In this study, the hourly variations of the mass concentrations of PM10, SO2, NOx and O3 at three sampling sites were observed in Beijing during dust storm occurrence period in April 2000. The PM2.5 samples were simultaneously collected. By comparing the hourly variations of the pollutant concentrations before, during and after dust storm event and haze pollution episode, the variation characteristics of the mass concentrations of PM10, SO2, NOx and O3during dust storm events were presented. The results show that the mass concentration of PM10 reached 1500 μg m−3 during dust storm events on April 6 and 25, 2000, which was 5–10 times that of the non-dust weather conditions, and this period of high mass concentration of PM10 lasted for about 14 h, and then the concentration level prior to the dust event was recovered in 6-h time period. Due to the strong wind, the concentrations of SO2, NOx, NO2and O3 during dust storm period were maintained at low levels, which was significantly different from those on non-dust storm and haze pollution conditions. A lot of coarse particles as well as a very large amount of fine particles were contained in the atmospheric particulates during dust storm period, and the concentration level of PM2.5 was comparable to that during haze pollution episode. During the dust storm period, the PM2.5 concentration was approximately 230 μg m−3, accounting for 30% of the total PM10 mass concentration, was four times that of non-dust weather conditions, and the crustal elements constituted about 66.4% of the chemical composition of PM2.5 while sulfate and nitrate contributed much less, which was quite different from the chemical composition of PM2.5 primarily constituted by sulfate, nitrate and organics on haze pollution day.
English education suffered a setback during the period of 1949-1976.The two decades between1977 and 1996 saw a period of restoration,growth and development.To welcome the arrival of thenew century,English education has moved on to the third stage:the period of reform.The paper argues for the need for English education reform,summarizes the work we have been doingsince 1997,lists the problems we have encountered,and gives some suggestions in the concluding remarks.
graph An efficient synthesis of large lptycenes appended with alkoxy and ethynyl substituents is reported. The rigid shape-persistent iptycene scaffold prevents interactions between the polymer backbones and can be used to solubilize polymers containing less soluble but readily accessible comonomers to prepare functional, solution-processible poly(p-phenyleneethynylene) (PPE)-conjugated polymers. These polymers are highly emissive in thin films without significant excimer/exciplex formation as a result of the effective chain isolation enforced by the iptycene units.
High DDT concentrations and o,p'-DDT/p,p-DDT ratios observed in the air over Taihu Lake, a lake near Shanghai, China, led us to suggest that current use of dicofol in the area north of the lake was the main source of the measured DDTs. To examine this hypothesis, samples of commercially available formulated dicofol in China were collected in 2003 to measure the impurities of DDT related compounds (DOTS). The o,p'-DDT/p,p'-DDT ratio in the samples was 7.0, close to the observed value in the air over Taihu Lake. Average contents of op'-DDT, pp'-Cl-DDT, op'-DDE, and p,p'-DDT in the samples were 114, 69, 44, and 17 g per kg dicofol, respectively. On the basis of a production and distribution survey, total input of DOTS to the environment from the dicofol use in China was estimated to be 8770 t between 1988 and 2002. "Dicofol type DDT pollution", defined as DDT pollution caused by dicofol use and characterized with high op'-DDT/pp'-DDT ratio, might be serious in China, especially in southern and eastern China. The conversion of pp'-Cl-DDT to pp DOE can lead to high pp'-DDE/p,p-DDT ratio and could mislead the evaluation of pp'-DDT resident time in the environment. Therefore, more studies on pp'-Cl-DDT in the environment are needed.