Can Silica Particles Reduce Air Pollution by Facilitating the Reactions of Aliphatic Aldehyde and NO₂?

This study investigated the heterogeneous atmospheric reactions of acetaldehyde, propanal, and butanal with NO₂ onto silica (SiO₂) clusters using a theoretical approach. By analyzing spectral features and adsorption parameters, the formation of hydrogen bonds and negative adsorption energies provide evidence that an efficient spontaneous uptake of aliphatic aldehydes onto SiO₂ could occur. The atmospheric reaction mechanisms show that when aldehydes and NO₂ react on the surface model, the H atom abstraction reaction from the aldehydic molecule by NO₂ is an exclusive channel, forming nitrous acid and acyl radicals. This study included kinetics exploring the reaction of aldehydes with NO₂ using a canonical variational transition state theory. The reaction rate constants are increased in the presence of SiO₂ between the temperatures 217 and 298 K. This may explain how aldehydes can temporarily stay on mineral particles without chemical reactions. The results suggest that silica can depress the rate at which the studied aldehydes react with NO₂ and possibly reduce air pollution generated by these atmospheric reactions