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Universidade de Aveiro (2016)

Estudo do aerossol (poeira do Sara) na região de Cabo Verde

Cardoso, João Gomes

Titre : Estudo do aerossol (poeira do Sara) na região de Cabo Verde

Auteur : Cardoso, João Gomes

Université de soutenance : Universidade de Aveiro

Grade : Doutoramento em Ciências e Engenharia do Ambiente 2016

Contexte
Within the CV-DUST research project a filed campaign was developed in Praia (14 ° 55 ’N, 23 ° 29 ’W) between January 2011 and January 2012. Aerosol concentration was quantified based on the gravimetric method, with sampling done in terms of PM10 and in size fractions using impactors. An optical particle counter was also used, which allows the continuous monitoring of the number of particles and their classification in 31 size class ranging between 0.25 and 32 μm. Chemical composition of samples was determined by focusing on the following components : inorganic ions solubles in water (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+ and Ca2+), total carbonate, elemental species (Si, Na, Al, Fe, Ca, Mg, K, Ti and Mn, Ba, Zn, Zr, Pb, Cu, Ce, Ni, Cr, V, Co, Sc, The Sm and Sb), and carbonaceous fraction (elemental carbon - EC and organic carbon - OC). Throughout the campaign, PM10 concentration shows a great variability, with daily mean values ranging between 10 and 507 μg/m3, the annual average concentration rounding 59 μg/m3. Higher concentrations (typically above 100 μg/m3) were registered during the dust events originated from North Africa (Saharan desert), the most intense observed in January, February and December 2011. Optical particle counter records made at 5 min intervals show that during the dust events the hourly average concentrations of PM10 and PM2.5 particles can exceed 700 μg/m3 and 200 μg/m3, respectively. Estimations based on the optical measurements reveal that the average contributions of particles size fractions PM1, PM(1-2.5) and PM(2.5-10) to PM10 mass were around of 11 %, 28 % and 61 %, respectively. Chemical composition of the aerosol varies considerably throughout the year and reveals the predominance of mineral particles and sea salt. Basing on chemical mass balance calculations, the contributions of these two main constituents were estimated in 47 % (mineral particles) and 17 % (sea salt). Secondary aerosols (represented by NH4+, NO3- and non sea salt fraction of SO42-) and carbonaceous aerosols (EC + MO with MO = 1.6 x OC) contribute each one to about 4 % and 3 %, respectively. The remained mass fraction (around 29 %) is composed by non analised species, but the contribution of water can be important. Chemical size resolution of the samples reveals the following composition for PM1, PM(1-2.5) and PM(2.5-10) particles : 5.2 %, 11.8 % and 20.7 % (sea salt contsituents) ; 8.6 %, 3.7 % and 3.1 % (secondary inorganic ions) ; 8.9 %, 1.5 % and 1.3 % (EC + OC).

Mots clés  : Ciências do ambiente Qualidade do ar - Monitorização - Cabo Verde Aerossóis atmosféricos - Cabo Verde Poeiras minerais - Sara Poluição do ar Efeitos da poluição

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Page publiée le 11 décembre 2016, mise à jour le 12 juin 2017