Desert dust contribution to the atmospheric aerosol in Cape Verde and in Portugal

Due to erosion processes, huge quantities of soil-derived particles are entrained into the atmosphere and transported away from the source, impacting air quality and affecting the Earth’s radiative budget. This Thesis addresses those land-atmosphere interactions, dealing with atmospheric mineral aerosol, with a main objective of improving the assessment of longrange transport of African dust focusing on Cape Verde and Portugal. To achieve the objective, dust modelling is employed and combined with observations, including size distributed particle concentrations and optical properties. Three different modelling systems are used, namely BSCDREAM8b, the NMMB/BSC-Dust model and WRF-CHIMERE, with distinct dust production models. In order to improve characterization of the dust size distribution at emission, a new parametrization is tested in this work, leading to a decrease in the emission fine fractions and an increase in the coarser ones, which has an impact in modelled downwind concentrations and optical parameters. Aerosol cycles are characterized and different methods to estimate the contribution of Saharan dust to regional PM levels are implemented and assessed. Significant dust intrusions from North West Africa severely affect Cape Verde PM surface concentrations during winter. In the summer dust is transported towards the region at higher altitudes, yielding high aerosol optical depths. On a yearly basis, and according to the methodology employed, roughly 42% of the PM10 mass observed in Cape Verde is associated with dust transported from North African deserts. Desert dust outbreaks are less severe in Portugal. Nevertheless, during 2016, at least two dust episodes, occurring in February and October, are responsible for regional exceedances of the PM10 daily limit value defined in the Air Quality Directive. This study intends to improve the scientific knowledge on processes and sources responsible for mineral dust loading into the atmosphere and to provide new means and valuable information for science-based decision making. Publications related to this Thesis International Journals included in the Science Citation Index (SCI) 1. Gama, C. , Monteiro, A. , Borrego, C. , Pio, C. , Baldasano, J.M. , Tchepel, O. Comparison of di erent methodologies for assessing desert dust contribution to regional PM10 and PM2.5 levels: a one-year study over Portugal. submitted to Aeolian Research [in review]. 2. Gama, C. , Monteiro, A. , Pio, C. , Miranda, A.I., Baldasano, J.M. , Tchepel, O. (2018) Temporal patterns and trends of particulate matter over Portugal: a long-term analysis of background concentrations. Air Quality, Atmosphere and Health. doi:10.1007/s11869-0180546-8 3. Gama, C. , Tchepel, O. , Baldasano, J.M. , Basart, S. , Ferreira, J., Pio, C. , Cardoso, J., Borrego, C. (2015) Seasonal patterns of Saharan dust over Cape Verde – a combined approach using observations and modelling. Tellus B 67, 24410. doi:10.3402/tellusb.v67. 24410. 4. Monteiro, A. , Fernandes, A.P., Gama, C. , Borrego, C. , Tchepel, O. (2015) Assessing the mineral dust from North Africa over Portugal region using BSC-DREAM8b model. Atmospheric Pollution Research 6, 70-81. doi:10.5094/APR.2015. 009. International Congresses and Workshops 1. Gama, C. , Monteiro, A. , Fernandes, A.P., Vieira, M. , Pio, C. , Miranda, A.I., Tchepel, O. (2016) Forecasting Saharan dust events over Portugal: analysis of the CHIMERE Dust module performance. 4th Iberian Meeting on Aerosol Science and Technology (RICTA 2016), 29 Jun.-01 Jul. 2016, Aveiro, Portugal. 2. Gama, C. , Basart, S. , Baldasano, J.M. , Pio, C. , Borrego, C. , Tchepel, O. (2016) Assessing the size distribution of dust in the NMMB/BSC-Dust model. 8th International Workshop on Sand/Duststorms and Associated Dustfall, 1-4 May 2016, Lisbon, Portugal. 3. Gama, C. , Basart, S. , Cardoso, J., Ferreira, J., Baldasano, J.M. , Pio, C. , Borrego, C. , Tchepel, O. (2015) Contribuição das poeiras do deserto para a degradação da qualidade do ar em Cabo Verde. XVII Encontro da Rede de Estudos Ambientais dos Países de Língua Portuguesa, 7-12 Sep., Praia, Santiago, Cape Verde. 4. Basart, S. , Gama, C. , Jorba, O. , Spada, M. , Pérez, C. , Baldasano, J.M. , Tchepel, O. , Pio, C. (2013) Desert dust and sea-salt evaluation of the NMMB/BSC-CTM model for North Africa. 7th International Workshop on Sand/Duststorms and Associated Dustfall, 2-4 Dec., Frascati, Italy. 5. Pio, C.A. , Cardoso, J., Nunes, T. , Cerqueira, M. , Tchepel, O. , Rocha, F. , Fialho, P., Alves, C. , Gonçalves, C. , Gama, C. , Ferreira, J., Almeida, S.M. , Almeida-Silva, M. , Reis, M. , Freitas, M.C. , Baldasano, J. (2013) Seasonal variability of atmospheric aerosol composition in Cape Verde islands under the influence of Sahara dust intrusions: results of the CV-Dust campaign. 1st Iberian Meeting on Aerosol Science and Technology (RICTA 2013), 1-3 Jul., Évora, Portugal. 6. Tchepel, O. , Ferreira, J., Fernandes, A.P., Gama, C. , Baldasano, J.M. , Borrego, C. , Cardoso, J., Almeida, S.M. , Pio, C. (2012) Modelling of long-range transport of mineral dust to Cape Verde. European Aerosol Conference. 2-7 Sep., Granada, Spain. National Conferences 1. Gama, C. , Basart, S. , Cardoso, J., Tchepel, O. , Baldasano, J.M. , Pio, C. , Borrego, C. (2015) One year of aerosol measurements and modelling of dust over Cape Verde. Research Day, 20 Maio, Aveiro, Portugal. 2. Gama, C. , Tchepel, O. , Ferreira, J., Baldasano, J.M. , Pio, C. (2013) Modelação das poeiras atmosféricas provenientes do deserto: aplicação à região de Cabo Verde. 10a Conferência Nacional do Ambiente. Repensar o ambiente: Luxo ou inevitabilidade? 6-8 Nov., Aveiro, Portugal.