Photoenhanced uptake of NO 2 on mineral dust: Laboratory experiments and model simulations

Mineral dust contains material such as TiO 2 that is well known to have photocatalytic activity. In this laboratory study, mixed TiO 2 ‐SiO 2 , Saharan dust and Arizona Test Dust were exposed to NO 2 in a coated wall flow tube reactor. While uptake in the dark was negligible, photoenhanced uptake of NO 2 was observed on all samples. For the mixed TiO 2 ‐SiO 2 , the uptake coefficients increased with increasing TiO 2 mass fraction, with BET uptake coefficients ranging from 0.12 to 1.9 × 10 −6 . HONO was observed from all samples, with varying yields, e.g., 80% for Saharan dust. Three‐dimensional modeling indicates that photochemistry of dust may reduce the NO 2 level up to 37% and ozone up to 5% during a dust event in the free troposphere.