Mineral dust aerosol is largely composed of soil particles lifted into the atmosphere by wind action. The flux of mineral dust into the troposphere varies greatly with location and season, but it is estimated that average annual emissions of mineral dust into the atmosphere total ~1000-3000Tg/yr with the Saharan Desert being the largest global contributor. The frequency and intensity of dust events, and ultimately the mineral aerosol loading in the atmosphere, are expected to continue to increase as long as improper land-use practices are driven by economic, social and political circumstances. By the year 2100, mineral aerosol production is anticipated to increase by 10% from its current level [IPCC Climate Change, 2001]. Mineral dust aerosol plays an important role in the coupled global processes of chemistry, climate, biogeochemical cycles, and health. Because mineral dust may undergo processing as it is transported in the atmosphere its impact on global processes may change over the course of its “life history”.

In our laboratory, we are trying to better understand how mineral dust can impact climate and biogeochemical cycles as described below.

Climate. Like atmospheric aerosols in general, mineral aerosol may affect local and global climate through the absorption and scattering of solar radiation. When aerosol particles absorb and scatter radiation themselves, the resulting radiative forcing is deemed “direct”, whereas if the particles influence the optical properties of clouds, then the radiative forcing is “indirect.” Positive radiative forcing values, measured in W m^-2, result in a warming effect on the Earth’s surface, and conversely, negative forcing has a cooling effect. Currently, researchers have a “very low level of scientific understanding” about the effect that mineral aerosol particles have on the radiative budget of the atmosphere, according to the latest report by the Intergovernmental Panel on Climate Change (IPCC), which estimates the net radiative forcing by mineral aerosol to range from –0.60 to +0.40 W m^-2. Most significant here is that not even the sign of the radiative forcing is known and ranges from both negative to positive values. That is to say it is completely uncertain whether mineral dust causes global warming or global cooling. The radiative impact of mineral dust in the atmosphere is quite unclear due to the incomplete understanding concerning the diverse nature, the transport and removal processes, and the chemical and physical properties of the particles. We are doing laboratory experiments and modeling analyses of mineral dust optical properties that will significantly enhance our understanding of the impact of mineral dust aerosol on global climate through direct radiative forcing, and, in particular, we are exploring how atmospheric aging (through chemical and physical processing) may alter the optical properties of the mineral dust and hence how it changes the impact that dust has on climate. This research is being done in collaboration with Professors Paul Kleiber (Physics) and Mark Young (Chemistry).

Biogeochemistry. It has been estimated that annually 360 to 500 Tg of mineral dust is deposited into the oceans, with approximately 50% of the total deposition occurring in the North Atlantic Ocean. Specifically, wind-transported mineral dust may play a large role in supplying soluble iron to the oceans, providing micronutrients to biological species, such as phytoplankton, and ultimately influencing the iron budget of the upper ocean. Chemical and photochemical processing of the mineral aerosols may reduce Fe(III) to a more soluble Fe(II) species. One of the goals of our laboratory studies is to better understand aerosol iron bioavailability and how atmospheric processing of Fe-containing mineral dust aerosol through heterogeneous chemistry plays a role in the amount of bioavailable iron. Laboratory studies could be important in better understanding and quantifying these reactions.