Titanium Dioxide Promotes New Particle Formation: A Smog Chamber Study.

TiO 2 is a widely used material in building coatings. Many studies have revealed that TiO 2 promotes the heterogeneous oxidation of SO 2 and the subsequent sulfate formation. However, whether and how much TiO 2 contributes to the gaseous H 2 SO 4 and subsequent new particle formation (NPF) still remains unclear. Herein, we used a 1 m 3 quartz smog chamber to investigate NPF in the presence of TiO 2 . The experimental results indicated that TiO 2 could greatly promote NPF. The increases in particle formation rate ( J ) and growth rate due to the presence of TiO 2 were quantified, and the promotion effect was attributed to the production of gaseous H 2 SO 4 . The promotion effect of TiO 2 on SO 2 oxidation and subsequent NPF decreased gradually due to the formation of surface sulfate but did not disappear completely, instead partly recovering after washing with water. Moreover, the promotion effect of TiO 2 on NPF was observed regardless of differences in RH, and the most significant promotion effect of TiO 2 associated with the strongest NPF occurred at an RH of 20%. Based on the experimental evidence, the environmental impact of TiO 2 on gaseous H 2 SO 4 and particle pollution in urban areas was estimated.