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Li X.,Beihang University | He K.,Tsinghua University | Li C.,Peking University | Yang F.,CAS Chongqing Institute of Green and Intelligent Technology | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

Distinct contrast of air quality and visibility before and during the 2008 Beijing Olympic Games provides a rare opportunity to investigate the links between PM2.5 mass, chemical composition, and light extinction in this megacity. Twenty-four hour integrated PM2.5 samples were collected, and light scattering coefficients and the concentrations of black carbon were measured at urban Beijing for this purpose during a measurement campaign from 1 July to 20 September 2008, which was classed into four stages according to the levels of emission control measures. Daily PM2.5 concentrations ranged from 15.9 to 156.7 μg m-3 with an average of 66.0 ± 35.1 μg m-3. The average PM2.5 mass during the Olympics decreased by 49% from the second stage (20 July to 7 August), mainly due to the reduction of secondary inorganic aerosols (i.e., sulfate, nitrate, and ammonium (SNA)). The counterintuitive increase of PM 2.5 mass (by 27% on average) during the second stage with two most serious haze episodes, although more rigorous emission control measures were in place, compared to the first stage (1-19 July), was mainly explained by the unfavorable meteorology and input of sulfate aerosols. A daily PM2.5 mass threshold of 50 μg m-3 was extracted for frequent haze occurrence. The extinction fractions of SNA and organic material were each approximately 30% during the 20% best visibility days but changed to 81.7% and 8.4%, respectively, during the 20% worst visibility days. The results indicated that the role of SNA was magnified in haze formation during the 2008 summer in Beijing. Key Points The dramatic PM2.5 mass decrease was mainly due to secondary inorganic species The threshold of PM2.5 concentration for the hazy day occurrence was estimated Ammonium sulfate was the largest single contributor to visibility degradation ©2013. American Geophysical Union. All Rights Reserved. Source


Huang Y.,University of Sichuan | Li R.,University of Sichuan | Feng J.,University of Sichuan | Qu L.,China Renewable Energy Engineering Institute | And 2 more authors.
Shuili Fadian Xuebao/Journal of Hydroelectric Engineering | Year: 2016

High dam spill, sudden warming and photosynthesis of nature water may result in supersaturation of water body with dissolved gases, such as dissolved oxygen and total dissolved gas, and this phenomenon might cause gas bubble disease and even mortality in fishes. To explore effective techniques for recovery of supersaturated water of this type, a series of aeration experiments were conducted in this work for the conditions of different aeration rates, water depths and aeration apertures. The results showed that aeration of water body can greatly accelerate the release of dissolved gas from supersaturated water body. When an aeration rate of 3.0 m3 h-1 was used, the release coefficient was increased to 0.48 min-1, or about 3000 times as large as that without aeration condition (0.00016 min-1). The release coefficient increased with the increasing aeration rate and decreased with the increasing aperture and water depth. A quantitative relationship of release coefficient versus water depth and aeration rate at given aeration apertures was developed. The present study lays a basis for further study and provides new ideas for design of practical measures. © 2016 All right reserved. Source


Ge F.,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters | Zhi X.,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters | Babar Z.A.,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters | Tang W.,Chongqing Institute of Environmental Science | Chen P.,Chongqing Meteorological Observatory
Theoretical and Applied Climatology | Year: 2016

The interannual variability of summer monsoon precipitation (1979–2011) over the Indochina Peninsula (ICP) is characterized using the first empirical orthogonal function of 5-month total precipitation (May to September). The leading mode, with a monopole pattern, accounts for 30.6 % of the total variance. Dynamic composites and linear regression analysis indicate that the rainy season precipitation over the ICP is linked to El Niño–Southern Oscillation (ENSO) on interannual scales. The preceding winter [D(−1)JF(0)] negative sea surface temperature (SST) over the Niño-3.4 region is predominantly correlated with the rainy season precipitation over the ICP. Notably, the simultaneous correlation between remote SST anomalies in the Niño-3.4 region and the rainy season precipitation over the ICP is weak. The interannual variation of tropical cyclones modulated by ENSO is a significant contributing factor to the rainy season precipitation over the ICP. However, this relationship is not homogeneous over the ICP if ENSO is considered. Before removing the ENSO signal, enhanced precipitation is present over the northeastern part of the ICP and reduced precipitation appears in the western ICP, especially in coastal areas. In contrast, after removing ENSO, only a minor significant positive precipitation anomaly occurs over the northeastern part of the ICP and the negative anomaly appears particularly in the western and eastern coastal regions. The results obtained through the present study are useful for our understanding of circulation mechanisms and provide information for assessing the ability of regional and global climate models in simulating the climate of Southeast Asia. © 2016 Springer-Verlag Wien Source


Ge F.,Nanjing University of Information Science and Technology | Babar Z.A.,Nanjing University of Information Science and Technology | Guo S.-L.,Nanjing University of Information Science and Technology | Zhi X.-F.,Nanjing University of Information Science and Technology | And 2 more authors.
Mausam | Year: 2014

Extreme weather events over Asia particularly in Pakistan are becoming more frequent in the present decade or so. This is contributing to the ever increasing human suffering of the region. In this study the whole energy parameter E from atmospheric energetic theory is derived. The characteristics of atmospheric energy conversion during the heavy rainfall in Pakistan for the period 27-29 July, 2010 are also discussed. The results show that due to the impact of the atmospheric circulation and terrain conditions, the kinetic energy is converted into potential energy, in the form of standing wave, during heavy rainfall development period. The conversion between kinetic and potential energy is significant in heavy rainfall spell. High energy value corresponds to the heavy rainfall region. Source


Yu D.-X.,Chongqing Shapingba Meteorological Bureau | Ma X.-X.,Beijing Guodian Futong Science and Technology Development Co. | Tan B.-Q.,Chongqing Shapingba Meteorological Bureau | Zhao D.-W.,Chongqing Institute of Environmental Science | And 2 more authors.
Huanjing Kexue/Environmental Science | Year: 2014

Although the total emission of sulphure dioxide (SO2) was reduced by more than 10% in the Eleventh Five-Year-Plan (2006-2010) in China, the total emission of nitrogen oxides (NOx) in the same period kept increasing. In order to evaluate the effects of the emission changes on acid depostion, a ten-year monitoring on forest throughfall was carried out from 2001 to 2010 at Tieshanping, Chongqing in Southwestern China. The results indicated there was a significantly decreasing trend of sulphur deposition and an increasing trend of nitrogen deposition, which coincided well with the dicreasing trend of SO2 emission and increasing tread of NOx emission in Chongqing, respectively. As the net effect, acid deposition was reduced by the emission contol. However, the total deposition of sulphur and nitrogen in 2010 was estimated to be 9.9 keq·(hm2·a)-1 and 4.5 keq·(hm2·a)-1, respectively according to the throughfall data, with the former probably overestimated by 28% and the latter underestimated by 50%. Since both the sulphur deposition and nitrogen deposition are higher than the highest levels in the history in Europe and North America, acid deposition is still a serious issue in Chongqing. Source

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