Boundary layer trace gas and particulate extinction measurements in the wavelength region from 320 nm to 680 nm have been performed by means of a differential optical absorption spectroscopy (DOAS) system at Cape Arkona (Island R¿gen/Germany). The wavelength-dependent extinction coefficient &sgr;e(&lgr;) is determined from the attenuation of radiation along two paths of different lengths. Nearly simultaneous recording of the concentrations of O3 and NO2 within the same air mass allows a correction of their contribution to &sgr;e(&lgr;). The extinction coefficients are compared with volume scattering coefficients measured by an open integrating nephelometer. Differences between the measurements can be attributed to atmospheric inhomogeneities. A simplified model involving monomodal log-normal distributions is applied to approximate the total particle surface area concentration and an upper limit of the accumulation mode radius. This allows a rough estimate of the particle number concentration. During the summer of 1995 the mean (median) surface area concentration was about 350 (250) &mgr;m2/cm3, and the particle number concentration ranged from about 100 cm-3 to some 1000 cm-3.¿ 1997 American Geophysical Union