Exploring the influence of mineral dust–pollutant interactions on dust photoreactivity and pollutant lifetimes

Abstract:

Mineral dust, a major source of atmospheric particulate matter (PM), can be transported for thousands of kilometers before settling. Field observations of mineral dust–pollutant mixing have motivated investigations of the influence of organic pollutants on cloud condensation nuclei activity and optical properties of mineral dust. Although mineral dust is photoactive, little is known about how components of internally mixed mineral dust can photochemically influence one another. Here, we explore this two-way avenue through two related projects.

In the first project, we use an aerosol flow tube to explore the influence of organic coatings on the photoenhanced uptake of ozone by TiO₂, which we use as a simple photoactive model for mineral dust. We find that uptake of ozone by TiO₂ coated with anthropogenic alkanes is reduced compared to that by uncoated TiO₂, and that the reduction in uptake is influenced by coating viscosity. In the second project, we investigate the photodegradation of methylene blue, which we use as a model organic pollutant, by natural Ti-containing minerals present in mineral dust. We demonstrate that the rate of photodegradation of methylene blue depends on both the adsorptive properties and inherent photoreactivities of each mineral sample.

Together, this work shows that mineral–dust pollutant mixing has the potential to influence both mineral dust photochemistry and the lifetime of organic pollutants present at the surface of mineral dust. These results will ultimately enable us to better understand the influence of mineral dust chemistry on air quality in polluted regions.