Impact of Sahara dust transport on Cape Verde atmospheric element particles
M. Almeida-Silva1,2*, S.M. Almeida1, C.A. Pio3, T. Nunes3, J. Cardoso3, 4
1
Escola Superior de Tecnologia da Saúde de Lisboa, Instituto Politécnico de Lisboa, Av. D. João
II 4.69.01, 1990-096 Lisboa, Portugal;
2
Instituto Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa,
Estrada Nacional 10, 2686-953 Sacavém, Portugal;
3
Aveiro University, CESAM, P-3810193 Aveiro, Portugal;
4
Cape Verde University, Campus do Palmarejo, Praia, Cape Verde
Corresponding Author: *[email protected]
Sahara desert is the most important source of mineral dust, contributing as much as 1900
million tons per year. Due to its localization, Cape Verde is ideal to quantify and to characterize
the dust transported from Sahara desert. Cape Verde is an archipelago composed by 10
islands, localized in Atlantic Ocean, near African coast. Santiago’s island is the biggest island of
Cape Verde, with an area of 991 km2 and was the selected to perform this study. This work was
developed within the project Atmospheric aerosol in Cape Verde region: seasonal evaluation of
composition, sources and transport (CV-Dust) - that aims to assess the transport of dust from
Sahara by using an integration of measuring and modelling tools.
Complementary tools were used to identify the likely Air Particulate Matter (APM)
provenance, such as back trajectory-based method, satellite images and APM chemical
analysis. PM10 was collected in Praia city (14º94’N; 23º49’W) with a Tecora® sampler in order
to characterize the element chemical composition. The collected filters were weighted by
gravimetry using a Mettler® Toledo balance with 0.1 µg readability, placed in a controlled clean
room (class 10,000). All samples were irradiated at the Portuguese Research Reactor (RPI-ITN;
nominal power: 1MW) during 5 h, and measured for 5-7 h after 2-5 days and 4 weeks of decay,
in high-purity and high-resolution germanium detectors. A comparator – Al-0.1% Au alloy disk
– was also irradiated and measured for application of the k0-INAA methodology.
Results showed that during the dust events PM10 concentrations increased significantly. The
maximum concentration of 494µg/m3 was reached in an event that occurred in February 2011.
k0-INAA showed to be very well suited to assess the Sahara dust contribution because this
technique can determine with accuracy the concentration of some crustal elements. The
measured crustal elements Fe, La, Sc and Sm presented significantly higher concentrations in
Cape Verde comparing with other studies performed in Lisbon by our research groups. These
elements reached the highest concentrations during air mass transport provided from Sahara
Desert.