Atmospheric ultrafine particles (UFP) are high in number but low in mass. Because of the ability to reach deeply into the lungs UFP can influence human health. Chemical analysis of UFP is to some extent possible after sampling by means of low pressure impactors. Main component classes of compounds in UFP are organic and elemental carbon and the water soluble ions ammonium, sulfate and nitrate. Single organic compounds such as polycyclic aromatic compounds, alkanes or levoglucosan can also be measured. Primary emissions of traffic and stationary combustion processes are one and secondary formation in the atmosphere from gaseous precursors is another major source. Organic matter and elemental carbon contribute up to 75?% to the mass of UFP. Parallel sampling at three locations, influenced by different emissions, helped to identify sources of particles.