Carbonaceous Aerosols in African Dust Over the Caribbean

African Dust (AD) particles transported by the trade winds from the North African desert make their way each year to the Caribbean, particularly during the summer months. Dust, as well as carbonaceous particles, influences the Earth's radiative budget directly by scattering and absorbing solar radiation in the atmosphere and indirectly by affecting cloud formation and, thus, cloud albedo. Yet the underlying physico-chemical processes and the interactions between dust and carbonaceous particles are poorly understood, especially if dust particles are as aged as those that travel from Africa to the Caribbean region. Here we present results on the chemical composition of aerosol samples sampled at several locations in the Caribbean in the presence and absence of African Dust. We performed chemical characterization of fine (Dp < 1.7 μm) and size-resolved samples focusing on the carbonaceous fraction (organic and elemental carbon (OC and EC)), the water-soluble organic carbon (WSOC)), and the water-soluble nitrogen (WSN). The presence of African dust was supported by aerosol optical thickness based on satellite images, results from the air masses backward trajectories calculated with the NOAA HYSPLIT model, the color of the filters after sampling, and chemical composition. Preliminary results showed limited increase in the concentrations of OC during dust events. The size-resolved samples showed three modes for the OC size distributions during the summer period, two in the fine fraction (Dp = 0.40 μm and 1.65 μm) and one in the coarse fraction (Dp = 6.70 μm). OC concentrations were also higher for the fine fraction (fine ~ 0.25 μg/m3 vs coarse 0.15 μg/m3). Additional results regarding OC, WSOC, WSN, and water-soluble ions together with the possible OC sources in the AD samples will be presented.