A look at aerosol formation using data mining techniques S. Hyvönen1, H. Junninen2, L. Laakso2, M. Dal Maso2, T. Grönholm2, B. Bonn2, P. Keronen2, P. Aalto2, V. Hiltunen3, T. Pohja3, S. Launiainen2, P. Hari4, H. Mannila1, and M. Kulmala2 1Helsinki Institute for Information Technology, Basic Research Unit, Department of Computer Science, University of Helsinki, P.O. Box 68, 00 014 University of Helsinki, Finland 2Department of Physics, University of Helsinki, P.O. Box 64, 00 014 University of Helsinki, Finland 3Hyytiälä Forestry Field Station, Hyytiäläntie 124, 35 500 Korkeakoski, Finland 4Department of Forest Ecology, Faculty of Agriculture and Forestry, P.O. Box 27, 00 014 University of Helsinki, Finland
Abstract. Atmospheric aerosol particle formation is frequently observed throughout the atmosphere, but despite
various attempts of explanation, the processes behind it remain unclear. In this study data mining
techniques were used to find the key parameters needed for atmospheric aerosol particle formation
to occur. A dataset of 8 years of 80 variables collected at the boreal forest station (SMEAR II)
in Southern Finland was used, incorporating variables such as radiation, humidity,
SO2, ozone and present aerosol surface area. This data was analyzed using clustering
and classification methods. The aim of this approach was to gain new parameters independent
of any subjective interpretation. This resulted in two key parameters, relative humidity and
preexisting aerosol particle surface (condensation sink), capable in explaining 88%
of the nucleation events. The inclusion of any further parameters did not improve the
results notably. Using these two variables it was possible to derive a nucleation probability
function. Interestingly, the two most important variables are related to mechanisms that
prevent the nucleation from starting and particles from growing, while parameters related
to initiation of particle formation seemed to be less important.
Nucleation occurs only with low relative humidity and condensation sink values. One possible
explanation for the effect of high water content is that it prevents biogenic hydrocarbon
ozonolysis reactions from producing sufficient amounts of low volatility compounds, which might be
able to nucleate. Unfortunately the most important biogenic hydrocarbon compound emissions were not
available for this study.
Another effect of water vapour may be due to its linkage to cloudiness which may prevent the
formation of nucleating and/or condensing vapours.
A high number of preexisting particles will act as a sink for condensable vapours that otherwise would
have been able to form sufficient supersaturation and initiate the nucleation process.
Citation: Hyvönen, S., Junninen, H., Laakso, L., Dal Maso, M., Grönholm, T., Bonn, B., Keronen, P., Aalto, P., Hiltunen, V., Pohja, T., Launiainen, S., Hari, P., Mannila, H., and Kulmala, M.: A look at aerosol formation using data mining techniques, Atmos. Chem. Phys., 5, 3345-3356, doi:10.5194/acp-5-3345-2005, 2005.