Heterogeneous Uptake of Gas-Phase Acetic Acid on the Surface of α-Al₂ O₃ Particles: Temperature Effects

Heterogeneous reactions are thought to play a significant role in the formation of haze, especially in wintertime, which suggests that temperature may affect the heterogeneous formation of organic aerosols. As the most-abundant carboxylic acid in the Earth's atmosphere, we chose acetic acid to study the effect of temperature on its heterogeneous reaction with α-Al₂ O₃ between 248 and 298 K. The products were characterized by in situ DRIFTS, which indicated that lowering the temperature slowed the formation of acetate, but promoted the formation of crystalline acetic acid. Moreover, low temperatures promoted a different reaction mechanism to that at room temperature. Owing to the formation of chain structures at low temperatures, crystalline acetic acid molecules covered the surface active sites on α-Al₂ O₃ , thereby inhibiting the formation of acetate. However, crystalline acetic acid reacted with α-Al₂ O₃ itself in a sequential manner. Furthermore, the reactive uptake coefficients, active energies, and acetic acid lifetimes at different temperatures were investigated.