Source strengths of ultrafine and fine particles due to cooking with a gas stove

Cooking, particularly frying, is an important source of particles indoors. Few studies have measured a full range of particle sizes, including ultrafine particles, produced during cooking. In this study, semicontinuous instruments with fine size discriminating ability were used to calculate particle counts in 124 size bins from 0.01 to 2.5 microm. Data were collected at 5 min intervals for 18 months in an occupied house. Tracer gas measurements were made every 10 min in each of 10 rooms of the house to establish air change rates. Cooking episodes (N = 44) were selected meeting certain criteria (high concentrations, no concurrent indoor sources, long smooth decay curves), and the number and volume of particles produced were determined for each size category. For each episode, the particle decay rate was determined and used to determine the source strength for each size category. The selected cooking episodes (mostly frying) were capable of producing about 10(14) particles over the length of the cooking period (about 15 min), more than 90% of them in the ultrafine (< 0.1 microm) range, with an estimated whole-house volume concentration of 50 (microm/cm)3. More than 60% of this volume occurred in the 0.1-0.3 microm range. Frying produced peak numbers of particles at about 0.06 microm, with a secondary peak at 0.01 microm. The peak volume occurred at a diameter of about 0.16 microm. Since the cooking episodes selected were biased toward higher concentrations, the particle concentrations measured during about 600 h of morning and evening cooking over a full year were compared to concentrations measured during noncooking periods at the same times. Cooking was capable of producing more than 10 times the ultrafine particle number observed during noncooking periods. Levels of PM2.5 were increased during cooking by a factor of 3. Breakfast cooking (mainly heating water for coffee and using an electric toaster) produced concentrations about half those produced from more complex dinnertime cooking. Although the number and volume concentrations observed depend on air change rates, house volume, and deposition rates due to fans and filters, the source strengths calculated here are independent of these variables and may be used to estimate number and volume concentrations in other types of homes with widely varying volumes, ventilation rates, and heating and air-conditioning practices.     

Centenary Review Article Beer Filtration

Beer filtration has been effected by sheet filters and various systems utilising filter aids for many decades. Cartridge filters, frequently utilising man-made polymeric media, are taking over the role of the sheet filter. While filter aid systems will be in use for some years, their long-term place in the Brewing Industry is being challenged by new developments in regenerable media depth filters and cross-flow microfilters. The advent of electronic particle size measurement has given detailed information on the physical character of beer particles and filter-aid particles. This enables accurate interpretation of filtration processes and the impact of materials such as β-glucans on the processes using the laws of filtration.     

Influence of surface charge distributions and particle size distributions on particle attachment in granular media filtration

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media.     

Retention and transport of amphiphilic colloids under unsaturated flow conditions: effect of particle size and surface property

The purpose of this study was to examine the mechanisms responsible for deposition and transport of amphiphilic colloids with a wide range of particle sizes (20-420 nm) through porous media. A series of saturated and unsaturated column experiments were conducted using amphiphilic latex microspheres and a hydrophilic silica colloid. We found that the amphiphilic latex particles were retained to a greater extentthan the hydrophilic silica colloid in unsaturated media. This was attributed to colloidal attachment atthe air-water interface due mainly to hydrophobic interactions. We also found that dependence of colloid retention on particle size was nonlinear. There existed a fraction of colloids with greater mobility than other fractions, which we referred to as the most mobile colloids. As particle size increased from 20 to 420 nm, colloid deposition rate first decreased to reach a minimum value at --100 nm then increased, indicating that different retention mechanisms were involved. We showed that conducting saturated transport experiments and analysis using filtration theory may be an effective approach for determining the most mobile colloid size(s) in porous media, perhaps even for unsaturated flow conditions. This study highlights the importance of including size effect and surface properties when predicting concentrations and fluxes of amphiphilic colloids or colloid-bound amphiphilic and hydrophobic contaminants in the subsurface environment.     

Aquasols: on the role of secondary minima

Experiments are presented that test the hypothesis of deposition into and reentrainment from secondary minima during flow through porous media. The release of deposited particles following a decrease in ionic strength is inconsistent with deposition in the primary minimum of either simple DLVO interaction energy curves (which suggest that deposition is irreversible) or Born-DLVO interaction energy curves (which create a finite primary minimum that deepens with decreasing ionic strength). The observed release of particles is, on the other hand, consistent with deposition in the secondary minimum because this energy minimum decreases and can disappear with decreasing ionic strength. The implications for colloid transport of a reversible deposition process in the secondary minimum are very different from those of a process involving irreversible deposition in the primary minimum. First, particles that are continually captured and released will travel much farther in the subsurface than might be expected if the classic irreversible filtration model is applied. Second, and perhaps more significantly, deposition in the secondary well can increase with increasing particle size. Although particle transport by convective diffusion increases as particle size decreases, particle "attachment" in secondary minima decreases with decreasing particle size. Thus, smaller particles (those with diameters in the order of a few tens of nanometers) would be more effective in the facilitated transport of highly sorbing contaminants such as hydrophobic organic molecules, metals, and radionuclides. Other contaminants are themselves particles, such as viruses (tens of nanometers in diameter) and bacteria (near 1 microm in diameter). Due to this difference in size, viruses could be transported over much larger distances than bacteria. Third, the transport of colloids and, hence, the transport of contaminants associated with them, depends on the Hamaker constant of the particle-water-aquifer media system. Colloids of lower Hamaker constant are likely to be transported farther than colloids of higher Hamaker constant. The extent of adsorption of specific contaminants and the Hamaker constant for the particle-aquifer system are both characteristics of the particles and contribute to the effectiveness of colloid-facilitated transport. Finally, the solution chemistry of the pore waters (through pH, ionic strength, types of solutes, and the valence of the ions) ultimately controls the deposition and release of colloidal particles in porous media. The pH determines the charge density and surface potential of the surfaces. When the surfaces are similarly charged, their interaction can be unfavorable, with an energy barrier and secondary minimum. The ionic strength and valence of the ions determines the shape of the interaction energy curve, including the presence and height of the energy barrier and the presence and depth of the secondary well. Since the subsequent release of a particle depends on the mode in which the particle is deposited (primary or secondary), these factors are particularly important in determining the extent of colloid transport in the subsurface.     

Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions

Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.     

Long duration tests of room air filters in cigarette smokers' homes

Information regarding the long-term performance of stand-alone room airfilters is limited. In this study, laboratory and field tests were carried out to determine the effectiveness and performance of room filters that are easily deployed in essentially any type of house. Tests were conducted in houses containing strong PM sources, specifically cigarette smokers. Using commercially available four-speed HEPA filter units, we tested flow rate, pressure drop, and power consumption as a function of fan speed and filter loading. Filters were then deployed in four single-family homes over a 2 month period. Between 15 and 40 cigarettes were smoked daily by several smokers in each home. Occupants were instructed to continuously operate the unit at one of the higher speeds. Periodically, we monitored filter usage, fan speed, particulate matter (PM) mass concentrations, PM number concentrations, volatile organic compound (VOC) levels, and other parameters with the filter fan operating and with filters both installed and removed. The filters decreased PM concentrations by 30-70%, depending on size fraction and occupant activities, and significantly reduced the half-life of PM3-1.0. The half-life of 1-5 microm particles, CO2 concentrations, and VOC concentrations, including 2,5-dimethyl furan (a tracer for environmental tobacco smoke), did not change, indicating that occupancy and cigarette smoking intensity did not change overthe monitoring periods. Occupants generally kept the filters operating at a moderate speed. Filter air flow rates decreased 7-14% with extended operation, largely due to the loading of prefilters. Air exchange rates, deposition loss rates, and clean air delivery rates were estimated from the field data. Continuous operation at an intermediate fan speed would incur a total annualized cost of $236. While acceptance of the filters was very high, occupants might benefit from instructions and reminders to clean the prefilter and to keep the unit on. We conclude that adequately sized room air filters can substantially lower PM concentrations in smoker's homes if air exchange rates are limited and that the filters can maintain their performance over extended periods.     

Excess colloid retention in porous media as a function of colloid size, fluid velocity, and grain angularity

The deposition and re-entrainment behaviors of five sizes of carboxylate-modified microspheres (ranging from 0.1 to 2.0 microm) were examined both in porous media and impinging jet systems under a variety of environmentally relevant pore fluid velocities (2-8 m day-'), and in both the absence and the presence of an energy barrier to deposition. The magnitudes of the deposition efficiencies were compared among the porous media and impinging jet systems under equivalent fluid velocities, solution chemistries, and surface chemistries. The observed deposition efficiencies were factors of about 5 to 50 greater in the porous media relative to the impinging jet across the entire size range of microspheres examined, demonstrating that this excess deposition in porous media is relevant to a wide range of colloid sizes. The magnitude of excess deposition increased with increasing fluid velocity, and was greatest for the smallest colloids (0.1 microm). A range between 15% and 40% of the excess retained colloids were released upon introduction of low ionic strength solution, indicating that they were retained via secondary energy minima without direct contact with the grain surfaces. The observations indicate that pore geometry is a critical governor of colloid deposition in the presence of an energy barrier, even in porous media composed of spherical collectors. A portion of this excess deposition results from retention in flow stagnation zones.     

In-situ measurements of engineered nanoporous particle transport in saturated porous media

Engineered nanoporous particles have become an important class of nanostructured materials that have been increasingly applied in energy, biomedical, and environmental researches and industries. The internal pore surfaces in the particles can be chemically functionalized for environmental applications to sequestrate metals and radionuclide contaminants from groundwater. The fate and transport of the nanoporous particles in subsurface environments, however, have not been studied. Here we present a scanning optical fiber fluorescence profiler that can be used to in situ monitor the transport of fluorescent particles in column systems. Engineered nanoporous silicate particles (ENSPs) that were covalently bounded with fluorescence-emitting, and uranium-chelating ligands in the intraparticle pore domains were synthesized and used as an example to investigate nanoporous particle transport and to demonstrate the application of the developed in situ measurement profiler. The profiler detected an "irreversible" or slowly detached fraction of ENSPs in a sand collector even under thermodynamically unfavorable conditions for particle attachment. Further, the in situ measurement system detected the spatial variability of ENSPs transport that deviated from one-dimensional, homogeneous assumption, which is typically used to model particle transport in column systems. Generally, however, both measured and model-calculated results indicated that the transport of ENSPs was consistent with that of nonporous colloidal particles subjected to coupled reversible attachment/detachment and straining processes. The developed system can also be applied to detect other fluorescent nanostructured or colloidal particles in porous media.     

Influence of media characteristics on energy dissipation in filter backwashing

Effective cleaning of granular filters during backwashing processes needs maximum turbulence and maximum shear in the fluid particle field. The energy dissipation in a backwashed filter as a particulate fluidized bed arises due to the suspending and random motions of particles and turbulent fluctuations in the bed. Size, density, and sphericity of the filter materials greatly influence the fluidization behavior of the media. In this study, a new model is proposed for predicting the energy dissipation parameters namely the hydrodynamic shear stress (tau(a)), the velocity gradient (G(a)), the turbulence dissipation coefficient (C(a)), and the turbulence parameter (C(a)0.5/Re) in backwashing of filters for different types of filter materials (sand, anthracite, and glass ball). The hydrodynamic shear stress is the dominant mechanism of filter cleaning and appears to increase with increasing the density and size of the filter media particles. Using the basic set of data, a step by step procedure is developed to compute the velocity gradient G(a), the turbulence dissipation coefficient C(a), the hydrodynamic shear stress tau(a), and the turbulent parameter (C(a)0.5/ Re).     

Continuous fractionation of fly ash particles by SPUTT for the investigation of PCDD/Fs levels in different sizes of insoluble particles

A combined analytical method has been developed to characterize the size dependent levels of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) contained in fly ash particles from a municipal solid waste incinerator (MSWI). Gravitational SPLITT fractionation (GSF), a relatively new technique for the fast and continuous separation of micron sized particles, was used to fractionate a fly ash sample, directly collected from a bag-filter house of MSWI in Korea, into six different size groups (<1.0, 1.0-2.5, 2.5-5.0, 5.0-10, 10-20, and 20-53 microm in diameter) in water solution, and the resulting fractions are examined by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) in order to determine the concentration of PCDD/Fs according to these particle sizes. The results from SPLITT fractionation show that approximately 54% of the fly ash particles (sieved fraction <53 microm) by weight have been found to be smaller than 5.0 microm excluding the water soluble matter in the sample. From the HRGC/HRMS measurements, particle fractions in the size range of PM 1.0-2.5 and 2.5-5.0 appear to carry about 76 and 79 ng/g of PCDD/Fs which are relatively larger than those found in other diameter ranges. Principal component analysis (PCA) shows that particles larger than 5.0 microm are clustered into a group predominantly containing low chlorinated dioxins and fractions smaller than 5.0 microm into another group with lower chlorinated furans. This study demonstrated that the combining GSF with a secondary analytical method such as HRGC/HRMS has the potential to obtain size dependent information of particulate materials in relation to their production processes, chemical compositions, environmental fates, and other factors.     

Size fractionation and characterisation of fresh water colloids and particles: split-flow thin-cell and electron microscopy analyses

Split-flow thin-cell (SPLITT) was employed in conventional mode (CSF), to size-fractionate colloids and particles from a selected freshwater. Imaging and quantification by calculations of particle size distributions (PSDs) and shape factors were performed on sample analyzed by conventional high vacuum scanning electron microscopy (SEM) and environmental SEM (ESEM), to investigate the ability of SPLITT to make accurate and nonperturbing separations. SEM and ESEM images of unperturbed and SPLITT-generated fractions were used in order to obtain qualitative and quantitative information about the properties of colloids and particles. Particle size distributions (PSDs) showed that separations were very good, agreeing with theoretical behavior. ESEM PSDs showed that up to 87-88% of the material in the a fraction (expected to be <1 microm) was in fact less than 1 microm and in the b fraction (>1 microm) 87-95% of the material was the expected size. The SEM data indicated a slightly higher contamination of the b fraction with the presence of submicron colloids. Moreover, analysis of conformations indicated significant nonsphericity in unfractionated colloids and particles, but after SPLITT fractionation, shape factors showed that particles were significantly more spherical than before separation.     

Indoor particulate matter of outdoor origin: importance of size-dependent removal mechanisms

Adverse human health effects have been observed to correlate with levels of outdoor particulate matter (PM), even though most human exposure to PM of outdoor origin occurs indoors. In this study, we apply a model and empirical data to explore the indoor PM levels of outdoor origin for two major building types: offices and residences. Typical ventilation rates for each building type are obtained from the literature. Published data are combined with theoretical analyses to develop representative particle penetration coefficients, deposition loss rates, and ventilation-system filter efficiencies for a broad particle size range (i.e., 0.001-10 microm). We apply archetypal outdoor number, surface area, and mass PM size distributions for both urban and rural airsheds. We also use data on mass-weighted size distributions for specific chemical constituents of PM: sulfate and elemental carbon. Predictions of the size-resolved indoor proportion of outdoor particles (IPOP) for various conditions and ambient particle distributions are then computed. The IPOP depends strongly on the ambient particle size distribution, building type and operational parameters, and PM metric. We conclude that an accurate determination of exposure to particles of ambient origin requires explicit consideration of how removal processes in buildings vary with particle size.     

Airborne bacterial spore counts by terbium-enhanced luminescence detection: pitfalls and real values

Bacterial spore determination by terbium(III)-dipicolinate luminescence has been reported by several investigators. We collected spore samples with a cyclone and extracted dipicolinic acid (DPA) in-line with hot aqueous dodecylamine, added Tb(III) in a continuous-flow system and detected the Tb(III)-DPA with a gated liquid core waveguide fluorescence detector with a flashlamp excitation source. The absolute limit of detection (LOD) for the system was equivalent to 540 B. subtilis spores (for a 1.8 m3 sample volume (t = 2 h, Q = 15 L/min), concentration LOD is 0.3 spores/L air). Extant literature suggests that, from office to home settings, viable spore concentrations range from 0.1 to 10 spores/L; however, these data have never been validated. Previously reported semiautomated instrumentation had an LOD of 50 spores/L. The present system was tested at five different location settings in Lubbock, Texas. The apparent bacterial spore concentrations ranged from 9 to 700 spores/L and only occasionally exhibited the same trend as the simultaneously monitored total optical particle counts in the > or = 0.5 microm size fraction. However, because the apparent spore counts sometimes were very large relative to the 0.5+ microm size particle counts, we investigated potential positive interferences. We show that aromatic acids are very likely large interferents. This interference typically constitutes approximately 70% of the signal and can be as high as 95%. It can be completely removed by prewashing the particles.     

Roughage Content and Particle Size: Their Effects on Size Reduction and Fiber Composition of Particles Passing Through the Gastrointestinal Tract of Sheep fed Corncob-Concentrate Diets

Pelleted diets varying either in content of corncobs (45.1, 35.1, 25.1, or 15.1% of the diet) or in fineness of grind of the corncob fraction (6.5, 5.4, 1.4, or .8 mm mean particle size) were fed to ruminal-, duodenal-, and ileal-cannulated sheep to evaluate changes of digesta mean particle size and fiber composition with passage of diets through the gastrointestinal tract. As diets decreased in quantity of corncobs (Experiment 1) or in mean particle size of the corncob fraction (Experiment 2), mean particle size of diet also decreased. Percentage dietary corncobs influenced fecal mean particle size (higher percentage corncobs in diets resulted in larger fecal mean particle sizes). Fecal mean particle size was not affected by mean particle size of the corncob fraction of the diet (Experiment 2). In both experiments, fiber concentration decreased as feed, digesta, and fecal particles decreased in size. The only exception was acid detergent lignin content of digesta and fecal particles where concentration decreased and then increased as particle size decreased. Fiber concentration of separated particles tended to increase as digesta moved through the gastrointestinal tract. Reduction of particle size was greater when dietary corncob amount was high. Particle size of the dietary corncob fraction altered fiber composition of particles and reduction of particle size of the diet with passage through the gastrointestinal tract of sheep.     

Quantification of the filterability of freshwater bacteria through 0.45, 0.22, and 0.1 microm pore size filters and shape-dependent enrichment of filterable bacterial communities

Micro-filtration is a standard process for sterilization in scientific research, medical, and industrial applications, and to remove particles in drinking water or wastewater treatment. It is generally assumed, and confirmed by quantifying filtration efficiency by plating, that filters with a 0.1-0.45 microm pore size can retain bacteria. In contrast to this assumption, we have regularly observed the passage of a significant fraction of natural freshwater bacterial communities through 0.45, 0.22, and 0.1 microm pore size filters. Flow cytometry and a regrowth assay were applied in the present study to quantify and cultivate filterable bacteria. Here we show for the first time a systematic quantification of their filterability, especially their ability to pass through 0.1 microm pore size filters. The filtered bacteria were subsequently able to grow on natural assimilable organic carbon (AOC) with specific growth rates up to 0.47 h(-1). We were able to enrich bacteria communities that pass preferentially through all three pore size filters at significantly increased percentages using successive filtration-regrowth cycles. In all instances, the dominant microbial populations comprised slender spirillum-shaped Hylemonella gracilis strains, suggesting shape-dependent selection during the filtration process. This quantification of the omnipresence of microfilterable bacterial in natural freshwater and their regrowth characteristics demand a change in the sterile filtration practice used in industrial and engineering applications as well as scientific research.     

Evaluation of microspheres as surrogates for Cryptosporidium parvum oocysts in filtration experiments

The size and surface characteristics of a surrogate particle and Cryptosporidium parvum oocysts are important in determining the ability of the particle to mimic the behavior of C. parvum oocysts in filtration and particle transport experiments. The zeta potential, hydrophobicity, and filterability of a surrogate particle, 5 microm carboxylated latex microspheres, and oocysts were compared for a variety of solution conditions. C. pervum oocysts had a slightly negative zeta potential (-1.5 to -12.5 mV) at pH 6.7 over a wide range of calcium concentration (10(-6)-10(-1) M), while the fluorescent microspheres were more negatively charged under the same conditions (-7.4 to -50.2 mV). After exposure to 5 mg of C/L of Suwanee River natural organic matter (NOM), the ; potentials of both particles became significantly more negative, with the microspheres consistently maintaining a more negative zeta potential than the oocysts. Alum was able to neutralize the negative zeta potentials of both particles when in the presence of NOM, but nearly twice the dosage was required for the microspheres. NOM also affected the hydrophobicity of the particles by increasing the hydrophobicity of the relatively hydrophilic oocysts and decreasing the hydrophobicity of the relatively hydrophobic microspheres. A bench-scale filtration system removed less microspheres (40.3 +/- 1.5%) than oocysts (49.7 +/- 2.9%) when 0.01 M CaCl2 was supplied as coagulant. After preexposure to 5 mg of C/L of NOM, the removals of both particles declined significantly, and the removals of microspheres (13.7 +/- 1.5%) and oocysts (16.3 +/- 1.5%) were similar. Finally, the removal efficiencies of microspheres and oocysts in the presence of NOM increased to 69.3 +/- 3.5% and 67.7 +/- 6.4%, respectively, when alum was supplied as coagulant at the optimum dosage needed to destabilize the oocysts. These experimental results suggest that microspheres can be used to provide a conservative estimate of oocyst removal in filters containing hydrophilic negatively charged filter media.     

Evaluation of an air quality model for the size and composition of source-oriented particle classes

Air quality model predictions of the size and composition of atmospheric particle classes are evaluated by comparison with aerosol time-of-flight mass spectrometry (ATOFMS) measurements of single-particle size and composition at Long Beach and Riverside, CA, during September 1996. The air quality model tracks the physical diameter, chemical composition, and atmospheric concentration of thousands of representative particles from different emissions classes as they are transported from sources to receptors while undergoing atmospheric chemical reactions. In the model, each representative particle interacts with a common gas phase but otherwise evolves separately from all other particles. The model calculations yield an aerosol population, in which particles of a given size may exhibit different chemical compositions. ATOFMS data are adjusted according to the known particle detection efficiencies of the ATOFMS instruments, and model predictions are modified to simulate the chemical sensitivities and compositional detection limits of the ATOFMS instruments. This permits a direct, semiquantitative comparison between the air quality model predictions and the single-particle ATOFMS measurements to be made. The air quality model accurately predicts the fraction of atmospheric particles containing sodium, ammonium, nitrate, carbon, and mineral dust, across all particle sizes measured by ATOFMS at the Long Beach site, and in the coarse particle size range (Da > or = 1.8 microm) atthe Riverside site. Given thatthis model evaluation is very likely the most stringent test of any aerosol air quality model to date, the model predictions show impressive agreement with the single-particle ATOFMS measurements.     

Concentration and distribution of heavy metals in urban airborne particulate matter in Frankfurt am Main, Germany

Heavy metal concentrations were measured in airborne dust collected at three sites with different traffic densities from August 2001 to July 2002 in the Frankfurt am Main area. Bulk samples of particulate matter (PM) with an aerodynamic equivalent diameter of <22 microm were collected on cellulose nitrate filters using air filtration devices. Fractionated samples of PM with an aerodynamic equivalent diameter of <10 microm were collected using an eight-stage Andersen impactor. Pb, Cd, Mn, Ni, Zn, V, As, Sb, Cu, Cr, Co, and Ce were determined by inductively coupled plasma sector field mass spectrometry, Pt and Rh were determined by adsorptive voltammetry, and Pd was determined by total reflection X-ray fluorescence analysis. The results show that the highest airborne heavy metal concentrations occurred at the main street with a large volume of traffic. With the exception of Co, V, Ce, and Mn, the heavy metals had an elevated enrichment factor compared to their concentrations in the continental crust. The main street site was especially contaminated with Sb, Zn, Cu, V, and Ni. Motor vehicles are the likely source of emissions. With the exception of Cr, Cu, and Zn, most of the airborne heavy metal concentrations determined for impactor samples deviate slightly from the results for total airborne dust. Heavy metal particle size distributions can be divided into three groups. For metals such as As, Cd, Pb, and V, the main fraction can be found in fine particles with a diameter of <2.1 microm, whereas Ce, Cr, Co, and Ni occur mainly in coarse particles with a diameter of >2.1 microm. Cu, Mn, Sb, Zn, Pt, Pd, and Rh occur in high concentrations in the medium range of the impactor stages (particle diameters of 1.1-4.7 microm). Metal concentrations in fine dust particles are needed to assess the human health risks of their inhalation.     

Distribution of aged 14C-PCB and 14C-PAH residues in particle-size and humic fractions of an agricultural soil

Organic matter is considered to be the single most importantfactor limiting availability and mobility of persistent organic pollutants (POPs) in soil. This study aimed to characterize the distribution of 14C-PCB (congeners 28 and 52) and 14C-PAH (fluoranthene and benzo[a]pyrene) residues in an Orthic Luvisol soil obtained from two lysimeter studies initiated in 1990 at the Agrosphere Institute (Forschungszentrum Jülich GmbH, Germany). The lysimeter soils contained a low-density OM fraction, isolated during soil washing, which contained a significant fraction (3-12%) of the total 14C-activity. Soils were also fractionated according to three particle sizes: >20, 20-2, and <2 microm. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) approximately (>20 microm) for the PCBs. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) > (>20 microm) for the PAHs. The distribution of 14C-PCB or 14C-PAH residues in the organic and inorganic matrixes of the particle-size fractions was determined using methyl isobutyl ketone (MIBK). 14C-PCB and 14C-PAH-associated activities were primarily located in the humin fraction of the 20-2 and <2 microm particle-size fractions of the soil. A small fraction was associated with the fulvic and humic acid fractions; these were quantitatively more important for the PAHs than the PCBs. There appeared to be a high degree of association of 14C-activity with the mineral fraction following MIBK separation of the humic fractions, ranging between 8 and 52% for 14C-PCBs and 57-80% for 14C-PAHs. The mineral (inorganic) component of the soils apparently played a significant (previously unreported) role in the sequestration of both PCBs 28 and 52 and the PAHs fluoranthene and benzo[a]pyrene.