Absolute reaction rate studies of NO₃ radicals with 4 aldehydes were performed in the atmosphere simulation chamber SAPHIR at the Research Center Jülich. Rate coefficients (ethanal: 2.6 ± 0.5, propanal: 5.8 ± 1.0, butanal: 11.9 ± 1.4, benzaldehyde: 2.2 ± 0.6; in 10⁻¹⁵ cm³ s⁻¹ at 300 K) were determined from measured concentration–time profiles of aldehydes and NO₃ at near ambient conditions. The values for the aliphatic aldehydes are in good agreement with the most recent recommendations (IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry: Evaluated kinetic and photochemical data for atmospheric chemistry, 2005, available at http://www.iupac-kinetic.ch.cam.ac.uk). The measured concentration-time profiles of precursor aldehydes, NO₃, NO₂, and of product aldehydes were compared to model calculations based on the MCM v3 (Jenkin et al., 2003; Saunders et al., 2003). Differences between measurements and model are attributed to a major interference of the GC system to peroxyacyl nitrates. In addition modifications to the rate constants in the MCM are suggested.