Tianjin is the third largest megacity and the fastest growth area in China,and consequently faces the problems of surface ozone and haze episodes.This study measures and characterizes volatile organic compounds （VOCs...Tianjin is the third largest megacity and the fastest growth area in China,and consequently faces the problems of surface ozone and haze episodes.This study measures and characterizes volatile organic compounds （VOCs）,which are ozone precursors,to identify their possible sources and evaluate their contribution to ozone formation in urban and suburban Tianjin,China during the HaChi （Haze in China） summer campaign in 2009.A total of 107 species of ambient VOCs were detected,and the average concentrations of VOCs at urban and suburban sites were 92 and 174 ppbv,respectively.Of those,51 species of VOCs were extracted to analyze the possible VOC sources using positive matrix factorization.The identified sources of VOCs were significantly related to vehicular activities,which specifically contributed 60％ to urban and 42％ to suburban VOCs loadings in Tianjin.Industrial emission was the second most prominent source of ambient VOCs in both urban and suburban areas,although the contribution of industry in the suburban area （36％） was much higher than that at the urban area （16％）.We conclude that controlling vehicle emissions should be a top priority for VOC reduction,and that fast industrialization and urbanization causes air pollution to be more complex due to the combined emission of VOCs from industry and daily life,especially in suburban areas.展开更多
The North China Plain(NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth.To explore regional air pollution...The North China Plain(NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth.To explore regional air pollution in the NCP,measurements of surface ozone(O3),nitrogen oxides(NOx),and sulfur dioxide(SO2) were carried out from May to November 2013 at a rural site(Xianghe) between the twin megacities of Beijing and Tianjin.The highest hourly ozone average was close to 240 ppbv in May,followed by around 160 ppbv in June and July.High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site.For NOx,an important ozone precursor,the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall.The occurrence of high NOx concentrations under calm conditions indicated that local emissions were dominant in Xianghe.The double-peak diurnal pattern found in NOxconcentrations and NO/NOx ratios was probably shaped by local emissions,photochemical removal,and dilution resulting from diurnal variations of surface wind speed and the boundary layer height.A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above,while the SO2-polluted air mass transported from possible emission sources,which differed between the non-heating(September and October) and heating(November) periods,was thought to be responsible for night-time high concentrations.展开更多
A 16-pole superconducting multipole wiggler with a large gap of 68 mm was designed and fabricated to serve as a multipole wiggler for HEPS-TF.The wiggler consists of 16 pairs of NbTi superconducting coils with a perio...A 16-pole superconducting multipole wiggler with a large gap of 68 mm was designed and fabricated to serve as a multipole wiggler for HEPS-TF.The wiggler consists of 16 pairs of NbTi superconducting coils with a period length of 170 mm,and its maximum peak field is 2.6 Tesla.In magnet design,magnet poles were optimized.Furthermore,the Lorentz force on the coils and electromagnetic force between the upper and lower halves were computed and analyzed along with the stored energy and inductance at different currents.To enhance the critical current of the magnet coil,all the pole coils selected for the magnet exhibited excellent performance,and appropriate prestress derived from the coil force analysis was applied to the pole coils during magnet assembly.The entire magnet structure was immersed in 4.2-K liquid helium in the cryostat cooled solely by four two-stage cryocoolers,and the performance test of the superconducting wiggler was appropriately completed.Based on the measured results,the first and second field integrals on the axis of the superconducting wiggler were significantly improved at different field levels after the compensation of the corrector coils.Subsequently,the wiggler was successfully installed in the storage ring of BEPCII operation with beams.展开更多
The impact of aerosols on the climate and atmospheric environment depends on the water uptake ability of particles;namely,hygroscopic growth and activation into cloud condensation nuclei(CCN).The size-resolved activat...The impact of aerosols on the climate and atmospheric environment depends on the water uptake ability of particles;namely,hygroscopic growth and activation into cloud condensation nuclei(CCN).The size-resolved activation ratios(SRAR),characterizing the fraction of aerosol particles that act as CCN at different particle sizes and supersaturations,can be measured using a combination of differential mobility analyzers(DMA) and particle counters.DMA-based measurements are influenced by the multiply charged particles and the quasi-mono-dispersed particles(effect of DMA transfer function) selected for each prescribed particle size.A theoretical study,assuming different particle number size distributions and hygroscopicity of aerosols,is performed to study the effects of the DMA transfer function and multiple charging on the measured SRAR and the derived hygroscopicity.Results show that the raw SRAR can be significantly skewed and hygroscopicity may be highly biased from the true value if the data are not corrected.The effect of the transfer function is relatively small and depends on the sample to sheath flow ratio.Multiply charged particles,however,can lead to large biases of the SRAR.These results emphasize that the inversion algorithm,which is used to correct the effects of the DMA transfer function and multiple charging,is necessary for accurate measurement of the SRAR.展开更多
研究多汁乳菇多糖的脱色工艺及抗氧化活性。以脱色率和多糖保留率为指标,评价不同类型树脂的脱色效果,并通过单因素试验和正交试验优化树脂法脱色的工艺条件。采用总抗氧化能力测定法评价脱色前后多糖样品的抗氧化活性。结果表明, D 20...研究多汁乳菇多糖的脱色工艺及抗氧化活性。以脱色率和多糖保留率为指标,评价不同类型树脂的脱色效果,并通过单因素试验和正交试验优化树脂法脱色的工艺条件。采用总抗氧化能力测定法评价脱色前后多糖样品的抗氧化活性。结果表明, D 202的脱色效果较好,其优化工艺条件为:温度60℃,树脂加入量15 g/100 mL,多糖质量浓度2 mg/mL,时间3 h。此条件下的多糖脱色率为95.25%±0.10%,多糖保留率为48.65%±0.28%。该法的脱色效果优于活性炭法和过氧化氢法。脱色前后多糖的抗氧化性能变化不大。树脂法对多汁乳菇多糖的脱色效果较好。展开更多
基金supported by the Tianjin Fundamental Research Program of the Tianjin Committee of Science and Technology (Grant No. 10JCYBJC050800)the National Special Science and Technology Program for Non-Profit Industry of the Ministry of Environmental Protection (Grant No. 200909022)+2 种基金the 973 Program (Grant No. 2011CB403402)the National Natural Science Foundation of China (NSFC) (Grant No. 40875001)the Basic Research Fund of the Chinese Academy of Meteorological Sciences (Grant No. 2008Z011)
文摘Tianjin is the third largest megacity and the fastest growth area in China,and consequently faces the problems of surface ozone and haze episodes.This study measures and characterizes volatile organic compounds （VOCs）,which are ozone precursors,to identify their possible sources and evaluate their contribution to ozone formation in urban and suburban Tianjin,China during the HaChi （Haze in China） summer campaign in 2009.A total of 107 species of ambient VOCs were detected,and the average concentrations of VOCs at urban and suburban sites were 92 and 174 ppbv,respectively.Of those,51 species of VOCs were extracted to analyze the possible VOC sources using positive matrix factorization.The identified sources of VOCs were significantly related to vehicular activities,which specifically contributed 60％ to urban and 42％ to suburban VOCs loadings in Tianjin.Industrial emission was the second most prominent source of ambient VOCs in both urban and suburban areas,although the contribution of industry in the suburban area （36％） was much higher than that at the urban area （16％）.We conclude that controlling vehicle emissions should be a top priority for VOC reduction,and that fast industrialization and urbanization causes air pollution to be more complex due to the combined emission of VOCs from industry and daily life,especially in suburban areas.
基金supported by the National Natural Science Foundation of China (Grant Nos.41305114 and 41175030)supported by Beijing Municipal Natural Science Foundation (Grant No.8121002)
文摘The North China Plain(NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth.To explore regional air pollution in the NCP,measurements of surface ozone(O3),nitrogen oxides(NOx),and sulfur dioxide(SO2) were carried out from May to November 2013 at a rural site(Xianghe) between the twin megacities of Beijing and Tianjin.The highest hourly ozone average was close to 240 ppbv in May,followed by around 160 ppbv in June and July.High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site.For NOx,an important ozone precursor,the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall.The occurrence of high NOx concentrations under calm conditions indicated that local emissions were dominant in Xianghe.The double-peak diurnal pattern found in NOxconcentrations and NO/NOx ratios was probably shaped by local emissions,photochemical removal,and dilution resulting from diurnal variations of surface wind speed and the boundary layer height.A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above,while the SO2-polluted air mass transported from possible emission sources,which differed between the non-heating(September and October) and heating(November) periods,was thought to be responsible for night-time high concentrations.
文摘A 16-pole superconducting multipole wiggler with a large gap of 68 mm was designed and fabricated to serve as a multipole wiggler for HEPS-TF.The wiggler consists of 16 pairs of NbTi superconducting coils with a period length of 170 mm,and its maximum peak field is 2.6 Tesla.In magnet design,magnet poles were optimized.Furthermore,the Lorentz force on the coils and electromagnetic force between the upper and lower halves were computed and analyzed along with the stored energy and inductance at different currents.To enhance the critical current of the magnet coil,all the pole coils selected for the magnet exhibited excellent performance,and appropriate prestress derived from the coil force analysis was applied to the pole coils during magnet assembly.The entire magnet structure was immersed in 4.2-K liquid helium in the cryostat cooled solely by four two-stage cryocoolers,and the performance test of the superconducting wiggler was appropriately completed.Based on the measured results,the first and second field integrals on the axis of the superconducting wiggler were significantly improved at different field levels after the compensation of the corrector coils.Subsequently,the wiggler was successfully installed in the storage ring of BEPCII operation with beams.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos.41205098 and 41305114)the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No.XDA05100000)
文摘The impact of aerosols on the climate and atmospheric environment depends on the water uptake ability of particles;namely,hygroscopic growth and activation into cloud condensation nuclei(CCN).The size-resolved activation ratios(SRAR),characterizing the fraction of aerosol particles that act as CCN at different particle sizes and supersaturations,can be measured using a combination of differential mobility analyzers(DMA) and particle counters.DMA-based measurements are influenced by the multiply charged particles and the quasi-mono-dispersed particles(effect of DMA transfer function) selected for each prescribed particle size.A theoretical study,assuming different particle number size distributions and hygroscopicity of aerosols,is performed to study the effects of the DMA transfer function and multiple charging on the measured SRAR and the derived hygroscopicity.Results show that the raw SRAR can be significantly skewed and hygroscopicity may be highly biased from the true value if the data are not corrected.The effect of the transfer function is relatively small and depends on the sample to sheath flow ratio.Multiply charged particles,however,can lead to large biases of the SRAR.These results emphasize that the inversion algorithm,which is used to correct the effects of the DMA transfer function and multiple charging,is necessary for accurate measurement of the SRAR.
基金Supported by the Fundamental Research Funds for the Central Universities (XDJK2019AC001)the Innovation Support Program for Chongqing Overseas Returnees (cx2019005)the National Natural Science Foundation of China (62173278)。
