Possible artifacts in filter sampling of atmospheric sulphuric acid and acidic sulphates

The possible artifacts involved in sulphuric acid sampling and analysis have been investigated with the aid of X-ray microanalysis, X-ray fluorescence spectrometry and radio thermal diffusion analysis. Experiments with a selection of different filters demonstrate that of the types tested Nuclepore^R and Mitex^R filters are best suited for sulphuric acid sampling. Even with these filters, severe interferences in the sampling technique due to reaction with gaseous ammonia, and reaction of the collected acid aerosol with previously sampled panicles are identified. This particle-to-particle interaction is favoured by an inhomogeneous distribution of the sampled aerosol over the filter surface.