Radiative Forcing Properties of Aging Saharan Dust Storms Entering the North Atlantic

The aerosol aging effects on Saharan dust storm radiative forcing contribution was characterized using ship-based measurements from the 2013, 2015, and 2017 Aerosol Ocean Science Expedition (AEROSE) campaigns in the Atlantic Ocean. The motivation behind this work was to address uncertainties in longwave emissive properties of the over 600 million tons of Saharan dust aerosolized per year. Although optical characterizations of Saharan soils exist, large uncertainties still remain in how these dust aerosols evolve throughout atmospheric transport due to chemical processing and gravitational settling known as aging. The AEROSE campaigns provided a unique opportunity to examine dust storm aging characteristics in conjunction with aerosol optical property measurements. Sunphotometer, optical particle counter, surface trace gas measurements, dust particulate chemical analysis, and back-trajectory techniques were leveraged to produce aerosol aging classifications of each observed dust storm event during the 2013, 2015, and 2017 AEROSE campaigns. The Marine Atmospheric Emitted Radiance Interferometer (M-AERI) provided upward and downward viewing infrared (IR) emission spectra from roughly 3-18 microns at 0.5 cm^-1 resolution during both dust-laden and clear sky periods of observation. Based on aerosol optical depth (AOD) and longwave infrared (LWIR) band ratio techniques, 2015 observations consisted of two heavy dust storms along with several elevated dust scenarios. Within the two heavy dust cases, significant differences were observed in aerosol size, composition, and resulting LWIR emission characteristics within the thermal IR atmospheric window region. It is anticipated that these rare dust storm characterizations at sea will provide the basis for climate modeling and satellite retrieval improvements of dust on North Atlantic heat budgets.