Source Apportionment of Particulate Matter Sampled in Cape Verde S.M. Almeida1*, M. Almeida-Silva1, C.A. Pio2, T. Nunes2, J. Cardoso3, M. Cerqueira2, M.A. Reis1, P.C. Chaves1, A. Taborda1 1 URSN,
IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa, Estrada Nacional 10, 2686-953 Sacavém, Portugal 2 3 Cape
CESAM, Aveiro University, 3810-193 Aveiro, Portugal
Universidade de Aveiro
Verde University, Campus do Palmarejo, Praia, Cape Verde
* Corresponding author:
[email protected]. pt
Aim: The objective of this study was (1) to perform a chemical characterization of the airborne particles sampled in Cape Verde, (2) to identify the main sources and origins of the particles and (3) to assess the influence of Sahara desert on local suspended particles. Introduction
Methodology
Sahara Desert is the most important source of mineral dust, contributing more
• PM10 was sampled during 2011.
than 1900 million tons per year and responsible for almost half of all the Aeolian
• Chemical characterization of particles was performed by: Neutron Activation Analysis and Particle Induced X-ray Emission for
material provided to the world’s oceans. Due to its geographical position, Cape Verde is highly affected by the transport of dust from the Sahara desert.
elemental measurements;
Therefore, it is essential to elucidate the role of Saharan dust may play in the
Ion Chromatography for the determination of water soluble ions;
degradation of Cape Verde air quality, human health, wellbeing, visibility, tourism
Thermal-optical system for the measurement of carbonaceous aerosol. • Source apportionment was performed by Positive Matrix Factorization and
and economy.
Cluster Analysis of Backward Trajectory.
Soil Sahara
Sea
Anthr. 1 / Soil
Anthr. 2
Results
EC
600 550
140
1
3
4
120 -3
Source contribution (g.m )
450 400 350 300 250 200 150
100
80
60
40
20
0 Soil Sahara
Sea
Anthr. 1 / Soil
Anthr. 2
EC
100 50
6-Jan
24-Dez
11-Dez
13-Nov
10-Out
7-Set
3-Ago
27-Jun
3-Jun
4-Mai
5-Abr
3-Mar
15-Fev
0
3-Fev
-3
Source contribution (g.m )
500
2
Figure 1: Source contribution for PM10 concentrations measured in Cape Verde during 2011. PMF identified 5 emission sources: Mineral dust from Sahara – identified by Al, Ce, Fe, Mn, Si, Sm, Ti, CO32- and K but also by some anthropogenic elements as As, Cr, Cu, Ni, Pb, V and Zn;
Figure 2: Cluster analysis applied to the backward trajectories and relative source contribution for each cluster.
Sea-spray composition – identified by Cl-, Na+, Mg2+ and Br; Local anthropogenic sources – identified by Ni, Cr, Sb, SO42- ; NO3- , Ca2+ and soil
• During trajectories from Sahara , the contribution of the mineral dust increased to more than 60%;
elements; Secondary aerosol – identified by NH4+, SO42- and NO3- ; Vehicles - identified by EC and OC.
• Sahara dust affected the aerosol in Cape Verde not only increasing the typical soil elements but also increasing As, Cr, Cu, Ni, Pb, V and Zn.
Conclusions • Cape Verde aerosol is affected principally by natural sources: dust coming from Sahara desert contributes on average to 48% of the total PM10 mass and sea salt spray contributes on average to 20%. • During trajectories from Sahara, dust contribution increases to more than 60% and PM10 concentrations reach concentrations 10 times higher than the EC limit values and WHO guidelines. We gratefully acknowledge the Portuguese Foundation for Science and Technology (FCT) for funding the project PTDC/AAC-CLI/100331/2008 - CVDust: Atmospheric Aerosol in Cape Verde Region: Seasonal Evaluation of Composition, Sources and Transport
