Development of a Local-Scale Spatially Refined Multimedia Fate Model (LSRMFM) for Urban-Scale Risk Assessment: Model Formulation, GIS-Based Preprocessing, and Case Study

A local-scale spatially refined multimedia fate model (LSRMFM) was developed to evaluate in detail the multimedia transport of organic compounds at a spatial level. The model was derived using a combination of an advection?Cdispersion?Creaction partial differential equation, a steady-state multimedia fugacity model, and a geographical information system. The model was applied to predicting four major volatile organic compounds that are produced as emissions (benzene, toluene, xylene, and styrene) in an urban and industrial area (the 50?×?50-km area was divided into 0.5?×?0.5-km segments) in Korea. To test the accuracy of the model, the LSRMFM was used to predict the extent of dispersion and the data compared with actual measured concentrations and the results of a generic multimedia fate model (GMFM). The results indicated that the method developed herein is appropriate for predicting long-term multimedia pollution. However, the comparison study also illustrated that the developed model has some limitations (e.g., steady-state assumption) in terms of explaining all the observed concentrations, and additional verification and study (e.g., validation using a large observed data set, integration with a more accurate runoff model) would be desirable. In comparing LSRMFM and GMFM, discrepancies between the LSRMFM and GMFM outputs were found, as the result of geographical effects, even though the environmental parameters were identical. The geographical variation for LSRMFM output indicated the existence of considerable local human and ecological risks, whereas the GMFM output indicated less average risk. These results demonstrate that the model has the potential for improving the management of pollutant levels under these refined spatial conditions.     

Effects of salinity and organic matter on the partitioning of perfluoroalkyl acid (PFAs) to clay particles

The influence of salinity and organic matter on the distribution coefficient (K(d)) for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in a brackish water-clay system was studied. The distribution coefficients (K(d)) for PFAs onto inorganic clay surfaces increased with salinity, providing evidence for electrostatic interaction for the sorption of PFAs, whereas the relationship between K(d) and organic carbon content (f(oc)) suggested that hydrophobic interaction is the primary driving force for the sorption of PFAs onto organic matter. The organic carbon normalized adsorption coefficient (K(oc)) of PFAs can be slightly overestimated due to the electrostatic interaction within uncoated inorganic surfaces. In addition, the dissolved organic matter released from coated clay particles seemed to solvate PFA molecules in solution, which contributed to a decrease in K(d). A positive relationship between K(d) and salinity was apparent, but an empirical relationship for the 'salting-out' effect was not evident. The K(d) values of PFAs are relatively small compared with those reported for persistent organic pollutants. Thus, sorption may not be a significant route of mass transfer of PFAs from water columns in estuarine environments. However, enhancement of sorption of PFAs to particulate matter at high salinity values could evoke potential risks to benthic organisms in estuarine areas.     

Photocatalytic oxidation of gas-phase elemental mercury by nanotitanosilicate fibers

Photocatalytic fibers were generated from the continuous evaporation of titanium tetraisopropoxide with tetraethyl orthosilicate through a flame burner. The morphology, the crystal form, and the components of the nanotitanosilicate fibers were analyzed by Raman spectroscopy, Field emission-scanning electron microscope, X-ray diffraction, and Brunauer-Emmett-Teller surface area analysis. The nanotitanosilicates prepared by three different carrier gases (air, N(2), and Ar) were tested for their photocatalytic ability to remove/oxidize gas-phase elemental mercury. Under UV black light, the Hg(0) capture efficiencies were 78%, 86%, and 85% for air, N(2), and Ar, respectively. For air, the value was close to 90%, even under household fluorescent light. The Hg(0) capture efficiency by nanotitanosilcate was measured under fluorescent light, UV black light, and sunlight.     

Exploratory studies of PM10 receptor and source profiling by GC/MS and principal component analysis of temporally and spatially resolved ambient samples

For a recent exploratory study of particulate matter (PM) compositions, origins, and impacts in the El Paso/Juarez (Paso del Norte) airshed, the authors relied on solvent extraction (SX)-gas chromatography/mass spectrometry (GC/MS) procedures to characterize 24-hr quartz fiber (QF) filter samples obtained from nine spatially distributed high-volume (Hi-Vol) PM10 samplers as well as on thermal desorption (TD)-GC/MS methods to characterize 45 time-resolved (2-hr) filter samples obtained with modified 1-m3/hr PM10 samplers. Principal component analysis and related chemometric techniques were used for data reduction and data fusion as well as for multiway data correlation. A high degree of correspondence (R2 = 0.821) was found between the rapid TD-GC/MS method (which can be carried out on 2-hr filter slices containing only microgram amounts of sample) and conventional SX-GC/MS procedures. The four main source patterns of organic PM components observed in GC/MS profiles of both temporally and spatially resolved receptor samples obtained in the El Paso/Juarez border airshed during the study period are interpreted to represent (1) vehicular emissions plus resuspended urban dust; (2) biomass combustion; (3) native vegetation detritus and resuspended agricultural dust; and (4) waste burning. Moreover, principal component analysis of combined, variance-weighted, temporally resolved TD-GC/MS data and spatially resolved SX-GC/MS data was used to determine approximate source locations for specific PM components identified in time-resolved receptor sample profiles. The same approach can be used to determine approximate circadian concentration profiles of specific PM components identified in spatially resolved receptor sample profiles.     

Formation and emission status of PCDDs/PCDFs in municipal solid waste incinerators in Korea

This study was carried out to examine the formation and the emission status of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs) in the flue gases of commercial-scale municipal solid waste (MSW) incinerators, and thus to provide the engineering data for the reduction of PCDDs/PCDFs emitted from MSW incinerators. The formation concentrations of the PCDDs/PCDFs generated at the outlet of waste heat boilers (WHB) were in the range of 1.18-29.61 ng-TEQ/N m3 (average 5.75 ng-TEQ/N m3), while the emission concentrations at the stacks were in the range of 0.026-4.548 ng-TEQ/N m3 (average 0.924 ng-TEQ/N m3). Two major 2,3,7,8-substituted congeners were 2,3,4,7,8-PeCDF and 2,3,4,6,7,8-HxCDF, and their concentrations were up to 50% and 64% of total TEQ values at the outlet of WHB and the stack, respectively. From the results of multi-regression analysis, the formation concentration of PCDDs/PCDFs could be predicted as follows with the correlation factor of r2 = 0.962: PCDDs/PCDFs (ng-TEQ/N m3) = 3.036 (Cl) + 0.094 (T1) - 0.472 (Combustibles) + 0.059 (CO) - 0.039 (THC) - 3.366 (H) + 22.157, where T1 (degrees C) is the temperature at the outlet of the WHB. Cl, Combustibles and H are given as percentages and the others are in parts per million.     

Combustion characteristics of simulated gas fuel in a 30 kg/h scale pyrolysis-melting incinerator

Combustion characteristics of gas fuel in a pyrolysis-melting incinerator having a 30kg/h capacity were investigated. Pyrolyzed gas from waste was simulated by propane that was injected in the combustion chamber, and burnt through multi-staged combustion by distributing the combustion air to primary, secondary, and tertiary air nozzles. Temperatures and the concentrations of gas components in the combustion chamber were measured. Combustion performance was evaluated with respect to the temperature distribution and combustion gas concentrations of O(2), CO and NO(x). Using secondary air and/or tertiary air, the combustion performance was improved, and, in particular, NO(x) concentration decreased significantly following the tertiary air injection.     

Characterization of particulate matter from diesel passenger cars tested on chassis dynamometers

Emission characterization of particle number as well as particle mass from three diesel passenger cars equipped with diesel particulate filter(DPF), diesel oxidation catalyst(DOC)and exhaust gas recirculation(EGR) under the vehicle driving cycles and regulatory cycle.Total particle number emissions(PNEs) decreased gradually during speed-up of vehicle from 17.3 to 97.3 km/hr. As the average vehicle speed increases, the size-segregated peak of particle number concentration shifts to smaller size ranges of particles. The correlation analysis with various particulate components such as particle number concentration(PNC),ultrafine particle number concentration(UFPNC) and particulate matter(PM) mass was conducted to compare gaseous compounds(CO, CO_2, HC and NOx). The UFPNC and PM were not only emitted highly in Seoul during severe traffic jam conditions, but also have good correlation with hydrocarbons and NOxinfluencing high potential on secondary aerosol generation. The effect of the dilution temperature on total PNC under the New European Driving Cycle(NEDC), was slightly higher than the dilution ratio. In addition, the nuclei mode(DP: ≤ 13 nm) was confirmed to be more sensitive to the dilution temperature rather than other particle size ranges. Comparison with particle composition between vehicle speed cycles and regulatory cycle showed that sulfate was slightly increased at regulatory cycle, while other components were relatively similar. During cold start test, semivolatile nucleation particles were increased due to effect of cold environment. Research on particle formation dependent on dilution conditions of diesel passenger cars under the NEDC is important to verify impact on vehicular traffic and secondary aerosol formation in Seoul.     

Application of eggshell waste for the immobilization of cadmium and lead in a contaminated soil

Liming materials have been used to immobilize heavy metals in contaminated soils. However, no studies have evaluated the use of eggshell waste as a source of calcium carbonate (CaCO₃) to immobilize both cadmium (Cd) and lead (Pb) in soils. This study was conducted to evaluate the effectiveness of eggshell waste on the immobilization of Cd and Pb and to determine the metal availability following various single extraction techniques. Incubation experiments were conducted by mixing 0–5% powdered eggshell waste and curing the soil (1,246 mg Pb kg^?1 soil and 17 mg Cd kg^?1 soil) for 30 days. Five extractants, 0.01 M calcium chloride (CaCl₂), 1 M CaCl₂, 0.1 M hydrochloric acid (HCl), 0.43 M acetic acid (CH₃COOH), and 0.05 M ethylendiaminetetraacetic acid (EDTA), were used to determine the extractability of Cd and Pb following treatments with CaCO₃ and eggshell waste. Generally, the extractability of Cd and Pb in the soils decreased in response to treatments with CaCO₃ and eggshell waste, regardless of extractant. Using CaCl₂ extraction, the lowest Cd concentration was achieved upon both CaCO₃ and eggshell waste treatments, while the lowest Pb concentration was observed using HCl extraction. The highest amount of immobilized Cd and Pb was extracted by CH₃COOH or EDTA in soils treated with CaCO₃ and eggshell waste, indicating that remobilization of Cd and Pb may occur under acidic conditions. Based on the findings obtained, eggshell waste can be used as an alternative to CaCO₃ for the immobilization of heavy metals in soils.     

Vaporization reduction characteristics of aqueous ammonia solutions by the addition of ethylene glycol, glycerol and glycine to the CO2 absorption process

Aqueous ammonia (NH₃) solution can be used as an alternative absorption for the control of CO₂ emitted from flue gases due to its high absorption capacity, fast absorption rate and low corrosion problem. The emission of CO₂ from iron and steel plants requires much attention, as they are higher than those emitted from power plants at a single point source. In the present work, low concentration ammonia liquor, 9 wt.%, was used with various additives to obtain the kinetic properties using the blast furnace gas model. Although a solution with a high ammonia concentration enables high CO₂ absorption efficiency, ammonium ions are lost as ammonia vapor, resulting in reduced CO₂ absorption due to the lower concentration of the ammonia absorbent. To decrease the vaporization of ammonia, ethylene glycol, glycerol and glycine, which contain more than one hydroxyl radical, were chosen. The experiments were conducted at 313 K similar to the CO₂ absorption conditions for the blast furnace gas model.     

Characteristics of metal contamination in paddy soils from three industrial cities in South Korea

Paddy soil contamination is directly linked to human dietary exposure to toxic chemicals via crop consumption. In Korea, rice paddy fields are often located around industrial complexes, a major anthropogenic source of metals. In this study, rice paddy soils were collected from 50 sites in three industrial cities to investigate the contamination characteristics and ecological risk of metals in the soils. The cities studied and their major industries are as follows: Ulsan (petrochemical, nonferrous, automobile, and shipbuilding), Pohang (iron and steel), and Gwangyang (iron and steel, nonmetallic, and petrochemical). Thirteen metals (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) were analyzed using inductively coupled plasma–optical emission spectrometry (ICP–OES). The mean concentration of Cd (1.98 mg/kg) exceeded the soil quality guideline of Canada (1.4 mg/kg), whereas concentrations of other metals were under the standards of both Korea and Canada. Generally, levels of metal concentrations decreased with increasing distance from industrial complexes. Among the three cities, Pohang showed high concentrations of Zn (142.2 mg/kg), and Ulsan and Gwangyang showed high concentrations of Cr (33.9 mg/kg) and Ba (126.4 mg/kg), respectively. These contamination patterns were influenced by the different major industries of each city, which was clearly demonstrated by the principal component analysis results. Pollution indices suggested that As, Cd, Pb, and Zn were enriched in the paddy soils via anthropogenic activities. Comprehensive potential ecological risk indices were at considerable levels for most sites, especially because of major contributions from As and Cd, which can pose potential ecological threats.