Source areas and effect of wet deposition on particles detected at SMEAR II measurement station as studied with FLEXPART

Aerosol particles are one of the most studied phenomena of modern days because their concretion and chemical compositions affect, both directly and indirectly, many aspects of society, for example, human health. The source areas of the particles affects their chemical composition and concentration and thus it is important to know where aerosols originate. In addition to the source areas of particles, it is important to understand the processes that affect the particles during transport through the atmosphere, for example, wet deposition. The aims of the thesis were to find out the characteristics in the source areas (1) and the effect of wet deposition (2) on the particles detected at SMEAR II (Hyytiälä, Finland) measurement station. Both aims were studied with the FLEXPART model and to study the first aim also the Hysplit model was used. FLEXPART is a Lagrangian particle dispersion model and Hysplit is traditional trajectory model. The both aims were studied with 14 case studies and each case study was studied with 96 hour backward in time simulations. The Hysplit simulations were made for each case study once and the FLEXPART simulations were made for each case study three times. The 14 case studies were selected based on observation made at the measurement station SMEAR II during the time period between February and April 2014. The case studies were divided into two classes: cloud and aerosol cases and the general characteristics of the cloud and aerosol cases were compared to each other. The extent and location of the source areas between FLEXPART and Hysplit were compared to define to source areas of the particles. The effect of wet deposition in the FLEXPART simulations was studied by comparing two simulation types: with default and with modified wet deposition parameterizations. The results of the thesis suggest that the measurement altitude, i.e. the release altitude in backward in time simulation, has a significant effect on the source areas of particles. The results also indicates that in cloud cases the particles originate more wider area than in aerosol cases. In cloud cases most of the trajectories come from South or South-West whereas in the aerosol cases most of the trajectories come from North or North-West which indicates that the source area of the particles could be in the background causing different interesting observations. The results suggest that wet deposition has a major role both in the amount of the mass and in the source areas of the particles detected in SMEAR II (Hyytiälä, Finland), especially in low pressure and cyclone situations, i.e. in cloud cases. Also the result indicates that the amount of scavenged mass is much higher in-cloud than below-cloud.