Particulate content of savanna fire emissions

As part of the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 1991, various aerosol samples were collected at ground level near prescribed fires or under local background conditions, to characterize the emissions of particulate matter from the burning of savanna vegetation. This paper deals with total aerosol (TPM) and carbon measurements. Detailed trace element and polycyclic hydrocarbon data are discussed in other papers presented in this issue.Near the fire plumes, the aerosols from biomass burning are primarily of a carbonaceous nature (C%70% of the aerosol mass) and consist predominantly of submicron particles (more than 90% in mass.) They are characterized by their organic nature (black to total carbon ratio Cb/Ct in the range 3–20%) and their high potassium content (K/Cb0.6). These aerosols undergo aging during their first minutes in the atmosphere causing slight alterations in their size distribution and chemical composition. However, they remain enriched in potassium (K/Cb=0.21) and pyrene, a polycyclic aromatic hydrocarbon, such that both of these species may be used as tracers of savanna burning aerosols. We show that during this period of the year, the background atmosphere experiences severe pollution from both terrigenous sources and regional biomass burning (44% of the aerosol). Daynight variations of the background carbon concentrations suggest that fire ignition and spreading occur primarily during the day. Simultaneous TPM and CO₂ real-time measurements point to a temporal and spatial heterogeneity of the burning so that the ratio of the above background concentrations (TPM/CO₂) varies from 2 to 400 g/kg C. Smoldering processes are intense sources of particles but particulate emissions may also be important during the rapidly spreading heading fires in connection with the generation of heavy brown smoke. We propose emission factor values (EF) for aerosols from the savanna biomass burning aerosols: EF (TPM)=11.4±4.6 and 69±25 g/kg C_{dry plant} and EF(Ct)=7.4±3.4 and 56±16 g C/kg C_{dry plant} for flaming and smoldering processes respectively. In these estimates, the range of uncertainty is mostly due to the intra-fire variability. These values are significantly lower than those reported in the literature for the combustion of other types of vegetation. But due to the large amounts of vegetation biomass being burnt in African savannas, the annual flux of particulate carbon into the atmosphere is estimated to be of the order of 8 Tg C, which rivals particulate carbon emissions from anthropogenic activities in temperate regions.     

贵州中三叠统烂泥沟金矿有机质的初步研究

烂泥沟金矿是以浊积岩为容矿岩石的微细浸染型金矿。有机岩石学分析表明,矿石与围岩中干酪根类型无明显差别,同属腐泥-腐植型。与围岩相比,矿石中干酪根成熟度(R₀=2.74%-3.06%)和含金性(6.15-24.8μg/g)均较高;干酪根总含金量在全岩中所占的比例是围岩高于矿石。氯仿沥青“A”的检测说明,矿石样品中可溶性有机质形成于强还原和高盐度环境,沥青质和含硫有机化合物发育。研究认为,干酪根含金性与碳的活化有关;不饱和的有机基因对金的动一定转换可能具有重要意义。     

我国藻菌生物成因的金矿研究

生物成矿作用分为生物直接成矿作用和生物间接成矿作用,生物直接成矿作用的标志结构为生物有机胶体结构。生物间接成矿作用的标志结构为“矿交代生物”结构,我国陕西二台子－半仓沟金矿,四川东北寨金矿、川甘拉尔玛金矿和云南金厂金矿等均为典型为实例,矿石中普遍含有多种金属矿物生物结构,还含多种生物有机组分。成矿物质具有多源性特征,硫同位素具混合型特征,矿床成型机制可与“人工碳吸附系统”聚金机制相类比,含金层位可     

Interferometric observations of HCN and CN towards carbon stars

Using the IRAM interferometer we have observed four carbon stars (U Cam, CIT6, Y CVn, IRC+40540) in the HCN(J=1 0) and CN(N=1 0) lines. Here we present some results for CIT6 and U Cam.     

Is C/O enhanced in NGC 253?

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.     

Ratios of stable carbon isotopes in some High Arctic plants and lake sediments

¹³C/¹²C ratios for a number of High Arctic vascular plants (51 determinations), mosses (11), and freshwater algae (11) show considerable variation, particularly among the freshwater algae (range from-6.9 to -36.3). In some cases the stable carbon ratios on modern and fossil materials provide guidance as to whether marine waters formerly occupied a given pond or lake basin. In other cases the ¹³C values for algae collected along the present-day shore of a pond or lake bear no relation to the values obtained on constituents preserved within the bottom sediments, suggesting that major changes have occurred in the last few thousand years.Geological Survey of Canada Contribution No. 17291. Contribution No. 41 from the Cape Herschel Project.     

Retailing local food in the Scottish-English borders: A supply chain perspective

Local food is championed as one alternative response to industrial systems of food production and supply. While advocacy for local food is high, there is a lack of empirical evidence about the actual shape and scale of such food supply chains, especially from a retail perspective. Using supply chain diagrams, this paper presents a summary of ‘new’ agro-food geographies for five different retail types—farm shops, butchers, caterers, specialist shops, supermarkets/department stores—that all source local food from suppliers in the Scottish-English borders. Presented as five separate ‘shopping trips’, the paper examines where, how and why retailers source local food. Results reveal the complex nature of local food systems, especially in terms of intra-sector competitive dynamics (with a notable tension between direct forms of retail and established (independent) retailers), links and overlaps with ‘normal’ food retail systems and elastic notions of the ‘local’. The paper also draws a key distinction between locally produced and locally supplied food products.     

An electrochemical study of pyrite oxidation in the presence of carbon coatings in cyanide medium

The anodic and cathodic behaviour of pyrite with clay and different carbon coatings of activated carbon, graphite and carbonaceous matter in cyanide medium was investigated using the potentiodynamic method. The presence of clay coating did not change the polarisation curve appearance for either the anodic oxidation of pyrite or the cathodic reduction of oxygen or the potential of the current plateau, but only decreased the plateau current especially at a higher coating thickness. The presence of the carbon coatings marginally shifted the rest potential for pyrite to a more anodic position and slightly changed the polarisation curve appearance for pyrite oxidation. The current density for pyrite oxidation largely increased in the presence of the carbon coatings, the potential at the plateau shifted to more cathodic positions, and the plateau width became smaller. These effects became more noticeable at a higher coating thickness. The activated carbon, graphite and carbonaceous matter coatings performed similarly in affecting pyrite oxidation at a similar thickness. The carbon coatings significantly increased the limiting current densities for oxygen reduction on pyrite, and the limiting current plateau became steeper at a higher coating thickness. The carbon coatings increased the limiting current density for oxygen reduction to a similar extent at a low coating thickness, but increased to varied extents at a higher coating thickness. The carbon coatings also greatly increased the cathodic current density for gold reduction on pyrite. The enhancement of pyrite oxidation and oxygen or gold reduction on pyrite by the carbon coatings was likely attributed to the electrochemical interaction between pyrite and the carbon materials with electron-rich surfaces and high conductivity. The presence of the carbon coatings significantly increased the oxidation of pyrite in aerated cyanide solutions and the preg-robbing of pyrite especially at a higher coating thickness.     

The effects of carbon dioxide leakage on fractures, and water quality of potable aquifers during geological sequestration of CO2

Since industrial revolution, the ＂greenhouse effect＂ is one of the most important global environmental issues. Of all the greenhouse gases, CO2 is responsible for about 64% of the enhanced ＂greenhouse effect＂, making it the target for mitigation, so reducing anthropogenic discharge of carbon dioxide attracts more and more attention. Geological sequestration of CO2 in deep saline aquifers is one of the most promising options. But because unknown fractures and faults may exist in the caprock layers which can prevent the leakage of CO2, CO2 will leak upward into upper potable aquifers, and lead to adverse impacts on the shallow potable aquifers. In order to assess the potential effect of CO2 leakage from underground storage reservoirs on fractures and water quality of potable aquifers, this study used the non-isothermal reactive geochemical transport code TOUGHREACT developed by Xu et al to establish a simplified 2-D model of CO2 underground sequestration system, which includes deep saline aquifers, caprock layers, and shallow potable aquifers, and study and analyze the changes of mineral and aqueous components. The simulation results indicated that the minerals of deep saline aquifers and fractures should be mainly composed of aluminosilicate and silicate minerals, which not only enhance the mass of CO2 sequestrated by mineral trapping, but also decrease the porosity and permeability of caprock layers and fractures to prevent and reduce CO2 leakage. The results from deep saline aquifers showed that the mass of carbon dioxide trapped by minerals and solution phases is limited, the rest remained as a supercritical phase, and so once the caprock aquifers have some unknown fractures, the free carbon dioxide phase may leak from CO2 geologic sequestration reservoirs by buoyancy.     

Correlations in aftershock and seismicity patterns

Correlations in space and time play a fundamental role in earthquake processes. One direct manifestation of the effects of correlations is the occurrence of aftershocks due to the stress transfer in the vicinity of a main shock. Less obvious and more speculative changes in correlations may occur in the background seismicity before large earthquakes. Using statistical physics it is possible to introduce a measure of spatial correlations through a correlation length. This quantity characterizes how local fluctuations can influence the occurrence of earthquakes over distances comparable with the correlation length. In this work, the physical basis of spatial correlations of earthquakes is discussed in the context of critical phenomena and the percolation problem. The method of two-point correlation function is applied to the seismicity of California. Well defined variations in time of the correlation length are found for aftershock sequences and background seismicity. The scaling properties of our obtained distributions are analyzed with respect to changes in several scaling parameters such as lower magnitude cutoff of earthquakes, the maximum time interval between earthquakes, and the spatial size of the area considered. This scaling behavior can be described in a unified manner by utilizing the multifractal fit. Utilizing the percolation approach the time evolution of clusters of earthquakes is studied with the correlation length defined in terms of the radius of gyration of clusters. This method is applied to the seismicity of California.