Temperature dependence of atmospheric PCB concentrations

An analysis of data from the U.S. Integrated Atmospheric Deposition Network (IADN) sites near the Great Lakes and a review of the literature shows that the temperature dependence of atmospheric PCB concentrations cannot be used to distinguish sites dominated by long-distance transport from those with local sources. We observe that calculations based on data sets with only approximately 25 measurements over a period of 1 year are unreliable indicators of the long-term temperature dependence at a given location, that temperature independence occurs at temperatures below freezing, and that low PCB concentrations can bias analyses toward a weaker temperature dependence. After accounting for these factors, a similar temperature dependence is observed at all IADN sites, and this temperature dependence increases for PCBs with increasing chlorination. Although previously described models do fit the data, the resulting calculated constants are not meaningful. Instead, a simple new model in which temperatures < 273 K are set equal to 273 K, and the Clausius-Clapeyron equation is used, can account for observed temperature dependence phenomena.     

Results from the Lake Michigan Mass Balance study: concentrations and fluxes of atmospheric polychlorinated biphenyls and trans-nonachlor

In this paper, we summarize the data and methods used to estimate atmospheric exchange of polychlorinated biphenyls (PCBs) and trans-nonachlor with Lake Michigan. This work was conducted as part of the Lake Michigan Mass Balance (LMMB) study. For the atmospheric component of the LMMB, more than 400 gas- and particulate-phase samples were collected at eight sites on the shore around the lake (shoreline) and at 14 sites on the lake (over-water). We review the quality of the data set; describe the concentrations in atmospheric gas and particulate phases; report local, instantaneous, net gas fluxes; and estimate annual deposition of the particle-associated compounds. The quality of the data set is high except for a subset of over-water samples where PCB contamination is suspected. Gas-phase trans-nonachlor concentrations (although not the resulting gas fluxes) are inversely correlated with latitude and positively correlated with temperature. Gas-phase sigmaPCBs (sum of 98 congener groups) are highest in concentration at the Chicago site and lowest at the Sleeping Bear Dunes site. The resulting sigmaPCB gas fluxes exhibit a seasonality that reflects elevated summertime gas-phase concentrations not compensated by temperature-corrected Henry's law coefficients. Particulate-phase deposition is much smaller in magnitude than gas fluxes, for either compound. Gas and particulate fluxes are comparable only at the Chicago site and only when large (> 10 microm) particulates are considered.     

Influence of local human population on atmospheric polycyclic aromatic hydrocarbon concentrations

Literature values of atmospheric polycyclic aromatic hydrocarbon (PAH) concentrations from sampling sites around the world were found, and using a high-resolution human population grid, the population within a 25-km radius of each sampling site was calculated. A regression of concentration vs population revealed much about PAH concentration differences among regions as well as site locations within a continent. The best fit for the regression was for sampling locations in North America. A small amount of scatter was present for the regression of all developed countries indicating slight differences in emission regulations or energy usage. The regression from this plot was used as a benchmark for the expected relationship between PAHs and human population. Sites located within 25 km of a coasttended to have concentrations lower than expected, due to dilution with clean ocean air, while sites near industrial outputs or other point sources had higher than expected concentrations. Sites from developing countries typically had PAH concentrations that were far higher than those of the rest of the world.     

Filament stretchability of biopolymer fluids and controlling factors

Filament stretchability of biopolymer fluids composed of casein and waxy maize starch has been investigated as a function of fluid properties (viscosity and viscoelasticity) and stretching speed. The stretching of a filament was conducted at a controlled speed using a Texture Analyzer and was monitored using a high speed camera. The maximum stretchable length, L_max, was used to quantify the stretchability of a filament. Influences of various contributing factors were analyzed using dimensionless numbers (Ohnesorge number Oh, Weber number We, and capillary number Ca). It was found that, for fluids that are dominantly viscous, the capillary number could be the dominant factor determining filament stretching, demonstrated by the master curve of the maximum stretchable length against the capillary number. However, for increasingly viscoelastic fluids, the stretching behaviour showed significant deviation from the master curve, suggesting that viscoelasticity could be another pronounced factor influencing the stretching of such biopolymer fluids.     

New peat bog record of atmospheric lead pollution in Switzerland: Pb concentrations,enrichment factors,isotopic composition,and organolead species

A peat core collected at Etang de la Gruère, an ombrotrophic bog in the Jura Mountains of Switzerland, was analyzed for organolead species (DEL, TEL, DML, and TML) using GC-MIP AES, Pb isotopes using TIMS, and total Pb using XRF and age-dated using 210Pb. The earliest occurrence of quantifiable alkyllead is found at a depth of 24 cm, which is dated at AD 1946 +/- 3; this finding is consistent with the introduction of leaded gasoline in Switzerland in 1947. The maximum concentration of alkyllead (2.89 ng/g) is found at 5 cm, which is dated at AD 1988 +/- 2. This same sample yielded 206Pb/207Pb = 1.1254, which is the least radiogenic value in the entire 2K core and comparable to the isotopic composition of Pb in leaded gasoline. The highest concentrations of DML (906 ng/g) and DEL (1906 ng/g) also were found in this sample. Total alkyllead never accounts for more than 0.02% of total Pb in any given sample. The spatial and temporal variations in organolead species is matched by the changes in the isotopic composition of Pb over the same interval. Despite this, the decline in anthropogenic Pb pre-dates the maximum in total alkyllead and minimum 206Pb/207Pb, indicating that atmospheric Pb emissions had already begun their decline prior to the introduction of unleaded gasoline. In fact the decline in anthropogenic Pb was probably in response to the introduction of legislation, first in Germany and later in the European Union, establishing a maximum allowable concentration of Pb in gasoline.     

Ratio of perfluorochemical concentrations as a tracer of atmospheric deposition to surface waters

A major question regarding the global distribution of perfluorochemicals (PFCs) is one of transport. It has been suggested that atmospheric transport of volatile precursor compounds to remote areas and subsequent degradation to the nonvolatile PFCs is responsible for contamination of biota. This paper presents surface water PFC concentrations aimed at identifying tracers of atmospheric sources. Concentrations of PFCs including perfluorocarboxylates from C6 to C10 and perfluorooctane sulfonate (PFOS) are presented here from urban surface waters with presumably both atmospheric and nonatmospheric sources of PFCs, remote waters with only atmospheric sources of PFCs, and Lake Michigan. Perfluoroheptanoic acid (PFHpA) and perfluorooctanoic acid (PFOA) were detected in all surface water samples, and PFOS was detected in all but two samples. PFOS concentrations ranged from nondetect to 1.2 ng/L and from 2.4 to 47 ng/L in remote and urban surface waters, respectively. PFOA concentrations ranged from 0.14 to 0.66 ng/L and from 0.45 to 19 ng/L in remote and urban surface waters, respectively. The ratio of PFHpA to PFOA increased with increasing distance from nonatmospheric sources suggesting that it can be used as a tracer of atmospheric deposition of PFCs to surface waters. The ratio ranged from 0.5 to 0.9 in urban areas and from 6 to 16 in remote areas. Applying this tracer to measurements from Lake Michigan indicates that the primary source of PFCs to Lake Michigan is nonatmospheric, most likely inputs from wastewater treatment effluent.     

Temporal and spatial trends of atmospheric polychlorinated biphenyl concentrations near the Great Lakes

Polychlorinated biphenyl (PCB) concentrations were measured in the atmosphere at six regionally representative sites near the five Great Lakes from 1990 to 2003 as part of the Integrated Atmospheric Deposition Network (IADN). Concentration data for several individual PCB congeners and for total PCBs were analyzed for temporal and spatial trends after correcting for the temperature dependency of the partial pressures. Atmospheric PCB concentrations are decreasing relatively slowly for tetra- and pentachlorinated congeners, an observation that is in agreement with primary emissions modeling. Relatively rapid decreases in PCB concentrations at the sites near Lakes Michigan and Ontario may reflect successful reduction efforts in Chicago and Toronto, respectively. Atmospheric PCB concentrations near Lakes Superior and Huron are now so low that the air and water concentrations may be close to equilibrium. Atmospheric PCB concentrations at sites near Lakes Michigan, Erie, and Ontario are relatively higher than those measured at sites near Lakes Superior and Huron. The highest PCB level was observed at the site near Lake Erie, most likely due to nearby urban activity. However, this relatively higher concentration is still 6-10 times lower than that previously reported at the Chicago site. A correlation between average gas-phase PCB concentration with local population indicates a strong urban source of PCBs. The temperature dependence of gas-phase PCB concentrations is similar at most sites except at Burnt Island on Lake Huron, where very low concentrations, approaching virtual elimination, prevent reliable temperature correlation calculations.     

有机硅改性丙烯酸酯乳液稳定性的影响因素及其控制方法

在简单分析乳液稳定性机理的基础上 ,着重讨论了影响有机硅改性丙烯酸酯乳液稳定性的影响因素 ,并提出了其控制方法。     

影响苹果酒的品质因素及控制措施

主要从苹果原料、酵母菌种、果汁处理、酒精发酵的控制、下胶和澄清等方面详细的分析了影响苹果酒的品质的因素,同时提出了苹果酒生产中的应注意的问题及一些相关的控制措施,以达到生产优质高档的苹果酒的目的。     

影响乳品质量的因素分析及控制方法

从原料奶包装材料、辅料、生产过程的控制和确认、工艺方法、设备的运行状态、设备及管路的清洗消毒、生产环境的卫生状况以及产品的防护、储存方式、员工的质量意识、质量知识等方面探讨和分析了影响乳品质量的因素,提出提高乳品质量必须从原料乳的质量、乳品生产过程的监督和确认、生产设备的维护和保养、设备及管路的清洗消毒、产品的配送管理、人员质量培训等关键环节来控制。     

Modeling kinetic processes controlling hydrogen and acetate concentrations in an aquifer-derived microcosm

Groundwater contaminants may degrade via fermentation to intermediate species, which are subsequently consumed by terminal electron-accepting processes (TEAPs). A numerical model of an aquifer-derived laboratory microcosm is developed to simulate the dynamic behavior of fermentation and respiration in groundwater by coupling microbial growth and substrate utilization kinetics with a formulation that also includes aqueous speciation and other geochemical reactions including surface complexation, mineral dissolution, and precipitation. The model is used to test approaches that currently make use of H2(aq) to diagnose prevalent TEAPs in groundwater. Competition between TEAPs is integral to the conceptual model of the simulation, and the results indicate that competitive exclusion is significant but with some overlap found in the temporal sequence of TEAPs. Steady-state H2(aq) concentrations observed during different TEAPs do not differ significantly. The results are not consistent with previous applications of the partial equilibrium approach since most TEAP redox pairs exhibit free energies that suggest a particular process is able to proceed, yet observations here show that this process does not proceed.     

Time trend analysis of atmospheric POPs concentrations in the Great Lakes region since 1990

Using a multiple linear regression model of the concentrations of several persistent organic pollutants in the atmospheric vapor and particle phases and in precipitation, we have analyzed a data set of about 700,000 values to determine the rate at which these concentrations are decreasing. These concentrations were measured as part of the Integrated Atmospheric Deposition Network (IADN), which has operated several sites near the North American Great Lakes since 1991. The pollutants measured include 83 polychlorinated biphenyl congeners, 17 polycyclic aromatic hydrocarbons, and 24 organochlorine pesticides. In the approach used here, for each of the three phases, the concentrations of a specific chemical at all the sites were combined and fitted with a regression incorporating the sine and cosine of the Julian Day (relative to 1 January 1990 and with a periodicity of one year) and the population living and working within a 25-km radius of the sampling site. Partial residuals were then calculated for each datum, all of the residuals for the three phases were combined, and an overall halving time was calculated from them. This relatively simple approach indicated that the concentrations of PCBs in air around the Great Lakes are decreasing with an overall halving time of 17 ± 2 years, which is slow for a substance that was banned about 35 years ago. Phenanthrene, chrysene, and endosulfan showed halving times on the order of 10 years. The concentrations of several organochlorine pesticides were decreasing more rapidly; for example α- and γ-HCH (lindane) have halving times of about 3.5 years.     

宁德市大气臭氧污染现状及影响因素

以宁德市蕉城区农机局、市监测站国控监测点2016年1月到2017年7月臭氧8小时监测值为基础,研究臭氧浓度的日变化、月变化趋势及臭氧相关影响因素,结果表明:在高温、低湿、低风速、晴朗无云的情况下,易形成高浓度臭氧;低温、高湿、少日照不利于臭氧的生成.现实情况中可能存在跨区域输送或区域内生成等情况都会导致臭氧污染的生成不...     

食品乳状液中脂质氧化的影响因素及抑制方法

脂质氧化是造成食品乳状液质量下降的一个主要原因。乳化体系中脂质氧化的机理及影响氧化的因素与均相体系中脂质的氧化有很大不同。综述了油脂、氧、抗氧化剂、界面特性、油滴大小以及体系中各成分对食品乳状液中脂质氧化的影响,对于了解食品乳状液中脂质氧化的机理和有效防止食品乳状液中脂质氧化具有实际意义。     

影响固态发酵的因素及控制策略

为了充分利用固态发酵法,分析了影响固态发酵过程的因素,主要有水分、温度、通风量、pH值、杂菌和接种量等因素,并就各因素的控制提出了一些策略     

Trace metal concentrations and water solubility in size-fractionated atmospheric particles and influence of road traffic

The abundance and the behavior of metals (Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Se, Ag, Cd, Sn, Ba, Pt, Hg, and Pb) and ions (Na+ K+ Mg2+ Ca2+, NH4+, Cl-, NO3-, SO4(2-), PO4(3-), and oxalate) in size-fractionated atmospheric particulate matter (PM) were studied in the U. K. and Ireland at four observation sites simulating extreme degrees of vehicular-traffic influence in the environment. Trace metals in urban PM showed distinct types of size-fractionated behavior depending on the particle sources from which they originate. In coarse PM (1.5 < Dp < 3.0 microm) the concentrations of copper, barium, and iron correlated closely across over 2 orders of magnitude in urban air, which is seen as evidence that major portions of transition metals (Cu, Ba, Fe, and Mn) are released through abrasive vehicular emissions, particularly the wear of brake linings. Further results are strongly indicative of a decoupling of coarse iron and calcium, the former arising predominantly from vehicles, the latter from soil resuspension. In fine PM (Dp < 0.5 microm), several combustion and secondary sources of particulates were identified, but these were much less unique in terms of elemental fingerprints. An analysis of the water solubility of trace metals yielded that solubility varies considerably with element and, to a lesser extent, with particle size. Notable differences were found to the elemental water solubilities determined in previous work, partially explained by differences in extraction procedures.     

Microstructural factors controlling the survival of food-borne pathogens in porous media.

The survival of Salmonella typhimurium LT2, Escherichia coli K-12 and Pseudomonas putida in several model porous media poised at a water activity of 0.94 is shown to depend critically on the microstructure of the particulate matrix and the microscopic water distribution. The porous media were made by randomly dispersing a liquid inoculum containing ca. 10(7) cells/ml throughout the pores and interparticle spaces of packed beds of silica particles and Sephadex microspheres. The purely "microstructural stress" effects were isolated by comparison with a homogeneous liquid growth medium having the same water activity. The possibility of exploiting similar microstructural stress effects in food preservation is discussed.