O ₃ and OH Multiphase Oxidation of Benzotriazole Ultraviolet Stabilizer UV-328

Benzotriazole ultraviolet stabilizers (BZT-UVs) are emerging contaminants whose presence in airborne dust, aerosol particles, and consumer products strongly suggests multiphase chemistry is important for their environmental fate. The first multiphase experiments of nm-thick films of 2-(2H-1,2,3-Benzotriazol-2-yl)-4,6-bis(2-methylbutan-2-yl)phenol (UV-328) with gas phase oxidants (OH, O 3 ) were conducted in a flow tube, with transformation products identified using liquid chromatography–high resolution mass spectrometry. With an OH exposure of ∼0.8 ppt for 3 days, oxidation products were identified with either 1 or 2 oxygen atoms added to the parent molecule and benzotriazole (BT). Reactions with O 3 at 250 ppb for 3 days produced only benzotriazole, whereas experiments at a much higher exposure led to a variety of ring-opened products with up to 4 oxygen atoms added to the parent molecule, including carboxylic acid and aldehyde groups. To act as a guide for the oxidative environmental fate of BZT-UVs, the observed products were used to propose reaction pathways for UV-328 with OH and O 3 . Analysis of a used traffic cone plastic sample identified UV-328 and two OH radical transformation products. This study identifies benzotriazole (C 6 H 5 N 3 ) as a multiphase transformation product for BZT-UVs.