α-Pinene, C10H16, represents one of the most important biogenic emissions into the atmosphere. The formation of RO2 radicals HO-C10H16O, x = 2-6, and their closed-shell products from the OH + α-pinene reaction has been measured for close to atmospheric reaction conditions in the presence of NO with concentrations of (1.7-490) × 109 molecules cm-3. Main closed-shell products are substances with the composition C10H16O2 and C10H16O4, most likely carbonyls, obtained with molar yields in the range 0.42-0.45 and 0.17-0.19, respectively, for NO concentrations >5 × 1010 molecules cm-3. The corresponding total product yields amount to 0.75-0.81, indicating efficient product detection by the mass spectrometric method applied. All stated molar yields represent lower limit values affected with an uncertainty of [Formula: see text]. Kinetic and product analysis consistently revealed the suppression of the formation of highly oxygenated organic molecules (HOMs) by a factor of 2-2.2 for the highest NO concentration used. The findings of this study provide insights into the RO2 radical processes of the OH + α-pinene reaction for atmospheric conditions and give an overview about the first-generation products.