Aerodynamic Equivalent Diameter Research Articles

Field Comparison of PM10 Samplers

Fugitive emissions of PM10 (particulate matter with equivalent aerodynamic diameter of 10 µm or less) are an increasing concern for concentrated animal feeding operations, including open-lot beef cattle feedlots. Various federal reference method (FRM) and equivalent samplers can be used to measure PM10 concentrations. This research compared the performance of Tapered Element Oscillating Microbalance™ (TEOM), FRM high-volume (HV), and low-volume (LV) PM10 samplers in measuring PM10 concentrations in the vicinity of large cattle feedlots in Kansas. Each of the three samplers was installed at the downwind and upwind perimeters of two commercial cattle feedlots (KS1 and KS2). Samplers were operated from May 2006 to February 2008 at KS1 and from February 2007 to February 2008 at KS2. PM10 concentration ranged from <10 to 832 µg m-3 at KS1 and from <10 to 713 µg m-3 at KS2. Comparison of collocated PM10 samplers showed that measured PM10 concentration was generally largest with the TEOM PM10 sampler and smallest with the LV PM10 sampler. Differences in PM10 concentration among samplers were affected by location and duration of sampling, season, and slightly by weather conditions.

Performance evaluation of six different aerosol samplers in a particulate matter generation chamber

The present study was carried out with the aim of evaluating the performance of six different aerosol samplers in terms of mass concentration, particle size distribution, and mass fraction for the international size-sampling conventions. The international size-sampling criteria were defined as inhalable, thoracic, and respirable mass fractions with 50% cutoff at an aerodynamic equivalent diameter of 100 μm, 10 μm, and 4 μm, respectively. Two Andersen, four total suspended particulate (TSP), two RespiCon, four PM 10, two DustTrak, and two SidePak samplers were selected and tested to quantitatively estimate human exposure in a carefully controlled particulate matter (PM) test chamber. The overall results indicate that (1) Andersen samplers underestimate total suspended PM and overestimate thoracic and respirable PM due to particle bounce and carryover between stages, (2) TSP samplers provide total suspended PM as reference samplers, (3) TSP samplers quantified by a coulter counter multisizer provide no information below an equivalent spherical diameter of 2 μm and therefore underestimate respirable PM, (4) RespiCon samplers are free from particle bounce as inhalable samplers but underestimate total suspended PM, (5) PM 10 samplers overestimate thoracic PM, and (6) DustTrak and SidePak samplers provide relative PM concentrations instead of absolute PM concentrations.

Influence of atmospheric ozone, PM 10 and meteorological factors on the concentration of airborne pollen and fungal spores

The increase of allergenic symptoms has been associated with air contaminants such as ozone, particulate matter, pollen and fungal spores. Considering the potential relevance of crossed effects of non-biological pollutants and airborne pollens and fungal spores on allergy worsening, the aim of this work was to evaluate the influence of non-biological pollutants and meteorological parameters on the concentrations of pollen and fungal spores using linear correlations and multiple linear regressions. For that, the seasonal variation of ozone, particulate matter with an equivalent aerodynamic diameter smaller than 10 μm, pollen and fungal spores were assessed and statistical correlations were analysed between those parameters. The data were collected through 2003–2005 in Porto, Portugal. The linear correlations showed that ozone and particulate matter had no significant influence on the concentration of pollen and fungal spores. On the contrary, when using multiple linear regressions those parameters showed to have some influence on the biological pollutants, although results were different depending on the year analysed. Among the meteorological parameters analysed, temperature was the one that most influenced the pollen and fungal spores airborne concentrations, both when using linear and multiple linear correlations. Relative humidity also showed to have some influence on the fungal spore dispersion when multiple linear regressions were used. Nevertheless, the conclusions for each pollen and fungal spore were different depending on the analysed period, which means that the correlations identified as statistically significant may not be, even so, consistent enough. Furthermore, the comparison of the results here presented with those obtained by other authors for only one period should be made carefully.

Bioaccessibility of selected trace metals in urban PM2.5 and PM10 samples: a model study

Bioaccessibility of trace metals originating from urban particulate matter was assessed in a worst case scenario to evaluate the uptake and thus the hazardous potential of these metals via gastric juice. Sampling was performed over a period of about two months at the Getreidemarkt in downtown Vienna. Concentrations of the assayed trace metals (Ti, Cr, Mn, Co, Ni, Cu, Zn, Mo, Ag, Cd, Sn, Sb, Tl and Pb) were determined in PM2.5 and PM10 samples by ICP-MS. The metal concentrations in sampled air were in the low picogram to high nanogram per cubic metre range. The concentrations in PM2.5 samples were generally lower than those in PM10 samples. The average daily intake of these metals by inhalation for a healthy adult was estimated to be in the range of <1 ng (Tl) to >1,000 ng (Zn). To estimate the accessibility of the inhaled and subsequently ingested metals (i.e. after lung clearance had taken place) in the size range from 2.5- to 10-microm aerodynamic equivalent diameter, a batch-extraction with synthetic gastric juice was performed. The data were used to calculate the bioaccessibility of the investigated trace metals. Extractable fractions ranged from 2.10% (Ti in PM2.5) to 91.0% (Cd in PM2.5), thus yielding bioaccessible fractions (PM(2.5-10)) from 0.16 ng (Ag) to 178 ng (Cu).

Open-Path Transmissometry to Determine Atmospheric Extinction Efficiency Associated with Feedyard Dust

Open-lot, concentrated animal feeding operations (CAFOs) in the southern High Plains, such as cattle feedyards and open-lot dairies, emit fugitive particulate matter (PM) that occasionally reduces downwind visibility. The long-path visibility transmissometer (LPV) can be used to measure changes in total atmospheric extinction, a direct measure of path-averaged visibility impairment. To our knowledge, no researchers have used transmissometry as a surrogate to estimate aerosol concentrations downwind of open-lot livestock facilities. We compare time-resolved PM mass concentrations (g m-3) and atmospheric extinction coefficients (km-1) measured simultaneously along the downwind boundary of a commercial cattle feedyard to compute extinction efficiency, the change in atmospheric extinction that results from a unit change in PM mass concentration. Expected values for the in-situ extinction efficiency of total suspended particulate (TSP) and its fraction less than 10 microns (PM10) aerodynamic equivalent diameter (AED) are 0.2 to 0.5 m2 g-1 and 0.4 to 0.8 m2 g-1, respectively. Determination of the atmospheric extinction efficiency of feedyard dust will enable transmissometry to be used as an intuitive, real-time surrogate for measuring time-averaged PM10 and/or TSP concentrations.

Aerosol Collection of the (Bladewerx Corporation) Breathing Zone Monitor and Portable Workplace Monitor

The Radiation Protection Group at the Los Alamos National Laboratory has a wind tunnel capable of measuring the aerosol collection efficiencies of air sampling devices. In the fall of 2005, the group received an internal Los Alamos request to perform aerosol collection efficiency tests on two air samplers manufactured by the Bladewerx Corporation (Rio Rancho, NM). This paper presents the results from tests performed in the wind tunnel facility at a test velocity of 0.5 m s. The SabreAlert (Portable Workplace Monitor) and the SabreBZM (Breathing Zone Monitor) are both designed to detect and measure the presence of alpha emitting isotopes in atmospheres. The SabreAlert was operated at two test air flow rates of 6 and 45 liters per minute (LPM), and the SabreBZM was operated at two test air flow rates of 3 and 19 LPM. The aerosol collection efficiencies of both samplers were evaluated with oleic acid (monodisperse) liquid droplet aerosols tagged with sodium fluorescein tracer. These test aerosols varied in size from about 2.3 to 17.2 microns (aerodynamic equivalent diameter). The SabreAlert was roughly 100% efficient in aerosol collection at a flow rate of 6 LPM, and had an aerodynamic cutpoint diameter of 11.3 microns at the 45 LPM flow rate. The SabreBZM had an aerodynamic cutpoint diameter of 6.7 microns at the 3 LPM flow rate, but the SabreBZM aerosol collection efficiency never exceeded 13.6% at the 19 LPM test flow rate condition.

Size distributions of fine and ultrafine particles in the city of Strasbourg: Correlation between number of particles and concentrations of NO x and SO 2 gases and some soluble ions concentration determination

An Electrical Low Pressure Impactor (ELPI) was used during spring and autumn 2003 in the centre of Strasbourg for the measurement of atmospheric aerosols size distribution. The concentration of NO x and SO 2 in air was simultaneously measured with specific analysers. Samples were collected in the range 0.007–10 μm in equivalent aerodynamic diameter size. Number distributions are representative of a pollution originating from urban traffic with a particle size distribution exhibiting a nucleation mode below 29 nm and an accumulation mode around 80 nm in size. A mean particle density equal to 39000±35000 total particles per cm 3 with a size ranging from 7 to 10 μm was obtained after a sampling period of 2 weeks in spring. About 86.9% of the number of particles have an aerodynamic diameter below 0.1 μm and 13.1% between 0.1 and 1 μm. Correlation coefficients between the number of particles impacted on each ELPI plate and gas concentrations (SO 2 and NO x ) showed that the numbers of particles with diameter between 0.10 and 0.62 μm are highly related to the NO x concentration. This result indicates that particles are traffic induced since NO x is mainly emitted by cars as shown by measurements on various sites. Particles are less clearly correlated to the SO 2 concentration. Particle analysis on different ELPI plates for a sampling period of 2 weeks in autumn showed high level of soluble NO 3 −, SO 4 2− and NH 4 + ions. Indeed, up to 90% b.w. of these three species were found in the particle range 0.1–1 μm. The formation of particulate NH 4NO 3 is favoured by high NO x concentration, which induces the formation of gaseous HNO 3.

Correlation Between Metallic and Acidic Components in High-Risk Particle Fraction in Zagreb Air

This paper presents the results of measurements of metallic (lead, manganese, cadmium) and acidic (chloride, nitrate, sulphate) components in high-risk particle fraction (PM2.5 particles with equivalent aerodynamic diameter less than 2.5 μ m ) in the city of Zagreb, Croatia. Sampling was carried out continouosly for one year (21 March 2001 – 20 March 2002). Twenty-four-hour samples of PM2.5 were collected on cellulose membrane filters from approximately 100 m3 of ambient air. The coarser particle fraction was removed from air stream using inertial impactor. Particle mass concentration was determined by gravimetry. Acidic anions (chloride, nitrate and sulphate) were analysed using ion chromatography. Metallic components (lead, manganese, cadmium) were determined by atomic absorption spectrometry. Results show that the concentration levels of all pollutants showed significant seasonal differences (P<0.001, ANOVA, one-way), with high values during winter. A significant correlation (P<0.05) was found between the measured pollutants, except between cadmium with chlorides, sulphates and lead. The overall median anion content in the high-risk particle fraction was 19%, and the overall median metall content was 0.22 %.

LABORATORY EVALUATION OF THE DUST-EMISSION POTENTIAL OF CATTLE FEEDLOT SURFACES

A laboratory apparatus was developed for measuring the dust-emission potential of cattle feedlot surfaces as affected by manure surface characteristics. A feedlot surface was simulated with a layer of dry, loose, sieved feedlot manure, either with or without a compacted soil layer underneath. The vertical action of the cattle hoof was reproduced by dropping a steel weight onto the manure surface. High-volume samplers for PM10 (particulate matter smaller than 10 .m aerodynamic equivalent diameter) were used to collect suspended PM10. The effects of kinetic energy of the falling weight, manure depth, manure moisture content, bulk density, and surface amendment (sawdust, wheat straw, and surface water application) were investigated. For each manure depth, PM10 emission was directly related to the kinetic energy of the falling weight. For each weight drop, PM10 emission did not differ significantly with manure depth. In addition, PM10 emission was inversely related to the manure moisture content. Compaction of the manure surface reduced PM10 emission. Increased amounts of water, sawdust, or wheat straw to the manure surface also significantly decreased PM10 emission in initial tests, but dislodging/displacement of wheat straw and penetration of the wetted surface crust by the falling weight increased the emission potential for subsequent tests. The weight drop test chamber developed is a simple and repeatable method that can be used to compare relative effectiveness of different dust abatement measures. While the measurements are reproducible, the vertical action of the cattle hoof is highly simplified; thus, the WDTC might not fully reproduce the actual vertical action of the cattle hoof on a feedlot surface. In addition, the resulting aerosol may not have similar physical characteristics as those of dust emitted from feedlots.

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.

Properties, use and health effects of depleted uranium

Depleted uranium (DU) has been claimed to contribute to health problems both in military personnel directly involved in war actions as well in military and civilian individuals who resided in areas where DU ammunition was expended. Due to the low specific radioactivity and the dominance of alpha-radiation, no acute health risk can be attributed to external exposure to DU. Internalised DU is both chemo- and radio-toxic. The major risk is from inhalation of DU dust or particles with less than 10 μm aerodynamic-equivalent diameter, formed when DU ammunitions hit hard targets (aerosol formation) or during weathering of DU penetrators. One major conclusion is that for all post-conflict situations, the inhaled DU quantities (central estimates) produced radiation doses that would be only a fraction of those normally received by the lung from natural radiation. Hence no long term lung effects due to these DU amounts can be expected. These conclusions also hold for whole-body exposure from ingestion of DU in local food and water.

DESIGN AND EVALUATION OF A LOW-VOLUME TOTAL SUSPENDED PARTICULATE SAMPLER

The regulation of particulate matter (PM) emitted by agricultural sources, e.g., cotton gins, feed mills, and concentrated animal feeding operations (CAFOs), is based on downwind concentrations of particulate matter less than 10 and 2.5 .m (PM10 and PM2.5) aerodynamic equivalent diameter (AED). Both PM10 and PM2.5 samplers operate by pre-separating PM larger than the size of interest (10 and 2.5 .m) prior to capturing the PM on the filter. It has been shown that Federal Reference Method (FRM) PM10 and PM2.5 samplers have concentration measurement errors when sampling PM with mass median diameters (MMD) larger than the size of interest in ambient air. It has also been demonstrated that most PM from agricultural sources typically have particle size distributions with MMDs larger than 10 .m AED. The PM10 concentration measurement error can be as much as 343% for ambient PM with MMD = 20 .m. These errors are a consequence of the PM10 pre-separator allowing a larger mass of PM greater than 10 .m to penetrate to the filter than the mass of PM less than 10 .m captured by the pre-separator. The mass of the particles greater than 10 .m that are allowed to penetrate to the filter introduces a substantial error in the calculated concentration of PM10. Researchers have reported that sampling PM larger than 2.5 .m AED resulted in a shift in the cutpoint of the pre-separator. If this is true for all PM10 and PM2.5 samplers, then the resulting errors in measurement of ambient concentrations could be even larger. One solution to this problem is to measure the concentration of total suspended particulate (TSP) matter and calculate the concentration of PM10 by determining the mass fraction of PM less than size of interest from the particle size distribution (PSD). The “standard” high-volume TSP sampler operates at a volume rate-of-flow in excess of 1.13 m3 min-1 (40 ft3 min-1). Most of the current PM10 and PM2.5 samplers operate at 1 m3 h-1 (0.589 ft3 min-1). Other researchers reported that TSP samplers have a cutpoint of a nominal 45 .m AED. The U.S. EPA specifies the engineering design parameters for TSP samplers. This article reports the engineering design and evaluation of a low-volume (1 m3 h-1) TSP sampler (TSPLV). The results suggest that the new TSPLV may be more robust and more accurate than the “standard” high-volume TSP sampler.

PERFORMANCE CHARACTERISTICS OF A LOW-VOLUME PM10 SAMPLER

Four identical PM10 pre-separators, along with four identical low-volume (1 m3 h-1) total suspended particulate(TSP) samplers were tested side-by-side in a controlled laboratory particulate matter (PM) chamber. The four PM10 and fourTSP samplers were also tested in an oil pipe cleaning field to evaluate the PM10 samplers performance characteristics. ThePMs used in the chamber tests had mass median diameters (MMDs) larger than 10 .m, whereas the PM emitted from the oilpipe cleaning system for the field tests had MMD smaller than 10 .m. The co-located TSP and PM10 sampler testing resultsindicate that PM10 samplers over-sample when exposed to ambient PM having MMD larger than 10 .m aerodynamicequivalent diameter (AED) and under-sample when exposed to ambient PM with MMD smaller than 10 .m. Theover-sampling and under-sampling rates varied with the change of MMD and the PM loading (TSP concentration). Thecutpoints and slopes of the PM10 pre-separator changed with the change of MMD of inlet PM.

The respiratory toxicity of airborne volcanic ash from the Soufrière Hills volcano, Montserrat

AbstractThe Soufrière Hills stratovolcano on the Caribbean island of Montserrat has been erupting since 18th July 1995. An enormous amount of respirable volcanic ash has been suspended into the atmosphere by the eruptions and wind re-suspension of deposited ash. The large amount of fine, airborne particulate matter, in particular the component 10 μm equivalent aerodynamic diameter (PM10), is a cause of medical concern. Airborne levels have frequently exceeded the UK environmental standard for PM10, (50 μg/m3), although it is noted that this standard was primarily set for urban PM10. The crystalline silica in the ash is mostly cristobalite, at reported levels up to 20%. The UK government’s Chief Medical Officer, referring to Montserrat, has suggested that long-term exposure to high levels of volcanic ash could lead to silicosis. These concerns have prompted government-funded investigations into the potential toxicity of well characterized volcanic ash samples from Montserrat. Given the well established toxicity of cristobalite, particular attention was paid to the amount of this mineral in the ash samples. Three ash samples were tested: (1) a vulcanian eruption ash, (2) ash released in a domecollapse pyroclastic flow, and (3) ash from a major vulcanian explosion that was wind-transported to, and deposited on, the neighbouring island of Antigua. Comparative toxicological studies were carried out on respirable preparations of these three samples together with appropriate control mineral dusts that matched the major components of the Montserrat samples: anorthite, labradorite, cristobalite/ obsidian and cristobalite. Alpha quartz (DQ12) was the positive control. All samples, including the controls, were characterized to establish particle-size distributions, particle morphologies, and to confirm the mineralogy. Rats were challenged with 1 mg via intratracheal instillation, and groups sacrificed at three time points (1, 3 and 9 weeks). Health assessment was made by examining endpoints of increasing lung damage such as inflammation, permeability (oedema), changes in epithelium, and increase in the size of broncho-thoracic lymph nodes. The data indicate that Montserrat respirable ash, derived from dome collapse pyroclastic flows or vulcanian explosions, has minimal acute bioreactivity in the lung. The feldspar standards showed low bioreactivity, in stark contrast to the cristobalite standard that showed progressive increases in lung damage. These results suggest that either the mass of cristobalite present in the Montserrat ash was insufficient to cause an effect in the lung, or the cristobalite in the ash was, for some as yet unknown reason, markedly less bioreactive than our pure cristobalite standard.

Comparison of wood-dust aerosol size-distributions collected by air samplers.

A method has been described previously for determining particle size distributions in the inhalable size range collected by personal samplers for wood dust. In this method, the particles collected by a sampler are removed, suspended, and re-deposited on a mixed cellulose-ester filter, and examined by optical microscopy to determine particle aerodynamic diameters. This method is particularly appropriate to wood-dust particles which are generally large and close to rectangular prisms in shape. The method was used to investigate the differences in total mass found previously in studies of side-by-side sample collection with different sampler types. Over 200 wood-dust samples were collected in three different wood-products industries, using the traditional 37 mm closed-face polystyrene/acrylonitrile cassette (CFC), the Institute of Occupational Medicine (IOM) inhalable sampler, and the Button sampler developed by the University of Cincinnati. Total mass concentration results from the samplers were found to be in approximately the same ratio as those from traditional long-term gravimetric samples, but about an order of magnitude higher. Investigation of the size distributions revealed several differences between the samplers. The wood dust particulate mass appears to be concentrated in the range 10-70 aerodynamic equivalent diameter (AED), but with a substantial mass contribution from particles larger than 100 microm AED in a significant number of samples. These ultra-large particles were found in 65% of the IOM samples, 42% of the CFC samples and 32% of the Button samples. Where present, particles of this size range dominated the total mass collected, contributing an average 53% (range 10-95%). However, significant differences were still found after removal of the ultra-large particles. In general, the IOM and CFC samplers appeared to operate in accordance with previous laboratory studies, such that they both collected similar quantities of particles at the smaller diameters, up to about 30-40 [micro sign]m AED, after which the CFC collection efficiency was reduced dramatically compared to the IOM. The Button sampler collected significantly less than the IOM at particle sizes between 10.1 and 50 microm AED. The collection efficiency of the Button sampler was significantly different from that of the CFC for particle sizes between 10.1 and 40 microm AED, and the total mass concentration given by the Button sampler was significantly less than that given by the CFC, even in the absence of ultra-large particles. The results are consistent with some relevant laboratory studies.

An HDI Polyisocyanate Aerosol Exposure System for Large-Scale Animal Experiments

An exposure system that allows large-scale exposure of animals to 1,6-hexamethylene diisocyanate (HDI)-based polyisocyanates at a stable concentration and aerosol size distribution was developed. The HDI polyisocyanate aerosol is generated by nebulizing a solution of a commercial polyisocyanate product dissolved in acetone. The aerosol is delivered with a constant airflow into a horizontal flow chamber. Complete mixing of aerosol in the chamber is ensured by a circulating fan. This method has been used to generate atmospheres containing HDI polyisocyanates at a concentration of 10.46±0.23 mg/m3 over a 5-hour period. The overall mass median aerodynamic equivalent diameter was found to be 1.42 µm with a geometric standard deviation of 1.26. The HDI monomer concentration was 0.15±0.04 mg/m3. The average chamber acetone concentration was determined to be 2481±222 ppm (mean±standard deviation). Different HDI polyisocyanate concentrations in the chamber can be achieved by altering the concentration of the comme...

An HDI polyisocyanate aerosol exposure system for large-scale animal experiments.

An exposure system that allows large-scale exposure of animals to 1,6-hexamethylene diisocyanate (HDI)-based polyisocyanates at a stable concentration and aerosol size distribution was developed. The HDI polyisocyanate aerosol is generated by nebulizing a solution of a commercial polyisocyanate product dissolved in acetone. The aerosol is delivered with a constant airflow into a horizontal flow chamber. Complete mixing of aerosol in the chamber is ensured by a circulating fan. This method has been used to generate atmospheres containing HDI polyisocyanates at a concentration of 10.46+/-0.23 mg/m(3) over a 5-hour period. The overall mass median aerodynamic equivalent diameter was found to be 1.42 microm with a geometric standard deviation of 1.26. The HDI monomer concentration was 0.15+/-0.04 mg/m(3). The average chamber acetone concentration was determined to be 2481+/-222 ppm (mean+/-standard deviation). Different HDI polyisocyanate concentrations in the chamber can be achieved by altering the concentration of the commercial polyisocyanate product in acetone and the chamber flow rate. The described exposure system will be useful for performing toxicological studies involving HDI polyisocyanates.

Determination of Pt, Pd and Rh by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in size-classified urban aerosol samples

Pt, Pd and Rh concentration levels related to particle size distribution were measured in Viennese aerosol. The urban aerosol was studied over a period of 1 month during summer 2002 in a heavy traffic area. A 6-stage cascade impactor collected classified particles with aerodynamic equivalent diameter (aed) <10 µm. Total suspended particulate matter (aed <30 µm) was assessed by filtering air (open face sampling head). The analysis of Pt, Pd and Rh in aerosol samples required a different strategy for each element to obtain accurate results and maximum sensitivity. Sample preparation was carried out by microwave-assisted acid digestion. For the determination of Pd an anion-exchange procedure was implemented. The digested samples were measured by ICP-SFMS in combination with ultrasonic nebulization and membrane desolvation, utilizing the high-resolution capabilities of this instrument for the determination of Rh. Pt and Pd were quantified by isotope dilution (IDMS), Rh by external calibration. Excellent detection limits of 0.07, 0.06 and 0.05 pg m−3 (impactor substrates) and 0.18, 0.22, 0.14 pg m−3 (open face sampling head substrates) for Pd, Pt and Rh, respectively, could be achieved. Since platinum group elements (PGE) are emitted from car catalysts as a result of mechanical processes, Pt, Pd and Rh were mainly found in the coarse fraction of urban aerosol. Summing up the concentrations assessed for the impactor stages (aed <10 µm) revealed a weekly average of 4.3 ± 1.7, 2.6 ± 0.6 and 0.4 ± 0.1 pg m−3 for Pt, Pd and Rh respectively. Concentration levels of samples collected with the open face sampling head (aed <30 µm) over the period of one week were significantly higher with average values of 38.1 ± 6.3, 14.4 ± 3.1 and 6.6 ± 2.4 pg m−3. Moreover, the presence of a collective of small particles containing the three investigated PGE was shown. Investigation of the impactor samples revealed an analogue size distribution for Pt, Rh and Pd with a maximum at 1–2.15 µm aed. These particles are toxicological relevant, as they penetrate deeply in human lungs (particles of 0.1–2.5 µm aed are deposited in the lung alveoli).

Relationship between particle mass and mobility for diesel exhaust particles.

We used the aerosol particle mass analyzer (APM) to measure the mass of mobility-classified diesel exhaust particles. This information enabled us to determine the effective density and fractal dimension of diesel particles as a function of engine load. We found that the effective density decreases as particle size increases. TEM images showed that this occurs because particles become more highly agglomerated as size increases. Effective density and fractal dimension increased somewhat as engine load decreased. TEM images suggest that this occurs because these particles contain more condensed fuel and/or lubricating oil. Also, we observed higher effective densities when high-sulfur EPA fuel (approximately 360 ppm S) was used than for Fischer-Tropsch fuel (approximately 0 ppm S). In addition, the effective density provides the relationship between mobility and aerodynamic equivalent diameters. The relationship between these diameters enables us to intercompare, in terms of a common measure of size, mass distributions measured with the scanning mobility particle sizer (SMPS) and a MOUDI impactor without making any assumptions about particle shape or density. We show that mass distributions of diesel particles measured with the SMPS-APM are in good agreement with distributions measured with a MOUDI and a nano-MOUDI for particles larger than approximately 60 nm. However, significantly more mass and greater variation were observed by the nano-MOUDI for particles smaller than 40 nm than by the SMPS-APM.

Phase separation and regrowth of aerosol matter collected after size fractionation in an impactor

Aerosol matter in the size range <2 μm was collected in a Berner impactor and subsequently analysed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. Owing to the low electron beam energy of 5 keV (occasionally 10 keV), analysis was restricted to elements with atomic numbers ⩽20 (Ca). Sub-micrometer aerosol matter was found to contain mostly S, O, and C as well as some K and Ca. Nitrogen appeared to escape detection, probably due to bombardment-induced sublimation of NO 3 and NH 4. During sampling at low to moderate relative humidity (<60%) the sulphur-rich fraction of the aerosol matter (most likely sulphates) regrew in the form of microcrystals with sizes up to 10 times larger than the mean aerodynamic diameter of the respective impactor stage. By contrast, when sampling during periods in course of which the relative humidity exceeded 70%, the aerosol matter regrew in the form of extended amorphous agglomerates. The aerosol deposits also contained large numbers of carbon nanoparticles, well separated from the regrown sulphate-rich matter. The nanoparticles were similar in size (∼20–40 nm), much smaller than the equivalent aerodynamic diameter of the impacting particles (63 nm–2 μm). Presumably, the carbon nanoparticles constituted the core of larger air-borne particles covered with sulphates (as well as with nitrates and organic carbon). The regrown microcrystals disappeared rapidly under electron bombardment at high current density, an observation that indicates high volatility at elevated temperatures. Aerosol matter collected in the size range between 1 and 2 μm contained large fractions of particles made of O, Si, P, K, and Ca (oxides). These particles were highly resistant to electron bombardment (hard) and showed little or no evidence for agglomeration or regrowth. After removing the soluble (acidic) material from the collected aerosol matter, only carbon nanoparticles and hard coarse particles were left behind. The observation of agglomerated or crystallized “soft” aerosol matter in combination with phase separation of carbon nanoparticles lends further support to the assertion that it is not possible to collect useful quantities of fine and ultrafine aerosol particles with as-suspended morphology. Some implications for health-related research are discussed.