A preliminary methods comparison for measurement of dissolved organic nitrogen in seawater

Routine determination of dissolved organic nitrogen (DON) is performed in numerous laboratories around the world using one of three families of methods: UV oxidation (UV), persulfate oxidation (PO), or high temperature combustion (HTC). Essentially all routine methods measure total dissolved nitrogen (TDN) and calculate DON by subtracting the dissolved inorganic nitrogen (DIN). While there is currently no strong suggestion that any of these methods is inadequate, there are continuing suspicions of slight inaccuracy by UV methods.This is a report of a broad community methods comparison where 29 sets (7 UV, 13 PO, and 9 HTC) of TDN analyses were performed on five samples with varying TDN and DIN concentrations. Analyses were done in a “blind” procedure with results sent to the first author. With editing out one set of extreme outliers (representing 5 out of 145 ampoules analyzed), the community comparability for analyzing the TDN samples was in the 8–28% range (coefficient of variation representing one standard deviation for the five individual samples by 28 analyses). When DIN concentrations were subtracted uniformly (single DIN value for each sample), the comparability was obviously worse (19–46% cv). This comparison represents a larger and more diverse set of analyses, but the overall comparability is only marginally better than that of the Seattle workshop of a decade ago. Grouping methods, little difference was seen other than inconclusive evidence that the UV methods gave TDN values for several of the samples higher than HTC methods. Since there was much scatter for each of the groups of methods and for all analyses when grouped, it is thought that more uniformity in procedures is probably needed. An important unplanned observation is that variability in DIN analyses (used in determining the final analyte in most UV and PO methods) is essentially as large as the variability in the TDN analyses.This exercise should not be viewed as a qualification exercise for the analysts, but should instead be considered a broad preliminary test of the comparison of the families of methods being used in various laboratories around the world. Based on many independent analyses here, none of the routinely used methods appears to be grossly inaccurate, thus, most routine TDN analyses being reported in the literature are apparently accurate. However, it is not reassuring that the ability of the international community to determine DON in deep oceanic waters continues to be poor. It is suggested that as an outgrowth of this paper, analysts using UV and PO methods experiment and look more carefully at the completeness of DIN conversion to the final analyte and also at the accuracy of their analysis of the final analyte. HTC methods appear to be relatively easy and convenient and have potential for routine adoption. Several of the authors of this paper are currently working together on an interlaboratory comparison on HTC methodology.     

Estimating the Sampling Uncertainty for the Analysis of Solid Refused Fuel

Uncertainty assessment of the parameters used for the reporting in the emissions trading system (ETS) to characterize fuels includes not only the processes in a laboratory but has to be expanded for inclusion of sampling and sample preparation. Analysis of variance was used to allocate the contributing uncertainties to the steps described. Apart from some specific results for sampling methods, it was observed that the uncertainty of sampling was in the same order of magnitude than the analytical and the sample preparation error. Several measures to enhance quality assurance in sampling and sample preparation could be derived from specific results. The results were used in the European Monitoring and Reporting Regulation, which set out the requirements for ETS. Sampling and sample preparation have to be included in uncertainty assessment as well as sampling procedures and sampling plans (including quality assurance) have to be agreed upon by the laboratories, carrying out the analytics of those samples.     

高超声速风洞进气道流量系数测量精度影响因素研究

进气道是飞行器动力装置的重要组成部分,准确测量进气道流量系数是进气道风洞试验的重要内容。对来流马赫数Ma=4.5,5.0和6.0状态下皮托管进气道开展流量系数测量研究,通过对比理论值和实测值,获取各状态流量系数修正系数。试验结果表明,随着来流马赫数增加,进气道流量系数与理论值偏差较明显,并逐渐增大。超声速风洞试验通常认为测量截面总温与来流总温相等,通过对测量截面总温与来流总温偏差以及测量截面流场畸变情况的分析,判断测量偏差主要是由测量截面总温等于来流总温的假设导致的。在高超声速风洞试验中,由于模型壁面热交换的存在,测量截面总温低于来流总温,进气道流量系数测量时需要进行总温修正,以提高流量测量精度。      

南昌市PM2.5中稳定碳同位素组成特征

近几年,PM2.5浓度上升导致灰霾事件频繁发生,已经引起了广泛的关注。碳组分是PM2.5中的重要组分,被认为是灰霾形成和转化的重要因素,因此,研究PM2.5中含碳组分的来源及其化学过程具有重要的意义。本研究于2016年12月至2017年8月期间在南昌地区共采集105个PM2.5样品,分析了PM2.5样品中总碳(TC)浓度及其碳同位素(δ^13C)。结果表明,采样期间TC的年平均浓度为(12.1±2.1)μg/m^3,总体上呈现冬季高、夏季低的变化趋势,可能是受不同季节气象因素和来源变化的影响。δ^13C的年平均值为(?26.1±0.2)‰,总体上呈现冬季高、春季低的变化趋势,可能是受不同来源的影响。利用贝叶斯模型计算南昌地区PM2.5中TC主要来源于C3植物燃烧和机动车尾气,年源贡献分别为49.3%和28.7%;其次是煤燃烧和C4植物燃烧,年源贡献分别为17.7%和4.2%。春季δ^13C值偏低是由于C3植物燃烧贡献相对较高,而冬季δ^13C值偏高则是煤燃烧贡献增加。     

基于模糊综合评判的煤自燃发火倾向性研究

自燃发火倾向性是煤自燃火灾的主要影响因素之一。通过对国内外煤自燃倾向性鉴定方法的分析, 指出了我国现行的煤自燃倾向性的不足之处。根据煤自燃机理的煤、氧复合理论,建立了依据煤在低温氧化过程中的吸氧率、放热强度和着火燃烧阶段的活化能作为鉴定煤自燃发火倾向性影响因素的模糊综合评判新方法。在此基础上,用热重分析方法测试了5种煤样在相同条件的指标参数,建立模糊综合评判模型,通过模糊运算得出评判5种煤样自燃发火倾向性的综合指标。验证表明,该方法有较强的实用性,其评判结果与5种煤样的实际自燃发火期趋势一致。      

燃煤过程中有害元素转化机理研究进展

综述了煤中有毒、有害元素经燃烧之后的存在形式与去向,元素在燃烧过程中的热解释放行为及其转化机理;强调煤中无机组分为主要存在许多有毒、爱元素在燃烧过程中会释放出来,然后再分异扩散到各种燃烧产物之中,地民人体廷民危害;指出今后研究不仅限于煤中有毒、有害元素的形成机理,更应侧重对燃烧产物中毒、有害元素的分异与去除方法作进一步的研究与试验,力求使燃煤对环境与人体健康产生的危害降低到最低程度。     

Comprehensive Combustion Performances of Water Hyacinth and Pistia stratiotes Pellet Fuels

For efficient combustion of aquatic biomass, the effects of heating rate on the combustion and dynamic characteristics of two typical aquatic species (water hyacinth, Pistia stratiotes), and the effects of temperature and additives on ash K and Cl concentrations are studied. The two types of pellets have ignition temperatures of 252.7 and 250.3 °C, respectively. At a heating rate of 10 °C min⁻¹, where combustion is most stable, the comprehensive combustion efficiencies reach their maximum at 4.7 × 10⁻⁶ and 2.2 × 10⁻⁶ mg²min⁻¹°C⁻², respectively. The K and Cl concentrations in the ash decrease steadily with increasing temperature, falling to 10.3% and 0.41% for water hyacinth and 11.1% and 1.85% for P. stratiotes, respectively. X-ray diffraction (XRD)shows that abundant Ca minerals form in the ash after the addition of CaO, which inhibit KCl formation, and K and Al silicates form in the ash after the addition of kaoline, which reserve K in the ash. These findings provide a starting point for the development of efficient aquatic biomass combustion.     

Comparison of HTC method and UV/persulphate method to determine colloidal organic carbon in seawater

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Relations between Light Hydrocarbon, Carbon Monoxide, and Carbon Dioxide Concentrations in the Plume from the Combustion of Plant Material in a Furnace

To systematically explain relations between light hydrocarbons, CO, and CO₂ concentrations/emissions of biomassburning, we measured concentrations/emissions of carbon gases – CO,CO₂, light hydrocarbons (CH₄, C₂H₆,C₂H₄, C₂H₂, C₃H₈, C₃H₆,n-C₄H₁₀, i-C₄H₁₀, n-C₅H₁₂,i-C₅H₁₂), and THC (total hydrocarbon) – in the burning of dead plant material, mainly Imperata grass, byclosed-chamber experiments and by time-series analyses of gas concentrations in combustion plumes in relatively efficient and inefficient combustion situations. Concentrations of hydrocarbons measured were well correlated to [CO] although [C₂H₂] was exceptionally well correlated to[CO₂]. The phase diagrams (relation between [CO]/ [CO₂] and [hydrocarbon]/ [CO₂]) obtained by the time-seriesexperiments well illustrated the variation in the overall emission rates of the closed-chamber experiments. The higher rates of decrease in hydrocarbon concentration with increasing carbon number in the efficient case compared with the inefficient case probably reflected the rate of oxidation and the amount of radicals. The overall concentrations (or emissions) of C₂H₄ and C₃H₆ were higher thanthose of C₂H₆ and C₃H₈, suggesting a linkage to mechanisms in whichthe predominant path of hydrocarbon oxidation is through the degradation of alkyl radicals, which can be immediately converted into or formed from alkenes. For C₃ and C₄ species, normal-chain species hadhigher emissions than iso-chain species under lower combustion efficiency. This may be attributable to the presence of tertiary C–H bonds in iso-species,which show more reactivity in the abstraction of H than secondary C–H bonds unless the carbon number is large.     

Chemical characteristics of fine particles during spring dust storm dominant period in two Chinese cities, Baotou and Wuwei

Mineral dust, including dust storm, fugitive and floating dust are the most important components of ambient aerosol in northern China during spring. Meanwhile, it goes through heating period when fossil fuel combustion acts as a dominant source. In order to understand the chemical characteristics of fine particles in North China, two sampling sites was established in Baotou City in the west of Inner Mongolia Autonomous Region and Wuwei City near the edge of Gobi to collect fine particles （PM 2.5） samples in the spring of 2004 and 2005, and analyze mass concentrations, ionic species and some element components of PM 2.5. The results indicated that dust events elevated the mass concentrations of particulate matter significantly, not only for coarse particles, but also for fine particles. Crustal components, organic matter and sulfates are three major compositions in fine particles, their mass concentrations and relative abundances are closely related with the frequency of dust events and coal combustion. The characteristics of fine particles are obviously diverse under different atmospheric conditions. （1） When the dust storms take place, the wind speeds are often higher than 10 m/s. A plenty of mineral aerosol is input from long distance, and also local soil dust is blown up to suspend in the air as particles. Therefore, the concentrations of PM 2.5 are enhanced dramatically. Mass concentrations and relative percentages of crustal components in PM 2.5 increased significantly during dust events. The mineral dust may help gas to particle conversation by heterogeneous reactions. Increases in mass concentrations of SO4^2-, NO3^- and NH4^＋ and organic matter in PM 2.5 were observed evidently. But their fractions in PM 2.5 do not increase simultaneously due to dilution of storing wind. （2） When wind velocity is lower （〈3 m/s）, air pollutants are accumulated, both mass concentrations of SO4^2-, NO3^- and NH4^＋ and organic matter, and their fractions in PM 2.5 increase, indicating severe anthropogenic pollution. The chemical characteristics of PM 2.5 in Baotou and Wuwei are also influenced by their industrial structure, topography and meteorological conditions.