Dynamical Effects of Mars on Asteroidal Dust Particles

Asteroidal dust particles resulting from family-forming events migrate from their source locations in the asteroid belt inwards towards the Sun under the effect of Poynting-Robertson (PR) drag. Understanding the distribution of these dust particle orbits in the inner solar system is of great importance to determining the asteroidal contribution to the zodiacal cloud, the accretion rate by the Earth, and the threat that these particles pose to spacecraft and satellites in near-Earth space. In order to correctly describe this distribution of orbits in the inner solar system, we must track the dynamical perturbations that the dust particle orbits experience as they migrate inwards. In a seminal paper Öpik (1951) determines that very few of the μm-cm sized dust particles suffer a collision with the planet face as they decay inwards past Mars. Here we re-analyze this problem, considering additionally the likelihood that the dust particle orbits pass through the Hill sphere of Mars (to various depths) and experience potentially significant perturbations to their orbits. We find that a considerable fraction of dust particle orbits will enter the Hill sphere of Mars. Furthermore, we find that there is a bias with inclination, particle size, and eccentricity of the particle orbits that enter the Martian Hill sphere. In particular the bias with inclination may create a bias towards higher-inclination sources in the proportions of asteroid family particles that reach near-Earth space.     

Meteor Outburst Profiles and Cometary Ejection Models

The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from the nucleus, including the mass distribution of ejected meteoroids.     

土壤剖面中粉煤灰垂向迁移的磁响应

对浙江省安吉县梅溪发电厂粉煤灰贮灰场附近的土壤短剖面进行环境磁学、元素含量及粒度研究.借助模糊聚类分析,分辨出粉煤灰原位堆积、富集、迁移深度及未受污染土壤特征.剖面上部0～14cm为粉煤灰的原位反映,多畴磁铁矿主导了该段样品磁性.其中11～14cm处磁性矿物和金属元素有所富集.14～21cm为粉煤灰在土壤中的迁移深度.迁移段土壤中亚铁磁性矿物及Pb、Zn等金属含量介于底部未污染土壤与上部粉煤灰原位堆积层之间.单畴斜交反铁磁性矿物及来源于上部粉煤灰的多畴磁铁矿共同主导了该段土壤的磁性特征.21cm以下土壤基本未受粉煤灰污染,单畴斜交反铁磁性矿物是其主要磁性矿物.指标聚类分析表明,亚铁磁性矿物主要赋存在粗粉砂中,单畴磁晶粒主要存在于细粉砂中.χ、ARM、SIRM与Cu、Mn、Pb、Zn呈显著相关.结合多元统计分析,磁参数可用于追踪、识别粉煤灰在土壤剖面中的垂向迁移.     

中国地区春季沙尘气溶胶短波辐射气候效应数值模拟研究

利用耦合了起沙模型(MEDM)的区域气候模式RegCM3,模拟研究了2000年春季中国地区沙尘气溶胶短波辐射气候效应。结果表明,春季中国沙尘气溶胶垂直负荷的大值区主要位于南疆盆地和阿拉善高原。引入沙尘气溶胶后,中国地区地表均出现负的辐射强迫,地面气温普遍降低,中低层(400 hPa层以下)大气温度则呈上升趋势。沙尘源区及其下游地区总云量及降水主要呈减少趋势,云量与降水的分布特征与空中流场的变化趋势一致性较好。     

Asian Dust effects on Total Suspended Particulate (TSP) compositions at Gosan in Jeju Island, Korea

The compositions of TSP between AD and NAD storm periods were compared to study their long-term variations and chemical characteristics. TSP samples were collected at Gosan site in Jeju Island of Korea from February to May of 1992–2004. The major ionic and elemental species of TSP aerosols were analyzed. During AD periods, the concentrations of crust components (nss-Ca²⁺, Al, Fe, Ca, Mg, Ba, Sr, Ti) increased remarkably, and the concentrations of anthropogenic components (nss-SO₄²⁻, NO₃⁻, S, Zn, Pb, Cr, Ni, Cd), with the exception of NH₄⁺, increased weakly. The concentration ratios of all major components between AD and NAD periods showed ranges from 1.2 to 8.5, except for NH₄⁺. The slope of the linear regression indicated that the contribution of CO₃²⁻ may have comprised up to 17% of the total anions. Our results suggested that the AD storm greatly influenced TSP compositions. Linear regression analyses indicated that NH₄⁺ was not correlated with NO₃⁻, but highly correlated with nss-SO₄²⁻ during both periods. The nss-SO₄²⁻ was also correlated with NH₄⁺, K⁺, nss-Mg²⁺, and nss-Ca²⁺ during both periods. Interestingly, NO₃⁻ was associated with nss-Ca²⁺ and nss-Mg²⁺ during AD periods. Of the metal elements, Fe, Ca, Mg, Ti, Mn, Ba, Sr, V, and Co were highly correlated with Al during both periods, signifying that these metals were mostly originated from soils.     

Influences of characteristic meteorological conditions on atmospheric carbonyls in Beijing, China

Atmospheric pollutants are controlled not only by their production rates but also by meteorological conditions. The influences of dust storm, sauna weather (haze with high temperature and high humidity), wet precipitation and wind speed on atmospheric carbonyls in Beijing were investigated. During a severe dust episode (April 17, 2006), the mixing ratios of carbonyls were significantly elevated to 13–27 ppbV from 7 to 13 ppbV in the previous non-dust days (April 15 and 16) with the increasing extents of 38–154%. The accumulating effect and the lower photolysis rate in the dust day may be responsible for the increases of carbonyls' levels. Additionally, the contribution from heterogeneous reactions occurring on dust particles to formaldehyde and acetaldehyde cannot be ruled out. During the period of typical sauna weather, the concentrations of atmospheric carbonyls increased to 18–60 ppbV from 10 to 17 ppbV before the sauna days. The air mass over Beijing during the sauna days was controlled by a subtropical anticyclone and the boundary layer became quite stable, which was beneficial to the rapid accumulation of air pollutants including carbonyls. Wet precipitation was found to be an effective removal process to the atmospheric carbonyls. After one-hour of rain in summer, the total concentrations of atmospheric carbonyls decreased to less than half of that before the rainfall. The similar temporal varying patterns of carbonyls and inorganic ions in rainwater indicated that carbonyls were mainly washed out from the atmosphere into rainwater as inorganic ions were. Strong wind could evidently dilute atmospheric carbonyls and a negative correlation was found between wind speeds and the concentrations of carbonyls in spring in Beijing.     

中国西北不同沙源地区起沙阈值的对比分析与研究

沙尘粒子进入大气所受到的空气动力因子和阴力因子分别用摩擦速度u,和临界摩擦速度u(?)来定量表示。临界摩擦速度是影响沙尘释放和输送的重要参数。文中利用2004年春季浑善达克沙地和2006年春季黄土高原与戈壁3种不同沙源地区开展的微气象学和沙尘暴观测资料,分析了沙尘天气过程中沙尘浓度随摩擦速度的变化关系,估算了临界起沙摩擦速度u(?),并与不同学者给出的结果进行对比。结果表明:沙尘天气过程中,临近起沙阶段,沙尘浓度较低,摩擦速度增加快,为起沙阶段提供了利的动力条件;起沙阶段,动力和热力湍流混合使得沙尘浓度迅速升高;沙尘天气减弱阶段,由于重力沉隆作用,沙尘浓度随摩擦速度近似呈线性递减关系。以空气中的沙尘浓度大于200μg/m~3作为起沙的判据条件,得到浑善达克沙地和戈壁地区的临界起沙摩擦速度分别为0.6和0.45 m/s。由于受地形及非均匀下垫面的影响,黄土高原的临界起沙摩擦速度与风向有关。西北风反映了来自西北方向毛乌素沙地的影响,u(?)为0.35 m/s,偏南风时对应观测站点南部黄土丘陵沟壑区的起沙特征,u(?)为0.7 m/s。黄土丘陵沟壑区的地表粗糙度值和土壤粒子间的相互作用力较大,从而导致了较大的临界起沙摩擦速度。不同的起沙阈值条件和风速频率分布与沙尘释放能力的不同相对应。     

Lessons from the Dust Bowl: Human-Environment Education on the Great Plains

Abstract

This article documents regional demand for human-environment educational resources via assessment of public knowledge of the environmental crisis known as the Dust Bowl. The steadily eroding knowledge-base on the topic is discussed along with the desire for enhanced Dust Bowl educational resources. Regionally focused educational activities utilizing geospatial technologies, family interviews, and repeat photography were created to help redress shortcomings in human-environment understanding of the Great Plains at a local level.     

Changes in mobility and speciation of heavy metals in clay-amended incinerator fly ash

The generation of municipal solid waste incinerator fly ash (MSWIF) has been increasing significantly over the recent past, and its disposal is problematic and costly due to high concentration of leachable heavy metals present in the material. This study explored a potential stabilization of MSWIF by blending with a natural sorbent material with low permeability, clay, and assessed the potential release of heavy metals from the stabilized mixtures under various simulated subsurface environments. The leachability of heavy metals such as Pb, Cd, Cr, Zn and Cu in the MSWIF-clay mixtures cured for 1 to 360 days was investigated by performing leaching tests and sequential chemical extractions (SCE). Leaching tests were performed at acidic, neutral and alkaline pH values. The leaching test results suggested that the natural clay could turn the MSWIF into non-hazardous material. All the MSWIF-clay mixtures demonstrated leaching behavior different from that of the original MSWIF. SCE results revealed that the acidic and reducing conditions were the most unfavorable to the immobilization of the heavy metals in the stabilized MSWIF-clay matrix. Conversely, the oxidizing and alkaline conditions were not critical to the stabilized MSWIF-clay mixtures. Apparently, clay in the mixtures could function as an adsorptive micro-barrier to retain the heavy metals within the MSWIF-clay matrices.     

Chromium and nickel distribution in soils, active river, overbank sediments and dust around the Burrel chromium smelter (Albania)

Chromium ore was treated to produce ferrochromium from 1979 until 2000 in a smelter in Burrel, 35 km NE of Tirana (Albania). As a consequence, large amounts of solid waste, i.e. slags (about 9.10⁶ m³) have been disposed next to the smelter, disfiguring the landscape. In an attempt to define contaminated sites, heavy metal content of the different sampling media have been compared with respective background samples.In the study area, the determination of background values in soil samples is complicated due to the different geological substrates. Cr and Ni background concentrations in serpentinite-derived soils, west of the smelting plant, are markedly higher than in the Pliocene gravel/sandy soils, where the smelter is situated (Cr 2147 and 193 mg/kg, respectively; Ni 2356 and 264 mg/kg). These values are clearly lower than those encountered around the smelter. Average total Cr and Ni concentrations in soils around the smelter are 3117 and 1243 mg/kg, respectively. The highest concentrations of Cr (up to 2.3 wt.%), were recorded in samples taken near the smelting compartment within the industrial plant and next to the slags clearly indicating that the smelter forms a point source of Cr contamination. The Cr / Fe ratio is the best indicator to differentiate non-polluted (Cr / Fe Serpentinite soil: 130–390; Pliocene soils: < 130) from polluted areas (> 390 smelting nearby of the slags).Cr and Ni values for local backgrounds in stream and overbank sediments were taken in the Mat river 6 km upstream and to the east of the smelter (268 and 430 mg/kg for Cr, and 306 and 604 mg/kg for Ni, respectively). Equivalent sediments taken from the Zalli i Germanit river, which drains the smelter area are respectively 816 and 1126 mg/kg for Cr and 1115 and 1185 mg/kg for Ni.Dust samples, taken from the lofts of houses up to 2 km from the smelter, display high concentrations of Cr, Ni and Zn (average contents of 2899, 436 and 902 mg/kg, respectively). The later concentrations in the dust samples have been confirmed by mineralogical analysis where Cr-bearing mineral phases such as ferrochromium and chromium oxides, clearly relate to the activity of the smelter. Consequently, atmospheric deposition of dust particles forms a serious problem and can also be responsible for the elevated contents encountered in soil samples around the smelter.All these data show that the degree of contamination caused by industrial activity of the Burrel Cr-smelter is severe, although no Cr(VI) was detected in soil water extractions nor in the surface or groundwater where concentrations were < 0.01 mg/kg.