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM(1.0) than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 70% and 40% of PM(1.0) and PM(2.5), respectively.
In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 mu m at BG was (1.7 +/- 0.8) x 10(4) cm(-3), about 40% lower than that at GZ, (2.9 +/- 1.1) x 10(4) cm(-3). The total particle volume concentration at BG was 94 +/- 34 mu m(3) cm(-3), similar to that at GZ, 96 +/- 43 mu m(3) cm(-3). More 20-100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100-660 nm particle number concentrations were similar at both sites as they are more regional. PM(2.5) values were similar at GZ (69 +/- 43 mu g m(-3)) and BG (69 +/- 58 mu g m(-3)) with R(2) of 0.71 for the daily average PM(2.5) at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 60% in 100-660 nm particle mass and PM(2.5) increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM(1.0) than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 70% and 40% of PM(1.0) and PM(2.5), respectively.
In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 mu m at BG was (1.7 +/- 0.8) x 10(4) cm(-3), about 40% lower than that at GZ, (2.9 +/- 1.1) x 10(4) cm(-3). The total particle volume concentration at BG was 94 +/- 34 mu m(3) cm(-3), similar to that at GZ, 96 +/- 43 mu m(3) cm(-3). More 20-100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100-660 nm particle number concentrations were similar at both sites as they are more regional. PM(2.5) values were similar at GZ (69 +/- 43 mu g m(-3)) and BG (69 +/- 58 mu g m(-3)) with R(2) of 0.71 for the daily average PM(2.5) at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 60% in 100-660 nm particle mass and PM(2.5) increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM(1.0) than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 70% and 40% of PM(1.0) and PM(2.5), respectively.
In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 mu m at BG was (1.7 +/- 0.8) x 10(4) cm(-3), about 40% lower than that at GZ, (2.9 +/- 1.1) x 10(4) cm(-3). The total particle volume concentration at BG was 94 +/- 34 mu m(3) cm(-3), similar to that at GZ, 96 +/- 43 mu m(3) cm(-3). More 20-100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100-660 nm particle number concentrations were similar at both sites as they are more regional. PM(2.5) values were similar at GZ (69 +/- 43 mu g m(-3)) and BG (69 +/- 58 mu g m(-3)) with R(2) of 0.71 for the daily average PM(2.5) at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 60% in 100-660 nm particle mass and PM(2.5) increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM(1.0) than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 70% and 40% of PM(1.0) and PM(2.5), respectively.
To study potential ecological impacts of CO2 leakage to shallow groundwater and soil/sediments from geologic CO2 sequestration (GCS) sites, this work investigated the viability and metal reduction of Shewanella oneidensis MR-1 under CO2 stress. While MR-1 could grow under high-pressure nitrogen gas (500 psi), the mix of 1% CO2 with N2 at total pressures of 15 or 150 psi significantly suppressed the growth of MR-1, compared to the N2 control. When CO2 partial pressures were over 15 psi, the growth of MR-1 stopped. The reduced bacterial viability was consistent with the pH decrease and cellular membrane damage under high pressure CO2. After exposure to 150 psi CO2 for 5 h, no viable cells survived, the cellular contents were released, and microscopy images confirmed significant cell structure deformation. However, after a relatively short exposure (25 min) to 150 psi CO2, MR-1 could fully recover their growth within 24 h after the stress was removed, and the reduction of MnO2 by MR-1 was observed right after the stress was removed. Furthermore, MR-1 survived better if the cells were aggregated rather than suspended, or if pH buffering minerals, such as calcite, were present. To predict the cell viability under different CO2 pressures and exposure times, a two-parameter mathematical model was developed.