Particle-associated benzotriazole ultraviolet stabilizers exhibit atmospheric persistence against ^•OH heterogeneous oxidation

Abstract. Benzotriazole ultraviolet stabilizers (BT-UVs) are ubiquitous in airborne particles due to continuous emissions from widespread usage in plastic and rubber, with several congeners recognized as Persistent Organic Pollutants (POPs) under the Stockholm Convention. While ^•OH-initiated heterogeneous oxidation is the primary atmospheric degradation pathway for particle-associated organics, the degradation kinetics and fate of particulate BT-UVs remain poorly constrained. Herein, an oxidation flow reactor (OFR) was utilized to systematically investigate the ^•OH-initiated heterogeneous oxidation processes of eight commonly used BT-UVs. The results revealed that the intrinsic second-order rate constants ranged from (4.12 ± 0.30) × 10^–13 to (13.2 ± 1.17) × 10^–13 cm³ molecules^–1 s^–1, corresponding to atmospheric lifetimes exceeding one week and significant potential for long-range environmental transport (LRET). Furthermore, elevated ambient humidity enhanced their degradation rates by approximately 30%, whereas coexisting soluble iron exhibited a marginal effect. The oxidation proceeded mainly through alkyl-group and phenyl-ring reactions, yielding 30 tentatively identified transformation products (TPs), 24 of which were subsequently confirmed in ambient PM_2.5. These findings quantitatively confirm the high persistence of particulate BT-UVs and highlight the necessity of evaluating the environmental risks and human inhalation hazards of their secondary transformation products.