Aerosol particles in a semi-clean savannah environment
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Helsinki University of Technology | Diplomityö
AbstractAerosol particles form at the moment the largest source of uncertainty in the current knowledge of earth radiative budget, but long time series of aerosol particle size distributions are nearly non-existent in Africa. This study is based on the first continuous combined Iong-term measurements of aerosol particle size distributions, air ions and trace gases in a semi-clean savannah environment. The effect of air mass history and the effect of wild fires from MODIS remote sensing observations are taken into account in the discussion. This thesis also presents the first detailed description of the measurement trailer built for the purpose of these measurements. New aerosol particle formation and subsequent growth was observed on 69 % of days, on only 4% of the days there certainly was not new particles formed. The formation and growth rates determined from the measurements are among highest observed globally. Based on the source area analysis the highest growth rates of the smallest air ions originate in the same areas as the highest sulphur dioxide concentrations observed in the measurement location. On the other hand the highest growth rates of the larger aerosol particles and air ions originate in less anthropogenically affected areas. This suggests the growth mechanisms or compounds to be different in the formation of new particles and the subsequent growth. A three-modal log-normal distribution was fitted in the measured aerosol size distribution. Presented this way the distribution can easily be used as comparison material for climate models covering the area and in development of the models. The effect of wild fires, which are common in the region, was seen as clearly increased trace gas concentrations and aerosol particle number concentrations in the Aitken and accumulation modes. The results of this study increase the knowledge of aerosol particle formation and growth in savannah environment and together with other studies offer valuable comparison data for global climate models.
Thesis advisorLaakso, Lauri
aerosol, aerosoli, Africa, Afrikka, savannah, savanni, MODIS, MODIS