During the decommissioning of the Fukushima Daiichi nuclear power plant,it is important to consider the retrieval of resolidified debris both in air and underwater configurations.For the subsequent retrieval of debris...During the decommissioning of the Fukushima Daiichi nuclear power plant,it is important to consider the retrieval of resolidified debris both in air and underwater configurations.For the subsequent retrieval of debris from the reactor building,the resolidified debris must be cut into smaller pieces using various cutting methods.During the cutting process,aerosol particles are expected to be generated at the submicron scale.It has been noted that such aerosols sizing within the Greenfield gap(0.1-1μm)are difficult to remove effectively using traditional spraying methods.Therefore,to improve the aerosol removal efficiency of the spray system,a new aerosol agglomeration method was recently proposed,which involves injecting water mist to enlarge the sizes of the aerosol particles before removing them using water sprays.In this study,a series of experiments were performed to clarify the proper spray configurations for effective aerosol scavenging and to improve the performance of the water mist.The experimental results showed that the spray flow rate and droplet characteristics are important factors for the aerosol-scavenging efficiency and performance of the water mist.The results obtained from this study will be helpful for the optimization of the spray system design for effective aerosol scavenging during the decommissioning of the Fukushima Daiichi plant.展开更多
The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which ...The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which are afterwards sublimated, and to examine the particles remaining after evaporation. The procedure takes into account only crystal with a maximum diameter of 20 μm, by assuming that small crystals do not scavenge aerosol during growth, and therefore that crystals contain only the effective nucleating particles. This assumption is questionable, however, as experiments have shown that even small ice crystals can scavenge aerosol. Another approach has been to compare the number and elemental composition of residual particles in small ice crystals and of aerosol near the cloud. By considering as example soot and black carbon aerosol, contradictory conclusions on their importance in the processes of ice nucleation have been reported in the literature. We suggest that, in addition to physico-chemical properties of soot/carbon aerosol particles, even the microphysical and environmental parameters involved in the transition of aerosol from gas phase to ice crystals in cloud should be considered. The contribution of phoretic forces should also be considered. After initial growth ice crystals can continue to grow by water vapour diffusion. Laboratory experiments confirm the contribution of diffusiophoresis with Stefan flow in the scavenging by snow crystals up to 3 mm in diameter. The particle scavenging efficiency of snow crystals is related to crystalline shape and depends on air relative humidity and temperature.展开更多
The below-cloud aerosol scavenging process by precipitation is one of the most important mechanisms to remove aerosols from the atmosphere.Due to its complexity and dependence on both aerosol and raindrop sizes,wet sc...The below-cloud aerosol scavenging process by precipitation is one of the most important mechanisms to remove aerosols from the atmosphere.Due to its complexity and dependence on both aerosol and raindrop sizes,wet scavenging process has been poorly treated,especially during the removal of fine particles.This makes the numerical simulation of below-cloud scavenging in large-scale aerosolmodels unrealistic.To consider the slip effects of submicron particles,a simplified expression for the diffusion scavenging was developed by approximating the Cunningham slip correction factor.The derived analytic solution was parameterized as a simple power function of rain intensity under the assumption of the lognormal size distribution of particles.The resultant approximated expression was compared to the observed data and the results of previous studies including a 3D atmospheric chemical transport model simulation.Compared with the default GEOS-Chem coefficient of 0.00106R0.61 and the observation-based coefficient of 0.0144R0.9268,the coefficient of a and b in∧m=aRb spread in the range of 0.0002-0.1959 for a and 0.3261-0.525 for b over a size distribution of GSD of 1.3–2.5 and a geometric mean diameter of 0.01-2.5μm.Overall,this study showed that the scavenging coefficient varies widely by orders of magnitude according to the size distribution of particles and rain intensity.This study also demonstrated that the obtained simplified expression could consider the theoretical approach of aerosol polydispersity.Our proposed analytic approach showed that results can be effectively applied for reduced computational burden in atmospheric modeling.展开更多
A closed-cell marine stratocumulus case during the Aerosol and Cloud Experiments in the Eastern North Atlantic(ACE-ENA)aircraft field campaign is selected to examine the heterogeneities of cloud and drizzle microphysi...A closed-cell marine stratocumulus case during the Aerosol and Cloud Experiments in the Eastern North Atlantic(ACE-ENA)aircraft field campaign is selected to examine the heterogeneities of cloud and drizzle microphysical properties and the aerosol-cloud-precipitation interactions.The spatial and vertical variabilities of cloud and drizzle microphysics are found in two different sets of flight legs:Leg-1 and Leg-2,which are parallel and perpendicular to the cloud propagation,respectively.The cloud along Leg-2 was close to adiabatic,where cloud-droplet effective radius and liquid water content linearly increase from cloud base to cloud top with less drizzle.The cloud along Leg-1 was sub-adiabatic with lower clouddroplet number concentration and larger cloud-droplet effective,but higher drizzle droplet number concentration,larger drizzle droplet median diameter and drizzle liquid water content.The heavier drizzle frequency and intensity on Leg-1 were enhanced by the collision-coalescence processes within cloud due to strong turbulence.The sub-cloud precipitation rate on Leg-1 was significantly higher than that along Leg-2.As a result,the sub-cloud accumulation mode aerosols and CCN on Leg-1 were depleted,but the coarse model aerosols increased.This further leads to a counter-intuitive phenomenon that the CCN is less than cloud-droplet number concentration for Leg-1.The average CCN loss rates are −3.89 cm^(-3)h^(-1)and −0.77 cm^(-3)h^(-1) on Leg-1 and Leg-2,respectively.The cloud and drizzle heterogeneities inside the same stratocumulus can significantly alter the sub-cloud aerosols and CCN budget.Hence it should be treated with caution in the aircraft assessment of aerosol-cloud-precipitation interactions.展开更多
This paper investigated the possibility that aerosol particles are scavenged during the first and fast diffusional growth of small ice crystals. After ice phase formation, riming, scavenging and aggregation may lead t...This paper investigated the possibility that aerosol particles are scavenged during the first and fast diffusional growth of small ice crystals. After ice phase formation, riming, scavenging and aggregation may lead to the collection of additional aerosol particles. Therefore, particles left after ice evaporation in hydrometeors, called ice residuals, may not currently be identical to ice nucleating particles. To overcome this problem, the largest ice crystals are removed during sampling in clouds and only crystals in the initial phase of growth, with diameters lower than 20 - 30 μm, are usually considered. Published papers assume that no aerosol scavenging takes place during the initial phase of growth of small ice crystals. The aim of this paper was to ascertain if this assumption is valid. Experiments were performed in a cold laboratory by considering ice crystals growing in the presence of supercooled droplets. Results showed that crystals can scavenge aerosol even in the first stage of growth. Theoretical considerations show that aerosol scavenging cannot be explained by Brownian diffusion, inertial impaction or interception processes. We suggest that the presence of aerosol in the pristine ice crystals may be due to diffusiophoretic force. During diffusive crystal growth, a flow called Stefan’s flow exists near the hydrometeor surface, driving the nearby aerosol particles towards the surface of the growing hydrometeors.展开更多
Scavenging experiments have been performed in a cloud chamber inside a cold room with different aerosol particles: Paraffin particles, NaCl particles, Magnesium oxide particles, Carbon particles, Sahara dust particles...Scavenging experiments have been performed in a cloud chamber inside a cold room with different aerosol particles: Paraffin particles, NaCl particles, Magnesium oxide particles, Carbon particles, Sahara dust particles. Essentially the experimental tests were carried on following the sequence of operations: the generation of the aerosol particles, their injection in the lower part of the cloud chamber, injection of water droplets in the whole chamber volume, nucleation of ice crystals, collection of ice crystals and their examination as for resulting scavenging efficiency. Evidence is given of the peculiar behaviour of soluble particles, individual and eventually inside mixed particles, leading to very much important scavenging efficiency, probably to be ascribed to aerodynamic capture. The evident peculiar behaviour of deliquescent particles can be oriented towards applications to an efficient abatement of specific effluents, on one side, and to weather modification experiments, both rain enhancement and hail prevention experiments.展开更多
The inter-conversion of nitrogen and sulfur species between the gas and particulate phases and their interaction with alkaline species influences the acidity of the aerosols and surface snow. To better understand thes...The inter-conversion of nitrogen and sulfur species between the gas and particulate phases and their interaction with alkaline species influences the acidity of the aerosols and surface snow. To better understand these processes, a short field campaign was undertaken in Ny-?lesund,Svalbard, during 13th April 2012 to 24th April 2012. Air measurements were carried out through a particulate sampler equipped with denuders and filter packs for simultaneous collection of trace gases(HNO_3, NO_2, SO_2 and reactive nitrogen compounds) and aerosols, with daily collection of snow samples. Ionic composition of the samples was analyzed using ion chromatography technique. The results suggested that nitrate-rich aerosols are formed when PAN(peroxy acetyl nitrate) disassociates to form NO_2 and HNO_3 which further hydrolyzes to form pNO_3^-(particulate nitrate). This resulted in a high contribution of pNO_3^-(62%) to the total nitrogen budget over the study area. The acidity of the aerosols and snow evaluated through cation/anion ratio(C/A)indicated alkaline conditions with C/A > 2. The bicarbonates/carbonates of Mg^(2+) played an important role in neutralization processes of surface snow while the role of NH_3 was dominant in aerosol neutralization processes. Such neutralization processes can increase the aerosol hygroscopicity causing warming. Chloride depletion in the snow was significant as compared to the aerosols, indicating two important processes, scavenging of coarse sea salt by the snow and gaseous adsorption of SO_2 on the snow surface. However, a more systematic and long term study is required for a better understanding of the neutralization processes and chemical interconversions.展开更多
Precipitation scavenging of aerosol particles is an important removal process in the atmosphere that can change aerosol physical and optical properties. This paper analyzes the changes in aerosol physical and optical ...Precipitation scavenging of aerosol particles is an important removal process in the atmosphere that can change aerosol physical and optical properties. This paper analyzes the changes in aerosol physical and optical properties before and after four rain events using in situ observations of mass concentration, number concentration, particle size distribution, scattering and absorption coefficients of aerosols in June and July 2013 at the Xianghe comprehensive atmospheric observation station in China. The results show the effect of rain scavenging is related to the rain intensity and duration, the wind speed and direction. During the rain events, the temporal variation of aerosol number concentration was consistent with the variation in mass concentration, but their size-resolved scavenging ratios were different. After the rain events, the increase in aerosol mass concentration began with an increase in particles with diameter ＆lt;0.8 μm [measured using an aerodynamic particle sizer（APS）], and fine particles with diameter ＆lt;0.1 μm [measured using a scanning mobility particle sizer（SMPS）]. Rainfall was most efficient at removing particles with diameter ～0.6 μm and greater than 3.5 μm. The changes in peak values of the particle number distribution（measured using the SMPS） before and after the rain events reflect the strong scavenging effect on particles within the 100–120 nm size range. The variation patterns of aerosol scattering and absorption coefficients before and after the rain events were similar, but their scavenging ratios differed, which may have been related to the aerosol particle size distribution and chemical composition.展开更多
基金financially supported by the Nuclear Energy Science and Technology and Human Resource Development Project of the Japan Atomic Energy Agency/Collaborative Laboratories for Advanced Decommissioning Science(No.R04I034)Ruicong Xu appreciates the scholarship(financial support)from the Chinese Scholarship Council(CSC No.202106380073).
文摘During the decommissioning of the Fukushima Daiichi nuclear power plant,it is important to consider the retrieval of resolidified debris both in air and underwater configurations.For the subsequent retrieval of debris from the reactor building,the resolidified debris must be cut into smaller pieces using various cutting methods.During the cutting process,aerosol particles are expected to be generated at the submicron scale.It has been noted that such aerosols sizing within the Greenfield gap(0.1-1μm)are difficult to remove effectively using traditional spraying methods.Therefore,to improve the aerosol removal efficiency of the spray system,a new aerosol agglomeration method was recently proposed,which involves injecting water mist to enlarge the sizes of the aerosol particles before removing them using water sprays.In this study,a series of experiments were performed to clarify the proper spray configurations for effective aerosol scavenging and to improve the performance of the water mist.The experimental results showed that the spray flow rate and droplet characteristics are important factors for the aerosol-scavenging efficiency and performance of the water mist.The results obtained from this study will be helpful for the optimization of the spray system design for effective aerosol scavenging during the decommissioning of the Fukushima Daiichi plant.
文摘The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which are afterwards sublimated, and to examine the particles remaining after evaporation. The procedure takes into account only crystal with a maximum diameter of 20 μm, by assuming that small crystals do not scavenge aerosol during growth, and therefore that crystals contain only the effective nucleating particles. This assumption is questionable, however, as experiments have shown that even small ice crystals can scavenge aerosol. Another approach has been to compare the number and elemental composition of residual particles in small ice crystals and of aerosol near the cloud. By considering as example soot and black carbon aerosol, contradictory conclusions on their importance in the processes of ice nucleation have been reported in the literature. We suggest that, in addition to physico-chemical properties of soot/carbon aerosol particles, even the microphysical and environmental parameters involved in the transition of aerosol from gas phase to ice crystals in cloud should be considered. The contribution of phoretic forces should also be considered. After initial growth ice crystals can continue to grow by water vapour diffusion. Laboratory experiments confirm the contribution of diffusiophoresis with Stefan flow in the scavenging by snow crystals up to 3 mm in diameter. The particle scavenging efficiency of snow crystals is related to crystalline shape and depends on air relative humidity and temperature.
基金supported by the FRIEND(Fine Particle Research Initiative in East Asia Considering National Differences)Project through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(No.2020M3G1A1114617)the Technology Development Program to Solve Climate Changes through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT(No.2019M1A2A2103953)+1 种基金the National Research Foundation of Korea Grant from the Korean Government(MSIT)(Nos.NRF2021M1A5A1065672/PN22011,NRF2021R1F1A1046878,and NRF2020R1A2C1003215)This research was also supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2020R1A6A1A03044834).
文摘The below-cloud aerosol scavenging process by precipitation is one of the most important mechanisms to remove aerosols from the atmosphere.Due to its complexity and dependence on both aerosol and raindrop sizes,wet scavenging process has been poorly treated,especially during the removal of fine particles.This makes the numerical simulation of below-cloud scavenging in large-scale aerosolmodels unrealistic.To consider the slip effects of submicron particles,a simplified expression for the diffusion scavenging was developed by approximating the Cunningham slip correction factor.The derived analytic solution was parameterized as a simple power function of rain intensity under the assumption of the lognormal size distribution of particles.The resultant approximated expression was compared to the observed data and the results of previous studies including a 3D atmospheric chemical transport model simulation.Compared with the default GEOS-Chem coefficient of 0.00106R0.61 and the observation-based coefficient of 0.0144R0.9268,the coefficient of a and b in∧m=aRb spread in the range of 0.0002-0.1959 for a and 0.3261-0.525 for b over a size distribution of GSD of 1.3–2.5 and a geometric mean diameter of 0.01-2.5μm.Overall,this study showed that the scavenging coefficient varies widely by orders of magnitude according to the size distribution of particles and rain intensity.This study also demonstrated that the obtained simplified expression could consider the theoretical approach of aerosol polydispersity.Our proposed analytic approach showed that results can be effectively applied for reduced computational burden in atmospheric modeling.
基金supported by the NSF grants AGS-2031750 and AGS-2031751supported as part of the “Enabling Aerosol-cloud interactions at GLobal convection-permitting scal ES (EAGLES)” project (74358),funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Earth System Modeling program with the subcontract to the University of Arizona
文摘A closed-cell marine stratocumulus case during the Aerosol and Cloud Experiments in the Eastern North Atlantic(ACE-ENA)aircraft field campaign is selected to examine the heterogeneities of cloud and drizzle microphysical properties and the aerosol-cloud-precipitation interactions.The spatial and vertical variabilities of cloud and drizzle microphysics are found in two different sets of flight legs:Leg-1 and Leg-2,which are parallel and perpendicular to the cloud propagation,respectively.The cloud along Leg-2 was close to adiabatic,where cloud-droplet effective radius and liquid water content linearly increase from cloud base to cloud top with less drizzle.The cloud along Leg-1 was sub-adiabatic with lower clouddroplet number concentration and larger cloud-droplet effective,but higher drizzle droplet number concentration,larger drizzle droplet median diameter and drizzle liquid water content.The heavier drizzle frequency and intensity on Leg-1 were enhanced by the collision-coalescence processes within cloud due to strong turbulence.The sub-cloud precipitation rate on Leg-1 was significantly higher than that along Leg-2.As a result,the sub-cloud accumulation mode aerosols and CCN on Leg-1 were depleted,but the coarse model aerosols increased.This further leads to a counter-intuitive phenomenon that the CCN is less than cloud-droplet number concentration for Leg-1.The average CCN loss rates are −3.89 cm^(-3)h^(-1)and −0.77 cm^(-3)h^(-1) on Leg-1 and Leg-2,respectively.The cloud and drizzle heterogeneities inside the same stratocumulus can significantly alter the sub-cloud aerosols and CCN budget.Hence it should be treated with caution in the aircraft assessment of aerosol-cloud-precipitation interactions.
文摘This paper investigated the possibility that aerosol particles are scavenged during the first and fast diffusional growth of small ice crystals. After ice phase formation, riming, scavenging and aggregation may lead to the collection of additional aerosol particles. Therefore, particles left after ice evaporation in hydrometeors, called ice residuals, may not currently be identical to ice nucleating particles. To overcome this problem, the largest ice crystals are removed during sampling in clouds and only crystals in the initial phase of growth, with diameters lower than 20 - 30 μm, are usually considered. Published papers assume that no aerosol scavenging takes place during the initial phase of growth of small ice crystals. The aim of this paper was to ascertain if this assumption is valid. Experiments were performed in a cold laboratory by considering ice crystals growing in the presence of supercooled droplets. Results showed that crystals can scavenge aerosol even in the first stage of growth. Theoretical considerations show that aerosol scavenging cannot be explained by Brownian diffusion, inertial impaction or interception processes. We suggest that the presence of aerosol in the pristine ice crystals may be due to diffusiophoretic force. During diffusive crystal growth, a flow called Stefan’s flow exists near the hydrometeor surface, driving the nearby aerosol particles towards the surface of the growing hydrometeors.
文摘Scavenging experiments have been performed in a cloud chamber inside a cold room with different aerosol particles: Paraffin particles, NaCl particles, Magnesium oxide particles, Carbon particles, Sahara dust particles. Essentially the experimental tests were carried on following the sequence of operations: the generation of the aerosol particles, their injection in the lower part of the cloud chamber, injection of water droplets in the whole chamber volume, nucleation of ice crystals, collection of ice crystals and their examination as for resulting scavenging efficiency. Evidence is given of the peculiar behaviour of soluble particles, individual and eventually inside mixed particles, leading to very much important scavenging efficiency, probably to be ascribed to aerodynamic capture. The evident peculiar behaviour of deliquescent particles can be oriented towards applications to an efficient abatement of specific effluents, on one side, and to weather modification experiments, both rain enhancement and hail prevention experiments.
基金National Centre for Antarctic and Ocean Research,Goa,for encouragement and the Ministry of Earth Sciences,Government of India for financial support on the project (Mo ES/P.O.(Seismo) 3(44)/2013)
文摘The inter-conversion of nitrogen and sulfur species between the gas and particulate phases and their interaction with alkaline species influences the acidity of the aerosols and surface snow. To better understand these processes, a short field campaign was undertaken in Ny-?lesund,Svalbard, during 13th April 2012 to 24th April 2012. Air measurements were carried out through a particulate sampler equipped with denuders and filter packs for simultaneous collection of trace gases(HNO_3, NO_2, SO_2 and reactive nitrogen compounds) and aerosols, with daily collection of snow samples. Ionic composition of the samples was analyzed using ion chromatography technique. The results suggested that nitrate-rich aerosols are formed when PAN(peroxy acetyl nitrate) disassociates to form NO_2 and HNO_3 which further hydrolyzes to form pNO_3^-(particulate nitrate). This resulted in a high contribution of pNO_3^-(62%) to the total nitrogen budget over the study area. The acidity of the aerosols and snow evaluated through cation/anion ratio(C/A)indicated alkaline conditions with C/A > 2. The bicarbonates/carbonates of Mg^(2+) played an important role in neutralization processes of surface snow while the role of NH_3 was dominant in aerosol neutralization processes. Such neutralization processes can increase the aerosol hygroscopicity causing warming. Chloride depletion in the snow was significant as compared to the aerosols, indicating two important processes, scavenging of coarse sea salt by the snow and gaseous adsorption of SO_2 on the snow surface. However, a more systematic and long term study is required for a better understanding of the neutralization processes and chemical interconversions.
基金supported by the National Natural Science Foundation of China(Grant No.41375155)the National Basic Program of China(973)(Grant No.2013CB955800)the China Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201306005)
文摘Precipitation scavenging of aerosol particles is an important removal process in the atmosphere that can change aerosol physical and optical properties. This paper analyzes the changes in aerosol physical and optical properties before and after four rain events using in situ observations of mass concentration, number concentration, particle size distribution, scattering and absorption coefficients of aerosols in June and July 2013 at the Xianghe comprehensive atmospheric observation station in China. The results show the effect of rain scavenging is related to the rain intensity and duration, the wind speed and direction. During the rain events, the temporal variation of aerosol number concentration was consistent with the variation in mass concentration, but their size-resolved scavenging ratios were different. After the rain events, the increase in aerosol mass concentration began with an increase in particles with diameter ＆lt;0.8 μm [measured using an aerodynamic particle sizer（APS）], and fine particles with diameter ＆lt;0.1 μm [measured using a scanning mobility particle sizer（SMPS）]. Rainfall was most efficient at removing particles with diameter ～0.6 μm and greater than 3.5 μm. The changes in peak values of the particle number distribution（measured using the SMPS） before and after the rain events reflect the strong scavenging effect on particles within the 100–120 nm size range. The variation patterns of aerosol scattering and absorption coefficients before and after the rain events were similar, but their scavenging ratios differed, which may have been related to the aerosol particle size distribution and chemical composition.
