Heterogeneous Reaction of OH Radicals with Terbuthylazine on Self-synthesized Silica Particles in an Aerosol Smog Chamber at Different Temperatures

Terbuthylazine (TBA) is regarded as a reference compound for the heterogeneous photooxidation of semi-volatile organic compounds (SVOCs) initiated by OH radicals, and the reaction rate constant has been used to evaluate the atmospheric lifetime of other pesticides/SVOCs. However, experiments on different carrier aerosols using different apparatus derived distinct results, therefore discussions were raised upon whether TBA should be regarded as persistent organic compounds (POPs) or not. In this study, we applied the self-synthesized silica particles (Stöber particles) as carrier aerosols, which could simulate the reactions on mineral particles in the atmosphere. We investigated the heterogeneous reaction of OH radicals with TBA, by exposing a sub-monolayer coating of TBA on the Stöber particles, to simulate the degradation of TBA on spherical particles in ambient air. The rate constants for the reaction of OH with TBA adsorbed on Stöber particles were determined to be 2.4 ± 0.3 (in units of 10^–12 cm³ molecule⁻¹ s⁻¹) at 25 °C. Heterogeneous reaction were also performed at 6.5 °C and − 10 °C, the rate constants were 2.3 ± 0.2 and 1.4 ± 0.1 (in units of 10^–12 cm³ molecule⁻¹ s⁻¹), respectively. The atmospheric half-lives of TBA on Stöber particles were estimated to be 53, 56, and 92 h at 25 °C, 6.5 °C, and -10 °C, respectively (based on the simulation parameter obtained from the Eley–Rideal (ER) mechanism). We also fit the experimental data to the Langmuir–Hinshelwood (LH) mechanism and the half-lives become shorter (33, 45, and 61 h at 25 °C, 6.5 °C, and -10 °C, respectively). There is no evidence from observation data that show that TBA could be transported to the remote region. TBA cannot be defined as a persistent organic pollutants (POPs). Reactions in the atmosphere might be a combined mechanism of both ER and LH theories.