Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributi...Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributions of salinity,nutrients [nitrate(NO_(3)^(-)),nitrite,ammonium,and phosphate],and the stable isotopic composition of NO_(3)^(-)(δ^(15)N and δ^(18)O) were used to investigate sources of dissolved inorganic nitrogen(DIN) to Hangzhou B ay.Spatial distributions of nitrate,salinity,and nitrate δ^(18)O indicate that the Qiantang River,the Changjiang River,and nearshore coastal waters may all contribute nitrate to the bay.Based on the isotopic compositions of nitrate in these potential source waters and conservative mixing of nitrate in our study area,we suggest that the NO_(3)^(- )in Hangzhou B ay was likely derived mainly from soils,synthetic N fertilizer,and manure and sewage.End-member modeling indicates that in the upper half of the bay,the Qiantang River was a very important DIN source,possibly contributing more than 50% of DIN in the bay head area.In the lower half of the bay,DIN was sourced mainly from strongly intruding coastal water.DIN coming directly from the Changjiang River made a relatively small contribution to Hangzhou Bay DIN in August 2019.展开更多
In this study,the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of n...In this study,the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of nitrite in the euphotic zone of the Southern Ocean.We found that primary nitrite maxima(PNMs)are widely present in the Amundsen Sea,where the depth of occurrence deepens from east to west and nitrite concentrations increases.Evidence from dual isotopes suggests that the formation of PNMs in all regions of the Amundsen Sea is dominated by ammonia oxidation.More importantly,the nitrogen and oxygen isotope compositions of nitrite in the Amundsen Sea mixed layer are abnormal,and their depth profiles are mirror symmetrical.Isotopic anomalies exhibit spatial variations,with central surface water having the lowest nitrogen isotope composition(−89.9‰±0.2‰)and western surface water having the highest oxygen isotope composition(63.3‰±0.3‰).Isotopic exchange reaction between nitrate and nitrite is responsible for these isotope anomalies,as both nitrogen and oxygen isotopes have large isotopic fractionation and opposite enrichment effects.This proves that isotopic exchange reaction operates extensively in different regions of the Amundsen Sea.Our study highlights the unique role of dual isotopes of nitrite in deepening the understanding of nitrogen cycle.Further studies on ammonia oxidation and isotopic exchange between nitrate and nitrite are warranted in the future to understand their roles in the nitrogen cycle in the Southern Ocean.展开更多
In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015...In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015 on the atmosphere over the Bohai Sea was explored.Results showed sharp increases in the concentrations of several important components of fine particulate matter(e.g.NO3−,SO42−,NH4+,organic carbon,elemental carbon)over Beihuangcheng Island after the explosion.Among them,NO3−was most affected(about 10 days),with a maximum concentration of 16.45μg m−3.Theδ15N-NO3−ranged from−1.58‰to+8.74‰,with an average of+2.79‰±3.32‰.Influenced by the explosion,δ15N-NO3−decreased significantly,which was in accordance with the industrial processes of explosives.Theδ18O-NO3−varied between+49.40‰and+69.52‰,and showed a marked increase(+66.62‰±3.92‰)in the explosion-affected period.Using Monte Carlo simulation,the•OH pathway for NO3−formation was 51.79%±10.94%at that time—much lower than in the regular period.The elevated dry deposition of NO3−caused by the explosion was 266.08μmol N m−2 d−1 over the Bohai Sea—again,much higher than in the regular period.With the dry nitrogen deposition of NH4+(42.41μmol N m−2 d−1),the total nitrogen deposition increased by 308.49μmol N m−2 d−1,leading to severe ecological risk.Through the inverse computation of the dry deposition flux of NO3−,the affected area over the Bohai Sea was less than 1.42×104 km2,which is about 20%of the total area.展开更多
Photocatalytic O_(2)activation to generate reactive oxygen species is crucially important for purifying organic pollutants,yet remains a challenge due to poor adsorption of O_(2)and low efficiency of electron transfer...Photocatalytic O_(2)activation to generate reactive oxygen species is crucially important for purifying organic pollutants,yet remains a challenge due to poor adsorption of O_(2)and low efficiency of electron transfer.Herein,we demonstrate that ultrafine MoO_(x)clusters anchored on graphitic carbon nitride(g-C_(3)N_(4))with dual nitrogen/oxygen defects promote the photocatalytic activation of O_(2)to generate·O_(2)−for the degradation of tetracycline hydrochloride(TCH).A range of characterization techniques and density functional theory(DFT)calculations reveal that the introduction of the nitrogen/oxygen dual defects and MoO_(x)clusters enhances the O_(2)adsorption energy from−2.77 to−2.94 eV.We find that MoO_(x)clusters with oxygen vacancies(Ov)and surface Ov-mediated Moδ+(3≥δ≥2)possess unpaired localized electrons,which act as electron capture centers to transfer electrons to the MoO_(x)clusters.These electrons can then transfer to the surface adsorbed O_(2),thus promoting the photocatalytic conversion of O_(2)to·O_(2)−and,simultaneously,realizing the efficient separation of photogenerated electron–hole pairs.Our fully-optimized MoO_(x)/g-C_(3)N_(4)catalyst with dual nitrogen/oxygen defects manifests outstanding photoactivities,achieving 79%degradation efficiency toward TCH within 120 min under visible light irradiation,representing nearly 7 times higher activity than pristine g-C_(3)N_(4).Finally,based on the results of liquid chromatograph mass spectrometry and DFT calculations,the possible photocatalytic degradation pathways of TCH were proposed.展开更多
The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other ...The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other chemical parameters in this area, were measured in spring to evaluate NO3 biogeochemical processes. A simple two end-members mixing model was used to examine the relative contribution of the Changjiang River Diluted Water and marine water to NO~ sources in the Changjiang Estuary and the adjacent East Chi- na Sea. The isotopic signals show that NO3 behaved relatively and conservatively in Transect F and Transect P where assimilation was weak possibly due to vertical mixing, while active assimilation and weak nitrifi- cation occurred in Transect D. Spatial difference in assimilation was indicated by the ~ 1：1 enrichment of S 15N and 6180 in the three transects, while spatial difference in nitrification was reflected by deviations of 15N and 6180 from assimilation line. Our results suggest that the input of the Changjiang River Diluted Wa- ter promoted NO3 assimilation possibly by stratifying the water column which favored the phytoplankton growth.展开更多
This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as th...This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.展开更多
基金The Zhejiang Provincial Natural Science Foundation of China under contract No.LZ22D060002the Key R&D Program of Zhejiang under contract No.2022C03044the National Key Research and Development Program of China under contract No.2021YFC3101702。
文摘Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributions of salinity,nutrients [nitrate(NO_(3)^(-)),nitrite,ammonium,and phosphate],and the stable isotopic composition of NO_(3)^(-)(δ^(15)N and δ^(18)O) were used to investigate sources of dissolved inorganic nitrogen(DIN) to Hangzhou B ay.Spatial distributions of nitrate,salinity,and nitrate δ^(18)O indicate that the Qiantang River,the Changjiang River,and nearshore coastal waters may all contribute nitrate to the bay.Based on the isotopic compositions of nitrate in these potential source waters and conservative mixing of nitrate in our study area,we suggest that the NO_(3)^(- )in Hangzhou B ay was likely derived mainly from soils,synthetic N fertilizer,and manure and sewage.End-member modeling indicates that in the upper half of the bay,the Qiantang River was a very important DIN source,possibly contributing more than 50% of DIN in the bay head area.In the lower half of the bay,DIN was sourced mainly from strongly intruding coastal water.DIN coming directly from the Changjiang River made a relatively small contribution to Hangzhou Bay DIN in August 2019.
基金The Impact and Response of Antarctic Seas to Climate Change under contract Nos IRASCC 02-01-01 and IRASCC 01-01-02Cthe National Natural Science Foundation of China under contract No.41721005.
文摘In this study,the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of nitrite in the euphotic zone of the Southern Ocean.We found that primary nitrite maxima(PNMs)are widely present in the Amundsen Sea,where the depth of occurrence deepens from east to west and nitrite concentrations increases.Evidence from dual isotopes suggests that the formation of PNMs in all regions of the Amundsen Sea is dominated by ammonia oxidation.More importantly,the nitrogen and oxygen isotope compositions of nitrite in the Amundsen Sea mixed layer are abnormal,and their depth profiles are mirror symmetrical.Isotopic anomalies exhibit spatial variations,with central surface water having the lowest nitrogen isotope composition(−89.9‰±0.2‰)and western surface water having the highest oxygen isotope composition(63.3‰±0.3‰).Isotopic exchange reaction between nitrate and nitrite is responsible for these isotope anomalies,as both nitrogen and oxygen isotopes have large isotopic fractionation and opposite enrichment effects.This proves that isotopic exchange reaction operates extensively in different regions of the Amundsen Sea.Our study highlights the unique role of dual isotopes of nitrite in deepening the understanding of nitrogen cycle.Further studies on ammonia oxidation and isotopic exchange between nitrate and nitrite are warranted in the future to understand their roles in the nitrogen cycle in the Southern Ocean.
基金This research was financially supported by a project funded by the China Postdoctoral Science Foundation[grant numbers 2017LH020 and 2017M622815]the National Natural Science Foundation of China[grant numbers 41977190 and 41907198].
文摘In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015 on the atmosphere over the Bohai Sea was explored.Results showed sharp increases in the concentrations of several important components of fine particulate matter(e.g.NO3−,SO42−,NH4+,organic carbon,elemental carbon)over Beihuangcheng Island after the explosion.Among them,NO3−was most affected(about 10 days),with a maximum concentration of 16.45μg m−3.Theδ15N-NO3−ranged from−1.58‰to+8.74‰,with an average of+2.79‰±3.32‰.Influenced by the explosion,δ15N-NO3−decreased significantly,which was in accordance with the industrial processes of explosives.Theδ18O-NO3−varied between+49.40‰and+69.52‰,and showed a marked increase(+66.62‰±3.92‰)in the explosion-affected period.Using Monte Carlo simulation,the•OH pathway for NO3−formation was 51.79%±10.94%at that time—much lower than in the regular period.The elevated dry deposition of NO3−caused by the explosion was 266.08μmol N m−2 d−1 over the Bohai Sea—again,much higher than in the regular period.With the dry nitrogen deposition of NH4+(42.41μmol N m−2 d−1),the total nitrogen deposition increased by 308.49μmol N m−2 d−1,leading to severe ecological risk.Through the inverse computation of the dry deposition flux of NO3−,the affected area over the Bohai Sea was less than 1.42×104 km2,which is about 20%of the total area.
基金supported by the National Natural Science Foundation of China(No.21972010)the National Key Research and Development Program of China(No.2022YFC2105900).
文摘Photocatalytic O_(2)activation to generate reactive oxygen species is crucially important for purifying organic pollutants,yet remains a challenge due to poor adsorption of O_(2)and low efficiency of electron transfer.Herein,we demonstrate that ultrafine MoO_(x)clusters anchored on graphitic carbon nitride(g-C_(3)N_(4))with dual nitrogen/oxygen defects promote the photocatalytic activation of O_(2)to generate·O_(2)−for the degradation of tetracycline hydrochloride(TCH).A range of characterization techniques and density functional theory(DFT)calculations reveal that the introduction of the nitrogen/oxygen dual defects and MoO_(x)clusters enhances the O_(2)adsorption energy from−2.77 to−2.94 eV.We find that MoO_(x)clusters with oxygen vacancies(Ov)and surface Ov-mediated Moδ+(3≥δ≥2)possess unpaired localized electrons,which act as electron capture centers to transfer electrons to the MoO_(x)clusters.These electrons can then transfer to the surface adsorbed O_(2),thus promoting the photocatalytic conversion of O_(2)to·O_(2)−and,simultaneously,realizing the efficient separation of photogenerated electron–hole pairs.Our fully-optimized MoO_(x)/g-C_(3)N_(4)catalyst with dual nitrogen/oxygen defects manifests outstanding photoactivities,achieving 79%degradation efficiency toward TCH within 120 min under visible light irradiation,representing nearly 7 times higher activity than pristine g-C_(3)N_(4).Finally,based on the results of liquid chromatograph mass spectrometry and DFT calculations,the possible photocatalytic degradation pathways of TCH were proposed.
基金The National Basic Research Program of China (973Program) under contract No.2010CB428903the National Natural Science Foundation of China under contract Nos 41006045 and 91128212+2 种基金National Science and Technology Pillar Program under contract No.2008BAC42B01China Postdoctoral Science Foundation under contract No.20100471690SIOSOA Project under contract Nos JT0707 and GCMAC1103
文摘The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other chemical parameters in this area, were measured in spring to evaluate NO3 biogeochemical processes. A simple two end-members mixing model was used to examine the relative contribution of the Changjiang River Diluted Water and marine water to NO~ sources in the Changjiang Estuary and the adjacent East Chi- na Sea. The isotopic signals show that NO3 behaved relatively and conservatively in Transect F and Transect P where assimilation was weak possibly due to vertical mixing, while active assimilation and weak nitrifi- cation occurred in Transect D. Spatial difference in assimilation was indicated by the ~ 1：1 enrichment of S 15N and 6180 in the three transects, while spatial difference in nitrification was reflected by deviations of 15N and 6180 from assimilation line. Our results suggest that the input of the Changjiang River Diluted Wa- ter promoted NO3 assimilation possibly by stratifying the water column which favored the phytoplankton growth.
基金supported by National Natural Science Foundation of China(Grant No.51265029)
文摘This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.
