Photoenhanced uptake of NO2 on mineral dust: Laboratory experiments and model simulations

Mineral dust contains material such as TiO2 that is well known to have photocatalytic activity. In this laboratory study, mixed TiO2‐SiO2, Saharan dust and Arizona Test Dust were exposed to NO2 in a coated wall flow tube reactor. While uptake in the dark was negligible, photoenhanced uptake of NO2 was observed on all samples. For the mixed TiO2‐SiO2, the uptake coefficients increased with increasing TiO2 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 NO2 level up to 37% and ozone up to 5% during a dust event in the free troposphere.