The investigations of aerosol particle formation in urban background area of Helsinki

In this study the possible conditions for new aerosol particle formation in a background area of Helsinki have been analysed. The measurements of aerosol particle size distribution, main gaseous pollutant compounds, UV spectra and meteorological parameters were performed during April-May 1993. The main interest was concentrated on the investigations of photochemical OH radical formation, the oxidation of gas phase SO 2 to H 2 SO 4 and the formation of H 2 SO 4 -H 2 O aerosol particles. The measurements were analysed using a model for OH radical formation and aerosol dynamics. The analysis of aerosol size distributions was carried out using positive matrix factorization. The main conclusion is that based on our model analysis no evidence of new particle formation in the vicinity of the measurement station was found. However, the high concentrations of aerosol particles in the ultrafine size range indicate that some other particle formation pathways are to be considered.