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Abstract

Diesel vehicles emit harmful soot particles. Soot can be removed effectively by after treatment systems, consisting of a particle filter and an oxidation catalyst. The filter removes soot particles, which are quasi-permanently burned using NO2, which is produced from motor NO in the oxidation catalyst. Unfortunately, SO2 is also oxidized to SO3, which results from the combustion of sulphur consisting fuels. SO3 reacts with water vapour to sulphuric acid. Due to its small vapour pressure gaseous H2SO4 can form nano particles by homogeneous nucleation with water vapour. Nano particles can intrude the lung and hence could be very harmful. Within the present work H2SO4 was measured by chemical ionisation mass spectrometry in the exhaust of a diesel engine. The formation of sulphuric acid in catalytic after treatment systems was verified and it was figured out, that the actual concentration in the exhaust is strongly influenced by store and release effects. Simultaneously measured aerosol particles show a correlation between the formation and growth of volatile nucleation particles and gaseous H2SO4. In addition a number of organic acids could be detected, some of which may also involved in nucleation processes.