首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
The characterisation of aggregates, like soot, firstly requires the determination of the size distribution of the primary particles. The primary particle size of combustion generated aggregates depends upon the combustion environment and the formation conditions, such as temperature, pressure and fuel-to-air ratio, among others. Since the combustion characteristics are different in the different types of burners, the characterisation of primary particles may offer the possibility to distinguish soot from different sources. In this paper, we present the signature of the primary particles and the aggregates of soot emitted by cars using diesel or biodiesel, by domestic heating, and by aircraft exhausts, which can be considered as the major sources as derived from measurements on transmission electron micrographs. The size distributions of all aggregates types with different aerodynamic diameter were log-normal and quasi-monodisperse. The size distribution of the primary particles for soot emitted by different sources showed minor differences. However, a comparison between the diameter of the primary particles and those obtained using a standard method for carbon black revealed discrepancies. The median diameter of the primary particles was combined with the median number of primary particles in an aggregate to calculate the relative particle surface area available for adsorption. In a similar way, the relative specific surface area was determined. The surface area was measured using the Brunauer-Emmett-Teller (B.E.T.) nitrogen adsorption method and the relative surface area available for adsorption was calculated.  相似文献   

2.
Combustion-derived particles emitted by various transport engines are analyzed with respect to their morphology and composition. Soot particles collected behind an aircraft gas turbine engine combustor, in the diesel engine exhaust pipe, and at the end of ship pipe demonstrate heterogeneous morphological structures and different chemical identities. Individual particle analysis allows the characterization of emitted soot particles into three fractions, namely C-O, C-O-S, and Fe-C-O, with the dominant presence of chain soot agglomerates, irregular internally mixed soot, and particles of distinct morphology, respectively. The influence of oxygen and sulfur concentrations on the ability of soot to uptake water is proposed as a method for categorizing transport engine-generated particles. Categories of hydrophobic and hydrophilic particles within non-hygroscopic soots can be defined based on the amount of water uptake relative to several reference laboratory-made soots comparable to transport engine emissions. This method of characterizing hydrophobic/hydrophilic and hygroscopic soots in combustion emissions will help to determine the potential impacts of the combustion emissions on CCN/IN formation in the atmosphere.  相似文献   

3.
Samples of airborne PM2.5 particles in Guangzhou urban area were collected during the autumn of 2006 and the spring of 2007. The morphologies and elemental compositions of individual particles were determined by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometer (SEM-EDX). The obtained images were further analyzed for size distribution by an image analysis system. Based on the morphology, particles in PM2.5 were classified into four groups: soot aggregates, minerals, fly ash and others. The amount of soot aggregates and minerals were higher than that of fly ashes. The distributions of particles by number and size in two seasons were bimodal with 90% less than 1.0 μm in diameter. The primary peak from the autumn samples was in the size range of 0.4 ~ 0.5 μm, and 0.3 ~ 0.4 μm for the spring samples. More soot aggregates (36.1%) and minerals (61.5%) were found than fly ash (2.4%) in autumn, but soot aggregates (89.9%) was the dominant particle type in spring. The size distribution of particles according to the volume was generally opposite to that according to the number. Particles less than 1.0 μm were as high as 89.5% in number but contributed only 18.9% in volume, indicating that fine particles contributed relatively little in volume although existing in large numbers.  相似文献   

4.
More than 3000 water droplets with soot particles immersed were monitored individually to identify the effect of heterogeneous freezing and establish the link between soot properties and freezing efficiency. A set of soot samples from many combustion sources, including an aircraft engine combustor were examined. The list of key soot properties affecting freezing were determined. It appears that soot effectiveness in causing the droplets to freeze mainly depends on the soot behaviour in water defined by the mass density of soot agglomerates, size and wetting. When large mass particles were homogeneously distributed through droplets and were stable to sedimentation effects median freezing temperatures of such droplets were significantly warmer than pure water droplets. The long-term presence of large soot agglomerates in water leads to an increase in the freezing efficiency over time because of the slow kinetics of wetting. Small sizes of soot agglomerates stimulate aggregative instability in droplets with large soot mass which decreases the total soot surface area and the freezing temperature. The highest freezing efficiency is found for homogeneously distributed soot agglomerates of high porosity. A gradual increase of the freezing temperature in correspondence with number density of active oxygen-containing sites is observed for soots having surfaces of low or intermediate polarity. However, highly soluble surface compounds, such as sulfates, may be easily dissolved in water leading to a decrease in the potential freezing efficiency. This was the case found for aircraft engine combustor generated soot. Therefore relatively hydrophobic soot with a significant number of oxygen-containing functional groups but not covered totally by hydrophilic sites and soluble compounds is proposed to act as the most efficient immersion freezing nuclei in the atmospheric cloud droplets.  相似文献   

5.
Size, morphology, microstructure, chemical composition and hygroscopic properties of aircraft engine combustor (AEC) soot particles are studied by using a combination of several methods, namely atomic force microscopy, transmission electron microscopy, gravimetry, ionic chromatography analysis and wetting observations. From the microstructure and the composition of soot agglomerates, we find that we can separate AEC soot in two fractions having quite different physico-chemical properties: a main fraction of particles containing essentially amorphous carbon with small amounts of oxygen, sulfur and iron and a fraction of impurities characterized by various structures and a large amount of impurities. These properties of aircraft engine combustor soot are compared to those of soot obtained by burning TC1 aviation kerosene in a laboratory burner. It is shown that TC1 soot can be a good surrogate of the AEC main fraction. Such a finding allows us to perform water uptake measurements and to conclude that the AEC main fraction is rather hydrophobic whereas the AEC fraction of impurities is highly hydrophilic The ability of the two fractions of aircraft engine combustor soot to act as cloud condensation nuclei is discussed with respect to their implication in contrail and cirrus formation.Associated to Université de la Méditerranée (Aix-Marseille II) and to Université Paul Cézanne (Aix-Marseille III)  相似文献   

6.
The effect of temperature (296–238 K) on the reaction of combustion soot (n-hexane) with ozone at low concentration (6–8 ppm) has been measured. Long optical path FTIR spectroscopy has revealed the rate law for ozone loss beyond initial stages, second order in O3, to be the same over this range of conditions. The reaction rate is 3.5 times lower at 238 K than at 296 K, and reveals an activation energy of 12.9 ± 0.5 kJ mol–1. The effect of humidity on the reaction has been estimated using its recently determined rate law dependence (p0.2). These data, differing from O3 reaction kinetics obtained from other types of carbonaceous particles used as surrogates for atmospheric soot, have implications for the role of combustion soot in atmospheric chemistry. Any involvement of aircraft soot in ozone depletion near the tropopause, for example, should be estimated using these temperature and humidity dependences.  相似文献   

7.
The dependence of specific properties of black carbon (BC) soots on fuel type and combustion conditions has been studied, and the effects of these properties on soot particle hydration and reaction with ozone determined. Series of soots were prepared from n-hexane, diesel and JP8 aircraft fuels, utilizing a flow combustion system designed for accurate control of the air/fuel ratio in premixed flames. It has been shown that, for each of these, linear relationships exist between the state of soot surface oxidation, surface area, unpaired electron spin density, and air/fuel ratio. The interrelationship of these properties potentially enables the preparation of soots with pre-selected characteristics by establishing combustion conditions for each fuel type. Predictable variations in these soot characteristics have been demonstrated through preparations near sea level and at higher elevation. Soot hydration and its reactivity with ozone are quantitatively related to surface oxidation and, thus, the air/fuel combustion ratio for soot's formation in premixed flames. The effect of relative humidity (RH) on the soot-ozone reaction over the O3 concentration and RH ranges 2–4.8 ppm and17–78%, respectively, is expressed by–d[O3]/dt =k[O3]2[H2O]0.2and is directly related to particle surface oxidation.  相似文献   

8.
The authors studied the size distributions of particles at an altitude of 2000 m by aircraft observation over eastern costal areas of China from Zhuhai, Guangdong to Dalian, Liaoning (0.3,7-30μm, 57 channels,including number concentration distribution, surface area concentration distribution and mass concentration distribution). In these cities, the average daily concentrations of PM10 are very high. They are among the most heavily polluted cities in China. The main pollution sources are anthropogenic activities such as wood, coal and oil burning. The observed size distributions show a broad spectrum and unique multi-peak characteristics, indicating no significant impacts of individual sources from urban areas. These results are far different from the distribution type at ground level. It may reflect the comprehensive effect of the regional pollution characteristics. Monitoring results over big cities could to some extent reflect their pollution characteristics.  相似文献   

9.
Characterizations of urban and regional sources of particulate matter (PM) were performed in the Milan area (North of Italy) during Föhn and stagnant (non-Föhn) conditions. The measurements were performed at two different places: in an urban area North of Milan (Bresso) and in a regional area at the EMEP-GAW station in Ispra (about 65 km NW from Milan) during the winter periods of the years 2002–2007. Particle size distributions and chemical bulk analysis of aerosols are combined with single particle mass spectrometry to obtain information about the chemical content of the particles and their mixing state. Föhn conditions are characterized by extremely clean background air from which background aerosol is scavenged, and consequently local sources (here defined as sources between the sampling sites and the mountain range top about 100–150 km away depending on the wind direction) determine the aerosol properties.It was observed that during Föhn events the accumulation mode in the size range 50 nm < d < 300 nm practically disappears and that the size fraction below 50 nm dominates the total number distribution. The significant change in the number size distribution and the large decrease in PM10 mass during Föhn events are accompanied by a significant change in the chemical composition of the particles. Results from bulk chemical analysis showed high amounts of carbonaceous compounds and very low concentrations of ammonium nitrate (as indicator for secondary chemistry) during Föhn episodes, in contrast to stagnant conditions, when secondary components are dominating the aerosol composition. Single particle measurements confirm the high contribution of carbonaceous compounds in locally emitted particles.It was concluded that particles that originated in the urban area come mainly from combustion processes, especially direct traffic emissions, domestic heating and industrial activities, whereas the regionally emitted particles are different with much less traffic contribution.We estimate that under prevailing (non-Föhn) winter conditions, about 50–65% of the aerosol mass load in the city of Milan are caused by local emissions, and about 35–50% come from regional background. This finding suggests that in order to improve air quality in a big city like Milan, it is important to combine local traffic restriction interventions with other long-term regional scale air-quality-measures.  相似文献   

10.
《Atmospheric Research》2009,91(2-4):159-169
Characterizations of urban and regional sources of particulate matter (PM) were performed in the Milan area (North of Italy) during Föhn and stagnant (non-Föhn) conditions. The measurements were performed at two different places: in an urban area North of Milan (Bresso) and in a regional area at the EMEP-GAW station in Ispra (about 65 km NW from Milan) during the winter periods of the years 2002–2007. Particle size distributions and chemical bulk analysis of aerosols are combined with single particle mass spectrometry to obtain information about the chemical content of the particles and their mixing state. Föhn conditions are characterized by extremely clean background air from which background aerosol is scavenged, and consequently local sources (here defined as sources between the sampling sites and the mountain range top about 100–150 km away depending on the wind direction) determine the aerosol properties.It was observed that during Föhn events the accumulation mode in the size range 50 nm < d < 300 nm practically disappears and that the size fraction below 50 nm dominates the total number distribution. The significant change in the number size distribution and the large decrease in PM10 mass during Föhn events are accompanied by a significant change in the chemical composition of the particles. Results from bulk chemical analysis showed high amounts of carbonaceous compounds and very low concentrations of ammonium nitrate (as indicator for secondary chemistry) during Föhn episodes, in contrast to stagnant conditions, when secondary components are dominating the aerosol composition. Single particle measurements confirm the high contribution of carbonaceous compounds in locally emitted particles.It was concluded that particles that originated in the urban area come mainly from combustion processes, especially direct traffic emissions, domestic heating and industrial activities, whereas the regionally emitted particles are different with much less traffic contribution.We estimate that under prevailing (non-Föhn) winter conditions, about 50–65% of the aerosol mass load in the city of Milan are caused by local emissions, and about 35–50% come from regional background. This finding suggests that in order to improve air quality in a big city like Milan, it is important to combine local traffic restriction interventions with other long-term regional scale air-quality-measures.  相似文献   

11.
We used both a conventional transmission electron microscope and an environmental transmission electron microscope (ETEM) to determine morphology, composition, and water uptake of 80 individual aerosol particles collected from the young smoke of flaming and smoldering fires during SAFARI-2000, a comprehensive air quality campaign in southern Africa. Six representative carbonaceous particle types are described, including soot, tar balls, and heterogeneously internally mixed particles containing C with S-, K-, Mg- or Na-rich inorganic phases. The hygroscopic behavior of these particles over the range 0–100% relative humidity (RH) was studied in detail. Soot and tar balls did not take up water, whereas the mixed organic–inorganic particles took up water between 55 and 100% RH, the exact value depending on the composition of their water-soluble phases. The inorganic phase appeared to determine the hygroscopic properties of all mixed organic–inorganic particles. Thus, incorporation of inorganic plant material or reactions with inorganic atmospheric components can dramatically alter the hygroscopic properties of carbonaceous particles in smoke plumes. The fraction of these mixed organic–inorganic particles plausibly increases with time, which will modulate the effects of smoke on radiative budgets.  相似文献   

12.
天津市总悬浮颗粒物浓度分布的数值模拟   总被引：5，自引：1，他引：4  
根据天津市总悬浮颗粒物的监测结果,用化学元素质量平衡法对监测点总悬浮颗粒物的来源进行了解析,简要介绍了天津市空气污染数值预报实验中总悬浮颗粒物的预报方法及其预报结果。  相似文献   

13.
Source attribution of urban smog episodes caused by coal combustion   总被引：1，自引：0，他引：1  
Stable weather conditions together with extensive use of coal combustion often lead to severe smog episodes in certain urban environments, especially in Eastern Europe. In order to identify the specific sources that cause the smog episodes in such environments, and to better understand the mixing state and atmospheric processing of aerosols, both single particle and bulk chemical characterization analysis of aerosols were performed in Krakow, Poland, during winter 2005.Real-time measurements of the bulk PM10 aerosol during a severe smog episode (PM10 mass > 400 µg m− 3) showed a stable concentration of black carbon in the aerosol, and an increase in the sulphate and chlorine mass contributions towards the end of the episode. Chemical characterization of single particles further helped to identify residential coal burning as the main source that caused this severe smog episode, consisting of single particles with major signals for carbon with simultaneous absence of sulphate, chlorine and calcium. Particles from industrial coal combustion gained importance towards the end of that episode, after residential coal combustion was switched off, indicated by an increase of the percentage of sulphate and chlorine containing particles. Traffic was not a significant source during the severe smog episode. During a lighter smog episode, residential and industrial coal combustion was still predominant, with an increased contribution of traffic and processed/aged aerosols. On a clean day, particle classes containing nitrate were the most abundant. In addition, the aerosol was more internally mixed showing that there were more sources contributing to the total aerosol population.  相似文献   

14.
北京地区PM2.5的成分特征及来源分析   总被引：12，自引：0，他引：12       下载免费PDF全文
选用2003—2004年初PM2.5连续观测资料，统计分析了北京地区PM2.5的特征、PM2.5与PM10以及PM2.5与地面气象要素的相互关系。结果表明:四季中夏季PM2.5浓度最低，冬、春两季浓度较高。PM2.5与PM10比值平均为0.55，非采暖期两者比值为0.52，采暖期两者比值为0.62；夏季该比值主要分布在0.3~0.6之间，春、秋两季该比值分布在0.3~0.8之间，冬季采暖期该比值分布在0.4~0.9之间。PM2.5与PM10比值日变化与气象条件日变化、人们日常生活习惯密切相关，沙尘天气和交通运输高峰期扬起地面粗颗粒物会导致PM2.5在PM10中的比例下降，而冬季取暖以及夏季光化学反应则会引起PM2.5的比例升高。PM2.5的浓度与地面气象要素中本站气压、相对湿度和风速有很好的的相关性，与气温的相关性较差。SO42-，NO3-和NH4+为北京地区PM2.5中主要离子。PMF源解析方法确定了北京地区5类细粒子污染源，分别是:土壤尘、煤燃烧、交通运输、海洋气溶胶以及钢铁工业。  相似文献   

15.
Hygroscopicity measurements of secondary organic aerosol (SOA) particles often show inconsistent results between the supersaturated and subsaturated regimes, with higher activity as cloud condensation nucleus (CCN) than indicated by hygroscopic growth. In this study, we have investigated the discrepancy between the two regimes in the Lund University (LU) smog chamber. Various anthropogenic SOA were produced from mixtures of different precursors: anthropogenic light aromatic precursors (toluene and m-xylene), exhaust from a diesel passenger vehicle spiked with the light aromatic precursors, and exhaust from two different gasoline-powered passenger vehicles. Three types of seed particles were used: soot aggregates from a diesel vehicle, soot aggregates from a flame soot generator and ammonium sulphate (AS) particles. The hygroscopicity of seed particles with condensed, photochemically produced, anthropogenic SOA was investigated with respect to critical supersaturation (sc) and hygroscopic growth factor (gf) at 90% relative humidity. The hygroscopicity parameter κ was calculated for the two regimes: κsc and κgf, from measurements of sc and gf, respectively. The two κ showed significant discrepancies, with a κgf /κsc ratio closest to one for the gasoline experiments with ammonium sulphate seed and lower for the soot seed experiments. Empirical observations of sc and gf were compared to theoretical predictions, using modified Köhler theory where water solubility limitations were taken into account. The results indicate that the inconsistency between measurements in the subsaturated and supersaturated regimes may be explained by part of the organic material in the particles produced from anthropogenic precursors having a limited solubility in water.  相似文献   

16.
利用机载云粒子探测设备入云进行观测是目前获取云粒子微物理特征最直接有效的手段。国内已有多家单位引进美国DMT（Droplet Measurement Technologies）公司的云粒子图像探头CIP（cloud imaging probe）。由于其配套软件不能输出逐个粒子的详细信息,在很大程度上限制了对云粒子图像探测数据的深入挖掘和分析。基于解析粒子图像原始数据,对粒子图像数据进行质量控制,并根据粒子形状几何特征将粒子形状分为8类（微小、线状、聚合状、霰状、球状、板状、枝状和不规则状）。利用2018年12月—2019年3月河南省3次冬季航测获取的灰度CIP探测数据,分析云粒子形状及各形状粒子面积的统计特征,并对比基于不同形状粒子的质量-尺度关系与将所有粒子视作球形液滴计算所得的粒子水凝物含量,发现后者超过前者约1个量级。  相似文献   

17.
为探究贵州省威宁地区雹暴过程中雹胚粒子的演变特征,本文在对X波段双线偏振雷达数据经过退折叠、滤波、自适应衰减订正后,运用Barnes插值方法对偏振参量进行插值,并结合模糊逻辑算法进行水成物粒子识别,然后对威宁县的两次典型雹暴过程进行了系统的分析,得到以下结论:(1)两次过程中高密度霰的来源均为冰晶聚合物和冻滴,低密度霰...  相似文献   

18.
In order to predict wind loading on trees (canopy height h) in partially harvested forests, it is necessary to characterize air flow and momentum transfer in progressively more complex patterns where groups of trees (or aggregates) are retained. In this study, we used large-eddy simulation to explore the effects of aggregate size, inter-aggregate spacing, and the ratio between the aggregate size and inter-aggregate spacing on air flow and momentum transfer. Forty-five grid points across an aggregate were needed to achieve an adequate level of turbulence. Using grid sizes of h/15 throughout was too viscous for the smaller aggregates. Vertical and horizontal flow deflection by the leading aggregates sheltered some of the downstream aggregates to varying degrees where turbulence increased for subsequent rows. The number of rows of protected aggregates decreased as aggregate dimensions and the space between aggregates increased. A theoretical treatment of time-dependent wind is presented for the lead aggregate and a simulation case is presented for the case of a gust of reduced wind passing through the aggregate pattern. The leading aggregate responded with decreasing moment for decreasing ambient wind speed as predicted by theory. However, downwind aggregates experienced substantial increases in bending moment. The overall results of the disruptive aspects of time dependence agrees with arguments regarding the role of irrotational (potential) flow to this problem. Our treatment of retention pattern design is only a first step and further research suggestions are presented.  相似文献   

19.
2004年北京秋季大气颗粒物的化学组分和来源特征   总被引：1，自引：0，他引：1  
2004年9月在北京城区进行了大气颗粒物采样,样品用PIXE方法进行了分析,得到了20种元素的浓度及其谱分布。并对北京颗粒物的谱分布、富集因子和来源进行了分析研究。发现K元素浓度分布呈细粒态单峰谱分布,细粒态K富集因子较高,表明了生物质燃烧的主要贡献。因子分析结果还表明,土壤尘、生物质燃烧、煤烟尘、工业源和汽车尾气排放源对秋季北京局地排放源有明显贡献。  相似文献   

20.
利用常规高空和地面气象观测资料、湘潭市空气质量监测数据并结合HYSPLIT4后向轨迹模式对2020年10月28-31日污染天气特征及成因进行分析。结果表明此次污染过程分为3个阶段:第1阶段为北方偏二次型传输阶段,此阶段北风风力较大,在强北风的推动下华北地区污染物(PM2.5)向南传输影响湘潭;第2阶段为大气高湿静稳条件下本地源(工业源、移动源、扬尘源、生物质燃烧源)排放累积阶段,此阶段地面转均压场,整层大气湿度接近饱和并出现弱降水,气态污染物在污染过程中发生二次转化,颗粒物吸湿增长,且近地面出现逆温,不利于污染物的垂直扩散,导致边界层内的污染物不断累积,污染加重,推高了湘潭的PM2.5浓度峰值;第3阶段为污染物缓慢清除阶段,随着新一波冷空气影响湘潭地区,水平扩散条件逐步改善,且上游空气质量优良,本地污染物得到有利扩散,此次污染过程结束。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号