The major part of the studies is performed in a large Aerosol Chamber (260 m³) under conditions close to those of the nightly atmospheric boundary layer. Presently the studies are focussed at the importance of organic aerosol components (e. g. organic coatings) for

• reactions on the surface of aerosol particles in particular with respect to the destruction and removal nitrogen oxides
• the partitioning of trace substances between the gas- and the condensed phases of the aerosol

Trace gas concentrations are monitored by in-chamber high resolution FTIR spectroscopy. The size distributions of the aerosols are measured with a scanning electrostatic classifier, an aerodynamic time of flight instrument and a light scattering instrument. The chemical composition of the particulate phase and its modification by the heterogeneous processes are determined by steam jet aerosol collection with subsequent ion chromatography and in the near future also by aerosol mass spectrometry. Kinetic and thermodynamic model calculations support the physico-chemical characterization of the observed heterogeneous processes and serve as pivotal point for the generalization of the chamber results for the atmosphere.

The chamber work is complemented by studies in an aerosol flow tube in which optical spectra (presently IR) and size distributions can be measured at the same time. This allows for the determination of optical constants of aerosols as function of their chemical composition by means of Mie calculations.

Formaldehyde is measured by an in-situ instrument that utilizes a fluorescence technique. In addition, we develop an on-line method for the measurement of formaldehyde and larger aldehydes based on HPLC analysis.