Absolute reaction rate studies of NO3 radicals with 4 aldehydes were performed in the atmosphere simulation chamber SAPHIR at the Research Center J¿lich. 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.