Humidity effects on gravitational settling and Brownian diffusion of atmospheric aerosol particles     

Gottfried Hänel 《Pure and Applied Geophysics》1977,115(4):775-797

The dependency on relative humidity of the settling velocity of aerosol particles in stagnant air and of the diffusion coefficient due to Brownian motion of aerosol particles was computed for six aerosol types and different particles sizes in dry state. The computations are based (1) on mean bulk densities of dry aerosol particles obtained from measurements or from the knowledge of the chemical composition of the particles, (2) on micro-balance measurements of the water uptake per unit mass of dry aerosol substance versus water activity at thermodynamic equilibrium, and (3) on measurements of the equilibrium water activity of aqueous sea salt solutions. The results show a significant dependence of the settling velocity and Brownian diffusion of aerosol particles on relative humidity and on the particle's chemical composition.Nomenclature A surface parameter of a particle - B surface parameter of a particle - c _L velocity of sound in moist air - C 1+Kn[A+Qexp(–B/Kn]=slip correction - D diffusion coefficient of a particle - D ₁ D(=1)=diffusion coefficient of a spherical particle - f P _w /P _we (T,P)=relative humidity (f=0 dry air,f=1 saturated air) - g acceleration due to gravity - g |g| - k 1.3804×10^–16 erg/°K=Boltzmann constant - Kn _L /r=Knudsen number of a particle - Kn _{0 0L} /r ₀=Knudsen number of a dry particle - m 4r ³/3=mass of a particle - m _L 4r ³ _L /3=mass of the moist air displaced by a particle - M mobility of a particle - M ₀ molar mass of dry air - M _w molar mass of water - Ma |u–u _L |/c _L =Mach number of the particles motion relative to the ambient air - n particle number per unit volume of air - P P ₀+P _w =pressure of the moist air - P ₀ partial pressure of the dry air - P _w partial pressure of the water vapour - P _we P _we (T,P)=equilibrium partial water vapour pressure over a plane surface of water saturated with air - Q surface parameter of a particle - r equivalent radius of a particle (radius of a sphere with the particles volume) - r ₀ equivalent radius of a particle in dry state - R 1+0.13Re ^0.85=inertia correction - R ₀ specific gas constant of dry air - R _w specific gas constant of water - Re 2r _L u–u _L / _L =Reynolds number of the particles motion relative to the ambient air - t time - T absolute temperature - u velocity of a particle - u (amount of the) settling velocity of a particle in stagnant air - u ₁ u(=1)=(amount of the) settling velocity of a spherical particle in stagnant air - u _L velocity of the ambient moist air (far enough from the particle where the flow pattern remains undistorted) - W drag coefficient of a particles equivalent sphere - empirical parameter in equation (3.1) - dynamic viscosity of a particles liquid cover - _L dynamic viscosity of moist air - _0L dynamic viscosity of dry air (at the same pressure and temperature like the moist air) - celsius temperature - dynamic shape factor of a particle (=1 for a sphere) - ₀ dynamic shape factor of a dry particle - _L mean free path of the molecules in moist air - _0L mean free path of the molecules in dry air (at the same pressure and temperature like the moist air) - _Po mean free path of the molecules in dry air at the pressureP ₀ of the dry air and the temperature given - factor of solid to liquid change-over (=1 for a solid particle) - mean bulk density of a particle - _L density of the moist air - _0L density of the dry air at the same pressure and temperature like the moist air - ₀ mean bulk density of a dry particle - ₀ mean diameter of the molecules of dry air - _w diameter of water molecules - relaxation time of a particle - gradient operation - 3.141593  相似文献   

Study of background aerosols in the Antarctic troposphere     

T. Ito 《Journal of Atmospheric Chemistry》1985,3(1):69-91

Systematic year-round observations of submicron aerosols were carried out at Syowa Station (69°00'S, 39°35'E) in 1978. On the basis of the results of these observations, it is concluded that two types of aerosols originating from different sources are present in the Antarctic croposphere. With the intrusion of maritime air, mostly in the polar night months, sea salt particles and ammonium sulfate particles contained originally in the clean maritime air are dominant. The size distribution of such aerosols is monomodal, having a single mode at around 0.03 m in radii. On the other hand, in the sunlit months, sulfuric acid droplets are predominant and the size distribution is bimodal, having an additional mode at around 0.005 m in radii. Those sulfuric acid particles seem to be formed photochemically within a specific layer in the mid to lower troposphere over Antarctica. Most Antarctic submicron particles are of tropospheric origin, not of stratospheric nor anthropogenic origin.  相似文献   

沙尘天气对榆林市环境空气质量的影响   总被引：1，自引：1，他引：0  

崔娟  王浩  刘杰  王越  卢立栋  陈洁 《中国沙漠》2021,41(2):59-66

基于2013—2018年榆林市沙尘天气和环境空气质量逐日数据,定量分析了沙尘天气对榆林市空气质量指数（AQI）、可吸入颗粒物（PM₁₀）和细颗粒物（PM_2.5）的绝对贡献和相对贡献率。结果表明：沙尘天气对榆林市AQI的贡献率为0.7%—11.1%（平均值±标准差6.4%±3.8%）;对PM₁₀的绝对贡献为1.0—13.1 μg·m^-3（平均8.2±5.4 μg·m^-3）,相对贡献率5.4%±3.5%;对PM_2.5的绝对贡献为-0.4—3.5 μg·m^-3,沙尘天气对PM_2.5的影响小于对PM₁₀。沙尘天气对榆林市空气质量的影响季节差异很大,春季贡献最大,秋冬季贡献较小。沙尘天气对榆林市区和郊区的影响程度不同,这可能与局部气象条件和地形条件等因素有关。  相似文献   

点电荷相互作用能与一类二重积分的算法     

朱世德  向安平 《成都信息工程学院学报》1999,(3)

在柱面坐标系下，点电荷的相互作用能是ｚ和ρ的具有极点的二重积分。此类积分有简单的解析解，但不容易数值计算。Ｍａｔｈｅｍａｔｉｃａ３．０和ＭａｐｌｅＶ不能求解此类积分；Ｇａｕｓｓ－Ｌｅｇｅｎｄｒｅ算法只能获得粗略结果，Ｒｕｎｇｅ－Ｋｕｔａ算法虽能成功地计算，但不能交换积分顺序。  相似文献   

同期采灌储能模式浅层咸水介质渗透性演化过程研究     

马玖辰  武春彬  刘雪玲  张志刚 《岩土力学》2015,36(7):1883-1891

针对地下浅层储能咸水介质复杂的水文地质条件与矿物构成的特殊性,开展可控三维物理模拟试验,基于表面化学与胶体稳定性理论,从介观尺度分析回灌溶液宏观参数变化与含水介质中微纳米颗粒重新分布过程的内在关联;探索复杂时空条件下咸水层孔隙结构变化规律;确定不同储能模式下低渗透帷幕带的形成区域。研究结果表明,回灌溶液温度、盐度变化是打破颗粒间受力平衡,造成含水介质渗透性能下降的诱导机制。在抽-注井固定与调换模式下,经历完整储能周期,含水层整体相对渗透率k/k0分别下降至63%、57%,表明由微纳米颗粒物质重组,导致含水介质空间结构变化具有不可逆性。两组储能试验中,由于形成机制不同,低渗透帷幕带分别形成于700～900 mm与500～700 mm的渗流单元。  相似文献   

粗粒料多边形表征及二维FEM/DEM分析     

严成增  郑宏  孙冠华  葛修润 《岩土力学》2015,36(Z2):95-103

考虑到颗粒形状对粗粒料的力学特性有重大影响,提出了一种新的表征颗粒形状的方法,即在椭圆上随机选取一系列点连接成多边形颗粒,表征狭长扁平的颗粒。新方法较圆上取点的方法能代表更多类型的颗粒形状,适用范围更广。提出了一种新的粗粒料投放算法,即先缩小颗粒,然采用随机算法将缩小的颗粒投放至给定区域,对颗粒划分好网格后,将颗粒放大到原来的大小,然后采用有限元-离散元(FEM/DEM)方法计算稳定后即生成了相应的试样。通过将上述颗粒生成及投放算法与FEM/DEM结合,应用于粗粒料的数值模拟。分析表明,FEM/DEM是研究粗粒料力学性质的较好方法,对复杂的颗粒形状也可简单建模,且因在颗粒内部划分了有限元网格,复杂的接触判断及接触力计算转化为标准统一的三角形和三角形之间的接触判断及接触力计算,所有的计算均可标准化、统一化。同时因为颗粒是可以变形的,依然保留了连续介质力学中应力和应变的概念,无须像PFC那样需通过测量圆来间接表示某点的应力、应变。最后,通过粗粒料的侧限压缩试验的数值模拟,展现了文中提出的一整套解决方案在模拟粗粒料方面的巨大潜力。  相似文献   

Using X‐ray observations to identify the particle acceleration mechanisms in VHE SNRs and “dark” VHE sources     

G. Pühlhofer 《Astronomische Nachrichten》2008,329(2):186-190

Very high energy (VHE) γ‐ray observations have proven to be very successful in localizing Galactic acceleration sites of VHE particles. Observations of shell‐type supernova remnants have confirmed that particles are accelerated to VHE energies in supernova blast waves; the interpretation of the γ‐ray data in terms of hadronic or leptonic particle components in these objects relies nevertheless strongly on input from X‐ray observations. The largest identified Galactic VHE source class consists of pulsar wind nebulae, as detected in X‐rays. Many of the remaining VHE sources remain however unidentified until now. With X‐ray observations of these enigmatic “dark” objects one hopes to solve the following questions: What is the astrophysical nature of these sources? Are they predominantly electron or hadron accelerators? And what is their contribution to the overall cosmic ray energy budget? The paper aims to provide an overview over the identification status of the Galactic VHE source population. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Supernova remnants,planetary nebulae and superbubbles: Prospects for new XMM‐Newton observations     

A. Decourchelle 《Astronomische Nachrichten》2008,329(2):178-181

Important results achieved over the last years on supernova remnants, planetary nebulae and superbubbles are briefly reviewed in the context of X‐ray observations. I intend to review the important open scientific questions in these fields, and the specific contributions that can be made by XMM‐Newton. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

TeV J2032+4130: a not-so-dark accelerator?     

Y. M. Butt  J. A. Combi  J. Drake  J. P. Finley  A. Konopelko  M. Lister  J. Rodriguez  D. Shepherd 《Monthly notices of the Royal Astronomical Society》2008,385(4):1764-1770

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Measuring the non-thermal pressure in early-type galaxy atmospheres: a comparison of X-ray and optical potential profiles in M87 and NGC 1399     

E. Churazov  W. Forman  A. Vikhlinin  S. Tremaine  O. Gerhard  C. Jones 《Monthly notices of the Royal Astronomical Society》2008,388(3):1062-1078

We compare the gravitational potential profiles of the elliptical galaxies NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived from X-ray and optical data. This comparison suggests that the combined contribution of cosmic rays, magnetic fields and microturbulence to the pressure is ∼10 per cent of the gas thermal pressure in the cores of NGC 1399 and M87, although the uncertainties in our model assumptions (e.g. spherical symmetry) are sufficiently large that the contribution could be consistent with zero. In the absence of any other form of non-thermal pressure support, these upper bounds translate into upper limits on the magnetic field of ∼10–20 μG at a distance of 1–2 arcmin from the centers of NGC 1399 and M87. We show that these results are consistent with the current paradigm of cool cluster cores, based on the assumption that active galactic nuclei regulate the thermal state of the gas by injecting energy into the intracluster medium. The limit of ∼10–20 per cent on the energy density in the form of relativistic protons applies not only to the current state of the gas, but also essentially to the entire history of the intracluster medium, provided that cosmic ray protons evolve adiabatically and that their spatial diffusion is suppressed.  相似文献