Alexander MacDonald

Chemical and Environmental Engineering

Investigating the Physicochemical Properties, Environmental, and Health Effects of Toxic Dust in Arizona

Aerosol particles have substantial effects on human health, Earth’s radiative balance, and nutrient and contaminant biogeochemical cycling. Dust particles can transport both vital nutrients and environmental toxins between different ecosystems. Respiratory diseases caused by wind-blown dust transport of toxic metals and metalloids (e.g., lead, arsenic, cadmium) from mining operations are a large health risk concern in the Southwest United States. Previous work by my research group has conducted measurements of size-resolved aerosol composition downwind of smelting and mining operations near Hayden and Winkelman, Arizona. They concluded that small fine particles are formed from condensation and coagulation of smelting vapors, whereas larger coarse particles likely originate as wind-eroded dust from mine tailing and other industrial sources. Coarse particles deposit in the upper respiratory tract due to inertial impact, while fine particles can effectively penetrate deep into the lungs. One issue that remains to be understood is how the particle’s chemical composition affects hygroscopic growth (i.e., the increase in size due to the condensation of water vapor onto the particle), hence modifying where and how much of the particles are deposited in the respiratory system. To better understand the relationship between aerosol chemical composition, hygroscopic growth, and deposition in the respiratory system, I am making use of the following: (1) size-resolved field measurements taken near the aforementioned mining sites, an inner-city site in Tucson, and a baseline site removed from anthropogenic emissions; (2) chemical analysis such as ion chromatography (IC), and inductively-coupled mass spectrometry (IC-PMS); (3) measurements of hygroscopic properties using a Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe (DASH-SP); (4) semi-empirical models of the human respiratory tract, as developed by the International Commission on Radiological Protection (IRCP).