S. Hoornaert

Single Particle Characterisation of the Aerosol in the Marine Boundary Layer and Free Troposphere over Tenerife, NE Atlantic, during ACE-2

In the framework of the 2nd Aerosol Characterization Experiment (ACE-2), in June and July 1997, size segregated samples were collected for single particle analysis on the island of Tenerife, in both the marine boundary layer (MBL) and the free troposphere (FT), to study the characteristics of the North Atlantic aerosol. A systematic assessment was made of the aerosol under background conditions and when the environment was perturbed by European emissions and/or Saharan dust. The aerosol particles were analysed by automated and manual SEM-EDX, followed by cluster analysis to identify the different particle types and their abundance. Basing on back trajectory calculations, particle numbers and volume concentrations, different periods can be identified regarding the origin of the sampled air masses. In the FT, the air masses were classified as clean Atlantic, Saharan dust from Africa or pollution from Europe. In the MBL, air masses were classified as clean, polluted or perturbed by emissions from Europe. For both the FT and MBL samples, the main changes in chemical composition were observed between the fine and coarse mode aerosol. The FT fine mode aerosol is dominated by S-poor aluminosilicates (62%) in the event of the dust samples or sulphates, carbonaceous particles (20%) and S-rich aluminosilicates (46%) in the polluted samples. For the larger fractions, a strong decreasing trend was observed for the sulphates (less than 20%) and carbonaceous particles (10%) in the polluted samples. The MBL fine mode was completely dominated by S-rich particles (polluted 55% and perturbed 59%), and to a lesser extent, carbonaceous and aged sea salt particles. In the coarse mode, the polluted air mass is dominated by sea salt particles (62%). Contrary to the fine fraction, the polluted air mass in the coarse fraction contained 5.3% of S-rich particles. The combined interpretation of the data from the analysis of size-fractioned particles and the calculated backward trajectories for air masses coming from Europe, Africa and the Atlantic, results in better insights on aerosol chemistry, especially for the comparison of the particle composition in the FT and the MBL.

Characterisation of Individual Aerosol Particles for Atmospheric and Cultural Heritage Studies

Microanalysis of individual particles allows straightforward and advanced characterisation of environmental samples. The most obvious technique to study large microparticle populations is still electron probe X-ray microanalysis (EPXMA). Recently, technical and methodological progress has been made to remedy some of the limitations of conventional EPXMA, as, for example, in the detection of low Z-elements. Recent examples of the use of EPXMA in various environmental fields are presented, namely concerning atmospheric deposition of micropollutants and nutrients to the sea, characterisation of aerosols in the context of their effect on Global Change (remote continental and biogenic aerosols) and aerosol deposition and soiling of paintings in museums.

Assessment of homogeneity of candidate reference material at the nanogram level and investigation on representativeness of single particle analysis using electron probe X-ray microanalysis

Abstract Particulate samples of a candidate reference material are evaluated on their homogeneity from bottle to bottle using electron probe X-ray microanalysis technique. The evaluation on the homogeneity is done by the utilization of the Kolmogorov–Smirnov statistics to the processing of the quantitative electron probe X-ray microanalysis data. Due to a limitation, existing even in computer controlled electron probe X-ray microanalysis, in terms of analysis time and expenses, the number of particles analyzed is much smaller compared to that in the sample. Therefore, it is investigated whether this technique provides representative analysis results for the characteristics of the sample, even though a very small portion of the sample is really analyzed. Furthermore, the required number of particles for the analysis to insure a certain level of reproducibility, e.g. 5% relative standard deviation, is determined by the application of the Ingamells sampling theory.

Electron probe X-ray microanalysis for the assessment of homogeneity of candidate reference materials at the nanogram level

A new approach to the assessment of homogeneity for powder samples of candidate reference materials with the help of electron probeX-ray micro-analysis (EPMA) is proposed. It is based on the utilisation of the Kolmogorov—Smirnov statistics coupled with the Akaike Information Criterion in the processing of the quantitative EPMA data. The evaluation of three IAEA candidate reference materials with the described approach is discussed.

Gypsum and other calcium-rich particles above the North Sea

Ca-containing particles, especially CaSO4 particles, have been encountered in several atmospheric aerosol studies. An overview is given of the different sources of airborne Ca-containing particles. The North Sea atmosphere is studied to identify the different Ca-containing particle types and to find the correlation between their occurrence and the source regions of the corresponding air masses. About 50 000 individual aerosol samples were collected above the Southern Bight of the North Sea for several wind directions and analyzed for their composition using electron probe X-ray microanalysis. Nonhierarchical cluster analysis is performed on the data to reveal the different particle types, their relative abundances and their sources. CaSO4 in most cases constitutes the largest fraction of the Ca-containing particles. Extremely high numbers of CaSO4 particles are found for northeastern winds, coming from the central part of Germany, suggesting that a great fraction is derived from anthropogenic sources loca...