1Division of Atmospheric Sciences, Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
2Finnish meteorological institute, Air Chemistry Laboratory, P.O. Box 503, 00 101 Helsinki, Finland
3STUK, Radiation and Nuclear Safety Authority, P.O. Box 14, 00881 Helsinki, Finland
4CSIRO – Commonwealth Scientific and Industrial Research Organisation, Marine and atmospheric research, P.O. Box 3023, ACT 2604, Canberra, Australia
Abstract. Formation of new aerosol particles by nucleation and growth is a significant source of aerosols in the atmosphere. New particle formation events usually take place during daytime, but in some locations they have been observed also at night. In the present study we have combined chamber experiments, quantum chemical calculations and aerosol dynamics models to study nocturnal new particle formation. All our approaches demonstrate, in a consistent manner, that the oxidation products of monoterpenes play an important role in nocturnal nucleation events. By varying the conditions in our chamber experiments, we were able to reproduce the very different types of nocturnal events observed earlier in the atmosphere. The exact strength, duration and shape of the events appears to be sensitive to the type and concentration of reacting monoterpenes, as well as the extent to which the monoterpenes are exposed to ozone and potentially other atmospheric oxidants.