THE INVESTIGATIONS OF AEROSOL-PARTICLE FORMATION IN URBAN BACKGROUND AREA OF HELSINKI

In this study the possible conditions for new aerosol particle formati on in a background area of Helsinki have been analysed, The measuremen ts of aerosol particle size distribution, main gaseous pollutant compo unds, UV spectra and meteorological parameters were performed during A pril-May 1993, The main interest was concentrated on the investigation s of photochemical OH radical formation, the oxidation of gas phase SO 2 to H2SO4 and the formation of H2SO4-H2O aerosol particles. The measu rements were analysed using a model for OH radical formation and aeros ol dynamics. The analysis of aerosol size distributions was carried ou t using positive matrix factorization. The main conclusion is that bas ed on our model analysis no evidence of new particle formation in the vicinity of the measurement station was found, However, the high conce ntrations of aerosol particles in the ultrafine size range indicate th at some other particle formation pathways are to be considered.