K. Van Cauwenberghe

Experiments on the distribution of organic pollutants between airborne particulate matter and the corresponding gas phase

Abstract Airborne particulate matter sampling was used in conjunction with gas phase sampling. Particulates were collected on glass fiber filters. Organic compounds not retained by the filter material were trapped from the gas phase on Tenax-GC polymer beads. Qualitative and quantitative analysis of the sample extracts was performed by gas chromatography-mass spectrometry with computerized data elaboration. More than 100 compounds were identified in the gas phase. About 50 of these compounds were quantified in both aerosol and gas samples with a precision of better than 10%. A distribution factor was defined for individual compounds as the ratio of the concentration of the compound in the particulate fraction over the concentration in the gas phase. Lower molecular weight compounds with high vapor pressure were present predominantly in the gas phase. High boiling compounds were preferentially retained on the filter material.

Determination of organic compounds in airborne particulate matter by gas chromatography-mass spectrometry

Abstract Airborne particulate matter from a residential town area was sampled by filtration through glass fiber filters. The benzene extractable compounds were subjected to a separation into neutral, acidic and basic substances. The acidic fraction was converted to the methylated derivatives before analysis. The partly evaporated residues were analyzed qualitatively by gas chromatography-mass spectrometry with computerized data acquisition. The generation of mass chromatograms for specific ion fragment masses permitted the location of mass spectra. Interpretation and comparison with reference data led to the identification of more than 100 compounds. In the neutral fraction, saturated aliphatic hydrocarbons, polynuclear aromatic hydrocarbons and polar oxygenated substances were identified. The acidic fraction consisted mainly of a homologue series of fatty acids and aromatic carboxylic acids some of them with hydroxysubstitution. The basic fraction consisted of the nitrogen containing analogues of the important polyaromatic hydrocarbons present in the neutral fraction. Estimates of the range of concentrations of various substances were made by the addition of standard amounts of a reference compound and the integration of the mass spectrometer output; some of the concentrations could not be determined very accurately because of the incomplete retention of the more volatile compounds during sampling.

The gas-particle distribution of organic aerosol constituents: measurement of the volatilisation artefact in Hi-Vol cascade impactor sampling

Abstract In order to determine quantitatively the volatilisation losses of organic aerosol constituents upon prolonged Hi-Vol sampling, an Integrated Gas Phase-Aerosol Sampling System was developed. The volatilisation artefact being measured, the actual distribution of the volatile organic compounds between the gas and the particulate phase as it exists in the atmosphere could be studied. Sampling was performed in a suburban and in a rural site during the four seasons. Determinations of the major organic aerosol components, including a series of unbranched aliphatic hydrocarbons, carboxylic acids and polycyclic aromatic hydrocarbons (PAH), were carried out by mass fragmentography. The volatilisation artefact is found to be important for the compounds with intermediate vapor pressure, e.g. n- alkanes from eicosane to tetracosane, acids from lauric to stearic acid, PAH from phenanthrene /anthracene to benz(a)anthracene/chrysene. The obvious influence of parameters such as the sampled volume and the average ambient air temperature is clearly reflected in the obtained data. The implications of these results with respect to the optimisation of Hi-Vol sampling procedures and to the use of the profile concept for emission source characterisation are discussed, as well as the problems, involved with the correction of particle size distribution data for aerosol constituents subjected to the volatilisation artefact. Generally, the particle size distribution profiles tend to widen as a consequence of the preferential depletion of the sub-μm fraction. The measured gas-particle distribution in the atmosphere reflects some important physico-chemical processes in aerosol formation and ageing. The gas-particle conversion of a young condensation aerosol in the suburb is compared to that of the aged, diluted one at the rural station. Aerodynamic elution of the most volatile n- alkanes is observed at the latter site.

Cascade impactor measurements of the size distribution of the major classes of organic pollutants in atmospheric particulate matter

Abstract Airborne particulate matter from a suburban area was fractionated in a 6-stage high volume cascade impactor and analysed for about 60 organic pollutants by programmed multiple ion detection gas chromatography-mass spectrometry. The distribution, as a function of particle size, has been measured for the aliphatic hydrocarbons, carboxylic acids, polynuclcar aromatic hydrocarbons (PAH) as well as some aza-heterocyclic polyaromatics. The observed distribution patterns are very similar. Most aliphatic hydrocarbons (85–90°) are found on particles below 3μm. The carboxylic acids are found for 90–95% below 3 μm. The PAH distribution is strongly subjected to seasonal variations : 95–98% below 3 μm and 70–80% below 1μm in winter. For the PAH eight different, but closely related types of distributions were measured. In winter, the distributions shift toward the smaller particles. Indications for artefacts produced by volatilisation are advanced : the lower PAH show a flatter distribution in the smaller size range. Also, the alternating concentration levels of even and uneven n -alkenes could be due to selective losses for the even alkenes, since there is a correlation with the molar heat of vaporisation of the homolog series.

On the aliphatic and polyaromatic hydrocarbon levels in urban and background aerosols from belgium and the netherlands

Concentrations of aliphatic hydrocarbons from eicosane up to tritriacontane, and of polycyclic aromatic hydrocarbons from anthracene and phenanthrene up to the dibenzanthracenes have been determined by GC-MS in ambient aerosol samples from seven different locations in Belgium, the Netherlands and Bolivia. Some of the sampling stations were situated in urban environments, others in residential suburban or rural sites. At one sampling station, the distribution of these hydrocarbons between the particulate and the gas phase was further investigated. The distribution patterns of aliphatic and polyaromatic hydrocarbons as a function of molecular weight or carbon number are reported for typical summer and winter samples collected under the most frequently occurring stable meteorological conditions, at two urban and one rural site in Belgium. Furthermore, hydrocarbon levels for two suburban stations are reported in terms of average concentrations over summer and winter periods as well as of frequency distributions. They are based on weekly samples collected over the whole year. The aliphatic hydrocarbon series shows a typical alternating pattern with higher concentrations for the compounds with odd carbon number in the range C27–C31. This effect is believed to result from natural emissions of biological origin (e.g. vegetation), whereas a more continuous distribution is observed for the anthropogenic emissions with a maximum around C24–C26. Gas phase contributions above C24 to the total aliphatic hydrocarbon levels are not significant. The polyaromatic hydrocarbon series shows a constant distribution pattern with an expected increase in winter due to increased fossil fuel combustion processes, mainly of the higher molecular weight compounds, such as chrysene/benzanthracene, benzofluoranthenes and benzopyrenes. Among these, only chrysene/benzanthracene is also significant in the gas phase. At the background stations, the natural emission of higher odd aliphatic hydrocarbons is enhanced in summer samples as can be seen from the carbon preference index. For the background stations the combined interpretation of industrial activity data and prevailing wind direction data allows a reasonable understanding of the changes in pollution levels. However, this approach was not successful for the suburban samples of the survey studies, where changing meteorological factors such as variable winds, inversion conditions or rain simultaneously affected the organic composition of the aerosol.

Nanotechnology in bio/clinical analysis

Nanotechnology is being exploited now in different fields of analytical chemistry: Single cell analysis; in chip/micro machined devices; hyphenated technology and sampling techniques. Secretory vesicles can be chemically and individually analyzed with a combination of optical trapping, capillary electrophoresis separation, and laser induced fluorescence detection. Attoliters (10(-18) l) can be introduced into the tapered inlets of separation capillaries. Chip technology has come of age in the field of genomics, allowing faster analyses, and will fulfil an important role in RNA and peptide/protein analysis. The introduction of nanotechnology in LC-MS and CE-MS has resulted in new findings in the study of DNA adduct formation caused by carcinogenic substances, including anticancer drugs. Sample handling and introduction also can benefit from nanotechnology: The downscaling of sample volumes to the picoliter level has resulted in zeptomole (10(-21)) detection limits in the single-shot mass spectrum of proteins.

Comparison between the organic fraction of suspended matter at a background and an urban station

Abstract Airborne particulate matter was sampled near the Cosmic Ray Laboratory of Chacaltaya, Bolivia, about 25 km NE of La Paz, at an altitude of 5200 m. Quantitative analysis of organic compounds was performed on two combined samples by gas chromatography-mass spectrometry with computerized data acquisition. Results are presented for aliphatic and polyaromatic hydrocarbons, fatty acids and heterocyclic arenes. A comparison is made with the results obtained from samples collected in a residential city area of Antwerp, Belgium. Polyaromatic hydrocarbons are found to be present in lower concentrations in the Bolivian samples by a factor of 10 to 300. For other compounds no meaningful differences are observed. The amount of the total suspended particulate matter per unit of volume is about three times lower in the remote area compared to the residential area.

Conversion of polycyclic aromatic hydrocarbons on diesel particulate matter upon exposure to ppm levels of ozone

Diesel exhaust particlulate matter samples were collected from a dilution tunnel using a Hi-Vol cascade impactor. The fraction of the aerosol with aerodynamic diameter below 0.5 μm, retained on the glass fiber back-up filter, was exposed to a flow of ozonised particle free air for periods of 0.5–4 h (1.5 ppm of O3, flow rate about 40 m3 h−1). Both exposed and non-exposed reference niters were Soxhlet-extracted with benzene and methanol, and the polycyclic aromatic hydrocarbon fraction (PAH) was isolated by a liquid-liquid partition procedure described in the literature, using cyclohexane and dimethylformamid-water as solvents, modified for quantitative recovery of PAH. The conversion yields of PAH upon exposure to O3 were determined by single ion monitoring mass spectrometry using a fused silica capillary column for their separation. Significant conversion was observed for PAH from molecular weight 226 to 276. Approximate half lives are of the order of 0.5–1 h for most PAH measured. This high reactivity of PAH on a carbonaceous matrix is probably related to the large specific surface of soot particles as well as to their high adsorptive capacity for gaseous compounds. Lower molecular weight PAH up to chrysene also undergo important physical losses by volatilisation and the extent to which chemical transformations occurred could not be determined accurately. Different reactivities are observed for several isomeric pairs of PAH: benzo(a)pyrene is much faster converted than benzo(e)pyrene, benz(a)anthracene reacts faster than chrysene. The benzo-fluoranthenes are most resistant toward O3 attack. The implications of these results with respect to atmospheric degradation of PAH, as well as to the occurrence of artefactual conversion upon Hi-Vol sampling are discussed.

On the size distribution of polycyclic aromatic hydrocarbon containing particles from a coke oven emission source

Abstract Two samples of particulate matter from a coke oven emission source were collected with an Andersen cascade impactof to obtain size-graded fractions. Analysis of 12 major polycyclic aromatic hydrocarbons was performed for all stages, by means of a gas chromatograph-mass spectrometer used in the mass fragmentography mode. Results illustrate that over 90% of polycyclic aromatic hydro-carbons is found on the particles smaller than 3 μm, which means that most of these compounds are within the respiratory size range. Similar size distribution curves were obtained for both the lower and higher molecular weight compounds.

Extraction of organic compounds from airborne particulate matter

The extraction of organic compounds from airborne particulate matter, obtained by glass fiber filtration, has been studied with different solvents and has been followed as a function of time.For many compounds, almost quantitative extraction was obtained after S h. Polyaromatic hydrocarbons and polar compounds often yielded higher extraction efficiencies with methanol than with benzene.The gas chromatographic mass spectrometric determination of these compounds is somewhat simplified by a separation of the sample into neutral, acidic and basic fractions.The efficiency of this procedure was tested on a mixture of compounds representative for the actual aerosol composition. It was concluded that the basic fraction yielded poor results.The techniques for these measurements included quantitative gas chromatography with electronic integration for standard mixtures and quantitative mass chromatography for natural sample extracts.