Quantifying road dust resuspension in urban environment by Multilinear Engine: A comparison with PMF2

Atmospheric PM pollution from traffic comprises not only direct emissions but also non-exhaust emissions because resuspension of road dust that can produce high human exposure to heavy metals, metalloids, and mineral matter. A key task for establishing mitigation or preventive measures is estimating the contribution of road dust resuspension to the atmospheric PM mixture. Several source apportionment studies, applying receptor modeling at urban background sites, have shown the difficulty in identifying a road dust source separately from other mineral sources or vehicular exhausts. The Multilinear Engine (ME-2) is a computer program that can solve the Positive Matrix Factorization (PMF) problem. ME-2 uses a programming language permitting the solution to be guided toward some possible targets that can be derived from a priori knowledge of sources (chemical profile, ratios, etc.). This feature makes it especially suitable for source apportionment studies where partial knowledge of the sources is available.In the present study ME-2 was applied to data from an urban background site of Barcelona (Spain) to quantify the contribution of road dust resuspension to PM₁₀ and PM_2.5 concentrations. Given that recently the emission profile of local resuspended road dust was obtained (Amato, F., Pandolfi, M., Viana, M., Querol, X., Alastuey, A., Moreno, T., 2009. Spatial and chemical patterns of PM₁₀ in road dust deposited in urban environment. Atmospheric Environment 43 (9), 1650–1659), such a priori information was introduced in the model as auxiliary terms of the object function to be minimized by the implementation of the so-called “pulling equations”.ME-2 permitted to enhance the basic PMF solution (obtained by PMF2) identifying, beside the seven sources of PMF2, the road dust source which accounted for 6.9 μg m^?3 (17%) in PM₁₀, 2.2 μg m^?3 (8%) of PM_2.5 and 0.3 μg m^?3 (2%) of PM₁. This reveals that resuspension was responsible of the 37%, 15% and 3% of total traffic emissions respectively in PM₁₀, PM_2.5 and PM₁. Therefore the overall traffic contribution resulted in 18 μg m^?3 (46%) in PM₁₀, 14 μg m^?3 (51%) in PM_2.5 and 8 μg m^?3 (48%) in PM₁. In PMF2 this mass explained by road dust resuspension was redistributed among the rest of sources, increasing mostly the mineral, secondary nitrate and aged sea salt contributions.     

Biodegradation potential of MTBE in a fractured chalk aquifer under aerobic conditions in long-term uncontaminated and contaminated aquifer microcosms

The potential for aerobic biodegradation of MTBE in a fractured chalk aquifer is assessed in microcosm experiments over 450 days, under in situ conditions for a groundwater temperature of 10 °C, MTBE concentration between 0.1 and 1.0 mg/L and dissolved O₂ concentration between 2 and 10 mg/L. Following a lag period of up to 120 days, MTBE was biodegraded in uncontaminated aquifer microcosms at concentrations up to 1.2 mg/L, demonstrating that the aquifer has an intrinsic potential to biodegrade MTBE aerobically. The MTBE biodegradation rate increased three-fold from a mean of 6.6 ± 1.6 μg/L/day in uncontaminated aquifer microcosms for subsequent additions of MTBE, suggesting an increasing biodegradation capability, due to microbial cell growth and increased biomass after repeated exposure to MTBE. In contaminated aquifer microcosms which also contained TAME, MTBE biodegradation occurred after a shorter lag of 15 or 33 days and MTBE biodegradation rates were higher (max. 27.5 μg/L/day), probably resulting from an acclimated microbial population due to previous exposure to MTBE in situ. The initial MTBE concentration did not affect the lag period but the biodegradation rate increased with the initial MTBE concentration, indicating that there was no inhibition of MTBE biodegradation related to MTBE concentration up to 1.2 mg/L. No minimum substrate concentration for MTBE biodegradation was observed, indicating that in the presence of dissolved O₂ (and absence of inhibitory factors) MTBE biodegradation would occur in the aquifer at MTBE concentrations (ca. 0.1 mg/L) found at the front of the ether oxygenate plume. MTBE biodegradation occurred with concomitant O₂ consumption but no other electron acceptor utilisation, indicating biodegradation by aerobic processes only. However, O₂ consumption was less than the stoichiometric requirement for complete MTBE mineralization, suggesting that only partial biodegradation of MTBE to intermediate organic metabolites occurred. The availability of dissolved O₂ did not affect MTBE biodegradation significantly, with similar MTBE biodegradation behaviour and rates down to ca. 0.7 mg/L dissolved O₂ concentration. The results indicate that aerobic MTBE biodegradation could be significant in the plume fringe, during mixing of the contaminant plume and uncontaminated groundwater and that, relative to the plume migration, aerobic biodegradation is important for MTBE attenuation. Moreover, should the groundwater dissolved O₂ concentration fall to zero such that MTBE biodegradation was inhibited, an engineered approach to enhance in situ bioremediation could supply O₂ at relatively low levels (e.g. 2–3 mg/L) to effectively stimulate MTBE biodegradation, which has significant practical advantages. The study shows that aerobic MTBE biodegradation can occur at environmentally significant rates in this aquifer, and that long-term microcosm experiments (100s days) may be necessary to correctly interpret contaminant biodegradation potential in aquifers to support site management decisions.     

Incorporating layer- and local-scale heterogeneities in numerical simulation of unsaturated flow and tracer transport

This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport.     

Influences of chemical activators on incinerator bottom ash

This research has applied different chemical activators to mechanically and thermally treated fine fraction (<14 mm) of incinerator bottom ash (IBA), in order to investigate the influences of chemical activators on this new pozzolanic material. IBA has been milled and thermally treated at 800 degrees C (TIBA). The TIBA produced was blended with Ca(OH)(2) and evaluated for setting time, reactivity and compressive strength after the addition of 0.0565 mole of Na(2)SO(4), K(2)SO(4), Na(2)CO(3), K(2)CO(3), NaOH, KOH and CaCl(2) into 100g of binder (TIBA+Ca(OH)(2)). The microstructures of activated IBA and hydrated samples have been characterized by X-ray diffraction (XRD) and thermogravimetry (TG) analysis. Thermal treatment is found to produce gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)) phases. The thermally treated IBA samples are significantly more reactive than the milled IBA. The addition of Na(2)CO(3) can increase the compressive strength and calcium hydroxide consumption at 28-day curing ages. However, the addition of Na(2)SO(4), K(2)SO(4), K(2)CO(3), NaOH and KOH reduces the strength and hydration reaction. Moreover, these chemicals produce more porous samples due to increased generation of hydrogen gas. The addition of CaCl(2) has a negative effect on the hydration of TIBA samples. Calcium aluminium oxide carbonate sulphide hydrate (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33)(H(2)O)(11)) is the main hydration product in the samples with activated IBA, except for the sample containing CaCl(2).     

A Sensitivity Analysis of an Integrated Modelling Approach to Assess the Risk of Wind-borne Spread of Foot-and-mouth Disease Virus from Infected Premises

The sensitivity of an integrated model to assess the potential for wind-borne spread of foot-and-mouth disease (FMD) to variations in key parameters controlling different physical and biological processes was evaluated. The estimated number of farms at risk is sensitive to the virus strain used and the accompanying effective contact rate. The C Noville strain increased the estimated number of exposed farms ranked as high and medium risk of being infected by a factor of 5, compared to the baseline, based on the O UKG 2001 strain. The inclusion of a model for biological ageing of the virus can also have a significant effect on the concentration patterns arising from transport and dispersion of the virus. Its inclusion has the practical advantage of markedly reducing the time required for the calculations. The estimated number of farms affected by exposure to high and medium virus concentrations is not grossly sensitive to attenuation caused by temperature or relative humidity effects. Changes in susceptibility to infection, as determined by the parameter θ in the exposure-risk model, does not change the configuration of the virus plumes, but it does change the distribution of farms at risk by risk category. These findings suggest that a good understanding of characteristics (excretion rates from infected animals, susceptibility of different species to infection, virus survival, etc.) of the virus strain involved in an FMD outbreak is necessary to provide a reliable assessment of the risk of wind-borne spread. In the event of an incursion of FMD, provision for laboratory studies on the virus will be an essential component of the disease response and should be factored into contingency plans.

Identification of soil heavy metal sources from anthropogenic activities and pollution assessment of Fuyang County, China

Understanding regional variations of soil heavy metals and their anthropogenic influence are very important for environmental planning. In this study, 286 surface soil samples were collected in Fuyang county, and the 'total' metals for copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd) and nickel (Ni) were measured in 2005. Statistic analysis showed that Cu, Zn, Pb and Cd had been added by exterior factors, and Ni was mainly controlled by natural factors. The combination of multivariate statistical and geostatistical analysis successfully grouped three groups (Cu, Zn and Pb; Cd; and Ni) of heavy metals from different sources. Through pollution evaluation, it was found that 15.76% of the study area for Cu, Zn and Pb, and 46.14% for Cd suffered from moderate or severe pollution. Further spatial analysis identified the limestone mining activities, paper mills, cement factory and metallurgic activities were the main sources for the concentration of Cu, Zn, Pb and Cd in soils, and soil Ni was mainly determined by the parent materials.     

Phosphate adsorption characteristics at the sediment–water interface and phosphorus fractions in Nansi Lake, China, and its main inflow rivers

Phosphorus fractions and phosphate adsorption characteristics of 16 sediments from a shallow freshwater lake (Nansi Lake, China) and its inflow estuaries were investigated. In the present study, the sediment phosphorus is fractionated into exchangeable P (exch-P), Al-P, Fe-P, Ca-P, organic P (OP), inorganic P (IP) and total P (TP). The results show that the total phosphorus (TP) content in the sediments ranges from 571.67 to 1,113.55 mg kg(-1), and calcium bound phosphorus (Ca-P) is the main fraction of IP. The biologically available phosphorus (BAP) ranges from 32.02 to 229.67 mg kg(-1) in the Nansi Lake sediments. Phosphate adsorption on the sediments mainly occurs within 10 h and is completed within 48 h. The content of native adsorbed phosphorus (omega(NAP)) varies greatly from 6.05 to 194.37 mg kg(-1), showing a significant correlation with the total maximal amount of phosphorus adsorbed (TQ(max)). Adsorption efficiency (m) ranges from 574.79 to 3,220.68 l kg(-1) and zero equilibrium phosphorus concentration (C(EPC)) ranges from 0.010 to 0.157 mg l(-1). After the South-to-North Water Diversion Project, the inherent phosphorus present in sediments will be a major threat to the diverted water quality and be a predominant factor determining the trophic status of the lake even if the external load is reduced.     

A storm event-based approach to TMDL development

It is vitally important to define the critical condition for a receiving water body in the total maximum daily load (TMDL) development process. One of the major disadvantages of using a continuous simulation approach is that there is no guarantee that the most critical condition will be covered within the subjectively selected representative hydrologic period, which is usually several years depending on the availability of data. Another limitation of the continuous simulation approach, compared to a design storm approach, is the lack of an estimate of the risk involved. Because of the above limitations, a storm event-based critical flow-storm (CFS) approach was previously developed to explicitly address the critical condition as a combination of a prescribed stream flow and a storm event of certain magnitude, both having a certain frequency of occurrence and when combined, would create a critical condition. The CFS approach was tested successfully in a TMDL study for Muddy Creek in Virginia. The present paper reports results of a comparative study on the applicability of the CFS approach in Taiwan. The Dy-yu creek watershed in northern Taiwan differs significantly from Muddy Creek in terms of climate, hydrology, terrain, and other characteristics. Results show that the critical condition for different watersheds might be also different, and that the CFS approach could clearly define that critical condition and should be considered as an alternative method for TMDL development to a continuous simulation approach.