Synergistic effect of nitrate-doped TiO₂ aerosols on the fast photochemical oxidation of formaldehyde.

ABSTRACT: The uptake of formaldehyde (HCHO) on mineral dust affects its budget as well as particle properties, yet the process has not yet been fully investigate. Here, TiO₂ and nitrate-doped TiO₂ aerosols were used as proxies for mineral dust, and the uptake of HCHO was explored in a chamber under both dark and illuminated conditions. The uptake loss of HCHO on UV-illuminated aerosols is 2-9 times faster than its gaseous photolysis in our experimental system. The uptake coefficient in the range of 0.43-1.68?×?10^-7 is 1-2 orders of magnitude higher than previous reports on model mineral dust particles. The reaction rate exhibits a Langmuir-Hinshelwood-type dependence on nitrate content and relative humidity, suggesting the competitive role of nitrate salts, water vapor and HCHO on the TiO₂ surface. The reaction produces carbon dioxide as the main product and gaseous formic acid as an important intermediate. The hydroxyl radical produced on illuminated TiO₂ primarily drives the fast oxidation of HCHO. The nitrate radical arising from the TiO₂-catalyzed photoreaction of nitrate synergistically promotes the oxidation process. This study suggests a novel oxidation route for HCHO in the atmosphere, taking into account high abundance of both mineral dust and anthropogenic TiO₂ aerosols.

SUBMITTER: Shang J 

PROVIDER: S-EPMC5430731 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature