A series of simulation chamber experiments has been performed on the atmospheric oxidation of acenaphthene at (293 ± 3) K in 1 atm of purified air. Rate coefficients for reaction with hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone have been determined using the relative rate technique. The values obtained for reaction with OH and O3 were (in units of cm3 molecule−1 s−1) (9.89 ± 0.51) × 10−11 and (1.79 ± 0.10) × 10−19 respectively. The rate coefficient for reaction with NO3 was found to be dependent on NO2 concentration and is given by (4.16 ± 0.70) × 10−13 + (3.45 ± 1.73) × 10−27[NO2] cm3 molecule−1 s−1. A denuder-filter sampling system coupled with off-line GC–MS analysis was used to collect and identify gas- and particle-phase products of the OH and NO3 initiated oxidation of acenaphthene. For the OH reaction, a range of ring-retaining and ring-opening products were identified in both phases, although some species, including nitroacenaphthene and 1,8-naphthalic anhydride, were found exclusively in the particle phase. In particular, the identification of 1-acenaphthenone and naphthalene-1,8-dicarbaldehyde amongst the products indicates that H-atom abstraction from the cyclopenta-fused ring is an important reaction pathway, along with OH addition to the aromatic ring. For the NO3 reaction, 1-acenaphthenone and nitroacenaphthene were identified as the major gas- and particle-phase products respectively. Possible reaction mechanisms for the formation of these products are proposed.