Chemical Variation as a Function of Size for Saharan Dust Plumes Observed During AEROSE 2015

The Saharan Desert is responsible for one of the largest contributors of natural aerosols emitted worldwide and has an immense yet poorly understood implication on climate, health, and ecosystems. Because of the remoteness and inhospitable conditions, observational data collection of Saharan dust can be a challenge. Fortunately, for nearly a decade the Saharan Dust Aerosols and Ocean Science Expedition (AEROSE) cruises have collected in-situ data of Saharan dust propagations as they enter the Atlantic Ocean. The AEROSE cruises support the National Oceanic and Atmospheric Administration (NOAA) mission of satellite and model improvement over the tropical Atlantic. Dust particle size influences aerosol lifetime, its efficiency as an ice nuclei, solar radiation interactions, and inhalation capabilities when it comes to human health. The objective of this investigation was to identify the chemical variability of dust plumes as a function of size. Using a two-stage and six-stage stage Staplex ™ Microbial Air Samplers, Saharan dust particulate were collected during the cruise intercepts of dust outflow events during the November 2015-December 2015 timeframe. The Staplex ™ Microbial Air Samplers allowed for collection of dust particles ranging from 0.65 to 10 microns onto quartz fiber filters that subsequently underwent micro-analytical chemical analysis.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been used to determine relative concentrations of distinctive elements such as Al, Ca, K, Na, Sr, Mg, and Fe for each size fraction collected.  Preliminary results indicate that external mixing on the dust samples was minimal indicating relatively homogeneous dust events without significant chemical mixing of urban or biomass burning air masses. Results from this investigation can be useful in understanding the dependence of the surface elemental distribution on particle size within Saharan dust plumes and its downstream implications on cloud microphysics.