Heterogeneous chemistry in the atmosphere of Mars

Hydrogen radicals are produced in the martian atmosphere by the photolysis of water vapour and subsequently initiate catalytic cycles that recycle carbon dioxide from its photolysis product carbon monoxide. These processes provide a qualitative explanation for the stability of the atmosphere of Mars, which contains 95 per cent carbon dioxide. Balancing carbon dioxide production and loss based on our current understanding of the gas-phase chemistry in the martian atmosphere has, however, proven to be difficult. Interactions between gaseous chemical species and ice cloud particles have been shown to be key factors in the loss of polar ozone observed in the Earth's stratosphere, and may significantly perturb the chemistry of the Earth's upper troposphere. Water-ice clouds are also commonly observed in the atmosphere of Mars and it has been suggested previously that heterogeneous chemistry could have an important impact on the composition of the martian atmosphere. Here we use a state-of-the-art general circulation model together with new observations of the martian ozone layer to show that model simulations that include chemical reactions occurring on ice clouds lead to much improved quantitative agreement with observed martian ozone levels in comparison with model simulations based on gas-phase chemistry alone. Ozone is readily destroyed by hydrogen radicals and is therefore a sensitive tracer of the chemistry that regulates the atmosphere of Mars. Our results suggest that heterogeneous chemistry on ice clouds plays an important role in controlling the stability and composition of the martian atmosphere.     

Atmospheric heterogeneous reaction of acetone:Adsorption and desorption kinetics and mechanisms on SiO_2 particles

Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmos-phere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are ad-sorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can de-crease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed.     

Atmospheric heterogeneous reaction of acetone: Adsorption and desorption kinetics and mechanisms on SiO2 particles

Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmos-phere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are adsorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can decrease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed.     

60 km 高空大气等离子体中离子密度随时间演化的数值模拟

利用建立的大气化学零维模型,模拟了60 km高空的大气化学反应,研究了带电粒子在化学反应中的动力学规律,计算得出电子在60 km高空的寿命为1.107 8×10-5 s,给出了电子密度及其他带电粒子密度随时间的演化图,并与地面附近的数值模拟进行了比较.所得结果对探讨大气物理化学反应的机制具有重要意义,为等离子体隐身及再入技术的研究和环境污染的监测提供了有用的参考.     

应用蒸汽相变机理脱除燃烧源PM2.5试验研究

对应用蒸汽相交原理作为脱除燃烧源PM2.5预调节措施的效果进行了试验研究.结果表明,蒸汽相变与常规除尘技术结合可有效脱除PM2.5,对燃煤、燃油PM2.5的脱除效率可分别提高80%,60%以上;相交核化室壁面性能,颗粒物化性质及蒸汽过饱和度对PM2.5凝并长大效果均有重要影响,采用低表面能的核化室壁面材料可明显改善蒸汽相变预调节的效果;强疏水性的燃油PM2.5颗粒凝并长大效果明显不及燃煤PM2.5颗粒,适当提高蒸汽添加量有助于增进相交效果.     

The sequestration of ethane on Titan in smog particles

Saturn's largest satellite, Titan, has a dense atmosphere of nitrogen with a few per cent of methane. At visible wavelengths its surface is hidden by dense orange-brown smog, which is produced in the stratosphere by photochemical reactions following the dissociation of methane by solar ultraviolet light. The most abundant of the products of these reactions is ethane, and enough of it should have been generated over the life of the Solar System to form a satellite-wide ocean one kilometre deep. Radar observations have found specular reflections in 75 per cent of the surface spots observed, but optical searches for a sun-glint off an ocean have been negative. Here I explain the mysterious absence or rarity of liquid ethane: it condenses onto the smog particles, instead of into liquid drops, at the cold temperatures in Titan's atmosphere. This dusty combination of smog and ethane, forming deposits several kilometres thick on the surface, including the observed dunes and dark areas, could be named 'smust'. This satellite-wide deposit replaces the ocean long thought to be an important feature of Titan.     

开放大气等离子体中带电粒子密度时间演化的数值模拟

利用大气化学反应的零维模型,模拟了地面附近的大气化学反应,研究了电子和主要离子在大气化学反应中的动力学规律和机制,给出了电子密度及其他带电粒子密度随时间的演化图.所得结果对进一步了解大气中的物理化学反应和空气动力学的机理具有重要意义,对飞机的等离子体隐身和大气环境污染与监测也具有一定的参考价值.     

Mechanical milling assisted by electrical discharge

Mechanical milling is an effective technique for the preparation of fine metallic and ceramic powders and can also be used to drive a wide range of chemical reactions. Milling devices include planetary machines, attritors and vibrational mills; products include amorphous, nanocrystalline and quasicrystalline materials, supersaturated solid solutions, reduced minerals, high-surface-area catalysts and reactive chemicals. During milling, solid-solid, solid-liquid and solid-gas reactions are initiated through repeated deformation and fracture of powder particles. A separate materials synthesis and processing technique involves reacting a material in a gas atmosphere under an electrical discharge. Here we show that the application of low-current, high-voltage electrical impulses during milling can result in both faster reactions and new synthesis and processing routes. We demonstrate the effects of glow (cold) and spark (hot) discharge milling on particle fracture for brittle, low-conductivity materials and ductile metals. Glow discharge milling was found to promote solid-gas reactions whereas spark discharge milling promotes fast fracturing, recrystallization, mineral reduction and solid-solid reactions.     

大气颗粒物PM2.5及其源解析

大气颗粒物的来源分为两类：一类是自然源;另一类是人为源。自然源主要包括：岩石土壤风化、森林大火、火山爆发、流星雨、沙尘暴、海盐粒子、植物花粉、真菌孢子、细菌体,以及各种有机物质的自燃过程等。人为源主要包括：汽车尾气排放、摩托车尾气排放、火车机车排放、飞机尾气排放、轮船排放、工业窑炉排放、民用炉灶排放、农用拖拉机排放、工业粉尘、交通道路扬尘、建筑工地扬尘、裸露地面扬尘、烹饪油烟、街头无序烧烤、垃圾焚烧、农田秸秆焚烧、燃放烟花爆竹、寺庙香火和烟民抽烟等。在大气颗粒物中,细颗粒物主要来自化石燃料和生物质的燃烧过程。专家们认为细颗粒物是导致北京地区雾霾灾害天气频繁出现的最主要因素。汽车尾气排放大量的空气污染物。有车族对北京市严重的大气污染和雾霾灾害的形成,负有首要责任。有车族,少开车,或者不开车,是解决目前北京严重的大气污染,阻止雾霾灾害天气频繁出现的根本出路。     

细粒菱铁矿、石英和赤铁矿吸附团聚的机理

含菱铁矿难选铁矿石在磨矿作业过程中,菱铁矿极易泥化,并大量吸附在脉石和有用矿物的表面上,恶化了后续选别作业.为了查明微细粒菱铁矿、石英和赤铁矿在矿浆中吸附团聚的本质及规律,利用DLVO理论探讨了微细粒菱铁矿与粗粒石英、微细粒菱铁矿与赤铁矿及细粒菱铁矿之间的作用机理.计算结果表明:微细粒菱铁矿容易吸附罩盖在粗粒石英和赤铁矿表面,微细粒菱铁矿和微细粒赤铁矿相互作用发生团聚现象,而微细粒菱铁矿之间不发生吸附团聚现象.     

An amorphous solid state of biogenic secondary organic aerosol particles

Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs). On a global scale, biogenic VOCs account for about 90% of VOC emissions and of SOA formation (90?billion kilograms of carbon per year). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth's radiation balance and climate. They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas-particle partitioning models usually assume that SOA particles are liquid, but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid-most probably glassy-state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles' ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles. Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.     

Sensitivity analysis of single-angle polarization reflectance observed by satellite

Two channels of the Cloud Aerosol Polarimetric Imager, onboard the TanSat-Chinese carbon dioxide observation satellite, are designed to detect the polarization state of radiation reflected by the earth-atmosphere system in a single-viewing angle. Aiming to understand how the earth and atmospheric parameters affect the polarization state of radiation, we conduct a sensitivity analysis of the polarized reflectance at the top of atmosphere （TOA） with respect to the aerosol microphysical parameters, atmo- spheric profiles, and surface polarization properties. It is found that （1） the TOA polarization reflectance at 0.66 μm is most sensitive to the real part of the aerosol complex refractive index, the mean radius of the fine mode aerosol particles, as well as atmospheric pressure and temperature profiles; （2） the TOA polarization reflectance at 1.64 μm is sensitive to the volume ratio between the coarse mode and fine mode particles as well, but it is not sensitive to atmospheric profiles; and （3） surface polarization properties have a relatively weak influence on the TOA polarization reflectance at both 0.66 and 1.64 μm.     

旱季广州大气中的硝酸盐粒子

利用复合薄膜法和总体分析,对旱季广州大气中的硝酸盐粒子进行了4年的观察.粒子通过一个二级粒子撞击器分为二部分粗大粒子(r>1.0μm)和微小粒子(r≤1.0tm).在电子显微镜下,一个粒子中所含的NO     

氧化铁微粒子表面积和孔径分布的测定

研究了微粒子氧化铁的表面性质,测定并计算了其孔径分布和比表面积。结果表明,用胶体化学法制制备的微粒子氧化铁,以中孔(20～50A)为主,在所测的两种试样中其比表面积分别为290m~2/g和830m~2/g。     

Volcanically emitted sodium chloride as a source for Io's neutral clouds and plasma torus

The atmosphere of Jupiter's satellite Io is extremely tenuous, time variable and spatially heterogeneous. Only a few molecules--SO2, SO and S2--have previously been identified as constituents of this atmosphere, and possible sources include frost sublimation, surface sputtering and active volcanism. Io has been known for almost 30 years to be surrounded by a cloud of Na, which requires an as yet unidentified atmospheric source of sodium. Sodium chloride has been recently proposed as an important atmospheric constituent, based on the detection of chlorine in Io's plasma torus and models of Io's volcanic gases. Here we report the detection of NaCl in Io's atmosphere; it constitutes only approximately 0.3% when averaged over the entire disk, but is probably restricted to smaller regions than SO2 because of its rapid photolysis and surface condensation. Although the inferred abundance of NaCl in volcanic gases is lower than predicted, those volcanic emissions provide an important source of Na and Cl in Io's neutral clouds and plasma torus.     

LHAASO实验中宇宙线次级粒子特性的模拟研究

高海拔宇宙线观测站(LHAASO)位于四川稻城海子山,海拔约4400 m,该实验采用多种手段,对进入大气层的宇宙线粒子进行精确的复合测量.高海拔区域,雷暴天气频繁,广延大气簇射中宇宙线次级粒子的数目、方向和能量都会受到雷暴电场的影响.本文利用Monte Carlo方法,模拟了宇宙线原初粒子进入大气层后的广延大气簇射过程,研究了次级粒子中光子、电子、μ子的纵向分布、横向分布和能量分布.结果表明,在LHAASO探测面,电子的数目比μ子多2～3倍、μ子横向分布范围比电子宽广、μ子的能量比电子大.若在雷暴期间,大气电场对电子(质量小、数目多)的影响将会更加明显.本工作对研究雷暴电场加速宇宙线次级带电粒子的物理机制具有重要意义,同时为理解地面实验的观测现象提供有用信息.     

蒸汽相变与撞击流耦合促进细颗粒物脱除

针对石灰石/石膏法湿式烟气脱硫(WFGD)工艺,考察了WFGD系统对烟气温湿度和细颗粒形貌与元素组成的影响,并分析了相变室中过饱和水汽环境的形成特性;在此基础上,采用蒸汽相变和撞击流耦合的方法,实验研究了撞击流相变室中应用蒸汽相变促进细颗粒物脱除的效果,并与普通蒸汽相变室进行了比较.结果表明:细颗粒经石灰石/石膏法脱硫...     

关于体育院系学风建设中的问题与对策

体育院系学风建设中存在的问题,不是孤立的,而是由多方面因素造成的,对生源的素质,教与学的处理,社会大环境的变化的影响.加强学风建设的具体研究对策:依托班级管理建好班风树立学风,注重师德教育;严谨治学,实施“教考分离”诚信教育,营造良好氛围,培育优良学风;促进学风建设.     

Dispersion characteristics of fine particles in water, ethanol and kerosene

Dispersion behavior of hydrophilic calcium carbonate particles and hydrophobic talcum particles in water, ethanol and kerosene media has been studied by sedimentation analysis. It is found that the dispersion of fine particles complies with the principle of polarity compatibility. That is to say, the dispersion effect will be improved when surface polarity of particles is similar to that of liquid media. The adsorption modets of oleic acid on the surface of particles in water and ethanol are proposed.     

湿法脱硫系统中应用蒸汽相变技术脱除细颗粒

通过在脱硫塔进口烟气、塔内脱硫液进口上方添加适量蒸汽等措施,在湿法烟气脱硫(WFGD)系统中进行了利用蒸汽相变原理高效脱除细颗粒的试验研究.考察了采用CaCO3, Na2CO3, NH3·H2O等3种不同脱硫剂时,WFGD系统对细颗粒的脱除性能及其脱硫剂、蒸汽添加量、液气比(体积比)、脱硫塔进口气液温差等的影响,并进行了添加蒸汽和喷雾化水的对比试验.结果表明,由于形成无机盐气溶胶细颗粒,采用CaCO3, NH3·H2O脱硫剂时,WFGD系统对细颗粒的脱除效果明显差于Na2CO3脱硫剂;在WFGD系统中应用蒸汽相变原理可显著促进细颗粒的脱除,在蒸汽添加量为0.05 kg/m3时,细颗粒数浓度脱除效率可增至60%～70%以上;液气比的影响与脱硫塔内是否存在蒸汽相变有关;提高脱硫塔进口气液温差有利于细颗粒脱除;烟气温度较高时,利用雾化液滴的蒸发替代添加蒸汽也能显著促进细颗粒的脱除.