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

[1] 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.