Retrieval of aerosol properties from boundary layer extinction measurements with a DOAS system

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 Rugen/Germany). The wavelength-dependent extinction coefficient sigma(e)(lambda) is determined from the attenuation of radiation along two paths of different lengths. Nearly simultaneous recording of the concentrations of O-3 and NO2 within the same air mass allows a correction of their contribution to sigma(e)(lambda). 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) mu m(2)/cm(3), and the particle number concentration ranged from about 100 cm(-3) to some 1000 cm(-3).