Studies on the influence of fly ash on the photosynthetic activity of Solidago canadensis L. were carried out in order to determine the importance of this material as an environmental impact agent. Leaf samples were dusted by fly ash and sprayed with water of different pH simulating acid rain. Fly ash was applied in quantities to model an accidental occasion of extremely high emission level of fly ash as a result of malfunctioning of the electrostatic filter of fossil fuel burning power plants. Leaf samples were analyzed to trace the distribution of fly ash compounds on the leaf epidermis by means of x-ray fluorescence analysis and single particle electron microprobe x-ray analysis (EPMA). Significant reduction of the photosynthetic activity compared to the control group was only observed when the dusted plants were sprayed by acid rain. The trace element study showed that the uptake of toxic elements by plants was not significant. A quartz microcrystal layer was detected in case of acid treatment by EPMA, which covered the entire leaf surface. It is supposed that this layer in addition to the fly ash particles themselves, absorbed the light significantly which played an important role in the decrease of the photo-synthetic activity.