Simulation of flow and shear stress distribution on the Oceano Dunes,implications for saltation and dust emissions

Environmental Fluid Mechanics - Wind-driven shear stresses drive saltation and dust emissions over sand dunes. However, the complex topography of coastal dunes and practical difficulties in...     

Chemical and colloidal analyses of natural seep water collected from the exploratory studies facility inside Yucca Mountain,Nevada, USA

Yucca Mountain is being considered as a geological repository for the USA’s spent nuclear fuel and high-level nuclear waste. Numerous groundwater seeps appeared during March 2005 within the exploratory studies facility (ESF), a tunnel excavated in the mountain. Because of the relevance to radionuclide transport and unsaturated zone-modeling studies, we analyzed the seep samples for major anions and cations, rare earth elements, and colloids. Major ion species and elemental concentrations in seep samples reflect interaction of the water with the volcanic rock and secondary calcites. Elemental fractograms from flow-injection field-flow fractionation ICP–MS scans detected Br, Ca, Cl, Cu, Fe, I, Mg, Si, Sr, W, and U at void fractions, suggesting they may be present in the form of dissolved anions. Colloids approximately 10 nm in hydrodynamic diameter, possibly calcite, were also present in the seepage samples. Geochemical calculations indicate, however, these may be an artifact (not present in the groundwater) which arose because of loss of CO₂ during sample collection and storage.     

Study of size distribution of atmospheric aerosol at Agra

Measurements on size distribution of atmospheric aerosol were made at Dayalbagh, Agra during July to September 1998. A 4-stage cascade particle sampler (CPS - 105) which fractionates particles in sizes ranging between 0.7 and >10.9 μm, was used. Samples were collected on Whatman 41 filters. The filters were analyzed for the major water-soluble ions. The anions (F, Cl, NO₃ and SO₄) were analyzed by Dionex DX-500 ion chromatograph while atomic absorption and colorimetric techniques were used for the analysis of cations (Na, K, Ca and Mg) and NH₄, respectively. The average mass of aerosol was found to be 131.6 μg m⁻³ and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and the ions NH₄, Cl, NO₃, K, Ca, Mg, SO₄ and Na was bimodal while that of F was unimodal. SO₄, F, K and NH₄ dominated in the fine mode while Ca, Mg, Cl and NO₃ were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO₄ and NO₃ have been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation on soil derived particles. Preponderance of K in fine mode is attributed to emissions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO₃ are largely soil derived and hence dominate in coarse fraction. Equivalent ratios of NH₄/(SO₄+NO₃) were calculated for both fine and coarse aerosols. The coarse mode ratio varied between 0.7 and 1.4 while in fine mode it ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline components while the basicity in fine mode is due to neutralization of acidity by NH₃.     

Field intercomparison of filter pack and denuder sampling methods for reactive gaseous and particulate pollutants

Atmospheric sulphate, nitrate, chloride and ammonium species have been measured with colocated filter pack and denuder samplers. In general the total amount of a species collected by the two types of sampler was almost the same, although there was evidence of better inlet efficiency for particles in the filter pack sampler. The filter pack gives slightly higher measurements of the volatile species HNO₃, HCl and NH₃ than the denuder, with a corresponding lower measure of particulate NO₃⁻, Cl⁻ and NH₄⁺, attributable to volatilization of ammonium salts from the filter pack pre-filter. In the context of most ambient measurements, the divergences between the techniques are small, and it is argued that differences in these measurement techniques are inevitably site, operator and apparatus-specific and data from one site or research group cannot readily be extrapolated to other sites.     

Applying guidance for methane emission estimation for landfills

Quantification of methane emission from landfills is important to evaluate measures for reduction of greenhouse gas emissions. Both the United Nations and the European Union have adopted protocols to ensure quantification of methane emission from individual landfills. The purpose of these protocols is to disclose emission data to regulators and the general public. Criteria such as timeliness, completeness, certainty, comparability, consistency and transparency are set for inclusion of emission data in a publicly accessible database. All methods given as guidance to landfill operators to estimate landfill methane emissions are based on models. In this paper the consequences of applying six different models for estimates of three landfills are explored. It is not the intention of this paper to criticise or validate models. The modelling results are compared with whole site methane emission measurements. A huge difference in results is observed. This raises doubts about the accuracy of the models. It also indicates that at least some of the criteria previously mentioned are not met for the tools currently available to estimate methane emissions from individual landfills. This will inevitably lead to compiling and comparing data with an incomparable origin. Harmonization of models is recommended. This may not necessarily reduce uncertainty, but it will at least result in comparable, consistent and transparent data.     

Characterizing the uncertainty of pesticide leaching in agricultural soils

A Monte-Carlo numerical simulation procedure for making regional assessments of pesticide leaching has been developed. This procedure uses probability density functions for organic matter, field capacity, and wilting point developed from information on approximately 3000 soils. Variations in climatic conditions were incorporated by random selection of yearly rainfall data. The procedure was demonstrated for aldicarb applied to corn grown in Ohio. A total of 2000 parameter sets were evaluated using the unsaturated zone model PRZM. The simulation results indicated that convergence of the 90th, 95th, and 99th percentiles for movement past 0.3, 0.6, 0.9, and 1.5 m was obtained after 500 simulations. The relative uncertainty associated with these percentiles was approximately 50% after 1500 simulations. The downward movement of aldicarb residues was most sensitive to changes in field capacity. These simulations, coupled with additional soil-specific simulations, indicated no significant movement of aldicarb residues beyond 1.8 m for applications to Ohio corn.     

Laboratory and field evaluation of real-time and near real-time PM2.5 smoke monitors

ABSTRACT

Increases in large wildfire frequency and intensity and a longer fire season in the western United States are resulting in a significant increase in air pollution, including concentrations of PM_2.5 (particulate matter <2.5 µm in aerodynamic diameter) that pose significant health risks to nearby communities. During wildfires, government agencies monitor PM_2.5 mass concentrations providing information and actions needed to protect affected communities; this requires continuously measuring instruments. This study assessed the performance of seven candidate instruments: (1) Met One Environmental beta attenuation monitor (EBAM), (2) Met One ES model 642 (ES642), (3) Grimm Environmental Dust Monitor 164 (EDM), (4) Thermo ADR 1500 (ADR), (5) TSI DRX model 8543 (DRX), (6) Dylos 1700 (Dylos), and (7) Purple Air II (PA-II) in comparison with a BAM 1020 (BAM) reference instrument. With the exception of the EBAM, all candidates use light scattering to determine PM_2.5 mass concentrations. Our comparison study included environmental chamber and field components, with two of each candidate instrument operating next to the reference instrument. The chamber component involved 6 days of comparisons for biomass combustion emissions. The field component involved operating all instruments in an air monitoring station for 39.5 days with hourly average relative humidity (RH) ranging from 19% to 98%. Goals were to assess instrument precision and accuracy and effects of RH, elemental carbon (EC), and organic carbon (OC) concentrations. All replicate candidate instruments showed high hourly correlations (R² ≥ 0.80) and higher daily average correlations (R² ≥ 0.90), where all instruments correlated well (R² ≥ 0.80) with the reference. The DRX and Purple Air overestimated PM_2.5 mass concentrations by a factor of ~two. Differences between candidates and reference were more pronounced at higher PM_2.5 concentrations. All optical instruments were affected by high RH and by the EC/OC ratio. Equations to convert candidate instruments data to FEM BAM type data are provided to enhance the usability of data from candidate instruments.

Implications: This study tested the performance of seven candidate PM_2.5 mass concentration measuring instruments in two settings - environmental chamber and field. The instruments were tested to determine their suitability for use during biomass combustion events and the effects of RH, PM mass concentrations, and concentrations of EC and OC on their performance. The accuracy and precision of each monitor and effect of RH, PM concentration, EC and OC concentrations are varied. The data show that most of these candidate instruments are suitable for measuring PM_2.5 concentration during biomass combustions with a proper correction factor for each instrument type.     

On a Temporal Investigation of Hurricane Strength and Frequency

Hurricanes originating in the West Atlantic often have devastating consequences on the cities in the US east coast, both monetary and otherwise, and hence pose a source of considerable concern to several authorities. The possibility of a connection between global warming in general and an increased frequency of these strong hurricanes is well researched, but is still actively debated. The present work tries to promote the use of a smoothing statistic termed empirical recurrence rates and to advocate the use of another, termed empirical recurrence rates ratio in a bid to better understand the rich history of these storms on one hand and to make appropriate inferences on the other, so that some light can be shed on the acceptability of conjectures held by renowned climate scientists. The methods introduced are intuitive and simple to implement and should find wide applications in diverse disciplines.

     

Does underweight amplify the relationship between short-term particulate matter exposure and blood pressure in children and adolescents: a large cross-sectional study in a metropolis of China

Environmental Science and Pollution Research - Overweight/obesity modified the effects of ambient particulate matter (PM) exposure on blood pressure (BP). This study aims to assess whether...