Polycyclic aromatic hydrocarbons (PAHs) are an ubiquitous class of compounds in the environment, mostly generated by anthropogenic processes. High time resolution measurements are necessary to gain further knowledge on the fate and diurnal pattern of these often carcinogenic and mutagenic compounds in the atmosphere. It is expected to find a strong correlation of the PAH levels with the strength and proximity to sources, as well as with meteorological parameters. To determine the fate of particle-bound PAHs, they were sampled in this study at an urban background site in Zurich, Switzerland, during summer 2002 and winter 2003. Particle-bound PAHs were collected with a rotating drum impactor and subsequently analyzed with two-step laser mass spectrometry. Using this combination of sampling and measurement, size-segregated (10-1.1, 1.1-0.3, and 0.3-0.1 microm) and high time resolution (20 min) data were obtained. The pronounced diurnal cycle (with day/night ratios of 0.1) was only altered during intensive atmospheric mixing periods (resulting in day/night ratios of up to 8) by cleaner air from upper atmospheric layers which was mixed into the boundary layer. During summer, signal intensities due to particle-bound PAHs were about a factor of 2-10 lower than during winter.