F. Bruynseels

Characterization of North-Sea aerosols by individual particle analyses

Abstract On aerosol and rain water samples, collected in the Southern Bight of the North Sea, single particle analyses were performed using both laser microprobe mass analysis and electron-probe X-ray microanalysis in combination with an automated image analysis system. In the aerosols collected from an air mass that had travelled from the Atlantic Ocean along the coast of North France, pure seasalt constituted the most abundant particle type, while aluminosilicates (mostly spherical fly-ash particles) amounted to about 20% and mixed seasalt/aluminosilicate, carbonaceous particles, CaSO 4 and spherical iron oxides contributed each 5–10 %. In air masses that had a longer residence time over the continent, spherical iron oxides, carbonaceous particles and ammonium sulfates together made up 70 % of the total particle load. Seasalt particles were nearly all enriched in sulfate or nitrate, but they were seen to be washed out efficiently after a rain shower. In rain water, some 40 % of the particles appeared to be spherical or irregularly shaped aluminosilicates, from fly-ash and dust dispersal, but more than 50 % consisted of SiO 2 . The high relative abundance of these particles in rain water may be the result of Al leaching from fly-ash, or of more efficient scavenging by rain droplets.

Direct detection of sulfate and nitrate layers on sampled marine aerosols by laser microprobe mass analysis

Abstract The direct detection of sulfate and nitrate layers on sampled marine aerosols was carried out by laser microprobe mass analysts.

Investigation of heterogeneous reactions of PAH's on particle surfaces using laser microprobe mass analysis

Abstract Artificially generated NaCl particles were coated with PAHs by using a condensation technique. These particles were exposed to reactive gases like ozone, bromine and nitrogen dioxide. The original as well as the exposed particles were investigated by fluorimetric analysis and by LAMMA (Laser Microprobe Mass Analysis) in the desorption mode, which allows the evaporation and characterization of surfaces of single particles. The results are interpreted in terms of possible heterogeneous atmospheric reactions. The reactivity of the considered PAHs towards nitrogen dioxide was found to be negligible. The structure of the reaction products formed with ozone was partially elucidated.

Study of inorganic ammonium compounds in individual marine aerosol particles by laser microprobe mass spectrometry

Abstract Ammonia is important in the atmosphere because it neutralizes acidic species. The relative importance of different inorganic ammonium compounds (chloride, nitrate and sulfate) in marine air chemistry was studied by single-particle characterization with the laser microprobe mass analyser. Standard aerosols were generated as a reference for compound identification, based on the fingerprint spectra obtained, and calculation of the relative sensitivity achieved for different ions in a marine aerosol matrix. The relative sensitivity for ammonium was low. Aerosol samples were collected in the Southern Bight of the North Sea under different meteorological conditions and examined for their ammonium compounds. Samples collected during an inversion period with continental influences showed a much higher content in all particles than samples collected under different meteorological conditions, where ammonium was mostly detected in the submicrometer particle-size range.

Molecular ion distributions in laser microprobe mass spectrometry of calcium oxide and calcium salts

Abstract Laser Microprobe Mass Spectrometry (LAMMA) is used to examine micrometric particles of calcium oxyanion salts (CaCO 3 , CaSO 4 , CaSO 4 ·2H 2 O) and calcium oxide, in both the positive and negative ion mode. The major molecular ions, appearing in the positive mass spectrum, can be divided into three series, namely Ca m O m -1 + , (CaO) m + and (CaO) m H + ( m = 1-4). In the case of the former two series the relative intensities of the mass peaks as a function of the fragment valence K = (1 + 2 n )/ m , for Ca m O n + , can be fitted to a Gaussian distribution curve, as was earlier demonstrated for secondary ion mass spectrometry. The high stability of the (CaO) m H + series can be explained by the favourable fragment valence of +2 corresponding to the usual oxidation state of calcium.

Recombination reactions and geometry effects in laser microprobe mass analysis studied with 12C/13C bilayers

Abstract Bilayers of carbon, consisting of a layer of natural carbon and a second layer highly enriched in 13 C, were investigated with the LAMMA 500- ® instrument. When such a bilayer is perforated by the laser beam, comparable amounts of 12 C and 13 C are evaporated and partly ionized so that geometry effects and recombination reactions during laser-induced ionization can straightforwardly be studied.

Characterization of Individual Particle Types in Coastal Air by Laser Microprobe Mass Analysis

Abstract Laser Microprobe Mass Analysis (LAMMA) was used in a preliminary study to characterize aerosol particles from a beach and inland sites and from a heavily industrialized area. As many as six types of both positive and negative mass spectra with different inorganic and organic signals could be distinguished in the different particle size ranges. Information about the elemental composition and the speciation of S and N was obtained. With increasing distance from sea, progressive uptake of nitrate in seasalt particles was found. Complex particles, containing soot and organic ammonium sulfate, were also detected.

Inorganic nitrogen speciation in single micrometer-size particles by laser microprobe mass analysis

Individual micrometer-size particles of inorganic nitrogen salts, such as NaNO3, NaNO2, (NH4)2SO4, NH4Cl, NH4NO3 and their mixtures, were analysed in the laser microprobe mass analyser. The cluster-ion distributions of the salts are systematically described and can be used to gain speciation information. The results can be used to study the distribution of the atmospheric aerosol inorganic nitrogen compounds and to investigate their chemical transformations under ambient conditions.

Characterization of Individual Environmental Particles

Abstract Recently, several micro-analysis techniques have been developed which can advantageously be applied to particulate environmental samples to complement measurements made by traditional bulk analysis methods. Automated electron probe X-ray microanalysis in combination with multivariate numerical analysis can, in a relatively short time, provide information about the major and minor elemental chemical composition of large numbers of aerosol and aqueous suspension particles. Relevant particle types can thus be identified and their behaviour can be followed as a function of time, location, wind direction or depth. In addition, laser microprobe mass analysis can yield complementary knowledge about the trace element distribution over the various particle types and, in some cases, about the particle surface layer characteristics. The potential and limitations of these methods are illustrated in applications to aerosol particles from the North Sea and the Amazon Basin, to particles from the sea surface microlayer, and to aqueous suspension particles from the Baltic Sea.

LAMMA and electron-microprobe analysis of atmospheric aerosols

A laser microprobe mass analyser and a highly automated electron probe X-ray microanalysis unit have been used to study the elemental composition, inorganic speciation and morphology of atmospheric aerosols collected at various remote to polluted and marine to continental locations