Acknowledgements

Sciences of the University of Helsinki. I want to thank Prof. Juhani Keinonen for providing the working facilities. I also want to thank Prof. Markku Kulmala for introducing me to aerosol science and also for his continuing guidance, encouragement and inspiration for my work. I am thankful to the Maj and Tor Nessling foundation for nancial support during the last two years of this work. Science today is born from co-operation, and this thesis would not exist without the input from a large number of people. I am grateful to all my coauthors for their expertise and collaboration. Especially I am grateful to Doc. Jyrki Makela and Dr. Pasi P. Aalto for patiently explaining me the ins and outs of working with aerosol size distributions. Prof. Kari Lehtinen and Prof. Veli-Matti Kerminen I wish to thank for sharing their profound knowledge on aerosol dynamics and on the art of writing. Doc. Hanna Vehkamaki I want to thank for helping me to start understanding nucleation. Doc. Aki Virkkula and Prof Marja-Liisa Riekkola I wish to thank for carefully proof-reading and thus improving this thesis