AbstractsBiology & Animal Science

Aerosol particles are important atmospheric constituents. They exist in both polluted and remote areas but the sizes and concentrations of these particles vary greatly depending on location. Aerosol particles damage human health via inhalation, reduce visibility with high mass loadings, and among all, contribute to climate change. Particles directly scatter and absorb solar radiation. In addition, particles that are large enough can participate in cloud formation and affect cloud properties by acting as cloud condensation nuclei (CCN). A notable fraction of submicron atmospheric aerosol mass consists of organic compounds, and a large fraction of this material has been formed through condensation of organic vapors onto aerosol particles (secondary organic aerosol, SOA). Most of the global SOA mass is deemed to be biogenic in origin, but recent studies suggest that a significant fraction of it may be controlled by anthropogenic pollution. However, due to poor understanding of this anthropogenic enhancement in biogenic SOA formation, it is not systematically accounted for in current atmospheric models. Due to these kind of uncertainties in global SOA mass burden and lack of detailed knowledge of chemical, physical and optical properties of SOA, estimates of organic aerosol effect on the climate are highly uncertain. To decrease the uncertainty in the climate effects of the organic aerosol, an improved understanding of the formation mechanisms and properties of SOA is needed. In addition, nanoparticle growth to CCN-sizes by condensation of secondary organic matter needs to be accurately described in atmospheric models. In this thesis the formation of SOA is investigated in the presence of both biogenic and anthropogenic compounds. The chemical and physical properties volatility and hygroscopicity of SOA are examined via field and laboratory experiments combined with process modeling. The thesis introduces improvements for the treatment of SOA related to nanoparticle growth in atmospheric models and evaluates their performance. The thesis shows that interactions between atmospheric biogenic and anthropogenic aerosol components can form aerosol material of low-volatility. For instance organic salt formation via chemical reactions between organic acids and inorganic salts can lower aerosol volatility. Particulate-phase processing may also alter aerosol hygroscopic properties. Description of nanoparticle growth by low-volatility secondary organics is important in improving the estimates of particle and CCN numbers. The thesis highlights the significance of biogenic organic matter formed under anthropogenic influence in the nanoparticle growth. This warrants future studies focusing on the formation mechanisms and properties of anthropogenically driven biogenic organic aerosol. Aerosolihiukkasia on ilmakehässä kaikkialla, niin saastuneilla kuin syrjäisemmilläkin alueilla. Ilmakehän aerosolihiukkaset aiheuttavat ihmisille vakavia terveyshaittoja ja huonontavat näkyvyyttä erityisesti saastuneissa suurkaupungeissa.…