Ultrafine Particles as Trace Catchers for Polycyclic Aromatic Hydrocarbons: The Photoelectric Aerosol Sensor as a Tool for in Situ Sorption and Desorption Studies

The adsorption, condensation, and desorption behavior of polycyclic aromatic hydrocarbons (PAHs) on the surface of ultrafine particles has been studied. Four different kinds of monodisperse primary particles—carbon, sodium chloride, aluminum oxide, and Aerosll 200—were subjected to PAH adsorption under well-defined conditions. The photoelectric aerosol sensor was used as a sensitive technique for “in situ” and “on-line” detection of the degree of surface coverage of the particles by PAHs. The results were controlled by fluorometric determination of the PAH amount from aerosol filter samples taken in parallel. The affinity of the PAHs to the particle material decreased from carbon to sodium chloride to aluminum oxide and had its minimum for Aerosll 200. In the second part of the study the thermal desorption of the adsorbed PAHs was investigated by application of a thermodenuder technique. From all particle materials tested the PAHs with the largest ring system desorbed at the highest temperature. By the study of a single PAH compound on the different carrier aerosols, it was demonstrated that the temperature necessary for desorption decreased in the sequence Aerosll 200 > aluminum oxide > NaCl = carbon. In case of aluminum oxide and Aerosll 200 a strong chemisorption of the PAHs is supposed to be the reason for the differences in the observed desorption temperatures.