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ld appear that this is only possible if the trace element carrier compounds which may possibly occur are known and the question of local incorporation into or onto individual dust particles can be clarified Past investigations show that only certain portion of the trace ele- ments present is incorporated in such compounds and would be accessible to dissolution pro- cesses after emission and could thus exert an environmentally-damaging influence The research project focuses primarily on investigating the following questions ) Are the trace elements present in the form of finely dispersed compounds of their own, or are they incorporated components of other compounds? ) Which traceelements are found in the glassof dust particlesfrom coal-fired powerstations and in the relict or newly formed minerals therein? ) Which trace element compounds form as condensates or sublimates on the surfaces of dust particles or at other sites of heterogeneous nucleation? ) Do certain trace element compounds, which are possibly water-soluble, accumulate on the surface of clean-gas particles? 2. Working steps Eight clean-gas dusts were investigated,six of which originated from coal-fired powerstations -three with dry and threewith slag tap furnaces - and twofrom refuse incineration lants The samples were taken downstream of the filter installations of the power stations gy experts from the VGB (Vereinigung der GroBkraftwerksbetreiber, Essen) The following examination procedure was employed on the clean-gas dusts ) The main components of the mineral content were analysed quantitatively with an -ray powder diffractometer, ) The particle size spectrum of the clean-gas dusts was determined using an analytical com- bination consisting of surface electron microscopy (SEM) and automatic image analysis, ~ 1 ) The analysis of individual dust particles and larger particle opulations was performed in the SEM using energy dispersive -ray microanalysis (EDSf ) The qualitat