This article presents the first study of the chemical reactivity of a photo-oxidation product of the 2-methyl-3-buten-2-ol (MBO) in the troposphere, the 2-hydroxy-2-methylpropanal (HMPr). Experiments were performed under controlled conditions for pressure (atmospheric pressure) and temperature (296±2 K) in the LISA indoor simulation chamber and in the EUPHORE outdoor simulation chamber to understand the transformations of HMPr in the atmosphere, using FTIR spectrometry. Reaction with OH radicals was studied in the presence and in the absence of NOx. All the kinetic studies were carried out by relative rate study using isoprene and/or n-butylether as the reference compound. The rate constants found for these reactions were J=(1.01±0.39)×10−5 s−1 and kHMPr+OH=(1.52±0.36)×10−11 molecule−1 cm3 s−1. For the reaction with OH radicals, an important production of acetone was observed, with a yield of Racetone=1.06±0.06.